Insulin secretion deficits in a Prader-Willi syndrome β-cell model are associated with a concerted downregulation of multiple endoplasmic reticulum chaperones

Abstract

Prader-Willi syndrome (PWS) is a multisystem disorder caused by loss of expression of a cluster of paternally-expressed, imprinted genes. Neonatal failure to thrive is followed by childhood-onset hyperphagia, obesity, neurobehavioral abnormalities, and hormonal deficits. Prior evidence from a mouse model with a deletion of the orthologous PWS-gene domain identified abnormal pancreatic islet development with deficient insulin secretion, hypoglucagonemia, and postnatal onset of progressive, lethal hypoglycemia. To investigate the role of PWS-genes in β-cell secretory function, we used CRISPR/Cas9 genome-editing to generate isogenic, clonal INS-1 insulinoma lines with 3.16 Mb deletions of the silent, maternal (control) or active, paternal (PWS) alleles. PWS β-cells showed a significant reduction in basal and glucose-stimulated insulin secretion, signifying a deficiency in cell-autonomous insulin secretion. Parallel proteome and transcriptome studies revealed reduced levels of secreted peptides and twelve endoplasmic reticulum (ER) chaperones, including HSPA5 and HSP90B1. In contrast to the dosage compensation previously seen for ER chaperones in Hspa5 or Hsp90b1 gene knockouts, compensation is precluded by the widespread deficiency of ER chaperones in PWS β-cells. Consistent with the reduced ER chaperone levels, PWS INS-1 β-cells are more sensitive to ER stress, leading to earlier activation of all three arms of the unfolded protein response. These results suggest that a chronic deficit of ER chaperones in PWS β-cells leads to a delay in ER transit and/or folding of insulin and other cargo along the secretory pathway. The findings illuminate the pathophysiological basis of hormone deficits in PWS and implicate PWS-imprinted genes in β-cell secretory pathway function.