UNDERSTANDING THE ROLE OF MITOCHONDRIAL QUALITY CONTROL

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Mitochondrial quality control (mQC), which refers to the mechanisms governing the regulated degradation of mitochondrial components, is an emerging facet in the field of mitochondrial biology. Indeed, several mQC mechanisms, the best known being mitophagy, have been uncovered recently, but their role in various cell types, their level of inter-relation, and their physiological relevance in vivo, remain poorly understood. This program aims to answer these questions using striated muscle and immune cells which have different designs and functions. We will focus on two mQC mechanisms: i) mitophagy (the selective clearance of whole mitochondria through autophagy), and ii) production of mitochondrial-derived vesicles (MDVs: the selective clearance of mitochondrial components through a vesicle secretion process).***Part 1: Mitochondrial QC in muscle cells: Maintenance of an adapted and optimally functioning pool of mitochondria is critical for normal contractile activity. For this reason we hypothesize that in myocytes mQC is commensurate to mitochondrial content/activity, and that these mechanisms act in a hierarchical manner. More specifically, we postulate that MDV production is a predominant mechanism for baseline mitochondrial housekeeping, and early response to mitochondrial stress, while mitophagy becomes more predominant when excessive damage to whole organelles is present. To test this, c2c12 myoblasts/myotubes will be used to characterize mitochondrial functions, mitophagy, MDV production, and cellular phenotype at baseline and in response to conditions known to force a mQC response. Genetic approaches will be used to specifically modulate mitophagy and MDV production in order to elucidate their role. This will also be studied in vivo in WT and transgenic mice using various approaches including quantitative morphological electron microscopy.***Part 2: Mitochondrial QC in macrophages (MΦ): In MΦ, mitochondria play a role the development of pro (M1) and anti (M2)-inflammatory responses, but the underlying mechanisms remain unclear. We hypothesize that modulation of mitophagy and MDV production, plays an important role in this process by altering mitochondrial functions, and mitochondrial antigen presentation for immune signalling. To test this Raw MΦ and primary bone marrow-derived MΦ will be exposed to pro- or anti-inflammatory stimuli in vitro. Mitochondrial functions will be analyzed together with mitophagy, MDV production, mitochondrial antigen presentation, and MΦ differentiation markers. Genetic approaches and transgenic mice will be used to modulate mitophagy and MDV production in order to elucidate their role in MΦ differentiation/activation. In vivo studies will also be conducted to examine the role of mQC on the immune response.***Overall this work will provide important information on the role of mQC in mitochondrial and cellular functions.**************