Sarcopenia Induced by Chronic Liver Disease in Mice Requires the Expression of the Bile Acids Membrane Receptor TGR5

Role of the ubiquitin-proteasome system in the sarcopenic-like phenotype induced by CCL5/RANTES

Sarcopenia is characterized by reduced muscle strength and mass and a decline in muscle fiber diameter and amount of sarcomeric proteins. Sarcopenia involves the activation of the ubiquitin-proteasome system (UPS). MuRF-1 and atrogin-1 are E3 ubiquitin ligases belonging to UPS, leading to proteolysis mediated by the PSMB 5, 6, and 7 subunits of 20S proteasome. CCL5/RANTES induces a sarcopenic-like effect in muscle cells. The present work explored the impact of CCL5 on UPS components and the influence of UPS on its sarcopenic-like effect. We demonstrated that CCL5 increased MuRF-1 and atrogin-1 protein levels and mRNA levels of subunits PSMB 5, 6, and 7. We used the MG132 inhibitor to elucidate the role of the 20S proteasome in the CCL5-induced sarcopenic-like effect. This inhibitor prevented the decrease in troponin and MHC protein levels and partially prevented the reduction in the diameter of single-isolated FDB muscle fibers induced by CCL5. These findings indicate that CCL5 actively modulates the UPS. Moreover, our results show the direct participation of UPS in the sarcopenic-like phenotype induced by CCL5.

Bile Acids as Signaling Molecules: Role of Ursodeoxycholic Acid in Cholestatic Liver Disease

Ursodeoxycholic acid (UDCA) is a natural substance physiologically produced in the liver. Initially used to dissolve gallstones, it is now successfully used in treating primary biliary cirrhosis and as adjuvant therapy for various hepatobiliary cholestatic diseases. However, the mechanisms underlying its beneficial effects still need to be clarified. Evidence suggests three mechanisms of action for UDCA that could benefit humans with cholestatic liver disease (CLD): protection of cholangiocytes against hydrophobic bile acid (BA) cytotoxicity, stimulation of hepatobiliary excretion, and protection of hepatocytes against BA-induced apoptosis. These mechanisms may act individually or together to potentiate them. At the molecular level, it has been observed that UDCA can generate modifications in the transcription and translation of proteins essential in the transport of BA, correcting the deficit in BA secretion in CLD, in addition to activating signaling pathways to translocate these transporters to the sites where they should fulfill their function. Inhibition of BA-induced hepatocyte apoptosis may play a role in CLD, characterized by BA retention in the hepatocyte. Thus, different mechanisms of action contribute to the improvement after UDCA administration in CLD. On the other hand, the effects of UDCA on tissues that possess receptors that may interact with BAs in pathological contexts, such as skeletal muscle, are still unclear. This work aims to describe the main molecular mechanisms by which UDCA acts in the human body, emphasizing the interaction in tissues other than the liver.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Osteoarthritis and sarcopenia-related traits: the cross-sectional study from NHANES 2011-2014 and Mendelian randomization study

BACKGROUND

Osteoarthritis (OA) and sarcopenia are common musculoskeletal disorders in the aged population, and a growing body of evidence indicated that they mutually influence one another. Nevertheless, there was still substantial controversy and uncertainty about the causal relationship between sarcopenia and OA. We explored the complex association between sarcopenia-related traits and OA using cross-sectional analysis and Mendelian randomization (MR).

METHODS

The cross-sectional study used the data from the National Health and Nutrition Examination Survey (NHANES) 2011-2014. Weighted multivariable-adjusted logistic regression and subgroup analyses were used to evaluate the correlation between sarcopenia, grip, appendicular lean mass (ALM) and the risk of OA. Then, we further performed MR analysis to examine the causal effect of sarcopenia-related traits (grip strength, ALM) on OA. Instrumental variables for grip strength and ALM were from the UK Biobank, and the summary-level data for OA was derived from the Genetics of Osteoarthritis (GO) Consortium GWAS (n = 826,690).

