Acta Physiologica最新文献

Aim

This work aimed to investigate the effects of the loss of Parkin in middle-aged mice skeletal muscle, focusing on different types of myofibers and in the analysis of proteins related to protein synthesis and degradation as well as the analysis of force generation and motor balance.

Methods

We used male mice C57BL/6J (WT) and Parkin knockout mice, Parkintm1Shn (Parkin^−/−) at 3 and 10 months of age. We used Walking Beam, Open Field, Spider Mice and Maximum Power Tests to assess motor, balance, and endurance functions. We used flexor digitorum brevis (FDB) muscle for force generation analysis, and tibial anterior (TA) and soleus (SOL) muscles were used for biomolecular techniques because of their difference in fiber type. These muscles were used to investigate markers of protein synthesis and degradation, mitochondrial respiration, and myofiber diameter.

Results

The Absence of Parkin in middle-aged mice leads to a reduction in isometric force generation but maintained overall motor and locomotion abilities, exhibited only minor balance deficits. In the SOL muscle of middle-aged Parkin^−/− mice, we observed a reduction of muscle mass and myofiber diameter, also a significant decrease in mitochondrial respiratory capacity and Complex V. In the same group, we observed a reduction in the phosphorylation of AKT and 4E-BP1, and an increase in MURF-1 while Ubiquitin K63 levels decreased. We did not observe relevant differences in the TA muscle.

Conclusion

Our results suggest middle-aged Parkin^−/− mice exhibited muscle atrophy and mitochondrial dysfunction primarily in oxidative myofibers before noticeable motor dysfunction occurs.

Aim

Podocytes, highly specialized epithelial cells located in the glomerulus of the kidney, are essential to the filtration barrier that ensures separation of blood and urine. These cells exhibit a unique architecture, characterized by an intricate network of foot processes interconnected by slit diaphragms, which serve as a critical selective filter for plasma ultrafiltration.

This review focusses on synthesizing current knowledge on podocyte physiology, emphasizing the roles of key proteins, signaling pathways, and environmental factors that influence their function.

Methods

Publications featuring current advances in molecular biology and imaging techniques were used to summarize new insights into the regulatory pathways governing podocyte homeostasis, as well as the mechanisms of injury and repair.

Results

The biology of podocytes encompasses diverse processes, including cytoskeletal dynamics, cellular signaling, and interactions with neighboring cells and the extracellular matrix. Disruption of podocyte structure or function is fundamental to a variety of glomerular diseases, which can lead to proteinuria and progressive kidney failure.

Conclusion

Understanding the intricate mechanisms involved in maintaining podocyte homeostasis offers potential therapeutic strategies to protect and restore podocyte integrity, addressing a critical need in nephrology. By highlighting the intricate balance required for podocyte survival, we reinforce their significance as both a cornerstone of renal filtration and a focal point in kidney disease research.

Aim

Distinguish the relative importance of intramuscular acidosis (hydrogen ion) and inorganic phosphate in skeletal muscle fatigue in vivo in rats.

Methods

We used direct sciatic nerve electrical stimulations to evoke twitches at different frequencies of contraction (0.25-, 0.50-, 0.75-, 1-, 2-, and 4-Hz) in the triceps surae to impose a range of intramuscular metabolic perturbations, quantified by phosphorus nuclear magnetic resonance spectroscopy. Linear mixed-effects models were used to analyze the relationships between peak twitch force and intramuscular hydrogen ion or inorganic phosphate concentration (as Z-scores) during the protocols that decreased peak twitch force (2- and 4-Hz).

Results

Although intramuscular hydrogen ion and inorganic phosphate concentrations increased with increasing frequencies of contraction, peak twitch force did not begin to decrease until a “threshold” inorganic phosphate concentration was reached. A given hydrogen ion accumulation was associated with a greater decrease in peak twitch force during 4-Hz compared to 2-Hz (β: −1.19 vs. −0.62, p < 0.001). In contrast, the decrease in peak twitch force for a given inorganic phosphate accumulation was not different between 4- and 2-Hz (β: −0.89 vs. −0.85, p = 0.889).

