Therapeutic effects of serelaxin in acute heart failure

AT1R-AT2R-RXFP1 Functional Crosstalk in Myofibroblasts: Impact on the Therapeutic Targeting of Renal and Cardiac Fibrosis

BACKGROUND

Recombinant human relaxin-2 (serelaxin), which has organ-protective actions mediated via its cognate G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1), has emerged as a potential agent to treat fibrosis. Studies have shown that serelaxin requires the angiotensin II (AngII) type 2 receptor (AT₂R) to ameliorate renal fibrogenesis in vitro and in vivo. Whether its antifibrotic actions are affected by modulation of the AngII type 1 receptor (AT₁R), which is expressed on myofibroblasts along with RXFP1 and AT₂R, is unknown.

METHODS

We examined the signal transduction mechanisms of serelaxin when applied to primary rat renal and human cardiac myofibroblasts in vitro, and in three models of renal- or cardiomyopathy-induced fibrosis in vivo.

RESULTS

The AT₁R blockers irbesartan and candesartan abrogated antifibrotic signal transduction of serelaxin via RXFP1 in vitro and in vivo. Candesartan also ameliorated serelaxin's antifibrotic actions in the left ventricle of mice with cardiomyopathy, indicating that candesartan's inhibitory effects were not confined to the kidney. We also demonstrated in a transfected cell system that serelaxin did not directly bind to AT₁Rs but that constitutive AT₁R-RXFP1 interactions could form. To potentially explain these findings, we also demonstrated that renal and cardiac myofibroblasts expressed all three receptors and that antagonists acting at each receptor directly or allosterically blocked the antifibrotic effects of either serelaxin or an AT₂R agonist (compound 21).

CONCLUSIONS

These findings have significant implications for the concomitant use of RXFP1 or AT₂R agonists with AT₁R blockers, and suggest that functional interactions between the three receptors on myofibroblasts may represent new targets for controlling fibrosis progression.

Relaxin mitigates microvascular damage and inflammation following cardiac ischemia-reperfusion

Microvascular obstruction (MVO) and leakage (MVL) forms a pivotal part of microvascular damage following cardiac ischemia-reperfusion (IR). We tested the effect of relaxin therapy on MVO and MVL in mice following cardiac IR injury including severity of MVO and MVL, opening capillaries, infarct size, regional inflammation, cardiac function and remodelling, and permeability of cultured endothelial monolayer. Compared to vehicle group, relaxin treatment (50 μg/kg) reduced no-reflow area by 38% and the content of Evans blue as a permeability tracer by 56% in jeopardized myocardium (both P < 0.05), effects associated with increased opening capillaries. Relaxin also decreased leukocyte density, gene expression of cytokines, and mitigated IR-induced decrease in protein content of VE-cadherin and relaxin receptor. Infarct size was comparable between the two groups. At 2 weeks post-IR, relaxin treatment partially preserved cardiac contractile function and limited chamber dilatation versus untreated controls by echocardiography. Endothelial cell permeability assay demonstrated that relaxin attenuated leakage induced by hypoxia-reoxygenation, H₂O₂, or cytokines, action that was independent of nitric oxide but associated with the preservation of VE-cadherin. In conclusion, relaxin therapy attenuates IR-induced MVO and MVL and endothelial leakage. This protection was associated with reduced regional inflammatory responses and consequently led to alleviated adverse cardiac remodeling.

Recent developments in relaxin mimetics as therapeutics for cardiovascular diseases

Cardiovascular disease is the most common cause of mortality worldwide, accounting for almost 50% of all deaths globally. Vascular endothelial dysfunction and fibrosis are critical in the pathophysiology of cardiovascular disease. Relaxin, an insulin-like peptide, is known to have beneficial actions in the cardiovascular system through its vasoprotective and anti-fibrotic effects. However, relaxin has several limitations of peptide-based drugs such as poor oral bioavailability, laborious, and expensive to synthesize. This review will focus on recent developments in relaxin mimetics, their pharmacology, associated signalling mechanisms, and their therapeutic potential for the management and treatment of cardiovascular disease.

