Macrophages in Renal Injury and Repair

Myeloid cell-derived coagulation tissue factor is associated with renal tubular damage in mice fed an adenine diet

Patients with chronic kidney disease (CKD) commonly exhibit hypercoagulability. Increased levels of uremic toxins cause thrombogenicity by increasing tissue factor (TF) expression and activating the extrinsic coagulation cascade. TF is induced in monocytes and macrophages under pathological conditions, such as inflammatory diseases. However, the role of monocyte myeloid cell TF in CKD progression remains unclear. We aimed to clarify this issue, and the present study found that patients with CKD had elevated levels of D-dimer, a marker of fibrin degradation, which was associated with decreased estimated glomerular filtration rate and increased serum levels of uremic toxins, such as indoxyl sulfate. In vitro studies showed that several uremic toxins increased cellular TF levels in monocytic THP-1 cells. Mice with TF specifically deleted in myeloid cells were fed an adenine diet to cause uremic kidney injury. Myeloid TF deletion reduced tubular injury and pro-inflammatory gene expression in the kidneys of adenine-induced CKD but did not improve renal function as measured by plasma creatinine or blood urea nitrogen. Collectively, our findings suggest a novel concept of pathogenesis of coagulation-mediated kidney injury, in which elevated TF levels in monocytes under uremic conditions is partly involved in the development of CKD.

Renal Mononuclear Phagocytes in Lupus Nephritis

Renal mononuclear phagocytes are a highly pleiotropic group of immune cells of myeloid origin that play multiple protective and pathogenic roles in tissue homeostasis, inflammation, repair, and fibrosis. Infiltration of kidneys with these cells is a hallmark of lupus nephritis and is associated with more severe disease and with increased risk of progression to end‐stage renal disease. This review presents current knowledge of the diversity of these cells and their involvement in kidney inflammation and resolution and describes how they contribute to the chronic inflammation of lupus nephritis. A better understanding of the subset heterogeneity and diverse functions of mononuclear phagocytes in the lupus nephritis kidney should provide fertile ground for the development of new therapeutic approaches that promote the differentiation and survival of protective subsets while targeting pathogenic cell subsets that cause inflammation and fibrosis.

Extracellular vesicle activities regulating macrophage- and tissue-mediated injury and repair responses

Macrophages are typically identified as classically activated (M1) macrophages and alternatively activated (M2) macrophages, which respectively exhibit pro- and anti-inflammatory phenotypes, and the balance between these two subtypes plays a critical role in the regulation of tissue inflammation, injury, and repair processes. Recent studies indicate that tissue cells and macrophages interact via the release of small extracellular vesicles (EVs) in processes where EVs released by stressed tissue cells can promote the activation and polarization of adjacent macrophages which can in turn release EVs and factors that can promote cell stress and tissue inflammation and injury, and vice versa. This review discusses the roles of such EVs in regulating such interactions to influence tissue inflammation and injury in a number of acute and chronic inflammatory disease conditions, and the potential applications, advantage and concerns for using EV-based therapeutic approaches to treat such conditions, including their potential role of drug carriers for the treatment of infectious diseases.

Reduced expression of MiR-125a-5p aggravates LPS-induced experimental acute kidney injury pathology by targeting TRAF6

AIMS

Patients with acute kidney injury (AKI) have higher mortality, and sepsis is among its main causes. MicroRNAs (miRNAs) are essential for regulating kidney function and could have curative potential. This study explored the possibility to treat AKI with miR-125a-5p and reveal the possible mechanism.

MATERIALS AND METHODS

LPS-induced mouse model and LPS-induced RAW264.7 cell model of AKI were established and treated with miR-125a-5p mimics or inhibitors. Serum creatinine and blood urea were measured to evaluate kidney function. The pathological changes of kidney tissues were detected by H&E and PAS staining technique, and the infiltration of macrophages were observed by immunohistochemistry. RAW264.7 cell viability, TRAF6 and cytokines expressions under LPS stimulation were measured. The role and therapeutic potential of miR-125a-5p were verified in vivo and in vitro after given miR-125a-5p mimics or inhibitors.

KEY FINDINGS

LPS-induced mice had increasing serum creatinine and urea, and evident pathological changes, including severe tubular dilatation and macrophages infiltration. TRAF6 expression in the kidney was significantly higher, while miR-125a-5p expression was suppressed. MiR-125a-5p targeted TRAF6, and its overexpression deactivated NF-κB signaling pathway, reducing downstream TNF-α, IL-1β and IL-6 expressions. MiR-125a-5p mimics rescued LPS-induced kidney damage and suppressed pro-inflammatory cytokines expression through inhibiting TRAF6/NF-κB axis.

SIGNIFICANCE

We highlighted that miR-125a-5p could inhibit LPS-induced acute inflammation in the kidney through targeting TRAF6/NF-κB axis. These results might contribute to the development of molecular therapy in AKI.

