bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Exhaustive Exercise, Carbohydrate Ingestion and Muscle Glycogen Content on Exercise‐Induced Circulatory Immune Responses
Authors: Dent Jessica R , Ogden Henry , Hazeldine Jon , Stocks Ben , Zemp Martina , Harrison Paul , Philp Andrew
Published: November 2023

Exercising in a state of reduced muscle glycogen content (“compete‐high, train‐low”) enhances metabolic adaptation in skeletal muscle. However, despite the increasing popularity of such regimes, how this training strategy affects post‐exercise immune disturbances and an athlete's susceptibility to acute upper respiratory tract infections (URTIs) is largely unknown. The present study therefore set out to investigate the influence of exhaustive exercise, carbohydrate (CHO) feeding and subsequent next‐day steady state (SS) exercise commenced in a ‘graded’ state of muscle glycogen availability on circulating immune markers. Eight healthy active males (mean ± SD: age 25 ± 2 yrs; height 176.3 ± 7.7 cm; body mass 78.7 ± 12.8 kg; 2 peak 45.6 ± 4.2 ml·kg‐1·min‐1) each completed three trials in a randomized crossover design. On each occasion, participants undertook an evening bout of muscle glycogen depleting cycle ergometry, before consuming 7 hours worth of CHO jelly and beverages at a rate of: 0.0 g.kg.h‐1 (LOW), 0.6 g.kg.h‐1 (MED) or 1.2 g.kg.h‐1 (HIG). The following morning, participants returned to perform one hour of SS cycling at 57% peak power output. Skeletal muscle biopsies were obtained pre‐depletion (trial 2), and immediately prior and post SS exercise. Blood samples were collected pre, post, 1 and 2 hours after both exhaustive and SS exercise bouts. Whole blood was used for the analysis of differential leukocyte counts and neutrophil function via the capacity for phagocytosis and production of superoxide following stimulation with opsonized E.Coli. The experimental design successfully produced three ‘graded’ levels of pre‐exercise muscle glycogen available prior to the commencement of SS exercise (p < 0.05). In each condition, lymphocyte/eosinophil count, neutrophil phagocytosis and oxidative burst were all suppressed following both exhaustive and SS exercise bouts (p < 0.05) when compared to pre‐depletion levels, whereas total leukocyte, neutrophil and monocyte counts were all increased (p < 0.05), and highest following SS exercise in the LOW trial (p < 0.05). To conclude, our data demonstrate little benefit for high or moderate CHO‐re‐feeding in the immediate hours following exhaustive exercise on immune function but lowered muscle glycogen may create greater immune disturbance following SS exercise. It may be suggested that CHO availability and its effect on exercise stress and tolerance, rather than a direct effect of CHO itself, confers benefits for immune function and an athlete's susceptibility to URTI's.

Support or Funding Information

This study was funded in part by a BBSRC New Investigator Award BB/L023547/1 to AP
Polyphenol Supplementation Does not Change the Post‐Resistance Exercise Circulating and Intramuscular TNF‐α or TNFR1 Response on Monocyte Subsets
Authors: Jajtner Adam , Hoffman Jay , Townsend Jeremy , Beyer Kyle , Varanoske Alyssa , Church David , Oliveira Leonardo , Herrlinger Kelli , Radom‐Aizik Shlomit , Fukuda David , Stout Jeffrey
Published: November 2023

OBJECTIVE

Examine the effect of a proprietary polyphenol blend (PPB) on the tumor necrosis factor – α (TNF‐α) and TNF receptor 1 (TNFR1) response to resistance exercise.

METHODS

Untrained men (n=38, 22.1±3.1 y; 174.0±7.9 cm; 77.8±14.5 kg) were randomized to: PPB (n=13), placebo (PL; n=15) or control (CON; n=10). PPB and PL were supplemented for 28 days prior to an acute bout of resistance exercise, consisting of 10 repetitions at 70% of the one repetition maximum for the squat (6 sets), leg press (4 sets) and leg extension (4 sets) exercises. Blood was obtained at pre (PRE), immediately (IP), 1 (1H), 5 (5H), 24 (24H) and 48 (48H) hours post‐exercise (PPB/PL), or rest (CON). Biopsies were obtained from the vastus lateralis at PRE, 1H, 5H and 48H. Plasma and intramuscular TNF‐α was assessed by multiplex assay. TNFR1 expression on classical (CLAS; CD14++/CD16−), intermediate (INT; CD14++/CD16+) and nonclassical (NC; CD14+/CD16+) circulating monocytes was assessed via flow cytometry. Repeated measures ANOVA were applied, and non‐normally distributed data were LN transformed. Area under the curve with respect to increase (AUCi) analyses were also performed. Data are presented as mean ± SD.

RESULTS

A time effect was observed for circulating (p=0.018), and intramuscular (p=0.021) TNF‐α. Circulating TNF‐α concentrations increased from PRE (19.4±16.7 pg·ml−1) to IP (23.3±22.7 pg·ml−1; p=0.026), while intramuscular protein content also increased from PRE (0.94±0.68 pg·mg−1) to IP (1.45±0.80 pg·mg−1; p=0.001). A time effect for TNFR1 expression on CLAS was observed (p<0.001), with changes from PRE at 1H (108.5±10.1%; p<0.001), 24H (115.5±24.8%; p=0.001) and 48H (105.6±12.8%; p=0.014). TNFR1 expression on CLAS AUCi was different between groups (p=0.050), with PPB (p=0.020) and PL (p=0.051) greater than CON. A time effect for TNFR1 expression on INT was observed (p<0.001), with changes from PRE at 1H (105.7±8.9%; p=0.001), and 24H (109.8±17.3%; p=0.002). TNFR1 expression on INT AUCi was different between groups (p=0.049) with PPB (p=0.020) and PL (p=0.048) greater than CON. A time effect was also observed for TNFR1 expression on NC (p=0.007), with changes from PR at 24H (108.0±16.0%; p=0.006). TNFR1 expression on NC AUCi was different between groups (p=0.034) with PPB (p=0.019) and PL (p=0.022) greater than CON.

