Investigations into the inhibitory effects of relaxin on renal myofibroblast differentiation.

Derived from fibroblasts, myofibroblasts are the principal cells that are responsible for the synthesis and reorganization of excess matrix in renal interstitial fibrosis. Recognized from their de novo expression of alpha-smooth muscle actin, myofibroblast differentiation and activity can be influenced by several factors, including a combination of growth factors and other soluble mediators, extracellular matrix components, and mechanical stress. Relaxin has previously been shown to inhibit renal myofibroblast differentiation in vitro, an effect partly mediated through its ability to interfere with the transforming growth factor-beta1 (TGF-beta1) pathway via inhibition of Smad2 phosphorylation and translocation. Furthermore, endogenous relaxin has been shown to protect the kidney from a myofibroblast-mediated model of injury in vivo. However, the pathways involved in the interaction between relaxin and TGF-beta1 remain unknown. In this report, the inhibitory actions of relaxin on TGF-beta1-induced renal myofibroblast differentiation are summarized to date, and the potential signaling pathways that are implicated in relaxin's inhibitory actions are discussed.

Relaxin inhibits renal myofibroblast differentiation via RXFP1, the nitric oxide pathway, and Smad2.

The hormone relaxin inhibits renal myofibroblast differentiation by interfering with TGF-beta1/Smad2 signaling. However, the pathways involved in the relaxin-TGF-beta1/Smad2 interaction remain unknown. This study investigated the signaling mechanisms by which human gene-2 (H2) relaxin regulates myofibroblast differentiation in vitro by examining its effects on mixed populations of fibroblasts and myofibroblasts propagated from injured rat kidneys. Cultures containing approximately 60-70% myofibroblasts were used to determine which relaxin receptors, G-proteins, and signaling pathways were involved in the H2 relaxin-mediated regulation of alpha-smooth muscle actin (alpha-SMA; a marker of myofibroblast differentiation). H2 relaxin only inhibited alpha-SMA immunostaining and collagen concentration in the presence of relaxin family peptide receptor 1 (RXFP1). H2 relaxin also induced a transient rise in cAMP in the presence of G(i/o) inhibition, and a sustained increase in extracellular signal-regulated kinase (ERK)-1/2 phosphorylation. Furthermore, inhibition of neuronal nitric oxide synthase (nNOS), NO, and cGMP significantly blocked the inhibitory effects of relaxin on alpha-SMA and Smad2 phosphorylation, while the NO inhibitor, L-nitroarginine methyl ester (hydrochloride) (L-NAME) significantly blocked the inhibitory actions of relaxin on collagen concentration in vivo. These findings suggest that relaxin signals through RXFP1, and a nNOS-NO-cGMP-dependent pathway to inhibit Smad2 phosphorylation and interfere with TGF-beta1-mediated renal myofibroblast differentiation and collagen production.

The effects of relaxin on extracellular matrix remodeling in health and fibrotic disease.

Since its discovery as a reproductive hormone 80 years ago, relaxin has been implicated in a number of pregnancy-related functions involving extracellular matrix (ECM) turnover and collagen degradation. It is now becoming evident that relaxin's ability to reduce matrix synthesis and increase ECM degradation has important implications in several nonreproductive organs, including the heart, lung, kidney, liver and skin. The identification of relaxin and RXFP1 (Relaxin family peptide receptor-1) mRNA and/or binding sites in cells or vessels of these nonreproductive tissues, has confirmed them as targets for relaxin binding and activity. Recent studies on Rln1 and Rxfp1 gene-knockout mice have established relaxin as an important naturally occurring and protective moderator of collagen turnover, leading to improved organ structure and function. Furthermore, through its ability to regulate the ECM and in particular, collagen at multiple levels, relaxin has emerged as a potent anti-fibrotic therapy, with rapid-occurring efficacy. It not only prevents fibrogenesis, but also reduces established scarring (fibrosis), which is a leading cause of organ failure and affects several tissues regardless of etiology. This chapter will summarize these coherent findings as a means of highlighting the significance and therapeutic potential of relaxin.

Nine novel COL4A3 and COL4A4 mutations and polymorphisms identified in inherited membrane diseases.

Both thin basement membrane nephropathy (TBMN) and autosomal recessive Alport syndrome result from mutations in the COL4A3 and COL4A4 genes, and this study documents further mutations and polymorphisms in these genes. Thirteen unrelated children with TBMN and five individuals with autosomal recessive Alport syndrome were examined for mutations in the 52 exons of COL4A3 and the 47 coding exons of COL4A4 using single-stranded conformation polymorphism (SSCP) analysis. Amplicons producing different electrophoretic patterns were sequenced, and mutations were defined as variants that changed an amino acid but were not present in 50 non-hematuric normals. Three further novel mutations were identified. These were IVS 22-5 T>A in the COL4A3 gene in a consanguineous family with autosomal recessive Alport syndrome, and R1677C and R1682Q in the COL4A4 gene. In addition, six novel polymorphisms (G455G, I462I, G736G and IVS 38-8 G>A in COL4A3, and L658L and A1577A in COL4A4) were demonstrated.Many different COL4A3 and COL4A4 mutations cause TBMN and autosomal recessive Alport syndrome. The identification of polymorphisms in these genes is particularly important to enable diagnostic laboratories to distinguish mutations from uncommon normal variants.

Endogenous relaxin is a naturally occurring modulator of experimental renal tubulointerstitial fibrosis.

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.

Endogenous relaxin regulates collagen deposition in an animal model of allergic airway disease.

