Matrix metalloproteinase-9 of tubular and macrophage origin contributes to the pathogenesis of renal fibrosis via macrophage recruitment through osteopontin cleavage

Matrix metalloproteinase-driven epithelial-mesenchymal transition: implications in health and disease

Epithelial-mesenchymal transition (EMT) is a process in which epithelial cells, defined by apical-basal polarity and tight intercellular junctions, acquire migratory and invasive properties characteristic of mesenchymal cells. Under normal conditions, EMT directs essential morphogenetic events in embryogenesis and supports tissue repair. When dysregulated, EMT contributes to pathological processes such as organ fibrosis, chronic inflammation, and cancer progression and metastasis. Matrix metalloproteinases (MMPs)-a family of zinc-dependent proteases that degrade structural components of the extracellular matrix-sit at the nexus of this transition by dismantling basement membranes, activating pro-EMT signaling pathways, and cleaving adhesion molecules. When normally regulated, MMPs promote balanced ECM turnover and support the cyclical remodeling necessary for proper development, wound healing, and tissue homeostasis. When abnormally regulated, MMPs drive excessive ECM turnover, thereby promoting EMT-related pathologies, including tumor progression and fibrotic disease. This review provides an integrated overview of the molecular mechanisms by which MMPs both initiate and sustain EMT under physiological and disease conditions. It discusses how MMPs can potentiate EMT through TGF-β and Wnt/β-catenin signaling, disrupt cell-cell junction proteins, and potentiate the action of hypoxia-inducible factors in the tumor microenvironment. It discusses how these pathologic processes remodel tissues during fibrosis, and fuel cancer cell invasion, metastasis, and resistance to therapy. Finally, the review explores emerging therapeutic strategies that selectively target MMPs and EMT, ranging from CRISPR/Cas-mediated interventions to engineered tissue inhibitors of metalloproteinases (TIMPs), and demonstrates how such approaches may suppress pathological EMT without compromising its indispensable roles in normal biology.

Osteopontin Promotes Cholangiocyte Secretion of Chemokines to Support Macrophage Recruitment and Fibrosis in MASH

BACKGROUND AND AIMS

Osteopontin (OPN) promotes the ductular reaction and is a major driver of chronic liver disease (CLD) progression. Although CLD is characterised by the accumulation of inflammatory cells including macrophages around the peri-portal regions, the influence of OPN on recruitment is unclear. We investigated the role of OPN in cholangiocyte chemokine production and macrophage recruitment by combining in vivo, in vitro, and in silico approaches.

METHODS

The effects of OPN on cholangiocyte chemokine production and macrophage migration were assessed in culture, alongside RNA-sequencing to identify genes and pathways affected by OPN depletion. Murine liver injury models were used to assess liver chemokine expression and liver macrophage/monocyte recruitment. OPN and chemokine expression were analysed in liver tissue and plasma from biopsy-proven metabolic dysfunction-associated alcoholic steatohepatitis (MASH) patients.

RESULTS

OPN-knockdown in cholangiocytes reduced chemokine secretion. RNA-sequencing showed OPN-related effects clustered around immunity, chemotaxis and chemokine production. Macrophage exposure to cholangiocyte-conditioned media showed OPN-supported migration via chemokines chemokine (C-C motif) ligand (CCL)2, CCL5 and chemokine (C-X-C motif) ligand (CXCL)1. These effects were related to NF-κB signalling. Murine liver fibrosis was accompanied by upregulated liver OPN, CCL2, CCL5 and CXCL1 mRNA, and accumulation of liver cluster of differentiation (CD)11b/F4/80+CC chemokine receptors (CCR2)high macrophages but treatment with OPN-specific neutralising aptamers reduced fibrosis, chemokine mRNAs and accumulation of liver CD11b/F4/80+CCR2high/lymphocyte antigen 6 complexhigh inflammatory monocytes. In human MASH, liver OPN correlated with chemokines CCL2 and IL8 in association with portal injury and fibrosis. Plasma OPN, serum CCL2 and IL8 also increased with fibrosis stage.

CONCLUSIONS

OPN promotes cholangiocyte chemokine secretion and the accumulation of pro-inflammatory monocytes. These data support neutralisation of OPN as an anti-inflammatory and anti-fibrotic strategy.

Matrix Metalloproteinases in Ureteropelvic Junction Obstruction: Their Role in Pathogenesis and Their Use as Clinical Markers

The obstruction of the urinary tract is responsible for obstructive nephropathy (ON), also known as uropathy, which may then evolve in a renal parenchymal disease (hydronephrosis). Regarding the etiology of ON, it has been linked to the perturbation of processes occurring during the urinary tract development such as morphogenesis, maturation, and growth. Despite the research carried out in recent years, there is still a pressing need to elucidate the molecular processes underlying the disease. This may then result in the definition of novel biomarkers that can help in patient stratification and the monitoring of therapeutic choices. Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases with key roles in extracellular matrix remodeling due to their wide cleavage specificity and ability to modulate the bioavailability of growth factors. Despite the known changes in the local tissue microenvironment at the site of the urinary tract obstruction, the role of MMPs in ureteropelvic junction obstruction (UPJO) and, therefore, in the pathogenesis of renal damage in ON is not well-documented. In this review, we underline the possible roles of MMPs both in the pathogenesis of UPJO and in the progression of related hydronephrosis. The potential use of MMPs as biomarkers detectable in bodily fluids (such as the patient's urine) is also discussed.

Cross-talk of renal cells through WNT signal transduction in the development of fibrotic kidneys

Chronic kidney disease (CKD) is a progressive condition that can lead to chronic renal failure (CRF), affecting 8%-16% of adults globally and imposing a significant burden on healthcare systems. Renal fibrosis is a key pathological hallmark of CKD progression and is linked to poor prognosis. Multiple signaling pathways, including WNT/β-catenin.Aberrant activation of WNT/β-catenin is implicated in renal fibrosis. The roles of renal macrophages and fibroblasts are pivotal in fibrosis progression and prognosis.

Targeting senescence to prevent diabetic kidney disease: Exploring molecular mechanisms and potential therapeutic targets for disease management

BACKGROUND/AIMS

As a microvascular complication, diabetic kidney disease is the leading cause of chronic kidney disease and end-stage renal disease worldwide. While the underlying pathophysiology driving transition of diabetic kidney disease to renal failure is yet to be fully understood, recent studies suggest that cellular senescence is central in disease development and progression. Consequently, understanding the molecular mechanisms which initiate and drive senescence in response to the diabetic milieu is crucial in developing targeted therapies that halt progression of renal disease.

METHODS

To understand the mechanistic pathways underpinning cellular senescence in the context of diabetic kidney disease, we reviewed the literature using PubMed for English language articles that contained key words related to senescence, inflammation, fibrosis, senescence-associated secretory phenotype (SASP), autophagy, and diabetes.

RESULTS

Aberrant accumulation of metabolically active senescent cells is a notable event in the progression of diabetic kidney disease. Through autocrine- and paracrine-mediated mechanisms, resident senescent cells potentiate inflammation and fibrosis through increased expression and secretion of pro-inflammatory cytokines, chemoattractants, recruitment of immune cells, myofibroblast activation, and extracellular matrix remodelling. Compounds that eliminate senescent cells and/or target the SASP - including senolytic and senomorphics drugs - demonstrate promising results in reducing the senescent cell burden and associated pro-inflammatory effect.

CONCLUSIONS

Here we evidence the link between senescence and diabetic kidney disease and highlight underlying molecular mechanisms and potential therapeutic targets that could be exploited to delay disease progression and improve outcomes for individuals with the disease. Trials are now required to translate their therapeutic potential to a clinical setting.

Proteinuria and tubular cells: Plasticity and toxicity

AIM

Proteinuria is the most robust predictive factors for the progression of chronic kidney disease (CKD), and interventions targeting proteinuria reduction have shown to be the most effective nephroprotective treatments to date. While glomerular dysfunction is the primary source of proteinuria, its consequences extend beyond the glomerulus and have a profound impact on tubular epithelial cells. Indeed, proteinuria induces notable phenotypic changes in tubular epithelial cells and plays a crucial role in driving CKD progression. This comprehensive review aims to elucidate the mechanisms involved in the tubular handling of proteins and explore the potential effects of proteinuria on the function of tubular epithelial cells.

METHODS

This paper is a narrative review. Litterature review was performed on PubMed from its inception until 2024, focusing on the effects of proteinuria on tubular cells.

