LRP-6 is a coreceptor for multiple fibrogenic signaling pathways in pericytes and myofibroblasts that are inhibited by DKK-1

Deficient RPE mitochondrial energetics leads to subretinal fibrosis in age-related neovascular macular degeneration

Subretinal fibrosis permanently impairs the vision of patients with neovascular age-related macular degeneration. Despite emerging evidence revealing the association between disturbed metabolism in retinal pigment epithelium (RPE) and subretinal fibrosis, the underlying mechanism remains unclear. In the present study, single-cell RNA sequencing revealed, prior to subretinal fibrosis, genes in mitochondrial fatty acid oxidation are downregulated in the RPE lacking very low-density lipoprotein receptor (VLDLR), especially the rate-limiting enzyme carnitine palmitoyltransferase 1A (CPT1A). We found that overexpression of CPT1A in the RPE of Vldlr-/- mice suppresses epithelial-to-mesenchymal transition and fibrosis. Mechanistically, TGFβ2 induces fibrosis by activating a Warburg-like effect, i.e. increased glycolysis and decreased mitochondrial respiration through ERK-dependent CPT1A degradation. Moreover, VLDLR blocks the formation of the TGFβ receptor I/II complex by interacting with unglycosylated TGFβ receptor II. In conclusion, VLDLR suppresses fibrosis by attenuating TGFβ2-induced metabolic reprogramming, and CPT1A is a potential target for treating subretinal fibrosis.

The fate and role of the pericytes in myocardial diseases

The adult mammalian heart contains a large population of pericytes that play important roles in homeostasis and disease. In the normal heart, pericytes regulate microvascular permeability and flow. Myocardial diseases are associated with marked alterations in pericyte phenotype and function. This review manuscript discusses the role of pericytes in cardiac homeostasis and disease. Following myocardial infarction (MI), cardiac pericytes participate in all phases of cardiac repair. During the inflammatory phase, pericytes may secrete cytokines and chemokines and may regulate leukocyte trafficking, through formation of intercellular gaps that serve as exit points for inflammatory cells. Moreover, pericyte contraction induces microvascular constriction, contributing to the pathogenesis of 'no-reflow' in ischemia and reperfusion. During the proliferative phase, pericytes are activated by growth factors, such as transforming growth factor (TGF)-β and contribute to fibrosis, predominantly through secretion of fibrogenic mediators. A fraction of pericytes acquires fibroblast identity but contributes only to a small percentage of infarct fibroblasts and myofibroblasts. As the scar matures, pericytes form a coat around infarct neovessels, promoting stabilization of the vasculature. Pericytes may also be involved in the pathogenesis of chronic heart failure, by regulating inflammation, fibrosis, angiogenesis and myocardial perfusion. Pericytes are also important targets of viral infections (such as SARS-CoV2) and may be implicated in the pathogenesis of cardiac complications of COVID19. Considering their role in myocardial inflammation, fibrosis and angiogenesis, pericytes may be promising therapeutic targets in myocardial disease.

Basic Fibroblast Growth Factor Supports the Function of Limbal Niche Cells via the Wnt/β-Catenin Pathway

Purpose: To test the effects and underlying mechanisms of basic fibroblast growth factor (bFGF) on the limbal niche cell (LNC) function ex vivo. Methods: By using different concentrations of bFGF (0, 4, 8, 12, and 16 ng/mL) and fibroblast growth factor receptor (FGFR) inhibitors, the effects of bFGF on LNC proliferation, expression of stem cell markers, and transcription levels of the β-catenin were investigated. Single-cell RNA sequencing (scRNA-seq) was used to analyze the action and mechanisms of FGFR subtypes and the Wnt/β-catenin pathway during LNC culture. An mature corneal epithelial cell (MCEC)/LNC three-dimensional model was constructed to verify whether bFGF activates the Wnt/β-catenin pathway in LNC by inhibiting FGFR or β-catenin targets. Results: scRNA-seq showed that FGFR1 is the main receptor in LNC, along with the molecules in the Wnt pathway, including WNT2, FZD7, LRP5, LRP6, and β-catenin. The 12 ng/mL bFGF treatment group showed higher LNC proliferation rate and transcription levels of OCT4, SOX2, NANOG, and β-catenin than any other groups (P < 0.001). In the MCEC/LNC co-culture model, MCEC/LNC treated with 12 ng/mL bFGF promoted the aggregation of the spheres than other groups, associated with increased transcription levels of P63α, WNT2, β-catenin, and a decreased transcription level of CK12 (P < 0.001). Wnt/β-catenin inhibitor LF3 treatment reversed the abovementioned effect of bFGF. Conclusions: bFGF could maintain and promote the stemness of LNC via the FGFR1/Wnt2/FZD7/LRP6 axis in a concentration-dependent manner.

DKK1 loss promotes endometrial fibrosis via autophagy and exosome-mediated macrophage-to-myofibroblast transition

INTRODUCTION

Intrauterine adhesions (IUA) manifest as endometrial fibrosis, often causing infertility or recurrent miscarriage; however, their pathogenesis remains unclear.

OBJECTIVES

This study assessed the role of Dickkopf WNT signaling pathway inhibitor 1 (DKK1) and autophagy in endometrial fibrosis, using clinical samples as well as in vitro and in vivo experiments.

METHODS

Immunohistochemistry, immunofluorescence and western blot were used to determine the localization and expression of DKK1 in endometrium; DKK1 silencing and DKK1 overexpression were used to detect the biological effects of DKK1 silencing or expression in endometrial cells; DKK1 gene knockout mice were used to observe the phenotypes caused by DKK1 gene knockout.

RESULTS

In patients with IUA, DKK1 and autophagy markers were down-regulated; also, α-SMA and macrophage localization were increased in the endometrium. DKK1 conditional knockout (CKO) mice showed a fibrotic phenotype with decreased autophagy and increased localization of α-SMA and macrophages in the endometrium. In vitro studies showed that DKK1 knockout (KO) suppressed the autophagic flux of endometrial stromal cells. In contrast, ectopic expression of DKK1 showed the opposite phenotype. Mechanistically, we discovered that DKK1 regulates autophagic flux through Wnt/β-catenin and PI3K/AKT/mTOR pathways. Further studies showed that DKK1 KO promoted the secretion of interleukin (IL)-8 in exosomes, thereby promoting macrophage proliferation and metastasis. Also, in DKK1 CKO mice, treatment with autophagy activator rapamycin partially restored the endometrial fibrosis phenotype.

CONCLUSION

Our findings indicated that DKK1 was a potential diagnostic marker or therapeutic target for IUA.

Endothelial Dickkopf-1 Promotes Smooth Muscle Cell-derived Foam Cell Formation via USP53-mediated Deubiquitination of SR-A During Atherosclerosis

Background: Shear stress-induced Dickkopf-1 (DKK1) secretion by endothelial cells (ECs) promotes EC dysfunction and accelerates atherosclerosis (AS). However, the paracrine role of endothelial DKK1 in modulating adjacent smooth muscle cells (SMCs) in atherosclerosis remains unclear. This study investigated the role of EC-secreted DKK1 in SMC-derived foam cell formation under shear stress, in vitro and in vivo. Methods: Parallel-plate co-culture flow system was used to explore the cellular communication between ECs and SMCs under shear stress in vitro. Endothelium-specific knockout of DKK1 (DKK1ECKO/APOE-/-) and endothelium-specific overexpression of DKK1 (DKK1ECTg) mice were constructed to investigate the role of endothelial DKK1 in atherosclerosis and SMC-derived foam cell formation in vivo. RNA sequencing (RNA-seq) was used to identify the downstream targets of DKK1. Reverse transcription quantitative polymerase chain reaction (RT-qPCR), western blot, coimmunoprecipitation (Co-IP) assays and chromatin immunoprecipitation (ChIP) experiments were conducted to explore the underlying regulatory mechanisms. Results: DKK1 is transcriptionally upregulated in ECs under conditions of low shear stress, but not in co-cultured SMCs. However, DKK1 protein in co-cultured SMCs is increased via uptake of low shear stress-induced endothelial DKK1, thereby promoting lipid uptake and foam cell formation in co-cultured SMCs via the post-translational upregulation of scavenger receptor-A (SR-A) verified in parallel-plate co-culture flow system, DKK1ECKO and DKK1ECTg mice. RNA sequencing revealed that DKK1-induced SR-A upregulation in SMCs is dependent on Ubiquitin-specific Protease 53 (USP53), which bound to SR-A via its USP domain and cysteine at position 41, exerting deubiquitination to maintain the stability of the SR-A protein by removing the K48 ubiquitin chain and preventing proteasomal pathway degradation, thereby mediating the effect of DKK1 on lipid uptake in SMCs. Moreover, DKK1 regulates the transcription of USP53 by facilitating the binding of transcription factor CREB to the USP53 promoter. SMC-specific overexpression of USP53 via adeno-associated virus serotype 2 vectors in DKK1ECKO/APOE-/- mice reversed the alleviation of atherosclerotic plaque burden, SR-A expression and lipid accumulation in SMCs within plaques resulting from DKK1 deficiency. Conclusions: Our findings demonstrate that, endothelial DKK1, induced by pathological low shear stress, acts as an intercellular mediator, promoted the foam cell formation of SMCs. These results suggest that targeted intervention with endothelial DKK1 may confer beneficial effects on atherosclerosis.

