Alternatively activated macrophages as therapeutic agents for kidney disease: in vivo stability is a key factor

Immunoregulation mechanism of VEGF signaling pathway inhibitors and its efficacy on the kidney

Angiogenesis and immunosuppression are closely related pathophysiologic processes. Widely prescribed in malignant tumor and proliferative retinal lesions, VEGF signaling pathway inhibitors may cause hypertension and renal injury in some patients, presenting with proteinuria, nephrotic syndrome, renal failure and thrombotic microangiopathy. VEGF signaling pathway inhibitors block the action of both VEGF-A and VEGF-C. However, VEGF-A and VEGF-C produced by podocytes are vital to maintain the physiological function of glomerular endothelial cells and podocytes. There is still no effective treatment for kidney disease associated with VEGF signaling pathway inhibitors and some patients have progressive renal failure even after withdrawal of the drug. Recent studies reveal that blocking of VEGF-A and VEGF-C can activate CD4 +and CD8+ T cells, augment antigen-presenting function of dendritic cells, enhance cytotoxicity of macrophages and initiate complement cascade activation. VEGF and VEGFR are expressed in immune cells, which are involved in the immunosuppression and cross-talk among immune cells. This review summarizes the expression and function of VEGF-A and VEGF-C in the kidney. The current immunoregulation mechanisms of VEGF signaling pathway inhibitors are reviewed. Finally, combinate strategies are summarized to highlight the proposal for VEGF signaling pathway inhibitors.

Macrophages derived from pluripotent stem cells: prospective applications and research gaps

Induced pluripotent stem cells (iPSCs) represent a valuable cell source able to give rise to different cell types of the body. Among the various pathways of iPSC differentiation, the differentiation into macrophages is a recently developed and rapidly growing technique. Macrophages play a key role in the control of host homeostasis. Their dysfunction underlies many diseases, including hereditary, infectious, oncological, metabolic and other disorders. Targeting macrophage activity and developing macrophage-based cell therapy represent promising tools for the treatment of many pathological conditions. Macrophages generated from human iPSCs (iMphs) provide great opportunities in these areas. The generation of iMphs is based on a step-wise differentiation of iPSCs into mesoderm, hematopoietic progenitors, myeloid monocyte-like cells and macrophages. The technique allows to obtain standardizable populations of human macrophages from any individual, scale up macrophage production and introduce genetic modifications, which gives significant advantages over the standard source of human macrophages, monocyte-derived macrophages. The spectrum of iMph applications is rapidly growing. iMphs have been successfully used to model hereditary diseases and macrophage-pathogen interactions, as well as to test drugs. iMph use for cell therapy is another promising and rapidly developing area of research. The principles and the details of iMph generation have recently been reviewed. This review systemizes current and prospective iMph applications and discusses the problem of iMph safety and other issues that need to be explored before iMphs become clinically applicable.

Macrophage polarization in hypoxia and ischemia/reperfusion: Insights into the role of energetic metabolism

Macrophages, the key cells of innate immunity, possess wide phenotypical and functional heterogeneity. In vitro studies showed that microenvironment signals could induce the so-called polarization of macrophages into two phenotypes: classically activated macrophages (M1) or alternatively activated macrophages (M2). Functionally, they are considered as proinflammatory and anti-inflammatory/pro-regenerative, respectively. However, in vivo studies into macrophage states revealed a continuum of phenotypes from M1 to M2 state instead of the clearly distinguished extreme phenotypes. An important role in determining the type of polarization of macrophages is played by energy metabolism, including the activity of oxidative phosphorylation. In this regard, hypoxia and ischemia that affect cellular energetics can modulate macrophage polarization. Here, we overview the data on macrophage polarization during metabolic shift-associated pathologies including ischemia and ischemia/reperfusion in various organs and discuss the role of energy metabolism potentially triggering the macrophage polarization.

