Caveolin-3 Deficiency Research Articles

Protein Expression of Canine and Feline Muscular Dystrophies

Muscular dystrophies in dogs and cats represent a heterogeneous group of inherited, sometimes congenital, but infrequently diagnosed, progressive neuromuscular disorders. A correct identification and characterization of canine and feline muscular dystrophies could increase diagnostic and treatment strategies for veterinary neurologists and could identify useful animal models for the study of human dystrophies. However, in dogs and cats, diagnosis of muscular dystrophies is challenging due to a nonspecific clinical phenotype and pathological lesions, thus is most likely underestimated. We performed immunofluorescence and Western blot techniques using a wide panel of antibodies against proteins involved in human dystrophies (dystrophin mid-rod and carboxyterminal domain, α, β, γ, and δ-sarcoglycan, α-dystroglycan, caveolin-3, emerin, merosin, dysferlin, calpain-3, spectrin epitopes), on 9 canine and 3 feline muscle biopsies characterized by myopathic changes. Dystrophin deficiency was detected in 3 dogs and 2 novel canine muscular dystrophies have been identified, characterized by deficiency of caveolin-3 and calpain-3, respectively. In 2 cats, deficiency of β-SG and carboxyterminal domain of dystrophin in all muscle fibers has been detected. Performing immunofluorescence and Western blot analyses with a wider panel of antibodies allowed a correct identification of muscular dystrophies in dogs and cats and provides a direction for subsequent targeted genetic testing.

EP.24Recessive mutations in CAV3 - a new differential diagnosis of early-onset neuromuscular disorders

Dominant CAV3 mutations account for a very wide phenotypical spectrum, including limb girdle muscular dystrophy (LGMD), rippling muscle disease (RMD), distal myopathy or asymptomatic hyperCKemia. Very few recessive cases have been reported to date with mild clinical features. Here we report a 19-month-old male presenting antenatally with reduced foetal movements from 36/40 and possible polyhydramnios. Family history had been unremarkable except for a history of speech and language delay in 2 siblings. He was delivered by elective Caesarean section at 38 weeks gestation. He was hypotonic at birth and was given facial oxygen and started on intravenous antibiotics until sepsis had been excluded. He quickly established spontaneous breathing and breast feeding. He was re-admitted to hospital when he was 2 months old with bronchiolitis when he was noted to have generalized hypotonia pronounced axially, with significant head lag and scarce antigrativity movements in his legs. There was bilateral talipes but there were no other contractures. DTR were difficult to elicit. He was not dysmorphic and did not have any facial weakness or ophthalmoplegia. CK was elevated up to 7398 IU/L. Brain MRI and cardiac evaluation were normal. His muscle biopsy showed abnormal variation in fibre size, increase in internal nuclei, necrosis and regeneration with modest endomysial chronic inflammation. Molecular analysis revealed a homozygous CAV3 mutation (c.10_17delGAAGAGCA; p.Glu4Hisfs*17) in trans. Further muscle biopsy IHC studies revealed complete caveolin-3 deficiency. Subsequently the patient achieved independent sitting at the age of 8 months, crawled from 1 year and walked independently at 18 months. No rippling of muscle was noted on further examination. This report expands the genetic and clinico-pathological spectrum of CAV3-associated disease, and suggests that recessive CAV3 mutations ought to be considered in the differential diagnosis of early-onset neuromuscular disorders.

Characteristic findings of skeletal muscle MRI in caveolinopathies

Caveolinopathies, caused by CAV3 mutations, can include several phenotypes such as rippling muscle disease, limb-girdle muscular dystrophy type 1C, distal myopathy, familial hypertrophic cardiomyopathy, and idiopathic hyperCKemia. Here we present characteristic skeletal muscle imaging findings in four patients with genetically defined childhood-onset RMD caused by CAV3 mutations and in one patient with congenital generalized lipodystrophy type 4 with muscular dystrophy due to polymerase I and transcript release factor (PTRF) mutations, which may have caused secondary deficiency of caveolin-3. Muscle MRI revealed that the rectus femoris and semitendinosus muscles were most commonly affected in the rippling muscle disease patients. Peripheral changes in the rectus femoris were specific and observed even in one of the younger patients in this study. Furthermore, muscle involvement extended to the semitendinosus muscles, biceps femoris, and gracilis with disease progression or increase in its severity. Similar patterns of involvement were observed on reviewing skeletal muscle images of various previously reported phenotypes of caveolinopathy; interestingly, patients with secondary deficiency of caveolin due to PTRF mutations revealed the same pattern. Thus, primary caveolinopathies and secondary deficiency of caveolin demonstrated specific findings on skeletal muscle imaging, regardless of the broad phenotypic spectrum of these two conditions.