The involvement of the Wnt/β-catenin signaling cascade in fibrosis progression and its therapeutic targeting by relaxin

Organ scarring, referred to as fibrosis, results from a failed wound-healing response to chronic tissue injury and is characterised by the aberrant accumulation of various extracellular matrix (ECM) components. Once established, fibrosis is recognised as a hallmark of stiffened and dysfunctional tissues, hence, various fibrosis-related diseases collectively contribute to high morbidity and mortality in developed countries. Despite this, these diseases are ineffectively treated by currently-available medications. The pro-fibrotic cytokine, transforming growth factor (TGF)-β1, has emerged as the master regulator of fibrosis progression, owing to its ability to promote various factors and processes that facilitate rapid ECM synthesis and deposition, whilst negating ECM degradation. TGF-β1 signal transduction is tightly controlled by canonical (Smad-dependent) and non-canonical (MAP kinase- and Rho-associated protein kinase-dependent) intracellular protein activity, whereas its pro-fibrotic actions can also be facilitated by the Wnt/β-catenin pathway. This review outlines the pathological sequence of events and contributing roles of TGF-β1 in the progression of fibrosis, and how the Wnt/β-catenin pathway contributes to tissue repair in acute disease settings, but to fibrosis and related tissue dysfunction in synergy with TGF-β1 in chronic diseases. It also outlines the anti-fibrotic and related signal transduction mechanisms of the hormone, relaxin, that are mediated via its negative modulation of TGF-β1 and Wnt/β-catenin signaling, but through the promotion of Wnt/β-catenin activity in acute disease settings. Collectively, this highlights that the crosstalk between TGF-β1 signal transduction and the Wnt/β-catenin cascade may provide a therapeutic target that can be exploited to broadly treat and reverse established fibrosis.

Drugs targeting CTGF in the treatment of pulmonary fibrosis

Pulmonary fibrosis represents the final alteration seen in a wide variety of lung disorders characterized by increased fibroblast activity and the accumulation of substantial amounts of extracellular matrix, along with inflammatory damage and the breakdown of tissue architecture. This condition is marked by a significant mortality rate and a lack of effective treatments. The depositing of an excessive quantity of extracellular matrix protein follows the damage to lung capillaries and alveolar epithelial cells, leading to pulmonary fibrosis and irreversible damage to lung function. It has been proposed that the connective tissue growth factor (CTGF) plays a critical role in the advancement of pulmonary fibrosis by enhancing the accumulation of the extracellular matrix and exacerbating fibrosis. In this context, the significance of CTGF in pulmonary fibrosis is examined, and a summary of the development of drugs targeting CTGF for the treatment of pulmonary fibrosis is provided.

miR-148a-3p regulates proliferation and apoptosis of idiopathic gingival fibroma by targeting NPTX1

OBJECTIVE

Idiopathic gingival fibromatosis (IGF) is a rare heterogeneous disease that results in the progressive and diffuse hyperplasia of gingival tissues. MicroRNAs are implicated in the development and progression of various tumors. The present study aimed to explore the potential roles and mechanisms of miR-148a-3p in IGF.

METHODS

Gingival fibroblasts (GFs) were transfected with miR-148a-3p mimics, miR-148a-3p inhibitors, or siNPTX1, and then, the proliferation and apoptosis of GFs and the expression of related genes were evaluated using Cell Counting Kit-8 assays, 5-ethynyl-2'-deoxyuridine assays, flow cytometry, reverse transcription-quantitative polymerase chain reaction, and western blot analysis, respectively.

RESULTS

miR-148a-3p was highly expressed in GFs of IGF (IGF-GFs) as compared with normal GFs (N-GFs). Overexpression of miR-148a-3p promoted the proliferation and inhibited the apoptosis of N-GFs, whereas downregulation of miR-148a-3p had the opposite effect in IGF-GFs. Knockdown of NPTX1 reversed miR-148a-3p-mediated effects in IGF-GFs. Dual-luciferase reporter assay confirmed that NPTX1 is a direct target of miR-148a-3p.

CONCLUSION

These findings identify that miR-148a-3p could regulate cell proliferation and apoptosis by targeting NPTX1, providing new insights for the further study of the molecular mechanism and treatment of IGF.

Update of pericytes function and their roles in kidney diseases

Studies have highlighted the significant involvement of kidney pericytes in renal fibrosis. Kidney pericytes, classified as interstitial mesenchymal cells, are extensively branched, collagen-producing cells that closely interact with endothelial cells. This article aims to provide an overview of the recent advancements in understanding the physiological functions of pericytes and their roles in kidney diseases. In a healthy kidney, pericytes have essential physiological function in angiogenesis, erythropoietin (EPO) production, and the regulation of renal blood flow. Nevertheless, pericyte-myofibroblast transition has been identified as the primary cause of disease progression in acute kidney injury (AKI)-to-chronic kidney disease (CKD) continuum. Our recent research has demonstrated that hypoxia-inducible factor-2α (HIF-2α) regulates erythropoietin production in pericytes. However, this production is repressed by EPO gene hypermethylation and HIF-2α downregulation which were induced by transforming growth factor-β1-activated DNA methyltransferase and activin receptor-like kinase-5 signaling pathway during renal fibrosis, respectively. Additionally, AKI induces epigenetic modifications in pericytes, rendering them more prone to extracellular matrix production, cell migration and proliferation, thereby contributing to subsequent capillary rarefaction and renal fibrosis. Further investigation into the specific functions and roles of different subpopulations of pericytes may contribute for the development of targeted therapies aimed at attenuating kidney disease and mitigating their adverse effects.

Mitochondrial Signaling, the Mechanisms of AKI-to-CKD Transition and Potential Treatment Targets

Acute kidney injury (AKI) is increasing in prevalence and causes a global health burden. AKI is associated with significant mortality and can subsequently develop into chronic kidney disease (CKD). The kidney is one of the most energy-demanding organs in the human body and has a role in active solute transport, maintenance of electrochemical gradients, and regulation of fluid balance. Renal proximal tubular cells (PTCs) are the primary segment to reabsorb and secrete various solutes and take part in AKI initiation. Mitochondria, which are enriched in PTCs, are the main source of adenosine triphosphate (ATP) in cells as generated through oxidative phosphorylation. Mitochondrial dysfunction may result in reactive oxygen species (ROS) production, impaired biogenesis, oxidative stress multiplication, and ultimately leading to cell death. Even though mitochondrial damage and malfunction have been observed in both human kidney disease and animal models of AKI and CKD, the mechanism of mitochondrial signaling in PTC for AKI-to-CKD transition remains unknown. We review the recent findings of the development of AKI-to-CKD transition with a focus on mitochondrial disorders in PTCs. We propose that mitochondrial signaling is a key mechanism of the progression of AKI to CKD and potential targeting for treatment.

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.

