Analysis of the autophagic pathway in the dystrophic muscle

Author(s)

Stephanie de Alcântara Fernandes

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2017-08-04

Examining board members

Mariz Vainzof; Merari de Fatima Ramires Ferrari; Helga Cristina Almeida da Silva; Edmar Zanoteli

• Advisor: Mariz Vainzof

Abstract

The skeletal muscle is a tissue that has the ability to regenerate upon lesion, whether it occurs pathologically or induced. Therefore, progenitor muscle cells, present in the adult muscle, act by fusing with each other or with damaged fibers in order to recover the tissue. The macroautophagy pathway, related to degradation and recycling of proteins and damaged organelles via lysosome, is essential for the maintenance of muscle mass, and it was also implicated in the differentiation and functioning of muscle progenitor cells. Besides that, this pathway is deregulated in several neuromuscular disorders, highlighting its important role in this tissue. In this study, the autophagic regulation was investigated in distinct contexts of muscle formation and degradation. To study the muscle differentiation process in vitro, we used a model of immortalized muscle cells from both a normal control and a patient with X-linked myopathy with excessive autophagy (XMEA). The genes and proteins p62, BNIP3, BECLIN1, VPS34, ATG12, LC3 and mTOR targets showed a similar pattern of expression in both undifferentiated myoblasts and differentiated myotubes, from both control cells and XMEA patient-derived cells. This fact suggests that autophagic deregulation might arise in later stages of the disease, in a pattern observed in disorders with protein accumulation. The investigation of muscle differentiation in the studied cells showed an enhancement of the myoblast fusion capacity in XMEA cells, which was not related to changes in the expression of myogenic genes. This observation indicates that the primary defect related to the XMEA pathology, as the deficiency of the vacuolar ATPase, might interfere in the process of muscle differentiation. In order to evaluate muscle in pathological conditions, we studied animal models for muscular dystrophies that have distinct patterns of muscle affection, such as the DMDmdx, model for the Duchenne muscular dystrophy, the SJL/J, model for the limb-girdle muscle dystrophy type 2B and the Largemyd, model for the congenital muscular dystrophy type 1D. We did not find any global alterations in the expression of autophagic genes and proteins. Additionally, each animal model had discrete changes, highlighting the absence of correlation between the pattern of muscle degeneration and alterations in the autophagy pathway. On the other hand, when a lesion is induced in normal muscle, there is a decrease in the expression of all studied genes, such as Bnip3, Beclin1, Vps34, Atg12, Lc3 and Gabarapl1, with a possible accumulation of the autophagic proteins p62 and Beclin1. With muscle recovery, five days after lesion, most of the studied genes had their expression returning to normal levels. These results indicate that the acute lesion is related to a drastic response and rapid recovery of the autophagic pathway. Together, our results show that autophagy is differentially affected depending on the stimulus given to the muscle, either of regeneration and formation of new muscle cells or degeneration. In that sense, this study may have implications for the development of therapies that target autophagy, since it indicates that the time point of therapeutic interventions may be important, as well as the stimulus that led to alterations in the skeletal muscle tissue (AU)

• FAPESP's process: 15/18130-3 - Analysis of the autophagic pathway in the dystrophic muscle.
• Grantee: Stephanie de Alcântara Fernandes
• Support Opportunities: Scholarships in Brazil - Master