Sustained expression of the transcription factor GLIS3 is required for normal beta cell function in adults.
Bottom Line: Genome-wide association studies identified GLIS3 as a susceptibility locus for type 1 and type 2 diabetes.GLIS3 controls beta cell proliferation in response to high-fat feeding at least partly by regulating Ccnd2 transcription.We conclude that normal Glis3 expression is required for pancreatic beta cell function and mass maintenance during adulthood, which impairment leads to diabetes in adults.
Affiliation: Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Diabetes and Endocrinology Research Center, Baylor College of Medicine, Houston, TX, USA.Show MeSH
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Mentions: As the glycaemic control in the insulin implanted TAM-treated Glis3fl/fl/Pdx1CreERT+ mice was less than perfect, it was not possible to rule out glucotoxicity-related insulin reduction and beta cell apoptosis in these mice. To further explore the role of Glis3 in the adult pancreas, we collected pancreata from TAM-treated Glis3fl/fl/Pdx1CreERT+ mice 10 days after TAM administration. Given that GLIS3 antibodies for are not available for immunocytochemical staining, we have determined the efficiency of Glis3 deletion in isolated islets by q-RT-PCR, which showed that Glis3 mRNA was reduced over 90% in the islets 10 days after TAM administration (Fig 7A). It should be noted that qRT-PCR underestimates Pdx1-Cre mediated Glis3 silencing in beta cells because Glis3 mRNA is also present in the non-beta islet cells (Senee et al, 2006). We further confirmed the efficiency of Glis3 deletion in the pancreatic islets by in situ hybridization 10 days after TAM or vehicle administration (Supporting Information Fig S5). At this early time point, the mice still displayed euglycaemia (Fig 7B) and a tendency towards glucose intolerance (Supporting Information Fig S6), in the presence of normal plasma insulin (Fig 7C). We observed that the mRNA expression of Pdx1, a mature beta cell marker (Jonsson et al, 1994; Offield et al, 1996; Ohlsson et al, 1993), was unchanged in the islets isolated from the two groups (Fig 7A). Importantly, the level of insulin mRNA (Fig 7A) and immunoreactive insulin (Fig 7D) was significantly decreased at this early stage of TAM treatment as compared with vehicle treatment in Glis3fl/fl/Pdx1CreERT+ mice. However, the number of apoptotic islet cells reflected by TUNEL assay was not different between the two groups (Fig 7E). To corroborate the absence of a difference in the very low percentage of TUNEL+ cells in the pancreatic islets of TAM and vehicle-treated Glis3fl/fl/Pdx1CreERT+ mice, we next performed TUNEL assay in Glis3-knockdown INS-1 derived 832/13 cells and again observed no difference in TUNEL-positive cells between control siRNA and Glis3 siRNA transfected cells (Fig 7F). Therefore, impairment in insulin expression at the mRNA and protein levels occurs early in TAM-treated Glis3fl/fl/Pdx1CreERT+ mice, an effect that precedes the onset of hyperglycaemia and the apoptosis that the latter induced.
Affiliation: Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Diabetes and Endocrinology Research Center, Baylor College of Medicine, Houston, TX, USA.