B7-H4 regulates β cell mass and insulin secretion by modulating cholesterol metabolism

Chronic islet inflammation is a hallmark of type 2 diabetes (T2D) and involves in the dysfunction of β cells. However, how β cells participate in this process remains unclear. Here, we report that the immune checkpoint molecule B7-H4(B7S1, B7x, VTCN1) expressed in β cells is critical to maintain β cell mass and insulin secretion. Lesion of B7-H4 in β cells results in glucose intolerance due to less β cell mass and deficient insulin secretion with upregulated cytokines and activated signal transducer and activator of transcription 5 (Stat5) signaling, while overexpression of B7-H4 in β cells ameliorates glucose intolerance in high-fat diet (HFD)-treated mice. Mechanistically, B7-H4 deficiency actives the Stat5 signaling, which inhibits the expression of Apolipoprotein F (ApoF), leading to reduced cholesterol efflux and accumulated cholesterol in β cells, thereby impairing the insulin processing and secretion. Inhibiting Stat5 activity or overexpression of ApoF in β cells can rescue the glucose intolerance and insulin secretion deficiency in β-cell-specific B7-H4 knockout (B7-H4 cKO) mice. Our study demonstrates that β cell expressed immune checkpoint molecule B7-H4 is essential for islet immune homeostasis and β cell function maintenance, and for the first time unravels the mechanism by which B7-H4 regulates insulin secretion through regulating cholesterol metabolism via Stat5 signaling, which may shed new light on the development of novel strategies for T2D treatment.