Bone marrow Ly6Chigh monocytes are selectively recruited to injured kidney and differentiate into functionally distinct populations

Lymphocytes and innate immune cells in acute kidney injury and repair

Acute kidney injury (AKI) is a common and serious disease entity that affects native kidneys and allografts but for which no specific treatments exist. Complex intrarenal inflammatory processes driven by lymphocytes and innate immune cells have key roles in the development and progression of AKI. Many studies have focused on prevention of early injury in AKI. However, most patients with AKI present after injury is already established. Increasing research is therefore focusing on mechanisms of renal repair following AKI and prevention of progression from AKI to chronic kidney disease. CD4+ and CD8+ T cells, B cells and neutrophils are probably involved in the development and progression of AKI, whereas regulatory T cells, double-negative T cells and type 2 innate lymphoid cells have protective roles. Several immune cells, such as macrophages and natural killer T cells, can have both deleterious and protective effects, depending on their subtype and/or the stage of AKI. The immune system not only participates in injury and repair processes during AKI but also has a role in mediating AKI-induced distant organ dysfunction. Targeted manipulation of immune cells is a promising therapeutic strategy to improve AKI outcomes.

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.

A Panoramic View of Cell Population Dynamics in Mammalian Aging

To elucidate the aging-associated cellular population dynamics throughout the body, here we present PanSci, a single-cell transcriptome atlas profiling over 20 million cells from 623 mouse tissue samples, encompassing a range of organs across different life stages, sexes, and genotypes. This comprehensive dataset allowed us to identify more than 3,000 unique cellular states and catalog over 200 distinct aging-associated cell populations experiencing significant depletion or expansion. Our panoramic analysis uncovered temporally structured, organ- and lineage-specific shifts of cellular dynamics during lifespan progression. Moreover, we investigated aging-associated alterations in immune cell populations, revealing both widespread shifts and organ-specific changes. We further explored the regulatory roles of the immune system on aging and pinpointed specific age-related cell population expansions that are lymphocyte-dependent. The breadth and depth of our 'cell-omics' methodology not only enhance our comprehension of cellular aging but also lay the groundwork for exploring the complex regulatory networks among varied cell types in the context of aging and aging-associated diseases.

Chemoradiotherapy treatment with gemcitabine improves renal function in locally advanced cervical cancer patients with renal dysfunction

BACKGROUND

Cervical cancer (CC) in Mexico is diagnosed mainly in locally advanced (LACC) and advanced (ACC) stages, where ureteral obstruction is more frequent. The standard treatment for this population is concurrent chemoradiotherapy (CCRT) with cisplatin, which is nephrotoxic and could lead to further deterioration of renal function in LACC patients with renal function decline. We aimed to evaluate the effect of CCRT with Gemcitabine on renal function in LACC patients.

METHODS

This retrospective study included LACC patients treated with CCRT with Gemcitabine as a radiosensitizer from February 2003 to December 2018. Data were collected from medical archives and electronic records. We assessed renal function before and after CCRT treatment and analyzed the patient's response to treatment and survival.

RESULTS

351 LACC patients treated were included and stratified into two groups: 198 with Glomerular Filtration Rate (GFR) ≥60ml/min (group A) and 153 with GFR<60ml/min (group B). An improvement in GFR was observed after CCRT in patients in group B, from 33 ml/min to 57.5 ml/min (p<0.001). Complete response was observed in 64.1% of patients in Group A and 43.8% in Group B (p<0.0001). Factors associated with increased risk of death included having a GFR of 15-29 ml/min (HR: 2.17; 1.08-4.35), having GFR<15 ml/min (HR: 3.08; 1.63-5.79), and receiving Boost treatment (HR: 2.09; 1.18-3.69). On the other hand, receiving brachytherapy is a positive predictor for OS (HR:0.51; 0.31-0.84).

CONCLUSION

CCRT with gemcitabine is an appropriate treatment option for patients diagnosed with LACC who present impaired renal function due to the disease's obstructive nature or other comorbidities.

Preclinical Animal Study and Pilot Clinical Trial of Using Enriched Peripheral Blood-Derived Mononuclear Cells for Intervertebral Disc Degeneration

Low back pain (LBP) is a leading cause of long-term disability globally. Intervertebral disk degeneration (IVDD) is mainly responsible for discogenic pain in LBP-affected young patients. There is no effective therapy to reverse disease severity and IVDD progression. This study investigates the effect of human peripheral blood-derived mononuclear cells (PBMCs) on pain relief and life quality improvement in IVDD patients. The enriched monocytes of the PBMCs could differentiate into CD14 and CD206 double-positive M2 macrophages in vitro. Preclinical evidence in rats showed that the transplanted PBMCs exhibited anti-inflammatory and moderate tissue-repair effects on controlling IVDD progress in the rat model. The PBMCs significantly steered the aggrecan and type II collagen expressions and attenuated the pro-inflammatory cytokines in the affected disk. Based on the animal results, 36 patients with chronic low back pain (CLBP) were included in clinical trials. The control group was conservative care only, and the experimental group was platelet-rich plasma (PRP) and PBMCs intradiscal injections. We first confirmed the single lumbar disk causing the discogenic pain by provocative discography or magnetic resonance imaging (MRI). Discogenic LBP participants received one intradiscal injection of autologous PBMCs and followed for 6 months. Our clinical trial showed that patients' LBP and disability were significantly ameliorated after the PBMCs transplantation rather than PRP. These preclinical and pilot clinical studies indicate that intradiscal injection of the enriched PBMCs might be a feasible and potential cell therapy to control pain and disability in IVDD patients.

Computational screening of biomarkers and potential drugs for arthrofibrosis based on combination of sequencing and large nature language model

Background

Arthrofibrosis (AF) is a fibrotic joint disease resulting from excessive collagen production and fibrous scar formation after total knee arthroplasty (TKA). This devastating complication may cause consistent pain and dramatically reduction of functionality. Unfortunately, the conservative treatments to prevent the AF in the early stage are largely unknown due to the lack of specific biomarkers and reliable therapeutic targets.

Methods

In this study, we extracted1782 fibrosis related genes (FRGs) from 373,461published literature based on the large natural language processing models (ChatGPT) and intersected with the 2750 differential expressed genes (DEGs) from mRNA microarray (GSE135854). A total of 311 potential AF biomarker genes (PABGs) were obtained and functional analysis were performed including gene ontology (GO) annotation and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses. Subsequently, we accomplished validation in AF animal models with immobilization of the unilateral knee joints of 16 rabbits for 1-week, 2-weeks, 3-weeks and 4-weeks. Finally, we tested the biomarkers in a retrospective cohort enrolled 35 AF patients and 35 control group patients.

Results

We identified G-protein-coupled receptor 17 (GPR17) as a reliable therapeutic biomarker for AF diagnosis with higher AUC (0.819) in the ROC curve. A total of 21 potential drugs targeted to GPR17 were screened. Among them, pranlukast and montelukast have achieved therapeutic effect in animal models. In addition, we established an online AF database for data integration (https://chenxi2023.shinyapps.io/afdbv1).

Conclusions

These results unveiling therapeutic biomarkers for AF diagnosis, and provide potential drugs for clinical treatment.

The translational potential of this article

Our study demonstrated that GPR17 holds significant promise as a potential biomarker and therapeutic target for arthrofibrosis. Moreover, pranlukast and montelukast targeted to GPR17 that could be instrumental in the treatment of AF.

