bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metformin Normalises Medullary Hypoxia in The Diabetic Rat Kidney
Authors: Christensen Michael , Schiffer Tomas , Nørregaard Rikke , Palm Fredrik 
Published: November 2023

BackgroundMetformin is the first choice treatment of type‐2 diabetes where it can lower the level of blood glucose by inhibiting hepatic gluconeogenesis and increase cellular glucose uptake. Besides the effect on blood glucose metformin has also shown protective effects in several renal diseases including diabetic nephropathy. The development of hypoxia in the kidney is suggested to be an important driving force for the development of diabetic nephropathy and we therefore wanted to investigate how metformin affects the oxygenation levels and mitochondrial function in the diabetic kidney.MethodsSprague Dawley rats were injected with streptozotocin (STZ) (50 mg/kg) and when rats were diabetic, metformin (250 mg/kg) was administrated in the drinking water. Rats were prepared for In Vivo measurements 25–30 days after STZ injection. Rats were anesthetized, placed on a heating pad, tracheotomized and a catheter was placed in the left femoral vein for infusion of Ringer solution containing H‐inulin and Para‐aminohippurate. The left femoral artery was catheterized for blood pressure measurements and blood sampling. The left kidney was exposed by a subcostal flank incision, immobilized in a plastic cup and catheters were placed in the left ureter as well as bladder for collection of urine. Intrarenal pO2 was measured in kidney cortex and medulla by oxygen microsensors. To assess mitochondrial function, mitochondria were isolated from kidney cortex and medulla and analyzed by high‐resolution respirometry (Oroboros, O2‐K)Important findingsDiabetic rats showed increased glomerular filtration rate (GFR), which was not affected by metformin treatment. PO2 was lower both in the outer medulla as well as cortex in the diabetic animals. Metformin treatment elevated PO2 in the outer medulla both in the control animals as well as in the diabetic animals. Isolated mitochondria from the outer medulla of diabetic rats showed a significantly higher GDP dependent respiration which was normalized by metformin treatment indicating inhibition of uncoupling protein 2 (UCP2) activity.ConclusionMetformin increases PO2 in the outer medulla both in control and diabetic animals, this could in part be mediated by inhibition of UCP2.
In Vivo Knockdown of I‐mfa Using The Targeted Nanoparticle Delivery System Ameliorated Renal Injury in Diabetic Mice
Authors: Ma Yuhong , Li Weizu , Jiang Hui , Wang Yanxia , Zuckerman Jonathan , Davis Mark , Ma Rong 
Published: November 2023

Accumulation of extracellular matrix (ECM) proteins in glomerulus is one of early features of diabetic nephropathy. Glomerular mesangial cell (MC) is the major source of ECM. Inhibitor of Myogenic Family isoform a (I‐mfa) is a cytosolic protein interacting with components of Wnt/β‐catenin pathway and of store‐operated Ca2+ signaling pathway, both of which are involved in the development of diabetic nephropathy. The present study was carried out to determine if I‐mfa in MCs contributed to renal injury in diabetic mice. Twelve male mice were randomly divided into 4 groups (3 mice each group): non‐diabetes, diabetes, diabetes treated with scramble siRNA, and diabetes treated with siRNA against I‐mfa. Diabetes was generated by multiple low‐dose streptozotocin (STZ, 50 mg/kg) injections (intraperitoneal, once one day for 5 days) at an age of 6 weeks. Mice in group of non diabetes were injected with 10 mM citrate buffer (vehicle). Diabetes was indicated by a fasting blood glucose level of > 300 mg/dl. Scramble or I‐mfa siRNA treatment started 24 weeks after STZ injection and the treatment lasted 2 weeks. All siRNAs (10 mg/kg body weight) were delivered by our recently established‐targeted nanoparticle/siRNA delivery system which is glomerular mesangial cell specific. We found that STZ treatment significantly increased blood glucose level after 4 weeks of injection and reduced body weight 26 weeks after treatment. I‐mfa siRNA treatment did not improve hyperglycemia, but lessened renal hypertrophy in STZ mice. Furthermore, diabetic mice showed significantly greater 24 hour urine output and this diabetic uresis was compromised by I‐mfa siRNA treatment. Although knocking down I‐mfa did not mitigate albuminuria, it lowered the level of blood urea nitrogen in diabetic mice. Consistent with the functional data, histological examination showed improved mesangial expansion and glomerular fibrosis in I‐mfa siRNA‐treated STZ mice. Immunohistochemical examination showed a significant reduction of protein abundance of glomerular fibronectin and collagen IV in the siRNA‐treated diabetic mice. Taken together, our data indicate that I‐mfa in MCs is involved in the development of diabetic kidney disease and thus, could be a potential therapeutic target for diabetic nephropathy.Support or Funding InformationAHA Southwestern Affiliate; Harry S. Moss Heart Trust; University Outstanding Talent Cultivated Projects of Anhui Province, China (gxfxZD2016118 and gxfxZD2016162)
GYY4137 modulates plasminogen activator inhibitor‐1‐dependent extracelluar matrix turnover in diabetic kidney via RAR/RXR signaling
Authors: John AM Sashi Papu , Pushpakumar Sathnur , Sen Utpal 
Published: November 2023

