Cellular Origin and Functional Relevance of Collagen I Production in the Kidney

Fisetin ameliorates fibrotic kidney disease in mice via inhibiting ACSL4-mediated tubular ferroptosis

Kidney fibrosis is the hallmark of chronic kidney disease (CKD) progression, whereas no effective anti-fibrotic therapies exist. Recent evidence has shown that tubular ferroptosis contributes to the pathogenesis of CKD with persistent proinflammatory and profibrotic responses. We previously reported that natural flavonol fisetin alleviated septic acute kidney injury and protected against hyperuricemic nephropathy in mice. In this study, we investigated the therapeutic effects of fisetin against fibrotic kidney disease and the underlying mechanisms. We established adenine diet-induced and unilateral ureteral obstruction (UUO)-induced CKD models in adult male mice. The two types of mice were administered fisetin (50 or 100 mg·kg-1·d-1, i.g.) for 3 weeks or 7 days, respectively. At the end of the experiments, the mice were euthanized, and blood and kidneys were gathered for analyzes. We showed that fisetin administration significantly ameliorated tubular injury, inflammation, and tubulointerstitial fibrosis in the two types of CKD mice. In mouse renal tubular epithelial (TCMK-1) cells, treatment with fisetin (20 μM) significantly suppressed adenine- or TGF-β1-induced inflammatory responses and fibrogenesis, and improved cell viability. By quantitative real-time PCR analysis of ferroptosis-related genes, we demonstrated that fisetin treatment inhibited ferroptosis in the kidneys of CKD mice as well as in injured TCMK-1 cells, as evidenced by decreased ACSL4, COX2, and HMGB1, and increased GPX4. Fisetin treatment effectively restored ultrastructural abnormalities of mitochondrial morphology and restored the elevated iron, the reduced GSH and GSH/GSSG as well as the increased lipid peroxide MDA in the kidneys of CKD mice. Notably, abnormally high expression of the ferroptosis key marker ACSL4 was verified in the renal tubules of CKD patients (IgAN, MN, FSGS, LN, and DN) as well as adenine- or UUO-induced CKD mice, and in injured TCMK-1 cells. In adenine- and TGF-β1-treated TCMK-1 cells, ACSL4 knockdown inhibited tubular ferroptosis, while ACSL4 overexpression blocked the anti-ferroptotic effect of fisetin and reversed the cytoprotective, anti-inflammatory, and anti-fibrotic effects of fisetin. In summary, we reveal a novel aspect of the nephroprotective effect of fisetin, i.e. inhibiting ACSL4-mediated tubular ferroptosis against fibrotic kidney diseases.

Thiobarbiturate-Derived Compound MHY1025 Alleviates Renal Fibrosis by Modulating Oxidative Stress, Epithelial Inflammation, and Fibroblast Activation

Chronic kidney disease (CKD) is a kidney structure and function abnormality. CKD development and progression are strongly influenced by oxidative stress and inflammatory responses, which can lead to tubulointerstitial fibrosis. Unfortunately, there are no effective or specific treatments for CKD. We investigated the potential of the thiobarbiturate-derived compound MHY1025 to alleviate CKD by reducing oxidative stress and inflammatory responses. In vitro experiments using NRK52E renal tubular epithelial cells revealed that MHY1025 significantly reduced LPS-induced oxidative stress and inhibited the activation of the NF-κB pathway, which is involved in inflammatory responses. Furthermore, treatment with MHY1025 significantly suppressed the expression of fibrosis-related genes and proteins induced by TGFβ in NRK49F fibroblasts. Furthermore, we analyzed the MHY1025 effects in vivo. To induce kidney fibrosis, mice were administered 250 mg/kg folic acid (FA) and orally treated with MHY1025 (0.5 mg/kg/day) for one week. MHY1025 effectively decreased the FA-induced inflammatory response in the kidneys. The group treated with MHY1025 exhibited a significant reduction in cytokine and chemokine expression and decreased immune cell marker expression. Decreased inflammatory response was associated with decreased tubulointerstitial fibrosis. Overall, MHY1025 alleviated renal fibrosis by directly modulating renal epithelial inflammation and fibroblast activation, suggesting that MHY1025 has the potential to be a therapeutic agent for CKD.

Obstructive nephropathy and molecular pathophysiology of renal interstitial fibrosis

The kidneys play a key role in maintaining total body homeostasis. The complexity of this task is reflected in the unique architecture of the organ. Ureteral obstruction greatly affects renal physiology by altering hemodynamics, changing glomerular filtration and renal metabolism, and inducing architectural malformations of the kidney parenchyma, most importantly renal fibrosis. Persisting pathological changes lead to chronic kidney disease, which currently affects ∼10% of the global population and is one of the major causes of death worldwide. Studies on the consequences of ureteral obstruction date back to the 1800s. Even today, experimental unilateral ureteral obstruction (UUO) remains the standard model for tubulointerstitial fibrosis. However, the model has certain limitations when it comes to studying tubular injury and repair, as well as a limited potential for human translation. Nevertheless, ureteral obstruction has provided the scientific community with a wealth of knowledge on renal (patho)physiology. With the introduction of advanced omics techniques, the classical UUO model has remained relevant to this day and has been instrumental in understanding renal fibrosis at the molecular, genomic, and cellular levels. This review details key concepts and recent advances in the understanding of obstructive nephropathy, highlighting the pathophysiological hallmarks responsible for the functional and architectural changes induced by ureteral obstruction, with a special emphasis on renal fibrosis.

Biomarkers of the End-Stage Renal Disease Progression: Beyond the GFR

Chronic kidney disease can progress to the end-stage renal disease (ESRD) characterized by a high risk of morbidity and mortality. ESRD requires immediate therapy or even dialysis or kidney transplantation, therefore, its timely diagnostics is critical for many patients. ESRD is associated with pathological changes, such as inflammation, fibrosis, endocrine disorders, and epigenetic changes in various cells, which could serve as ESRD markers. The review summarizes information on conventional and new ESRD biomarkers that can be assessed in kidney tissue, blood, and urine. Some biomarkers are specific to a particular pathology, while others are more universal. Here, we suggest several universal inflammatory, fibrotic, hormonal, and epigenetic markers indicative of severe deterioration of renal function and ESRD progression for improvement of ESRD diagnostics.

Defining the molecular correlate of arteriolar hyalinosis in kidney disease progression by integration of single cell transcriptomic analysis and pathology scoring

Arteriolar hyalinosis in kidneys is an independent predictor of cardiovascular disease, the main cause of mortality in chronic kidney disease (CKD). The underlying molecular mechanisms of protein accumulation in the subendothelial space are not well understood. Using single cell transcriptomic data and whole slide images from kidney biopsies of patients with CKD and acute kidney injury in the Kidney Precision Medicine Project, the molecular signals associated with arteriolar hyalinosis were evaluated. Co-expression network analysis of the endothelial genes yielded three gene set modules as significantly associated with arteriolar hyalinosis. Pathway analysis of these modules showed enrichment of transforming growth factor beta / bone morphogenetic protein (TGFβ / BMP) and vascular endothelial growth factor (VEGF) signaling pathways in the endothelial cell signatures. Ligand-receptor analysis identified multiple integrins and cell adhesion receptors as over-expressed in arteriolar hyalinosis, suggesting a potential role of integrin-mediated TGFβ signaling. Further analysis of arteriolar hyalinosis associated endothelial module genes identified focal segmental glomerular sclerosis as an enriched term. On validation in gene expression profiles from the Nephrotic Syndrome Study Network cohort, one of the three modules was significantly associated with the composite endpoint (> 40% reduction in estimated glomerular filtration rate (eGFR) or kidney failure) independent of age, sex, race, and baseline eGFR, suggesting poor prognosis with elevated expression of genes in this module. Thus, integration of structural and single cell molecular features yielded biologically relevant gene sets, signaling pathways and ligand-receptor interactions, underlying arteriolar hyalinosis and putative targets for therapeutic intervention.

TLR7 activation by miR-21 promotes renal fibrosis by activating the pro-inflammatory signaling pathway in tubule epithelial cells

BACKGROUND

Toll-like receptor 7 (TLR7) is an endosomal TLR activated by single-stranded RNA, including endogenous microRNAs. Although TLR7 is known to promote inflammatory responses in pathophysiological conditions, its role in renal fibrosis has not been investigated. Here, we aim to investigate the inflammatory roles of TLR7 in kidney inflammation and fibrosis.

METHODS

TLR7 knockout mice (Tlr7 -/-) subjected to AD-induced kidney injury were utilized to examine the role of TLR7 in kidney fibrosis. To elucidate the role of TLR7 in renal epithelial cells, NRK52E rat renal tubule epithelial cells were employed.