Conclusions

The inconsistent relationship between the decrease in twitch force and intramuscular hydrogen ion accumulation is not congruent with the primary mechanisms by which acidosis is thought to mediate muscle fatigue. In contrast, the discernible twitch force–inorganic phosphate breakpoint and the consistent relationship between the decrease in twitch force and intramuscular inorganic phosphate accumulation are congruent with the concept of a critical concentration beyond which inorganic phosphate mediates muscle fatigue.

Aim

To evaluate the effect of carotid sinus nerve stimulation (CSNS) in the progression of cardiorenal syndrome type 1 (CRS1), 3 days after acute myocardial infarction (AMI).

Methods

Male rats were divided into four groups. CSNS was applied daily for 10 min over 3 days. Cardiac, renal, and inflammatory parameters characterized the CRS1 and the electroceutical effects of CSNS.

Results

CSNS reduced the ischemic zone compared to the AMI group not exposed to CSNS (32.7% ± 2.2% vs. 8.0% ± 1.8%). Heart rate (bpm) was increased in the AMI group, showing 440 ± 7.6 at 48 h and 428 ± 1.0 at 60 h post-AMI. Additionally, arterial pressure (mmHg) was increased in the AMI group at 48 h, as follows: mean: 98 ± 1.7, diastolic: 89 ± 2.1, and systolic: 122 ± 5.3. In contrast, the CSNS + AMI group showed significant reductions of these parameters: mean: 79 ± 2.0, diastolic, 66 ± 1.7, and systolic: 99 ± 2.7. Renal injury was confirmed by increased apoptosis in the AMI group. A significant increase in TNF-α was observed in both heart and kidneys (pg/mg of tissue) in the AMI group and reduced IL-6 and IL-1β levels in the CSNS + AMI group, indicating an attenuation of the inflammatory responses by CSNS.

Conclusions

This study demonstrates early cardiac and renal dysfunction in CRS1 following AMI, associated with elevated inflammatory markers (TNF-α, IL-6, and IL-1β) and renal apoptosis. Therefore, CSNS appears to be a promising electroceutical approach for CRS1. Besides, on the basis of previous studies from our laboratory, CSNS involves stimulation of the baroreflex, activating the parasympathetic and inhibiting the sympathetic nervous system.

Background

Bone is a dynamic tissue undergoing constant remodeling mediated by osteoblasts and osteoclasts. An imbalance between these cells can lead to reduced bone mass, disrupted microarchitecture, and ultimately osteoporosis. O-GlcNAcylation is a dynamic and reversible posttranslational modification where uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) is added or removed from serine/threonine residues of proteins by OGT and OGA, respectively. Emerging evidence indicates that appropriate O-GlcNAcylation is essential for bone remodeling, although its specific effects remain controversial.

Aims

This review aims to summarize the process of O-GlcNAcylation and critically evaluate its specific effects on osteoblast-mediated and osteoclast-mediated bone remodeling.

Materials & Methods

Based on a comprehensive analysis of published scientific literature, we synthesized the current evidence regarding the role of O-GlcNAcylation in bone cell differentiation and function, and its association with osteoporosis.

Results

Our analysis reveals that cellular demands for O-GlcNAcylation vary during osteoblastic and osteoclastic differentiation. Moderate O-GlcNAcylation is essential for osteoblast differentiation, whereas dynamic alterations in O-GlcNAcylation are crucial for osteoclast differentiation. Furthermore, elevated O-GlcNAcylation levels are consistently observed in both primary and secondary osteoporosis cases, suggesting a potential pathogenic role in the dysregulation of bone remodeling.

Discussion

These findings indicate that the effects of O-GlcNAcylation are cell type- and differentiation stage-dependent in bone. The observed elevation of O-GlcNAcylation in osteoporosis underscores its potential contribution to the dysregulation of bone remodeling pathways.

