Macrophages and neutrophils are necessary for ER stress-induced ß cell loss.

Persistent endoplasmic reticulum (ER) stress induces islet inflammation and ß cell loss. How islet inflammation contributes to ß cell loss remains uncertain. We have reported previously that chronic overnutrition-induced ER stress in ß cells causes Ripk3-mediated islet inflammation, macrophage recruitment, and a reduction of ß cell numbers in a zebrafish model. We show here that ß cell loss results from the intricate communications among ß cells, macrophages, and neutrophils. Macrophage-derived Tnfa induces cxcl8a in ß cells. Cxcl8a, in turn, attracts neutrophils to macrophage-contacted "hotspots" where ß cell loss occurs. We also show potentiation of chemokine expression in stressed mammalian ß cells by macrophage-derived TNFA. In Akita and db/db mice, there is an increase in CXCL15-positive ß cells and intra-islet neutrophils. Blocking neutrophil recruitment in Akita mice preserves ß cell mass and slows diabetes progression. These results reveal an important role of neutrophils in persistent ER stress-induced ß cell loss.

Genome-wide CRISPR screen identified a role for commander complex mediated ITGB1 recycling in basal insulin secretion.

OBJECTIVES: Pancreatic beta cells secrete insulin postprandially and during fasting to maintain glucose homeostasis. Although glucose-stimulated insulin secretion (GSIS) has been extensively studied, much less is known about basal insulin secretion. Here, we performed a genome-wide CRISPR/Cas9 knockout screen to identify novel regulators of insulin secretion. METHODS: To identify genes that cell autonomously regulate insulin secretion, we engineered a Cas9-expressing MIN6 subclone that permits irreversible fluorescence labeling of exocytic insulin granules. Using a fluorescence-activated cell sorting assay of exocytosis in low glucose and high glucose conditions in individual cells, we performed a genome-wide CRISPR/Cas9 knockout screen. RESULTS: We identified several members of the COMMD family, a conserved family of proteins with central roles in intracellular membrane trafficking, as positive regulators of basal insulin secretion, but not GSIS. Mechanistically, we show that the Commander complex promotes insulin granules docking in basal state. This is mediated, at least in part, by its function in ITGB1 recycling. Defective ITGB1 recycling reduces its membrane distribution, the number of focal adhesions and cortical ELKS-containing complexes. CONCLUSIONS: We demonstrated a previously unknown function of the Commander complex in basal insulin secretion. We showed that by ITGB1 recycling, Commander complex increases cortical adhesions, which enhances the assembly of the ELKS-containing complexes. The resulting increase in the number of insulin granules near the plasma membrane strengthens basal insulin secretion.