Role of MICU2 in the regulation of mitochondrial functions and cell physiology

Abstract

The ability of mitochondria to transport Ca2+ in a highly regulated manner makes them essential players in Ca2+ signaling. Mitochondrial functions are fine-tuned by changes in both matrix and/or intermembrane space [Ca2+]. Alterations in the composition of the mitochondrial calcium uniporter complex (MCUc) have emerged as an important mechanism to regulate mitochondrial Ca2+ transport either under physiological or pathological contexts. Among MCUc components, less is known about the role and mechanistic regulation of the mitochondrial calcium uptake protein 2 (MICU2). We have previously demonstrated that MICU2 content is decreased (~25%) in mitochondria isolated from the liver and kidneys of calorically restricted (CR) rodents, which correlates with higher rates in which they uptake Ca2+. Kidney mitochondria from CR rats release higher amounts of oxidants, which render them more prone to Ca2+-induced permeability transition. Despite this, we didn't observe an increase in oxidative damage markers. Indeed, other mitochondrial functions are preserved or even improved. As CR is well known to protect kidneys against ischemia/reperfusion-induced damage, we believe that retrograde redox signaling from mitochondria, as a consequence of MICU2 decrease and higher mitochondrial Ca2+ content, may prime cells to improve their antioxidant systems. Additionally, mitochondrial quality control systems, such as mitophagy and mitochondrially-derived vesicle (MDV) formation, should be able to cope with the extra damaged components. In this project, we aim to elucidate the role of MICU2 in the control of mitochondrial functions and its consequences for whole-cell physiology. First, using NRK and AML12 cell lines, we will clarify the role of MICU2 in mitochondrial Ca2+ uptake. We will characterize the effect of MICU2 KD on cell growth/survival, cell metabolism, redox balance, mitochondrial bioenergetics, morphology, and quality control, with a focus on mitophagy and MDV formation. The mechanistic basis of the MICU2 KD phenotype will be studied. Then, we will identify how MICU2 is regulated under basal state and conditions that mimic in-vitro CR and fasting. (AU)