Pathogenic and protective role of macrophages in kidney disease

Glycyrrhizin attenuates renal inflammation in a mouse Con A-hepatitis model via the IL-25/M2 axis

Glycyrrhizin (GL) has immunoregulatory effects on various inflammatory diseases including hepatitis and nephritis. However, the mechanisms underlying the anti-inflammatory effect of GL on renal inflammation are not fully understood. Hepatorenal syndrome (HRS) is a functional acute renal impairment that occurs in severe liver disease, and we found that kidney injury also occurs in Con A-induced experimental hepatitis in mice. We previously found that GL can alleviate Con A-induced hepatitis by regulating the expression of IL-25 in the liver. We wanted to investigate whether GL can alleviate Con A-induced nephritis by regulating IL-25. IL-25 regulates inflammation by modulating type 2 immune responses, but the mechanism by which IL-25 affects kidney disease remains unclear. In this study, we found that the administration of GL enhanced the expression of IL-25 in renal tissues; the latter promoted the generation of type 2 macrophages (M2), which inhibited inflammation in the kidney caused by Con A challenge. IL-25 promoted the secretion of the inhibitory cytokine IL-10 by macrophages but inhibited the expression of the inflammatory cytokine IL-1β by macrophages. Moreover, IL-25 downregulated the Con A-mediated expression of Toll-like receptor (TLR) 4 on macrophages. By comparing the roles of TLR2 and TLR4, we found that TLR4 is required for the immunoregulatory effect of IL-25 on macrophages. Our data revealed that GL has anti-inflammatory effects on Con A-induced kidney injury and that the GL/IL-25/M2 axis participates in the anti-inflammatory process. This study suggested that GL is a potential therapeutic for protecting against acute kidney injury.

Responses of peritubular macrophages and the testis transcriptome profiles of peripubertal and adult rodents exposed to an acute dose of MEHP

Exposure of rodents to mono-(2-ethylhexyl) phthalate (MEHP) is known to disrupt the blood-testis barrier and cause testicular germ cell apoptosis. Peritubular macrophages (PTMφ) are a newly identified type of testicular macrophage that aggregates near the spermatogonial stem cell niche. We have previously reported that MEHP exposure increased the numbers of PTMφs by 6-fold within the testis of peripubertal rats. The underlying mechanism(s) accounting for this change in PTMφs and its biological significance is unknown. This study investigates if MEHP-induced alterations in PTMφs occur in rodents (PND 75 adult rats and PND 26 peripubertal mice) that are known to be less sensitive to MEHP-induced testicular toxicity. Results show that adult rats have a 2-fold higher basal level of PTMφ numbers than species-matched peripubertal animals, but there was no significant increase in PTMφ numbers after MEHP exposure. Peripubertal mice have a 5-fold higher basal level of PTMφ compared with peripubertal rats but did not exhibit increases in number after MEHP exposure. Further, the interrogation of the testis transcriptome was profiled from both the MEHP-responsive peripubertal rats and the less sensitive rodents via 3' Tag sequencing. Significant changes in gene expression were observed in peripubertal rats after MEHP exposure. However, adult rats showed lesser changes in gene expression, and peripubertal mice showed only minor changes. Collectively, the data show that PTMφ numbers are associated with the sensitivity of rodents to MEHP in an age- and species-dependent manner.

Role of renal tubular epithelial cells and macrophages in cisplatin-induced acute renal injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a sudden and continuous decline in renal function. The drug cisplatin is commonly used as chemotherapy for solid tumors, and cisplatin-induced acute kidney injury (CI-AKI), which is characterized by acute tubular necrosis and inflammation, frequently occurs in tumor patients. Renal tubular epithelial cells (RTECs) are severely damaged early in this process and play an important role in renal tubular injury and the recruitment of immune cells. Macrophages are the most common infiltrating immune cells in the kidney and have a significant impact on CI-AKI and subsequent repair. This article reviews the latest research progress on the effects of RTECs and macrophages on CI-AKI and their interactions in AKI to provide a direction for identifying therapeutic targets for treating AKI.

Mirabegron, dependent on β3-adrenergic receptor, alleviates mercuric chloride-induced kidney injury by reversing the impact on the inflammatory network, M1/M2 macrophages, and claudin-2

The β3-adrenergic receptor (β3-AR) agonism mirabegron is used to treat overactive urinary bladder syndrome; however, its role against acute kidney injury (AKI) is not unveiled, hence, we aim to repurpose mirabegron in the treatment of mercuric chloride (HgCl2)-induced AKI. Rats were allocated into normal, normal + mirabegron, HgCl2 untreated, HgCl2 + mirabegron, and HgCl2 + the β3-AR blocker SR59230A + mirabegron. The latter increased the mRNA of β3-AR and miR-127 besides downregulating NF-κB p65 protein expression and the contents of its downstream targets iNOS, IL-4, -13, and -17 but increased that of IL-10 to attest its anti-inflammatory capacity. Besides, mirabegron downregulated the protein expression of STAT-6, PI3K, and ERK1/2, the downstream targets of the above cytokines. Additionally, it enhanced the transcription factor PPAR-α but turned off the harmful hub HNF-4α/HNF-1α and the lipid peroxide marker MDA. Mirabegron also downregulated the CD-163 protein expression, which besides the inhibited correlated cytokines of M1 (NF-κB p65, iNOS, IL-17) and M2 (IL-4, IL-13, CD163, STAT6, ERK1/2), inactivated the macrophage phenotypes. The crosstalk between these parameters was echoed in the maintenance of claudin-2, kidney function-related early (cystatin-C, KIM-1, NGAL), and late (creatinine, BUN) injury markers, besides recovering the microscopic structures. Nonetheless, the pre-administration of SR59230A has nullified the beneficial effects of mirabegron on the aforementioned parameters. Here we verified that mirabegron can berepurposedto treat HgCl2-induced AKI by activating the β3-AR. Mirabegron signified its effect by inhibiting inflammation, oxidative stress, and the activated M1/M2 macrophages, events that preserved the proximal tubular tight junction claudin-2 via the intersection of several trajectories.

New biomarkers in acute kidney injury

Acute kidney injury (AKI) is a commonly encountered clinical syndrome. Although it often complicates community acquired illness, it is more common in hospitalized patients, particularly those who are critically ill or who have undergone major surgery. Approximately 20% of hospitalized adult patients develop an AKI during their hospital care, and this rises to nearly 60% in the critically ill, depending on the population being considered. In general, AKI is more common in older adults, in those with preexisting chronic kidney disease and in those with known risk factors for AKI (including diabetes and hypertension). The development of AKI is associated with an increase in both mortality and morbidity, including the development of post-AKI chronic kidney disease. Currently, AKI is defined by a rise in serum creatinine from either a known or derived baseline value and/or oliguria or anuria. However, clinicians may fail to recognize the initial development of AKI because of a delay in the rise of serum creatinine or because of inaccurate urine output monitoring. This, in turn, delays any putative measures to treat AKI or to limit its degree. Consequently, efforts have focused on new biomarkers associated with AKI that may allow early recognition of this syndrome with the intent that this will translate into improved patient outcomes. Here we outline current biomarkers associated with AKI and explore their potential in aiding diagnosis, understanding the pathophysiology and directing therapy.

Oxalate disrupts monocyte and macrophage cellular function via Interleukin-10 and mitochondrial reactive oxygen species (ROS) signaling

Oxalate is a small compound found in certain plant-derived foods and is a major component of calcium oxalate (CaOx) kidney stones. Individuals that consume oxalate enriched meals have an increased risk of forming urinary crystals, which are precursors to CaOx kidney stones. We previously reported that a single dietary oxalate load induces nanocrystalluria and reduces monocyte cellular bioenergetics in healthy adults. The purpose of this study was to extend these investigations to identify specific oxalate-mediated mechanisms in monocytes and macrophages. We performed RNA-Sequencing analysis on monocytes isolated from healthy subjects exposed to a high oxalate (8 mmol) dietary load. RNA-sequencing revealed 1,198 genes were altered and Ingenuity Pathway Analysis demonstrated modifications in several pathways including Interleukin-10 (IL-10) anti-inflammatory cytokine signaling, mitochondrial metabolism and function, oxalic acid downstream signaling, and autophagy. Based on these findings, we hypothesized that oxalate induces mitochondrial and lysosomal dysfunction in monocytes and macrophages via IL-10 and reactive oxygen species (ROS) signaling which can be reversed with exogenous IL-10 or Mitoquinone (MitoQ; a mitochondrial targeted antioxidant). We exposed monocytes and macrophages to oxalate in an in-vitro setting which caused oxidative stress, a decline in IL-10 cytokine levels, mitochondrial and lysosomal dysfunction, and impaired autophagy in both cell types. Administration of exogenous IL-10 and MitoQ attenuated these responses. These findings suggest that oxalate impairs metabolism and immune response via IL-10 signaling and mitochondrial ROS generation in both monocytes and macrophages which can be potentially limited or reversed. Future studies will examine the benefits of these therapies on CaOx crystal formation and growth in vivo.