Caveolin-3 is aberrantly expressed in skeletal muscle cells in myasthenia gravis

Caveolin-3 is a muscle-specific membrane protein that localizes to the sarcolemma and T-tubule system. Caveolin-3 is needed for muscle repair and skeletal muscle development. The objective of this study was to compare caveolin-3 expression in myasthenia gravis (MG) and control muscles. Caveolin-3 was abnormally expressed in the MG muscle membrane, with partial loss of expression and overexpression in 5/15 and 10/15 patients, respectively. Caveolin-3 mRNA and protein levels were higher in MG than in control muscles, suggesting that partial deficiency of caveolin-3 is occasionally detected in MG muscle and that caveolin-3 overexpression may be required after MG muscle damage.

Abstract 14809: Murc/cavin-4 Regulates Cardiac Function via β-adrenergic Receptor Signaling

Background: Muscle-restricted coiled-coil protein (MURC), also referred to as Cavin-4, is a member of the cavin family, which regulates caveolae function together with caveolins. In cardiomyocytes, caveolin-3, a critical and muscle-specific component of caveolae, regulates caveolar structure and function and forms a complex with MURC/Cavin-4. Caveolin-3 overexpression induces cardiac protection, and caveolin-3 deficiency causes progressive cardiomyopathy. The caveolin-3 scaffolding domain peptide inhibits type 5 adenylyl cyclase (AC5), which is an enzyme to synthesize cAMP and an effector of β-adrenergic receptor (AR) signaling. Mutations in MURC/Cavin-4 have been identified in patients with dilated cardiomyopathy. However, molecular mechanisms of MURC as a caveolar component in cardiac function remain unknown. Methods and results: To assess the role of MURC/Cavin-4 in cardiac function, wild-type (WT) and MURC/Cavin-4-knockout (MURC-KO) mice were subjected to a model of pressure overload induced by transverse aortic constriction (TAC). After TAC, WT mice showed cardiac hypertrophy and heart failure, whereas MURC-KO mice were resistant to pressure overload-induced cardiac hypertrophy and heart failure accompanied by fibrosis. We then focused on β-AR signaling, because β1-AR signaling is one of the essential parts in heart failure. MURC/Cavin-4 was co-localized with β1-AR in cardiomyocytes. Isoproterenol (ISO) treatment induced cardiac hypertrophy with fibrosis in WT mice, while ISO-induced cardiac hypertrophy and fibrosis was markedly attenuated in MURC-KO mice. In cardiomyocytes, MURC/Cavin-4 knockdown suppressed ISO-induced cAMP production, while MURC/Cavin-4 overexpression and caveolin-3 knockdown stimulated cAMP production, indicating that caveolin-3 and MURC/Cavin-4 have opposite effects on cAMP production. MURC/Cavin-4 bound to caveolin-3 and interferes with the association between caveolin-3 and AC5. Moreover, MURC-knockdown suppressed ISO-induced PKA activity and phospholamban phosphorylation. Conclusion: Our findings suggest that MURC/Cavin-4 regulates cardiac function via β-AR signaling.

Caveolinopathies in Greece.

Mutations in the CAV3 gene are usually inherited in an autosomal dominant manner and lead to distinct disorders including limb-girdle muscular dystrophy 1C, rippling muscle disease, and isolated creatine kinase elevation. The features of the first patients with caveolin-3 deficiency from Greece are presented. Patients' phenotypes ranged from asymptomatic creatine kinase elevation to severe weakness of lower extremities. Clinical evaluation disclosed muscle hypertrophy in 2 patients, whereas percussion-induced muscle mounding was a consistent finding in all of them. Muscle histopathology was variable and unrelated with disease severity. The diagnosis was based on the immunohistochemical study of caveolin-3 expression and molecular analysis of the caveolin-3 gene. Clinical manifestations and histochemical findings in caveolinopathy patients may be mild or nonspecific or overlapping with features of other muscular dystrophies. Immunohistochemical study of caveolin-3 expression on muscle biopsy should be routinely performed when investigating isolated hyperCKemia or undetermined myopathy especially in the presence of percussion-induced muscle mounding.