Major signaling pathways and key mediators of macrophages in acute kidney injury (Review)

Acute kidney injury (AKI) has become a global public health problem with high morbidity and mortality rates, as well as high healthcare costs. Immune cells, particularly macrophages, which regulate tissue development, destroy pathogens, control homeostasis and repair wounds, play crucial and complex roles in AKI. In various types of AKI, numerous rapidly recruited monocytes and tissue-resident macrophages act in a coordinated manner. Thus, elucidating the phenotypic and functional characteristics of macrophages in AKI is essential for identifying potential therapeutic targets. Macrophage-sensing mediators and macrophage-derived mediators participate in the major macrophage-related signaling pathways in AKI, which regulate macrophage polarization and determine disease progression. In conclusion, macrophages change their roles and regulatory mechanisms during the occurrence and development of AKI. The aim of the present review was to contribute to an improved understanding of AKI and to the identification of novel therapeutic targets for this condition.

Hydroxychloroquine Inhibits Macrophage Activation and Attenuates Renal Fibrosis After Ischemia-Reperfusion Injury

Chronic kidney disease (CKD), which is associated with high morbidity, remains a worldwide health concern, while effective therapies remain limited. Hydroxychloroquine (HCQ), which mainly targets toll-like receptor-7 (TLR-7) and TLR-9, is associated with a lower risk of incident CKD. Taking into account that TLR-9 is involved in the development of renal fibrosis and serves as a potential therapy target for CKD, we investigated whether HCQ could attenuate CKD via TLR-9 signal pathway. The effects of HCQ on renal tubulointerstitial fibrosis were further explored using a mouse model of renal tubulointerstitial fibrosis after ischemia/reperfusion injury. Bone marrow-derived macrophages were isolated to explore the effects of HCQ in vitro. Judicious use of HCQ efficiently inhibited the activation of macrophages and MAPK signaling pathways, thereby attenuating renal fibrosis in vivo. In an in vitro model, results showed that HCQ promoted apoptosis of macrophages and inhibited activation of macrophages, especially M2 macrophages, in a dose-dependent manner. Because TLR-7 is not involved in the development of CKD post-injury, a TLR-9 knockout mouse was used to explore the mechanisms of HCQ. The effects of HCQ on renal fibrosis and macrophages decreased after depletion of TLR-9 in vivo and in vitro. Taken together, this study indicated that proper use of HCQ could be a new strategy for anti-fibrotic therapy and that TLR-9 could be a potential therapeutic target for CKD following acute kidney injury.

The Restoration of Vitamin D Levels Slows the Progression of Renal Ischemic Injury in Rats Previously Deficient in Vitamin D

Chronic kidney disease (CKD) remains a global public health problem. The initial damage after ischemia/reperfusion (I/R) injury plays an important role in the pathogenesis of acute kidney injury (AKI) and predisposition to CKD. Several studies have been showing that nontraditional risk factors such as AKI and hypovitaminosis D could also be involved in CKD progression. Vitamin D deficiency (VDD) is associated with hemodynamic changes, activation of inflammatory pathways and renal disease progression (RDP) following I/R-AKI. Strategies for prevention and/or slowing RDP have been determined and the sufficiency of vitamin D has been emerging as a renoprotective factor in many diseases. Therefore, we investigated the effect of the restoration of vitamin D levels in the progression of I/R injury (IRI) in rats previously deficient in vitamin D. On day 30, male Wistar rats were submitted to bilateral 45 min IRI and divided into three groups: IRI, standard diet for 120 days; VDD+IRI, vitamin D-free diet for 120 days; and VDD+IRI+R, vitamin D-free diet in the first 30 days and just after I/R, we reintroduced the standard diet in the last 90 days. After the 120-day protocol, VDD+IRI+R rats presented an improvement in the renal function and renal protein handling followed by a smaller fractional interstitial area. Furthermore, those animals exhibited a reestablishment regarding the hemodynamic parameters and plasma levels of aldosterone, urea and PTH. In addition, the restoration of vitamin D levels reestablished the amount of MCP1 and the renal expressions of CD68+ and CD3+ cells in the VDD+IRI+R rats. Also, VDD+IRI+R rats showed a restoration regarding the amount of collagen type III and renal expressions of fibronectin, vimentin and α-SMA. Such changes were also accompanied by a reestablishment on the renal expression of VDR, Klotho, JG12, and TGF-β1. Our findings indicate that the restoration of vitamin D levels not only improved the renal function and hemodynamics but also reduced the inflammation and fibrosis lesions observed in I/R-AKI associated with VDD. Thus, monitoring of vitamin D status as well as its replacement in the early stages of kidney injury may be a therapeutic alternative in the mitigation of renal disease progression.

Deciphering the Role of Heme Oxygenase-1 (HO-1) Expressing Macrophages in Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), which contributes to the development of chronic kidney disease (CKD). Renal IRI combines major events, including a strong inflammatory immune response leading to extensive cell injuries, necrosis and late interstitial fibrosis. Macrophages act as key players in IRI-induced AKI by polarizing into proinflammatory M1 and anti-inflammatory M2 phenotypes. Compelling evidence exists that the stress-responsive enzyme, heme oxygenase-1 (HO-1), mediates protection against renal IRI and modulates macrophage polarization by enhancing a M2 subset. Hereafter, we review the dual effect of macrophages in the pathogenesis of IRI-induced AKI and discuss the critical role of HO-1 expressing macrophages.