IntroductionDiabetic kidney is associated with dysregulation of retinoic acid metabolism. Retinoic acid receptor (RARs) and Retinoid X receptor (RXRs) are nuclear receptors that function as transcriptional regulators of several genes involved in renal pathology; however, their role in the development of renal fibrosis in diabetes remains unknown. Further, peroxisome proliferator‐activated receptors (PPARs) and RAR is known to control RXR signaling leading to differential gene expression. A recent study has also linked RAR and RXR to increased expression of Plasminogen activator inhibitor‐1 (PAI‐1), a serine protease implicated in extracellular matrix (ECM) accumulation in diabetic nephropathy (DN). Hydrogen sulfide (H2S), a gasotransmitter with potent antioxidant and anti‐inflammatory property has been shown to mitigate adverse effects in DN; however, its role in targeting other molecular events in ECM turnover remains unexplored. The purpose of this study was to determine the role of RAR and RXR in the progression of DN and whether GYY4137, a H2S donor can mitigate ECM accumulation by modulation of PPAR/RAR controlled RXR signaling.MethodsC57BL6/‐Ins2Akita/J, (Akita) mice representing type‐I diabetes and C57BL6/J (WT) mice were treated without or with GYY4137 (0.5 mg/Kg/d, IP, × 8 weeks). In vitro studies were done in mouse glomerular endothelial cells (MGECs) and treated with GYY4137 (250uM) for 24 h.ResultsIn diabetic kidneys, the mRNA and protein expression of PPARγ was decreased and the expressions of RARs, RXRs and PAI‐1 were upregulated. Diabetic kidneys demonstrated increased matrix metalloproteinase‐9 expression and activity. Further, MMP‐13 was upregulated in diabetic mice. Immunohistochemistry showed increased collagen IV, laminin and fibronectin in the glomerular and interstitial areas. GYY4137 treatment reversed the changes above. In vitro studies demonstrated that PPARγ antagonism and RAR agonism in MGECs resulted in increased RXR signaling and PAI‐1 expression and was reversed following GYY4137 treatment. In addition, GYY4137 reduced the mRNA levels of Collagen IV, laminin and fibronectin and normalized the levels of elastin.In conclusion, our data suggests that RXR signaling plays a significant role in excessive ECM turnover and GYY4137 modulates RXR signaling to reduce PAI‐1 mediated renal fibrosis in type‐I diabetes.Support or Funding InformationDK104653, HL104103 and 15SDG25840013
A ventral medial prefrontal cortex–dorsomedial hypothalamus monosynaptic pathway that drives sympathetic stress responses
Authors: Kataoka Naoya , Nakamura Kazuhiro 
Published: November 2023

