Tetraspanin7-mediated inhibition of β-cell voltage-dependent Ca2+ channels regulates glucose-stimulated insulin secretion.

Glucose-stimulated insulin secretion (GSIS) is regulated by Ca2+ influx into pancreatic β-cells through voltage-dependent Ca2+ channels (VDCCs). As some tetraspanin (TSPAN) transmembrane proteins control Ca2+ handling they may also modulate GSIS. TSPAN7 is the most abundant TSPAN in mouse and human islets. TSPAN7 autoantibodies are also found in type 1 diabetic serum, suggesting a link between TSPAN7 and diabetes. The aim herein was to determine if TSPAN7 controls β-cell Ca2+ handling and insulin secretion. Immunofluorescence imaging of mouse and human pancreatic slices indicated that TSPAN7 is highly expressed in β- and α-cells. shRNA-mediated TSPAN7 knockdown (KD) in mouse and human β-cells augmented glucose-stimulated Ca2+ influx (by 32.3±9.5% and 33.8±15.1% respectively) as well as KCl-stimulated Ca2+ influx (45 mM; 34.5±9.6%, human). Mouse β-cell Ca2+ oscillation frequency was also accelerated by TSPAN7 KD (by 29.4±10.1%). As TSPANs interact with and regulate VDCCs, we examined the effect of TSPAN7 on VDCC currents. TSPAN7 KD increased peak L-type VDCC currents in mouse and human β-cells (by 4.1±1.3 pA/pF and 2.0±0.9 pA/pF respectively). Heterologous expression of TSPAN7 with L-type VDCCs in HEK293 cells also decreased VDCC currents (CaV1.2: 4.3±1.8 pA/pF; CaV1.3: 17.5±5.4 pA/pF) and reduced KCl-stimulated (50 mM) Ca2+ influx (CaV1.2: 51.0±7.1%; CaV1.3: 28.4±7.5%). Furthermore, TSPAN7 coimmunoprecipitated with CaV1.2 and CaV1.3 from primary human β-cells and when heterologously expressed in HEK293 cells. Finally, TSPAN7 KD in human β-cells increased basal (5.6 mM glucose; 8.3±5.5 ng*hr-1) and stimulated (45 mM KCl+14 mM glucose; 20.4±17.1 ng*hr-1) insulin secretion. These findings reveal that TSPAN7 modulation of β-cell L-type VDCCs limits glucose-stimulated Ca2+ influx and insulin secretion.

Disclosure

M. Dickerson: None. P. Dadi: None. R.B. Butterworth: None. D. Jacobson: None.

Funding

American Diabetes Association (1-17-IBS-024 to D.J.); National Institutes of Health (T32DK101003, DK097392, DK115620); Vanderbilt University Medical Center Diabetes Research and Training Center (P60DK20593)

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