Relaxin and the progression of kidney disease

Fine Tuning Mesenchymal Stromal Cells - Code For Mitigating Kidney Diseases

Kidney Disease (KD), has a high global prevalence and accounts for one of the most prominent causes of morbidity and mortality in the twenty-first century. Despite the advances in our understanding of its pathophysiology, the only available therapy options are dialysis and kidney transplantation. Mesenchymal stem cells (MSCs) have proven to be a viable choice for KD therapy due to their antiapoptotic, immunomodulatory, antioxidative, and pro-angiogenic activities. However, the low engraftment, low survival rate, diminished paracrine ability, and delayed delivery of MSCs are the major causes of the low clinical efficacy. A number of preconditioning regimens are being tested to increase the therapeutic capabilities of MSCs. In this review, we highlight the various strategies to prime MSCs and their protective effects in kidney diseases.

Beyond Prostate Cancer: An Androgen Receptor Splice Variant Expression in Multiple Malignancies, Non-Cancer Pathologies, and Development

Multiple studies have demonstrated the importance of androgen receptor (AR) splice variants (SVs) in the progression of prostate cancer to the castration-resistant phenotype and their utility as a diagnostic. However, studies on AR expression in non-prostatic malignancies uncovered that AR-SVs are expressed in glioblastoma, breast, salivary, bladder, kidney, and liver cancers, where they have diverse roles in tumorigenesis. AR-SVs also have roles in non-cancer pathologies. In granulosa cells from women with polycystic ovarian syndrome, unique AR-SVs lead to an increase in androgen production. In patients with nonobstructive azoospermia, testicular Sertoli cells exhibit differential expression of AR-SVs, which is associated with impaired spermatogenesis. Moreover, AR-SVs have been identified in normal cells, including blood mononuclear cells, neuronal lipid rafts, and the placenta. The detection and characterization of AR-SVs in mammalian and non-mammalian species argue that AR-SV expression is evolutionarily conserved and that AR-SV-dependent signaling is a fundamental regulatory feature in multiple cellular contexts. These discoveries argue that alternative splicing of the AR transcript is a commonly used mechanism that leads to an expansion in the repertoire of signaling molecules needed in certain tissues. Various malignancies appropriate this mechanism of alternative AR splicing to acquire a proliferative and survival advantage.

Enhancing the Therapeutic Potential of Mesenchymal Stromal Cell-Based Therapies with an Anti-Fibrotic Agent for the Treatment of Chronic Kidney Disease

Chronic kidney disease (CKD) affects 1 in 10 members of the general population, placing these patients at an increasingly high risk of kidney failure. Despite the significant burden of CKD on various healthcare systems, there are no effective cures that reverse or even halt its progression. In recent years, human bone-marrow-derived mesenchymal stromal cells (BM-MSCs) have been recognised as a novel therapy for CKDs, owing to their well-established immunomodulatory and tissue-reparative properties in preclinical settings, and their promising safety profile that has been demonstrated in patients with CKDs from several clinical trials. However, renal fibrosis (scarring), a hallmark of CKD, has been shown to impair the viability and functionality of BM-MSCs post-transplantation. This has suggested that BM-MSCs might require a pre-treatment or adjunct therapy that can enhance the viability and therapeutic efficacy of these stromal cells in chronic disease settings. To address this, recent studies that have combined BM-MSCs with the anti-fibrotic drug serelaxin (RLX), have demonstrated the enhanced therapeutic potential of this combination therapy in normotensive and hypertensive preclinical models of CKD. In this review, a critical appraisal of the preclinical data available on the anti-fibrotic and renoprotective actions of BM-MSCs or RLX alone and when combined, as a treatment option for normotensive vs. hypertensive CKD, is discussed.

