Molecular Mechanism of Brown Adipose Tissue Regression

Abstract Our preliminary data demonstrates that in both Adipoq and UCP1-specific Stx4 knockout mice results in the activation of pyroptotic brown adipocyte cell death through the NLRP1 (NOD-like receptor protein 1) signaling pathway. In parallel, brown adipose function and to a lesser extent mass declines during aging and this age-associated decline in BAT thermogenesis occur concomitant with the induction of pyroptosis. Furthermore, in both modes the regression of BAT results in the reduction in insulin sensitivity, energy expenditure and cold tolerance that can be reversed by over expression of Stx4 in brown/beige adipocytes (UCP1-Stx4 transgenic mice) or by blocking of pyroptosis using an inhibitor of caspase 1. In addition, aged and Stx4 knockout mice have reduced protein levels of the cell survival receptors Ntrk3, a brown adipocyte selective tyrosine receptor kinase within brown adipose tissue. Based upon these data, we are proposing a multi-principal investigator (MPI) application to understand the molecular basis for the decline in brown adipose tissue mass and function during the normal development of aging and the functional/physiological consequences of preserving brown mass and function, in terms of energy balance, insulin sensitivity and metabolic homeostasis. In this proposal, we will determine 1) the specific pathways and signaling events responsible for brown adipocyte pyroptosis and functional consequences of preserving BAT using both pharmacological and genetic interventions; 2) the functional role of the neurotropic tyrosine receptor kinase Ntrk3 in regulating BAT mass, function and brown adipocyte pyroptosis; and 3) changes in tissue cellular identity and its role during age-dependent BAT dysfunction and regression. The findings obtained from this proposal will then allow to develop strategies to prevent age-dependent regression of BAT that will likely provide a more tractable and effective therapeutic approach than the induction of beige adipose tissue to improve glucose metabolism, increase energy expenditure and prevent weight gain.