Myeloid PFKFB3-mediated glycolysis promotes kidney fibrosis

Excessive renal fibrosis is a common pathology in progressive chronic kidney diseases. Inflammatory injury and aberrant repair processes contribute to the development of kidney fibrosis. Myeloid cells, particularly monocytes/macrophages, play a crucial role in kidney fibrosis by releasing their proinflammatory cytokines and extracellular matrix components such as collagen and fibronectin into the microenvironment of the injured kidney. Numerous signaling pathways have been identified in relation to these activities. However, the involvement of metabolic pathways in myeloid cell functions during the development of renal fibrosis remains understudied. In our study, we initially reanalyzed single-cell RNA sequencing data of renal myeloid cells from Dr. Denby's group and observed an increased gene expression in glycolytic pathway in myeloid cells that are critical for renal inflammation and fibrosis. To investigate the role of myeloid glycolysis in renal fibrosis, we utilized a model of unilateral ureteral obstruction in mice deficient of Pfkfb3, an activator of glycolysis, in myeloid cells (Pfkfb3 ΔMϕ ) and their wild type littermates (Pfkfb3 WT). We observed a significant reduction in fibrosis in the obstructive kidneys of Pfkfb3 ΔMϕ mice compared to Pfkfb3 WT mice. This was accompanied by a substantial decrease in macrophage infiltration, as well as a decrease of M1 and M2 macrophages and a suppression of macrophage to obtain myofibroblast phenotype in the obstructive kidneys of Pfkfb3 ΔMϕ mice. Mechanistic studies indicate that glycolytic metabolites stabilize HIF1α, leading to alterations in macrophage phenotype that contribute to renal fibrosis. In conclusion, our study implicates that targeting myeloid glycolysis represents a novel approach to inhibit renal fibrosis.

Mannan-binding lectin ameliorates renal fibrosis by suppressing macrophage-to-myofibroblast transition

Mannan-binding lectin (MBL) is a pattern-recognition molecule that plays a crucial role in innate immunity. MBL deficiency correlates with an increased risk of chronic kidney disease (CKD). However, the molecular mechanisms are not fully defined. Here, we established a CKD model in wild-type (WT) and MBL-deficient (MBL-/-) mice via unilateral ureteral obstruction (UUO). The result showed that MBL deficiency aggravated the pathogenesis of renal fibrosis in CKD mice. Strikingly, the in vivo macrophage depletion investigation revealed that macrophages play an essential role in the MBL-mediated suppression of renal fibrosis. We found that MBL limited the progression of macrophage-to-myofibroblast transition (MMT) in kidney tissues of UUO mice. Further in vitro study showed that MBL-/- macrophages exhibited significantly increased levels of fibrotic-related molecules compared with WT cells upon transforming growth factor beta (TGF-β) stimulation. We demonstrated that MBL inhibited the MMT process by suppressing the production of matrix metalloproteinase 9 (MMP-9) and activation of Akt signaling. In summary, our study revealed an expected role of MBL on macrophage transition during renal fibrosis, thus offering new insight into the potential of MBL as a therapeutic target for CKD.

Lipin-1 restrains macrophage lipid synthesis to promote inflammation resolution

Macrophages are critical to maintaining and restoring tissue homeostasis during inflammation. The lipid metabolic state of macrophages influences their function, but a deeper understanding of how lipid metabolism is regulated in pro-resolving macrophage responses is needed. Lipin-1 is a phosphatidic acid phosphatase with a transcriptional coregulatory activity (TC) that regulates lipid metabolism. We previously demonstrated that lipin-1 supports pro-resolving macrophage responses, and here, myeloid-associated lipin-1 is required for inflammation resolution, yet how lipin-1-regulated cellular mechanisms promote macrophage pro-resolution responses is unknown. We demonstrated that the loss of lipin-1 in macrophages led to increased free fatty acid, neutral lipid, and ceramide content and increased phosphorylation of acetyl-CoA carboxylase. The inhibition of the first step of lipid synthesis and transport of citrate from the mitochondria in macrophages reduced lipid content and restored efferocytosis and inflammation resolution in lipin-1mKO macrophages and mice. Our findings suggest macrophage-associated lipin-1 restrains lipid synthesis, promoting pro-resolving macrophage function in response to pro-resolving stimuli.

Impact of intestinal microenvironments in obesity and bariatric surgery on shaping macrophages

Obesity is associated with alterations in tissue composition, systemic cellular metabolism, and low-grade chronic inflammation. Macrophages are heterogenous innate immune cells ubiquitously localized throughout the body and are key components of tissue homeostasis, inflammation, wound healing, and various disease states. Macrophages are highly plastic and can switch their phenotypic polarization and change function in response to their local environments. Here, we discuss how obesity alters the intestinal microenvironment and potential key factors that can influence intestinal macrophages as well as macrophages in other organs, including adipose tissue and hematopoietic organs. As bariatric surgery can induce metabolic adaptation systemically, we discuss the potential mechanisms through which bariatric surgery reshapes macrophages in obesity.

Systemic Mutation of Ncf1 Ameliorates Obstruction-Induced Renal Fibrosis While Macrophage-Rescued NCF1 Further Alleviates Renal Fibrosis

Aims: NCF1, a subunit of the NADPH oxidase 2 (NOX2), first described the expression in neutrophils and macrophages and participated in the pathogenesis from various systems. However, there are controversial findings on the role of NCF1 in different kinds of kidney diseases. In this study, we aim to pinpoint the specific role of NCF1 in the progression of renal fibrosis induced by obstruction. Results: In this study, NCF1 expression was upregulated in kidney biopsies of chronic kidney disease patients. The expression level of all subunits of the NOX2 complex was also significantly increased in the unilateral ureteral obstruction (UUO) kidney. Then, we used wild-type mice and Ncf1 mutant mice (Ncf1m1j mice) to perform UUO-induced renal fibrosis. Results demonstrated that Ncf1m1j mice exhibited mild renal fibrosis but increased macrophages count and CD11b+Ly6Chi macrophage proportion. Next, we compared the renal fibrosis degree between Ncf1m1j mice and Ncf1 macrophage-rescued mice (Ncf1m1j.Ncf1Tg-CD68 mice). We found that rescuing NCF1 expression in macrophages further alleviated renal fibrosis and decreased macrophage infiltration in the UUO kidney. In addition, flow cytometry data showed fewer CD11b+Ly6Chi macrophages in the kidney of the Ncf1m1j.Ncf1Tg-CD68 group than the Ncf1m1j group. Innovation: We first used the Ncf1m1j mice and Ncf1m1j.Ncf1Tg-CD68 mice to detect the role of NCF1 in the pathological process of renal fibrosis induced by obstruction. Also, we found that NCF1 expressed in different cell types exerts opposing effects on obstructive nephropathy. Conclusion: Taken together, our findings support that systemic mutation of Ncf1 ameliorates renal fibrosis induced by obstruction, and rescuing NCF1 in macrophages further alleviates renal fibrosis.

Conjunctival infiltrates and cytokines in an experimental immune-mediated blepharoconjunctivitis rat model

Purpose

To characterize the histopathological and immunological findings of a rat model of allergic blepharoconjunctivitis (BC) and demonstrate its potential utility for the assessment of BC therapies.

Methods

Sprague-Dawley (SD) rats were immunized with ovalbumin (OVA) and topically challenged with OVA (BC group) or PBS (control group), while a corticosteroid group was pre-treated with triamcinolone acetate 24 h before the challenge. Morphological features were evaluated and tissues were harvested for histological, flow cytometry and cytokine analysis.

Results

The BC group rats developed eyelid excoriations, redness, and conjunctival edema 24 h after the OVA challenge, while corticosteroid pre-treated and PBS-challenged rats were unaffected. The BC features were reduced despite repeated challenges for 5 days. Massive immune cell infiltration was observed in conjunctivae of BC rats, while no significant infiltration was seen in the other groups. Populations of T cells, mono-macrophages, neutrophils, and NK cells made up more than 77% of CD45⁺7AAD^- cells in the conjunctival tissues. T cell proportions were increased at 96 h compared to 24 h post-challenge, while macrophages decreased during the same time period. Eosinophils and intraepithelial neutrophils were detected in the BC rats, but not in the PBS and corticosteroid groups. BC eyes had significantly higher levels of IFN-γ and IL-2, while IL-4 and IL-6 levels were similar to controls.

Conclusion

A robust BC response was detected in this rat model which was suppressed by corticosteroid pre-treatment. Immune cell composition and cytokine profiles changed over time.