Relaxin inhibits renal fibrosis and the epithelial-to-mesenchymal transition via the Wnt/β-catenin signaling pathway

Renal fibrosis is a common characteristic and the final pathological mechanism of chronic kidney disease (CKD). Although CKD remains incurable, inhibition of renal fibrosis is beneficial to inhibit the CKD process. Relaxin alleviates renal fibrosis in some experimental models, but its mechanism remains unclear. In the following, we studied the regulatory effect of relaxin on epithelial-mesenchymal transition (EMT) after unilateral ureteral obstruction (UUO). Our results demonstrate that relaxin could downregulate Wnt/β-catenin signaling and decrease EMT, thus protecting against loss of transporters in tubular epithelial cells (TECs) and abrogate renal interstitial fibrosis following UUO. We confirmed that relaxin can downregulate Wnt/β-catenin signaling and decrease EMT in NRK52E, thus abrogating G2 cell cycle arrest in vitro experiments. Therefore, a novel mechanism by which relaxin is antifibrotic is that relaxin regulates the EMT program of TECs via Wnt/β-catenin signaling pathway. The inhibition of EMT contributes to protecting the functional capabilities of TECs and promoting the regeneration of TECs.

Differential Expression of the Androgen Receptor, Splice Variants and Relaxin 2 in Renal Cancer

Background: The role of the androgen receptor (AR) in renal cell carcinoma (RCC) is unclear. We aimed to analyze the expression of AR and its splice variants (SVs) and their correlation with relaxin 2 (RLN2) and cytokines in RCC. Methods: We investigated the expression of RLN2 and AR variants in 25 clear cell RCC (ccRCC) and 9 papillary (pRCC) tumor tissues and the corresponding controls using quantitative PCR and serum RLN2, testosterone and cytokine levels in matched samples using ELISA and chemiluminescent immunometric assay, respectively. Results: ccRCC tissues but not pRCC tissues more frequently expressed AR and the SVs than did normal tissues. All pRCC samples expressed more AR than did ccRCC samples. The highest expression of all AR variants except AR-V12 was found in low-stage tumors, with dominant expression of AR-V7. In males in the ccRCC cohort, the expression of AR-FL, AR-V1 and AR-V3 was significantly correlated with that of RLN2. The secretion pattern of proinflammatory IL-6 was higher in ccRCC than in pRCC. Conclusions: The results highlight additional molecular differences between ccRCC and pRCC, suggesting the influence of external factors on the whole kidney or genetic predispositions to developing certain types of renal cancer, and may support further pathological analysis and studies of targeted hormone therapy.

Relaxin receptor deficiency promotes vascular inflammation and impairs outward remodeling in arteriovenous fistulas

The pathophysiology of arteriovenous fistula (AVF) maturation failure is not completely understood but impaired outward remodeling (OR) and intimal hyperplasia are thought to be contributors. This adverse vascular response after AVF surgery results from interplay between vascular smooth muscle cells (VSMCs), the extracellular matrix (ECM), and inflammatory cells. Relaxin (RLN) is a hormone that acts on the vasculature via interaction with RLN/insulin-like peptide family receptor 1 (RXFP1), resulting in vasodilatation, ECM remodeling, and decreased inflammation. In the present study, we evaluated the consequences of RXFP1 knockout ( Rxfp1-/-) on AVF maturation in a murine model of AVF failure. Rxfp1-/- mice showed a 22% decrease in vessel size at the venous outflow tract 14 d after AVF surgery. Furthermore, a 43% increase in elastin content was observed in the lesions of Rxfp1-/- mice and coincided with a 41% reduction in elastase activity. In addition, Rxfp1-/- mice displayed a 6-fold increase in CD45+ leukocytes, along with a 2-fold increase in monocyte chemoattractant protein 1 (MCP1) levels, when compared with wild-type mice. In vitro, VSMCs from Rxfp1-/- mice exhibited a synthetic phenotype, as illustrated by augmentation of collagen, fibronectin, TGF-β, and platelet-derived growth factor mRNA. In addition, VSMCs derived from Rxfp1-/- mice showed a 5-fold increase in cell migration. Finally, RXFP1 and RLN expression levels were increased in human AVFs when compared with unoperated cephalic veins. In conclusion, RXFP1 deficiency hampers elastin degradation and results in induced vascular inflammation after AVF surgery. These processes impair OR in murine AVF, suggesting that the RLN axis could be a potential therapeutic target for promoting AVF maturation.-Bezhaeva, T., de Vries, M. R., Geelhoed, W. J., van der Veer, E. P., Versteeg, S., van Alem, C. M. A., Voorzaat, B. M., Eijkelkamp, N., van der Bogt, K. E., Agoulnik, A. I., van Zonneveld, A.-J., Quax, P. H. A., Rotmans, J. I. Relaxin receptor deficiency promotes vascular inflammation and impairs outward remodeling in arteriovenous fistulas.

