Role of MCP-1/CCR2 axis in renal fibrosis: Mechanisms and therapeutic targeting

TGF-β: elusive target in diabetic kidney disease

Transforming growth factor-beta (TGF-β), a cytokine with near omnipresence, is an integral part of many vital cellular processes across the human body. The family includes three isoforms: Transforming growth factor-beta 1, 2, and 3. These cytokines play a significant role in the fibrosis cascade. Diabetic kidney disease (DKD), a major complication of diabetes, is increasing in prevalence daily, and the classical diagnosis of diabetes is based on the presence of albuminuria. The occurrence of nonalbuminuric DKD has provided new insight into the pathogenesis of this disease. The emphasis on multifactorial pathways involved in developing DKD has highlighted some markers associated with tissue fibrosis. In diabetic nephropathy, TGF-β is significantly involved in its pathology. Its presence in serum and urine means that it could be a diagnostic tool while its regulation provides potential therapeutic targets. Completely blocking TGF-β signaling could reach untargeted regions and cause unanticipated effects. This paper reviews the basic details of TGF-β as a cytokine, its role in DKD, and updates on research carried out to validate its candidacy.

Advances and challenges in kidney fibrosis therapeutics

Chronic kidney disease (CKD) is a major global health burden that affects more than 10% of the adult population. Current treatments, including dialysis and transplantation, are costly and not curative. Kidney fibrosis, defined as an abnormal accumulation of extracellular matrix in the kidney parenchyma, is a common outcome in CKD, regardless of disease aetiology, and is a major cause of loss of kidney function and kidney failure. For this reason, research efforts have focused on identifying mediators of kidney fibrosis to inform the development of effective anti-fibrotic treatments. Given the prominent role of the transforming growth factor-β (TGFβ) family in fibrosis, efforts have focused on inhibiting TGFβ signalling. Despite hopes raised by the efficacy of this approach in preclinical models, translation into clinical practice has not met expectations. Antihypertensive and antidiabetic drugs slow the decline in kidney function and could slow fibrosis but, owing to the lack of technologies for in vivo renal imaging, their anti-fibrotic effect cannot be truly assessed at present. The emergence of new drugs targeting pro-fibrotic signalling, or enabling cell repair and cell metabolic reprogramming, combined with better stratification of people with CKD and the arrival of nanotechnologies for kidney-specific drug delivery, open up new perspectives for the treatment of this major public health challenge.

Therapeutically Induced Lymphangiogenesis Is Ineffective in Resolving Established Kidney Disease in Mice

Key Points

Background

CKD counts AKI as one of its many underlying causes. Lymphatic vessels are important in modulating inflammation postinjury. Manipulating lymphatic vessel expansion thus has the potential to alter CKD progression. Previously, we demonstrated that renal lymphatic expansion before injury reduced CKD progression after an AKI. Here, we test whether inducing lymphangiogenesis affects established CKD.

Methods

After CKD progression, kidney lymphatics were expanded by transgenic induction of kidney-specific overexpression of vascular endothelial growth factor-D in aristolochic acid (AA) nephropathy and cisplatin injury aggravated with chronic high phosphate diet (CisPi) models or by infusion of kidney-targeting nanoparticles loaded with the vascular endothelial growth factor receptor-3 specific ligand vascular endothelial growth factor-C C156S in a progressive proteinuria (POD) model. Renal fibrosis and lymphatic density were determined by picrosirius red staining and immunofluorescence, respectively. Renal function was assessed by creatinine clearance rate, serum creatinine, BUN, and urinary albumin-creatinine ratio. Renal proinflammatory and fibrotic markers expression were measured by quantitative RT-PCR.

Results

Kidney-specific overexpression of vascular endothelial growth factor-D+ mice demonstrated expanded renal lymphatics, while nanoparticles treatment minimally expanded lymphatics. In neither the AA nor POD model did lymphangiogenesis improve renal function or fibrosis. AA mice showed decreased Tgfb1 expression and POD mice showed increased Col4a1 expression. Expansion worsened function in CisPi CKD and increased fibrosis. CisPi kidneys also demonstrated increased expression of Mcp-1, Il1b, Col1a1, and Tgfb1 and increased macrophage numbers.

