Role of RyR2 phosphorylation in heart failure and arrhythmias: protein kinase A-mediated hyperphosphorylation of the ryanodine receptor at serine 2808 does not alter cardiac contractility or cause heart failure and arrhythmias.

This Controversies in Research article discusses the hypothesis that protein kinase A (PKA)-mediated phosphorylation of the Ryanodine Receptor (RyR) at a single serine (RyRS2808) is essential for normal sympathetic regulation of cardiac myocyte contractility and is responsible for the disturbed Ca(2+) regulation that underlies depressed contractility in heart failure. Studies supporting this hypothesis have associated hyperphosphorylation of RyRS2808 and heart failure progression in animals and humans and have shown that a phosphorylation defective RyR mutant mouse (RyRS2808A) does not respond normally to sympathetic agonists and does not exhibit heart failure symptoms after myocardial infarction. Studies to confirm and extend these ideas have failed to support the original data. Experiments from many different laboratories have convincingly shown that PKA-mediated RyRS2808 phosphorylation does not play any significant role in the normal sympathetic regulation of sarcoplasmic reticulum Ca2+ release or cardiac contractility. Hearts and myocytes from RyRS2808A mice have been shown to respond normally to sympathetic agonists, and to increase Ca(2+) influx, Ca(2+) transients, and Ca(2+) efflux. Although the RyR is involved in heart failure-related Ca(2+) disturbances, this results from Ca(2+)-calmodulin kinase II and reactive oxygen species-mediated regulation rather than by RyR2808 phosphorylation. Also, a new study has shown that RyRS2808A mice are not protected from myocardial infarction. Collectively, there is now a clear consensus in the published literature showing that dysregulated RyRs contribute to the altered Ca(2+) regulatory phenotype of the failing heart, but PKA-mediated phosphorylation of RyRS2808 has little or no role in these alterations.

Estudo clínico, histológico e molecular da miopatia centronuclear / A clinical, histological and molecular study of centronuclear myopathy

Introdução: A miopatia centronuclear é uma doença muscular congênita com apresentação clínica heterogênea, caracterizada histologicamente pela proeminência de fibras musculares com núcleos centralizados. Três formas são reconhecidas: neonatal grave, com herança ligada ao X e envolvimento do gene MTM1; autossômica dominante, com início geralmente tardio e curso mais leve, associada a mutações no gene DNM2; e autossômica recessiva, com gravidade intermediária entre as outras formas e envolvimento dos genes BIN1, RYR1 ou TTN. Apesar da identificação dos principais genes responsáveis pela doença, os métodos usuais de diagnóstico genético não encontram mutações em cerca da metade dos casos. Objetivo: O objetivo deste estudo foi a caracterização clínica, histológica e molecular de pacientes brasileiros portadores de miopatia centronuclear. Métodos: Laudos de dois bancos de biópsia muscular foram usados para identificar pacientes com diagnóstico de miopatia centronuclear nos últimos dez anos. As lâminas das biópsias foram revisadas e analisadas, e as famílias correspondentes convocadas para aplicação de protocolo clínico e coleta de sangue periférico para extração de DNA genômico. As famílias foram estudadas para os genes conhecidos por sequenciamento Sanger, MLPA, painel de genes implicados em doenças neuromusculares ou sequenciamento de exoma. Resultados: Foram convocados 24 pacientes provenientes de 21 famílias, em 16 das quais foi possível estabelecer o diagnóstico molecular. As 7 famílias com a forma neonatal grave constituíam um grupo homogêneo clínica e histologicamente, e mutações novas e conhecidas foram encontradas no gene MTM1 em 6 destas. Dois meninos deste grupo, com evolução estável, tiveram óbito súbito por choque hipovolêmico subsequente a rompimento de cisto hepático. O gene MTM1 também foi implicado em uma menina portadora manifestante, com quadro mais leve, na forma de uma macrodeleção em heterozigose, detectada por MPLA...

Introduction: Centronuclear myopathy is a heterogeneous congenital muscle disease, characterized by the prominence of centralized nuclei in muscle fibers. Three disease forms are recognized: a severe neonatal, X-linked form caused by mutations in the MTM1 gene; an autosomal dominant, late-onset milder form, associated to the DNM2 gene; and an autosomal recessive form, with intermediate severity, so far with the BIN1, RYR1 or TTN genes implicated. In spite of the identification of these genes, usual molecular diagnostic methods don't yield a molecular diagnosis in about half of cases. Objetives: The aim of this work was to study clinical, histological, and molecular aspects of centronuclear myopathy Brazilian patients. Methods: Reports taken from two muscle biopsy banks were used to identify centronuclear myopathy patients in the last ten years. Biopsy slides were reviewed and analyzed, and corresponding families recruited to apply a clinical protocol and to draw peripheral blood to extract genomic DNA. Families were studied for known genes via Sanger sequencing, MLPA, panel of genes implicated in neuromuscular diseases, or exome sequencing. Results: Twentyfour patients out of 21 families were recruited, and in 16 families molecular diagnosis was established. The 7 families with the severe neonatal form amounted to a clinically and histologically homogeneous group, and mutations, both known and novel, were found in the MTM1 gene in 6 of these. Two boys of this group, with a stable course, died suddenly of hypovolemic shock due to a hepatic cyst rupture. The MTM1 gene was also implicated in the case of a mild manifesting carrier girl with a heterozygous macrodeletion detected via MLPA...