Peptide hormone relaxin: from bench to bedside

The peptide hormone relaxin has numerous roles both within and independent of pregnancy and is often thought of as a “pleiotropic hormone.” Relaxin targets several tissues throughout the body, and has many functions associated with extracellular matrix remodeling and the vasculature. This review considers the potential therapeutic applications of relaxin in cervical ripening, in vitro fertilization, preeclampsia, acute heart failure, ischemia-reperfusion, and cirrhosis. We first outline the animal models used in preclinical studies to progress relaxin into clinical trials and then discuss the findings from these studies. In many cases, the positive outcomes from preclinical animal studies were not replicated in human clinical trials. Therefore, the focus of this review is to evaluate the various animal models used to develop relaxin as a potential therapeutic and consider the limitations that must be addressed in future studies. These include the use of human relaxin in animals, duration of relaxin treatment, and the appropriateness of the clinical conditions being considered for relaxin therapy.

Short-term (48 hours) intravenous serelaxin infusion has no effect on myogenic tone or vascular remodeling in rat mesenteric arteries

BACKGROUND

Short-term IV sRLX (recombinant human relaxin-2) infusion enhances endothelium-dependent relaxation in mesenteric arteries. This is initially underpinned by increased NO followed by a transition to prostacyclin. The effects of short-term IV sRLX treatment on pressure-induced myogenic tone and vascular remodeling in these arteries are unknown. Therefore, we investigated the effects of sRLX infusion on pressure-induced myogenic tone and passive mechanical wall properties in mesenteric arteries.

METHODS

Mesenteric artery myogenic tone and passive mechanics were examined after 48-hours and 10-days infusion of sRLX. Potential mechanisms of action were assessed by pressure myography, qPCR, and Western blot analysis.

RESULTS

Neither 48-hours nor 10-days sRLX treatment had significant effects on myogenic tone, passive arterial wall stiffness, volume compliance, or axial lengthening. However, in 48-hours sRLX -treated rats, incubation with the NO synthase blocker L-NAME significantly increased myogenic tone (P<.05 vs placebo), demonstrating an increased contribution of NO to the regulation of myogenic tone. eNOS dimerization, but not phosphorylation, was significantly upregulated in the arteries of sRLX -treated rats.

CONCLUSION

In mesenteric arteries, 48-hours sRLX treatment upregulates the role of NO in the regulation of myogenic tone by enhancing eNOS dimerization, without altering overall myogenic tone or vascular remodeling.

Effects of serelaxin on renal microcirculation in rats under control and high-angiotensin environments

Serelaxin is a novel recombinant human relaxin-2 that has been investigated for the treatment of acute heart failure. However, its effects on renal function, especially on the renal microcirculation, remain incompletely characterized. Our immunoexpression studies localized RXFP1 receptors on vascular smooth muscle cells and endothelial cells of afferent arterioles and on principal cells of collecting ducts. Clearance experiments were performed in male and female normotensive rats and Ang II-infused male rats. Serelaxin increased mean arterial pressure slightly and significantly increased renal blood flow, urine flow, and sodium excretion rate. Group analysis of all serelaxin infusion experiments showed significant increases in GFR. During infusion with subthreshold levels of Ang II, serelaxin did not alter mean arterial pressure, renal blood flow, GFR, urine flow, or sodium excretion rate. Heart rates were elevated during serelaxin infusion alone (37 ± 5%) and in Ang II-infused rats (14 ± 2%). In studies using the in vitro isolated juxtamedullary nephron preparation, superfusion with serelaxin alone (40 ng/ml) significantly dilated afferent arterioles (10.8 ± 1.2 vs. 13.5 ± 1.1 µm) and efferent arterioles (9.9 ± 0.9 vs. 11.9 ± 1.0 µm). During Ang II superfusion, serelaxin did not alter afferent or efferent arteriolar diameters. During NO synthase inhibition (l-NNA), afferent arterioles also did not show any vasodilation during serelaxin infusion. In conclusion, serelaxin increased overall renal blood flow, urine flow, GFR, and sodium excretion and dilated the afferent and efferent arterioles in control conditions, but these effects were attenuated or prevented in the presence of exogenous Ang II and NO synthase inhibitors.

