Sonic hedgehog signaling in kidney fibrosis: a master communicator

The role of cyclic adenosine monophosphate (cAMP) in pathophysiology of fibrosis

Fibrosis, the excessive production and disorganised deposition of extracellular matrix proteins, can occur in any organ system, disrupting functionality and causing fatality. The number, efficacy and safety of antifibrotic drugs are incredibly limited. Therapeutics which elevate intracellular cyclic adenosine monophosphate (cAMP) offer a potential solution. In this review, we present the signalling mechanisms involved in fibrosis pathophysiology, how cAMP and its effectors might interact with these pathways, and the current preclinical and clinical efforts in this field. cAMP elevating agents have the potential to be future antifibrotic drug candidates, but further studies are required, particularly to develop tissue specific therapeutics.

Modulation of renal fibrosis-related signaling pathways by traditional Chinese medicine: molecular mechanisms and experimental evidence

Renal fibrosis (RF), characterized by excessive deposition of extracellular matrix leading to tissue damage and scar formation, represents a refractory disease and a pivotal pathological basis for the progression to end-stage renal disease. The pathogenesis of RF is intricate, prominently implicating multiple key signaling pathways, including adenosine monophosphate-activated protein kinase/mammalian target of rapamycin (AMPK/mTOR), phosphoinositide 3-kinase/protein kinase B (PI3K/Akt), transforming growth factor-β1/small mother against decapentaplegic (TGF-β1/Smad), toll-like receptor 4/nuclear factor kappa B (TLR4/NF-κB), wingless integrated/β-catenin (Wnt/β-catenin), hypoxia-inducible factor-1α (HIF-1α), Hedgehog, and mitogen-activated protein kinase (MAPK). The current Western medical practices primarily rely on supportive and replacement therapies, which are often costly and suboptimal in efficacy. In contrast, traditional Chinese medicine (TCM), with its inherent advantages of multi-target, multi-pathway, and multi-effect modulation, emerges as a promising new strategy for RF treatment. However, a systematic, comprehensive, and detailed summary of these advancements remains absent. Therefore, this review consolidates the recent research progress on TCM modulation of RF-related signaling pathways, aiming to provide a theoretical foundation for further investigations into RF and the development of TCM interventions.

Extracellular vesicles play a central role in linking podocyte injury to mesangial activation in glomerular disease

Background: Podocyte injury leading to proteinuria is the primary feature of a vast majority of glomerular diseases, while mesangial cell activation is the hallmark of glomerulosclerosis. Whether and how these two events are connected remains elusive. In this study, we investigated the role of extracellular vesicles (EVs) in linking podocyte injury to mesangial activation in glomerular disease. Methods: EVs were characterized by nanoparticle tracking analysis and electron microscopy. Differentially expressed proteins from podocyte-derived EVs were analyzed by protein microarray. The role and mechanism by which EVs-packaged sonic hedgehog (Shh) mediates mesangial cell activation were investigated in vitro and in vivo. Results: An increased production of EVs in mouse podocytes (MPC5) was observed after injury induced by angiotensin II (Ang II). Shh and N-Shh were identified as major constituents of the proteins encapsulated in EVs isolated from Ang II-treated MPC5 cells (Ang II-EVs). In vitro, Ang II-EVs induced the activation and proliferation of rat mesangial cells (HBZY-1), whereas inhibition of EV secretion with dimethyl amiloride, depletion of EVs from conditioned media or knockdown of Shh expression abolished the ability of Ang II-EVs to induce HBZY-1 activation. In vivo, intravenous injection of Ang II-EVs exacerbated glomerulosclerosis, which was negated by hedgehog inhibitor. Furthermore, blocking EV secretion also ameliorated glomerulosclerosis in mouse model of glomerular disease. Conclusions: These findings suggest that podocyte injury can cause mesangial cell activation and glomerulosclerosis by releasing Shh-enriched EVs. Therefore, strategies targeting EVs may be a novel way to ameliorate proteinuric kidney disease.

Inhibition of hedgehog signaling ameliorates severity of chronic pancreatitis in experimental mouse models

Chronic pancreatitis (CP) is a fibro-inflammatory disease of the pancreas with no specific cure. Research highlighting the pathogenesis and especially the therapeutic aspect remains limited. Aberrant activation of developmental pathways in adults has been implicated in several diseases. Hedgehog pathway is a notable embryonic signaling pathway, known to promote fibrosis of various organs when overactivated. The aim of this study is to explore the role of the hedgehog pathway in the progression of CP and evaluate its inhibition as a novel therapeutic strategy against CP. CP was induced in mice by repeated injections of l-arginine or caerulein in two separate models. Mice were administered with the FDA-approved pharmacological hedgehog pathway inhibitor, vismodegib during or after establishing the disease condition to inhibit hedgehog signaling. Various parameters of CP were analyzed to determine the effect of hedgehog pathway inhibition on the severity and progression of the disease. Our study shows that hedgehog signaling was overactivated during CP and its inhibition was effective in improving the histopathological parameters associated with CP. Vismodegib administration not only halted the progression of CP but was also able to resolve already-established fibrosis. In addition, inhibition of hedgehog signaling resulted in the reversal of pancreatic stellate cell activation ex vivo. Findings from our study justify conducting clinical trials using vismodegib against CP and, thus, could lead to the development of a novel therapeutic strategy for the treatment of CP.NEW & NOTEWORTHY Hedgehog signaling is activated in human and experimental models of CP. Inhibition of hedgehog signaling using an FDA-approved inhibitor, vismodegib, leads to the resolution of fibrosis and improves CP. This study has immense and immediate translational benefits.

Exploring disulfiram mechanisms in renal fibrosis: insights from biological data and computational approaches

Background

Disulfiram (DSF) is an anti-alcoholic drug that has been reported to inhibit the epithelial-to-mesenchymal transition and crosslinking during fibrosis, pyroptosis, and inflammatory NF-κB and Nrf-2 signaling pathways. However, there is insufficient evidence to support the mechanisms of DSF in preventing renal fibrosis (RF). Therefore, the current study aimed to elucidate the DSF-modulated targets and pathways in renal fibrosis.

Methods

The common proteins between DSF and RF were screened for protein-protein interaction, pathway enrichment, cluster, and gene ontology analysis. Molecular docking was executed for core genes using AutoDock Vina through the POAP pipeline. Molecular dynamics (MD) simulation (100 ns) was performed to infer protein-ligand stability, and conformational changes were analyzed by free energy landscape (FEL).

Results

A total of 78 targets were found to be common between DSF and RF, of which NFKB, PIK3CA/R1, MTOR, PTGS2, and MMP9 were the core genes. PI3K-Akt signaling followed by JAK-STAT, TNF, Ras, ErbB, p53, phospholipase D, mTOR, IL-17, NF-κB, AMPK, VEGF, and MAPK signaling pathways were modulated by DSF in RF. DSF showed a direct binding affinity with active site residues of core genes, and except for DSF with NF-κB, all other complexes, including the standard, were found to be stable during 100 ns MD simulation with minimal protein-ligand root mean squared deviation and residual fluctuations and higher compactness with broad conformational changes.

Conclusion

DSF protects against renal fibrosis, and this study paves the way for experimental investigation to repurpose DSF for treating RF.

Advances in the mechanisms of vascular calcification in chronic kidney disease

Vascular calcification (VC) is common in patients with advanced chronic kidney disease (CKD).A series of factors, such as calcium and phosphorus metabolism disorders, uremic toxin accumulation, inflammation and oxidative stress and cellular senescence, cause osteoblast-like differentiation of vascular smooth muscle cells, secretion of extracellular vesicles, and imbalance of calcium regulatory factors, which together promote the development of VC in CKD. Recent advances in epigenetics have provided better tools for the investigation of VC etiology and new approaches for finding more accurate biomarkers. These advances have not only deepened our understanding of the pathophysiological mechanisms of VC in CKD, but also provided valuable clues for the optimization of clinical predictors and the exploration of potential therapeutic targets. The aim of this article is to provide a comprehensive overview of the pathogenesis of CKD VC, especially the new advances made in recent years, including the various key factors mentioned above. Through the comprehensive analysis, we expect to provide a solid theoretical foundation and research direction for future studies targeting the specific mechanisms of CKD VC, the establishment of clinical predictive indicators and the development of potential therapeutic strategies.