Abstract 220: Transcriptional Analysis Of Caveolin And Cavin In The Male And Female Ageing Mouse Heart Following Ischemic Stress

Cardioprotection against infarction and dysfunction in the myocardium involves G-protein-coupled receptor signalling orchestrated by specialised membrane microdomains termed caveolae. The caveolin protein family consist of three subtypes: caveolin-1, −2 and −3 (Cav1-3) and are responsible for the formation of caveolae and hypothesized to orchestrate cardioprotective signalling. Caveolin-3 deficiency and overexpression has been shown to attenuate and restore cardioprotection, respectively. Recently, a family of four related proteins known as cavins (Cavin1-4) have been implicated as regulators of caveolae formation and function. The roles and expression distribution of the cavin family is currently unknown in cardiac tissue. In this study hearts were isolated from 8, 16, 32 and 48 week male and female mice and subjected to normoxic perfusion (80 min) or ischemic stress (20 min global ischemia, 60 min reperfusion). RT-qPCR was used to assess differential gene expression of caveolin and cavin subtypes across these ages in both sexes. Decreased post-ischemic pressure development and increased LDH release were observed in 32 and 48 week old relative to 8 week old male hearts hearts, indicative of age-related loss of ischemic tolerance. Females showed greater tolerance to ischemia at 32 and 48 week old hearts when compared to male counterparts. In normoxic male 48 week old hearts, Cav1,-2,-3 and Cavin1 were significantly repressed, whilst post-ischemic male 48 week old hearts demonstrated significant repression of Cav3 and Cavin1 only. Normoxic female hearts showed no significant changes in caveolin and cavin transcript expression over the aging time course. However, post-ischemic female 48 week old hearts showing significant down-regulation of Cav3 only. Taken together, alterations in caveolin and cavin expression may contribute to the age-related loss of ischemic tolerance and G-protein-coupled receptor-mediated protection in aging male and female mice hearts.

Electrically Active Immune-mediated Rippling Muscle Disease Preceding Breast Cancer

Rippling muscle disease (RMD) is a rare disorder of muscle hyperexcitability clinically characterized by painful muscle stiffness, rippling phenomenon, percussion-induced muscle mounding, and rapid contraction. RMD is typically considered to be electrically silent, but electrical activity during the muscle rippling has been occasionally described. RMD could be genetically determined or immune-mediated (iRMD). The association between cancer and iRMD is extremely rare. We present here a patient with electrically active iRMD preceding the diagnosis of breast cancer. The patient had acetylcholine receptor binding antibodies but no clinical or electrophysiological signs of myasthenia. Muscle biopsy revealed inflammatory changes and a mosaic distribution of sarcolemmal caveolin-3 deficiency. Sequencing of caveolin-3 gene detected no mutation. Immunotherapy led to the resolution of the RMD and disappearance of the serum acetylcholine receptor antibodies. The abnormal electrical activity in this patient suggests that an acquired neuromuscular hyperexcitability syndrome represents a continuum of disorders. The close temporal relationship between the onset of iRMD and the diagnosis of breast cancer raises the possibility that iRMD might be paraneoplastic.

SNP-array based whole genome homozygosity mapping: A quick and powerful tool to achieve an accurate diagnosis in LGMD2 patients

A large number of novel disease genes have been identified by homozygosity mapping and the positional candidate approach. In this study we used single nucleotide polymorphism (SNP) array-based, whole genome homozygosity mapping as the first step to a molecular diagnosis in the highly heterogeneous muscle disease, limb girdle muscular dystrophy (LGMD). In a consanguineous family, both affected siblings showed homozygous blocks on chromosome 15 corresponding to the LGMD2A locus. Direct sequencing of CAPN3, encoding calpain-3, identified a homozygous deletion c.483delG (p.Ile162SerfsX17). In a sporadic LGMD patient complete absence of caveolin-3 on Western blot was observed. However, a mutation in CAV3 could not be detected. Homozygosity mapping revealed a large homozygous block at the LGMD2I locus, and direct sequencing of FKRP encoding fukutin-related-protein detected the common homozygous c.826 C>A (p.Leu276Ile) mutation. Subsequent re-examination of this patient's muscle biopsy showed aberrant α-dystroglycan glycosylation. In summary, we show that whole-genome homozygosity mapping using low cost SNP arrays provides a fast and non-invasive method to identify disease-causing mutations in sporadic patients or sibs from consanguineous families in LGMD2. Furthermore, this is the first study describing that in addition to PTRF, encoding polymerase I and transcript release factor, FKRP mutations may cause secondary caveolin-3 deficiency.

