CaMKK2 in macrophages promotes obesity-induced insulin resistance and inflammation

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Project Summary/Abstract The obesity pandemic is a growing crisis that predisposes afflicted individuals to comorbidities of the metabolic syndrome including hypertension, Type 2 diabetes and liver disease. Clinically, obesity is defined as a low-grade inflammatory disease that is influenced by macrophage infiltration and activation. Resolving this perturbed inflammatory response could be a means by which the onset and progression of metabolic syndrome is circumvented. Activation of the calcium/calmodulin kinase cascade has been implicated in abnormal metabolic processes and a contributor to diet-induced obesity. We identified that Ca2+/Calmodulin-Dependent Protein Kinase Kinase 2 (CaMKK2) is highly expressed in macrophages and is synergistically activated by Ca2+ and long-chain fatty acids, two signals that are elevated during obesity. We have shown that mice devoid of CaMKK2 are refractory to diseases typically associated with caloric overload, and that pharmacological inhibition of CaMKK2 reverses hepatic steatosis and regresses hepatic tumor growth. Furthermore, loss of CaMKK2 reduces expression of several inflammatory markers, indicating the importance of CaMKK2 in regulating the inflammatory response. To clarify the role of CaMKK2 in macrophages, we developed a myeloid-specific CaMKK2 knockout (CaMKK2MKO) and evaluated its response to chronic high-fat diet feeding. Resulting macrophage ablation of CaMKK2 conferred protection against the detrimental effects of caloric overload by improving peripheral insulin sensitivity, reducing hepatic steatosis and decreasing central adiposity. Additionally, RNA-Seq analysis from epidydimal white adipose tissue (eWAT) shows that CaMKK2MKO mice have a robust activation of fatty-acid metabolic programs and a concomitant reduction in pro-inflammatory signaling. Assessment of mitochondrial performance reveals that loss or inhibition of CaMKK2 confers a reprogramming of naïve macrophages to more efficiently metabolize fatty-acid substrates. These results are corroborated with b-oxidation assays that show macrophages devoid of CaMKK2 have a significantly improved capacity to utilize fatty-acids and retain elevated oxidation levels despite inflammatory stimuli. Based on these findings, we hypothesize that CaMKK2 functions as a metabolic sensor in macrophages to modulate the balance of fuel utilization between glycolytic and oxidative pathways, reprogramming the cell’s ability to respond to metabolic stimuli. I will test this hypothesis in Aim 1 by determining the role of CaMKK2 in the regulation of macrophage fuel preference and function. Building on this information, Aim 2 will focus on characterizing the mechanism(s) by which CaMKK2 reprograms macrophage metabolic capability by examining the downstream functions of Mitofusin-2 (Mfn2) on mitochondrial dynamics. We have developed the necessary tools to identify novel interactants and substrates of CaMKK2 in macrophages in the hopes of providing a mechanistic explanation to support the metabolic benefits associated with inhibition or loss of CaMKK2. Collectively, our findings highlight an unappreciated role of CaMKK2 as a driver of metabolic dysfunction and expose a new target for therapeutic intervention of metabolic syndrome.