Relaxin-mediated renal vasodilation in the rat is associated with falls in glomerular blood pressure

Relaxin (RLX) is a pleiotropic peptide hormone with marked renal vasodilatory actions that are physiologically important during pregnancy. RLX also has potent antifibrotic actions and is being tested therapeutically in various fibrotic diseases, including chronic kidney disease (CKD). Since renal vasodilation may expose the glomerulus to increased blood pressure [glomerular capillary pressure (PGC)], which exacerbates progression of CKD, we assessed the glomerular hemodynamic actions of acute (0.89 µg·100 g body wt-1·h-1 iv over 75 min) and chronic (1.5 µg·100 g body wt-1·h-1 sc) administration of RLX. Both acute and chronic RLX produced marked renal vasodilation and increased renal plasma flow (RPF) in euvolemic, anesthetized male rats. Glomerular filtration rate also increased with RLX, but the magnitude of the rise was much less than the increase in RPF due to concomitant decreases in filtration fraction. The fall in filtration fraction was the result of significant decreases in PGC, despite a slight increase in mean arterial blood pressure (MAP) with acute RLX and no net change in MAP with chronic RLX. This fall in PGC occurred because of the "in-series" arrangement of the afferent and efferent arteriolar resistance vessels, which can regulate PGC independently of MAP. With both acute and chronic RLX, efferent arteriolar resistance vessels relaxed to a greater extent than afferent arteriolar resistance vessels, thus producing falls in PGC. Based on this finding, RLX has a beneficial hemodynamic impact on the kidney, which, together with the antifibrotic actions of RLX, suggests a strong therapeutic potential for use in CKD.

Relaxin abrogates renal interstitial fibrosis by regulating macrophage polarization via inhibition of Toll-like receptor 4 signaling

Renal fibrosis is a common feature of chronic kidney disease (CKD). To inhibit the CKD process, it is important to prevent renal fibrosis, though CKD remains incurable. Renal fibrosis can be inhibited by relaxin in several experimental models, but the mechanism of relaxin for antifibrotic potential is still not clear. And here we have studied the role of relaxin in macrophage polarization and renal inflammation after unilateral ureteral obstruction (UUO). Our results show that relaxin can downregulate the Toll-like receptor (TLR) 4 signaling, shift macrophage polarization toward the M2 phenotype and ameliorat renal fibrosis in the early stages of UUO. In vitro experiments, it has been confirmed that relaxin can downregulate the TLR4 signaling and induce the M2 macrophage transition. Furthermore, the transitional actions of macrophage phenotype induced by relaxin are significantly blocked by TAK-242, a TLR4 antagonist, in vitro experiments. Thus, there is a novel mechanism of relaxin for antifibrosis that shifts macrophage polarization toward the M2 phenotype via inhibition of TLR4 signaling.

Effects of serelaxin in acute heart failure patients with renal impairment: results from RELAX-AHF

BACKGROUND

Serelaxin showed beneficial effects on clinical outcome and trajectories of renal markers in patients with acute heart failure. We aimed to study the interaction between renal function and the treatment effect of serelaxin.

METHODS

In the current post hoc analysis of the RELAX-AHF trial, we included all patients with available estimated glomerular filtration rate (eGFR) at baseline (n = 1132). Renal impairment was defined as an eGFR <60 ml/min/1.73 m(2) estimated by creatinine.

