SIRT3 enables neuronal β-oxidation and protects against lipotoxicity

Sirtuin3 is a mitochondrial NAD⁺-dependent deacetylase that controls adaptive responses to metabolic challenges. As a result, SIRT3KO mice are obese, insulin resistant and exhibit mitochondrial dysfunction. Yet, the function of SIRT3 in neurons is less clear. Here, we overexpress SIRT3 in hypothalamic neurons and assess its function on mitochondrial activity and insulin sensitivity in normal and lipotoxic conditions.

The murine hypothalamic cell line CLU183 was used for all experiments. We stably overexpressed SIRT3 and stimulated cells with 125µM BSA or 250µM Palmitate for 16h followed by 100nM insulin stimulation. Gene and protein expression were assessed using Western Blot and qPCR techniques. Mitochondrial function and morphology were characterized via Seahorse XFe Analyzer and electron microscopy.

SIRT3OE neurons exhibited decreased insulin-induced phosphorylation of IGF1/Insulin Receptor compared to control, and decreased basal and maximal mitochondrial respiration, concomitant with reduced expression of the mitochondrial chaperones Hsp60 and Hsp10, whose reduction has been shown to induce mitochondrial dysfunction and insulin resistance. Yet, when SIRT3OE were pretreated with palmitate, SIRT3 overexpression reversed the palmitate-induced decrease in AKT-S473 phosphorylation and mitochondrial dysfunction. This was accompanied by increased mitochondrial biogenesis as evidenced by increased PGC1alpha expression and increased mitochondrial size. Interestingly, SIRT3OE neurons were able to metabolize palmitate and showed increased β-oxidation compared to control. Accordingly, these cells showed increased expression of short-chain acyl-CoA dehydrogenase and mitochondrial transporter VDAC, which was shown to improve CPT1 activity, facilitating palmitoyl-CoA transfer into mitochondria.

Thus we identify a novel feature of SIRT3 enabling metabolic flexibility in neurons and protecting against lipotoxicity.