Author: Rakhvinder Kaur Kashmir Singh
Kashmir Singh, Rakhvinder Kaur, 2012 The Mechanism of glucose-induced RCAN1 expression in beta-cells, Flinders University, School of Medicine
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Regulator of calcineurin 1 (RCAN1) is a gene located on chromosome 21 that is highly expressed in the brain, heart, and also in numerous endocrine cells. RCAN1 is an endogenous inhibitor of the protein phosphatase calcineurin which is essential for β cell function and circulatory insulin levels. Changes in RCAN1 expression regulate exocytosis, mitochondrial function, apoptosis, proliferation and susceptibility to oxidative stress. Previous work with RCAN1 in β cells, showed that elevated expression of RCAN1 has a profound effect on β cell function resulting in altered gene expression, elevated ROS accumulation, reduced insulin secretion, hypoinsulinemia and fasting hyperglycemia. Furthermore, an increase in RCAN1 expression is also seen in chronic hyperglycemia in pancreatic islets. However, the mechanisms underlying this in β cells are unknown. As RCAN1 expression is induced by oxidative stress in neuronal cultures and oxidative stress can occur in β cells during periods of cell stress such as hypoxia, there could potentially be a role of RCAN1 in hypoxia. Hence, the aims of this study were firstly to investigate potential mechanisms underlying the glucose-induced expression of RCAN1 followed by the effects of hypoxia on the expression of RCAN1 in MIN6 β cells. Glucose induction of both the RCAN1 isoforms, RCAN1-1 and RCAN1-4, was dependent on the production of ROS and Ca2+ entry in the MIN6 β cells at the gene and protein level. This is because reversal of the glucose-induction of these RCAN1 isoforms was seen in the presence of antioxidants and Ca2+ channel blockers. However, the inhibition of calcineurin via the usage of FK506 and Cyclosporine A was seen to effect the expression of RCAN1-4 significantly at the gene and protein level but not that of RCAN1-1. These results suggest a common ROS and Ca2+-associated pathway for the control of both RCAN1 isoforms but a calcineurin-associated pathway regulating RCAN1-4 expression but not RCAN1-1. Hypoxia at various levels and durations had no effect on the expression of either of the RCAN1 isoforms. This study provides new insights into the mechanisms by which glucose induces the expression of RCAN1. Given that increased RCAN1 has negative effects on β cell function and induces diabetes, the findings further our understanding of the mechanisms linking chronic high glucose and β cell dysfunction.
Keywords: glucose,beta-cells,RCAN1,MIN6,Calcineurin,RCAN1-1,RCAN 1-4,calcium-induced,glucose responsive,RT-PCR,Western Blotting,hypoxia,calcineurin inhibitors
Subject: Medicine thesis
Thesis type: Masters
School: School of Medicine
Supervisor: Dr. Damien Keating