Accumulation of caveolin-3 protein is limited in damaged muscle in chicken muscular dystrophy

Members of the caveolin family are the main component of caveolae, and caveolin-3 is a muscle-specific protein. Caveolin-3 deficiency induces a muscular dystrophic phenotype, while its overexpression is also harmful to muscle cells. Increased caveolae were observed in chicken muscular dystrophy; however, the underlying mechanism causing the onset remains unclear. Therefore, the current study analyzes the expression of caveolin-3 and other caveola-related proteins in dystrophic chickens. Western blotting and semi-quantitative RT-PCR analysis revealed that (1) caveolin-3 is highly expressed in the damaged muscle of dystrophic chickens (7.12-fold); (2) the amount of caveolin-3 protein is regulated in posttranslational modification, since no significant increase is observed at the mRNA level (1.09-fold); and (3) the expression pattern of other caveola-related proteins is similar to that of caveolin-3. These results suggest that the accumulation of caveolin-3 protein may be associated with the causative process of chicken muscular dystrophy.

Bedside diagnosis of rippling muscle disease in CAV3 p.A46T mutation carriers

Thirty-nine members, ages 1 to 67 years, of a Swedish family with rippling muscle disease (RMD) were investigated to assess genotype-phenotype correlations. Clinical, neurophysiological, and muscle morphological examinations were performed. Genetic analysis was performed in 38 individuals. Twenty-three patients had percussion-induced muscle mounding (PIMM) and percussion-induced rapid contractions (PIRC). Rippling and hyperCKemia were not found in all patients. Weakness was minor or absent. The electromyogram showed absence of electrical activity in ripples and PIMM, and muscle biopsy specimens confirmed caveolin-3 deficiency and absence of caveolae. Genetic analysis revealed a CAV3 c.G136A transition resulting in a p.A46T missense mutation in affected family members. The phenotype in these 23 cases of RMD with this mutation appears to be homogenous, benign, and nonprogressive. The presence of PIMM and PIRC seems to be diagnostic at all ages, whereas the absence of hyperCKemia and rippling does not exclude the diagnosis.

Caveolinopathies: from the biology of caveolin-3 to human diseases

In muscle tissue the protein caveolin-3 forms caveolae--flask-shaped invaginations localized on the cytoplasmic surface of the sarcolemmal membrane. Caveolae have a key role in the maintenance of plasma membrane integrity and in the processes of vesicular trafficking and signal transduction. Mutations in the caveolin-3 gene lead to skeletal muscle pathology through multiple pathogenetic mechanisms. Indeed, caveolin-3 deficiency is associated to sarcolemmal membrane alterations, disorganization of skeletal muscle T-tubule network and disruption of distinct cell-signaling pathways. To date, there have been 30 caveolin-3 mutations identified in the human population. Caveolin-3 defects lead to four distinct skeletal muscle disease phenotypes: limb girdle muscular dystrophy, rippling muscle disease, distal myopathy, and hyperCKemia. In addition, one caveolin-3 mutant has been described in a case of hypertrophic cardiomyopathy. Many patients show an overlap of these symptoms and the same mutation can be linked to different clinical phenotypes. This variability can be related to additional genetic or environmental factors. This review will address caveolin-3 biological functions in muscle cells and will describe the muscle and heart disease phenotypes associated with caveolin-3 mutations.