Psychological stress causes a variety of sympathetic responses in mammals, which help the body react quickly and effectively to the stressor. We have reported that stress induces thermogenesis in brown adipose tissue (BAT), hyperthermia and tachycardia by activating a direct neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe (rMR). However, the mechanism by which stress signals activate the DMH neurons driving the sympathetic stress responses remains unknown. Here we demonstrate that the ventral medial prefrontal cortex (vmPFC) is a major source of the stress signals to the DMH by performing in vivo physiological, optogenetic and neuroanatomical experiments in rats. Indicating the importance of glutamatergic inputs to the DMH in sympathetic stress responses, blockade of glutamate receptors in the DMH with bilateral nanoinjections of AP5/CNQX diminished BAT thermogenesis and hyperthermia evoked by social defeat stress, a sociopsychological stress model. Retrograde neural tracing from the DMH revealed numerous projections from the mPFC to the DMH, and anterograde tracing visualized putative synaptic connections of vmPFC‐derived glutamatergic axons to DMH neurons projecting to the rMR. Rats exposed to social defeat stress exhibited increased expression of Fos, a marker for neuronal activation, in DMH‐projecting neurons in the vmPFC, and inactivation of vmPFC neurons with bilateral muscimol nanoinjections diminished BAT thermogenic, hyperthermic, tachycardic and pressor responses evoked by social defeat stress. In contrast, inhibition of neurons in the dorsal part of the mPFC (dmPFC) exhibited a weaker inhibitory effect on these stress responses. Selective stimulation of vmPFC–DMH monosynaptic transmission using an in vivo optogenetic technique elicited BAT thermogenesis and tachycardia, which were both blocked by bilateral AP5/CNQX injections into the DMH. However, selective stimulation of dmPFC–DMH transmission did not increase BAT thermogenesis or tachycardia. These results indicate that the vmPFC–DMH glutamatergic monosynaptic pathway provides the DMH with excitatory stress signals to activate the DMH– rMR sympathoexcitatory pathway driving sympathetic stress responses.Support or Funding InformationFunding: Grants‐in‐Aids for Scientific Research from MEXT, Japan (16K19006 to NK, 16H05128 & 15H05932 to KN); Takeda Science Foundation (KN); Uehara Memorial Foundation (KN); Brain Science Foundation (KN).
Four weeks of exposure to environmentally relevant levels of second hand smoke decreases heart rate variability—but not baroreflex sensitivity—in mice
Authors: Karey Emma , Pan Shiyue , Chen Yi‐Je , Pinkerton Kent E , Chen Chao 
Published: November 2023

BACKGROUNDSecond hand smoke (SHS), a source of environmental air pollution exposure, is a significant risk factor for cardiovascular morbidity and mortality. Impaired autonomic function, as indexed by decreased heart rate variability (HRV), has been implicated as one of the underlying mechanisms of increased arrhythmia susceptibility that often precedes sudden cardiac death. We previously showed, in mice, that short term (3 days) exposure to a high level of SHS (30 mg/m3, 6 hr/d) reduced HRV that persisted after this acute window of SHS exposure. However, we have limited information on the time course of SHS‐induced cardiovascular dysfunction at more environmentally relevant concentrations. Here, we sought to test the hypothesis that an environmentally relevant level of SHS decreases HRV and baroreflex sensitivity (BRS), while increasing blood pressure (BP) and BP variability (BPV).METHODSAdult male C57BL/6J mice were implanted with BP/ECG telemetry devices. Two weeks after recovering from surgery, mice were randomly assigned to either filtered air (FA, n=10 for HRV, n=5 for BPV and BRS) or SHS (n=6) groups. SHS exposure level was similar to that of a “smoky bar” (3 mg/m3) for 6hr/d, 5d/wk for 4wk. Weekly, 36 hours of continuous BP and ECG recordings were performed after five days of exposure. Data were divided into three 12‐hour periods: the dark cycle immediate after the 5th day of exposure and the following light and dark cycles. Standard time domain HRV parameters were determined from normal‐to‐normal R wave intervals (SDNN, CV% and rMSSD). BRS was determined with the sequence method using systolic BP.RESULTSSHS exposure for four weeks did not change BP and HR in either dark or light cycle. SHS significantly decreased short term HRV (rMSSD) during the light cycle in as few as two weeks of exposure (28% lower than FA group, p<0.05). However, there was no significant change in overall HRV (SDNN and CV%) after four weeks of SHS exposure. These data suggest that the initial change in cardiac autonomic regulation is likely mediated by reduced vagal regulation. There was a trend, but not statistically significant effect, for an increase in BPV (12% higher than FA group) after four weeks of SHS exposure; however, no change in BRS was observed after four weeks of SHS exposure. These data suggest that changes in cardiac regulation precede changes in BP regulation, and that the cardiac vagal limb of the autonomic nervous system is particularly sensitive to SHS exposure.CONCLUSIONSWe conclude that this environmentally relevant dose of SHS can impair cardiovascular regulation in a time‐dependent manner, further emphasizing the importance of regulating and limiting exposure to SHS.Support or Funding InformationR01 ES025229; T32 HL086350
Pressor Hyperreactivity to Stress Corresponds to Greater Vasoconstriction and Sympathetic Responsiveness and is Prevented by Renal Denervation
Authors: Knuepfer Mark M , Burris Sarah K , Perry Jeffrey L 
Published: November 2023