RESULTS

817 (72.2 %) patients had a baseline eGFR <60 ml/min/1.73 m(2). In placebo-treated patients, baseline renal impairment was related to a higher 180 day cardiovascular (HR 3.12, 95 % CI 1.33-7.30) and all-cause mortality (HR 2.81, 95 % CI 1.34-5.89). However, in serelaxin-treated patients, the risk of cardiovascular and all-cause mortality was less pronounced (HR 1.19, 95 % CI 0.54 -2.64; p for interaction = 0.106, and HR 1.15 95 % CI 0.56-2.34 respectively; p for interaction = 0.088). In patients with renal impairment, treatment with serelaxin resulted in a more pronounced all-cause mortality reduction (HR 0.53, 95 % CI 0.34-0.83), compared with patients without renal impairment (HR 1.30, 95 % CI 0.51-3.29).

CONCLUSION

Renal dysfunction was associated with higher cardiovascular and all-cause mortality in placebo-treated patients, but not in serelaxin-treated patients. The observed reduction in (cardiovascular) mortality in RELAX-AHF was more pronounced in patients with renal dysfunction. These observations need to be confirmed in the ongoing RELAX-AHF-2 trial.

Relaxin Treatment in an Ang-II-Based Transgenic Preeclamptic-Rat Model

Relaxin is a peptide related to pregnancy that induces nitric oxide-related and gelatinase-related effects, allowing vasodilation and pregnancy-related adjustments permitting parturition to occur. Relaxin controls the hemodynamic and renovascular adaptive changes that occur during pregnancy. Interest has evolved regarding relaxin and a therapeutic principle in preeclampsia and heart failure. Preeclampsia is a pregnancy disorder, featuring hypertension, proteinuria and placental anomalies. We investigated relaxin in an established transgenic rat model of preeclampsia, where the phenotype is induced by angiotensin (Ang)-II production in mid pregnancy. We gave recombinant relaxin to preeclamtic rats at day 9 of gestation. Hypertension and proteinuria was not ameliorated after relaxin administration. Intrauterine growth retardation of the fetus was unaltered by relaxin. Heart-rate responses and relaxin levels documented drug effects. In this Ang-II-based model of preeclampsia, we could not show a salubrious effect on preeclampsia.

Combination therapy of mesenchymal stem cells and serelaxin effectively attenuates renal fibrosis in obstructive nephropathy

Chronic kidney disease (CKD) results from the development of fibrosis, ultimately leading to end-stage renal disease (ESRD). Although human bone marrow-derived mesenchymal stem cells (MSCs) can accelerate renal repair following acute injury, the establishment of fibrosis during CKD may affect their potential to influence regeneration capacity. Here we tested the novel combination of MSCs with the antifibrotic serelaxin to repair and protect the kidney 7 d post-unilateral ureteral obstruction (UUO), when fibrosis is established. Male C57BL6 mice were sham-operated or UUO-inured (n = 4-6) and received vehicle, MSCs (1 × 10(6)), serelaxin (0.5 mg/kg per d), or the combination of both. In vivo tracing studies with luciferin/enhanced green fluorescent protein (eGFP)-tagged MSCs showed specific localization in the obstructed kidney where they remained for 36 h. Combination therapy conferred significant protection from UUO-induced fibrosis, as indicated by hydroxyproline analysis (P < 0.001 vs. vehicle, P < 0.05 vs. MSC or serelaxin alone). This was accompanied by preserved structural architecture, decreased tubular epithelial injury (P < 0.01 vs. MSCs alone), macrophage infiltration, and myofibroblast localization in the kidney (both P < 0.01 vs. vehicle). Combination therapy also stimulated matrix metalloproteinase (MMP)-2 activity over either treatment alone (P < 0.05 vs. either treatment alone). These results suggest that the presence of an antifibrotic in conjunction with MSCs ameliorates established kidney fibrosis and augments tissue repair to a greater extent than either treatment alone.

Recombinant human relaxin-2: (how) can a pregnancy hormone save lives in acute heart failure?

