Distinct roles for telethonin N‐versus C‐terminus in sarcomere assembly and maintenance

The N‐terminus of telethonin forms a unique structure linking two titin N‐termini at the Z‐disc. While a specific role for the C‐terminus has not been established, several studies indicate it may have a regulatory function. Using a morpholino approach in Xenopus, we show that telethonin knockdown leads to embryonic paralysis, myocyte defects, and sarcomeric disruption. These myopathic defects can be rescued by expressing full‐length telethonin mRNA in morpholino background, indicating that telethonin is required for myofibrillogenesis. However, a construct missing C‐terminal residues is incapable of rescuing motility or sarcomere assembly in cultured myocytes. We, therefore, tested two additional constructs: one where four C‐terminal phosphorylatable residues were mutated to alanines and another where terminal residues were randomly replaced. Data from these experiments support that the telethonin C‐terminus is required for assembly, but in a context‐dependent manner, indicating that factors and forces present in vivo can compensate for C‐terminal truncation or mutation. Developmental Dynamics 239:1124–1135, 2010. © 2010 Wiley‐Liss, Inc.     

Malignant and benign mutations in familial cardiomyopathies: Insights into mutations linked to complex cardiovascular phenotypes

Cardiomyopathies, familial or sporadic, have become recognized as one of the leading cardiac threats. Hypertrophic cardiomyopathy (HCM) affects 0.2% of the population and is the leading cause of sudden death in young adults. Dilated cardiomyopathy (DCM) and restrictive cardiomyopathy (RCM) are associated with sudden death as well as heart transplantations. Ventricular noncompaction cardiomyopathy (VNCM) is associated with heart failure and arrhythmias. Currently, more than 630 mutations in 10 sarcomeric genes associated with cardiomyopathy have been identified. HCM is associated with more than 550 mutations, whereas DCM, RCM and VNCM are associated with 52, 14 and 17 mutations, respectively. In many cases, the genes affected present a varying range of phenotypic and pathological severity. Recent data suggest that at least two main genetic determinants are involved in the pathogenesis and phenotypic variability within families afflicted by the same disease-linked gene. Individuals that are homozygous for a mutation or heterozygous for two or more mutations often show more severe phenotypes. Secondly, genetic modifiers are present in some cardiomyopathy patients and are associated with a poorer prognosis. At the protein level, changes in protein-protein interactions may also be important in determining the type of cardiomyopathy caused by different mutations. This review provides insight into the complex cardiovascular phenotypes and genetic variability associated with HCM, DCM, RCM and VNCM.     

A pilot study of muscle plasma protein changes after exercise

Introduction: Creatine kinase (CK) and myoglobin (Mb) do not possess all good qualities as biomarkers of skeletal muscle damage. We investigated the utility of troponin I (TnI) and telethonin (Tcap) as markers and examined their temporal profiles after skeletal muscle damage. Methods: Plasma profiles were measured before and after exercise in 3 groups: subjects affected by either Becker muscular dystrophy or McArdle disease, and healthy subjects. Results: Mb and TnI appeared early in the blood, and the increase of TnI was only observed in patients with muscle disease. The CK increase was more delayed in plasma. Tcap was not detectable at any time. Conclusions: Our results suggest that TnI is a marker of more severe damage signifying sarcomeric damage, and it could therefore be an important supplement to CK and Mb in clinical practice. Tcap is not useful as a marker for skeletal muscle damage. Muscle Nerve 49 : 261–266, 2014     

Telethonin与MSTN在进行性肌营养不良患者肌肉中的表达

目的Telethon in是一种重要的肌节蛋白,肌肉抑制素(myostatin,MSTN)是骨骼肌生长发育抑制因子,本文主要目的是探讨Telethon in和MSTN基因与进行性肌营养不良病理发生的相关性。方法采用W estern b lot方法分析肌营养不良患者中Telethon in和MSTN蛋白的表达水平;为进一步分析Telethon in蛋白对肌营养不良病理发生的作用,构建了Telethon in的反义表达载体,转染肌原性细胞系C2C12,研究阻断Telethon in基因表达(Knockdown)对成肌细胞增殖分化的影响。结果发现在一些肌营养不良患者中Telethon in蛋白表达缺失,而在这些患者的肌肉组织中MSTN蛋白表达正常但存在加工障碍;此结果提示,Telethon in蛋白可能参与MSTN蛋白的加工成熟过程。采用反义技术阻断Telethon in基因表达后,C2C12细胞增殖受到明显抑制。结论Telethon in和MSTN可能与一些类型肌营养不良的病理发生密切相关。     

Localization of Sarcomeric Proteins During Myofibril Assembly in Cultured Mouse Primary Skeletal Myotubes

It is important to understand how muscle forms normally in order to understand muscle diseases that result in abnormal muscle formation. Although the structure of myofibrils is well understood, the process through which the myofibril components form organized contractile units is not clear. Based on the staining of muscle proteins in avian embryonic cardiomyocytes, we previously proposed that myofibrils formation occurred in steps that began with premyofibrils followed by nascent myofibrils and ending with mature myofibrils. The purpose of this study was to determine whether the premyofibril model of myofibrillogenesis developed from studies developed from studies in avian cardiomyocytes was supported by our current studies of myofibril assembly in mouse skeletal muscle. Emphasis was on establishing how the key sarcomeric proteins, F‐actin, nonmuscle myosin II, muscle myosin II, and α‐actinin were organized in the three stages of myofibril assembly. The results also test previous reports that nonmuscle myosins II A and B are components of the Z‐bands of mature myofibrils, data that are inconsistent with the premyofibril model. We have also determined that in mouse muscle cells, telethonin is a late assembling protein that is present only in the Z‐bands of mature myofibrils. This result of using specific telethonin antibodies supports the approach of using YFP‐tagged proteins to determine where and when these YFP‐sarcomeric fusion proteins are localized. The data presented in this study on cultures of primary mouse skeletal myocytes are consistent with the premyofibril model of myofibrillogenesis previously proposed for both avian cardiac and skeletal muscle cells. Anat Rec, 297:1571–1584, 2014. © 2014 Wiley Periodicals, Inc.     

Maintenance of muscle mass,fiber size,and contractile function in mice lacking the Z-disc protein myotilin

Abstract

Background. Myofibrillar myopathies constitute a rare group of congenital neuromuscular disorders, frequently associated with mutations in Z-disc proteins such as myotilin. Myotilin location and interactions with other Z-disc proteins are clearly defined, but its role in the regulation of muscle structure and function remains unknown. The present study aims at investigating this specific role of myotilin.

Methods. Skeletal and cardiac muscles were collected from adult mice with a targeted deletion of myotilin (myo^-/-) and wild-type animals (myo^+/+).

Results and conclusion. Similar skeletal and cardiac muscle weights were observed in myo^-/- and myo^+/+ mice. At the muscle cell level, the size and force production of single membrane permeabilized fibers were identical between myo^-/- and myo^+/+ rodents. Thus, myotilin does not have a significant influence on muscle mass, muscle fiber size, or regulation of muscle contraction. Alternatively, compensatory over-expressions of other elements including proteins from the same subfamily, or Z-disc proteins such as telethonin, or intermediate filaments may compensate for the lack of myotilin.