Caveolin-3 deficiency associated with the dystrophy P104L mutation impairs skeletal muscle mitochondrial form and function

CAV3 alleviates diabetic cardiomyopathy via inhibiting NDUFA10-mediated mitochondrial dysfunction

BACKGROUND

The progression of diabetic cardiomyopathy (DCM) is noticeably influenced by mitochondrial dysfunction. Variants of caveolin 3 (CAV3) play important roles in cardiovascular diseases. However, the potential roles of CAV3 in mitochondrial function in DCM and the related mechanisms have not yet been elucidated.

METHODS

Cardiomyocytes were cultured under high-glucose and high-fat (HGHF) conditions in vitro, and db/db mice were employed as a diabetes model in vivo. To investigate the role of CAV3 in DCM and to elucidate the molecular mechanisms underlying its involvement in mitochondrial function, we conducted Liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis and functional experiments.

RESULTS

Our findings demonstrated significant downregulation of CAV3 in the cardiac tissue of db/db mice, which was found to be associated with cardiomyocyte apoptosis in DCM. Importantly, cardiac-specific overexpression of CAV3 effectively inhibited the progression of DCM, as it protected against cardiac dysfunction and cardiac remodeling associated by alleviating cardiomyocyte mitochondrial dysfunction. Furthermore, mass spectrometry analysis and immunoprecipitation assays indicated that CAV3 interacted with NDUFA10, a subunit of mitochondrial complex I. CAV3 overexpression reduced the degradation of lysosomal pathway in NDUFA10, restored the activity of mitochondrial complex I and improved mitochondrial function. Finally, our study demonstrated that CAV3 overexpression restored mitochondrial function and subsequently alleviated DCM partially through NDUFA10.

CONCLUSIONS

The current study provides evidence that CAV3 expression is significantly downregulated in DCM. Upregulation of CAV3 interacts with NDUFA10, inhibits the degradation of lysosomal pathway in NDUFA10, a subunit of mitochondrial complex I, restores the activity of mitochondrial complex I, ameliorates mitochondrial dysfunction, and thereby protects against DCM. These findings indicate that targeting CAV3 may be a promising approach for the treatment of DCM.

The C5aR1 complement receptor: A novel immunomodulator of insulin action in skeletal muscle

The complement system constitutes an integral component of the innate immune system and plays a critical role in adaptive immunity. Activation of this system engenders the production of complement peptide fragments, including C5a, which engage G-protein coupled receptors predominantly expressed in immune-associated cells, such as neutrophils, initiating pro-inflammatory responses. Intriguingly, our investigation has unveiled the presence of C5a receptor 1 (C5aR1) expression within skeletal muscle, a key metabolic tissue and primary target of insulin. Herein, we demonstrate that C5aR1 activation by C5a in differentiated human skeletal muscle cells elicits acute suppression of insulin signalling. This suppression manifests as impaired insulin-dependent association between IRS1 and the p85 subunit of PI3-kinase, a 50% reduction in Akt phosphorylation, and a 60% decline in insulin-stimulated glucose uptake. This impairment in insulin signalling is associated with a three-fold elevation in intramyocellular diacylglycerol (DAG) levels and a two-fold increase in cytosolic calcium content, which promote PKC-mediated IRS1 inhibition via enhanced phosphorylation at IRS1 Ser1101. Significantly, our findings demonstrate that structurally diverse C5aR1 antagonists, along with genetic deletion or stable silencing of C5aR1 by 80% using short-hairpin RNA, effectively attenuate repression of insulin signalling by C5a in LHCN-M2 human skeletal myotubes. These results underscore the potential of heightened C5aR1 activation, characteristic of obesity and chronic inflammatory conditions, to detrimentally impact insulin function within skeletal muscle cells. Additionally, the study suggests that agents targeting the C5a-C5aR axis, originally devised for mitigating complement-dependent inflammatory conditions, may offer therapeutic avenues to ameliorate immune-driven insulin resistance in key peripheral metabolic tissues, including skeletal muscle.

Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors

Sarcopenia is a geriatric disorder characterized by a progressive decline in muscle mass and function. This disorder has been associated with a range of adverse health outcomes, including fractures, functional deterioration, and increased mortality. The pathophysiology of sarcopenia is highly complex and multifactorial, involving both genetic and environmental factors as key contributors. This review consolidates current knowledge on the genetic factors influencing the pathogenesis of sarcopenia, particularly focusing on the altered gene expression of structural and metabolic proteins, growth factors, hormones, and inflammatory cytokines. While the influence of environmental factors such as physical inactivity, chronic diseases, smoking, alcohol consumption, and sleep disturbances on sarcopenia is relatively well understood, there is a dearth of studies examining their mechanistic roles. Therefore, this review emphasizes the interplay between genetic and environmental factors, elucidating their cumulative role in exacerbating the progression of sarcopenia beyond their individual effects. The unique contribution of this review lies in synthesizing the latest evidence on the genetic factors and their interaction with environmental factors, aiming to inform the development of novel therapeutic or preventive interventions for sarcopenia.

Caveolin-3 loss linked with the P104L LGMD-1C mutation modulates skeletal muscle mTORC1 signalling and cholesterol homeostasis

BACKGROUND

Caveolins are the principal structural components of plasma membrane caveolae. Dominant pathogenic mutations in the muscle-specific caveolin-3 (Cav3) gene isoform, such as the limb girdle muscular dystrophy type 1C (LGMD-1C) P104L mutation, result in dramatic loss of the Cav3 protein and pathophysiological muscle weakness/wasting. We hypothesize that such muscle degeneration may be linked to disturbances in signalling events that impact protein turnover. Herein, we report studies assessing the effects of Cav3 deficiency on mammalian or mechanistic target of rapamycin complex 1 (mTORC1) signalling in skeletal muscle cells.

METHODS

L6 myoblasts were stably transfected with Cav3P104L or expression of native Cav3 was abolished by CRISPR/Cas9 genome editing (Cav3 knockout [Cav3KO]) prior to performing subcellular fractionation and immunoblotting, analysis of real-time mitochondrial respiration or fixed cell immunocytochemistry. Skeletal muscle from wild-type and Cav3-/- mice was processed for immunoblot analysis of downstream mTORC1 substrate phosphorylation.

RESULTS

Cav3 was detected in lysosomal-enriched membranes isolated from L6 myoblasts and observed by confocal microscopy to co-localize with lysosomal-specific markers. Cav3P104L expression, which results in significant (~95%) loss of native Cav3, or CRISPR/Cas9-mediated Cav3KO, reduced amino acid-dependent mTORC1 activation. The decline in mTORC1-directed signalling was detected by immunoblot analysis of L6 muscle cells and gastrocnemius Cav3-/- mouse muscle as judged by reduced phosphorylation of mTORC1 substrates that play key roles in the initiation of protein synthesis (4EBP1S65 and S6K1T389 ). S6K1T389 and 4EBP1S65 phosphorylation reduced by over 75% and 80% in Cav3KO muscle cells and by over 90% and 30% in Cav3-/- mouse skeletal muscle, respectively. The reduction in protein synthetic capacity in L6 muscle cells was confirmed by analysis of puromycylated peptides using the SUnSET assay. Cav3 loss was also associated with a 26% increase in lysosomal cholesterol, and pharmacological manipulation of lysosomal cholesterol was effective in replicating the reduction in mTORC1 activity observed in Cav3KO cells. Notably, re-expression of Cav3 in Cav3KO myoblasts normalized lysosomal cholesterol content, which coincided with a recovery in protein translation and an associated increase in mTORC1-directed phosphorylation of downstream targets.

CONCLUSIONS

Our findings indicate that Cav3 can localize on lysosomal membranes and is a novel regulator of mTORC1 signalling in muscle. Cav3 deficiency associated with the Cav3P104L mutation impairs mTORC1 activation and protein synthetic capacity in skeletal muscle cells, which may be linked to disturbances in lysosomal cholesterol trafficking and contribute to the pathology of LGMD-1C.

