• Critical role of zinc in a new murine model of enterotoxigenic Escherichia coli diarrhea

      Bolick, D.T.; Medeiros, P.H.Q.S.; Ledwaba, S.E. (American Society for Microbiology, 2018)
      Enterotoxigenic Escherichia coli (ETEC) is a major cause of traveler's diarrhea as well as of endemic diarrhea and stunting in children in developing areas. However, a small-mammal model has been badly needed to better understand and assess mechanisms, vaccines, and interventions. We report a murine model of ETEC diarrhea, weight loss, and enteropathy and investigate the role of zinc in the outcomes. ETEC strains producing heat-labile toxins (LT) and heat-stable toxins (ST) that were given to weaned C57BL/6 mice after antibiotic disruption of normal microbiota caused growth impairment, watery diarrhea, heavy stool shedding, and mild to moderate intestinal inflammation, the latter being worse with zinc deficiency. Zinc treatment promoted growth in zinc-deficient infected mice, and subinhibitory levels of zinc reduced expression of ETEC virulence genes cfa1, cexE, sta2, and degP but not of eltA in vitro. Zinc supplementation increased shedding and the ileal burden of wild-type (WT) ETEC but decreased shedding and the tissue burden of LT knockout (LTKO) ETEC. LTKO ETEC-infected mice had delayed disease onset and also had less inflammation by fecal myeloperoxidase (MPO) assessment. These findings provide a new murine model of ETEC infection that can help elucidate mechanisms of growth, diarrhea, and inflammatory responses as well as potential vaccines and interventions. Copyright 2018 American Society for Microbiology.
    • Insulin secretion by β-cell-like cells derived from pulp stem cells depends on augmented cytosolic zinc levels than gaba levels

      Kim, Gyuyoup; Chung, Man Kyo; Pae, Eung Kwon (MDPI AG, 2020-11-01)
      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. © 2020 by the authors.