CONCLUSIONS

Data indicate the TNFR1 response to resistance exercise may be biphasic on CLAS and INT with increases at 1H, followed by a return to baseline at 5H, and increases again at 24H. Expression on NC, however, appear to be delayed, with increased expression only observed at 24H. Furthermore, chronic polyphenol supplementation does not appear to impact this post‐exercise response.

Support or Funding Information

Funded by Kemin Foods, L.C.
Influence of physical exercise on skeletal muscle trophism and myostatin signaling in rats subjected to intermittent feeding
Authors: Martinez Paula F , Oliveira Ana Priscila C , Gois Priscilla B , Gomes Mariana J , Pagan Luana U , Morais Camila S , Muzili Nayara A , Ota Gabriel E , Carvalho Marianna R , Souza Albert S , Okoshi Katashi U , Okoshi Marina P , Oliveira‐Junior Silvio A
Published: November 2023

Background

Intermittent feeding (IF) is often used as an alternative to caloric restriction and characterized by alternating cycles of ad libitum feeding and fasting. The main consequence of caloric restriction on skeletal muscle is fiber size reduction, which pathophysiological mechanism is not well known. This study aimed to evaluate the influence of exercise on skeletal muscle morphology and myostatin signaling in rats subjected to intermittent feeding.

Methods

Male Wistar rats (n=40) were allocated into four groups: sedentary control (C‐S), control + physical exercise (C‐Ex), sedentary intermittent feeding (IF‐S), and intermittent feeding + physical exercise (IF‐Ex). The C‐S and C‐Ex groups were fed ad libitum, and IF‐S and IF‐Ex groups had ad libitum access to food on alternating days. Rats from C‐Ex and IF‐Ex underwent into a treadmill‐exercise protocol for 90 days. Functional capacity was assessed by maximal exercise test on treadmill. Myostatin and follistatin protein expression was evaluated by Western blot in soleus and gastrocnemius (white portion) muscles. Statistics: two‐way ANOVA and Tukey.

Results

Functional capacity was improved in exercised groups compared to respective controls. Exercise, as an independent factor, reduced myostatin expression in gastrocnemius muscle (C‐S 1.0±0.3; IF‐S 0.9±0.3; C‐Ex 0.8±0.1; IF‐Ex 0.8±0.1). There was no difference between groups for myostatin expression in soleus muscle, and follistatin expression in both gastrocnemius and soleus muscle. Other results are shown in Table.

Conclusion

Intermittent feeding promotes a physical exercise‐reversible atrophy in soleus muscle, but not in white gastrocnemius muscle of rats. Although myostatin may be modulated by physical exercise, it does not seem to participate on intermittent feeding‐induced muscle atrophy.

Support or Funding Information

Financial support: CAPES

Variables
C‐S
IF‐S
C‐Ex
IF‐Ex

Gastrocnemius mass (g)
2.36±0.28
1.92±0.27*
2.35±0.17
2.12±0.13#†

Soleus mass (g)
0.18±0.03
0.14±02*
0.17±0.02
0.16±0.02

Gastrocnemius CSA (μm2)
3878±308
3156±434*
3667±270
3101±398†

Soleus CSA (μm2)
3982±543
3177±314*
3649±354
3617±160#

CSA: fiber cross‐sectional area. Mean ± standard deviation. Two‐way ANOVA and Tukey;

p<0.05 vs. C‐S;

p<0.05 vs. IF‐S;

p<0.05 vs. C‐Ex.
Strings attached: Sound perception and brain wiring enabled by cadherins
Authors: Sotomayor Marcos
Published: November 2023

Cadherins form a large superfamily of proteins essential for morphogenesis, neuronal connectivity, and tissue integrity. Two atypical members of this superfamily, cadherin‐23 (cdh23) and protocadherin‐15 (pcdh15), are also involved in hereditary deafness and blindness. In the inner ear, these two proteins interact to form the tip link, a fine filament that pulls open transduction channels to initiate a cascade of events leading to sensory perception. Here we present structural, computational, and biophysical experiments that reveal unique properties of the tip link's extracellular cadherin (EC) repeats. Our crystal structures, simulations, and binding assays show how the N‐terminus of pcdh15 and several of its variants form a calcium‐dependent heterophilic complex with the N‐terminus of cdh23. In addition, structures and simulations of other domains of cdh23 and pcdh15 reveal unusual inter‐repeat linker regions that may alter the tertiary structure and elasticity of these proteins. Overall, our results provide a molecular view of tip link mechanics and identify the structural determinants of cdh23 and pcdh15 function in vertebrate mechanosensation.

Support or Funding Information

NIH NIDCD and Alfred P. Sloan Foundation.
Muscle Activation Assessed with Electromyography is Suboptimal During Physical Therapy in Mechanically Ventilated Patients
Authors: Supinski Gerald S. , Netzel Paul F. , Valentine Emily N , Callahan Leigh Ann
Published: November 2023