Limb-Girdle Muscular Dystrophies Classification and Therapies

Limb-girdle muscular dystrophies (LGMDs) are caused by mutations in multiple genes. This review article presents 39 genes associated with LGMDs. Some forms are inherited in a dominant fashion, while for others this occurs recessively. The classification of LGMDs has evolved through time. Lately, to be considered an LGMD, the mutation has to cause a predominant proximal muscle weakness and must be found in two or more unrelated families. This article also presents therapies for LGMDs, examining both available treatments and those in development. For now, only symptomatic treatments are available for patients. The goal is now to solve the problem at the root of LGMDs instead of treating each symptom individually. In the last decade, multiple other potential treatments were developed and studied, such as stem-cell transplantation, exon skipping, gene delivery, RNAi, and gene editing.

Measurement of GLUT4 Traffic to and from the Cell Surface in Muscle Cells

Elevated blood glucose following a meal is cleared by insulin-stimulated glucose entry into muscle and fat cells. The hormone increases the amount of the glucose transporter GLUT4 at the plasma membrane in these tissues at the expense of preformed intracellular pools. In addition, muscle contraction also increases glucose uptake via a gain in GLUT4 at the plasma membrane. Regulation of GLUT4 levels at the cell surface could arise from alterations in the rate of its exocytosis, endocytosis, or both. Hence, methods that can independently measure these traffic parameters for GLUT4 are essential to understanding the mechanism of regulation of membrane traffic of the transporter. Here, we describe cell population-based assays to measure the steady-state levels of GLUT4 at the cell surface, as well as to separately measure the rates of GLUT4 endocytosis and endocytosis. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Measuring steady-state cell surface GLUT4myc Basic Protocol 2: Measuring steady-state cell surface GLUT4-HA Basic Protocol 3: Measuring GLUT4myc endocytosis Basic Protocol 4: Measuring GLUT4myc exocytosis.

Structural analysis of the P132L disease mutation in caveolin-1 reveals its role in the assembly of oligomeric complexes

Caveolin-1 (CAV1) is a membrane-sculpting protein that oligomerizes to generate flask-shaped invaginations of the plasma membrane known as caveolae. Mutations in CAV1 have been linked to multiple diseases in humans. Such mutations often interfere with oligomerization and the intracellular trafficking processes required for successful caveolae assembly, but the molecular mechanisms underlying these defects have not been structurally explained. Here, we investigate how a disease-associated mutation in one of the most highly conserved residues in CAV1, P132L, affects CAV1 structure and oligomerization. We show that P132 is positioned at a major site of protomer-protomer interactions within the CAV1 complex, providing a structural explanation for why the mutant protein fails to homo-oligomerize correctly. Using a combination of computational, structural, biochemical, and cell biological approaches, we find that despite its homo-oligomerization defects P132L is capable of forming mixed hetero-oligomeric complexes with WT CAV1 and that these complexes can be incorporated into caveolae. These findings provide insights into the fundamental mechanisms that control the formation of homo- and hetero-oligomers of caveolins that are essential for caveolae biogenesis, as well as how these processes are disrupted in human disease.

Characterization of lncRNA/circRNA-miRNA-mRNA network to reveal potential functional ceRNAs in the skeletal muscle of chicken

Skeletal muscle, comprising approximately 40% of body mass, is a highly complex and heterogeneous tissue serving a multitude of functions in the organism. Non-coding RNAs (ncRNAs) are known to participate in skeletal muscle development as critical regulators. However, the regulatory mechanisms of ncRNAs on chicken muscle traits are not well understood. In the present study, we collected the leg muscle from male embryos of Tibetan chicken at embryonic (E) 10 and E18 for RNA sequencing. A total of 6,583 differentially expressed mRNAs (DEMs) including 3,055 down-regulated and 3,528 up-regulated were identified in E18. We identified 695 differentially expressed lncRNAs (DELs) (187 down-regulated and 508 up-regulated) and 1,906 differentially expressed circRNAs (DECs) (1,224 down-regulated and 682 up-regulated) in E18. Among the 130 differentially expressed miRNAs (DEMIs), 59 were up-regulated and 71 were down-regulated in E18. Numerous DEMs and target genes for miRNAs/lncRNAs were significantly enriched in the muscle system process and cell cycle. We constructed a miRNA-gene-pathway network by considering target relationships between genes related to skeletal muscle development and miRNAs. A competing endogenous RNA (ceRNA) network was also constructed by integrating competing relationships between DEMs, DELs, and DECs. Several DELs and DECs were predicted to regulate the ADRA1B, ATP2A2, ATP2B1, CACNA1S, CACNB4, MYLK2, and ROCK2 genes. We discovered the crosstalk between the ncRNAs and their competing mRNAs, which provides insights into ceRNA function and mechanisms in the skeletal muscle development of chicken.

