4-phenylbutyric acid attenuates diabetes mellitus secondary to thiamine-responsive megaloblastic anaemia syndrome by modulating endoplasmic reticulum stress.

Introduction: Thiamine-responsive megaloblastic anaemia syndrome (TRMA) is a rare genetic disease caused by mutations in the SLC19A2 gene that encodes thiamine transporter 1 (THTR-1). The common manifestations are diabetes, anaemia, and deafness. The pathogenic mechanism has not yet been clarified.

Material and methods: Rat pancreatic islet tumour cells INS.1 were used to construct cell lines stably overexpressing wild-type SLC19A2 and SLC19A2 (c.1409insT) mutants. The mRNA and protein expressions of THTR-1 and endoplasmic reticulum stress (ERS)-associated factors were detected by real-time fluorescence quantitative polymerase chain reaction (PCR) and western blot methods, respectively. Flow cytometry and cell counting kit-8 were used to analyse the effects of SLC19A2 (c.1409insT) mutation on cell apoptosis and proliferation, respectively. 4-Phenylbutyric acid (4-PBA), an ERS inhibitor, was administered to SLC19A2 (c.1409insT)-mutated INS.1 cells, and then the mRNA and protein expressions of ERS-related factors in cells were detected.

Results: Mutations in the SLC19A2 (c.1409insT) promote apoptosis and inhibit cell proliferation, thereby upregulating the mRNA and protein levels of ERS-associated factors glucose-regulated protein 78, protein kinase R-like endoplasmic reticulum kinase, C/EBP homologous protein, and activating transcription factor 4. 4-PBA could inhibit ERS caused by SLC19A2 (c.1409insT) mutations, downregulate mRNA and protein expression levels of GRP78, CHOP, and phosphorylated eukaryotic initiation factor 2α, and protect pancreatic islet β-cells.

Conclusion: THTR-1 deficiency triggers diabetes in TRMA patients through ERS, and 4-PBA protects pancreatic islet β-cells by inhibiting ERS, which provides new ideas and intervention targets for the prevention and treatment of TRMA and diabetes.