Relaxin-2 in Cardiometabolic Diseases: Mechanisms of Action and Future Perspectives

Despite the great effort of the medical community during the last decades, cardiovascular diseases remain the leading cause of death worldwide, increasing their prevalence every year mainly due to our new way of life. In the last years, the study of new hormones implicated in the regulation of energy metabolism and inflammation has raised a great interest among the scientific community regarding their implications in the development of cardiometabolic diseases. In this review, we will summarize the main actions of relaxin, a pleiotropic hormone that was previously suggested to improve acute heart failure and that participates in both metabolism and inflammation regulation at cardiovascular level, and will discuss its potential as future therapeutic target to prevent/reduce cardiovascular diseases.

Cardiac Fibrosis and Arrhythmogenesis

Myocardial injury, mechanical stress, neurohormonal activation, inflammation, and/or aging all lead to cardiac remodeling, which is responsible for cardiac dysfunction and arrhythmogenesis. Of the key histological components of cardiac remodeling, fibrosis either in the form of interstitial, patchy, or dense scars, constitutes a key histological substrate of arrhythmias. Here we discuss current research findings focusing on the role of fibrosis, in arrhythmogenesis. Numerous studies have convincingly shown that patchy or interstitial fibrosis interferes with myocardial electrophysiology by slowing down action potential propagation, initiating reentry, promoting after-depolarizations, and increasing ectopic automaticity. Meanwhile, there has been increasing appreciation of direct involvement of myofibroblasts, the activated form of fibroblasts, in arrhythmogenesis. Myofibroblasts undergo phenotypic changes with expression of gap-junctions and ion channels thereby forming direct electrical coupling with cardiomyocytes, which potentially results in profound disturbances of electrophysiology. There is strong evidence that systemic and regional inflammatory processes contribute to fibrogenesis (i.e., structural remodeling) and dysfunction of ion channels and Ca2+ homeostasis (i.e., electrical remodeling). Recognizing the pivotal role of fibrosis in the arrhythmogenesis has promoted clinical research on characterizing fibrosis by means of cardiac imaging or fibrosis biomarkers for clinical stratification of patients at higher risk of lethal arrhythmia, as well as preclinical research on the development of antifibrotic therapies. At the end of this review, we discuss remaining key questions in this area and propose new research approaches. © 2017 American Physiological Society. Compr Physiol 7:1009-1049, 2017.

Distinct activation modes of the Relaxin Family Peptide Receptor 2 in response to insulin-like peptide 3 and relaxin

Relaxin family peptide receptor 2 (RXFP2) is a GPCR known for its role in reproductive function. It is structurally related to the human relaxin receptor RXFP1 and can be activated by human gene-2 (H2) relaxin as well as its cognate ligand insulin-like peptide 3 (INSL3). Both receptors possess an N-terminal low-density lipoprotein type a (LDLa) module that is necessary for activation and is joined to a leucine-rich repeat domain by a linker. This linker has been shown to be important for H2 relaxin binding and activation of RXFP1 and herein we investigate the role of the equivalent region of RXFP2. We demonstrate that the linker’s highly-conserved N-terminal region is essential for activation of RXFP2 in response to both ligands. In contrast, the linker is necessary for H2 relaxin, but not INSL3, binding. Our results highlight the distinct mechanism by which INSL3 activates RXFP2 whereby ligand binding mediates reorientation of the LDLa module by the linker region to activate the RXFP2 transmembrane domains in conjunction with the INSL3 A-chain. In contrast, relaxin activation of RXFP2 involves a more RXFP1-like mechanism involving binding to the LDLa-linker, reorientation of the LDLa module and activation of the transmembrane domains by the LDLa alone.