Renal denervation is effective in reducing arterial pressure in some patients with resistant hypertension. The cardiovascular reactivity hypothesis proposes that enhanced pressor responsiveness to stressful stimuli in humans predicts predisposition to develop hypertension and cardiovascular disease. Clinical studies have suggested, but not always verified, that pressor hyperreactivity correlates with greater muscle sympathetic nerve activity (SNA) responses. Our laboratory has shown that outbred Sprague‐Dawley male rats have variable pressor responsiveness to acute stress (air jet or cold water exposure). We reported that rats with larger acute pressor responses to stress lose this greater sensitivity after renal denervation or selective deafferentation using intrarenal capsaicin administration. We hypothesized that greater pressor sensitivity in the rat model reflects greater sympathetic responsiveness and dependence on renal sensory input to promote sympathetic tone. Rats were instrumented for recording arterial pressure (AP), heart rate, ascending aortic blood flow as a measure of cardiac output and both renal and adrenal SNA. After recovery, rats were tested with a brief air jet (1 sec, 30 psi) to the face, and with cold water exposure (1 cm deep for 1 min) while recording hemodynamic and sympathetic variables. As expected, both renal and adrenal SNA were significantly increased, particularly during the initial few seconds after onset of the stressor exposure. Rats were separated into those with larger and those with smaller pressor responses (32.5 ±1.5 vs 23.6±0.9 mmHg) to cold stress. The differences correlated with greater increases in calculated systemic vascular resistance (44.1±3.3 vs 33.4±2.4%). They also correlated with greater increases in renal SNA (660±54 vs 488±32%, p<0.013) and greater increases in adrenal SNA (713±99 vs 450±48%, p<0.034). As noted, the differences in hemodynamic responses were prevented by renal denervation in a separate group of rats. After renal denervation, all rats had similar pressor and vasoconstrictor responses to cold water stress. We conclude that rats have variable pressor responsiveness that is correlated with greater renal and adrenal SNA. We predict that this model may reveal a means to study sympathetic hyperreactivity and how this is related to predisposition to develop cardiovascular disease. In the future, we will verify that SNA responses are also normalized by renal denervation.Support or Funding InformationSupported by USPHS DA13256 and St. Louis University.
Small‐conductance Ca2+‐activated K+ (SK) channels regulate pre‐sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) and parasympathetic cardiomotor neurons (CMN) in the nucleus ambiguus (NA): Pathological changes
Authors: Cheng Zixi , Lin Ming , Toney Glenn M. , Chen Qinghui 
Published: November 2023

SK channels regulate action potential (AP) firing patterns and neuronal excitability in a Ca2+ dependent manner. Here, we report on (1) the functional role of SK channels in pre‐sympathetic neurons of the PVN and parasympathetic CMN of the NA and (2) the pathological contributions of SK channels in salt‐sensitive hypertension (SSH), maternal diabetes (MD) and chronic intermittent hypoxia (CIH). For PVN: Whole cell patch‐clamp recordings were made in brain slices from PVN neurons retrogradely labelled from the rostral ventrolateral medulla (RVLM). In current‐clamp recordings, we found that depolarizing current injections evoked action potentials that underwent spike‐frequency adaptation (SFA). Bath application of apamin increased PVN‐RVLM neuronal excitability, while attenuating current evoked SFA and the amplitude of the ensuing after hyperpolarization potential (AHP). In voltage‐clamp recordings, step depolarization elicited a Ca2+‐dependent delayed outward current (IAHP) that temporally corresponded to the AHP. IAHP was nearly abolished by the SK channel blocker apamin. Neurons from rats with SSH had diminished SK currents and enhanced excitability, which reflected reduced SFA and diminished AHP amplitude. Collectively, these data indicate that SK channels in PVN‐RVLM neurons play an important role in regulating excitability and suggest that diminished SK channel current in SSH could lead to increased neuronal discharge and thereby contribute to sympathoexcitation in this model of neurogenic hypertension. For CMN: The tracer XRITC was injected into the pericardial space to label parasympathetic CMN in mice. Two days later, whole cell recordings were made from labeled CMN in brainstem slices. In current‐clamp recordings, depolarizing current injections evoked spike trains that underwent SFA. Bath application of apamin increased neuronal excitability, abolished SFA and suppressed the amplitude of the AHP. In voltage clamp recordings, a Ca2+‐dependent, apamin‐sensitive IAHP was identified. In mice with MD and mice exposed to CIH, the apamin sensitive IAHP was enhanced and excitability was reduced, suggesting that SK channels negatively regulate AP discharge of CMN and could contribute to impaired vagal baroreflex control of the heart in these disease models. Ongoing studies in disease models seek to determine mechanisms to explain why SK channel function is diminished in PVN pre‐sympathetic neurons but enhanced in NA parasympathetic neurons.Support or Funding InformationSupport: HL‐79636 (ZC), HL‐088052 (GMT) and HL‐122952 (QHC).
Physiological Plasticity and Tolerance of Fundulid Killifish Species to Aquatic Hypoxia
Authors: Hoffman Ryan , Borowiec Brittney , Scott Graham , Adams Chelsea , Galvez Fernando 
Published: November 2023

