Expression patterns of initiator and effector caspases in denervated human skeletal muscle

A novel variant in the QRICH1 gene was identified in a patient with severe developmental delay

BACKGROUND

QRICH1 encodes the glutamine-rich protein 1, which contains one caspase activation recruitment domain and is likely to be involved in apoptosis and inflammation. However, the function of the QRICH1 gene was largely unknown. Recently, several studies have reported de novo variants in QRICH1, and the variants have been associated with Ververi-Brady syndrome characterized by developmental delay, nonspecific facial dysmorphism, and hypotonia.

MATERIALS AND METHODS

Whole exome sequencing, clinical examinations, and functional experiments were performed to identify the etiology of our patient.

RESULTS

Here, we added another patient with severe growth retardation, atrial septal defect, and slurred speech. Whole exome sequencing identified a novel truncation variant in the QRICH1 gene (MN_017730.3: c.1788dupC, p.Tyr597Leufs*9). Furthermore, the functional experiments confirmed the effect of genetic variation.

CONCLUSION

Our findings expand the QRICH1 variant spectrum in developmental disorders and provide evidence for the application of whole exome sequencing in Ververi-Brady syndrome.

A case of Ververi-Brady syndrome due to QRICH1 loss of function and the literature review

Ververi-Brady syndrome (VBS), first reported in 2018, is characterized by intellectual disability, speech delay, and mild dysmorphic facial features. VBS has been linked to de novo loss-of-function variants in the glutamine-rich protein 1 (QRICH1) on chromosome 3p21 and was reported until lately in only five individuals. Four additional cases have just been described substantiating the notion that children with VBS are mildly dysmorphic, mildly to moderately intellectually disabled, have linear growth shortage, are picky eaters, and have notable attention and social behavioral deficits. We describe a new patient and review the clinical and genetic information, on all previously reported VBS cases. The child here reported is noted for maladaptive behavior, sensory hypersensitivity, and slow linear growth. He is mainly hyperactive, distractible, impulsive, and inattentive. His speech, initially delayed, is fair and his verbal comprehension age adequate.

Loss of membrane integrity drives myofiber death in lipin1-deficient skeletal muscle

Mutations in lipin1 are suggested to be a common cause of massive rhabdomyolysis episodes in children; however, the molecular mechanisms involved in the regulation of myofiber death caused by the absence of lipin1 are not fully understood. Loss of membrane integrity is considered as an effective inducer of cell death in muscular dystrophy. In this study, we utilized a mouse line with selective homozygous lipin1 deficiency in the skeletal muscle (Lipin1Myf5cKO ) to determine the role of compromised membrane integrity in the myofiber death in lipin1-deficient muscles. We found that Lipin1Myf5cKO muscles had significantly elevated proapoptotic factors (Bax, Bak, and cleaved caspase-9) and necroptotic proteins such as RIPK1, RIPK3, and MLKL compared with WT mice. Moreover, Lipin1Myf5cKO muscle had significantly higher membrane disruptions, as evidenced by increased IgG staining and elevated uptake of Evans Blue Dye (EBD) and increased serum creatine kinase activity in Lipin1Myf5cKO muscle fibers. EBD-positive fibers were strongly colocalized with apoptotic or necroptotic myofibers, suggesting an association between compromised plasma membrane integrity and cell death pathways. We further show that the absence of lipin1 leads to a significant decrease in the absolute and specific muscle force (normalized to muscle mass). Our work indicates that apoptosis and necroptosis are associated with a loss of membrane integrity in Lipin1Myf5cKO muscle and that myofiber death and dysfunction may cause a decrease in contractile force.

