Novel homozygous mutation of the caveolin-3 gene in rippling muscle disease with extraocular muscle paresis

Unraveling calcium dysregulation and autoimmunity in immune mediated rippling muscle disease

Rippling Muscle Disease (RMD) is a rare skeletal myopathy characterized by abnormal muscular excitability manifesting with wave-like muscle contractions and percussion-induced muscle mounding. Hereditary RMD is associated with caveolin-3 or cavin-1 mutations. Recently, we identified cavin 4 autoantibodies as a biomarker of immune-mediated RMD (iRMD), though the underlying disease-mechanisms remain poorly understood. Transcriptomic studies were performed on muscle biopsies of 8 patients (5 males; 3 females; ages 26-to-80) with iRMD. Subsequent pathway analysis compared iRMD to human non-disease control and disease control (dermatomyositis) muscle samples. Transcriptomic studies demonstrated changes in key pathways of muscle contraction and development. All iRMD samples had significantly upregulated cavin-4 expression compared to controls, likely compensatory for autoantibody-mediated protein degradation. Proteins involved in muscle relaxation (including SERCA1, PMCA and PLN) were significantly increased in iRMD compared to controls. Comparison of iRMD to dermatomyositis transcriptomics demonstrated significant overlap in immune pathways, and the IL-6 signaling pathway was markedly increased in all iRMD patient muscle biopsies and increased in the majority of iRMD patients' serum. This study represents the first muscle transcriptomic analysis of iRMD patients and dissects underlying disease mechanisms. Increase of sarcolemmal and cellular calcium channels as well as PLN, an inhibitor of the SERCA pump for calcium into the sarcoplasm, likely alters the calcium dynamics in iRMD. These changes in crucial components of muscle relaxation may underlie rippling by altering calcium flux. Our findings provide crucial insights into the differential expression of genes regulating muscle relaxation and highlight potential disease pathomechanisms.

The spectrum of rippling muscle disease

Rippling muscle disease (RMD) is a rare disorder of muscle hyperexcitability. It is characterized by rippling wave-like muscle contractions induced by mechanical stretch or voluntary contraction followed by sudden stretch, painful muscle stiffness, percussion-induced rapid muscle contraction (PIRC), and percussion-induced muscle mounding (PIMM). RMD can be hereditary (hRMD) or immune-mediated (iRMD). hRMD is caused by pathogenic variants in caveolin-3 (CAV3) or caveolae-associated protein 1/ polymerase I and transcript release factor (CAVIN1/PTRF). CAV3 pathogenic variants are autosomal dominant or less frequently recessive while CAVIN1/PTRF pathogenic variants are autosomal recessive. CAV3-RMD manifests with a wide spectrum of clinical phenotypes, ranging from asymptomatic creatine kinase elevation to severe muscle weakness. Overlapping phenotypes are common. Muscle caveolin-3 immunoreactivity is often absent or diffusely reduced in CAV3-RMD. CAVIN1/PTRF-RMD is characterized by congenital generalized lipodystrophy (CGL, type 4) and often accompanied by several extra-skeletal muscle manifestations. Muscle cavin-1/PTRF immunoreactivity is absent or reduced while caveolin-3 immunoreactivity is reduced, often in a patchy way, in CAVIN1/PTRF-RMD. iRMD is often accompanied by other autoimmune disorders, including myasthenia gravis. Anti-cavin-4 antibodies are the serological marker while the mosaic expression of caveolin-3 and cavin-4 is the pathological feature of iRMD. Most patients with iRMD respond to immunotherapy. Rippling, PIRC, and PIMM are usually electrically silent. Different pathogenic mechanisms have been postulated to explain the disease mechanisms. In this article, we review the spectrum of hRMD and iRMD, including clinical phenotypes, electrophysiological characteristics, myopathological findings, and pathogenesis.

Coexistence of a Heterozygous Caveolin-3 Deletion and a Novel Dystrophin Gene Mutation in a Duchenne Muscular Dystrophy Patient

Inherited muscular abnormalities are debilitating disorders that greatly diminish the quality of life in affected individuals. Mutations in proteins such as dystrophin and caveolin, which together with other proteins form structural connections between the cytoskeleton and the extracellular matrix, are frequently the culprit of muscular dystrophies. In this case report, we describe a patient with a novel pathogenic dystrophin mutation co-existing with a caveolin-3 deletion. While genetically composed of this unique combination, the patient phenotypically presented with a primary clinical manifestation of Duchenne muscular dystrophy (DMD) in contrast to other cases of dual mutations in dystrophin and dystrophin-associated proteins.

Expanding the Clinical and Genetic Spectrum of Caveolinopathy in Korea

Purpose: Caveolinopathy is a disease caused by caveolin-3 (CAV3) mutations that shows a wide clinical spectrum, including isolated hyperCKemia and limb-girdle muscular dystrophy. While recent advances in next-generation sequencing (NGS) have enabled earlier diagnosis of this disease, it remains difficult to predict the clinical course of each patient.Methods: This study summarizes the clinical presentations of 13 genetically confirmed caveolinopathy patients in four Korean families. Genetic diagnosis was performed using NGS technologies for probands and Sanger sequencing for the other family members.Results: Four coding mutations were found (p.Val103_Val104del, p.Asp28Glu, p.Pro105Leu, and p.Arg27Gln), and each family showed autosomal dominant inheritance. While all 13 cases had hyperCKemia, only five of them showed some myopathic features including ankle contracture, calf hypertrophy, exercise intolerance, and muscle cramping. This high proportion of asymptomatic cases suggests both that these mutations may be associated with a mild phenotype and that caveolinopathy may be an underdiagnosed disease.Conclusion: This study extends our understanding of caveolinopathy; in particular, the findings suggest the need to consider caveolinopathy in patients with incidental findings of CK elevation. NGS may be a useful method in the differential diagnosis of such cases.

Role of aquaglyceroporins and caveolins in energy and metabolic homeostasis

Aquaglyceroporins and caveolins are submicroscopic integral membrane proteins that are particularly abundant in many mammalian cells. Aquaglyceroporins (AQP3, AQP7, AQP9 and AQP10) encompass a subfamily of aquaporins that allow the movement of water, but also of small solutes, such as glycerol, across cell membranes. Glycerol constitutes an important metabolite as a substrate for de novo synthesis of triacylglycerols and glucose as well as an energy substrate to produce ATP via the mitochondrial oxidative phosphorylation. In this sense, the control of glycerol influx/efflux in metabolic organs by aquaglyceroporins plays a crucial role with the dysregulation of these glycerol channels being associated with metabolic diseases, such as obesity, insulin resistance, non-alcoholic fatty liver disease and cardiac hypertrophy. On the other hand, caveolae have emerged as relevant plasma membrane sensors implicated in a wide range of cellular functions, including endocytosis, apoptosis, cholesterol homeostasis, proliferation and signal transduction. Caveolae-coating proteins, namely caveolins and cavins, can act as scaffolding proteins within caveolae by concentrating signaling molecules involved in free fatty acid and cholesterol uptake, proliferation, insulin signaling or vasorelaxation, among others. The importance of caveolae in whole-body homeostasis is highlighted by the link between homozygous mutations in genes encoding caveolins and cavins with metabolic diseases, such as lipodystrophy, dyslipidemia, muscular dystrophy and insulin resistance in rodents and humans. The present review focuses on the role of aquaglyceroporins and caveolins on lipid and glucose metabolism, insulin secretion and signaling, energy production and cardiovascular homeostasis, outlining their potential relevance in the development and treatment of metabolic diseases.

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.