TLR4 mediates lipotoxic β-cell dysfunction by inhibiting the TMEM24/PI3K/AKT pathway.

Immune imbalance is the core pathophysiological mechanism of the deterioration of β-cell function driven by lipid metabolism disorders. Toll-like receptor 4 (TLR4) inflammatory signaling is a key pathway that mediates lipotoxic injury in β-cells, but the underlying mechanism needs to be further elucidated. Transmembrane protein 24 (TMEM24) is a key transporter that regulates pulsatile insulin secretion, but its pathophysiology in lipotoxicity remains unclear. In this study, we investigate whether TLR4-mediated lipotoxicity is affected by the inhibition of TMEM24 expression. The PPI network shows that TLR4 is associated with both insulin secretion and ER stress proteins in islets from obese rats. Using in vitro lipotoxic β-cell models, we found that TMEM24 is the target signal of palmitic acid (PA)-induced insulin secretion impairment in islet β-cells, and TLR4 plays a mediating role in this process. Mechanistically, TLR4 mediates lipotoxicity by binding to TMEM24 and downregulating its protein expression to suppress PI3K/AKT signaling, leading to β-cell dysfunction. TLR4 knockout ameliorates islet function impairment through TMEM24/PI3K/AKT signaling in HFD-induced obese rats. Taken together, our results show that TLR4 mediates lipotoxicity in islet β-cells by inhibiting the TMEM24/PI3K/AKT pathway, and the mechanism of TLR4-mediated lipotoxicity is elucidated from the perspective of insulin vesicular secretion.