Acute heart failure (AHF) syndrome, characterized by pulmonary and/or venous congestion owing to increased cardiac filling pressures with or without diminished cardiac output, is still associated with high post-discharge mortality and hospitalization rates. Many novel and promising therapeutic approaches, among them endothelin-1, vasopressin and adenosine antagonists, calcium sensitization, and recombinant B-type natriuretic hormone, have failed in large studies. Likewise, the classic drugs, vasodilators, diuretics, and inotropes, have never been shown to lower mortality.The phase III trial RELAX-AHF tested recombinant human relaxin-2 (rhRlx) and found it to improve clinical symptoms moderately, to be neutral regarding the combination of death and hospitalization at day 60, to be safe, and to lower mortality at day 180. This review focuses on basic research and pre-clinical findings that may account for the benefit of rhRlx in AHF. The drug combines short-term hemodynamic advantages, such as moderate blood pressure decline and functional endothelin-1 antagonism, with a wealth of protective effects harboring long-term benefits, such as anti-inflammatory, anti-fibrotic, and anti-oxidative actions. These pleiotropic effects are exerted through a complex and intricate signaling cascade involving the relaxin-family peptide receptor-1, the glucocorticoid receptor, nitric oxide, and a cell type-dependent variety of kinases and transcription factors.

Detection of relaxin receptor in the dorsoradial ligament, synovium, and articular cartilage of the trapeziometacarpal joint

Basilar thumb osteoarthritis (OA) is postulated to occur due to ligament attenuation of the trapeziometacarpal (TM) joint. Relaxin is a peptide hormone, which loosens ligaments before childbirth, through remodeling of the extracellular matrix via upregulation of matrix metalloproteases (MMPs). We postulated that relaxin family peptide receptor 1 (RXFP-1), the receptor for circulating relaxin, was present in tissues of the TM joint. Ligaments and synovium were sampled from 15 patients during surgery for TM arthritis. We obtained trapezial cartilage from two autopsy donors and four patients. Tissues were fixed, paraffin embedded, and sectioned at 5 µm, then were immunostained for RXFP-1, as well as MMP-1, and MMP-13, using rabbit anti-human polyclonal antibodies. Eight DRL samples showed positive immunostaining for relaxin receptor, with 14/15 positively stained in synovium. Greater staining was seen in specimens obtained from women with more severe TM arthritis. Trapezial cartilage demonstrated receptor staining within chondrocytes in the middle and deep zones. Immunostaining for MMPs co-localized with relaxin receptor staining. Relaxin receptors are present at the ligament, cartilage, and synovium of the TM joint, indicating that it is a potential target for relaxin. This suggests that circulating relaxin may impact joint stability. The role of relaxin in cartilage and synovium may be related to its role in collagen regulation as a possible tissue response to OA.

Relaxin does not improve Angiotensin II-induced target-organ damage

Relaxin is a corpus-luteum produced protein hormone with vasodilatatory, anti-fibrotic, and angiogenic properties that are opposite to angiotensin (Ang) II. We investigated whether or not relaxin ameliorates Ang II-induced target-organ damage. We used double transgenic rats harboring both human renin and angiotensinogen genes (dTGR) that develop severe hypertension, target-organ damage, and die untreated within 7–8 weeks. Recombinant relaxin at a low (26 μg/kg/d) and a high dose (240 μg/kg/d) was given to 4 week-old dTGR and age-matched Sprague-Dawley rats (SD). Systolic blood pressure increased progressively in untreated dTGRs from 162±3 mmHg at week 5 to 225±5 mmHg at week 7. Relaxin had no effect on blood pressure whereas SD rats were normotensive (106±1 mmHg). Untreated and relaxin-treated dTGR had similarly severe cardiac hypertrophy indices. Relaxin did not ameliorate albuminuria and did not prevent matrix-protein deposition in the heart and kidney in dTGR. Finally, relaxin treatment did not reduce mortality. These data suggest that pharmacological doses of relaxin do not reverse severe effects of Ang II.

Relationship of relaxin hormone and thumb carpometacarpal joint arthritis

BACKGROUND

The female predominance in thumb carpometacarpal (CMC) joint arthritis has led to speculation that reproductive hormones or hypermobility are responsible. Evidence shows that patients with pathologic laxity have a higher rate of thumb CMC arthritis. Relaxin hormone increases laxity in the pelvic ligaments through upregulation of matrix metalloproteases (MMPs). It is thus a hormone of interest in the development of thumb CMC arthritis.

