Metabolic stressors common to type 2 diabetes (T2D) lead to perturbations of β-cell’s transcriptional identity which provide β-cells an adaptive survival advantage at the expense of compromised function (i.e., dedifferentiation). Increase in the intracellular pH (pHi alkalization) is a characteristic feature of cancer cell dedifferentiation and survival. Interestingly, a recent single-cell transcriptomic study of human pancreas identified SLC4A4 (encoding Na+-coupled HCO3- cotransporter, NBCe1) as one of the few genes enriched in dedifferentiated T2D β-cells. Indeed, NBCe1 is a key regulator pHi alkalization; however, its role in human β-cell dysfunction in T2D is unknown. To address this we first defined whether aberrant SLC4A4/NBCe1 expression marks failing human β-cells in T2D. First, utilizing immunofluorescence analysis of human autopsy pancreas we observed near complete absence of NBCe1 expression in β-cells of lean nondiabetic individuals (ND) and robust expression of NBCe1 in obese T2D β-cells (∼10 fold increase in T2D vs. ND, p<.01). Moreover, NBCe1 expression occurred in conjunction with the nuclear to cytoplasmic redistribution of NKX6.1 and with an increase in ALDH1a3-positive β-cells, both key markers of β-cell dedifferentiation in T2D. Moreover, we independently procured ND and T2D isolated human islets (12 independent shipments) and observed ∼ 3-fold increase in SLC4A4 mRNA in T2D islets (p<.05 vs. ND). Since the primary function of NBCe1 is HCO3- import, T2D islet cells also exhibited significantly higher pHi (p<.001 vs. ND). Finally, NBCe1 activity inhibition (with selective inhibitor, S0859) reversed β-cell dysfunction in isolated T2D islets by significantly enhancing β-cell GSIS (p<.01 vs. UT). Taken together, our study suggests that induction of β-cell SLC4A4/NBCe1 expression and consequent increase in pHi may play a previously unappreciated role in β-cell dysfunction and dedifferentiation in T2D.
M. Brown: None. A. Stiller: None. M.F. Romero: None. A. Matveyenko: None.