Delivery of nitric oxide with a pH-responsive nanocarrier for the treatment of renal fibrosis

Fibrosis is an excessive accumulation of extracellular matrix (ECM) that may cause severe organ dysfunction. Nitric oxide (NO), a multifunctional gaseous signaling molecule, may inhibit fibrosis, and delivery of NO may serve as a potential antifibrotic strategy. However, major limitations in the application of NO to treat fibrotic diseases include its nonspecificity, short half-life and low availability in fibrotic tissue. Herein, we aimed to develop a stimuli-responsive drug carrier to deliver NO to halt kidney fibrosis. We manufactured a nanoparticle (NP) composed of pH-sensitive poly[2-(diisopropylamino)ethyl methacrylate (PDPA) polymers to encapsulate a NO donor, a dinitrosyl iron complex (DNIC; [Fe₂(μ-SEt)₂(NO)₄]). The NPs were stable at physiological pH 7.4 but disintegrated at pH 4.0-6.0. The NPs showed significant cytotoxicity to cultured human myofibroblasts and were able to inhibit the activation of myofibroblasts, as indicated by a lower expression level of α-smooth muscle actin and the synthesis of a major ECM component, collagen I, in cultured human myofibroblasts. When given to mice treated with unilateral ureteral ligation/obstruction (UUO) to induce kidney fibrosis, these NPs remained in blood at a stable concentration for as long as 24 h and might enter the fibrotic kidneys to suppress myofibroblast activation and collagen I production, leading to a 70% reduction in the fibrotic area. In summary, our strategy to assemble a NO donor, the iron nitrosyl complex DNIC, into pH-responsive NPs proves effective in treating renal fibrosis and warrants further investigation for its therapeutic potential.

Enriched Peripheral Blood-Derived Mononuclear Cells for Treating Knee Osteoarthritis

Osteoarthritis (OA) is a common chronic skeletal disease in the elderly. There is no effective therapy to reverse disease severity and knee OA (KOA) progression, particularly at the late stage. This study aims to examine the effect of peripheral blood-derived mononuclear cells (PBMNCs) on pain and motor function rescue in patients with Kellgren-Lawrence (KL) grade II to IV KOA. Participants received one intra-articular (IA) injection of autologous PBMNCs. The mononuclear cells were isolated from peripheral blood, enriched by a specialized medium (MoFi medium), and separated by Ficoll-Paque solution. The isolated and enriched PBMNCs could differentiate into M1 and M2 macrophages in vitro. The in vivo anti-inflammatory effect of the PBMNCs was similar to that of bone marrow mesenchymal stem cells, evaluated by complete Freund's adjuvant-induced arthritis in rodents. A single-arm and open-label pilot study showed that patients' knee pain and motor dysfunction were significantly attenuated after the cell transplantation, assessed by visual analogue scale (VAS) and Knee injury and Osteoarthritis Outcome Score (KOOS) at 6 and 12 months post-treatment. Notably, the therapeutic effect of the PBMNCs treatment can be stably maintained for 24 months, as revealed by the KOOS scores. These preclinical and pilot clinical data suggest that IA injection of MoFi-PBMNCs might serve as a novel medical technology to control the pain and the progress of KOA.

Interleukin-3 protects against viral pneumonia in sepsis by enhancing plasmacytoid dendritic cell recruitment into the lungs and T cell priming

Rationale

Sepsis, a global health burden, is often complicated by viral infections leading to increased long-term morbidity and mortality. Interleukin-3 (IL-3) has been identified as an important mediator amplifying acute inflammation in sepsis; however, its function in the host response to viral infections during sepsis remains elusive.

Objectives

To investigate the role of IL-3 during viral pneumonia in sepsis.

Methods

We included septic patients from two different cohorts and used in vitro and in vivo assays. The obtained data were substantiated using a second model (SARS-CoV-2 infections).

Measurements and main results

Low plasma IL-3 levels were associated with increased herpes simplex virus (HSV) airway infections in septic patients, resulting in reduced overall survival. Likewise, Il-3-deficient septic mice were more susceptible to pulmonary HSV-1 infection and exhibited higher pulmonary inflammation than control mice. Mechanistically, IL-3 increases innate antiviral immunity by promoting the recruitment of circulating plasmacytoid dendritic cells (pDCs) into the airways and by enhancing pDC-mediated T cell activation upon viral stimulation. Interestingly, the ability of IL-3 to improve adaptive immunity was confirmed in patients with SARS-CoV-2 infections.

Conclusion

Our study identifies IL-3 as a predictive disease marker for viral reactivation in sepsis and reveals that IL-3 improves antiviral immunity by enhancing the recruitment and the function of pDCs.

Development of Cell Therapies for Renal Disease and Regenerative Medicine

The incidence of renal disease is gradually increasing worldwide, and this condition has become a major public health problem because it is a trigger for many other chronic diseases. Cell therapies using multipotent mesenchymal stromal cells, hematopoietic stem cells, macrophages, and other cell types have been used to induce regeneration and provide a cure for acute and chronic kidney disease in experimental models. This review describes the advances in cell therapy protocols applied to acute and chronic kidney injuries and the attempts to apply these treatments in a clinical setting.

Effect of M2-like macrophages of the injured-kidney cortex on kidney cancer progression

Chronic kidney disease (CKD) affects kidney cancer patients' mortality. However, the underlying mechanism remains unknown. M2-like macrophages have pro-tumor functions, also exist in injured kidney, and promote kidney fibrosis. Thus, it is suspected that M2-like macrophages in injured kidney induce the pro-tumor microenvironment leading to kidney cancer progression. We found that M2-like macrophages present in the injured kidney promoted kidney cancer progression and induced resistance to anti-PD1 antibody through its pro-tumor function and inhibition of CD8⁺ T cell infiltration. RNA-seq revealed Slc7a11 was upregulated in M2-like macrophages. Inhibition of Slc7a11 with sulfasalazine inhibited the pro-tumor function of M2-like macrophages and synergized with anti-PD1 antibody. Moreover, SLC7A11-positive macrophages were associated with poor prognosis among kidney cancer patients. Collectively, this study dissects the characteristic microenvironment in the injured kidney that contributed to kidney cancer progression and anti-PD1 antibody resistance. This insight offers promising combination therapy with anti-PD1 antibody and macrophage targeted therapy.

Macrophages in Lupus Nephritis: Exploring a potential new therapeutic avenue

Lupus nephritis (LN) is a serious complication of systemic lupus erythematosus (SLE) that occurs in about half of patients. LN is characterized by glomerular deposition of immune complexes, leading to subendothelial, mesangial and subepithelial electron dense deposits, triggering immune cell infiltration and glomerular as well as tubulointerstitial injury. Monocytes and macrophages are abundantly present in inflammatory lesions, both in glomeruli and the tubulointerstitium. Here we discuss how monocytes and macrophages are involved in this process and how monocytes and macrophages may represent specific therapeutic targets to control LN.

Transcriptional profile changes after treatment of ischemia reperfusion injury-induced kidney fibrosis with 18β-glycyrrhetinic acid

Introduction

Chronic kidney disease (CKD) is characterized by renal fibrosis without effective therapy. 18β-Glycyrrhetinic acid (GA) is reported to have detoxification and anti-inflammatory functions and promotes tissue repair. However, the role of GA in CKD remains unclear. In this study, we investigated whether GA has a potential therapeutic effect in kidney fibrosis.

Methods

A renal fibrosis mouse model was established by ischemia/reperfusion (I/R) injury via clamping unilateral left renal pedicle for 45 min; then, the mice were treated with vehicle or GA. Kidney tissues and blood samples were extracted 14 days after reperfusion and renal function, histopathological staining, quantitative PCR, and western blotting were performed. RNA-seq was performed to explore the changes in the transcriptional profile after GA treatment.

Results

Renal function, pathological and molecular analysis displayed that fibrosis was successfully induced in the I/R model. In the GA treatment group, the severity of fibrosis gradually reduced with the best effect seen at a concentration of 25 mg kg ⁻¹. A total of 970 differentially expressed genes were identified. Pathway enrichment showed that reduced activation and migration of inflammatory cells and decreased chemokine interaction in significant pathways. Protein–protein interaction networks were constructed and 15 hub genes were selected by degree rank, including chemokines, such as C3, Ccl6, Ccr2, Ptafr, Timp1, and Pf4.

Conclusions

GA may alleviate renal fibrosis by inhibiting the inflammatory response. GA is a promising therapy that may perhaps be used in treating renal fibrosis and CKD.

Renal fibrosis as a hallmark of diabetic kidney disease: Potential role of targeting transforming growth factor-beta (TGF-β) and related molecules

INTRODUCTION

Diabetic kidney disease (DKD) is the most common cause of end-stage renal disease (ESRD) worldwide. Currently, there is no effective treatment to completely prevent DKD progression to ESRD. Renal fibrosis and inflammation are the major pathological features of DKD, being pursued as potential therapeutic targets for DKD.

