Loss of tetraspanin-7 expression reduces pancreatic beta-cell exocytosis Ca2+ sensitivity but has limited effect on systemic metabolism.
McLaughlin K., Acreman S., Nawaz S., Cutteridge J., Clark A., Knudsen JG., Denwood G., Spigelman AF., Manning Fox JE., Singh SP., MacDonald PE., Hastoy B., Zhang Q.
BACKGROUND: Tetraspanin-7 (Tspan7) is an islet autoantigen involved in autoimmune type 1 diabetes and known to regulate beta-cell L-type Ca2+ channel activity. However, the role of Tspan7 in pancreatic beta-cell function is not yet fully understood. METHODS: Histological analyses were conducted using immunostaining. Whole-body metabolism was tested using glucose tolerance test. Islet hormone secretion was quantified using static batch incubation or dynamic perifusion. Beta-cell transmembrane currents, electrical activity and exocytosis were measured using whole-cell patch-clamping and capacitance measurements. Gene expression was studied using mRNA-sequencing and quantitative PCR. RESULTS: Tspan7 is expressed in insulin-containing granules of pancreatic beta-cells and glucagon-producing alpha-cells. Tspan7-knockout mice (Tspan7y/- mouse) exhibit reduced body weight and ad libitum plasma glucose but normal glucose tolerance. Tspan7y/- islets have normal insulin content and glucose- or tolbutamide-stimulated insulin secretion. Depolarisation-triggered Ca2+ current was enhanced in Tspan7y/- beta-cells, but beta-cell electrical activity and depolarisation-evoked exocytosis were unchanged suggesting that exocytosis was less sensitive to Ca2+ . TSPAN7 knockdown (KD) in human pseudo-islets led to a significant reduction in insulin secretion stimulated by 20 mM K+ . Transcriptomic analyses show that TSPAN7 KD in human pseudo-islets correlated with changes in genes involved in hormone secretion, apoptosis and ER stress. Consistent with rodent beta-cells, exocytotic Ca2+ sensitivity was reduced in a human beta-cell line (EndoC-βH1) following Tspan7 KD. CONCLUSION: Tspan7 is involved in the regulation of Ca2+ -dependent exocytosis in beta-cells. Its function is more significant in human beta-cells than their rodent counterparts.