QUESTIONS/PURPOSES

Our goals were to identify demographic and hormonal factors associated with joint laxity in patients with CMC arthritis and to evaluate the relationship among serum relaxin, relaxin receptors, and MMPs in the anterior oblique ligament (AOL) of the thumb. We hypothesized that serum relaxin was correlated with joint laxity as well as with relaxin receptors and MMPs in the AOL.

METHODS

Forty-nine patients undergoing thumb CMC arthroplasty underwent laxity examination, blood draw, and AOL sampling. Ligaments were analyzed for relaxin receptor and MMPs 1 and 3 using quantitative reverse-transcriptase polymerase chain reaction.

RESULTS

Women demonstrated more joint laxity than men (p < 0.001). RNA analysis confirmed relaxin receptors in the AOL as well as MMPs 1 and 3. There was a significant correlation between serum relaxin and MMP-1 (p = 0.04). Detectable serum relaxin was negatively correlated with relaxin receptors in the AOL (p = 0.02).

CONCLUSIONS

Further studies are needed to evaluate the role of laxity and sex hormones in thumb CMC arthritis.

CLINICAL RELEVANCE

Relaxin hormone may play a role in the development of arthritis at the thumb CMC joint.

LEVEL OF EVIDENCE

Level I, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

Acute treatment with relaxin protects the kidney against ischaemia/reperfusion injury

Although recent preclinical and clinical studies have demonstrated that recombinant human relaxin (rhRLX) may have important therapeutic potential in acute heart failure and chronic kidney diseases, the effects of acute rhRLX administration against renal ischaemia/reperfusion (I/R) injury have never been investigated. Using a rat model of 1-hr bilateral renal artery occlusion followed by 6-hr reperfusion, we investigated the effects of rhRLX (5 μg/Kg i.v.) given both at the beginning and after 3 hrs of reperfusion. Acute rhRLX administration attenuated the functional renal injury (increase in serum urea and creatinine), glomerular dysfunction (decrease in creatinine clearance) and tubular dysfunction (increase in urinary excretion of N-acetyl-β-glucosaminidase) evoked by renal I/R. These beneficial effects were accompanied by a significant reduction in local lipid peroxidation, free radical-induced DNA damage and increase in the expression/activity of the endogenous antioxidant enzymes MnSOD and CuZnSOD superoxide dismutases (SOD). Furthermore, rhRLX administration attenuated the increase in leucocyte activation, as suggested by inhibition of myeloperoxidase activity, intercellular-adhesion-molecule-1 expression, interleukin (IL)-1β, IL-18 and tumour necrosis factor-α production as well as increase in IL-10 production. Interestingly, the reduced oxidative stress status and neutrophil activation here reported were associated with rhRLX-induced activation of endothelial nitric oxide synthase and up-regulation of inducible nitric oxide synthase, possibly secondary to activation of Akt and the extracellular signal-regulated protein kinase (ERK) 1/2, respectively. Thus, we report herein that rhRLX protects the kidney against I/R injury by a mechanism that involves changes in nitric oxide signalling pathway.

Relationship of serum relaxin to generalized and trapezial-metacarpal joint laxity

PURPOSE

The reproductive hormone relaxin acts to loosen pelvic ligaments in preparation for childbirth and is thought to be a mediator of joint laxity. The purpose of this study was to evaluate the correlation of serum relaxin with radiographic laxity at the trapezial-metacarpal joint and with generalized joint laxity.

METHODS

We enrolled 289 healthy subjects prospectively. Participants completed a demographic questionnaire and were examined for generalized joint hypermobility using the Beighton-Horan scale. Stress radiographs of the trapezial-metacarpal joint were obtained in 163 subjects (56%). Blood samples were collected, and serum relaxin was measured for 287 subjects using enzyme-linked immunosorbent assay for human relaxin-2.

RESULTS

The mean serum relaxin level among all subjects was 1.84 pg/mL (range, 0-45.25 pg/mL). Relaxin was not detectable in 166 of 287 samples, whereas the mean serum relaxin level among the 121 subjects with a detectable relaxin level (of 287 total relaxin samples) was 4.37 pg/mL (range, 0.46-45.25 pg/mL). Mean trapezial-metacarpal subluxation ratio scores were higher among those with a detectable relaxin level compared to those without a detectable relaxin level (0.34 vs 0.30 pg/mL). The average Beighton-Horan laxity score was 1.8 (range, 0-9). There was no correlation between generalized joint laxity measures and serum relaxin levels.