An Avascular Niche Created by Axitinib-Loaded PCL/Collagen Nanofibrous Membrane Stabilized Subcutaneous Chondrogenesis of Mesenchymal Stromal Cells

Engineered cartilage derived from mesenchymal stromal cells (MSCs) always fails to maintain the cartilaginous phenotype in the subcutaneous environment due to the ossification tendency. Vascular invasion is a prerequisite for endochondral ossification during the development of long bone. As an oral antitumor medicine, Inlyta (axitinib) possesses pronounced antiangiogenic activity, owing to the inactivation of the vascular endothelial growth factor (VEGF) signaling pathway. In this study, axitinib-loaded poly(ε-caprolactone) (PCL)/collagen nanofibrous membranes are fabricated by electrospinning for the first time. Rabbit-derived MSCs-engineered cartilage is encapsulated in the axitinib-loaded nanofibrous membrane and subcutaneously implanted into nude mice. The sustained and localized release of axitinib successfully inhibits vascular invasion, stabilizes cartilaginous phenotype, and helps cartilage maturation. RNA sequence further reveals that axitinib creates an avascular, hypoxic, and low immune response niche. Timp1 is remarkably upregulated in this niche, which probably plays a functional role in inhibiting the activity of matrix metalloproteinases and stabilizing the engineered cartilage. This study provides a novel strategy for stable subcutaneous chondrogenesis of mesenchymal stromal cells, which is also suitable for other medical applications, such as arthritis treatment, local treatment of tumors, and regeneration of other avascular tissues (cornea and tendon).

Synapsin-Promoted Caveolin-1 Overexpression Maintains Mitochondrial Morphology and Function in PSAPP Alzheimer's Disease Mice

Mitochondrial dysfunction plays a pivotal role in the Alzheimer's Disease (AD) pathology. Disrupted mitochondrial dynamics (i.e., fusion/fission balance), which are essential for normal mitochondria structure and function, are documented in AD. Caveolin-1 (Cav-1), a membrane/lipid raft (MLR) scaffolding protein regulates metabolic pathways in several different cell types such as hepatocytes and cancer cells. Previously, we have shown decreased expression of Cav-1 in the hippocampus of 9-month (m) old PSAPP mice, while hippocampal overexpression of neuron-targeted Cav-1 using the synapsin promoter (i.e., SynCav1) preserved cognitive function, neuronal morphology, and synaptic ultrastructure in 9 and 12 m PSAPP mice. Considering the central role of energy production in maintaining normal neuronal and synaptic function and survival, the present study reveals that PSAPP mice exhibit disrupted mitochondrial distribution, morphometry, and respiration. In contrast, SynCav1 mitigates mitochondrial damage and loss and enhances mitochondrial respiration. Furthermore, by examining mitochondrial dynamics, we found that PSAPP mice showed a significant increase in the phosphorylation of mitochondrial dynamin-related GTPase protein (DRP1), resulting in excessive mitochondria fragmentation and dysfunction. In contrast, hippocampal delivery of SynCav1 significantly decreased p-DRP1 and augmented the level of the mitochondrial fusion protein, mitofusin1 (Mfn1) in PSAPP mice, a molecular event, which may mechanistically explain for the preserved balance of mitochondria fission/fusion and metabolic resilience in 12 m PSAPP-SynCav1 mice. Our data demonstrate the critical role for Cav-1 in maintaining normal mitochondrial morphology and function through affecting mitochondrial dynamics and explain a molecular and cellular mechanism underlying the previously reported neuroprotective and cognitive preservation induced by SynCav1 in PSAPP mouse model of AD.

