SWELL1 is a glucose sensor required for β-cell excitability and insulin secretion

Insulin secretion from the pancreatic β-cell initiated by activation of voltage-gated Ca2+ channels (VGCC) to trigger Ca2+-mediated insulin vesicle fusion with the β-cell plasma membrane. The firing of VGCC depends on the β-cell membrane potential, which is in turn mediated by the balance of depolarizing (excitatory) and hyperpolarizing (inhibitory) ionic currents1-3. While much attention has focused on inhibitory potassium currents4-10 there is little knowledge about the excitatory currents required to depolarize the β-cell, including the molecular identity of these excitatory currents3. Here we show that SWELL1 (LRRC8a) mediates a swell-activated, depolarizing chloride current (ICl,SWELL) in β-cells. Hypotonic and glucose-stimulated β-cell swelling activates SWELL1-mediated ICl,SWELL and this is required for both glucose-stimulated and hypotonic swell-mediated activation of VGCC-dependent intracellular calcium signaling in β-cells. SWELL1 KO MIN6 cells and β-cell targeted SWELL1 KO murine islets exhibit significantly impaired glucose-stimulated insulin secretion, with preserved insulin content in vitro. Tamoxifen-inducible β-cell targeted SWELL1 KO mice have normal fasting insulin levels but display markedly impaired glucose-stimulated insulin secretion. Our results reveal a physiological role for SWELL1 as a glucose sensor - linking glucose-mediated β-cell swelling to SWELL1-dependent activation of VGCC-triggered calcium signaling, and highlights SWELL1-mediated “swell-secretion” coupling as required for glucose-stimulated insulin secretion.


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To determine the impact of SWELL1-dependent glucose-stimulated Ca 2+ signaling on insulin 145 secretion in β-cells we measured glucose-stimulated insulin secretion (GSIS) in WT and SWELL1 KO 146 MIN6 cells. We find that the glucose-dependent increase in insulin secretion in WT MIN6 cells is 147 significantly diminished in SWELL1 KO MIN6 cells (Fig. 4a), particularly at higher glucose concentration 148 (30 mM), despite no change in total insulin content (Fig. 4b). We next isolated islets from SWELL1 fl/fl 149 mice followed by transduction with either Ad-RIP1-RFP (WT) or Ad-RIP1-Cre-P2A-RFP (SWELL1 KO;

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and in β-cell-targeted SWELL1 KO murine islets (Fig. 4d). However, with glucose-stimulation (2 g/kg 163 i.p.) we find that insulin secretion is significantly impaired in KO Ins1Cre ERT2 mice compared to WT mice 164 ( Fig. 4j). Overall, these data are consistent with a requirement of β-cell SWELL1 for glucose-stimulated,

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Ca 2+ -dependent insulin secretion both in vitro and in vivo.

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VRAC/I Cl,SWELL has been studied for decades through electrophysiological recordings in numerous cell 168 types 29-31 , but only recently has it been discovered that SWELL1/LRRC8a, and associated LRRC8 169 isoforms b-e, form the VRAC channel complex in common cell lines [11][12][13] . Accordingly, the physiological 170 role of SWELL1-mediated VRAC in primary cells remains unexplored. We recently showed that 171 SWELL1 is required for VRAC in adipocytes where it senses adipocyte hypertrophy in the setting of 172 obesity and regulates insulin-PI3K-AKT2-GLUT4 mediated glucose uptake and systemic glycemia 32 .

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Here we asked whether SWELL1 is required for VRAC described previously in the pancreatic β-cell [16][17][18] 174 and whether the VRAC hypothesis 33 can be explained by a putative glucose-mediated swell sensing