RESULTS

Under fibrotic conditions induced by an adenine diet (AD), TLR7 was significantly increased in damaged tubule epithelial cells, where macrophages were highly infiltrated. TLR7 deficiency protected against AD-induced tubular damage, inflammation, and renal fibrosis. Under in vitro conditions, TLR7 activation increased NF-κB activity and induced chemokine expression, whereas TLR7 inhibition effectively blocked NF-κB activation. Furthermore, among the known TLR7 endogenous ligands, miR-21 was significantly upregulated in the tubular epithelial regions. In NRK52E cells, miR-21 treatment induced pro-inflammatory responses, which could be blocked by a TLR7 inhibitor. When the TLR7 inhibitor, M5049, was administered to the AD-induced renal fibrosis model, TLR7 inhibition significantly attenuated AD-induced renal inflammation and fibrosis.

CONCLUSIONS

Overall, activation of TLR7 by endogenous miR-21 in renal epithelial cells contributes to inflammatory responses in a renal fibrosis model, suggesting a possible therapeutic target for the treatment of renal fibrosis. Video Abstract.

Molecular MR Imaging of Renal Fibrogenesis in Mice

BACKGROUND

In most CKDs, lysyl oxidase oxidation of collagen forms allysine side chains, which then form stable crosslinks. We hypothesized that MRI with the allysine-targeted probe Gd-oxyamine (OA) could be used to measure this process and noninvasively detect renal fibrosis.

METHODS

Two mouse models were used: hereditary nephritis in Col4a3-deficient mice (Alport model) and a glomerulonephritis model, nephrotoxic nephritis (NTN). MRI measured the difference in kidney relaxation rate, ΔR1, after intravenous Gd-OA administration. Renal tissue was collected for biochemical and histological analysis.

RESULTS

ΔR1 was increased in the renal cortex of NTN mice and in both the cortex and the medulla of Alport mice. Ex vivo tissue analyses showed increased collagen and Gd-OA levels in fibrotic renal tissues and a high correlation between tissue collagen and ΔR1.

CONCLUSIONS

Magnetic resonance imaging using Gd-OA is potentially a valuable tool for detecting and staging renal fibrogenesis.

Cold Shock Domain Protein DbpA Orchestrates Tubular Cell Damage and Interstitial Fibrosis in Inflammatory Kidney Disease

DNA-binding protein A (DbpA) belongs to the Y-box family of cold shock domain proteins that exert transcriptional and translational activities in the cell via their ability to bind and regulate mRNA. To investigate the role of DbpA in kidney disease, we utilized the murine unilateral ureter obstruction (UUO) model, which recapitulates many features of obstructive nephropathy seen in humans. We observed that DbpA protein expression is induced within the renal interstitium following disease induction. Compared with wild-type animals, obstructed kidneys from Ybx3-deficient mice are protected from tissue injury, with a significant reduction in the number of infiltrating immune cells as well as in extracellular matrix deposition. RNAseq data from UUO kidneys show that Ybx3 is expressed by activated fibroblasts, which reside within the renal interstitium. Our data support a role for DbpA in orchestrating renal fibrosis and suggest that strategies targeting DbpA may be a therapeutic option to slow disease progression.

Extracellular Targets to Reduce Excessive Scarring in Response to Tissue Injury

Excessive scar formation is a hallmark of localized and systemic fibrotic disorders. Despite extensive studies to define valid anti-fibrotic targets and develop effective therapeutics, progressive fibrosis remains a significant medical problem. Regardless of the injury type or location of wounded tissue, excessive production and accumulation of collagen-rich extracellular matrix is the common denominator of all fibrotic disorders. A long-standing dogma was that anti-fibrotic approaches should focus on overall intracellular processes that drive fibrotic scarring. Because of the poor outcomes of these approaches, scientific efforts now focus on regulating the extracellular components of fibrotic tissues. Crucial extracellular players include cellular receptors of matrix components, macromolecules that form the matrix architecture, auxiliary proteins that facilitate the formation of stiff scar tissue, matricellular proteins, and extracellular vesicles that modulate matrix homeostasis. This review summarizes studies targeting the extracellular aspects of fibrotic tissue synthesis, presents the rationale for these studies, and discusses the progress and limitations of current extracellular approaches to limit fibrotic healing.

Localization and characterization of proenkephalin-A as a potential biomarker for kidney disease in murine and human kidneys

INTRODUCTION

Exact measurement of renal function is essential for the treatment of patients. Elevated serum-creatinine levels, while established, are influenced by other parameters and show a significant time-lag. This drives the search for novel biomarkers of renal function and injury. Beside Lipocalin-2 and kidney-injury-molecule-1 (KIM-1), the endogenous opioid precursor proenkephalin-A (Penk) has recently emerged as a promising marker for renal function. But the cellular origin and regulation of Penk outside the brain has not yet been investigated in depth.

MATERIALS AND METHODS

This study characterizes the cellular origin of Penk expression with high-resolution in situ hybridization in two models of renal fibrosis in mice and human tissue.

RESULTS

Interstitial cells are the main expression site for renal Penk. This classifies Penk as biomarker for interstitial damage as opposed to tubular damage markers like Lipocalin-2 and KIM-1. Furthermore, our data indicate that renal Penk expression is not regulated by classical profibrotic pathways.

DISCUSSION

This study characterizes changing Penk expression in the kidneys. The similarity of Penk expression across species gives rise to further investigations into the function of Penk in healthy and injured kidneys.

CONCLUSION

Penk is a promising biomarker for interstitial renal damage that warrants further studies to utilize its predictive potential.Clinical significanceKnowledge of real-time renal function is essential for proper treatment of critically ill patients and in early diagnosis of acute kidney injury (AKI). Proenkephalin-A has been measured in a number of patient cohorts as a highly accurate and predictive biomarker of renal damage.The present study identifies Penk as a biomarker for interstitial damage in contrast to the tubular biomarkers such as Lipocalin-2 or KIM-1.Our data show that Penk is regulated independently of classical profibrotic or proinflammatory pathways, indicating it might be more robust against extra-renal influences.Data presented in this study provide fundamental information about cell type-specific localization and regulation of the potential new biomarker Penk across species as foundation for further research.

Diminished Tubule Epithelial Farnesoid X Receptor Expression Exacerbates Inflammation and Fibrosis Response in Aged Rat Kidney

The age-associated functional decline of the kidney is accompanied by structural changes including glomerular sclerosis and interstitial fibrosis. Aging kidneys also exhibit increased vulnerability in stressful environmental conditions. In this study, we assessed the differences in responses between young and aged animals to folic acid (FA)-induced renal fibrosis. To monitor the effects of aging on FA-induced kidney fibrosis, we administered FA (250 mg/kg) to young (6-month old) and aged (20-month old) rats. The development of severe fibrosis was only detected in aged rat kidneys, which was accompanied by increased kidney injury and inflammation. Furthermore, we found that FA-treated aged rats had significantly lower farnesoid X receptor (FXR) expression in the tubular epithelial cells than the rats not treated with FA. Interestingly, the extent of inflammation was severe in the kidneys of aged rat, where the FXR expression was low. To explore the role of FXR in kidney inflammation, in vitro studies were performed using NRK52E kidney tubule epithelial cells. NF-κB activation by lipopolysaccharide treatment induces chemokine production in NRK52E cells. The activation of FXR by obeticholic acid significantly reduced the transcriptional activity of NF-κB and chemokine production. In contrast, FXR knockdown increased LPS-induced chemokine production in NRK52E cells. Finally, FXR-knockout mice that were administered FA showed increased inflammation and severe fibrosis. In summary, we demonstrated that diminished FXR expression in the epithelial cells of the renal tubules exacerbated the fibrotic response in aged rat kidneys by upregulating pro-inflammatory NF-κB activation.

Zhen Wu decoction represses renal fibrosis by invigorating tubular NRF2 and TFAM to fuel mitochondrial bioenergetics

BACKGROUND

Zhen Wu Decoction (ZWD) is a prescription from the classical text "Treatise on Exogenous Febrile Disease" and has been extensively used to control kidney diseases since the time of the Eastern Han Dynasty.

HYPOTHESIS

We hypothesized that ZWD limits tubular fibrogenesis by reinvigorating tubular bio-energetic capacity.

STUDY DESIGN / METHODS

A mouse model of chronic kidney disease (CKD) was established using unilateral ureteral obstruction (UUO). Three concentrations of ZWD, namely 25.2 g/kg (high dosage), 12.6 g/kg (middle dosage), and 6.3 g/kg (low dosage), were included to study the dose-effect relationship. Real-time qPCR was used to observe gene transcription in blood samples from patients with CKD. Different siRNAs were designed to study the role of mitochondrial transcription factor A (TFAM) and nuclear factor (erythroid-derived 2)-related factor 2 (NRF2) in transforming growth factor (TGF)-β1 induced fibrogenesis and mitochondrial damage.