Proteomic and bioinformatic analysis of differentially expressed proteins in denervated skeletal muscle

The aim of this study was to improve our understanding and the current treatment of denervation-induced skeletal muscle atrophy. We used isobaric tags for relative and absolute quantification (iTRAQ) coupled with two-dimensional liquid chromatography-tandem mass spectrometry (2D LC-MS/MS) to identify the differentially expressed proteins in the tibialis anterior (TA) muscle of rats at 1 and 4 weeks following sciatic nerve transection. A total of 110 proteins was differentially expressed and was further classified using terms from the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases to unravel their molecular functions. Among the differentially expressed metabolic enzymes involved in glycolysis, Krebs cycle and oxidative phosphorylation, α- and β-enolase displayed an increased and decreased expression, respectively, which was further validated by western blot analysis and immunohistochemistry. These findings suggest that the enolase isozymic switch during denervation-induced muscle atrophy is the reverse of that occurring during muscle maturation. Notably, protein‑protein interaction analysis using the STRING database indicated that the protein expression of tumor necrosis factor receptor-associated factor-6 (TRAF6), muscle ring-finger protein 1 (MuRF1) and muscle atrophy F-box (MAFBx) was also upregulated during denervation‑induced skeletal muscle atrophy, which was confirmed by western blot analysis. TRAF6 knockdown experiments in L6 myotubes suggested that the decreased expression of TRAF6 attenuated glucocorticoid‑induced myotube atrophy. Therefore, we hypothesized that the upregulation of TRAF6 may be involved in the development of denervation‑induced muscle atrophy, at least in part, by regulating the expression of MAFBx and MuRF1 proteins. The data from the present study provide valuable insight into the molecular mechanisms regulating denervation-induced muscle atrophy.

Mitochondrial pathways in sarcopenia of aging and disuse muscle atrophy

Muscle loss during aging and disuse is a highly prevalent and disabling condition, but knowledge about cellular pathways mediating muscle atrophy is still limited. Given the postmitotic nature of skeletal myocytes, the maintenance of cellular homeostasis relies on the efficiency of cellular quality control mechanisms. In this scenario, alterations in mitochondrial function are considered a major factor underlying sarcopenia and muscle atrophy. Damaged mitochondria are not only less bioenergetically efficient, but also generate increased amounts of reactive oxygen species, interfere with cellular quality control mechanisms, and display a greater propensity to trigger apoptosis. Thus, mitochondria stand at the crossroad of signaling pathways that regulate skeletal myocyte function and viability. Studies on these pathways have sometimes provided unexpected and counterintuitive results, which suggests that they are organized into a complex, heterarchical network that is currently insufficiently understood. Untangling the complexity of such a network will likely provide clinicians with novel and highly effective therapeutics to counter the muscle loss associated with aging and disuse. In this review, we summarize the current knowledge on the mechanisms whereby mitochondrial dysfunction intervenes in the pathogenesis of sarcopenia and disuse atrophy, and highlight the prospect of targeting specific processes to treat these conditions.

Muscle apoptotic response to denervation, disuse, and aging

Apoptosis is a tightly regulated biological process that plays an important role in coordinating cellular proliferation and differentiation. The pathological consequences of aberrant regulation of apoptosis have been widely demonstrated in carcinogenesis, neurodegenerative diseases, autoimmune diseases, viral infections, and acquired immunodeficiency syndrome. The study of apoptosis has been initiated in skeletal muscle biology. Consistent data have indicated the activation of apoptotic events in muscle atrophic conditions including neuromuscular diseases, muscle disuse, and sarcopenia. Although these results seem to link apoptosis to muscle atrophy, the causative role of apoptosis in this process still needs to be established. Further perspective studies are desired to reveal the precise mechanism and the exact physiologic role of apoptosis in muscle adaptation. This article aims to stimulate research into apoptosis in skeletal muscle. It reviews the apoptotic response of skeletal muscle to the atrophic conditions, namely, denervation, disuse, and aging, and discusses the proposed potential physiological links of apoptosis with muscle loss.

Muscle atrophy induced by SOD1G93A expression does not involve the activation of caspase in the absence of denervation

Background

The most remarkable feature of skeletal muscle is the capacity to adapt its morphological, biochemical and molecular properties in response to several factors. Nonetheless, under pathological conditions, skeletal muscle loses its adaptability, leading to atrophy or wasting. Several signals might function as physiopathological triggers of muscle atrophy. However, the specific mechanisms underlying the atrophic phenotype under different pathological conditions remain to be fully elucidated. In this paper, we address the involvement of caspases in the induction of muscle atrophy in experimental models of amyotrophic lateral sclerosis (ALS) expressing the mutant SOD1^G93A transgene either locally or ubiquitously.