Conclusions

Therapeutically induced lymphatic expansion is ineffective in resolving established CKD and has the potential to further worsen CKD progression.

Dressed in Collagen: 2D and 3D Cardiac Fibrosis Models

Cardiovascular diseases (CVD), the leading cause of death worldwide, and their strong association with fibrosis highlight the pressing need for innovative antifibrotic therapies. In vitro models have emerged as valuable tools for replicating cardiac fibrosis 'in a dish', facilitating the study of disease mechanisms and serving as platforms for drug testing and development. These in vitro systems encompass 2D and 3D models, each with its own limitations and advantages. 2D models offer high reproducibility, cost-effectiveness, and high-throughput capabilities, but they oversimplify the complex fibrotic environment. On the other hand, 3D models provide greater biological relevance but are more complex, harder to reproduce, and less suited for high-throughput screening. The choice of model depends on the specific research question and the stage of drug development. Despite significant progress, challenges remain, including the integration of immune cells in cardiac fibrosis and optimizing the scalability and throughput of highly biomimetic systems. Herein, we review recent in vitro cardiac fibrosis models, with a focus on their shared characteristics and remaining challenges, and explore how in vitro fibrosis models of other organs could inspire novel approaches in cardiac research, showcasing potential strategies that could be adapted to refine myocardial fibrosis models.

The Diagnostic Value of Serum MCP-1 Combined with OPN Detection for Early Renal Injury in Gout Patients

Objective

To explore the changes in serum Monocyte chemoattractant protein-1 (MCP-1) and Osteopontin (OPN) in gout patients and their diagnostic value for early renal injury.

Methods

In this research, 174 gout patients (January 2022-October 2024) were divided into the early renal injury group (50 cases) and non-early renal injury group (124 cases). Additionally, 169 healthy individuals were included as controls. Clinical indicators such as serum creatinine, cystatin C (CysC), and GFR were recorded. MCP-1 and OPN levels were measured using ELISA. Pearson's correlation was used to analyze relationships; Logit regression was applied to identify influencing factors, and ROC curves assessed diagnostic value, with AUC comparisons via Z-test.

Results

Serum MCP-1 and OPN levels were significantly higher in the gout group compared to controls (P<0.05) and further elevated in the early renal injury group (P<0.05). MCP-1 and OPN correlated positively with creatinine and CysC and negatively with GFR (P<0.05). Logit regression identified MCP-1 (OR: 2.765, 95% CI: 1.308-5.846) and OPN (OR: 3.019, 95% CI: 1.468-6.210) as independent risk factors (P<0.05). The AUC for diagnosing early renal injury was 0.775 (MCP-1), 0.827 (OPN), and 0.938 (combined), with the combination significantly outperforming either marker alone (Z=3.075, 2.273, P<0.05).

Conclusion

The combination of serum MCP-1 and OPN in gout patients has a higher diagnostic value for early renal injury, it is obviously higher than the individual diagnosis of each indicator, and demonstrates significant clinical implications.

Effect of immunostimulatory RNA on the fibrosis development in Bleomycin- or LPS-induced mouse models

Previously, we described a 19-base pair double-stranded RNA with 3'-trinucleotide overhangs, acting as immunostimulatory RNA (isRNA). This molecule demonstrated notable antiproliferative effects on cancer cells, inhibited tumor growth, and elicited immunostimulatory and antiviral responses by inducing cytokine and interferon production. Within this study, we compared the efficiency of lung fibrosis development, initiated in mice by BLM or LPS using different schemes of induction. Then we compared the effect of isRNA used in a preventive or therapeutic regimen on the development of fibrosis in selected BLM- and LPS-induced mouse models and showed that isRNA can be used in pathological conditions accompanied by the development of inflammation and the risk of fibrosis formation, without adverse side effects. Prophylactic regimen of isRNA application is beneficial for prevention of the development of pulmonary fibrosis.