The role of regulatory T cells in the pathogenesis of acute kidney injury

The incidence of acute kidney injury (AKI) is on the rise and is associated with high mortality; however, there are currently few effective treatments. Moreover, the relationship between Tregs and other components of the immune microenvironment (IME) in the pathogenesis of AKI remains unclear. We downloaded four publicly accessible AKI datasets, GSE61739, GSE67401, GSE19130, GSE81741, GSE19288 and GSE106993 from the gene expression omnibus (GEO) database. Additionally, we gathered two kidney single-cell sequencing (scRNA-seq) samples from the Department of Organ Transplantation at Zhujiang Hospital of Southern Medical University to investigate chronic kidney transplant rejection (CKTR). Moreover, we also collected three samples of normal kidney tissue from GSE131685. By analysing the differences in immune cells between the AKI and Non-AKI groups, we discovered that the Non-AKI group contained a significantly greater number of Tregs than the AKI group. Additionally, the activation of signalling pathways, such as inflammatory molecules secretion, immune response, glycolytic metabolism, NOTCH, FGF, NF-κB and TLR4, was significantly greater in the AKI group than in the Non-AKI group. Additionally, analysis of single-cell sequencing data revealed that Tregs in patients with chronic kidney rejection and in normal kidney tissue have distinct biology, including immune activation, cytokine production, and activation fractions of signalling pathways such as NOTCH and TLR4. In this study, we found significant differences in the IME between AKI and Non-AKI, including differences in Tregs cells and activation levels of biologically significant signalling pathways. Tregs were associated with lower activity of signalling pathways such as inflammatory response, inflammatory molecule secretion, immune activation, glycolysis.

Arginase 2 Promotes Cisplatin-Induced Acute Kidney Injury by the Inflammatory Response of Macrophages

Acute kidney injury (AKI) is a complex clinical syndrome with a rapid decrease in renal function caused by several different etiologies, including sepsis, ischemia, and the administration of nephrotoxic drugs. Tubular arginase 2 (ARG2), an arginine-metabolic enzyme, is a potential therapeutic target for AKI, but it has not been confirmed under various AKI conditions. The aim of this study was to investigate ARG2 as a therapeutic target for cisplatin-induced AKI. Cisplatin-treated mice with a genetic deficiency in Arg2 had significant amelioration of renal dysfunction, characterized by decreased acute tubular damage and apoptosis. In contrast, cisplatin-induced tubular toxicity was not ameliorated in proximal tubule cells derived from Arg2-deficient mice. Immunohistochemical analysis demonstrated the increased infiltration of ARG2-positive macrophages in kidneys damaged by cisplatin. Importantly, cisplatin-treated Arg2 knockout mice exhibited a significant reduction in kidney inflammation, characterized by the decreased infiltration of inflammatory macrophages and reduced gene expression of interleukin (IL)-6 and IL-1β. The secretion of IL-6 and IL-1β induced by lipopolysaccharides was decreased in bone marrow-derived macrophages isolated from Arg2-deficient mice. Furthermore, the lipopolysaccharide-induced elevation of mitochondrial membrane potential and production of reactive oxygen species were reduced in bone marrow-derived macrophages lacking Arg2. These findings indicate that ARG2 promotes the inflammatory responses of macrophages through mitochondrial reactive oxygen species, resulting in the exacerbation of AKI. Therefore, targeting ARG2 in macrophages may constitute a promising therapeutic approach for AKI.

Chronic treatment with IL-25 increases renal M2 macrophages and reduces renal injury in obese Dahl salt-sensitive rats during the prepubescent stage

Recently, we have reported that the early progression of proteinuria in the obese Dahl salt-sensitive (SS) leptin receptor mutant (SSLepRmutant) strain was associated with increased renal macrophage infiltration before puberty. Macrophages can be divided into two distinct phenotypes: M1 (proinflammatory) and M2 (anti-inflammatory). Moreover, previous studies have demonstrated that interleukin (IL)-25 converts resting macrophages and M1 into M2. Therefore, the present study examined whether treatment with IL-25 would reduce the early progression of renal injury in SSLepRmutant rats by increasing renal M2. We also investigated the impact of IL-25 on M2 subtypes: M2a (wound healing/anti-inflammatory), M2b (immune mediated/proinflammatory), M2c (regulatory/anti-inflammatory), and M2d (tumor associated/proangiogenic). Four-wk-old SS and SSLepRmutant rats were treated with either control (IgG) or IL-25 (1 µg/day ip every other day) for 4 wk. The kidneys from SSLepRmutant rats displayed progressive proteinuria and renal histopathology versus SS rats. IL-25 treatment had no effect on these parameters in SS rats. However, in the SSLepRmutant strain, proteinuria was markedly reduced after IL-25 treatment. Chronic treatment with IL-25 significantly decreased glomerular and tubular injury and renal fibrosis in the SSLepRmutant strain. Although the administration of IL-25 did not change total renal macrophage infiltration in both SS and SSLepRmutant rats, IL-25 increased M2a by >50% and reduced M1 by 60% in the kidneys of SSLepRmutant rats. Overall, these data indicate that IL-25 reduces the early progression of renal injury in SSLepRmutant rats by inducing M2a and suppressing M1 and suggest that IL-25 may be a therapeutic target for renal disease associated with obesity. NEW & NOTEWORTHY For the past few decades, immune cells and inflammatory cytokines have been demonstrated to play an important role in the development of renal disease. The present study provides strong evidence that interleukin-25 slows the early progression of renal injury in obese Dahl salt-sensitive rats before puberty by increasing systemic anti-inflammatory cytokines and renal M2a macrophages.

Peroxiredoxin 1 aggravates acute kidney injury by promoting inflammation through Mincle/Syk/NF-κB signaling

Damage-associated molecular patterns (DAMPs) are a cause of acute kidney injury (AKI). Our knowledge of these DAMPs remains incomplete. Here, we report serum peroxiredoxin 1 (Prdx1) as a novel DAMP for AKI. Lipopolysaccharide (LPS) and kidney ischemia/reperfusion injury instigated AKI with concurrent increases in serum Prdx1 and reductions of Prdx1 expression in kidney tubular epithelial cells. Genetic knockout of Prdx1 or use of a Prdx1-neutralizing antibody protected mice from AKI and this protection was impaired by introduction of recombinant Prdx1 (rPrdx1). Mechanistically, lipopolysaccharide increased serum and kidney proinflammatory cytokines, macrophage infiltration, and the content of M1 macrophages. All these events were suppressed in Prdx1-/- mice and renewed upon introduction of rPrdx1. In primary peritoneal macrophages, rPrdx1 induced M1 polarization, activated macrophage-inducible C-type lectin (Mincle) signaling, and enhanced proinflammatory cytokine production. Prdx1 interacted with Mincle to initiate acute kidney inflammation. Of note, rPrdx1 upregulated Mincle and the spleen tyrosine kinase Syk system in the primary peritoneal macrophages, while knockdown of Mincle abolished the increase in activated Syk. Additionally, rPrdx1 treatment enhanced the downstream events of Syk, including transcription factor NF-κB signaling pathways. Furthermore, serum Prdx1 was found to be increased in patients with AKI; the increase of which was associated with kidney function decline and inflammatory biomarkers in patient serum. Thus, kidney-derived serum Prdx1 contributes to AKI at least in part by activating Mincle signaling and downstream pathways.

The Potential Biotherapeutic Targets of Contrast-Induced Acute Kidney Injury

Contrast-induced acute kidney injury (CI-AKI) is manifested by an abrupt decline in kidney function as a consequence of intravascular exposure to contrast media. With the increased applicability of medical imaging and interventional procedures that utilize contrast media for clinical diagnosis, CI-AKI is becoming the leading cause of renal dysfunction. The pathophysiological mechanism associated with CI-AKI involves renal medullary hypoxia, the direct toxicity of contrast agents, oxidative stress, apoptosis, inflammation, and epigenetic regulation. To date, there is no effective therapy for CI-AKI, except for the development of strategies that could reduce the toxicity profiles of contrast media. While most of these strategies have failed, evidence has shown that the proper use of personalized hydration, contrast medium, and high-dose statins may reduce the occurrence of CI-AKI. However, adequate risk predication and attempts to develop preventive strategies can be considered as the key determinants that can help eliminate CI-AKI. Additionally, a deeper understanding of the pathophysiological mechanism of CI-AKI is crucial to uncover molecular targets for the prevention of CI-AKI. This review has taken a step further to solidify the current known molecular mechanisms of CI-AKI and elaborate the biomarkers that are used to detect early-stage CI-AKI. On this foundation, this review will analyze the molecular targets relating to apoptosis, inflammation, oxidative stress, and epigenetics, and, thus, provide a strong rationale for therapeutic intervention in the prevention of CI-AKI.