Results

We demonstrate that SOD1^G93A-mediated muscle atrophy is independent from caspase activity. In particular, the expression of SOD1^G93A promotes a reduction of the phosphatidylinositol 3-kinase/Akt pathway associated with activation of forkhead box O3. In contrast, the activation of caspases occurs later and is causally linked to motor neuron degeneration, which is associated with exacerbation of the atrophic phenotype and a shift in fiber-type composition.

Conclusion

This study suggests that muscle atrophy induced by the toxic effect of SOD1^G93A is independent from the activation of apoptotic markers and that caspase-mediated apoptosis is a process activated upon muscle denervation.

Effect of electromyostimulation on apoptosis-related factors in denervation and reinnervation of rat skeletal muscles

Electromyostimulation (EMS) has been utilized to reduce muscle atrophy, but its effect on denervated muscles is controversial. This study was performed to determine the effect of EMS on intramuscular changes and apoptosis during denervation and reinnervation following nerve damage. Rat sciatic nerves were denervated completely (CD) or partially (PD), and EMS was applied for 2 weeks. The same numbers of cases were followed without EMS. Nerve conduction studies, muscle weights, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to measure apoptotic changes, and Western blot were done 4, 8, and 12 weeks after injury. TUNEL-positive nuclei of CD muscles (18.6 +/- 5.5%) were more prevalent than those of PD muscles (7.5 +/- 3.3%). The EMS group showed greater muscle weight, fewer positive nuclei (4.7 +/- 1.9%), and lower BAX and Bcl-2 expression levels compared with the non-EMS group at 4 weeks after PD but not after CD. Denervated muscle atrophy delayed by EMS may be linked with enhanced anti-apoptosis under the control of apoptosis-related factors.

Coordinated patterns of gene expressions for adult muscle build-up in transgenic mice expressing myostatin propeptide

Background

Skeletal muscle growth and maintenance are essential for human health. One of the muscle regulatory genes, namely myostatin, a member of transforming growth factor-β, plays a dominant role in the genetic control of muscle mass. Myostatin is synthesized as a precursor protein, which generates the N-terminal propeptide and the C-terminal mature myostatin peptide by a post-translational cleavage event. Previously, transgenic over-expression of myostatin propeptide in skeletal muscle results in significant muscle growth in early stages of development. The objectives of present study were to further characterize muscle growth in later stages of life and to identify genes and their expression patterns that are responsible for adult muscle build-up by myostatin propeptide.

Results

Immunohistochemical staining with an antibody to the N-terminus indicates a high level of myostatin propeptide present in the muscles of transgenic mice while there were no apparent differences in myostatin protein distribution in the muscle fibers between the transgenic and wild-type mice. Main individual muscles increased by 76–152% in the transgenic mice over their wild-type littermate mice at 12 months of age. A large number of nuclei were localized in the central and basal lamina of the myofibers in the transgenic mice as the number of nuclei per fiber and 100 μm² area was significantly higher in transgenic mice than wild-type mice. By systemic comparisons of global mRNA expression patterns between transgenic mice and wild-type littermates using microarray and qRT-PCR techniques, we have identified distinct gene expression patterns to support adult muscle build-up by myostatin propeptide, which are comprised of enhanced expressions of myogenic regulatory factors and extracelullar matrix components, and differentially down-regulated expressions of genes related to protein degradation and mitochondrial ATP synthesis.

Conclusion

The results present a coordinated pattern of gene expressions for reduced energy utilization during muscle build-up in adult stage. Enhanced muscle buildup by myostatin propeptide is sustained by reduced ATP synthesis as a result of a decreased activity of protein degradation. Myostatin propeptide may have a therapeutic application to the treatment of clinical muscle wasting problems by depressing myostatin activity.

