TGF-β/Smad3 signalling regulates the transition of bone marrow-derived macrophages into myofibroblasts during tissue fibrosis

Targeting interferon regulatory factor 7 alleviates renal fibrosis by inhibiting macrophage-to-myofibroblast transition

The development of effective therapeutic strategies for renal fibrosis is a key centerpiece in addressing the progression of Chronic Kidney Disease (CKD) to end-stage renal disease (ESRD). Macrophage-to-myofibroblast transition (MMT) is thought to exacerbate the progression of renal fibrosis. Therefore, targeting MMT may be a promising therapeutic strategy for treating renal fibrosis. This study aimed to identify the key effector molecules and specific mechanisms of MMT in renal fibrosis and to provide new ideas for developing drugs for treating renal fibrosis. Analysis of transcriptomic data from Renal interstitial fibrosis (RIF) patients showed that Interferon regulatory factor 7 (IRF7) plays an important role in MMT. Further, the unilateral ureteral obstruction (UUO) model established in IRF7 knockout mice and the MMT model established in IRF7 deficiency macrophage, respectively, found that IRF7 was able to promote MMT by regulating the transcriptional activation of Cathepsin S (CTSS), increasing the number of myofibroblasts, leading to a persistent production of extracellular matrix (ECM) and ultimately exacerbating renal fibrosis. This process is dependent on the regulation of the TGF-β/Smad3 signaling pathway. In addition, we found that human umbilical cord mesenchymal stem cell-derived exosomes mimetic extracellular nanovesicles treatment of renal fibrosis may similarly depend on IRF7-mediated MMT to function. In conclusions, in renal fibrosis, upregulation of IRF7 expression depends on the regulation of the TGF-β/Smad3 signaling pathway and exacerbates renal fibrosis by regulating MMT through the IRF7-CTSS axis. These mechanisms suggest that targeting IRF7 may be the key to future treatment of renal fibrosis.

Cellular senescence promotes macrophage-to-myofibroblast transition in chronic ischemic renal disease

Cellular senescence participates in the pathophysiology of post-stenotic kidney damage, but how it regulates tissue remodeling is incompletely understood. Macrophage-myofibroblast transition (MMT) contributes to the development of tissue fibrosis. We hypothesized that cellular senescence contributes to MMT and renal fibrosis in mice with renal artery stenosis (RAS). INK-ATTAC mice expressing p16INK-4a and green fluorescent protein in senescent cells were assigned to control or unilateral RAS, untreated or treated with AP20187 (an apoptosis inducer in p16INK-4a-expressing cells) for 4 weeks. Renal perfusion was studied in vivo using micro-MRI, and kidney morphology, senescence, and MMT ex vivo. Cellular senescence was induced in human renal proximal tubular epithelial cells (HRPTEpiC) in vitro, and interferon-induced transmembrane protein-3 (IFITM3), a cellular senescence vector, was silenced (siRNA) or over-expressed (plasmid). HRPTEpiC were then co-incubated with macrophages with silenced integrin-3 (ITGB3), a regulator of mesenchymal transitions. CD68/p16INK-4a/α-SMA co-expression and senescence markers were studied. Murine RAS kidneys showed increased expression of p16INK-4a and MMT markers (F4/80, α-SMA) vs. controls, which decreased after AP20187, as did renal fibrosis and plasma creatinine, whereas renal perfusion increased. IFITM3 and ITGB3 expression were upregulated in senescent HRPTEpiC or co-cultured macrophages, respectively. MMT markers and TGF-β/Smad3 expression also rose in these macrophages and decreased after IFITM3 or ITGB3 silencing. p16INK-4a-expressing macrophages may regulate interstitial fibrosis in RAS via MMT. This process is associated with elevated expression of ITGB3 and TGF-β/Smad3 pathway activation through neighboring senescent cell-derived IFITM3. These findings may implicate MMT as a therapeutic target in ischemic kidneys.

LncRNAs and IgA nephropathy: underlying molecular pathways and clinical applications

IgA nephropathy (IgAN), also known as Berger's disease, is a prevalent kidney disorder caused by the accumulation of IgA antibodies in the glomerular tissue. Long noncoding RNAs (lncRNAs), a class of noncoding RNAs longer than 200 nucleotides, play crucial roles in regulating various cellular and molecular processes, including translation, chromatin remodeling, and transcriptional efficiency. Research has highlighted the significant impact of lncRNA imbalances on the development and progression of kidney diseases, including IgAN. These molecules influence several key signaling pathways, such as PI3K/AKT/mTOR, PTEN, Notch, JNK, and immune-related pathways, with their dysregulation contributing to IgAN pathogenesis. This review aims to provide a comprehensive analysis of the molecular signaling pathways involving lncRNAs in IgAN, underscoring their potential as biomarkers for screening, diagnosis, and prevention. Furthermore, it explores the therapeutic potential of lncRNAs as precise targets for personalized treatment strategies.

Macrophage-to-Myofibroblast Transition Contributes to Cutaneous Scarring Formation Through the TGF-β/Smad3 Signaling Pathways

Cutaneous scarring typically arises after surgery, trauma, and infection, occurring when normal skin tissue is replaced by fibrous tissue during the healing process. Myofibroblasts have been identified as a significant contributor to this scarring. While the differentiation of fibroblasts into myofibroblasts is well-recognized as essential for wound healing and tissue repair, the mechanisms underlying the macrophage-myofibroblast transition (MMT) remain largely unexplored. This study aimed to investigate the role and potential mechanisms of MMT in cutaneous scarring. In specimens of hypertrophic scars, keloid and scleroderma, we confirmed the coexistence of MMT markers CD68 and α-smooth muscle actin (α-SMA) in areas of skin fibrosis. Additionally, most MMT cells in human cutaneous scar co-expressed the M2-type macrophage marker CD206. Fate-mapping in Lyz2-Cre/Rosa26-tdTomato mice further demonstrated that the majority of myofibroblasts in cutaneous scars were derived from bone marrow macrophages. Furthermore, higher levels of TGF-β were released from scar fibroblasts, which contributed to MMT through the Smad3 pathways. In vivo studies inhibiting Smad3 reduced MMT and scarring. Macrophage depletion with clodronate liposomes also reduced cutaneous scar formation. Our findings indicate that MMT plays a pivotal role in cutaneous scarring through the TGF-β/Smad3 pathways. Consequently, inhibiting MMT may be a novel strategy for the treatment of cutaneous scarring.

Innate immune cells in acute and chronic kidney disease

Acute kidney injury (AKI) and chronic kidney disease (CKD) are inter-related clinical and pathophysiological disorders. Cells of the innate immune system, such as granulocytes and macrophages, can induce AKI through the secretion of pro-inflammatory mediators such as cytokines, chemokines and enzymes, and the release of extracellular traps. In addition, macrophages and dendritic cells can drive the progression of CKD through a wide range of pro-inflammatory and pro-fibrotic mechanisms, and by regulation of the adaptive immune response. However, innate immune cells can also promote kidney repair after acute injury. These actions highlight the multifaceted nature of the way by which innate immune cells respond to signals within the kidney microenvironment, including interaction with the complement and coagulation cascades, cells of the adaptive immune system, intrinsic renal cells and infiltrating mesenchymal cells. The factors and mechanisms that underpin the ability of innate immune cells to contribute to renal injury or repair and to drive the progression of CKD are of great interest for understanding disease processes and for developing new therapeutic approaches to limit AKI and the AKI-to-CKD transition.

MMP12-dependent myofibroblast formation contributes to nucleus pulposus fibrosis

Intervertebral disc degeneration (IDD) is associated with low back pain, a leading cause of disability worldwide. Fibrosis of nucleus pulposus (NP) is a principal component of IDD, featuring an accumulation of myofibroblast-like cells. Previous study indicates that matrix metalloproteinase 12 (MMP12) expression is upregulated in IDD, but its role remains largely unexplored. We here showed that TGF-β1 could promote myofibroblast-like differentiation of human NP cells along with an induction of MMP12 expression. Intriguingly, MMP12 knockdown not only ameliorated the myofibroblastic phenotype but also increased chondrogenic marker expression. Transcriptome analysis revealed that the MMP12-mediated acquisition of myofibroblast phenotype was coupled to processes related to fibroblast activation and osteogenesis and to pathways mediated by MAPK and Wnt signaling. Injury induced mouse IDD showed NP fibrosis with marked increase of collagen deposition and αSMA-expressing cells. In contrast, MMP12-KO mice exhibited largely reduced collagen I and III but increased collagen II and aggrecan deposition, indicating an inhibition of NP fibrosis along with an enhanced cartilaginous matrix remodeling. Consistently, an increase of SOX9+ and CNMD+ but decrease of αSMA+ NP cells was found in the KO. Altogether, our findings suggest a pivotal role of MMP12 in myofibroblast generation, thereby regulating NP fibrosis in IDD.