Phospholipids: Identification and Implication in Muscle Pathophysiology

Phospholipids (PLs) are amphiphilic molecules that were essential for life to become cellular. PLs have not only a key role in compartmentation as they are the main components of membrane, but they are also involved in cell signaling, cell metabolism, and even cell pathophysiology. Considered for a long time to simply be structural elements of membranes, phospholipids are increasingly being viewed as sensors of their environment and regulators of many metabolic processes. After presenting their main characteristics, we expose the increasing methods of PL detection and identification that help to understand their key role in life processes. Interest and importance of PL homeostasis is growing as pathogenic variants in genes involved in PL biosynthesis and/or remodeling are linked to human diseases. We here review diseases that involve deregulation of PL homeostasis and present a predominantly muscular phenotype.

Skeletal Muscle Mitochondria Dysfunction in Genetic Neuromuscular Disorders with Cardiac Phenotype

Mitochondrial dysfunction is considered the major contributor to skeletal muscle wasting in different conditions. Genetically determined neuromuscular disorders occur as a result of mutations in the structural proteins of striated muscle cells and therefore are often combined with cardiac phenotype, which most often manifests as a cardiomyopathy. The specific roles played by mitochondria and mitochondrial energetic metabolism in skeletal muscle under muscle-wasting conditions in cardiomyopathies have not yet been investigated in detail, and this aspect of genetic muscle diseases remains poorly characterized. This review will highlight dysregulation of mitochondrial representation and bioenergetics in specific skeletal muscle disorders caused by mutations that disrupt the structural and functional integrity of muscle cells.

Transcriptomic investigation of embryonic pectoral muscle reveals increased myogenic processes in Shitou geese compared to Wuzong geese

1.Embryonic stages before birth are crucial for poultry muscle development, as this determines muscle mass in adulthood. This study characterised the distinction in embryonic pectoral muscle development between Wuzong (WZE, small) and Shitou (STE, large) geese (two indigenous goose breeds in Guangdong Province, China) at embryonic days 15 (E15), 23 (E23) and the day of hatching (P1) to gain insights into the regulatory mechanisms of muscle development.2.The results showed that STE had significantly higher myofibre density during E15-P1 and had significantly larger myofibre diameter at E15 than WZE. By RNA-sequencing analysis, 19 507 genes were detected, and 7121 differentially expressed genes (DEGs) were identified.3.Gene expression distinctions between breeds began increasing from E23, and WZE had different gene expression profiles compared to STE. A GO analysis of DEGs indicated that myo-genes involved at E15 may influence distinct pectoral muscle development characteristics between WZE and STE. The RT-qPCR results were consistent with the RNA-sequencing analysis. Four muscle structure protein coding genes (MYL2, MYL3, TNNI2 and TNNC2 and three other functional genes (CAV3, CACNA1S and NOS1) were identified in a predicted interaction network. These functional genes may interact with muscle structural protein coding genes to regulate embryonic pectoral muscle development in WZE and STE geese.4.The study revealed that STE and WZE had divergent embryonic pectoral muscle development patterns and these differences may begin before E15.

A Role for Caveolin-3 in the Pathogenesis of Muscular Dystrophies

Caveolae are the cholesterol-rich small invaginations of the plasma membrane present in many cell types including adipocytes, endothelial cells, epithelial cells, fibroblasts, smooth muscles, skeletal muscles and cardiac muscles. They serve as specialized platforms for many signaling molecules and regulate important cellular processes like energy metabolism, lipid metabolism, mitochondria homeostasis, and mechano-transduction. Caveolae can be internalized together with associated cargo. The caveolae-dependent endocytic pathway plays a role in the withdrawal of many plasma membrane components that can be sent for degradation or recycled back to the cell surface. Caveolae are formed by oligomerization of caveolin proteins. Caveolin-3 is a muscle-specific isoform, whose malfunction is associated with several diseases including diabetes, cancer, atherosclerosis, and cardiovascular diseases. Mutations in Caveolin-3 are known to cause muscular dystrophies that are collectively called caveolinopathies. Altered expression of Caveolin-3 is also observed in Duchenne’s muscular dystrophy, which is likely a part of the pathological process leading to muscle weakness. This review summarizes the major functions of Caveolin-3 in skeletal muscles and discusses its involvement in the pathology of muscular dystrophies.

