Myostatin and muscle atrophy during chronic kidney disease

Skeletal Muscle Injury in Chronic Kidney Disease-From Histologic Changes to Molecular Mechanisms and to Novel Therapies

Chronic kidney disease (CKD) is associated with significant reductions in lean body mass and in the mass of various tissues, including skeletal muscle, which causes fatigue and contributes to high mortality rates. In CKD, the cellular protein turnover is imbalanced, with protein degradation outweighing protein synthesis, leading to a loss of protein and cell mass, which impairs tissue function. As CKD itself, skeletal muscle wasting, or sarcopenia, can have various origins and causes, and both CKD and sarcopenia share common risk factors, such as diabetes, obesity, and age. While these pathologies together with reduced physical performance and malnutrition contribute to muscle loss, they cannot explain all features of CKD-associated sarcopenia. Metabolic acidosis, systemic inflammation, insulin resistance and the accumulation of uremic toxins have been identified as additional factors that occur in CKD and that can contribute to sarcopenia. Here, we discuss the elevation of systemic phosphate levels, also called hyperphosphatemia, and the imbalance in the endocrine regulators of phosphate metabolism as another CKD-associated pathology that can directly and indirectly harm skeletal muscle tissue. To identify causes, affected cell types, and the mechanisms of sarcopenia and thereby novel targets for therapeutic interventions, it is important to first characterize the precise pathologic changes on molecular, cellular, and histologic levels, and to do so in CKD patients as well as in animal models of CKD, which we describe here in detail. We also discuss the currently known pathomechanisms and therapeutic approaches of CKD-associated sarcopenia, as well as the effects of hyperphosphatemia and the novel drug targets it could provide to protect skeletal muscle in CKD.

Caffeic acid alleviates skeletal muscle atrophy in 5/6 nephrectomy rats through the TLR4/MYD88/NF-kB pathway

Skeletal muscle atrophy is a common complication of chronic kidney disease (CKD) that affects the quality of life and prognosis of patients. We aimed to investigate the effects and mechanisms of caffeic acid (CA), a natural phenolic compound, on skeletal muscle atrophy in CKD rats. Male Sprague-Dawley rats underwent 5/6 nephrectomy (NPM) and were treated with CA (20, 40, or 80 mg/kg/day) for 10 weeks. The body and muscle weights, renal function, hemoglobin, and albumin were measured. The histological, molecular, and biochemical changes in skeletal muscles were evaluated using hematoxylin-eosin staining, quantitative real-time PCR, malondialdehyde/catalase/superoxide dismutase/glutathione level detection, and enzyme-linked immunosorbent assay. Western blotting and network pharmacology were applied to identify the potential targets and pathways of CA, CKD, and muscle atrophy. The results showed that CA significantly improved NPM-induced muscle-catabolic effects, reduced the expression of muscle atrophy-related proteins (muscle atrophy F-box and muscle RING finger 1) and proinflammatory cytokines (interleukin [IL]-6, tumor necrosis factor-alpha, and IL-1β), and attenuated muscle oxidative stress. Network pharmacology revealed that CA modulated the response to oxidative stress and nuclear factor kappa B (NF-κB) signaling pathway and that Toll-like receptor 4 (TLR4) was a key target. In vivo experiment confirmed that CA inhibited the TLR4/myeloid differentiation primary response 88 (MYD88)/NF-kB signaling pathway, reduced muscle iron levels, and restored glutathione peroxidase 4 activity, thereby alleviating ferroptosis and inflammation in skeletal muscles. Thus, CA might be a promising therapeutic agent for preventing and treating skeletal muscle atrophy in CKD by modulating the TLR4/MYD88/NF-κB pathway and ferroptosis.

The phase angle cut-off point capable of discriminating hemodialysis patients with reduced exercise tolerance: a cross-sectional study

BACKGROUND

Phase angle (PhA) is a prognostic marker of all-cause mortality in chronic kidney disease. However, no study has investigated this marker as a predictor of exercise intolerance in hemodialysis (HD) patients. The aim of this study was to determine a cut-off point for the PhA capable of discriminating HD patients with reduced exercise tolerance.

METHODS

Thirty-one patients (80.6% men, median age 69 years) were included. The evaluations were performed on three different days, before the HD session. The outcomes evaluated were: biochemical markers, inflammatory and nutritional status, body composition, peripheral muscle strength and exercise tolerance. Performance ≤50% of the predicted value in the six-minute step test (6MST) was defined as reduced exercise tolerance.

RESULTS

Patients presented an average of 67.6 steps (50.5% of predicted) in the 6MST. Fifteen patients (48.4%) were classified with reduced exercise tolerance. The receiver operating characteristic curve indicated a cut-off point of 3.73° for the PhA (sensitivity = 87%, specificity = 81%, and area under the curve = 0.88 [95% CI: 0.76-1.00]; p < 0.001). Patients with reduced exercise tolerance had worse inflammatory and nutritional status, lower PhA and greater impairment of peripheral muscle strength.

CONCLUSION

The cut-off point of 3.73° for the PhA is sensitive and specific to discriminate HD patients with reduced exercise tolerance.

TRIAL REGISTRATION

This study was registered in the Clinical Trials database (no. NCT03779126, date of first registration 19/12/2018).