Resveratrol Protects Against Renal Damage via Attenuation of Inflammation and Oxidative Stress in High-Fat-Diet-Induced Obese Mice

Oxidative stress and inflammation play an important role in the chronic kidney disease associated with obesity. Resveratrol (RSV) has been reported to exhibit a wide range of biological activities including antioxidant and anti-inflammatory properties. The objective of the present study was to investigate the effects of RSV on renal inflammation and oxidative stress in obese mice induced by high-fat diet. Male C57BL/6 mice were induced to have nephropathy associated obesity by high-fat diet for 12 weeks. After 8 weeks of feeding, oral supplementation with 100 mg RSV/kg body weight/day was applied with the high-fat-diet feeding for another 4 weeks. The results showed that RSV treatment protected against renal damage induced by high-fat diet, as evidenced by the decreased serum creatinine and urea nitrogen levels, alleviation of glomerular damage, and tubular vacuolization. In addition, RSV enhanced the antioxidant enzyme activity; improved the expression of genes related to inflammation; and decreased the malondialdehyde, tumor necrosis factor-α, and interleukin-6 concentrations in the kidney of high-fat-diet mice. In conclusion, RSV could alleviate renal damage in obese mice induced by high-fat diet via suppressing inflammation and oxidative stress.

Aquaporin-1 attenuates macrophage-mediated inflammatory responses by inhibiting p38 mitogen-activated protein kinase activation in lipopolysaccharide-induced acute kidney injury

Objective

This study was designed to investigate the role of AQP1 in the development of LPS-induced AKI and its potential regulatory mechanisms in the inflammatory responses of macrophages.

Methods

Male Wistar rats were injected intraperitoneally with LPS, and biochemical and histological renal damage was assessed. The levels of inflammatory mediators, macrophage markers and AQP1 in blood and kidney tissues were assessed by ELISA. RTPCR was used to assess changes in the relative levels of AQP1 mRNA induced by LPS. Western blot and immunofluorescence analyses were performed to assay the activation of the p38 MAPK and NF-κB pathways, respectively. The same detection methods were used in vitro to determine the regulatory mechanisms underlying AQP1 function.

Results

AQP1 mRNA levels were dramatically decreased in AKI rats following the increased expression of inflammatory factors. In vitro experiments demonstrated that silencing the AQP1 gene increased inflammatory mediator secretion, altered the classical activation of macrophages, greatly enhanced the phosphorylation of p38 and accelerated the translocation of NF-κB. Furthermore, these results were blocked by doramapimod, a p38 inhibitor. Therefore, these effects were mediated by the increased phosphorylation of p38 MAPK.

Conclusion

Our results suggest that altered AQP1 expression may be associated with the development of inflammation in AKI. AQP1 plays a protective role in modulating acute renal injury and can attenuate macrophage-mediated inflammatory responses by downregulating p38 MAPK activity in LPS-induced RAW264.7 cells. The pharmacological targeting of AQP1-mediated p38 MAPK signalling may provide a novel treatment approach for AKI.

Significance of M2 macrophage in tubulointerstitial disease secondary to primary Sjogren's disease

Objective: M2 Macrophages could improve tubulointerstitial disease in animal models. HIF-1αpromotes macrophage polarization and is involved in tubular injury. The study aims to observe the clinicopathologic significance of M2 macrophage and HIF-1α in tubulointerstitial injury secondary to primary Sjogren's disease.

Methods: Renal tissue samples from patients with tubulointerstitial disease secondary to primary Sjogren's disease (SS, n = 10), chronic tubulointerstitial nephritis secondary to drug (CIN, n = 8) were included in this study. The expression of CD163, CD68 and HIF-1α were examined by immunohistochemistry or immunofluorescence.

Results: (1) Renal involvement was the first manifestation in seven of ten (7/10) patients with pSS, including proteinuria, renal dysfunction, renal tubular acidosis and multiple renal stone; and two patient had intractable hypokalemia. (2) There were numerous CD163- positive cells and CD68- positive cells infiltration in tubulointerstitial injury of pSS, especially in patients with hypokalemia. CD163 positive cells and HIF-1αwere mainly expressed in acute tubulointerstitial injury of pSS, which positively correlated to N-acetyl-β-D-glucosaminidase and β2-microglobulin. (3) Compared with CIN, patients with pSS had higher serum globulin level, erythrocyte sedimentation rate (ESR) and lower urinary osmotic pressure. (4) During follow-up of one year, six patients with pSS and acute tubular injury acquired improved renal function on therapy of steroid and total glucosides of peony. The remaining four patients with pSS had stable renal function.