Fat mass- and obesity-associated (FTO) gene promoted myoblast differentiation through the focal adhesion pathway in chicken

The action of FTO on myoblasts proliferation and differentiation and molecular mechanism underlying it were investigated by transfecting with FTO lentiviral overexpression vector and gene expression profile sequencing. Compared with the control group, myoblasts with FTO transfection was significantly enhanced proliferation; the expression of MYOG and MYOD mRNA was significantly increased. In cells transfected with FTO, 129 differentially expressed genes were determined compared with control group, with 104 up-regulated and 25 down-regulated genes. Twelve pathways (Phagosome, Focal adhesion, Adrenergic signaling in cardiomyocytes, Endocytosis, Cardiac muscle contraction, Toll-like receptor, Ribosome, Tight junction, Regulation of actin cytoskeleton, Cytokine-cytokine receptor interaction, Adrenergic signaling in cardiomyocytes and MAPK) were significantly enriched. Eight genes known to be directly or indirectly related to skeletal muscle development (LAMA5, SPP1, CAV3, RASGRF1, FAK, PDGFB, PDGFRα, and RAC2) were enriched in the focal adhesion and expressed differentially. Altogether, these data suggested that FTO stimulated differentiation of myoblasts through regulation of eight genes enriched in the focal adhesion.

Caveolin-3 deficiency associated with the dystrophy P104L mutation impairs skeletal muscle mitochondrial form and function

BACKGROUND

Caveolin-3 (Cav3) is the principal structural component of caveolae in skeletal muscle. Dominant pathogenic mutations in the Cav3 gene, such as the Limb Girdle Muscular Dystrophy-1C (LGMD1C) P104L mutation, result in substantial loss of Cav3 and myopathic changes characterized by muscle weakness and wasting. We hypothesize such myopathy may also be associated with disturbances in mitochondrial biology. Herein, we report studies assessing the effects of Cav3 deficiency on mitochondrial form and function in skeletal muscle cells.

METHODS

L6 myoblasts were stably transfected with Cav3^P104L or expression of native Cav3 repressed by shRNA or CRISPR/Cas9 genome editing prior to performing fixed/live cell imaging of mitochondrial morphology, subcellular fractionation and immunoblotting, or analysis of real time mitochondrial respiration. Skeletal muscle from wild-type and Cav3^-/- mice was processed for analysis of mitochondrial proteins by immunoblotting.

RESULTS

Caveolin-3 was detected in mitochondrial-enriched membranes isolated from mouse gastrocnemius muscle and L6 myoblasts. Expression of Cav3^P104L in L6 myoblasts led to its targeting to the Golgi and loss of native Cav3 (>95%), including that associated with mitochondrial membranes. Cav3^P104L reduced mitochondrial mass and induced fragmentation of the mitochondrial network that was associated with significant loss of proteins involved in mitochondrial biogenesis, respiration, morphology, and redox function [i.e. PGC1α, succinate dehyrdogenase (SDHA), ANT1, MFN2, OPA1, and MnSOD). Furthermore, Cav3^P104L myoblasts exhibited increased mitochondrial cholesterol and loss of cardiolipin. Consistent with these changes, Cav3^P104L expression reduced mitochondrial respiratory capacity and increased myocellular superoxide production. These morphological, biochemical, and functional mitochondrial changes were phenocopied in myoblasts in which Cav3 had been silenced/knocked-out using shRNA or CRISPR. Reduced mitochondrial mass, PGC1α, SDHA, ANT1, and MnSOD were also demonstrable in Cav3^-/- mouse gastrocnemius. Strikingly, Cav3 re-expression in Cav3KO myoblasts restored its mitochondrial association and facilitated reformation of a tubular mitochondrial network. Significantly, re-expression also mitigated changes in mitochondrial superoxide, cholesterol, and cardiolipin content and recovered cellular respiratory capacity.

CONCLUSIONS

Our results identify Cav3 as an important regulator of mitochondrial homeostasis and reveal that Cav3 deficiency in muscle cells associated with the Cav3^P104L mutation invokes major disturbances in mitochondrial respiration and energy status that may contribute to the pathology of LGMD1C.