Matrix metalloproteinase-12 deficiency attenuates experimental crescentic anti-glomerular basement membrane glomerulonephritis

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.

CD4+ T cells produce GM-CSF and drive immune-mediated glomerular disease by licensing monocyte-derived cells to produce MMP12

GM-CSF in glomerulonephritisDespite glomerulonephritis being an immune-mediated disease, the contributions of individual immune cell types are not clear. To address this gap in knowledge, Paust et al. characterized pathological immune cells in samples from patients with glomerulonephritis and in samples from mice with the disease. The authors found that CD4+ T cells producing granulocyte-macrophage colony-stimulating factor (GM-CSF) licensed monocytes to promote disease by producing matrix metalloproteinase 12 and disrupting the glomerular basement membrane. Targeting GM-CSF to inhibit this axis reduced disease severity in mice, implicating this cytokine as a potential therapeutic target for patients with glomerulonephritis. -CM.

Add-On Cyclic Angiotensin-(1-7) with Cyclophosphamide Arrests Progressive Kidney Disease in Rats with ANCA Associated Glomerulonephritis

Rapidly progressive crescentic glomerulonephritis associated with anti-neutrophil cytoplasmic antibodies (ANCA-GN) is a major cause of renal failure. Current immunosuppressive therapies are associated with severe side effects, intensifying the need for new therapeutic strategies. The activation of Mas receptor/Angiotensin-(1-7) axis exerted renoprotection in chronic kidney disease. Here, we investigated the effect of adding the lanthionine-stabilized cyclic form of angiotensin-1-7 [cAng-(1-7)] to cyclophosphamide in a rat model of ANCA-GN. At the onset of proteinuria, Wistar Kyoto rats with ANCA-GN received vehicle or a single bolus of cyclophosphamide, with or without daily cAng-(1-7). Treatment with cAng-(1-7) plus cyclophosphamide reduced proteinuria by 85% vs. vehicle, and by 60% vs. cyclophosphamide, and dramatically limited glomerular crescents to less than 10%. The addition of cAng-(1-7) to cyclophosphamide protected against glomerular inflammation and endothelial rarefaction and restored the normal distribution of parietal epithelial cells. Ultrastructural analysis revealed a preserved GBM, glomerular endothelium and podocyte structure, demonstrating that combination therapy provided an additional layer of renoprotection. This study demonstrates that adding cAng-(1-7) to a partially effective dose of cyclophosphamide arrests the progression of renal disease in rats with ANCA-GN, suggesting that cAng-(1-7) could be a novel clinical approach for sparing immunosuppressants.

Mice with Established Diabetes Show Increased Susceptibility to Renal Ischemia/Reperfusion Injury: Protection by Blockade of Jnk or Syk Signaling Pathways

Patients with diabetes are at an increased risk for acute kidney injury (AKI) after renal ischemia/reperfusion injury (IRI). However, there is a lack preclinical models of IRI in established diabetes. The current study characterized renal IRI in mice with established diabetes and investigated potential therapies. Diabetes was induced in C57BL/6J mice by low-dose streptozotocin injection. After 7 weeks of sustained diabetes, mice underwent 13 minutes of bilateral renal ischemia and were euthanized after 24 hours of reperfusion. Age-matched, nondiabetic controls underwent the same surgical procedure. Renal IRI induced two- and sevenfold increases in plasma creatinine level in nondiabetic and diabetic mice, respectively (P < 0.001). Kidney damage, as indicated by histologic damage, tubular cell death, tubular damage markers, and inflammation, was more severe in the diabetic IRI group. The diabetic IRI group showed greater accumulation of spleen tyrosine kinase (Syk)-expressing cells, and increased c-Jun N-terminal kinase (Jnk) signaling in tubules compared to nondiabetic IRI. Prophylactic treatment with a Jnk or Syk inhibitor substantially reduced the severity of AKI in the diabetic IRI model, with differential effects on neutrophil infiltration and Jnk activation. In conclusion, established diabetes predisposed mice to renal IRI-induced AKI. Two distinct proinflammatory pathways, JNK and SYK, were identified as potential therapeutic targets for anticipated AKI in patients with diabetes.

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.

Glomerular endothelial cell heterogeneity in Alport syndrome

Glomerular endothelial cells (GEC) are a crucial component of the glomerular physiology and their damage contributes to the progression of chronic kidney diseases. How GEC affect the pathology of Alport syndrome (AS) however, is unclear. We characterized GEC from wild type (WT) and col4α5 knockout AS mice, a hereditary disorder characterized by progressive renal failure. We used endothelial-specific Tek-tdTomato reporter mice to isolate GEC by FACS and performed transcriptome analysis on them from WT and AS mice, followed by in vitro functional assays and confocal and intravital imaging studies. Biopsies from patients with chronic kidney disease, including AS were compared with our findings in mice. We identified two subpopulations of GEC (dim^tdT and bright^tdT) based on the fluorescence intensity of the Tek^tdT signal. In AS mice, the bright^tdT cell number increased and presented differential expression of endothelial markers compared to WT. RNA-seq analysis revealed differences in the immune and metabolic signaling pathways. In AS mice, dim^tdT and bright^tdT cells had different expression profiles of matrix-associated genes (Svep1, Itgβ6), metabolic activity (Apom, Pgc1α) and immune modulation (Apelin, Icam1) compared to WT mice. We confirmed a new pro-inflammatory role of Apelin in AS mice and in cultured human GEC. Gene modulations were identified comparable to the biopsies from patients with AS and focal segmental glomerulosclerosis, possibly indicating that the same mechanisms apply to humans. We report the presence of two GEC subpopulations that differ between AS and healthy mice or humans. This finding paves the way to a better understanding of the pathogenic role of GEC in AS progression and could lead to novel therapeutic targets.