Indoxyl sulfate inhibits muscle cell differentiation via Myf6/MRF4 and MYH2 downregulation

BACKGROUND

Chronic kidney disease (CKD) is associated with a significant decrease in muscle strength and mass, possibly related to muscle cell damage by uremic toxins. Here, we studied in vitro and in vivo the effect of indoxyl sulfate (IS), an indolic uremic toxin, on myoblast proliferation, differentiation and expression of myogenic regulatory factors (MRF)-myoblast determination protein 1 (MyoD1), myogenin (Myog), Myogenic Factor 5 (Myf5) and myogenic regulatory factor 4 (Myf6/MRF4)-and expression of myosin heavy chain, Myh2.

METHODS

C2C12 myoblasts were cultured in vitro and differentiated in myotubes for 7 days in the presence of IS at a uremic concentration of 200 µM. Myocytes morphology and differentiation was analyzed after hematoxylin-eosin staining. MRF genes' expression was studied using reverse transcription polymerase chain reaction in myocytes and 5/6th nephrectomized mice muscle. Myf6/MRF4 protein expression was studied using enzyme-linked immunosorbent assay; MYH2 protein expression was studied using western blotting. The role of Aryl Hydrocarbon Receptor (AHR)-the cell receptor of IS-was studied by adding an AHR inhibitor into the cell culture milieu.

RESULTS

In the presence of IS, the myotubes obtained were narrower and had fewer nuclei than control myotubes. The presence of IS during differentiation did not modify the gene expression of the MRFs Myf5, MyoD1 and Myog, but induced a decrease in expression of Myf6/MRF4 and MYH2 at the mRNA and the protein level. AHR inhibition by CH223191 did not reverse the decrease in Myf6/MRF4 mRNA expression induced by IS, which rules out the implication of the ARH genomic pathway. In 5/6th nephrectomized mice, the Myf6/MRF4 gene was down-regulated in striated muscles.

CONCLUSION

In conclusion, IS inhibits Myf6/MRF4 and MYH2 expression during differentiation of muscle cells, which could lead to a defect in myotube structure. Through these new mechanisms, IS could participate in muscle atrophy observed in CKD.

Relation between myostatin levels and malnutrition and muscle wasting in hemodialysis patients

BACKGROUND AND AIM

Malnutrition is one of the most troublesome comorbidities among hemodialysis patients (HD). Myostatin (MSTN) belongs to the transforming growth factor-β superfamily. In HD patients, MSTN effects are not limited to skeletal muscle growth. The present study aimed to assess MSTN levels in HD patients and its relation to various clinical and biochemical parameters.

PATIENTS AND METHODS

The present case control study included 60 patients on HD for at least three years. In addition, there were age and sex-matched healthy subjects who constitutes the control group. Nutritional status was evaluated using the malnutrition inflammation score (MIS). Muscle wasting in the present study was evaluated using the lean tissue index (LTI) as assessed by the body composition monitor (BCM). Rectus Femoris Muscle (RFM) thickness was also measured as indicator for nutritional status of patient.

RESULTS

The present study included 60 HD patients, and ageand sex-matched healthy controls. Patients expressed significantly higher myostatin levels when compared to controls [median (IQR): 221.3 (153.5-688.2) versus 144.8 (97.0-281.7), p < 0.001]. According to MIS, patients were classified into those with no/mild malnutrition (n = 22) and others with moderate/severe malnutrition (n = 38). Comparison between the two subgroups revealed that the former group had significantly lower myostatin levels [167.7 (150.3-236.3) versus 341.7 (160.9-955.9), p = 0.004]. According to LTI, patients were classified into those with muscle wasting (n = 23) and others without muscle wasting (n = 37). Comparative analysis showed that patients in the former group had significantly higher myostatin levels [775.1 (325.1-2133.7) versus 161.8 (142.6-302.3), p < 0.001].

CONCLUSIONS

Myostatin seems to be a promising marker for identification of malnutrition and muscle wasting in HD patients.

The Potential Influence of Uremic Toxins on the Homeostasis of Bones and Muscles in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) often experience a high accumulation of protein-bound uremic toxins (PBUTs), specifically indoxyl sulfate (IS) and p-cresyl sulfate (pCS). In the early stages of CKD, the buildup of PBUTs inhibits bone and muscle function. As CKD progresses, elevated PBUT levels further hinder bone turnover and exacerbate muscle wasting. In the late stage of CKD, hyperparathyroidism worsens PBUT-induced muscle damage but can improve low bone turnover. PBUTs play a significant role in reducing both the quantity and quality of bone by affecting osteoblast and osteoclast lineage. IS, in particular, interferes with osteoblastogenesis by activating aryl hydrocarbon receptor (AhR) signaling, which reduces the expression of Runx2 and impedes osteoblast differentiation. High PBUT levels can also reduce calcitriol production, increase the expression of Wnt antagonists (SOST, DKK1), and decrease klotho expression, all of which contribute to low bone turnover disorders. Furthermore, PBUT accumulation leads to continuous muscle protein breakdown through the excessive production of reactive oxygen species (ROS) and inflammatory cytokines. Interactions between muscles and bones, mediated by various factors released from individual tissues, play a crucial role in the mutual modulation of bone and muscle in CKD. Exercise and nutritional therapy have the potential to yield favorable outcomes. Understanding the underlying mechanisms of bone and muscle loss in CKD can aid in developing new therapies for musculoskeletal diseases, particularly those related to bone loss and muscle wasting.

