Role of the P2X7 receptor in the renal vasculature in a mouse model of chronic kidney disease

Abstract

Chronic kidney disease (CKD) is a global disease affecting 10% of the world population and is largely treated by dialysis and organ transplant at late stages of disease. As rates of CKD rise, it is increasingly evident that novel drug targets are required for intervention before these late stages are reached. The purinergic receptor sub-type 7 (P2X7) may represent such a drug target. P2X7, an ATP-gated ion channel, is part of the purinergic signalling pathway and antagonists are safe and well-tolerated in clinical trials as a treatment for inflammatory disease. These trials did not show therapeutic benefit, but recent findings suggest that vascular, rather than immune, functions of P2X7 may be important for renal disease. This project aimed to investigate the expression and role of P2X7 in the renal vasculature in both normal and hypertensive mice. A mouse model of multi-hit renal vascular injury was established and characterised through the administration of angiotensin II (ANGII), deoxycorticosterone (DOCA) and a high salt diet (ANGII DOCA salt model). ANGII DOCA salt mice exhibited mild hypertension, moderate albuminuria, vascular dysfunction, perivascular fibrosis, and a marked increase in renal injury markers in both whole kidney and urine, compared to sham-operated (Sham) littermates. A systematic immunofluorescence study localised P2X7 to the endothelium of renal vessels and glomerular capillaries in both Sham and ANGII DOCA salt mice, as well as localising to areas of injury in ANGII DOCA salt mouse kidneys. The P2X7 antagonist A438079 was able to inhibit ATP-stimulated release of IL-1B in LPS-primed mouse macrophages and was therefore used to assess vascular function in isolated aorta by wire myography. These studies found that activation of P2X7 via agonist BzATP led to vasoconstriction in both mouse groups, an effect that was amplified upon P2X7 inhibitions. Following these findings, it is possible that this is due to a shift in the expression of different P2X7 isoforms with potentially opposing vasoactivity in ANGII DOCA salt mice, compared to Sham mice. This is supported by the observation of differential expression of P2X7 according to the tissue used, the method of detection used, and the disease model investigated. This thesis highlights the importance of considering splice variation under normo- and pathophysiological conditions, both their expressional and functional differences.