Electrogenic sodium bicarbonate cotransporter NBCe1 regulates pancreatic β cell function in type 2 diabetes
Matthew R. Brown, … , Michael F. Romero, Aleksey V. Matveyenko
Matthew R. Brown, … , Michael F. Romero, Aleksey V. Matveyenko
Published September 1, 2021
Citation Information: J Clin Invest. 2021;131(17):e142365. https://doi.org/10.1172/JCI142365.
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Research Article Cell biology Endocrinology

Electrogenic sodium bicarbonate cotransporter NBCe1 regulates pancreatic β cell function in type 2 diabetes

Abstract

Pancreatic β cell failure in type 2 diabetes mellitus (T2DM) is attributed to perturbations of the β cell’s transcriptional landscape resulting in impaired glucose-stimulated insulin secretion. Recent studies identified SLC4A4 (a gene encoding an electrogenic Na+-coupled HCO3– cotransporter and intracellular pH regulator, NBCe1) as one of the misexpressed genes in β cells of patients with T2DM. Thus, in the current study, we set out to test the hypothesis that misexpression of SLC4A4/NBCe1 in T2DM β cells contributes to β cell dysfunction and impaired glucose homeostasis. To address this hypothesis, we first confirmed induction of SLC4A4/NBCe1 expression in β cells of patients with T2DM and demonstrated that its expression was associated with loss of β cell transcriptional identity, intracellular alkalinization, and β cell dysfunction. In addition, we generated a β cell–selective Slc4a4/NBCe1-KO mouse model and found that these mice were protected from diet-induced metabolic stress and β cell dysfunction. Importantly, improved glucose tolerance and enhanced β cell function in Slc4a4/NBCe1-deficient mice were due to augmented mitochondrial function and increased expression of genes regulating β cell identity and function. These results suggest that increased β cell expression of SLC4A4/NBCe1 in T2DM plays a contributory role in promotion of β cell failure and should be considered as a potential therapeutic target.

Authors

Matthew R. Brown, Heather Holmes, Kuntol Rakshit, Naureen Javeed, Tracy K. Her, Alison A. Stiller, Satish Sen, Gary E. Shull, Y.S. Prakash, Michael F. Romero, Aleksey V. Matveyenko

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Figure 4

Generation and validation of a β cell–selective Slc4a4-null mouse model.

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Generation and validation of a β cell–selective Slc4a4-null mouse model....
(A) Targeting strategy for β cell–selective deletion of Slc4a4 (left). Representative PCR analyses of tail DNA using primers for identification of Slc4a4 floxed allele and Cre recombinase (right). (B) Diagram of study design indicating that 2-month-old control (β-Slc4a4+/+ Slc4a4fl/fl+/+ and +/+Ins2Cre/+) and β cell Slc4a4-KO (β-Slc4a4–/– Slc4a4fl/flIns2Cre/+) mice were treated for 8 weeks with either chow diet or 60% HFD. In vivo characterization of glucose metabolism occurred at 0, 4, and 8 weeks. Islets were isolated from the mice for functional and transcriptomic profiling; pancreata were isolated for morphological assessment. (C) Slc4a4 expression from β-Slc4a4+/+ (Slc4a4fl/fl+/+) and β-Slc4a4–/– (Slc4a4fl/flIns2Cre/+) pancreatic islets exposed to either 8 weeks of chow or HFD. ***P < 0.001 denotes statistical significance versus β-Slc4a4+/+ chow (unpaired, 2-tailed t test; n = 6 mice per genotype and diet) (top). pHi measured in β-Slc4a4+/+ (Slc4a4fl/fl+/+) and β-Slc4a4–/– (Slc4a4fl/flIns2Cre/+) islet cells exposed to either 8 weeks of chow or HFD. *P < 0.05, **P < 0.01 denotes statistical significance (1-way ANOVA with Tukey’s method for multiple comparisons; n = 62–87 independent cells from n = 2 mice per genotype and diet) (bottom). (D) Representative examples of pancreatic sections and individual islets immunostained for insulin (green), glucagon (white), NBCe1 (red), and DAPI (blue) imaged at 20× original magnification obtained from β-Slc4a4+/+ (Slc4a4fl/fl+/+) and β-Slc4a4–/– (Slc4a4fl/flIns2Cre/+) mice exposed to 8 weeks of chow or HFD. Scale bars: 20 μm. Images are representative of n = 3 mice per genotype and diet. (E) Percentage change in body mass from baseline of β-Slc4a4+/+ (Slc4a4fl/fl+/+) and β-Slc4a4–/– (Slc4a4fl/flIns2Cre/+) mice exposed to either 8 weeks of chow or HFD. *P < 0.05 denotes statistical significance versus β-Slc4a4+/+ chow (2-way ANOVA with Dunnett’s method for multiple comparisons; n = 5–7 mice per genotype and diet). All values are represented as mean ± SEM.