Altered ATP-Sensitive P2 Receptor Subtype Expression in the Han:SPRD cy/+ Rat, a Model of Autosomal Dominant Polycystic Kidney Disease

The effects of extracellular ATP on fluid secretion and reabsorption by renal epithelial cells, as well as its known effects on cell proliferation and death, are potentially important contributory factors in the development and growth of renal cysts. In this study, we have investigated the protein and mRNA expression of several P2Y receptor subtypes (P2Y_1,2,4,6), as well as the P2X₅ and P2X₇ receptors, in kidney tissue from the Han:SPRD (cy/+) rat model of polycystic kidney disease. All of the P2Y receptors tested for, and the P2X₅ and P2X₇ subtypes, were located on the cyst-lining cells of Han:SPRD (cy/+) rat polycystic kidneys; most immunostaining was cytosolic and we could not confidently localize it to one or other membrane. However, the staining pattern for P2Y₆ was uniquely granular when compared with the other P2 receptors. P2Y₂ and P2Y₆ receptor mRNA was increased in both homozygote (cy/cy) and heterozygote (cy/+) rat kidneys when compared with unaffected littermates. The protein levels of P2Y₂ and P2Y₆ receptors were also increased, being undetectable or at a low level, respectively, in control tissue. Finally, P2X₇ receptor mRNA was increased in cy/+, but not in cy/cy rat kidneys. Our results show that a number of P2Y receptor subtypes, as well as the P2X₅ and P2X₇ receptors, are clearly expressed in cyst-lining cells in the Han:SPRD (cy/+) rat model of renal cystic disease. Furthermore, P2Y₂ and P2Y₆ receptor mRNA and protein levels are markedly increased in cystic rat kidneys compared with normal rats of the same genetic background. Thus, the most consistent findings were an increase in the expression of P2Y₂, P2Y₆ and P2X₇ receptors in cystic tissue. Given the widely reported effects of stimulating these P2 receptor subtypes in epithelial and other renal cells, they could contribute to the development and growth of renal cysts: extracellular ATP and its products ‘trapped’ in cyst fluid may activate P2 receptors expressed by cyst-lining cells, causing cyst expansion from increased fluid secretion and/or reduced reabsorption, as well as an increase in cell turnover (re-modeling).