Transforming growth factor-β and renal graft fibrosis:

Molecular and clinical response to angiotensin II receptor antagonist in kidney transplant patients with chronic allograft nephropathy

Chronic allograft nephropathy (CAN) represents an important cause of graft loss after kidney transplantation. TGF-beta1 is a key factor in fibrogenesis, and the angiotensin II receptor antagonist losartan may decrease the intra-graft synthesis of TGF-beta1. The aim of this study was to determine the clinical and molecular effect of losartan in kidney transplant patients (KTPs) with CAN. We studied nine KTPs, after the first year of transplantation, with proteinuria (more than 500 mg/24 h), stable renal function, and histological signs of CAN. Immunosuppression was cyclosporine, azathioprine, and corticoids. Kidney biopsy was performed in all patients at the beginning of the study and 12 weeks after treatment with 50 mg/day of losartan. Quantitation of intra-graft expression of TGF-beta1 was performed in all biopsies, by real-time PCR. After losartan treatment there were no differences in patients' BP and blood creatinine level. The proteinuria significantly dropped to 414.2+/-377 mg/24 h, P=0.001. Intra-graft expression of TGF-beta1 was decreased after treatment. In conclusion, losartan significantly decreases the intra-graft expression of TGF-beta1 and proteinuria in KTPs with CAN.

Urinary amino-terminal propeptide of type III procollagen (PIIINP) as a marker of interstitial fibrosis in renal transplant recipients

BACKGROUND

Interstitial fibrosis in the protocol biopsy specimens of transplanted kidneys is regarded as the most reliable predictor of future impaired renal function. Type I and III collagens are the main components of renal fibrosis. During the synthesis and deposition of type III collagen, an amino-terminal propeptide (PIIINP) of a molecular weight of 44 kDa is degraded from the collagen and secreted into surroundings. Increased circulating PIIINP has been shown to reflect ongoing fibrotic processes.

METHODS

The extent of interstitial fibrosis in 6-month protocol biopsy specimens was recorded, and the urinary excretion of PIIINP in 24-hr urine specimens was measured in 79 graft patients. We also measured the urinary excretion of transforming growth factor (TGF)-beta 1, alpha(1)-microglobulin (alpha(1)M), and albumin and recorded the changes in creatinine clearance during 0.5 to 6 (mean, 4.3) posttransplant follow-up years.

RESULTS

The urinary excretion of PIIINP was significantly lower in patients with no interstitial fibrosis compared with patients with mild or moderate interstitial fibrosis (P<0.01). The urinary PIIINP-to-creatinine ratio correlated closely with the extent of interstitial fibrosis (r=0.410, P<0.001), with TGF-beta 1-to-creatinine (r=0.585, P<0.001) and alpha(1)M-to-creatinine (r=0.438, P<0.001) but not with the albumin-to-creatinine ratio. There was a close correlation between urinary TGF-beta 1 and alpha(1)M (r=0.508, P<0.001), whereas no correlation was found between urinary and serum PIIINP or between urinary PIIINP-to-creatinine ratio and glomerular filtration rate (GFR). During the follow-up, the GFR decreased in 42% of patients with a PIIINP-to-creatinine ratio over 100 ng/mmol, but only in 8% of patients with a ratio less than 100 ng/mmol (P<0.01).

CONCLUSIONS

These findings show that the urinary PIIINP-to-creatinine ratio reflects the ongoing fibrotic processes in the kidney. Tubular epithelial cell injury may initiate the fibrotic processes, and elevated concentrations of urinary TGF-beta 1 and alpha(1)M may associate with the increased production and deposition of collagen type III in the graft. We conclude that measurements of urinary excretion of PIIINP can be used as an early noninvasive indicator of renal fibrosis after kidney transplantation.

Cytokine gene expression by alloactivated cells in SCID mice

OBJECTIVES

The severe combined immune deficient (SCID) mouse provides a neutral environment to study human immune responses. We therefore tested human gene expression of Interleukin (IL) 2, 4 and 10, interferon gamma (IFNgamma); transforming growth factor beta 1 (TGFbeta1); and CD40 ligand (CD40L) in splenic extracts of SCID mice after engraftment of PBLs from two persons (direct MLR) or one person plus allopeptides (indirect MLR) in the presence or absence of cyclosporin A (CsA) or FK506.

METHODS

Cytokine gene expression was detected by RT and quantitative (for IFN-gamma, TGFbeta1 and CD40L) PCR. All cells, allopeptides, CsA (25 mg/kg/day for 7 days) or FK 506 (0.5 mg/kg/day for 7 days) were administered intraperitoneally (IP).

RESULTS

In both direct and indirect MLR the numbers of SCID mice expressing the human cytokine genes varied between 33% for IL4 and 100% for IL10, IFN-gamma, TGFbeta1, and CD40L. There was significant interpersonal variation in levels of gene expression. Concomitant CsA or FK506 administration for 7 days did not abrogate early or late (1 week after discontinuation of CsA or FK506) cytokine gene expression in either the direct or indirect MLR, but paradoxically enhanced levels of IFN-gamma, TGFbeta1 and CD40L gene expression in some experiments.

CONCLUSIONS

The results explain late rejection after rapid calcineurin inhibitor withdrawal or reduction, and illustrate the potential use of SCID mice as a surrogate model to study graft outcome by determination levels of gene expression and sensitivity to immunosuppressive agents in the in vivo alloresponse.

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 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.