Baicalein Alleviates Fibrosis and Inflammation in Scleroderma Through Regulating B Cell Abnormalities

Background Scleroderma (Systemic sclerosis, SSc) is an autoimmune disorder characterized by multisystem extensive fibrosis, vascular changes and immunological dysregulation. B cell abnormalities play an essential role in the fibrotic pathogenesis of scleroderma by promoting autoantibodies and cytokines release as well as modulating the inflammatory processes. Baicalein, a phenolic flavonoid derived from the Chinese herb Scutellaria baicalensis Georgi, has been used in the treatment of the pathological processes of various fibrotic and inflammatory diseases. Here, we aimed to investigate the effect of baicalein on the major pathological characteristics of SSc both in vitro and in vivo, including fibrosis, B cell abnormalities and inflammation. Methods The effect of baicalein on collagen accumulation and expression of fibrogenic markers in human dermal fibroblasts were analyzed. The antifibrotic features of baicalein and its mechanisms were investigated in the bleomycin (BLM)-induced dermal fibrosis mice model by histologic examination, hydroxyproline assay, enzyme-linked immunosorbent assay and flow cytometry. Results 5-120 µM baicalein significantly abrogated total collagen deposition, decreased soluble collagen secretion, and inhibited the expression of various fibrogenesis molecules, including collagen(COL)1A1, COL1A2, COL3A1, connective tissue growth factor (CTGF), fibronectin, transforming growth factor β1 (TGF-β1) and alpha-smooth muscle actin (α-SMA) in both TGF β1- and PDGF-induced human CCC-ESF-1 dermal fibroblasts. In BLM-induced dermal fibrosis mice model, 25-100 mg/kg baicalein markedly attenuated dermal thickness and collagen accumulation in dose-dependent manners. Baicalein reduced the proportion of B220+ B cells, while increased the percentage of CD27+ memory B cells in the spleen of BLM-induced mice. Consistent with reversing B cell abnormalities, baicalein treatment potently attenuated serum levels of cytokines(IL-1β, IL-2, IL-4, IL6, IL-17A, TNF-α), chemokines (MCP-1, MIP-1β) and autoantibodies (anti-Scl-70, anti-PM-Scl, anti-centromeres and anti-dsDNA). Conclusions Baicalein inhibits TGF-β1 and PDGF- mediated ECM accumulation in human dermal fibroblasts and alleviates the development of experimental dermal fibrosis by reversing B cell abnormalities, reducing autoantibody production and ameliorating inflammation. Baicalein may have the potential to be further developed as a therapeutic candidate against SSc.

Scleroderma-like Impairment in the Network of Telocytes/CD34+ Stromal Cells in the Experimental Mouse Model of Bleomycin-Induced Dermal Fibrosis

Considerable evidence accumulated over the past decade supports that telocytes (TCs)/CD34+ stromal cells represent an exclusive type of interstitial cells identifiable by transmission electron microscopy (TEM) or immunohistochemistry in various organs of the human body, including the skin. By means of their characteristic cellular extensions (telopodes), dermal TCs are arranged in networks intermingled with a multitude of neighboring cells and, hence, they are thought to contribute to skin homeostasis through both intercellular contacts and releasing extracellular vesicles. In this context, fibrotic skin lesions from patients with systemic sclerosis (SSc, scleroderma) appear to be characterized by a disruption of the dermal network of TCs, which has been ascribed to either cell degenerative processes or possible transformation into profibrotic myofibroblasts. In the present study, we utilized the well-established mouse model of bleomycin-induced scleroderma to gain further insights into the TC alterations found in cutaneous fibrosis. CD34 immunofluorescence revealed a severe impairment in the dermal network of TCs/CD34+ stromal cells in bleomycin-treated mice. CD31/CD34 double immunofluorescence confirmed that CD31−/CD34+ TC counts were greatly reduced in the skin of bleomycin-treated mice compared with control mice. Ultrastructural signs of TC injury were detected in the skin of bleomycin-treated mice by TEM. The analyses of skin samples from mice treated with bleomycin for different times by either TEM or double immunostaining and immunoblotting for the CD34/α-SMA antigens collectively suggested that, although a few TCs may transition to α-SMA+ myofibroblasts in the early disease stage, most of these cells rather undergo degeneration, and then are lost. Taken together, our data demonstrate that TC changes in the skin of bleomycin-treated mice mimic very closely those observed in human SSc skin, which makes this experimental model a suitable tool to (i) unravel the pathological mechanisms underlying TC damage and (ii) clarify the possible contribution of the TC loss to the development/progression of dermal fibrosis. In perspective, these findings may have important implications in the field of skin regenerative medicine.