Conclusion: M2 macrophages are involved in acute tubular injury in patients with primary Sjogren's disease. Early intervention can improve renal function of tubulointerstitial injury secondary to primary Sjogren's disease.

Comparison of the characteristics of macrophages derived from murine spleen, peritoneal cavity, and bone marrow

Macrophages have a diverse set of functions based upon their activation states. The activation states, including resting (M0) and polarizing (M1 and M2) states, of macrophages derived from the mouse bone marrow, spleen, and peritoneal cavity (BMs, SPMs, and PCMs, respectively) were compared. We evaluated the macrophage yield per mouse and compared the surface markers major histocompatibility complex (MHC) II and CD86 by flow cytometry. The relative mRNA levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, mannose receptor (MR), and Ym1 in the M0, M1, and M2 states were also compared using real-time polymerase chain reaction (PCR) analysis. Bone marrow yielded the most macrophages with the best homogeneity, but they were polarized toward the M2 phenotype. All three types of macrophages had the capacity to polarize into the M1 and M2 states, but SPMs had a stronger capacity to polarize into M1. The three types of macrophages showed no differences in their capacity to polarize into the M2 state. Therefore, the three types of macrophages have distinct characteristics regardless of their resting or polarizing states. Although bone marrow can get large amounts of homogeneous macrophages, the macrophages cannot replace tissue-derived macrophages.

The Untapped Pharmacopeic Potential of Helminths

The dramatic rise in immunological disorders that occurs with socioeconomic development is associated with alterations in microbial colonization and reduced exposure to helminths. Excretory-secretory (E/S) helminth products contain a mixture of proteins and low-molecular-weight molecules representing the primary interface between parasite and host. Research has shown great pharmacopeic potential for helminth-derived products in animal disease models and even in clinical trials. Although in its infancy, the translation of worm-derived products into therapeutics is highly promising. Here, we focus on important key aspects in the development of immunomodulatory drugs, also highlighting novel approaches that hold great promise for future development of innovative research strategies.

Circulating CD14+CD163+CD206+ M2 Monocytes Are Increased in Patients with Early Stage of Idiopathic Membranous Nephropathy

Aim

To analyze changes in peripheral blood monocytes and their clinical significance in patients with early stage of idiopathic membranous nephropathy (IMN).

Methods

A total of 27 patients with early stage of IMN and 16 age- and sex-matched healthy controls (HCs) were recruited for the study. The monocyte subset counts in circulation were measured by flow cytometry, and serum interleukin- (IL-) 10 and IL-12 concentrations were tested by enzyme-linked immunosorbent assay. The potential association between clinical signs and monocyte subset counts was analyzed statistically.

Results

Compared with the HCs, the patients with early stage of IMN had higher counts of CD14⁺CD163⁺, CD14⁺CD163⁺CD206⁺, and CD14⁺CD163⁺CD206⁺CD115⁺ M2-like monocytes. The CD14⁺CD163⁺CD206⁺ M2-like cell counts and intracellular IL-10 concentrations in the monocytes were positively correlated with progression in proteinuria. The levels of serum IL-10 were significantly higher in early IMN patients than in the HCs. Furthermore, CD14⁺CD163⁺CD206⁺ M2-like cell counts in the patients with incipient IMN were also positively related with 24 h urinary albumin levels and the values of serum M-type phospholipase A2 receptor (PLA2R).

Conclusion

CD14⁺CD163⁺CD206⁺ M2-like monocytes may contribute to the pathologic process in early-stage IMN and could serve as potential markers for evaluating the disease severity.

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.

PAI-1 (Plasminogen Activator Inhibitor-1) Expression Renders Alternatively Activated Human Macrophages Proteolytically Quiescent

OBJECTIVE

Macrophages are versatile immune cells capable of polarizing into functional subsets depending on environmental stimulation. In atherosclerotic lesions, proinflammatory polarized macrophages are associated with symptomatic plaques, whereas Th2 (T-helper cell type 2) cytokine-polarized macrophages are inversely related with disease progression. To establish a functional cause for these observations, we analyzed extracellular matrix degradation phenotypes in polarized macrophages.