TSC1 Affects the Process of Renal Ischemia-Reperfusion Injury by Controlling Macrophage Polarization

Renal ischemia-reperfusion injury (IRI) contributes to acute kidney injury (AKI), increases morbidity and mortality, and is a significant risk factor for chronic kidney disease (CKD). Macrophage infiltration is a common feature after renal IRI, and infiltrating macrophages can be polarized into the following two distinct types: M1 macrophages, i.e., classically activated macrophages, which can not only inhibit infection but also accelerate renal injury, and M2 macrophages, i.e., alternatively activated macrophages, which have a repair phenotype that can promote wound healing and subsequent fibrosis. The role of TSC1, which is a negative regulator of mTOR signaling that regulates macrophage polarization in inflammation-linked diseases, has been well documented, but whether TSC1 contributes to macrophage polarization in the process of IRI is still unknown. Here, by using a mouse model of renal ischemia-reperfusion, we found that myeloid cell-specific TSC1 knockout mice (termed Lyz-TSC1 cKO mice) had higher serum creatinine levels, more severe histological damage, and greater proinflammatory cytokine production than wild-type (WT) mice during the early phase after renal ischemia-reperfusion. Furthermore, the Lyz-TSC1 cKO mice showed attenuated renal fibrosis during the repair phase of IRI with decreased levels of M2 markers on macrophages in the operated kidneys, which was further confirmed in a cell model of hypoxia-reoxygenation (H/R) in vitro. Mechanistically, by using RNA sequencing of sorted renal macrophages, we found that the expression of most M1-related genes was upregulated in the Lyz-TSC1 cKO group (Supplemental Table 1) during the early phase. However, C/EBPβ and CD206 expression was decreased during the repair phase compared to in the WT group. Overall, our findings demonstrate that the expression of TSC1 in macrophages contributes to the whole process of IRI but serves as an inflammation suppressor during the early phase and a fibrosis promoter during the repair phase.

Glomerular Macrophages in Human Auto- and Allo-Immune Nephritis

Macrophages are involved in tissue homeostasis. They participate in inflammatory episodes and are involved in tissue repair. Macrophages are characterized by a phenotypic heterogeneity and a profound cell plasticity. In the kidney, and more particularly within glomeruli, macrophages are thought to play a maintenance role that is potentially critical for preserving a normal glomerular structure. Literature on the glomerular macrophage role in human crescentic glomerulonephritis and renal transplantation rejection with glomerulitis, is sparse. Evidence from preclinical models indicates that macrophages profoundly modulate disease progression, both in terms of number-where depletion has resulted in a reduced glomerular lesion-and sub-phenotype-M1 being more profoundly detrimental than M2. This evidence is corroborated by better outcomes in patients with a lower number of glomerular macrophages. However, due to the very limited biopsy sample size, the type and role of macrophage subpopulations involved in human proliferative lesions is more difficult to precisely define and synthesize. Therefore, specific biomarkers of macrophage activation may enhance our ability to assess their role, potentially enabling improved monitoring of drug activity and ultimately allowing the development of novel therapeutic strategies to target these elusive cellular players.

Molecular Aspects of Volatile Anesthetic-Induced Organ Protection and Its Potential in Kidney Transplantation

Ischemia reperfusion injury (IRI) is inevitable in kidney transplantation and negatively impacts graft and patient outcome. Reperfusion takes place in the recipient and most of the injury following ischemia and reperfusion occurs during this reperfusion phase; therefore, the intra-operative period seems an attractive window of opportunity to modulate IRI and improve short- and potentially long-term graft outcome. Commonly used volatile anesthetics such as sevoflurane and isoflurane have been shown to interfere with many of the pathophysiological processes involved in the injurious cascade of IRI. Therefore, volatile anesthetic (VA) agents might be the preferred anesthetics used during the transplantation procedure. This review highlights the molecular and cellular protective points of engagement of VA shown in in vitro studies and in vivo animal experiments, and the potential translation of these results to the clinical setting of kidney transplantation.

Downregulation of XBP1 protects kidney against ischemia-reperfusion injury via suppressing HRD1-mediated NRF2 ubiquitylation

Ischemia-reperfusion (IR) injury to the renal epithelia is associated with endoplasmic reticulum stress (ERS) and mitochondria dysfunction, which lead to oxidative stress-induced acute kidney injury (AKI). X-box binding protein 1 (XBP1), an ERS response protein, could play a prominent role in IR-induced AKI. In this study, we revealed that XBP1 and its downstream target HRD1 participated in the crosstalk between ERS and mitochondrial dysfunction via regulation of NRF2/HO-1-mediated reactive oxidative stress (ROS) signaling. Mice with reduced expression of XBP1 (heterozygous Xbp1±) were resistant to IR-induced AKI due to the enhanced expression of NRF2/HO-1 and diminished ROS in the kidney. Downregulation of XBP1 in renal epithelial cells resulted in reduced HRD1 expression and increased NRF2/HO-1 function, accompanied with enhanced antioxidant response. Furthermore, HRD1 served as an E3-ligase to facilitate the downregulation of NRF2 through ubiquitination-degradation pathway, and the QSLVPDI motif on NRF2 constituted an active site for its interaction with HRD1. Thus, our findings unveil an important physiological role for XBP1/HRD1 in modulating the antioxidant function of NRF2/HO-1 in the kidney under stress conditions. Molecular therapeutic approaches that target XBP1-HRD1-NRF2 pathway may represent potential effective means to treat renal IR injury.