Fibroblast expression of transmembrane protein smoothened governs microenvironment characteristics after acute kidney injury

The smoothened (Smo) receptor facilitates hedgehog signaling between kidney fibroblasts and tubules during acute kidney injury (AKI). Tubule-derived hedgehog is protective in AKI, but the role of fibroblast-selective Smo is unclear. Here, we report that Smo-specific ablation in fibroblasts reduced tubular cell apoptosis and inflammation, enhanced perivascular mesenchymal cell activities, and preserved kidney function after AKI. Global proteomics of these kidneys identified extracellular matrix proteins, and nidogen-1 glycoprotein in particular, as key response markers to AKI. Intriguingly, Smo was bound to nidogen-1 in cells, suggesting that loss of Smo could affect nidogen-1 accessibility. Phosphoproteomics revealed that the 'AKI protector' Wnt signaling pathway was activated in these kidneys. Mechanistically, nidogen-1 interacted with integrin β1 to induce Wnt in tubules to mitigate AKI. Altogether, our results support that fibroblast-selective Smo dictates AKI fate through cell-matrix interactions, including nidogen-1, and offers a robust resource and path to further dissect AKI pathogenesis.

Recent Advances of MSCs in Renal IRI: From Injury to Renal Fibrosis

Renal fibrosis is a pathological endpoint of maladaptation after ischemia-reperfusion injury (IRI), and despite many attempts, no good treatment has been achieved so far. At the core of renal fibrosis is the differentiation of various types of cells into myofibroblasts. MSCs were once thought to play a protective role after renal IRI. However, growing evidence suggests that MSCs have a two-sided nature. In spite of their protective role, in maladaptive situations, MSCs start to differentiate towards myofibroblasts, increasing the myofibroblast pool and promoting renal fibrosis. Following renal IRI, it has been observed that Bone Marrow-Derived Mesenchymal Stem Cells (BM-MSCs) and Renal Resident Mesenchymal Stem Cells (RR-MSCs) play important roles. This review presents evidence supporting their involvement, discusses their potential mechanisms of action, and suggests several new targets for future research.

Cell-cell communication in kidney fibrosis

Kidney fibrosis is a common outcome of a wide variety of chronic kidney diseases, in which virtually all kinds of renal resident and infiltrating cells are involved. As such, well-orchestrated intercellular communication is of vital importance in coordinating complex actions during renal fibrogenesis. Cell-cell communication in multicellular organisms is traditionally assumed to be mediated by direct cell contact or soluble factors, including growth factors, cytokines and chemokines, through autocrine, paracrine, endocrine and juxtacrine signaling mechanisms. Growing evidence also demonstrates that extracellular vesicles, lipid bilayer-encircled particles naturally released from almost all types of cells, can act as a vehicle to transfer a diverse array of biomolecules including proteins, mRNA, miRNA and lipids to mediate cell-cell communication. We recently described a new mode of intercellular communication via building a special extracellular niche by insoluble matricellular proteins. Kidney cells, upon injury, produce and secrete different matricellular proteins, which incorporate into the local extracellular matrix network, and regulate the behavior, trajectory and fate of neighboring cells in a spatially confined fashion. This extracellular niche-mediated cell-cell communication is unique in that it restrains the crosstalk between cells within a particular locality. Detailed delineation of this unique manner of intercellular communication will help to elucidate the mechanism of kidney fibrosis and could offer novel insights in developing therapeutic intervention.

Temporal gene signature of myofibroblast transformation in Peyronie's disease: first insights into the molecular mechanisms of irreversibility

BACKGROUND

Transformation of resident fibroblasts to profibrotic myofibroblasts in the tunica albuginea is a critical step in the pathophysiology of Peyronie's disease (PD). We have previously shown that myofibroblasts do not revert to the fibroblast phenotype and we suggested that there is a point of no return at 36 hours after induction of the transformation. However, the molecular mechanisms that drive this proposed irreversibility are not known.

AIM

Identify molecular pathways that drive the irreversibility of myofibroblast transformation by analyzing the expression of the genes involved in the process in a temporal fashion.

METHODS

Human primary fibroblasts obtained from tunica albuginea of patients with Peyronie's disease were transformed to myofibroblasts using transforming growth factor beta 1 (TGF-β1). The mRNA of the cells was collected at 0, 24, 36, 48, and 72 hours after stimulation with TGF-β1 and then analyzed using a Nanostring nCounter Fibrosis panel. The gene expression results were analyzed using Reactome pathway analysis database and ANNi, a deep learning-based inference algorithm based on a swarm approach.

OUTCOMES

The study outcome was the time course of changes in gene expression during transformation of PD-derived fibroblasts to myofibroblasts.

RESULTS

The temporal analysis of the gene expression revealed that the majority of the changes at the gene expression level happened within the first 24 hours and remained so throughout the 72-hour period. At 36 hours, significant changes were observed in genes involved in MAPK-Hedgehog signaling pathways.

CLINICAL TRANSLATION

This study highlights the importance of early intervention in clinical management of PD and the future potential of new drugs targeting the point of no return.

STRENGTHS AND LIMITATIONS

The use of human primary cells and confirmation of results with further RNA analysis are the strengths of this study. The study was limited to 760 genes rather than the whole transcriptome.

CONCLUSION

This study is to our knowledge the first analysis of temporal gene expression associated with the regulation of the transformation of resident fibroblasts to profibrotic myofibroblasts in PD. Further research is warranted to investigate the role of the MAPK-Hedgehog signaling pathways in reversibility of PD.

Sonic hedgehog-heat shock protein 90β axis promotes the development of nonalcoholic steatohepatitis in mice

Sonic hedgehog (SHH) and heat shock protein 90β (HSP90β) have been implicated in nonalcoholic steatohepatitis (NASH) but their molecular mechanisms of action remain elusive. We find that HSP90β is a key SHH downstream molecule for promoting NASH process. In hepatocytes, SHH reduces HSP90β ubiquitylation through deubiquitylase USP31, thus preventing HSP90β degradation and promoting hepatic lipid synthesis. HSP90β significantly increases in NASH mouse model, leading to secretion of exosomes enriched with miR-28-5p. miR-28-5p directly targetes and decreases Rap1b levels, which in turn promotes NF-κB transcriptional activity in macrophages and stimulates the expression of inflammatory factors. Genetic deletion, pharmacological inhibition of the SHH-HSP90β axis, or delivery of miR-28-5p to macrophages in the male mice liver, impairs NASH symptomatic development. Importantly, there is a markedly higher abundance of miR-28-5p in NASH patient sera. Taken together, the SHH-HSP90β-miR-28-5p axis offers promising therapeutic targets against NASH, and serum miR-28-5p may serve as a NASH diagnostic biomarker.

Serum levels of sonic hedgehog in patients with IgA nephropathy are closely associated with intrarenal arteriolar lesions

BACKGROUND

Intrarenal arteriolar disease is a major risk factor for poor prognosis in immunoglobulin A nephropathy (IgAN). The morphologic factor sonic hedgehog (SHH) plays an important role in a variety of vascular diseases, so it may be directly or indirectly involved in the process of renal arteriolar disease. The purpose of this study was to investigate the correlation between serum SHH levels and renal arteriole disease in patients with IgAN.

METHODS

Subjects with primary IgAN diagnosed by renal biopsy performed between October 2018 and August 2019 at the First Medical Center of the Chinese PLA General Hospital were recruited. Blood specimens were collected from the patients within 1 week before renal biopsy after they signed an informed consent form, and healthy controls were recruited for blood specimen collection during the same period. The concentration of serum SHH was measured by enzyme-linked immunosorbent assay in this population.

RESULTS

Serum SHH levels were significantly lower in the IgAN group than in the control group. 41 of the 94 subjects diagnosed with IgAN had severe renal arteriolosclerosis and, compared to their less severely affected counterparts, were older, more hypertensive, and characterized by lower levels of SHH, higher levels of tubular atrophy/interstitial fibrosis and a higher Lee's classification. Serum SHH concentration was found to be an independent predictor of severe intrarenal arteriolosclerosis in IgAN subjects after correction using multivariate analysis.

CONCLUSION

In this study, serum SHH levels were found to be significantly lower in patients with IgAN than in healthy subjects. Serum SHH may serve as a noninvasive biomarker of intrarenal arteriolosclerosis in patients with IgAN.