We examined the relationship among relaxin (a peptide hormone that stimulates collagen degradation), airway fibrosis, other changes of airway remodeling, and airway hyperresponsiveness (AHR) in an animal model of allergic airway disease. Eight- to 10-wk-old relaxin gene-knockout (RLX(-/-)) and wild-type (RLX(+/+)) mice were sensitized with ovalbumin (OVA) or saline ip at d 0 and 14 and challenged three times per week for 6 wk with nebulized 2.5% OVA or saline. Saline-treated control RLX(+/+) and RLX(-/-) mice had equivalent collagen expression and baseline airway responses. OVA-treated RLX(-/-) mice developed airway inflammation equivalent to that in OVA-treated RLX(+/+) mice. However, OVA-treated RLX(-/-) mice had markedly increased lung collagen deposition as compared with OVA-treated RLX(+/+) and saline-treated mice (all P < 0.05). Collagen was predominantly deposited in the subepithelial basement membrane region and submucosal regions in both OVA-treated RLX(+/+) and RLX(-/-) mice. The increased collagen measured in OVA-treated RLX(-/-) mice was associated with reduced matrix metalloproteinase (MMP)-9 (P < 0.02) expression and failure to up-regulate matrix metalloproteinase-2 expression, compared with levels in OVA-treated RLX(+/+) mice. Goblet cell numbers were equivalent in OVA-treated RLX(-/-) and RLX(+/+) mice and increased, compared with saline-treated animals. Both OVA-treated RLX(+/+) and RLX(-/-) mice developed similar degrees of AHR after OVA treatment. These findings demonstrate a critical role for relaxin in the inhibition of lung collagen deposition during an allergic inflammatory response. Increased deposition of collagen per se did not influence airway epithelial structure or AHR.

Relaxin regulates collagen overproduction associated with experimental progressive renal fibrosis.

Progressive fibrosis due to excess extracellular matrix (primarily collagen) is the final common pathway in all forms of chronic renal disease, regardless of etiology, and leads to tissue dysfunction, when normal tissue is replaced by scar tissue. Emerging work from ourselves and others suggests that the naturally occurring hormone relaxin has the potential to limit renal collagen production and reorganization, while increasing its degradation. The outlined studies demonstrate relaxin's potential as an antifibrotic agent against experimental progressive renal disease.

Relaxin modulates fibroblast function, collagen production, and matrix metalloproteinase-2 expression by cardiac fibroblasts.

Cardiac fibrosis is a hallmark of heart disease and involves recruitment, proliferation, and differentiation of extracellular matrix-producing fibroblasts, leading to overproduction of collagen within the myocardium. In this study, the effects of relaxin in inhibiting these processes were investigated. We used neonatal rat atrial and ventricular fibroblasts, which respond to pro-fibrotic stimuli (i.e., transforming growth factor-beta and angiotensin II) and naturally express the relaxin receptor LGR7. Relaxin significantly inhibited TGF-beta- and angiotensin II-mediated fibroblast function and collagen production over a 72-h period, while increasing MMP-2 expression and activity in the presence of both profibrotic factors (all P < .05). These studies demonstrate that relaxin may have therapeutic potential in diseased states characterized by cardiac fibrosis.

Investigating the role of relaxin in the regulation of airway fibrosis in animal models of acute and chronic allergic airway disease.

Airway remodeling is a characteristic feature of asthma that leads to chronic irreversible airway obstruction. Fibrosis in the basement membrane region is a hallmark of remodeling in asthma that is not found in other diseases. In the outlined studies, we investigated the relationship between relaxin and airway fibrosis in asthma using acute and chronic models of allergic airway disease. These studies confirm a critical role for relaxin, in the regulation of collagen deposition in the airway/lung in animal models of allergic airway disease.

Relaxin modulates cardiac fibroblast proliferation, differentiation, and collagen production and reverses cardiac fibrosis in vivo.

Cardiac fibrosis is a key component of heart disease and involves the proliferation and differentiation of matrix-producing fibroblasts. The effects of an antifibrotic peptide hormone, relaxin, in inhibiting this process were investigated. We used rat atrial and ventricular fibroblasts, which respond to profibrotic stimuli and express the relaxin receptor (LGR7), in addition to two in vivo models of cardiac fibrosis. Cardiac fibroblasts, when plated at low density or stimulated with TGF-beta or angiotensin II (Ang II), accelerated fibroblast differentiation into myofibroblasts, as demonstrated by significantly increased alpha-smooth muscle actin expression, collagen synthesis, and collagen deposition (by up to 95% with TGF-beta and 40% with Ang II; all P < 0.05). Fibroblast proliferation was significantly increased by 10(-8) m and 10(-7) m Ang II (63-75%; P < 0.01) or 0.1-1 microg/ml IGF-I (27-40%; P < 0.05). Relaxin alone had no marked effect on these parameters, but it significantly inhibited Ang II- and IGF-I-mediated fibroblast proliferation (by 15-50%) and Ang II- and TGF-beta-mediated fibroblast differentiation, as detected by decreased expression of alpha-smooth muscle actin (by 65-88%) and collagen (by 60-80%). Relaxin also increased matrix metalloproteinase-2 expression in the presence of TGF-beta (P < 0.01) and Ang II (P < 0.05). Furthermore, relaxin decreased collagen overexpression when administered to two models of established fibrotic cardiomyopathy, one due to relaxin deficiency (by 40%; P < 0.05) and the other to cardiac-restricted overexpression of beta2-adrenergic receptors (by 58%; P < 0.01). These coherent findings indicate that relaxin regulates fibroblast proliferation, differentiation, and collagen deposition and may have therapeutic potential in diseased states characterized by cardiac fibrosis.