Module 4-Deficient CCN2/Connective Tissue Growth Factor Attenuates the Progression of Renal Fibrosis via Suppression of Focal Adhesion Kinase Phosphorylation in Tubular Epithelial Cells

CCN2/connective tissue growth factor (CTGF) potentially serves as a therapeutic target for chronic kidney disease. Here we investigated CCN2 module-4, encoded by Ccn2 exon 5, through the generation of Ccn2 exon 5 knockout mice (Ex5-/- mice). To investigate renal fibrosis pathogenesis, Ex5-/- mice were employed to model unilateral ureteral obstruction (UUO), unilateral ischemic-reperfusion injury (UIRI), and 5/6 nephrectomy. Interstitial fibrosis was significantly attenuated in the Ex5-/- mice in the three models. Furthermore, phosphorylated focal adhesion kinase (FAK) levels in tubular epithelial cells were significantly lower in the kidneys of the UUO- and UIRI-Ex5-/- mice than those of the Ex5+/+ mice. Moreover, CCN2 module 4-mediated renal tubule FAK and promoted fibrosis. These findings indicate that CCN2 module-4-FAK pathway components will serve as therapeutic targets for effectively attenuating renal fibrosis.

Research advances in cochlear pericytes and hearing loss

Pericytes are specialized mural cells surrounding endothelial cells in microvascular beds. They play a role in vascular development, blood flow regulation, maintenance of blood-tissue barrier integrity, and control of angiogenesis, tissue fibrosis, and wound healing. In recent decades, understanding of the critical role played by pericytes in retina, brain, lung, and kidney has seen significant progress. The cochlea contains a large population of pericytes. However, the role of cochlear pericytes in auditory pathophysiology is, by contrast, largely unknown. The present review discusses recent progress in identifying cochlear pericytes, mapping their distribution, and defining their role in regulating blood flow, controlling the blood-labyrinth barrier (BLB) and angiogenesis, and involvement in different types of hearing loss.

Pregnane X receptor activation alleviates renal fibrosis in mice via interacting with p53 and inhibiting the Wnt7a/β-catenin signaling

Renal fibrosis is a common pathological feature of chronic kidney disease (CKD) with various etiologies, which seriously affects the structure and function of the kidney. Pregnane X receptor (PXR) is a member of the nuclear receptor superfamily and plays a critical role in regulating the genes related to xenobiotic and endobiotic metabolism in mammals. Previous studies show that PXR is expressed in the kidney and has protective effect against acute kidney injury (AKI). In this study, we investigated the role of PXR in CKD. Adenine diet-induced CKD (AD) model was established in wild-type and PXR humanized (hPXR) mice, respectively, which were treated with pregnenolone-16α-carbonitrile (PCN, 50 mg/kg, twice a week for 4 weeks) or rifampicin (RIF, 10 mg·kg-1·d-1, for 4 weeks). We showed that both PCN and RIF, which activated mouse and human PXR, respectively, improved renal function and attenuated renal fibrosis in the two types of AD mice. In addition, PCN treatment also alleviated renal fibrosis in unilateral ureter obstruction (UUO) mice. On the contrary, PXR gene deficiency exacerbated renal dysfunction and fibrosis in both adenine- and UUO-induced CKD mice. We found that PCN treatment suppressed the expression of the profibrotic Wnt7a and β-catenin in AD mice and in cultured mouse renal tubular epithelial cells treated with TGFβ1 in vitro. We demonstrated that PXR was colocalized and interacted with p53 in the nuclei of tubular epithelial cells. Overexpression of p53 increased the expression of Wnt7a, β-catenin and its downstream gene fibronectin. We further revealed that p53 bound to the promoter of Wnt7a gene to increase its transcription and β-catenin activation, leading to increased expression of the downstream profibrotic genes, which was inhibited by PXR. Taken together, PXR activation alleviates renal fibrosis in mice via interacting with p53 and inhibiting the Wnt7a/β-catenin signaling pathway.

Cardiac Pericytes Acquire a Fibrogenic Phenotype and Contribute to Vascular Maturation After Myocardial Infarction

BACKGROUND

Pericytes have been implicated in tissue repair, remodeling, and fibrosis. Although the mammalian heart contains abundant pericytes, their fate and involvement in myocardial disease remains unknown.

METHODS

We used NG2Dsred;PDGFRαEGFP pericyte:fibroblast dual reporter mice and inducible NG2CreER mice to study the fate and phenotypic modulation of pericytes in myocardial infarction. The transcriptomic profile of pericyte-derived cells was studied using polymerase chain reaction arrays and single-cell RNA sequencing. The role of transforming growth factor-β (TGF-β) signaling in regulation of pericyte phenotype was investigated in vivo using pericyte-specific TGF-β receptor 2 knockout mice and in vitro using cultured human placental pericytes.

RESULTS

In normal hearts, neuron/glial antigen 2 (NG2) and platelet-derived growth factor receptor α (PDGFRα) identified distinct nonoverlapping populations of pericytes and fibroblasts, respectively. After infarction, a population of cells expressing both pericyte and fibroblast markers emerged. Lineage tracing demonstrated that in the infarcted region, a subpopulation of pericytes exhibited transient expression of fibroblast markers. Pericyte-derived cells accounted for ~4% of PDGFRα+ infarct fibroblasts during the proliferative phase of repair. Pericyte-derived fibroblasts were overactive, expressing higher levels of extracellular matrix genes, integrins, matricellular proteins, and growth factors, when compared with fibroblasts from other cellular sources. Another subset of pericytes contributed to infarct angiogenesis by forming a mural cell coat, stabilizing infarct neovessels. Single-cell RNA sequencing showed that NG2 lineage cells diversify after infarction and exhibit increased expression of matrix genes, and a cluster with high expression of fibroblast identity markers emerges. Trajectory analysis suggested that diversification of infarct pericytes may be driven by proliferating cells. In vitro and in vivo studies identified TGF-β as a potentially causative mediator in fibrogenic activation of infarct pericytes. However, pericyte-specific TGF-β receptor 2 disruption had no significant effects on infarct myofibroblast infiltration and collagen deposition. Pericyte-specific TGF-β signaling was involved in vascular maturation, mediating formation of a mural cell coat investing infarct neovessels and protecting from dilative remodeling.

CONCLUSIONS

In the healing infarct, cardiac pericytes upregulate expression of fibrosis-associated genes, exhibiting matrix-synthetic and matrix-remodeling profiles. A fraction of infarct pericytes exhibits expression of fibroblast identity markers. Pericyte-specific TGF-β signaling plays a central role in maturation of the infarct vasculature and protects from adverse dilative remodeling, but it does not modulate fibrotic remodeling.

Promising therapeutic mechanism for Chinese herbal medicine in ameliorating renal fibrosis in diabetic nephropathy

Diabetic nephropathy (DN) is one of the most serious chronic microvascular abnormalities of diabetes mellitus and the major cause of uremia. Accumulating evidence has confirmed that fibrosis is a significant pathological feature that contributes to the development of chronic kidney disease in DN. However, the exact mechanism of renal fibrosis in DN is still unclear, which greatly hinders the treatment of DN. Chinese herbal medicine (CHM) has shown efficacy and safety in ameliorating inflammation and albuminuria in diabetic patients. In this review, we outline the underlying mechanisms of renal fibrosis in DN, including oxidative stress (OS) generation and OS-elicited ASK1-p38/JNK activation. Also, we briefly summarize the current status of CHM treating DN by improving renal fibrosis. The treatment of DN by inhibiting ASK1 activation to alleviate renal fibrosis in DN with CHM will promote the discovery of novel therapeutic targets for DN and provide a beneficial therapeutic method for DN.

The PI3K-Akt-mTOR pathway mediates renal pericyte-myofibroblast transition by enhancing glycolysis through HKII

BACKGROUND

Pericyte-myofibroblast transition (PMT) has been confirmed to contribute to renal fibrosis in several kidney diseases, and transforming growth factor-β1 (TGF-β1) is a well-known cytokine that drives PMT. However, the underlying mechanism has not been fully established, and little is known about the associated metabolic changes.

METHODS

Bioinformatics analysis was used to identify transcriptomic changes during PMT. PDGFRβ + pericytes were isolated using MACS, and an in vitro model of PMT was induced by 5 ng/ml TGF-β1. Metabolites were analyzed by ultraperformance liquid chromatography (UPLC) and tandem mass spectrometry (MS). 2-Deoxyglucose (2-DG) was used to inhibit glycolysis via its actions on hexokinase (HK). The hexokinase II (HKII) plasmid was transfected into pericytes for HKII overexpression. LY294002 or rapamycin was used to inhibit the PI3K-Akt-mTOR pathway for mechanistic exploration.

