Intragraft messenger RNA expression of angiotensinogen: relationship with transforming growth factor beta-1 and chronic allograft nephropathy in kidney transplant patients

Abstract

Transforming growth factor (TGF)-beta1 is important in fibrogenesis and has been involved in the pathogenesis of chronic allograft nephropathy (CAN). The angiotensinogen (AGT) gene encodes the only glycoprotein known to be a precursor of the vasopressor angiotensin II. Angiotensin II is also a growth factor and a profibrogenic cytokine. It mediates the induction of TGF-beta1. We studied the relationship among the intragraft expression of AGT, TGF-beta1, and CAN in stable renal transplant patients (RTP). We used a competitive quantitative reverse transcriptase-polymerase chain reaction (RT-PCR)-ELISA assay to identify intragraft amounts of AGT expression in RTP and correlated it with TGF-beta1 mRNA expression. We studied and performed kidney biopsies on 12 RTP with long-functioning grafts and 6 RTP in the immediate posttransplantation period (7 days) who had acute tubular necrosis as control. Histology was based on Banff working classification criteria. Total RNA was isolated from biopsy specimens. For RT-PCR-ELISA, we created heterologous RNA competitors that coamplified with the same primers as AGT and TGF-beta1. Six of 12 long RTP had proteinuria >1000 mg/24 hr and 6 had proteinuria <1000 mg/24 hr. The differences between Banff grades (P =0.03), AGT, and TGF-beta1 levels by RT-PCR-ELISA were statistically significant between both groups (106.2+/-60.7 vs. 34.1+/-11.9 pg/microg total RNA [P =0.01] and 5954+/-5612 vs. 436+/-517 transcripts/microg total RNA [P =0.01], respectively). The control group showed AGT levels of 25+/-12.2 pg/microg total RNA and TGF-beta1 levels of 228+/-111 transcripts/microg total RNA, significant only for the higher proteinuria group (P=0.01 and P=0.04, respectively). There was a correlation between AGT and TGF-beta1 in both groups (r=0.96, P=0.001). We showed a relationship between mRNA expression of AGT and TGF-beta1 in kidney transplant patients with different grades of CAN and proteinuria.