Prostatic Escherichia coli infection drives CCR2-dependent recruitment of fibrocytes and collagen production

Prostate fibrosis contributes to lower urinary tract dysfunction (LUTD). To develop targeted treatments for prostate fibrosis, it is necessary to identify the cell types and molecular pathways required for collagen production. We used a genetic approach to label and track potential collagen-producing cell lineages in mouse prostate through a round of Escherichia coli UTI89-mediated prostate inflammation. E. coli increased collagen density and production in Gli1+, S100a4+, Lyz2+ and Cd2+ cell lineages, but not in Myh11+ or Srd5a2+ cell lineages, in the mouse prostate. Molecular phenotyping revealed GLI1+LYZ+S100A4+ cells (fibrocytes) in histologically inflamed human prostate. These fibrocytes colocalized with regions of increased collagen in men with LUTD. Fibrocyte recruitment and collagen synthesis was impaired in Ccr2 null mice but restored by allotransplantation of Rosa-GFP donor bone marrow-derived cells. These results suggest that bone marrow-derived fibrocytes are a mediator of prostatic collagen accumulation.

LLLT accelerates experimental wound healing under microgravity conditions via PI3K/AKT-CCR2 signal axis

Background and Purpose

The risk of skin injuries in space is increasing with longer space missions and a growing astronaut population. This highlights the importance of understanding the adverse effects of weightlessness on wound healing. The objective of this research was to examine the therapeutic potential of Low-Level Light Therapy (LLLT) on skin healing processes under simulated microgravity (SMG) conditions and uncover the underlying molecular mechanisms, thus providing innovative solutions and a sound theoretical basis for space skin injuries.

Methods

Hindlimb unloading (HU) mice models were used to simulate weightlessness conditions, with or without a complete management of LLLT for 14 days. A systematic testing consisting of HE, Masson and immunohistochemical staining was performed against the standardized mouse tissue specimens. In vitro assessment of cellular biological functions under SMG conditions was carried out in the rotation system of culture (RSOC) using HaCaT and NIH3T3 cell-lines.

Results

Under SMG conditions, LLLT significantly reduced skin wound area in HU mice, especially on Days 10 (p < 0.001), accompanied by increased collagen deposition and elevated levels of Ki67 and CD31. Moreover, LLLT showed impressive anti-inflammatory effects represented by the reduced in pro-inflammatory markers including LY6G, F4/80 and CD86, as well as the decreased levels of IL-1β, IL-6 and TNF-α. Conversely, an elevation in the anti-inflammatory marker CD206 was observed. By employing bioinformatics technology, we further found the PI3K/AKT signaling was prominent in the KEGG pathway analysis and CCR2 acted as a hub gene in the interaction network. Therefore, we demonstrated that LLLT could enhance the phosphorylation of PI3K/AKT and reduce CCR2 expression under SMG conditions, while CCR2 knockdown promoted the phosphorylation of PI3K/AKT, suggesting an important role of CCR2/PI3K/AKT signal axis in LLLT-accelerated wound healing under SMG conditions.

Conclusion

LLLT induced activation of the PI3K/AKT signaling pathway through suppression of CCR2 expression, which significantly enhanced skin wound healing under SMG conditions.s.