RESULTS

An increase in carbon metabolism during PMT was detected through bioinformatics and metabolomics analysis. We first detected increased levels of glycolysis and HKII expression in pericytes after stimulation with TGF-β1 for 48 h, accompanied by increased expression of α-SMA, vimentin and desmin. Transdifferentiation was blunted when pericytes were pretreated with 2-DG, an inhibitor of glycolysis. The phosphorylation levels of PI3K, Akt and mTOR were elevated during PMT, and after inhibition of the PI3K-Akt-mTOR pathway with LY294002 or rapamycin, glycolysis in the TGF-β1-treated pericytes was decreased. Moreover, PMT and HKII transcription and activity were blunted, but the plasmid-mediated overexpression of HKII rescued PMT inhibition.

CONCLUSIONS

The expression and activity of HKII as well as the level of glycolysis were increased during PMT. Moreover, the PI3K-Akt-mTOR pathway regulates PMT by increasing glycolysis through HKII regulation.

Klotho Supplementation Reverses Renal Dysfunction and Interstitial Fibrosis in Remnant Kidney

INTRODUCTION

While recent investigations show that klotho exerts renoprotective actions, it has not been fully addressed whether klotho protein supplementation reverses renal damage.

METHODS

The impacts of subcutaneous klotho supplementation on rats with subtotal nephrectomy were examined. Animals were divided into 3 groups: group 1 (short remnant [SR]): remnant kidney for 4 weeks, group 2 (long remnant [LR]): remnant kidney for 12 weeks, and group 3 (klotho supplementation [KL]): klotho protein (20 μg/kg/day) supplementation on the remnant kidney. Blood pressure, blood and urine compositions with conventional methods such as enzyme-linked immunosorbent assay and radioimmunoassay, kidney histology, and renal expressions of various genes were analyzed. In vitro studies were also performed to support in vivo findings.

RESULTS

Klotho protein supplementation decreased albuminuria (-43%), systolic blood pressure (-16%), fibroblast growth factor (FGF) 23 (-51%) and serum phosphate levels (-19%), renal angiotensin II concentration (-43%), fibrosis index (-70%), renal expressions of collagen I (-55%), and transforming growth factor β (-59%) (p < 0.05 for all). Klotho supplementation enhanced fractional excretion of phosphate (+45%), glomerular filtration rate (+76%), renal expressions of klotho (+148%), superoxide dismutase (+124%), and bone morphogenetic protein (BMP) 7 (+174%) (p < 0.05 for all).

CONCLUSION

Our data indicated that klotho protein supplementation inactivated renal renin-angiotensin system, reducing blood pressure and albuminuria in remnant kidney. Furthermore, exogenous klotho protein supplementation elevated endogenous klotho expression to increase phosphate excretion with resultant reductions in FGF23 and serum phosphate. Finally, klotho supplementation reversed renal dysfunction and fibrosis in association with improved BMP7 in remnant kidney.

Mesenchymal cells in the Lung: Evolving concepts and their role in fibrosis

Mesenchymal cells in the lung are crucial during development, but also contribute to the pathogenesis of fibrotic disorders, including idiopathic pulmonary fibrosis (IPF), the most common and deadly form of fibrotic interstitial lung diseases. Originally thought to behave as supporting cells for the lung epithelium and endothelium with a singular function of producing basement membrane, mesenchymal cells encompass a variety of cell types, including resident fibroblasts, lipofibroblasts, myofibroblasts, smooth muscle cells, and pericytes, which all occupy different anatomic locations and exhibit diverse homeostatic functions in the lung. During injury, each of these subtypes demonstrate remarkable plasticity and undergo varying capacity to proliferate and differentiate into activated myofibroblasts. Therefore, these cells secrete high levels of extracellular matrix (ECM) proteins and inflammatory cytokines, which contribute to tissue repair, or in pathologic situations, scarring and fibrosis. Whereas epithelial damage is considered the initial trigger that leads to lung injury, lung mesenchymal cells are recognized as the ultimate effector of fibrosis and attempts to better understand the different functions and actions of each mesenchymal cell subtype will lead to a better understanding of why fibrosis develops and how to better target it for future therapy. This review summarizes current findings related to various lung mesenchymal cells as well as signaling pathways, and their contribution to the pathogenesis of pulmonary fibrosis.

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.

Dickkopf-1 drives tumor immune evasion by inducing PD-L1 expression in hepatocellular carcinoma

Understanding the mechanisms regulating PD-L1 expression in hepatocellular carcinoma (HCC) is important to improve the response rate to PD-1/PD-L1 blockade therapy. Here, we show that DKK1 expression is positively associated with PD-L1 expression and inversely correlated with CD8⁺ T cell infiltration in human HCC tumor specimens. In a subcutaneous xenograft tumor model, overexpression of DKK1 significantly promotes tumor growth, tumoral PD-L1 expression, but reduces tumoral CD8⁺ T cell infiltration; whereas knockdown of DKK1 has opposite effects. Moreover, enforced expression of DKK1 dramatically promotes PD-L1 expression, Akt activation, β-catenin phosphorylation and total protein expression in HCC cells. By contrast, knockdown of DKK1 inhibits all, relative to controls. In addition, CKAP4 depletion, Akt inhibition, or β-catenin depletion remarkably abrogates DKK1 overexpression-induced transcriptional expression of PD-L1 in HCC cells. Reconstituted expression of the active Akt1 largely increased PD-L1 transcriptional expression in HCC cells. Similarly, expression of WT β-catenin, but not the phosphorylation-defective β-catenin S552A mutant, significantly promotes PD-L1 expression. Correlation analysis of human HCC tumor specimens further revealed that DKK1 and PD-L1 expression were positively correlated with p-β-catenin expression. Together, our findings revealed that DKK1 promotes PD-L1 expression through the activation of Akt/β-catenin signaling, providing a potential strategy to enhance the clinical efficacy of PD-1/PD-L1 blockade therapy in HCC patients.

Characterization of an ablative fractional CO2 laser-induced wound-healing model based on in vitro 3D reconstructed skin

OBJECTIVE

This study describes the development and characterization of a novel in vitro wound-healing model based on a full-thickness reconstructed skin by exposing the tissue to fractional ablative laser treatment.

METHOD

A 3D full-thickness skin model was fabricated and treated with fractional ablative CO₂ laser. Wound-healing process was characterized by HE staining, noninvasive OCT imaging, immunostaining, as well as transepidermal water loss measurement. Cytokines and proteins involved in the inflammatory and dermal remodeling process were studied by ELISA and protein array assays.

RESULTS

Fractional ablative CO₂ treatment induced a wound zone of 9 mm in diameter, containing 56 micro-wounds with 200 μm diameter and 500-700 μm in depth on reconstructed full-thickness skin model. HE staining revealed a typical wound morphology and healing process with migration of keratinocytes, formation and extrusion of necrotic tissue, and cell inclusion in dermis, which correlates with clinical observations. Based on OCT and TEWL measurements, the re-epithelialization took place over 2 days. Laser-triggered keratinocytes proliferation and differentiation were demonstrated by activated Ki67 and Filaggrin expression respectively. Injury-invoked cytokine ICAM-1 showed instant upregulation on Day 1. Decreased epidermis thickness and depression of IGFBP-2 protein level synergistically indicated the unavoidable thermal side effects from laser treatment. Downregulated DKK-1 protein level and upregulation of α-SMA together implicated the risk of potential fibrosis post-laser treatment.

CONCLUSION

This in vitro laser wounded reconstructed skin model captured the key events of wound-healing process, could be used to investigate the mechanisms of wound-healing triggered by a commonly used beauty procedure, and also provides a valuable tool for evaluating the efficacy of novel actives for the post-procedure application.

Cancer-associated fibroblasts in gynecological malignancies: are they really allies of the enemy?

Molecular and cellular components of the tumor microenvironment are essential for cancer progression. The cellular element comprises cancer cells and heterogeneous populations of non-cancer cells that satisfy tumor needs. Immune, vascular, and mesenchymal cells provide the necessary factors to feed the tumor mass, promote its development, and favor the spread of cancer cells from the primary site to adjacent and distant anatomical sites. Cancer-associated fibroblasts (CAFs) are mesenchymal cells that promote carcinogenesis and progression of various malignant neoplasms. CAFs act through the secretion of metalloproteinases, growth factors, cytokines, mitochondrial DNA, and non-coding RNAs, among other molecules. Over the last few years, the evidence on the leading role of CAFs in gynecological cancers has notably increased, placing them as the cornerstone of neoplastic processes. In this review, the recently reported findings regarding the promoting role that CAFs play in gynecological cancers, their potential use as therapeutic targets, and the new evidence suggesting that they could act as tumor suppressors are analyzed and discussed.