CD161a-positive natural killer (NK) cells and α-smooth muscle actin-positive myofibroblasts were upregulated by extrarenal DPP4 in a rat model of acute renal rejection

AIMS

Systemic inhibition of dipeptidyl peptidase 4 (DPP4) showed a protective effect in several transplant models. Here we assessed the specific role of extrarenal DPP4 in renal transplant rejection.

METHODS

Kidneys from wildtype (wt) F344 rats were either transplanted in wt Dark Agouti or congenic rats not expressing DPP4. The remaining, not transplanted donor kidney served as healthy controls. To investigate early inflammatory events rats were sacrificed 3 days after transplantation and kidneys were evaluated for inflammatory cells, capillary rarefaction, proliferation, apoptosis and myofibroblasts by immunohistochemistry.

RESULTS

Capillary ERG-1-positive endothelial cells were significantly more abundant in renal cortex when transplanted into DPP4 deficient compared to wt recipients. In contrast, TGF-ß and myofibroblasts were reduced by more than 25% in kidneys transplanted into DPP4 deficient compared to wt recipients. Numbers of CD161a-positive NK-cells were significantly lower in allografts in DPP4 deficient compared to wt recipients. Numbers of all other investigated immune cells were not affected by the lack of extrarenal DPP4.

CONCLUSION

In early transplant rejection extrarenal DPP4 is involved in the recruitment of NK-cells and early fibrosis. Beneficial effects were less pronounced than reported for systemic DPP4 inhibition, indicating that renal DPP4 is an important player in transplantation-mediated injury.

Endothelial-Derived miR-17∼92 Promotes Angiogenesis to Protect against Renal Ischemia-Reperfusion Injury

BACKGROUND

Damage to the renal microvasculature is a hallmark of renal ischemia-reperfusion injury (IRI)-mediated AKI. The miR-17∼92 miRNA cluster (encoding miR-17, -18a, -19a, -20a, -19b-1, and -92a-1) regulates angiogenesis in multiple settings, but no definitive role in renal endothelium during AKI pathogenesis has been established.

METHODS

Antibodies bound to magnetic beads were utilized to selectively enrich for renal endothelial cells from mice. Endothelial-specific miR-17∼92 knockout (miR-17∼92endo-/- ) mice were generated and given renal IRI. Mice were monitored for the development of AKI using serum chemistries and histology and for renal blood flow using magnetic resonance imaging (MRI) and laser Doppler imaging. Mice were treated with miRNA mimics during renal IRI, and therapeutic efficacies were evaluated.

RESULTS

miR-17, -18a, -20a, -19b, and pri-miR-17∼92 are dynamically regulated in renal endothelial cells after renal IRI. miR-17∼92endo-/- exacerbates renal IRI in male and female mice. Specifically, miR-17∼92endo-/- promotes renal tubular injury, reduces renal blood flow, promotes microvascular rarefaction, increases renal oxidative stress, and promotes macrophage infiltration to injured kidneys. The potent antiangiogenic factor thrombospondin 1 (TSP1) is highly expressed in renal endothelium in miR-17∼92endo-/- after renal IRI and is a target of miR-18a and miR-19a/b. miR-17∼92 is critical in the angiogenic response after renal IRI, which treatment with miR-18a and miR-19b mimics can mitigate.

CONCLUSIONS

These data suggest that endothelial-derived miR-17∼92 stimulates a reparative response in damaged renal vasculature during renal IRI by regulating angiogenic pathways.

TGF-β1 Signaling: Immune Dynamics of Chronic Kidney Diseases

Chronic kidney disease (CKD) is a major cause of morbidity and mortality worldwide, imposing a great burden on the healthcare system. Regrettably, effective CKD therapeutic strategies are yet available due to their elusive pathogenic mechanisms. CKD is featured by progressive inflammation and fibrosis associated with immune cell dysfunction, leading to the formation of an inflammatory microenvironment, which ultimately exacerbating renal fibrosis. Transforming growth factor β1 (TGF-β1) is an indispensable immunoregulator promoting CKD progression by controlling the activation, proliferation, and apoptosis of immunocytes via both canonical and non-canonical pathways. More importantly, recent studies have uncovered a new mechanism of TGF-β1 for de novo generation of myofibroblast via macrophage-myofibroblast transition (MMT). This review will update the versatile roles of TGF-β signaling in the dynamics of renal immunity, a better understanding may facilitate the discovery of novel therapeutic strategies against CKD.

The varying roles of macrophages in kidney injury and repair

PURPOSE OF REVIEW

Macrophages play an important role in regulating homeostasis, kidney injury, repair, and tissue fibrogenesis. The present review will discuss recent advances that explore the novel subsets and functions of macrophage in the pathogenesis of kidney damage and hypertension.

RECENT FINDINGS

Macrophages differentiate into a variety of subsets in microenvironment-dependent manner. Although the M1/M2 nomenclature is still applied in considering the pro-inflammatory versus anti-inflammatory effects of macrophages in kidney injury, novel, and accurate macrophage phenotypes are defined by flow cytometric markers and single-cell RNA signatures. Studies exploring the crosstalk between macrophages and other cells are rapidly advancing with the additional recognition of exosome trafficking between cells. Using murine conditional mutants, actions of macrophage can be defined more precisely than in bone marrow transfer models. Some studies revealed the opposing effects of the same protein in renal parenchymal cells and macrophages, highlighting a need for the development of cell-specific immune therapies for translation.