AREAS COVERED

Inflammation and renal fibrosis are involved in the pathogenesis of DKD. Anti-inflammatory drugs have been developed to combat DKD but without efficacy demonstrated. Thus, we have focused on the mechanisms of TGF-β-induced renal fibrosis in DKD, as well as discussing the important molecules influencing the TGF-β signaling pathway and their potential development into new pharmacotherapies, rather than targeting the ligand TGF-β and/or its receptors, such options include Smads, microRNAs, histone deacetylases, connective tissue growth factor, bone morphogenetic protein 7, hepatocyte growth factor, and cell division autoantigen 1.

EXPERT OPINION

TGF-β is a critical driver of renal fibrosis in DKD. Molecules that modulate TGF-β signaling rather than TGF-β itself are potentially superior targets to safely combat DKD. A comprehensive elucidation of the pathogenesis of DKD is important, which requires a better model system and access to clinical samples via collaboration between basic and clinical researchers.

Bone marrow adipocytes drive the development of tissue invasive Ly6Chigh monocytes during obesity

During obesity and high fat-diet (HFD) feeding in mice, sustained low-grade inflammation includes not only increased pro-inflammatory macrophages in the expanding adipose tissue, but also bone marrow (BM) production of invasive Ly6C^high monocytes. As BM adiposity also accrues with HFD, we explored the relationship between the gains in BM white adipocytes and invasive Ly6C^high monocytes by in vivo and ex vivo paradigms. We find a temporal and causal link between BM adipocyte whitening and the Ly6C^high monocyte surge, preceding the adipose tissue macrophage rise during HFD in mice. Phenocopying this, ex vivo treatment of BM cells with conditioned media from BM adipocytes or bona fide white adipocytes favoured Ly6C^high monocyte preponderance. Notably, Ly6C^high skewing was preceded by monocyte metabolic reprogramming towards glycolysis, reduced oxidative potential and increased mitochondrial fission. In sum, short-term HFD changes BM cellularity, resulting in local adipocyte whitening driving a gradual increase and activation of invasive Ly6C^high monocytes.

Immune-mediated tubule atrophy promotes acute kidney injury to chronic kidney disease transition

Incomplete repair after acute kidney injury can lead to development of chronic kidney disease. To define the mechanism of this response, we compared mice subjected to identical unilateral ischemia-reperfusion kidney injury with either contralateral nephrectomy (where tubule repair predominates) or contralateral kidney intact (where tubule atrophy predominates). By day 14, the kidneys undergoing atrophy had more macrophages with higher expression of chemokines, correlating with a second wave of proinflammatory neutrophil and T cell recruitment accompanied by increased expression of tubular injury genes and a decreased proportion of differentiated tubules. Depletion of neutrophils and T cells after day 5 reduced tubular cell loss and associated kidney atrophy. In kidney biopsies from patients with acute kidney injury, T cell and neutrophil numbers negatively correlated with recovery of estimated glomerular filtration rate. Together, our findings demonstrate that macrophage persistence after injury promotes a T cell- and neutrophil-mediated proinflammatory milieu and progressive tubule damage.

Myeloperoxidase as a Marker to Differentiate Mouse Monocyte/Macrophage Subsets

Macrophages are present in every tissue in the body and play essential roles in homeostasis and host defense against microorganisms. Some tissue macrophages derive from the yolk sac/fetal liver that populate tissues for life. Other tissue macrophages derive from monocytes that differentiate in the bone marrow and circulate through tissues via the blood and lymphatics. Circulating monocytes are very plastic and differentiate into macrophages with specialized functions upon entering tissues. Specialized monocyte/macrophage subsets have been difficult to differentiate based on cell surface markers. Here, using a combination of "pan" monocyte/macrophage markers and flow cytometry, we asked whether myeloperoxidase (MPO) could be used as a marker of pro-inflammatory monocyte/macrophage subsets. MPO is of interest because of its potent microbicidal activity. In wild-type SPF housed mice, we found that MPO⁺ monocytes/macrophages were present in peripheral blood, spleen, small and large intestines, and mesenteric lymph nodes, but not the central nervous system. Only monocytes/macrophages that expressed cell surface F4/80 and/or Ly6C co-expressed MPO with the highest expression in F4/80^HiLy6C^Hi subsets regardless of tissue. These cumulative data indicate that MPO expression can be used as an additional marker to differentiate between monocyte/macrophage subsets with pro-inflammatory and microbicidal activity in a variety of tissues.

Heat acclimation ameliorated heat stress-induced acute kidney injury and prevented changes in kidney macrophages and fibrosis

Heatstroke can cause acute kidney injury (AKI), which reportedly progresses to chronic kidney disease. Kidney macrophages may be involved in such injury. Although heat acclimation (HA) provides thermal resilience, its renoprotective effect and mechanism remain unclear. To investigate heat stress-induced kidney injuries in mice and the mitigating effect of HA on them, male C57/BL6J mice were exposed to heat stress (40℃, 1 h), with or without 5-day HA (38℃, 3 h/day) prior to heat stress. Heat stress damaged kidney proximal tubules with elevation of urinary kidney injury molecule-1 (KIM-1). Kidney fibrosis was observed on day 7 and correlated with the urinary KIM-1 levels on day 3. Kidney resident macrophages decreased on day 1, whereas the number of infiltrating macrophages in the kidney did not change. Both subsets of macrophages polarized to the pro-inflammatory M1 phenotype on day 1; however, they polarized to the anti-inflammatory M2 phenotype on day 7. HA significantly ameliorated heat stress-induced proximal tubular damage and kidney fibrosis. HA substantially increased heat shock protein 70 (Hsp70) expression in the tubules before heat stress and reduced an elevation of cleaved caspase-3 expression after heat stress. HA also induced the Hsp70 expression of resident macrophages and prevented heat stress-induced changes in both subsets of kidney macrophages. These results provide pathophysiological data supporting the renoprotective effect of HA. Further studies are needed to confirm that HA can prevent kidney damage due to heat stress in humans.

High Levels of MFG-E8 Confer a Good Prognosis in Prostate and Renal Cancer Patients

Simple Summary

In the present study, we analyzed the distribution and prognostic impact of milk fat globule-epidermal growth factor-8 (MFG-E8) protein expression in patients with prostate and renal cancers. Our data highlighted MFG-E8 expression by tumor cells in the epithelium. Our results also showed that low levels of MFG-E8 in prostate and renal cancers were associated with worse clinical outcomes. Furthermore, higher numbers of CD206⁺ cells were found in the peripheral regions of renal clear cell carcinoma that expressed lower MFG-E8 levels. Globally, our results suggest that MFG-E8 expression could potentially be used as a prognostic marker in prostate and renal cancers.

Abstract

Milk fat globule-epidermal growth factor-8 (MFG-E8) is a glycoprotein secreted by different cell types, including apoptotic cells and activated macrophages. MFG-E8 is highly expressed in a variety of cancers and is classically associated with tumor growth and poor patient prognosis through reprogramming of macrophages into the pro-tumoral/pro-angiogenic M2 phenotype. To date, correlations between levels of MFG-E8 and patient survival in prostate and renal cancers remain unclear. Here, we quantified MFG-E8 and CD68/CD206 expression by immunofluorescence staining in tissue microarrays constructed from renal (n = 190) and prostate (n = 274) cancer patient specimens. Percentages of MFG-E8-positive surface area were assessed in each patient core and Kaplan–Meier analyses were performed accordingly. We found that MFG-E8 was expressed more abundantly in malignant regions of prostate tissue and papillary renal cell carcinoma but was also increased in the normal adjacent regions in clear cell renal carcinoma. In addition, M2 tumor-associated macrophage staining was increased in the normal adjacent tissues compared to the malignant areas in renal cancer patients. Overall, high tissue expression of MFG-E8 was associated with less disease progression and better survival in prostate and renal cancer patients. Our observations provide new insights into tumoral MFG-E8 content and macrophage reprogramming in cancer.