ML290 is a biased allosteric agonist at the relaxin receptor RXFP1

Activation of the relaxin receptor RXFP1 has been associated with improved survival in acute heart failure. ML290 is a small molecule RXFP1 agonist with simple structure, long half-life and high stability. Here we demonstrate that ML290 is a biased agonist in human cells expressing RXFP1 with long-term beneficial actions on markers of fibrosis in human cardiac fibroblasts (HCFs). ML290 did not directly compete with orthosteric relaxin binding and did not affect binding kinetics, but did increase binding to RXFP1. In HEK-RXFP1 cells, ML290 stimulated cAMP accumulation and p38MAPK phosphorylation but not cGMP accumulation or ERK1/2 phosphorylation although prior addition of ML290 increased p-ERK1/2 responses to relaxin. In human primary vascular endothelial and smooth muscle cells that endogenously express RXFP1, ML290 increased both cAMP and cGMP accumulation but not p-ERK1/2. In HCFs, ML290 increased cGMP accumulation but did not affect p-ERK1/2 and given chronically activated MMP-2 expression and inhibited TGF-β1-induced Smad2 and Smad3 phosphorylation. In vascular cells, ML290 was 10x more potent for cGMP accumulation and p-p38MAPK than for cAMP accumulation. ML290 caused strong coupling of RXFP1 to Gα_s and Gα_oB but weak coupling to Gα_i3. ML290 exhibited signalling bias at RXFP1 possessing a signalling profile indicative of vasodilator and anti-fibrotic properties.

Relaxin and Matrix Metalloproteinase-9 in Angiotensin II-Induced Abdominal Aortic Aneurysms

BACKGROUND

This study determined whether relaxin or matrix metalloproteinase (MMP)-9 influences angiotensin II (AngII)-induced abdominal aortic aneurysms (AAA).Methods and Results:Male C57BL/6 or apolipoprotein E^-/-mice were infused with AngII with or without relaxin. Relaxin did not influence AngII-induced AAA in either mouse strain. Infusion of AngII reduced, but relaxin increased, MMP-9 mRNA in macrophages. We then determined the effects of MMP-9 deficiency on AAA in apolipoprotein E^-/-mice. MMP-9 deficiency led to AAA formation in the absence of AngII, and augmented AngII-induced aortic rupture and AAA incidence.

CONCLUSIONS

MMP-9 deficiency augmented AngII-induced AAA.

Serelaxin in clinical development: past, present and future

The availability of highly purified recombinant human relaxin, serelaxin, has allowed clinical trials to be conducted in several indications and the elucidation of its pharmacology in human subjects. These studies have demonstrated that serelaxin has unique haemodynamic properties that are likely to contribute to organ protection and long-term outcome benefits in acute heart failure. Clinical observations support its consideration for therapeutic use in other patient populations, including those with chronic heart failure, coronary artery disease, portal hypertension and acute renal failure.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Novel Therapies for Heart Failure - Where Do They Stand?

Despite advances in therapy, patients with heart failure (HF) continue to experience unacceptably high rates of hospitalization and death, as well as poor quality of life. As a consequence, there is an urgent need for new treatments that can improve the clinical course of the growing worldwide population of HF patients. Serelaxin and ularatide, both based on naturally occurring peptides, have potent vasodilatory as well as other effects on the heart and kidneys. For both agents, phase 3 studies that are designed to determine whether they improve outcomes in patients with acute HF have completed enrollment. TRV027, a biased ligand for the type 1 angiotensin receptor with effects that extend beyond traditional angiotensin-receptor blockers is also being studied in the acute HF population. Omecamtiv mecarbil, an inotropic agent that improves myocardial contractility by a novel mechanism, and vericiguat, a drug that stimulates soluble guanylate cyclase, are both being developed to treat patients with chronic HF. Finally, despite the negative results of the CUPID study, gene transfer therapy continues to be explored as a means of improving the function of the failing heart. The basis for the use of these drugs and their current status in clinical trials are discussed. (Circ J 2016; 80: 1882-1891).

