Ketone-body receptor GPR109A suppresses hepatic inflammation via gut-liver axis regulation
The ketogenic diet (KD) promotes ketone body synthesis and has been used as an effective treatment for disorders such as epilepsy. Although elevated ketone bodies, including {beta}-hydroxybutyrate ({beta}HB) and acetoacetate, are thought to meditate the beneficial effects of the KD, the mechanisms underlying their metabolic actions remain incompletely understood. In this study, we focused on GPR109A, a receptor for {beta}HB with an unclear role in metabolic homeostasis. We employed KD and fasting models to examine metabolic changes under two distinct ketogenic conditions. Under KD conditions, Gpr109a-/- mice exhibited increased hepatic lipid accumulation, and subsequent hepatic inflammation and fibrosis. However, Gpr109a deletion did not exacerbate hepatic lipid accumulation or inflammation during short-term fasting, suggesting that GPR109A-mediated liver protection is specific to KD-induced metabolic stress rather than under fasting conditions. Mechanistic analysis revealed that GPR109A protects the liver from inflammation by maintaining intestinal barrier integrity. These findings highlight the novel protective mechanism of GPR109A, via the gut-liver axis, to sustain metabolic homeostasis during the KD. This study provides valuable insights into the physiological effects of ketone bodies.