RESULTS

The review highlights the toxic effects of plasma proteins on tubular epithelial cells through signal transduction pathways, as well as endoplasmic reticulum stress activation, oxidative stress, and metabolic alterations. Additionally, it provides an updated understanding of the dynamic phenotypic changes occurring within the nephron in response to proteinuria.

CONCLUSIONS

By examining the intricate interplay between proteinuria and tubular epithelial cells, this review sheds light on key factors contributing to CKD progression and unveils potential targets for therapeutic interventions.

Enter the Matrix: Fibroblast-immune cell interactions shape extracellular matrix deposition in health and disease

Fibroblasts, non-hematopoietic cells of mesenchymal origin, are tissue architects which regulate the topography of tissues, dictate tissue resident cell types, and drive fibrotic disease. Fibroblasts regulate the composition of the extracellular matrix (ECM), a 3-dimensional network of macromolecules that comprise the acellular milieu of tissues. Fibroblasts can directly and indirectly regulate immune responses by secreting ECM and ECM-bound molecules to shape tissue structure and influence organ function. In this review, we will highlight recent studies which elucidate the mechanisms by which fibroblast-derived ECM factors (e.g., collagens, fibrillar proteins) regulate ECM architecture and subsequent immune responses, with a focus on macrophages. As examples of fibroblast-derived ECM proteins, we examine Collagen Triple Helix Repeat Containing 1 (CTHRC1) and Transforming Growth Factor-β-inducible protein (TGFBI), also known as BIGH3. We address the need for investigation into how diverse fibroblast populations coordinate immune responses by modulating ECM, including the fibroblast-ECM-immune axis and the precise molecular mediators and pathways which regulate these processes. Finally, we will outline how novel research identifying key regulators of ECM deposition is critical for therapeutic development for fibrotic diseases and cancer.

Unveiling the bidirectional role of MMP9: A key player in kidney injury

Matrix metalloproteinases (MMPs) are a group of zinc-dependent proteolytic metalloenzymes that are involved in numerous pathological conditions, including nephropathy. MMP9, a member of the MMPs family, is categorized as a constituent of the gelatinase B subgroup, and its involvement in extracellular matrix (ECM) remodeling and renal fibrosis highlights its importance in the development and progression of renal diseases. The exact role of MMP9 in the development of kidney diseases is still controversial. This study investigated the dual role of MMP9 in kidney injury, discussing its implications in the pathogenesis of kidney diseases and investigating the design and mechanism of MMP9 inhibitors based on previous studies. This study provides an effective basis for the development of novel and selective MMP9 inhibitors for treating renal diseases.

Renal tubular epithelial cell quality control mechanisms as therapeutic targets in renal fibrosis

Renal fibrosis is a devastating consequence of progressive chronic kidney disease, representing a major public health challenge worldwide. The underlying mechanisms in the pathogenesis of renal fibrosis remain unclear, and effective treatments are still lacking. Renal tubular epithelial cells (RTECs) maintain kidney function, and their dysfunction has emerged as a critical contributor to renal fibrosis. Cellular quality control comprises several components, including telomere homeostasis, ubiquitin-proteasome system (UPS), autophagy, mitochondrial homeostasis (mitophagy and mitochondrial metabolism), endoplasmic reticulum (ER, unfolded protein response), and lysosomes. Failures in the cellular quality control of RTECs, including DNA, protein, and organelle damage, exert profibrotic functions by leading to senescence, defective autophagy, ER stress, mitochondrial and lysosomal dysfunction, apoptosis, fibroblast activation, and immune cell recruitment. In this review, we summarize recent advances in understanding the role of quality control components and intercellular crosstalk networks in RTECs, within the context of renal fibrosis.

Identification of immune infiltration and immune-related biomarkers of periprosthetic joint infection

BACKGROUND

The immune response associated with periprosthetic joint infection (PJI) is an emerging but relatively unexplored topic. The aim of this study was to investigate immune cell infiltration in periprosthetic tissues and identify potential immune-related biomarkers.

METHODS

The GSE7103 dataset from the GEO database was selected as the data source. Differentially expressed genes (DEGs) and significant modular genes in weighted correlation network analysis (WGCNA) were identified. Functional enrichment analysis and transcription factor prediction were performed on the overlapping genes. Next, immune-related genes from the ImmPort database were matched. The protein-protein interaction (PPI) analysis was performed to identify hub genes. CIBERSORTx was used to evaluate the immune cell infiltration pattern. Spearman correlation analysis was used to evaluate the relationship between hub genes and immune cells.

RESULTS

A total of 667 DEGs were identified between PJI and control samples, and 1847 PJI-related module genes were obtained in WGCNA. Enrichment analysis revealed that the common genes were mainly enriched in immune and host defense-related terms. TFEC, SPI1, and TWIST2 were the top three transcription factors. Three hub genes, SDC1, MMP9, and IGF1, were identified in the immune-related PPI network. Higher levels of plasma cells, CD4+ memory resting T cells, follicular helper T cells, resting mast cells, and neutrophils were found in the PJI group, while levels of M0 macrophages were lower. Notably, the expression of all three hub genes correlated with the infiltration levels of seven types of immune cells.

CONCLUSION

The present study revealed immune infiltration signatures in the periprosthetic tissues of PJI patients. SDC1, MMP9, and IGF1 were potential immune-related biomarkers for PJI.

The role of matrix metalloproteinase 9 in fibrosis diseases and its molecular mechanisms

Fibrosis is a process of tissue repair that results in the slow creation of scar tissue to replace healthy tissue and can affect any tissue or organ. Its primary feature is the massive deposition of extracellular matrix (mainly collagen), eventually leading to tissue dysfunction and organ failure. The progression of fibrotic diseases has put a significant strain on global health and the economy, and as a result, there is an urgent need to find some new therapies. Previous studies have identified that inflammation, oxidative stress, some cytokines, and remodeling play a crucial role in fibrotic diseases and are essential avenues for treating fibrotic diseases. Among them, matrix metalloproteinases (MMPs) are considered the main targets for the treatment of fibrotic diseases since they are the primary driver involved in ECM degradation, and tissue inhibitors of metalloproteinases (TIMPs) are natural endogenous inhibitors of MMPs. Through previous studies, we found that MMP-9 is an essential target for treating fibrotic diseases. However, it is worth noting that MMP-9 plays a bidirectional regulatory role in different fibrotic diseases or different stages of the same fibrotic disease. Previously identified MMP-9 inhibitors, such as pirfenidone and nintedanib, suffer from some rather pronounced side effects, and therefore, there is an urgent need to investigate new drugs. In this review, we explore the mechanism of action and signaling pathways of MMP-9 in different tissues and organs, hoping to provide some ideas for developing safer and more effective biologics.

The pathogenic role of succinate-SUCNR1: a critical function that induces renal fibrosis via M2 macrophage

BACKGROUND

Renal fibrosis significantly contributes to the progressive loss of kidney function in chronic kidney disease (CKD), with alternatively activated M2 macrophages playing a crucial role in this progression. The serum succinate level is consistently elevated in individuals with diabetes and obesity, both of which are critical factors contributing to CKD. However, it remains unclear whether elevated succinate levels can mediate M2 polarization of macrophages and contribute to renal interstitial fibrosis.

METHODS

Male C57/BL6 mice were administered water supplemented with 4% succinate for 12 weeks to assess its impact on renal interstitial fibrosis. Additionally, the significance of macrophages was confirmed in vivo by using clodronate liposomes to deplete them. Furthermore, we employed RAW 264.7 and NRK-49F cells to investigate the underlying molecular mechanisms.

RESULTS

Succinate caused renal interstitial macrophage infiltration, activation of profibrotic M2 phenotype, upregulation of profibrotic factors, and interstitial fibrosis. Treatment of clodronate liposomes markedly depleted macrophages and prevented the succinate-induced increase in profibrotic factors and fibrosis. Mechanically, succinate promoted CTGF transcription via triggering SUCNR1-p-Akt/p-GSK3β/β-catenin signaling, which was inhibited by SUCNR1 siRNA. The knockdown of succinate receptor (SUCNR1) or pretreatment of anti-CTGF(connective tissue growth factor) antibody suppressed the stimulating effects of succinate on RAW 264.7 and NRK-49F cells.

CONCLUSIONS

The causative effects of succinate on renal interstitial fibrosis were mediated by the activation of profibrotic M2 macrophages. Succinate-SUCNR1 played a role in activating p-Akt/p-GSK3β/β-catenin, CTGF expression, and facilitating crosstalk between macrophages and fibroblasts. Our findings suggest a promising strategy to prevent the progression of metabolic CKD by promoting the excretion of succinate in urine and/or using selective antagonists for SUCNR1.