Bone marrow granulocytes downregulate IL-1β and TNF production and the microbicidal activity of inflammatory macrophages

Macrophages play critical roles in inflammation and defense against pathogens, as well as in the return to tissue homeostasis. Macrophage subpopulations displaying antagonistic phenotypes are generally classified as proinflammatory M1, implicated in antipathogen and antitumoral activities, or as anti-inflammatory M2, associated with tissue repair. Granulocytic and monocytic myeloid-derived suppressor cells recruited from the bone marrow to tissues and phagocytosis of apoptotic neutrophils can attenuate macrophage microbicidal activity. Here, we showed that bone marrow neutrophils, but not thioglycollate-recruited neutrophils, directly suppress the responses of macrophages that were previously committed to an inflammatory phenotype. Cocultures of inflammatory macrophages with bone marrow CD11b+Ly6Ghi granulocytes led to reduced release of IL-1β, TNF-α, and IL-6 by macrophages after lipopolysaccharide stimulation. The suppressive activity was unrelated to granulocyte apoptosis or to secreted factors and required cell-to-cell contact. The suppressive effect was paralleled by reduction in the nuclear levels of the NF-κB p65 subunit, but not of the p50 subunit. Furthermore, bone marrow granulocytes decreased the phagocytic activity of macrophages and their capacity to kill intracellular Escherichia coli. Taken together, these results show that bone marrow granulocytes can function as suppressors of the proinflammatory activity and microbial-killing responses of macrophages.

Occurrences and Functions of Ly6Chi and Ly6Clo Macrophages in Health and Disease

Macrophages originating from the yolk sac or bone marrow play essential roles in tissue homeostasis and disease. Bone marrow-derived monocytes differentiate into Ly6C^hi and Ly6C^lo macrophages according to the differential expression of the surface marker protein Ly6C. Ly6C^hi and Ly6C^lo cells possess diverse functions and transcriptional profiles and can accelerate the disease process or support tissue repair and reconstruction. In this review, we discuss the basic biology of Ly6C^hi and Ly6C^lo macrophages, including their origin, differentiation, and phenotypic switching, and the diverse functions of Ly6C^hi and Ly6C^lo macrophages in homeostasis and disease, including in injury, chronic inflammation, wound repair, autoimmune disease, and cancer. Furthermore, we clarify the differences between Ly6C^hi and Ly6C^lo macrophages and their connections with traditional M1 and M2 macrophages. We also summarize the limitations and perspectives for Ly6C^hi and Ly6C^lo macrophages. Overall, continued efforts to understand these cells may provide therapeutic approaches for disease treatment.

Loss of CD11b Accelerates Lupus Nephritis in Lyn-Deficient Mice Without Disrupting Glomerular Leukocyte Trafficking

Systemic lupus erythematosus (SLE) is a complex, heterogeneous autoimmune disease. A common manifestation, lupus nephritis, arises from immune complex deposition in the kidney microvasculature promoting leukocyte activation and infiltration, which triggers glomerular damage and renal dysfunction. CD11b is a leukocyte integrin mainly expressed on myeloid cells, and aside from its well-ascribed roles in leukocyte trafficking and phagocytosis, it can also suppress cytokine production and autoreactivity. Genome-wide association studies have identified loss-of-function polymorphisms in the CD11b-encoding gene ITGAM that are strongly associated with SLE and lupus nephritis; however, it is not known whether these polymorphisms act alone to induce disease or in concert with other risk alleles. Herein we show using Itgam^-/- mice that loss of CD11b led to mild inflammatory traits, which were insufficient to trigger autoimmunity or glomerulonephritis. However, deficiency of CD11b in autoimmune-prone Lyn-deficient mice (Lyn^-/-Itgam^-/-) accelerated lupus-like disease, driving early-onset immune cell dysregulation, autoantibody production and glomerulonephritis, impacting survival. Migration of leukocytes to the kidney in Lyn^-/- mice was unhindered by lack of CD11b. Indeed, kidney inflammatory macrophages were further enriched, neutrophil retention in glomerular capillaries was increased and kidney inflammatory cytokine responses were enhanced in Lyn^-/-Itgam^-/- mice. These findings indicate that ITGAM is a non-monogenic autoimmune susceptibility gene, with loss of functional CD11b exacerbating disease without impeding glomerular leukocyte trafficking when in conjunction with other pre-disposing genetic mutations. This highlights a primarily protective role for CD11b in restraining inflammation and autoimmune disease and provides a potential therapeutic avenue for lupus treatment.

Peroxisome Proliferator-Activated Receptor-γ Agonist Attenuates Vocal Fold Fibrosis in Rats via Regulation of Macrophage Activation

Macrophages aid in wound healing by changing their phenotype and can be a key driver of fibrosis. However, the contribution of macrophage phenotype to fibrosis following vocal fold injury remains unclear. Peroxisome proliferator-activated receptor-γ (PPARγ) is expressed mainly by macrophages during early wound healing and regulates the macrophage phenotype. This study aimed to evaluate the effects of pioglitazone (PIO), a PPARγ agonist, on the macrophage phenotype and fibrosis following vocal fold injury in rats. PIO was injected into the rat vocal folds on days 1, 3, 5, and 7 after injury, and the vocal fold lamina propria was evaluated on days 4 and 56 after injury. Moreover, THP-1-derived macrophages were treated with PIO, and the expression of proinflammatory cytokines under lipopolysaccharide/interferon-γ stimulation was analyzed. PIO reduced the expression of Ccl2 both in vivo and in vitro. Furthermore, PIO decreased the density of inducible nitric oxide synthase⁺ CD68⁺ macrophages and inhibited the expression of fibrosis-related factors on day 4 after injury. On day 56 after injury, PIO inhibited fibrosis, tissue contracture, and hyaluronic acid loss in a PPARγ-dependent manner. These results indicate that PPARγ activation could inhibit accumulation of inflammatory macrophages and improve tissue repair. Taken together, these findings imply that inflammatory macrophages play a key role in vocal fold fibrosis.

PLX5622 Reduces Disease Severity in Lethal CNS Infection by Off-Target Inhibition of Peripheral Inflammatory Monocyte Production

PLX5622 is a CSF-1R inhibitor and microglia-depleting reagent, widely used to investigate the biology of this central nervous system (CNS)-resident myeloid population, but the indirect or off-target effects of this agent remain largely unexplored. In a murine model of severe neuroinflammation induced by West Nile virus encephalitis (WNE), we showed PLX5622 efficiently depleted both microglia and a sub-population of border-associated macrophages in the CNS. However, PLX5622 also significantly depleted mature Ly6C^hi monocytes in the bone marrow (BM), inhibiting their proliferation and lethal recruitment into the infected brain, reducing neuroinflammation and clinical disease scores. Notably, in addition, BM dendritic cell subsets, plasmacytoid DC and classical DC, were depleted differentially in infected and uninfected mice. Confirming its protective effect in WNE, cessation of PLX5622 treatment exacerbated disease scores and was associated with robust repopulation of microglia, rebound BM monopoiesis and markedly increased inflammatory monocyte infiltration into the CNS. Monoclonal anti-CSF-1R antibody blockade late in WNE also impeded BM monocyte proliferation and recruitment to the brain, suggesting that the protective effect of PLX5622 is via the inhibition of CSF-1R, rather than other kinase targets. Importantly, BrdU incorporation in PLX5622-treated mice, suggest remaining microglia proliferate independently of CSF-1 in WNE. Our study uncovers significantly broader effects of PLX5622 on the myeloid lineage beyond microglia depletion, advising caution in the interpretation of PLX5622 data as microglia-specific. However, this work also strikingly demonstrates the unexpected therapeutic potential of this molecule in CNS viral infection, as well as other monocyte-mediated diseases.

Different Roles of Resident and Non-resident Macrophages in Cardiac Fibrosis

Cardiac fibrosis is a key pathological link of various cardiovascular diseases to heart failure. It is of great significance to deeply understand the development process of cardiac fibrosis and the cellular and molecular mechanisms involved. Macrophages play a special role in promoting heart development, maintaining myocardial cell homeostasis and heart function. They are involved in the whole process from inflammatory to cardiac fibrosis. This article summarizes the relationship between inflammation and fibrosis, discusses the bidirectional regulation of cardiac fibrosis by macrophages and analyses the functional heterogeneity of macrophages from different sources. It is believed that CCR2^– cardiac resident macrophages can promote cardiac function, but the recruitment and infiltration of CCR2⁺ cardiac non-resident macrophages aggravate cardiac dysfunction and heart remodeling. After heart injury, damage associated molecular patterns (DAMPs) are released in large quantities, and the inflammatory signal mediated by macrophage chemoattractant protein-1 (MCP-1) promotes the infiltration of CCR2⁺ monocytes and transforms into macrophages in the heart. These CCR2⁺ non-resident macrophages not only replace part of the CCR2^– resident macrophage subpopulation in the heart, but also cause cardiac homeostasis and hypofunction, and release a large number of mediators that promote fibroblast activation to cause cardiac fibrosis. This article reveals the cell biology mechanism of resident and non-resident macrophages in regulating cardiac fibrosis. It is believed that inhibiting the infiltration of cardiac non-resident macrophages and promoting the proliferation and activation of cardiac resident macrophages are the key to improving cardiac fibrosis and improving cardiac function.