SUMMARY

Macrophage-targeted therapies hold potential for limiting kidney injury and hypertension. To realize this potential, future studies will be required to understand precise mechanisms in macrophage polarization, crosstalk, proliferation, and maturation in the setting of renal disease.

The orchestrated cellular and molecular responses of the kidney to endotoxin define a precise sepsis timeline

Sepsis is a dynamic state that progresses at variable rates and has life-threatening consequences. Staging patients along the sepsis timeline requires a thorough knowledge of the evolution of cellular and molecular events at the tissue level. Here, we investigated the kidney, an organ central to the pathophysiology of sepsis. Single-cell RNA-sequencing in a murine endotoxemia model revealed the involvement of various cell populations to be temporally organized and highly orchestrated. Endothelial and stromal cells were the first responders. At later time points, epithelial cells upregulated immune-related pathways while concomitantly downregulating physiological functions such as solute homeostasis. Sixteen hours after endotoxin, there was global cell–cell communication failure and organ shutdown. Despite this apparent organ paralysis, upstream regulatory analysis showed significant activity in pathways involved in healing and recovery. This rigorous spatial and temporal definition of murine endotoxemia will uncover precise biomarkers and targets that can help stage and treat human sepsis.

The Blockade of TACE-Dependent EGF Receptor Activation by Losartan-Erlotinib Combination Attenuates Renal Fibrosis Formation in 5/6-Nephrectomized Rats Under Vitamin D Deficiency

Chronic kidney disease (CKD) has been considered a major public health issue. In addition to cardiovascular diseases and infections, hypovitaminosis D has been considered a non-traditional aggravating factor for CKD progression. Interstitial fibrosis is a hallmark of CKD strongly correlated with deterioration of renal function. Transforming growth factor β (TGF-β) is the major regulatory profibrotic cytokine in CKD. Many injurious stimuli converge on the TGF-β pathway, which has context-dependent pleiotropic effects and interacts with several related renal fibrosis formation (RFF) pathways. Epidermal growth factor receptor (EGFR) is critically involved in CKD progression, exerting a pathogenic role in RFF associated with TGF-β-related fibrogenesis. Among others, EGFR pathway can be activated by a disintegrin and a metalloproteinase known as tumor necrosis factor α-converting enzyme (TACE). Currently no effective therapy is available to completely arrest RFF and slow the progression of CKD. Therefore, we investigated the effects of a double treatment with losartan potassium (L), an AT1R antagonist, and the tyrosine kinase inhibitor erlotinib (E) on the alternative pathway of RFF related to TACE-dependent EGFR activation in 5/6-nephrectomized rats under vitamin D deficiency (D). During the 90-day protocol, male Wistar rats under D, were submitted to 5/6 nephrectomy (N) on day 30 and randomized into four groups: N+D, no treatment; N+D+L, received losartan (50 mg/kg/day); N+D+E, received erlotinib (6 mg/kg/day); N+D+L+E received losartan+erlotinib treatment. N+D+L+E data demonstrated that the double treatment with losartan+erlotinib not only blocked the TACE-dependent EGF receptor activation but also prevented the expression of TGF-β, protecting against RFF. This renoprotection by losartan+erlotinib was corroborated by a lower expression of ECM proteins and markers of phenotypic alteration as well as a lesser inflammatory cell infiltrate. Although erlotinib alone has been emerging as a renoprotective drug, its association with losartan should be considered as a potential therapeutic strategy on the modulation of RFF.

M2 macrophage-derived exosomal miR-25-3p improves high glucose-induced podocytes injury through activation autophagy via inhibiting DUSP1 expression

Diabetic nephropathy (DN) is the primary reason of chronic kidney disease. The aim of our study is to explore the role and action mechanism of M2 macrophage-derived exosomes in high glucose (HG)-induced podocytes injury. Here, 30 mmol/L of HG was used to induce podocytes injury. Annexin V-FITC/PI double staining was performed to measure podocytes apoptosis, and western blot was carried out to ensure proteins expression. The shape of exosomes was identified using TEM. Besides, the expression of miR-25-3p was determined by qRT-PCR, FAM-labeled miR-25-5p combined with DiI-labeled exosomes were utilized to explore the uptake of podocytes to exosomes. Relationship between miR-25-3p and DUSP family members was ensued by luciferase activity assay. In the beginning, we found that M2 macrophage ameliorated HG-induced podocytes apoptosis and epithelial-mesenchymal transition through secreting exosomes. Subsequently, highly expressed miR-25-3p was found in M2 macrophage-derived exosomes that effectively improved HG-induced podocytes injury. Furthermore, inhibition of miR-25-3p in M2 macrophage inefficiently repressed HG-induced podocytes injury, thus we proposed that M2 macrophage attenuated podocytes injury through secreting exosomal miR-25-3p. Then, we used an autophagy inhibitor to stimulate podocytes, and demonstrated that M2 macrophage-derived exosomal miR-25-3p improved HG-induced podocytes injury through activating autophagy. Finally, DUSP1 was proved to be a downstream target and mediated the inhibition of exosomal miR-25-3p to HG-induced podocytes injury. Our results indicated that M2 macrophage could improve HG-induced podocytes injury via secreting exosomal miR-25-3p to activate autophagy of the cells through suppressing DUSP1 expression. We proved a newly potential therapy strategy for DN treatment.

