Atf4 protects islet ß-cell identity and function under acute glucose-induced stress but promotes ß-cell failure in the presence of free fatty acid.

Glucolipotoxicity, caused by combined hyperglycemia and hyperlipidemia, results in ß-cell failure and type 2 diabetes (T2D) via cellular stress-related mechanisms. Activating transcription factor 4 (Atf4) is an essential effector of stress response. We show here that Atf4 expression in ß-cells is dispensable for glucose homeostasis in young mice, but it is required for ß-cell function during aging and under obesity-related metabolic stress. Henceforth, aged Atf4- deficient ß-cells display compromised secretory function under acute hyperglycemia. In contrast, they are resistant to acute free fatty acid-induced loss-of identity and dysfunction. At molecular level, Atf4 -deficient ß-cells down-regulate genes involved in protein translation, reducing ß-cell identity gene products under high glucose. They also upregulate several genes involved in lipid metabolism or signaling, likely contributing to their resistance to free fatty acid-induced dysfunction. These results suggest that Atf4 activation is required for ß-cell identity and function under high glucose, but this paradoxically induces ß-cell failure in the presence of high levels of free fatty acids. Different branches of Atf4 activity could be manipulated for protecting ß-cells from metabolic stress-induced failure. Highlights: Atf4 is dispensable in ß-cells in young miceAtf4 protects ß-cells under high glucoseAtf4 exacerbate fatty acid-induced ß-cell defectsAtf4 activates translation but depresses lipid-metabolism.

Endocrine islet ß-cell subtypes with differential function are derived from biochemically distinct embryonic endocrine islet progenitors that are regulated by maternal nutrients.

Endocrine islet b cells comprise heterogenous cell subsets. Yet when/how these subsets are produced and how stable they are remain unknown. Addressing these questions is important for preventing/curing diabetes, because lower numbers of b cells with better secretory function is a high risk of this disease. Using combinatorial cell lineage tracing, scRNA-seq, and DNA methylation analysis, we show here that embryonic islet progenitors with distinct gene expression and DNA methylation produce b-cell subtypes of different function and viability in adult mice. The subtype with better function is enriched for genes involved in vesicular production/trafficking, stress response, and Ca2+-secretion coupling, which further correspond to differential DNA methylation in putative enhancers of these genes. Maternal overnutrition, a major diabetes risk factor, reduces the proportion of endocrine progenitors of the b-cell subtype with better-function via deregulating DNA methyl transferase 3a. Intriguingly, the gene signature that defines mouse b-cell subtypes can reliably divide human cells into two sub-populations while the proportion of b cells with better-function is reduced in diabetic donors. The implication of these results is that modulating DNA methylation in islet progenitors using maternal food supplements can be explored to improve b-cell function in the prevention and therapy of diabetes.