RESULTS

In this cross-sectional analysis, we observed that sarcopenia, grip were significantly linked with the risk of OA (OR 1.607, 95% CI 1.233-2.094, P < 0.001), (OR 0.972, 95% CI 0.964-0.979, P < 0.001). According to subgroup analyses stratified by gender, body mass index (BMI), and age, the significant positive relationship between sarcopenia and OA remained in males, females, the age (46-59 years) group, and the BMI (18.5-24.9 kg/m²) group (P < 0.05). Furthermore, MR analysis and sensitivity analyses showed causal associations between right grip, left grip and KOA (OR 0.668; 95% CI 0.509 to 0.877; P = 0.004), (OR 0.786; 95% CI 0.608 to 0.915; P = 0.042). Consistent directional effects for all analyses were observed in both the MR-Egger and weighted median methods. Subsequently, sensitivity analyses revealed no heterogeneity, directional pleiotropy or outliers for the causal effect of grip strength on KOA (P > 0.05).

CONCLUSIONS

Our research provided evidence that sarcopenia is correlated with an increased risk of OA, and there was a protective impact of genetically predicted grip strength on OA. These findings needed to be verified in further prospective cohort studies with a large sample size.

Cholic and deoxycholic acids induce mitochondrial dysfunction, impaired biogenesis and autophagic flux in skeletal muscle cells

BACKGROUND

Skeletal muscle is sensitive to bile acids (BA) because it expresses the TGR5 receptor for BA. Cholic (CA) and deoxycholic (DCA) acids induce a sarcopenia-like phenotype through TGR5-dependent mechanisms. Besides, a mouse model of cholestasis-induced sarcopenia was characterised by increased levels of serum BA and muscle weakness, alterations that are dependent on TGR5 expression. Mitochondrial alterations, such as decreased mitochondrial potential and oxygen consumption rate (OCR), increased mitochondrial reactive oxygen species (mtROS) and unbalanced biogenesis and mitophagy, have not been studied in BA-induced sarcopenia.

METHODS

We evaluated the effects of DCA and CA on mitochondrial alterations in C₂C₁₂ myotubes and a mouse model of cholestasis-induced sarcopenia. We measured mitochondrial mass by TOM20 levels and mitochondrial DNA; ultrastructural alterations by transmission electronic microscopy; mitochondrial biogenesis by PGC-1α plasmid reporter activity and protein levels by western blot analysis; mitophagy by the co-localisation of the MitoTracker and LysoTracker fluorescent probes; mitochondrial potential by detecting the TMRE probe signal; protein levels of OXPHOS complexes and LC3B by western blot analysis; OCR by Seahorse measures; and mtROS by MitoSOX probe signals.

RESULTS

DCA and CA caused a reduction in mitochondrial mass and decreased mitochondrial biogenesis. Interestingly, DCA and CA increased LC3II/LC3I ratio and decreased autophagic flux concordant with raised mitophagosome-like structures. In addition, DCA and CA decreased mitochondrial potential and reduced protein levels in OXPHOS complexes I and II. The results also demonstrated that DCA and CA decreased basal, ATP-linked, FCCP-induced maximal respiration and spare OCR. DCA and CA also reduced the number of cristae. In addition, DCA and CA increased the mtROS. In mice with cholestasis-induced sarcopenia, TOM20, OXPHOS complexes I, II and III, and OCR were diminished. Interestingly, the OCR and OXPHOS complexes were correlated with muscle strength and bile acid levels.

CONCLUSION

Our results showed that DCA and CA decreased mitochondrial mass, possibly by reducing mitochondrial biogenesis, which affects mitochondrial function, thereby altering potential OCR and mtROS generation. Some mitochondrial alterations were also observed in a mouse model of cholestasis-induced sarcopenia characterised by increased levels of BA, such as DCA and CA.

Ursodeoxycholic acid induces sarcopenia associated with decreased protein synthesis and autophagic flux

BACKGROUND

Skeletal muscle generates force and movements and maintains posture. Under pathological conditions, muscle fibers suffer an imbalance in protein synthesis/degradation. This event causes muscle mass loss and decreased strength and muscle function, a syndrome known as sarcopenia. Recently, our laboratory described secondary sarcopenia in a chronic cholestatic liver disease (CCLD) mouse model. Interestingly, the administration of ursodeoxycholic acid (UDCA), a hydrophilic bile acid, is an effective therapy for cholestatic hepatic alterations. However, the effect of UDCA on skeletal muscle mass and functionality has never been evaluated, nor the possible involved mechanisms.

