The IL-4 receptor α has a critical role in bone marrow-derived fibroblast activation and renal fibrosis

Iguratimod prevents renal fibrosis in unilateral ureteral obstruction model mice by suppressing M2 macrophage infiltration and macrophage-myofibroblast transition

Iguratimod is a novel synthetic, small-molecule immunosuppressive agent used to treat rheumatoid arthritis. Through ongoing exploration of its role and mechanisms of action, iguratimod has been observed to have antifibrotic effects in the lung and skin; however, its effect on renal fibrosis remains unknown. This study aimed to investigate whether iguratimod could affect renal fibrosis progression. Three different concentrations of iguratimod (30 mg/kg/day, 10 mg/kg/day, and 3 mg/kg/day) were used to intervene in unilateral ureteral obstruction (UUO) model mice. Iguratimod at 10 mg/kg/day was observed to be effective in slowing UUO-mediated renal fibrosis. In addition, stimulating bone marrow-derived macrophages with IL-4 and/or iguratimod, or with TGF-β and iguratimod or SRC inhibitors in vitro, suggested that iguratimod mitigates the progression of renal fibrosis in UUO mice, at least in part, by inhibiting the IL-4/STAT6 signaling pathway to attenuate renal M2 macrophage infiltration, as well as by impeding SRC activation to reduce macrophage-myofibroblast transition. These findings reveal the potential of iguratimod as a treatment for renal disease.

The role of macrophages in fibrosis of chronic kidney disease

Macrophages are widely distributed throughout various tissues of the body, and mounting evidence suggests their involvement in regulating the tissue microenvironment, thereby influencing disease onset and progression through direct or indirect actions. In chronic kidney disease (CKD), disturbances in renal functional homeostasis lead to inflammatory cell infiltration, tubular expansion, glomerular atrophy, and subsequent renal fibrosis. Macrophages play a pivotal role in this pathological process. Therefore, understanding their role is imperative for investigating CKD progression, mitigating its advancement, and offering novel research perspectives for fibrosis treatment from an immunological standpoint. This review primarily delves into the intrinsic characteristics of macrophages, their origins, diverse subtypes, and their associations with renal fibrosis. Particular emphasis is placed on the transition between M1 and M2 phenotypes. In late-stage CKD, there is a shift from the M1 to the M2 phenotype, accompanied by an increased prevalence of M2 macrophages. This transition is governed by the activation of the TGF-β1/SMAD3 and JAK/STAT pathways, which facilitate macrophage-to-myofibroblast transition (MMT). The tyrosine kinase Src is involved in both signaling cascades. By thoroughly elucidating macrophage functions and comprehending the modes and molecular mechanisms of macrophage-fibroblast interaction in the kidney, novel, tailored therapeutic strategies for preventing or attenuating the progression of CKD can be developed.

The renoprotective activity of amikacin-gamma-amino butyric acid-chitosan nanoparticles: a comparative study

The development of nanoparticles (NPs) with active components with upgraded stability, and prolonged release helps in enhanced tissue regeneration. In addition, NPs are feasible strategy to boost antibiotic effectiveness and reduce drug side effects. Our study focuses on the use of amikacin (AMK) and gamma amino butyric acid (GABA) unloaded combinations or loaded on chitosan nanoparticles (CSNPs) for kidney protection. The AMK-GABA-CSNPs were prepared with the ionic gelation method, the morphology was studied using transmission electron microscopy (TEM), zetasizer and the Fourier transform-infrared spectroscopy (FT-IR) spectrum of the synthesized NPs was observed. The average size of AMK-GABA-CSNPs was 77.5 ± 16.5 nm. Zeta potential was + 38.94 ± 2.65 mV. AMK-GABA-CSNPs revealed significant in vitro antioxidant, anti-coagulation, non-hemolytic properties and good cell compatibility. To compare the effects of the unloaded AMK-GABA combination and AMK-GABA-CSNPs on the renal tissue, 42 healthy Sprague-Dawley rats were divided into seven groups. G1: normal control (NC), normal saline; G2: low-dose nephrotoxic group (LDN), AMK (20 mg/kg/day; i.p.); G3: unloaded AMK (20 mg/kg/day; i.p.) and GABA (50 mg/kg/day; i.p.); G4: AMK-GABA-CSNPs (20 mg/kg/day; i.p.); G5: high-dose nephrotoxic group (HDN), AMK (30 mg/kg/day; i.p.); G6: unloaded AMK (30 mg/kg/day; i.p.) and GABA (50 mg/kg/day; i.p.) and G7: AMK-GABA-CSNPs (30 mg/kg/day; i.p.). The results showed that AMK-GABA-CSNPs formulation is superior to unloaded AMK-GABA combination as it ameliorated kidney functions, oxidative stress and displayed a significant homeostatic role via suppression of inflammatory cytokines of Th1, Th2 and Th17 types. Hence, AMK-GABA-CSNPs could afford a potential nano-based therapeutic formula for the management of AMK-nephrotoxicity.

Critical Role of histone deacetylase 3 in the regulation of kidney inflammation and fibrosis

Chronic kidney disease (CKD) is characterized by kidney inflammation and fibrosis. However, the precise mechanisms leading to kidney inflammation and fibrosis are poorly understood. Since histone deacetylase is involved in inflammation and fibrosis in other tissues, we examined the role of histone deacetylase 3 (HDAC3) in the regulation of inflammation and kidney fibrosis. HDAC3 is induced in the kidneys of animal models of CKD but mice with conditional HDAC3 deletion exhibit significantly reduced fibrosis in the kidneys compared with control mice. The expression of proinflammatory and profibrotic genes was significantly increased in the fibrotic kidneys of control mice, which was impaired in mice with HDAC3 deletion. Genetic deletion or pharmacological inhibition of HDAC3 reduced the expression of proinflammatory genes in cultured monocytes/macrophages. Mechanistically, HDAC3 deacetylates Lys122 of NF-κB p65 subunit turning on transcription. RGFP966, a selective HDAC3 inhibitor, reduced fibrosis in cells and in animal models by blocking NF-κB p65 binding to κB-containing DNA sequences. Thus, our study identified HDAC3 as a critical regulator of inflammation and fibrosis of the kidney through deacetylation of NF-κB unlocking its transcriptional activity. Hence, targeting HDAC3 could serve as a novel therapeutic strategy for CKD.

Remimazolam attenuates inflammation and kidney fibrosis following folic acid injury

The transition of acute kidney injury (AKI) to chronic kidney disease (CKD) is characterized by intense inflammation and progressive fibrosis. Remimazolam is widely used for procedural sedation in intensive care units, such as AKI patients. Remimazolam has been shown to possess anti-inflammatory and organ-protective properties. However, the role of remimazolam in inflammation and renal fibrosis following AKI remains unclear. Here, we explored the effects of remimazolam on the inflammatory response and kidney fibrogenesis of mice subjected to folic acid (FA) injury. Our results showed that remimazolam treatment alleviated kidney damage and dysfunction. Mice treated with remimazolam presented less collagen deposition in FA-injured kidneys compared with FA controls, which was accompanied by a reduction of extracellular matrix proteins accumulation and fibroblasts activation. Furthermore, remimazolam treatment reduced inflammatory cells infiltration into the kidneys of mice with FA injury and inhibited proinflammatory or profibrotic molecules expression. Finally, remimazolam treatment impaired the activation of bone marrow-derived fibroblasts and blunted the transformation of macrophages to myofibroblasts in FA nephropathy. Additionally, the benzodiazepine receptor antagonist PK-11195 partially reversed the protective effect of remimazolam on the FA-injured kidneys. Overall, remimazolam attenuates the inflammatory response and renal fibrosis development following FA-induced AKI, which may be related to the peripheral benzodiazepine receptor pathway.

Immunosuppressive tumor microenvironment and uterine fibroids: Role in collagen synthesis

Uterine fibroids (UF), also called uterine leiomyoma, is one of the most prevalent uterine tumors. UF represents a serious women's health global problem with a significant physical, emotional, and socioeconomic impact. Risk factors for UF include racial disparities, age, race, hormonal factors, obesity, and lifestyle (diet, physical activity, and stress. There are several biological contributors to UF pathogenesis such as cellular proliferation, angiogenesis, and extracellular matrix (ECM) accumulation. This review addresses tumor immune microenvironment as a novel mediator of ECM deposition. Polarization of immune microenvironment towards the immunosuppressive phenotype has been associated with ECM deposition. Immunosuppressive cells include M2 macrophage, myeloid-derived suppressor cells (MDSCs), and Th17 cells, and their secretomes include interleukin 4 (IL-4), IL-10, IL-13, IL-17, IL-22, arginase 1, and transforming growth factor-beta (TGF-β1). The change in the immune microenvironment not only increase tumor growth but also aids in collagen synthesis and ECM disposition, which is one of the main hallmarks of UF pathogenesis. This review invites further investigations on the change in the UF immune microenvironment as well as a novel targeting approach instead of the traditional UF hormonal and supportive treatment.