The actions of relaxin on the human cardiovascular system

The insulin-like peptide relaxin, originally identified as a hormone of pregnancy, is now known to exert a range of pleiotropic effects including vasodilatory, anti-fibrotic, angiogenic, anti-apoptotic and anti-inflammatory effects in both males and females. Relaxin produces these effects by binding to a cognate receptor RXFP1 and activating a variety of signalling pathways including cAMP, cGMP and MAPKs as well as by altering gene expression of TGF-β, MMPs, angiogenic growth factors and endothelin receptors. The peptide has been shown to be effective in halting or reversing many of the adverse effects including fibrosis in animal models of cardiovascular disease including ischaemia/reperfusion injury, myocardial infarction, hypertensive heart disease and cardiomyopathy. Relaxin given to humans is safe and produces favourable haemodynamic changes. Serelaxin, the recombinant form of relaxin, is now in extended phase III clinical trials for the treatment of acute heart failure. Previous clinical studies indicated that a 48 h infusion of relaxin improved 180 day mortality, yet the mechanism underlying this effect is not clear. This article provides an overview of the cellular mechanism of effects of relaxin and summarizes its beneficial actions in animal models and in the clinic. We also hypothesize potential mechanisms for the clinical efficacy of relaxin, identify current knowledge gaps and suggest new ways in which relaxin could be useful therapeutically.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Association Between Serum Relaxin and Subsequent Shoulder Instability

Ligamentous laxity correlates with shoulder instability. Relaxin is a hormone that has been linked to laxity in the knee and has been shown to be a risk factor for anterior cruciate ligament (ACL) injury. This study prospectively evaluated the association between relaxin and acute shoulder instability. A prospective cohort study of 1050 young athletes was performed between 2006 and 2010. The authors conducted a nested case-control analysis within this cohort to evaluate the association between preinjury serum relaxin concentration and the likelihood of subsequent shoulder instability. The study compared 53 patients who had shoulder instability and 53 control subjects who were matched for sex, age, height, and weight. The serum relaxin concentration in preinjury baseline samples was tested with enzyme-linked immunosorbent assay analysis in duplicate. Independent t tests were performed to identify differences in mean serum relaxin concentration between patients with shoulder instability and uninjured control subjects. Logistic regression was used to evaluate whether preinjury baseline serum relaxin concentration was associated with the subsequent likelihood of shoulder instability. Of the 53 patients with instability, 13 (25%) had a detectable serum relaxin concentration compared with 9 (17%) of uninjured control subjects (P=.34). Mean serum relaxin concentration in the injury group was 3.69±1.78 pg/mL and 2.20±0.97 pg/mL in uninjured control subjects (P=.02). Increased serum relaxin concentration was associated with the subsequent likelihood of acute shoulder instability. Subjects were 2.18 times (odds ratio, 2.18; 95% confidence interval, 1.01-4.76) more likely to have acute shoulder instability during the follow-up period for every 1-pg/mL increase in serum relaxin concentration at baseline. The findings suggest that serum relaxin concentration is associated with a risk of subsequent shoulder instability in young athletes. Further research on the role of relaxin in shoulder instability is warranted. [Orthopedics. 2016; 39(4):e724-e728.].

Serelaxin: A Novel Therapeutic for Vascular Diseases

Vascular dysfunction is an important hallmark of cardiovascular disease. It is characterized by increased sensitivity to vasoconstrictors, decreases in the endothelium-derived vasodilators nitric oxide (NO) and prostacyclin (PGI2), and endothelium-derived hyperpolarization (EDH). Serelaxin (recombinant human relaxin) has gained considerable attention as a new vasoactive drug, largely through its beneficial therapeutic effects in acute heart failure. In this review we first describe the contribution of endogenous relaxin to vascular homeostasis. We then provide a comprehensive overview of the novel mechanisms of serelaxin action in blood vessels that differentiate it from other vasodilator drugs and explain how this peptide could be used more widely as a therapeutic to alleviate vascular dysfunction in several cardiovascular diseases.