Perivascular PDGFRB+ cells accompany lesion formation and clinical evolution differentially in two different EAE models

BACKGROUND

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) that may lead to progressive disability. Here, we explored the behavioral pattern and the role of vasculature especially PDGFRB+ pericytes/ perivascular cells, in MS pathogenesis.

METHODS

We have evaluated vascular changes in two different experimental allergic encephalomyelitis (EAE) mice models (MOG and PLP-induced). PDGFRB+ cells demonstrated distinct and different behavioral patterns. In both models, fibrosis formation was detected via collagen, fibronectin, and extracellular matrix accumulation.

RESULTS

The PLP-induced animal model revealed that fibrosis predominantly occurs in perivascular locations and that PDGFRB+ cells are accumulated around vessels. Also, the expression of fibrotic genes and genes coding extracellular matrix (ECM) proteins are upregulated. Moreover, the perivascular thick wall structures in affected vessels of this model presented primarily increased PDGFRB+ cells but not NG2+ cells in the transgenic NG2-DsRed transgenic animal model. On the other hand, in MOG induced model, PDGFRB+ perivascular cells were accumulated at the lesion sites. PDGFRB+ cells colocalized with ECM proteins (collagen, fibronectin, and lysyl oxidase L3). Nevertheless, both MOG and PLP-immunized mice showed increasing EAE severity, and disability parallel with enhanced perivascular cell accumulation as the disease progressed from earlier (day 15) to later (day 40).

CONCLUSION

As a result, we have concluded that PDGFRB+ perivascular cells may be participating in lesion progression and as well as demonstrating different responses in different EAE models.

The fibrogenic niche in kidney fibrosis: components and mechanisms

Kidney fibrosis, characterized by excessive deposition of extracellular matrix (ECM) that leads to tissue scarring, is the final common outcome of a wide variety of chronic kidney diseases. Rather than being distributed uniformly across the kidney parenchyma, renal fibrotic lesions initiate at certain focal sites in which the fibrogenic niche is formed in a spatially confined fashion. This niche provides a unique tissue microenvironment that is orchestrated by a specialized ECM network consisting of de novo-induced matricellular proteins. Other structural elements of the fibrogenic niche include kidney resident and infiltrated inflammatory cells, extracellular vesicles, soluble factors and metabolites. ECM proteins in the fibrogenic niche recruit soluble factors including WNTs and transforming growth factor-β from the extracellular milieu, creating a distinctive profibrotic microenvironment. Studies using decellularized ECM scaffolds from fibrotic kidneys show that the fibrogenic niche autonomously promotes fibroblast proliferation, tubular injury, macrophage activation and endothelial cell depletion, pathological features that recapitulate key events in the pathogenesis of chronic kidney disease. The concept of the fibrogenic niche represents a paradigm shift in understanding of the mechanism of kidney fibrosis that could lead to the development of non-invasive biomarkers and novel therapies not only for chronic kidney disease, but also for fibrotic diseases of other organs.

Hormonal Regulation of Renal Fibrosis

Fibrosis is a severe complication of many acute and chronic kidney pathologies. According to current concepts, an imbalance in the synthesis and degradation of the extracellular matrix by fibroblasts is considered the key cause of the induction and progression of fibrosis. Nevertheless, inflammation associated with the damage of tissue cells is among the factors promoting this pathological process. Most of the mechanisms accompanying fibrosis development are controlled by various hormones, which makes humoral regulation an attractive target for therapeutic intervention. In this vein, it is particularly interesting that the kidney is the source of many hormones, while other hormones regulate renal functions. The normal kidney physiology and pathogenesis of many kidney diseases are sex-dependent and thus modulated by sex hormones. Therefore, when choosing therapy, it is necessary to focus on the sex-associated characteristics of kidney functioning. In this review, we considered renal fibrosis from the point of view of vasoactive and reproductive hormone imbalance. The hormonal therapy possibilities for the treatment or prevention of kidney fibrosis are also discussed.

Follistatin-like 1 (FSTL1) interacts with Wnt ligands and Frizzled receptors to enhance Wnt/β-catenin signaling in obstructed kidneys in vivo

Follistatin (FS)-like 1 (FSTL1) is a member of the FS-SPARC (secreted protein, acidic and rich in cysteine) family of secreted and extracellular matrix proteins. The functions of FSTL1 have been studied in heart and lung injury as well as in wound healing; however, the role of FSTL1 in the kidney is largely unknown. Here, we show using single-cell RNA-Seq that Fstl1 was enriched in stromal cells in obstructed mouse kidneys. In addition, immunofluorescence demonstrated that FSTL1 expression was induced in fibroblasts during kidney fibrogenesis in mice and human patients. We demonstrate that FSTL1 overexpression increased renal fibrosis and activated the Wnt/β-catenin signaling pathway, known to promote kidney fibrosis, but not the transforming growth factor β (TGF-β), Notch, Hedgehog, or Yes-associated protein (YAP) signaling pathways in obstructed mouse kidneys, whereas inhibition of FSTL1 lowered Wnt/β-catenin signaling. Importantly, we show that FSTL1 interacted with Wnt ligands and the Frizzled (FZD) receptors but not the coreceptor lipoprotein receptor–related protein 6 (LRP6). Specifically, we found FSTL1 interacted with Wnt3a through its extracellular calcium–binding (EC) domain and von Willebrand factor type C–like (VWC) domain, and with FZD4 through its EC domain. Furthermore, we show that FSTL1 increased the association of Wnt3a with FZD4 and promoted Wnt/β-catenin signaling and fibrogenesis. The EC domain interacting with both Wnt3a and FZD4 also enhanced Wnt3a signaling. Therefore, we conclude that FSTL1 is a novel extracellular enhancer of the Wnt/β-catenin pathway.

CTGF-D4 Amplifies LRP6 Signaling to Promote Grafts of Adult Epicardial-derived Cells That Improve Cardiac Function After Myocardial Infarction

Transplantation of stem/progenitor cells holds promise for cardiac regeneration in patients with myocardial infarction (MI). Currently, however, low cell survival and engraftment after transplantation present a major barrier to many forms of cell therapy. One issue is that ligands, receptors, and signaling pathways that promote graft success remain poorly understood. Here, we prospectively isolate uncommitted epicardial cells from the adult heart surface by CD104 (β-4 integrin) and demonstrate that C-terminal peptide from connective tissue growth factor (CTGF-D4), when combined with insulin, effectively primes epicardial-derived cells (EPDC) for cardiac engraftment after MI. Similar to native epicardial derivatives that arise from epicardial EMT at the heart surface, the grafted cells migrated into injured myocardial tissue in a rat model of MI with reperfusion. By echocardiography, at 1 month after MI, we observed significant improvement in cardiac function for animals that received epicardial cells primed with CTGF-D4/insulin compared with those that received vehicle-primed (control) cells. In the presence of insulin, CTGF-D4 treatment significantly increased the phosphorylation of Wnt co-receptor LRP6 on EPDC. Competitive engraftment assays and neutralizing/blocking studies showed that LRP6 was required for EPDC engraftment after transplantation. Our results identify LRP6 as a key target for increasing EPDC engraftment after MI and suggest amplification of LRP6 signaling with CTGF-D4/insulin, or by other means, may provide an effective approach for achieving successful cellular grafts in regenerative medicine.

LRG1 as a novel therapeutic target in eye disease

Retinal and choroidal diseases are major causes of blindness and visual impairment in the developed world and on the rise due to an ageing population and diabetes epidemic. Standard of care is centred around blockade of vascular endothelial growth factor (VEGF), but despite having halved the number of patients losing sight, a high rate of patient non-response and loss of efficacy over time are key challenges. Dysregulation of vascular homoeostasis, coupled with fibrosis and inflammation, are major culprits driving sight-threatening eye diseases. Improving our knowledge of these pathological processes should inform the development of new drugs to address the current clinical challenges for patients. Leucine-rich α-2 glycoprotein 1 (LRG1) is an emerging key player in vascular dysfunction, inflammation and fibrosis. Under physiological conditions, LRG1 is constitutively expressed by the liver and granulocytes, but little is known about its normal biological function. In pathological scenarios, such as diabetic retinopathy (DR) and neovascular age-related macular degeneration (nvAMD), its expression is ectopically upregulated and it acquires a much better understood pathogenic role. Context-dependent modulation of the transforming growth-factor β (TGFβ) pathway is one of the main activities of LRG1, but additional roles have recently been emerging. This review aims to highlight the clinical and pre-clinical evidence for the pathogenic contribution of LRG1 to vascular retinopathies, as well as extrapolate from other diseases, functions which may be relevant to eye disease. Finally, we will provide a current update on the development of anti-LRG1 therapies for the treatment of nvAMD.