EZH2-mediated macrophage-to-myofibroblast transition contributes to calcium oxalate crystal-induced kidney fibrosis

Long-term nephrocalcinosis leads to kidney injury, fibrosis, and even chronic kidney disease (CKD). Macrophage-to-myofibroblast transition (MMT) has been identified as a new mechanism in CKD, however, the effect of MMT in calcium oxalate (CaOx)-induced kidney fibrosis remains unclear. In this study, abundant MMT cells are identified by immunofluorescence (IF) and flow cytometry in kidney tissues of patients with CaOx-related CKD, a male mouse model, and CaOx-treated macrophages. Clodronate liposome (CLO)-mediated macrophage depletion attenuates fibrosis in male nephrocalcinosis mice. Transcriptomic sequencing reveals that histone methyltransferase (HMTs), EZH2, is highly expressed in nephrocalcinosis. Ezh2 inducible knock-out or inhibition by GSK-126 attenuates MMT and renal fibrosis. Mechanistically, ChIP and transcriptomic sequencing show that EZH2 inhibition reduces the enrichment of H3K27me3 on the Dusp23 gene promoter and elevates Dusp23 expression. The Co-IP and molecular docking analysis shows that DUSP23 mediates the dephosphorylation of pSMAD3 (Ser423/425). Thus, our study found that EZH2 promotes kidney fibrosis by meditating MMT via the DUSP23/SMAD3 pathway in nephrocalcinosis.

Modulation of TGF-β signaling new approaches toward kidney disease and fibrosis therapy

The prevalence of chronic kidney disease (CKD) is increasing worldwide, posing a significant healthcare challenge. Despite the immense burden of CKD, optimal therapies remain limited in impact. Kidney fibrosis is a common mediator of all CKD progression, characterized by excessive extracellular matrix deposition and scarring of kidney parenchyma. Transforming growth factor-β (TGF-β) is a potent pro-fibrotic cytokine that signals through canonical and non-canonical pathways to promote kidney cell damage and fibrosis progression, thus garnering much interest as an optimal therapeutic target for CKD. However, the clinical translation of TGF-β inhibition in CKD and other disease settings has faced substantial challenges, particularly due to the highly pleiotropic effects of TGF-β in organ homeostasis and disease. Here, we review the kidney cell-specific biological effects of TGF-β signaling, discuss the current challenges in therapeutic targeting TGF-β in CKD, and provide the rationale for alternative targeting strategies of TGF-β signaling as potential approaches in CKD therapy. Selective inhibition of TGF-β signaling modulators to fine-tune TGF-β inhibition without a broad blockade may lead to new and safer treatments for CKD.

Effect of macrophage-to-myofibroblast transition on silicosis

BACKGROUND

The aim was to explore the effect of macrophage polarization and macrophage-to-myofibroblast transition (MMT) in silicosis.

METHODS

Male Wistar rats were divided into a control group and a silicosis group developed using a HOPE MED 8050 dynamic automatic dusting system. Murine macrophage MH-S cells were randomly divided into a control group and an SiO2 group. The pathological changes in lung tissue were observed using hematoxylin and eosin (HE) and Van Gieson (VG) staining. The distribution and location of macrophage marker (F4/80), M1 macrophage marker (iNOS), M2 macrophage marker (CD206), and myofibroblast marker (α-smooth muscle actin [α-SMA]) were detected using immunohistochemical and immunofluorescent staining. The expression changes in iNOS, Arg, α-SMA, vimentin, and type I collagen (Col I) were measured using Western blot.

RESULTS

The results of HE and VG staining showed obvious silicon nodule formation and the distribution of thick collagen fibers in the lung tissue of the silicosis group. Macrophage marker F4/80 increased gradually from 8 to 32 weeks after exposure to silica. Immunohistochemical and immunofluorescent staining results revealed that there were more iNOS-positive cells and some CD206-positive cells in the lung tissue of the silicosis group at 8 weeks. More CD206-positive cells were found in the silicon nodules of the lung tissues in the silicosis group at 32 weeks. Western blot analysis showed that the expressions of Inducible nitric oxide synthase and Arg protein in the lung tissues of the silicosis group were upregulated compared with those of the control group. The results of immunofluorescence staining showed the co-expression of F4/80, α-SMA, and Col I, and CD206 and α-SMA were co-expressed in the lung tissue of the silicosis group. The extracted rat alveolar lavage fluid revealed F4/80+α-SMA+, CD206+α-SMA+, and F4/80+α-SMA+Col I+ cells using immunofluorescence staining. Similar results were also found in MH-S cells induced by SiO2.

CONCLUSIONS

The development of silicosis is accompanied by macrophage polarization and MMT.

Intracellular iron accumulation throughout the progression of sepsis influences the phenotype and function of activated macrophages in renal tissue damage

Sepsis, the most common cause of acute kidney injury, remains a major socioeconomic burden. A dysregulated immune response leads to progressive organ dysfunction. Although numerous inflammatory pathways were described, most are still vague and need to be studied in terms of the mechanisms to improve the therapeutic intervention. We tackled the relationship between intracellular iron overload and macrophage polarization within 6, 24, and 72 h of sepsis induction. In our study, sepsis-induced kidney injury was caused by using the cecal ligation and puncture (CLP) model. Our results indicated severe renal tissue damage with a progressive increase in serum BUN and creatinine with architectural tissue damage and positive PAS staining. There was increased expression of CD8+ CD68+ M1 macrophage markers with upregulation of iNOS and co-expression of CD163+. Alternatively, Arg1+ Fizz1+ M2 macrophage markers were downregulated with increased iNOS/Arg1 ratio. TFR1, cubilin, and DMT1, as iron transport systems, were increased compared to sham but were significant after 72 h, while ZIP8 showed no significant change. There was a correlation between iron overload and M1 macrophage polarization with CD163+ phenotype, together with fibrotic changes. The intracellular iron overload with downregulation of ferritin was strongly related to macrophage polarization that was exaggerated at 72 h. Finally, early introduced therapy to target free iron during sepsis is a proposed novel solution for protecting the renal tissue from acute injury due to macrophage activation that may end up with chronic kidney injury, if not mortality.

Kupffer cells, the limelight in the liver regeneration

Kupffer cells are pivotal in initiating hepatocyte proliferation and establishing connections between different cell types during liver regeneration following partial hepatectomy. As resident macrophages within the liver, Kupffer cells collaborate with hepatocytes and non-parenchymal cells to release various inflammatory mediators that promote hepatocyte proliferation through induction signals like STAT3 phosphorylation. Additionally, the regeneration and replenishment of Kupffer cells themselves are integral components of liver regeneration. The supplementation of the Kupffer cell pool primarily occurs through two pathways: one involves local proliferation of Kupffer cells in their original location, while the other entails infiltration of circulating monocytes into the liver, followed by acquiring Kupffer cell phenotypes under the combined influence of multiple inducing factors. Extensive research has focused on intercellular crosstalk among various types of liver cells during liver regeneration, highlighting the crucial role played by Kupffer cells. This article aims to introduce Kupffer cells and their involvement in liver regeneration, as well as discuss the steady-state balance of Kupffer cell pools during this process.

