CCR2 antagonism leads to marked reduction in proteinuria and glomerular injury in murine models of focal segmental glomerulosclerosis (FSGS)

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/CCR2 axis in renal fibrosis: Mechanisms and therapeutic targeting

Renal fibrosis is a common pathological manifestation in various chronic kidney diseases. Inflammation plays a central role in renal fibrosis development. Owing to their significant participation in inflammation and autoimmunity, chemokines have always been the hot spot and focus of scientific research and clinical intervention. Among the chemokines, monocyte chemoattractant protein-1 (MCP-1), also known as C-C motif chemokine ligand 2, together with its main receptor C-C chemokine receptor type 2 (CCR2) are important chemokines in renal fibrosis. The MCP-1/CCR2 axis is activated when MCP-1 binds to CCR2. Activation of MCP-1/CCR2 axis can induce chemotaxis and activation of inflammatory cells, and initiate a series of signaling cascades in renal fibrosis. It mediates and promotes renal fibrosis by recruiting monocyte, promoting the activation and transdifferentiation of macrophages. This review summarizes the complex physical processes of MCP-1/CCR2 axis in renal fibrosis and addresses its general mechanism in renal fibrosis by using specific examples, together with the progress of targeting MCP-1/CCR2 in renal fibrosis with a view to providing a new direction for renal fibrosis treatment.

Effect of CCR2 Knockout on Tendon Biomechanical Properties in a Mouse Model of Delayed Rotator Cuff Repair

BACKGROUND

The high incidence of incomplete or failed healing after rotator cuff repair (RCR) has led to an increased focus on the biologic factors that affect tendon-to-bone healing. Inflammation plays a critical role in the initial tendon-healing response. C-C chemokine receptor type 2 (CCR2) is a chemokine receptor linked to the recruitment of monocytes in early inflammatory stages and is associated with an increase in pro-inflammatory macrophages. The purpose of this study was to evaluate the role of CCR2 in tendon healing following RCR in C57BL/6J wildtype (WT) and CCR2-/- knockout (CCR2KO) mice in a delayed RCR model.

METHODS

Fifty-two 12-week-old, male mice were allocated to 2 groups (WT and CCR2KO). All mice underwent unilateral supraspinatus tendon (SST) detachment at the initial surgical procedure, followed by a delayed repair 2 weeks later. The primary outcome measure was biomechanical testing. Secondary measures included histology, gene expression analysis, flow cytometry, and gait analysis.

RESULTS

The mean load-to-failure was 1.64 ± 0.41 N in the WT group and 2.50 ± 0.42 N in the CCR2KO group (p = 0.030). The mean stiffness was 1.43 ± 0.66 N/mm in the WT group and 3.00 ± 0.95 N/mm in the CCR2KO group (p = 0.008). Transcriptional profiling demonstrated 7 differentially expressed genes (DEGs) when comparing the CCR2KO and WT groups (p < 0.05) and significant differences in Type-I and Type-II interferon pathway scores (p < 0.01). Flow cytometry demonstrated significant differences between groups for the percentage of macrophages present (8.1% for the WT group compared with 5.8% for the CCR2KO group; p = 0.035). Gait analysis demonstrated no significant differences between groups.

CONCLUSIONS

CCR2KO may potentially improve tendon biomechanical properties by decreasing macrophage infiltration and/or by suppressing inflammatory mediator pathways in the setting of delayed RCR.

CLINICAL RELEVANCE

CCR2 may be a promising target for novel therapeutics that aim to decrease failure rates following RCR.

CCR2 deficiency alters activation of microglia subsets in traumatic brain injury

In traumatic brain injury (TBI), a diversity of brain resident and peripherally derived myeloid cells have the potential to worsen damage and/or to assist in healing. We define the heterogeneity of microglia and macrophage phenotypes during TBI in wild-type (WT) mice and Ccr2^−/− mice, which lack macrophage influx following TBI and are resistant to brain damage. We use unbiased single-cell RNA sequencing methods to uncover 25 microglia, monocyte/macrophage, and dendritic cell subsets in acute TBI and normal brains. We find alterations in transcriptional profiles of microglia subsets in Ccr2^−/− TBI mice compared to WT TBI mice indicating that infiltrating monocytes/macrophages influence microglia activation to promote a type I IFN response. Preclinical pharmacological blockade of hCCR2 after injury reduces expression of IFN-responsive gene, Irf7, and improves outcomes. These data extend our understanding of myeloid cell diversity and crosstalk in brain trauma and identify therapeutic targets in myeloid subsets.

