Background: Studying patients with rare Mendelian diabetes has highlighted molecular mechanisms regulating β-cell pathophysiology. Previous, experimental studies have shown that Class IIa histone deacetylases (HDAC4, 5, 7, and 9) modulate mammalian pancreatic endocrine cell differentiation, function and finally glucose homeostasis.
Methods: We performed exome sequencing in one adolescent boy with non-autoimmune diabetes and his parents. He carried a heterozygous de novo HDAC4 variant (p.His227Arg) with predicted, deleterious protein function. We additionally sequenced a cohort of 94 individuals with paediatric-onset, non-immune diabetes, and lack of mutations in genes up-to-date associated with monogenic diabetes. In mouse pancreatic β-cell lines (Min6 and SJ cells), we performed insulin secretion assay and quantitive RT-PCR to measure the β-cell function transfected with the detected HDAC4 variants and wildtype. We carried out immunostaining, Western blot and immunoprecipitation to investigate rare HDAC4 variants from our cohort whether one key porcess, the cellular translocation and acetylation of Forkhead box protein O1 (FoxO1) in pancreatic β-cells specifically was influenced.
Results: We discovered three HDAC4 mutations (p.His227Arg, p.Asp234Asn, and p.Glu374Lys) in unrelated individuals that had non-autoimmune diabetes with various degrees of β-cell loss. In mouse pancreatic β-cell lines, we found that these three HDAC4 mutations decrease insulin secretion, down-regulate β-cell-specific transcriptional factors, all compared to wild-type HDAC4. Finally, overexpression of all pathogenic HDAC4 mutations cause nuclear exclusion of acetylated FoxO1 in β-cells.
Conclusion: Mutations in HDAC4 disrupt the deacetylation of FoxO1 and thus lead to its nuclear exclusion. Subsequently in-vitro β-cell function was decreased and cellular mechanisms identified in-vitro might cause diabetes in individuals carrying HDAC4 mutations.
19 Sep 2019 - 21 Sep 2019