CONCLUSIONS

In a large volunteer population, we demonstrated a relationship between circulating relaxin and trapezial-metacarpal joint laxity. However, we were unable to show a direct link between serum relaxin and generalized joint laxity.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic II.

Relaxin: new pathophysiological aspects and pharmacological perspectives for an old protein

Human relaxin-2 (hereafter simply defined as "relaxin") is a 6-kDa peptidic hormone best known for the physiological role played during pregnancy in the growth and differentiation of the reproductive tract and in the renal and systemic hemodynamic changes. This factor can also be involved in the pathophysiology of arterial hypertension and heart failure, in the molecular pathways of fibrosis and cancer, and in angiogenesis and bone remodeling. It belongs to the relaxin peptide family, whose members comprehensively exert numerous effects through interaction with different types of receptors, classified as relaxin family peptide (RXFP) receptors (RXFP1, RXFP2, RXFP3, RXFP4). Research looks toward the in-depth examination and complete understanding of relaxin in its various pleiotropic actions. The intent is to evaluate the likelihood of employing this substance for therapeutic purposes, for instance in diseases where a deficit could be part of the underlying pathophysiological mechanisms, also avoiding any adverse effect. Relaxin is already being considered as a promising drug, especially in acute heart failure. A careful study of the different RXFPs and their receptors and the comprehension of all biological activities of these hormones will probably provide new drugs with a potential wide range of therapeutic applications in the near future.

Fibrosis in the kidney: is a problem shared a problem halved?

Fibrotic disorders are commonplace, take many forms and can be life-threatening. No better example of this exists than the progressive fibrosis that accompanies all chronic renal disease. Renal fibrosis is a direct consequence of the kidney's limited capacity to regenerate after injury. Renal scarring results in a progressive loss of renal function, ultimately leading to end-stage renal failure and a requirement for dialysis or kidney transplantation. Although it manifests itself histologically as an increase in extracellular matrix, we know that the histological appearance can be caused by a de novo synthesis of matrix (primarily collagen), or a disproportionate loss of renal parenchyma. In both cases the process depends on a resident mesenchymal cell, the so-called myofibroblast, and is independent of disease etiology. Potentially we can ameliorate fibrosis, either indirectly by modifying the environment the kidney functions in, or more directly by interfering with activation and function of myofibroblasts. However, while renal fibrosis shares many features in common with the wound healing response in other organs, we also recognise that the consequences can be highly kidney specific. This review highlights the similarities and differences between this process in the kidney and other organs, and considers the therapeutic implications.

Relaxin and castration in male mice protect from, but testosterone exacerbates, age-related cardiac and renal fibrosis, whereas estrogens are an independent determinant of organ size

This study determined the effects of castration and hormone replacement therapy on the age-related cardiac and renal pathology of male relaxin gene-knockout (RlnKO) and age-matched wild-type (RlnWT) mice and that of aged male aromatase knockout (ArKO) mice, which lack estrogens and have 5-10 times the androgen levels of male wild-type mice. One-month-old RlnWT and RlnKO mice were bilaterally gonadectomized or sham operated and maintained until 12 months. Subgroups of castrated animals received testosterone or 17β-estradiol treatment from 9 to 12 months. Male ArKO mice and aromatase wild-type mice were aged to 12 months. Collected heart and kidney tissues were assessed for changes in organ size and fibrosis. Castration reduced body, heart, left ventricle, and kidney weights in both RlnKO and RlnWT mice, and the cardiac/renal fibrosis that was seen in sham RlnKO animals (all P < 0.05 vs. respective sham). Testosterone normalized organ weights and organ weight to body weight ratio of castrated animals and increased cardiac/renal collagen concentration to levels measured in or beyond that of sham RlnKO mice (all P < 0.05 vs. respective castrated mice). Furthermore, expression of TGF-β1, mothers against decapentaplegic homolog 2 (Smad2), and myofibroblast differentiation paralleled the above changes (all P < 0.05 vs. respective castrated mice), whereas matrix metalloproteinase-13 was decreased in testosterone-treated RlnKO mice. Conversely, 17β-estradiol only restored changes in organ size. Consistent with these findings, intact ArKO mice demonstrated increased cardiac/renal fibrosis in the absence of changes in organ size. These findings suggest that relaxin and castration protect, whereas androgens exacerbate, cardiac and renal fibrosis during ageing, whereas estrogens, in synergy with relaxin, regulates age-related changes in organ size.