RESULTS

We showed that ZWD efficiently attenuates renal function impairment and reduces renal interstitial fibrosis. TFAM and NRF2 were repressed, and the stimulator of interferon genes (STING) was activated in CKD patient blood sample. We further confirmed that ZWD activated TFAM depended on NRF2 as an important negative regulator of STING in mouse kidneys. Treatment with ZWD significantly reduced oxidative stress and inflammation by regulating the levels of oxidative phosphorylation (OXPHOS) and pro-inflammatory factors, such as interleukin-6, interleukin-1β, tumor necrosis factor receptor 1, and mitochondrial respiratory chain subunits. NRF2 inhibitors can weaken the ability of ZWD to increase TFAM expression and heal injured mitochondria, playing a similar role to that of STING inhibitors. Our study showed that ZWD elevates the expression of TFAM and mitochondrial respiratory chain subunits by promoting NRF2 activation, after suppressing mitochondrial membrane damage and cristae breakdown and restricting mitochondrial DNA (mtDNA) leakage into the cytoplasm to reduce STING activation.

CONCLUSION

ZWD maintains mitochondrial integrity and improves OXPHOS which represents an innovative insight into "strengthening Yang-Qi" theory. ZWD limits tubular fibrogenesis by reinvigorating tubular bioenergetic capacity.

Chrysophanol, a main anthraquinone from Rheum palmatum L. (rhubarb), protects against renal fibrosis by suppressing NKD2/NF-κB pathway

PURPOSE

Chronic kidney disease (CKD), characterized as renal dysfunction and multi-system damage, has become a serious public health problem with high prevalence and mortality. Rheum palmatum L. (rhubarb) is one of the most widely used Chinese herb with renal protective activity. However, the active components and underlying mechanisms of rhubarb remain unknown. In this work, we tried to explore the pharmacological mechanism of chrysophanol, a main anthraquinone from rhubarb, against CKD by in vivo and in vitro models.

STUDY DESIGN

The therapeutic effect of chrysophanol and its underlying mechanism were investigated using CKD mouse model induced by unilateral ureteral occlusion (UUO), and human kidney 2 (HK-2) cells stimulated by TGF-β1 in vivo.

METHODS

The impact of chrysophanol on renal function, inflammation, fibrosis of CKD mice were evaluated. Then, the protein expressions of FN1, collagen ɑI, α-SMA, NF-κB and naked keratinocyte homolog 2 (NKD2) were investigated. In vitro studies, the inhibition on inflammation and fibrogenesis by chrysophanol was further validated in TGF-β1-stimulated HK2 cells, and the regulation of chrysophanol on NKD2/NF-κB pathway was analyzed. Moreover, NKD2 was overexpressed in HK-2 cells to confirm the role of NKD2/NF-κB pathway in chrysophanol-mediated efficacy. Finally, the binding mode of chrysophanol with NKD2 was studied using in silico molecular docking and microscale thermophoresis (MST) assay.

RESULTS

Chrysophanol could significantly improve the kidney dysfunction, alleviate renal pathology, and reverse the elevated levels of renal fibrosis markers such as FN1, collagen ɑI and α-SMA. Furthermore, chrysophanol effectively inhibited TNF-α, IL-6, and IL-1β production, and suppressed NF-κB activation and NKD2 expression. The findings of in vitro study were consistent with those of animal expriment. Using NKD2-overexpressing HK-2 cells, we also demonstrated that overexpression of NKD2 significantly compromised the anti-fibrotic effects of chrysophanol. In addition, molecular docking and MST analysis revealed that NKD2 was a direct target of chrysophanol.

CONCLUSION

Together, our work demonstrated for the first time that chrysophanol could effectively ameliorate renal fibrosis by inhibiting NKD2/NF-κB pathway. Chrysophanol can potentially prevent CKD by suppressing renal NKD2 expression directly.

Opposing roles of hepatic stellate cell subpopulations in hepatocarcinogenesis

Hepatocellular carcinoma (HCC), the fourth leading cause of cancer mortality worldwide, develops almost exclusively in patients with chronic liver disease and advanced fibrosis1,2. Here we interrogated functions of hepatic stellate cells (HSCs), the main source of liver fibroblasts3, during hepatocarcinogenesis. Genetic depletion, activation or inhibition of HSCs in mouse models of HCC revealed their overall tumour-promoting role. HSCs were enriched in the preneoplastic environment, where they closely interacted with hepatocytes and modulated hepatocarcinogenesis by regulating hepatocyte proliferation and death. Analyses of mouse and human HSC subpopulations by single-cell RNA sequencing together with genetic ablation of subpopulation-enriched mediators revealed dual functions of HSCs in hepatocarcinogenesis. Hepatocyte growth factor, enriched in quiescent and cytokine-producing HSCs, protected against hepatocyte death and HCC development. By contrast, type I collagen, enriched in activated myofibroblastic HSCs, promoted proliferation and tumour development through increased stiffness and TAZ activation in pretumoural hepatocytes and through activation of discoidin domain receptor 1 in established tumours. An increased HSC imbalance between cytokine-producing HSCs and myofibroblastic HSCs during liver disease progression was associated with increased HCC risk in patients. In summary, the dynamic shift in HSC subpopulations and their mediators during chronic liver disease is associated with a switch from HCC protection to HCC promotion.

P2Y12 inhibitor clopidogrel inhibits renal fibrosis by blocking macrophage-to-myofibroblast transition

Clopidogrel, a P2Y12 inhibitor, is a novel anti-fibrosis agent for chronic kidney disease (CKD), but its mechanisms remain unclear, which we investigated by silencing P2Y12 or treating unilateral ureteral obstruction (UUO) in LysM-Cre/Rosa Tomato mice with clopidogrel in vivo and in vitro. We found that P2Y12 was significantly increased and correlated with progressive renal fibrosis in CKD patients and UUO mice. Phenotypically, up to 82% of P2Y12-expressing cells within the fibrosing kidney were of macrophage origin, identified by co-expressing CD68/F4/80 antigens or a macrophage-lineage-tracing marker Tomato. Unexpectedly, more than 90% of P2Y12-expressing macrophages were undergoing macrophage-to-myofibroblast transition (MMT) by co-expressing alpha smooth muscle actin (α-SMA), which was also confirmed by single-cell RNA sequencing. Functionally, clopidogrel improved the decline rate of the estimated glomerular filtration rate (eGFR) in patients with CKD and significantly inhibited renal fibrosis in UUO mice. Mechanistically, P2Y12 expression was induced by transforming growth factor β1 (TGF-β1) and promoted MMT via the Smad3-dependent mechanism. Thus, silencing or pharmacological inhibition of P2Y12 was capable of inhibiting TGF-β/Smad3-mediated MMT and progressive renal fibrosis in vivo and in vitro. In conclusion, P2Y12 is highly expressed by macrophages in fibrosing kidneys and mediates renal fibrosis by promoting MMT via TGF-β/Smad3 signaling. Thus, P2Y12 inhibitor maybe a novel and effective anti-fibrosis agent for CKD.

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.

Siglec-F-expressing neutrophils are essential for creating a pro-fibrotic microenvironment in the renal fibrosis

The roles of neutrophils in renal inflammation are currently unclear. On examining these cells in the unilateral ureteral obstruction murine model of chronic kidney disease, we found that the injured kidney bore a large and rapidly expanding population of neutrophils that expressed the eosinophil marker Siglec-F. We first confirmed that these cells were neutrophils. Siglec-F+ neutrophils were recently detected for the first time by several studies on other disease contexts. We then showed that (i) these cells were derived from conventional neutrophils in the renal vasculature by TGF-β1 and GM-CSF, (ii) they differed from their parent cells by more frequent hypersegmentation, higher expression of pro-fibrotic inflammatory cytokines, and, notably, expression of Collagen 1, and (iii) their depletion reduced collagen deposition and disease progression, but adoptive transfer increased renal fibrosis. These findings have thus unveiled a subtype of neutrophils that participate in renal fibrosis and maybe a new therapeutic target in chronic kidney disease.

Current kidney function parameters overestimate kidney tissue repair in reversible experimental kidney disease

Although underlying mechanisms and the clinical course of kidney disease progression are well described, less is known about potential disease reversibility. Therefore, to analyze kidney recovery, we adapted a commonly used murine chronic kidney disease (CKD) model of 2,8- dihydroxyadenine (2,8-DHA) crystal-induced nephropathy to study disease recovery and efficacy of disease-modifying interventions. The recovery phase after CKD was characterized by improved kidney function after two weeks which remained stable thereafter. By contrast, even after eight weeks recovery, tubular injury and inflammation were only partially reduced and fibrosis persisted. Deep-learning-based histologic analysis of 8,604 glomeruli and 596,614 tubular cross sections revealed numerous tubules had undergone either prominent dilation or complete atrophy, leading to atubular glomeruli and irreversible nephron loss. We confirmed these findings in a second CKD model, reversible unilateral ureteral obstruction, in which a rapid improvement of glomerular filtration rate during recovery also did not reflect the permanent histologic kidney injury. In 2,8-DHA nephropathy, increased drinking volume was highly effective in disease prevention. However, in therapeutic approaches, high fluid intake was only effective in moderate but not severe CKD and established tissue injury was again poorly reflective of kidney function parameters. The injury was particularly localized in the medulla, which is often not analyzed. Thus, recovery after crystal- or obstruction-induced CKD is characterized by ongoing tissue injury, fibrosis, and nephron loss, but not reflected by standard measures of kidney function. Hence, our data might aid in designing kidney recovery studies and suggest the need for biomarkers specifically monitoring intra-kidney tissue injury.