HLA class II antibody activation of endothelial cells induces M2 macrophage differentiation in peripheral blood

BACKGROUND

Donor-specific human leukocyte antigen (HLA) class II antibodies (HLA-II Abs) combined with allogeneic endothelial cells (ECs) mediate high-risk rejection in kidney transplant patients. Macrophage accumulation is a significant histological feature of antibody-mediated rejection (AMR) in kidney transplant patients. Here, we further investigated the effect of HLA-II Abs on macrophage phenotypes to provide theoretical basis for clinical treatment of AMR.

METHODS

We prepared an experimental model containing HLA-II Ab-stimulated microvascular ECs and peripheral blood mononuclear cells (PBMCs) co-culture and explored the potential relationship of HLA-II Ab, ECs activation, and macrophage differentiation. Immune phenotype of macrophage subsets was analyzed and quantified by flow cytometry. HLA-II Ab activation of ECs induces M2 macrophage differentiation signal pathways which were investigated by qPCR and western blotting.

RESULTS

The stimulation of ECs by F(ab')₂ fragment of HLA-II Abs led to phosphorylation of PI3K, Akt, and mTOR, which mediated IL-10, ICAM-1, VCAM-1 secretion. The enhanced ICAM-1 and IL-10 promoted the migration of PBMCs and their differentiation into CD68⁺ and CD163⁺ (M2-type) macrophages, respectively, but not CD86⁺ macrophages.

CONCLUSION

These findings revealed the PI3K/Akt/mTOR signal pathways activated by HLA-II Abs in ECs and the immune regulation ability of HLA-II Abs to induce PBMC differentiation.

Macrophages in Renal Injury, Repair, Fibrosis Following Acute Kidney Injury and Targeted Therapy

Acute kidney injury (AKI) is a renal disease with a high incidence and mortality. Currently, there are no targeted therapeutics for preventing and treating AKI. Macrophages, important players in mammalian immune response, are involved in the multiple pathological processes of AKI. They are dynamically activated and exhibit a diverse spectrum of functional phenotypes in the kidney after AKI. Targeting the mechanisms of macrophage activation significantly improves the outcomes of AKI in preclinical studies. In this review, we summarize the role of macrophages and the underlying mechanisms of macrophage activation during kidney injury, repair, regeneration, and fibrosis and provide strategies for macrophage-targeted therapies.

Biomimetic Micelles to Accurately Regulate the Inflammatory Microenvironment for Glomerulonephritis Treatment

Glomerulonephritis is a key factor in leading to end-stage renal disease. Mesangial cell proliferation and macrophage infiltration are two prominent features linked in a vicious circle mechanism for glomerulonephritis progression. Herein, a novel biomimetic pH-sensitive nanomicelle (MM/HA-DXM) was constructed to synergize hyaluronic acid (HA)-activated macrophage phenotypic remodeling and dexamethasone (DXM)-mediated mesangial cell killing for precise treatment of glomerulonephritis. Owing to the camouflaged coating with endogenous macrophage membrane (MM), MM/HA-DXM could escape from RES phagocytosis and then be recruited to inflammatory glomerulus by active homing effect. Afterwards, HA-DXM nanomicelles ruptured in response to the weakly acidic glomerulonephritis microenvironment, to locally release HA and DXM. On the one hand, DXM can inhibit the abnormal proliferation of mesangial cells. On the other hand, HA transformed pro-inflammatory M1 macrophages into anti-inflammatory M2 phenotype to improve the glomerular inflammatory microenvironment. In doxorubicin-induced glomerulonephritis models, results revealed that MM/HA-DXM could specifically "homing" to inflammatory renal tissue with 4.33-fold improvement in targeting performance. In addition, in vivo pharmacodynamic results proved that after treatment with MM/HA-DXM, the proteinuria level decreased to 2.33 times, as compared with that of control group, demonstrating a superior therapeutic effect on glomerulonephritis via this collaborative two-pronged anti-inflammatory therapy strategy.

Rho GTPases in kidney physiology and diseases

Rho family GTPases are molecular switches best known for their pivotal role in dynamic regulation of the actin cytoskeleton, but also of cellular morphology, motility, adhesion and proliferation. The prototypic members of this family (RhoA, Rac1 and Cdc42) also contribute to the normal kidney function and play important roles in the structure and function of various kidney cells including tubular epithelial cells, mesangial cells and podocytes. The kidney's vital filtration function depends on the structural integrity of the glomerulus, the proximal portion of the nephron. Within the glomerulus, the architecturally actin-based cytoskeleton podocyte forms the final cellular barrier to filtration. The glomerulus appears as a highly dynamic signalling hub that is capable of integrating intracellular cues from its individual structural components. Dynamic regulation of the podocyte cytoskeleton is required for efficient barrier function of the kidney. As master regulators of actin cytoskeletal dynamics, Rho GTPases are therefore of critical importance for sustained kidney barrier function. Dysregulated activities of the Rho GTPases and of their effectors are implicated in the pathogenesis of both hereditary and idiopathic forms of kidney diseases. Diabetic nephropathy is a progressive kidney disease that is caused by injury to kidney glomeruli. High glucose activates RhoA/Rho-kinase in mesangial cells, leading to excessive extracellular matrix production (glomerulosclerosis). This RhoA/Rho-kinase pathway also seems involved in the post-transplant hypertension frequently observed during treatment with calcineurin inhibitors, whereas Rac1 activation was observed in post-transplant ischaemic acute kidney injury.

Immunomodulatory Effects of Mesenchymal Stem Cells on Drug-Induced Acute Kidney Injury

Drug-induced nephrotoxicity is an important and increasing cause of acute kidney injury (AKI), which accounts for approximately 20% of hospitalized patients. Previous reviews studies on immunity and AKI focused mainly on ischemia-reperfusion (IR), whereas no systematic review addressing drug-induced AKI and its related immune mechanisms is available. Recent studies have provided a deeper understanding on the mechanisms of drug-induced AKI, among which acute tubular interstitial injury induced by the breakdown of innate immunity was reported to play an important role. Emerging research on mesenchymal stem cell (MSC) therapy has revealed its potential as treatment for drug-induced AKI. MSCs can inhibit kidney damage by regulating the innate immune balance, promoting kidney repair, and preventing kidney fibrosis. However, it is important to note that there are various sources of MSCs, which impacts on the immunomodulatory ability of the cells. This review aims to address the immune pathogenesis of drug-induced AKI versus that of IR-induced AKI, and to explore the immunomodulatory effects and therapeutic potential of MSCs for drug-induced AKI.

Uremic toxin indoxyl sulfate promotes proinflammatory macrophage activation by regulation of β-catenin and YAP pathways

Evidence has been shown that indoxyl sulfate (IS) could impair kidney and cardiac functions. Moreover, macrophage polarization played important roles in chronic kidney disease and cardiovascular disease. IS acts as a nephron-vascular toxin, whereas its effect on macrophage polarization during inflammation is still not fully elucidated. In this study, we aimed to investigate the effect of IS on macrophage polarization during lipopolysaccharide (LPS) challenge. THP-1 monocytes were incubated with phorbol 12-myristate-13-acetate (PMA) to differentiate into macrophages, and then incubated with LPS and IS for 24 h. ELISA was used to detect the levels of TNFα, IL-6, IL-1β in THP-1-derived macrophages. Western blot assay was used to detect the levels of arginase1 and iNOS in THP-1-derived macrophages. Percentages of HLA-DR-positive cells (M1 macrophages) and CD206-positive cells (M2 macrophages) were detected by flow cytometry. IS markedly increased the production of the pro-inflammatory factors TNFα, IL-6, IL-1β in LPS-stimulated THP-1-derived macrophages. In addition, IS induced M1 macrophage polarization in response to LPS, as evidenced by the increased expression of iNOS and the increased proportion of HLA-DR+ macrophages. Moreover, IS downregulated the level of β-catenin, and upregulated the level of YAP in LPS-stimulated macrophages. Activating β-catenin signaling or inhibiting YAP signaling suppressed the IS-induced inflammatory response in LPS-stimulated macrophages by inhibiting M1 polarization. IS induced M1 macrophage polarization in LPS-stimulated macrophages via inhibiting β-catenin and activating YAP signaling. In addition, this study provided evidences that activation of β-catenin or inhibition of YAP could alleviate IS-induced inflammatory response in LPS-stimulated macrophages. This finding may contribute to the understanding of immune dysfunction observed in chronic kidney disease and cardiovascular disease.

Design, synthesis and biological evaluation of novel arylpropionic esters for the treatment of acute kidney injury

Acute kidney injury (AKI) is associated with a strong inflammatory response, and inhibiting the response effectively prevents or ameliorates AKI. A series of novel arylpropionic esters were designed, synthesized and evaluated their biological activity in LPS-stimulated RAW264.7 cells. Novel arylpropionic esters bearing multi-functional groups showed significant anti-inflammatory activity, in which, compound 13b exhibited the most potent activity through dose-dependent inhibiting the production of nitric oxide (NO, IC₅₀ = 3.52 μM), TNF-α and IL-6 (84.1% and 33.6%, respectively), as well as suppressing the expression of iNOS, COX-2 and TLR4 proteins. In C57BL/6 mice with cisplatin-induced AKI, compound 13b improved kidney function, inhibited inflammatory development, and reduced pathological damage of kidney tissues. In brief, this arylpropionic ester scaffold may be developed as anti-inflammatory agents.

