THE ROLE OF MICAL2 IN PHYSIOLOGICAL AND PATHOLOGICAL MYOGENIC COMMITMENT : De rol van MICAL2 in fysiologische en pathologische myogenese

Muscle tissue represents 40% of human body mass and provides locomotion, posture support and breathing. Contractile myofibre units are mainly composed of two crucial components: thick myosin and thin actin (F-actin) filaments. F-Actin interacts with Microtubule Associated Monooxygenase, Calponin And LIM Domain Containing 2 (MICAL2), capable to make oxidation-reduction reactions by its FAD domain. Indeed, MICAL2 modifies actin subunits and promotes actin turnover by severing disaggregation and preventing repolymerisation. An adequate supply of oxygen is essential during myogenesis and muscle fibres need to modify their oxygen demand from rest to cell contraction. The striking capability of MICAL2 to directly and mechanistically connect oxygen availability with F-actin depolymerisation, and hence cytoskeleton dynamics, was thought to be implicated into the process of myogenic differentiation. Therefore, we hypothesised that MICAL2 is involved in smooth, skeletal and cardiac muscle differentiations. Gaining this knowledge might help to understand the role of MICAL2 in muscle pathological conditions, including muscular dystrophies and rhabdomyosarcoma (RMS). Hence, unravelling MICAL2 involvement in muscle differentiation in physiological and pathological conditions was the main aim of this project. The role of MICAL2 was deciphered firstly during differentiation to skeletal, smooth and cardiac muscle cells from myogenic progenitors. In this setting, MICAL2 was found more expressed in myogenic differentiated cells compared to their relative progenitors. Secondly, MICAL2 expression was assessed in dystrophic conditions where the pool of adult stem cells was exhausted. In this case, MICAL2 was more present when a degeneration/regeneration process occurred, localising in centrally-nucleated fibres, in both acute and chronic conditions. Loss and gain of function studies in C2C12 and satellite cells demonstrated that silencing or overexpressing MICAL2 had an impact on both proliferation and myogenic differentiation potential. Indeed, silencing MICAL2 resulted in an enhanced proliferation state of progenitor cells, with a consequent skeletal muscle differentiation impairment. While, on the contrary, overexpressing MICAL2 inmyogenic precursors differentiating towards skeletal muscle positively impacted on myotube formation compared to control cells. Moreover, RMS cell lines were explored for MICAL2 expression, showing an abundant presence of MICAL2 in these cancer cells. Loss of function experiments were performed to unveil the molecular impact of MICAL2, resulting in a slower and decreased proliferative stage. Further modulation of MICAL2 might reduce the tumorigenic capacity of RMS cells and might induce differentiation towards skeletal muscle. In conclusion, our data indicate that MICAL2 is a novel regulator of myogenic differentiation, also outlining its multifaceted effects in determining the cellular response to the environment. In particular, in the pathophysiological context MICAL2 affects proliferation and cell migration, and controls muscle regeneration. Thus, we propose MICAL2 as potent modulator of skeletal myogenesis and perhaps crucial also for cardiac and smooth muscle progenitor cell fate. ispartof: pages:1-134 status: published