METHODS

We assessed the ability of UDCA to generate sarcopenia in C57BL6 mice and develop a sarcopenic-like phenotype in C₂C₁₂ myotubes and isolated muscle fibers. In mice, we measured muscle strength by a grip strength test, muscle mass by bioimpedance and mass for specific muscles, and physical function by a treadmill test. We also detected the fiber's diameter and content of sarcomeric proteins. In C₂C₁₂ myotubes and/or isolated muscle fibers, we determined the diameter and troponin I level to validate the cellular effect. Moreover, to evaluate possible mechanisms, we detected puromycin incorporation, p70S6K, and 4EBP1 to evaluate protein synthesis and ULK1, LC3 I, and II protein levels to determine autophagic flux. The mitophagosome-like structures were detected by transmission electron microscopy.

RESULTS

UDCA induced sarcopenia in healthy mice, evidenced by decreased strength, muscle mass, and physical function, with a decline in the fiber's diameter and the troponin I protein levels. In the C₂C₁₂ myotubes, we observed that UDCA caused a reduction in the diameter and content of MHC, troponin I, puromycin incorporation, and phosphorylated forms of p70S6K and 4EBP1. Further, we detected increased levels of phosphorylated ULK1, the LC3II/LC3I ratio, and the number of mitophagosome-like structures. These data suggest that UDCA induces a sarcopenic-like phenotype with decreased protein synthesis and autophagic flux.

CONCLUSIONS

Our results indicate that UDCA induces sarcopenia in mice and sarcopenic-like features in C₂C₁₂ myotubes and/or isolated muscle fibers concomitantly with decreased protein synthesis and alterations in autophagic flux.

Lithocholic acid promotes skeletal muscle regeneration through the TGR5 receptor

<p indent="0mm">Lithocholic acid (LCA) is a classical secondary bile acid formed by the metabolism of gut microbiota. The TGR5 receptor (also known as G protein-coupled receptor 1, GPBAR1) is an important bile acid membrane receptor that mediates a variety of metabolic processes <italic>in vivo</italic>. In recent years, most studies have focused on the role of bile acid receptors in the intestine and liver. However, there are few reports on its effect on skeletal muscle regeneration, and the specific mechanism remains unclear. Therefore, it is necessary to investigate the mechanism of the TGR5 receptor in the regulation of skeletal muscle regeneration. The results demonstrate that muscle injection with LCA significantly reduces the necrosis rate of injured muscle and improves muscle injury. Moreover, treatment of C2C12 cells with LCA significantly increases AKT/mTOR/FoxO3 phosphorylation through the TGR5 receptor, enhances MyoG transcription and reduces FBXO32 transcription. These findings indicate that LCA can activate the TGR5/AKT signaling pathway, inhibit protein degradation and promote protein synthesis to enhance the myogenic process and promote skeletal muscle regeneration. </p>.

Differential Fibrotic Response of Muscle Fibroblasts, Myoblasts, and Myotubes to Cholic and Deoxycholic Acids

Fibrosis is a condition characterized by an increase in the components of the extracellular matrix (ECM). In skeletal muscle, the cells that participate in the synthesis of ECM are fibroblasts, myoblasts, and myotubes. These cells respond to soluble factors that increase ECM. Fibrosis is a phenomenon that develops in conditions of chronic inflammation, extensive lesions, or chronic diseases. A pathological condition with muscle weakness and increased bile acids (BA) in the blood is cholestatic chronic liver diseases (CCLD). Skeletal muscle expresses the membrane receptor for BA called TGR5. To date, muscle fibrosis in CCLD has not been evaluated. This study aims to assess whether BA can induce a fibrotic condition in muscle fibroblasts, myoblasts, and myotubes. The cells were incubated with deoxycholic (DCA) and cholic (CA) acids, and fibronectin protein levels were evaluated by Western blot. In muscle fibroblasts, both DCA and CA induced an increase in fibronectin protein levels. The same response was found in fibroblasts when activating TGR5 with the specific receptor agonist (INT-777). Interestingly, DCA reduced fibronectin protein levels in both myoblasts and myotubes, while CA did not show changes in fibronectin protein levels in myoblasts and myotubes. These results suggest that DCA and CA can induce a fibrotic phenotype in muscle-derived fibroblasts. On the other hand, DCA decreased the fibronectin in myoblasts and myotubes, whereas CA did not show any effect in these cell populations. Our results show that BA has different effects depending on the cell population to be analyzed.