Pregnane X receptor (PXR) protects against cisplatin-induced acute kidney injury in mice

Cisplatin-induced acute kidney injury (CAKI) has been recognized as one of the most serious side effects of cisplatin. Pregnane X receptor (PXR) is a ligand-dependent nuclear receptor and serves as a master regulator of xenobiotic detoxification. Increasing evidence also suggests PXR has many other functions including the regulation of cell proliferation, inflammatory response, and glucose and lipid metabolism. In this study, we aimed to investigate the role of PXR in cisplatin-induced nephrotoxicity in mice. CAKI model was performed in wild-type or PXR knockout mice. Pregnenolone 16α‑carbonitrile (PCN), a mouse PXR specific agonist, was used for PXR activation. The renal function, biochemical, histopathological and molecular alterations were examined in mouse blood, urine or renal tissues. Whole transcriptome analysis was performed by RNA sequencing. We found that PXR activation significantly attenuated CAKI as reflected by improved renal function, reduced renal tubular apoptosis, ameliorated oxidative and endoplasmic reticulum stress, and suppressed inflammatory gene expression. RNA sequencing analysis revealed that the renoprotective effect of PXR was associated with multiple crucial signaling pathways, especially the PI3K/AKT pathway. In vitro study further revealed that PXR protected against cisplatin-induced apoptosis of cultured proximal tubule cells in a PI3K-dependent manner. Our results demonstrate that PXR activation can preserve renal function in cisplatin-induced AKI and suggest a possibility of PXR as a novel protective target for cisplatin-induced nephrotoxicity.

Conversion of extracellular ATP into adenosine: a master switch in renal health and disease

ATP and its ultimate degradation product adenosine are potent extracellular signalling molecules that elicit a variety of pathophysiological functions in the kidney through the activation of P2 and P1 purinergic receptors, respectively. Extracellular purines can modulate immune responses, balancing inflammatory processes and immunosuppression; indeed, alterations in extracellular nucleotide and adenosine signalling determine outcomes of inflammation and healing processes. The functional activities of ectonucleotidases such as CD39 and CD73, which hydrolyse pro-inflammatory ATP to generate immunosuppressive adenosine, are therefore pivotal in acute inflammation. Protracted inflammation may result in aberrant adenosinergic signalling, which serves to sustain inflammasome activation and worsen fibrotic reactions. Alterations in the expression of ectonucleotidases on various immune cells, such as regulatory T cells and macrophages, as well as components of the renal vasculature, control purinergic receptor-mediated effects on target tissues within the kidney. The role of CD39 as a rheostat that can have an impact on purinergic signalling in both acute and chronic inflammation is increasingly supported by the literature, as detailed in this Review. Better understanding of these purinergic processes and development of novel drugs targeting these pathways could lead to effective therapies for the management of acute and chronic kidney disease.

α1-Acid Glycoprotein Attenuates Adriamycin-Induced Nephropathy via CD163 Expressing Macrophage Induction

BACKGROUND

Recent clinical studies have shown that proteinuria is a critical factor in the progression of CKD and onset of cardiovascular disease. Inflammation and infiltration of macrophages into renal tissue are implicated as causes of proteinuria. α₁-Acid glycoprotein (AGP), an acute-phase plasma protein, is leaked into the urine in patients with proteinuria. However, the relationship between urinary leakage of AGP, renal inflammation, and proteinuria remains unclear.

METHODS

Human AGP (hAGP) was exogenously administrated for 5 consecutive days to adriamycin-induced nephropathy model mice.

RESULTS

Adriamycin treatment increased urinary AGP, accompanied by decreased plasma AGP in mice. Exogenous hAGP administration to adriamycin-treated mice suppressed proteinuria, renal histologic injury, and inflammation. hAGP administration increased renal CD163 expression, a marker of anti-inflammatory macrophages. Similar changes were observed in PMA-differentiated THP-1 cells treated with hAGP. Even in the presence of LPS, hAGP treatment increased CD163/IL-10 expression in differentiated THP-1 cells.

CONCLUSIONS

AGP alleviates proteinuria and renal injury in mice with proteinuric kidney disease via induction of CD163-expressing macrophages with anti-inflammatory function. The results demonstrate that endogenous AGP could work to protect against glomerular disease. Thus, AGP supplementation could be a possible new therapeutic intervention for patients with glomerular disease.

Substance P Improves Renal Ischemia Reperfusion Injury Through Modulating Immune Response

Substance P (SP), an injury-inducible messenger that mobilizes bone marrow stem cells and modulates the immune response, has been suggested as a novel target for therapeutic agents. We evaluated the role of SP as an immune cell modulator during the progression of renal ischemic/reperfusion injury (IRI). Unilateral IRI induced the transient expression of endogenous SP and the infiltration of CCR7⁺ M1 macrophages in injured kidneys. However, SP altered the intrarenal macrophage polarization from CCR7⁺ M1 macrophages to CD206⁺ M2 macrophages in injured kidneys. SP also modulated bone marrow-derived neutrophils and mesenchymal stromal cells after IRI. SP treatment for 4 weeks starting one week after unilateral IRI significantly preserved kidney size and length and normal tubular structures and alleviated necrotic tubules, inflammation, apoptosis, and tubulointerstitial fibrosis. The beneficial effects of SP were accompanied by attenuation of intrarenal recruitment of CD4, CD8, and CD20 cells and abnormal angiogenesis. The immunomodulatory effect of SP suggested that SP could be a promising therapeutic target for preventing the progression of acute kidney injury to chronic kidney disease.

Sex differences in redox homeostasis in renal disease

Sex differences in redox signaling in the kidney present new challenges and opportunities for understanding the physiology and pathophysiology of the kidney. This review will focus on reactive oxygen species, immune-related signaling pathways and endothelin-1 as potential mediators of sex-differences in redox homeostasis in the kidney. Additionally, this review will highlight male-female differences in redox signaling in several major cardiovascular and renal disorders namely acute kidney injury, diabetic nephropathy, kidney stone disease and salt-sensitive hypertension. Furthermore, we will discuss the contribution of redox signaling in the pathogenesis of postmenopausal hypertension and preeclampsia.

Macrophage Depletion Improves Chronic Rejection in Rats With Allograft Heart Transplantation

BACKGROUND

Macrophages may be important in chronic rejection after organ transplantation. This study aimed to investigate the possibility of depleting macrophages for a certain amount of time to alleviate chronic rejection in a heart transplant model of Fischer to Lewis rats.

METHODS

Clodronate liposome was injected abdominally to deplete macrophages for 2 time frames. The expression levels of ectodysplasin 1, arginase 1 (Arg1), chitinase-like lectin (Ym1), interferon gamma, tumor necrosis factor α (TNF-α), smooth muscle α-actin (α-SMA), monocyte chemoattractant protein 1 (MCP-1), and interleukin 10 (IL-10) were detected.

RESULTS

1. The expression levels of α-SMA, interferon gamma, TNF-α, and MCP-1 and the transformation of peripheral T cells were lower after macrophage depletion for 2 or 4 weeks. 2. The expression levels of α-SMA, TNF-α, and MCP-1 and the transformation of peripheral T cells were even lower after 4 weeks compared with 2 weeks, except for interferon gamma. 3. A higher level of expression of Arg1 and Ym1 after macrophage depletion for 2 weeks was observed. 4. A higher level of expression of IL-10 after macrophage depletion for 2 weeks, but not 4 weeks, was also observed.

CONCLUSIONS

Macrophage clearance after heart transplantation alleviated chronic rejection probably via M2 polarization of regenerated macrophages, reduced T-lymphocyte proliferation, and changed the expression levels of interferon gamma, TNF-α, MCP-1, and IL-10.

Peritoneal M2 macrophage transplantation as a potential cell therapy for enhancing renal repair in acute kidney injury

Acute kidney injury (AKI) is a clinical condition that is associated with high morbidity and mortality. Inflammation is reported to play a key role in AKI. Although the M2 macrophages exhibit antimicrobial and anti‐inflammatory activities, their therapeutic potential has not been evaluated for AKI. This study aimed to investigate the protective effect of peritoneal M2 macrophage transplantation on AKI in mice. The macrophages were isolated from peritoneal dialysates of mice. The macrophages were induced to undergo M2 polarization using interleukin (IL)‐4/IL‐13. AKI was induced in mice by restoring the blood supply after bilateral renal artery occlusion for 30 minutes. The macrophages were injected into the renal cortex of mice. The changes in renal function, inflammation and tubular proliferation were measured. The M2 macrophages were co‐cultured with the mouse primary proximal tubular epithelial cells (PTECs) under hypoxia/reoxygenation conditions in vitro. The PTEC apoptosis and proliferation were analysed. The peritoneal M2 macrophages effectively alleviated the renal injury and inflammatory response in mice with ischaemia‐reperfusion injury (IRI) and promoted the PTEC proliferation in vivo and in vitro. These results indicated that the peritoneal M2 macrophages ameliorated AKI by decreasing inflammatory response and promoting PTEC proliferation. Hence, the peritoneal M2 macrophage transplantation can serve as a potential cell therapy for renal diseases.

