A window in time for β-cell regeneration

In vivo regeneration of β cells provides hope for self-renewal of functional insulin-secreting cells following β-cell failure, a historically fatal condition now sustainable only by administration of exogenous insulin. Despite advances in the treatment of diabetes mellitus, the path toward endogenous renewal of β-cell populations has remained elusive. Intensive efforts have focused on elucidating pancreatic transcriptional programs that can drive the division and (trans-)differentiation of non-β cells to produce insulin. A surprise has been the identification of an essential role of the molecular circadian clock in the regulation of competent insulin-producing β cells. In this issue of Genes & Development, work by Petrenko and colleagues (pp. 1650-1665) now shows a requirement for the intrinsic clock in the regenerative capacity of insulin-producing cells following genetic ablation of β cells. These studies raise the possibility that enhancing core clock activity may provide an adjuvant in cell replacement therapies.

The core clock transcription factor BMAL1 drives circadian β-cell proliferation during compensatory regeneration of the endocrine pancreas

Circadian clocks in pancreatic islets participate in the regulation of glucose homeostasis. Here we examined the role of these timekeepers in β-cell regeneration after the massive ablation of β cells by doxycycline-induced expression of diphtheria toxin A (DTA) in Insulin-rtTA/TET-DTA mice. Since we crossed reporter genes expressing α- and β-cell-specific fluorescent proteins into these mice, we could follow the fate of α- and β cells separately. As expected, DTA induction resulted in an acute hyperglycemia, which was accompanied by dramatic changes in gene expression in residual β cells. In contrast, only temporal alterations of gene expression were observed in α cells. Interestingly, β cells entered S phase preferentially during the nocturnal activity phase, indicating that the diurnal rhythm also plays a role in the orchestration of β-cell regeneration. Indeed, in arrhythmic Bmal1-deficient mice, which lack circadian clocks, no compensatory β-cell proliferation was observed, and the β-cell ablation led to aggravated hyperglycemia, hyperglucagonemia, and fatal diabetes.