M2a macrophages regulate fibrosis and affect the outcome after stroke via PU.1/mTOR pathway in fibroblasts

The moderate formation of the fibrotic scar plays an important role in functional recovery after stroke. M2a macrophages have been identified as an important source of early fibrosis after cerebral ischemia. However, the underlying mechanisms by which macrophages interact with fibroblasts in this context remain largely unknown. Therefore, our study aimed to further investigate the potential mechanisms underlying the effects of macrophages on fibroblasts following ischemic stroke. In vitro and in vivo, recombinant rat interleukin 4 (IL4) was used to induce macrophages to polarize into M2a macrophages. In vitro, primary Sprague-Dawley newborn rat meningeal-derived fibroblasts were treated with PU.1 knockdown, the PU.1 inhibitor DB1976 or the mTOR inhibitor rapamycin, which were then co-cultured with M2a macrophage conditioned medium (MCM). In vivo, Sprague-Dawley adult rats were infected with negative control adenoviruses or PU.1-shRNA adenoviruses. Ten days after infection, an injury model of middle cerebral artery occlusion/reperfusion (MCAO/R) was constructed. Subsequently, IL4 was injected intracerebroventricularly to induce M2a macrophages polarization. In vitro, M2a MCM upregulated PU.1 expression and promoted the differentiation, proliferation, migration and extracellular matrix generation of fibroblasts, which could be reversed by treatment with the PU.1 inhibitor DB1976 or PU.1 knockdown. In vivo, PU.1 expression in fibroblasts was increased within ischemic core following MCAO/R, and this upregulation was further enhanced by exposure to IL4. Treatment with IL4 promoted fibrosis, increased angiogenesis, reduced apoptosis and infarct volume, as well as mitigated neurological deficits after MCAO/R, and these effects could be reversed by PU.1 knockdown. Furthermore, both in vivo and in vitro studies showed that IL4 treatment increased the levels of phosphorylated Akt and mTOR proteins, which were markedly decreased by PU.1 knockdown. Additionally, the use of an mTOR inhibitor rapamycin obviously suppressed the migration and differentiation of fibroblasts, and Col1 synthesis. In conclusion, our findings suggest for the first time that M2a macrophages, at least in part, regulate fibrosis and affect the outcome after cerebral ischemic stroke via the PU.1/mTOR signaling pathway in fibroblasts.

Macrophages polarization in renal inflammation and fibrosis animal models (Review)

Chronic kidney disease (CKD) is a significant public health concern. Renal fibrosis is the final common pathway in the progression of kidney diseases, irrespective of the initial injury. Substantial evidence underscores the pivotal role of renal inflammation in the genesis of renal fibrosis. The presence of macrophages within normal renal tissue is significantly increased within diseased renal tissue, indicative of their crucial regulatory function in inflammation and fibrosis. Macrophages manifest a high degree of heterogeneity, exhibiting distinct phenotypic and functional traits in response to diverse stimuli within the local microenvironment in various types of kidney diseases. Broadly, macrophages are categorized into two principal groups: Classically activated, designated as M1 macrophages and alternatively activated, designated as M2 macrophages. A number of experimental models are widely used to study the underlying mechanisms driving renal inflammation and fibrosis progression. The present review delineated the phenotypic and functional attributes of macrophages present in diverse induced models, analyzing their disposition in relation to M1 and M2 polarization states.

Inflammatory Markers Involved in the Pathogenesis of Dupuytren's Contracture

Dupuytren's disease is a common fibroproliferative disease that can result in debilitating hand deformities. Partial correction and return of deformity are common with surgical or clinical treatments at present. While current treatments are limited to local procedures for relatively late effects of the disease, the pathophysiology of this connective tissue disorder is associated with both local and systemic processes (e.g., fibrosis, inflammation). Hence, a better understanding of the systemic circulation of Dupuytren related cytokines and growth factors may provide important insights into disease progression. In addition, systemic biomarker analysis could yield new concepts for treatments of Dupuytren that attenuate circulatory factors (e.g., anti-inflammatory agents, neutralizing antibodies). Progress in the development of any disease modifying biologic treatment for Dupuytren has been hampered by the lack of clinically useful biomarkers. The characterization of nonsurgical Dupuytren biomarkers will permit disease staging from diagnostic and prognostic perspectives, as well as allows evaluation of biologic responses to treatment. Identification of such markers may transcend their use in Dupuytren treatment, because fibrotic biological processes fundamental to Dupuytren are relevant to fibrosis in many other connective tissues and organs with collagen-based tissue compartments. There is a wide range of potential Dupuytren biomarker categories that could be informative, including disease determinants linked to genetics, collagen metabolism, as well as immunity and inflammation (e.g., cytokines, chemokines). This narrative review provides a broad overview of previous studies and emphasizes the importance of inflammatory mediators as candidate circulating biomarkers for monitoring Dupuytren's disease.

Precisely Regulating M2 Subtype Macrophages for Renal Fibrosis Resolution

Macrophages are central to the pathogenesis of kidney disease and serve as an effective therapeutic target for kidney injury and fibrosis. Among them, M2-type macrophages have double-edged effects regarding anti-inflammatory effects and tissue repair. Depending on the polarization of the M2 subtypes (M2a or M2c) in the diseased microenvironment, they can either mediate normal tissue repair or drive tissue fibrosis. In renal fibrosis, M2a promotes disease progression through macrophage-to-myofibroblast transition (MMT) cells, while M2c possesses potent anti-inflammatory functions and promotes tissue repair, and is inhibited. The mechanisms underlying this differentiation are complex and are currently not well understood. Therefore, in this study, we first confirmed that M2a-derived MMT cells are responsible for the development of renal fibrosis and demonstrated that the intensity of TGF-β signaling is a major factor determining the differential polarization of M2a and M2c. Under excessive TGF-β stimulation, M2a undergoes a process known as MMT cells, whereas moderate TGF-β stimulation favors the polarization of M2c phenotype macrophages. Based on these findings, we employed targeted nanotechnology to codeliver endoplasmic reticulum stress (ERS) inhibitor (Ceapin 7, Cea or C) and conventional glucocorticoids (Dexamethasone, Dex or D), precisely modulating the ATF6/TGF-β/Smad3 signaling axis within macrophages. This approach calibrated the level of TGF-β stimulation on macrophages, promoting their polarization toward the M2c phenotype and suppressing excessive MMT polarization. The study indicates that the combination of ERS inhibitor and a first-line anti-inflammatory drug holds promise as an effective therapeutic approach for renal fibrosis resolution.

JMJD3 ablation in myeloid cells confers renoprotection in mice with DOCA/salt-induced hypertension

Hypertension-induced renal injury is characterized by robust inflammation and tubulointerstitial fibrosis. Jumonji domain containing-3 (JMJD3) is closely linked with inflammatory response and fibrogenesis. Here we examined the effect of myeloid JMJD3 ablation on kidney inflammation and fibrosis in deoxycorticosterone acetate (DOCA)/salt hypertension. Our results showed that JMJD3 is notably induced in the kidneys with hypertensive injury. DOCA/salt stress causes an elevation in blood pressure that was no difference between myeloid specific JMJD3-deficient mice and wild-type control mice. Compared with wild-type control mice, myeloid JMJD3 ablation ameliorated kidney function and injury of mice in response to DOCA/salt challenge. Myeloid JMJD3 ablation attenuated collagen deposition, extracellular matrix proteins expression, and fibroblasts activation in injured kidneys following DOCA/salt treatment. Furthermore, myeloid JMJD3 ablation blunts inflammatory response in injured kidneys after DOCA/salt stress. Finally, myeloid JMJD3 ablation precluded myeloid myofibroblasts activation and protected against macrophages to myofibroblasts transition in injured kidneys. These beneficial effects were accompanied by reduced expression of interferon regulator factor 4. In summary, JMJD3 ablation in myeloid cells reduces kidney inflammation and fibrosis in DOCA salt-induced hypertension. Inhibition of myeloid JMJD3 may be a novel potential therapeutic target for hypertensive nephropathy. Myeloid JMJD3 deficiency reduces inflammatory response, myeloid fibroblasts activation, macrophages to myofibroblasts transition, and delays kidney fibrosis progression.

Interferon regulatory factor 4 deletion protects against kidney inflammation and fibrosis in deoxycorticosterone acetate/salt hypertension

BACKGROUND

Inflammation and renal interstitial fibrosis are the main pathological features of hypertensive nephropathy. Interferon regulatory factor 4 (IRF-4) has an important role in the pathogenesis of inflammatory and fibrotic diseases. However, its role in hypertension-induced renal inflammation and fibrosis remains unexplored.