Pharmacological Activation of Sirt1 Ameliorates Cisplatin-Induced Acute Kidney Injury by Suppressing Apoptosis, Oxidative Stress, and Inflammation in Mice

Sirtuin 1 (Sirt1) is an essential modulator of cellular metabolism and has pleiotropic effects. It was recently reported that Sirt1 overexpression in kidney tubule ameliorates cisplatin-induced acute kidney injury (AKI). However, whether pharmacological activation of Sirt1 also has a beneficial effect against the disease remains unclear. In this study, we aimed to evaluate whether SRT1720, a potent and specific activator of Sirt1, could ameliorate cisplatin-induced AKI. We found that SRT1720 treatment ameliorated cisplatin-induced acute renal failure and histopathological alterations. Increased levels of tubular injury markers in kidneys were significantly attenuated by SRT1720. SRT1720 treatment also suppressed caspase-3 activation and apoptotic cell death. Increased expression of 4-hydroxynonenal, elevated malondialdehyde level, and decreased ratio of reduced glutathione/oxidized glutathione after cisplatin injection were significantly reversed by SRT1720. In addition, SRT1720 treatment decreased renal expression of pro-inflammatory cytokines and prevented macrophage infiltration into damaged kidneys. We also showed that the therapeutic effects of SRT1720 were associated with reduced acetylation of p53 and nuclear factor kappa-B p65 and preservation of peroxisome function, as evidenced by recovered expression of markers for number and function of peroxisome. These results suggest that Sirt1 activation by SRT1720 would be a useful therapeutic option for cisplatin-induced AKI.

Galectin 3 protects from cisplatin-induced acute kidney injury by promoting TLR-2-dependent activation of IDO1/Kynurenine pathway in renal DCs

Strategies targeting cross-talk between immunosuppressive renal dendritic cells (DCs) and T regulatory cells (Tregs) may be effective in treating cisplatin (CDDP)-induced acute kidney injury (AKI). Galectin 3 (Gal-3), expressed on renal DCs, is known as a crucial regulator of immune response in the kidneys. In this study, we investigated the role of Gal-3 for DCs-mediated expansion of Tregs in the attenuation of CDDP-induced AKI. Methods: AKI was induced in CDDP-treated wild type (WT) C57BL/6 and Gal-3 deficient (Gal-3^-/-) mice. Biochemical, histological analysis, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry, real-time PCR, magnetic cell sorting, flow cytometry and intracellular staining of renal-infiltrated immune cells were used to determine the differences between CDDP-treated WT and Gal-3^-/- mice. Newly synthesized selective inhibitor of Gal-3 (Davanat) was used for pharmacological inhibition of Gal-3. Recombinant Gal-3 was used to demonstrate the effects of exogenously administered soluble Gal-3 on AKI progression. Pam3CSK4 was used for activation of Toll-like receptor (TLR)-2 in DCs. Cyclophosphamide or anti-CD25 antibody were used for the depletion of Tregs. 1-Methyl Tryptophan (1-MT) was used for pharmacological inhibition of Indoleamine 2,3-dioxygenase-1 (IDO1) in TLR-2-primed DCs which were afterwards used in passive transfer experiments. Results: CDDP-induced nephrotoxicity was significantly more aggravated in Gal-3^-/- mice. Significantly reduced number of immunosuppressive TLR-2 and IDO1-expressing renal DCs, lower serum levels of KYN, decreased presence of IL-10-producing Tregs and significantly higher number of inflammatory IFN-γ and IL-17-producing neutrophils, Th1 and Th17 cells were observed in the CDDP-injured kidneys of Gal-3^-/- mice. Pharmacological inhibitor of Gal-3 aggravated CDDP-induced AKI in WT animals while recombinant Gal-3 attenuated renal injury and inflammation in CDDP-treated Gal-3^-/- mice. CDDP-induced apoptosis, driven by Bax and caspase-3, was aggravated in Gal-3^-/- animals and in WT mice that received Gal-3 inhibitor (CDDP+Davanat-treated mice). Recombinant Gal-3 managed to completely attenuate CDDP-induced apoptosis in CDDP-injured kidneys of Gal-3^-/- mice. Genetic deletion as well as pharmacological inhibition of Gal-3 in renal DCs remarkably reduced TLR-2-dependent activation of IDO1/KYN pathway in these cells diminishing their capacity to prevent transdifferentiation of Tregs in inflammatory Th1 and Th17 cells. Additionally, Tregs generated by Gal-3 deficient DCs were not able to suppress production of IFN-γ and IL-17 in activated neutrophils. TLR-2-primed DCs significantly enhanced capacity of Tregs for attenuation of CDDP-induced AKI and inflammation and expression of Gal-3 on TLR-2-primed DCs was crucially important for their capacity to enhance nephroprotective and immunosuppressive properties of Tregs. Adoptive transfer of TLR-2-primed WTDCs significantly expanded Tregs in the kidneys of CDDP-treated WT and Gal-3^-/- recipients resulting in the suppression of IFN-γ and IL-17-driven inflammation and alleviation of AKI. Importantly, this phenomenon was not observed in CDDP-treated WT and Gal-3^-/- recipients of TLR-2-primed Gal-3^-/-DCs. Gal-3-dependent nephroprotective and immunosuppressive effects of renal DCs was due to the IDO1-induced expansion of renal Tregs since either inhibition of IDO1 activity in TLR-2-primed DCs or depletion of Tregs completely diminished DCs-mediated attenuation of CDDP-induced AKI. Conclusions: Gal-3 protects from CDDP-induced AKI by promoting TLR-2-dependent activation of IDO1/KYN pathway in renal DCs resulting in increased expansion of immunosuppressive Tregs in injured kidneys. Activation of Gal-3:TLR-2:IDO1 pathway in renal DCs should be further explored as new therapeutic approach for DC-based immunosuppression of inflammatory renal diseases.

Tubular GM-CSF Promotes Late MCP-1/CCR2-Mediated Fibrosis and Inflammation after Ischemia/Reperfusion Injury

BACKGROUND

After bilateral kidney ischemia/reperfusion injury (IRI), monocytes infiltrate the kidney and differentiate into proinflammatory macrophages in response to the initial kidney damage, and then transition to a form that promotes kidney repair. In the setting of unilateral IRI (U-IRI), however, we have previously shown that macrophages persist beyond the time of repair and may promote fibrosis.

METHODS

Macrophage homing/survival signals were determined at 14 days after injury in mice subjected to U-IRI and in vitro using coculture of macrophages and tubular cells. Mice genetically engineered to lack Ccr2 and wild-type mice were treated ±CCR2 antagonist RS102895 and subjected to U-IRI to quantify macrophage accumulation, kidney fibrosis, and inflammation 14 and 30 days after the injury.

RESULTS

Failure to resolve tubular injury after U-IRI results in sustained expression of granulocyte-macrophage colony-stimulating factor by renal tubular cells, which directly stimulates expression of monocyte chemoattractant protein-1 (Mcp-1) by macrophages. Analysis of CD45⁺ immune cells isolated from wild-type kidneys 14 days after U-IRI reveals high-level expression of the MCP-1 receptor Ccr2. In mice lacking Ccr2 and wild-type mice treated with RS102895, the numbers of macrophages, dendritic cells, and T cell decreased following U-IRI, as did the expression of profibrotic growth factors and proimflammatory cytokines. This results in a reduction in extracellular matrix and kidney injury markers.

CONCLUSIONS

GM-CSF-induced MCP-1/CCR2 signaling plays an important role in the cross-talk between injured tubular cells and infiltrating immune cells and myofibroblasts, and promotes sustained inflammation and tubular injury with progressive interstitial fibrosis in the late stages of U-IRI.