Identifying fibrogenic cells following salivary gland obstructive injury

Fibrosis results from excess extracellular matrix accumulation, which alters normal tissue architecture and impedes function. In the salivary gland, fibrosis can be induced by irradiation treatment for cancer therapy, Sjögren's Disease, and other causes; however, it is unclear which stromal cells and signals participate in injury responses and disease progression. As hedgehog signaling has been implicated in fibrosis of the salivary gland and other organs, we examined contributions of the hedgehog effector, Gli1, to fibrotic responses in salivary glands. To experimentally induce a fibrotic response in female murine submandibular salivary glands, we performed ductal ligation surgery. We detected a progressive fibrotic response where both extracellular matrix accumulation and actively remodeled collagen significantly increased at 14 days post-ligation. Macrophages, which participate in extracellular matrix remodeling, and Gli1+ and PDGFRα+ stromal cells, which may deposit extracellular matrix, both increased with injury. Using single-cell RNA-sequencing, Gli1 + cells were not found in discrete clusters at embryonic day 16 but were found in clusters expressing the stromal genes Pdgfra and/or Pdgfrb. In adult mice, Gli1+ cells were similarly heterogeneous but more cells co-expressed PDGFRα and PDGFRβ. Using Gli1-CreERT2; ROSA26tdTomato lineage-tracing mice, we found that Gli1-derived cells expand with ductal ligation injury. Although some of the Gli1 lineage-traced tdTomato+ cells expressed vimentin and PDGFRβ following injury, there was no increase in the classic myofibroblast marker, smooth muscle alpha-actin. Additionally, there was little change in extracellular matrix area, remodeled collagen area, PDGFRα, PDGFRβ, endothelial cells, neurons, or macrophages in Gli1 null salivary glands following injury when compared with controls, suggesting that Gli1 signaling and Gli1+ cells have only a minor contribution to mechanical injury-induced fibrotic changes in the salivary gland. We used scRNA-seq to examine cell populations that expand with ligation and/or showed increased expression of matrisome genes. Some Pdgfra + /Pdgfrb + stromal cell subpopulations expanded in response to ligation, with two stromal cell subpopulations showing increased expression of Col1a1 and a greater diversity of matrisome genes, consistent with these cells being fibrogenic. However, only a few cells in these subpopulations expressed Gli1, consistent with a minor contribution of these cells to extracellular matrix production. Defining the signaling pathways driving fibrotic responses in stromal cell sub-types could reveal future therapeutic targets.

Identifying Fibrogenic Cells Following Salivary Gland Obstructive Injury

Fibrosis results from excess extracellular matrix accumulation, which alters normal tissue architecture and impedes function. In the salivary gland, fibrosis can be induced by irradiation treatment for cancer therapy, Sjögren's Disease, and other causes; however, it is unclear which stromal cells and signals participate in injury responses and disease progression. As hedgehog signaling has been implicated in fibrosis of the salivary gland and other organs, we examined contributions of the hedgehog effector, Gli1, to fibrotic responses in salivary glands. To experimentally induce a fibrotic response in female murine submandibular salivary glands, we performed ductal ligation surgery. We detected a progressive fibrotic response where both extracellular matrix accumulation and actively remodeled collagen trended upwards at 7 days and significantly increased at 14 days post- ligation. Macrophages, which participate in extracellular matrix remodeling, Gli1 + and PDGFRα + stromal cells, which may deposit extracellular matrix, both increased with injury. Using single-cell RNA-sequencing, we found that a majority of Gli1 + cells at embryonic day 16 also express Pdgfra and/or Pdgfrb. However, in adult mice, only a small subset of Gli1 + cells express PDGFRα and/or PDGFRβ at the protein level. Using lineage-tracing mice, we found that Gli1-derived cells expand with ductal ligation injury. Although some of the Gli1 lineage-traced tdTomato + cells expressed vimentin and PDGFRβ following injury, there was no increase in the classic myofibroblast marker, smooth muscle alpha-actin. Additionally, there was little change in extracellular matrix area, remodeled collagen area, PDGFRα, PDGFRβ, endothelial cells, neurons, or macrophages in Gli1 null salivary glands following injury when compared with controls, suggesting that Gli1 signaling and Gli1 + cells have only a minor contribution to mechanical injury-induced fibrotic changes in the salivary gland. We used scRNA-seq to examine cell populations that expand with ligation and/or showed increased expression of matrisome genes. Pdgfra + /Pdgfrb + stromal cell subpopulations both expanded in response to ligation, showed increased expression and a greater diversity of matrisome genes expressed, consistent with these cells being fibrogenic. Defining the signaling pathways driving fibrotic responses in stromal cell sub-types could reveal future therapeutic targets.

Senescent renal tubular epithelial cells activate fibroblasts by secreting Shh to promote the progression of diabetic kidney disease

Introduction

Diabetic kidney disease (DKD) is one of the complications of diabetes; however, the pathogenesis is not yet clear. A recent study has shown that senescence is associated with the course of DKD. In the present study, we explored whether senescent renal tubular cells promote renal tubulointerstitial fibrosis by secreting Sonic hedgehog (Shh) which mediates fibroblast activation and proliferation in DKD.

Methods

A 36-week-old db/db mice model and the renal tubular epithelial cells were cultured in high glucose (HG, 60 mmol/L) medium for in vivo and in vitro experiments.

Results

Compared to db/m mice, blood glucose, microalbuminuria, serum creatinine, urea nitrogen, and UACR (microalbuminuria/urine creatinine) were markedly increased in db/db mice. Collagen III, monocyte chemoattractant protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-α) were also increased in db/db mice kidneys, suggesting fibrosis and inflammation in the organ. Moreover, the detection of SA-β-galactosidase (SA-β-Gal) showed that the activity of SA-β-Gal in the cytoplasm of renal tubular epithelial cells increased, and the cell cycle inhibition of the expression of senescence-related gene cell cycle inhibitor p16 ^INK4A protein and p21 protein increased, indicating that renal fibrosis in db/db mice was accompanied by cell senescence. Furthermore, Shh is highly expressed in the injured renal tubules and in the kidney tissue of db/db mice, as detected by enzyme-linked immunosorbent assay (ELISA). The results of immunofluorescence staining showed increased positive staining for Shh in renal tubular epithelial cells of db/db mice and decreased positive staining for Lamin B1, but increased positive staining for γH2A.X in cells with high Shh expression; similar results were obtained in vitro. In addition, HG stimulated renal tubular epithelial cells to secrete Shh in the supernatant of the medium. D-gal treatment of renal tubular epithelial cells increased the protein levels of Shh and p21. We also found enhanced activation and proliferation of fibroblasts cultured with the supernatant of renal tubular epithelial cells stimulated by HG medium but the proliferative effect was significantly diminished when co-cultured with cyclopamine (CPN), an inhibitor of the Shh pathway.

Discussion

In conclusion, HG induces renal tubular epithelial cell senescence, and the secretion of senescence-associated proteins and Shh mediates inflammatory responses and fibroblast activation and proliferation, ultimately leading to renal fibrosis.

Oxy210, a Semi-Synthetic Oxysterol, Inhibits Profibrotic Signaling in Cellular Models of Lung and Kidney Fibrosis

Oxy210, a semi-synthetic oxysterol derivative, displays cell-selective inhibition of Hedgehog (Hh) and transforming growth factor beta (TGF-β) signaling in epithelial cells, fibroblasts, and macrophages as well as antifibrotic and anti-inflammatory efficacy in models of liver fibrosis. In the present report, we examine the effects of Oxy210 in cellular models of lung and kidney fibrosis, such as human lung fibroblast cell lines IMR-90, derived from healthy lung tissue, and LL97A, derived from an idiopathic pulmonary fibrosis (IPF) patient. In addition, we examine the effects of Oxy210 in primary human renal fibroblasts, pericytes, mesangial cells, and renal tubular epithelial cells, known for their involvement in chronic kidney disease (CKD) and kidney fibrosis. We demonstrate in fibroblasts that the expression of several profibrotic TGF-β target genes, including fibronectin (FN), collagen 1A1 (COL1A1), and connective tissue growth factor (CTGF) are inhibited by Oxy210, both at the basal level and following TGF-β stimulation in a statistically significant manner. The inhibition of COL1A1 gene expression translated directly to significantly reduced COL1A1 protein expression. In human primary small airway epithelial cells (HSAECs) and renal tubular epithelial cells, Oxy210 significantly inhibited TGF-β target gene expression associated with epithelial-mesenchymal transition (EMT). Oxy210 also inhibited the proliferation of fibroblasts, pericytes, and mesangial cells in a dose-dependent and statistically significant manner.

Kaempferol inhibits renal fibrosis by suppression of the sonic hedgehog signaling pathway

BACKGROUND

Most chronic kidney diseases (CKDs) develop to end-stage renal disease (ESRD), which is characterized by fibrosis and permanent tissue and function loss. As a result, better and more effective remedies are essential. Kaempferol (KAE) is a common flavonoid extracted from plants. It can control the progression of kidney fibrosis and the epithelial-to-mesenchymal transition (EMT) of the renal tubular system.