Neurogenic tachykinin mechanisms in experimental nephritis of rats

We demonstrated earlier that renal afferent pathways combine very likely “classical” neural signal transduction to the central nervous system and a substance P (SP)–dependent mechanism to control sympathetic activity. SP content of afferent sensory neurons is known to mediate neurogenic inflammation upon release. We tested the hypothesis that alterations in SP-dependent mechanisms of renal innervation contribute to experimental nephritis. Nephritis was induced by OX-7 antibodies in rats, 6 days later instrumented for recording of blood pressure (BP), heart rate (HR), drug administration, and intrarenal administration (IRA) of the TRPV1 agonist capsaicin to stimulate afferent renal nerve pathways containing SP and electrodes for renal sympathetic nerve activity (RSNA). The presence of the SP receptor NK-1 on renal immune cells was assessed by FACS. IRA capsaicin decreased RSNA from 62.4 ± 5.1 to 21.6 ± 1.5 mV s (*p < 0.05) in controls, a response impaired in nephritis. Suppressed RSNA transiently but completely recovered after systemic administration of a neurokinin 1 (NK1-R) blocker. NK-1 receptors occurred mainly on CD11⁺ dendritic cells (DCs). An enhanced frequency of CD11c⁺NK1R⁺ cell, NK-1 receptor⁺ macrophages, and DCs was assessed in nephritis. Administration of the NK-1R antagonist aprepitant during nephritis reduced CD11c⁺NK1R⁺ cells, macrophage infiltration, renal expression of chemokines, and markers of sclerosis. Hence, SP promoted renal inflammation by weakening sympathoinhibitory mechanisms, while at the same time, substance SP released intrarenally from afferent nerve fibers aggravated immunological processes i.e. by the recruitment of DCs.

Clusterin regulates macrophage expansion, polarization and phagocytic activity in response to inflammation in the kidneys

Clusterin (CLU) is a multifunctional protein localized extracellularly and intracellularly. Although CLU-knockout (KO) mice are more susceptible to renal ischemia-reperfusion injury (IRI), the mechanisms underlying the actions of CLU in IRI are not fully understood. Macrophages are key regulators of IRI severity and tissue repair. Therefore, we investigated the role of CLU in macrophage polarization and phagocytosis. Renal IRI was induced in wild-type (WT) or CLU-KO C57BL/6 mice by clamping the renal pedicles for 30 min at 32°C. Peritoneal macrophages were activated via an intraperitoneal injection of lipopolysaccharide (LPS). Renal tissue damage was examined using histology, whereas leukocyte phenotypes were assessed using flow cytometry and immunohistochemistry. We found that monocytes/macrophages expressed the CLU protein that was upregulated by hypoxia. The percentages of macrophages (F4/80⁺ , CD11b⁺ or MAC3⁺ ) infiltrating the kidneys of WT mice were significantly less than those in CLU-KO mice after IRI. The M1/M2 phenotype ratio of the macrophages in WT kidneys decreased at day 7 post-IRI when the injury was repaired, whereas that in KO kidneys increased consistently as tissue injury persisted. In response to LPS stimulation, WT mice produced fewer M1 macrophages, but not M2, than the control did. Phagocytosis was stimulated by CLU expression in macrophages compared with the CLU null controls and by the exogenous CLU protein. In conclusion, CLU suppresses macrophage infiltration and proinflammatory M1 polarization during the recovery period following IRI, and enhances phagocytic activity, which may be partly responsible for tissue repair in the kidneys of WT mice after injury.

Human amniotic epithelial cells ameliorate kidney damage in ischemia-reperfusion mouse model of acute kidney injury

BACKGROUND

Acute kidney injury (AKI) is a common clinical disease with complex pathophysiology and limited therapeutic choices. This prompts the need for novel therapy targeting multiple aspects of this disease. Human amnion epithelial cell (hAEC) is an ideal stem cell source. Increasing evidence suggests that exosomes may act as critical cell-cell communicators. Accordingly, we assessed the therapeutic potential of hAECs and their derived exosomes (hAECs-EXO) in ischemia reperfusion mouse model of AKI and explored the underlying mechanisms.

METHODS

The hAECs were primary cultured, and hAECs-EXO were isolated and characterized. An ischemic-reperfusion injury-induced AKI (IRI-AKI) mouse model was established to mimic clinical ischemic kidney injury with different disease severity. Mouse blood creatinine level was used to assess renal function, and kidney specimens were processed to detect cell proliferation, apoptosis, and capillary density. Macrophage infiltration was analyzed by flow cytometry. hAEC-derived exosomes (hAECs-EXO) were used to treat hypoxia-reoxygenation (H/R) injured HK-2 cells and mouse bone marrow-derived macrophages to evaluate their protective effect in vitro. Furthermore, hAECs-EXO were subjected to liquid chromatography-tandem mass spectrometry for proteomic profiling.

RESULTS

We found that systematically administered hAECs could improve mortality and renal function in IRI-AKI mice, decrease the number of apoptotic cells, prevent peritubular capillary loss, and modulate kidney local immune response. However, hAECs showed very low kidney tissue integration. Exosomes isolated from hAECs recapitulated the renal protective effects of their source cells. In vitro, hAECs-EXO protected HK-2 cells from H/R injury-induced apoptosis and promoted bone marrow-derived macrophage polarization toward M2 phenotype. Proteomic analysis on hAECs-EXO revealed proteins involved in extracellular matrix organization, growth factor signaling pathways, cytokine production, and immunomodulation. These findings demonstrated that paracrine of exosomes might be the key mechanism of hAECs in alleviating renal ischemia reperfusion injury.