Senescent renal tubular cells derived extracellular vesicles transported miR-20a and miR-21 induced macrophage-to-myofibroblast transition in renal fibrosis after ischemia reperfusion injury

In our investigation, we aimed to shed light on the role of senescent cells in renal fibrosis, considering the observed correlation between renal tubular epithelial cell senescence and the presence of renal fibrosis. Our findings confirm the manifestation of senescence characteristics in renal tubular epithelial cells during renal fibrosis and establish their capacity to trigger a transition from macrophages to myofibroblasts, known as macrophage-myofibroblast transition (MMT). Additionally, our study uncovered that extracellular vesicles released by senescent HK-2 cells (sHK-2) play a pivotal role in facilitating MMT. Subsequently, we investigated the miRNA profile in sHK-2-derived extracellular vesicles (sHK-2-EVs) and confirmed the elevated abundance of specific miRNAs, including miR-20a-5p and miR-21-5p, compared to normal HK-2-EVs. Notably, these miRNAs possess the capability to induce M2-like polarization in macrophages and enhance the expression of TGF-β. Moreover, TGF-β can stimulate macrophages to produce miR-20a-5p and miR-21-5p, establishing a positive feedback loop that amplifies the TGF-β/Smad pathway and facilitates the process of macrophage-myofibroblast transition.

Regulatory mechanisms of macrophage-myofibroblast transdifferentiation: A potential therapeutic strategy for fibrosis

Macrophage-myofibroblast transdifferentiation (MMT), a fibrotic process impacting diverse tissue types, has garnered recent scholarly interest. Within damaged tissues, the role of myofibroblasts is pivotal in the accumulation of excessive fibrous connective tissue, leading to persistent scarring or organ dysfunction. Consequently, the examination of MMT-related fibrosis is imperative. This review underscores MMT as a fundamental mechanism in myofibroblast generation during tissue fibrosis, and its exploration is crucial for elucidating the regulatory mechanisms underlying this process. Gaining insight into these mechanisms promises to facilitate the development of therapeutic approaches aimed at inhibiting and reversing fibrosis, thereby offering potential avenues for the treatment of fibrotic diseases.

Macrophages in organ fibrosis: from pathogenesis to therapeutic targets

Fibrosis, an excessive self-repair response, is an age-related pathological process that universally affects various major organs such as the heart, liver, kidney, and lungs. Continuous accumulation of pathological tissue fibrosis destroys structural integrity and causes loss of function, with consequent organ failure and increased mortality. Although some differences exist in the triggering mechanisms and pathophysiologic manifestations of organ-specific fibrosis, they usually share similar cascading responses and features, including chronic inflammatory stimulation, parenchymal cell injury, and macrophage recruitment. Macrophages, due to their high plasticity, can polarize into different phenotypes in response to varied microenvironments and play a crucial role in the development of organ fibrosis. This review examined the relationship between macrophages and the pathogenesis of organ fibrosis. Moreover, it analyzed how fibrosis can be modulated by targeting macrophages, which may become a novel and promising therapeutic strategy for 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.

Macrophage erythropoietin signaling promotes macrophage-myofibroblast transformation and fibroblast-myofibroblast differentiation

While myofibroblasts are the key cause of abnormal extracellular matrix accumulation, the origin of which has not yet been fully elucidated. Recently, it has been found that macrophage-myofibroblast transformation (MMT) defined by the expression of both macrophage markers (F4/80 or CD68) and myofibroblast markers (α-SMA) is one of its important sources. In the process of MMT, it is unclear whether epor is involved. In this study, when BMDM was induced by tgf-β1, the number of F4/80+α-SMA+ cells increased, the cells polarized toward M2, and the expression of tgf-β1 increased. After the activation of epor, the number of F4/80 +α-SMA + cells and the polarization level of M2 were further increased. At the same time, we found that the conditioned medium from MMT cells could induce the activation of 3T3 cells with increased the expression of α-SMA and col-1. In contrast, the number of F4/80+α-SMA + cells, the polarization of M2, and the expression of Tgf-β1 decreased after epor was inhibited by siRNA. Our results demonstrate that the activation of epor in BMDMs could promote the transformation of macrophage-myofibroblast induced by TGF-β1.

Roles of macrophages in lupus nephritis

LN is a serious complication of systemic lupus erythematosus (SLE), affecting up to 60% of patients with SLE and may lead to end-stage renal disease (ESRD). Macrophages play multifaceted roles in the pathogenesis of LN, including clearance of immune complexes, antigen presentation, regulation of inflammation, and tissue repair. Macrophages are abundant in the glomeruli and tubulointerstitium of LN patients and are positively correlated with serum creatinine levels and the severity of renal pathology. It has been shown that the infiltration of macrophages is closely associated with several clinical indicators, such as serum creatinine and complement C3 levels, anti-dsDNA antibody titers, Austin score, interstitial fibrosis and renal tubular atrophy. Moreover, cytokines expressed by macrophages were upregulated at LN onset and downregulated after remission, suggesting that macrophages may serve as markers of LN pathogenesis and remission. Therapies targeting macrophages have been shown to alleviate LN. There are two main types of macrophages in the kidney: kidney-resident macrophages (KRMs) and monocyte-derived macrophages (MDMs). KRMs and MDMs play different pathological roles in LN, with KRMs promoting leukocyte recruitment at sites of inflammation by expressing monocyte chemokines, while MDMs may exacerbate autoimmune responses by presenting immune complex antigens. Macrophages exhibit high plasticity and can differentiate into various phenotypes in response to distinct environmental stimuli. M1 (proinflammatory) macrophages are linked to the progression of active SLE, whereas the M2 (anti-inflammatory) phenotype is observed during the remission phase of LN. The polarization of macrophages in LN can be manipulated through multiple pathways, such as the modulation of signaling cascades including TLR 2/1, S1P, ERS, metabolic reprogramming, and HMGB1. This paper provides a comprehensive overview of the role of macrophages in the progression of lupus nephritis (LN), and elucidates how these cells and their secretory products function as indicators and therapeutic targets for the disease in the context of diagnosis and treatment of LN.

Advances in macrophage-myofibroblast transformation in fibrotic diseases

Macrophage-myofibroblast transformation (MMT) has emerged as a discovery in the field of fibrotic disease research. MMT is the process by which macrophages differentiate into myofibroblasts, leading to organ fibrosis following organ damage and playing an important role in fibrosis formation and progression. Recently, many new advances have been made in studying the mechanisms of MMT occurrence in fibrotic diseases. This article reviews some critical recent findings on MMT, including the origin of MMT in myofibroblasts, the specific mechanisms by which MMT develops, and the mechanisms and effects of MMT in the kidneys, lungs, heart, retina, and other fibrosis. By summarizing the latest research related to MMT, this paper provides a theoretical basis for elucidating the mechanisms of fibrosis in various organs and developing effective therapeutic targets for fibrotic diseases.

Transformation of macrophages into myofibroblasts in fibrosis-related diseases: emerging biological concepts and potential mechanism

Macrophage-myofibroblast transformation (MMT) transforms macrophages into myofibroblasts in a specific inflammation or injury microenvironment. MMT is an essential biological process in fibrosis-related diseases involving the lung, heart, kidney, liver, skeletal muscle, and other organs and tissues. This process consists of interacting with various cells and molecules and activating different signal transduction pathways. This review deeply discussed the molecular mechanism of MMT, clarified crucial signal pathways, multiple cytokines, and growth factors, and formed a complex regulatory network. Significantly, the critical role of transforming growth factor-β (TGF-β) and its downstream signaling pathways in this process were clarified. Furthermore, we discussed the significance of MMT in physiological and pathological conditions, such as pulmonary fibrosis and cardiac fibrosis. This review provides a new perspective for understanding the interaction between macrophages and myofibroblasts and new strategies and targets for the prevention and treatment of MMT in fibrotic diseases.

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.

TGF‑β/Smad signaling in chronic kidney disease: Exploring post‑translational regulatory perspectives (Review)

The TGF‑β/Smad signaling pathway plays a pivotal role in the onset of glomerular and tubulointerstitial fibrosis in chronic kidney disease (CKD). The present review delves into the intricate post‑translational modulation of this pathway and its implications in CKD. Specifically, the impact of the TGF‑β/Smad pathway on various biological processes was investigated, encompassing not only renal tubular epithelial cell apoptosis, inflammation, myofibroblast activation and cellular aging, but also its role in autophagy. Various post‑translational modifications (PTMs), including phosphorylation and ubiquitination, play a crucial role in modulating the intensity and persistence of the TGF‑β/Smad signaling pathway. They also dictate the functionality, stability and interactions of the TGF‑β/Smad components. The present review sheds light on recent findings regarding the impact of PTMs on TGF‑β receptors and Smads within the CKD landscape. In summary, a deeper insight into the post‑translational intricacies of TGF‑β/Smad signaling offers avenues for innovative therapeutic interventions to mitigate CKD progression. Ongoing research in this domain holds the potential to unveil powerful antifibrotic treatments, aiming to preserve renal integrity and function in patients with CKD.