Physical therapy (PT) is a standard component of care for mechanically ventilated (MV) patients. Recent studies have raised concerns, however, that this treatment may be relatively ineffective. The purpose of the present study was to objectively analyze the effect of PT on leg strength in MV patients. Studies were performed on 22 MV patients receiving PT for 2 weeks. To assess PT intensity, we measured: (a) exercise duration, (b) PT types (range of motion, transfers, exercise machine usage, walking, resistance training), and (c) the intensity of muscle activation using wireless electromyogram (EMG) recordings of four leg muscles. To assess the response to PT, we measured quadriceps force generation evoked by magnetic femoral nerve stimulation. We found that response to PT was poor, and leg strength before and following PT (8.6 ± 3.4 and 7.6 ± 2.8 N) was not significantly different. EMG recordings indicated that patient effort during exercises was also poor. In particular, integrated normalized EMG activity fell substantially over time during training sessions in the majority of patients (the EMG index had a median of 30.3 (25–75% CI of 16.7–46.1) for the initial exercise and decreased to 18.1 (25–75% CI of 2.6–24.4) for the final exercise, p=0.039). There was dramatic patient‐to‐patient variation in the effort made during specific types of PT, resulting in substantial time spent performing ineffective exercises. We also found that, in many cases, the weakest patients received far less PT than patients with normal strength. These data provide a potential explanation why PT in MV patients is largely ineffective. We speculate that use of novel techniques to direct exercises (EMG targeting) and to accurately measure the response to PT (magnetic twitch assessment of strength) may dramatically improve responses of MV patients to PT.

Support or Funding Information

R01HL113494, 5I01BX002132, R01HL112085
An analysis of how consumer physical activity monitors are used in biomedical research
Authors: Wright Stephen P , Collier Scott R , Brown Tyish S , Sandberg Kathryn
Published: November 2023

BACKGROUND

Biomedical researchers are very interested in measuring physical activity because sedentary lifestyle and lack of physical activity are well‐established risk factors for chronic disease and adverse health outcomes. Many consumer physical activity monitors have accuracies similar to research‐grade monitors for measuring steps and offer a relatively new tool for measuring physical activity in an ecological setting.

AIM

To analyze how consumer physical activity monitors are currently used in biomedical research.

METHOD

Searches were conducted in Ovid Medline, PubMed Medline, clinicaltrials.gov, and NIH RePorter using search terms including Fitbit, Jawbone, Apple watch, Garmin, Polar, Microsoftband, Misfit, Nike, Withings, and Xiaomi. Results were quantitated by category: condition/topic, intervention, enrollment status, study type and design, participant age, funding mechanism, and primary outcome.

RESULTS

Fitbit devices were the most common consumer physical activity monitors used in published work (89%), clinical trials (83%), and NIH‐funded research (95%). Validity studies represented the plurality (19/40) of published studies involving consumer physical activity monitors. The design of the majority of clinical trials (116/127) and unique NIH‐funded grants (20/25) involving Fitbit are interventional. The most common primary outcome measure reported in clinical trials using Fitbit is physical activity (50/127), with biomarkers of health (e.g., blood pressure, HbA1c, fasting glucose) being the second most prominent. The most common clinical conditions studied in clinical trials are mental and brain related (74/127), second most being body weight related (62/127).

CONCLUSION

The current state and potential growth of the consumer monitor technology is transforming biomedical research, and is enabling us to ask new and more granular questions about physical activity in health and disease.

Support or Funding Information

This work was supported by the following grants: TL1‐TR001431 (SPW), UL1‐TR001409 (TSHB, SPW, SRC, KS) and R01‐HL119380 (KS).
ADRB2 Variations do not Influence Body Composition in Duchenne Muscular Dystrophy
Authors: Kelley Eli F , Uithoven Katelyn E , Zavala Hanan , Karachunski Peter I , Snyder Eric M
Published: November 2023

Introduction

Duchenne muscular dystrophy (DMD) is an inherited x‐link disease caused by the deletion of the dystrophin gene. DMD is characterized by progressive muscle weakness and degeneration of skeletal, cardiac and respiratory muscles resulting in severe functional impairment. The beta‐2 adrenergic receptor (ADRB2) plays a functional role in muscle size, strength and regeneration through regulation of multiple downstream mechanisms. Multiple polymorphisms of the ADRB2 have been identified as including a glycine (Gly) for arginine (Arg) substitution at amino acid 16. This polymorphism (Gly16) has been shown to have higher receptor density on lymphocytes and be more resistant to receptor down regulation. Although not specifically studied previously, human subjects with the Gly16 polymorphism tend to have a greater body mass index, despite greater fitness levels, possibly suggesting greater muscle mass. Therefore, the Gly16 polymorphism may attenuate skeletal muscle degeneration.

Purpose

To investigate the relationship between ADRB2 genotype and body composition in DMD patients.

Methods

Sixteen patients were recruited through the University of Minnesota Fairview Clinic. DNA was collected via buccal swabs and analyzed for ADRB2 genotype. Medical records were then accessed to obtain retrospective data on dual energy x‐ray absorptiometry (DEXA) body composition measures.

Results

There were no differences between genotype groups in age, height, weight, or BMI (age = 10.8 ± 2.8yrs, 9.8 ± 3.7yrs, 10.9 ± 3.5yrs, height = 138.1 ± 14.6cm, 130.2 ± 17.1cm, 136.6 ± 17.9cm, weight = 52.8 ± 26.5kg, 42.3 ± 25.1kg, 44.8 ± 19.3kg, and BMI = 26.5 ± 7.6, 23.2 ± 9.1, 22.8 ± 5.9, for AA, AG, and GG, respectively). Additionally, there were no differences between genotype groups in lower lumbar density (L1–L4), total body density (TBD), lean body mass (LBM), or lean body mass corrected for body surface area (LBM/BSA) (L1–L4 = 0.74 ± 0.16gm/cm2, 0.62 ± 0.12gm/cm2, 0.68 ± 0.09gm/cm2, TBD = 0.74 ± 0.11gm/cm2, 0.66 ± 0.13gm/cm2, 0.64 ± 0.01gm/cm2, LBM = 55.3 ± 16.7%, 67.7 ± 16.9%, 65.5 ± 19.9%, LBM/BSA = 43.4 ± 23.7, 66 ± 33.8, 59.1 ± 33.8, for AA, AG, and GG, respectively).

Conclusions

Although ADRB2 genotype has been implicated in the regulation of muscle size and strength, these data suggest ADRB2 genotype does not influence body composition in DMD.