Conclusion

This review provides novel mechanistic insights into osteoporosis pathogenesis via dysregulation of the O-GlcNAcylation post-translational modification. Understanding these mechanisms will facilitate the development of novel therapeutic strategies targeting O-GlcNAcylation to restore balanced bone remodeling.

Aim

Chronic obstructive pulmonary disease (COPD) is frequently associated with skeletal muscle dysfunction, having a considerable impact on exercise tolerance and patient prognosis. Mitochondria play a role in skeletal muscle weakness and exercise intolerance in COPD, but the majority of studies on mitochondrial function are biased by the fact that physical activity is greater in healthy subjects than in patients. Furthermore, exercise training (ET) has been proposed as a therapeutic strategy to prevent skeletal muscle dysfunction in COPD, but very few results are available on mitochondrial adaptation in response to ET.

Methods

Skeletal muscle mitochondrial function and the potential efficacy of ET on this function were compared between 12 patients with COPD and 21 healthy subjects with similar low levels of physical activity. Various markers of mitochondrial respiration, oxidative stress, biogenesis, and dynamics were assessed.

Results

Lower oxidative phosphorylation (OxPhos; p < 0.001) and increased nonphosphorylating respiration (p = 0.025) and mitochondrial oxidative damage (lipid peroxidation (p = 0.014) and protein carbonylation (p = 0.020)) were observed in patients. While ET increased OxPhos efficiency (p = 0.011) and reduced nonphosphorylating respiration (p < 0.001) and lipid peroxidation (p < 0.001) in patients' muscle mitochondria, it fails to improve maximal respiration (p = 0.835) and expression of the antioxidant enzyme MnSOD (p = 0.606), mitochondrial transcription factor TFAM (p = 0.246), and mitochondrial complexes I, III, and IV (p = 0.816, p = 0.664, p = 0.888, respectively) as observed in healthy subjects.

Conclusion

The mitochondrial dysfunction and the defects in mitochondrial adaptation to ET that we observe in the muscle of patients with COPD are intrinsic to the disease and do not arise from muscle disuse.

Aim

Metabolic disturbances challenge pH homeostasis in cardiomyocytes. The electroneutral Na⁺,HCO₃⁻-cotransporter NBCn1/Slc4a7 mediates net acid extrusion, and genetic variation in SLC4A7 contributes to human hypertension and cardiovascular risk. Nonetheless, the cardiac consequences of disrupted NBCn1 expression and function remain unclear. Here, we test the hypothesis that NBCn1, either directly or indirectly, influences cardiac structure, contractile function, and electrophysiological properties.

Methods

Based on mice with global loss of NBCn1, we measure intracellular pH in atria and ventricles of the heart (fluorescence microscopy), membrane potential responses (patch clamping), electro- and echocardiographic variables, blood pressure (telemetry), and cardiac dimensions (in vivo and postmortem analyses).

Results

We find that protein and mRNA expression of NBCn1 are more prominent in atrial than in ventricular cardiomyocytes. Disruption of NBCn1 expression lowers Na⁺,HCO₃⁻-cotransport activity more than 50% in atria without significantly influencing net acid extrusion activity of ventricular cardiomyocytes. Loss of NBCn1 is associated with hypertension (blood pressure increased by ~15 mmHg), cardiac hypertrophy (heart/body weight increased by ~10%), and prolonged ventricular isovolumic relaxation time (increased by ~25%). NBCn1 knockout does not affect cardiomyocyte size, collagen content in the heart wall, overall cardiac contractile function, electrophysiological properties of ventricular cardiomyocytes, or the electrocardiogram.

Conclusion

NBCn1 is a main mechanism of Na⁺,HCO₃⁻-cotransport in atrial tissue and contributes substantially to net acid extrusion during intracellular acidification. NBCn1 does not play any major direct role in ventricular cardiomyocytes of unchallenged mice, but global knockout of NBCn1 increases systemic blood pressure and results in the development of cardiac hypertrophy.