Tissue fibroblasts are versatile immune regulators: An evaluation of their impact on the aging process

Fibroblasts are abundant stromal cells which not only control the integrity of extracellular matrix (ECM) but also act as immune regulators. It is known that the structural cells within tissues can establish an organ-specific immunity expressing many immune-related genes and closely interact with immune cells. In fact, fibroblasts can modify their immune properties to display both pro-inflammatory and immunosuppressive activities in a context-dependent manner. After acute insults, fibroblasts promote tissue inflammation although they concurrently recruit immunosuppressive cells to enhance the resolution of inflammation. In chronic pathological states, tissue fibroblasts, especially senescent fibroblasts, can display many pro-inflammatory and immunosuppressive properties and stimulate the activities of different immunosuppressive cells. In return, immunosuppressive cells, such as M2 macrophages and myeloid-derived suppressor cells (MDSC), evoke an excessive conversion of fibroblasts into myofibroblasts, thus aggravating the severity of tissue fibrosis. Single-cell transcriptome studies on fibroblasts isolated from aged tissues have confirmed that tissue fibroblasts express many genes coding for cytokines, chemokines, and complement factors, whereas they lose some fibrogenic properties. The versatile immune properties of fibroblasts and their close cooperation with immune cells indicate that tissue fibroblasts have a crucial role in the aging process and age-related diseases.

Role of Culinary Indian Spices in the Regulation of TGF-β Signaling Pathway in Inflammation-Induced Liver Cancer

SCOPE

Hepatocellular carcinoma (HCC) results from various etiologies, such as Hepatitis B and C, Alcoholic and Non-alcoholic fatty liver disorders, fibrosis, and cirrhosis. About 80 to 90% of HCC cases possess cirrhosis, which is brought on by persistent liver inflammation. TGF-β is a multifunctional polypeptide molecule that acts as a pro-fibrogenic marker, inflammatory cytokine, immunosuppressive agent, and pro-carcinogenic growth factor during the progression of HCC. The preclinical and clinical evidence illustrates that TGF-β can induce epithelial-to-mesenchymal transition, promoting progression and hepatocyte immune evasion. Therefore, targeting the TGF-β pathway can be a promising therapeutic option against HCC.

METHODS AND RESULTS

We carry out a systemic analysis of eight potentially selected culinary Indian spices: Turmeric, Black pepper, Ginger, Garlic, Fenugreek, Red pepper, Clove, Cinnamon, and their bioactives in regulation of the TGF-β pathway against liver cancer.

CONCLUSION

Turmeric and its active constituent, curcumin, possess the highest therapeutic potential in treating inflammation-induced HCC and they also have the maximum number of ongoing in-vivo and in-vitro studies.

Macrophage-derived macrophage migration inhibitory factor mediates renal injury in anti-glomerular basement membrane glomerulonephritis

Macrophages are a rich source of macrophage migration inhibitory factor (MIF). It is well established that macrophages and MIF play a pathogenic role in anti-glomerular basement membrane crescentic glomerulonephritis (anti-GBM CGN). However, whether macrophages mediate anti-GBM CGN via MIF-dependent mechanism remains unexplored, which was investigated in this study by specifically deleting MIF from macrophages in MIFf/f-lysM-cre mice. We found that compared to anti-GBM CGN induced in MIFf/f control mice, conditional ablation of MIF in macrophages significantly suppressed anti-GBM CGN by inhibiting glomerular crescent formation and reducing serum creatinine and proteinuria while improving creatine clearance. Mechanistically, selective MIF depletion in macrophages largely inhibited renal macrophage and T cell recruitment, promoted the polarization of macrophage from M1 towards M2 via the CD74/NF-κB/p38MAPK-dependent mechanism. Unexpectedly, selective depletion of macrophage MIF also significantly promoted Treg while inhibiting Th1 and Th17 immune responses. In summary, MIF produced by macrophages plays a pathogenic role in anti-GBM CGN. Targeting macrophage-derived MIF may represent a novel and promising therapeutic approach for the treatment of immune-mediated kidney diseases.

Exploring unconventional targets in myofibroblast transdifferentiation outside classical TGF-β signaling in renal fibrosis

We propose that the key initiators of renal fibrosis are myofibroblasts which originate from four predominant sources-fibroblasts, pericytes, endothelial cells and macrophages. Increased accumulation of renal interstitial myofibroblasts correlates with an increase in collagen, fibrillar proteins, and fibrosis severity. The canonical TGF-β pathway, signaling via Smad proteins, is the central molecular hub that initiates these cellular transformations. However, directly targeting these classical pathway molecules has proven challenging due their integral roles in metabolic process, and/or non-sustainable effects involving compensatory cross-talk with TGF-β. This review explores recently discovered alternative molecular targets that drive transdifferentiation into myofibroblasts. Discovering targets outside of the classical TGF-β/Smad pathway is crucial for advancing antifibrotic therapies, and strategically targeting the development of myofibroblasts offers a promising approach to control excessive extracellular matrix deposition and impede fibrosis progression.

Cell type-specific transforming growth factor-β (TGF-β) signaling in the regulation of salivary gland fibrosis and regeneration

Salivary gland damage and hypofunction result from various disorders, including autoimmune Sjögren's disease (SjD) and IgG4-related disease (IgG4-RD), as well as a side effect of radiotherapy for treating head and neck cancers. There are no therapeutic strategies to prevent the loss of salivary gland function in these disorders nor facilitate functional salivary gland regeneration. However, ongoing aquaporin-1 gene therapy trials to restore saliva flow show promise. To identify and develop novel therapeutic targets, we must better understand the cell-specific signaling processes involved in salivary gland regeneration. Transforming growth factor-β (TGF-β) signaling is essential to tissue fibrosis, a major endpoint in salivary gland degeneration, which develops in the salivary glands of patients with SjD, IgG4-RD, and radiation-induced damage. Though the deposition and remodeling of extracellular matrix proteins are essential to repair salivary gland damage, pathological fibrosis results in tissue hardening and chronic salivary gland dysfunction orchestrated by multiple cell types, including fibroblasts, myofibroblasts, endothelial cells, stromal cells, and lymphocytes, macrophages, and other immune cell populations. This review is focused on the role of TGF-β signaling in the development of salivary gland fibrosis and the potential for targeting TGF-β as a novel therapeutic approach to regenerate functional salivary glands. The studies presented highlight the divergent roles of TGF-β signaling in salivary gland development and dysfunction and illuminate specific cell populations in damaged or diseased salivary glands that mediate the effects of TGF-β. Overall, these studies strongly support the premise that blocking TGF-β signaling holds promise for the regeneration of functional salivary glands.

Targeting Interactions between Fibroblasts and Macrophages to Treat Cardiac Fibrosis

Excessive extracellular matrix (ECM) deposition is a defining feature of cardiac fibrosis. Most notably, it is characterized by a significant change in the concentration and volume fraction of collagen I, a disproportionate deposition of collagen subtypes, and a disturbed ECM network arrangement, which directly affect the systolic and diastolic functions of the heart. Immune cells that reside within or infiltrate the myocardium, including macrophages, play important roles in fibroblast activation and consequent ECM remodeling. Through both direct and indirect connections to fibroblasts, monocyte-derived macrophages and resident cardiac macrophages play complex, bidirectional, regulatory roles in cardiac fibrosis. In this review, we discuss emerging interactions between fibroblasts and macrophages in physiology and pathologic conditions, providing insights for future research aimed at targeting macrophages to combat cardiac fibrosis.

