Investigating the role of the transducin-like enhancer of split proteins in maintenance of pancreatic beta cell phenotype

Abstract

The relative contribution of pancreatic beta cell dysfunction and cell death to the decline in insulin production in type 2 diabetes (T2D) is debated. Although, undoubtedly, some cell death is occurring, studies have shown, in times of high metabolic stress, beta cells undergo changes to less mature cells (dedifferentiation) or even gain characteristics of other endocrine cell types (transdifferentiation) to ‘hide away’ from the constant demand for insulin secretion. Our first aim was to assess the impact of glucotoxicity on beta cell phenotype and function. To achieve this, INS1E cells were cultured in high glucose and gene expression and functional assays were performed. A reduction in beta cell genes and insulin content were observed alongside upregulation of glucagon gene expression and protein levels, suggesting a transition to an alpha-cell phenotype. Next, we aimed to assess the role particular proteins play in this phenotypic shift. Tle3, a member of the Groucho family of co-repressors, has been implicated as a repressor of the alpha-cell fate and has a potential role in beta cell function through interaction with transcription factor Pdx1. To investigate this further, Tle3 knockdown was performed in vitro using INS1E cells and isolated rodent islets. Both cell types showed a loss of beta cell phenotype and function and gain of alpha-cell characteristics. Finally, we aimed to determine whether transdifferentiation is occurring in human T2D and what role TLE1, the human functional equivalent of Tle3, plays in this process. Immunohistochemistry techniques were used to analyse beta-, alpha- and bihormonal cells in relation to TLE1 expression in control and diabetic patients. Our findings demonstrated an overall loss of beta cells and TLE1 expression in diabetic donors alongside increases in both alpha- and bihormonal cells. Together, these studies provide evidence for transdifferentiation during T2D and show a potential role for Tle3/1 in the maintenance of the beta cell phenotype and function.