Myostatin Overexpression and Smad Pathway in Detrusor Derived from Pediatric Patients with End-Stage Lower Urinary Tract Dysfunction

Cell therapies and tissue engineering approaches using smooth muscle cells (SMCs) may provide treatment alternatives for end-stage lower urinary tract dysfunction (ESLUTD). Myostatin, a negative regulator of muscle mass, is a promising target to improve muscle function through tissue engineering. The ultimate goal of our project was to investigate the expression of myostatin and its potential impact in SMCs derived from healthy pediatric bladders and pediatric ESLUTD patients. Human bladder tissue samples were evaluated histologically, and SMCs were isolated and characterized. The proliferation of SMCs was assessed by WST-1 assay. The expression pattern of myostatin, its pathway and the contractile phenotype of the cells were investigated at gene and protein levels by real-time PCR, flow cytometry, immunofluorescence, WES and gel contraction assay. Our results show that myostatin is expressed in human bladder smooth muscle tissue and in isolated SMCs at gene and protein levels. A higher expression of myostatin was detected in ESLUTD-derived compared to control SMCs. Histological assessment of bladder tissue confirmed structural changes and decreased muscle-to-collagen ratios in ESLUTD bladders. A decrease in cell proliferation and in the expression of key contractile genes and proteins, α-SMA, calponin, smoothelin and MyH11, as well as a lower degree of in vitro contractility was observed in ESLUTD-derived compared to control SMCs. A reduction in the myostatin-related proteins Smad 2 and follistatin, and an upregulation in the proteins p-Smad 2 and Smad 7 were observed in ESLUTD SMC samples. This is the first demonstration of myostatin expression in bladder tissue and cells. The increased expression of myostatin and the changes in the Smad pathways were observed in ESLUTD patients. Therefore, myostatin inhibitors could be considered for the enhancement of SMCs for tissue engineering applications and as a therapeutic option for patients with ESLUTD and other smooth muscle disorders.

Chronic kidney disease-induced muscle atrophy: Molecular mechanisms and promising therapies

Chronic kidney disease (CKD) is a high-risk chronic catabolic disease due to its high morbidity and mortality. CKD is accompanied by many complications, leading to a poor quality of life, and serious complications may even threaten the life of CKD patients. Muscle atrophy is a common complication of CKD. Muscle atrophy and sarcopenia in CKD patients have complex pathways that are related to multiple mechanisms and related factors. This review not only discusses the mechanisms by which inflammation, oxidative stress, mitochondrial dysfunction promote CKD-induced muscle atrophy but also explores other CKD-related complications, such as metabolic acidosis, vitamin D deficiency, anorexia, and excess angiotensin II, as well as other related factors that play a role in CKD muscle atrophy, such as insulin resistance, hormones, hemodialysis, uremic toxins, intestinal flora imbalance, and miRNA. We highlight potential treatments and drugs that can effectively treat CKD-induced muscle atrophy in terms of complication treatment, nutritional supplementation, physical exercise, and drug intervention, thereby helping to improve the prognosis and quality of life of CKD patients.

Serum myostatin levels are associated with physical function and hospitalization in peritoneal dialysis patients

BACKGROUND

Myostatin functions as a negative regulator of skeletal muscle growth. The association of myostatin with muscle parameters in dialysis patients is inconsistent, and there are no studies associating myostatin with physical function and outcomes in peritoneal dialysis (PD) patients. Therefore, we assessed the association of serum myostatin with lean mass, physical function, and hospitalization in a prospective cohort of PD patients.

METHODS

Lean mass, physical function, and serum myostatin were assessed at baseline. Patients were followed up for at least 24 months and hospitalization was recorded.

RESULTS

Serum myostatin levels were positively correlated with handgrip strength and Appendicular Lean Mass Index among male patients. Binary logistic regression models were performed including myostatin levels and physical function parameters as independent variables. Serum myostatin, handgrip strength, gait speed, and Short Physical Performance Battery were associated with hospitalization.

CONCLUSION

Lower serum myostatin and physical function were associated with hospitalization in PD patients.

Crosstalk between bone and muscle in chronic kidney disease

With increasing life expectancy, the related disorders of bone loss, metabolic dysregulation and sarcopenia have become major health threats to the elderly. Each of these conditions is prevalent in patients with chronic kidney disease (CKD), particularly in more advanced stages. Our current understanding of the bone-muscle interaction is beyond mechanical coupling, where bone and muscle have been identified as interrelated secretory organs, and regulation of both bone and muscle metabolism occurs through osteokines and myokines via autocrine, paracrine and endocrine systems. This review appraises the current knowledge regarding biochemical crosstalk between bone and muscle, and considers recent progress related to the role of osteokines and myokines in CKD, including modulatory effects of physical exercise and potential therapeutic targets to improve musculoskeletal health in CKD patients.