[Slowing chronic kidney disease progression: hopes and disappointments. Vascular repair of chronic kidney]

In chronic kidney disease patients, inexorable renal function decline is reduced by renin-angiotensin system (RAS) blockers. ACE inhibitors and angiotensin receptor blockers decrease blood pressure and proteinuria. Guidelines recommend a reduction of blood pressure to less than 130/80 mmHg and urinary protein excretion below 0.5 g/d. The combined use of a diuretic increases anti-proteinuric effect and blood pressure control of RAS blockers. Drugs as mineralo-corticocoids receptor antagonist and endothelin receptor antagonists reduce further albuminuria in combination with RAS blocker, but side effects need to be precised. Both metabolic acidosis and hyperuricemia represent new therapeutic goals to slow renal function decline in CKD patients. Renal fibrosis treatment and regenerative medicine are stemming and will be important issues for kidney and other organs in the future.

Kidney aging--inevitable or preventable?

The aging process affects all organs, including the kidneys. As part of this process, progressive scarring and a measurable decline in renal function occur in most people over time. The improved understanding of the processes that can lead to and/or hasten scarring and loss of renal function over time parallels advances in our understanding of the aging process. Clinical factors, including hypertension, diabetes mellitus, obesity, abnormal lipid levels and vitamin D deficiency, have been associated with increasing renal sclerosis with age. In addition, tissue factors such as angiotensin II, advanced glycation end products, oxidative stress and Klotho are associated with renal aging. These associations and possible interventions, including the control of blood pressure, blood sugar, weight, diet and calorie restriction might make renal aging more preventable than inevitable.

Antifibrotic properties of relaxin: in vivo mechanism of action in experimental renal tubulointerstitial fibrosis

This study examined the efficacy and in vivo mechanism of action of the antifibrotic hormone, relaxin, in a mouse model of unilateral ureteric obstruction (UUO). Kidney fibrosis was assessed in recombinant human gene-2 relaxin-treated animals maintained for 3 and 9 d after UUO. Results were compared with untreated and unoperated animals (d 0). Total collagen, collagen subtypes (I, IV), TGF-β2 production, mothers against decapentaplegic homolog 2 (Smad2) phosphorylation, myofibroblast differentiation, mitosis, and apoptosis were all progressively increased by UUO (all P<0.05 vs. d 0 group at d 3 and d 9), whereas TGF-β1 production was increased and vascular endothelial growth factor expression (angiogenesis) decreased at d 9 (both P<0.05 vs. d 0). A progressive increase in matrix metalloproteinase (MMP)-2 after UUO suggested that it was reactive to the increased fibrogenesis. Conversely, MMP-9 was decreased at d 9, whereas its inhibitor tissue inhibitor of metalloproteinase-1 progressively decreased after UUO. Human gene-2 relaxin pretreatment of animals from 4 d prior to UUO ameliorated the increase in total collagen, collagen IV, Smad2 phosphorylation, and myofibroblasts at both time points (all P<0.05 vs. untreated groups) and inhibited TGF-β2 production and cell proliferation (both P<0.05 vs. untreated groups) with a trend toward normalizing vascular endothelial growth factor expression at d 9, with no effect on TGF-β1 production or apoptosis. The relaxin-mediated regulation of MMPs and tissue inhibitor of metalloproteinases in this model was not consistent with its antifibrotic properties. The beneficial effects of relaxin were lost when treatment was stopped. These findings establish that relaxin can inhibit both early and established phases of tubulointerstitial fibrosis, primarily by suppressing cell proliferation, myofibroblast differentiation, and collagen production. Not all of these effects paralleled changes to TGF-β-Smad signaling.