PURPOSE

We aim to investigate the effect of KAE therapy on extracellular matrix deposition and stimulation of EMT in vitro and in vivo to elucidate the treatment mechanisms regulating these effects.

STUDY DESIGN

Chronic hypertension-induced kidney fibrosis was studied in spontaneously hypertensive rats with chronic kidney disease. Biochemical analysis, histological staining, and the expression level of relative proteins were used to assess the effect of KAE on renal function and fibrosis. The direct impact of KAE on proliferation and migration was evaluated using human renal tubular epithelial cells (HK-2) induced by transforming growth factor-β1 (TGF-β1), which can then induce EMT. The molecular mechanism of KAE was verified using co-IP assay and immunofluorescence.

RESULTS

KAE could reduce blood pressure and decrease the extracellular matrix (ECM) components (including collagen I and collagen Ш), TGF-β1, and α-SMA in the kidneys of hypertension-induced rats with chronic kidney disease. Moreover, in HK-2 cell treated with TGF-β1, KAE administration significantly suppressed proliferation, migration, and EMT via increasing the expression of E-cadherin, while reducing the N-cadherin and α-SMA. Sufu was exceedingly repressed in HK-2 cells treated with TGF-β1. KAE inhibited the activation of Shh and Gli through increasing the expression of Sufu, thereby blocking the nuclear translocation of Gli1 in vitro.

CONCLUSION

KAE ameliorated kidney fibrosis and EMT by inhibiting the sonic hedgehog signaling pathway, thereby to attenuate the pathological progression of hypertensive kidney fibrosis.

Effective dose/duration of natural flavonoid quercetin for treatment of diabetic nephropathy: A systematic review and meta-analysis of rodent data

BACKGROUND

Given the challenges on diabetic nephropathy (DN) treatment, research has been carried out progressively focusing on dietary nutrition and natural products as a novel option with the objective of enhancing curative effect and avoiding adverse reactions. As a representative, Quercetin (Qu) has proved to be of great value in current data.

PURPOSE

We aimed to synthetize the evidence regarding the therapeutic effect and specific mechanism of quercetin on DN via systematically reviewing and performing meta-analysis.

METHODS

Preclinical literature published prior to August 2021, was systematical retrieval and manually filtrated across four major databases including PubMed, Web of Science, EMBASE and Cochrane library. Pooled overall effect sizes of results were generated by STATA 16.0, and underlying mechanisms were summarized. Three-dimensional dose/time-effect analyses and radar maps were conducted to examine the dosage/time-response relations between Qu and DN.

RESULTS

This paper pools all current available evidence in a comprehensive way, and shows the therapeutic benefits as well as potential action mechanisms of Qu in protecting the kidney against damage. A total of 304 potentially relevant citations were identified, of which 18 studies were enrolled into analysis. Methodological quality was calculated, resulting in an average score of 7.06/10. This paper provided the preliminary evidence that consumption of Qu could induce a statistical reduction in mesangial index, Scr, BUN, 24-h urinary protein, serum urea, BG, kidney index, TC, TG, LDL-C, AST, MDA, AGE, TNF-α, TGF-β1, TGF-β1 mRNA, CTGF and IL-1β, whereas HDL-C, SOD, GSH, GSH-Px, CAT and smad-7 were significantly increased. Furthermore, Qu could remarkably improve the renal pathology. In terms of the mechanisms underlying therapy of DN, Qu exerts anti-diabetic nephropathy properties possibly through PI3K/PKB, AMPK-P38 MAPK, SCAP/SREBP2/LDLr, mtROS-TRX/TXNIP/NLRP3/IL-1β, TGF-β1/Smad, Nrf2/HO-1, Hippo, mTORC1/p70S6K and SHH pathways. Dose/time-response images predicted a modest association between Qu dosage consumption/administration length and therapeutic efficacy, with the optimal dosage at 90-150 mg/kg/d and administration length ranging from 8 weeks to 12 weeks.

CONCLUSIONS

Quercetin exhibit highly pleiotropic actions, which simultaneously contributes to prevent fundamental progression of DN, such as hyperglycemia, dyslipidemia, inflammation, fibrotic lesions and oxidative stress. The therapeutic effect becomes stronger when Qu administration at higher dosages lasts for longer durations. Taken together, quercetin could be used in patients with DN as a promising agent, which has well-established safety profiles and nontoxicity according to existing literature.

Natural products: potential drugs for the treatment of renal fibrosis

With the increasing prevalence and mortality, chronic kidney disease (CKD) has become a world public health problem. As the primary pathological manifestation in CKD, renal fibrosis is often used as a critical target for the treatment of CKD and inhibits the progression of CKD to end-stage renal disease (ESRD). As a potential drug, natural products have been confirmed to have the potential as a routine or supplementary therapy for chronic kidney disease, which may target renal fibrosis and act through various pharmacological activities such as anti-inflammatory and anti-oxidation of natural products. This article briefly introduces the pathological mechanism of renal fibrosis and systematically summarizes the latest research on the treatment of renal fibrosis with natural products of Chinese herbal medicines.

Inhibitory Effects of Rhein on Renal Interstitial Fibrosis via the SHH-Gli1 Signal Pathway

Background. Rhein is the main extract of Rheum palmatum L., which has been proved to improve the renal function of chronic kidney disease, but its mechanism is not clear. Therefore, this experiment explored the potential pharmacological effect of rhein on renal interstitial fibrosis rats. Methods. This study explores the potential pharmacological action of rhein. In this work, we investigate the potential pharmacological action of rhein in unilateral urethral obstruction (UUO) rats. Thirty Sprague Dawley rats were randomly divided into three groups: sham, UUO, and rhein (rhein-treated UUO rats) groups. The left ureters of the UUO group rats were exposed and bluntly dissected. The rhein group rats were administered an intragastric gavage of rhein (2 mg·kg−1·d−1) for 14 d. Kidney function-related indicators were monitored in these rats, while indexes of pathologic aspects were determined histologically. The expression of α-SMA, TGF-β1, SHH, Gli1, and Snail was quantified using real-time polymerase chain reaction and western blotting. The NRK-49F cells were incubated with and without SHH (100 ng·ml−1) for 48 hours. The SHH-activated NRK-49F cells were incubated with cyclopamine (CNP, 20 umol L−1) or rhein (1 ng·ml−1). The Gli1 and Snail mRNA and protein level were detected. Results. In the in vivo experiment, the results exhibited that UUO caused renal pathological damages. However, these changes could be significantly reversed by the administration of rhein. Compared with the untreated UUO group, the rhein group showed reduced kidney tubular atrophy and necrosis, interstitial fibrosis, hyperplasia, and abnormal deposition of extracellular matrix. Rhein reduced the RNA and protein expression of SHH, Gli1, and Snail of the UUO rats. In the in vitro experiment, CNP or rhein treatment decreased the expression of Gli1 and Snail on mRNA and protein levels in SHH-induced NRK-49F cells, suggesting that CNP or rhein suppresses SHH-induced NRK-49F activation. Taken together, these results demonstrated that rhein suppresses SHH-Gli1-Snail signal pathway activation, with potential implications for the treatment of renal fibrosis. Conclusions. Treatment with rhein remarkably ameliorated renal interstitial fibrosis in UUO rats by regulating the SHH-Gli1-Snail signal pathway.

Plants with Therapeutic Potential for Ischemic Acute Kidney Injury: A Systematic Review

Acute kidney injury (AKI) is a complex condition which has an intricate pathology mostly involving hemodynamic, inflammatory, and direct toxic effects at the cellular level with high morbidity and mortality ratios. Renal ischemic reperfusion injury (RIRI) is the main factor responsible for AKI, most often observed in different types of shock, kidney transplantation, sepsis, and postoperative procedures. The RIRI-induced AKI is accompanied by increased reactive oxygen species generation together with the activation of various inflammatory pathways. In this context, plant-derived medicines have shown encouraging nephroprotective properties. Evidence provided in this systemic review leads to the conclusion that plant-derived extracts and compounds exhibit nephroprotective action against renal ischemic reperfusion induced-AKI by increasing endogenous antioxidants and decreasing anti-inflammatory cytokines. However, there is no defined biomarker or target which can be used for treating AKI completely. These plant-derived extracts and compounds are only tested in selected transgenic animal models. To develop the results obtained into a therapeutic entity, one should apply them in proper vertebrate multitransgenic animal models prior to further validation in humans.

Shen-Shuai-Ling Formulation Attenuates Renal Interstitial Fibrosis in Chronic Kidney Disease by Regulating SHH-Gli1 Signaling Pathway

Background

Shen-Shuai-Ling Formulation (SSLF) has apparent effects on improving renal function, delaying the progression of chronic kidney disease (CKD).