Skeletal Muscle Complications in Chronic Kidney Disease

PURPOSE OF REVIEW

To provide an overview of the recent literature investigating the pathophysiology of skeletal muscle changes, interventions for skeletal muscle, and effects of exercise in chronic kidney disease (CKD).

RECENT FINDINGS

There are multiple CKD-related changes that negatively impact muscle size and function. However, the variability in the assessment of muscle size, in particular, hinders the ability to truly understand the impact it may have in CKD. Exercise interventions to improve muscle size and function demonstrate inconsistent responses that warrant further investigation to optimize exercise prescription. Despite progress in the field, there are many gaps in the knowledge of the pathophysiology of sarcopenia of CKD. Identifying these gaps will help in the design of interventions that can be tested to target muscle loss and its consequences such as impaired mobility, falls, and poor quality of life in patients with CKD.

Allograft function and muscle mass evolution after kidney transplantation

BACKGROUND

Advanced chronic kidney disease is associated with muscle wasting, but how glomerular filtration rate (GFR) recovery after kidney transplantation is associated with muscle mass is unknown.

METHODS

We took advantage of the simultaneous measurement of GFR (using iohexol plasma clearance; ioGFR) and creatinine excretion rate (a surrogate marker of muscle mass; CER) performed 3 months after transplantation and at a later time point at our institution to investigate the interplay between allograft function, muscle mass, and outcome in kidney transplant recipients.

RESULTS

Between June 2005 and October 2019, 1319 successive kidney transplant recipients (mean age 50.4 ± 14.6; 38.7% female) underwent GFR measurement at our institution 3 months after kidney transplantation. CER (CER₃ ) and ioGFR (ioGFR₃ ) were 7.7 ± 2.6 μmol/min and 53 ± 17.1 mL/min/1.73 m² , respectively. Multivariable analysis identified female gender, older donor and recipient age, reduced body mass index, coronary disease, dialysis history, proteinuria, and reduced ioGFR₃ as independent predictors of low CER₃ (ioGFR₃ : β coefficient 0.19 [95% confidence interval 0.14 to 0.24]). A total of 1165 patients had a subsequent CER measurement after a median follow-up of 9.5 months. Of them, 373 (32%) experienced an increase in CER > 10%, while 222 (19%) showed a CER decrease of more than 10%. Multivariable analysis adjusted for CER₃ and other confounders identified ioGFR₃ as an independent predictor of CER at follow-up (β coefficient 0.11 [95% confidence interval 0.07 to 0.16]). In multivariable Cox analysis, reduced CER at 3 months or at follow-up were consistently associated with mortality (hazard ratio [95% confidence interval] at 3 months: 0.82 [0.74 to 0.91]; at follow-up: 0.79 [0.69 to 0.99]) but not with graft loss.

CONCLUSIONS

Glomerular filtration rate recovery is a determinant of muscle mass variation after kidney transplantation. Early interventions targeting muscle mass gain may be beneficial for kidney transplant recipients.

Sarcopenia and cardiovascular disease in patients with and without kidney disease: what do we know?

Cardiovascular disease (CVD) incidence is high in patients with chronic kidney disease (CKD) and is the most frequent cause of mortality in this population. Advanced age, hypertension, uremic toxins, endothelial dysfunction, atherosclerosis, hyperhomocysteinemia, oxidative stress, and inflammation are among the leading causes of increased CVD in advanced stages of CKD. Although defined as a decrease in muscle strength associated with aging, sarcopenia is also prevalent in CKD patients. Sarcopenia causes physical disability, low quality of life, and mortality. Regular exercise and nutritional supplementation may slow the progression of sarcopenia. Recent studies have shown that sarcopenia increases the risk of CVD and mortality in people with or without kidney disease. This review discusses the relationship between sarcopenia and CVD in light of the current literature.

Enhanced Myogenesis by Silencing Myostatin with Nonviral Delivery of dCas9 Ribonucleoprotein Complex

Stress urinary incontinence (SUI) and pelvic floor disorder (PFD) are common conditions with limited treatment options in women worldwide. Regenerative therapy to restore urethral striated and pelvic floor muscles represents a valuable therapeutic approach. We aim to determine the CRISPR interference-mediated gene silencing effect of the nonviral delivery of nuclease-deactivated dCas9 ribonucleoprotein (RNP) complex on muscle regeneration at the cellular and molecular level. We designed four myostatin (MSTN)-targeting sgRNAs and transfected them into rat myoblast L6 cells together with the dCas9 protein. Myogenesis assay and immunofluorescence staining were performed to evaluate muscle differentiation, while CCK8 assay, cell cycle assay, and 5-ethynyl-2'-deoxyuridine staining were used to measure muscle proliferation. Reverse transcription-polymerase chain reaction and Western blotting were also performed to examine cellular signaling. Myogenic factors (including myosin heavy chain, MSTN, myocardin, and serum response factor) increased significantly after day 5 during myogenesis. MSTN was efficiently silenced after transfecting the dCas9 RNP complex, which significantly promoted more myotube formation and a higher fusion index for L6 cells. In cellular signaling, MSTN repression enhanced the expression of MyoG and MyoD, phosphorylation of Smad2, and the activity of Wnt1/GSK-3β/β-catenin pathway. Moreover, MSTN repression accelerated L6 cell growth with a higher cell proliferation index as well as a higher expression of cyclin D1 and cyclin E. Nonviral delivery of the dCas9 RNP complex significantly promoted myoblast differentiation and proliferation, providing a promising approach to improve muscle regeneration for SUI and PFD. Further characterization and validation of this approach in vivo are needed.