Caveolinopathy – New mutations and additional symptoms

Mutations in the caveolin-3 gene (CAV3) can lead to a broad spectrum of clinical phenotypes. Phenotypes that have so far been associated with primary caveolin-3 deficiency include limb girdle muscular dystrophy, rippling muscle disease, distal myopathy and hyperCKaemia. This is the first report describing the clinical, pathological and genetic features of patients with caveolinopathy from the UK. Ten patients (six families) were identified via the National Commissioning Group (NCG) service for patients with limb girdle muscle dystrophy in Newcastle. Myalgia was the most prominent symptom in our cohort of patients and for 50% it was the reason for referral. Muscle weakness was only found in 60% of the patients, whereas rippling muscle movement was present in 80%. One of the patients reported episodes of myoglobinuria and another one episodes of hypoglycaemia. Five different mutations were identified, two of which were novel and three that had previously been described. Caveolinopathy needs to be considered as a differential diagnosis in a range of clinical situations, including in patients who do not have any weakness. Indeed, rippling muscles are a more frequent symptom than weakness, and can be detected in childhood. Presentation with myalgia is common and management of it as well as of myoglobinuria and hypoglycaemia may have a major impact on the patients’ quality of life.

A novel missense mutation in the caveolin‐3 gene in rippling muscle disease

Rippling muscle disease (RMD) is a benign myopathy with symptoms and signs of muscular hyperirritability. We report a 17-year-old patient who presented with muscular hypertrophy, local mounding on percussion, and a rippling phenomenon. Needle electromyography showed electrical silence during the rippling phenomenon. Muscle protein immunohistochemical analysis showed a partial deficiency of caveolin-3. Molecular analysis revealed a novel heterozygous A>C transition at nucleotide position 140 in exon 2 of the caveolin-3 gene. We associated this novel mutation with RMD.

Two novel CAV3 gene mutations in Japanese families

Caveolin-3 deficiency is a rare, autosomal dominant, muscle disorder caused by caveolin-3 gene ( CAV3) mutations and consists of four clinical phenotypes: limb-girdle muscular dystrophy type 1C (LGMD-1C), rippling muscle disease, distal myopathy, and familial hyperCKemia. So far, only 13 mutations have been reported. We here report two novel heterozygous mutations, 96C>G (N32K) and 128T>A (V43E), in the CAV3 gene in two unrelated Japanese families with LGMD-1C. Both probands presented with elevated serum CK level with calf muscle hypertrophy in their childhood but without apparent muscle weakness. However, their mothers showed mild limb-girdle weakness in addition to high CK level. Caveolin-3 was deficient and caveolae were lacking in muscles from both patients. Our data confirm that caveolin-3 deficiency causes LGMD-1C and expand the variability in CAV3 gene mutations.

A CAV3 microdeletion differentially affects skeletal muscle and myocardium.

Caveolin-3 is the muscle-specific protein product of the caveolin gene family and an integral membrane component of caveolae. Mutations in the gene encoding caveolin-3 (CAV3) underlie four distinct disorders of skeletal muscle: the autosomal dominant form of limb-girdle muscular dystrophy type 1C (LGMD-1C), rippling muscle disease (RMD), sporadic and familial forms of hyperCKemia, and distal myopathy. To characterize a multigenerational Italian family affected by an autosomal dominant myopathic disorder and to assess the expression of caveolin-3, dystrophin, dystrophin-associated glycoproteins, and neuronal nitric oxide synthase in the myocardium of an affected patient. Clinical analysis involved 15 family members. Skeletal muscle expression of sarcolemmal proteins was evaluated by immunohistochemistry and western blot analysis in three affected individuals. Caveolar structures were analyzed through electron microscopy in muscle biopsies and in one heart biopsy. CAV3 genetic analysis showed a heterozygous 3-bp microdeletion (328-330del) in affected individuals, resulting in the loss of a phenylalanine (Phe97del) in the transmembrane domain. In the skeletal muscle, the mutation was associated with severe caveolin-3 deficiency and caveolar disorganization, whereas the expression of the other analyzed muscle proteins was unaltered. Remarkably, caveolin-3 was expressed in myocardium at a level corresponding to about 60% of that of control individuals and was correctly localized at the myocardial cell membranes, with preservation of cardiac myofiber caveolar structures. Clinical analysis revealed the concomitant presence in this family of the following phenotypes: RMD, LGMD, and hyperCKemia. Intrafamilial phenotypic heterogeneity is associated with caveolin-3 Phe97 microdeletion. The molecular network interacting with caveolin-3 in skeletal muscle and heart may differ.

Variable reduction of caveolin-3 in patients with LGMD2B/MM.