Methods

Fifty male SD rats were randomly divided into 5 groups: Sham group, Model group, SSLF group, CPN group, and C + S group. The morphological changes and the collagen fibers of the rat kidneys were observed by HE staining. The expression of α-SMA, Col I, SHH, Gli1, and snail1 was detected by Western blot and qPCR. Then, the cells were divided into the control group, SHH group, and SHH + SSLF serum group.

Results

Compared with the Model group, the fibrosis in SSLF, CPN, and C + S groups was significantly alleviated. And, compared with those in the Model group, the expression of α-SMA, Col I, SHH, Gli1, Snail in SSLF, CPN, and C + S groups decreased remarkably.

Conclusions

SSLF remarkably improves renal function and alleviates renal interstitial fibrosis in UUO rats.

Renal primary cilia lengthen in the progression of diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease, and its early pathogenesis is critical. Shear stress caused by glomerular hyperfiltration contributes to the initiation of kidney injury in diabetes. The primary cilium of renal tubular epithelial cells (RTECs) is an important mechanical force sensor of shear stress and regulates energy metabolism homeostasis in RTECs to ensure energy supply for reabsorption functions, but little is known about the alterations in the renal cilium number and length during the progression of DKD. Here, we demonstrate that aberrant ciliogenesis and dramatic increase in the cilium length, the number of ciliated cells, and the length of cilia are positively correlated with the DKD class in the kidney biopsies of DKD patients by super-resolution imaging and appropriate statical analysis methods. This finding was further confirmed in STZ-induced or db/db diabetic mice. These results suggest that the number and length of renal cilia may be clinically relevant indicators and that cilia will be attractive therapeutic targets for DKD.

The Hedgehog Signaling Pathway in Idiopathic Pulmonary Fibrosis: Resurrection Time

The hedgehog (Hh) pathway is a sophisticated conserved cell signaling pathway that plays an essential role in controlling cell specification and proliferation, survival factors, and tissue patterning formation during embryonic development. Hh signal activity does not entirely disappear after development and may be reactivated in adulthood within tissue-injury-associated diseases, including idiopathic pulmonary fibrosis (IPF). The dysregulation of Hh-associated activating transcription factors, genomic abnormalities, and microenvironments is a co-factor that induces the initiation and progression of IPF.

Pirfenidone is a renal protective drug: Mechanisms, signalling pathways, and preclinical evidence

Renal fibrosis, a characteristic of all chronic kidney diseases, lacks effective therapeutic drugs currently. Pirfenidone (PFD), a small molecule drug with good oral bioavailability, is widely used in idiopathic pulmonary fibrosis and exerts anti-fibrotic, anti-inflammatory, antioxidant, and anti-apoptotic effects. These effects have been attributed to the suppression of cell growth factors (in particular, but not exclusively, transforming growth factor-β) and the epithelial-mesenchymal transition, as well as the possible down-regulation of pro-inflammatory mediators (such as tumour necrosis factor-α), the protection of mitochondrial function, and the regulation of inflammatory cells. Considering the activation of similar anti-fibrotic pathways in lung and kidney disease and the broad activity of PFD, this drug has improved the treatment of the renal fibrotic disease. In this review, we briefly summarize the pharmacokinetics and safety of PFD as well as the mechanisms of PFD focusing on kidney disease. We summarize the effects of PFD on renal function and pathological alterations based on animal experiments, as well as changes in growth factors based on both animal and renal cell experiments. Moreover, given the activation of similar profibrotic pathways in pulmonary diseases and other disorders, we reviewed in-depth the possible signalling pathways targeted by PFD to attenuate renal fibrosis and protect renal function. Finally, we provide an overview of the current clinical trials of PFD for the treatment of renal fibrosis.

Nupr1 mediates renal fibrosis via activating fibroblast and promoting epithelial-mesenchymal transition

Renal interstitial fibrosis (RIF) is a pathological process that fibrotic components are excessively deposited in the renal interstitial space due to kidney injury, resulting in impaired renal function and chronic kidney disease. The molecular mechanisms controlling renal fibrosis are not fully understood. In this present study, we identified Nuclear protein 1 (Nupr1), a transcription factor also called p8, as a novel regulator promoting renal fibrosis. Unilateral ureteral obstruction (UUO) time-dependently induced Nupr1 mRNA and protein expression in mouse kidneys while causing renal damage and fibrosis. Nupr1 deficiency (Nupr1^-/- ) attenuated the renal tubule dilatation, tubular epithelial cell atrophy, and interstitial collagen accumulation caused by UUO. Consistently, Nupr1^-/- significantly decreased the expression of type I collagen, myofibroblast markers smooth muscle α-actin (α-SMA), fibroblast-specific protein 1 (FSP-1), and vimentin in mouse kidney that were upregulated by UUO. These results suggest that Nupr1 protein was essential for fibroblast activation and/or epithelial-mesenchymal transition (EMT) during renal fibrogenesis. Indeed, Nupr1 was indispensable for TGF-β-induced myofibroblast activation of kidney interstitial NRK-49F fibroblasts, multipotent mesenchymal C3H10T1/2 cells, and the EMT of kidney epithelial NRK-52E cells. It appears that Nupr1 mediated TGF-β-induced α-SMA expression and collagen synthesis by initiating Smad3 signaling pathway. Importantly, trifluoperazine (TFP), a Nupr1 inhibitor, alleviated UUO-induced renal fibrosis. Taken together, our results demonstrate that Nupr1 promotes renal fibrosis by activating myofibroblast transformation from both fibroblasts and tubular epithelial cells.

A Review of Traditional Chinese Medicine in Treating Renal Interstitial Fibrosis via Endoplasmic Reticulum Stress-Mediated Apoptosis

Renal interstitial fibrosis (RIF) is the main pathological manifestation of end-stage renal disease. Recent studies have shown that endoplasmic reticulum (ER) stress is involved in the pathogenesis and development of RIF. Traditional Chinese medicine (TCM), as an effective treatment for kidney diseases, can improve kidney damage by affecting the apoptotic signaling pathway mediated by ER stress. This article reviews the apoptotic pathways mediated by ER stress, including the three major signaling pathways of unfolded protein response, the main functions of the transcription factor C/EBP homologous protein. We also present current research on TCM treatment of RIF, focusing on medicines that regulate ER stress. A new understanding of using TCM to treat kidney disease by regulating ER stress will promote clinical application of Chinese medicine and discovery of new drugs for the treatment of RIF.

Polysaccharides extracted from balanophora polyandra Griff (BPP) ameliorate renal Fibrosis and EMT via inhibiting the Hedgehog pathway

Renal interstitial fibrosis (RIF) is a crucial pathological change leading to chronic kidney disease (CKD). Currently, no effective medicines have been available for treating it. In our research, we examined the effects of polysaccharides extracted from Balanophora polyandra Griff (BPPs) on kidney fibrosis and epithelial to mesenchymal transition (EMT) in vivo and in vitro, aiming to explore the underlying mechanisms. By using the mice with unilateral urethral obstruction (UUO) as experimental subjects, we examined the medicinal values of BPPs on alleviating RIF. The effects of BPPs were evaluated by examining the histological staining and relative mRNA and protein expression levels of the related genes. The possible underlying mechanisms were further explored with human normal renal proximal tubular epithelia (HK‐2 cells) as in vitro model. In UUO mice, BPP treatment could significantly alleviate interstitial fibrosis through reducing the components (Collagens I, III and IV) of extracellular matrix (ECM), and reducing the activation of fibroblasts producing these components, as revealed by inhibiting the hallmarks (fibronectin and α‐SMA) of fibroblast activation. Furthermore, BPP administration increased the expression levels of matrix metalloproteinases (MMPs) and declined those of tissue inhibitors of metalloproteinases (TIMPs). BPPs markedly ameliorated EMT in both the kidneys of UUO mice and TGF‐β1 treated HK‐2 cells. Moreover, BPP treatment decreased the expression levels of several transcriptional factors involved in regulating E‐cadherin expression, including snail, twist and ZEB1. Additionally, the Hedgehog pathway was found to be closely correlated with renal fibrosis and EMT. Altogether, our results clearly demonstrated that BPP treatment effectively inhibited the Hedgehog pathway both in renal tissues of UUO mice and TGF‐β1‐treated HK‐2 cells. Thus, BPPs ameliorated RIF and EMT in vivo and in vitro via suppressing Hedgehog signalling pathway.

