Modelling pancreatic facets of Johanson-Blizzard syndrome in a dish

Johanson-Blizzard syndrome (JBS) is a rare genetic disorder with autosomal recessive inheritance. The condition is characterized by congenital exocrine pancreatic insufficiency, aplasia of the nasal wings, and multiple other symptoms of varying severity. We could previously identify mutations in the UBR1 gene encoding one of several E3 ubiquitin ligases of the N-end rule pathway as the cause of the disease. As mouse models incompletely recapitulate the phenotype of the disease, we employ pluripotent stem cells (PSCs) to investigate pancreatic facets of JBS. We have implemented two independent but complimentary PSC models by editing human embryonic stem cells via CRISPR/Cas9 and by generating induced PSCs from two patients sharing a severe pancreatic phenotype. Stepwise pancreatic lineage differentiation of UBR1 mutant PSCs did not reveal an early developmental defect in agreement with a normal pancreatic anlage in JBS patients. Global quantitative proteomics, however, revealed a stage-specific upregulation of a set of proteins in UBR1 ablated cells. Specifically, a list of candidate proteins with described roles in cellular homeostasis were significantly upregulated. Upon repair of one allele of iPSCs from one patient the deregulation of such proteins could be successfully rescuedin vitro. Whether these proteins are direct UBR1 substrates and contribute to the JBS phenotype in the pancreas is part of our ongoing analysis. In summary, the thorough analysis of our established JBS cellular models focusing on viability and cellular homeostasis together with quantitative proteome analysis will provide us a comprehensive picture of JBS in the pancreas.

Publication History

Article published online:
19 August 2022