Renal tubular PAR2 promotes interstitial fibrosis by increasing inflammatory responses and EMT process

Renal fibrosis is defined by excessive extracellular matrix (ECM) accumulation and is associated with a decreased kidney function. Increased inflammation and infiltration of inflammatory cells are the key features of renal fibrosis development; however, the mechanism of how inflammation starts is still un-known. Here, we show that the activation of epithelial Protease-activating receptor 2 (PAR2) signaling plays an important role in the initiation of inflammation via increased chemokine expression and inflammatory cell induction. In the adenine diet-induced renal fibrosis mouse model, PAR2 expression was significantly increased in the renal tubule region. Kidneys from PAR2-knockout mice were protected from adenine diet-induced renal fibrosis, kidney dysfunction, and inflammation. Using NRK52E kidney epithelial cells, we further elucidated the mechanisms underlying these processes. Activation of PAR2 signaling pathway by PAR2 agonist specifically increased the levels of chemokines, including MCP1 and MCP3, via the MAPK-NF-κB signaling pathway. Inhibition of the MAPK signaling pathway attenuated PAR2 agonist-induced NF-κB activation, chemokine expression, and macrophage cell induction. Furthermore, PAR2 activation directly increased mesenchymal cell markers in epithelial cells. Taken together, we found that increased PAR2 expression and the PAR2/MAPK signaling pathway promote renal fibrosis by increasing the inflammatory responses and promoting EMT process.

Macrophages in the kidney in health, injury and repair

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

Adenosine/A1R signaling pathway did not play dominant roles on the influence of SGLT2 inhibitor in the kidney of BSA‐overloaded STZ‐induced diabetic mice

Aims/Introduction

Sodium–glucose cotransporter 2 inhibitors (SGLT2i) have been shown to display excellent renoprotective effects in diabetic kidney disease with macroalbuminuria/proteinuria. Regarding the renoprotective mechanism of SGLT2i, a sophisticated hypothesis was made by explaining the suppression of glomerular hypertension/hyperfiltration through the adenosine/adenosine type 1 receptor (A1R) signaling‐mediated restoration of the tubuloglomerular feedback mechanism; however, how such A1R signaling is relevant for renoprotection by SGLT2i in diabetic kidney disease with proteinuria has not been elucidated.

Materials and Methods

Streptozotocin‐induced diabetic CD‐1 mice were injected with bovine serum albumin (BSA) and treated with SGLT2i in the presence/absence of A1R inhibitor administration.

Results

We found that the influences of SGLT2i are essentially independent of the activation of A1R signaling in the kidney of BSA‐overloaded streptozotocin‐induced diabetic mice. BSA‐overloaded diabetic mice showed the trend of kidney damage with higher glomerular filtration rate (GFR) and the significant induction of fibrogenic genes, such as transforming growth factor‐β2 and collagen type III. SGLT2i TA‐1887 suppressed diabetes‐induced GFR in BSA‐overloaded diabetic mice was associated with the significant suppression of transforming growth factor‐β2 and collagen type III; A1R‐specific inhibitor 8‐cyclopentyl‐1,3‐dipropylxanthine did not cancel the effects of TA‐1887 on either GFR or associated gene levels. Both TA‐1887 and 8‐cyclopentyl‐1,3‐dipropylxanthine‐treated BSA‐overloaded diabetic mice showed suppressed glycated hemoglobin levels associated with the increased food intake. When analyzing the association among histological evaluation, GFR and potential fibrogenic gene levels, each group of mice showed distinct correlation patterns.

Conclusions

A1R signaling activation was not the dominant mechanism on the influence of SGLT2i in the kidney of BSA‐overloaded diabetic mice.

Donor-But Not Recipient-Derived Cells Produce Collagen-1 in Chronically Rejected Cardiac Allografts

Fibrosis is a prominent feature of chronic allograft rejection, caused by an excessive production of matrix proteins, including collagen-1. Several cell types produce collagen-1, including mesenchymal fibroblasts and cells of hematopoietic origin. Here, we sought to determine whether tissue-resident donor-derived cells or allograft-infiltrating recipient-derived cells are responsible for allograft fibrosis, and whether hematopoietic cells contribute to collagen production. A fully MHC-mismatched mouse heterotopic heart transplantation model was used, with transient depletion of CD4⁺ T cells to prevent acute rejection. Collagen-1 was selectively knocked out in recipients or donors. In addition, collagen-1 was specifically deleted in hematopoietic cells. Tissue-resident macrophages were depleted using anti-CSF1R antibody. Allograft fibrosis and inflammation were quantified 20 days post-transplantation. Selective collagen-1 knock-out in recipients or donors showed that tissue-resident cells from donor hearts, but not infiltrating recipient-derived cells, are responsible for production of collagen-1 in allografts. Cell-type-specific knock-out experiments showed that hematopoietic tissue-resident cells in donor hearts substantially contributed to graft fibrosis. Tissue resident macrophages, however, were not responsible for collagen-production, as their deletion worsened allograft fibrosis. Donor-derived cells including those of hematopoietic origin determine allograft fibrosis, making them attractive targets for organ preconditioning to improve long-term transplantation outcomes.

COL1A1 Gene Expression in Hepatitis B Virus (HBV) Related Hepatocellular Carcinoma (HCC) Egyptian's Patients

Introduction:

Collagens are the most abundant proteins in the human body, accounting for one-third of total proteins. Over the last few years, accumulated evidence have indicated that some collagens are differentially expressed in cancer. The aim of the study was to assess COL1A1 gene expression as a novel marker for the progression of hepatitis B cirrhosis into hepatocellular carcinoma.

Methods:

This cohort study included 348 subjects and was conducted between May 2018 and June 2019. Subjects were divided into 4 groups: group1 included HBV positive hepatocellular carcinoma patients “HCC” (n= 87), group II included HBV positive patients with liver cirrhosis “LC” (n = 87), group III included chronic hepatitis B patients with neither HCC nor cirrhosis “ C-HBV” (n = 87) and group IV consisted of healthy volunteers as controls (n = 87). Fasting venous blood samples (10 ml) were collected from each participant in this study and were used for assessment of aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin, albumin and alfa-fetoprotein (AFP). Another portion of blood was collected in 2 vacutainer tubes containing EDTA, one for Complete blood count and the other for gene expression of COL1A1.

Results:

The gene expression of collagen was 6.9 ± 8.8 in group 1 (HBV positive hepatocellular carcinoma patients) and this was a significant increase in comparison with the other groups. In group 2 (HBV positive patients with liver cirrhosis), the gene expression (collagen) was 3.7±1.5 and it was significantly increased when compared with group 4 (healthy volunteers).

Conclusion:

COL1A1 gene expression can be used as an indicator of the progression of hepatitis B cirrhosis into hepatocellular carcinoma.

Chronic exposure to MC-LR increases the risks of microcytic anemia: Evidence from human and mice

Microcystins (MCs) produced by cyanobacteria are potent toxins to humans that cannot be ignored. However, the toxicity of MCs to humans remains largely unknown. The study explored the role of MCs in the development of hematological parameters through human observations and a chronic mouse model to explore related mechanisms. The adjusted odds ratio of MC-LR to the risk of anemia was 4.954 (95 % CI, 2.423-10.131) in a case-control study in Nanjing. An inverse correlation between serum MC-LR and hemoglobin (HGB), hematocrit (HCT), mean corpuscular volume (MCV), and red blood cell count (RBC) was observed. MC-LR in the serum of the population was an independent risk factor for microcytic anemia. Animal experiments demonstrated that MC-LR resulted in microcytic anemia, which is associated with inflammation, dysregulation of iron homeostasis, and erythropoiesis. We first identified the possible signaling pathway of MC-LR-induced anemia that MC-LR significantly upregulated the levels of hepcidin via EPO/EPOR signaling pathway and the decreased levels of Twsg1 and Gdf15, thereby resulting in the decreased levels of Hbb and Fpn, and the increased expression of Fth1, and Tf in a chronic mouse model. Our study first identified that prolonged environmental exposure to MCs probably contribute to the occurrence of microcytic anemia in humans, which provides new insights into the toxicity of MCs for public health.