Targeting Macrophages: Therapeutic Approaches in Diabetic Kidney Disease

Diabetes is not solely a metabolic disorder but also involves inflammatory processes. The immune response it incites is a primary contributor to damage in target organs. Research indicates that during the initial phases of diabetic nephropathy, macrophages infiltrate the kidneys alongside lymphocytes, initiating a cascade of inflammatory reactions. The interplay between macrophages and other renal cells is pivotal in the advancement of kidney disease within a hyperglycemic milieu. While M1 macrophages react to the inflammatory stimuli induced by elevated glucose levels early in the disease progression, their subsequent transition to M2 macrophages, which possess anti-inflammatory and tissue repair properties, also contributes to fibrosis in the later stages of nephropathy by transforming into myofibroblasts. Comprehending the diverse functions of macrophages in diabetic kidney disease and regulating their activity could offer therapeutic benefits for managing this condition.

Periodontitis deteriorates renal fibrosis and macrophage infiltration in rats with chronic kidney disease

OBJECTIVE

The objective of this study was to examine the effect of periodontitis on renal function and morphology in rats with or without nephrectomy (Nx)-induced chronic kidney disease (CKD).

METHODS

Rats were divided into sham surgery (Sham), Sham with tooth ligation (ShamL), Nx, and NxL groups. Periodontitis was induced by tooth ligation at 16-week olds. Creatinine, alveolar bone area, and renal histopathology were analyzed at 20-week olds.

RESULTS

Creatinine did not differ between the Sham and ShamL groups or between the Nx and NxL groups. The ShamL and NxL groups (both p = 0.002) had less alveolar bone area than the Sham group. The NxL group had fewer glomeruli than the Nx group (p < 0.000). The periodontitis groups demonstrated more tubulointerstitial fibrosis (Sham vs. ShamL p = 0.002, Nx vs. NxL p < 0.000) and macrophage infiltration (Sham vs. ShamL p = 0.002, Nx vs. NxL p = 0.006) than the groups without periodontitis. Only the NxL group had greater renal TNFα expression than the Sham group (p < 0.003).

CONCLUSIONS

These suggest that periodontitis increases renal fibrosis and inflammation in the presence or absence of CKD but does not affect renal function. Periodontitis also increases TNFα expression in the presence of CKD.

From inflammation to renal fibrosis: A one-way road in autoimmunity?

Renal fibrosis is now recognized as a main determinant of renal pathology to include chronic kidney disease. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space, and around arterioles predicts and contributes to the functional demise of the nephron and its surrounding vasculature. The recent identification of the major cell populations of fibroblast precursors in the kidney interstitium such as pericytes and tissue-resident mesenchymal stem cells, or bone-marrow-derived macrophages, and in the glomerulus such as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process thought the lens of involved immunological pathways. Besides, a growing body of evidence is supporting the role of the lymphatic system in modulating the immunological response potentially leading to inflammation and ultimately renal damage. These notions have moved our understanding of renal fibrosis to be recognized as a clinical entity and new main player in autoimmunity, impacting directly the management of patients.

Macrophage-Myofibroblast Transition as a Potential Origin for Skeletal Muscle Fibrosis After Injury via Complement System Activation

BACKGROUND

Acute skeletal muscle injury is common in sports. The injured muscle cannot fully recover due to fibrosis resulting from myofibroblasts. Understanding the origin of fibroblasts is, therefore, important for the development of anti-fibrotic therapies. Accumulating evidence shows that a mechanism called macrophage-myofibroblast transition (MMT) can lead to tissue or organ fibrosis, yet it is still unclear whether MMT exists in skeletal muscle and the exact mechanisms.

METHODS

Single-cell transcriptome of mice skeletal muscle after acute injury was analyzed with a specific attention on the process of MMT. Cell-cell interaction network, pseudotime trajectory analysis, Gene Ontology (GO), and Kyoto Genome Encyclopedia (KEGG) were conducted. A series of experiments in vivo and in vitro were launched for verification.

RESULTS

Single cell transcriptomic analysis indicated that, following acute injury, there were much interactions between macrophages and myofibroblasts. A detailed analysis on macrophages indicated that, CD68+α-SMA+ cells, which represented the status of MMT, mainly appeared at five days post-injury. KEGG/GO analysis underlined the involvement of complement system, within which C3ar1, C1qa, C1qb, and C1qc were up-regulated. Trajectory analysis also confirmed a potential shift from macrophages to myofibroblasts. These findings were verified by histological study in mice skeletal muscle, that there were much MMT cells at five days, declined gradually, and vanished 14 days after trauma, when there was remarkable fibrosis formation within the injured muscle. Moreover, C3a stimulation could directly induce MMT in BMDMs.

CONCLUSION

Fibrosis following acute injury is disastrous to skeletal muscle, but the origin of myofibroblasts remains unclear. We proved that, following acute injury, macrophage-myofibroblast transition happened in skeletal muscle, which may contribute to fibrosis formation. This phenomenon mainly occurred at five days post-injury. The complement system can activate MMT. More evidence is needed to directly support the pro-fibrotic role of MMT in skeletal muscle fibrosis after acute injury.

Collagenase-based wound debridement agent induces extracellular matrix supporting phenotype in macrophages

Macrophages assume diverse phenotypes and functions in response to cues from the microenvironment. Earlier we reported an anti-inflammatory effect of Collagenase Santyl® Ointment (CSO) and the active constituent of CSO (CS-API) on wound macrophages in resolving wound inflammation indicating roles beyond debridement in wound healing. Building upon our prior finding, this study aimed to understand the phenotypes and subsets of macrophages following treatment with CS-API. scRNA-sequencing was performed on human blood monocyte-derived macrophages (MDM) following treatment with CS-API for 24 h. Unbiased data analysis resulted in the identification of discrete macrophage subsets based on their gene expression profiles. Following CS-API treatment, clusters 3 and 4 displayed enrichment of macrophages with high expression of genes supporting extracellular matrix (ECM) function. IPA analysis identified the TGFβ-1 pathway as a key hub for the CS-API-mediated ECM-supportive phenotype of macrophages. Earlier we reported the physiological conversion of wound-site macrophages to fibroblasts in granulation tissue and impairment of such response in diabetic wounds, leading to compromised ECM and tensile strength. The findings that CSO can augment the physiological conversion of macrophages to fibroblast-like cells carry significant clinical implications. This existing clinical intervention, already employed for wound care, can be readily repurposed to improve the ECM response in chronic wounds.

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.

ALA-PDT promotes the death and contractile capacity of hypertrophic scar fibroblasts through inhibiting the TGF-β1/Smad2/3/4 signaling pathway

BACKGROUND

Hypertrophic scars, an abnormal wound-healing response to burn injuries, are characterized by massive fibroblast proliferation and excessive deposition of extracellular matrix and collagen. 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT) is a promising therapy for hypertrophic scar, details of the mechanisms remain to be elucidated. In this study, we aimed to investigate the molecular mechanisms involved in ALA-PDT against hypertrophic scar fibroblasts.

METHODS

The morphologies of hypertrophic scar fibroblasts (HSFs) treated with ALA-PDT were observed under a light microscopy. The viability of HSFs was detected using the CCK-8 assay. HSFs-populated collagen gel contraction assays were conducted to examine the fibroblast contractility and the cytotoxicity of HSFs in 3D collagen tissues were observed using confocal microscopy. The effect of ALA-PDT on TGF-β1/Smad2/3/4 signaling pathway activation and effector gene expression were verified by immunoprecipitation, western blot and real-time quantitative PCR analysis.

RESULTS

We observed significant changes in cell morphology after ALA-PDT treatment of HSFs. As ALA concentration and light dose increased, the viability of HSFs significantly decreased. ALA-PDT can significantly alleviate the contractile capacity and promote the death of HSFs induced by TGF-β1 treatment in a three-dimensional collagen culture model. TGF-β1 treatment of HSFs can significantly induce phosphorylation of Smad2/3 (p-Smad2/3) in whole cells, as well as p-Smad2/3 and Smad4 proteins into the nucleus and increase the mRNA levels of collagen 1/3 and α-SMA. ALA-PDT hampers the TGF-β1-Smad2/3/4 signaling pathway activation by inducing K48-linked ubiquitination and degradation of Smad4.

