The role of regulator of Calcineurin 1 (RCAN1) in the adipose tissue and pancreatic β-cells

Author: Pauline Yap

Yap, Pauline, 2020 The role of regulator of Calcineurin 1 (RCAN1) in the adipose tissue and pancreatic β-cells, Flinders University, College of Medicine and Public Health

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Obesity, characterised by excess fat, is a huge risk factor for both insulin resistance and Type 2 diabetes (T2D). Current treatments are only partially effective. Regulator of Calcineurin 1 (RCAN1), a gene on chromosome 21, is highly expressed in the brain, heart and metabolic tissues such as the adipose tissue and pancreatic β-cells. RCAN1 is an endogenous inhibitor of the protein phosphatase, calcineurin, in the calcineurin-NFAT pathway. Recently, it was shown that RCAN1 was a candidate driver of β-cell dysfunction in T2D (Peiris et al., 2012, Peiris et al., 2016) and was increased with obesity. Rcan1-/- mice on a high fat diet (HFD) exhibited a lean phenotype and had increase browning of white adipose tissue (WAT) (Rotter et al., 2018). However, it is unknown if other mechanisms, apart from thermogenesis, are responsible for this phenotype. The recent discovery of a novel suite of drugs that inhibits RCAN1 could be a potential therapeutic for obesity and T2D. This is possible if the drugs are successful in decreasing lipid storage in adipocytes, increasing proliferation and decreasing apoptosis in pancreatic β-cells.

Therefore, the aims of this research include determining the minimum concentration of five inhibitors of RCAN1-calcineurin association (IRCA) drugs that were not lethal to cells and are effective in reducing fat storage in adipocytes, increase proliferation and decrease apoptosis in β-cells. Additionally, to extend our understanding of mechanisms in the adipose tissue that could drive the anti-obesity effects in Rcan1-/- mice, we aimed to investigate gene expression changes associated with lipolysis, adipogenesis and lipogenesis in the WAT of Rcan1-/- mice compared to wild-type. To investigate possible factors that might induce RCAN1 expression, several factors were investigated in adipocytes.

The results of this study showed an increase in fat storage in adipocytes, instead of a reduction, when the effective minimum concentration of IRCA drugs were determined. This was observed only in more diluted concentrations of the IRCA drugs used, suggesting possible off-target effects not specific to RCAN1-calcineruin interaction. The effective minimum concentration of IRCA drugs on β-cells were determined and their effects on proliferation and apoptosis-associated gene expression were tested. Whilst no expression changes were found, a significant increase in real-time proliferation was found when IRCA1 was used to treat β-cells compared to control. Furthermore, there were gene expression changes associated with lipolysis, lipogenesis and adipogenesis in WAT from Rcan1-/- mice and WT mice fed a low-fat diet (LFD) and a HFD. These novel pieces of data add to our understanding of the lack of HFD-induced obesity phenotype seen in our Rcan1-/- mice in a recent publication (Rotter et al., 2018). Moreover, the use of several factors significantly increased gene expression of RCAN1 isoforms, Rcan1.1 and Rcan1.4, in adipocytes. Overall, the findings of this research provide exciting and new insights into possible mechanisms involved in Rcan1-/- mice adipocyte function. We have also identified a potential new therapeutic that increases the proliferation in β-cells and we now have a broad overview of factors that could upregulate or downregulate RCAN1 gene expression in adipocytes.

Keywords: Type 2 Diabetes, Obesity, metabolism, Adipose tissue, Pancreas, β-cells, Adipocytes, RCAN1, IRCA drugs, Calcineurin-NFAT, Therapeutics

Subject: Medical Science thesis

Thesis type: Masters
Completed: 2020
School: College of Medicine and Public Health
Supervisor: Professor Damien Keating