The association between plasma proteomics and incident cardiovascular disease identifies MMP-12 as a promising cardiovascular risk marker in patients with chronic kidney disease

BACKGROUND AND AIMS

Previous proteomics efforts in patients with chronic kidney disease (CKD) have predominantly evaluated urinary protein levels. Therefore, our aim was to investigate the association between plasma levels of 80 cardiovascular disease-related proteins and the risk of major adverse cardiovascular events (MACE) in patients with CKD.

METHODS

Individuals with CKD stages 3-5 (eGFR below 60 ml min-1 [1.73 m]-2) from three community-based cohorts (PIVUS, ULSAM, SAVA), one diabetes cohort (CARDIPP) and one cohort with peripheral artery disease patients (PADVA) with information on 80 plasma protein biomarkers, assessed with a proximity extension assay, and follow-up data on incident MACE, were used as discovery sample. To validate findings and to asses generalizability to patients with CKD in clinical practice, an outpatient CKD-cohort (Malnutrition, Inflammation and Vascular Calcification (MIVC)) was used as replication sample.

RESULTS

In the discovery sample (total n = 1316), 249 individuals experienced MACE during 7.0 ± 2.9 years (range 0.005-12.9) of follow-up, and in the replication sample, 71 MACE events in 283 individuals over a mean ± SD change of 2.9 ± 1.2 years (range 0.1-4.0) were documented. Applying Bonferroni correction, 18 proteins were significantly associated with risk of MACE in the discovery cohort, adjusting for age and sex in order of significance, GDF-15, FGF-23, REN, FABP4, IL6, TNF-R1, AGRP, MMP-12, AM, KIM-1, TRAILR2, TNFR2, CTSL1, CSF1, PlGF, CA-125, CCL20 and PAR-1 (p < 0.000625 for all). Only matrix metalloproteinase 12 (MMP-12) was significantly associated with an increased risk of MACE in the replication sample (hazard ratio (HR) per SD increase, 1.36, 95% CI (1.07-1.75), p = 0.013).

CONCLUSIONS

Our proteomics analyses identified plasma MMP-12 as a promising cardiovascular risk marker in patients with CKD.

Macrophages: versatile players in renal inflammation and fibrosis

Macrophages have important roles in immune surveillance and in the maintenance of kidney homeostasis; their response to renal injury varies enormously depending on the nature and duration of the insult. Macrophages can adopt a variety of phenotypes: at one extreme, M1 pro-inflammatory cells contribute to infection clearance but can also promote renal injury; at the other extreme, M2 anti-inflammatory cells have a reparative phenotype and can contribute to the resolution phase of the response to injury. In addition, bone marrow monocytes can differentiate into myeloid-derived suppressor cells that can regulate T cell immunity in the kidney. However, macrophages can also promote renal fibrosis, a major driver of progression to end-stage renal disease, and the CD206⁺ subset of M2 macrophages is strongly associated with renal fibrosis in both human and experimental diseases. Myofibroblasts are important contributors to renal fibrosis and recent studies provide evidence that macrophages recruited from the bone marrow can transition directly into myofibroblasts within the injured kidney. This process is termed macrophage-to-myofibroblast transition (MMT) and is driven by transforming growth factor-β1 (TGFβ1)-Smad3 signalling via a Src-centric regulatory network. MMT may serve as a key checkpoint for the progression of chronic inflammation into pathogenic fibrosis.

An inhibitor of spleen tyrosine kinase suppresses experimental crescentic glomerulonephritis

Non-selective inhibitors of spleen tyrosine kinase (SYK) efficiently suppress disease in T cell-dependent models of crescentic glomerulonephritis. However, the therapeutic potential of selective SYK inhibitors in this disease has not been established. In addition, we lack knowledge regarding SYK expression in non-myeloid cells in glomerulonephritis. We addressed these two issues in a rat model of nephrotoxic serum nephritis (NTN) using a SYK inhibitor, GS-492429. Disease was induced in Sprague-Dawley rats (Study 1) or Wistar-Kyoto (WKY) rats (Study 2) by immunization with sheep IgG and administration of sheep anti-rat nephrotoxic serum. Animals were untreated or received GS-492429 (30 mg/kg/bid) or vehicle treatment from 2 h before nephrotoxic serum injection until being killed 3 or 24 h later (Study 1) or 14 days later (Study 2). Two-colour confocal microscopy found that SYK expression in NTN kidney was restricted to myeloid cells and platelets, with no evidence of SYK expression by T cells, mesangial cells, podocytes or tubular epithelial cells. In Study 1, GS-492429 treatment significantly reduced glomerular neutrophil and macrophage infiltration, with protection from glomerular thrombosis and proteinuria. In Study 2, GS-492429 treatment reduced glomerular crescent formation by 70% on day 14 NTN in conjunction with reduced glomerular thrombosis, glomerulosclerosis and tubular damage. This was accompanied by a marked reduction in markers of inflammation (CCL2, TNF-α, NOS2, MMP-12). Importantly, the protective effects of GS-492429 were independent of T cell infiltration and activation and independent of JAK/STAT3 signalling. In conclusion, this study demonstrates that a SYK inhibitor can suppress the development of crescentic glomerulonephritis through effects upon myeloid cells and platelets.