Sarcopenia in chronic kidney disease: prevalence by different definitions and relationship with adiposity

This was a cross-sectional study with Chronic Kidney Disease (CKD) patients under non-dialysis-dependent (NDD), hemodialysis (HD) and kidney transplant (KTx) treatment aimed to evaluate the prevalence of sarcopenia using the European Working Group on Sarcopenia in Older People (EWGSOP2) and the Foundation of the National Institutes of Health (FNIH) guidelines; also analyze the relationship between sarcopenia and its components with body adiposity. Body composition was assessed by dual energy X-ray absorptiometry (DXA) and anthropometry. Bioelectrical impedance provided data of phase angle and body water. The prevalence of sarcopenia in total sample (n=243; 53% men, 48±10 y) was 7% by FNIH and 5% by EWGSOP2 criteria; and was low in each CKD group independently of the criteria applied (max 11% prevalence). Low muscle mass was present in 39% (FNIH) and 36% (EWGSOP2) and dynapenia in 10% of patients. Sarcopenic patients by EWGSOP2 criteria presented low body adiposity. Conversely, sarcopenic patients by FNIH presented high adiposity. This study suggests that in CKD (i) sarcopenia and low muscle mass prevalence varies according to the diagnostic criteria, (ii) are common conditions, (iii) association with body adiposity depends on the criteria used to define low muscle mass, (iv) FNIH criteria detected high adiposity in individuals with sarcopenia. Novelty bullets: Prevalence of sarcopenia and low muscle mass in CKD varied according to the diagnostic criteria; association of excess adiposity with sarcopenia and low muscle mass depends on muscle mass index applied; FNIH criteria detected higher adiposity in individuals with sarcopenia. NOVELTY BULLETS Prevalence of sarcopenia and low muscle mass in CKD varied according to the diagnostic criteria; Association of excess adiposity with sarcopenia and low muscle mass depends on muscle mass index applied; FNIH criteria detected higher adiposity in individuals with sarcopenia and low muscle mass.

Low serum creatinine to cystatin C ratio is independently associated with sarcopenia and high carotid plaque score in patients with type 2 diabetes

BACKGROUND AND AIMS

Low serum creatinine (Cr) to cystatin C (cysC) ratio has been suggested to be associated with low muscle mass and strength and poor prognosis in various chronic disease. We investigated the associations of CCR with sarcopenia and carotid plaque score (PS) in patients with type 2 diabetes mellitus.

METHODS AND RESULTS

A total of 1577 patients with type 2 diabetes were enrolled. High PS was defined as PS ≥ 3. Sarcopenia was assessed by the measurement of appendicular skeletal muscle mass (ASM) and grip strength (GS). Compared to the highest CCR group, the lowest tertile group was older; had higher C-reactive protein levels, CIMT, and PS, but lower cysC-based estimated glomerular filtration rate (cysC-eGFR), ASM/BMI, and GS. Positive correlations between CCR and ASM/BMI (r = 0.239 in men and 0.303 in women, p < 0.001) and GS (r = 0.282 in men and 0.270 in women, p < 0.001) were observed in both genders. Odds ratios and 95% confidence intervals for high PS after adjusting for age and sex were 1.22 (0.92-1.61, p = 0.18) in the middle and 1.74 (1.31-2.30, p < 0.001) in the lowest tertiles, respectively, with those of the lowest tertile remaining significant after further adjusting for multiple confounders.

CONCLUSIONS

Low CCR was independently associated with sarcopenia and high PS in patients with type 2 diabetes mellitus, especially after adjusting for ASM/BMI and GS.

Muscle Wasting in Chronic Kidney Disease: Mechanism and Clinical Implications—A Narrative Review

Muscle wasting, known to develop in patients with chronic kidney disease (CKD), is a deleterious consequence of numerous complications associated with deteriorated renal function. Muscle wasting in CKD mainly involves dysregulated muscle protein metabolism and impaired muscle cell regeneration. In this narrative review, we discuss the cardinal role of the insulin-like growth factor 1 and myostatin signaling pathways, which have been extensively investigated using animal and human studies, as well as the emerging concepts in microRNA- and gut microbiota-mediated regulation of muscle mass and myogenesis. To ameliorate muscle loss, therapeutic strategies, including nutritional support, exercise programs, pharmacological interventions, and physical modalities, are being increasingly developed based on advances in understanding its underlying pathophysiology.