High-Fat Diet Induced Hedgehog Signaling Modifications during Chronic Kidney Damage

Excessive consumption of dietary fats leads to the deposition of unnecessary metabolites and multiple organ damage. Lipids, important key regulators of Hedgehog signaling, are involved in triggering fibrotic chronic kidney disease. The present study encompasses the assessment of renal morphofunctional modifications and alteration of lipid metabolism influencing the changes in gene expression of hedgehog signaling pathway genes. Fifteen male Rattus norvegicus of 200 ± 25 grams weight were equally divided into three groups: control (standard rat chow), D-1 (unsaturated high-fat diet) and D-2 (saturated high-fat diet). Animals were provided with respective diets and were followed for 16 weeks. Both HFD-fed groups did not show overall body weight gain as compared to the control. While significant downregulation of hedgehog pathway genes was found in fatty diet groups. In comparison with the control group, Shh, Gli1, Gli2, and Gli3 were downregulated after the consumption of both unsaturated and saturated fatty diets. Ihh and Smo exhibit a similar downregulation in the D-1 group, but an upregulation was detected in the D-2 group. D-2 group also had an increased serum urea concentration as compared to the control (P = 0.0023). Furthermore, renal histopathology revealed tubular necrosis, glomerular edema, glomerular shrinkage, and hypocellularity. Collagen deposition in both HFD groups marks the extent of fibrosis summary figure. Extravagant intake of dietary fats impaired normal kidney functioning and morphofunctionally anomalous kidney triggers on Hh signaling in adult rats. These anomalies can be linked to an escalated risk of chronic kidney disease in adults strongly recommending the reduced uptake of fatty diets to prevent impaired metabolism and renal lipotoxicity.

Shenkang VII Recipe Attenuates Unilateral Ureteral Obstruction-induced Renal Fibrosis via TGF-β/Smad, NF-κB and SHH Signaling Pathway

This study aimed to explore the protective effects of the traditional Chinese Medicine formula Shenkang VII recipe (SK-7) on renal fibrosis and the mechanisms. Renal fibrosis was induced by unilateral ureteral obstruction (UUO) in rats. The rats were then divided into 5 groups: control group (Sham operation), UUO model group, UUO model plus low to high doses of SK-7 (0.5, 1.0, or 2.0 g/kg/day, for 14 days) groups. The animals were sacrificed on the 7th or 14th day. Kidney tissues were collected for histopathological examinations (hematoxylin and eosin and Masson's trichrome staining). Immunohistochemistry was used to detect the expression of collagen type III (Col III), fibronectin (FN), α-smooth muscle actin (α-SMA), TIMP metallopeptidase inhibitor 2 (TIMP2), matrix metallopeptidase 2 (MMP2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and monocyte chemotactic protein-1 (MCP-1). The TGF-β1/Smad, NF-kB and Sonic hedgehog signaling proteins were detected by Western blotting. Our results showed that SK-7 prevented UUO-induced renal injury and accumulation of collagen fibrils. Renal fibrosis biomarkers Col III, FN, α-SMA and TIMP2 were increased in the rats after UUO and decreased by SK-7, while MMP2 was upregulated after treatment. SK-7 also suppressed the levels of TNF-α, IL-1β and MCP-1 in UUO rats. In addition, SK-7 inhibited activation of the TGF-β/Smad, NF-κB and sonic hedgehog signaling (SHH) pathways. Taken together, these findings suggest that SK-7 may regulate the synthesis and degradation of extracellular matrix, reduce inflammation and suppress the proliferation of fibroblasts, by blocking the TGF-β1/Smad, NF-κB and SHH signaling pathways to exert its anti-renal fibrosis effect in UUO rats.

Integrative microRNA and mRNA expression profiling in acute aristolochic acid nephropathy in mice

In acute aristolochic acid nephropathy (AAN), aristolochic acid (AA) induces renal injury and tubulointerstitial fibrosis. However, the roles of microRNAs (miRNAs/miRs) and mRNAs involved in AAN are not clearly understood. The aim of the present study was to examine AA‑induced genome‑wide differentially expressed (DE) miRNAs and DE mRNAs using deep sequencing in mouse kidneys, and to analyze their regulatory networks. In the present self‑controlled study, mice were treated with 5 mg/kg/day AA for 5 days, following unilateral nephrectomy. AA‑induced renal injury and tubulointerstitial fibrosis were detected using hematoxylin and eosin staining and Masson's trichrome staining in the mouse kidneys. A total of 82 DE miRNAs and 4,605 DE mRNAs were identified between the AA‑treated group and the self‑control group. Of these DE miRNAs and mRNAs, some were validated using reverse transcription‑quantitative PCR. Expression levels of the profibrotic miR‑21, miR‑433 and miR‑132 families were significantly increased, whereas expression levels of the anti‑fibrotic miR‑122‑5p and let‑7a‑1‑3p were significantly decreased. Functions and signaling pathways associated with the DE miRNAs and mRNAs were analyzed using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG). A total of 767 DE pairs (in opposing directions) of miRNAs and their mRNA targets were identified. Among these, regulatory networks of miRNAs and mRNAs were analyzed using KEGG to identify enriched signaling pathways and extracellular matrix‑associated pathways. In conclusion, the present study identified genome‑wide DE miRNAs and mRNAs in the kidneys of AA‑treated mice, as well as their regulatory pairs and signaling networks. The present results may improve the understanding of the role of DE miRNAs and their mRNA targets in the pathophysiology of acute AAN.

Microcystin-leucine-arginine induces liver fibrosis by activating the Hedgehog pathway in hepatic stellate cells

Microcystin-leucine-arginine (MC-LR), produced by cyanobacteria, accumulates in the liver through blood circulation. We investigated the impact of MC-LR on liver fibrosis. Mice received a daily injection of MC-LR at various concentrations for 14 consecutive days aa and then mouse liver was obtained for histopathological and immunoblot analysis. Next, a human hepatic stellate cell line (LX-2) was treated with MC-LR at various concentrations followed by measurement of cell viability, cell cycle and relevant protein expression levels. Our data confirmed the induction of mouse liver fibrosis after exposure to MC-LR at 15 μg/kg and 30 μg/kg. Furthermore, we demonstrated that LX-2 cells could uptake MC-LR, resulting in cell proliferation and differentiation through impacting the Hedgehog signaling after the treatment of MC-LR at 50 nM. Our data supported that MC-LR could induce liver fibrosis by modulating the expression of the transcription factor Gli2 in the Hedgehog signaling in hepatic stellate cells.

Tubule-derived exosomes play a central role in fibroblast activation and kidney fibrosis

Extracellular vesicles such as exosomes are involved in mediating cell-cell communication by shuttling an assortment of proteins and genetic information. Here, we tested whether renal tubule-derived exosomes play a central role in mediating kidney fibrosis. The production of exosomes was found to be increased in the early stage of unilateral ureteral obstruction, ischemia reperfusion injury or 5/6 nephrectomy models of kidney disease. Exosome production occurred primarily in renal proximal tubular epithelium and was accompanied by induction of sonic hedgehog (Shh). In vitro, upon stimulation with transforming growth factor-β1, kidney proximal tubular cells (HKC-8) increased exosome production. Purified exosomes from these cells were able to induce renal interstitial fibroblast (NRK-49F) activation. Conversely, pharmacologic inhibition of exosome secretion with dimethyl amiloride, depletion of exosome from the conditioned media or knockdown of Shh expression abolished the ability of transforming growth factor-β1-treated HKC-8 cells to induce NRK-49F activation. In vivo, injections of tubular cell-derived exosomes aggravated kidney injury and fibrosis, which was negated by an Shh signaling inhibitor. Blockade of exosome secretion in vivo ameliorated renal fibrosis after either ischemic or obstructive injury. Furthermore, knockdown of Rab27a, a protein that is essential for exosome formation, also preserved kidney function and attenuated renal fibrotic lesions in mice. Thus, our results suggest that tubule-derived exosomes play an essential role in renal fibrogenesis through shuttling Shh ligand. Hence, strategies targeting exosomes could be a new avenue in developing therapeutics against renal fibrosis.

Molecular pathways involved in injury-repair and ADPKD progression

The major hallmark of Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the formation of many fluid-filled cysts in the kidneys, which ultimately impairs the normal renal structure and function, leading to end-stage renal disease (ESRD). A large body of evidence suggests that injury-repair mechanisms are part of ADPKD progression. Once cysts have been formed, proliferation and fluid secretion contribute to the cyst size increase, which eventually causes stress on the surrounding tissue resulting in local injury and fibrosis. In addition, renal injury can cause or accelerate cyst formation. In this review, we will describe the various mechanisms activated during renal injury and tissue repair and show how they largely overlap with the molecular mechanisms activated during PKD progression. In particular, we will discuss molecular mechanisms such as proliferation, inflammation, cell differentiation, cytokines and growth factors secretion, which are activated following the renal injury to allow the remodelling of the tissue and a proper organ repair. We will also underline how, in a context of PKD-related gene mutations, aberrant or chronic activation of these developmental pathways and repair/remodelling mechanisms results in exacerbation of the disease.

