Expression and significance of the P2X7 purinoceptor in Diabetic Nephropathy

Diabetic kidney disease (diabetic nephropathy) is a serious and increasingly prevalent complication of diabetes; it is characterised by progressive scarring of the kidney glomeruli (the filtration units). Despite improvements in the treatment of diabetes, renal function in many patients continues to decline, eventually requiring dialysis or transplantation. Current treatments slow progression in a proportion of patients but do not prevent this, and there is a pressing need for new forms of treatment.
An ATP receptor known as the P2X7 receptor (P2X7R) that can be expressed on the surface of cells in the kidney has been linked to kidney injury, including in diabetes. The aim of this proposal is to investigate whether this receptor is involved in diabetic nephropathy. The studies outlined involve a combined approach using human kidney biopsy sections and urine samples, and a model of diabetes in mice that do not express P2X7R (if P2X7R is important in diabetes, lack of this receptor should reduce disease severity), as well as in vitro kidney cell cultures, to define the mechanisms whereby P2X7R may cause disease. Demonstrating a role for P2X7R in diabetic nephropathy could lead to development of a novel therapy for this intractable disease.

Diabetic nephropathy (DN) is a major cause of renal failure in developed and developing countries; its pathology involves altered glomerular cytokine expression, accumulation of extracellular matrix (ECM), and cell loss. The ATP-sensitive cell-surface receptor P2X7 (P2X7R) is expressed mainly, though not exclusively, in immune cells, and it can affect cytokine production and also cause cell death by apoptosis or necrosis.
Our previous studies have linked P2X7R to several forms of renal injury, including DN. A combined in vivo and in vitro approach will be used to investigate this further. Preliminary data show that glomerular expression of P2X7R occurs in a rat model of diabetes and in renal biopsies from diabetic patients.
The pattern of renal expression of P2X7R will be examined in a mouse model of DN induced by streptozotocin (STZ) compared with vehicle treated-controls, and in renal biopsies from patients with DN compared with non-diabetic controls. Co-localisation with cell-specific markers will identify the cell types expressing P2X7R and expression will be correlated with histological and biochemical markers of disease progression.
The effect of genetic ablation of P2X7R on the pathogenesis of DN will be examined in P2X7R knockout (KO) mice, and wild-type (WT) littermates, with STZ-induced diabetes.
P2X7R expression is not evident in normal renal tissue and expression is increased in biopsies from diabetic patients. Renal biopsy is invasive and it would be useful to have a non-invasive method of detection. To this end, P2X7R will be looked for in human urinary exosomes as a potential non-invasive biomarker of DN.
Since the early changes in DN occur in the glomerulus, and preliminary data suggest glomerular expression of P2X7R, in vitro studies will be confined to mesangial cells and podocytes. Cultured cells will be used to examine the effects of known diabetic stimuli on P2X7R expression. The functional role of P2X7R in cytokine and ECM production, and apoptosis, will be assessed using an ATP analogue (agonist) or antagonist.
These combined studies will establish whether P2X7R is involved in the pathogenesis of DN, and if it is a potential therapeutic target. The proposed studies will also provide research training in a wide range of in vivo and in vitro experimental techniques.