Aquatic hypoxia is a naturally occurring phenomenon in waters subject to high primary production, eutrophication, and salinity‐derived stratification. Fish utilize a suite of physiological responses in order to cope with aquatic hypoxia. Species that regularly experience repeated bouts of hypoxia may rely more heavily on compensatory responses in order to survive. We hypothesized that species from hypoxia‐prone environments such as estuaries are more tolerant to hypoxia than species living in stable environments. We also hypothesized that species from variable environments would show a greater scope for phenotypic plasticity in their physiological acclimation responses to hypoxia. Fundulid killifish species from different ecological niches (marine‐tolerant Lucania parva and Fundulus confluentus and freshwater‐tolerant L. goodei and F. rathbuni) were acclimated for 21–28 d to either constant hypoxia or diurnal cycles of intermittent hypoxia (12 h normoxia: 12 h hypoxia). We then assessed the resting O2 consumption rates and hypoxia tolerance (critical O2 tension, O2 tension at loss of equilibrium, and time to loss of equilibrium at 0.6 kPa O2). Our results show that F. confluentus, an estuarine killifish, demonstrated much greater hypoxia tolerance than F. rathbuni, which inhabits freshwater rivers and creeks. Also, the sister taxa, Lucania parva and L. goodei demonstrated very similar baseline hypoxia tolerance. Acclimation to intermittent or constant hypoxia often (but not always) significantly improved hypoxia tolerance, but there were no clear patterns of variation in this plasticity between species from different environments. Our data suggest that plasticity can vary between even closely related species. Future work will compare the unique physiological strategies of each species for coping with hypoxia.Support or Funding InformationWe would like to thank the American Physiological Society's Undergraduate Summer Research Fellowship program, Louisiana Sea Grant, Louisiana State University, McMaster University, the Society of Experimental Biology, the National Science Foundation, and the Natural Sciences and Engineering Research Council of Canada for funding and support.
Diving Mice vs. Torpid Mice: A Comparison of Cardiovascular Regulation
Authors: Hult Elissa M , Bingaman Mark Jake , Swoap Steven John 
Published: November 2023

The diving response is a coordinated physiological response to submersion into water, and is used widely amongst mammals. The physiological response is composed of three primary effects: an immediate drop in heart rate, a reduced drive to breathe, and constriction of peripheral blood vessels. The diving response is important, not only because of its dramatic influence of the autonomic nervous system, but also because it inhibits or alters normal homeostatic reflexes such as the drive to breathe. We hypothesized that the cardiovascular effects and neural circuitry involved in the murine dive response are similar to those used in daily torpor. In this study, telemeters that measure arterial pressure and body temperature were implanted into female C57Bl/6J mice. These mice were trained to swim then voluntarily dive underwater for a distance of 60 cm over a 5 second period. After a recovery period, the same mice were calorically restricted to induce a bout of torpor. Just before the dive, the interbeat interval (IBI) was 87±3 msec and diastolic pressure was 100±8 mmHg. Diving caused a dramatic bradycardia immediately at the onset of each dive (IBI increased to 464±60 msec) and diastolic pressure dropped to 56±9 mmHg, that coincided with elevated peripheral resistance. Mice experienced a short bout (~5 sec) hypertension (diastolic pressure rose to 133±9 mmHg) upon emergence. The bradycardia and hypotension were dependent on vagal influence, as pre‐treatment with atropine blocked these responses. The same absolute changes to heart rate, blood pressure, and total peripheral resistance were observed in the torpid mouse, albeit at a different time scale. These data suggest that the drivers of the cardiovascular changes during a bout of torpor and during the diving response are likely shared.Support or Funding InformationSupported by 1R15HL120072‐01A1 to SJS