The primary cilia in diabetic kidney disease: A tubulocentric view?

Diabetic kidney disease is growing exponentially. This review aims to discuss alternate therapeutic approaches beyond the glomerulocentric view and to consider a novel tubulocentric approach with focus on the primary cilia. Renin-angiotensin-aldosterone system blockade to decrease glomerular capillary pressure and prevent albuminuria has been the mainstay of treatment for diabetic and non-diabetic proteinuric kidney disease. Landmark clinical trials have also shown cardiorenal benefit with sodium-glucose linked co-transporter 2 inhibitors and glucagon-like peptide 1 receptor analogues in patients with type 2 diabetes. Effective renoprotective drugs seem to have a common mechanistic mode of reducing glomerular hyperfiltration/hypertension. In the tubules, primary cilia act as "antennae" to detect mechanosensory changes such as glomerular hyperfiltration and trgger intracellular signalling pathways. They are also implicated in obesity and metabolic disorders linked to diabetes. To conclude, primary cilia of the kidney tubules offer a novel therapeutic target and may complement the current glomerulocentric approaches.

Targeting the progression of chronic kidney disease

Chronic kidney disease (CKD) is a devastating condition that is reaching epidemic levels owing to the increasing prevalence of diabetes mellitus, hypertension and obesity, as well as ageing of the population. Regardless of the underlying aetiology, CKD is slowly progressive and leads to irreversible nephron loss, end-stage renal disease and/or premature death. Factors that contribute to CKD progression include parenchymal cell loss, chronic inflammation, fibrosis and reduced regenerative capacity of the kidney. Current therapies have limited effectiveness and only delay disease progression, underscoring the need to develop novel therapeutic approaches to either stop or reverse progression. Preclinical studies have identified several approaches that reduce fibrosis in experimental models, including targeting cytokines, transcription factors, developmental and signalling pathways and epigenetic modulators, particularly microRNAs. Some of these nephroprotective strategies are now being tested in clinical trials. Lessons learned from the failure of clinical studies of transforming growth factor β1 (TGFβ1) blockade underscore the need for alternative approaches to CKD therapy, as strategies that target a single pathogenic process may result in unexpected negative effects on simultaneously occurring processes. Additional promising avenues include preventing tubular cell injury and anti-fibrotic therapies that target activated myofibroblasts, the main collagen-producing cells.

Quercetin inhibits kidney fibrosis and the epithelial to mesenchymal transition of the renal tubular system involving suppression of the Sonic Hedgehog signaling pathway

Quercetin is the most ubiquitous flavonoid in fruits, herbs, vegetables and products made from them. It shows the potential to inhibit the progression of kidney fibrosis and the epithelial to mesenchymal transition (EMT) of the renal tubular system, but the molecular mechanism behind this is still not known. In our study, we explored the effect of quercetin treatment on extracellular matrix (ECM) deposition and stimulation of the EMT in vitro and in vivo and tried to deduce the mechanisms regulating these effects. In rats having unilateral ureter obstruction (UUO), quercetin treatment significantly prevented renal function decline. Quercetin reduced the TGF-β1 expression and inhibited the epithelial cell to mesenchymal cell phenotypic switch, as well as ECM deposition in rats with UUO. In cultured epithelial cells of the renal tubular region (NRK-52E), quercetin markedly ameliorated the EMT and ECM synthesis induced by TGF-β1. Activation of the Hedgehog pathway was closely related to EMT induction. Quercetin effectively suppressed the hyperactive Hedgehog pathway in NRK-52E cells treated with TGF-β1 and in kidney obstructed rats, which reduced the EMT, ECM deposition and cellular proliferation. Moreover, we examined certain transcriptional factors (slug, snail, ZEB-1 and twist) that govern the E-cadherin expression at the level of transcription. The results unveiled that the four transcriptional factors were highly repressed in NRK-52E cells treated with TGF-β1 and also in obstructed kidneys by quercetin-mediated inhibition. Therefore, these outcomes indicate that quercetin could alleviate fibrosis and the EMT in vitro and in vivo by inhibiting the activation of Hedgehog signaling and could act as a therapeutic agent for patients having several kinds of renal fibrotic diseases.

Sonic hedgehog connects podocyte injury to mesangial activation and glomerulosclerosis

Glomerular disease is characterized by proteinuria and glomerulosclerosis, two pathologic features caused by podocyte injury and mesangial cell activation, respectively. However, whether these two events are linked remains elusive. Here, we report that sonic hedgehog (Shh) is the mediator that connects podocyte damage to mesangial activation and glomerulosclerosis. Shh was induced in glomerular podocytes in various models of proteinuric chronic kidney diseases (CKD). However, mesangial cells in the glomeruli, but not podocytes, responded to hedgehog ligand. In vitro, Shh was induced in podocytes after injury and selectively promoted mesangial cell activation and proliferation. In a miniorgan culture of isolated glomeruli, Shh promoted mesangial activation but did not affect the integrity of podocytes. Podocyte-specific ablation of Shh in vivo exhibited no effect on proteinuria after adriamycin injection but hampered mesangial activation and glomerulosclerosis. Consistently, pharmacologic blockade of Shh signaling decoupled proteinuria from glomerulosclerosis. In humans, Shh was upregulated in glomerular podocytes in patients with CKD and its circulating level was associated with glomerulosclerosis but not proteinuria. These studies demonstrate that Shh mechanistically links podocyte injury to mesangial activation in the pathogenesis of glomerular diseases. Our findings also illustrate a crucial role for podocyte-mesangial communication in connecting proteinuria to glomerulosclerosis.

Early activation of fibroblasts is required for kidney repair and regeneration after injury

Acute kidney injury (AKI) is a devastating condition with high morbidity and mortality. AKI is characterized by tubular injury, inflammation, and vascular impairment. However, the role of interstitial fibroblasts in the pathogenesis of AKI is largely unknown. Here, we show that fibroblasts were activated, as defined by vimentin expression, at 1 h after AKI triggered by ischemia-reperfusion injury (IRI). They rapidly entered the cell cycle with Ki-67-positive staining, which started at 1 h and peaked at 12 h after IRI, whereas tubular cell proliferation peaked at 3 d. The trigger for such an early activation of fibroblasts was identified as sonic hedgehog (Shh), which was rapidly induced in renal tubules and could target interstitial fibroblasts. Tubule-specific knockout of Shh in mice inhibited fibroblast activation and aggravated kidney injury and functional decline after IRI. Likewise, pharmacologic inhibition of Shh signaling with cyclopamine also hindered fibroblast activation and exacerbated kidney damage. These studies uncover that tubule-derived Shh triggers the early activation of fibroblasts, which is required for kidney repair and regeneration. Our findings for the first time illustrate a previously unrecognized importance of interstitial fibroblasts in conferring renal protection in AKI.-Zhou, D., Fu, H., Liu, S., Zhang, L., Xiao, L., Bastacky, S. I., Liu, Y. Early activation of fibroblasts is required for kidney repair and regeneration after injury.

Sonic hedgehog selectively promotes lymphangiogenesis after kidney injury through noncanonical pathway

Kidney fibrosis is associated with an increased lymphangiogenesis, characterized by the formation and expansion of new lymphatic vessels. However, the trigger and underlying mechanism responsible for the growth of lymphatic vessels in diseased kidney remain poorly defined. Here, we report that tubule-derived sonic hedgehog (Shh) ligand is a novel lymphangiogenic factor that plays a crucial role in mediating lymphatic endothelial cell proliferation and expansion. Shh was induced in renal tubular epithelium in various models of fibrotic chronic kidney disease, and this was accompanied by an expansion of lymphatic vessels in adjacent areas. In vitro, Shh selectively promoted the proliferation of human dermal lymphatic endothelial cells (HDLECs) but not human umbilical vein endothelial cells, as assessed by cell counting, MTT assay, and bromodeoxyuridine incorporation. Shh also induced the expression of vascular endothelial growth factor receptor-3, cyclin D1, and proliferating cell nuclear antigen in HDLECs. Shh did not affect the expression of Gli1, the downstream target and readout of canonical hedgehog signaling, but activated ERK-1/2 in HDLECs. Inhibition of Smoothened with small-molecule inhibitor or blockade of ERK-1/2 activation abolished the lymphatic endothelial cell proliferation induced by Shh. In vivo, inhibition of Smoothened also repressed lymphangiogenesis and attenuated renal fibrosis. This study identifies Shh as a novel mitogen that selectively promotes lymphatic, but not vascular, endothelial cell proliferation and suggests that tubule-derived Shh plays an essential role in mediating lymphangiogenesis after kidney injury.

