bluuebunny/crossref_metadata_2025_split huggingface dataset:
Active Shortening Protects Against Stretch‐Induced Force Deficits in Human Skeletal Muscle
Authors: Saripalli Anjali L. , Sugg Kristoffer B. , Mendias Christopher L. , Brooks Susan V. , Claflin Dennis R. 
Published: November 2023

Skeletal muscle contraction results from molecular interactions of myosin “crossbridges” with adjacent actin filament binding sites. The binding of myosin to actin can be “weak” or “strong”, and only strong binding states contribute to force production. During active shortening, the number of strongly‐bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences whereas stretch of an isometrically (fixed‐length) contracting muscle causes ultrastructural damage and a decline in force‐generating capability. Our working hypothesis is that stretch‐induced damage is uniquely attributable to the population of crossbridges that are strongly‐bound. We tested the hypothesis that stretch‐induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and either allowed to generate maximum isometric force (Fo), or to shorten at velocities that resulted in force maintenance of ≈50% Fo or ≈2% Fo. For each test condition, a rapid stretch equivalent to 0.1 × optimal fiber length was applied. Relative to pre‐stretch Fo, force deficits resulting from stretches applied during force maintenance of 100%, ≈50%, and ≈2% Fo were 23.2 ± 8.6%, 7.8 ± 4.2% and 0.3 ± 3.3%, respectively (mean ± SD, n=20). We conclude that stretch‐induced damage declines with increasing shortening velocity, in support of the possibility that the fraction of strongly‐bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch‐induced damage.Support or Funding InformationNIH R01‐AG050676, R01‐AR063649, F32‐AR067086
Human Skeletal Muscle Proteins and Metabolic Pathways are Susceptible to Dicarbonyl Stress
Authors: Mey Jacob T , Haus Jacob M 
Published: November 2023

INTRODUCTIONIndividuals with Type 2 Diabetes Mellitus (T2DM) present with hyperglycemia concomitant with increased generation of methylglyoxal (MG), a highly reactive dicarbonyl and glycolytic intermediate. MG modifies proteins at arginine residues creating the advanced glycation endproduct methylglyoxal‐derived hydroimidazolone (MG‐H1). Accumulation of MG‐modified proteins has been referred to as dicarbonyl stress and has been implicated in the etiology of T2DM and development of future complications. The mechanisms and tissue specificity underlying MG‐directed protein modifications are largely unknown, but MG has been hypothesized to target the regulatory gamma subunit of AMPK (AMPKγ), due to exposed arginine residues within the AMPKγ catalytic site.PURPOSETherefore, the purpose of this study was to investigate the effects of hyperglycemia or exogenous MG treatment on the formation of total MG‐modified proteins and specific AMPKγ protein modifications in primary human skeletal muscle cells (HSKMCs). Skeletal muscle tissue was selected given the paucity of evidence and the importance to whole body glucose metabolism.METHODSHSKMCs were incubated in euglycemic (5.5mM glucose) or hyperglycemic (30mM glucose) media and total MG‐directed protein modifications were assessed at 24 hrs and 5 days in cell lysates via immunoblotting of MG‐H1 residues. Specific MG‐modifications of AMPKγ were assessed by incubating HSKMCs in MG‐supplemented media (0, 5, 50, 100, or 500μM MG) for 4 hours after which AMPKγ was immunoprecipitated and immunoblotted for MG‐H1 residues. We also examined the effects of MG treatment on AMPK activity, with and without AICAR stimulation (2mM), as assessed by the expression of phosphorylated acetyl coa carboxylase β (pACCβ), a commonly used surrogate marker for AMPK activity in skeletal muscle.RESULTSHyperglycemia showed no effect on total MG‐modified proteins at 24 hrs (p>0.05), but increased MG‐modified proteins by 50±18% (p<0.035) at 5 days. Experimental MG treatment did not increase MG‐modifications of AMPKγ at any MG concentration. However, ACCβ phosphorylation increased in stepwise fashion with increasing MG concentrations, becoming significant at 10μM (141±4%, p=0.0066), 50 μM (202±9%, p=0.0007) and peaking at 100μM (342±27%, p=0.0010). Interestingly, pre‐incubating HSKMCs with low dose MG (10μM) was additive to AICAR stimulated AMPK activity as the combination increased pACCβ expression by 24±4% compared to AICAR alone (p=0.011). However, pre‐incubating cells with MG at high doses showed no additional effect or abolished pACC expression (500μM, no different from Control).CONCLUSIONThese data suggest that hyperglycemia increases dicarbonyl stress in HSKMCs and that exogenous MG treatment augments AMPK activity in the absence of AMPKγ specific MG‐modifications. The biphasic response in AMPK activity in response to exogenous MG requires further investigation.
Development of a chronic irradiation and simulated microgravity facility
Authors: Chowdhury Parimal , Griffin Robert J. , Narayanasamy Ganesh , Pathak Rupak , Hauer‐Jensen Martin , Boerma Marjan , Dobretsov Maxim 
Published: November 2023

