Exploring the in vivo role of the mitochondrial calcium uniporter in brown fat bioenergetics

The mitochondrial calcium uniporter has been proposed to coordinate the organelle's energetics with cytosolic calcium signaling. Previous studies have shown that the uniporter current is extremely high in mitochondria from brown adipose tissue (BAT), yet the contribution of the uniporter to BAT physiology in vivo is not known. Here, we report the generation and characterization of a mouse model lacking Mcu, the pore forming subunit of the uniporter, specifically in BAT (BAT-Mcu-KO). BAT-Mcu-KO mice are born in Mendelian ratios on a C57BL6/J genetic background, without any overt phenotypes. Although uniporter based calcium uptake is selectively ablated in BAT mitochondria, these mice are able to defend their body temperature in response to cold challenge and exhibit a normal body weight trajectory on a high fat diet. BAT transcriptional profiles at baseline and following cold-challenge are intact and not impacted by loss of Mcu. Unexpectedly, we found that cold powerfully activates the ATF4-dependent integrated stress response in BAT, and increases both circulating FGF21 and GDF15 levels, raising the hypothesis that the integrated stress response partly underlies the pleiotropic effects of BAT on systemic metabolism. Our study demonstrates that the uniporter is largely dispensable for BAT thermogenesis, and unexpectedly, uncovers a striking activation of the integrated stress response of BAT to cold challenge. Overall design: RNA-seq was performed on BAT RNA isolated from BAT-Mcu-KO and control animals housed for 6 hours at 4C or room temp (RT). Samples include 6 control animals at RT; 5 control animals at 4C; 6 BAT-Mcu-KO animals at RT; and 6 BAT-Mcu-KO animals at 4C.

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Flicker D, Sancak Y, Mick E, Goldberger O, Mootha VK