Support or Funding Information

NIH grant: 5R01HL108962‐03
Transient cerebral ischemic stroke activates multiple catabolic signaling pathways in skeletal muscle
Authors: Tuntevski Kiril , Alway Stephen E. , Mohamed Junaith S.
Published: November 2023

Stroke is the fifth leading cause of death in the United States, and even with optimal acute therapy, about two‐thirds of the patients remain in a state of incomplete recovery after stroke. Skeletal muscle is the primary target organ of stroke after the brain, therefore muscle atrophy and dysfunction are the leading cause of the functional disability in stroke patients. However, the underlying mechanism that causes the loss of muscle mass and function after stroke have not been investigated in detail. The objective of this study is to identify the mechanism that initiates muscle wasting and impairment in a mouse model of ischemic stroke. Using a mouse model of transient middle cerebral artery occlusion (tMCAO), changes in various catabolic activation in muscle tissue was studied. Muscle wasting (muscle mass), muscle catabolism, and proteasome activity were assessed. Post‐stroke mice displayed severe muscle wasting. Catabolic signaling such as apoptosis, atrophy and autophagy, and proteasome pathways were activated in the ipsilateral leg when compare to the contralateral leg in the post‐stroke mice. Our study indicates that muscle wasting after ischemic stroke is caused mainly by the synergetic activation of multiple catabolic pathways, suggesting that identification of the upstream factor (s) that initiates activation of the above catabolic pathways in response to stroke might provide improved treatment tactics for the stroke patients.

Support or Funding Information

WVU CoBRE Pilot Grant P20 GM109098‐03 (Simpkins, J; PI)
Resistance training with short interval does not induce skeletal muscle hypertrophy in rats
Authors: Takegaki Junya , Kotani Takaya , Ogasawara Riki , Tsutaki Arata , Nakazato Koichi , Ishii Naokata
Published: November 2023

Resistance training is an effective tool for increasing the skeletal muscle mass and strength. The resistance training effect is recognized to depend on the training frequency, together with intensity, volume, etc. However, the detailed response according to the training frequency remains unclear.

Purpose

To see changes in skeletal muscle hypertrophy and relating factors after equal sessions of resistance exercise by changing the training interval.

Methods

Male Sprague‐Dawley rats were randomly assigned into three groups: resistance‐trained with 18 bouts at interval of 72h (72H), 24h (24H), and 8h (8H). The resistance exercise consisted of 50 repetitions of maximal isometric contraction of the gastrocnemius muscle. The right gastrocnemius muscle was used as trained muscle, and the left was used as internal control. The muscle contraction was induced by transcutaneous electrical stimulation under anesthesia. Muscle samples were collected 48h after the final exercise session, and kept frozen until analysis.

Results

Gastrocnemius wet weight was increased in 72H and 24H, but not in 8H. Mitochondria content was increased in 72H and 24H, but not in 8H. The protein ubiquitination was observed in all groups, and the ubiquitination was increased with shortening of training interval.

Conclusion

The present results suggest that resistance training with 8h interval does not cause skeletal muscle hypertrophy, and the hostile environment for anti‐catabolism is one of the possible causes for this.

Support or Funding Information

This work was supported by grants‐in‐aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (15H03078 to N.I.).
Cytokines IL‐6 and LIF can differentially regulate myotube protein synthesis
Authors: GAO SONG , Carson James A.
Published: November 2023

IL‐6 and LIF are members of the IL‐6 family of cytokines that have recognized paradoxical regulatory roles in skeletal muscle mass, but there are gaps in our understanding of the cellular mechanisms that contribute to this regulatory dichotomy. The IL‐6 family of cytokines can induce several upstream regulators of mTORC1, including PI3K/Akt, ERK1/2 and AMPK; these pathways have the ability to regulate muscle mTORC1 signaling and protein synthesis. However, mTORC1 signaling regulation of by the IL‐6 family of cytokines remains poorly understood. Therefore, we investigated the effects of IL‐6 and LIF dose and duration on mTORC1 signaling and protein synthesis in myotubes. C2C12 myotubes were treated with varying doses of IL‐6 or LIF for either a short (1–4h) or long duration (24h). Signaling through the gp130 receptor and downstream effectors, including PI3K/Akt, STAT3 and AMPK were investigated by specific siRNA or pharmaceutical inhibitors administration. The Akt‐mTORC1 signaling axis and protein synthesis was induced by short term IL‐6 or LIF administration, which was blocked by siRNA knock‐down of gp130 receptor or pharmaceutical inhibition of Akt signaling. Interestingly, inhibition of mTOR or STAT3 signaling decreased basal myotube protein synthesis, but did not block the protein synthesis induction by short term IL‐6 or LIF administration. Long term IL‐6 or LIF administration suppressed Akt‐mTORC1 signaling and protein synthesis, which coincided with increased AMPK phosphorylation. However, inhibition of AMPK signaling by siRNA knock‐down did not rescue the protein synthesis suppression by long term IL‐6 or LIF treatment. These results demonstrate that IL‐6 family of cytokines have the capacity to either activate or suppress myotube mTORC1 signaling and protein synthesis, and the ultimate effect depends on the degree of the cytokine exposure.