Soluble very low-density lipoprotein receptor (sVLDLR) inhibits fibrosis in neovascular age-related macular degeneration

Subretinal fibrosis is a key pathological feature in neovascular age‐related macular degeneration (nAMD). Previously, we identified soluble very low‐density lipoprotein receptor (sVLDLR) as an endogenous Wnt signaling inhibitor. This study investigates whether sVLDLR plays an anti‐fibrogenic role in nAMD models, including Vldlr^−/− mice and laser‐induced choroidal neovascularization (CNV). We found that fibrosis factors including P‐Smad2/3, α‐SMA, and CTGF were upregulated in the subretinal area of Vldlr^−/− mice and the laser‐induced CNV model. The antibody blocking Wnt co‐receptor LRP6 significantly attenuated the overexpression of fibrotic factors in these two models. Moreover, there was a significant reduction of sVLDLR in the interphotoreceptor matrix (IPM) in the laser‐induced CNV model. A transgenic strain (sVLDLR‐Tg) with sVLDLR overexpression in the IPM was generated. Overexpression of sVLDLR ameliorated the profibrotic changes in the subretinal area of the laser‐induced CNV model. In addition, Wnt and TGF‐β signaling synergistically promoted fibrogenesis in human primary retinal pigment epithelium (RPE) cells. CRISPR/Cas9‐mediated LRP6 gene knockout (KO) attenuated this synergistic effect. The disruption of VLDLR expression promoted, while the overexpression of sVLDLR inhibited TGF‐β‐induced fibrosis. These findings suggest that overactivated Wnt signaling enhances the TGF‐β pathway in subretinal fibrosis. sVLDLR confers an antifibrotic effect, at least partially, through the inhibition of Wnt signaling and thus, has therapeutic potential for fibrosis.

ZBTB38 suppresses prostate cancer cell proliferation and migration via directly promoting DKK1 expression

Prostate cancer is still one of the most common malignancies in men all around the world. The mechanism of how prostate cancer initiates and develops is still not clear. Here in this study, we show that tumor suppressor ZBTB38 could suppress the migration and proliferation of prostate cancer cells. We find lower ZBTB38 expression in prostate cancer tissues, which also strongly predicts a poorer prognosis of prostate cancer. ZBTB38 binds DKK1 (Dickkopf WNT signaling pathway inhibitor 1) locus and promotes DKK1 expression in prostate cancer cell lines. Consistently, reduction of DKK1 expression significantly restores ZBTB38-mediated suppression of migration and proliferation of prostate cancer cell lines. Mechanistically, we find that ZBTB38 primarily binds the promoters of target genes, and differentially regulates the expression of 1818 genes. We also identify PRKDC (protein kinase, DNA-activated, catalytic subunit) as a ZBTB38-interacting protein that could repress the function of ZBTB38 in suppressing migration and proliferation of prostate cancer cells. Taken together, our results indicate that ZBTB38 could repress cell migration and proliferation in prostate cancer via promoting DKK1 expression, and also provide evidence supporting ZBTB38 as a potential prognosis marker for prostate cancer.

The Expressions of Dickkopf-Related Protein 1 and Frizzled-Related Protein Are Negatively Correlated to Local Inflammation and Osteoarthritis Severity

OBJECTIVE

To investigate the presence of WNT antagonists Dickkopf-related protein 1 (DKK1), Frizzled-related protein (FRZB) and BMP antagonist Gremlin 1 (GREM1) in synovial fluid (SF) and serum, respectively, from end-stage knee osteoarthritis (OA) patients, and correlate their expression with other markers of OA.

DESIGN

In a cross-sectional study, SF and serum were collected from OA patients (n = 132). The concentrations of DKK1, FRZB and GREM1 in SF and serum were determined using immunoassays. Correlation measurements were performed between groups and previously assessed disease markers, such as synovium nitric oxide (NO), inerleukin-1β (IL1β), tumor necrosis factor-α (TNFα), and prostaglandin E2 (PGE2).

RESULTS

The OA patients with the celecoxib treatment till surgery have higher median SF FRZB values compared with the control (no treatment); the celecoxib 3-days before surgery stopped treatment group has higher median serum FRZB values than the control and the naproxen treatment group. The combinational analysis of SF DKK1 and SF FRZB negatively correlated with macroscopic cartilage scores and histological synovium scores in OA patients. The expression of DKK1 and FRZB in SF showed the same expression trend as their expression in serum. Furthermore, the SF concentration of DKK1 was positively correlated with FRZB in both SF and serum. In contrast, it was negatively correlated with synovium NO and IL1β. SF FRZB was negatively correlated with synovium NO, IL1β, cartilage PGE2, and age.

CONCLUSIONS

Our findings suggest DKK1 and FRZB were negatively correlated with OA severity and multiple pro-inflammatory cytokines. Our data indicate that DKK1 and FRZB can be joint disease-specific biomarkers.

LRP5 and LRP6 in Wnt Signaling: Similarity and Divergence

The canonical Wnt/β-catenin signaling plays a fundamental role in regulating embryonic development, injury repair and the pathogenesis of human diseases. In vertebrates, low density lipoprotein receptor-related proteins 5 and 6 (LRP5 and LRP6), the single-pass transmembrane proteins, act as coreceptors of Wnt ligands and are indispensable for Wnt signal transduction. LRP5 and LRP6 are highly homologous and widely co-expressed in embryonic and adult tissues, and they share similar function in mediating Wnt signaling. However, they also exhibit distinct characteristics by interacting with different protein partners. As such, each of them possesses its own unique functions. In this review, we systematically discuss the similarity and divergence of LRP5 and LRP6 in mediating Wnt and other signaling in the context of kidney diseases. A better understanding of the precise role of LRP5 and LRP6 may afford us to identify and refine therapeutic targets for the treatment of a variety of human diseases.

Aging modulates the effects of ischemic injury upon mesenchymal cells within the renal interstitium and microvasculature

The renal mesenchyme contains heterogeneous cells, including interstitial fibroblasts and pericytes, with key roles in wound healing. Although healing is impaired in aged kidneys, the effect of age and injury on the mesenchyme remains poorly understood. We characterized renal mesenchymal cell heterogeneity in young vs old animals and after ischemia‐reperfusion‐injury (IRI) using multiplex immunolabeling and single cell transcriptomics. Expression patterns of perivascular cell markers (α‐SMA, CD146, NG2, PDGFR‐α, and PDGFR‐β) correlated with their interstitial location. PDGFR‐α and PDGFR‐β co‐expression labeled renal myofibroblasts more efficiently than the current standard marker α‐SMA, and CD146 was a superior murine renal pericyte marker. Three renal mesenchymal subtypes; pericytes, fibroblasts, and myofibroblasts, were recapitulated with data from two independently performed single cell transcriptomic analyzes of murine kidneys, the first dataset an aging cohort and the second dataset injured kidneys following IRI. Mesenchymal cells segregated into subtypes with distinct patterns of expression with aging and following injury. Baseline uninjured old kidneys resembled post‐ischemic young kidneys, with this phenotype further exaggerated following IRI. These studies demonstrate that age modulates renal perivascular/interstitial cell marker expression and transcriptome at baseline and in response to injury and provide tools for the histological and transcriptomic analysis of renal mesenchymal cells, paving the way for more accurate classification of renal mesenchymal cell heterogeneity and identification of age‐specific pathways and targets.

Wnt/β-Catenin in Acute Kidney Injury and Progression to Chronic Kidney Disease

Acute kidney injury (AKI) portends a poor clinical prognosis and increases the risk for the development of chronic kidney disease (CKD). Currently, there are no therapies to treat AKI or prevent its progression to CKD. Wnt/β-catenin is a critical regulator of kidney development that is up-regulated after injury. Most of the literature support a beneficial role for Wnt/β-catenin in AKI, but suggest that this pathway promotes the progression of tubulointerstitial fibrosis, the hallmark of CKD progression. We review the role of Wnt/β-catenin in renal injury with a focus on its potential as a therapeutic target in AKI and in AKI to CKD transition.