Upregulation of CCL5/RANTES Gene Expression in the Diaphragm of Mice with Cholestatic Liver Disease

Chronic liver diseases are a group of pathologies affecting the liver with high prevalence worldwide. Among them, cholestatic chronic liver diseases (CCLD) are characterized by alterations in liver function and increased plasma bile acids. Secondary to liver disease, under cholestasis, is developed sarcopenia, a skeletal muscle dysfunction with decreased muscle mass, strength, and physical function. CCL5/RANTES is a chemokine involved in the immune and inflammatory response. Indeed, CCL5 is a myokine because it is produced by skeletal muscle. Several studies show that bile acids induce CCL5/RANTES expression in liver cells. However, it is unknown if the expression of CCL5/RANTES is changed in the skeletal muscle of mice with cholestatic liver disease. We used a murine model of cholestasis-induced sarcopenia by intake of hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC diet), in which we detected the mRNA levels for ccl5. We determined that mice fed the DDC diet presented high levels of serum bile acids and developed typical features of sarcopenia. Under these conditions, we detected the ccl5 gene expression in diaphragm muscle showing elevated mRNA levels compared to mice fed with a standard diet (chow diet). Our results collectively suggest an increased ccl5 gene expression in the diaphragm muscle concomitantly with elevated serum bile acids and the development of sarcopenia.

Bile Acids Alter the Autophagy and Mitogenesis in Skeletal Muscle Cells

Muscle atrophy decreases muscle mass with the subsequent loss of muscle function. Among the mechanisms that trigger sarcopenia is mitochondrial dysfunction. Mitochondria, whose primary function is to produce ATP, are dynamic organelles that present the process of formation (mitogenesis) and elimination (mitophagy). Failure of any of these processes contributes to mitochondrial malfunction. Mitogenesis is mainly controlled by Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1α), a transcriptional coactivator that regulates the expression of TFAM, which participates in mitogenesis. Mitophagy is a process of selective autophagy. Autophagy corresponds to a degradative pathway of protein complexes and organelles. Liver disease caused sarcopenia and increased bile acids in the blood. We demonstrated that the treatment with cholic (CA) or deoxycholic (DCA) bile acids generates mitochondrial dysfunction and loss of biomass. This work assessed whether CA and DCA alter autophagy and mitogenesis. For this, western blot evaluated the autophagy process by determining the protein levels of the LC3II/LC3I ratio. In addition, we assessed mitogenesis using a luciferase-coupled plasmid reporter for the PGC-1α promoter and the protein levels of TFAM by western blot. Our results indicate that treatment with CA or DCA induces autophagy, represented by an increase in the LC3II/LC3I ratio. In addition, a decreased autophagic flux was observed. On the other hand, when treated with CA or DCA, a decrease in the activity of the PGC-1α promoter was observed. However, the levels of TFAM increased in myotubes incubated with CA and DCA. Our results demonstrate that CA and DCA modulate autophagy ad mitogenesis in C₂C₁₂ myotubes.

Bile Acids Induce Alterations in Mitochondrial Function in Skeletal Muscle Fibers

Cholestatic chronic liver disease is characterized by developing sarcopenia and elevated serum levels of bile acids. Sarcopenia is a skeletal muscle disorder with the hallmarks of muscle weakness, muscle mass loss, and muscle strength decline. Our previous report demonstrated that deoxycholic acid (DCA) and cholic acid (CA), through the membrane receptor TGR5, induce a sarcopenia-like phenotype in myotubes and muscle fibers. The present study aimed to evaluate the impact of DCA and CA on mitochondrial mass and function in muscle fibers and the role of the TGR5 receptor. To this end, muscle fibers obtained from wild-type and TGR5^−/− mice were incubated with DCA and CA. Our results indicated that DCA and CA decreased mitochondrial mass, DNA, and potential in a TGR5-dependent fashion. Furthermore, with TGR5 participation, DCA and CA also reduced the oxygen consumption rate and complexes I and II from the mitochondrial electron transport chain. In addition, DCA and CA generated more mitochondrial reactive oxygen species than the control, which were abolished in TGR5^−/− mice muscle fibers. Our results indicate that DCA and CA induce mitochondrial dysfunction in muscle fibers through a TGR5-dependent mechanism.