Bone marrow-derived Ly6C- macrophages promote ischemia-induced chronic kidney disease

Macrophages play an important role in renal injury and repair after acute kidney injury (AKI) and the subsequent chronic kidney disease (CKD) that often results. However, as macrophages have a high degree of plasticity and heterogeneity, the function(s) of macrophage subtypes in AKI-to-CKD progression are not fully understood. Here, we focused on Ly6C⁻ macrophages, which are derived from the embryonic yolk sac and post-development become resident in the kidneys. We found that C–C chemokine receptor type 2 (CCR2) deficiency, which blocks the migration of Ly6C⁺ macrophages from the bone marrow to the sites of injury, alleviated ischemia-induced AKI in mice. Unexpectedly, though, CCR2 deficiency worsened the subsequent renal fibrosis, which was marked by notable intra-renal infiltration of Ly6C⁻ macrophages. These Ly6C⁻ macrophages were greater in number in both the acute and chronic phases after ischemia reperfusion (I/R) in kidneys of wild type (WT) mice, and we showed them to be derived from the bone marrow by bone marrow chimerism. Clodronate Liposomes (CLs)-mediated depletion of renal Ly6C⁻ macrophages in CCR2^−/− mice or in WT mice after I/R alleviated the renal injury and fibrosis. On the contrary, adoptive transfer of Ly6C⁻ macrophages from injured kidneys of WT mice into immune-deficient mice was sufficient to induce renal injury and fibrosis. Transcriptome sequencing of Ly6C⁻ macrophages from injured kidneys revealed that they secreted various cytokines and growth factors, which were associated with the transdifferentiation of fibroblasts into myofibroblasts. This transdifferentiation effect was further supported by in vitro studies showing that Ly6C⁻ macrophages induced the secretion of extracellular matrix proteins from co-cultured fibroblasts. In conclusion, the presence of bone marrow-derived Ly6C⁻ macrophages after ischemia induces AKI and worsens subsequent CKD.

Inflammatory Mediators and Renal Fibrosis

Renal inflammation is the initial, healthy response to renal injury. However, prolonged inflammation promotes the fibrosis process, which leads to chronic pathology and eventually end-stage kidney disease. There are two major sources of inflammatory cells: first, bone marrow-derived leukocytes that include neutrophils, macrophages, fibrocytes and mast cells, and second, locally activated kidney cells such as mesangial cells, podocytes, tubular epithelial cells, endothelial cells and fibroblasts. These activated cells produce many profibrotic cytokines and growth factors that cause accumulation and activation of myofibroblasts, and enhance the production of the extracellular matrix. In particular, activated macrophages are key mediators that drive acute inflammation into chronic kidney disease. They produce large amounts of profibrotic factors and modify the microenvironment via a paracrine effect, and they also transdifferentiate to myofibroblasts directly, although the origin of myofibroblasts in the fibrosing kidney remains controversial. Collectively, understanding inflammatory cell functions and mechanisms during renal fibrosis is paramount to improving diagnosis and treatment of chronic kidney disease.

Macrophages in Renal Fibrosis

Monocytes/macrophages are highly involved in the process of renal injury, repair and fibrosis in many aspects of experimental and human renal diseases. Monocyte-derived macrophages, characterized by high heterogeneity and plasticity, are recruited, activated, and polarized in the whole process of renal fibrotic diseases in response to local microenvironment. As classically activated M1 or CD11b⁺/Ly6C^high macrophages accelerate renal injury by producing pro-inflammatory factors like tumor necrosis factor-alpha (TNFα) and interleukins, alternatively activated M2 or CD11b⁺/Ly6C^intermediate macrophages may contribute to kidney repair by exerting anti-inflammation and wound healing functions. However, uncontrolled M2 macrophages or CD11b⁺/Ly6C^low macrophages promote renal fibrosis via paracrine effects or direct transition to myofibroblast-like cells via the process of macrophage-to-myofibroblast transition (MMT). In this regard, therapeutic strategies targeting monocyte/macrophage recruitment, activation, and polarization should be emphasized in the treatment of renal fibrosis.

Pharmacological Inhibition of Caspase-1 Ameliorates Cisplatin-Induced Nephrotoxicity through Suppression of Apoptosis, Oxidative Stress, and Inflammation in Mice

Caspase-1 is a proinflammatory caspase responsible for the proteolytic conversion of the precursor forms of interleukin-1β to its active form and plays an important role in the pathogenesis of various inflammatory diseases. It was reported that genetic deficiency of caspase-1 prevented cisplatin-induced nephrotoxicity. However, whether pharmacological inhibition of caspase-1 also has a preventive effect against cisplatin-induced kidney injury has not been evaluated. In this study, we examined the effect of Ac-YVAD-cmk, a potent caspase-1-specific inhibitor, on renal function and histology in cisplatin-treated mice and explored its underlying mechanisms. We found that administration of Ac-YVAD-cmk effectively attenuated cisplatin-induced renal dysfunction, as evidenced by reduced plasma levels of blood urea nitrogen and creatinine, and histological abnormalities, such as tubular cell death, dilatation, and cast formation. Administration of Ac-YVAD-cmk inhibited caspase-3 activation as well as caspase-1 activation and attenuated apoptotic cell death, as assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, in the kidneys of cisplatin-treated mice. Cisplatin-induced G2/M arrest of renal tubular cells was also reduced by caspase-1 inhibition. In addition, administration of Ac-YVAD-cmk reversed increased oxidative stress and depleted antioxidant capacity after cisplatin treatment. Moreover, increased macrophage accumulation and elevated expression of cytokines and chemokines were attenuated by caspase-1 inhibition. Taken together, these results suggest that caspase-1 inhibition by Ac-YVAD-cmk protects against cisplatin-induced nephrotoxicity through inhibition of renal tubular cell apoptosis, oxidative stress, and inflammatory responses. Our findings support the idea that caspase-1 may be a promising pharmacological target for the prevention of cisplatin-induced kidney injury.

Trichosanthes kirilowii lectin ameliorates streptozocin-induced kidney injury via modulation of the balance between M1/M2 phenotype macrophage

BACKGROUND

Macrophage polarization has been reported to induce podocyte injury, which is a typical characteristic of diabetic nephropathy (DN). Trichosanthes kirilowii is an herb showing renal protective effect as well as immune-regulating effect. Therefore, it was hypothesized that the renal protective effect of Trichosanthes kirilowii was associated with its modulation on macrophage polarization. In the current study, we tested the hypothesis by subjecting DN rats to treatment of Trichosanthes kirilowii lectin (TKL), an active component of Trichosanthes kirilowii.

METHOD

DN was induced using streptozocin (STZ) method, and after 3 days, treatments were performed with different doses of TKL for eight weeks. The effect of TKL on the renal function, structure, and inflammation was assessed. To explain the pathway mediating the effect of TKL on renal tissues, the expressions of markers involved in macrophage polarization, podocyte proliferation, and Notch signaling were determined. Moreover, the DN rats were further administrated with Notch signaling inhibitor, Dibenzazepine (DIB), to verify the key role of Notch signaling in the renal protective effect of TKL.

RESULTS

STZ induced damages in renal function and structure, which was attenuated by TKL of different doses. Moreover, STZ also increased the production of TNF-α and iNOS while suppressed the production of IL-10 and arginase-1 (Arg-1). The induced inflammation by STZ was inhibited by TKL. The polarization of macrophage into M1 type during the development of DN was blocked by TKL, contributing to the increased proliferation potential of podocytes. Regarding Notch signaling, TKL administration inhibited the activation of the pathway by suppressing the expression of Notch1, NICD1, and Hes1. The administration of DIB had similar effect to that of TKL administration on renal function and structure.

CONCLUSIONS

The study for the first time showed that TKL attenuated deterioration in renal structure and function by increasing M2 macrophage proportion via inhibition of Notch signaling.

Renal immune surveillance and dipeptidase-1 contribute to contrast-induced acute kidney injury

Radiographic contrast agents cause acute kidney injury (AKI), yet the underlying pathogenesis is poorly understood. Nod-like receptor pyrin containing 3-deficient (Nlrp3-deficient) mice displayed reduced epithelial cell injury and inflammation in the kidney in a model of contrast-induced AKI (CI-AKI). Unexpectedly, contrast agents directly induced tubular epithelial cell death in vitro that was not dependent on Nlrp3. Rather, contrast agents activated the canonical Nlrp3 inflammasome in macrophages. Intravital microscopy revealed diatrizoate (DTA) uptake within minutes in perivascular CX3CR1+ resident phagocytes in the kidney. Following rapid filtration into the tubular luminal space, DTA was reabsorbed and concentrated in tubular epithelial cells via the brush border enzyme dipeptidase-1 in volume-depleted but not euvolemic mice. LysM-GFP+ macrophages recruited to the kidney interstitial space ingested contrast material transported from the urine via direct interactions with tubules. CI-AKI was dependent on resident renal phagocytes, IL-1, leukocyte recruitment, and dipeptidase-1. Levels of the inflammasome-related urinary biomarkers IL-18 and caspase-1 were increased immediately following contrast administration in patients undergoing coronary angiography, consistent with the acute renal effects observed in mice. Taken together, these data show that CI-AKI is a multistep process that involves immune surveillance by resident and infiltrating renal phagocytes, Nlrp3-dependent inflammation, and the tubular reabsorption of contrast via dipeptidase-1.