Chronic irradiation (IR) and microgravity (MG) are associated with multiple physiological, cellular, molecular, and genetic alterations and thus it is a risk factor during long term human space exploration missions. However, studies on the combined effects of chronic IR and MG on biological systems are largely unknown, because of lack of appropriate facilities. Ground based studies on in‐vivo or/in‐vitro models of simulated MG (SMG) have targeted studies on acute exposure to IR (and usually at relatively high doses). In contrast, relatively few studies with hind‐limb suspended rodents (model of SMG) studies were conducted at various time points following a single or repetitive exposure to IR. The effects of chronic low dose IR administered under conditions of SMG or without are even less studied. Thus in order to study the effects of chronic SMG and IR administered either in combination or in isolation we have planned to build a facility capable of delivering both stresses to small animals. Our approach calls for immediate need of developing facilities in which space flight conditions (SMG and continuous low grade IR with occasional bursts of IR (solar sparks) can be mimicked with a reasonable reliability. Here we discuss the minimal requirements for such facility and provide further arguments showing that without such facility we will unlikely be able to address the question about combined and dissociated effects of IR and MG on human health. Furthermore, having the facility will allow enhanced development of targeted countermeasures diminishing the deteriorating effects of prolonged space flight on human crew health and operational capacity.Support or Funding InformationArkansas Space Grant Consortium
Contribution of Prostaglandins to the Inspiratory Muscle Metaboreflex‐Induced Cardiovascular Consequences
Authors: Smith Joshua R , Didier Kaylin D , Hammer Shane M , Alexander Andrew M , Kurti Stephanie P , Barstow Thomas J , Harms Craig A 
Published: November 2023

