PROJECT SUMMARY There is a fundamental gap in our knowledge of how mitochondria homeostasis contributes to immune re- sponses to infectious pathogens. The overall objective of this proposal is to define how the tripartite motif con- taining protein TRIM14 regulates STAT3 activity to modulate mitochondria health and innate immune outcomes during Mycobacterium tuberculosis (Mtb) infection. Recent studies have shown that TRIM14 negatively regulates type I IFN responses during Mtb infection through interactions with the cytosolic DNA sensing kinase TBK1 and the transcription factor STAT3. Specifically, TRIM14 was shown to be required for TBK1 phosphorylation of STAT3 at S727, which controls STAT3’s ability to translocate to the nucleus and turn on expression of negative regulators of IFNAR to dampen type I IFN responses. Interestingly, additional studies of Trim14-/- macrophages demonstrated several mitochondrial-related defects, including altered metabolic profiles during Mtb infection and a propensity to undergo intrinsic apoptosis. STAT3 is a classical transcription factor, but recent studies have highlighted its role in mitochondrial respiration, generation of reactive oxygen species, and maintaining mito- chondrial membrane potential. These connections prompted interest into how this novel TRIM14-TBK1-STAT3 axis influences mitochondrial health and how disruption of this pathway impacts innate immune responses to the intracellular bacterial pathogen Mycobacterium tuberculosis. This proposal is designed to test the hypothesis that TRIM14 is a critical player in maintaining the integrity of the mitochondrial network by directing TBK1 phos- phorylation of STAT3 and promoting STAT3 accumulation in the mitochondrial matrix. Aim 1 of this proposal will define how TRIM14 alters TBK1’s ability to phosphorylate STAT3 and how STAT3 phosphorylation alters its subcellular localization. Aim 2 will investigate how TRIM14 and STAT3 control mitochondria depolarization and apoptosis during Mtb infection. Aim 3 will investigate how TRIM14’s regulation of mitochondria metabolism, apoptosis, and changes to innate immune cell populations alter the outcome of Mtb infection in a mouse model of disease. This work will further fundamental understanding of how the TRIM14-TBK1-STAT3 axis regulates mitochondria health, which may inform novel therapeutic interventions that could help control Mtb and improve tuberculosis patient outcomes.