Support or Funding Information

R01 CA121249 to J. A. Carson from the National Cancer Institute, P20 RR‐017698 to J. A. Carson from National Center for Research Resources Grant
Characterizing the Role of Muscle‐Specific RING Finger 1 (MuRF1) as a Regulator of Atrophy‐Induced Gene Expression
Authors: Kakareka Karina , Waddell David
Published: November 2023

Skeletal muscle wasting occurs as a consequence of numerous physiological conditions, including denervation, immobilization, and aging. The E3 ubiquitin ligases, MuRF1 and MAFbx, are induced under nearly all atrophy conditions and are believed to play a key role in protein degradation. Preliminary data presented here provides intriguing evidence that MuRF1 may also act as a transcriptional modulator of muscle atrophy‐induced gene expression. The transcriptional regulation of MuRF1 and MAFbx were analyzed using a reporter gene system and exhibited repression in C2C12 cells overexpressing MuRF1. Furthermore, ectopic expression of the myogenic regulatory factors (MRFs), MyoD and myogenin, caused significant activation of the MuRF1 and MAFbx reporter gene constructs, while co‐overexpression of MuRF1 with MRFs resulted in reversal of MRF induction of reporter gene activity. Ectopic expression of a catalytically dead MuRF1 RING mutant failed to reverse MRF activation of the reporters, suggesting that ubiquitin ligase activity may be important for MuRF1 transcriptional regulation. In order to further investigate a potential mechanism for MuRF1 modulation of MRF activity, Western blot analysis was performed to analyze MRF protein expression levels in C2C12 cells overexpressing MuRF1 or MuRF1 RING mutant. Cells with ectopic MuRF1 or MuRF1 RING mutant showed repressed levels of myogenin. Additionally, cells overexpressing MuRF1 and MuRF1 RING mutant treated with MG132 showed a modest rescue of myogenin, but myogenin protein levels were still reduced. Finally, chromatin immunoprecipitation (ChIP) was performed in order to analyze MRF occupancy of the MuRF1 promoter. As expected, MRF overexpression resulted in increased MuRF1 promoter immunoprecipitation. Interestingly, co‐overexpression of MuRF1 with MRFs resulted in a reversal of promoter occupancy. These findings suggest that MuRF1 may regulate MRF transcriptional activity by interfering with promoter binding, which provides additional insight into the potential mechanism by which MuRF1 may act to transcriptionally regulate atrophy‐induced gene expression.

Support or Funding Information

This work was supported by University of North Florida Transformational Learning Opportunity Grants to D.W.
Deletion of Kvβ2 Alters Murine Skeletal Muscle Morphology and Phenotype
Authors: Tipparaju Srinivas M , Tur Jared , Chapalamadugu Kalyan C
Published: November 2023

Introduction

Mammalian skeletal muscle expresses various potassium channels that regulate myogenesis. Recent evidence points to the role of Kv1.5 in cell cycle progression in myoblasts as pharmacological inhibition of this channel in L6E9 cells inhibited G0/G1 transition. Additionally, skeletal muscle also expresses voltage‐gated potassium channel beta subunits 1–3 (Kvβ, 2, 3) of aldo‐keto reductases (AK6) family, although their role in skeletal myogenesis is not yet known. Given that Kvβ subunits binds to and regulate members of Kv1 family including Kv1.5, it is plausible that Kvβ subunits play a significant role in skeletal myogenesis.

Hypothesis

we hypothesized that Kvβ2 modulates skeletal myogenesis.

Methods

Age matched, 8–12 week old, wild type (Wt) and Kvβ2 knockout mice (KO) mice were used in this study. Transcript expression analysis of key transcription factors, muscle growth regulators and contractile genes was conducted utilizing real time quantitative PCR (qPCR). Myofiber size was estimated in biceps femoris muscle cross‐sections using Hematoxylin and eosin staining. Protein expression was assessed by Western blots in lysates isolated from Biceps femoris muscle.

Results

Body weight of KO mice recorded at 6, 11 or 16 weeks of age, was significantly (p < 0.05) less than that of age matched Wt mice. Body weight normalized to tibia length in 16 week old KO mice was nearly 30% less than that of age matched Wt mice. Biceps femoris muscle cross‐sections in KO mice revealed significantly smaller myofiber area when compared to that of Wt mice (p < 0.05). Myosin heavy chain mRNA expression profiles were also significantly different between the KO and Wt mice. when compared with that of Wt mice, gastrocnemius and biceps femoris of KO mice showed marginal (p < 0.1) to significantly (p < 0.05) higher expression of myosin heavy chain IIA and IIX isoforms, while myosin heavy chain I mRNA expression was not different between the groups. Soleus muscle of KO mice showed significantly higher myosin heavy chain I expression, while the expression of myosin heavy chain 2B was profoundly (p < 0.05) decreased. Interestingly, the expression of major myogenic regulatory factors was unchanged between the two genotypes, with the exception that MyoD expression showed a consistently decreasing trend in all three muscles of KO mice when compared with that of Wt. In C2C12 cells, Kvβ2 mRNA expression declined steadily during the course of differentiation reaching to approximately 10% of that observed before differentiation (p < 0.05).

Conclusion

Our data suggest that Kvβ2 subunit is essential for skeletal myogenesis. Kvβ2 appear to effect muscle fitness by altering myosin heavy chain composition, suggesting a significant role of Kvβ subunits in skeletal muscle size and phenotype determination.
Does Vehicle Matter on Skeletal Muscle Regeneration Study?
Authors: Srikuea Ratchakrit , Suhatcho Kanokwan
Published: November 2023