CONCLUSIONS

Our results provide evidence that ALA-PDT can inhibit fibroblast contraction and promote cell death by inhibiting the activation of the TGF-β1 signaling pathway that mediates hypertrophic scar formation, which may be the basis for the efficacy of ALA-PDT in the treatment of hypertrophic scars.

AMPK signaling inhibits the differentiation of myofibroblasts: impact on age-related tissue fibrosis and degeneration

Disruption of the extracellular matrix (ECM) and an accumulation of fibrotic lesions within tissues are two of the distinctive hallmarks of the aging process. Tissue fibroblasts are mesenchymal cells which display an impressive plasticity in the regulation of ECM integrity and thus on tissue homeostasis. Single-cell transcriptome studies have revealed that tissue fibroblasts exhibit a remarkable heterogeneity with aging and in age-related diseases. Excessive stress and inflammatory insults induce the differentiation of fibroblasts into myofibroblasts which are fusiform contractile cells and abundantly secrete the components of the ECM and proteolytic enzymes as well as many inflammatory mediators. Detrimental stresses can also induce the transdifferentiation of certain mesenchymal and myeloid cells into myofibroblasts. Interestingly, many age-related stresses, such as oxidative and endoplasmic reticulum stresses, ECM stiffness, inflammatory mediators, telomere shortening, and several alarmins from damaged cells are potent inducers of myofibroblast differentiation. Intriguingly, there is convincing evidence that the signaling pathways stimulated by the AMP-activated protein kinase (AMPK) are potent inhibitors of myofibroblast differentiation and accordingly AMPK signaling reduces fibrotic lesions within tissues, e.g., in age-related cardiac and pulmonary fibrosis. AMPK signaling is not only an important regulator of energy metabolism but it is also able to control cell fate determination and many functions of the immune system. It is known that AMPK signaling can delay the aging process via an integrated signaling network. AMPK signaling inhibits myofibroblast differentiation, e.g., by suppressing signaling through the TGF-β, NF-κB, STAT3, and YAP/TAZ pathways. It seems that AMPK signaling can alleviate age-related tissue fibrosis and degeneration by inhibiting the differentiation of myofibroblasts.

Crosstalk between fibroblasts and immunocytes in fibrosis: From molecular mechanisms to clinical trials

BACKGROUND

The impact of fibroblasts on the immune system provides insight into the function of fibroblasts. In various tissue microenvironments, multiple fibroblast subtypes interact with immunocytes by secreting growth factors, cytokines, and chemokines, leading to wound healing, fibrosis, and escape of cancer immune surveillance. However, the specific mechanisms involved in the fibroblast-immunocyte interaction network have not yet been fully elucidated.

MAIN BODY AND CONCLUSION

Therefore, we systematically reviewed the molecular mechanisms of fibroblast-immunocyte interactions in fibrosis, from the history of cellular evolution and cell subtype divisions to the regulatory networks between fibroblasts and immunocytes. We also discuss how these communications function in different tissue and organ statuses, as well as potential therapies targeting the reciprocal fibroblast-immunocyte interplay in fibrosis. A comprehensive understanding of these functional cells under pathophysiological conditions and the mechanisms by which they communicate may lead to the development of effective and specific therapies targeting fibrosis.

Mitophagy in renal interstitial fibrosis

As a high energy consumption organ, kidney relies on a large number of mitochondria to ensure normal physiological activities. Under specific stimulation, mitophagy and mitochondrial dynamics (fission, fusion) cooperatively regulate mitochondrial quality and participate in many life activities such as energy metabolism, inflammatory response, oxidative stress, cell senescence and death. Mitophagy plays a key role in the progression of acute kidney injury and chronic kidney disease. The early induction of oxidative stress in renal parenchyma, the activation of pro-inflammatory cytokines and TGF-β signal pathway are closely related to renal interstitial fibrosis. Macrophage reprogramming is also considered to be an important participant in the progression of kidney fibrosis. This review summarizes the molecular mechanism of mitochondrial autophagy and its relationship with the pathway of promoting fibrosis, and discusses the possibility of restoring mitophagy balance as a pharmacological target for the treatment of renal interstitial fibrosis, so as to provide new ideas for more efficient anti-fibrosis and delay the progress of chronic kidney disease.

STAT6 promoting oxalate crystal deposition-induced renal fibrosis by mediating macrophage-to-myofibroblast transition via inhibiting fatty acid oxidation

OBJECTIVE AND DESIGN

Kidney stones commonly occur with a 50% recurrence rate within 5 years, and can elevate the risk of chronic kidney disease. Macrophage-to-myofibroblast transition (MMT) is a newly discovered mechanism that leads to progressive fibrosis in different forms of kidney disease. In this study, we aimed to investigate the role of MMT in renal fibrosis in glyoxylate-induced kidney stone mice and the mechanism by which signal transducer and activator of transcription 6 (STAT6) regulates MMT.

METHODS

We collected non-functioning kidneys from patients with stones, established glyoxylate-induced calcium oxalate stone mice model and treated AS1517499 every other day in the treatment group, and constructed a STAT6-knockout RAW264.7 cell line. We first screened the enrichment pathway of the model by transcriptome sequencing; detected renal injury and fibrosis by hematoxylin eosin staining, Von Kossa staining and Sirius red staining; detected MMT levels by multiplexed immunofluorescence and flow cytometry; and verified the binding site of STAT6 at the PPARα promoter by chromatin immunoprecipitation. Fatty acid oxidation (FAO) and fibrosis-related genes were detected by western blot and real-time quantitative polymerase chain reaction.

RESULTS

In this study, we found that FAO was downregulated, macrophages converted to myofibroblasts, and STAT6 expression was elevated in stone patients and glyoxylate-induced kidney stone mice. The promotion of FAO in macrophages attenuated MMT and upregulated fibrosis-related genes induced by calcium oxalate treatment. Further, inhibition of peroxisome proliferator-activated receptor-α (PPARα) eliminated the effect of STAT6 deletion on FAO and fibrosis-associated protein expression. Pharmacological inhibition of STAT6 also prevented the development of renal injury, lipid accumulation, MMT, and renal fibrosis. Mechanistically, STAT6 transcriptionally represses PPARα and FAO through cis-inducible elements located in the promoter region of the gene, thereby promoting MMT and renal fibrosis.

CONCLUSIONS

These findings establish a role for STAT6 in kidney stone injury-induced renal fibrosis, and suggest that STAT6 may be a therapeutic target for progressive renal fibrosis in patients with nephrolithiasis.

Macrophage polarization in tissue fibrosis

Fibrosis can occur in all major organs with relentless progress, ultimately leading to organ failure and potentially death. Unfortunately, current clinical treatments cannot prevent or reverse tissue fibrosis. Thus, new and effective antifibrotic therapeutics are urgently needed. In recent years, a growing body of research shows that macrophages are involved in fibrosis. Macrophages are highly heterogeneous, polarizing into different phenotypes. Some studies have found that regulating macrophage polarization can inhibit the development of inflammation and cancer. However, the exact mechanism of macrophage polarization in different tissue fibrosis has not been fully elucidated. This review will discuss the major signaling pathways relevant to macrophage-driven fibrosis and profibrotic macrophage polarization, the role of macrophage polarization in fibrosis of lung, kidney, liver, skin, and heart, potential therapeutics targets, and investigational drugs currently in development, and hopefully, provide a useful review for the future treatment of fibrosis.