By single-cell RNA sequencing of traumatically injured and normal brains from wild-type and Ccr2^−/− mice, Somebang et al. define microglia, macrophage, and dendritic cell phenotypes in TBI. Targeting mouse and/or human CCR2 reduces specific TBI brain CNS myeloid compartments, dampens type I interferon responses, and improves cognition after TBI.

Therapeutic trials in adult FSGS: lessons learned and the road forward

Focal segmental glomerulosclerosis (FSGS) is not a specific disease entity but a lesion that primarily targets the podocyte. In a broad sense, the causes of the lesion can be divided into those triggered by a presumed circulating permeability factor, those that occur secondary to a process that might originate outside the kidneys, those caused by a genetic mutation in a podocyte or glomerular basement membrane protein, and those that arise through an as yet unidentifiable process, seemingly unrelated to a circulating permeability factor. A careful attempt to correctly stratify patients with FSGS based on their clinical presentation and pathological findings on kidney biopsy is essential for sound treatment decisions in individual patients. However, it is also essential for the rational design of therapeutic trials in FSGS. Greater recognition of the pathophysiology underlying podocyte stress and damage in FSGS will increase the likelihood that the cause of an FSGS lesion is properly identified and enable stratification of patients in future interventional trials. Such efforts will facilitate the identification of effective therapeutic agents.

CD73 Overexpression in Podocytes: A Novel Marker of Podocyte Injury in Human Kidney Disease

The CD73 pathway is an important anti-inflammatory mechanism in various disease settings. Observations in mouse models suggested that CD73 might have a protective role in kidney damage; however, no direct evidence of its role in human kidney disease has been described to date. Here, we hypothesized that podocyte injury in human kidney diseases alters CD73 expression that may facilitate the diagnosis of podocytopathies. We assessed the expression of CD73 and one of its functionally important targets, the C-C chemokine receptor type 2 (CCR2), in podocytes from kidney biopsies of 39 patients with podocytopathy (including focal segmental glomerulosclerosis (FSGS), minimal change disease (MCD), membranous glomerulonephritis (MGN) and amyloidosis) and a control group. Podocyte CD73 expression in each of the disease groups was significantly increased in comparison to controls (p < 0.001–p < 0.0001). Moreover, there was a marked negative correlation between CD73 and CCR2 expression, as confirmed by immunohistochemistry and immunofluorescence (Pearson r = −0.5068, p = 0.0031; Pearson r = −0.4705, p = 0.0313, respectively), thus suggesting a protective role of CD73 in kidney injury. Finally, we identify CD73 as a novel potential diagnostic marker of human podocytopathies, particularly of MCD that has been notorious for the lack of pathological features recognizable by light microscopy and immunohistochemistry.

Calcineurin inhibitors in the treatment of primary focal segmental glomerulosclerosis: A protocol of systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Evidence suggesting a role for including calcineurin inhibitors(CNIs) in early therapy remains limited for low quality and mainly based on small observation cohort study. We will conduct a systematic reviews to explore the effect and adverse effect of calcineurin inhibitors compared with other interventions in the treatment of primary focal segmental glomerulosclerosis (FSGS).

METHODS

A comprehensive literature search of MEDLINE (through PubMed), EMBASE, The Cochrane Library, Cochrane Central Register of Controlled Trials (CENTRAL) will be conducted. Two investigators will independently select studies, extract data and assess the quality of the included study. Extracted information will include study characteristics, the contents of included randomized controlled trials, outcomes, the quality of randomized controlled trials and etc. A risk of bias tool will be used to assess the methodological quality. Any disagreement will be resolved by the third investigator. There is no requirement of ethical approval and informed consent.

RESULTS

This study will provide high-quality evidence for treatment of FSGS in terms of effectiveness and safety.

CONCLUSION

This systematic review aims to provide evidence for treatment of FSGS in different CNIs.

REGISTRATION

The systematic review and meta-analysis is registered in the OSF REGISTERS (10.17605/OSF.IO/3B7DE) international prospective register of systematic review.

Autoimmunity in Focal Segmental Glomerulosclerosis: A Long-Standing Yet Elusive Association

Focal segmental glomerulosclerosis (FSGS) is a histological term that describes a pathologic renal entity affecting both adults and children, with a wide array of possible underlying etiologies. Podocyte damage with scarring, the hallmark of this condition, leads to altered permeability of the glomerular barrier, which may result in massive proteinuria and relentless renal function deterioration. A definite cause of focal segmental glomerulosclerosis can be confirmed in a minority of cases, while most forms have been traditionally labeled as primary or idiopathic. Despite this definition, increasing evidence indicates that primary forms are a heterogenous group rather than a single disease entity: several circulating factors that may affect glomerular permeability have been proposed as potential culprits, and both humoral and cellular immunity have been implicated in the pathogenesis of the disease. Consistently, immunosuppressive drugs are considered as the cornerstone of treatment for primary focal segmental glomerulosclerosis, but response to these agents and long-term outcomes are highly variable. In this review we provide a summary of historical and recent advances on the pathogenesis of primary focal segmental glomerulosclerosis, focusing on implications for its differential diagnosis and treatment.