Although lipid‐soluble and water‐soluble vehicles were routinely used in research investigation and clinical application, however, whether these vehicles have the effect on skeletal muscle regeneration after intramuscular injection are currently unseeing. Therefore, this study was designed to investigate the effects of intramuscular injections of lipid‐soluble vehicles [olive oil, 40% dimethyl sulfoxide (DMSO), and 40% propylene glycol (PG)] and water‐soluble vehicles [0.9% NaCl, phosphate‐buffered saline (PBS), 0.1% ethanol, and distilled water] on skeletal muscle regenerative capacity. Tibialis anterior muscle of young adult C57BL/6 mice was injured by 1.2% BaCl2 solution to induce skeletal muscle regeneration. Histological analysis on regenerating muscle fiber morphology was evaluated using hematoxylin and eosin staining. Expression of proteins that regulate skeletal muscle regeneration including skeletal muscle stem cell differentiation (myogenin) and regenerative muscle fiber formation (EbMHC) were investigated using immunohistochemical analysis. The results revealed that regenerating muscle fiber morphology, myogenin positive nuclei, and EbMHC protein expression were not significantly changed in almost tested vehicles compared to no vehicle administration. Nevertheless, presence of degenerative muscle fibers paralleled with increased number of myogenin positive nuclei and EbMHC protein expression were evident after intramuscular injections of 40% DMSO and 40% PG. In contrast, this deteriorate effect did not observe after intramuscular injections of 0.9% NaCl and distilled water which were the solutions that used for 40% DMSO and 40% PG preparation in this study. Moreover, the effects of 40% DMSO and 40% PG was comparable with 2% trypsin (degenerative substance) administration. These results suggest that intramuscular injections of 40% DMSO and 40% PG into regenerating muscle could lead to the recurrent of muscle injury during skeletal muscle regeneration. Hence, the applications of DMSO and PG as vehicle for intramuscular injection could potentially affect the experimental results that obtain during skeletal muscle regeneration study.

Support or Funding Information

This research project is supported by Mahidol University.
Regulation Of Histone 3 Acetylation By Intermittent Hypoxia
Authors: Nanduri Jayasri , Wang Ning , Semenza Gregg L , Prabhakar Nanduri R
Published: November 2023

Acetylation of nucleosome core histone proteins determines the structure of chromatin, which regulates the accessibility of DNA sequences to the transcriptional machinery. In general, histone hyperacetylation activates gene transcription and histone hypoacetylation leads to gene silencing. Intermittent hypoxia (IH), a hallmark feature of sleep apnea, induces transcriptional activation of several genes. Whether histone acetylation contributes to IH‐induced gene transcription is not known. The goal of the present study was to determine the effects of IH on histone acetylation and assess the underlying mechanisms. Experiments were performed on rat pheochromocytoma (PC12) cells exposed to alternating cycles of 1.5% O2 for 30 sec followed by 20% O2 for 5 min. Exposure of cells to 60 cycles of IH increased global acetylation of histone 3 (H3) but not histone 4 (H4) in a stimulus‐dependent and reversible manner compared to cell exposed to normoxia (20% O2). Specific lysine residues K9, K14, K18 and K27 contributed to increased H3 acetylation by IH. Histone deacetylase (HDAC) inhibitors mimicked IH‐increased H3 acetylation under normoxic conditions. IH reduced HDAC3 and HDAC5 protein expression. Pharmacological blockade of NADPH oxidase with triazolo pyrimidine (VAS‐2870), a specific Nox inhibitor inhibited the increased H3 acetylation and decreased HDAC expression that were induced by IH. These results suggest that ROS generated by NADPH oxidase triggers IH‐induced HDAC downregulation, leading to increased H3 acetylation.

Support or Funding Information

Supported by NIH‐PO1‐HL90554.
Chronic Intermittent Hypoxia Promotes Multiple Myeloma Development in Black/6 Mice
Authors: Kowkuntla Sandeep , Xu Hongwei , Tomasson Michael H , Bates Melissa
Published: November 2023

Multiple myeloma (MM) is an incurable malignancy of bone marrow plasma B cells and is associated with obesity. Decreased levels of the lipokine adiponectin are associated with disease risk in obese patients with MM, but the mechanisms by which obesity contributes to MM remain unclear. Obesity is also associated with sleep apnea and chronic intermittent hypoxia (CIH) and MM cells develop aggressive features when exposed to hypoxia, so we hypothesized that CIH would facilitate disease progression in a mouse model of MM. 5TGM1 cells are a murine MM cell line derived from KaLwRij strain that fail to engraft efficiently in Black6 strain mice. We injected 5TGM1 MM cells into two cohorts of Black/6 mice, one control and one exposed to intermittent hypoxia for one week prior to injection and another three weeks after injection for a total of four weeks. None of the control mice developed disease after two months, but two of five (40%) CIH mice developed MM disease characterized by hind limb paralysis and bone marrow infiltration with GFP‐positive 5TGM1 cells. These results suggest that CIH may contribute to the development of MM. Further studies are warranted.

Support or Funding Information

University of Iowa Start‐Up Fund
Remodeling of neuronal properties in the preBötzinger Complex (preBötC) causes destabilized rhythm generation following chronic intermittent hypoxia (CIH)
Authors: Garcia Alfredo , Dashevskiy Tatiana , Ramirez Jan‐Marino
Published: November 2023

CIH is a cardinal trait of conditions such as apneas of prematurity and sleep apnea. We have previously reported that CIH increases the irregularity of rhythm generation from the preBötC which leads to failed transmission to hypoglossal motor pool. This ongoing study aims to further understand how CIH affects preBötC neurons responsible for premotor generation of the inspiratory rhythm. Electrophysiological studies were conducted in the preBötC of isolated brainstem slices prepared from mice either exposed to room air or to CIH (10 days). Intracellular recordings from synaptically isolated preBötC neurons reveals that CIH exposure causes an increased rheobase and increased threshold for action potential generation. Moreover, in network, preBötC neurons generated fewer action potentials and tended to fire later during the network burst. Computational modeling of the respiratory network suggests that changes in intrinsic properties of preBötC neurons may alter their firing phenotypes (i.e., tonic vs. silent vs. burster). These may lead to relative changes in network composition that destabilizes rhythm generation. We conclude that intrinsic reconfiguration at the neuronal level is necessary for preserving network rhythm generation when experiencing recurrent perturbation such as CIH.

