Cloning a novel form of rat PDGF A-chain with a unique 5'-UT: regulation during development and in glomerulonephritis

Contribution of androgens to chronic allograft nephropathy is mediated by dihydrotestosterone

BACKGROUND

Donor and recipient gender influence long-term allograft outcome after kidney transplantation. Sex hormones are likely to contribute to these gender-related differences. The present study investigated the role of androgens and their inhibition on the development of chronic allograft nephropathy.

METHODS

Male or female Fisher (F344) kidneys were orthotopically transplanted into intact male Lewis recipients. Animals were treated either with testosterone, the antiandrogen flutamide, the 5alpha-reductase inhibitor finasteride, or vehicle. Twenty weeks after transplantation animals were harvested for histology, immunohistology, and molecular analysis.

RESULTS

Testosterone treatment resulted in an increased proteinuria as well as profound glomerulosclerosis, tubulointerstitial fibrosis, and mononuclear cell infiltration that paralleled enhanced intragraft mRNA levels of transforming growth factor-beta (TGF-beta) and platelet-derived growth factor-A and -B chain (PDGF-A and -B). In contrast, flutamide and finasteride reduced glomerulosclerosis as well as the inflammatory cell infiltration associated with decreased TGF-beta, PDGF-A, and -B chain mRNA expression. No gender-related donor differences were noted between the groups.

CONCLUSIONS

Our data suggest that dihydrotestosterone mediates the adverse effects of androgens on chronic allograft nephropathy. The inhibition of androgens improves long-term allograft outcome after kidney transplantation.

Recipient age and weight affect chronic renal allograft rejection in rats

Nephron doses and immune responses change with age. Therefore, age is a potential risk factor for graft survival after kidney transplantation. The aim of this study was to determine whether age-related differences are of importance for long-term outcomes after renal transplantation. Kidneys from Fisher 344 rats were orthotopically transplanted into nephrectomized Lewis rats. Kidneys were transplanted using donors and recipients of three age levels, i.e., young (8 wk of age), adult (16 wk of age), and old (40 wk of age). Rats were killed 24 wk after transplantation, and functional, morphologic, and molecular evaluations were performed. Recipient age, rather than donor age, determined graft survival rates. No significant correlation was observed between donor kidney weight on the day of transplantation and morphologic results. Advanced recipient age was associated with reduced creatinine clearance, more severe histologic injuries, including extended glomerular sclerosis, interstitial fibrosis, and vascular lesions, more pronounced cellular infiltration, and greater expression of transforming growth factor-beta and platelet-derived growth factor A and B chains. Although no significant correlation between donor age or kidney weight on the day of transplantation and morphologic results was observed, there was a significant correlation between recipient body weight on the day of transplantation and allograft injury. It is concluded that recipient age and weight affect chronic renal rejection. Renal allografts may benefit from young recipient age but may deteriorate in old recipients, suggesting effects of recipient functional demand on long-term outcomes.

Effect of angiotensin-converting enzyme inhibition on growth factor mRNA in chronic renal allograft rejection in the rat

BACKGROUND

Despite considerable progress in immunosuppression, the incidence of chronic renal allograft rejection has not decreased. Recent studies have revealed that angiotensin-converting enzyme (ACE) inhibition ameliorates graft arteriosclerosis, glomerulosclerosis, and tubular atrophy. Moreover, it decreases systemic and glomerular capillary hydrostatic pressure in a rat kidney allograft model. We evaluated the effects of the ACE inhibitor enalapril on cytokine and growth factor expression in chronically rejecting rat kidney allografts.

METHODS

Kidneys of Fisher (F344) rats were orthotopically transplanted into Lewis (Lew) rats. To prevent acute rejection, cyclosporine A (1.5 mg/kg/day) was given to all recipients during the first 10 days after transplantation. Enalapril (60 mg/L) or vehicle was added to the drinking water 10 days after transplantation. Animals were harvested 20 weeks after transplantation for histologic and immunohistologic studies, as well as for evaluation of cytokine and growth factor mRNA by semiquantitative polymerase chain reaction.

RESULTS

Controls developed severe signs of chronic rejection, such as glomerular and vascular lesions, associated with a large number of infiltrating leukocytes. Enalapril-treated animals developed less proteinuria and other signs of chronic rejection. The mRNA levels of transforming growth factor-beta 1 (TGF-beta 1), platelet-derived growth factor A and B chain (PDGF A and B), insulin-like growth factor-I (IGF-I), interleukin-1 (IL-1), and monocyte chemoattractant protein-1 (MCP-1) were significantly reduced in the enalapril group and were most pronounced for IL-1 and PDGF A. In addition, we found an increased level of renal angiotensinogen mRNA after treatment with enalapril.

CONCLUSIONS

Treatment with enalapril attenuated the development of proteinuria, ameliorated morphological damage, decreased leukocyte infiltration, and prevented a rise in renal mRNA levels of growth factors and cytokines in kidney grafts in a rat model of chronic renal allograft rejection.

SDZ-RAD prevents manifestation of chronic rejection in rat renal allografts

BACKGROUND

Chronic rejection remains the most frequent cause of renal graft loss over the long term. However, effective treatment of this process is not yet available. SDZ-RAD (40-O-[2-hydroxyethyl]-rapamycin) is a new, orally active rapamycin derivative with potent immunosuppressive activity. We have examined the effects of SDZ-RAD in a well-established model of chronic renal allograft rejection in rats.

METHODS

Kidneys of Fisher (F334) rats were orthotopically transplanted into bilaterally nephrectomized Lewis recipients. To suppress an initial episode of acute rejection, rats were briefly treated with low doses of cyclosporine for the first 10 days. Thereafter they received either SDZ-RAD (0.5 mg/kg(day) or vehicle. At 24 weeks, functional evaluations were performed, kidneys were harvested, and histological, immunohistological, and reverse transcription-polymerase chain reaction evaluations were performed.

RESULTS

Animals treated with SDZ-RAD developed lower proteinuria and less glomerulosclerosis as compared with controls. Additionally SDZ-RAD reduced the infiltration of macrophages and lymphocytes and the expression of intercellular adhesion molecule-1, laminin, and fibronectin. Furthermore, we observed a reduced expression of growth factor mRNA (transforming growth factor-beta and platelet-derived growth factor-AA) in these animals.

CONCLUSION

Our results demonstrated that SDZ-RAD effectively ameliorates chronic renal allograft rejection in rats, probably mediated by suppression of growth factors.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.