Macrophage-Myofibroblast Transition Contributes to Myofibroblast Formation in Proliferative Vitreoretinal Disorders

Inflammation and fibrosis are key features of proliferative vitreoretinal disorders. We aimed to define the macrophage phenotype and investigate the role of macrophage-myofibroblast transition (MMT) in the contribution to myofibroblast populations present in epiretinal membranes. Vitreous samples from proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR) and nondiabetic control patients, epiretinal fibrovascular membranes from PDR patients and fibrocellular membranes from PVR patients, human retinal Müller glial cells and human retinal microvascular endothelial cells (HRMECs) were studied by ELISA, immunohistochemistry and flow cytometry analysis. Myofibroblasts expressing α-SMA, fibroblast activation protein-α (FAP-α) and fibroblast-specific protein-1 (FSP-1) were present in all membranes. The majority of CD68+ monocytes/macrophages co-expressed the M2 macrophage marker CD206. In epiretinal membranes, cells undergoing MMT were identified by co-expression of the macrophage marker CD68 and myofibroblast markers α-SMA and FSP-1. Further analysis revealed that CD206+ M2 macrophages co-expressed α-SMA, FSP-1, FAP-α and ß-catenin. Soluble (s) CD206 and sFAP-α levels were significantly higher in vitreous samples from PDR and PVR patients than in nondiabetic control patients. The proinflammatory cytokine TNF-α and the hypoxia mimetic agent cobalt chloride induced upregulation of sFAP-α in culture media of Müller cells but not of HRMECs. The NF-ĸß inhibitor BAY11-7085 significantly attenuated TNF-α-induced upregulation of sFAP-α in Müller cells. Our findings suggest that the process of MMT might contribute to myofibroblast formation in epiretinal membranes, and this transition involved macrophages with a predominant M2 phenotype. In addition, sFAP-α as a vitreous biomarker may be derived from M2 macrophages transitioned to myofibroblasts and from Müller cells.

Epithelial-Mesenchymal Transition Mechanisms in Chronic Airway Diseases: A Common Process to Target?

Epithelial-to-mesenchymal transition (EMT) is a reversible process, in which epithelial cells lose their epithelial traits and acquire a mesenchymal phenotype. This transformation has been described in different lung diseases, such as lung cancer, interstitial lung diseases, asthma, chronic obstructive pulmonary disease and other muco-obstructive lung diseases, such as cystic fibrosis and non-cystic fibrosis bronchiectasis. The exaggerated chronic inflammation typical of these pulmonary diseases can induce molecular reprogramming with subsequent self-sustaining aberrant and excessive profibrotic tissue repair. Over time this process leads to structural changes with progressive organ dysfunction and lung function impairment. Although having common signalling pathways, specific triggers and regulation mechanisms might be present in each disease. This review aims to describe the various mechanisms associated with fibrotic changes and airway remodelling involved in chronic airway diseases. Having better knowledge of the mechanisms underlying the EMT process may help us to identify specific targets and thus lead to the development of novel therapeutic strategies to prevent or limit the onset of irreversible structural changes.

Vitamin A and retinoid signaling in the kidneys

Vitamin A (VA, retinol) and its metabolites (commonly called retinoids) are required for the proper development of the kidney during embryogenesis, but retinoids also play key roles in the function and repair of the kidney in adults. Kidneys filter 180-200 liters of blood per day and each kidney contains approximately 1 million nephrons, which are often referred to as the 'functional units' of the kidney. Each nephron consists of a glomerulus and a series of tubules (proximal tubule, loop of Henle, distal tubule, and collecting duct) surrounded by a network of capillaries. VA is stored in the liver and converted to active metabolites, most notably retinoic acid (RA), which acts as an agonist for the retinoic acid receptors ((RARs α, β, and γ) to regulate gene transcription. In this review we discuss some of the actions of retinoids in the kidney after injury. For example, in an ischemia-reperfusion model in mice, injury-associated loss of proximal tubule (PT) differentiation markers occurs, followed by re-expression of these differentiation markers during PT repair. Notably, healthy proximal tubules express ALDH1a2, the enzyme that metabolizes retinaldehyde to RA, but transiently lose ALDH1a2 expression after injury, while nearby myofibroblasts transiently acquire RA-producing capabilities after injury. These results indicate that RA is important for renal tubular injury repair and that compensatory mechanisms exist for the generation of endogenous RA by other cell types upon proximal tubule injury. ALDH1a2 levels also increase in podocytes, epithelial cells of the glomeruli, after injury, and RA promotes podocyte differentiation. We also review the ability of exogenous, pharmacological doses of RA and receptor selective retinoids to treat numerous kidney diseases, including kidney cancer and diabetic kidney disease, and the emerging genetic evidence for the importance of retinoids and their receptors in maintaining or restoring kidney function after injury. In general, RA has a protective effect on the kidney after various types of injuries (eg. ischemia, cytotoxic actions of chemicals, hyperglycemia related to diabetes). As more research into the actions of each of the three RARs in the kidney is carried out, a greater understanding of the actions of vitamin A is likely to lead to new insights into the pathology of kidney disorders and the development of new therapies for kidney diseases.

Promising small molecule anti-fibrotic agents: Newly developed or repositioned drugs targeting myofibroblast transdifferentiation

Fibrosis occurs in all organs and tissues except the brain, and its progression leads to dysfunction of affected organs. Fibrosis-induced organ dysfunction results from the loss of elasticity, strength, and functionality of tissues due to the extracellular matrix secreted by myofibroblasts that express smooth muscle-type actin as a marker. Myofibroblasts, which play a major role in fibrosis, were once thought to originate exclusively from activated fibroblasts; however, it is now clear that myofibroblasts are diverse in origin, from epithelial cells, endothelial cells, adipocytes, macrophages, and other cells. Fibrosis of vital organs, such as the heart, lungs, kidneys, and liver, is a serious chronic disease that ultimately leads to death. Currently, anti-cancer drugs have made remarkable progress, as evidenced by the development of many molecular-targeted drugs, and are making a significant contribution to improving the prognosis of cancer treatment. However, the development of anti-fibrotic agents, which also play an important role in prognosis, has lagged. In this review, the current knowledge regarding myofibroblasts is summarized, with particular attention given to their origin and transdifferentiation signaling pathways (e.g., TGF-β, Wnt/β-catenin, YAP/TAZ and AMPK signaling pathways). The development of new small molecule anti-fibrotic agents and the repositioning of existing drugs targeting myofibroblast transdifferentiation are discussed.

Research Progress of Cordyceps sinensis and Its Fermented Mycelium Products on Ameliorating Renal Fibrosis by Reducing Epithelial-to-Mesenchymal Transition

Renal fibrosis is a hallmark and common outcome of various chronic kidney diseases (CKDs) and manifests pathologically as accumulation and deposition of extracellular matrix (ECM) in the kidney. Epithelial-to-mesenchymal transition (EMT) has been shown to be an important mechanism involved in renal fibrosis. Cordyceps sinensis, a traditional Chinese medicine, has long been used for the treatment of renal fibrosis. As research on the mycelium of C. sinensis progressed, a variety of medicines developed from fermented mycelium were used to treat CKD. However, their efficacies and mechanisms have not been fully summarized. In this review, five medicines developed from fermented mycelium of C. sinensis are presented. The pharmacodynamic effects of C. sinensis on different animal models of renal fibrosis are summarized. The in vitro studies and related mechanisms of C. sinensis on renal cells are detailed. Finally, the application and efficacy of these five commercial medicines that meet national standards in different types of CKD are summarized. From this review, it can be concluded that C. sinensis can alleviate various causes of renal fibrosis to some extent, and its mechanism is related to TGF-β1 dependent signaling, inhibition of inflammation, and improvement of renal function. Further research on rigorously designed, large-sample, clinically randomized controlled trial studies and detailed mechanisms should be conducted.

Fibrocytes enhance mammary gland fibrosis in obesity

Obesity rates continue to rise, and obese individuals are at higher risk for multiple types of cancer, including breast cancer. Obese mammary fat is a site of chronic, macrophage-driven inflammation, which enhances fibrosis within adipose tissue. Elevated fibrosis within the mammary gland may contribute to risk for obesity-associated breast cancer. To understand how inflammation due to obesity enhanced fibrosis within mammary tissue, we utilized a high-fat diet model of obesity and elimination of CCR2 signaling in mice to identify changes in immune cell populations and their impact on fibrosis. We observed that obesity increased a population of CD11b+ cells with the ability to form myofibroblast-like colonies in vitro. This population of CD11b+ cells is consistent with fibrocytes, which have been identified in wound healing and chronic inflammatory diseases but have not been examined in obesity. In CCR2-null mice, which have limited ability to recruit myeloid lineage cells into obese adipose tissue, we observed reduced mammary fibrosis and diminished fibrocyte colony formation in vitro. Transplantation of myeloid progenitor cells, which are the cells of origin for fibrocytes, into the mammary glands of obese CCR2-null mice resulted in significantly increased myofibroblast formation. Gene expression analyses of the myeloid progenitor cell population from obese mice demonstrated enrichment for genes associated with collagen biosynthesis and extracellular matrix remodeling. Together these results show that obesity enhances recruitment of fibrocytes to promote obesity-induced fibrosis in the mammary gland.