Support or Funding Information

R01 HL126523; P01 HL090554
Response to Sustained Handgrip Exercise and Post‐Exercise Circulatory Arrest in Renal Denervation Responders and Non‐Responders
Authors: Hearon Christopher M , Howden Erin J , Verhees Myrthe , Lawley Justin S , East Cara , Stickford Abigail , Fu Qi , Levine Benjamin D
Published: November 2023

PURPOSE

Hypertension is characterized by an exaggerated hemodynamic response to sympathoexcitatory stimuli such as exercise and metaboreflex activation. Renal Denervation (RDN) lowers blood pressure in some individuals with resistant hypertension, however the effect of RDN on reflex control of blood pressure remains unclear.

METHODS

A subset of subjects from the simplicity HTN‐3 study who underwent RDN (n=11) were classified as responders (R; n=7, 6M:1F, 61±10 years) or non‐responders (NR; n=4, 3M:1F, 57±4 years) based on a target decrease in office blood pressure of 20mmHg observed on at least 3 occasions post‐RDN (~27 months). Heart rate (HR), mean arterial blood pressure (MAP; plethysmography), and muscle sympathetic nervous system activity (MSNA, microneurography) were measured during supine rest, sustained handgrip exercise to fatigue (HGE; 40% maximal voluntary contraction), and post‐exercise circulatory arrest (PECA; 2 mins). Maximal changes (Δ) in HR, MAP, and MSNA (frequency: burst/min and total MSNA: AU/min) were calculated from baseline in response to HGE and PECA, and comparisons made using unpaired t‐tests and reported as mean ± SEM.

RESULTS

During supine rest, R had lower MAP (R: 97±7; NR: 118±8 mmHg, P<0.05), and similar HR (R: 70±4; NR: 75±9, P=0.26) and MSNA (R: 41.8±4; NR: 41±3 burst/min, P=0.50) compared to NR. During HGE, R had a similar rise in bursts frequency and a larger rise in total MSNA (ΔMSNA: R: 2897±825; NR: 382±573 AU/min, P<0.05) compared to NR. Despite this increase, the HR and BP response to HGE was similar between groups (ΔHR: R: 17±4; NR: 11±3 beats/min; ΔMAP: R: 33±8; NR: 27±7 mmHg, both P>0.05). During PECA, MSNA tended to remain elevated (ΔMSNA: R: 2345±687; NR: 775±493 AU/min, P=0.10) and HR was higher (ΔHR: R: 9±3; NR: −1±2 beats/min, P=0.02) in R compared to NR, while MAP was not different between groups (ΔMAP: R: 25±5; NR: 15±6 mmHg, P=0.21).

CONCLUSION

R had a greater rise in MSNA in response to the same sympathoexcitatory stimuli (HGE, PECA) compared to NR. Despite this larger increase in MSNA, the HR and BP response to HGE and PECA was similar between groups. Thus, RDN may impact both central integration, and end organ responsiveness to sympathoexcitatory stimuli.
Leptin Increases Blood Pressure Acting via Transient Receptor Potential (TRP) Channels in the Carotid Body
Authors: Shin Mi Kyung , Hwang Min Woo , Yeung Bonnie Ho‐yee , Shirahata Machiko , Tang Winnie Wan‐yee , Sham James S.K. , Polotsky Vsevolod Y
Published: November 2023

Rationale

Obesity leads to cardiovascular morbidity and mortality acting via multiple mechanisms including hypertension and obstructive sleep apnea. Obesity leads to high levels of adipokine leptin. Increased leptin levels have been previously reported in sleep apnea and implicated in increased sympathetic activity and the pathogenesis of hypertension. However, mechanisms of the effects of leptin on blood pressure are unclear. The carotid bodies (CB) express leptin receptor (LepR), but the mechanisms and consequences of leptin action in CB are unknown. We have previously demonstrated that leptin enhances carotid sinus nerve activity in response to hypoxia and this effect is abolished by non‐selective blockers of transient receptor potential (TRP) channels (Shirahata et al., 2015). We hypothesized that high levels of circulating leptin signal via LepR in CB leading to hypertension and that leptin's effect is mediated via TRP channels.

Methods

1) Male C57BL/6J mice (n=6) were implanted with telemetry in the left femoral artery for blood pressure monitoring at baseline, during leptin infusion (120ug/day for 3 days via a SC pump) before and after CB denervation; 2) LepR deficient db/db mice were implanted with telemetry; blood pressure measurements were performed followed by infection with adenovirus carrying the LepR gene (Ad‐LepR, n=5) or luciferase (control, Ad‐Luc, n=5) followed by BP measurements; 3) Expression of different TRP channels was measured in CB of wildype C57BL/6J, leptin deficient ob/ob mice and LepR deficient db/db mice; 4) TRP channel expression was measured in db/db mice infected with Ad‐LepR vs Ad‐Luc; 5) blood pressure monitoring was performed in male C57BL/6J mice (n= 9) at baseline, during leptin infusion with or without Trpm7 inhibitor, FTY720 (10mg/kg, sc, n=3) for 24 hrs.

Results

1) In mice with intact CB, leptin increased mean arterial pressure by 13 mm Hg during the day and by 16 mm Hg at night (p = 0.003 for the effect of leptin). CB denervation completely abolished leptin‐induced hypertension (p < 0.001). 2) wildtype C57BL/6J mice showed significantly higher CB expression of Trpm7 compared to ob/ob and db/db mice; 3) LepR expression in CB of db/db mice dramatically increased Trpm7 expression; 4) Trpm7 inhibitor FTY720 abolished leptin‐induced hypertension.

Conclusions

Leptin increases blood pressure by acting via LepR and downstream Trpm7 channels in the CB.

