OxPhos in adipose tissue macrophages regulated by BTK enhances their M2-like phenotype and confers a systemic immunometabolic benefit in obesity

Abstract

Brutons tyrosine kinase (BTK) is a non-receptor bound kinase involved in pro-inflammatory signalling in activated macrophages, however, its role within adipose tissue macrophages remains unclear. We have demonstrated that BTK signalling regulates macrophage M2-like polarisation state by up-regulating subunits of mitochondrially encoded electron transport chain Complex I (ND4 and NDL4) and Complex IV (mt-CO1, mt-CO2 and mt-CO3) resulting in an enhanced rate of oxidative phosphorylation (OxPhos) in an NF-{kappa}B independent manner. Critically, BTK expression is elevated in adipose tissue macrophages from obese individuals with diabetes, while key mitochondrial genes (mtC01, mtC02 and mtC03) are decreased in inflammatory myeloid cells from obese individuals. Inhibition of BTK signalling either globally (Xid mice) or in myeloid cells (LysMCreBTK), or therapeutically (Acalabrutinib) protects HFD-fed mice from developing glycaemic dysregulation by improving signalling through the IRS1/Akt/GSK3b pathway. The beneficial effects of acalabrutinib treatment are lost in macrophage ablated mice. Inhibition of BTK signalling in myeloid cells but not B-cells, induced a phenotypic switch in adipose tissue macrophages from a pro-inflammatory M1-state to a pro-resolution M2-like phenotype, by shifting macrophage metabolism towards OxPhos. This reduces both local and systemic inflammation and protects mice from the immunometabolic consequences of obesity. Therefore, in BTK we have identified a macrophage specific, druggable target that can regulate adipose tissue polarisation and cellular metabolism that can confer systematic benefit in metabolic syndrome. Article high lightsObesity and diabetes are associated with inflammation, particularly within the adipose tissue. We have found a new druggable target called Brutons tyrosine kinase (BTK) that is highly expressed in adipose tissue macrophages. When BTK is inhibited in macrophages, it allows these cells to undergo a phenotypic switch towards an M2-like pro-resolution macrophage. This achieved by increasing expression of key mitochondrially encoded components of the electron transport chain allowing for enhanced OxPhos. Inhibition of BTK signalling in myeloid cells but not B-cells protects HFD-fed mice from developing glycaemic dysregulation.