APPROACH AND RESULTS

We provide evidence that proinflammatory polarized macrophages rely on membrane-bound proteases including MMP-14 (matrix metalloproteinase-14) and the serine protease uPA (urokinase plasminogen activator) together with its receptor uPAR for extracellular matrix degradation. In contrast, Th2 cytokine alternatively primed macrophages do not show different proteolytic activity in comparison to unpolarized macrophages and lack increased localization of MMP-14 and uPA receptor to the cell membrane. Nonetheless, they express the highest amount of the serine protease uPA. However, uPA activity is blocked by similarly increased expression of its inhibitor PAI-1 (plasminogen activator inhibitor 1). When inhibiting PAI-1 or when analyzing macrophages deficient in PAI-1, Th2 cytokine-polarized macrophages display the same matrix degradation capability as proinflammatory-primed macrophages. Within atherosclerotic lesions, macrophages positive for the alternative activation marker CD206 express high levels of PAI-1. In addition, to test changed tissue remodeling capacities of alternatively activated macrophages, we used a bleomycin lung injury model in mice reconstituted with PAI-1-/- bone marrow. These results supported an enhanced remodeling phenotype displayed by increased fibrosis and elevated MMP activity in the lung after PAI-1 loss.

CONCLUSIONS

We were able to demonstrate matrix degradation dependent on membrane-bound proteases in proinflammatory stimulated macrophages and a forced proteolytical quiescence in alternatively polarized macrophages by the expression of PAI-1.

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.

Transfusion of CD206+ M2 Macrophages Ameliorates Antibody-Mediated Glomerulonephritis in Mice

Macrophages are multifunctional immune cells that may either drive or modulate disease pathogenesis, depending on the activated phenotype. In this study, we investigated the protective effects of CD206⁺ M2 macrophages against nephrotoxic serum nephritis in mice. We found that these immunosuppressive macrophages, derived from bone marrow and stimulated with IL-4/IL-13 [CD206⁺ M2 bone marrow-derived macrophages (M2BMMs)], protected against renal injury, decreased proteinuria, and diminished the infiltration of CD68⁺ macrophages, neutrophils, and T cells into glomerular tissue. Comparable therapeutic results were obtained with CD206⁺ M2 cells derived from induced pluripotent stem cells. Notably, CD206⁺ M2BMMs, which retained an M2 signature, could elicit a switch of M1 to M2 phenotype in co-cultured macrophages. Moreover, these cells were found to induce the production of regulatory T cells in the spleen and renal draining lymph node. Accordingly, mRNA expression of the T helper 1 cytokines tumor necrosis factor-α, interferon-β, interferon-γ, and IL-12 was significantly reduced in kidneys from mice treated with CD206⁺ M2BMMs. Taken together, the data suggest that CD206⁺ M2 may have therapeutic potential against antibody-mediated glomerular injury and presents its therapeutic value for the treatment of crescentic nephritis in humans.

Significance of CD163-Positive Macrophages in Proliferative Glomerulonephritis

BACKGROUND

CD163, a marker of M2 macrophages, possesses anti-inflammatory properties. This study aims to investigate the clinicopathological significance of CD163-positive macrophages in proliferative glomerulonephritis.

METHODS

Renal tissue samples from patients with lupus nephritis (LN, n = 22), antineutrophil cytoplasmic autoantibody (ANCA)-associated pauci-immune necrotizing glomerulonephritis (PNGN, n = 10), type 1 membranoproliferative glomerulonephritis (n = 5), minimal change disease (n = 8) and normal control kidneys (n = 3) were included in this study. The expression of CD163, CD68, CD20 and CD3 in renal tissues was detected by immunohistochemistry or immunofluorescence. The level of urinary neutrophil gelatinase-associated lipocalin (NGAL) was determined by enzyme-linked immunosorbent assay.

