Chronic β-Cell Depolarization Impairs β-Cell Identity by Disrupting a Network of Ca2+-Regulated Genes

Abstract

We used mice lacking <i>Abcc8</i>, a key component of the β-cell K_ATP-channel, to analyze the effects of a sustained elevation in the intracellular Ca²⁺ concentration ([Ca²⁺]_i) on β-cell identity and gene expression. Lineage tracing analysis revealed the conversion of β-cells lacking <i>Abcc8</i> into pancreatic polypeptide cells but not to α- or δ-cells. RNA-sequencing analysis of FACS-purified <i>Abcc8^-/-</i> β-cells confirmed an increase in <i>Ppy</i> gene expression and revealed altered expression of more than 4,200 genes, many of which are involved in Ca²⁺ signaling, the maintenance of β-cell identity, and cell adhesion. The expression of <i>S100a6</i> and <i>S100a4</i>, two highly upregulated genes, is closely correlated with membrane depolarization, suggesting their use as markers for an increase in [Ca²⁺]_i Moreover, a bioinformatics analysis predicts that many of the dysregulated genes are regulated by common transcription factors, one of which, <i>Ascl1</i>, was confirmed to be directly controlled by Ca²⁺ influx in β-cells. Interestingly, among the upregulated genes is <i>Aldh1a3</i>, a putative marker of β-cell dedifferentiation, and other genes associated with β-cell failure. Taken together, our results suggest that chronically elevated β-cell [Ca²⁺]_i in <i>Abcc8^-/-</i> islets contributes to the alteration of β-cell identity, islet cell numbers and morphology, and gene expression by disrupting a network of Ca²⁺-regulated genes.