HSCI Retreat 2020 Abstract 5

ABSTRACT

Stem cell-derived organoids that recapitulate endogenous physiology could transform disease research and therapy, yet most methods yield products that function like fetal, not adult tissues. Organoids are typically grown in constant environments, whereas our tissues turn functionally mature in the presence of daily physiological rhythms. To better understand maturation-driving mechanisms, we studied epigenome dynamics during the stepwise formation of pancreatic islet organoids from human pluripotent stem cells (Fig.1A) (Alvarez-Dominguez et al., 2019, Cell Stem Cell, 26, 108–122 e110). We devised tools to purify intermediates across islet lineage progression, and profiled their DNA methylation, accessibility, and histone modification changes. Unexpectedly, we found BMAL1/CLOCK footprints enriched at genomic sites activated as organoids gain glucose-responsive insulin secretion. Moreover, we uncovered transcriptional loops between circadian effectors DEC1/2 and factors linked to mature insulin responses. This suggested circadian clocks may foster organoid maturation. Indeed, entrainment to 12h feeding-fasting cycles (Fig.1B) induces organoid clocks, eliciting pulsatile synthesis of energy metabolism and insulin secretion effectors, including antiphasic insulin-glucagon pulses. This triggers metabolic rhythms and cyclic insulin responses with higher glucose threshold and single-cell secretion (Fig.1B,C), a hallmark of islet maturity. Clock-entrained organoids gain stable epigenetic changes at genes enabling mature insulin responses, and function within days of transplant. Clock control of islet maturity effectors depends on Dec1 binding their promoters/enhancers, and Dec1 loss causes insulin responses with low secretion and glucose threshold. Accordingly, β cell-specific Dec1 deletion renders mice diabetic, despite intact islet mass, insulin content, and Bmal1/Clock function. This reveals a mechanism linking circadian rhythms to metabolic maturity, which can be harnessed to further maturation of stem cell-derived organoids.