Endoplasmic Reticulum Stress in the Pathogenesis of Hyperglycemia Induced by Thiamine-Responsive Megaloblastic Anemia

Thiamine responsive megaloblastic anemia (TRMA) is a genetic disease caused by SLC19A2 gene mutation. This study aimed to preliminarily explore the relationship between endoplasmic reticulum stress (ERS)-PERK signaling pathway and the pathogenesis of hyperglycemia induced by TRMA.

Islet β (INS.1 and β-TC-6) and HEK293T cell line models with stable overexpression of SLC19A2 and SLC19A2 (c.1409insT) were established. The cells were divided into empty virus group (control), wild-type group (overexpressed SLC19A2), and mutation group (overexpressed SLC19A2 (c.1409insT)). Quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and western blotting were used to detect the expression levels of ERS-PERK signaling pathway-related proteins, including glucose-regulated protein 78 (GRP78), protein kinase R-like ER kinase (PERK), and eukaryotic initiation factor 2 (eIF2α), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) in islet β cells. Protein localization was assessed by immunofluorescence staining.

Compared with the control group, the mRNA expression levels of SLC19A2 in wild-type and mutant islet β cells (INS.1 and β-TC-6) and HEK293T cells were significantly upregulated (all p < 0.05). Compared with the control group and the wild-type group, the mRNA expression levels of GRP78, PERK, eIF2α, ATF4, and CHOP were increased (all p < 0.05) in the mutant islet β cells; the protein expression levels of PERK, GRP78, and eIF2α were elevated (all p < 0.05). In addition, the results of immunofluorescence staining showed that SLC19A2 (c.1409insT) mutation changed the localization of the proteins in the cells. Thus, they were not located on the cell surface, but in the cytoplasm and nuclei, and protein aggregation occurred in the cytoplasm.

1. Islet β and HEK293Tcell lines, stably overexpressing SLC19A2 and SLC19A2 (c.1409insT) mutations, were successfully constructed. 2. SLC19A2 (c.1409insT) mutation could raise the expression levels of ERS-PERK signaling pathway-related proteins (GRP78, PERK, eIF2α, ATF4, and CHOP), and activate apoptosis pathway. 3. SLC19A2 (c.1409insT) mutation could change the localization of proteins and produce protein aggregation in cells. It could lead to protein misfolding and ERS, which would participate in the pathological mechanism of hyperglycemia induced by TRMA.