METHOD AND RESULTS

We showed that deoxycorticosterone acetate (DOCA)-salt resulted in an elevation of blood pressure and that there was no difference between wild-type and IRF-4 knockout mice. IRF-4 -/- mice presented less severe renal dysfunction, albuminuria, and fibrotic response after DOCA-salt stress compared with wild-type mice. Loss of IRF-4 inhibited extracellular matrix protein deposition and suppressed fibroblasts activation in the kidneys of mice subjected to DOCA-salt treatment. IRF-4 disruption impaired bone marrow-derived fibroblasts activation and macrophages to myofibroblasts transition in the kidneys in response to DOCA-salt treatment. IRF-4 deletion impeded the infiltration of inflammatory cells and decreased the production of proinflammatory molecules in injured kidneys. IRF-4 deficiency activated phosphatase and tensin homolog and weakened phosphoinositide-3 kinase/AKT signaling pathway in vivo or in vitro . In cultured monocytes, TGFβ1 also induced expression of fibronectin and α-smooth muscle actin and stimulated the transition of macrophages to myofibroblasts, which was blocked in the absence of IRF-4. Finally, macrophages depletion blunted macrophages to myofibroblasts transition, inhibited myofibroblasts accumulation, and ameliorated kidney injury and fibrosis.

CONCLUSION

Collectively, IRF-4 plays a critical role in the pathogenesis of kidney inflammation and fibrosis in DOCA-salt hypertension.

Enhancer of zeste homolog 2 promotes renal fibrosis after acute kidney injury by inducing epithelial-mesenchymal transition and activation of M2 macrophage polarization

Long-term follow-up data indicates that 1/4 patients with acute kidney injury (AKI) will develop to chronic kidney disease (CKD). Our previous studies have demonstrated that enhancer of zeste homolog 2 (EZH2) played an important role in AKI and CKD. However, the role and mechanisms of EZH2 in AKI-to-CKD transition are still unclear. Here, we demonstrated EZH2 and H3K27me3 highly upregulated in kidney from patients with ANCA-associated glomerulonephritis, and expressed positively with fibrotic lesion and negatively with renal function. Conditional EZH2 deletion or pharmacological inhibition with 3-DZNeP significantly improved renal function and attenuated pathological lesion in ischemia/reperfusion (I/R) or folic acid (FA) mice models (two models of AKI-to-CKD transition). Mechanistically, we used CUT & Tag technology to verify that EZH2 binding to the PTEN promoter and regulating its transcription, thus regulating its downstream signaling pathways. Genetic or pharmacological depletion of EZH2 upregulated PTEN expression and suppressed the phosphorylation of EGFR and its downstream signaling ERK1/2 and STAT3, consequently alleviating the partial epithelial-mesenchymal transition (EMT), G2/M arrest, and the aberrant secretion of profibrogenic and proinflammatory factors in vivo and vitro experiments. In addition, EZH2 promoted the EMT program induced loss of renal tubular epithelial cell transporters (OAT1, ATPase, and AQP1), and blockade of EZH2 prevented it. We further co-cultured macrophages with the medium of human renal tubular epithelial cells treated with H₂O₂ and found macrophages transferred to M2 phenotype, and EZH2 could regulate M2 macrophage polarization through STAT6 and PI3K/AKT pathways. These results were further verified in two mice models. Thus, targeted inhibition of EZH2 might be a novel therapy for ameliorating renal fibrosis after acute kidney injury by counteracting partial EMT and blockade of M2 macrophage polarization.

Kidney fibrosis: from mechanisms to therapeutic medicines

Chronic kidney disease (CKD) is estimated to affect 10-14% of global population. Kidney fibrosis, characterized by excessive extracellular matrix deposition leading to scarring, is a hallmark manifestation in different progressive CKD; However, at present no antifibrotic therapies against CKD exist. Kidney fibrosis is identified by tubule atrophy, interstitial chronic inflammation and fibrogenesis, glomerulosclerosis, and vascular rarefaction. Fibrotic niche, where organ fibrosis initiates, is a complex interplay between injured parenchyma (like tubular cells) and multiple non-parenchymal cell lineages (immune and mesenchymal cells) located spatially within scarring areas. Although the mechanisms of kidney fibrosis are complicated due to the kinds of cells involved, with the help of single-cell technology, many key questions have been explored, such as what kind of renal tubules are profibrotic, where myofibroblasts originate, which immune cells are involved, and how cells communicate with each other. In addition, genetics and epigenetics are deeper mechanisms that regulate kidney fibrosis. And the reversible nature of epigenetic changes including DNA methylation, RNA interference, and chromatin remodeling, gives an opportunity to stop or reverse kidney fibrosis by therapeutic strategies. More marketed (e.g., RAS blockage, SGLT2 inhibitors) have been developed to delay CKD progression in recent years. Furthermore, a better understanding of renal fibrosis is also favored to discover biomarkers of fibrotic injury. In the review, we update recent advances in the mechanism of renal fibrosis and summarize novel biomarkers and antifibrotic treatment for CKD.

Mesenchymal stem cells in fibrotic diseases-the two sides of the same coin

Fibrosis is caused by extensive deposition of extracellular matrix (ECM) components, which play a crucial role in injury repair. Fibrosis attributes to ~45% of all deaths worldwide. The molecular pathology of different fibrotic diseases varies, and a number of bioactive factors are involved in the pathogenic process. Mesenchymal stem cells (MSCs) are a type of multipotent stem cells that have promising therapeutic effects in the treatment of different diseases. Current updates of fibrotic pathogenesis reveal that residential MSCs may differentiate into myofibroblasts which lead to the fibrosis development. However, preclinical and clinical trials with autologous or allogeneic MSCs infusion demonstrate that MSCs can relieve the fibrotic diseases by modulating inflammation, regenerating damaged tissues, remodeling the ECMs, and modulating the death of stressed cells after implantation. A variety of animal models were developed to study the mechanisms behind different fibrotic tissues and test the preclinical efficacy of MSC therapy in these diseases. Furthermore, MSCs have been used for treating liver cirrhosis and pulmonary fibrosis patients in several clinical trials, leading to satisfactory clinical efficacy without severe adverse events. This review discusses the two opposite roles of residential MSCs and external MSCs in fibrotic diseases, and summarizes the current perspective of therapeutic mechanism of MSCs in fibrosis, through both laboratory study and clinical trials.

Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism

Fibrotic ligament diseases (FLDs) are diseases caused by the pathological accumulation of periarticular fibrotic tissue, leading to functional disability around joint and poor life quality. Relaxin (RLX) has been reported to be involved in the development of fibrotic lung and liver diseases. Previous studies have shown that RLX can block pro-fibrotic process by reducing the excess extracellular matrix (ECM) formation and accelerating collagen degradation in vitro and in vivo. Recent studies have shown that RLX can attenuate connective tissue fibrosis by suppressing TGF-β/Smads signaling pathways to inhibit the activation of myofibroblasts. However, the specific roles and mechanisms of RLX in FLDs remain unclear. Therefore, in this review, we confirmed the protective effect of RLX in FLDs and summarized its mechanism including cells, key cytokines and signaling pathways involved. In this article, we outline the potential therapeutic role of RLX and look forward to the application of RLX in the clinical translation of FLDs.

The IL-4/IL-13 signaling axis promotes prostatic fibrosis

Background

Lower urinary tract symptoms (LUTS) are a costly and pervasive medical problem for millions of aging men. Recent studies have showed that peri-urethral tissue fibrosis is an untreated pathobiology contributing to LUTS. Fibrosis results from excessive extracellular matrix deposition which increases transition zone and peri-urethral tissue stiffness and compromises prostatic urethral flexibility and compliance, producing urinary obstructive symptoms. Inflammatory cells, including neutrophils, macrophages, and T-lymphocytes, secrete a medley of pro-fibrotic proteins into the prostatic microenvironment, including IFNγ, TNFα, CXC-type chemokines, and interleukins, all of which have been implicated in inflammation-mediated fibrosis. Among these, IL-4 and IL-13 are of particular interest because they share a common signaling axis that, as shown here for the first time, promotes the expression and maintenance of IL-4, IL-13, their cognate receptors, and ECM components by prostate fibroblasts, even in the absence of immune cells. Based on studies presented here, we hypothesize that the IL-4/IL-13 axis promotes prostate fibroblast activation to ECM-secreting cells.

Methods

N1 or SFT1 immortalized prostate stromal fibroblasts were cultured and treated, short- or long-term, with pro-fibrotic proteins including IL-4, IL-13, TGF-β, TNF-α, IFNγ, with or without prior pre-treatment with antagonists or inhibitors. Protein expression was assessed by immunohistochemistry, immunofluorescence, ELISA, immunoblot, or Sircoll assays. Transcript expression levels were determined by qRT-PCR. Intact cells were counted using WST assays.

Results

IL-4Rα, IL-13Rα1, and collagen are concurrently up-regulated in human peri-urethral prostate tissues from men with LUTS. IL-4 and IL-13 induce their own expression as well as that of their cognate receptors, IL-4Rα and IL-13Rα1. Low concentrations of IL-4 or IL-13 act as cytokines to promote prostate fibroblast proliferation, but higher (>40ng/ml) concentrations repress cellular proliferation. Both IL-4 and IL-13 robustly and specifically promote collagen transcript and protein expression by prostate stromal fibroblasts in a JAK/STAT-dependent manner. Moreover, IL-4 and IL-13-mediated JAK/STAT signaling is coupled to activation of the IL-4Rα receptor.