Activation of the inspiratory muscle metaboreflex leads to increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) as well as decreases in limb blood flow (Q̇L). Inhibition of prostaglandin synthesis has previously been shown to attenuate skeletal muscle metaboreflex‐induced increases in muscle sympathetic nerve activity. However, it is not known if inhibition of prostaglandins will also attenuate the cardiovascular consequences of the inspiratory muscle metaboreflex.PurposeThe purpose of this study was to determine the contribution of prostaglandins to the inspiratory muscle metaboreflex. We hypothesized that compared to placebo, inhibition of prostaglandin synthesis would attenuate inspiratory muscle metaboreflex‐induced1) increases in MAP and LVR and 2) decreases in Q̇L.MethodsSeven college‐aged men were recruited and visited the laboratory on three different occasions. Subjects orally consumed ibuprofen (IB, 10mg/kg) or placebo (PLA) 90min prior to a cold pressor test (CPT) and inspiratory resistive breathing task (IRBT) at 65% of their maximal inspiratory mouth pressure. During the IRBTs, the breathing frequency was 20 breaths per min with a 50% duty cycle. At rest and during the IRBTs, MAP was measured via automated oscillometry, Q̇L was measured via Doppler ultrasound, and LVR was calculated. End tidal CO2 remained at baseline levels during the IRBTs. EMG was recorded on the leg to ensure no muscle contraction occurred.ResultsDuring the 65% IRBT, compared to PLA, IB led to greater (p<0.01) increases in MAP (IB: 16.8±6.7 mmHg; PLA: 8.4±4.7 mmHg) and LVR (IB: 68.6±27.7 %; PLA: 51.7±22.2 %). The decrease in Q̇L was not different (p=0.72) between IB (−27.7±11.0 %) and PLA (−26.7±9.3 %). The increase in MAP during the CPT was not different (p=0.87) between IB (IB: 24.7±10.9 mmHg) and PLA (PLA: 24.1±5.9 mmHg).ConclusionContrary to our hypotheses, inhibition of prostaglandin synthesis, via ibuprofen, led to greater inspiratory muscle metaboreflex‐induced increases in MAP and LVR.Support or Funding InformationSupported by ACSM Foundation Doctoral Grant
The role played by oxidative stress in evoking the exercise pressor reflex in health and simulated peripheral artery disease
Authors: Harms Jonathan E , Kim Joyce S , Kuczmarski J Matthew , Thomas Gail D , Kaufman Marc P 
Published: November 2023

Contraction of skeletal muscle evokes the exercise pressor reflex (EPR), which is expressed in part by increases in heart rate and arterial pressure. Patients with peripheral artery disease (PAD) show an exaggerated EPR, sometimes report pain when walking and have an increased risk for cardiac arrthymias. Previous research has suggested that reactive oxygen species (ROS) mediate the exaggerated EPR associated with PAD. To examine the effects of ROS on the exercise pressor reflex, we infused a superoxide scavenger, Tiron, into the superficial epigastric artery of decerebrated rats. In some of these rats, we simulated PAD by ligating a femoral artery for 72 hours before the experiment. The peak EPR in ligated rats during saline infusion into the superficial epigastric artery averaged 31 ± 4 mmHg; n=12), whereas the peak EPR in these rats during Tiron infusion (1g/kg/hour) averaged (13 ± 2; p<0.001); the attenuating effect of Tiron on the EPR was partly reversed when saline was reinfused into the superficial epigastric artery (21 ± 2; p<0.01 vs tiron). Tiron infusion had no effect on the EPR in rats with patent femoral arteries (n=9). Western blots showed that the triceps surae muscles taken from rats whose femoral arteries were ligated expressed more Nox2 and p67phox, which are components of NADPH oxidase, than did triceps surae muscles taken from rats whose femoral arteries were freely perfused. Tiron added to muscle homogenates reduced ROS production in vitro. Our results provide further evidence that ROS mediates the exaggeration of EPR in rats with simulated PAD.Support or Funding InformationFunded by NIH R01 AR059397, NIH R01 HL130987, and NIH P01 HL096570
Sestrin 2 and 3 Gene Expressions Correlate with Homeostasis Model Assessment of Insulin Resistance and Beta Cell Secretory Status in Older Men
Authors: Zeng Nina , Sharma Pankaja , Ramzan Farha , Mitchell Sarah M. , D'Souza Randall F. , Prodhan Utpal , Milan Amber M. , Mitchell Cameron J. , Cameron‐Smith David 
Published: November 2023