Paeoniflorin Ameliorates Skeletal Muscle Atrophy in Chronic Kidney Disease via AMPK/SIRT1/PGC-1α-Mediated Oxidative Stress and Mitochondrial Dysfunction

Skeletal muscle atrophy is a common and serious complication of chronic kidney disease (CKD). Oxidative stress and mitochondrial dysfunction are involved in the pathogenesis of muscle atrophy. The aim of this study was to explore the effects and mechanisms of paeoniflorin on CKD skeletal muscle atrophy. We demonstrated that paeoniflorin significantly improved renal function, calcium/phosphorus disorders, nutrition index and skeletal muscle atrophy in the 5/6 nephrectomized model rats. Paeoniflorin ameliorated the expression of proteins associated with muscle atrophy and muscle differentiation, including muscle atrophy F-box (MAFbx/atrogin-1), muscle RING finger 1 (MuRF1), MyoD and myogenin (MyoG). In addition, paeoniflorin modulated redox homeostasis by increasing antioxidant activity and suppressing excessive accumulation of reactive oxygen species (ROS). Paeoniflorin alleviated mitochondrial dysfunction by increasing the activities of electron transport chain complexes and mitochondrial membrane potential. Furthermore, paeoniflorin also regulates mitochondrial dynamics. Importantly, paeoniflorin upregulated the expression of silent information regulator 1 (SIRT1), peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), and phosphorylation of AMP-activated protein kinase (AMPK). Similar results were observed in C2C12 myoblasts treated with TNF-α and paeoniflorin. Notably, these beneficial effects of paeoniflorin on muscle atrophy were abolished by inhibiting AMPK and SIRT1 and knocking down PGC-1α. Taken together, this study showed for the first time that paeoniflorin has great therapeutic potential for CKD skeletal muscle atrophy through AMPK/SIRT1/PGC-1α-mediated oxidative stress and mitochondrial dysfunction.

Exercise Therapy for People With Sarcopenic Obesity: Myokines and Adipokines as Effective Actors

Sarcopenic obesity is defined as a multifactorial disease in aging with decreased body muscle, decreased muscle strength, decreased independence, increased fat mass, due to decreased physical activity, changes in adipokines and myokines, and decreased satellite cells. People with sarcopenic obesity cause harmful changes in myokines and adipokines. These changes are due to a decrease interleukin-10 (IL-10), interleukin-15 (IL-15), insulin-like growth factor hormone (IGF-1), irisin, leukemia inhibitory factor (LIF), fibroblast growth factor-21 (FGF-21), adiponectin, and apelin. While factors such as myostatin, leptin, interleukin-6 (IL-6), interleukin-8 (IL-8), and resistin increase. The consequences of these changes are an increase in inflammatory factors, increased degradation of muscle proteins, increased fat mass, and decreased muscle tissue, which exacerbates sarcopenia obesity. In contrast, exercise, especially strength training, reverses this process, which includes increasing muscle protein synthesis, increasing myogenesis, increasing mitochondrial biogenesis, increasing brown fat, reducing white fat, reducing inflammatory factors, and reducing muscle atrophy. Since some people with chronic diseases are not able to do high-intensity strength training, exercises with blood flow restriction (BFR) are newly recommended. Numerous studies have shown that low-intensity BFR training produces the same increase in hypertrophy and muscle strength such as high-intensity strength training. Therefore, it seems that exercise interventions with BFR can be an effective way to prevent the exacerbation of sarcopenia obesity. However, due to limited studies on adipokines and exercises with BFR in people with sarcopenic obesity, more research is needed.

The Correlation of Serum Myostatin Levels with Gait Speed in Kidney Transplantation Recipients

The primary role of myostatin is to negatively regulate skeletal muscle growth. The gait speed is a noninvasive, reliable parameter that predicts cardiovascular risk and mortality. This study evaluated the relationship between serum myostatin concentrations and gait speeds in patients who had undergone kidney transplantation (KT). A total of 84 KT recipients were evaluated. A speed of less than 1.0 m/s was categorized into the low gait speed group. We measured serum myostatin concentrations with a commercial enzyme-linked immunosorbent assay. KT recipients in the low gait speed group had significantly older age, as well as higher body weight, body mass index (BMI), skeletal muscle index, serum triglyceride levels, glucose levels, and blood urea nitrogen levels, lower estimated glomerular filtration rates and serum myostatin levels, a higher percentage of steroid use, and a lower proportion of mycophenolate mofetil use. Multivariable logistic regression analysis revealed that lower myostatin levels and lower frequency of mycophenolate mofetil use were independently associated with low gait speed. In multivariable stepwise linear regression analysis, myostatin levels were positively correlated with gait speeds, and age and BMI were negatively correlated with gait speeds. In the study, serum myostatin levels were significantly lower in the low gait speed group. Subjects in the low gait speed group also had greater BMI and older age.

Effects of hormonal changes on sarcopenia in chronic kidney disease: where are we now and what can we do?

