Insulin Secretion by β-Cell-Like Cells Derived from Pulp Stem Cells Depends on Augmented Cytosolic Zinc Levels than GABA Levels

Abstract

Background: Stem cells harvested from human exfoliated deciduous teeth (SHED) are pluripotent and can be differentiated into insulin-secreting β-cells, i.e., SHED β-cells. Previously, we showed that zinc upregulates insulin secretion from SHED β-cells, potentially providing an extra source for insulin. Rationale: In this study, we determined the role of ionotropic γ-aminobutyric acid A (GABAA) receptor in zinc-enhanced insulin secretion from SHED β-cells. Autocrine/paracrine activation of GABAA receptors by GABA elevates calcium influx in pancreatic β-cells, in which intracellular chloride is maintained at high levels. Method and Findings: Differentiating SHED into SHED β-cells resulted in an increase in the expression of GABAA receptor subunits and Zrt-/irt-like protein3 (ZIP3), a zinc uptake transporter. Zinc pretreatment elevated the insulin gene transcription, whereas knockdown of ZIP3 reduced levels of intracellular zinc, and concomitantly reduced insulin secretion by SHED β-cells. Zinc-pretreated SHED β-cells exhibited a GABA-induced increase in Ca2+ influx, detected with a ratiometric calcium-sensitive dye, suggesting zinc-mediated regulation of GABAA receptors. Conclusion: Our results indicate that elevated levels of zinc and GABAA receptors are indispensable for efficient insulin secretion by SHED β-cells. These findings suggest an opportunity for using SHED β-cells for treating diabetes.

Intermittent Hypoxia Interferes with Autocrine Effects of GABA on Insulin Secretion in Postnatal Rodents—Implications for Pediatric Obstructive Sleep Apnea

“…GABA is an excellent secretagogue of insulin [ 9 , 19 , 26 ]. Exogenous GABA increased the intracellular calcium ion levels, as shown in Figure 2 , a finding consistent with previous reports [ 27 , 28 ].…”

“…Ratiometric Ca 2+ imaging analysis was performed as described previously in detail [ 19 ]. Dissociated islet cells were loaded with Fura2-AM (Molecular Probes) for 40 min at 37 °C in a calcium-imaging buffer (CIB) containing 130 mM NaCl, 3 mM KCl, 0.5 mM MgCl 2 , 0.9 mM CaCl 2 , 10 mM HEPES, 10 mM sucrose, 1.2 mM NaHCO 3 pH 7.45 and 320 mOsm (adjusted with mannitol).…”