Sestrins are a family of stress‐inducible proteins composed of three members (Sesn 1/2/3). They are involved in many physiological processes such as protecting organisms against oxidative stress by acting as antioxidants and playing a critical role in metabolic and glucose homeostasis by activating AMP‐activated Protein Kinase (AMPK), Mammalian Target of Rapamycin Complex 2 (mTORC2) and inhibiting mTORC1. Sesn3 has been observed to be upregulated in muscle biopsies obtained from patients with type 2 diabetes. Recent identification of the 3D structure of the human Sestrin 2 revealed a leucine‐binding pocket in its C‐terminal domain, suggesting a role as an intracellular leucine sensor.The objective of the study was to further characterise the gene expression of each individual Sestrin members in the skeletal muscle of a non‐diabetic population.Fasted plasma and muscle biopsies from vastus lateralis were collected from twenty‐eight men (74.1 ± 3.6 years). Plasma levels of fasting amino acid, glucose, insulin and lipid profiles were characterised. The Homeostasis Model Assessment (HOMA) software was used to estimate insulin sensitivity (HOMA %S) and beta cell secretory status (HOMA %B), as percentages of a normal reference population. The gene expressions of Sesn 1/2/3 were determined and correlated with the baseline blood chemistry and HOMA‐index.The average HOMA%S of the subjects was 94.0 ± 44.0 % and HOMA%B was 86.2 ± 20.2%, while insulin resistance (HOMA‐IR) was 1.3 ± 0.6. HOMA‐IR and HOMA%B were positively correlated with body mass index, waist circumference, body fat mass, percent body fat and triglyceride (all p values <0.05 and r >0.45).The gene expressions of Sesn2/3 correlated positively with insulin (p=0.03, 0.04; r=0.42, 0.39); HOMA‐IR (p= 0.04, 0.05; r=0.40, 0.38) and HOMA%B (p=0.002, 0.03; r=0.57, 0.41) respectively. Circulating baseline leucine concentration correlated positively with only Sesn 2 (p=0.01, r=0.45). Furthermore, the gene expressions of Sesn1 did not correlate with Sesn2/3.Although Sesn 1/2/3 share strong sequence homology, their expressed genes are differentially regulated, with Sesn2 correlating to plasma leucine, whilst Sens2 and 3 correlate to insulin sensitivity. Each Sestrin paralog appears to play a unique physiological role.
Muscle‐Specific Calpastatin Overexpression Prevents Sarcopenia of Aging
Authors: Schroder Elizabeth A , Song Xiao‐Hong , Wang Lin , Supinski Gerald S , Callahan Leigh Ann 
Published: November 2023

Sarcopenia is a major cause of disability. The precise mechanisms responsible for aging‐related muscle weakness and atrophy are not known. However, recent studies suggest that pathologic activation of calpain modulates skeletal muscle dysfunction in aging. We tested the hypothesis that skeletal muscle‐specific overexpression of calpastatin, the endogenous inhibitor of calpain, would ameliorate aging‐associated decrements in muscle function. Five month old and 25 month old wild type (WT) and muscle‐specific calpastatin overexpressing (CalpOX) male mice (n=23) were studied. Grip strength was used as an index of total forelimb strength. To assess hindlimb strength, we measured extensor digitorum longus (EDL) mass and muscle specific force generation. Aging significantly reduced fore‐limb grip strength (0.94 ± 0.06 vs 1.47 ± 0.06N for old WT vs young WT, respectively, p<0.001). Importantly, calpastatin overexpression mitigated the aging‐induced reductions in fore‐limb grip strength (0.94 ± 0.06 vs 1.22 ± 0.05 for old WT vs old CalpOX, respectively, p=0.007). Aging also induced loss of EDL mass; calpastatin overexpression significantly ameliorated these reductions (7.63 ± 0.33 vs. 9.17 ± 0.45 mg for old WT vs old CalpOX, respectively, p=0.02). While calpastatin overexpression increased EDL muscle mass, EDL force per unit mass was similar between old WT and old CalpOX animals. To our knowledge, this is the first report of the effects of muscle‐specific calpastatin overexpression on skeletal muscle function in aging rodents. These findings support the concept that calpain activation plays a role in aging‐induced sarcopenia. We speculate that therapeutic agents which attenuate calpain activation may preserve muscle function in the elderly.Support or Funding InformationR01HL112085, 5I01BX002132, R01HL113494
Hypothalamic Pathways Involved in Adenosine A1 Receptor Agonist‐Induced Hibernation in the Arctic Ground Squirrel (Urocitellus paryii)
Authors: Frare Carla , Drew Kelly L. 
Published: November 2023