Tissue-specific parameters for the design of ECM-mimetic biomaterials

The extracellular matrix (ECM) is a complex network of biomolecules that mechanically and biochemically directs cell behavior and is crucial for maintaining tissue function and health. The heterogeneous organization and composition of the ECM varies within and between tissue types, directing mechanics, aiding in cell-cell communication, and facilitating tissue assembly and reassembly during development, injury and disease. As technologies like 3D printing rapidly advance, researchers are better able to recapitulate in vivo tissue properties in vitro; however, tissue-specific variations in ECM composition and organization are not given enough consideration. This is in part due to a lack of information regarding how the ECM of many tissues varies in both homeostatic and diseased states. To address this gap, we describe the components and organization of the ECM, and provide examples for different tissues at various states of disease. While many aspects of ECM biology remain unknown, our goal is to highlight the complexity of various tissues and inspire engineers to incorporate unique components of the native ECM into in vitro platform design and fabrication. Ultimately, we anticipate that the use of biomaterials that incorporate key tissue-specific ECM will lead to in vitro models that better emulate human pathologies. STATEMENT OF SIGNIFICANCE: Biomaterial development primarily emphasizes the engineering of new materials and therapies at the expense of identifying key parameters of the tissue that is being emulated. This can be partially attributed to the difficulty in defining the 3D composition, organization, and mechanics of the ECM within different tissues and how these material properties vary as a function of homeostasis and disease. In this review, we highlight a range of tissues throughout the body and describe how ECM content, cell diversity, and mechanical properties change in diseased tissues and influence cellular behavior. Accurately mimicking the tissue of interest in vitro by using ECM specific to the appropriate state of homeostasis or pathology in vivo will yield results more translatable to humans.

Endothelin receptors in renal interstitial cells do not contribute to the development of fibrosis during experimental kidney disease

Renal interstitial fibrosis is characterized by the development of myofibroblasts, originating from resident renal and immigrating cells. Myofibroblast formation and extracellular matrix production during kidney damage are triggered by various factors. Among these, endothelins have been discussed as potential modulators of renal fibrosis. Utilizing mouse models of adenine nephropathy (AN) and unilateral ureter occlusion (UUO), this study aimed to investigate the contribution of endothelin signaling in stromal mesenchymal resident renal interstitial cells. We found in controls that adenine feeding and UUO caused marked upregulations of endothelin-1 (ET-1) gene expression in endothelial and in tubular cells and a strong upregulation of ET_A-receptor (ET_A-R) gene expression in interstitial and mesangial cells, while the gene expression of ET_B-receptor (ET_B-R) did not change. Conditional deletion of ET_A-R and ET_B-R gene expression in the FoxD1 stromal cell compartment which includes interstitial cells significantly reduced renal ET_A-R gene expression and moderately lowered renal ET_B-R gene expression. ET receptor (ET-R) deletion exerted no apparent effects on kidney development nor on kidney function. Adenine feeding and UUO led to similar increases in profibrotic and proinflammatory gene expression in control as well as in ET_A^flflET_B^flfl FoxD1^Cre+ mice (ET-Ko). In summary, our findings suggest that adenine feeding and UUO activate endothelin signaling in interstitial cells which is due to upregulated ET_A-R expression and enhanced renal ET-1 production Our data also suggest that the activation of endothelin signaling in interstitial cells has less impact for the development of experimentally induced fibrosis.

GSDME-mediated pyroptosis promotes inflammation and fibrosis in obstructive nephropathy

Renal tubular cell (RTC) death and inflammation contribute to the progression of obstructive nephropathy, but its underlying mechanisms have not been fully elucidated. Here, we showed that Gasdermin E (GSDME) expression level and GSDME-N domain generation determined the RTC fate response to TNFα under the condition of oxygen-glucose-serum deprivation. Deletion of Caspase-3 (Casp3) or Gsdme alleviated renal tubule damage and inflammation and finally prevented the development of hydronephrosis and kidney fibrosis after ureteral obstruction. Using bone marrow transplantation and cell type-specific Casp3 knockout mice, we demonstrated that Casp3/GSDME-mediated pyroptosis in renal parenchymal cells, but not in hematopoietic cells, played predominant roles in this process. We further showed that HMGB1 released from pyroptotic RTCs amplified inflammatory responses, which critically contributed to renal fibrogenesis. Specific deletion of Hmgb1 in RTCs alleviated caspase11 and IL-1β activation in macrophages. Collectively, our results uncovered that TNFα/Casp3/GSDME-mediated pyroptosis is responsible for the initiation of ureteral obstruction-induced renal tubule injury, which subsequentially contributes to the late-stage progression of hydronephrosis, inflammation, and fibrosis. This novel mechanism will provide valuable therapeutic insights for the treatment of obstructive nephropathy.

Thiol-ene cross-linked alginate hydrogel encapsulation modulates the extracellular matrix of kidney organoids by reducing abnormal type 1a1 collagen deposition

Differentiated kidney organoids from induced pluripotent stem cells hold promise as a treatment for patients with kidney diseases. Before these organoids can be translated to the clinic, shortcomings regarding their cellular and extracellular compositions, and their developmental plateau need to be overcome. We performed a proteomic analysis on kidney organoids cultured for a prolonged culture time and we found a specific change in the extracellular matrix composition with increased expression of types 1a1, 2 and 6a1 collagen. Such an excessive accumulation of specific collagen types is a hallmark of renal fibrosis that causes a life-threatening pathological condition by compromising key functions of the human kidney. Here we hypothesized the need for a three-dimensional environment to grow the kidney organoids, which could better mimic the in vivo surroundings of the developing kidney than standard culture on an air-liquid interface. Encapsulating organoids for four days in a soft, thiol-ene cross-linked alginate hydrogel resulted in decreased type 1a1 collagen expression. Furthermore, the encapsulation did not result in any changes of organoid structural morphology. Using a biomaterial to modulate collagen expression allows for a prolonged kidney organoid culture in vitro and a reduction of abnormal type 1a1 collagen expression bringing kidney organoids closer to clinical application.

Promotion of cholangiocarcinoma growth by diverse cancer-associated fibroblast subpopulations

Cancer-associated fibroblasts (CAF) are a poorly characterized cell population in the context of liver cancer. Our study investigates CAF functions in intrahepatic cholangiocarcinoma (ICC), a highly desmoplastic liver tumor. Genetic tracing, single-cell RNA sequencing, and ligand-receptor analyses uncovered hepatic stellate cells (HSC) as the main source of CAF and HSC-derived CAF as the dominant population interacting with tumor cells. In mice, CAF promotes ICC progression, as revealed by HSC-selective CAF depletion. In patients, a high panCAF signature is associated with decreased survival and increased recurrence. Single-cell RNA sequencing segregates CAF into inflammatory and growth factor-enriched (iCAF) and myofibroblastic (myCAF) subpopulations, displaying distinct ligand-receptor interactions. myCAF-expressed hyaluronan synthase 2, but not type I collagen, promotes ICC. iCAF-expressed hepatocyte growth factor enhances ICC growth via tumor-expressed MET, thus directly linking CAF to tumor cells. In summary, our data demonstrate promotion of desmoplastic ICC growth by therapeutically targetable CAF subtype-specific mediators, but not by type I collagen.

Tumor restriction by type I collagen opposes tumor-promoting effects of cancer-associated fibroblasts

Cancer-associated fibroblasts (CAF) may exert tumor-promoting and tumor-suppressive functions, but the mechanisms underlying these opposing effects remain elusive. Here, we sought to understand these potentially opposing functions by interrogating functional relationships among CAF subtypes, their mediators, desmoplasia, and tumor growth in a wide range of tumor types metastasizing to the liver, the most common organ site for metastasis. Depletion of hepatic stellate cells (HSC), which represented the main source of CAF in mice and patients in our study, or depletion of all CAF decreased tumor growth and mortality in desmoplastic colorectal and pancreatic metastasis but not in nondesmoplastic metastatic tumors. Single-cell RNA-Seq in conjunction with CellPhoneDB ligand-receptor analysis, as well as studies in immune cell-depleted and HSC-selective knockout mice, uncovered direct CAF-tumor interactions as a tumor-promoting mechanism, mediated by myofibroblastic CAF-secreted (myCAF-secreted) hyaluronan and inflammatory CAF-secreted (iCAF-secreted) HGF. These effects were opposed by myCAF-expressed type I collagen, which suppressed tumor growth by mechanically restraining tumor spread, overriding its own stiffness-induced mechanosignals. In summary, mechanical restriction by type I collagen opposes the overall tumor-promoting effects of CAF, thus providing a mechanistic explanation for their dual functions in cancer. Therapeutic targeting of tumor-promoting CAF mediators while preserving type I collagen may convert CAF from tumor promoting to tumor restricting.

The Role of Tubule-Interstitial Crosstalk in Renal Injury and Recovery

Renal epithelial cells show remarkable regenerative capacity to recover from acute injury, which involves specific phenotypic changes, but also significant profibrotic tubule-interstitial crosstalk. Tubule-derived profibrotic stimuli and subsequent myofibroblast activation and extracellular matrix deposition have been linked closely with decline of renal function and nephron loss. However, recent data have questioned the view of purely detrimental effects of myofibroblast activation in the injured kidney and even suggested its beneficial role for epithelial regeneration. This article reviews the current understanding of the underlying mechanisms of tubular cell turnover, new suggested pathways of proregenerative tubular-interstitial crosstalk, and relevant insights of proliferation-enhancing effects of myofibroblasts on epithelial cells in nonrenal tissues.