Mitochondrial death effectors: relevance to sarcopenia and disuse muscle atrophy

Accelerated apoptosis in skeletal muscle is increasingly recognized as a potential mechanism contributing to the development of sarcopenia of aging and disuse muscle atrophy. Given their central role in the regulation of apoptosis, mitochondria are regarded as key players in the pathogenesis of myocyte loss during aging and other atrophying conditions. Oxidative damage to mitochondrial constituents, impaired respiration and altered mitochondrial turnover have been proposed as potential triggering events for mitochondrial apoptotic signaling. In addition, iron accumulation within mitochondria may enhance the susceptibility to apoptosis during the development of sarcopenia and possibly acute muscle atrophy, likely through exacerbation of oxidative stress. Mitochondria can induce myocyte apoptosis via both caspase-dependent and independent pathways, although the apoptogenic mediators involved may be different depending on age, muscle type and specific atrophying conditions. Despite the considerable advances made, additional research is necessary to establish a definite causal link between apoptotic signaling and the development of sarcopenia and acute atrophy. Furthermore, a translational effort is required to determine the role played by apoptosis in the pathogenesis of sarcopenia and disuse-induced muscle loss in human subjects.

Apoptotic-Related Protein Expression in the Diaphragm and the Effect of Dopamine During Inspiratory Resistance Loading

Dopamine (DA) is a free radical scavenger that attenuates apoptosis. We studied the effects of normal saline (NS) and DA on diaphragm apoptotic protein expression following 60 min of inspiratory resistance loading in rats. We tested for 27 apoptotic-related proteins and found 12 in the diaphragm. Of the 12 proteins, superoxide dismutase copper zinc (SOD [CuZn]) and proprioceptive event related potential (PERP) were significantly higher in the DA group than in the NS and sham groups ( p = .002, p = .007). DA group diaphragms had significantly greater expression of SOD (CuZn) than the NS ( p = .005) and sham group diaphragms ( p = .003). Likewise, the DA group had significantly greater expression of PERP than the NS group ( p = .008). These results suggest that DA decreases diaphragm apoptosis through elevated expression of SOD (CuZn). The identification of 12 apoptotic-related proteins will assist investigators as they study diaphragm apoptosis.

SMAC-expression in denervated human skeletal muscle as a potential inhibitor of coexpressed inhibitor-of-apoptosis proteins

In multinucleated skeletal muscle fibers, apoptotic muscle fiber loss is mediated by a consecutive disassembly of single fiber segments. During this period of time, proapoptotic and antiapoptotic factors compete for promotion or inhibition of apoptotic fiber degradation. In 16 patients with a neurogenic muscular atrophy, we studied the immunohistochemical expression of the inhibitor-of-apoptosis proteins (IAP) survivin, cIAP1, and XIAP and also of second mitochondria-derived activator of caspase (SMAC), which is released during apoptosis and binds to IAPs to prevent them from inhibiting caspases. Although normal control muscle fibers show no expression of SMAC and IAPs, there was a distinct sarcoplasmic expression of SMAC (12.0%+/-3.5%), survivin (10.2%+/-4.0%), cIAP1 (9.0%+/-3.1%), and XIAP (11.0%+/-4.6%) in varying numbers of muscle fibers in neurogenic muscular atrophy. Coexpression of SMAC and IAPs varied. Some denervated muscle fibers displayed up-regulation of either SMAC or IAPs. Other groups of atrophic muscle fibers showed coexpression of SMAC and IAPs. All factors were exclusively up-regulated in atrophic muscle fibers. These findings indicate that IAPs may inhibit apoptotic degradation of denervated muscle fibers. However, IAPs are finally insufficient to counterbalance and prevent muscle fiber apoptosis, as up-regulated expression of SMAC can antagonize this antiapoptotic potential and promote apoptotic muscle fiber disassembly and loss. The interplay between IAPs and SMAC may represent a threshold for muscle fiber-degrading caspase activities. If this bears a therapeutic potential in the prevention of loss of denervated muscle fibers, it remains highly speculative.