Role of CCR2-Positive Macrophages in Pathological Ventricular Remodelling

Even with recent advances in care, heart failure remains a major cause of morbidity and mortality, which urgently needs new treatments. One of the major antecedents of heart failure is pathological ventricular remodelling, the abnormal change in the size, shape, function or composition of the cardiac ventricles in response to load or injury. Accumulating immune cell subpopulations contribute to the change in cardiac cellular composition that occurs during ventricular remodelling, and these immune cells can facilitate heart failure development. Among cardiac immune cell subpopulations, macrophages that are recognized by their transcriptional or cell-surface expression of the chemokine receptor C-C chemokine receptor type 2 (CCR2), have emerged as playing an especially important role in adverse remodelling. Here, we assimilate the literature that has been generated over the past two decades describing the pathological roles that CCR2+ macrophages play in ventricular remodelling. The goal is to facilitate research and innovation efforts in heart failure therapeutics by drawing attention to the importance of studying the manner by which CCR2+ macrophages mediate their deleterious effects.

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.

Gut Microbiota, Macrophages and Diet: An Intriguing New Triangle in Intestinal Fibrosis

Intestinal fibrosis is a common complication in inflammatory bowel disease (IBD) without specific treatment. As macrophages are the key actors in inflammatory responses and the wound healing process, they have been extensively studied in chronic diseases these past decades. By their exceptional ability to integrate diverse stimuli in their surrounding environment, macrophages display a multitude of phenotypes to underpin a broad spectrum of functions, from the initiation to the resolution of inflammation following injury. The hypothesis that distinct macrophage subtypes could be involved in fibrogenesis and wound healing is emerging and could open up new therapeutic perspectives in the treatment of intestinal fibrosis. Gut microbiota and diet are two key factors capable of modifying intestinal macrophage profiles, shaping their specific function. Defects in macrophage polarisation, inadequate dietary habits, and alteration of microbiota composition may contribute to the development of intestinal fibrosis. In this review, we describe the intriguing triangle between intestinal macrophages, diet, and gut microbiota in homeostasis and how the perturbation of this discreet balance may lead to a pro-fibrotic environment and influence fibrogenesis in the gut.

Macrophage-Specific MCPIP1/Regnase-1 Attenuates Kidney Ischemia-Reperfusion Injury by Shaping the Local Inflammatory Response and Tissue Regeneration

Sterile inflammation either resolves the initial insult or leads to tissue damage. Kidney ischemia/reperfusion injury (IRI) is associated with neutrophilic infiltration, enhanced production of inflammatory mediators, accumulation of necrotic cells and tissue remodeling. Macrophage-dependent microenvironmental changes orchestrate many features of the immune response and tissue regeneration. The activation status of macrophages is influenced by extracellular signals, the duration and intensity of the stimulation, as well as various regulatory molecules. The role of macrophage-derived monocyte chemoattractant protein-induced protein 1 (MCPIP1), also known as Regnase-1, in kidney ischemia-reperfusion injury (IRI) and recovery from sterile inflammation remains unresolved. In this study, we showed that macrophage-specific Mcpip1 deletion significantly affects the kidney phenotype. Macrophage-specific Mcpip1 transgenic mice displayed enhanced inflammation and loss of the tubular compartment upon IRI. We showed that MCPIP1 modulates sterile inflammation by negative regulation of Irf4 expression and accumulation of IRF4+ cells in the tissue and, consequently, suppresses the post-ischemic kidney immune response. Thus, we identified MCPIP1 as an important molecular sentinel of immune homeostasis in experimental acute kidney injury (AKI) and renal fibrosis.

15-Lipoxygenase worsens renal fibrosis, inflammation, and metabolism in a murine model of ureteral obstruction

15-Lipoxygenase (15-LO) is a nonheme iron-containing dioxygenase that has both pro- and anti-inflammatory roles in many tissues and disease states. 15-LO is thought to influence macrophage phenotype, and silencing 15-LO reduces fibrosis after acute inflammatory triggers. The goal of the present study was to determine whether altering 15-LO expression influences inflammation and fibrogenesis in a murine model of unilateral ureteral obstruction (UUO). C57BL/6J mice, 15-LO knockout (Alox15-/-) mice, and 15-LO transgenic overexpressing (15LOTG) mice were subjected UUO, and kidneys were analyzed at 3, 10, and 14 days postinjury. Histology for fibrosis, inflammation, cytokine quantification, flow cytometry, and metabolomics were performed on injured tissues and controls. PD146176, a specific 15-LO inhibitor, was used to complement experiments involving knockout animals. Compared with wild-type animals undergoing UUO, Alox15-/- mouse kidneys had less proinflammatory, profibrotic message along with less fibrosis and macrophage infiltration. PD146176 inhibited 15-LO and resulted in reduced fibrosis and macrophage infiltration similar to Alox15-/- mice. Flow cytometry revealed that Alox15-/- UUO-injured kidneys had a dynamic change in macrophage phenotype, with an early blunting of CD11bHiLy6CHi "M1" macrophages and an increase in anti-inflammatory CD11bHiLy6CInt "M2c" macrophages and reduced expression of the fractalkine receptor chemokine (C-X3-C motif) receptor 1. Many of these findings were reversed when UUO was performed on 15LOTG mice. Metabolomics analysis revealed that wild-type kidneys developed a glycolytic shift postinjury, while Alox15-/- kidneys exhibited increased oxidative phosphorylation. In conclusion, 15-LO manipulation by genetic or pharmacological means induces dynamic changes in the inflammatory microenvironment in the UUO model and appears to be critical in the progression of UUO-induced fibrosis.NEW & NOTEWORTHY 15-Lipoxygenase (15-LO) has both pro- and anti-inflammatory functions in leukocytes, and its role in kidney injury and repair is unexplored. Our study showed that 15-LO worsens inflammation and fibrosis in a rodent model of chronic kidney disease using genetic and pharmacological manipulation. Silencing 15-LO promotes an increase in M2c-like wound-healing macrophages in the kidney and alters kidney metabolism globally, protecting against anaerobic glycolysis after injury.

Kidney VISTA prevents IFNγ-IL-9 axis-mediated tubulointerstitial fibrosis after acute glomerular injury

Severe glomerular injury ultimately leads to tubulointerstitial fibrosis that determines patient outcome, but the immunological molecules connecting these processes remain undetermined. The present study addressed whether V-domain Ig suppressor of T cell activation (VISTA), constitutively expressed in kidney macrophages, plays a protective role in tubulointerstitial fibrotic transformation after acute antibody-mediated glomerulonephritis. After acute glomerular injury using nephrotoxic serum, tubules in the VISTA-deficient (Vsir–/–) kidney suffered more damage than those in WT kidneys. When interstitial immune cells were examined, the contact frequency of macrophages with infiltrated T cells increased and the immunometabolic features of T cells changed to showing high oxidative phosphorylation and fatty acid metabolism and overproduction of IFN-γ. The Vsir–/– parenchymal tissue cells responded to this altered milieu of interstitial immune cells as more IL-9 was produced, which augmented tubulointerstitial fibrosis. Blocking antibodies against IFN-γ and IL-9 protected the above pathological process in VISTA-depleted conditions. In human samples with acute glomerular injury (e.g., antineutrophil cytoplasmic autoantibody vasculitis), high VISTA expression in tubulointerstitial immune cells was associated with low tubulointerstitial fibrosis and good prognosis. Therefore, VISTA is a sentinel protein expressed in kidney macrophages that prevents tubulointerstitial fibrosis via the IFN-γ/IL-9 axis after acute antibody-mediated glomerular injury.

