Endogenous Relaxin Is a Naturally Occurring Modulator of Experimental Renal Tubulointerstitial Fibrosis

Abstract

Relaxin is a naturally occurring regulator of collagen turnover. In this study, we determined the role of endogenous relaxin in the pathogenesis of primary tubulointerstitial fibrosis after unilateral ureteric obstruction (UUO). Four- to 6-wk-old relaxin (RLX) gene-knockout (RLX(-/-)) and age-matched wild-type (RLX(+/+)) mice, with equivalent baseline collagen levels, were subjected to UUO. Obstructed and contralateral kidneys were collected at d 0, 3, and 10 after surgery and analyzed for changes in inflammatory and fibrosis-related markers. UUO was associated with a progressive increase in fibrosis in all obstructed, but not contralateral kidneys. The increase in total collagen (hydroxyproline analysis) was associated with more alpha-smooth muscle actin (alpha-SMA) staining (myofibroblasts) and interstitial collagen sub-types (SDS-PAGE; types I, III, and V), whereas gelatin zymography demonstrated increased expression of matrix metalloproteinase-2 after surgery. By d 10 after UUO, there was a 5-fold decrease in RLX mRNA expression (quantitative RT-PCR) in RLX(+/+) animals. Total collagen and alpha-SMA expression were significantly greater in the obstructed kidneys of RLX(-/-) mice 3 d after UUO (both P < 0.05 vs. RLX(+/+) D3 after UUO), but comparable to that in RLX(+/+) animals 10 d after UUO. Administration of recombinant H2 relaxin to RLX(-/-) mice 4 d before UUO ameliorated the increase in collagen and alpha-SMA expression (both P < 0.05 vs. untreated RLX(-/-) mice) by d 3 after UUO. Expression of monocyte chemoattractant protein-1 and macrophage infiltration (inflammation) in addition to that of matrix metalloproteinases was unaffected by genotype after UUO. These combined data demonstrate that endogenous RLX acts as a modulating factor in tubulointerstitial fibrosis, a hallmark of progressive renal disease. This is likely to be via direct effects on renal myofibroblast function.

Drugs of the future: the hormone relaxin

“…At 3 days post-UUO, total collagen and myofibroblast accumulation were significantly greater in Rln1À/À mice than their Rln1+/+ counterparts [49]. This increase in collagen and myofibroblast accumulation was reversed by the administration of H2 relaxin to Rln1À/À mice 3 days post-UUO, again confirming that relaxin played a specific role in regulating collagen in this model.…”

“…This increase in collagen and myofibroblast accumulation was reversed by the administration of H2 relaxin to Rln1À/À mice 3 days post-UUO, again confirming that relaxin played a specific role in regulating collagen in this model. Furthermore, no significant differences in inflammation or MMP expression were observed between genotypes, suggesting that the ability of relaxin to inhibit renal fibrosis was mediated through inhibition of renal myofibroblast activity in this model [49] By 10 days post-UUO, the rapid progression of disease resulted in Rln1+/+ mice having equivalent levels of collagen and myofibroblast accumulation to that measured in Rln1À/À mice, suggesting that endogenous relaxin only delays but does not prevent the progression of fibrosis in such a rapid model of scarring. Nevertheless, the results indicate that even the very low levels of relaxin found endogenously are sufficient to modulate fibrosis.…”

Relaxin inhibits renal myofibroblast differentiationviaRXFP1, the nitric oxide pathway, and Smad2

“…Our in vitro studies have also demonstrated that relaxin mediates its therapeutic effects in the kidney (10) and other organs (11), in part, by an ability to inhibit myofibroblast differentiation and the subsequent ability of these cells to produce collagen. More recently, we have also demonstrated that endogenous relaxin protects the injured kidney from the progression of tubulointerstitial renal fibrosis in vivo (12). This was paralleled by a reduction in myofibroblast accumulation and was independent of upstream effects on renal inflammation.…”

Human Umbilical Cord Mesenchymal Stem Cells Reduce Fibrosis of Bleomycin-Induced Lung Injury

“…25 Briefly, lungs were lyophilized, hydrolyzed in HCl, and the absorbance measured at 558 nm using a Varian series 634 digital spectrophotometer (Varian Australia Pty Ltd, Melbourne, Australia). Collagen content was calculated by multiplying the hydroxyproline measurements by 6.94 and then expressed as a proportion of the dry weight tissue to yield collagen concentration.…”