RFX6haploinsufficiency predisposes to diabetes through impaired beta cell functionality

Abstract

Regulatory factor X 6 (RFX6) is indispensable for pancreatic endocrine development and differentiation. The RFX6 protein-truncating variant p.His293LeufsTer7 is significantly enriched in the Finnish population with almost 1:250 individuals as a carrier. Importantly, the FinnGen study indicates a high predisposition for heterozygous carriers to develop type 2 diabetes (T2D) and gestational diabetes. To understand the role of this variant in β-cell development and function, we generated allelic series of isogenic pluripotent stem cell models and directed them into pancreatic islet lineages (SC-islets). Expectedly,in-vitromodels of the homozygousRFX6−/−variant failed to generate pancreatic endocrine cells, recapitulating the phenotype in Mitchell-Riley syndrome. Notably, heterozygousRFX6+/−derived SC-islets showed reduced β-cell maturation markers and calcium oscillations, resulting in defective insulin secretion, without affecting β-cell number or insulin content. The reduced insulin secretion is sustained duringin-vivoimplantation studies, consistent with the susceptibility of the carriers to develop diabetes.TeaserModelingRFX6-assocciated neonatal and type-2 diabetes using allelic series stem cell-derived isletsin-vitroandin-vivo.

Deletion of RFX6, a Diabetes-Associated Gene, Impairs iPSC-Derived Islet Organoid Development and Survival, With No Impact on the Generation of PDX1+/NKX6.1+ Progenitors

“…Furthermore, we developed an isogenic KO platform using human iPSC-derived islets to investigate the molecular and cellular alterations at different stages of human islet cell development carrying loss-of-function mutations in RFX6. Our findings are consistent with previous studies, showing the following results: (i) the absence of INS-, GCG-, and SST-producing cells and an increase in PPY cell production due to RFX6 loss; (ii) significant downregulation of genes related to pancreatic endocrine differentiation, insulin secretion, and ion transport in association with RFX6 loss [4, 24, 25]. In addition, our study unveils novel insights into the role of RFX6 during pancreatic islet development.…”

“…Our findings revealed a significant decrease in PDX1 expression in RFX6 KO-PF compared to WT-PF, consistent with recent findings [25]. However, the absence of RFX6 did not impact the co-expression of PDX1 and NKX6.1 (PDX1 + /NKX6.1 + ) in PPs.…”

“…Conversely, the expression of TFs like PDX1, NKX6.1, SOX9, and FOXA2, specific to PPs [30] remained unaffected by the absence of RFX6 in the PPs, while endocrine TFs like PAX4, NEUROG3, and NKX2.2, were increased in the EPs due to RFX6 deficiency. These findings are consistent with recent results indicating that RFX6 loss does not affect SOX9 expression and increases the expression of NEUROG3, PAX4, and NKX2.2 [25]. During pancreatic development, it has been demonstrated that RFX6 operates downstream of proendocrine TF NEUROG3 [1], which directly controls the expression of PAX4 [31].…”

“…Recent studies have highlighted the pivotal role of RFX6 in the development and function of human pancreatic islets, linking it to the development of diabetes [24] [25] [17] [3]. Nonetheless, a comprehensive understanding of its specific function during human pancreatic islet development and its exact role in diabetes pathogenesis is still poorly understood.…”