Conclusions

Taken together, these studies show that IL-4 and IL-13 signal through the IL-4Rα receptor to activate JAK/STAT signaling, thereby promoting their own expression, that of their cognate receptors, and collagens. These finding suggest that the IL-4/IL-13 signaling axis is a powerful, but therapeutically targetable, pro-fibrotic mechanism in the lower urinary tract.

Jmjd3/IRF4 axis aggravates myeloid fibroblast activation and m2 macrophage to myofibroblast transition in renal fibrosis

Renal fibrosis commonly occurs in the process of chronic kidney diseases. Here, we explored the role of Jumonji domain containing 3 (Jmjd3)/interferon regulatory factor 4 (IRF4) axis in activation of myeloid fibroblasts and transition of M2 macrophages into myofibroblasts transition (M2MMT) in kidney fibrosis. In mice, Jmjd3 and IRF4 were highly induced in interstitial cells of kidneys with folic acid or obstructive injury. Jmjd3 deletion in myeloid cells or Jmjd3 inhibitor reduced the levels of IRF4 in injured kidneys. Myeloid Jmjd3 depletion impaired bone marrow-derived fibroblasts activation and M2MMT in folic acid or obstructive nephropathy, resulting in reduction of extracellular matrix (ECM) proteins expression, myofibroblasts formation and renal fibrosis progression. Pharmacological inhibition of Jmjd3 also prevented myeloid fibroblasts activation, M2MMT, and kidney fibrosis development in folic acid nephropathy. Furthermore, IRF4 disruption inhibited myeloid myofibroblasts accumulation, M2MMT, ECM proteins accumulation, and showed milder fibrotic response in obstructed kidneys. Bone marrow transplantation experiment showed that wild-type mice received IRF4^-/- bone marrow cells presented less myeloid fibroblasts activation in injured kidneys and exhibited much less kidney fibrosis after unilateral ureteral obstruction. Myeloid Jmjd3 deletion or Jmjd3 inhibitor attenuated expressions of IRF4, α-smooth muscle actin and fibronectin and impeded M2MMT in cultured monocytes exposed to IL-4. Conversely, overexpression IRF4 abrogated the effect of myeloid Jmjd3 deletion on M2MMT. Thus, Jmjd3/IRF4 signaling has a crucial role in myeloid fibroblasts activation, M2 macrophages to myofibroblasts transition, extracellular matrix protein deposition, and kidney fibrosis progression.

Pharmacological Inhibition of S100A4 Attenuates Fibroblast Activation and Renal Fibrosis

The TGF-β/Smad3 signaling pathway is an important process in the pathogenesis of kidney fibrosis. However, the molecular mechanisms are not completely elucidated. The current study examined the functional role of S100A4 in regulating TGF-β/Smad3 signaling in fibroblast activation and kidney fibrosis development. S100A4 was upregulated in the kidney in a murine model of renal fibrosis induced by folic acid nephropathy. Further, S100A4 was predominant in the tubulointerstitial cells of the kidney. Pharmacological inhibition of S100A4 with niclosamide significantly attenuated fibroblast activation, decreased collagen content, and reduced extracellular matrix protein expression in folic acid nephropathy. Overexpression of S100A4 in cultured renal fibroblasts significantly facilitated TGF-β1-induced activation of fibroblasts by increasing the expression of α-SMA, collagen-1 and fibronectin. In contrast, S100A4 knockdown prevented TGF-β1-induced activation of fibroblast and transcriptional activity of Smad3. Mechanistically, S100A4 interacts with Smad3 to stabilize the Smad3/Smad4 complex and promotes their translocation to the nucleus. In conclusion, S100A4 facilitates TGF-β signaling via interaction with Smad3 and promotes kidney fibrosis development. Manipulating S100A4 may provide a beneficial therapeutic strategy for chronic kidney disease.

The role of the macrophage-to-myofibroblast transition in renal fibrosis

Renal fibrosis causes structural and functional impairment of the kidney, which is a dominant component of chronic kidney disease. Recently, a novel mechanism, macrophage-to-myofibroblast transition (MMT), has been identified as a crucial component in renal fibrosis as a response to chronic inflammation. It is a process by which bone marrow-derived macrophages differentiate into myofibroblasts during renal injury and promote renal fibrosis. Here, we summarized recent evidence and mechanisms of MMT in renal fibrosis. Understanding this phenomenon and its underlying signal pathway would be beneficial to find therapeutic targets for renal fibrosis in chronic kidney disease.

Pharmacological Inhibition of STING/TBK1 Signaling Attenuates Myeloid Fibroblast Activation and Macrophage to Myofibroblast Transition in Renal Fibrosis

Renal fibrosis is an important pathological biomarker of chronic kidney disease (CKD). Stimulator of interferon genes/TANK binding kinase 1 (STING/TBK1) axis has been identified as the main regulator of innate immune response and closely related to fibrotic disorder. However, the role of STING/TBK1 signaling pathway in kidney fibrosis is still unknown. In this study, we investigated the effect of pharmacological inhibition of STING/TBK1 signaling on renal fibrosis induced by folic acid (FA). In mice, TBK1 was significantly activated in interstitial cells of FA-injured kidneys, which was markedly inhibited by H-151 (a STING inhibitor) treatment. Specifically, pharmacological inhibition of STING impaired bone marrow-derived fibroblasts activation and macrophage to myofibroblast transition in folic acid nephropathy, leading to reduction of extracellular matrix proteins expression, myofibroblasts formation and development of renal fibrosis. Furthermore, pharmacological inhibition of TBK1 by GSK8612 reduced myeloid myofibroblasts accumulation and impeded macrophage to myofibroblast differentiation, resulting in less deposition of extracellular matrix protein and less severe fibrotic lesion in FA-injured kidneys. In cultured mouse bone marrow-derived monocytes, TGF-β1 activated STING/TBK1 signaling. This was abolished by STING or TBK1 inhibitor administration. In addition, GSK8612 treatment decreased levels of α-smooth muscle actin and extracellular matrix proteins and prevents bone marrow-derived macrophages to myofibroblasts transition in vitro. Collectively, our results revealed that STING/TBK1 signaling has a critical role in bone marrow-derived fibroblast activation, macrophages to myofibroblasts transition, and kidney fibrosis progression.

Macrophages in the kidney in health, injury and repair

Macrophages are a key component of the renal mononuclear phagocyte system, playing a major role in defense against infection, renal injury and repair. Yolk sac macrophage precursors seed the early embryonic kidney and are important for renal development. Later, renal macrophages are derived from hematopoietic stem cells and in adult life, there is a significant contribution from circulating monocytes, which is enhanced in response to infection or injury. Macrophages are highly plastic and can alter their phenotype in response to cues from parenchymal renal cells. Danger-associated molecules released from injured kidney cells may activate macrophages toward a pro-inflammatory phenotype, mediating further recruitment of inflammatory cells, exacerbating renal injury and activating renal fibroblasts to promote scarring. In acute kidney injury, once the injury stimulus has abated, macrophages may adopt a more reparative phenotype, dampening the immune response and promoting repair of renal tissue. However, in chronic kidney disease ongoing activation of pro-inflammatory monocytes and persistence of reparative macrophages leads to glomerulosclerosis and tubulointerstitial fibrosis, the hallmarks of end-stage kidney disease. Several strategies to inhibit the recruitment, activation and secretory products of pro-inflammatory macrophages have proven beneficial in pre-clinical models and are now undergoing clinical trials in patients with kidney disease. In addition, macrophages may be utilized in cell therapy as a "Trojan Horse" to deliver targeted therapies to the kidney. Single-cell RNA sequencing has identified a previously unappreciated spectrum of macrophage phenotypes, which may be selectively present in injury or repair, and ongoing functional analyses of these subsets may identify more specific targets for therapeutic intervention.

Neutrophil Gelatinase-Associated Lipocalin From Macrophages Plays a Critical Role in Renal Fibrosis Via the CCL5 (Chemokine Ligand 5)-Th2 Cells-IL4 (Interleukin 4) Pathway

NGAL (neutrophil gelatinase-associated lipocalin; or lipocalin 2, Lcn2) is a novel mineralocorticoid target in the cardiovascular system. We showed that Lcn2 gene invalidation protects against proteinuria and renal injury upon mineralocorticoid excess and we hypothesized that NGAL produced from macrophages promotes the expression of chemoattractant molecules involved these renal lesions. The role of NGAL was analyzed using myeloid-specific (MΦ KO NGAL) Lcn2 knockout mice challenged with uni-nephrectomy, aldosterone, and salt (NAS) for 6 weeks. The role of the CCL5 (chemokine ligand 5) and IL4 (interleukin 4) in kidney fibrosis was studied by administration of the CCL5 receptor antagonist maraviroc or by injections of an anti-IL4 neutralizing antibody. In CTL mice, NAS increased the renal expression of extracellular matrix proteins, such as collagen I, αSMA, and fibronectin associated with interstitial fibrosis which were blunted in MΦ KO NGAL mice. The expression of CCL5 was blunted in sorted macrophages from MΦ KO NGAL mice challenged by NAS and in macrophages obtained from KO NGAL mice and challenged ex vivo with aldosterone and salt. The pharmacological blockade of the CCL5 receptor reduced renal fibrosis and the CD4⁺ Th cell infiltration induced by NAS. Neutralization of IL4 in NAS mice blunted kidney fibrosis and the overexpression of profibrotic proteins, such as collagen I, αSMA, and fibronectin. In conclusion, NGAL produced by macrophages plays a critical role in renal fibrosis and modulates the CCL5/IL4 pathway in mice exposed to mineralocorticoid excess.