Legumain, an asparaginyl endopeptidase, mediates the effect of M2 macrophages on attenuating renal interstitial fibrosis in obstructive nephropathy

Two distinct macrophage phenotypes contribute to kidney injury and repair during the progression of renal interstitial fibrosis; proinflammatory (M1) and antiinflammatory (M2) macrophages. Legumain, an asparaginyl endopeptidase of the cysteine protease family, is overexpressed in macrophages in some pathological conditions. However, the macrophage subtype and function of macrophage-derived legumain remains unclear. To resolve this we tested whether M2 macrophages contribute to the accumulation of legumain in the unilateral ureteral obstruction model. Legumain-null mice exhibited more severe fibrotic lesions after obstruction compared with wild-type control. In vitro, IL4-stimulated M2 polarization led to the overexpression and secretion of legumain. The levels of fibronectin and collagen I/III, major components of the extracellular matrix, were reduced in the conditioned medium of TGF-β1-stimulated tubular epithelial cells or fibroblasts after treatment with legumain or conditioned medium from IL4-stimulated macrophages. Administration of the legumain inhibitor RR-11a exacerbated fibrotic lesions following obstruction. Therapeutically, adoptive transfer of legumain-overexpressing macrophages or IL4-stimulated macrophages ameliorated the deposition of collagen and fibronectin induced by ureteral obstruction, either in the wild-type mice or in lgmn^-/- mice. Thus, M2 macrophages overexpress and secret legumain and legumain mediates the anti-fibrotic effect of M2 macrophages in obstructive nephropathy.

Relaxin abrogates renal interstitial fibrosis by regulating macrophage polarization via inhibition of Toll-like receptor 4 signaling

Renal fibrosis is a common feature of chronic kidney disease (CKD). To inhibit the CKD process, it is important to prevent renal fibrosis, though CKD remains incurable. Renal fibrosis can be inhibited by relaxin in several experimental models, but the mechanism of relaxin for antifibrotic potential is still not clear. And here we have studied the role of relaxin in macrophage polarization and renal inflammation after unilateral ureteral obstruction (UUO). Our results show that relaxin can downregulate the Toll-like receptor (TLR) 4 signaling, shift macrophage polarization toward the M2 phenotype and ameliorat renal fibrosis in the early stages of UUO. In vitro experiments, it has been confirmed that relaxin can downregulate the TLR4 signaling and induce the M2 macrophage transition. Furthermore, the transitional actions of macrophage phenotype induced by relaxin are significantly blocked by TAK-242, a TLR4 antagonist, in vitro experiments. Thus, there is a novel mechanism of relaxin for antifibrosis that shifts macrophage polarization toward the M2 phenotype via inhibition of TLR4 signaling.

Macrophage in chronic kidney disease

Chronic kidney disease (CKD) has become a major health problem worldwide. This review describes the role of macrophages in CKD and highlights the importance of anti-inflammatory M2 macrophage activation in both renal fibrosis and wound healing processes. Furthermore, the mechanisms by which M2 macrophages induce renal repair and regeneration are still under debate and currently demand more attention. The M1/M2 macrophage balance is related to the renal microenvironment and could influence CKD progression. In fact, an inflammatory renal environment and M2 plasticity can be the major hurdles to establishing macrophage cell-based therapies in CKD. M2 macrophage cell-based therapy is promising if the M2 phenotype remains stable and is 'fixed' by in vitro manipulation. However, a greater understanding of phenotype polarization is still required. Moreover, better strategies and targets to induce reparative macrophages in vivo should guide future investigations in order to abate kidney diseases.

Rescue therapy with Tanshinone IIA hinders transition of acute kidney injury to chronic kidney disease via targeting GSK3β

Acute kidney injury (AKI) remains challenging for clinical practice and poses a risk of developing progressive chronic kidney disease (CKD) with no definitive treatment available yet. Tanshinone IIA, an active ingredient of Chinese herbal Salvia miltiorrhiza, has been widely used in Asia for the remarkable organoprotective activities. Its effect on established AKI, however, remains unknown. In mice with folic acid-induced AKI, delayed treatment with Tanshinone IIA, commenced early or late after injury, diminished renal expression of kidney injury markers, reduced apoptosis and improved kidney dysfunction, concomitant with mitigated histologic signs of AKI to CKD transition, including interstitial fibrosis and tubular atrophy, and with an ameliorated inflammatory infiltration in tubulointerstitium and a favored M2-skewed macrophage polarization. Mechanistically, Tanshinone IIA blunted glycogen synthase kinase (GSK)3β overactivity and hyperactivation of its downstream mitogen-activated protein kinases that are centrally implicated in renal fibrogenesis and inflammation. Inhibition of GSK3β is likely a key mechanism mediating the therapeutic activity of Tanshinone IIA, because sodium nitroprusside, a GSK3β activator, largely offset its renoprotective effect. In confirmatory studies, rescue treatment with Tanshinone IIA likewise ameliorated ischemia/reperfusion-induced kidney destruction in mice. Our data suggest that Tanshinone IIA represents a valuable treatment that improves post-AKI kidney salvage via targeting GSK3β.

HMGB1/TLR4 signaling induces an inflammatory response following high-pressure renal pelvic perfusion in a porcine model

Percutaneous nephrolithotomy (PCNL) causes a rapid increase in renal pelvic pressure in the kidney, which induces an inflammatory response. High-mobility group box-1 (HMGB1) is known to trigger the recruitment of inflammatory cells and the release of proinflammatory cytokines following ischemia reperfusion injury in the kidney, but the contribution of HMGB1 to the inflammatory response following high-pressure renal pelvic perfusion has not been investigated. In this study, high-pressure renal pelvic perfusion was induced in anesthetized pigs to examine the effect of HMGB1 on the inflammatory response. HMGB1 levels in the kidney increased following high-pressure renal pelvic perfusion, together with elevated levels of inflammatory cytokines in the plasma and kidney and an accumulation of neutrophils and macrophages. Inhibition of HMGB1 alleviated this inflammatory response while perfusion with recombinant HMGB1 had an augmentative effect, confirming the involvement of HMGB1 in the inflammatory response to high-pressure renal pelvic perfusion. HMGB1 regulated the inflammatory response by activating Toll-like receptor 4 (TLR4) signaling. In conclusion, this study has demonstrated that HMGB1/TLR4 signaling contributes to the inflammatory response following high-pressure renal pelvic perfusion in a porcine model and has implications for the management of inflammation after PCNL.

SREBP inhibition ameliorates renal injury after unilateral ureteral obstruction

Tubulointerstitial fibrosis is a major feature associated with declining kidney function in chronic kidney disease of diverse etiology. No effective means as yet exists to prevent the progression of fibrosis. We have shown that the transcription factor sterol-regulatory element-binding protein 1 (SREBP-1) is an important mediator of the profibrotic response to transforming growth factor-β (TGF-β) and angiotensin II, both key cytokines in the fibrotic process. Here, we examined the role of SREBP in renal interstitial fibrosis in the unilateral ureteral obstruction (UUO) model. The two isoforms of SREBP (-1 and -2) were activated by 3 days after UUO, with SREBP-1 showing a more sustained activation to 21 days. We then examined whether SREBP1/2 inhibition with the small-molecule inhibitor fatostatin could attenuate fibrosis after 14 days of UUO. SREBP activation was confirmed to be inhibited by fatostatin. Treatment decreased interstitial fibrosis, TGF-β signaling, and upregulation of α-smooth muscle actin (SMA), a marker of fibroblast activation. Fatostatin also attenuated inflammatory cell infiltrate and apoptosis. Associated with this, fatostatin preserved proximal tubular mass. The significant increase in atubular glomeruli observed after UUO, known to correlate with irreversible renal functional decline, was also decreased by treatment. In cultured primary fibroblasts, TGF-β1 induced the activation of SREBP-1 and -2. Fatostatin blocked TGF-β1-induced α-SMA and matrix protein upregulation. The inhibition of SREBP is thus a potential novel therapeutic target in the treatment of fibrosis in chronic kidney disease.

Therapeutic effects and mechanism of conditioned media from human mesenchymal stem cells on anti-GBM glomerulonephritis in WKY rats

Recent studies have demonstrated that conditioned media derived from mesenchymal stem cells (MSC-CM) have therapeutic effects in various experimental diseases. However, the therapeutic mechanism is not fully understood. In the present study, we investigated the therapeutic effects and mechanism of MSC-CM in experimental antiglomerular basement membrane glomerulonephritis. We administered either MSC-CM or vehicle from day 0 to day 10 after the induction of nephrotoxic serum nephritis in Wistar-Kyoto rats. In vitro, we analyzed the effects of MSC-CM on TNF-α-mediated cytokine production in cultured normal human mesangial cells, proximal tubular (HK-2) cells, human umbilical vein endothelial cells, and monocytes (THP-1 and peripheral blood mononuclear cells). Compared with vehicle treatment, MSC-CM treatment improved proteinuria and renal dysfunction. Histologically, MSC-CM-treated rats had reduced crescent formation and glomerular ED1+ macrophage infiltration and increased glomerular ED2+ macrophage infiltration. Increased serum monocyte chemoattractant protein (MCP)-1 levels were observed in MSC-CM-treated rats. Renal cortical mRNA expression levels of proinflammatory cytokines, such as TNF-α and IL-6, and of the T helper cell 1 cytokine interferon-γ were greatly decreased by MSC-CM treatment. In vitro, pretreatment with MSC-CM blocked TNF-α-mediated IL-8 release in normal human mesangial cells and HK-2 cells. TNF-α-mediated MCP-1 release was enhanced by pretreatment with MSC-CM in human umbilical vein endothelial cells and HK-2 cells and was strikingly enhanced in THP-1 cells. Stimulation of peripheral blood mononuclear cells with a combination of MCP-1 and IL-4 enhanced the expression of M2-associated genes compared with IL-4 alone. We demonstrated that MSC-CM had therapeutic effects in experimental antiglomerular basement membrane glomerulonephritis that were mediated through anti-inflammatory effects that were partly due to acceleration of M2 macrophage polarization, which might be mediated by MCP-1 enhancement.