ASK1 inhibitor treatment suppresses p38/JNK signalling with reduced kidney inflammation and fibrosis in rat crescentic glomerulonephritis

Activation of p38 mitogen‐activated protein kinase (MAPK) and c‐Jun amino terminal kinase (JNK) is prominent in human crescentic glomerulonephritis. p38 and JNK inhibitors suppress crescentic disease in animal models; however, the upstream mechanisms inducing activation of these kinases in crescentic glomerulonephritis are unknown. We investigated the hypothesis that apoptosis signal‐regulating kinase 1 (ASK1/MAP3K5) promote p38/JNK activation and renal injury in models of nephrotoxic serum nephritis (NTN); acute glomerular injury in SD rats, and crescentic disease in WKY rats. Treatment with the selective ASK1 inhibitor, GS‐444217 or vehicle began 1 hour before nephrotoxic serum injection and continued until animals were killed on day 1 (SD rats) or 14 (WKY rats). NTN resulted in phosphorylation (activation) of p38 and c‐Jun in both models which was substantially reduced by ASK1 inhibitor treatment. In SD rats, GS‐444217 prevented proteinuria and glomerular thrombosis with suppression of macrophage activation on day 1 NTN. In WKY rats, GS‐444217 reduced crescent formation, prevented renal impairment and reduced proteinuria on day 14 NTN. Macrophage activation, T‐cell infiltration and renal fibrosis were also reduced by GS‐444217. In conclusion, GS‐444217 treatment inhibited p38/JNK activation and development of renal injury in rat NTN. ASK1 inhibitors may have therapeutic potential in rapidly progressive glomerulonephritis.

The role of transcriptional factor D-site-binding protein in circadian CCL2 gene expression in anti-Thy1 nephritis

Mesangial proliferative glomerulonephritis (MsPGN) is an inflammatory disease, but both the nature of disease progression and its regulation remain unclear. In the present study, we monitored the course of anti-Thy1 nephritis from days 1 to 5 and established gene expression profiles at each time point using microarrays to explore the development of inflammation. According to the gene expression profiles, macrophage infiltration (triggered by CCL2 activation) was evident on day 1 and enhanced inflammation over the next few days. We screened for genes with expression levels similar to CCL2 and found that the upregulation of the circadian gene albumin D-site-binding protein (DBP) was involved in CCL2 activation in mesangial cells. More importantly, CCL2 expression showed oscillatory changes similar to DBP, and DBP induced peak CCL2 expression at 16:00 a clock on day 1 in the anti-Thy1 nephritis model. We knocked down DBP through transfection with a small interfering RNA (siRNA) and used RNA sequencing to identify the DBP-regulated TNF-α-CCL2 pathway. We performed chromatin immunoprecipitation sequencing (ChIP-Seq) and the dual luciferase assay to show that DBP bound to the TRIM55 promoter, regulating gene expression and in turn controlling the TNF-α-CCL2 pathway. In conclusion, DBP-regulated circadian CCL2 expression by the TRIM55-TNF pathway in injured mesangial cells at an early stage, which promoted macrophage recruitment and in turn triggered infiltration and inflammation in a model of anti-Thy1 nephritis.

Urinary metal and metalloid biomarker study of Henoch-Schonlein purpura nephritis using inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry

To obtain a better understanding as to whether concentration alterations of metals and metalloids in urine were related to Henoch-Schonlein purpura nephritis (HSPN), the profiles of as many as 29 elements in urine were compared among three groups, the Henoch-Schonlein purpura (HSP), HSPN and a healthy control group. To this end, a reliable method has been developed for the simultaneous quantification of multiple elements including Li, Be, B, Al, Sc, Ti, V, Cr, Mn, Fe, Ni, Co, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Mo, Cd, Sn, Sb, Cs, Ba, Tl, Pb and Bi in urine using inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (ICP-oa-TOF-MS). The process of sample pre-treatment used a direct 20-fold dilution method with centrifuged urine. The internal standard element used for quantification was ¹⁰³Rh, and 1,4-butanediol was chosen as a matrix matching reagent. The method detection limits of these 29 elements were in the range of 0.04-12ngmL^-1. Results of statistical analysis revealed that the concentrations of 15 elements and the element homeostasis were significantly different among these three groups. Our study provides a potential method for HSPN metal and metalloid biomarker discovery.