Sarcopenia or muscle wasting is a progressive and generalized skeletal muscle disorder involving the accelerated loss of muscle mass and function, often associated with muscle weakness (dynapenia) and frailty. Whereas primary sarcopenia is related to ageing, secondary sarcopenia happens independent of age in the context of chronic disease states such as chronic kidney disease (CKD). Sarcopenia has become a major focus of research and public policy debate due to its impact on patient's health-related quality of life, health-care expenditure, morbidity, and mortality. The development of sarcopenia in patients with CKD is multifactorial and it may occur independently of weight loss or cachexia including under obese sarcopenia. Hormonal imbalances can facilitate the development of sarcopenia in the general population and is a common finding in CKD. Hormones that may influence the development of sarcopenia are testosterone, growth hormone, insulin, thyroid hormones, and vitamin D. Although the relationship between free testosterone level that is low in uraemic patients and sarcopenia in CKD is not well-defined, functional improvement may be seen. Unlike testosterone, it is known that vitamin D is associated with muscle strength, muscle size, and physical performance in patients with CKD. Outcomes after vitamin D replacement therapy are still controversial. The half-life of growth hormone (GH) is prolonged in patients with CKD. Besides, IGF-1 levels are normal in patients with Stage 4 CKD-a minimal reduction is seen in the end-stage renal disease. Unresponsiveness or resistance of IGF-1 and changes in the GH/IGF-1 axis are the main causes of sarcopenia in CKD. Low serum T3 level is frequent in CKD, but the net effect on sarcopenia is not well-studied. CKD patients develop insulin resistance (IR) from the earliest period even before GFR decline begins. IR reduces glucose utilization as an energy source by hepatic gluconeogenesis, decreasing muscle glucose uptake, impairing intracellular glucose metabolism. This cascade results in muscle protein breakdown. IR and sarcopenia might also be a new pathway for targeting. Ghrelin, oestrogen, cortisol, and dehydroepiandrosterone may be other players in the setting of sarcopenia. In this review, we mainly examine the effects of hormonal changes on the occurrence of sarcopenia in patients with CKD via the available data.

Molecular and Metabolic Mechanism of Low-Intensity Pulsed Ultrasound Improving Muscle Atrophy in Hindlimb Unloading Rats

Low-intensity pulsed ultrasound (LIPUS) has been proved to promote the proliferation of myoblast C2C12. However, whether LIPUS can effectively prevent muscle atrophy has not been clarified, and if so, what is the possible mechanism. The aim of this study is to evaluate the effects of LIPUS on muscle atrophy in hindlimb unloading rats, and explore the mechanisms. The rats were randomly divided into four groups: normal control group (NC), hindlimb unloading group (UL), hindlimb unloading plus 30 mW/cm² LIPUS irradiation group (UL + 30 mW/cm²), hindlimb unloading plus 80 mW/cm² LIPUS irradiation group (UL + 80 mW/cm²). The tails of rats in hindlimb unloading group were suspended for 28 days. The rats in the LIPUS treated group were simultaneously irradiated with LIPUS on gastrocnemius muscle in both lower legs at the sound intensity of 30 mW/cm² or 80 mW/cm² for 20 min/d for 28 days. C2C12 cells were exposed to LIPUS at 30 or 80 mW/cm² for 5 days. The results showed that LIPUS significantly promoted the proliferation and differentiation of myoblast C2C12, and prevented the decrease of cross-sectional area of muscle fiber and gastrocnemius mass in hindlimb unloading rats. LIPUS also significantly down regulated the expression of MSTN and its receptors ActRIIB, and up-regulated the expression of Akt and mTOR in gastrocnemius muscle of hindlimb unloading rats. In addition, three metabolic pathways (phenylalanine, tyrosine and tryptophan biosynthesis; alanine, aspartate and glutamate metabolism; glycine, serine and threonine metabolism) were selected as important metabolic pathways for hindlimb unloading effect. However, LIPUS promoted the stability of alanine, aspartate and glutamate metabolism pathway. These results suggest that the key mechanism of LIPUS in preventing muscle atrophy induced by hindlimb unloading may be related to promoting protein synthesis through MSTN/Akt/mTOR signaling pathway and stabilizing alanine, aspartate and glutamate metabolism.

Performance of Bioelectrical Impedance and Anthropometric Predictive Equations for Estimation of Muscle Mass in Chronic Kidney Disease Patients

Background: Patients with chronic kidney disease (CKD) are vulnerable to loss of muscle mass due to several metabolic alterations derived from the uremic syndrome. Reference methods for body composition evaluation are usually unfeasible in clinical settings.

Aims: To evaluate the accuracy of predictive equations based on bioelectrical impedance analyses (BIA) and anthropometry parameters for estimating fat free mass (FFM) and appendicular FFM (AFFM), compared to dual energy X-ray absorptiometry (DXA), in CKD patients.

Methods: We performed a longitudinal study with patients in non-dialysis-dependent, hemodialysis, peritoneal dialysis and kidney transplant treatment. FFM and AFFM were evaluated by DXA, BIA (Sergi, Kyle, Janssen and MacDonald equations) and anthropometry (Hume, Lee, Tian, and Noori equations). Low muscle mass was diagnosed by DXA analysis. Intra-class correlation coefficient (ICC), Bland-Altman graphic and multiple regression analysis were used to evaluate equation accuracy, linear regression analysis to evaluate bias, and ROC curve analysis and kappa for reproducibility.

Results: In total sample and in each CKD group, the predictive equation with the best accuracy was AFFM_Sergi (men, n = 137: ICC = 0.91, 95% CI = 0.79–0.96, bias = 1.11 kg; women, n = 129: ICC = 0.94, 95% CI = 0.92–0.96, bias = −0.28 kg). AFFM_Sergi also presented the best performance for low muscle mass diagnosis (men, kappa = 0.68, AUC = 0.83; women, kappa = 0.65, AUC = 0.85). Bias between AFFM_Sergi and AFFM_DXA was mainly affected by total body water and fat mass. None of the predictive equations was able to accurately predict changes in AFFM and FFM, with all ICC lower than 0.5.

