Urine acidification has no effect on peroxisome proliferator-activated receptor (PPAR) signaling or epidermal growth factor (EGF) expression in rat urinary bladder urothelium

Abstract

We previously reported prevention of urolithiasis and associated rat urinary bladder tumors by urine acidification (via diet acidification) in male rats treated with the dual peroxisome proliferator-activated receptor (PPAR)α/γ agonist muraglitazar. Because urine acidification could potentially alter PPAR signaling and/or cellular proliferation in urothelium, we evaluated urothelial cell PPARα, PPARδ, PPARγ, and epidermal growth factor receptor (EGFR) expression, PPAR signaling, and urothelial cell proliferation in rats fed either a normal or an acidified diet for 5, 18, or 33 days. A subset of rats in the 18-day study also received 63 mg/kg of the PPARγ agonist pioglitazone daily for the final 3 days to directly assess the effects of diet acidification on responsiveness to PPARγ agonism. Urothelial cell PPARα and γ expression and signaling were evaluated in the 18- and 33-day studies by immunohistochemical assessment of PPAR protein (33-day study only) and quantitative real-time polymerase chain reaction (qRT-PCR) measurement of PPAR-regulated gene expression. In the 5-day study, EGFR expression and phosphorylation status were evaluated by immunohistochemical staining and egfr and akt2 mRNA levels were assessed by qRT-PCR. Diet acidification did not alter PPARα, δ, or γ mRNA or protein expression, PPARα- or γ-regulated gene expression, total or phosphorylated EGFR protein, egfr or akt2 gene expression, or proliferation in urothelium. Moreover, diet acidification had no effect on pioglitazone-induced changes in urothelial PPARγ-regulated gene expression. These results support the contention that urine acidification does not prevent PPARγ agonist-induced bladder tumors by altering PPARα, γ, or EGFR expression or PPAR signaling in rat bladder urothelium.