Brown adipose tissue (BAT) dissipates energy for thermogenesis which reduces or prevents obesity and metabolic dysfunction. AMP-activated protein kinase (AMPK) is a master regulator of energy metabolism and its activity is inhibited in the developing BAT due to obesity. We previously found that AMPK is required for brown fat development and thermogenic function, but the non-brown adipogenic differentiation of progenitor cells due to AMPK alpha 1 deficiency has not been defined. We found that, in vivo, the thermogenic capacity and morphology of BAT were compromised due to AMPK deficiency, which was correlated with decreased progenitor density in BAT. In addition, the expression of fibrogenic markers was higher in AMPK deficient compared to wild-type mice. Furthermore, we transplanted AMPK alpha 1 wild type (WT) and floxed BAT into the same recipient mice; following tamoxifen induced AMPK alpha 1 knockout in floxed BAT, the fibrogenesis was enhanced compared to WT mice. Taken together, our data demonstrated that AMPK alpha 1 deficiency suppressed brown adipogenesis in favor of fibrogenesis during BAT development. (C) 2017 Elsevier Inc. All rights reserved.