Central Acting Hsp10 Regulates Mitochondrial Function, Fatty Acid Metabolism, and Insulin Sensitivity in the Hypothalamus.

Mitochondria are critical for hypothalamic function and regulators of metabolism. Hypothalamic mitochondrial dysfunction with decreased mitochondrial chaperone expression is present in type 2 diabetes (T2D). Recently, we demonstrated that a dysregulated mitochondrial stress response (MSR) with reduced chaperone expression in the hypothalamus is an early event in obesity development due to insufficient insulin signaling. Although insulin activates this response and improves metabolism, the metabolic impact of one of its members, the mitochondrial chaperone heat shock protein 10 (Hsp10), is unknown. Thus, we hypothesized that a reduction of Hsp10 in hypothalamic neurons will impair mitochondrial function and impact brain insulin action. Therefore, we investigated the role of chaperone Hsp10 by introducing a lentiviral-mediated Hsp10 knockdown (KD) in the hypothalamic cell line CLU-183 and in the arcuate nucleus (ARC) of C57BL/6N male mice. We analyzed mitochondrial function and insulin signaling utilizing qPCR, Western blot, XF96 Analyzer, immunohistochemistry, and microscopy techniques. We show that Hsp10 expression is reduced in T2D mice brains and regulated by leptin in vitro. Hsp10 KD in hypothalamic cells induced mitochondrial dysfunction with altered fatty acid metabolism and increased mitochondria-specific oxidative stress resulting in neuronal insulin resistance. Consequently, the reduction of Hsp10 in the ARC of C57BL/6N mice caused hypothalamic insulin resistance with acute liver insulin resistance.

Insulin action in the brain regulates mitochondrial stress responses and reduces diet-induced weight gain.

OBJECTIVE: Insulin action in the brain controls metabolism and brain function, which is linked to proper mitochondrial function. Conversely, brain insulin resistance associates with mitochondrial stress and metabolic and neurodegenerative diseases. In the present study, we aimed to decipher the impact of hypothalamic insulin action on mitochondrial stress responses, function and metabolism. METHODS: To investigate the crosstalk of insulin action and mitochondrial stress responses (MSR), namely the mitochondrial unfolded protein response (UPRmt) and integrated stress response (ISR), qPCR, western blotting, and mitochondrial activity assays were performed. These methods were used to analyze the hypothalamic cell line CLU183 treated with insulin in the presence or absence of the insulin receptor as well as in mice fed a high fat diet (HFD) for three days and STZ-treated mice without or with insulin therapy. Intranasal insulin treatment was used to investigate the effect of acute brain insulin action on metabolism and mitochondrial stress responses. RESULTS: Acute HFD feeding reduces hypothalamic mitochondrial stress responsive gene expression of Atf4, Chop, Hsp60, Hsp10, ClpP, and Lonp1 in C57BL/6N mice. We show that insulin via ERK activation increases the expression of MSR genes in vitro as well as in the hypothalamus of streptozotocin-treated mice. This regulation propagates mitochondrial function by controlling mitochondrial proteostasis and prevents excessive autophagy under serum deprivation. Finally, short-term intranasal insulin treatment activates MSR gene expression in the hypothalamus of HFD-fed C57BL/6N mice and reduces food intake and body weight development. CONCLUSIONS: We define hypothalamic insulin action as a novel master regulator of MSR, ensuring proper mitochondrial function by controlling mitochondrial proteostasis and regulating metabolism.