C-C chemokine receptor type 2 mediates glomerular injury and interstitial fibrosis in focal segmental glomerulosclerosis

BACKGROUND

Glomerulosclerosis and tubulointerstitial fibrosis are hallmarks of chronic kidney injury leading to end-stage renal disease. Inflammatory mechanisms contribute to glomerular and interstitial scarring, including chemokine-mediated recruitment of leucocytes. In particular, accumulation of C-C chemokine receptor type 2 (CCR2)-expressing macrophages promotes renal injury and fibrotic remodelling in diseases like glomerulonephritis and diabetic nephropathy. The functional role of CCR2 in the initiation and progression of primary glomerulosclerosis induced by podocyte injury remains to be characterized.

METHODS

We analysed glomerular expression of CCR2 and its chemokine ligand C-C motif chemokine ligand 2 (CCL2) in human focal segmental glomerulosclerosis (FSGS). Additionally, CCL2 expression was determined in stimulated murine glomeruli and glomerular cells in vitro. To explore pro-inflammatory and profibrotic functions of CCR2 we induced adriamycin nephropathy, a murine model of FSGS, in BALB/c wild-type and Ccr2-deficient mice.

RESULTS

Glomerular expression of CCR2 and CCL2 significantly increased in human FSGS. In adriamycin-induced FSGS, progressive glomerular scarring and reduced glomerular nephrin expression was paralleled by induced glomerular expression of CCL2. Adriamycin exposure stimulated secretion of CCL2 and tumour necrosis factor-α (TNF) in isolated glomeruli and mesangial cells and CCL2 in parietal epithelial cells. In addition, TNF induced CCL2 expression in all glomerular cell populations, most prominently in podocytes. In vivo, Ccr2-deficient mice with adriamycin nephropathy showed reduced injury, macrophage and fibrocyte infiltration and inflammation in glomeruli and the tubulointerstitium. Importantly, glomerulosclerosis and tubulointerstitial fibrosis were significantly ameliorated.

CONCLUSIONS

Our data indicate that CCR2 is an important mediator of glomerular injury and progression of FSGS. CCR2- targeting therapies may represent a novel approach for its treatment.

CCR2 inhibition reduces tumor myeloid cells and unmasks a checkpoint inhibitor effect to slow progression of resistant murine gliomas

Immunotherapy directed at the PD-L1/PD-1 axis has produced treatment advances in various human cancers. Unfortunately, progress has not extended to glioblastoma (GBM), with phase III clinical trials assessing anti-PD-1 monotherapy failing to show efficacy in newly diagnosed and recurrent tumors. Myeloid-derived suppressor cells (MDSCs), a subset of immunosuppressive myeloid derived cells, are known to infiltrate the tumor microenvironment of GBM. Growing evidence suggests the CCL2-CCR2 axis is important for this process. This study evaluated the combination of PD-1 blockade and CCR2 inhibition in anti-PD-1-resistant gliomas. CCR2 deficiency unmasked an anti-PD-1 survival benefit in KR158 glioma-bearing mice. CD11b⁺/Ly6C^hi/PD-L1⁺ MDSCs within established gliomas decreased with a concomitant increase in overall CCR2⁺ cells and MDSCs within bone marrow of CCR2-deficient mice. The CCR2 antagonist CCX872 increased median survival as a monotherapy in KR158 glioma-bearing animals and further increased median and overall survival when combined with anti-PD-1. Additionally, combination of CCX872 and anti-PD-1 prolonged median survival time in 005 GSC GBM-bearing mice. In both models, CCX872 decreased tumor associated MDSCs and increased these cells within the bone marrow. Examination of tumor-infiltrating lymphocytes revealed an elevated population, increased IFNγ expression, indicating enhanced cytolytic activity, as well as decreased expression of exhaustion markers in CD4⁺ and CD8⁺ T cells following combination treatment. These data establish that combining CCR2 and PD-1 blockade extends survival in clinically relevant murine glioma models and provides the basis on which to advance this combinatorial treatment toward early-phase human trials.