Mutations in the human dysferlin gene ( DYSF) cause autosomal recessive muscular dystrophies characterized by degeneration and weakness of proximal and/or distal muscles: limb girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM). Recently, an interaction between caveolin-3 and dysferlin in normal and dystrophic muscle (primary caveolin-3 deficiency; LGMD1C) was shown. In this study, clinical,morphological and genetic analysis was carried out in four independent LGMD2B/MM patients. All patients presented with an adult-onset, slowly progressive muscular dystrophy with variable involvement of proximal and distal muscles. We found complete lack of dysferlin in the four LGMD2B/MM patients. Secondary reduction of caveolin-3 was detected in three out of the four patients. Regular caveolae were detected along the basal lamina in two patients by electron microscopy. We provide further evidence that dysferlin and caveolin-3 interact in human skeletal muscle. It remains to be elucidated whether the loss of this interaction contributes to pathogenic events in muscular dystrophy.

Impairment of Caveolae Formation and T-System Disorganization in Human Muscular Dystrophy with Caveolin-3 Deficiency

Caveolin-3, a muscle specific caveolin-related protein, is the principal structural protein of caveolar membranes. We have recently identified an autosomal dominant form of limb girdle muscular dystrophy (LGMD-1C) that is due to caveolin-3 deficiency and caveolin-3 gene mutations. Here, we studied by electron microscopy, including freeze-fracture and lanthanum staining, the distribution of caveolae and the organization of the T-tubule system in caveolin-3 deficient human muscle fibers. We found a severe impairment of caveolae formation at the muscle cell surface, demonstrating that caveolin-3 is essential for the formation and organization of caveolae in muscle fibers. In addition, we also detected a striking disorganization of the T-system openings at the sub-sarcolemmal level in LGMD-1C muscle fibers. These observations provide new perspectives in our understanding of the role of caveolin-3 in muscle and of the pathogenesis of muscle weakness in caveolin-3 deficient muscle.

Caveolin-3 Null Mice Show a Loss of Caveolae, Changes in the Microdomain Distribution of the Dystrophin-Glycoprotein Complex, and T-tubule Abnormalities

Caveolin-3, a muscle-specific caveolin-related protein, is the principal structural protein of caveolae membrane domains in striated muscle cells. Recently, we identified a novel autosomal dominant form of limb-girdle muscular dystrophy (LGMD-1C) in humans that is due to mutations within the coding sequence of the human caveolin-3 gene (3p25). These LGMD-1C mutations lead to an approximately 95% reduction in caveolin-3 protein expression, i.e. a caveolin-3 deficiency. Here, we created a caveolin-3 null (CAV3 -/-) mouse model, using standard homologous recombination techniques, to mimic a caveolin-3 deficiency. We show that these mice lack caveolin-3 protein expression and sarcolemmal caveolae membranes. In addition, analysis of skeletal muscle tissue from these caveolin-3 null mice reveals: (i) mild myopathic changes; (ii) an exclusion of the dystrophin-glycoprotein complex from lipid raft domains; and (iii) abnormalities in the organization of the T-tubule system, with dilated and longitudinally oriented T-tubules. These results have clear mechanistic implications for understanding the pathogenesis of LGMD-1C at a molecular level.

Transgenic mice expressing mutant caveolin-3 show severe myopathy associated with increased nNOS activity.

Caveolin-3 is the muscle-specific isoform of the caveolin protein family, which is a major component of caveolae, small membrane invaginations found in most cell types. Caveolins play important roles in the formation of caveola membranes, acting as scaffolding proteins to organize and concentrate lipid-modified signaling molecules, and modulate a signaling pathway. For instance, caveolin-3 interacts with neuronal nitric oxide synthase (nNOS) and inhibits its catalytic activity. Recently, specific mutations in the caveolin-3 gene, including the Pro104Leu missense mutation, have been shown to cause an autosomal dominant limb-girdle muscular dystrophy (LGMD1C), which is characterized by the deficiency of caveolin-3 in the sarcolemma. However, the molecular mechanism by which these mutations cause the deficiency of caveolin-3 and muscle cell degeneration remains elusive. Here we generated transgenic mice expressing the Pro104Leu mutant caveolin-3. They showed severe myopathy accompanied by the deficiency of caveolin-3 in the sarcolemma, indicating a dominant negative effect of mutant caveolin-3. Interestingly, we also found a great increase of nNOS activity in their skeletal muscle, which, we propose, may play a role in muscle fiber degeneration in caveolin-3 deficiency.