Hibernation is an adaptive strategy characterized by metabolic suppression and regulation of thermogenesis to maintain energy balance in adverse environmental conditions. Previous study shows the role of adenosine A1 receptor agonist in promoting hibernation in the arctic ground squirrels. N6‐cyclohexyladenosine (CHA), an adenosine A1 receptor agonist, suppresses thermogenesis in a seasonally dependent manner. CHA induces hibernation in winter, while the effect is transient in summer: arctic ground squirrels counteract an initial decrease in metabolism restoring their euthermic values. These observations suggest that a higher order process regulates the seasonal CHA‐response, but if this phenomenon is driven by a seasonal modulation of thermogenesis is not known. The hypothalamus controls energy homeostasis regulating thermogenesis, in part, via the hypothalamic‐pituitary‐thyroid (HPT) axis. The intent of this research is to identify the hypothalamic nuclei activated in a seasonally dependent manner in response to CHA. Arctic ground squirrels were treated with CHA or vehicle at different seasonal points (summer and winter) and brains were collected 3h after treatment. Immunohistochemistry was used to localize active nuclei as indicated by cFos‐immunoreactivity (mouse anti‐cFos 1:20,000, Santa Cruz) focusing on the nuclei involved in thermoregulation and energy homeostasis. Specific markers (e.g. rabbit anti pro‐TRH 1:10,000 gift from Eva Redei) were used to define the phenotype of cFos‐ir neurons. Data show similar cFos‐ir in the paraventricular nucleus. These results suggest that mechanisms downstream to hypothalamic modulation of thermogenesis contribute to the higher order process regulating the seasonal CHA‐response.Support or Funding InformationNIH R15NS070779 and Alaska INBRE P20GM103395
AICAR Attenuates Olanzapine‐Induced Hyperglycaemia and Insulin Resistance in C57BL6 Mice
Authors: Bush Natasha , Castellani Laura , Wright David C 
Published: November 2023

Olanzapine (OLZ), an antipsychotic drug used in the treatment of schizophrenia, induces undesirable side effects including hyperglycaemia, glucose intolerance, dyslipidaemia, weight gain and insulin resistance, often resulting in the development of Type 2 Diabetes (T2D). The acute effects of OLZ on blood glucose are likely caused by a reduction in insulin secretion, the development of insulin resistance and increases in liver glucose production. 5′AMP‐activated protein kinase (AMPK) is a cellular energy sensor activated during exercise that has been shown to increase insulin sensitivity and increase insulin‐independent glucose uptake. Though having some off‐target effects, 5‐aminoimidazole‐4‐carboxamide riboside (AICAR) is a pharmacological agent that can activate AMPK in vivo. The purpose of this investigation was to determine if co‐treatment with AICAR would prevent acute OLZ‐induced increases in blood glucose in C57BL6 mice. AMPK and ACC phosphorylation was increased in liver, epididymal adipose tissue and triceps muscles 30 minutes following an injection of (AICAR) (250 mg/kg, IP injection) compared to vehicle treated mice. OLZ (5 mg/kg) caused rapid (15 minutes) and sustained increases in blood glucose that was prevented with AICAR co‐treatment. Treatment with OLZ attenuated the ability of insulin (0.75 U/kg, IP) to reduce blood glucose levels and this was partially prevented by AICAR. OLZ led to an exaggerated increase in blood glucose during a pyruvate tolerance test (2 g/kg, IP) and this was mitigated by AICAR. The results of the current study provide evidence that AICAR prevents OLZ‐induced hyperglycemia by preventing the development of peripheral insulin resistance and blunting increases in liver glucose output.Support or Funding InformationD.C.W. is a Tier II Canada Research Chair. This research was funded by a NSERC Discovery Grant to D.C.W. N.B. was funded by CGS‐M (CIHR).
The Cellular Response to C‐peptide is Dependent on the Concentration of Glucose and Insulin
Authors: Rossiter Jackie Lee , Kolar Grant R , Yosten Gina LC 
Published: November 2023