Kidney pericyte hypoxia-inducible factor regulates erythropoiesis but not kidney fibrosis

Prolyl hydroxylase domain enzyme (PHD) inhibitors are effective in the treatment of chronic kidney disease (CKD)-associated anemia by stabilizing hypoxia inducible factor (HIF), thereby increasing erythropoietin and consequently erythropoiesis. However, concern for CKD progression needs to be addressed in clinical trials. Although pre-clinical studies showed an anti-inflammatory effect in kidney disease models, the effect of PHD inhibitors on kidney fibrosis was inconsistent probably because the effects of HIF are cell type and context dependent. The major kidney erythropoietin-producing cells are pericytes that produce erythropoietin through HIF-2α-dependent gene transcription. The concern for the impact of HIF in pericytes on kidney fibrosis arises from the fact that pericytes are the major precursor cells of myofibroblasts in CKD. Since cells expressing Gli1 fulfill the morphologic and anatomic criteria for pericytes, we induced Gli1⁺ cell-specific HIF stabilization or knockout to study the impact of HIF in pericytes on kidney pathology of mice with or without fibrotic injury induced by unilateral ureteral obstruction. Compared with the littermate controls, mice with pericyte-specific HIF stabilization due to von Hippel-Lindau protein or PHD2 knockout showed increased serum erythropoietin and polycythemia rather than a discernible difference in kidney fibrosis. Compared with Gli1⁺ pericytes sorted from littermate controls, Gli1⁺ pericytes sorted from PHD2 knockout mice showed increased erythropoietin gene expression rather than discernible changes in Col1a1 or Acta2 expression. Furthermore, pericyte-specific knockout of HIF-1α or HIF-2α did not affect kidney fibrosis. Thus, our study supports the absence of negative effects of PHD inhibitors on kidney fibrosis of mice despite HIF stabilization in pericytes.

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.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

Inhibitory effect of caffeic acid on advanced glycation end product-induced renal fibrosis in vitro: A potential therapeutic target

Advanced glycation end products (AGEs) are formed from amino acids and reducing sugars through nonenzymatic Maillard reaction. AGEs are known to induce oxidative stress, which may cause fibrosis or cancer. In this study, we investigated the protective effect of caffeic acid (CA) on AGE-mediated kidney epithelial to mesenchymal transition (EMT) in human HK-2 cells. Exposure to 100 µg/mL of AGEs by kidney epithelial cells raised the production of reactive oxygen species by 5.2-fold and decreased levels of glutathione. In addition, cardamonin, a β-catenin inhibitor, was used to determine the signaling pathway for β-catenin in which cardamonin inhibited the AGEs-induced translocation of β-catenin into the nucleus, resulting in an inhibition of the EMT process. Similarly, our findings showed that, close to the control level, CA treatment decreased AGE-mediated oxidative stress, loss of E-cadherin expression, and overexpression of α-smooth muscle actin and fibronectin by inactivation of the β-catenin pathway. Furthermore, AGE treatment enhanced the expression of collagen type I (1.99-fold) as well as the activity of metalloproteinases 2 (1.86-fold) and 9 (2.79-fold), but such increase was inhibited by the pretreatment of CA. In conclusion, this study determined the inhibitory effect of CA on AGE-induced β-catenin signaling, which prevented the occurrence of EMT in kidney epithelial cells. This suggests that CA may be a potential target for AGE-induced renal fibrosis. PRACTICAL APPLICATION: Exposure of kidney epithelial cells to advanced glycation end products (AGEs) leads to a rise in reactive oxygen species and a decrease in glutathione, thereby increasing oxidative stress that may cause fibrosis. However, treatment of kidney cells with caffeic acid (CA) prior to their exposure to AGEs lowers oxidative stress and decreases fibrosis. This research reveals the beneficial influence of CA on renal fibrosis in laboratory-cultured kidney cells (in vitro), which makes CA a potential therapeutic target for AGE-induced fibrosis.

Balanced Wnt/Dickkopf-1 signaling by mesenchymal vascular progenitor cells in the microvascular niche maintains distal lung structure and function

The well-described Wnt inhibitor Dickkopf-1 (DKK1) plays a role in angiogenesis as well as in regulation of growth factor signaling cascades in pulmonary remodeling associated with chronic lung diseases (CLDs) including emphysema and fibrosis. However, the specific mechanisms by which DKK1 influences mesenchymal vascular progenitor cells (MVPCs), microvascular endothelial cells (MVECs), and smooth muscle cells (SMCs) within the microvascular niche have not been elucidated. In this study, we show that knockdown of DKK1 in Abcg2pos lung mouse adult tissue resident MVPCs alters lung stiffness, parenchymal collagen deposition, microvessel muscularization and density as well as loss of tissue structure in response to hypoxia exposure. To complement the in vivo mouse modeling, we also identified cell- or disease-specific responses to DKK1, in primary lung chronic obstructive pulmonary disease (COPD) MVPCs, COPD MVECs, and SMCs, supporting a paradoxical disease-specific response of cells to well-characterized factors. Cell responses to DKK1 were dose dependent and correlated with varying expressions of the DKK1 receptor, CKAP4. These data demonstrate that DKK1 expression is necessary to maintain the microvascular niche whereas its effects are context specific. They also highlight DKK1 as a regulatory candidate to understand the role of Wnt and DKK1 signaling between cells of the microvascular niche during tissue homeostasis and during the development of chronic lung diseases.

Diverse origins and activation of fibroblasts in cardiac fibrosis

Cardiac fibroblasts (cFBs) have emerged as a heterogenous cell population. Fibroblasts are considered the main cell source for synthesis of the extracellular matrix (ECM) and as such a dysregulation in cFB function, activity, or viability can lead to disrupted ECM structure or fibrosis. Fibrosis can be initiated in response to different injuries and stimuli, and can be reparative (beneficial) or reactive (damaging). FBs need to be activated to myofibroblasts (MyoFBs) which have augmented capacity in synthesizing ECM proteins, causing fibrosis. In addition to the resident FBs in the myocardium, a number of other cells (pericytes, fibrocytes, mesenchymal, and hematopoietic cells) can transform into MyoFBs, further driving the fibrotic response. Multiple molecules including hormones, cytokines, and growth factors stimulate this process leading to generation of activated MyoFBs. Contribution of different cell types to cFBs and MyoFBs can result in an exponential increase in the number of MyoFBs and an accelerated pro-fibrotic response. Given the diversity of the cell sources, and the array of interconnected signalling pathways that lead to formation of MyoFBs and subsequently fibrosis, identifying a single target to limit the fibrotic response in the myocardium has been challenging. This review article will delineate the importance and relevance of fibroblast heterogeneity in mediating fibrosis in different models of heart failure and will highlight important signalling pathways implicated in myofibroblast activation.

Connective Tissue Growth Factor: From Molecular Understandings to Drug Discovery

Connective tissue growth factor (CTGF) is a key signaling and regulatory molecule involved in different biological processes, such as cell proliferation, angiogenesis, and wound healing, as well as multiple pathologies, such as tumor development and tissue fibrosis. Although the underlying mechanisms of CTGF remain incompletely understood, a commonly accepted theory is that the interactions between different protein domains in CTGF and other various regulatory proteins and ligands contribute to its variety of functions. Here, we highlight the structure of each domain of CTGF and its biology functions in physiological conditions. We further summarized main diseases that are deeply influenced by CTGF domains and the potential targets of these diseases. Finally, we address the advantages and disadvantages of current drugs targeting CTGF and provide the perspective for the drug discovery of the next generation of CTGF inhibitors based on aptamers.

WNT-β-catenin signalling - a versatile player in kidney injury and repair

The WNT-β-catenin system is an evolutionary conserved signalling pathway that is of particular importance for morphogenesis and cell organization during embryogenesis. The system is usually suppressed in adulthood; however, it can be re-activated in organ injury and regeneration. WNT-deficient mice display severe kidney defects at birth. Transient WNT-β-catenin activation stimulates tissue regeneration after acute kidney injury, whereas sustained (uncontrolled) WNT-β-catenin signalling promotes kidney fibrosis in chronic kidney disease (CKD), podocyte injury and proteinuria, persistent tissue damage during acute kidney injury and cystic kidney diseases. Additionally, WNT-β-catenin signalling is involved in CKD-associated vascular calcification and mineral bone disease. The WNT-β-catenin pathway is tightly regulated, for example, by proteins of the Dickkopf (DKK) family. In particular, DKK3 is released by 'stressed' tubular epithelial cells; DKK3 drives kidney fibrosis and is associated with short-term risk of CKD progression and acute kidney injury. Thus, targeting the WNT-β-catenin pathway might represent a promising therapeutic strategy in kidney injury and associated complications.