STAT6 Deficiency Attenuates Myeloid Fibroblast Activation and Macrophage Polarization in Experimental Folic Acid Nephropathy

Renal fibrosis is a pathologic feature of chronic kidney disease, which can lead to end-stage kidney disease. Myeloid fibroblasts play a central role in the pathogenesis of renal fibrosis. However, the molecular mechanisms pertaining to myeloid fibroblast activation remain to be elucidated. In the present study, we examine the role of signal transducer and activator of transcription 6 (STAT6) in myeloid fibroblast activation, macrophage polarization, and renal fibrosis development in a mouse model of folic acid nephropathy. STAT6 is activated in the kidney with folic acid nephropathy. Compared with folic-acid-treated wild-type mice, STAT6 knockout mice had markedly reduced myeloid fibroblasts and myofibroblasts in the kidney with folic acid nephropathy. Furthermore, STAT6 knockout mice exhibited significantly less CD206 and PDGFR-β dual-positive fibroblast accumulation and M2 macrophage polarization in the kidney with folic acid nephropathy. Consistent with these findings, STAT6 knockout mice produced less extracellular matrix protein, exhibited less severe interstitial fibrosis, and preserved kidney function in folic acid nephropathy. Taken together, these results have shown that STAT6 plays a critical role in myeloid fibroblasts activation, M2 macrophage polarization, extracellular matrix protein production, and renal fibrosis development in folic acid nephropathy. Therefore, targeting STAT6 may provide a novel therapeutic strategy for fibrotic kidney disease.

IRF-4 deficiency reduces inflammation and kidney fibrosis after folic acid-induced acute kidney injury

The chronic phase following toxin-induced acute kidney injury (AKI) is characterized by robust inflammation and progressive kidney fibrosis. Interferon regulatory factor 4 (IRF-4) is a type of multifunctional transcription factor that has been deeply linked to inflammation and fibrotic diseases. However, the role of IRF-4 in kidney damage and renal fibrosis after toxin-induced AKI remain to be explored. In this work, we examined the effect of IRF-4 deficiency on inflammation and kidney fibrosis in an AKI-chronic kidney disease (CKD) transition model induced by folic acid (FA) injury. We showed that FA treatment resulted in severe acute tubular injury followed by inflammatory reaction and interstitial fibrosis in wild-type mice. A sharp elevation of IRF-4 levels was observed in FA-injured kidneys. IRF-4 knockout led to a substantial reduction of extracellular matrix (ECM) proteins deposition and inhibited myofibroblasts transformation in the kidneys of mice subjected to FA treatment. In addition, IRF-4 ablation impaired F4/80+ macrophages and CD3+ T lymphocytes infiltration into the FA-injured kidneys. Loss of IRF-4 reduced the production of inflammatory molecules such as CXCL16, IL-18, IL-6, and TGF-β1 in the kidneys in response to FA stress. Following FA injury, the kidneys of IRF-4 knockout mice had fewer bone marrow-derived myofibroblasts than wild-type controls. Moreover, IRF-4 disruption inhibited macrophages to myofibroblasts differentiation in the kidneys in response to FA stimuli. In vitro, IL-4 stimulated expression of α-smooth muscle actin and ECM proteins and promoted M2 macrophages to myofibroblasts transition in mouse bone marrow-derived monocytes, which was abolished in the absence of IRF-4. Thus, we identified an important role of IRF-4 in the pathogenesis of progressive CKD following FA-induced AKI.

Identification of circular RNA expression profiles in renal fibrosis induced by obstructive injury

INTRODUCTION

Advancing renal fibrosis is the common histopathological feature of chronic obstructive nephropathy, representing the final pathway of nearly all chronic and progressive nephropathies. Increasing evidences suggest that circular RNAs (circRNAs) are crucial regulatory molecules present at virtually every level of the cellular pathophysiological process. Nonetheless, there are a few evidences for the role of circRNAs in renal fibrosis induced by obstructive nephropathy.

AIMS

We performed RNA-seq analysis to analyze the expression profiles of circRNAs in the obstructed kidneys to identify the potential circRNAs and their network.

METHODS

With silk ligated the left ureter to establish a mice unilateral ureteral obstruction (UUO) model. Renal tissue circRNAs were obtained and were screened by a circRNA microarray. The circRNA-miRNA-mRNA regulatory network and the target genes were visualized using Cytoscape software.

RESULTS

The microarray results showed that 5454 and 2935 circRNAs were detected in the control and UUO group, respectively. There were 605 circRNAs up-regulated and 745 circRNAs down-regulated in the obstructive kidneys. The top 5 up-regulated and down-regulated circRNAs were chosen for predicting the circRNA/miRNA/target mRNAs triple network. The GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis showed that these circRNAs and the triple network were enriched in the process of apoptosis, p53 signaling pathway, cell growth and cell death, which might participate in the pathogenesis of obstructive nephrology.

CONCLUSION

Our results show that the dis-regulated circRNAs might play crucial roles in the pathogenesis of obstructive nephropathy, which proceeds to identify novel therapeutic targets for chronic kidney disease.

Pharmacological Inhibition of STAT6 Ameliorates Myeloid Fibroblast Activation and Alternative Macrophage Polarization in Renal Fibrosis

A hallmark of chronic kidney disease is renal fibrosis, which can result in progressive loss of kidney function. Currently, there is no effective therapy for renal fibrosis. Therefore, there is an urgent need to identify potential drug targets for renal fibrosis. In this study, we examined the effect of a selective STAT6 inhibitor, AS1517499, on myeloid fibroblast activation, macrophage polarization, and development of renal fibrosis in two experimental murine models. To investigate the effect of STAT6 inhibition on myeloid fibroblast activation, macrophage polarization, and kidney fibrosis, wild-type mice were subjected to unilateral ureteral obstruction or folic acid administration and treated with AS1517499. Mice treated with vehicle were used as control. At the end of experiments, kidneys were harvested for analysis of myeloid fibroblast activation, macrophage polarization, and renal fibrosis and function. Unilateral ureteral obstruction or folic acid administration induced STAT6 activation in interstitial cells of the kidney, which was significantly abolished by AS1517499 treatment. Mice treated with AS1517499 accumulated fewer myeloid fibroblasts and myofibroblasts in the kidney with ureteral obstruction or folic acid nephropathy compared with vehicle-treated mice. Moreover, AS1517499 significantly suppressed M2 macrophage polarization in the injured kidney. Furthermore, AS1517499 markedly reduced the expression levels of extracellular matrix proteins, and development of kidney fibrosis and dysfunction. These findings suggest that AS1517499 inhibits STAT6 activation, suppresses myeloid fibroblast activation, reduces M2 macrophage polarization, attenuates extracellular matrix protein production, and preserves kidney function. Therefore, targeting STAT6 with AS1517499 is a novel therapeutic approach for chronic kidney disease.

The Role of Macrophages in Kidney Fibrosis

The phenotypic heterogeneity and functional diversity of macrophages confer on them complexed roles in the development and progression of kidney diseases. After kidney injury, bone marrow-derived monocytes are rapidly recruited to the glomerulus and tubulointerstitium. They are activated and differentiated on site into pro-inflammatory M1 macrophages, which initiate Th1-type adaptive immune responses and damage normal tissues. In contrast, anti-inflammatory M2 macrophages induce Th2-type immune responses, secrete large amounts of TGF-β and anti-inflammatory cytokines, transform into αSMA+ myofibroblasts in injured kidney, inhibit immune responses, and promote wound healing and tissue fibrosis. Previous studies on the role of macrophages in kidney fibrosis were mainly focused on inflammation-associated injury and injury repair. Apart from macrophage-secreted profibrotic cytokines, such as TGF-β, evidence for a direct contribution of macrophages to kidney fibrosis is lacking. However, under inflammatory conditions, Wnt ligands are derived mainly from macrophages and Wnt signaling is central in the network of multiple profibrotic pathways. Largely underinvestigated are the direct contribution of macrophages to profibrotic signaling pathways, macrophage phenotypic heterogeneity and functional diversity in relation to kidney fibrosis, and on their cross-talk with other cells in profibrotic signaling networks that cause fibrosis. Here we aim to provide an overview on the roles of macrophage phenotypic and functional diversity in their contribution to pro-fibrotic signaling pathways, and on the therapeutic potential of targeting macrophages for the treatment of kidney fibrosis.