MiR-320a induces diabetic nephropathy via inhibiting MafB

Multiple studies indicate that microRNAs (miRNAs) are involved in diabetes. However, the roles of miRNA in the target organ damages in diabetes remain unclear. This study investigated the functions of miR-320a in diabetic nephropathy (DN). In this study, db/db mice were used to observe the changes in podocytes and their function in vivo, as well as in cultured mouse podocyte cells (MPC5) exposed to high glucose in vitro. To further explore the role of miR-320a in DN, recombinant adeno-associated viral particle was administered intravenously to manipulate the expression of miR-320a in db/db mice. Overexpression of miR-320a markedly promoted podocyte loss and dysfunction in DN, including mesangial expansion and increased levels of proteinuria, serum creatinine and urea nitrogen. Furthermore, MafB was identified as a direct target of miR-320a through AGO2 co-immunoprecipitation, luciferase reporter assay, and Western blotting. Moreover, re-expression of MafB rescued miR-320a-induced podocyte loss and dysfunction by upregulating the expressions of Nephrin and glutathione peroxidase 3 (Gpx3). Our data indicated that miR-320a aggravated renal disfunction in DN by targeting MafB and downregulating Nephrin and Gpx3 in podocytes, which suggested that miR-320a could be a potential therapeutic target of diabetic nephropathy.

Expression and significance of the Hedgehog signal transduction pathway in oxygen-induced retinal neovascularization in mice

Aim

The aim of the study was to investigate the signal transduction mechanism of Hedgehog–vascular endothelial growth factor in oxygen-induced retinopathy (OIR) and the effects of cyclopamine on OIR.

Methods

An OIR model was established in C57BL/6J mice exposed to hyperoxia. Two hundred mice were randomly divided into a control group, an OIR group, an OIR-control group (treated with isometric phosphate-buffered saline by intravitreal injection), and a cyclopamine group (treated with cyclopamine by intravitreal injection), with 50 mice in each group. The retinal vascular morphology was observed using adenosine diphosphatase and number counting using hematoxylin and eosin-stained image. Quantitative real-time quantitative polymerase chain reaction was used to detect mRNA expression. Protein location and expression were evaluated using immunohistochemistry and Western blot.

Results

The OIR group and OIR-control group demonstrated large-area pathological neovascularization and nonperfused area when compared with the control group (both P<0.05). The area of nonperfusion and neovascularization in the cyclopamine group was significantly reduced compared with the OIR and OIR-control groups (both P<0.05). Compared with the control group, the OIR and OIR-control groups had more vascular endothelial cells breaking through the inner limiting membrane. The number of new blood vessel endothelial cell nuclei in the cyclopamine group was significantly reduced (both P<0.05) when compared with the OIR and OIR-control groups. The mRNA and protein expressions of Smoothened, Gli1, and vascular endothelial growth factor in the signal pathway of the OIR and OIR-control groups were significantly higher than those of the control group; however, in the cyclopamine group, these factors were reduced when compared with the OIR and OIR-control groups (all P<0.05).

Conclusion

Our data suggest that abnormal expression of the Hedgehog signaling pathway may be closely associated with the formation of OIR. Inhibiting the Smoothened receptor using cyclopamine could control retinal neovascularization, providing new ideas and measures for the prevention of oxygen-induced retinal neovascularization.

The Injury-Related Activation of Hedgehog Signaling Pathway Modulates the Repair-Associated Inflammation in Liver Fibrosis

Liver fibrosis is a wound healing response initiated by inflammation responding for different iterative parenchymal damages caused by diverse etiologies. Immune cells, which exert their ability of either inducing injury or promoting repair, have been regarded as crucial participants in the fibrogenic response. A characteristic feature of the fibrotic microenvironment associated with chronic liver injury is aberrant activation of hedgehog (Hh) signaling pathway. Growing evidence from a number of different studies in vivo and in vitro has indicated that immune-mediated events involved in liver fibrogenesis are regulated by Hh signaling pathway. In this review, we emphasize the impacts of injury-activated Hh signaling on liver fibrogenesis through modulating repair-related inflammation and focus on the regulatory action of aberrant Hh signaling on repair-related inflammatory responses mediated by hepatic classical and non-classical immune cell populations in the progression of liver fibrosis. Moreover, we also assess the potentiality of Hh pathway inhibitors as good candidates for anti-fibrotic therapeutic agents because of their immune regulation actions for fibrogenic liver repair. The identification of immune-modulatory mechanisms of Hh signaling pathway underlying the fibrotic process of chronic liver diseases might provide a basis for Hh-centered therapeutic strategies for liver fibrosis.

Tubule-Derived Wnts Are Required for Fibroblast Activation and Kidney Fibrosis

Cell-cell communication via Wnt ligands is necessary in regulating embryonic development and has been implicated in CKD. Because Wnt ligands are ubiquitously expressed, the exact cellular source of the Wnts involved in CKD remains undefined. To address this issue, we generated two conditional knockout mouse lines in which Wntless (Wls), a dedicated cargo receptor that is obligatory for Wnt secretion, was selectively ablated in tubular epithelial cells or interstitial fibroblasts. Blockade of Wnt secretion by genetic deletion of Wls in renal tubules markedly inhibited myofibroblast activation and reduced renal fibrosis after unilateral ureteral obstruction. This effect associated with decreased activation of β-catenin and downstream gene expression and preserved tubular epithelial integrity. In contrast, fibroblast-specific deletion of Wls exhibited little effect on the severity of renal fibrosis after obstructive or ischemia-reperfusion injury. In vitro, incubation of normal rat kidney fibroblasts with tubule-derived Wnts promoted fibroblast proliferation and activation. Furthermore, compared with kidney specimens from patients without CKD, biopsy specimens from patients with CKD also displayed increased expression of multiple Wnt proteins, predominantly in renal tubular epithelium. These results illustrate that tubule-derived Wnts have an essential role in promoting fibroblast activation and kidney fibrosis via epithelial-mesenchymal communication.

Fibrotic Changes Mediating Acute Kidney Injury to Chronic Kidney Disease Transition

End-stage renal disease (ESRD) is common, costly, and it results from progressive chronic kidney disease (CKD). ESRD claims many lives every year. It is increasingly recognized that episodes of acute kidney injury (AKI) predispose to the future development of CKD and ESRD. While our understanding of the pathophysiology of the AKI to CKD transition is improving, there are no validated therapeutic strategies to prevent this transition. In this review, we summarize the recent progress made in defining the cellular and molecular events underlying the AKI to CKD transition and highlight potential therapeutic targets and strategies to reduce the incidence of CKD following AKI.

Tenascin-C Is a Major Component of the Fibrogenic Niche in Kidney Fibrosis

Kidney fibrosis initiates at certain focal sites in which the fibrogenic niche provides a specialized microenvironment that facilitates fibroblast activation and proliferation. However, the molecular identity of these fibrogenic niches is poorly characterized. Here, we determined whether tenascin-C (TNC), an extracellular matrix glycoprotein, is a component of the fibrogenic niche in kidney fibrosis. In vivo, TNC expression increased rapidly in kidneys subjected to unilateral ureteral obstruction or ischemia/reperfusion injury and predominantly localized at the foci rich in fibroblasts in renal interstitium. In vitro, TNC selectively promoted renal interstitial fibroblast proliferation, bromodeoxyuridine incorporation, and the expression of proliferation-related genes. The mitogenic activity of TNC required the integrin/focal adhesion kinase/mitogen-activated protein kinase signaling cascade. Using decellularized extracellular matrix scaffolds, we found that TNC-enriched scaffolds facilitated fibroblast proliferation, whereas TNC-deprived scaffolds inhibited proliferation. Matrix scaffold prepared from fibrotic kidney also promoted greater ex vivo fibroblast proliferation than did scaffolds prepared from healthy kidney. Conversely, small interfering RNA-mediated knockdown of TNC in vivo repressed injury-induced fibroblast expansion and renal fibrosis. These studies identify TNC as a major constituent of the fibrogenic niche that promotes fibroblast proliferation, and illustrate a pivotal role for the TNC-enriched microenvironment in kidney fibrogenesis.