Identification of potential mediators of oxidative damage and targets for novel treatments for chronic kidney disease

Abstract

Chronic kidney disease (CKD) is a common and serious problem causing a significant burden to healthcare systems and, most importantly, the affected individual. Despite this, few successful treatments exist for CKD. Understanding the pathophysiological features that are common to chronic kidney pathologies is vital to identify targets for treatment. Oxidative stress has been implicated in all chronic diseases, acting via highly conserved pathways of disease progression.However, evidence to date shows limited benefit of antioxidants as therapies for CKD patients, suggesting a need to better identify the pathways that are stimulated.This thesis focuses on the role of oxidative stress, the regulation of mitochondrial homeostasis, the action of antioxidant compounds, and the disruption of oxidant signalling networks in chronic kidney pathologies (reviewed in Chapter 1). The aims of this project were to: (1) to use an in vitro model of oxidative stress-induced kidney injury to determine how a failure in balance between oxidative stress and oxidant control causes the cellular characteristics of CKD, then to determine whether exogenous antioxidants can prevent and restore renal cell bioenergetics and reduce cell injury; (2) to use an in vivo model of oxidative stress-induced kidney injury with molecular and metabolic imaging to measure potential biomarkers identified in Aim 1, in association with changes in kidney structure and function, and determine whether treatment with an antioxidant therapy modulates kidney disease pathology; and (3) to explore the links between biomarkers of oxidative stress and clinical characteristics of CKD in patients to determine whether a lifestyle intervention in conjunction with standard nephrology care improve systemic oxidative stress and whether this influences kidney function. The renal specific in vitro, in vivo, and clinical models and the methods used are explained in Chapter 2.Chapter 3 reports the separate and cumulative effects of oxidative stress, mitochondrial dysfunction and cell senescence in promoting loss of renal cells in an in vitro model of kidney disease. The results demonstrate that oxidative stress and cell senescence cause mitochondrial destabilization and kidney tubular epithelial cell loss. This may contribute to the development of cellular and tissue atrophy seen in CKD.Chapter 4 further defines the role of mitochondrial alterations as a consequence of a specificallyimpaired oxidant signalling regulatory mechanism, namely, peroxisome proliferator-activated receptor-gamma (PPARγ)-regulated mitochondrial biogenesis. Oxidative stress promoted mitochondrial destabilisation in kidney proximal tubular epithelial cells, in association with ii increased PPARγ Serine 112 phosphorylation. Despite their positive effects in other tissues, PPARγ agonists failed to protect proximal tubular epithelial (PTE) cells, and appear to be detrimental to kidney PTE cell health when oxidative stress induces the cell damage.Chapter 5 examined mediators of oxidative stress in an in...