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Title: Mechanisms and models of insulin receptor substrate-2 signalling in the kidney
Author: Lavin, Deborah Philomena
ISNI:       0000 0004 6424 6288
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2017
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Diabetic nephropathy (DN) is one of three interrelated microvascular complications of diabetes. DN is characterised by renal fibrosis and the progressive decline in renal function partly due to the incessant loss of operational nephrons. Current treatments for DN such as controlling blood pressure and blood glucose levels, delay, but do not prevent patient progression to end stage renal disease (ESRD). Diabetes is a major risk factor for the development of acute kidney injury (AKI) which can be pre-renal, intrinsic/ intra-renal, or post-renal, and is characterised by a swift reduction in renal function. The molecular mechanisms that underpin these renal diseases remain to be elucidated. Insulin receptor substrate-2 (IRS2) is a cellular scaffolding protein which mediates signalling from the activated insulin receptor to downstream signalling molecules such as those involved in the PI3K/MAPK pathway. IRS2 is pressed in the tubular epithelium and collecting ducts of the kidney, and upregulated in DN patients where it correlates with poor renal function. The overarching aim of this thesis was to elucidate mechanisms and models of IRS2 signalling in the kidney, its regulation by hypoxia and high glucose among other mediators, and the role of IRS2 in AKI. We demonstrate that chemical-induced HIF stabilisation via DMOG and subsequent IRS2 accumulation occurs in a number of cell types in the kidney, namely epithelial cells, and podocytes. However, we also showed that this was not a global effect in all kidney cells. We confirmed these data by exposing cells to 1 % 02 and we also detected differential patterns of HIF-1a, HIF-2a, and IRS2 protein expression in hypoxia. siRNA targeting HIF-1a or HIF-2a showed that both HIF-1a and HIF-2a influence IRS2 accumulation as a result of chemical-induced or physiological HIF stabilisation. In vivo, DMOG did not stabilise HIF or cause IRS2 accumulation. We observed that combination of DMOG or hypoxia with ITS stimulation induced an upwards shift in IRS proteins and increased downstream insulin signalling, evidenced by increased Akt phosphorylation. We determined that DMOG- or hypoxia-induced IRS2 accumulation was not dependent on the proteasome. We observed TGFpi signalling via IRS2, and found that high glucose prevented IRS2 accumulation in hypoxia. We found that the morphology of the Irs2-/- kidney was similar to the wild-type kidney, yet we observed elevated p- catenin staining and increased Akt signalling in the Irs2-/- kidney. Increases in fibrosis associated genes were also detected in Irs2-/- kidneys. Lastly, we determined that in a folic-acid induced model of AKI, Irs2-/- mice presented with somewhat exacerbated renal fibrosis as evidenced by higher inflammatory F4/80 staining. These data provide preliminary evidence for IRS2 as a potential therapeutic target in DN, through modulation of HIF stabilisation. However, further work is required to develop strategies to successfully increase renal IRS2 expression in vivo and examine what effect this will have on insulin signalling in the kidney. The long-term impact of these approaches would be improving or increasing insulin signalling in the diabetic kidney as a means of preventing DN development or progression.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available