Histone deacetylase 3-selective inhibitor RGFP966 ameliorates impaired glucose tolerance through β-cell protection

Highights

• RGFP966 ameliorated blood glucose level in low-dose of STZ-induced pre-diabetic mice.

• RGFP966 improved β cell function in low-dose of STZ-induced pre-diabetic mice.

• RGFP966 promoted insulin secretion in vivo and in vitro.

• RGFP966 partially attenuated apoptosis induced by PA via HDAC3/Erk1/2 /caspase 3 in vitro.

Abstract

The potential therapeutic effect of histone deacetylase 3 (HDAC3) pharmacologic inhibition on diabetes has been focused recently. RGFP966, as a highly-selective HDAC3 inhibitor, its possible roles and underlying mechanism in the treatment of diabetes needs to be clarified. In this study, low-dose streptozotocin (STZ)-induced pre-diabetic mice were used to test the regulatory ability of RGFP966 in blood glucose and insulin. We isolated the islets both from normal C57BL/6 J mice and KKA^y mice with spontaneous type 2 diabetes to determine the potency of RGFP966 on glucose-stimulated insulin secretion. NIT-1 pancreatic β-cells induced by sodium palmitate (PA) were applied to identify the protective effects of RGFP966 against β-cell apoptosis. The results showed that administration of RGFP966 in the pre-diabetic mice not only significantly reduced hyperglycemia, promoted phase I insulin secretion, improved morphology of islets, but also increased glucose infusion rate (GIR) during hyperglycemic clamp test. When treated in vitro, RGFP966 enhanced insulin secretion and synthesis in islets of normal C57BL/6J mice and diabetic KKA^y mice. In addition, it partially attenuated PA-induced apoptosis in NIT-1 cells. Therefore, our research suggests that RGFP966, probably through selective inhibition of HDAC3, might serve as a novel potential preventive and therapeutic candidate for diabetes.

Introduction

Diabetes, as a chronic disease that causes hyperglycemia, poses a great threat to human health. β cells in the islets of the pancreas are the only type of cells that downregulate blood glucose levels by secreting insulin hormone. β-cell dysfunction is the main cause of onset and/or development in both type 1 and type 2 diabetes. In the stage of pre-diabetes, also known as impaired glucose tolerance, β-cell dysfunction is also present (Prentki and Nolan, 2006). However, to date, most small molecule anti-diabetic drugs have little effect on restoring the function of β cells.

Histone deacetylase 3 (HDAC3) is a member of the class I HDACs, which also includes HDAC1, HDAC2, and HDAC8. Histone deacetylases regulate gene expression through deacetylation of histone proteins, which modulate chromatin structure (Haberland et al., 2009; Verdin and Ott, 2015). As a class I HDAC, HDAC3 is the predominant HDAC associated with nuclear receptor co-repressors, silencing mediator of retinoic acid and thyroid hormone receptor (SMRT or NCoR2), and nuclear receptor co-repressor 1 (NCoR1 or NCoR). It is also the only class I HDAC found in endogenous SMRT and NCoR complexes (Guenther et al., 2000; Li et al., 2000; Wen et al., 2000). In addition, its catalytic function requires a physical interaction with the deacetylase-activating domain, a conserved domain in SMRT and NCoR proteins (Watson et al., 2012; You et al., 2013). In recent years, multiple studies have shown that HDAC3 inhibitors not only serve as anti-cancer agents, but can also treat metabolic disorders (Emmett et al., 2017; West and Johnstone, 2014). One study showed that BRD3308, a specific HDAC3 inhibitor, improved glycemia and insulin secretion in obese diabetic rats (Lundh et al., 2015). Deletion of HDAC3 in adult β cells can promote glucose tolerance via increasing insulin secretion (Remsberg et al., 2017).

In the past several years, the HDAC3-specific inhibitor RGFP966 has been shown to have multiple effects. It causes decreased cell growth in cutaneous T cell lymphoma by disrupting the DNA replication of rapidly cycling tumor cells (Wells et al., 2013); enhances extinction of drug-seeking behavior by influencing gene expression within the infralimbic cortex, hippocampus, and nucleus accumbens (Malvaez et al., 2013); may have an effective role in developing therapeutics for inflammatory lung diseases because of its anti-inflammatory properties (Leus et al., 2016); can prevent retinal ganglion cell loss following optic nerve crush (Schmitt et al., 2018); and can also prevent diabetes-induced aortic pathologies by regulating relative gene expression in the liver (Zhang et al., 2018a).

However, it remains unknown if RGFP966 has similar roles in β-cell function as other HDAC3 inhibitors such as BRD3308. The results of this study showed that in β cells, the HDAC3 specific-inhibitor RGFP966 not only promotes insulin secretion, but also prevents apoptosis induced by sodium palmitate (PA). Besides, it protects β cells function in pre-diabetic stage.