DaiTongXiao improves gout nephropathy by inhibiting inflammatory response through the TLR4/MyD88/NF-κB pathway

Introduction: Gouty nephropathy (GN) arises from factors like excessive purine intake, metabolic disorders or abnormal synthesis, and uric acid hypersaturation in the blood, leading to urate crystal deposition in kidney tissue. DaiTongXiao (DTX) is a remedy used by the Dai people of China. It shows efficacy in lowering uric acid levels and exhibits anti-inflammatory and kidney-protective properties. Methods: A GN rat model was induced using adenine and potassium oxonate. Following DTX administration, various parameters were assessed in urine, serum, and kidney tissue. Western blot analysis evaluated TLR4/MyD88/NF-κB signaling proteins, while immunofluorescence examined NF-κB nuclear expression. Results: DTX treatment improved kidney morphology, increased body weight, and kidney index and enhanced urinary levels of blood urea nitrogen (Bun), 24-h urinary protein, uric acid (UA), and allantoin in GN rats, reducing UA, Bun, creatinine (Cre), cystatin C (CysC), serum amyloid A (SAA), α1-microglobulin (MG), and β2-MG in serum analysis. Renal tissue assessments showed decreased xanthine oxidase (XOD), hydroxyproline (Hyp), α-smooth muscle actin (α-SMA), and collage type Ⅳ (COL-Ⅳ). Kidney damage severity was notably reduced. DTX lowered serum inflammatory factors like interleukin (IL) -18, tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), transforming growth factor-β1 (TGF-β1), and IL-1β in the rat serum, reducing chemokine monocyte chemoattractant protein-1 (MCP-1) and adhesion factor vascular cell adhesion molecule-1(VCAM-1). Western blotting demonstrated the downregulation of TLR4/MyD88/NF-κB pathway proteins, and immunofluorescence revealed reduced NF-κB expression in renal tissue. Discussion: DTX exhibits significant anti-GN effects by modulating TLR4/MyD88/ NF-κB pathway protein expression, reducing inflammatory factor release, and inhibiting GN progression.

Renal macrophages and NLRP3 inflammasomes in kidney diseases and therapeutics

Macrophages are exceptionally diversified cell types and perform unique features and functions when exposed to different stimuli within the specific microenvironment of various kidney diseases. In instances of kidney tissue necrosis or infection, specific patterns associated with damage or pathogens prompt the development of pro-inflammatory macrophages (M1). These M1 macrophages contribute to exacerbating tissue damage, inflammation, and eventual fibrosis. Conversely, anti-inflammatory macrophages (M2) arise in the same circumstances, contributing to kidney repair and regeneration processes. Impaired tissue repair causes fibrosis, and hence macrophages play a protective and pathogenic role. In response to harmful stimuli within the body, inflammasomes, complex assemblies of multiple proteins, assume a pivotal function in innate immunity. The initiation of inflammasomes triggers the activation of caspase 1, which in turn facilitates the maturation of cytokines, inflammation, and cell death. Macrophages in the kidneys possess the complete elements of the NLRP3 inflammasome, including NLRP3, ASC, and pro-caspase-1. When the NLRP3 inflammasomes are activated, it triggers the activation of caspase-1, resulting in the release of mature proinflammatory cytokines (IL)-1β and IL-18 and cleavage of Gasdermin D (GSDMD). This activation process therefore then induces pyroptosis, leading to renal inflammation, cell death, and renal dysfunction. The NLRP3-ASC-caspase-1-IL-1β-IL-18 pathway has been identified as a factor in the development of the pathophysiology of numerous kidney diseases. In this review, we explore current progress in understanding macrophage behavior concerning inflammation, injury, and fibrosis in kidneys. Emphasizing the pivotal role of activated macrophages in both the advancement and recovery phases of renal diseases, the article delves into potential strategies to modify macrophage functionality and it also discusses emerging approaches to selectively target NLRP3 inflammasomes and their signaling components within the kidney, aiming to facilitate the healing process in kidney diseases.