The Anti-fibrotic Actions of Relaxin Are Mediated Through a NO-sGC-cGMP-Dependent Pathway in Renal Myofibroblasts In Vitro and Enhanced by the NO Donor, Diethylamine NONOate

INTRODUCTION

The anti-fibrotic hormone, relaxin, has been inferred to disrupt transforming growth factor (TGF)-β1/Smad2 phosphorylation (pSmad2) signal transduction and promote collagen-degrading gelatinase activity via a nitric oxide (NO)-dependent pathway. Here, we determined the extent to which NO, soluble guanylate cyclase (sGC) and cyclic guanosine monophosphate (cGMP) were directly involved in the anti-fibrotic actions of relaxin using a selective NO scavenger and sGC inhibitor, and comparing and combining relaxin's effects with that of an NO donor.

METHODS AND RESULTS

Primary renal cortical myofibroblasts isolated from injured rat kidneys were treated with human recombinant relaxin (RLX; 16.8 nM), the NO donor, diethylamine NONOate (DEA/NO; 0.5-5 μM) or the combined effects of RLX (16.8 nM) and DEA/NO (5 μM) over 72 h. The effects of RLX (16.8 nM) and DEA/NO (5 μM) were also evaluated in the presence of the NO scavenger, hydroxocobalamin (HXC; 100 μM) or sGC inhibitor, ODQ (5 μM) over 72 h. Furthermore, the effects of RLX (30 nM), DEA/NO (5 μM) and RLX (30 nM) + DEA/NO (5 μM) on cGMP levels were directly measured, in the presence or absence of ODQ (5 μM). Changes in matrix metalloproteinase (MMP)-2, MMP-9 (cell media), pSmad2 and α-smooth muscle actin (α-SMA; a measure myofibroblast differentiation) (cell layer) were assessed by gelatin zymography and Western blotting, respectively. At the highest concentration tested, both RLX and DEA/NO promoted MMP-2 and MMP-9 levels by 25-33%, while inhibiting pSmad2 and α-SMA expression by up to 50% (all p < 0.05 vs. untreated and vehicle-treated cells). However, 5μM of DEA/NO was required to produce the effects seen with 16.8 nM of RLX over 72 h. The anti-fibrotic effects of RLX or DEA/NO alone were completely abrogated by HXC and ODQ (both p < 0.01 vs. RLX alone or DEA/NO alone), but were significantly enhanced when added in combination (all p < 0.05 vs. RLX alone). Additionally, the direct cGMP-promoting effects of RLX, DEA/NO and RLX+DEA/NO (which all increased cGMP levels by 12-16-fold over basal levels; all p < 0.01 vs. vehicle-treated cells) were significantly inhibited by pre-treatment of ODQ (all p < 0.05 vs. the respective treatments alone).

CONCLUSION

These findings confirmed that RLX mediates its TGF-β1-inhibitory and gelatinase-promoting effects via a NO-sGC-cGMP-dependent pathway, which was additively augmented by co-administration of DEA/NO.

Serelaxin for the treatment of acute heart failure: a review with a focus on end-organ protection

Acute heart failure (AHF) is a complex clinical syndrome characterized by fluid overload and haemodynamic abnormalities (short-term clinical consequences) and the development of end-organ damage (long-term consequences). Current therapies for the treatment of AHF, such as loop diuretics and vasodilators, help to relieve haemodynamic imbalance and congestion, but have not been shown to prevent (and may even contribute to) end-organ damage, or to provide long-term clinical benefit. Serelaxin is the recombinant form of human relaxin-2, a naturally occurring hormone involved in mediating haemodynamic changes during pregnancy. Preclinical and clinical studies have investigated the effects mediated by serelaxin and the suitability of this agent for the treatment of patients with AHF. Data suggest that serelaxin acts via multiple pathways to improve haemodynamics at the vascular, cardiac, and renal level and provide effective congestion relief. In addition, this novel agent may protect the heart, kidneys, and liver from damage by inhibiting inflammation, oxidative stress, cell death, and tissue fibrosis, and stimulating angiogenesis. Serelaxin may therefore improve both short- and long-term outcomes in patients with AHF. In this review, we examine the unique mechanisms underlying the potential benefits of serelaxin for the treatment of AHF, in particular, those involved in mediating end-organ protection.