Tubular epithelial cells derived-exosomes containing CD26 protects mice against renal ischemia/reperfusion injury by maintaining proliferation and dissipating inflammation

Ischemia-reperfusion injury (IR) is the leading cause of acute kidney injury (AKI). No effective drugs to treat IR-related AKI are currently available. Recent pre-clinical trials have evaluated the therapeutic potential of extracellular vesicles-exosomes to chronic kidney disease. Here, we found exosomes derived from the tubular epithelial cell in IR condition (Exo^IR) enriched CD26, compared with control (Exo^Normal). Tracking exosomes in vivo certified tubular epithelial cell uptake exosomes. We have isolated exosomes with overexpression of CD26 (Exo^CD26+) from culture media from tubular epithelial cell line transferred by adenovirus vectors. After administration of exosomes (100 mg) or bovine serum albumin (BSA, equivalent protein control) in IR or sham operation mice after 72 h via tail vein injection, the renal function impairment and histology injury were relived in mice receiving Exo^CD26+. Immunofluorescence staining with proliferating cell nuclear antigen revealed Exo^CD26+ recovered proliferation of cells partly after IR injury. Cell cycle modulator, p53 and p21 were upregulated in IR mice receiving BSA control, Exo^Normal, and Exo^IR. Exo^CD26+ significantly blunt this protein upregulation. Inflammatory cell infiltration and chemokine receptor (CXCR4) were dissipated in IR mice receiving Exo^CD26+. Downstream chemokine of CXCR4, stromal derived factor-1 (SDF1) also decreased after administration of Exo^CD26+ in IR mice. Finally, Exo^CD26+ suppressed inundant collagenⅠ expression in IR kidney. In conclusion, Tubular epithelial cells derived-exosomes containing CD26 might be one of the therapy modes for IR-AKI by maintaining proliferation and dissipating inflammation.

Inhibition of transforming growth factor β1 signaling in resident interstitial cells attenuates profibrotic gene expression and preserves erythropoietin production during experimental kidney fibrosis in mice

Kidney fibrosis is characterized by the development of myofibroblasts originating from resident kidney and immigrating cells. Myofibroblast formation and extracellular matrix production during kidney damage are triggered by various cytokines. Among these, transforming growth factor β1 (TGFβ1) is considered a central trigger for kidney fibrosis. We found a highly upregulated expression of TGFβ1 and TGFβ receptor 2 (TGFβ-R2) mRNAs in kidney interstitial cells in experimental fibrosis. Here, we investigated the contribution of TGFβ1 signaling in resident kidney interstitial cells to organ fibrosis using the models of adenine induced nephropathy and unilateral ureteral occlusion in mice. For this purpose TGFβ1 signaling was interrupted by inducible deletion of the TGFβ-R2 gene in interstitial cells expressing the fibroblast marker platelet derived growth factor receptor-β. Expression of profibrotic genes was attenuated up to 50% in kidneys lacking TGFβ-R2 in cells positive for platelet derived growth factor receptor-β. Additionally, deletion of TGFβ-R2 prevented the decline of erythropoietin production in ureter ligated kidneys. Notably, fibrosis associated expression of α-smooth muscle actin as a myofibroblast marker and deposits of extracellular collagens were not altered in mice with targeted deletion of TGFβ-R2. Thus, our findings suggest an enhancing effect of TGFβ1 signaling in resident interstitial cells that contributes to profibrotic gene expression and the downregulation of erythropoietin production, but not to the development of myofibroblasts during kidney fibrosis.

ClC-5 Downregulation Induces Osteosarcoma Cell Apoptosis by Promoting Bax and tBid Complex Formation

Osteosarcoma is the most common malignant bone tumor. Chloride (Cl^-) channels-mediated Cl^- movement plays an important role in regulating the functions of various cancer cells, but its role in osteosarcoma remains unclear. In this study, we found that ClC-5 was increased in osteosarcoma tissues compared with normal bone tissues. Patients with high ClC-5 expression showed poor overall survival relative to those patients with low ClC-5 expression. Higher ClC-5 expression and lower intracellular Cl^- concentration ([Cl^-]_i) were observed in osteosarcoma cells compared with normal osteoblasts. Lowering [Cl^-]_i increased the viability of osteosarcoma cells, which was markedly blocked by ClC-5 downregulation. Knockdown of ClC-5 significantly induced osteosarcoma cell apoptosis and increased the release of cytochrome c from mitochondria to cytosol, concomitantly with cleavage of caspase-9, caspase-3, and PARP. The effect of ClC-5 downregulation on osteosarcoma cell apoptosis and viability was abolished by caspase-3 and caspase-9 inhibitors, but not caspase-8 inhibitor. Furthermore, ClC-5 inhibition promoted Bax translocation from cytosol to mitochondria. Immunoprecipitation showed that ClC-5 interacted with Bax and ClC-5 downregulation enhanced Bax and tBid complex formation. Collectively, we demonstrate that ClC-5 downregulation induces osteosarcoma cell apoptosis via mitochondria-dependent apoptotic pathway activation by promoting Bax and tBid association and subsequent Bax translocation.

Molecular characterization of the human kidney interstitium in health and disease

The gene expression signature of the human kidney interstitium is incompletely understood. The cortical interstitium (excluding tubules, glomeruli, and vessels) in reference nephrectomies (N = 9) and diabetic kidney biopsy specimens (N = 6) was laser microdissected (LMD) and sequenced. Samples underwent RNA sequencing. Gene signatures were deconvolved using single nuclear RNA sequencing (snRNAseq) data derived from overlapping specimens. Interstitial LMD transcriptomics uncovered previously unidentified markers including KISS1, validated with in situ hybridization. LMD transcriptomics and snRNAseq revealed strong correlation of gene expression within corresponding kidney regions. Relevant enriched interstitial pathways included G-protein coupled receptor. binding and collagen biosynthesis. The diabetic interstitium was enriched for extracellular matrix organization and small-molecule catabolism. Cell type markers with unchanged expression (NOTCH3, EGFR, and HEG1) and those down-regulated in diabetic nephropathy (MYH11, LUM, and CCDC3) were identified. LMD transcriptomics complements snRNAseq; together, they facilitate mapping of interstitial marker genes to aid interpretation of pathophysiology in precision medicine studies.

SGLT2 inhibition requires reconsideration of fundamental paradigms in chronic kidney disease, 'diabetic nephropathy', IgA nephropathy and podocytopathies with FSGS lesions

In 2020, the Dapagliflozin and Prevention of Adverse Outcomes in Chronic Kidney Disease (DAPA-CKD) trial first demonstrated that inhibition of the sodium-glucose transporter-2 (SGLT2) with dapagliflozin attenuates the progression of chronic kidney disease (CKD) with proteinuria in patients with or without diabetes at an unprecedented effect size. These results have far-reaching implications for a series of traditional concepts in Nephrology. It now became obvious that CKD with and without diabetes involves a predominant SGLT2-driven pathophysiology compared with the other pathogenic pathways currently under consideration. As SGLT2 inhibition is similarly efficacious in diabetic and non-diabetic CKD with proteinuria, treating CKD rather than 'diabetic nephropathy' becomes the central paradigm. Indeed, in older adults with type 2 diabetes, CKD is rather of multifactorial origin. As the DAPA-CKD trial included more patients with immunoglobulin A nephropathy (IgAN) than any of the previous IgAN trials, dual renin-angiotensin/SGLT2 inhibition may become the new standard. The same applies for patients with podocytopathy-related focal segmental glomerulosclerosis lesions. From now on, IgAN and podocytopathy trials without SGLT2 inhibition as background therapy and without glomerular filtration rate decline as primary outcome criterion will be of limited value. These and other potential implications will trigger broad discussions and secondary research activities with conclusions difficult to predict today. However, one is for sure: Nephrology after the DAPA-CKD trial will be not the same as it was before. Finally!

Profibrotic Circulating Proteins and Risk of Early Progressive Renal Decline in Patients With Type 2 Diabetes With and Without Albuminuria

OBJECTIVE

The role of fibrosis in early progressive renal decline in type 2 diabetes is unknown. Circulating WFDC2 (WAP four-disulfide core domain protein 2) and matrix metalloproteinase 7 (MMP-7; Matrilysin) are postulated to be biomarkers of renal fibrosis. This study examined an association of circulating levels of these proteins with early progressive renal decline.

RESEARCH DESIGN AND METHODS

Individuals with type 2 diabetes enrolled in the Joslin Kidney Study with an estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² were monitored for 6-12 years to ascertain fast early progressive renal decline, defined as eGFR loss ≥5 mL/min/1.73 m²/year.

RESULTS

A total of 1,181 individuals were studied: 681 without and 500 with albuminuria. Median eGFR and albumin-to-creatinine ratio (ACR) at baseline were 97 mL/min/1.73 m² and 24 mg/g, respectively. During follow-up, 152 individuals experienced fast early progressive renal decline: 6.9% in those with normoalbuminuria and 21% with albuminuria. In both subgroups, the risk of renal decline increased with increasing baseline levels of WFDC2 (P < 0.0001) and MMP-7 (P < 0.0001). After adjustment for relevant clinical characteristics and known biomarkers, an increase by one quartile in the fibrosis index (combination of levels of WFDC2 and MMP-7) was associated with higher risk of renal decline (odds ratio 1.63; 95% CI 1.30-2.04). The association was similar and statistically significant among patients with and without albuminuria.