CONCLUSIONS

We reported hAECs could improve survival and ameliorate renal injury in mice with IRI-AKI. The anti-apoptotic, pro-angiogenetic, and immunomodulatory capabilities of hAECs are at least partially, through paracrine pathways. hAECs-EXO might be a promising clinical therapeutic tool, overcoming the weaknesses and risks associated with the use of native stem cells, for patients with AKI.

CP-25 improves nephropathy in collagen-induced arthritis rats by inhibiting the renal inflammatory response

Paeoniflorin-6'-O-benzene sulfonate (CP-25) is a derivative of paeoniflorin. We previously confirmed that CP-25 inhibits inflammatory responses in several arthritis animal models. The aim of the present study was to investigate the beneficial effects of CP-25 on renal damage in rats with collagen-induced arthritis (CIA). CIA was induced in rats, which were orally administered CP-25 (25, 50 and 100 mg/kg/day) for 24 days. The levels of plasma blood urea nitrogen (BUN) and urine protein in CIA rats were measured. Pathological changes in renal tissues and joints were observed, and inflammatory cell infiltration was evaluated by immunohistochemistry. Moreover, renal inflammatory mediators and transporters were measured by western blotting. We found that CP-25 not only inhibited arthritis manifestations but also improved renal pathological manifestations and kidney injury by decreasing serum BUN and urine protein levels. Further study revealed that CP-25 treatment reduced the number of renal CD68+ cells and downregulated the levels of MCP-1, TNF-α and IL-6 in CIA rats. On the other hand, we noted that CP-25 decreased the ratios of phosphorylated NF-κB p65 (p-p65) to total p65 and p-IκBα to total IκBα in CIA rats, suggesting that CP-25 blocked NF-κB activation. Finally, we observed that CP-25 restored the abnormal expression of OAT1 and OCT1 in the renal tissues of CIA rat. Our data indicate that CP-25 ameliorates kidney damage in CIA rats, and this beneficial effect is closely related to inhibiting renal inflammation and the abnormal expression of transporters.

BAY61-3606 protects kidney from acute ischemia/reperfusion injury through inhibiting spleen tyrosine kinase and suppressing inflammatory macrophage response

Acute kidney injury (AKI) is a highly prevalent clinical syndrome with high mortality and morbidity. Previous studies indicated that inflammation promotes tubular damage and plays a key role in AKI progress. Spleen tyrosine kinase (Syk) has been linked to macrophage-related inflammation in AKI. Up to date, however, no Syk-targeted therapy for AKI has been reported. In this study, we employed both cell model of LPS-induced bone marrow-derived macrophage (BMDM) and mouse model of ischemia/reperfusion injury (IRI)-induced AKI to evaluate the effects of a Syk inhibitor, BAY61-3606 (BAY), on macrophage inflammation in vitro and protection of kidney from AKI in vivo. The expression and secretion of inflammatory cytokines, both in vitro and in vivo, were significantly inhibited even back to normal levels by BAY. The upregulated serum creatinine and blood urea nitrogen levels in the AKI mice were significantly reduced after administration of BAY, implicating a protective effect of BAY on kidneys against IRI. Further analyses from Western blot, immunofluorescence staining and flow cytometry revealed that BAY inhibited the Mincle/Syk/NF-κB signaling circuit and reduced the inflammatory response. BAY also inhibited the reactive oxygen species (ROS), which further decreased the formation of inflammasome and suppressed the mature of IL-1β and IL-18. Notably, these inhibitory effects of BAY on inflammation and inflammasome in BMDM were significantly reversed by Mincle ligand, trehalose-6,6-dibehenate. In summary, these findings provided compelling evidence that BAY may be an efficient inhibitor of the Mincle/Syk/NF-κB signaling circuit and ROS-induced inflammasome, which may help to develop Syk-inhibitors as novel therapeutic agents for AKI.

Mutation of RORγT reveals a role for Th17 cells in both injury and recovery from renal ischemia-reperfusion injury

To investigate T helper type 17 (Th17) cells in the setting of acute kidney injury, the gene encoding the master regulator of Th17 cell differentiation, that is, RAR-related orphan receptor-γ (RORγT), was mutated in Lewis rats using CRISPR/Cas9 technology. In response to 40 min of bilateral renal ischemia-reperfusion (I/R), RAR-related orphan receptor C (Rorc)^-/- rats were resistant to injury relative to wild-type Rorc^+/+ rats. This protection was associated with inhibition of IL-17 expression and reduced infiltration of CD4⁺ cells, CD8⁺ cells, B cells, and macrophages. To evaluate the effect of Th17 cells on repair, ischemia was increased to 50 min in Rorc^-/- rats. This maneuver equalized the initial level of injury in Rorc^-/- and Rorc^+/+ rats 1 to 2 days post-I/R based on serum creatinine values. However, Rorc^-/- rats, but not Rorc^+/+ rats, failed to successfully recover renal function and had high mortality by 4 days post-I/R. Histological assessment of kidney tubules showed evidence of repair by day 4 post-I/R in Rorc^+/+ rats but persistent necrosis and elevated cell proliferation in Rorc^-/- rats. Adoptive transfer of CD4⁺ cells from the spleen of Rorc^+/+ rats or supplementation of exogenous rIL-17 by an osmotic minipump improved renal function and survival of Rorc^-/- rats following 50 min of I/R. This was associated with a relative decrease in the number of M₁-type macrophages and a relative increase in the percentage of T regulatory cells. Taken together, these data suggest that Th17 cells have both a deleterious and a beneficial role in kidney injury and recovery, contributing to early postischemic injury and inflammation but also possibly being critical in the resolution of inflammation during kidney repair.