Relaxin increases sympathetic nerve activity and activates spinally projecting neurons in the paraventricular nucleus of nonpregnant, but not pregnant, rats

Pregnancy is characterized by increased blood volume and baseline sympathetic nerve activity (SNA), vasodilation, and tachycardia. Relaxin (RLX), an ovarian hormone elevated in pregnancy, activates forebrain sites involved in control of blood volume and SNA through ANG II-dependent mechanisms and contributes to adaptations during pregnancy. In anesthetized, arterial baroreceptor-denervated nonpregnant (NP) rats, RLX microinjected into the subfornical organ (SFO; 0.77 pmol in 50 nl) produced sustained increases in lumbar SNA (8 ± 3%) and mean arterial pressure (MAP; 26 ± 4 mmHg). Low-dose intracarotid artery infusion of RLX (155 pmol·ml(-1)·h(-1); 1.5 h) had minor transient effects on AP and activated neurons [increased Fos-immunoreactivity (IR)] in the SFO and in spinally projecting (19 ± 2%) and arginine-vasopressin (AVP)-IR (21 ± 5%) cells in the paraventricular nucleus of the hypothalamus of NP, but not pregnant (P), rats. However, mRNA for RLX and ANG II type 1a receptors in the SFO was preserved in pregnancy. RLX receptor-IR is present in the region of the SFO in NP and P rats and is localized in astrocytes, the major source of angiotensinogen in the SFO. These data provide an anatomical substrate for a role of RLX in the resetting of AVP secretion and increased baseline SNA in pregnancy. Since RLX and ANG II receptor expression was preserved in the SFO of P rats, we speculate that the lack of response to exogenous RLX may be due to maximal activation by elevated endogenous levels of RLX in near-term pregnancy.

MMI-0100 inhibits cardiac fibrosis in myocardial infarction by direct actions on cardiomyocytes and fibroblasts via MK2 inhibition

The cell-permeant peptide inhibitor of MAPKAP kinase 2 (MK2), MMI-0100, inhibits MK2 and downstream fibrosis and inflammation. Recent studies have demonstrated that MMI-0100 reduces intimal hyperplasia in a mouse vein graft model, pulmonary fibrosis in a murine bleomycin-induced model and development of adhesions in conjunction with abdominal surgery. MK2 is critical to the pathogenesis of ischemic heart injury as MK2(-/-) mice are resistant to ischemic remodeling. Therefore, we tested the hypothesis that inhibiting MK2 with MMI-0100 would protect the heart after acute myocardial infarction (AMI) in vivo. AMI was induced by placing a permanent LAD coronary ligation. When MMI-0100 peptide was given 30 min after permanent LAD coronary artery ligation, the resulting fibrosis was reduced/prevented ~50% at a 2 week time point, with a corresponding improvement in cardiac function and decrease in left ventricular dilation. In cultured cardiomyocytes and fibroblasts, MMI-0100 inhibited MK2 to reduce cardiomyocyte caspase 3/7 activity, while enhancing primary cardiac fibroblast caspase 3/7 activity, which may explain MMI-0100's salvage of cardiac function and anti-fibrotic effects in vivo. These findings suggest that therapeutic inhibition of MK2 after acute MI, using rationally-designed cell-permeant peptides, inhibits cardiac fibrosis and maintains cardiac function by mechanisms that involve inhibiting cardiomyocyte apoptosis, while enhancing primary cardiac fibroblast cell death.