Brown adipocytes (BA) are a specialized fat cell which possesses a high capacity for fuel oxidation combined with heat production. The maintenance of high metabolic activity in BA requires elevated oxidation of fuel through the tricarboxylic acid cycle. Pyruvate carboxylase (PC) was previously proposed to be essential for coordination between fuel oxidation and thermogenesis. By differentiating human pluripotent stem cells to mature BA in vitro, we showed that ablation of PC gene by CRISPR Cas9 genome engineering did not impair the ability of stem cells to generate mature BA. However, brown adipocytes deficient for PC expression displayed a 35% reduction in ATP-linked respiration, but not thermogenesis under both basal and isoproterenol-stimulated conditions. This relatively mild impairment of ATP-link respiration in PC knockout BA was protected by increased spare mitochondrial respiratory capacity. Taken together, this study highlights the role of PC in supporting fuel oxidation rather than thermogenesis in human BA.
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