Chronic overexpression of neuropeptide Y in the skin is sufficient to induce inflammation and epidermal and dermal pathology

Neuropeptide Y (NPY) is a pleiotropic peptide produced in the central nervous system and peripheral organs. Despite conjectures that NPY may have a role in skin physiology and pathology, the effects of NPY in this organ remain poorly understood. We reported that a knock-in mouse with entopic NPY overexpression exhibits significantly elevated NPY in the skin, accompanied by premature and progressive hair graying secondary to depletion of melanocyte stem cells within hair follicles. However, the question remains as to whether NPY overexpression in the skin can induce non-melanocyte pathology. In this study, we employed this mouse to investigate the consequences of skin-specific overexpression of NPY. Our findings show that chronic NPY overexpression in the skin induces dermal fibrosis and epidermal hyperkeratosis. Additionally, NPY overexpression induces significant accumulation of macrophages and regulatory T cells in the dermis. RNA sequencing of whole skin from NPY-overexpressing mice further reveals NPY-mediated transcriptional changes consistent with inflammatory processes and inflammation-associated skin changes and highlights novel cell types involved in the NPY-mediated response in the skin. Together, these results provide long-awaited evidence of NPY’s involvement in skin pathology, providing a background for defining the precise role of NPY in the regulation of cutaneous homeostasis and disease.

Loss of Protein Kinase D2 Activity Protects Against Bleomycin-induced Dermal Fibrosis in Mice

BackgroundDermal fibrosis occurs in many human diseases, particularly systemic sclerosis (SSc) where persistent inflammation leads to collagen deposition and fiber formation in skin and multiple organs. The family of protein kinase D (PKD) has been linked to inflammatory responses in various pathological conditions, however, its role in inflammation-induced dermal fibrosis has not been well defined. Here, using a murine fibrosis model that gives rise to dermal lesions similar to those in SSc, we investigated the role of PKD in dermal fibrosis in mice lacking PKD2 activity.MethodsHomozygous kinase-dead PKD2 knock-in mice (PKD2SSAA/SSAA-KI) were obtained through intercrossing mice heterozygous for PKD2S707A/S711A (PKD2SSAA). The wild-type and KI mice were subjected to repeated subcutaneous injection of bleomycin (BLM) to induce dermal inflammation and fibrosis. As controls, mice were injected with PBS. At the end of the experiment, mouse skin at the injection site was dissected, stained, and analyzed for morphological changes and expression of inflammatory and fibrotic markers. PKD-regulated signaling pathways were examined by real-time RT-qPCR and Western blotting. In a separate experiment, BLM-treated mice were administered with or without a PKD inhibitor, CRT0066101 (CRT). The effects of CRT on dermal fibrosis were analyzed similarly. The identity of the PKD expressing cells were probed using myeloid lineage markers CD45, CD68 in BLM-treated mouse tissues.ResultsDermal thickness and collagen fibers of kinase-dead PKD2-KI mice were significantly reduced in response to BLM treatment as compared to the wild-type mice. These mice also exhibited reduced α-smooth muscle actin (α-SMA) and collagen expression. At molecular levels, both transforming growth factor β1 (TGF-β1) and interleukin-6 (IL-6) mRNAs were decreased in the KI mice treated with BLM as compared to those in the wild-type mice. Similarly, CRT significantly blocked BLM-induced dermal fibrosis and inhibited the expression of α-SMA, collagen, and IL-6 expression. Further analysis indicated that PKD2 was mainly expressed in CD45+/CD68+ myeloid cells that could be recruited to the lesional sites to promote the fibrotic process of the skin in response to BLM.ConclusionsKnock-in of the kinase-dead PKD2 or inhibition of PKD activity in mice protected against BLM-induced dermal fibrosis by reducing dermis thickness and expression of fibrotic biomarkers including α-SMA, collagen, and inflammatory/fibrotic mediators including TGF-β1 and IL-6. PKD2 does this potentially through modulating the recruitment and function of myeloid cells in skin of BLM-treated mice. Overall, our study demonstrated a potential critical role of PKD catalytic activity in inflammation-induced dermal fibrosis.

Inhibition of Hsp90 Counteracts the Established Experimental Dermal Fibrosis Induced by Bleomycin

Our previous study demonstrated that heat shock protein 90 (Hsp90) is overexpressed in the involved skin of patients with systemic sclerosis (SSc) and in experimental dermal fibrosis. Pharmacological inhibition of Hsp90 prevented the stimulatory effects of transforming growth factor-beta on collagen synthesis and the development of dermal fibrosis in three preclinical models of SSc. In the next step of the preclinical analysis, herein, we aimed to evaluate the efficacy of an Hsp90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG), in the treatment of established experimental dermal fibrosis induced by bleomycin. Treatment with 17-DMAG demonstrated potent antifibrotic and anti-inflammatory properties: it decreased dermal thickening, collagen content, myofibroblast count, expression of transforming growth factor beta receptors, and pSmad3-positive cell counts, as well as leukocyte infiltration and systemic levels of crucial cytokines/chemokines involved in the pathogenesis of SSc, compared to vehicle-treated mice. 17-DMAG effectively prevented further progression and may induce regression of established bleomycin-induced dermal fibrosis to an extent comparable to nintedanib. These findings provide further evidence of the vital role of Hsp90 in the pathophysiology of SSc and characterize it as a potential target for the treatment of fibrosis with translational implications due to the availability of several Hsp90 inhibitors in clinical trials for other indications.