Overexpression of Smad7 in hypothalamic POMC neurons disrupts glucose balance by attenuating central insulin signaling

Sep 24, 2020Molecular metabolism

Increasing Smad7 in brain hunger-control neurons may disturb blood sugar by weakening insulin signals in the brain

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Abstract

Smad7 expression was increased in POMC neurons in the hypothalamic arcuate nucleus of high-fat diet-fed or middle-aged mice.

Overexpression of Smad7 in POMC neurons disrupted glucose balance.
Deletion of Smad7 in POMC neurons prevented glucose disorders associated with diet or age.
The effects of Smad7 on glucose metabolism appeared to be independent of body weight or food intake changes.
Overexpression of AKT in the arcuate nucleus reversed the impact of excess Smad7.
Smad7 decreased AKT phosphorylation by activating protein phosphatase 1c in hypothalamic primary neurons.

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OBJECTIVE: Although the hypothalamus is crucial for peripheral metabolism control, the signals in specific neurons involved remain poorly understood. The aim of our current study was to explore the role of the hypothalamic gene mothers against decapentaplegic homolog 7 (Smad7) in peripheral glucose disorders.

METHODS: We studied glucose metabolism in high-fat diet (HFD)-fed mice and middle-aged mice with Cre-mediated recombination causing 1) overexpression of Smad7 in hypothalamic proopiomelanocortin (POMC) neurons, 2) deletion of Smad7 in POMC neurons, and 3) overexpression of protein kinase B (AKT) in arcuate nucleus (ARC) in Smad7 overexpressed mice. Intracerebroventricular (ICV) cannulation of insulin was used to test the hypothalamic insulin sensitivity in the mice. Hypothalamic primary neurons were used to investigate the mechanism of Smad7 regulating hypothalamic insulin signaling.

RESULTS: We found that Smad7 expression was increased in POMC neurons in the hypothalamic ARC of HFD-fed or middle-aged mice. Furthermore, overexpression of Smad7 in POMC neurons disrupted the glucose balance, and deletion of Smad7 in POMC neurons prevented diet- or age-induced glucose disorders, which was likely to be independent of changes in body weight or food intake. Moreover, the effect of Smad7 was reversed by overexpression of AKT in the ARC. Finally, Smad7 decreased AKT phosphorylation by activating protein phosphatase 1c in hypothalamic primary neurons.

CONCLUSIONS: Our results demonstrated that an excess of central Smad7 in POMC neurons disrupts glucose balance by attenuating hypothalamic insulin signaling. In addition, we found that this regulation was mediated by the activity of protein phosphatase 1c.

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Overexpression of Smad7 in hypothalamic POMC neurons disrupts glucose balance by attenuating central insulin signaling

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