Effect of Compound 21, a Selective Angiotensin II Type 2 Receptor Agonist, in a Murine Xenograft Model of Dupuytren Disease

AT2R Activation Improves Wound Healing in a Preclinical Mouse Model

Abnormal skin healing resulting in chronic wounds or hypertrophic scarring remains a major healthcare burden. Here, the antifibrotic angiotensin II type 2 receptor (AT2R) signaling pathway was modulated to determine its impact on cutaneous wound healing. Balb/c mice received two splinted full-thickness wounds. Topical treatments with the selective AT2R agonist compound 21 (C21) and/or selective antagonist PD123319 or saline vehicle were administered until sacrifice on post-wounding days 7 or 10. The rate of wound re-epithelialization was accelerated by PD123319 and combination treatments. In vitro, C21 significantly reduced human fibroblast migration. C21 increased both collagen and vascular densities at days 7 and 10 post-wounding and collagen I:III ratio at day 10, while PD123319 and combination treatments decreased them. Genes associated with regeneration and repair were upregulated by C21, while PD123319 treatment increased the expression of genes associated with inflammation and immune cell chemotaxis. C21 treatment reduced wound total leukocyte and neutrophil staining densities, while PD123319 increased these and macrophage densities. Overall, AT2R activation with C21 yields wounds that mature more quickly with structural, cellular, and gene expression profiles more closely approximating unwounded skin. These findings support AT2R signal modulation as a potential therapeutic target to improve skin quality during wound healing.

Catch your breath: The protective role of the angiotensin AT2 receptor for the treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive interstitial lung disease whereby excessive deposition of extracellular matrix proteins (ECM) ultimately leads to respiratory failure. While there have been advances in pharmacotherapies for pulmonary fibrosis, IPF remains an incurable and irreversible disease. There remains an unmet clinical need for treatments that reverse fibrosis, or at the very least have a more tolerable side effect profile than currently available treatments. Transforming growth factor β1(TGFβ1) is considered the main driver of fibrosis in IPF. However, as our understanding of the role of the pulmonary renin-angiotensin system (PRAS) in the pathogenesis of IPF increases, it is becoming clear that targeting angiotensin receptors represents a potential novel treatment strategy for IPF - in particular, via activation of the anti-fibrotic angiotensin type 2 receptor (AT2R). This review describes the current understanding of the pathophysiology of IPF and the mediators implicated in its pathogenesis; focusing on TGFβ1, angiotensin II and related peptides in the PRAS and their contribution to fibrotic processes in the lung. Preclinical and clinical assessment of currently available AT2R agonists and the development of novel, highly selective ligands for this receptor will also be described, with a focus on compound 21, currently in clinical trials for IPF. Collectively, this review provides evidence of the potential of AT2R as a novel therapeutic target for IPF.

Effect of nanoparticle-mediated delivery of SFRP4 siRNA for treating Dupuytren disease

Dupuytren disease (DD) is a progressive fibrous proliferative disease. It invades the palmar aponeurosis and extends to the finger fascia, eventually leading to flexion contracture of the metacarpophalangeal or interphalangeal joint. At present, surgical resection and the local injection of collagenase are the main methods for the treatment of DD, but postoperative complications and high recurrence rates often occur. Bioinformatics analysis showed that the increased expression of SFRP4 protein was closely related to the incidence of DD. Persistent and effective inhibition of SFRP4 expression may be a promising treatment for DD. We prepared SFRP4 siRNA/nanoparticle complexes (si-SFRP4) and negative siRNA/nanoparticle complexes (NC) and applied them in vitro and in vivo. Flow cytometry analysis showed that si-SFRP4 could be successfully transfected into DD cells. MTT and EdU staining assays showed that the OD values and percentage of EdU-positive cells in the si-SFRP4 group were significantly lower than those in the NC group. Scratch tests showed that the wound healing rate of the si-SFRP4 group was lower than that of the NC group, and the difference was statistically significant. The expression of SFRP4 and α-SMA protein in the si-SFRP4 group significantly decreased in both DD cells and xenografts. Compared with the NC group, the xenograft quality of the si-SFRP4 group was significantly reduced. Masson's trichrome staining showed that the collagen and fibrous cells in the si-SFRP4 group were more uniform, slender, parallel and regular. The above experimental results suggest that the proliferation and metabolism of palmar aponeurosis cells and the quality of metacarpal fascia xenografts were both significantly decreased. We speculated that nanoparticle-mediated SFRP4 siRNA can be used as a potential new method for the treatment of DD.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Therapeutic candidates for keloid scars identified by qualitative review of scratch assay research for wound healing