Crosstalk between proximal tubular epithelial cells and other interstitial cells in tubulointerstitial fibrosis after renal injury

The energy needs of tubular epithelial components, especially proximal tubular epithelial cells (PTECs), are high and they heavily depend on aerobic metabolism. As a result, they are particularly vulnerable to various injuries caused by factors such as ischemia, proteinuria, toxins, and elevated glucose levels. Initial metabolic and phenotypic changes in PTECs after injury are likely an attempt at survival and repair. Nevertheless, in cases of recurrent or prolonged injury, PTECs have the potential to undergo a transition to a secretory state, leading to the generation and discharge of diverse bioactive substances, including transforming growth factor-β, Wnt ligands, hepatocyte growth factor, interleukin (IL)-1β, lactic acid, exosomes, and extracellular vesicles. By promoting fibroblast activation, macrophage recruitment, and endothelial cell loss, these bioactive compounds stimulate communication between epithelial cells and other interstitial cells, ultimately worsening renal damage. This review provides a summary of the latest findings on bioactive compounds that facilitate the communication between these cellular categories, ultimately leading to the advancement of tubulointerstitial fibrosis (TIF).

(5R)-5-hydroxytriptolide ameliorates diabetic kidney damage by inhibiting macrophage infiltration and its cross-talk with renal resident cells

OBJECTIVE

Diabetic nephropathy (DN) is the main cause of end-stage renal disease, and there are no targeted treatment options at present. The efficacy of the new immunosuppressive drug (5R)-5-hydroxytriptolide (LLDT8) in improving kidney inflammation has been demonstrated in multiple studies. The present study was intended to investigate the preventive and therapeutic effects of LLDT8 on DN and to reveal its potential pharmacological mechanisms.

METHODS

The effects of LLDT8 on liver and kidney functions, and urine microprotein of Streptozotocin (STZ) induced DN mice were detected. The protective effect of LLDT8 on the kidney tissue was observed by pathological staining and transmission electron microscopy. Cell culture experiments were performed to detect the effects of LLDT8 on the expression of chemokines and epithelial-mesenchymal transition (EMT) in high glucose-induced TCMK1 cells using real-time polymerase chain reaction (RT-PCR) and western blot (WB) techniques and to detect the influence of LLDT8 on the secretion of pro-inflammatory and pro-fibrotic factors in high glucose-induced RAW264.7 cells.

RESULTS

In animal experiments, treatment with high-dose LLDT8 (0.25 mg/kg/2d) reduced 24 h urinary albumin excretion, improved structural kidney damage, and delayed fibrosis progression in DN mice. Immunofluorescence results showed that LLDT8 intervention reduced macrophage infiltration in kidney tissues of DN mice. PCR and WB results of kidney tissues showed reduced expressions of chemokines CCL2 and M-CSF1 in the LLDT8 intervention group compared to the DN group. In cellular assays, LLDT8 treatment reduced chemokine secretion in high glucose-induced TCMK1 cells, but had no effect on EMT of TCMK1 cells. LLDT8 treatment reduced the secretion of pro-inflammatory and pro-fibrotic factors in high glucose-induced RAW264.7 cells.

CONCLUSIONS

The present study suggests that LLDT8 could effectively inhibit the secretion of pro-inflammatory and pro-fibrotic factors by macrophages, which could alleviate high glucose-induced renal tissue injury and slow down the process of tissue fibrosis and DN.

The Expression and Molecular Mechanisms of Matrix Metalloproteinase- 9 and Vascular Endothelial Growth Factor in Renal Interstitial Fibrosis in Rats

OBJECTIVE

To explore a new approach for the treatment of renal interstitial fibrosis (RIF), we detected the expression of matrix metalloproteinase-9 (MMP9) and vascular endothelial growth factor (VEGF).

METHODS

Twenty-four male Sprague Dawley (SD) rats were randomly divided into 2- week normal control (2NC) group, 4-week NC (4NC) group, 2-week unilateral ureteral obstruction (2UUO) group, and 4-week UUO (4UUO) group. We performed left ureteral ligation on UUO groups. Then, we sacrificed the rats of the 2NC group and 2UUO group at 2 weeks and the other groups at 4 weeks after the surgery. Immunohistochemistry and western blot were applied to detect the expression of MMP9, VEGF, fibronectin (FN), type IV collagen (Col-IV), and transforming growth factor-β1 (TGF-β1). MMP9 levels reduced after UUO surgery. Its expression was less in the 4UUO group than in the 2UUO group (P<0.05). The expression of VEGF, TGF- β1, FN, and Col-IV was higher in UUO groups than in NC groups (P<0.05). The expression of these indicators was higher in the 4UUO group than in the 2UUO group (P<0.05).

RESULTS

In the correlation analysis, MMP9 levels in UUO groups had a negative correlation with the expression of TGF-β1, VEGF, Col-IV, FN, and RIF index (all P<0.05). In UUO groups, VEGF levels had a positive correlation with the expression of TGF-β1, Col-IV, FN, and RIF index (all P<0.05).

CONCLUSION

In conclusion, with the aggravation of RIF lesions, MMP9 levels decreased, and VEGF levels increased. Whether there is a mutual inhibition relationship between them remains to be confirmed by further experiments.

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

BACKGROUND

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

MAIN BODY AND CONCLUSION

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

Renal Fibrosis and Oxidative Stress Induced by Silica Nanoparticles in Male Rats and Its Molecular Mechanisms

Background

The utilization of amorphous silica nanoparticles (SiNPs) is gaining popularity in various applications, but it poses a potential risk to human and environmental health. However, the underlying causes and mechanisms of SiNPs-induced kidney damage are still largely unknown.

Objectives

This study aimed to investigate the SiNPs-induced damage in the kidney and further explore the possible mechanisms of SiNPs-induced nephrotoxicity.

Methods

Thirty adult male rats were divided into 3 different groups. Rats in groups 2 and 3 were administered SiNPs at 2 dosage levels (25 and 100 mg/kg of body weight), while the rats in the control group received no treatment for 28 days. Reactive oxygen species (ROS), antioxidant enzyme activities (glutathione peroxidase [GPx], superoxide dismutase [SOD], and catalase [CAT]), glutathione (GSH) levels, and oxidation markers (such as lipid peroxidation [malondialdehyde (MDA)] and protein oxidation [protein carbonyl (PCO)]) were analyzed in the kidney tissue. Additionally, renal fibrogenesis was studied through histopathological examination and the expression levels of fibrotic biomarkers.

Results

The findings revealed that in vivo treatment with SiNPs significantly triggered oxidative stress in kidney tissues in a dose-dependent manner. This was characterized by increased production of ROS, elevated levels of MDA, PCO, and nitric oxide (NO), along with a significant decline in the activities of SOD, CAT, GPx, and reduced GSH. These changes were consistent with the histopathological analysis, which indicated interstitial fibrosis with mononuclear inflammatory cell aggregation, tubular degeneration, glomerulonephritis, and glomerular atrophy. The fibrosis index was confirmed using Masson's trichrome staining. Additionally, there was a significant upregulation of fibrosis-related genes, including transforming growth factor-beta 1 (TGF-β1), matrix metalloproteinases 2 and 9 (MMP-2/9), whereas the expression of tissue inhibitor of metalloproteinase 2 (TIMP2) was downregulated.

Conclusions

This study provided a new research clue for the role of ROS and deregulated TGF-β signaling pathway in SiNPs nephrotoxicity.

The critical role of osteopontin (OPN) in fibrotic diseases

Fibrosis is a pathological condition characterized by the excessive deposition of extracellular matrix components in tissues and organs, leading to progressive architectural remodelling and contributing to the development of various diseases. Osteopontin (OPN), a highly phosphorylated glycoprotein, has been increasingly recognized for its involvement in the progression of tissue fibrosis. This review provides a comprehensive overview of the genetic and protein structure of OPN and focuses on our current understanding of the role of OPN in the development of fibrosis in the lungs and other tissues. Additionally, special attention is given to the potential of OPN as a biomarker and a novel therapeutic target in the treatment of fibrosis.

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.