Canonical Wnts Mediate CD8+ T Cell Noncytolytic Anti-HIV-1 Activity and Correlate with HIV-1 Clinical Status

CD8⁺ T cells do not rely solely on cytotoxic functions for significant HIV control. Moreover, the noncytotoxic CD8⁺ T cell antiviral response is a primary mediator of natural HIV control such as that seen in HIV elite controllers and long-term nonprogressors that does not require combined antiretroviral therapy. In this study, we investigated the biological factors contributing to the noncytotoxic control of HIV replication mediated by primary human CD8⁺ T cells. We report that canonical Wnt signaling inhibits HIV transcription in an MHC-independent, noncytotoxic manner and that mediators of this pathway correlate with HIV controller clinical status. We show that CD8⁺ T cells express all 19 Wnts and CD8⁺ T cell-conditioned medium (CM) induced canonical Wnt signaling in infected recipient cells while simultaneously inhibiting HIV transcription. Antagonizing canonical Wnt activity in CD8⁺ T cell CM resulted in increased HIV transcription in infected cells. Further, Wnt2b expression was upregulated in HIV controllers versus viremic patients, and in vitro depletion of Wnt2b and/or Wnt9b from CD8⁺ CM reversed HIV inhibitory activity. Finally, plasma concentration of Dkk-1, an antagonist of canonical Wnt signaling, was higher in viremic patients with lower CD4 counts. This study demonstrates that canonical Wnt signaling inhibits HIV and significantly correlates with HIV controller status.

R-Spondin 2 Induces Odontogenic Differentiation of Dental Pulp Stem/Progenitor Cells via Regulation of Wnt/β-Catenin Signaling

Odontoblast cells generated from human dental pulp stem/progenitor cells (hDPSCs) secrete reparative dentin in responds to an injury. Endogenous Wnt signaling is also activated during this process, and these Wnt-activated cells are responsible for the following repair response. R-spondin 2 (Rspo2) is a potent stem cell growth factor, which strongly potentiates Wnt/β-catenin signaling and plays a vital role in cell differentiation and regeneration. However, the role of Rspo2 during odontoblast differentiation in hDPSCs has not yet been completely understood. This study investigated the effects of Rspo2 on hDPSCs to provide therapeutic insight into dentin regeneration and reparative dentin formation. HDPSCs were extracted from human molars or premolars. Immunofluorescence staining and flow cytometric analysis were used to detect the mesenchymal stem cell markers in hDPSCs. EdU assay and Cell Counting Kit-8 (CCK-8) were performed to explore cell proliferation. The odontogenic differentiation levels were determined by measuring the mRNA and protein expression of DSPP, DMP-1, ALP, and BSP. Immunofluorescence staining was performed to detect the localization of β-catenin. The biological effects of Rspo2 on hDPSCs was investigated using the Lentivirus-based Rspo2 shRNA and recombined human Rspo2 (rhRspo2). Recombined human DKK-1 (rhDKK-1) and recombined human Wnt3a (rhWnt3a) were used for further investigation. The cells generated from human dental pulp expressed mesenchymal stem cell markers Vimentin, Stro-1, Nestin, C-kit, CD90, and CD73, while were negative for CD3, CD31, and CD34. The mRNA expression levels of the odontogenic-related genes DSPP, DMP-1, ALP, and BSP were upregulated in the rhRspo2 treated cells. Silencing Rspo2 suppressed the proliferation and differentiation of the hDPSCs. Blockade of Wnt signaling with DKK-1 inhibited Rspo2-induced activation of Wnt/β-catenin signaling and cell differentiation. The combined use of rhWnt3a and rhRspo2 created a synergistic effect to improve the activation of Wnt/β-catenin signaling. Rspo2 promoted the proliferation and odontogenic differentiation of hDPSCs by regulating the Wnt/β-catenin signaling pathway.

Contribution of the Low-Density Lipoprotein Receptor Family to Breast Cancer Progression

The low-density lipoprotein receptor (LDLR) family comprises 14 single-transmembrane receptors sharing structural homology and common repeats. These receptors specifically recognize and internalize various extracellular ligands either alone or complexed with membrane-spanning co-receptors that are then sorted for lysosomal degradation or cell-surface recovery. As multifunctional endocytic receptors, some LDLR members from the core family were first considered as potential tumor suppressors due to their clearance activity against extracellular matrix-degrading enzymes. LDLRs are also involved in pleiotropic functions including growth factor signaling, matricellular proteins, and cell matrix adhesion turnover and chemoattraction, thereby affecting both tumor cells and their surrounding microenvironment. Therefore, their roles could appear controversial and dependent on the malignancy state. In this review, recent advances highlighting the contribution of LDLR members to breast cancer progression are discussed with focus on (1) specific expression patterns of these receptors in primary cancers or distant metastasis and (2) emerging mechanisms and signaling pathways. In addition, potential diagnosis and therapeutic options are proposed.

Wnt signaling pathway in aging-related tissue fibrosis and therapies

Fibrosis is the final hallmark of pathological remodeling, which is a major contributor to the pathogenesis of various chronic diseases and aging-related organ failure to fully control chronic wound-healing and restoring tissue function. The process of fibrosis is involved in the pathogenesis of the kidney, lung, liver, heart and other tissue disorders. Wnt is a highly conserved signaling in the aberrant wound repair and fibrogenesis, and sustained Wnt activation is correlated with the pathogenesis of fibrosis. In particular, mounting evidence has revealed that Wnt signaling played important roles in cell fate determination, proliferation and cell polarity establishment. The expression and distribution of Wnt signaling in different tissues vary with age, and these changes have key effects on maintaining tissue homeostasis. In this review, we first describe the major constituents of the Wnt signaling and their regulation functions. Subsequently, we summarize the dysregulation of Wnt signaling in aging-related fibrotic tissues such as kidney, liver, lung and cardiac fibrosis, followed by a detailed discussion of its involvement in organ fibrosis. In addition, the crosstalk between Wnt signaling and other pathways has the potential to profoundly add to the complexity of organ fibrosis. Increasing studies have demonstrated that a number of Wnt inhibitors had the potential role against tissue fibrosis, specifically in kidney fibrosis and the implications of Wnt signaling in aging-related diseases. Therefore, targeting Wnt signaling might be a novel and promising therapeutic strategy against aging-related tissue fibrosis.

Acoustic Trauma Causes Cochlear Pericyte-to-Myofibroblast-Like Cell Transformation and Vascular Degeneration, and Transplantation of New Pericytes Prevents Vascular Atrophy

Acoustic trauma disrupts cochlear blood flow and damages sensory hair cells. Damage and regression of capillaries after acoustic trauma have long been observed, but the underlying mechanism of pathology has not been understood. We show herein that loud sound causes change of phenotype from neural/glial antigen 2 positive/α-smooth muscle actin negative to neural/glial antigen 2 positive/α-smooth muscle actin positive in some pericytes (PCs) on strial capillaries that is strongly associated with up-regulation of transforming growth factor-β1. The acoustic trauma also reduced capillary density and increased deposition of matrix proteins, particularly in the vicinity of transformed PCs. In a newly established in vitro three-dimensional endothelial cell (EC) and PC co-culture model, transformed PCs induced thicker capillary-like branches in ECs and increased collagen IV and laminin expression. Transplantation of exogenous PCs derived from neonatal day 10 mouse cochleae to acoustic traumatized cochleae, however, significantly attenuated the decreased vascular density in the stria. Transplantation of PCs pretransfected with adeno-associated virus 1-vascular endothelial growth factor-A165 under control of a hypoxia-response element markedly promotes vascular volume and blood flow, increased proliferation of PCs and ECs, and attenuated loud sound-caused loss in endocochlear potential and hearing. Our results indicate that loud sound-triggered PC transformation contributes to capillary wall thickening and regression, and young PC transplantation effectively rehabilitates the vascular regression and improves hearing.