Tanshinone IIA Protects Against Folic Acid-Induced Acute Kidney Injury

Tanshinone IIA is a diterpene extracted from Salvia miltiorrhiza, a popular and safe herb medicine that has been widely used in China and other Asian countries. Previous studies have demonstrated the pleiotropic effects of Tanshinone IIA on many disease treatments via its antitoxicity, anti-inflammation, anti-oxidative stress, as well as antifibrosis activities. However, its effect on acute kidney injury (AKI) has not been fully investigated. Here, we show for the first time that systemic administration of Tanshinone IIA can lead to improved kidney function in folic acid-induced kidney injury mice. In the acute phase of AKI, Tanshinone IIA attenuated renal tubular epithelial injury, as determined by histologic changes and the detection of Neutrophil gelatinase-associated lipocalin (NGAL) in the kidney and urine. Additionally, Tanshinone IIA treatment resulted in elevated proliferating cell nuclear antigen (PCNA) expression and decreased inflammatory cells infiltration as well as chemokine expression, suggesting that Tanshinone IIA promoted renal repair following AKI and inhibited local inflammatory response in the injured kidney. This led to decreased long-term fibrosis in the injured kidney, characterized by less accumulation of fibronectin and collagen I in tubulointerstitium. Taken together, these results suggest that Tanshinone IIA may represent a potential approach for AKI treatment.

Macrophages in kidney injury, inflammation, and fibrosis

Macrophages are found in normal kidney and in increased numbers in diseased kidney, where they act as key players in renal injury, inflammation, and fibrosis. Macrophages are highly heterogeneous cells and exhibit distinct phenotypic and functional characteristics in response to various stimuli in the local microenvironment in different types of kidney disease. In kidney tissue necrosis and/or infection, damage- and/or pathogen-associated molecular patterns induce pro-inflammatory macrophages, which contribute to further tissue injury, inflammation, and subsequent fibrosis. Apoptotic cells and anti-inflammatory factors in post-inflammatory tissues induced anti-inflammatory macrophages, which can mediate kidney repair and regeneration. This review summarizes the role of macrophages with different phenotypes in kidney injury, inflammation, and fibrosis in various acute and chronic kidney diseases. Understanding alterations of kidney microenvironment and the factors that control the phenotype and functions of macrophages may offer an avenue for the development of new cellular and cytokine/growth factor-based therapies as alternative treatment options for patients with kidney disease.

The complement receptor C5aR1 contributes to renal damage but protects the heart in angiotensin II-induced hypertension

Adaptive and innate immune responses contribute to hypertension and hypertensive end-organ damage. Here, we determined the role of anaphylatoxin C5a, a major inflammatory effector of the innate immune system that is generated in response to complement activation, in hypertensive end-organ damage. For this purpose, we assessed the phenotype of C5a receptor 1 (C5aR1)-deficient mice in ANG II-induced renal and cardiac injury. Expression of C5aR1 on infiltrating and resident renal as well as cardiac cells was determined using a green fluorescent protein (GFP)-C5aR1 reporter knockin mouse. Flow cytometric analysis of leukocytes isolated from the kidney of GFP-C5aR1 reporter mice showed that 28% of CD45-positive cells expressed C5aR1. Dendritic cells were identified as the major C5aR1-expressing population (88.5%) followed by macrophages and neutrophils. Using confocal microscopy, we detected C5aR1 in the kidney mainly on infiltrating cells. In the heart, only infiltrating cells stained C5aR1 positive. To evaluate the role of C5aR1 deficiency in hypertensive injury, an aggravated model of hypertension was used. Unilateral nephrectomy was performed followed by infusion of ANG II (1.5 ng·g(-1)·min(-1)) and salt in wild-type (n = 34) and C5aR1-deficient mice (n = 32). C5aR1-deficient mice exhibited less renal injury, as evidenced by significantly reduced albuminuria. In contrast, cardiac injury was accelerated with significantly increased cardiac fibrosis and heart weight in C5aR1-deficient mice after ANG II infusion. No effect was found on blood pressure. In summary, the C5a:C5aR1 axis drives end-organ damage in the kidney but protects from the development of cardiac fibrosis and hypertrophy in experimental ANG II-induced hypertension.

Monocyte Mitochondrial Function in Calcium Oxalate Stone Formers

OBJECTIVE

To investigate whether mitochondrial function is altered in circulating immune cells from calcium oxalate (CaOx) stone formers compared to healthy subjects.

MATERIALS AND METHODS

Adult healthy subjects (n = 18) and CaOx stone formers (n = 12) were included in a pilot study. Data collection included demographic and clinical values from electronic medical records. Bioenergetic function was assessed in monocytes, lymphocytes, and platelets isolated from blood samples using the Seahorse XF96 Analyzer. Plasma interleukin-6 (IL-6) was measured using enzyme-linked immunosorbent assay.

RESULTS

All participants were age matched (44.5 ± 3.0 years for healthy subjects vs 42.3 ± 4.8 years for CaOx stone formers, P = .6905). CaOx stone formers did not have urinary tract infection, ureteral stones, or obstructing renal stones. Monocyte mitochondrial function was decreased in CaOx stone formers compared to healthy subjects. Specifically, mitochondrial maximal respiration (P = .0011) and reserve capacity (P < .0001) were significantly lower. In contrast, lymphocyte and platelet mitochondrial function was similar between the 2 groups. The bioenergetic health index, an integrated value of mitochondrial function, was significantly lower in monocytes from CaOx stone formers compared to healthy subjects (P = .0041). Lastly, plasma IL-6 levels were significantly increased (P = .0324).

CONCLUSION

The present pilot study shows that CaOx stone formers have decreased monocyte mitochondrial function. Plasma IL-6 was also increased in this cohort. These data suggest that impaired monocyte mitochondrial function and inflammation may be linked to CaOx kidney stone formation. Further studies are needed to confirm these findings in a larger cohort of patients.

Insight into Reepithelialization: How Do Mesenchymal Stem Cells Perform?

Wound reepithelialization is a cooperative multifactorial process dominated by keratinocyte migration, proliferation, and differentiation that restores the intact epidermal barrier to prevent infection and excessive moisture loss. However, in wounds that exhibit impaired wound healing, such as chronic nonhealing wounds or hypertrophic scars, the reepithelialization process has failed. Thus, it is necessary to explore a suitable way to mitigate these abnormalities to promote reepithelialization and achieve wound healing. Mesenchymal stem cells (MSCs) have the capacity for self-renewal as well as potential multipotency. These cells play important roles in many biological processes, including anti-inflammation, cell migration, proliferation, and differentiation, and signal pathway activation or inhibition. The mechanism of the involvement of MSCs in reepithelialization is still not fully understood. An abundance of evidence has shown that MSCs participate in reepithelialization by inhibiting excessive inflammatory responses, secreting important factors, differentiating into multiple skin cell types, and recruiting other host cells. This review describes the evidence for the roles that MSCs appear to play in the reepithelialization process.

P311 promotes renal fibrosis via TGFβ1/Smad signaling

P311, a gene that was identified in 1993, has been found to have diverse biological functions in processes such as cell proliferation, migration and differentiation. However, its role in fibrosis is unknown. We previously observed that P311 is highly expressed in skin hypertrophic scars. In this study, P311 over-expression was detected in a subset of tubular epithelial cells in clinical biopsy specimens of renal fibrosis; this over-expression, was found concurrent with α-smooth muscle actin (α-SMA) and transforming growth factor beta1 (TGFβ1) expression. Subsequently, these results were verified in a mouse experimental renal fibrosis model induced by unilateral ureteral obstruction. The interstitial deposition of collagen, α-SMA and TGF-β1 expression, and macrophage infiltration were dramatically decreased when P311 was knocked out. Moreover, TGFβ/Smad signaling had a critical effect on the promotion of renal fibrosis by P311. In conclusion, this study demonstrate that P311 plays a key role in renal fibrosis via TGFβ1/Smad signaling, which could be a novel target for the management of renal fibrosis.