A spatially anchored transcriptomic atlas of the human kidney papilla identifies significant immune injury in patients with stone disease

Kidney stone disease causes significant morbidity and increases health care utilization. In this work, we decipher the cellular and molecular niche of the human renal papilla in patients with calcium oxalate (CaOx) stone disease and healthy subjects. In addition to identifying cell types important in papillary physiology, we characterize collecting duct cell subtypes and an undifferentiated epithelial cell type that was more prevalent in stone patients. Despite the focal nature of mineral deposition in nephrolithiasis, we uncover a global injury signature characterized by immune activation, oxidative stress and extracellular matrix remodeling. We also identify the association of MMP7 and MMP9 expression with stone disease and mineral deposition, respectively. MMP7 and MMP9 are significantly increased in the urine of patients with CaOx stone disease, and their levels correlate with disease activity. Our results define the spatial molecular landscape and specific pathways contributing to stone-mediated injury in the human papilla and identify associated urinary biomarkers.

Structural insights into regulation of CCN protein activities and functions

CCN proteins play important functions during development, in repair mechanisms following tissue injury, as well as in pathophysiologic mechanisms of metastasis of cancer. CCNs are secreted proteins that have a multimodular structure and are categorized as matricellular proteins. Although the prevailing view is that CCN proteins regulate biologic processes by interacting with a wide array of other proteins in the microenvironment of the extracellular matrix, the molecular mechanisms of action of CCN proteins are still poorly understood. Not dissuading the current view, however, the recent appreciation that these proteins are signaling proteins in their own right and may even be considered preproproteins controlled by endopeptidases to release a C-terminal bioactive peptide has opened new avenues of research. Also, the recent resolution of the crystal structure of two of the domains of CCN3 have provided new knowledge with implications for the entire CCN family. These resolved structures in combination with structural predictions based upon the AlphaFold artificial intelligence tool provide means to shed new light on CCN functions in context of the notable literature in the field. CCN proteins have emerged as important therapeutic targets in several disease conditions, and clinical trials are currently ongoing. Thus, a review that critically discusses structure - function relationship of CCN proteins, in particular as it relates to interactions with other proteins in the extracellular milieu and on the cell surface, as well as to cell signaling activities of these proteins, is very timely. Suggested mechanism for activation and inhibition of signaling by the CCN protein family (graphics generated with BioRender.com ).

MMP-3-mediated cleavage of OPN is involved in copper oxide nanoparticle-induced activation of fibroblasts

BACKGROUND

Copper oxide nanoparticles (Nano-CuO) are one of the most produced and used nanomaterials. Previous studies have shown that exposure to Nano-CuO caused acute lung injury, inflammation, and fibrosis. However, the mechanisms underlying Nano-CuO-induced lung fibrosis are still unclear. Here, we hypothesized that exposure of human lung epithelial cells and macrophages to Nano-CuO would upregulate MMP-3, which cleaved osteopontin (OPN), resulting in fibroblast activation and lung fibrosis.

METHODS

A triple co-culture model was established to explore the mechanisms underlying Nano-CuO-induced fibroblast activation. Cytotoxicity of Nano-CuO on BEAS-2B, U937* macrophages, and MRC-5 fibroblasts were determined by alamarBlue and MTS assays. The expression or activity of MMP-3, OPN, and fibrosis-associated proteins was determined by Western blot or zymography assay. Migration of MRC-5 fibroblasts was evaluated by wound healing assay. MMP-3 siRNA and an RGD-containing peptide, GRGDSP, were used to explore the role of MMP-3 and cleaved OPN in fibroblast activation.

RESULTS

Exposure to non-cytotoxic doses of Nano-CuO (0.5 and 1 µg/mL) caused increased expression and activity of MMP-3 in the conditioned media of BEAS-2B and U937* cells, but not MRC-5 fibroblasts. Nano-CuO exposure also caused increased production of cleaved OPN fragments, which was abolished by MMP-3 siRNA transfection. Conditioned media from Nano-CuO-exposed BEAS-2B, U937*, or the co-culture of BEAS-2B and U937* caused activation of unexposed MRC-5 fibroblasts. However, direct exposure of MRC-5 fibroblasts to Nano-CuO did not induce their activation. In a triple co-culture system, exposure of BEAS-2B and U937* cells to Nano-CuO caused activation of unexposed MRC-5 fibroblasts, while transfection of MMP-3 siRNA in BEAS-2B and U937* cells significantly inhibited the activation and migration of MRC-5 fibroblasts. In addition, pretreatment with GRGDSP peptide inhibited Nano-CuO-induced activation and migration of MRC-5 fibroblasts in the triple co-culture system.

CONCLUSIONS

Our results demonstrated that Nano-CuO exposure caused increased production of MMP-3 from lung epithelial BEAS-2B cells and U937* macrophages, which cleaved OPN, resulting in the activation of lung fibroblasts MRC-5. These results suggest that MMP-3-cleaved OPN may play a key role in Nano-CuO-induced activation of lung fibroblasts. More investigations are needed to confirm whether these effects are due to the nanoparticles themselves and/or Cu ions.

Analysis of the potential biological mechanisms of diosmin against renal fibrosis based on network pharmacology and molecular docking approach

BACKGROUND

Interstitial fibrosis is involved in the progression of various chronic kidney diseases and renal failure. Diosmin is a naturally occurring flavonoid glycoside that has antioxidant, anti-inflammatory, and antifibrotic activities. However, whether diosmin protects kidneys by inhibiting renal fibrosis is unknown.

METHODS

The molecular formula of diosmin was obtained, targets related to diosmin and renal fibrosis were screened, and interactions among overlapping genes were analyzed. Overlapping genes were used for gene function and KEGG pathway enrichment analysis. TGF-β1 was used to induce fibrosis in HK-2 cells, and diosmin treatment was administered. The expression levels of relevant mRNA were then detected.

RESULTS

Network analysis identified 295 potential target genes for diosmin, 6828 for renal fibrosis, and 150 hub genes. Protein-protein interaction network results showed that CASP3, SRC, ANXA5, MMP9, HSP90AA1, IGF1, RHOA, ESR1, EGFR, and CDC42 were identified as key therapeutic targets. GO analysis revealed that these key targets may be involved in the negative regulation of apoptosis and protein phosphorylation. KEGG indicated that pathways in cancer, MAPK signaling pathway, Ras signaling pathway, PI3K-Akt signaling pathway, and HIF-1 signaling pathway were key pathways for renal fibrosis treatment. Molecular docking results showed that CASP3, ANXA5, MMP9, and HSP90AA1 stably bind to diosmin. Diosmin treatment inhibited the protein and mRNA levels of CASP3, MMP9, ANXA5, and HSP90AA1. Network pharmacology analysis and experimental results suggest that diosmin ameliorates renal fibrosis by decreasing the expression of CASP3, ANXA5, MMP9, and HSP90AA1.

CONCLUSIONS

Diosmin has a potential multi-component, multi-target, and multi-pathway molecular mechanism of action in the treatment of renal fibrosis. CASP3, MMP9, ANXA5, and HSP90AA1 might be the most important direct targets of diosmin.

Aristolocholic acid I promotes renal tubular epithelial fibrosis by upregulating matrix metalloproteinase-9 expression via activating the C3a/C3aR axis of macrophages

Aristolochic acid I (AAI) can cause nephrotoxicity and is characterized by interstitial fibrosis. The C3a/C3aR axis of macrophages and matrix metalloproteinase-9 (MMP-9) play important roles in fibrosis, but whether they are involved in AAI-induced renal interstitial fibrosis and are related remains to be elucidated. In this study, we investigated whether C3a/C3aR axis of macrophages promotes renal interstitial fibrosis by regulating MMP-9 in aristolochic acid nephropathy (AAN). Intraperitoneal injection of AAI for 28 days successfully induced AAN in C57bl/6 mice. The content of C3a in the kidney of AAN mice was increased, and there was a significant distribution of macrophages in the renal tubules. The same results were observed in the in vitro experiment. We also explored the role and mechanism of macrophages after AAI administration in the epithelial-mesenchymal transformation (EMT) of renal tubular epithelial cells (RTECs) and found that AAI could activate the C3a/C3aR axis of macrophages to upregulate p65 expression in macrophages. p65 upregulated MMP-9 expression in macrophages not only directly but also by promoting the secretion if interleukin-6 by macrophages and then activating STAT3 in RTECs. The upregulation of MMP-9 expression could promote the EMT of RTECs. Taken together, our study demonstrated that the AAI-activated the C3a/C3aR axis of macrophages, which induced MMP-9 production, was one of the causes of renal interstitial fibrosis. Therefore, targeting the C3a/C3aR axis of macrophages is an effective therapeutic strategy for the prevention and treatment of renal interstitial fibrosis in AAN.