Endoplasmic reticulum stress in myotonic dystrophy type 1 muscle

In myotonic dystrophy type 1 (DM1), alternative splicing of ryanodine receptor 1 (RyR1) and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) genes has been reported. These proteins are essential for maintaining intracellular Ca2+ in skeletal muscle. To clarify involvement of endoplasmic reticulum (ER) stress in DM1 muscles, we examined the activation of ER stress-related proteins by immunohistochemistry, western blot analysis and RT-PCR. In four of five DM1 muscle biopsies, except for a muscle biopsy from a patient with the shortest CTG expansion and no myotonia, increased expression of GRP78 and calnexin, and phosphorylation of PERK and eIF-2 alpha were revealed in fibers with sarcoplasmic masses and in highly atrophic fibers with pyknotic nuclear clumps. Caspase-3 and -7 were also expressed in these fibers. Increased expression of GRP78 in these DM1 muscles was confirmed by western blot analysis. GRP78 mRNA and spliced isoform of XBP1 mRNA were also increased in DM1 muscle biopsies. Furthermore, we demonstrated increased expression of GRP78 in highly atrophic fibers with pyknotic nuclear clumps in all three muscle biopsies from neurogenic muscular atrophies. However, five muscle biopsies from central core disease presumably with disturbed intracellular Ca2+ homeostasis and a muscle biopsy from paramyotonia congenita with myotonia showed no activation of these proteins. Taken together, ER stress is involved in muscle wasting in DM1. However, it seems to be evoked not only by disrupted intracellular Ca2+ homeostasis.

Apoptosis in muscle atrophy: relevance to sarcopenia

The loss of muscle mass with aging, or sarcopenia, is an important contributor to the functional decline and loss of independence observed with aging. Little is known about the role of apoptosis in sarcopenia. Studies in adult animals have shown that apoptosis is involved in the loss of muscle nuclei during acute disuse atrophy, and caspase-3 dependent pathways play an important role in this process. Elevated apoptosis has also been observed in muscles of aged animals, but this does not depend upon caspase-3 pathways to the same extent as disuse atrophy. Moreover, disuse atrophy induced in aged animals is associated with a higher amount of apoptosis than in young and intracellular mechanisms are different from those in young, depending more on caspase-independent pathways. The functional relevance of the increase in apoptosis with respect to the loss of muscle fibers and muscle cross-sectional area with aging remains to be determined and interventions to decrease apoptosis in muscle need to be evaluated.

Nuclear translocation of EndoG at the initiation of disuse muscle atrophy and apoptosis is specific to myonuclei

Skeletal muscle atrophy is associated with an increase in apoptosis, and we showed previously that endonuclease G (EndoG) is localized to nuclei following unloading. The goal of this study was to determine whether the onset of apoptosis in response to disuse was consistent with the hypothesis that EndoG is involved in myofiber nuclear loss. Atrophy was induced by hindlimb suspension for 12 h or 1, 2, 4 and 7 days in 6-mo-old rats. Soleus myofiber cross-sectional area decreased significantly by 2 days, whereas muscle mass and muscle-to-body mass ratio decreased by 4 and 7 days, respectively. By contrast, a significant increase in apoptosis, evidenced by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive nuclei, occurred as early as 12 h after suspension, preceding the elevation in muscle atrophy F-box gene expression. The early increase in apoptosis appeared to be specific to myofiber nuclei, whereas TUNEL-positive interstitial cells did not become significantly elevated until 2 days after suspension. Furthermore, TUNEL-positive myofiber nuclei colocalized with EndoG as early as 12 h after suspension, and no such localization was observed in interstitial cells. Although no significant change in total activated caspase-3, -7, or -12 protein abundance was apparent, activated caspase-3 was expressed in interstitial cells undergoing apoptosis, some of which were endothelial cells. These data indicate that apoptosis is an early, and therefore possibly causative, event in the process of muscle atrophy, and that EndoG nuclear translocation is specific for myofiber nuclear apoptosis, whereas interstitial cells may undergo apoptosis via a more classical, caspase-dependent pathway.