Conclusion: The predictive equation with the best performance to asses muscle mass in CKD patients was AFFM_Sergi, including evaluation of low muscle mass diagnosis. However, assessment of changes in body composition was biased, mainly due to variations in fluid status together with adiposity, limiting its applicability for longitudinal evaluations.

Maintenance of Skeletal Muscle to Counteract Sarcopenia in Patients with Advanced Chronic Kidney Disease and Especially Those Undergoing Hemodialysis

Life extension in modern society has introduced new concepts regarding such disorders as frailty and sarcopenia, which has been recognized in various studies. At the same time, cutting-edge technology methods, e.g., renal replacement therapy for conditions such as hemodialysis (HD), have made it possible to protect patients from advanced lethal chronic kidney disease (CKD). Loss of muscle and fat mass, termed protein energy wasting (PEW), has been recognized as prognostic factor and, along with the increasing rate of HD introduction in elderly individuals in Japan, appropriate countermeasures are necessary. Although their origins differ, frailty, sarcopenia, and PEW share common components, among which skeletal muscle plays a central role in their etiologies. The nearest concept may be sarcopenia, for which diagnosis techniques have recently been reported. The focus of this review is on maintenance of skeletal muscle against aging and CKD/HD, based on muscle physiology and pathology. Clinically relevant and topical factors related to muscle wasting including sarcopenia, such as vitamin D, myostatin, insulin (related to diabetes), insulin-like growth factor I, mitochondria, and physical inactivity, are discussed. Findings presented thus far indicate that in addition to modulation of the aforementioned factors, exercise combined with nutritional supplementation may be a useful approach to overcome muscle wasting and sarcopenia in elderly patients undergoing HD treatments.

Muscle-Bone Crosstalk in Chronic Kidney Disease: The Potential Modulatory Effects of Exercise

Chronic kidney disease (CKD) is a prevalent worldwide public burden that increasingly compromises overall health as the disease progresses. Two of the most negatively affected tissues are bone and skeletal muscle, with CKD negatively impacting their structure, function and activity, impairing the quality of life of these patients and contributing to morbidity and mortality. Whereas skeletal health in this population has conventionally been associated with bone and mineral disorders, sarcopenia has been observed to impact skeletal muscle health in CKD. Indeed, bone and muscle tissues are linked anatomically and physiologically, and together regulate functional and metabolic mechanisms. With the initial crosstalk between the skeleton and muscle proposed to explain bone formation through muscle contraction, it is now understood that this communication occurs through the interaction of myokines and osteokines, with the skeletal muscle secretome playing a pivotal role in the regulation of bone activity. Regular exercise has been reported to be beneficial to overall health. Also, the positive regulatory effect that exercise has been proposed to have on bone and muscle anatomical, functional, and metabolic activity has led to the proposal of regular physical exercise as a therapeutic strategy for muscle and bone-related disorders. The detection of bone- and muscle-derived cytokine secretion following physical exercise has strengthened the idea of a cross communication between these organs. Hence, this review presents an overview of the impact of CKD in bone and skeletal muscle, and narrates how these tissues intrinsically communicate with each other, with focus on the potential effect of exercise in the modulation of this intercommunication.

The Relevance of a Physical Active Lifestyle and Physical Fitness on Immune Defense: Mitigating Disease Burden, With Focus on COVID-19 Consequences

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is a fast spreading virus leading to the development of Coronavirus Disease-2019 (COVID-19). Severe and critical cases are characterized by damage to the respiratory system, endothelial inflammation, and multiple organ failure triggered by an excessive production of proinflammatory cytokines, culminating in the high number of deaths all over the world. Sedentarism induces worse, continuous, and progressive consequences to health. On the other hand, physical activity provides benefits to health and improves low-grade systemic inflammation. The aim of this review is to elucidate the effects of physical activity in physical fitness, immune defense, and its contribution to mitigate the severe inflammatory response mediated by SARS-CoV-2. Physical exercise is an effective therapeutic strategy to mitigate the consequences of SARS-CoV-2 infection. In this sense, studies have shown that acute physical exercise induces the production of myokines that are secreted in tissues and into the bloodstream, supporting its systemic modulatory effect. Therefore, maintaining physical activity influence balance the immune system and increases immune vigilance, and also might promote potent effects against the consequences of infectious diseases and chronic diseases associated with the development of severe forms of COVID-19. Protocols to maintain exercise practice are suggested and have been strongly established, such as home-based exercise (HBE) and outdoor-based exercise (OBE). In this regard, HBE might help to reduce levels of physical inactivity, bed rest, and sitting time, impacting on adherence to physical activity, promoting all the benefits related to exercise, and attracting patients in different stages of treatment for COVID-19. In parallel, OBE must improve health, but also prevent and mitigate COVID-19 severe outcomes in all populations. In conclusion, HBE or OBE models can be a potent strategy to mitigate the progress of infection, and a coadjutant therapy for COVID-19 at all ages and different chronic conditions.