Androgen receptor blockade by flutamide down-regulates renal fibrosis, inflammation, and apoptosis pathways in male rats

AIM

this study aims to explore the effect of androgen receptor (AR) blockade by flutamide on some renal pathologic changes such as inflammation, apoptosis, and fibrosis in male rats.

MAIN METHODS

Firstly, we investigated the potential effect of AR blockade on renal inflammatory intermediates including IL-1β, IL-6, TNF-α, NF-Қβ proteins, and the renal gene expression of NF-Қβ. Besides inflammation, we also assessed the apoptosis pathways including the caspases 3 & 9, mTOR, pAKT proteins, and BAX gene expression. Besides inflammation and apoptosis pathways, we also investigated the effect of androgen blockade on renal fibrosis intermediates including vimentin, TGFβ-1, α-SMA, MMP-9, collagen type-III, collagen type-IV, and the renal expression of the col1A1 gene. Besides previous pathological pathways, we assessed the expression of chloride channel protein-5 (ClC-5), as an important regulator of many renal pathological changes. Finally, we assessed the impact of previous pathological changes on renal function at biochemical and pathological levels.

KEY FINDINGS

We found that AR blockade by flutamide was associated with the down-regulation of renal inflammation, apoptosis, and fibrosis markers. It was associated with expression down-regulation of IL-1β & IL-6, TNF-α, NF-Қβ, caspases 3 & 9, mTOR, MMP-9, collagens, TGFβ-1, and α-SMA. Away from down-regulation, we also found that AR blockade has upregulated ClC-5 and pAKT proteins.

SIGNIFICANCE

AR is a major player in androgens-induced nephrotoxicity. AR blockade downregulates renal fibrosis, inflammation, and apoptosis pathways. It may be helpful as a strategy for alleviation of renal side effects associated with some drugs. However; this needs further investigations.

Bioinformatics analysis reveals the potential role of matrix metalloproteinases in immunity and urolithiasis

Background

The pathogenesis of urolithiasis remains unclear, making the development of medications for treatment and prevention stagnant. Randall’s plaques (RPs) begin as interstitial calcium phosphate crystal deposits, grow outward and breach the renal papillary surface, acting as attachment for CaOx stones. Since matrix metalloproteinases (MMPs) can degrade all components of extracellular matrix (ECM), they might participate in the breach of RPs. Besides, MMPs can modulate the immune response and inflammation, which were confirmed to be involved in urolithiasis. We aimed to investigate the role of MMPs in the development of RPs and stone formation.

Methods

The public dataset GSE73680 was mined to identify differentially expressed MMPs (DEMMPs) between normal tissues and RPs. WGCNA and three machine learning algorithms were performed to screen the hub DEMMPs. In vitro experiments were conducted for validation. Afterwards, RPs samples were classified into clusters based on the hub DEMMPs expression. Differentially expressed genes (DEGs) between clusters were identified and functional enrichment analysis and GSEA were applied to explore the biological role of DEGs. Moreover, the immune infiltration levels between clusters were evaluated by CIBERSORT and ssGSEA.

Results

Five DEMMPs, including MMP1, MMP3, MMP9, MMP10, and MMP12, were identified between normal tissues and RPs, and all of them were elevated in RPs. Based on WGCNA and three machine learning algorithms, all of five DEMMPs were regarded as hub DEMMPs. In vitro validation found the expression of hub DEMMPs also increased in renal tubular epithelial cells under lithogenic environment. RPs samples were divided into two clusters and cluster A exhibited higher expression of hub DEMMPs compared to cluster B. Functional enrichment analysis and GSEA found DEGs were enriched in immune-related functions and pathways. Moreover, increased infiltration of M1 macrophages and enhanced levels of inflammation were observed in cluster A by immune infiltration analysis.

Conclusion

We assumed that MMPs might participate in RPs and stone formation through ECM degradation and macrophages-mediated immune response and inflammation. Our findings offer a novel perspective on the role of MMPs in immunity and urolithiasis for the first time, and provide potential biomarkers to develop targets for treatment and prevention.

Hesperidin protects against aluminum-induced renal injury in rats via modulating MMP-9 and apoptosis: biochemical, histological, and ultrastructural study

Aluminum, one of the most abundant metallic elements, is known to be toxic to multiple organs including the kidneys. This study aimed to investigate the pleiotropic nephroprotective effects of Hesperidin in aluminum chloride (ALCL3)-induced renal injury, highlighting the potential molecular mechanisms underlying. Twenty-four male albino rats were divided into four groups: control, Hesperidin (80 mg/kg BW, orally), ALCL3 (10 mg/kg BW, IP), and ALCL3 + Hesperidin groups. By the end of the study, blood samples were collected, and tissue samples were harvested at sacrifice. ALCL3 rats showed dramatically declined renal function, enhanced intrarenal oxidative stress, inflammation, apoptosis, and extravagant renal histopathological damage with interstitial fibrosis as shown by a higher Endothelial, Glomerular, Tubular, and Interstitial (EGTI) score. Hesperidin significantly reversed all the aforementioned detrimental effects in ALCL3-treated rats. The study verified the nephroprotective effects of Hesperidin on ALCL3-induced renal damage and confirmed the critical role of extracellular matrix (ECM) remodeling and apoptosis inhibition.

Urinary markers differentially associate with kidney inflammatory activity and chronicity measures in patients with lupus nephritis

OBJECTIVE

Lupus nephritis (LN) is diagnosed by biopsy, but longitudinal monitoring assessment methods are needed. Here, in this preliminary and hypothesis-generating study, we evaluate the potential for using urine proteomics as a non-invasive method to monitor disease activity and damage. Urinary biomarkers were identified and used to develop two novel algorithms that were used to predict LN activity and chronicity.

METHODS

Baseline urine samples were collected for four cohorts (healthy donors (HDs, n=18), LN (n=42), SLE (n=17) or non-LN kidney disease biopsy control (n=9)), and over 1 year for patients with LN (n=42). Baseline kidney biopsies were available for the LN (n=46) and biopsy control groups (n=9). High-throughput proteomics platforms were used to identify urinary analytes ≥1.5 SD from HD means, which were subjected to stepwise, univariate and multivariate logistic regression modelling to develop predictive algorithms for National Institutes of Health Activity Index (NIH-AI)/National Institutes of Health Chronicity Index (NIH-CI) scores. Kidney biopsies were analysed for macrophage and neutrophil markers using immunohistochemistry (IHC).

RESULTS

In total, 112 urine analytes were identified from LN, SLE and biopsy control patients as both quantifiable and overexpressed compared with HDs. Regression analysis identified proteins associated with the NIH-AI (n=30) and NIH-CI (n=26), with four analytes common to both groups, demonstrating a difference in the mechanisms associated with NIH-AI and NIH-CI. Pathway analysis of the NIH-AI and NIH-CI analytes identified granulocyte-associated and macrophage-associated pathways, and the presence of these cells was confirmed by IHC in kidney biopsies. Four markers each for the NIH-AI and NIH-CI were identified and used in the predictive algorithms. The NIH-AI algorithm sensitivity and specificity were both 93% with a false-positive rate (FPR) of 7%. The NIH-CI algorithm sensitivity was 88%, specificity 96% and FPR 4%. The accuracy for both models was 93%.

CONCLUSIONS

Longitudinal predictions suggested that patients with baseline NIH-AI scores of ≥8 were most sensitive to improvement over 6-12 months. Viable approaches such as this may enable the use of urine samples to monitor LN over time.

