Mechanistic link between mitochondrial cristae integrity and Th1 responses

PROJECT SUMMARY Genetic and environmental factors determine individuals’ susceptibility to autoimmunity. Genome-wide association studies of human subjects provide valuable information; however, the interpretation of these results is complex due to intrinsic and extrinsic variations. This proposal aims to uncover the genetic basis underlying the intrinsic propensity of T cells towards autoimmunity using a hybrid mouse system with minimum extrinsic variations and to elucidate the molecular mechanism underlying these genetic differences. We performed a forward genetics screen using a hybrid mouse diversity panel of 107 common and recombinant inbred strains to examine T cell propensity. We have uncovered four significant genetic loci associated with expression of proinflammatory cytokines. A targeted screen using deletion of candidate genes within these loci uncovered a mitochondrial cristae morphology regulator, TMEM11, as a genetic determinant of the Th1 response. Tmem11- /- mice show normal development and homeostasis of T cells. However, while T cell differentiation was not affected, selective effector functions of Th1 cells, including expression of IFNg, were impaired due to the loss of TMEM11. This impairment decreased the severity of an animal model of autoimmunity, experimental autoimmune encephalomyelitis (EAE). Further analyses revealed that Tmem11-/- Th1 cells showed impairment in cristae integrity and mitochondrial respiration. Among these defects, excessive mitochondrial reactive oxygen species (mtROS) production was the underlying cause of impaired Th1 function since mitigating mtROS rescued the defect. We also found that excessive mtROS decreased histone acetylation and activation of the Ca2+-NFAT pathway, which are important for Ifng transcription. Based on these findings, we propose to 1) uncover the mechanism regulating mitochondrial cristae morphology in effector T cells using high-resolution imaging techniques and proteomics, 2) understand the relationship between mitochondrial cristae integrity and effector T cell responses by checking the role of excessive mtROS in histone modification and the NFAT signaling pathway, and 3) Determine the role of mitochondrial cristae integrity in T cell-mediated autoimmunity using active and passive EAE models. This study is innovative because our forward and reverse genetics approaches uncovered a unique tool to investigate the roles of cristae integrity and mtROS in effector T cells. Knockout of Tmem11 provides an ideal system to determine the physiological role of cristae morphology and integrity because TMEM11 is a regulatory protein but not a core subunit of the cristae junctional complex, and its deficiency, hence does not influence mitochondrial biogenesis or global cellular physiology. The outcome of this study will positively impact our understanding of the roles of mitochondrial cristae integrity and oxidative stress in effector T cell functions and autoimmunity, which need further investigations.