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

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 post-transplantation 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-beta 1 levels by RT-PCR-ELISA were statistically significant between both groups (106.2 +/- 60.7 vs. 34.1 +/- 11.9 pg/mu g total RNA [P=0.01] and 5954 +/- 5612 vs. 436 +/- 517 transcripts/mu g total RNA [P=0.01], respectively). The control group showed AGT levels of 25 mu 12.2 pg/mu g total RNA and TGF-beta 1 levels of 228 +/- 111 transcripts/mu g 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-beta 1 in both groups (r=0.96, P=0.001). We showed a relationship between mRNA expression of AGT and TGF-beta 1 in kidney transplant patients with different grades of CAN and proteinuria.