Our lab has been focusing for many years on the intrinsic stress experienced by pancreatic islet β-cells, which (even in healthy states) live under a strict metabolic mandate to continuously produce and secrete insulin at intensely high rates that predispose these professional secretory cells to secretory exhaustion. β-cells evolved a high-capacity endoplasmic reticulum (ER) organelle in which the insulin precursor, proinsulin, undergoes initial oxidative protein folding and structural maturation. However, whenever secretory demand outpaces folding capacity, unfolded proteins begin to accumulate in the ER—a condition called “ER stress”.
ER stress activates an intracellular signaling pathway called the unfolded protein response (UPR) that augments ER chaperones and protein-modifying activities by triggering adaptive (‘A’)-UPR transcriptional and translational programs. But if ER stress remains unresolved, the adaptive UPR outputs wane and are replaced by “terminal” (‘T’)-UPR programs that actively promote loss of differentiated cell identity, cause sterile inflammation and senescence, and ultimately trigger apoptosis. Mounting evidence shows that high ER stress/and consequent A>T-UPR conversion causes β-cell apoptosis, leading to diabetes in mouse models of T1D. However, it remains unclear whether human islets also demonstrate an A- to T-UPR switch during progression to T1D.