Glucosidase inhibitor, Nimbidiol ameliorates renal fibrosis and dysfunction in type-1 diabetes

Diabetic nephropathy is characterized by excessive accumulation of extracellular matrix (ECM) leading to renal fibrosis, progressive deterioration of renal function, and eventually to end stage renal disease. Matrix metalloproteinases (MMPs) are known to regulate synthesis and degradation of the ECM. Earlier, we demonstrated that imbalanced MMPs promote adverse ECM remodeling leading to renal fibrosis in type-1 diabetes. Moreover, elevated macrophage infiltration, pro-inflammatory cytokines and epithelial‒mesenchymal transition (EMT) are known to contribute to the renal fibrosis. Various bioactive compounds derived from the medicinal plant, Azadirachta indica (neem) are shown to regulate inflammation and ECM proteins in different diseases. Nimbidiol is a neem-derived diterpenoid that is considered as a potential anti-diabetic compound due to its glucosidase inhibitory properties. We investigated whether Nimbidiol mitigates adverse ECM accumulation and renal fibrosis to improve kidney function in type-1 diabetes and the underlying mechanism. Wild-type (C57BL/6J) and type-1 diabetic (C57BL/6-Ins2^Akita/J) mice were treated either with saline or with Nimbidiol (0.40 mg kg^-1 d^-1) for eight weeks. Diabetic kidney showed increased accumulation of M1 macrophages, elevated pro-inflammatory cytokines and EMT. In addition, upregulated MMP-9 and MMP-13, excessive collagen deposition in the glomerular and tubulointerstitial regions, and degradation of vascular elastin resulted to renal fibrosis in the Akita mice. These pathological changes in the diabetic mice were associated with functional impairments that include elevated resistive index and reduced blood flow in the renal cortex, and decreased glomerular filtration rate. Furthermore, TGF-β1, p-Smad2/3, p-P38, p-ERK1/2 and p-JNK were upregulated in diabetic kidney compared to WT mice. Treatment with Nimbidiol reversed the changes to alleviate inflammation, ECM accumulation and fibrosis and thus, improved renal function in Akita mice. Together, our results suggest that Nimbidiol attenuates inflammation and ECM accumulation and thereby, protects kidney from fibrosis and dysfunction possibly by inhibiting TGF-β/Smad and MAPK signaling pathways in type-1 diabetes.

Plasticity towards Rigidity: A Macrophage Conundrum in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic, and ultimately fatal diffuse parenchymal lung disease. The molecular mechanisms of fibrosis in IPF patients are not fully understood and there is a lack of effective treatments. For decades, different types of drugs such as immunosuppressants and antioxidants have been tested, usually with unsuccessful results. Although two antifibrotic drugs (Nintedanib and Pirfenidone) are approved and used for the treatment of IPF, side effects are common, and they only slow down disease progression without improving patients' survival. Macrophages are central to lung homeostasis, wound healing, and injury. Depending on the stimulus in the microenvironment, macrophages may contribute to fibrosis, but also, they may play a role in the amelioration of fibrosis. In this review, we explore the role of macrophages in IPF in relation to the fibrotic processes, epithelial-mesenchymal transition (EMT), and their crosstalk with resident and recruited cells and we emphasized the importance of macrophages in finding new treatments.

New insights into fibrosis from the ECM degradation perspective: the macrophage-MMP-ECM interaction

Fibrosis is a pathological feature of a variety of chronic inflammatory diseases that can affect almost all organs, which can cause severe consequences and even lead to death. Fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) due to disruption of the balance between ECM production and degradation. Although overabundance of ECM proteins has long been the focus of studies on fibrosis, another facet of the problem-impaired degradation of the ECM-is gaining increasing attention. Matrix metalloproteinase (MMP) and the tissue inhibitor of metalloproteinase (TIMP) system is the main molecular system contributing to ECM degradation, and macrophages are the major regulators of ECM. However, the relationship among macrophages, the MMP/TIMP system and the ECM is not fully understood in the context of fibrosis. Here, we discuss in detail the role played by the ECM in the development of fibrosis and highlight the macrophage-MMP-ECM interaction that is involved in fibrogenesis and may be a potential therapeutic target for fibrosis.

Interaction Between Intrinsic Renal Cells and Immune Cells in the Progression of Acute Kidney Injury

A growing number of studies have confirmed that immune cells play various key roles in the pathophysiology of acute kidney injury (AKI) development. After the resident immune cells and intrinsic renal cells are damaged by ischemia and hypoxia, drugs and toxins, more immune cells will be recruited to infiltrate through the release of chemokines, while the intrinsic cells promote macrophage polarity conversion, and the immune cells will promote various programmed deaths, phenotypic conversion and cycle arrest of the intrinsic cells, ultimately leading to renal impairment and fibrosis. In the complex and dynamic immune microenvironment of AKI, the bidirectional interaction between immune cells and intrinsic renal cells affects the prognosis of the kidney and the progression of fibrosis, and determines the ultimate fate of the kidney.

Association of osteopontin with kidney function and kidney failure in chronic kidney disease patients: the GCKD study

BACKGROUND

Osteopontin (OPN), synthesized in the thick ascending limb of Henle's loop and in the distal tubule, is involved in the pathogenesis of kidney fibrosis, a hallmark of kidney failure (KF). In a cohort of chronic kidney disease (CKD) patients, we evaluated OPN's association with kidney markers and KF.

METHODS

OPN was measured from baseline serum samples of German Chronic Kidney Disease study participants. Cross-sectional regression models for estimated glomerular filtration rate (eGFR) and urinary albumin-to-creatinine ratio (UACR) as well as Cox regression models for all-cause mortality and KF were evaluated to estimate the OPN effect. Additionally, predictive ability, of OPN and time-dependent population-attributable fraction were evaluated.

RESULTS

Over a median follow-up of 6.5 years, 471 KF events and 629 deaths occurred among 4,950 CKD patients. One-unit higher log(OPN) was associated with 5.5 mL/min/1.73m2 lower eGFR (95%CI: [-6.4,-4.6]) and 1% change in OPN with 0.7% higher UACR (estimated effect 0.7, 95%CI: [0.6,0.8]). Moreover, higher OPN levels were associated with a higher risk of KF (hazard ratio [HR] 1.4, 95%CI: [1.2,1.7]) and all-cause mortality (HR 1.5, 95%CI: [1.3,1.8]). After 6 years, 31% of the KF events could be attributed to higher OPN levels (95%CI: [3%,56%]).

CONCLUSIONS

In this study, higher OPN levels were associated with kidney function markers worsening, and a higher risk for adverse outcomes. A larger proportion of KF could be attributed to higher OPN levels warranting further research on OPN with regards to its role in CKD progression and possible treatment options.

Matrix metalloproteinase-21 promotes metastasis via increasing the recruitment and M2 polarization of macrophages in HCC

MMP-21 is a newly identified member of the matrix metalloproteinase family and has been reported to regulate both embryonic development and tumor progression. However, the roles of MMP-21 in hemofiltrate C-C chemokine (HCC) remain largely unclear. In this study, we used western blot, qPCR and immunohistochemistry (IHC) to determine the upregulation of MMP-21 in HCC tissues, and showed that the increase in MMP-21 was associated with vascular invasion and poor prognosis. Although changing levels of MMP-21 in HCC cell lines had no significant effect on cell migration or invasion abilities in in vitro transwell tests, both IHC analysis and in vivo mouse models proved that upregulated MMP-21 promoted metastasis. Functional enrichments of MMP-21 using The Cancer Genome Atlas (TCGA) data suggested that MMP-21 might regulate metastasis via macrophages. Further experiments proved that MMP-21 enhanced macrophage recruitment by increasing CCL-14 levels and promoted M2-type polarization of macrophage by elevating the expression of CSF-1 and FGF-1. Taken together, this study revealed that MMP-21 controlled the tumor microenvironment remodeling and functional regulation of macrophages to regulate HCC metastasis.

CircACTR2 in macrophages promotes renal fibrosis by activating macrophage inflammation and epithelial-mesenchymal transition of renal tubular epithelial cells

The crosstalk between macrophages and tubular epithelial cells (TECs) actively regulates the progression of renal fibrosis. In the present study, we revealed the significance of circular RNA ACTR2 (circACTR2) in regulating macrophage inflammation, epithelial-mesenchymal transition (EMT) of TECs, and the development of renal fibrosis. Our results showed UUO-induced renal fibrosis was associated with increased inflammation and EMT, hypertrophy of contralateral kidney, up-regulations of circACTR2 and NLRP3, and the down-regulation of miR-561. CircACTR2 sufficiently and essentially promoted the activation of NLRP3 inflammasome, pyroptosis, and inflammation in macrophages, and through paracrine effect, stimulated EMT and fibrosis of TECs. Mechanistically, circACTR2 sponged miR-561 and up-regulated NLRP3 expression level to induce the secretion of IL-1β. In TECs, IL-1β induced renal fibrosis via up-regulating fascin-1. Knocking down circACTR2 or elevating miR-561 potently alleviated renal fibrosis in vivo. In summary, circACTR2, by sponging miR-561, activated NLRP3 inflammasome, promoted macrophage inflammation, and stimulated macrophage-induced EMT and fibrosis of TECs. Knocking down circACTR2 and overexpressing miR-561 may, thus, benefit the treatment of renal fibrosis.