Natural killer T cell/IL-4 signaling promotes bone marrow-derived fibroblast activation and M2 macrophage-to-myofibroblast transition in renal fibrosis

Renal fibrosis is a histological manifestation of chronic kidney disease. Natural killer T (NKT) cells have a critical role in the pathogenesis of fibrotic disorder. However, the role of NKT cells in regulating kidney fibrosis remains largely unknown. In the current study, we showed that the percentages of NKT⁺ cells and NKT⁺-IL-4⁺ cells were notably increased in folic acid (FA) and obstructive nephropathy. CD1d deficiency protected mice from renal fibrosis induced by FA and obstructive injury. Specifically, Loss of CD1d reduced bone marrow-derived myofibroblasts and CD206⁺/α-smooth muscle actin⁺ cells in the kidneys of injured mice. But mice treated with α-galactosylceramide (α-GC, a specific activator of NKT cells) developed more severe fibrosis, accumulated more myeloid myofibroblasts and M2 macrophages-myofibroblasts transition (M2MMT) cells in FA injured kidneys. Furthermore, IL-4 expression was markedly reduced in CD1d deficiency mice but increased in α-GC-treated mice. Administration of IL-4 abrogates the inhibiting effect of CD1d deficiency on renal fibrosis, bone marrow-derived fibroblasts activation, and M2MMT in FA injured kidneys. Conversely, pharmacological inhibition of IL-4 attenuated the development of renal fibrosis, decreased bone marrow-derived myofibroblasts, and suppressed M2MMT. Thus, this study revealed a novel role of NKT cells in the bone marrow-derived fibroblasts activation and M2MMT during renal fibrosis. Targeting NKT cell/IL-4 signaling may be an effective treatment for renal fibrosis.

The Mechanism of CD8+ T Cells for Reducing Myofibroblasts Accumulation during Renal Fibrosis

Renal fibrosis is a hallmark of chronic kidney disease (CKD) and a common manifestation of end-stage renal disease that is associated with multiple types of renal insults and functional loss of the kidney. Unresolved renal inflammation triggers fibrotic processes by promoting the activation and expansion of extracellular matrix-producing fibroblasts and myofibroblasts. Growing evidence now indicates that diverse T cells and macrophage subpopulations play central roles in the inflammatory microenvironment and fibrotic process. The present review aims to elucidate the role of CD8⁺ T cells in renal fibrosis, and identify its possible mechanisms in the inflammatory microenvironment.

Pharmacological inhibition of SETD7 by PFI-2 attenuates renal fibrosis following folic acid and obstruction injury

Renal fibrosis is the common pathological hallmark of chronic kidney disease, and SET domain containing lysine methyltransferase 7 (SETD7) promote considerably renal fibrosis. However, the signaling mechanisms underlying SETD7 driving renal fibrosis are not fully understood. Here, we investigated the role of SETD7 in M2 macrophages-myofibroblasts transition and the myeloid fibroblasts activation in folic acid and obstruction-induced renal fibrosis. Mice treated with PFI-2, an inhibitor of SETD7, presented less bone marrow-derived myofibroblasts, fewer CD206+/α-smooth muscle actin + cells and developed less renal fibrosis (P＜0.01). Furthermore, SETD7 inhibition reduced the infiltration of inflammatory cells and decreased the production of pro-inflammatory cytokines and chemokines in the kidneys after folic acid treatment (P＜0.01). Finally, SETD7 inhibition suppressed the accumulation of NF-κB p65+ cells in folic acid nephropathy (P＜0.01). Taken together, SETD7 mediates M2 macrophages-myofibroblasts transition, bone marrow-derived myofibroblasts activation, and inflammation response in the development of renal fibrosis.

Ex Vivo Expanded 3D Human Kidney Spheres Engraft Long Term and Repair Chronic Renal Injury in Mice

End-stage renal disease is a worldwide epidemic requiring renal replacement therapy. Harvesting tissue from failing kidneys and autotransplantation of tissue progenitors could theoretically delay the need for dialysis. Here we use healthy and end-stage human adult kidneys to robustly expand proliferative kidney epithelial cells and establish 3D kidney epithelial cultures termed "nephrospheres." Formation of nephrospheres reestablishes renal identity and function in primary cultures. Transplantation into NOD/SCID mice shows that nephrospheres restore self-organogenetic properties lost in monolayer cultures, allowing long-term engraftment as tubular structures, potentially adding nephron segments and demonstrating self-organization as critical to survival. Furthermore, long-term tubular engraftment of nephrospheres is functionally beneficial in murine models of chronic kidney disease. Remarkably, nephrospheres inhibit pro-fibrotic collagen production in cultured fibroblasts via paracrine modulation, while transplanted nephrospheres induce transcriptional signatures of proliferation and release from quiescence, suggesting re-activation of endogenous repair. These data support the use of human nephrospheres for renal cell therapy.

Bixin Protects Against Kidney Interstitial Fibrosis Through Promoting STAT6 Degradation

Bixin, a natural carotenoid extracted from the seeds of Bixa orellana, has antioxidant and anti-inflammation effects. However, the pharmacological effects and underlying mechanisms of bixin in kidney interstitial fibrosis remain unknown. Partial epithelial-to-mesenchymal transition (EMT) of tubular cells has been linked to renal interstitial fibrosis. Here, we found that in the unilateral ureteral obstruction model, bixin administration could ameliorate kidney interstitial fibrosis. The expression of signal transducer and activator of transcription 6 (STAT6) was dramatically increased in renal tubular cells. Bixin treatment inhibited STAT6 induction. The activation of STAT6 signaling was essential for transforming growth factor β1, fibrotic markers, and EMT-related protein expression in HK2 cells, which was confirmed by using the Stat6^-/- mice. Ubiquitination, but not the acetylation level of STAT6, was induced by bixin treatment and promoted the suppression of phosphorylation and stability of STAT6. P62-dependent autophagy might be involved in this process. The study demonstrated that bixin can be exploited therapeutically to alleviate renal interstitial fibrosis by targeting STAT6 signaling deactivation.

The role of Treg subtypes in glomerulonephritis

While Th1 and Th17 T effector cells are pathogenic drivers of glomerulonephritis (GN), regulatory T cells (Tregs) potently protect from renal tissue injury. Recently, it has become evident that different Treg subtypes exist. Among these are lineage specific Treg1 and Treg17 cells, which are specialized to down regulate either Th1 or Th17 T effector cell responses. Interestingly, programming of specialized Tregs and the corresponding T helper effector cells depend on the same lineage specific master transcription factors Tbet (Th1/Treg1) and STAT3 (Th17/Treg17). Furthermore, early control of T effector cell priming in secondary lymphoid organs by specialized Tregs was described. One central mechanism of T effector cell control by the corresponding Treg subtype seems to be expression of the same chemokine receptor repertoire, which facilitates their co-localization. More recently, another intriguing Treg subset was identified, which expresses Foxp3 together with the Th17 characteristic transcription factor RORγt. While these Foxp3⁺RORγt⁺ Tregs were shown to be highly immunosuppressive, studies in GN also identified pro-inflammatory potential via secretion of IL-17. Many questions regarding this unusual Treg subset remain, including their origin, stability, and mechanisms of action. Further characterization of the renal Treg landscape during GN will help to identify novel immunosuppressive mechanisms and develop successful Treg-directed therapies. In this review, we summarize the currently available data about specialized Treg subsets and discuss their role in GN.

AMP-activated protein kinase contributes to cisplatin-induced renal epithelial cell apoptosis and acute kidney injury

Cisplatin, a commonly used anticancer drug, has been shown to induce acute kidney injury, which limits its clinical use in cancer treatment. Emerging evidence has suggested that AMP-activated protein kinase (AMPK), which functions as a cellular energy sensor, is activated by various cellular stresses that deplete cellular ATP. However, the potential role of AMPK in cisplatin-induced apoptosis of renal tubular epithelial cells has not been studied. In this study, we demonstrated that cisplatin activates AMPK (Thr¹⁷² phosphorylation) in cultured renal tubular epithelial cells in a time-dependent manner, which was associated with p53 phosphorylation. Compound C, a selective AMPK inhibitor, suppressed cisplatin-induced AMPK activation, p53 phosphorylation, Bax induction, and caspase 3 activation. Furthermore, silencing AMPK expression by siRNA attenuated cisplatin-induced p53 phosphorylation, Bax induction, and caspase 3 activation. In a mouse model of cisplatin-induced kidney injury, compound C inhibited p53 phosphorylation, Bax expression, caspase 3 activation, and apoptosis, protecting the kidney from injury and dysfunction. Taken together, these results suggest that the AMPK-p53-Bax signaling pathway plays a crucial role in cisplatin-induced tubular epithelial cell apoptosis.

