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: Pancreatic beta cell mass expansion is a normal response to an increased demand for insulin, as occurs when mice are fed a HFD, total beta cell mass being modulated by cell proliferation and/or apoptosis (Ackermann & Gannon, 2007; Sachdeva & Stoffers, 2009). As we detected no difference in the number of apoptotic beta cells in Glis3+/+ and Glis3+/− islets (Fig 2I), we examined beta cell proliferation as reflected by proliferating cell nuclear antigen (PCNA) staining and found that HFD feeding led to a significant increase in the number of PCNA+ beta cells in the islets of Glis3+/+ mice but no change in Glis3+/− mice (Fig 2J). D-type cyclins, particularly cyclin D2 (Ccnd2) and D1, are essential for maintaining postnatal pancreatic beta cell mass (Georgia & Bhushan, 2004; Kushner et al, 2005). We therefore examined mRNA expression of D-type cyclins and other cell cycle-related genes in the isolated islets of these mice. qRT-PCR showed that the expression of Ccnd2, a predominant D-type cyclin in pancreatic beta cells (Georgia & Bhushan, 2004; Kushner et al, 2005) which was reported to be crucial for beta cell mass expansion (Georgia et al, 2010), was downregulated in the islets of Glis3+/− mice compared to Glis3+/+ mice fed the same diets (Fig 3A); the expression of cyclin-dependent kinase inhibitor 2a (Cdkn2a) was upregulated in the islets of Glis3+/− mice compared to Glis3+/+ mice fed regular chow; no difference in the expression of Ccnd1, Ccnd3, cyclin-dependent kinase 4 (Cdk4), Cdkn1a, Cdkn1b or Cdkn2c was detected (Fig 3A). We further confirmed by qRT-PCR that the mRNA expression of Ccnd2 was downregulated in the islets of beta cell-specific Glis3-deficient mice (Fig 3B) and in Glis3-knockdown 832/13 cells (Fig 3C), while it was upregulated in Glis3-overexpressing 832/13 cells (Fig 3D and E). To corroborate these findings at the mRNA level, we found that at the protein level CCND2 was lower in the islets of Glis3+/− mice fed either a chow or a HFD (Fig 3F) and in the islets of beta cell-specific Glis3-deficient mice (Fig 3G) as well as in Glis3-knockdown 832/13 cells (Fig 3H).
Affiliation: Division of Diabetes, Endocrinology and Metabolism, Department of Medicine, Diabetes and Endocrinology Research Center, Baylor College of Medicine, Houston, TX, USA.