A2BAR Antagonism Decreases the Glomerular Expression and Secretion of Chemoattractants for Monocytes and the Pro-Fibrotic M2 Macrophages Polarization during Diabetic Nephropathy

Some chemoattractants and leukocytes such as M1 and M2 macrophages are known to be involved in the development of glomerulosclerosis during diabetic nephropathy (DN). In the course of diabetes, an altered and defective cellular metabolism leads to the increase in adenosine levels, and thus to changes in the polarity (M1/M2) of macrophages. MRS1754, a selective antagonist of the A2B adenosine receptor (A2BAR), attenuated glomerulosclerosis and decreased macrophage-myofibroblast transition in DN rats. Therefore, we aimed to investigate the effect of MRS1754 on the glomerular expression/secretion of chemoattractants, the intraglomerular infiltration of leukocytes, and macrophage polarity in DN rats. Kidneys/glomeruli of non-diabetic, DN, and MRS1754-treated DN rats were processed for transcriptomic analysis, immunohistopathology, ELISA, and in vitro macrophage migration assays. The transcriptomic analysis identified an upregulation of transcripts and pathways related to the immune system in the glomeruli of DN rats, which was attenuated using MRS1754. The antagonism of the A2BAR decreased glomerular expression/secretion of chemoattractants (CCL2, CCL3, CCL6, and CCL21), the infiltration of macrophages, and their polarization to M2 in DN rats. The in vitro macrophages migration induced by conditioned-medium of DN glomeruli was significantly decreased using neutralizing antibodies against CCL2, CCL3, and CCL21. We concluded that the pharmacological blockade of the A2BAR decreases the transcriptional expression of genes/pathways related to the immune response, protein expression/secretion of chemoattractants, as well as the infiltration of macrophages and their polarization toward the M2 phenotype in the glomeruli of DN rats, suggesting a new mechanism implicated in the antifibrotic effect of MRS1754.

Obesity and Fibrosis: Setting the Stage for Breast Cancer

Obesity is a rising health concern and is linked to a worsened breast cancer prognosis. Tumor desmoplasia, which is characterized by elevated numbers of cancer-associated fibroblasts and the deposition of fibrillar collagens within the stroma, may contribute to the aggressive clinical behavior of breast cancer in obesity. A major component of the breast is adipose tissue, and fibrotic changes in adipose tissue due to obesity may contribute to breast cancer development and the biology of the resulting tumors. Adipose tissue fibrosis is a consequence of obesity that has multiple sources. Adipocytes and adipose-derived stromal cells secrete extracellular matrix composed of collagen family members and matricellular proteins that are altered by obesity. Adipose tissue also becomes a site of chronic, macrophage-driven inflammation. Macrophages exist as a diverse population within obese adipose tissue and mediate the development of fibrosis through the secretion of growth factors and matricellular proteins and interactions with other stromal cells. While weight loss is recommended to resolve obesity, the long-term effects of weight loss on adipose tissue fibrosis and inflammation within breast tissue are less clear. Increased fibrosis within breast tissue may increase the risk for tumor development as well as promote characteristics associated with tumor aggressiveness.

“Long COVID-19” and viral “fibromyalgia-ness”: Suggesting a mechanistic role for fascial myofibroblasts (Nineveh, the shadow is in the fascia)

The coronavirus pandemic has led to a wave of chronic disease cases; “Long COVID-19” is recognized as a new medical entity and resembles “fibromyalgia” which, likewise, lacks a clear mechanism. Observational studies indicate that up to 30%–40% of convalescent COVID-19 patients develop chronic widespread pain and fatigue and fulfill the 2016 diagnostic criteria for “fibromyalgia.” A recent study suggested a theoretical neuro-biomechanical model (coined “Fascial Armoring”) to help explain the pathogenesis and cellular pathway of fibromyalgia, pointing toward mechanical abnormalities in connective tissue and fascia, driven by contractile myo/fibroblasts and altered extracellular matrix remodeling with downstream corresponding neurophysiological aberrations. This may help explain several of fibromyalgia’s manifestations such as pain, distribution of pain, trigger points/tender spots, hyperalgesia, chronic fatigue, cardiovascular abnormalities, metabolic abnormalities, autonomic abnormalities, small fiber neuropathy, various psychosomatic symptoms, lack of obvious inflammation, and silent imaging investigations. Pro-inflammatory and pro-fibrotic pathways provide input into this mechanism via stimulation of proto/myofibroblasts. In this hypothesis and theory paper the theoretical model of Fascial Armoring is presented to help explain the pathogenesis and manifestations of “long COVID-19” as a disease of immuno-rheumo-psycho-neurology. The model is also used to make testable experimental predictions on investigations and predict risk and relieving factors.

Quercetin Alleviates Pulmonary Fibrosis in Silicotic Mice by Inhibiting Macrophage Transition and TGF-β-Smad2/3 Pathway

Silicosis is a pulmonary disease caused by the inhalation of silica. There is a lack of early and effective prevention, diagnosis, and treatment methods, and addressing silicotic fibrosis is crucial. Quercetin, a flavonoid with anti-carcinogenic, anti-inflammatory, and antiviral properties, is known to have a suppressive effect on fibrosis. The present study aimed to determine the therapeutic effect of quercetin on silicotic mice and macrophage polarity. We found that quercetin suppressed silicosis in mice. It was observed that SiO₂ activated macrophage polarity and the macrophage-to-myofibroblast transition (MMT) by transforming the growth factor-β (TGF-β)-Smad2/3 signaling pathway in silicotic mice and MH-S cells. Quercetin also attenuated the MMT and the TGF-β-Smad2/3 signaling pathway in vivo and in vitro. The present study demonstrated that quercetin is a potential therapeutic agent for silicosis, which acts by regulating macrophage polarity and the MMT through the TGF-β-Smad2/3 signaling pathway.

Tissue transglutaminase exacerbates renal fibrosis via alternative activation of monocyte-derived macrophages

Macrophages are important components in modulating homeostatic and inflammatory responses and are generally categorized into two broad but distinct subsets: classical activated (M1) and alternatively activated (M2) depending on the microenvironment. Fibrosis is a chronic inflammatory disease exacerbated by M2 macrophages, although the detailed mechanism by which M2 macrophage polarization is regulated remains unclear. These polarization mechanisms have little in common between mice and humans, making it difficult to adapt research results obtained in mice to human diseases. Tissue transglutaminase (TG2) is a known marker common to mouse and human M2 macrophages and is a multifunctional enzyme responsible for crosslinking reactions. Here we sought to identify the role of TG2 in macrophage polarization and fibrosis. In IL-4-treated macrophages derived from mouse bone marrow and human monocyte cells, the expression of TG2 was increased with enhancement of M2 macrophage markers, whereas knockout or inhibitor treatment of TG2 markedly suppressed M2 macrophage polarization. In the renal fibrosis model, accumulation of M2 macrophages in fibrotic kidney was significantly reduced in TG2 knockout or inhibitor-administrated mice, along with the resolution of fibrosis. Bone marrow transplantation using TG2-knockout mice revealed that TG2 is involved in M2 polarization of infiltrating macrophages derived from circulating monocytes and exacerbates renal fibrosis. Furthermore, the suppression of renal fibrosis in TG2-knockout mice was abolished by transplantation of wild-type bone marrow or by renal subcapsular injection of IL4-treated macrophages derived from bone marrow of wild-type, but not TG2 knockout. Transcriptome analysis of downstream targets involved in M2 macrophages polarization revealed that ALOX15 expression was enhanced by TG2 activation and promoted M2 macrophage polarization. Furthermore, the increase in the abundance of ALOX15-expressing macrophages in fibrotic kidney was dramatically suppressed in TG2-knockout mice. These findings demonstrated that TG2 activity exacerbates renal fibrosis by polarization of M2 macrophages from monocytes via ALOX15.