Fibrinogen-like protein 2 deficiency aggravates renal fibrosis by facilitating macrophage polarization

Renal fibrosis has no effective target for its prevention or reversal. Fibinogen-like protein 2 (Fgl2) is a novel prothrombinase exhibiting coagulation activity and immunomodulatory effects. Although Fgl2 is known to play a vital role in the development of liver and interstitial fibrosis, its function in renal fibrosis remains unclear. In this study, Fgl2 expression was found to be markedly increased in kidney tissues from mice with unilateral ureteral obstruction (UUO)-induced renal fibrosis and patients with chronic kidney disease. However, Fgl2 deficiency aggravated UUO-induced renal fibrosis, as evidenced by the significantly increasing collagen I, fibronectin, and α-SMA expression, extracellular matrix deposition, and profibrotic factor (TGF-β1) secretion. Administration of rmFgl2 (recombinant mouse Fgl2) significantly alleviated UUO-induced renal fibrosis in mice, suggesting that the increased fibrosis can be reversed by supplementing rmFgl2. Although there was no difference in the percentages of total macrophages between Fgl2^+/+ and Fgl2^-/- mice, Fgl2 deficiency remarkably facilitated M2 macrophage polarization and accelerated M1 macrophage polarization to a low degree, during UUO-induced renal fibrosis development in mice. Similar results were observed when Fgl2^+/+ and Fgl2^-/- mice bone marrow-derived macrophages were treated for M1 or M2 polarization. Moreover, Fgl2 deficiency significantly increased the phosphorylation of STAT6, a critical mediator of M2 polarization, in both UUO-induced fibrotic kidney tissues and bone marrow-derived M2 macrophages. In conclusion, the aggravation of renal fibrosis by Fgl2 deficiency is facilitated by the p-STAT6-dependent upregulation of macrophage polarization, especially of M2.

STAT signaling in polycystic kidney disease

The most common form of polycystic kidney disease (PKD) in humans is caused by mutations in the PKD1 gene coding for polycystin1 (PC1). Among the many identified or proposed functions of PC1 is its ability to regulate the activity of transcription factors of the STAT family. Most STAT proteins that have been investigated were found to be aberrantly activated in kidneys in PKD, and some have been shown to be drivers of disease progression. In this review, we focus on the role of signal transducer and activator of transcription (STAT) signaling pathways in various renal cell types in healthy kidneys as compared to polycystic kidneys, on the mechanisms of STAT regulation by PC1 and other factors, and on the possibility to target STAT signaling for PKD therapy.

Application of either nano fibrillated cellulose methotrexate or nano silicon dioxide methotrexate composites against renal fibrosis in leukemia rat model

Cellulose derivatives have got growing interest due to their relative abundance and ability to sustain the release of medicaments. In this study, micro- and nano-fibrillated cellulose were prepared from rice straw and used as drug carriers. Both carriers in addition to another one which is nano silicon dioxide were characterized with various techniques. Methotrexate was chosen to be loaded on nano-fibrillated cellulose and nano silicon dioxide. Both methotrexate carriers were evaluated for their possible protective role against renal fibrosis induced by methotrexate in leukemia rat model. Results of this study exhibited that loading methotrexate on either nano-fibrillated cellulose or nano silicon dioxide seems to have an ameliorative role on renal function tests, inflammatory and fibrotic markers of renal tissues. Moreover, the sustained release of methotrexate for long time period maintained by nano-fibrillated cellulose carrier gives it more priority than nano silicon dioxide to be used as an effective novel drug carrier in further medical applications with minimal side effects on kidney tissue in leukemia model.

The IL-4/IL-13 axis in skin fibrosis and scarring: mechanistic concepts and therapeutic targets

Skin fibrosis, characterized by excessive fibroblast proliferation and extracellular matrix deposition in the dermis, is the histopathologic hallmark of dermatologic diseases such as systemic sclerosis, hypertrophic scars, and keloids. Effective anti-scarring therapeutics remain an unmet need, underscoring the complex pathophysiologic mechanisms of skin fibrosis. The Th2 cytokines interleukin (IL)-4 and IL-13 have been implicated as key mediators in the pathogenesis of fibroproliferative disorders. The goal of this article is to summarize the current understanding of the role of the IL-4/IL-13 axis in wound healing and skin fibrosis. We conducted a literature search to identify research studies investigating the roles of IL-4 and IL-13 in fibrotic skin diseases. While transforming growth factor-beta has long been regarded as the main driver of fibrotic processes, research into the cellular and molecular biology of wound healing has revealed other pathways that promote scar tissue formation. IL-4 and IL-13 are important mediators of skin fibrosis, supported by evidence from in vitro data, animal models of fibrosis, and clinical studies. Overactive signaling of the IL-4/IL-13 axis contributes to the initiation and perpetuation of fibrotic skin diseases. Further insights into the IL-4/IL-13 axis may reveal potential targets for the development of novel therapies that prevent or treat fibrotic skin diseases.

IL-4 Receptor α Chain Protects the Kidney Against Tubule-Interstitial Injury Induced by Albumin Overload

Increasing evidence has highlighted the role of tubule-interstitial injury (TII) as a vital step in the pathogenesis of acute kidney injury (AKI). Incomplete repair of TII during AKI could lead to the development of chronic kidney disease. Changes in albumin endocytosis in proximal tubule epithelial cells (PTECs) is linked to the development of TII. In this context, interleukin (IL)-4 has been shown to be an important factor in modulating recovery of TII. We have studied the possible role of IL-4 in TII induced by albumin overload. A subclinical AKI model characterized by albumin overload in the proximal tubule was used, without changing glomerular function. Four groups were generated: (1) CONT, wild-type mice treated with saline; (2) BSA, wild-type mice treated with 10 g/kg/day bovine serum albumin (BSA); (3) KO, IL4Rα^–/– mice treated with saline; and (4) KO + BSA, IL4Rα^–/– mice treated with BSA. As reported previously, mice in the BSA group developed TII without changes in glomerular function. The following parameters were increased in the KO + BSA group compared with the BSA group: (1) tubular injury score; (2) urinary γ-glutamyltransferase; (3) CD4⁺ T cells, dendritic cells, macrophages, and neutrophils are associated with increases in renal IL-6, IL-17, and transforming growth factor β. A decrease in M2-subtype macrophages associated with a decrease in collagen deposition was observed. Using LLC-PK1 cells, a model of PTECs, we observed that (1) these cells express IL-4 receptor α chain associated with activation of the JAK3/STAT6 pathway; (2) IL-4 alone did not change albumin endocytosis but did reverse the inhibitory effect of higher albumin concentration. This effect was abolished by JAK3 inhibitor. A further increase in urinary protein and creatinine levels was observed in the KO + BSA group compared with the BSA group, but not compared with the CONT group. These observations indicate that IL-4 has a protective role in the development of TII induced by albumin overload that is correlated with modulation of the pro-inflammatory response. We propose that megalin-mediated albumin endocytosis in PTECs could work as a sensor, transducer, and target during the genesis of TII.

Advances in Understanding the Effects of Erythropoietin on Renal Fibrosis

Renal fibrosis is the common manifestation of the pathogenesis of end-stage renal disease that results from different types of renal insult, and is a hallmark of chronic kidney disease (CKD). The main pathologic characteristics of renal fibrosis are renal interstitial fibroblast hyperplasia and the aberrant and excessive deposition of extracellular matrix, pathologies that lead to the destruction of normal renal tubules and interstitial structures. However, the biological significance of fibrosis during the progression of CKD is not clear, and there are no approved clinical treatments for delaying or reversing renal fibrosis. Studies of the mechanism of renal fibrosis and of potential measures of prevention and treatment have focused on erythropoietin (EPO), a hormone best known as a regulator of red blood cell production. These recent studies have found that EPO may also provide efficient protection against renal fibrosis. Future therapeutic approaches using EPO offer new hope for patients with CKD. The aim of the present review is to briefly discuss the role of EPO in renal fibrosis, to identify its possible mechanisms in preventing renal fibrosis, and to provide novel ideas for the use of EPO in future treatments of renal fibrosis.

Current Approaches Targeting the Wound Healing Phases to Attenuate Fibrosis and Scarring

Cutaneous fibrosis results from suboptimal wound healing following significant tissue injury such as severe burns, trauma, and major surgeries. Pathologic skin fibrosis results in scars that are disfiguring, limit normal movement, and prevent patient recovery and reintegration into society. While various therapeutic strategies have been used to accelerate wound healing and decrease the incidence of scarring, recent studies have targeted the molecular regulators of each phase of wound healing, including the inflammatory, proliferative, and remodeling phases. Here, we reviewed the most recent literature elucidating molecular pathways that can be targeted to reduce fibrosis with a particular focus on post-burn scarring. Current research targeting inflammatory mediators, the epithelial to mesenchymal transition, and regulators of myofibroblast differentiation shows promising results. However, a multimodal approach addressing all three phases of wound healing may provide the best therapeutic outcome.