CONCLUSIONS

Elevation of circulating profibrotic proteins is associated with the development of early progressive renal decline in type 2 diabetes. This association is independent from albuminuria status and points to the importance of the fibrotic process in the development of early renal decline.

Fibrosis and Immune Cell Infiltration Are Separate Events Regulated by Cell-Specific Receptor Notch3 Expression

BACKGROUND

Kidney injuries that result in chronic inflammation initiate crosstalk between stressed resident cells and infiltrating immune cells. In animal models, whole-body receptor Notch3 deficiency protects from leukocyte infiltration and organ fibrosis. However, the relative contribution of Notch3 expression in tissue versus infiltrating immune cells is unknown.

METHODS

Chimeric mice deficient for Notch3 in hematopoietic cells and/or resident tissue cells were generated, and kidney fibrosis and inflammation after unilateral ureteral obstruction (UUO) were analyzed. Adoptive transfer of labeled bone marrow-derived cells validated the results in a murine Leishmania ear infection model. In vitro adhesion assays, integrin activation, and extracellular matrix production were analyzed.

RESULTS

Fibrosis follows UUO, but inflammatory cell infiltration mostly depends upon Notch3 expression in hematopoietic cells, which coincides with an enhanced proinflammatory milieu (e.g., CCL2 and CCL5 upregulation). Notch3 expression on CD45⁺ leukocytes plays a prominent role in efficient cell transmigration. Functionally, leukocyte adhesion and integrin activation are abrogated in the absence of receptor Notch3. Chimeric animal models also reveal that tubulointerstitial fibrosis develops, even in the absence of prominent leukocyte infiltrates after ureteral obstruction. Deleting Notch3 receptors on resident cells blunts kidney fibrosis, ablates NF-κB signaling, and lessens matrix deposition.

CONCLUSIONS

Cell-specific receptor Notch3 signaling independently orchestrates leukocyte infiltration and organ fibrosis. Interference with Notch3 signaling may present a novel therapeutic approach in inflammatory as well as fibrotic diseases.

Neural transcription factor Pou4f1 promotes renal fibrosis via macrophage-myofibroblast transition

Unresolved inflammation can lead to tissue fibrosis and impaired organ function. Macrophage-myofibroblast transition (MMT) is one newly identified mechanism by which ongoing chronic inflammation causes progressive fibrosis in different forms of kidney disease. However, the mechanisms underlying MMT are still largely unknown. Here, we discovered a brain-specific homeobox/POU domain protein Pou4f1 (Brn3a) as a specific regulator of MMT. Interestingly, we found that Pou4f1 is highly expressed by macrophages undergoing MMT in sites of fibrosis in human and experimental kidney disease, identified by coexpression of the myofibroblast marker, α-SMA. Unexpectedly, Pou4f1 expression peaked in the early stage in renal fibrogenesis in vivo and during MMT of bone marrow-derived macrophages (BMDMs) in vitro. Mechanistically, chromatin immunoprecipitation (ChIP) assay identified that Pou4f1 is a Smad3 target and the key downstream regulator of MMT, while microarray analysis defined a Pou4f1-dependent fibrogenic gene network for promoting TGF-β1/Smad3-driven MMT in BMDMs at the transcriptional level. More importantly, using two mouse models of progressive renal interstitial fibrosis featuring the MMT process, we demonstrated that adoptive transfer of TGF-β1-stimulated BMDMs restored both MMT and renal fibrosis in macrophage-depleted mice, which was prevented by silencing Pou4f1 in transferred BMDMs. These findings establish a role for Pou4f1 in MMT and renal fibrosis and suggest that Pou4f1 may be a therapeutic target for chronic kidney disease with progressive renal fibrosis.

COL4A1 promotes the growth and metastasis of hepatocellular carcinoma cells by activating FAK-Src signaling

BACKGROUND

Collagens are the most abundant proteins in extra cellular matrix and important components of tumor microenvironment. Recent studies have showed that aberrant expression of collagens can influence tumor cell behaviors. However, their roles in hepatocellular carcinoma (HCC) are poorly understood.

METHODS

In this study, we screened all 44 collagen members in HCC using whole transcriptome sequencing data from the public datasets, and collagen type IV alpha1 chain (COL4A1) was identified as most significantly differential expressed gene. Expression of COL4A1 was detected in HCC samples by quantitative real-time polymerase chain reaction (qRT-PCR), western blot and immunohistochemistry (IHC). Finally, functions and potential mechanisms of COL4A1 were explored in HCC progression.

RESULTS

COL4A1 is the most significantly overexpressed collagen gene in HCC. Upregulation of COL4A1 facilitates the proliferation, migration and invasion of HCC cells through FAK-Src signaling. Expression of COL4A1 is upregulated by RUNX1 in HCC. HCC cells with high COL4A1 expression are sensitive to the treatment with FAK or Src inhibitor.

CONCLUSION

COL4A1 facilitates growth and metastasis in HCC via activation of FAK-Src signaling. High level of COL4A1 may be a potential biomarker for diagnosis and treatment with FAK or Src inhibitor for HCC.

Collagen, stiffness, and adhesion: the evolutionary basis of vertebrate mechanobiology

The emergence of collagen I in vertebrates resulted in a dramatic increase in the stiffness of the extracellular environment, supporting long-range force propagation and the development of low-compliant tissues necessary for the development of vertebrate traits including pressurized circulation and renal filtration. Vertebrates have also evolved integrins that can bind to collagens, resulting in the generation of higher tension and more efficient force transmission in the extracellular matrix. The stiffer environment provides an opportunity for the vertebrates to create new structures such as the stress fibers, new cell types such as endothelial cells, new developmental processes such as neural crest delamination, and new tissue organizations such as the blood-brain barrier. Molecular players found only in vertebrates allow the modification of conserved mechanisms as well as the design of novel strategies that can better serve the physiological needs of the vertebrates. These innovations collectively contribute to novel morphogenetic behaviors and unprecedented increases in the complexities of tissue mechanics and functions.

Janus-Faced: Molecular Mechanisms and Versatile Nature of Renal Fibrosis

Renal fibrosis is a major hallmark of CKD, regardless of the underlying etiology. In fibrosis development and progression, myofibroblasts play a pivotal role, producing extracellular matrix and interacting with various resident cells in the kidney. Over the past decade, the origin of myofibroblasts has been thoroughly investigated. Emerging evidence suggests that renal myofibroblasts originate from several cellular sources, including resident fibroblasts, pericytes, and bone marrow-derived cells. The contribution of resident fibroblasts is most crucial, and currently available data strongly suggest the importance of functional heterogeneity and plasticity of fibroblasts in kidney disease progression. Resident fibroblasts acquire distinct phenotypes based on their local microenvironment and exert multifactorial functions. For example, age-dependent alterations of renal fibroblasts make a significant contribution to the formation of tertiary lymphoid tissues, which promote local inflammation after injury in the aged kidney. In conjunction with fibrosis development, dysfunction of resident fibroblasts provokes unique pathologic conditions including renal anemia and peritubular capillary loss, both of which are major complications of CKD. Although renal fibrosis is considered detrimental in general, recent studies suggest it has beneficial roles, such as maintaining functional crosstalk with injured proximal tubular cells and supporting their regeneration. These findings provide novel insight into the mechanisms of renal fibrosis, which could be regarded as an adaptive process of kidney injury and repair. Precise understanding of the functional heterogeneity of resident fibroblasts and myofibroblasts has the potential to facilitate the development of novel therapeutics against kidney diseases. In this review, we describe the current perspective on the origin of myofibroblasts and fibroblast heterogeneity, with special emphasis on the dual aspects of renal fibrosis, both beneficial and detrimental, in CKD progression.

Application of Histone Deacetylase Inhibitors in Renal Interstitial Fibrosis

BACKGROUND

Renal interstitial fibrosis is characterized by the accumulation of extracellular matrix proteins, which is a common feature of chronic kidney diseases.

SUMMARY

Increasing evidence has shown the aberrant expression of histone deacetylases (HDACs) in the development and progression of renal fibrosis, suggesting the possibility of utilizing HDAC inhibitor (HDACi) as therapeutics for renal fibrosis. Recent studies have successfully demonstrated the antifibrotic effects of HDACis in various animal models, which are associated with multiple signaling pathways including TGF-β signaling, EGRF signaling, signal transducer and activator of transcription 3 pathway, and JNK/Notch2 signaling. This review will focus on the utilization of HDACi as antifibrotic agents and its relative molecular mechanisms.

KEY MESSAGES

HDACis have shown promising results in antifibrotic therapy, and it is rational to anticipate that HDACis will improve clinical outcomes of renal fibrosis in the future.

miR-196b-5p-enriched extracellular vesicles from tubular epithelial cells mediated aldosterone-induced renal fibrosis in mice with diabetes

INTRODUCTION

Aldosterone is a mediator of progressive renal disease, but the mechanisms for aldosterone-mediated renal impairment in mice with diabetes are not fully defined.

