Pancreatic islet cellular oscillators have been recently demonstrated to play a critical role in regulating glucose homeostasis in physiological conditions. However, little is known about changes of molecular clockwork upon islet dysfunction, and its role in beta (b)-cell regeneration. We aimed to assess diurnal regulation of b-cell proliferation and circadian transcriptome of alpha (a)- and b-cells following massive b-cell ablation in rtTA/TET-DTA mouse model. Diurnal proliferation of remnant b-cells was assessed by injecting bromodeoxyuridine (BrdU) before sacrificing in several time-points across 24 h. The role of functional islet oscillators in b-cell regeneration was studies in clock deficient mice. Our data suggest that both absolute levels and diurnal profiles of blood glucose, insulin and glucagon are altered following b-cell ablation. Temporal RNAseq analyses suggest massive changes in b-cell temporal transcriptome landscape, with modest alterations in a-cell transcriptional regulation. Complimentary differential RNAseq analysis of b-cells between intact islets and after ablation showed altered expression of genes involved in hormone secretory pathway, and activation of transcripts responsible for cell proliferation. In line with the circadian rhythmicity of cell-cycle related transcripts, the incorporation of BrdU by residual b-cells exhibited circadian rhythmicity. Moreover, we show that also in young pups, b-cell proliferation follows diurnal pattern. Importantly, the arrhythmic Bmal1 KO mice failed to regenerate b-cells after ablation.
To conclude, loss of b-cell mass in rtTA/TET-DTA mice affects gene transcription in residual b-cells, but not in a-cells, while the temporal transcriptome profile is perturbed in both cell types, paralleled with impaired daily secretion of insulin and glucagon. Noteworthy, the key component of molecular clock Bmal1 is required for proper regeneration and functional recovery after massive b-cell ablation.
V. Petrenko: None. M. Stolovich-Rain: None. B. Vandereycken: None. S. Chera: None. Y. Dor: None. C. Dibner: None.
Swiss National Science Foundation (31003A_166700/1, 310030_184708/1)