The role of insulin in the regulation of blood glucose has been the subject of extensive research. Insulin and C‐peptide, a 31 amino acid peptide, are co‐produced and co‐secreted by pancreatic beta islet cells. In 2013, a candidate receptor for C‐peptide was identified by our group to be the G‐protein coupled receptor, GPR 146. On release the relative concentrations of insulin to C‐peptide are 1:1, however due to differences in sites and rates of catabolism, in plasma the relative ratios of insulin to C‐peptide are 1:5. There is a growing body of evidence to support a physiologic role for C‐peptide in the prevention of co‐morbidities associated with microvascular damage in individuals with diabetes. These co‐morbidities include increased incidence of cardiovascular disease, retinopathies, renal failure and poor wound healing. We hypothesized that the cellular response to C‐peptide is dependent on the relative concentrations of C‐peptide, glucose, and insulin. In this study, HEK293 cells were incubated with varying levels of glucose (40 mg/dl, 115mg/dl, or 450 mg/dl), C‐peptide (0, 0.1nM, 1.0nM, or 10nM), or insulin (0, 100pM, 1000pM, or 2000pM). HEK293 cell responses were evaluated by comparing relative levels of cFOS, GPR146, and insulin receptor (IR) mRNA expression. Incubation of HEK293 in high glucose with basal levels (0.1nM) of C‐peptide resulted in HEK293 activation as measured by cFOS mRNA. Basal (0.1nM) C‐peptide induces production of GPR146 mRNA in conditions of low and high glucose but had no significant effect in normal glucose conditions. However, for HEK293 cells incubated with basal C‐peptide and high glucose, the addition of insulin ameliorated cellular activation induced by C‐peptide. Thus, the cellular responses to C‐peptide were dependent on ambient levels of glucose and insulin. These findings have important implications for the development of C‐peptide based therapies. C‐peptide therapeutics may be of benefit in high glucose conditions, however those benefits may be confounded the presence of exogenous insulin that exceeds physiologic parameters of insulin to C‐peptide (1:5).Support or Funding InformationHL121456
Effect of resistance exercise training in mitophagy of diabetic rats
Authors: Jorge luciana , Silva Kleiton Augusto , Luiz Rafael S , Rampaso Rodolfo R , Schor Nestor 
Published: November 2023

Diabetic nephropathy (DN) is a progressive complication arising from diabetes. The repertoire of kidney cell response to injury includes cell division, cell hypertrophy, apoptosis and mitochondrial dysfunction. Increasing evidence indicates that the disruption of mitochondrial may be important in the development and progression of DN. On the other hand, the resistance exercise training is fundamental as non‐pharmacological intervention to prevent those complications. In this study, we investigated the effect of resistance exercise training (RET) on the DN pathogenesis. Male Wistar rats were divided into 4 groups: control (C=8), control trained (CT=8), diabetic (D=8) and diabetic trained (DT=8). Diabetes Mellitus (DM) (glycemia>250mg/dL) was induced by streptozootocina (STZ) (50mg/kg, i.v.). Trained groups were submitted to resistance exercise training protocol on ladder climb for 8 weeks. DN were accompanied by urinary volume and microalbuminuria and the expression of DRP‐1 and LC3 protein was evaluated by western blotting. The results indicate RET improved renal parameters in the DT group showing a decreased urinary volume (DS:160; DT:120; CS:13 and CT:14ml), microalbuminuria (DS:8.7; DT:4.7; CS:1.5; CT:2.3mg/24h). The renal expression of DRP‐1 and LC3 were enhanced in DS group and RET normalized this expression. Our findings demonstrated that RET increases in physical capacity and mitochondrial and renal benefits following training protocol, regardless of any improvement in glycemic controlSupport or Funding InformationCNPQ, CAPES, Fapesp, FOC