Loss of tetraspanin-7 expression reduces pancreatic β-cell exocytosis Ca 2+ sensitivity but has limited effect on systemic metabolism.

Background: Tetraspanin-7 (Tspan7) is an islet autoantigen involved in autoimmune type 1 diabetes and known to regulate β-cell L-type Ca ²⁺ channel activity. However, the role of Tspan7 in pancreatic β-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. β-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 β-cells and glucagon-producing α-cells. Tspan7 knockout mice (Tspan7 ^y/- mouse) exhibit reduced body weight and ad libitum plasma glucose but normal glucose tolerance. Tspan7 ^y/- islets have normal insulin content and glucose- or tolbutamide-stimulated insulin secretion. Depolarisation-triggered Ca ²⁺ current was enhanced in Tspan7 ^y/- β-cells, but β-cell electrical activity and depolarisation-evoked exocytosis were unchanged suggesting that exocytosis was less sensitive to Ca ²⁺ . 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 β-cells, exocytotic Ca ²⁺ sensitivity was reduced in a human β-cell line (EndoC-βH1) following Tspan7 KD.
Conclusion: Tspan7 is involved in the regulation of Ca ²⁺ -dependent exocytosis in β-cells. Its function is more significant in human β-cells than their rodent counterparts.
(© 2022 The Authors. Diabetic Medicine published by John Wiley & Sons Ltd on behalf of Diabetes UK.)