METHODS

Aldosterone and/or mineralocorticoid receptor antagonist eplerenone were used to treat the db/db mice with diabetes. Proximal tubule epithelial cells (PTECs) and fibroblasts were cultured. Blood and kidney samples from patients with diabetes with or without diabetic kidney disease (DKD) were used to verify the findings from animals and cultured cells.

RESULTS

We found that aldosterone promoted proteinuria and tubulointerstitial extracellular matrix (ECM) accumulation in db/db mice with diabetes while eplerenone mitigated the adverse effect of aldosterone. However, coculture of PTECs and fibroblasts found that when PTECs-derived extracellular vesicles (EVs) were taken up by fibroblasts, ECM production increased remarkably. Moreover, C57BL/6 mice injected with EVs from renal cortex of aldosterone-treated db/db mice showed increased ECM accumulation. Function of the ingredients of PTECs-derived EVs were analyzed, and RNAs were identified to be responsible for the EVs-induced fibroblast dysfunction. Furthermore, microRNA (miRNA) array analysis revealed that miR-196b-5p was the most remarkably increased miRNA in PTECs-derived EVs with aldosterone stimulation. Overexpression of miR-196b-5p in fibroblasts increased ECM production, accompanied by inhibition of the SOCS2 expression and enhanced STAT3 phosphorylation. In addition, plasma levels of miR-196b-5p was higher in patients with DKD as compared with patients without DKD and miR-196b-5p levels positively correlated with the albuminuria concentration. In kidney specimens from patients with diabetes, expression of miR-196b-5p, located mainly in PTECs, increased in patients with DKD as compared with the non-DKD.

CONCLUSION

This study demonstrates the involvement of miR-196b-5p-EVs pathway as a novel mechanism in aldosterone-induced renal fibrosis in diabetes. EVs rich in miR-196b-5p mediate the crosstalk between PTECs and fibroblast during the development of renal fibrosis, which might be associated with STAT3/SOCO2 signaling pathway.

Cyclophilin A Promotes Inflammation in Acute Kidney Injury but Not in Renal Fibrosis

Cyclophilin A (CypA) is a highly abundant protein in the cytoplasm of most mammalian cells. Beyond its homeostatic role in protein folding, CypA is a Damage-Associated Molecular Pattern which can promote inflammation during tissue injury. However, the role of CypA in kidney disease is largely unknown. This study investigates the contribution of CypA in two different types of kidney injury: acute tubular necrosis and progressive interstitial fibrosis. CypA (Ppia) gene deficient and wild type (WT) littermate controls underwent bilateral renal ischaemia/reperfusion injury (IRI) and were killed 24 h later or underwent left unilateral ureteric obstruction (UUO) and were killed 7 days later. In the IRI model, CypA^−/− mice showed substantial protection against the loss of renal function and from tubular cell damage and death. This was attributed to a significant reduction in neutrophil and macrophage infiltration since CypA^−/− tubular cells were not protected from oxidant-induced cell death in vitro. In the UUO model, CypA^−/− mice were not protected from leukocyte infiltration or renal interstitial fibrosis. In conclusion, CypA promotes inflammation and acute kidney injury in renal IRI, but does not contribute to inflammation or interstitial fibrosis in a model of progressive kidney fibrosis.

Origin and functional heterogeneity of fibroblasts

The inherent plasticity and resiliency of fibroblasts make this cell type a conventional tool for basic research. But where do they come from, are all fibroblasts the same, and how do they function in disease? The first fibroblast lineages in mammalian development emerge from the ooze of primary mesenchyme during gastrulation. They are cells that efficiently create and negotiate the extracellular matrix of the mesoderm in order to migrate and meet their developmental fate. Mature fibroblasts in epithelial tissues live in the interstitial spaces between basement membranes that spatially delimit complex organ structures. While the function of resident fibroblasts in healthy tissues is largely conjecture, the accumulation of fibroblasts in pathologic lesions offers insight into biologic mechanisms that control their function; fibroblasts are poised to coordinate fibrogenesis in tissue injury, neoplasia, and aging. Here, we examine the developmental origin and plasticity of fibroblasts, their molecular and functional definitions, the epigenetic control underlying their identity and activation, and the evolution of their immune regulatory functions. These topics are reviewed through the lens of fate mapping using genetically engineered mouse models and from the perspective of single-cell RNA sequencing. Recent observations suggest dynamic and heterogeneous functions for fibroblasts that underscore their complex molecular signatures and utility in injured tissues.

Pathology and natural history of organ fibrosis

Histopathological assessment of fibrosis focusing on morphological patterns provides important information for the management of patients with chronic diseases of the kidney, liver and the lung. This review summarizes key histopathological features of pulmonary, renal and hepatic fibrosis and discusses advances in the understanding of the pathogenesis of pulmonary fibrosis and pathogenetic insights with translational implications for renal fibrosis. The review also tackles new staging approaches based on liver fibrosis dynamics and evaluation of fibrosis regression, digital pathology and second harmonic generation microscopy methods for hepatic fibrosis assessment and critical appraisal of non-invasive tests for liver and renal fibrosis evaluation.

The p21 dependent G2 arrest of the cell cycle in epithelial tubular cells links to the early stage of renal fibrosis

Renal fibrosis is accompanied by the progression of chronic kidney disease. Despite a number of past and ongoing studies, our understanding of the underlying mechanisms remains elusive. Here we explored the progression of renal fibrosis using a mouse model of unilateral ureter obstruction. We found that in the initial stage of damage, where extracellular matrix was not yet deposited, proximal tubular cells arrested at G2 of the cell cycle. Further analyses indicated that the cyclin-dependent kinase inhibitor p21 is partially involved in the G2 arrest after the damage. A newly produced monoclonal antibody against p21 revealed that levels of p21 were sharply upregulated in response to the damage during the initial stage but dropped toward the later stage. To investigate the requirement of p21 for the progression of renal fibrosis, we constructed the novel p21 deficient mice by i-GONAD method. Compared with wild-type mice, p21 deficient mice showed exacerbation of the fibrosis. Thus we propose that during the initial stage of the renal damage, tubular cells arrest in G2 partially depending on p21, thereby safeguarding kidney functions.

An immortalized cell line derived from renal erythropoietin-producing (REP) cells demonstrates their potential to transform into myofibroblasts

The erythroid growth factor erythropoietin (Epo) is produced by renal interstitial fibroblasts, called REP (renal Epo-producing) cells, in a hypoxia-inducible manner. In chronic kidney disease (CKD), REP cells lose their Epo-production ability, leading to renal anaemia. Concurrently, REP cells are suggested to be transformed into myofibroblasts, which are the major player of renal fibrosis. Although establishment of cultured cell lines derived from REP cells has been a long-term challenge, we here successfully established a REP-cell-derived immortalized and cultivable cell line (Replic cells) by using a genetically modified mouse line. Replic cells exhibited myofibroblastic phenotypes and lost their Epo-production ability, reflecting the situation in renal fibrosis. Additionally, we found that cell-autonomous TGFβ signalling contributes to maintenance of the myofibroblastic features of Replic cells. Furthermore, the promoters of genes for Epo and HIF2α, a major activator of Epo gene expression, were highly methylated in Replic cells. Thus, these results strongly support our contention that REP cells are the origin of myofibroblasts in fibrotic kidneys and demonstrate that cell-autonomous TGFβ signalling and epigenetic silencing are involved in renal fibrosis and renal anaemia, respectively, in CKD. The Replic cell line is a useful tool to further investigate the molecular mechanisms underlying renal fibrosis.

Extracellular Matrix in Kidney Fibrosis: More Than Just a Scaffold

Kidney fibrosis is the common histological end-point of progressive, chronic kidney diseases (CKDs) regardless of the underlying etiology. The hallmark of renal fibrosis, similar to all other organs, is pathological deposition of extracellular matrix (ECM). Renal ECM is a complex network of collagens, elastin, and several glycoproteins and proteoglycans forming basal membranes and interstitial space. Several ECM functions beyond providing a scaffold and organ stability are being increasingly recognized, for example, in inflammation. ECM composition is determined by the function of each of the histological compartments of the kidney, that is, glomeruli, tubulo-interstitium, and vessels. Renal ECM is a dynamic structure undergoing remodeling, particularly during fibrosis. From a clinical perspective, ECM proteins are directly involved in several rare renal diseases and indirectly in CKD progression during renal fibrosis. ECM proteins could serve as specific non-invasive biomarkers of fibrosis and scaffolds in regenerative medicine. The gold standard and currently only specific means to measure renal fibrosis is renal biopsy, but new diagnostic approaches are appearing. Here, we discuss the localization, function, and remodeling of major renal ECM components in healthy and diseased, fibrotic kidneys and the potential use of ECM in diagnostics of renal fibrosis and in tissue engineering.