The scratch assay is an in vitro technique used to analyze cell migration, proliferation, and cell-to-cell interaction. In the assay, cells are grown to confluence and then ‘scratched’ with a sterile instrument. For the cells in the leading edge, the resulting polarity induces migration and proliferation in attempt to ‘heal’ the modeled wound. Keloid scars are known to have an accelerated wound closure phenotype in the scratch assay, representing an overactivation of wound healing. We performed a qualitative review of the recent literature searching for inhibitors of scratch assay activity that were already available in topical formulations under the hypothesis that such compounds may offer therapeutic potential in keloid treatment. Although several shortcomings in the scratch assay literature were identified, caffeine and allicin successfully inhibited the scratch assay closure and inflammatory abnormalities in the commercially available keloid fibroblast cell line. Caffeine and allicin also impacted ATP production in keloid cells, most notably with inhibition of non-mitochondrial oxygen consumption. The traditional Chinese medicine, shikonin, was also successful in inhibiting scratch closure but displayed less dramatic impacts on metabolism. Together, our results partially summarize the strengths and limitations of current scratch assay literature and suggest clinical assessment of the therapeutic potential for these identified compounds against keloid scars may be warranted.

Current Concepts in the Management of Dupuytren Disease of the Hand

Dupuytren disease is a fibroproliferative disorder of the palmar fascia of the hand. Little agreement and remarkable variability exists in treatment algorithms between surgeons. Because the cellular and molecular etiology of Dupuytren has been elucidated, ongoing efforts have been made to identify potential chemotherapeutic targets that could modulate the phenotypic expression of the disease. Although these efforts may dramatically alter the approach to treating this disease in the future, these approaches are largely experimental at this point. Over the past decade, the mainstay nonsurgical options have continued to be percutaneous needle aponeurotomy and collagenase Clostridium hystoliticum, and the most common surgical option is limited fasciectomy.

Angiotensin II Type 2 Receptor Modulates Synovial Macrophage Polarization by Inhibiting GRK2 Membrane Translocation in a Rat Model of Collagen-Induced Arthritis

The chronic inflammatory autoimmune disease rheumatoid arthritis (RA) is characterized by an infiltration of activated proinflammatory immune cells into the joint that is accompanied by an overproduction of various mediators, leading to destruction of cartilage and bone erosion. Angiotensin II type 2 receptor (AT2R) is involved in antioxidative, anti-inflammatory, and antifibrotic responses. Synovial macrophages (SMs) are a type of tissue macrophages that are derived from bone marrow cells. SMs plays a central role in synovial regional immunization, which is significantly increased in both collagen-induced mice with arthritis mice and RA patients. AT2R activation caused a reversal of the polarization of SMs in the joint from the proinflammatory M1 SM to the tolerogenic, benign M2 SM. In consequence, this switch resulted in an attenuated form of the joint pathology in a rat model of collagen-induced arthritis. These results were mechanistically linked to the observation that GRK2 was translocated into cytoplasm, and ERK1/2 and NF-κB activation were inhibited. These findings open the way to a new therapeutic approach using an activation of AT2R to subvert joint inflammation in RA.

The Selective Angiotensin II Type 2 Receptor Agonist Compound 21 Reduces Abdominal Adhesions in Mice

BACKGROUND

Abdominal adhesions (AAs) are post-traumatic fibrous bands that connect visceral and/or peritoneal surfaces, leading to possible long-term complications. The effect of a novel antifibrotic selective angiotensin II type 2 receptor agonist, compound 21 (C21) on AA formation was assessed in a murine model.

METHODS

Female BALB/c mice were laparotomized and the cecum and overlying parietal peritoneum abraded. C21 (10 μg/kg) or saline (vehicle) were administered orally or intraperitoneally daily. Mice were sacrificed 8 days after surgery, adhesions graded, and peritoneal fluid collected for transforming growth factor (TGF)-β levels. Laparotomy incisions were excised for immunohistochemistry. In vitro, scratch assays were performed using primary parietal peritoneal fibroblasts and visceral mesothelial cells treated with C21 (10 μM), angiotensin II (1 μM), or both. Western blot analysis of primary cell lysates was performed for total and phosphorylated SMAD 2/3.