Gut microbiota in sarcopenia and heart failure

Sarcopenia is common in aging and in patients with heart failure (HF) who may experience worse outcomes. Patients with muscle wasting are more likely to experience falls and can have serious complications when undergoing cardiac procedures. While intensive nutritional support and exercise rehabilitation can help reverse some of these changes, they are often under-prescribed in a timely manner, and we have limited insights into who would benefit. Mechanistic links between gut microbial metabolites (GMM) have been identified and may contribute to adverse clinical outcomes in patients with cardio-renal diseases and aging. This review will examine the emerging evidence for the influence of the gut microbiome-derived metabolites and notable signaling pathways involved in both sarcopenia and HF, especially those linked to dietary intake and mitochondrial metabolism. This provides a unique opportunity to gain mechanistic and clinical insights into developing novel therapeutic strategies that target these GMM pathways or through tailored nutritional modulation to prevent progressive muscle wasting in elderly patients with heart failure.

Redox-Dependent Effects in the Physiopathological Role of Bile Acids

Bile acids (BA) are recognized by their role in nutrient absorption. However, there is growing evidence that BA also have endocrine and metabolic functions. Besides, the steroidal-derived structure gives BA a toxic potential over the biological membrane. Thus, cholestatic disorders, characterized by elevated BA on the liver and serum, are a significant cause of liver transplant and extrahepatic complications, such as skeletal muscle, central nervous system (CNS), heart, and placenta. Further, the BA have an essential role in cellular damage, mediating processes such as membrane disruption, mitochondrial dysfunction, and the generation of reactive oxygen species (ROS) and oxidative stress. The purpose of this review is to describe the BA and their role on hepatic and extrahepatic complications in cholestatic diseases, focusing on the association between BA and the generation of oxidative stress that mediates tissue damage.

Baicalin and the liver-gut system: Pharmacological bases explaining its therapeutic effects

With the development of high-throughput screening and bioinformatics technology, natural products with a range of pharmacological targets in multiple diseases have become important sources of new drug discovery. These compounds are derived from various plants, including the dried root of Scutellaria baicalensis Georgi, which is often used as a traditional Chinese herb named Huangqin, a popular medication used for thousands of years in China. Many studies have shown that baicalin, an extract from Scutellaria baicalensis Georgi, exerts various protective effects on liver and gut diseases. Baicalin plays a therapeutic role mainly by mediating downstream apoptosis and immune response pathways induced by upstream oxidative stress and inflammation. During oxidative stress regulation, PI3K/Akt/NRF2, Keap-1, NF-κB and HO-1 are key factors associated with the healing effects of baicalin on NAFLD/NASH, ulcerative colitis and cholestasis. In the inflammatory response, IL-6, IL-1β, TNF-α, MIP-2 and MIP-1α are involved in the alleviation of NAFLD/NASH, cholestasis and liver fibrosis by baicalin, as are TGF-β1/Smads, STAT3 and NF-κB. Regarding the apoptosis pathway, Bax, Bcl-2, Caspase-3 and Caspase-9 are key factors related to the suppression of hepatocellular carcinoma and attenuation of liver injury and colorectal cancer. In addition to immune regulation, PD-1/PDL-1 and TLR4-NF-κB are correlated with the alleviation of hepatocellular carcinoma, ulcerative colitis and colorectal cancer by baicalin. Moreover, baicalin regulates intestinal flora by promoting the production of SCFAs. Furthermore, BA is involved in the interactions of the liver-gut axis by regulating TGR5, FXR, bile acids and the microbiota. In general, a comprehensive analysis of this natural compound was conducted to determine the mechanism by which it regulates bile acid metabolism, the intestinal flora and related signaling pathways, providing new insights into the pharmacological effects of baicalin. The mechanism linking the liver and gut systems needs to be elucidated to draw attention to its great clinical importance.