Editors' ChoiceMetabolism

Gut microbes help turn up the heat?

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Sci. Signal.  01 Aug 2017:
Vol. 10, Issue 490, eaao4947
DOI: 10.1126/scisignal.aao4947

Cold temperatures induce a switch in cholesterol metabolism that alters the gut microbiota and facilitates thermogenesis.

In cold temperatures, mammals generate body heat through energy-consuming processes involving brown adipose tissue (BAT) and increased uptake of various nutrients, particularly carbohydrates and lipid-related metabolites. The gut microbiota also contributes to metabolic homeostasis. Worthmann et al. (see also Kuipers and Groen) found that the gut microbiota may facilitate thermogenesis involving a cold-induced switch in the metabolism of cholesterol. In male mice fed a high-fat, high-cholesterol diet, the amount of plasma triglycerides and cholesterol was decreased, and the amount of fecal bile acids was increased when mice were housed in the cold. Radiolabeling revealed that a greater proportion of absorbed dietary cholesterol was converted to bile acids in cold-housed mice. Cold exposure also altered the bacterial composition of the gut microbiome. The cold-induced metabolic and microbiome effects were prevented by blocking cholesterol uptake or knocking down CYP7B1, an enzyme associated with the “alternative pathway” of bile acid synthesis in the liver. In contrast, the cold-associated effects were observed in mice at ambient temperatures after overexpression of CYP7B1 or β-adrenergic stimulation of BAT. Further exploration will reveal whether and how specifically the microbiome contributes to cold-induced thermogenesis. Nonetheless, the findings identify a multitissue axis involving a change in cholesterol metabolism that enables mammals (or at least mice) to adapt to the cold.

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