Senescent macrophages alter fibroblast fibrogenesis in response to SARS-CoV-2 infection

SARS-CoV-2 has, since its emergence in 2019, become a global pandemic. Disease outcomes are worsened in older patients who are infected. The causes for this is multifactorial, but one potential cause for this disparity is increased rates of cellular senescence in older individuals, particularly in immune cells. Cellular senescence, the accumulation of factors resulting in cell growth arrest and apoptosis resistance, increases as individuals age. In immune cells, senescence is associated with increased inflammation, and alterations in immune response. We utilized a co-culture system consisting of senescent or non-senescent macrophages directly cultured with fibroblasts, and infected with SARS-CoV-2. We assessed the expression of collagen and fibronectin, important molecules in the extracellular matrix, as well as a number of fibrogenic factors. We observed that infection with SARS-CoV-2 induced collagen production in co-cultures with senescent, but not non-senescent macrophages. Fibronectin expression was decreased in both co-culture conditions. While significant results were not observed, concentrations of other fibrogenic molecules were consistent with the collagen results. These data demonstrate that senescence in macrophages alters the production of fibrotic molecules from fibroblasts in a SARS-CoV-2 infection model. As collagen and fibronectin expression are generally directly correlated, this suggests that senescence dysregulates fibrogenesis in response to infection with SARS-CoV-2. There is a need to further investigate the mechanisms for these changes.

mTOR activity is essential for retinal pigment epithelium regeneration in zebrafish

The retinal pigment epithelium (RPE) plays numerous critical roles in maintaining vision and this is underscored by the prevalence of degenerative blinding diseases like age-related macular degeneration (AMD), in which visual impairment is caused by progressive loss of RPE cells. In contrast to mammals, zebrafish possess the ability to intrinsically regenerate a functional RPE layer after severe injury. The molecular underpinnings of this regenerative process remain largely unknown yet hold tremendous potential for developing treatment strategies to stimulate endogenous regeneration in the human eye. In this study, we demonstrate that the mTOR pathway is activated in RPE cells post-genetic ablation. Pharmacological and genetic inhibition of mTOR activity impaired RPE regeneration, while mTOR activation enhanced RPE recovery post-injury, demonstrating that mTOR activity is essential for RPE regeneration in zebrafish. RNA-seq of RPE isolated from mTOR-inhibited larvae identified a number of genes and pathways dependent on mTOR activity at early and late stages of regeneration; amongst these were components of the immune system, which is emerging as a key regulator of regenerative responses across various tissue and model systems. Our results identify crosstalk between macrophages/microglia and the RPE, wherein mTOR activity is required for recruitment of macrophages/microglia to the RPE injury site. Macrophages/microglia then reinforce mTOR activity in regenerating RPE cells. Interestingly, the function of macrophages/microglia in maintaining mTOR activity in the RPE appeared to be inflammation-independent. Taken together, these data identify mTOR activity as a key regulator of RPE regeneration and link the mTOR pathway to immune responses in facilitating RPE regeneration.

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.

Olfactory receptors contribute to progression of kidney fibrosis

Olfactory receptors (ORs) which are mainly known as odor-sensors in the olfactory epithelium are shown to be expressed in several non-sensory tissues. Despite the specified role of some of these receptors in normal physiology of the kidney, little is known about their potential effect in renal disorders. In this study, using the holistic view of systems biology, it was determined that ORs are significantly changed during the progression of kidney fibrosis. For further validation, common differentially expressed ORs resulted from reanalysis of two time-course microarray datasets were selected for experimental evaluation in a validated murine model of unilateral ureteral obstruction (UUO). Transcriptional analysis by real-time quantitative polymerase chain reaction demonstrated considerable changes in the expression pattern of Olfr433, Olfr129, Olfr1393, Olfr161, and Olfr622 during the progression of kidney fibrosis. For localization of these ORs, single-cell RNA-sequencing datasets of normal and UUO mice were reanalyzed. Results showed that Olfr433 is highly expressed in macrophages in day-2 and 7 post-injury in UUO mice and not in normal subgroups. Besides, like previous findings, Olfr1393 was shown to be expressed prominently in the proximal tubular cells of the kidney. In conclusion, our combinatorial temporal approach to the underlying mechanisms of chronic kidney disease highlighted the potential role of ORs in progression of fibrosis. The expression of Olfr433 in the macrophages provides some clue about its relation to molecular mechanisms promoted in the fibrotic kidney. The proposed ORs in this study could be the subject of further functional assessments in the future.

Inhibition of renal fibrosis with a human CXCL9‐derived glycosaminoglycan‐binding peptide

Objectives

Renal fibrosis accompanies all chronic kidney disorders, ultimately leading to end‐stage kidney disease and the need for dialysis or even renal replacement. As such, renal fibrosis poses a major threat to global health and the search for effective therapeutic strategies to prevent or treat fibrosis is highly needed. We evaluated the applicability of a highly positively charged human peptide derived from the COOH‐terminal domain of the chemokine CXCL9, namely CXCL9(74–103), for therapeutic intervention. Because of its high density of net positive charges at physiological pH, CXCL9(74–103) competes with full‐length chemokines for glycosaminoglycan (GAG) binding. Consequently, CXCL9(74–103) prevents recruitment of inflammatory leucocytes to sites of inflammation.

Methods

CXCL9(74–103) was chemically synthesised and tested in vitro for anti‐fibrotic properties on human fibroblasts and in vivo in the unilateral ureteral obstruction (UUO) mouse model.

Results

CXCL9(74–103) significantly reduced the mRNA and/or protein expression of connective tissue growth factor (CTGF), alpha‐smooth muscle actin (α‐SMA) and collagen III by transforming growth factor (TGF)‐β1‐stimulated human fibroblasts. In addition, administration of CXCL9(74–103) inhibited fibroblast migration towards platelet‐derived growth factor (PDGF), without affecting cell viability. In the UUO model, CXCL9(74–103) treatment significantly decreased renal α‐SMA, vimentin, and fibronectin mRNA and protein expression. Compared with vehicle, CXCL9(74–103) attenuated mRNA expression of TGF‐β1 and the inflammatory markers/mediators MMP‐9, F4/80, CCL2, IL‐6 and TNF‐α. Finally, CXCL9(74–103) treatment resulted in reduced influx of leucocytes in the UUO model and preserved tubular morphology. The anti‐fibrotic and anti‐inflammatory effects of CXCL9(74–103) were mediated by competition with chemokines and growth factors for GAG binding.

Conclusions

Our findings provide a scientific rationale for targeting GAG–protein interactions in renal fibrotic disease.

Molecular Mechanisms of Kidney Injury and Repair

Chronic kidney disease (CKD) will become the fifth global cause of death by 2040, thus emphasizing the need to better understand the molecular mechanisms of damage and regeneration in the kidney. CKD predisposes to acute kidney injury (AKI) which, in turn, promotes CKD progression. This implies that CKD or the AKI-to-CKD transition are associated with dysfunctional kidney repair mechanisms. Current therapeutic options slow CKD progression but fail to treat or accelerate recovery from AKI and are unable to promote kidney regeneration. Unraveling the cellular and molecular mechanisms involved in kidney injury and repair, including the failure of this process, may provide novel biomarkers and therapeutic tools. We now review the contribution of different molecular and cellular events to the AKI-to-CKD transition, focusing on the role of macrophages in kidney injury, the different forms of regulated cell death and necroinflammation, cellular senescence and the senescence-associated secretory phenotype (SAPS), polyploidization, and podocyte injury and activation of parietal epithelial cells. Next, we discuss key contributors to repair of kidney injury and opportunities for their therapeutic manipulation, with a focus on resident renal progenitor cells, stem cells and their reparative secretome, certain macrophage subphenotypes within the M2 phenotype and senescent cell clearance.

Doxycycline Alters the Porcine Renal Proteome and Degradome during Hypothermic Machine Perfusion

Ischemia-reperfusion injury (IRI) is a hallmark for tissue injury in donation after circulatory death (DCD) kidneys. The implementation of hypothermic machine perfusion (HMP) provides a platform for improved preservation of DCD kidneys. Doxycycline administration has shown protective effects during IRI. Therefore, we explored the impact of doxycycline on proteolytic degradation mechanisms and the urinary proteome of perfused kidney grafts. Porcine kidneys underwent 30 min of warm ischemia, 24 h of oxygenated HMP (control/doxycycline) and 240 min of ex vivo reperfusion. A proteomic analysis revealed distinctive clustering profiles between urine samples collected at T15 min and T240 min. High-efficiency undecanal-based N-termini (HUNTER) kidney tissue degradomics revealed significantly more proteolytic activity in the control group at T-10. At T240, significantly more proteolytic activity was observed in the doxycycline group, indicating that doxycycline alters protein degradation during HMP. In conclusion, doxycycline administration during HMP led to significant proteomic and proteolytic differences and protective effects by attenuating urinary NGAL levels. Ultimately, we unraveled metabolic, and complement and coagulation pathways that undergo alterations during machine perfusion and that could be targeted to attenuate IRI induced injury.

