Project Grant F32GM167154

NOVEL FUNCTIONS OF BNIP3 IN LIPID HOMEOSTASIS IN THE LIVER - PROJECT SUMMARY HUMAN HEALTH RELIES ON MITOCHONDRIAL HOMEOSTASIS. MITOCHONDRIA ARE NECESSARY FOR A PLETHORA OF PURPOSES IN THE CELL SUCH AS ENERGY PRODUCTION, LIPID AND ION HOMEOSTASIS, REDOX HOMEOSTASIS, COFACTOR SYNTHESIS, AND APOPTOSIS. TO ENSURE THAT EACH OF THESE FUNCTIONS ARE PROPERLY EXECUTED THE CELL AND MITOCHONDRIA EVOLVED TO INCLUDE SELF- DEFENSE MECHANISMS, REFERRED TO AS MITOCHONDRIAL QUALITY CONTROL (MQC), TO COMBAT ENDOGENOUS AND EXOGENOUS STRESS STIMULI. ONE SUCH DEFENSE MECHANISM IS MITOPHAGY, OR MITOCHONDRIAL TURNOVER. BRIEFLY, MITOPHAGY IS THE SELECTIVE DEGRADATION OF PORTIONS OF THE MITOCHONDRIAL NETWORK TO CONTROL MITOCHONDRIAL MASS AND MITIGATE THE ACCUMULATION OF STRESS AND DAMAGED MOLECULES WITHIN MITOCHONDRIA. MITOPHAGY IS MEDIATED BY SEVERAL PATHWAYS, BUT HERE I WILL FOCUS ON MITOPHAGY MEDIATED BY THE MITOCHONDRIAL CARGO RECEPTOR BNIP3. BNIP3 IS, PRIMARILY, A STRESS-INDUCED PROTEIN THAT UPON ACTIVATION LOCALIZES TO THE OUTER MITOCHONDRIAL MEMBRANE (OMM) AND INITIATES MITOPHAGY AND AUTOPHAGOSOME FORMATION AND ENGULFMENT. BNIP3 EXPRESSION AND ACTIVATION ARE REGULATED BOTH TRANSCRIPTIONALLY AND POST-TRANSLATIONALLY. IN THE LIVER, BNIP3 IS HIGHLY EXPRESSED COMPARED TO OTHER TISSUES AND PLAYS A CRITICAL ROLE IN LIVER HOMEOSTASIS AND LIPID METABOLISM, AS DESCRIBED PREVIOUSLY BY THE MACLEOD LAB. BNIP3 DEFICIENCY RESULTS IN THE ACCUMULATION OF PHOSPHOLIPIDS, TRIACYLGLYCERIDES, AND LIPID DROPLETS. FROM A PHYSIOLOGICAL PERSPECTIVE, LOSS OF BNIP3 ENHANCES THE DEVELOPMENT OF SEVERE LIVER DISEASES AND HEPATOCELLULAR CARCINOMA. MORE RECENTLY, MY UNPUBLISHED STUDIES SHOW THAT RECOMBINANT BNIP3 BINDS DIRECTLY TO SPECIFIC PHOSPHOLIPIDS IN VITRO. MOREOVER, THESE STUDIES ALSO REVEALED THAT BNIP3 MODULATED FERROPTOSIS INDUCTION BY A CURRENTLY UNKNOWN MECHANISM. THESE DATA INDICATE THAT BNIP3 RESIDES WITHIN THE MITOCHONDRIA-LIPID METABOLISM NEXUS. MITOCHONDRIA AND LIPID METABOLISM ARE ALREADY CLOSELY LINKED. MITOCHONDRIA DEPEND ON LIPID METABOLISM TO PROVIDE THE LIPIDS TO BUILD THE OMM AND THE INNER MITOCHONDRIAL MEMBRANE WHILE ALSO PLAYING A ROLE IN OXIDATIVE PHOSPHORYLATION AND THERMOGENESIS. CONVERSELY, MITOCHONDRIA TRAFFIC AND MODIFY PHOSPHOLIPIDS, SYNTHESIZE LIPOIC ACID, AND GENERATE ENERGY THROUGH THE OXIDATION OF FATTY ACIDS. WE HYPOTHESIZE THAT (1) BNIP3 BINDS DIRECTLY TO PHOSPHOLIPIDS TO MAINTAIN PROPER BALANCE BETWEEN LIPID STORAGE AND DEGRADATION AND THAT (2) BNIP3 MODULATES LIPID METABOLISM AND FERROPTOSIS VIA MITOPHAGY AND LIPID BINDING. THESE HYPOTHESES WILL BE TESTED IN PRIMARY HEPATOCYTES AND THE HEPATOCELLULAR CARCINOMA CELL LINE, HEPG2, THROUGH THE FOLLOWING AIMS: AIM 1- DEFINING THE LIPID BINDING CAPABILITIES OF BNIP3 AND THEIR IMPACT ON CELLULAR HOMEOSTASIS AND AIM 2- DELINEATING THE ROLE OF BNIP3 IN MODULATING MITOPHAGY AND LIPID METABOLISM. SUCCESSFUL COMPLETION OF THE PROPOSED AIMS WILL PROVIDE CRITICAL INSIGHT TOWARDS THE MOLECULAR MECHANISMS CONTROLLING LIPID METABOLISM AND MITOCHONDRIAL HOMEOSTASIS IN THE LIVER. ACQUIRING A PROPER UNDERSTANDING OF THESE MECHANISMS WILL ALLOW FOR THE FURTHER ADVANCEMENT AND DEVELOPMENT OF EFFECTIVE TREATMENTS AND THERAPIES FOR LIVER-ASSOCIATED METABOLIC DISORDERS AND LIVER CANCERS.