Interplay of immune and kidney resident cells in the formation of tertiary lymphoid structures in lupus nephritis

Kidney involvement confers significant morbidity and mortality in patients with systemic lupus erythematosus (SLE). The pathogenesis of lupus nephritis (LN) involves diverse mechanisms instigated by elements of the autoimmune response which alter the biology of kidney resident cells. Processes in the glomeruli and in the interstitium may proceed independently albeit crosstalk between the two is inevitable. Podocytes, mesangial cells, tubular epithelial cells, kidney resident macrophages and stromal cells with input from cytokines and autoantibodies present in the circulation alter the expression of enzymes, produce cytokines and chemokines which lead to their injury and damage of the kidney. Several of these molecules can be targeted independently to prevent and reverse kidney failure. Tertiary lymphoid structures with true germinal centers are present in the kidneys of patients with lupus nephritis and have been increasingly recognized to associate with poorer renal outcomes. Stromal cells, tubular epithelial cells, high endothelial vessel and lymphatic venule cells produce chemokines which enable the formation of structures composed of a T-cell-rich zone with mature dendritic cells next to a B-cell follicle with the characteristics of a germinal center surrounded by plasma cells. Following an overview on the interaction of the immune cells with kidney resident cells, we discuss the cellular and molecular events which lead to the formation of tertiary lymphoid structures in the interstitium of the kidneys of mice and patients with lupus nephritis. In parallel, molecules and processes that can be targeted therapeutically are presented.

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.

Apamin inhibits renal fibrosis via suppressing TGF-β1 and STAT3 signaling in vivo and in vitro

Renal fibrosis is a progressive and chronic process that influences kidneys with chronic kidney disease (CKD), irrespective of cause, leading to irreversible failure of renal function and end-stage kidney disease. Among the signaling related to renal fibrosis, transforming growth factor-β1 (TGF-β1) signaling is a major pathway that induces the activation of myofibroblasts and the production of extracellular matrix (ECM) molecules. Apamin, a component of bee venom (BV), has been studied in relation to various diseases. However, the effect of apamin on renal interstitial fibrosis has not been investigated. The aim of this study was to estimate the beneficial effect of apamin in unilateral ureteral obstruction (UUO)-induced renal fibrosis and TGF-β1-induced renal fibroblast activation. This study revealed that obstructive kidney injury induced an inflammatory response, tubular atrophy, and ECM accumulation. However, apamin treatment suppressed the increased expression of fibrotic-related genes, including α-SMA, vimentin, and fibronectin. Administration of apamin also attenuated the renal tubular cells injury and tubular atrophy. In addition, apamin attenuated fibroblast activation, ECM synthesis, and inflammatory cytokines such as TNF-α, IL-1β, and IL-6 by suppressing the TGF-β1-canonical and non-canonical signaling pathways. This study showed that apamin inhibits UUO-induced renal fibrosis in vivo and TGF-β1-induced renal fibroblasts activation in vitro. Apamin inhibited the inflammatory response, tubular atrophy, ECM accumulation, fibroblast activation, and renal interstitial fibrosis through suppression of TGF-β1/Smad2/3 and STAT3 signaling pathways. These results suggest that apamin might be a potential therapeutic agent for renal fibrosis. KEY MESSAGES: UUO injury can induce renal dysfunction; however, apamin administration prevents renal failure in UUO mice. Apamin inhibited renal inflammatory response and ECM deposition in UUO-injured mice. Apamin suppressed the activation of myofibroblasts in vivo and in vitro. Apamin has the anti-fibrotic effect on renal fibrosis via regulation of TGF-β1 canonical and non-canonical signaling.

PP2Acα promotes macrophage accumulation and activation to exacerbate tubular cell death and kidney fibrosis through activating Rap1 and TNFα production

Macrophage accumulation and activation play an essential role in kidney fibrosis; however, the underlying mechanisms remain to be explored. By analyzing the kidney tissues from patients and animal models with kidney fibrosis, we found a large induction of PP2Acα in macrophages. We then generated a mouse model with inducible macrophage ablation of PP2Acα. The knockouts developed less renal fibrosis, macrophage accumulation, or tubular cell death after unilateral ureter obstruction or ischemic reperfusion injury compared to control littermates. In cultured macrophages, PP2Acα deficiency resulted in decreased cell motility by inhibiting Rap1 activity. Moreover, co-culture of PP2Acα^-/- macrophages with tubular cells resulted in less tubular cell death attributed to downregulated Stat6-mediated tumor necrosis factor α (TNFα) production in macrophages. Together, this study demonstrates that PP2Acα promotes macrophage accumulation and activation, hence accelerates tubular cell death and kidney fibrosis through regulating Rap1 activation and TNFα production.

Twist1 in podocytes ameliorates podocyte injury and proteinuria by limiting CCL2-dependent macrophage infiltration

The transcription factor Twist1 regulates several processes that could impact kidney disease progression, including epithelial cell differentiation and inflammatory cytokine induction. Podocytes are specialized epithelia that exhibit features of immune cells and could therefore mediate unique effects of Twist1 on glomerular disease. To study Twist1 functions in podocytes during proteinuric kidney disease, we employed a conditional mutant mouse in which Twist1 was selectively ablated in podocytes (Twist1-PKO). Deletion of Twist1 in podocytes augmented proteinuria, podocyte injury, and foot process effacement in glomerular injury models. Twist1 in podocytes constrained renal accumulation of monocytes/macrophages and glomerular expression of CCL2 and the macrophage cytokine TNF-α after injury. Deletion of TNF-α selectively from podocytes had no impact on the progression of proteinuric nephropathy. By contrast, the inhibition of CCL2 abrogated the exaggeration in proteinuria and podocyte injury accruing from podocyte Twist1 deletion. Collectively, Twist1 in podocytes mitigated urine albumin excretion and podocyte injury in proteinuric kidney diseases by limiting CCL2 induction that drove monocyte/macrophage infiltration into injured glomeruli. Myeloid cells, rather than podocytes, further promoted podocyte injury and glomerular disease by secreting TNF-α. These data highlight the capacity of Twist1 in the podocyte to mitigate glomerular injury by curtailing the local myeloid immune response.

Kidney organoid systems for studies of immune-mediated kidney diseases: challenges and opportunities

Acute and chronic kidney diseases are major contributors to morbidity and mortality in the global population. Many nephropathies are considered to be immune-mediated with dysregulated immune responses playing an important role in the pathogenesis. At present, targeted approaches for many kidney diseases are still lacking, as the underlying mechanisms remain insufficiently understood. With the recent development of organoids—a three-dimensional, multicellular culture system, which recapitulates important aspects of human tissues—new opportunities to investigate interactions between renal cells and immune cells in the pathogenesis of kidney diseases arise. To date, kidney organoid systems, which reflect the structure and closer resemble critical aspects of the organ, have been established. Here, we highlight the recent advances in the development of kidney organoid models, including pluripotent stem cell-derived kidney organoids and primary epithelial cell-based tubuloids. The employment and further required advances of current organoid models are discussed to investigate the role of the immune system in renal tissue development, regeneration, and inflammation to identify targets for the development of novel therapeutic approaches of immune-mediated kidney diseases.

Single-Cell RNA Sequencing Reveals the Immunological Profiles of Renal Allograft Rejection in Mice

Allograft rejection is a common immunological feature in renal transplantation and is associated with reduced graft survival. A mouse renal allograft rejection model was induced and single-cell RNA sequencing (scRNA-seq) data of CD45+ leukocytes in kidney allografts on days 7 (D7) and 15 (D15) after operation was analyzed to reveal a full immunological profiling. We identified 20 immune cell types among 10,921 leukocytes. Macrophages and CD8+ T cells constituted the main populations on both timepoints. In the process from acute rejection (AR) towards chronic rejection (CR), the proportion of proliferating and naïve CD8+ T cells dropped significantly. Both B cells and neutrophils decreased by about 3 folds. On the contrary, the proportion of macrophages and dendritic cells (DCs) increased significantly, especially by about a 4.5-fold increase in Ly6cloMrc1+ macrophages and 2.6 folds increase in Ly6cloEar2+ macrophages. Moreover, myeloid cells harbored the richest ligand and receptor (LR) pairs with other cells, particularly for chemokine ligands such as Cxcl9, Cxcl10, Cxcl16 and Yars. However, macrophages with weak response to interferon gamma (IFNg) contributed to rejection chronicization. To conclude, reduction in CD8 T cells, B cells and neutrophils while increasing in Ly6cloMrc1+ macrophages and Ly6cloEar2+ macrophages, may contribute significantly to the progress from AR towards CR.

