Fine architectonics and protein turnover rate in myofibrils of glucocorticoid caused myopathic rats

Abstract

Priit Kaasik, Maria Umnova, Karin Alev, Anne Selart, Teet Seene

Objective: The purpose of this study was to assess the relationship between the synthesis and degradation rate of thick and thin myofilaments, and changes in fine architectonics of myofibrils of glycolytic muscle fibers of glucocorticoid caused myopathic rats. Methods: Male Wistar rats receive dexamethasone to induce myopathy. Protein synthesis rate degradation and structure of myofibrils was measured. Results: Myofibrils from glycolytic muscle fibers of 16-week-old male rats of the Wistar Strain were used for analysis. Myofibrils of glucocorticoid caused myopathic rats were thinner than in the control group (1.10 ± 0.05 µm 2 and 2.56 ± 0.08 µm 2 , respectively) and thick and thin myofilaments in myopathic muscle disappeared from 22.0 ± 2.7% of the myofibrils cross-section area. In the control group, myofilaments were absent from 1.8 ± 0.5%. In the myopathic group, a positive correlation was found between the area of myofibrils where myofilaments disappeared and the myofibrillar protein degradation rate (r=0.849; p<0.001). A positive correlation was found between myofibrils cross-sectional area and thick myofilaments synthesis rate (r=0.933; p<0.001). Conclusions: Increased myofibrillar protein degradation rate, decreased myosin heavy chain (MyHC) and actin synthesis rate and a decrease in MyHCIIb isoform relative content in myopathic glycolytic muscle are related to qualitative remodeling of the myofibrillar apparatus in myopathic glycolytic muscle fibers.