Immune Mechanisms and Related Targets for the Treatment of Fibrosis in Various Organs

Inflammation and fibrosis are two inter-related disease pathologies with several overlapping components. Three specific cell types, macrophages, T helper cells and myofibroblasts, each play important roles in regulating both processes. Following tissue injury, an inflammatory stimulus is often necessary to initiate tissue repair, where cytokines released from infiltrating and resident immune and inflammatory cells stimulate the proliferation and activation of extracellular matrix-producing myofibroblasts. However, persistent tissue injury drives an inappropriate pro-fibrotic response. Additionally, activated myofibroblasts can take on the role of traditional antigen-presenting cells, secrete pro-inflammatory cytokines, and recruit inflammatory cells to fibrotic foci, amplifying the fibrotic response in a vicious cycle. Moreover, inflammatory cells have been shown to play contradictory roles in the initiation, amplification and resolution of fibrotic disease processes. The central role of the inflammasome molecular platform in contributing to fibrosis is only beginning to be fully appreciated. In this review, we discuss the immune mechanisms that can lead to fibrosis, the inflammasomes that have been implicated in the fibrotic process in the context of the immune response to injury, and also discuss current and emerging therapies that target inflammasome-induced collagen deposition to treat organ fibrosis.

Matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases in kidney disease

Matrix metalloproteinases (MMPs) are a group of zinc and calcium endopeptidases which cleave extracellular matrix (ECM) proteins. They are also involved in the degradation of cell surface components and regulate multiple cellular processes, cell to cell interactions, cell proliferation, and cell signaling pathways. MMPs function in close interaction with the endogenous tissue inhibitors of matrix metalloproteinases (TIMPs), both of which regulate cell turnover, modulate various growth factors, and participate in the progression of tissue fibrosis and apoptosis. The multiple roles of MMPs and TIMPs are continuously elucidated in kidney development and repair, as well as in a number of kidney diseases. This chapter focuses on the current findings of the significance of MMPs and TIMPs in a wide range of kidney diseases, whether they result from kidney tissue changes, hemodynamic alterations, tubular epithelial cell apoptosis, inflammation, or fibrosis. In addition, the potential use of these endopeptidases as biomarkers of renal dysfunction and as targets for therapeutic interventions to attenuate kidney disease are also explored in this review.

Is the Macrophage Phenotype Determinant for Fibrosis Development?

Fibrosis is a pathophysiological process of wound repair that leads to the deposit of connective tissue in the extracellular matrix. This complication is mainly associated with different pathologies affecting several organs such as lung, liver, heart, kidney, and intestine. In this fibrotic process, macrophages play an important role since they can modulate fibrosis due to their high plasticity, being able to adopt different phenotypes depending on the microenvironment in which they are found. In this review, we will try to discuss whether the macrophage phenotype exerts a pivotal role in the fibrosis development in the most important fibrotic scenarios.

Tubular lysosomes harbor active ion gradients and poise macrophages for phagocytosis

Lysosomes are organelles that also act as cell-signaling hubs. They regulate functions ranging from antigen presentation to autophagy. Spherical lysosomes can spontaneously elongate into tubules in starving or inflamed immune cells. We describe a DNA-based reagent, denoted Tudor, that tubulates lysosomes in macrophages without triggering either an immune response or autophagy. Chemical imaging revealed that tubular lysosomes differ from vesicular ones in terms of their pH, calcium, and proteolytic activity. Tudor revealed a role for tubular lysosomes in that they enhance MMP9 secretion and phagocytosis in resting macrophages. The ability to tubulate lysosomes in resting immune cells without starving or inflaming them may help reveal new insights into how tubular lysosomes function.

Lysosomes adopt dynamic, tubular states that regulate antigen presentation, phagosome resolution, and autophagy. Tubular lysosomes are studied either by inducing autophagy or by activating immune cells, both of which lead to cell states where lysosomal gene expression differs from the resting state. Therefore, it has been challenging to pinpoint the biochemical properties lysosomes acquire upon tubulation that could drive their functionality. Here we describe a DNA-based assembly that tubulates lysosomes in macrophages without activating them. Proteolytic activity maps at single-lysosome resolution revealed that tubular lysosomes were less degradative and showed proximal to distal luminal pH and Ca²⁺ gradients. Such gradients had been predicted but never previously observed. We identify a role for tubular lysosomes in promoting phagocytosis and activating MMP9. The ability to tubulate lysosomes without starving or activating immune cells may help reveal new roles for tubular lysosomes.

GYY4137 Regulates Extracellular Matrix Turnover in the Diabetic Kidney by Modulating Retinoid X Receptor Signaling

Diabetic kidney is associated with an accumulation of extracellular matrix (ECM) leading to renal fibrosis. Dysregulation of retinoic acid metabolism involving retinoic acid receptors (RARs) and retinoid X receptors (RXRs) has been shown to play a crucial role in diabetic nephropathy (DN). Furthermore, RARs and peroxisome proliferator-activated receptor γ (PPARγ) are known to control the RXR-mediated transcriptional regulation of several target genes involved in DN. Recently, RAR and RXR have been shown to upregulate plasminogen activator inhibitor-1 (PAI-1), a major player involved in ECM accumulation and renal fibrosis during DN. Interestingly, hydrogen sulfide (H₂S) has been shown to ameliorate adverse renal remodeling in DN. We investigated the role of RXR signaling in the ECM turnover in diabetic kidney, and whether H₂S can mitigate ECM accumulation by modulating PPAR/RAR-mediated RXR signaling. We used wild-type (C57BL/6J), diabetic (C57BL/6-Ins2^Akita/J) mice and mouse mesangial cells (MCs) as experimental models. GYY4137 was used as a H₂S donor. Results showed that in diabetic kidney, the expression of PPARγ was decreased, whereas upregulations of RXRα, RXRβ, and RARγ1 expression were observed. The changes were associated with elevated PAI-1, MMP-9 and MMP-13. In addition, the expressions of collagen IV, fibronectin and laminin were increased, whereas elastin expression was decreased in the diabetic kidney. Excessive collagen deposition was observed predominantly in the peri-glomerular and glomerular regions of the diabetic kidney. Immunohistochemical localization revealed elevated expression of fibronectin and laminin in the glomeruli of the diabetic kidney. GYY4137 reversed the pathological changes. Similar results were observed in in vitro experiments. In conclusion, our data suggest that RXR signaling plays a significant role in ECM turnover, and GYY4137 modulates PPAR/RAR-mediated RXR signaling to ameliorate PAI-1-dependent adverse ECM turnover in DN.

The Role of Myeloid Cells in Acute Kidney Injury and Kidney Repair

AKI remains highly prevalent, yet no optimal therapy is available to prevent it or promote recovery after initial insult. Experimental studies have demonstrated that both innate and adaptive immune responses play a central role during AKI. In response to injury, myeloid cells are first recruited and activated on the basis of specific signals from the damaged microenvironment. The subsequent recruitment and activation state of the immune cells depends on the stage of injury and recovery, reflecting a dynamic and diverse spectrum of immunophenotypes. In this review, we highlight our current understanding of the mechanisms by which myeloid cells contribute to injury, repair, and fibrosis after AKI.

Redox signaling pathways in unilateral ureteral obstruction (UUO)-induced renal fibrosis

Unilateral ureteral obstruction (UUO) is an experimental rodent model that mimics renal fibrosis associated with obstructive nephropathy in an accelerated manner. After UUO, the activation of the renin-angiotensin system (RAS), nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) and mitochondrial dysfunction lead to reactive oxygen species (ROS) overproduction in the kidney. ROS are secondary messengers able to induce post-translational modifications (PTMs) in redox-sensitive proteins, which activate or deactivate signaling pathways. Therefore, in UUO, it has been proposed that ROS overproduction causes changes in said pathways promoting inflammation, oxidative stress, and apoptosis that contribute to fibrosis development. Furthermore, mitochondrial metabolism impairment has been associated with UUO, contributing to renal damage in this model. Although ROS production and oxidative stress have been studied in UUO, the development of renal fibrosis associated with redox signaling pathways has not been addressed. This review focuses on the current information about the activation and deactivation of signaling pathways sensitive to a redox state and their effect on mitochondrial metabolism in the fibrosis development in the UUO model.

The Role of Macrophages in Kidney Fibrosis

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