Role of collagen VI in skeletal muscle homeostasis
Year: 2011
Type: dissertation
Abstract: Collagen VI (ColVI) is an extracellular matrix protein forming a microfilamentous network in various tissues, and composed by three chains, α1(VI), α2(VI) and α3(VI), encoded by separate genes. Mutations of ColVI genes in humans cause various muscle diseases, including Bethlem Myopathy and Ullrich Congenital Muscular Dystrophy (UCMD). Mice lacking ColVI (Col6a1-/-) display a myopathic phenotype with mitochondrial dysfunction and spontaneous apoptosis of muscle fibers. Analysis of muscle biopsies and primary cultures of UCMD patients revealed a similar phenotype, which could be normalized by treatment with cyclosporin A or its non-immunosuppressive derivatives. During the first two years of my PhD work, I focused on studies aimed at elucidating collagen VI pathomolecular defects in human disorders, characterizing three novel ColVI chains in humans and mice and understanding molecular pathways underlying the phenotype of Col6a1-/- mice. Considering the remarkable apoptotic phenotype displayed by Col6a1-/- and UCMD myoblasts, and persuaded by the regenerative effect of cyclosporin A treatment in UCMD patients, during the second half of my PhD work I started investigating muscle regeneration and satellite cell (SC) activity in the Col6a1-/- mouse model. SCs are an adult stem cell population of skeletal muscle, representing the main player in skeletal muscle regeneration. Under physiological condition, I found that Col6a1-/- mice display an altered regenerative activity when compared to wild-type mice. In order to investigate further muscle regeneration capability of Col6a1-/- mice, I analyzed the regenerative response after muscle injury, induced either by cardiotoxin injection or by muscle training by voluntary exercise on running wheels. Light microscopy showed that after repeated cardiotoxin injury Col6a1-/- mice lose the ability to properly regenerate muscles, compared to wild type mice. Further studies, using Pax7 as a marker for SCs, revealed that in Col6a1-/- muscles SCs are able to complete muscle regeneration, but are unable to expand and maintain their pool. Interestingly, during the first stages of regeneration wild-type muscles showed a marked increase of ColVI deposition in the regenerating area, where Pax7-positive cells were found to proliferate extensively. In addition, almost all Pax7-positive cells were found in close contact with ColVI, and some of these cells were totally surrounded by the protein. Moreover, apoptotic nuclei were found to be strongly increased in Col6a1–/– muscles during starting events of regeneration, when compared to both untreated Col6a1–/– and cardiotoxin-treated wild-type muscles. In order to perform further studies on SC activity, I set up an in vitro experimental system with single myofiber cultures derived from wild-type and Col6a1–/– EDL muscles. These in vitro studies showed that wild-type SCs doubled during myofiber culture and gave origin both to activated cells (Pax7+MyoD+) and cell returned to the quiescence state (Pax7+MyoD-). Conversely, the number of quiescent Pax7-positive cells per fiber was strongly reduced in Col6a1–/– cultures compared to both wild-type cultures and freshly isolated Col6a1–/– myofibers. Altogether, these in vivo and in vitro studies strongly suggest a new role for ColVI in skeletal muscle regeneration and indicate that in Col6a1–/– muscles SCs have an impaired ability to expand and maintain the stem cell pool. We are currently investigating the mechanism through which ColVI signals are transduced in SCs in vivo and in vitro.
Author: Anna Urciuolo
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2462143133