A flow cytometry approach reveals heterogeneity in conventional subsets of murine renal mononuclear phagocytes

Mononuclear phagocytes (MNPs) participate in inflammation and repair after kidney injury, reflecting their complex nature. Dissection into refined functional subunits has been challenging and would benefit understanding of renal pathologies. Flow cytometric approaches are limited to classifications of either different MNP subsets or functional state. We sought to combine these two dimensions in one protocol that considers functional heterogeneity in each MNP subset. We identified five distinct renal MNP subsets based on a previously described strategy. In vitro polarization of bone marrow-derived macrophages (BMDM) into M1- and M2-like cells suggested functional distinction of CD86 + MHCII + CD206- and CD206 + cells. Combination of both distinction methods identified CD86 + MHCII + CD206- and CD206 + cells in all five MNP subsets, revealing their heterologous nature. Our approach revealed that MNP composition and their functional segmentation varied between different mouse models of kidney injury and, moreover, was dynamically regulated in a time-dependent manner. CD206 + cells from three analyzed MNP subsets had a higher ex vivo phagocytic capacity than CD86 + MHCII + CD206- counterparts, indicating functional uniqueness of each subset. In conclusion, our novel flow cytometric approach refines insights into renal MNP heterogeneity and therefore could benefit mechanistic understanding of renal pathology.

The Role of Ageing and Parenchymal Senescence on Macrophage Function and Fibrosis

In this review, we examine senescent cells and the overlap between the direct biological impact of senescence and the indirect impact senescence has via its effects on other cell types, particularly the macrophage. The canonical roles of macrophages in cell clearance and in other physiological functions are discussed with reference to their functions in diseases of the kidney and other organs. We also explore the translational potential of different approaches based around the macrophage in future interventions to target senescent cells, with the goal of preventing or reversing pathologies driven or contributed to in part by senescent cell load in vivo.

Chess Not Checkers: Complexities Within the Myeloid Response to the Acute Kidney Injury Syndrome

Immune dysregulation in acute kidney injury (AKI) is an area of intense interest which promises to enhance our understanding of the disease and how to manage it. Macrophages are a heterogeneous and dynamic population of immune cells that carry out multiple functions in tissue, ranging from maintenance to inflammation. As key sentinels of their environment and the major immune population in the uninjured kidney, macrophages are poised to play an important role in the establishment and pathogenesis of AKI. These cells have a profound capacity to orchestrate downstream immune responses and likely participate in skewing the kidney environment toward either pathogenic inflammation or injury resolution. A clear understanding of macrophage and myeloid cell dynamics in the development of AKI will provide valuable insight into disease pathogenesis and options for intervention. This review considers evidence in the literature that speaks to the role and regulation of macrophages and myeloid cells in AKI. We also highlight barriers or knowledge gaps that need to be addressed as the field advances.

Macrophage Heterogeneity in Kidney Injury and Fibrosis

Kidney macrophages are central in kidney disease pathogenesis and have therapeutic potential in preventing tissue injury and fibrosis. Recent studies highlighted that kidney macrophages are notably heterogeneous immune cells that fulfill opposing functions such as clearing deposited pathogens, maintaining immune tolerance, initiating and regulating inflammatory responses, promoting kidney fibrosis, and degrading the extracellular matrix. Macrophage origins can partially explain macrophage heterogeneity in the kidneys. Circulating Ly6C⁺ monocytes are recruited to inflammatory sites by chemokines, while self-renewed kidney resident macrophages contribute to kidney repair and fibrosis. The proliferation of resident macrophages or infiltrating monocytes provides an alternative explanation of macrophage accumulation after kidney injury. In addition, dynamic Ly6C expression on infiltrating monocytes accompanies functional changes in handling kidney inflammation and fibrosis. Mechanisms underlying kidney macrophage heterogeneity, either by recruiting monocyte subpopulations, regulating macrophage polarization, or impacting distinctive macrophage functions, may help develop macrophage-targeted therapies for kidney diseases.

Kidney pericyte hypoxia-inducible factor regulates erythropoiesis but not kidney fibrosis

Prolyl hydroxylase domain enzyme (PHD) inhibitors are effective in the treatment of chronic kidney disease (CKD)-associated anemia by stabilizing hypoxia inducible factor (HIF), thereby increasing erythropoietin and consequently erythropoiesis. However, concern for CKD progression needs to be addressed in clinical trials. Although pre-clinical studies showed an anti-inflammatory effect in kidney disease models, the effect of PHD inhibitors on kidney fibrosis was inconsistent probably because the effects of HIF are cell type and context dependent. The major kidney erythropoietin-producing cells are pericytes that produce erythropoietin through HIF-2α-dependent gene transcription. The concern for the impact of HIF in pericytes on kidney fibrosis arises from the fact that pericytes are the major precursor cells of myofibroblasts in CKD. Since cells expressing Gli1 fulfill the morphologic and anatomic criteria for pericytes, we induced Gli1⁺ cell-specific HIF stabilization or knockout to study the impact of HIF in pericytes on kidney pathology of mice with or without fibrotic injury induced by unilateral ureteral obstruction. Compared with the littermate controls, mice with pericyte-specific HIF stabilization due to von Hippel-Lindau protein or PHD2 knockout showed increased serum erythropoietin and polycythemia rather than a discernible difference in kidney fibrosis. Compared with Gli1⁺ pericytes sorted from littermate controls, Gli1⁺ pericytes sorted from PHD2 knockout mice showed increased erythropoietin gene expression rather than discernible changes in Col1a1 or Acta2 expression. Furthermore, pericyte-specific knockout of HIF-1α or HIF-2α did not affect kidney fibrosis. Thus, our study supports the absence of negative effects of PHD inhibitors on kidney fibrosis of mice despite HIF stabilization in pericytes.

Respiratory and systemic impacts following MWCNT inhalation in B6C3F1/N mice

Background

A very pure multi-walled carbon nanotube (MWCNT) that was shown to have very low toxicity in vitro, was evaluated for lung and systemic effects and distribution following inhalation exposure.

Methods

B6C3F1/N mice were exposed to varying doses (0, 0.06, 0.2, and 0.6 mg/m³) of the (99.1% carbon) MWCNT by inhalation for 30 days (excluding weekends). Ten days following the last exposure, the lungs and spleen were harvested and processed for histology and immune cell population assessment. In addition, lung lavage cells and fluid were analyzed. Stimulated Raman scattering (SRS) was used to identify particles in the lungs, spleen, kidneys, liver, mediastinal and brachial lymph nodes, and olfactory bulb. Splenic tissue sections were stained with hematoxylin and eosin (H&E) for light microscopic histopathology assessment. Blood plasma was analyzed for cytokines and cathepsins. A section of the spleen was processed for RNA isolation and relative gene expression for 84 inflammation-related cytokines/chemokines.

Results

Following MWCNT exposure, particles were clearly evident in the lungs, spleens, lymph nodes and olfactory bulbs, (but not livers or kidneys) of exposed mice in a dose-dependent manner. Examination of the lavaged lung cells was unremarkable with no significant inflammation indicated at all particle doses. In contrast, histological examination of the spleen indicated the presence of apoptotic bodies within T cells regions of the white pulp area. Isolated splenic leukocytes had significant changes in various cells including an increased number of proinflammatory CD11b⁺Ly6C⁺ splenic cells. The gene expression studies confirmed this observation as several inflammation-related genes were upregulated particularly in the high dose exposure (0.6 mg/m³). Blood plasma evaluations showed a systemic down-regulation of inflammatory cytokines and a dose-dependent up-regulation of lysosomal cathepsins.

Conclusions

The findings in the lungs were consistent with our hypothesis that this MWCNT exposure would result in minimal lung inflammation and injury. However, the low toxicity of the MWCNT to lung macrophages may have contributed to enhanced migration of the MWCNT to the spleen through the lymph nodes, resulting in splenic toxicity and systemic changes in inflammatory mediators.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00408-z.