ABSTRACT: Various forms of fasting, including time-restricted feeding, alternate day fasting, and periodic fasting have shown promise in clinical and pre-clinical studies to normalize body weight, improve metabolic health, and protect against disease. Recent studies suggest that β-hydroxybutyrate (βOHB), a characteristic ketone body of the fasted metabolic state, acts as a potential signaling molecule mediating the beneficial effects of the various forms of fasting, potentially by acting as a histone deacetylase inhibitor. In the first part we investigated whether βOHB, in comparison to the well-established histone deacetylase inhibitor butyrate, influences cellular differentiation in vitro. In C2C12 myotubes, 3T3-L1 adipocytes, and THP-1 monocytes, millimolar concentrations of βOHB did not alter differentiation, as determined by gene expression and histological assessment, whereas equimolar concentrations of butyrate potently impaired differentiation in all cell types. RNA-sequencing revealed that unlike butyrate, βOHB minimally impacted gene expression in adipocytes, macrophages, and hepatocytes. However, in myocytes, βOHB upregulated genes involved in the TCA cycle and oxidative phosphorylation, while downregulating genes belonging to cytokine and chemokine signal transduction. Overall, our data do not support the notion that βOHB serves as a powerful signaling molecule regulating gene expression in adipocytes, macrophages and hepatocytes, but suggest that βOHB may act as a niche signaling molecule in muscle.
