Transcriptional regulation by the CaMKK2/AMPK/SRC-3 signaling pathway in NAFLD

York, Brian

Abstract

Chronicnutritionaloverloadimposesstressontheliverthatpromoteshepaticsteatosis,leadingtoacceleration ofnon-alcoholicfattyliverdisease(NAFLD),insulinresistanceandtype2diabetesmellitus(T2DM).Restoring the capacity of the liver to manage excess energy burden improves peripheral insulin sensitivity, even in the presence of high fat diet-induced obesity. We discovered that calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is required for obesity-driven hepatic steatosis and our preliminary studies found that pharmacological inhibition of CaMKK2 reverses obesity-induced NAFLD and improves whole body glycemia. The aberrant metabolism of lipids by the liver resulting from high fat diet-induced obesity induces stress responses in the endoplasmic reticulum (ER), which perturb the delicate intrahepatic balance of calcium and fattyacidhomeostasis.Ourpreliminarystudiesestablishthatcalciumandlongchainfattyacidssynergistically convergetodirectlyactivateCaMKK2,suggestingamechanismbywhichthesesignalscoordinatetopromote NAFLD.TheoverarchinggoalofourresearchistoelucidatethedownstreammechanismsbywhichCaMKK2 activation promotes hepatic steatosis in response to overnutrition. To this end, we have identified a novel pathwaywherebyCaMKK2activationsignalstoAMPKa?2andSteroidReceptorCoactivator-3(SRC-3)todrive transcriptionofERstressgeneprogramsthatpromoteNAFLD.Thesefindingssupportthehypothesisthatthis signalingaxisdriveshepatictranscriptionalreprogrammingduringovernutritiontostimulateNAFLD.
In Aim1, wewilldefinethemechanismsgoverningtranscriptionalregulationofERstressbyCaMKK2/AMPKa?2/SRC-3.
Aim2 willdefinetheroleofCaMKK2asanintegratorofcalciumandfattyacidsignalingthatpromotesobesity- driven NAFLD and define its potential as a therapeutic target. Our research is expected to identify the molecular and physiological mechanisms by which the CaMKK2/AMPKa?2/SRC-3 signaling axis promotes obesity-driven NAFLD. Our observations linking CaMKK2 to aberrant Ca2+ and fatty acid signals induced by overnutrition exposes an uncharacterized pathway by which these obesity-driven signals converge to exacerbate hepatic steatosis. Experiments to determine how CaMKK2 reprograms hepatic transcriptional programs to favor steatosis is expected to define new mechanisms for therapeutic intervention of obesity- drivenhepaticpathologies.PUBLICHEALTH

Public Health Relevance

NAFLD,insulinresistanceandT2DMarechronic health problems driven by rampant obesity in the United States. Discovery of innovative mechanisms to overcomehepaticsteatosisandrestorelivermetaboliccapacitythatimprovesinsulinsensitivityrepresentnew paradigmsforclinicalmanagementofobesity-relateddiseases.