Podocyte-Specific Deletion of MCP-1 Fails to Protect against Angiotensin II- or Adriamycin-Induced Glomerular Disease

Investigating the role of podocytes in proteinuric disease is imperative to address the increasing global burden of chronic kidney disease (CKD). Studies strongly implicate increased levels of monocyte chemoattractant protein-1 (MCP-1/CCL2) in proteinuric CKD. Since podocytes express the receptor for MCP-1 (i.e., CCR2), we hypothesized that podocyte-specific MCP-1 production in response to stimuli could activate its receptor in an autocrine manner, leading to further podocyte injury. To test this hypothesis, we generated podocyte-specific MCP-1 knockout mice (Podo-Mcp-1fl/fl) and exposed them to proteinuric injury induced by either angiotensin II (Ang II; 1.5 mg/kg/d, osmotic minipump) or Adriamycin (Adr; 18 mg/kg, intravenous bolus). At baseline, there were no between-group differences in body weight, histology, albuminuria, and podocyte markers. After 28 days, there were no between-group differences in survival, change in body weight, albuminuria, kidney function, glomerular injury, and tubulointerstitial fibrosis. The lack of protection in the knockout mice suggests that podocyte-specific MCP-1 production is not a major contributor to either Ang II- or Adr-induced glomerular disease, implicating that another cell type is the source of pathogenic MCP-1 production in CKD.

Role of MCP-1 as an inflammatory biomarker in nephropathy

The Monocyte chemoattractant protein-1 (MCP-1), also referred to as chemokine ligand 2 (CCL2), belongs to the extensive chemokine family and serves as a crucial mediator of innate immunity and tissue inflammation. It has a notable impact on inflammatory conditions affecting the kidneys. Upon binding to its receptor, MCP-1 can induce lymphocytes and NK cells' homing, migration, activation, differentiation, and development while promoting monocytes' and macrophages' infiltration, thereby facilitating kidney disease-related inflammation. As a biomarker for kidney disease, MCP-1 has made notable advancements in primary kidney diseases such as crescentic glomerulonephritis, chronic glomerulonephritis, primary glomerulopathy, idiopathic proteinuria glomerulopathy, acute kidney injury; secondary kidney diseases like diabetic nephropathy and lupus nephritis; hereditary kidney diseases including autosomal dominant polycystic kidney disease and sickle cell kidney disease. MCP-1 not only predicts the occurrence, progression, prognosis of the disease but is also closely associated with the severity and stage of nephropathy. When renal tissue is stimulated or experiences significant damage, the expression of MCP-1 increases, demonstrating a direct correlation with the severity of renal injury.

Prolonged Antibiotic Use in a Preclinical Model of Gulf War Chronic Multisymptom-Illness Causes Renal Fibrosis-like Pathology via Increased micro-RNA 21-Induced PTEN Inhibition That Is Correlated with Low Host Lachnospiraceae Abundance

Gulf War (GW) veterans show gastrointestinal disturbances and gut dysbiosis. Prolonged antibiotic treatments commonly employed in veterans, especially the use of fluoroquinolones and aminoglycosides, have also been associated with dysbiosis. This study investigates the effect of prolonged antibiotic exposure on risks of adverse renal pathology and its association with gut bacterial species abundance in underlying GWI and aims to uncover the molecular mechanisms leading to possible renal dysfunction with aging. Using a GWI mouse model, administration of a prolonged antibiotic regimen involving neomycin and enrofloxacin treatment for 5 months showed an exacerbated renal inflammation with increased NF-κB activation and pro-inflammatory cytokines levels. Involvement of the high mobility group 1 (HMGB1)-mediated receptor for advanced glycation end products (RAGE) activation triggered an inflammatory phenotype and increased transforming growth factor-β (TGF-β) production. Mechanistically, TGF-β- induced microRNA-21 upregulation in the renal tissue leads to decreased phosphatase and tensin homolog (PTEN) expression. The above event led to the activation of protein kinase-B (AKT) signaling, resulting in increased fibronectin production and fibrosis-like pathology. Importantly, the increased miR-21 was associated with low levels of Lachnospiraceae in the host gut which is also a key to heightened HMGB1-mediated inflammation. Overall, though correlative, the study highlights the complex interplay between GWI, host gut dysbiosis, prolonged antibiotics usage, and renal pathology via miR-21/PTEN/AKT signaling.