RESULTS

CD163 was mainly expressed in active crescentic glomerulonephritis, proliferative glomerular lesions and areas of tubulointerstitial injury. Patients with LN-IV and PNGN had numerous CD163-positive cells in glomerular and acute tubulointerstitial lesions. CD163-positive cells in glomeruli positively correlated to proteinuria yet negatively correlated to estimated glomerular filtration rate. There was a positive correlation between the number of CD163 cells in acute tubulointerstitial lesions and NGAL levels, whereas a negative correlation between CD163 numbers and estimated glomerular filtration rate. The number of CD163-positive cells in crescentic glomerulonephritis was more than other groups. In LN, the number of CD163 cells in the tubulointerstitial and glomerular lesions had a positive correlation with activity index. Dual staining showed that CD163-positive cells also expressed CD68, although they did not show any staining for CD20 or CD3.

CONCLUSIONS

CD163-positive macrophages were involved in the pathogenesis of proliferative glomerular lesions, active crescentic glomerulonephritis and acute tubular injury of patients with PNGN and active LN.

The Elusive Antifibrotic Macrophage

Fibrotic diseases, especially of the liver, the cardiovascular system, the kidneys, and the lungs, account for approximately 45% of deaths in Western societies. Fibrosis is a serious complication associated with aging and/or chronic inflammation or injury and cannot be treated effectively yet. It is characterized by excessive deposition of extracellular matrix (ECM) proteins by myofibroblasts and impaired degradation by macrophages. This ultimately destroys the normal structure of an organ, which leads to loss of function. Most efforts to develop drugs have focused on inhibiting ECM production by myofibroblasts and have not yielded many effective drugs yet. Another option is to stimulate the cells that are responsible for degradation and uptake of excess ECM, i.e., antifibrotic macrophages. However, macrophages are plastic cells that have many faces in fibrosis, including profibrotic behavior-stimulating ECM production. This can be dependent on their origin, as the different organs have tissue-resident macrophages with different origins and a various influx of incoming monocytes in steady-state conditions and during fibrosis. To be able to pharmacologically stimulate the right kind of behavior in fibrosis, a thorough characterization of antifibrotic macrophages is necessary, as well as an understanding of the signals they need to degrade ECM. In this review, we will summarize the current state of the art regarding the antifibrotic macrophage phenotype and the signals that stimulate its behavior.

Macrophage polarization in kidney diseases

Macrophage accumulation associates closely with the degree of renal structural injury and renal dysfunction in human kidney diseases. Depletion of macrophages reduces while adoptive transfer of macrophages worsens inflammation in animal models of the renal injury. However, emerging evidence support that macrophage polarization plays a critical role in the progression of a number of kidney diseases including obstructive nephropathy, ischemia-reperfusion injury, glomerulonephritis, diabetic nephropathy, and other kidney diseases. In this mini-review, we briefly summarize the macrophage infiltration and polarization in these inflammatory and fibrotic kidney diseases, discussing the results mostly from studies in animal models. In view of the critical role of macrophage in the progression of these diseases, manipulating macrophage phenotype may be a potential effective strategy to treat various kidney diseases.

Resveratrol attenuates lipopolysaccharide-induced acute kidney injury by suppressing inflammation driven by macrophages

SCOPE

Acute kidney injury (AKI) is the most frequent and serious complication in sepsis, a potentially deadly inflammatory response induced by bacterial, viral, or fungal infection. LPS-induced AKI is associated with an abnormal inflammatory response, including renal endothelial dysfunction and renal inflammation. Resveratrol, a natural phytoalexin with low toxicity and anti-inflammatory properties, is known to protect endothelial cells and modulate the immune response in sepsis.

METHODS AND RESULTS

This study investigates the potential protective effects of resveratrol on AKI induced by LPS exposure of mice. Resveratrol was administered as a pre- and posttreatment, or as a posttreatment alone following LPS injection and compared to control groups. Resveratrol significantly improved kidney function and lowered serum and kidney tissue inflammatory cytokine levels. Consistently, resveratrol prevented endotoxin-induced disruption of endothelial cell permeability and inhibited inflammation of kidney tissue. Resveratrol treatment attenuated the effects of LPS on macrophages, with significant inhibition of activation, cytokine release, and Toll-like receptor 4 activation. Resveratrol treatment also resulted in decreased expression of iNOS, Bcl-2, and Bcl-xL in macrophages, which was linked with induction of apoptosis in macrophages.

CONCLUSION

Our studies suggest that resveratrol might represent a novel therapeutic agent to prevent and treat sepsis-induced AKI.