Tan, C.H.; (2011) The cell biology of the mitochondrial protein IF1. Doctoral thesis , UCL (University College London).

Abstract

Mitochondria are important organelles that regulate processes such as energy homeostasis and apoptosis. Dysregulation of mitochondrial function contributes to pathophysiology of diseases including ischaemia-reperfusion injury and cancer. When mitochondrial respiration is disturbed during oxygen deprivation, the mitochondrial ATP synthase runs ‘backwards’ as an ATPase, consuming ATP whilst maintaining mitochondrial membrane potential. The depletion of ATP can drive cell death. In this thesis, I have studied the roles of the endogenous inhibitor of ATPase, IF1, in regulating progression and outcome of cellular injury in models of necrosis and apoptosis. I first studied localisation and expression profiles of IF1 in HeLa and HL-1 cells. IF1 localised exclusively to mitochondria in both cell types. In HL-1 cells, IF1 expression profile changed dramatically with confluency, correlating with changes in cell differentiation. IF1 overexpression increased viability of HL-1 cardiomyocytes following oxygen and glucose deprivation, a model of ischaemia-reperfusion. A pivotal step in triggering apoptosis is the release of cytochrome c from mitochondrial intracristal space, activating cytosolic enzymatic cascades which cause cell death. It has been suggested that cristae remodelling facilitates cytochrome c release. As IF1 increases cristae density, I studied the impact of IF1 overexpression on cytochrome c release following exposure of HeLa cells to staurosporine. IF1 upregulation delayed cytochrome c release, possibly as a result of altered cristae structure. It has been suggested that cytochrome c release increases calcium release from endoplasmic reticulum (ER), promoting a positive feedback system that accelerates complete cytochrome c release. I found that cytochrome c release correlated with ER calcium efflux, depletion of ER calcium and with mitochondrial depolarisation, mediated by permeability transition pore opening. These processes were reduced following IF1 overexpression, suggesting that IF1 plays a significant role in progression of apoptosis. Thus, IF1 modulates progression and outcome of cell injury and death through necrotic and apoptotic pathways.

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