Diabetes develops as a result of both genetic and environmental influences; however, low concordance rates of type 1 diabetes between monozygotic twins and increased penetrance of type 2 diabetes during aging suggests an, as yet, poorly understood epigenetic role in diabetes development and progression. The epigenetic code, of which lysine acetylation (Kac) is a major histone post-translational modification, regulates the structure and dynamics of chromatin leading to epigenetically-controlled changes in gene accessibility toward transcription factors. Histone acetylation is regulated by histone acetyltransferases and deacetylases which write and erase sites of histone acetylation, respectively. SIRT1 is a key protein deacetylase in the control of glucose homeostasis. Decreased SIRT1 can lead to impaired insulin signaling, therefore drugs that enhance either SIRT1 expression or enzymatic activity may treat insulin resistance. Bromodomains are epigenetic readers that interpret the complex pattern of histone acetylation by binding Kac residues on histones and other nuclear proteins. Of particular interest are the bromodomain and extraterminal domain (BET) family of bromodomain-containing proteins, which have recently emerged as a potential target to treat or prevent diabetes. Interestingly, we recently found that treatment of β-cells with BET bromodomain inhibitors leads to increased SIRT1 expression levels, although the underlying mechanism was unclear. Here, we use an insulinoma β-cell line (INS832/13) and primary rat islets to determine the mechanism through which BET proteins suppress SIRT1 expression. To modulate SIRT1 and BET protein levels and activity, we used a combination of small molecules that either inhibit or degrade BET proteins, in conjunction with CRISPR/Cas9 knockout β-cell lines of both SIRT1 and the individual BET proteins.
In summary, BET inhibitors may provide an indirect means to increase SIRT1 activity in β-cells and improve β-cell function in the context of diabetes.
R.A. Jones Lipinski: None. S. Wynia-Smith: None. J. Nord: None. B.C. Smith: None.
American Diabetes Association (1-18-IBS-068 to B.C.S.); National Institute of Diabetes and Digestive and Kidney Diseases (R01DK119359)