Support or Funding Information

HL133100, HL128970
GPR37L1 Expressed in Renal Proximal Tubule Cells Regulates Sodium Transport
Authors: Konkalmatt Prasad , Zheng Xiaoxu , Asico Larry D , Armando Ines , Jose Pedro A
Published: November 2023

GPR37L1 is a G protein‐coupled receptor that is expressed mainly in brain glial cells and muscle‐myenteric nerve layers in the GI tract. GPR37L1 knockout (KO) mice have increased systolic blood pressure. Prosaposin (PSAP) is a precursor for saposins A, B, C, and D. PSAP was identified as a ligand for GPR37L1 although recent reports showed conflicting results on the role of PSAP as ligand for GPR37L1. There is no report on the expression or function of GPR37L1 in the kidney. Our studies using immunostaining and immunoblotting showed that GPR37L1 is expressed in the apical membrane of mouse renal proximal tubules but not collecting duct cells; RT‐PCR on proximal tubule and collecting duct cells obtained by laser‐capture microdissection of mouse kidney sections, confirmed these findings. Live‐cell imaging of human renal proximal tubule cells (hRPTC) expressing GPR37L1‐GFP protein showed the internalization of the membrane GPR37L1‐GFP following exposure to prosaptide, a 14 amino acid peptide derived from the neurotropic region in the N‐terminal portion of saposin C. cAMP production was increased in hRPTC expressing GPR37L1 treated with prosaptide (4.2 ± 1.4‐fold, P<0.05). In addition, chronic high salt intake increased the renal expression of PSAP suggesting that PSAP is a ligand for GPR37L1 and has a role in renal function. To determine the role of GPR37L1 in renal Na+ transport, we over‐expressed or silenced the expression of GPR37L1 in hRPTC. Over‐ expression of GPR37L1 in hRPTC increased intracellular Na+ (3.2 ± 0.6‐fold, P<0.001) compared with mock‐transfected cells. Treatment with prosaptide blunted the GPR37L1‐ enhanced increase in intracellular Na+, suggesting that prosaptide binding to GPR37L1 may inhibit Na+ entry into the cell. Treatment with a selective NHE3 inhibitor (S3226) decreased intracellular Na+ in GPR37L1‐over expressing, as well as mock‐transfected hRPTC. Treatment with Na+, K+‐ATPase inhibitor (ouabain) showed no effect on the GPR37L1 enhancement of intracellular Na+ in GPR37L1 over‐expressing hRPTC. Silencing of GPR37L1 expression decreased the basal level of intracellular Na+ in the hRPTC. Immunoblot analyses showed increased phosphorylation of Erk1/2 (1.73 ± 0.11‐fold, P<0.05) and ribosomal S6 protein (1.49 ± 0.08‐fold, P<0.01) in hRPTC over‐expressing GPR37L1, compared with mock‐transfected hRPTC. Taken together, these results show that GPR37L1 is expressed in the renal proximal tubule cells, signals via the Erk1/2 pathway, and plays a role in renal Na+ transport and may be a novel target to design drugs to treat patients with hypertension.
High salt promotes NADPH oxidase‐dependent formation and activation of dendritic cells
Authors: Barbaro Natalia , Foss Jason David , Montaniel Kim Ramil , Chen Wei , Harrison David Glenn , Kirabo Annet
Published: November 2023

It has become apparent that sodium can accumulate in the interstitium and promote inflammation through poorly defined mechanisms. We have previously shown that increased NADPH oxidase‐ dependent oxidative stress in dendritic cells (DCs) leads to formation of isolevuglandin (IsoLG)‐ modified proteins which act as neo‐antigens to activate T cells. We hypothesized that increasing sodium chloride (NaCl) in excess of the physiological interstitial space concentrations leads to monocyte differentiation into DCs in an NADPH oxidase‐dependent manner and formation of immunogenic IsoLGs. We exposed murine bone marrow cells to normal physiological NaCl (NS: 150 mM/L), elevated NaCl concentrations (HS: 190 mM/L), or HS plus gp91dstat, an inhibitor of the NADPH oxidase assembly. Compared to NS, HS significantly increased the number cells expressing the DC marker CD11c (NS: 14.4 ± 7.0 vs HS: 52 ± 11.7 % p<0.001), and this was prevented by co‐treatment with gp91dstat (39.8 ± 16.0 p<0.05 vs HS). In additional experiments, we found that exposure of monocytes isolated from human volunteers to HS, but not mannitol, caused a 2‐fold increase in formation of IsoLG‐modified proteins. This was associated with an increase in activation marker CD86 (NS: 466 ± 192 vs HS: 596 ± 324 MFI p<0.05) and production of inflammatory cytokines IL‐6, IL‐β and TNF‐α. Interestingly, these cells expressed surface markers indicative of transformation to activated DCs, as evidenced by their acquisition of surface marker CD83. In additional studies, we found that monocytes exposed to high salt for 7 days acquire a DC like morphology. Moreover, using flow cytometry, we confirmed that high salt exposure causes these cells to lose the monocyte marker CD14 (NS: 41.1 ± 15.4 vs HS: 19.9 ± 6.4 MFI; p<0.05), and gain the DC marker CD209 (NS: 24.2 ± 1.0 vs HS: 49.3 ± 0.7 MFI; p<0.001). Co‐treatment with gp91dstat and scavenging of IsoLGs during high salt exposure prevented conversion of monocytes into DCs. High salt dramatically increased mRNA expression of GM‐CSF (NS: 758 ± 440.8 vs HS: 5476 ± 2268 MFI; p<0.05), IL‐4 NS: 1868 ± 560.6 vs HS: 4867 ± 1152 MFI; p<0.05) and Flt3 (NS: 2526 ± 636.8 vs HS: 10014 ± 2370 MFI; p<0.05), which are known to mediate monocyte conversion to DCs. Thus, we have defined a novel pathway whereby high NaCl concentrations lead to transformation of monocytes to DCs due to increased formation of immunogenic isoketals. These observations provide insight into how elevated sodium environments lead to an inflammatory state.

Support or Funding Information

This work was supported by the American Heart Association grants 16POST29090001 and 14SFRN20420046, and National Institutes of Health grants 1K01HL13049701, 1R01HL12586501, and 5R01HL03900626