Aim

Vascular calcification (VC), a characteristic feature of peripheral artery disease in patients with diabetes and chronic kidney disease, has been associated with poor prognosis. We hypothesize that hyperglycemia drives VC through alterations in metabolomic and transcriptomic profiles.

Methods

Human coronary artery smooth muscle cells (SMCs) were cultured with 0, 5.5, and 25 mM glucose under calcifying conditions. Untargeted metabolomic and transcriptomic analyses were performed at different time points. Mitochondrial respiration was examined using Seahorse analysis.

Results

Glucose-treated SMCs promoted extracellular matrix (ECM) calcification in a concentration- and time-dependent manner. The absence of glucose entirely abolished SMC calcification but reduced SMC proliferation in control and calcifying conditions compared to 25 mM glucose. Multi-omics data integration revealed key players from the hypotaurine/taurine metabolic pathway as the center hub of the reconstructed network. Glucose promoted the hypotaurine secretion, while its intracellular abundance was not altered. Blocking hypotaurine production by propargylglycine increased ECM calcification, while hypotaurine treatment prevented it. Furthermore, omics data suggest energy remodeling in calcifying SMCs under hyperglycemia. Calcifying SMCs exhibited decreased oxygen consumption that was partially restored by hypotaurine. Validation of our in vitro models using the murine warfarin model demonstrated reduced hypotaurine/taurine transporter (TAUT) expression in SMCs.

Conclusions

Our multi-omics analysis revealed a role of the hypotaurine/taurine metabolic pathway in glucose-induced SMC calcification. Moreover, our data suggest a glucose-dependent energy remodeling in calcifying SMCs and that increasing glucose concentrations fuel ECM calcification. Our work highlights potential novel therapeutic targets that warrant further investigation in hyperglycemia-dependent in vitro SMC calcification.

Aim

Dilatory microvascular function is impaired in ischemia/reperfusion injury in the kidney. Nitric oxide independent activators of soluble guanylyl cyclase (sGC) provide renal protection by dilating microvessels and preserving perfusion, but their efficacy declines after severe hypoxia. This study explores whether lipocalin-2 (Lcn2), a key iron-transporting protein, can restore the sGC-mediated dilation in mouse afferent arterioles (AAs) after hypoxia/reoxygenation (H/R) and kidney transplantation.

Methods

Dilation of isolated, angiotensin II (Ang II) pre-constricted, AAs was induced by application of sGC activator cinaciguat after pre-constriction with Ang II following H/R (H: 30 min, R: 10 min ± holo-rLcn2, apo-rLcn2, deferoxamine) and syngeneic kidney transplantation (cold ischemia: 30 min or 5.5 h, reperfusion: 20 h ± holo-rLcn2) in C57BL/6 mice. To corroborate the dilatory function at the organ level, vascular relaxation was assessed using an isolated mouse kidney perfusion system.

Results

Dilation of AAs was impaired following H/R. Pretreatment with holo-rLcn2 (iron-bound) preserved dilation, whereas apo-rLcn2 (iron-free) had no effect. The reversal of holo-rLcn2's effect by deferoxamine confirmed the role of iron. AAs from kidney transplants showed reduced dilation compared to sham-operated controls, with greater impairment following prolonged ischemia. Treatment with holo-rLcn2 significantly improved dilatory function after extended cold ischemia (5.5 h), restoring it to levels seen with shorter ischemia (30 min). Ex vivo perfusion of the isolated mouse kidney with holo-rLcn2 enhanced cinaciguat-induced vascular relaxation, confirming its beneficial effect at the organ level.

Conclusion

This study identifies a novel role for holo-rLcn2 in preserving renal vascular function post-H/R and kidney transplantation, apparently by upholding iron levels in vascular cells.