RESULTS

Oral and intraperitoneal C21 reduced AA formation and TGF-β levels in peritoneal fluid. Surgical incisions demonstrated decreased α-smooth muscle actin expression in C21-treated animals, but no difference in vascularity, macrophage infiltration, collagen I/III distribution and density, and dermal thickness. Migration and expression of phosphorylated SMAD 2/3 was reduced in parietal peritoneal fibroblasts and visceral mesothelial cells treated with C21.

CONCLUSIONS

Local and systemic C21 administration reduced or completely prevented AA formation. These findings may be attributed to decreased intraperitoneal TGF-β in vivo and decreased migration of peritoneal fibroblasts and visceral mesothelial cells. Importantly, C21 did not have histologically quantifiable effects on laparotomy wounds, suggesting C21 could reduce AA formation without compromising laparotomy healing.

Attenuation of Dupuytren's fibrosis via targeting of the STAT1 modulated IL-13Rα1 response

Fibrotic disorders represent common complex disease pathologies that are therapeutically challenging. Inflammation is associated with numerous fibrotic pathogeneses; however, its role in the multifaceted mechanisms of fibrosis remains unclear. IL-13 is implicated in aberrant responses involved in fibrotic disease, and we aimed to understand its role in the inflammatory processes of a common fibrotic disorder, Dupuytren's disease. We demonstrated T-cells produced IFN-g, which induced IL-13 secretion from mast cells and up-regulated IL-13Ra1 on fibroblasts, rendering them more reactive to IL-13. Consequently, diseased myofibroblasts demonstrated enhanced fibroproliferative effects upon IL-13 stimulation. We established IFN-g and IL-13 responses involved STAT dependent pathways, and STAT targeting (tofacitinib) could inhibit IL-13 production from mast cells, IL-13Ra1 up-regulation in fibroblasts and fibroproliferative effects of IL-13 on diseased myofibroblasts. Accordingly, utilizing Dupuytren's as an accessible human model of fibrosis, we propose targeting STAT pathways may offer previously unidentified therapeutic approaches in the management of fibrotic disease.

Targeting the renin-angiotensin-aldosterone system in fibrosis

Fibrosis is characterized by excessive deposition of extracellular matrix components such as collagen in tissues or organs. Fibrosis can develop in the heart, kidneys, liver, skin or any other body organ in response to injury or maladaptive reparative processes, reducing overall function and leading eventually to organ failure. A variety of cellular and molecular signaling mechanisms are involved in the pathogenesis of fibrosis. The renin-angiotensin-aldosterone system (RAAS) interacts with the potent Transforming Growth Factor β (TGFβ) pro-fibrotic pathway to mediate fibrosis in many cell and tissue types. RAAS consists of both classical and alternative pathways, which act to potentiate or antagonize fibrotic signaling mechanisms, respectively. This review provides an overview of recent literature describing the roles of RAAS in the pathogenesis of fibrosis, particularly in the liver, heart, kidney and skin, and with a focus on RAAS interactions with TGFβ signaling. Targeting RAAS to combat fibrosis represents a promising therapeutic approach, particularly given the lack of strategies for treating fibrosis as its own entity, thus animal and clinical studies to examine the impact of natural and synthetic substances to alter RAAS signaling as a means to treat fibrosis are reviewed as well.

Anti-fibrotic mechanisms of angiotensin AT2 -receptor stimulation

The angiotensin AT₂ -receptor is a main receptor of the protective arm of the renin-angiotensin system. Understanding of this unconventional G-protein coupled receptor has significantly advanced during the past decade, largely because of the availability of a selective non-peptide AT₂ -receptor agonist, which allowed the conduct of a multitude of studies in animal disease models. This article reviews such preclinical studies that in their entirety provide strong evidence for an anti-fibrotic effect mediated by activation of the AT₂ -receptor. Prevention of the development of fibrosis by AT₂ -receptor stimulation has been demonstrated in lungs, heart, blood vessels, kidney, pancreas and skin. In lungs, AT₂ -receptor stimulation was even able to reverse existing fibrosis. The article further discusses intracellular signalling mechanisms mediating the AT₂ -receptor-coupled anti-fibrotic effect, including activation of phosphatases and subsequent interference with pro-fibrotic signalling pathways, induction of matrix-metalloproteinases and hetero-dimerization with the AT₁ -receptor, the TGF-βRII-receptor or the RXFP1-receptor for relaxin. Knowledge of the anti-fibrotic effects of the AT₂ -receptor is of particular relevance because drugs targeting this receptor have entered clinical development for indications involving fibrotic diseases.