Investigation of differentially expressed proteins in rat gastrocnemius muscle during denervation-reinnervation

To have a better insight into the molecular events involved in denervation-induced atrophy and reinnervation-induced regeneration of skeletal muscles, it is important to investigate the changes in expression levels of a great multitude of muscle proteins during the process of denervation-reinnervation. In this study, we employed an experimental model of rat sciatic nerve crush to examine the differentially expressed proteins in the rat gastrocnemius muscle at different time points (0, 1, 2, 3, 4 weeks) after sciatic nerve crush by using two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS), collectively referred to as the modern proteomic analysis. The results showed that 16 proteins in the rat gastrocnemius muscle exhibited two distinct types of change pattern in their relative abundance: (1) The relative expression levels of 11 proteins (including alpha actin, myosin heavy chain, etc.) were decreased either within 1 or 2 weeks post-sciatic nerve injury, followed by restoration during the ensuing days until 4 weeks. (2) The other 5 proteins (including alpha enolase, beta enolase, signal peptide peptidase-like 3, etc.) displayed an up-regulation in their relative expression levels within 1 week following sciatic nerve injury, and a subsequent gradual decrease in their relative expression levels until 4 weeks. Moreover, the significance of the changes in expression levels of the 16 proteins during denervation-reinnervation has been selectively discussed.

Characterization of initiator and effector caspase expressions in dystrophinopathies

There is evidence that apoptotic cell death mechanisms contribute to muscle fiber loss in dystrophin-deficient muscle but there is little knowledge about the final degrading events of muscle fiber apoptosis. In muscle biopsy specimens from 14 patients with a dystrophinopathy (10 patients with DMD, two with Becker MD, two DMD carriers), expression of APAF-1 and caspase-9, upstream members of the apoptotic protease cascade, as well as of the downstream executioners caspase-2, -6 and -7, were studied by immunohistochemistry and Western blots. Besides predominant immunoreactivity in regenerating muscle fibers, which may contribute to apoptotic events during new muscle fiber formation, caspase-9, -6 and -7 displayed upregulation in non-regenerating, light microscopically intact but atrophic muscle fibers. Western blot analyses confirmed the upregulations. These findings indicate that, once activated, caspase-9 initiates a proteolytic, muscle fiber degrading cascade involving the downstream executioners caspase-6 and -7. However, lacking coexpression of APAF-1 suggests the existence of other pathways of caspase-9 activation than through the "apoptosome" in dystrophinopathies.

Molecular characterization of muscle atrophy and proteolysis associated with spawning in rainbow trout

Severe muscle deterioration is a physiological response to the energetic demands of fish spawning. This response represents a suitable model to study mechanisms of muscle degradation in fish where typical tetrapod methods, such as muscle unloading, are not applicable. Enzyme activities and mRNA accumulations of genes in major proteolytic pathways, including cathepsins, calpains and the multi-catalytic proteasome, were measured in white muscles of rainbow trout during spawning and post-spawning seasons of gravid fish for comparisons to sterile fish. Fertile fish at spawning had less muscle tissue and less muscle protein compared to sterile fish and post-spawning fertile fish. Muscle deterioration of the fertile fish during spawning was associated with greater mRNA accumulation and elevated activity of cathepsin-L. Concurrently, muscle of spawning fish showed increased mRNA accumulations of cathepsin-D, the calpain regulatory subunit and the proteasome catalytic subunit alpha without corresponding increases in enzyme activities. In addition, elevated activity and increased mRNA accumulation of caspase-9, but not caspase-3, were observed in fertile fish during spawning. This study indicates that cathepsins mediate protein catabolism during spawning in rainbow trout and the catabolic process may involve activation of the apoptosis mediator, caspase-9, but not the apoptosis executioner, caspase-3.

Muscle-fiber apoptosis in neuromuscular diseases

Muscle-fiber loss is a characteristic of many progressive neuromuscular disorders. Over the past decade, identification of a growing number of apoptosis-associated factors and events in pathological skeletal muscle provided increasing evidence that apoptotic cell-death mechanisms account significantly for muscle-fiber atrophy and loss in a wide spectrum of neuromuscular disorders. It became obvious that there is not one specific pathway for muscle fibers to undergo apoptotic degradation. In contrast, certain neuromuscular diseases seem to involve characteristic expression patterns of apoptosis-related factors and pathways. Furthermore, there are some characteristics of muscle-fiber apoptosis that rely on the muscle fiber itself as an extremely specified cell type. Multinucleated muscle fibers with successive muscle-fiber segments controlled by individual nuclei display some specifics different from apoptosis of mononucleated cells. This review focuses on the expression patterns of apoptosis-associated factors in different primary and secondary neuromuscular disorders and gives a synopsis of current knowledge.