Disruption of CXCR6 Ameliorates Kidney Inflammation and Fibrosis in Deoxycorticosterone Acetate/Salt Hypertension

Circulating cells have a pathogenic role in the development of hypertensive nephropathy. However, how these cells infiltrate into the kidney are not fully elucidated. In this study, we investigated the role of CXCR6 in deoxycorticosterone acetate (DOCA)/salt-induced inflammation and fibrosis of the kidney. Following uninephrectomy, wild-type and CXCR6 knockout mice were treated with DOCA/salt for 3 weeks. Blood pressure was similar between wild-type and CXCR6 knockout mice at baseline and after treatment with DOCA/salt. Wild-type mice develop significant kidney injury, proteinuria, and kidney fibrosis after three weeks of DOCA/salt treatment. CXCR6 deficiency ameliorated kidney injury, proteinuria, and kidney fibrosis following treatment with DOCA/salt. Moreover, CXCR6 deficiency inhibited accumulation of bone marrow–derived fibroblasts and myofibroblasts in the kidney following treatment with DOCA/salt. Furthermore, CXCR6 deficiency markedly reduced the number of macrophages and T cells in the kidney after DOCA/salt treatment. In summary, our results identify a critical role of CXCR6 in the development of inflammation and fibrosis of the kidney in salt-sensitive hypertension.

H2S alleviates renal injury and fibrosis in response to unilateral ureteral obstruction by regulating macrophage infiltration via inhibition of NLRP3 signaling

Renal fibrosis is a key pathological feature in chronic kidney diseases (CKDs). Dysregulation of hydrogen sulfide (H₂S) homeostasis is implicated in the pathogenesis of CKDs. Here, C57/BL6 mice were allocated to Sham and unilateral ureteral obstruction (UUO) groups, which were treated with NaHS or NLRP3 inflammasome inhibitor 16673-34-0 for 3-14 days. UUO mice displayed downregulation of H₂S production and increased macrophage infiltration in obstructed kidneys. H₂S donor NaHS treatment attenuated renal damage and fibrosis and inhibited M1 and M2 macrophage infiltration. NLPR3 inflammasome was activated and levels of phosphorylated nuclear factor κB (NF-κB) p65 subunit, phosphorylated signal transducer and activator of transcription 6 (STAT6) and interleukin (IL)-4 protein were increased in the kidneys after UUO. NLRP3 inhibitor inactivated NF-κB and IL-4/STAT6 signaling, suppressed M1 and M2 macrophage infiltration and attenuated renal damage and fibrosis in UUO mice. NaHS treatment also suppressed NLRP3, NF-κB and IL-4/STAT6 activation in the obstructed kidneys. In conclusion, the therapeutic effects of H₂S on UUO-induced renal injury and fibrosis are at least in part by inhibition of M1 and M2 macrophage infiltration. H₂S suppresses NLRP3 activation and subsequently inactivates NF-κB and IL-4/STAT6 signaling, which may contribute to the anti-inflammatory and anti-fibrotic effects of H₂S.

C/EBP Homologous Protein (CHOP) Activates Macrophages and Promotes Liver Fibrosis in Schistosoma japonicum-Infected Mice

CCAAT/enhancer-binding homologous protein (CHOP), a transcriptional regulator induced by endoplasmic reticulum stress (ER stress) is a pivotal factor in the ER stress-mediated apoptosis pathway. Previous studies have shown that CHOP is involved in the formation of fibrosis in a variety of tissues and is associated with alternative macrophage activation. The role of CHOP in the pathologic effects of liver fibrosis in schistosomiasis has not been reported, and underlying mechanisms remain unclear. This study is aimed at understanding the effect of CHOP on liver fibrosis induced by Schistosoma japonicum (S. japonicum) in vivo and clarifying its mechanism. C57BL/6 mice were infected with cercariae of S. japonicum through the abdominal skin. The liver fibrosis was examined. The level of IL-13 was observed. The expressions of CHOP, Krüppel-like factor 4 (KLF4), signal transducer and activator of transcription 6 (STAT6), phosphorylation STAT6, interleukin-13 receptor alpha 1 (IL-13Rα1), and interleukin-4 receptor alpha (IL-4Rα) were analysed. The eosinophilic granuloma and collagen deposition were found around the eggs in mice infected for 6 and 10 weeks. IL-13 in plasma and IL-13Rα1 and IL-4Rα in liver tissue were significantly increased. The phosphorylated STAT6 was enhanced while Krüppel-like factor 4 (KLF4) was decreased in liver tissue. The expression of CHOP and colocalization of CHOP and CD206 were increased. Overall, these results suggest that CHOP plays a critical role in hepatic fibrosis induced by S. japonicum, likely through promoting alternative activation of macrophages.

EZH2 plays a crucial role in ischemia/reperfusion-induced acute kidney injury by regulating p38 signaling

OBJECTIVE AND DESIGN

Renal ischemia-reperfusion (IR)-induced acute kidney injury (AKI) remains a major challenge in clinic. The histone methyltransferases enhancer of zest homolog-2 (EZH2) is associated with the development of renal injury. However, the molecular mechanism has not been fully elucidated.

MATERIALS

AKI in C57BL/6 mice was generated by renal IR.

TREATMENTS

The 3-deazaneplanocin A (DZNeP), a selective EZH2 inhibitor, or vehicle was administrated in mice after IR. HK-2 cells were exposed to hypoxia-reoxygenation (H/R) stress.

METHODS

Apoptosis was detected by TUNEL assay or flow cytometry. EZH2, caspase-3, p38, F4/80⁺ macrophages, and CD3⁺ T cells were examined by immunohistochemistry or Western blot. Tumor necrosis factor (TNF)-α, monocyte chemoattractant protein (MCP)-1, IL-6, and IL-18 were measured using RT-PCR.

RESULTS

Mice treated with DZNeP exhibited less severe renal dysfunction and tubular injury following IR. EZH2 inhibition decreased apoptotic cells while reducing activation of caspase-3 in kidneys under IR condition. Moreover, EZH2 inhibition impaired the recruitment of CD3⁺ T cells and F4/80⁺ cells in kidneys with IR. Administration of DZNeP suppressed the production of TNF-α, MCP-1, IL-6, and IL-18 in IR-treated kidneys. Of note, EZH2 inhibition reduced p38 phosphorylation in kidneys after IR. In H/R-treated HK-2 cells, DZNeP treatment or EZH2 knockdown reduced apoptosis. EZH2 inhibition inactivated p38 resulting in reduction of active caspase-3 and proinflammatory molecules. By contrast, EZH2 overexpression induced p38 phosphorylation, caspase-3 activation, and production of proinflammatory molecules, which was reversed by SB203580.

CONCLUSIONS

EZH2 plays a crucial role in IR-induced AKI via modulation of p38 signaling. Targeting EZH2/p38 signaling pathway may offer novel strategies to protect kidneys from acute kidney injury induced by ischemia-reperfusion.

Cerebrospinal fluid cytokine/chemokine/growth factor profiles in idiopathic hypertrophic pachymeningitis

Hypertrophic pachymeningitis (HP) is a rare neurologic disease causing inflammatory fibrous thickening of the brain and spinal dura mater. We investigated the cerebrospinal fluid cytokine profile of HP by measuring 28 cytokines/chemokines/growth factors with a multiplexed fluorescent immunoassay in 8 patients with HP (6 idiopathic, 1 IgG4-related, 1 anti-neutrophil cytoplasmic antibody-related), and 11 with other non-inflammatory neurologic diseases (OND). Interleukin (IL)-4, IL-5, IL-9, IL-10, TNF-α, and CXCL8/IL-8 levels were significantly higher in idiopathic HP (IHP) than OND. Cluster analyses disclosed two major clusters: one mainly consisted of IHP and the other of OND, suggesting a unique cytokine profile in IHP.

Macrophages: versatile players in renal inflammation and fibrosis

Macrophages have important roles in immune surveillance and in the maintenance of kidney homeostasis; their response to renal injury varies enormously depending on the nature and duration of the insult. Macrophages can adopt a variety of phenotypes: at one extreme, M1 pro-inflammatory cells contribute to infection clearance but can also promote renal injury; at the other extreme, M2 anti-inflammatory cells have a reparative phenotype and can contribute to the resolution phase of the response to injury. In addition, bone marrow monocytes can differentiate into myeloid-derived suppressor cells that can regulate T cell immunity in the kidney. However, macrophages can also promote renal fibrosis, a major driver of progression to end-stage renal disease, and the CD206⁺ subset of M2 macrophages is strongly associated with renal fibrosis in both human and experimental diseases. Myofibroblasts are important contributors to renal fibrosis and recent studies provide evidence that macrophages recruited from the bone marrow can transition directly into myofibroblasts within the injured kidney. This process is termed macrophage-to-myofibroblast transition (MMT) and is driven by transforming growth factor-β1 (TGFβ1)-Smad3 signalling via a Src-centric regulatory network. MMT may serve as a key checkpoint for the progression of chronic inflammation into pathogenic fibrosis.