Trichostatin A Alleviates Renal Interstitial Fibrosis Through Modulation of the M2 Macrophage Subpopulation

Mounting evidence indicates that an increase in histone deacetylation contributes to renal fibrosis. Although inhibition of histone deacetylase (HDAC) can reduce the extent of fibrosis, whether HDAC inhibitors exert the antifibrotic effect through modulating the phenotypes of macrophages, the key regulator of renal fibrosis, remains unknown. Moreover, the functional roles of the M2 macrophage subpopulation in fibrotic kidney diseases remain incompletely understood. Herein, we investigated the role of HDAC inhibitors on renal fibrogenesis and macrophage plasticity. We found that HDAC inhibition by trichostatin A (TSA) reduced the accumulation of interstitial macrophages, suppressed the activation of myofibroblasts and attenuated the extent of fibrosis in obstructive nephropathy. Moreover, TSA inhibited M1 macrophages and augmented M2 macrophage infiltration in fibrotic kidney tissue. Interestingly, TSA preferentially upregulated M2c macrophages and suppressed M2a macrophages in the obstructed kidneys, which was correlated with a reduction of interstitial fibrosis. TSA also repressed the expression of proinflammatory and profibrotic molecules in cultured M2a macrophages and inhibited the activation of renal myofibroblasts. In conclusion, our study was the first to show that HDAC inhibition by TSA alleviates renal fibrosis in obstructed kidneys through facilitating an M1 to M2c macrophage transition.

MiRNA-133a aggravates inflammatory responses in sepsis by targeting SIRT1

BACKGROUND

Sepsis is a systemic inflammatory response syndrome. MicroRNA (miRNA) plays an important role in immune cell activation, inflammatory cytokine release and immune response. However, the mechanism of miR-133a in sepsis remains largely unknown.

METHODS

Sepsis mice models were established by applying the cecal ligation and puncture (CLP) method. Quantitative real-time polymerase chain reaction (qRT-PCR) assay was performed to detect the relative expression of miR-133a and inflammatory cytokines. Hematoxylin and eosin (H&E) staining and enzyme-linked immunosorbent assay (Elisa) were used to evaluate organ injury and inflammatory response. Besides, lipopolysaccharide (LPS)-induced RAW264.7 macrophages were used to construct sepsis cell models. Further, dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were carried out to confirm the relationship between miR-133a and sirtuin-1 (SIRT1). In addition, western blot (WB) assay was performed to measure the relative SIRT1 protein level.

RESULTS

MiR-133a was highly expressed in sepsis patients and CLP mice models. Knockdown of miR-133a inhibited sepsis-induced lung, liver and kidney injuries and inflammatory response in CLP mice models. Besides, miR-133a inhibitor also alleviated the inflammatory response of RAW264.7 macrophages induced by LPS. SIRT1 was a target of miR-133a, and silenced SIRT1 could reverse the anti-inflammatory effect of miR-133a inhibitor on LPS-induced sepsis cell models.

CONCLUSION

MiR-133a promoted the inflammatory response of sepsis by inhibiting the expression of SIRT1, which might provide a new therapeutic strategy for sepsis.

CSF-1R inhibition attenuates ischemia-induced renal injury and fibrosis by reducing Ly6C+ M2-like macrophage infiltration

Acute kidney injury (AKI) to chronic kidney disease (CKD) progression has become a life-threatening disease. However, an effective therapeuticstrategyis still needed. The pathophysiology of AKI-to-CKD progression involves chronic inflammation and renal fibrosis driven by macrophage activation, which is physiologically dependent on colony-stimulating factor-1 receptor (CSF-1R) signaling. In this study, we modulated macrophage infiltration through oral administration of the CSF-1R inhibitor GW2580 in an ischemia-reperfusion (I/R)-induced AKI model to evaluate its therapeutic effects on preventing the progression of AKI to CKD. We found that GW2580 induced a significant reduction in the number of macrophages in I/R-injured kidneys and attenuated I/R-induced renal injury and subsequent interstitial fibrosis. By flow cytometry, we observed that the reduced macrophages were primarily Ly6C⁺ inflammatory macrophages in the GW2580-treated kidneys, while there was no significant difference in the number and percentage of Ly6C^-CX3CR1⁺ macrophages. We further found that these reduced macrophages also demonstrated some characteristics of M2-like macrophages, which have been generally regarded as profibrotic subtypes in chronic inflammation. These results indicate the existence of phenotypic and functional crossover between Ly6C⁺ and M2-like macrophages in I/R kidneys, which induces AKI worsening to CKD. In conclusion, therapeutic GW2580 treatment alleviates acute renal injury and subsequent fibrosis by reducing Ly6C⁺ M2-like macrophage infiltration in ischemia-induced AKI.

Role of promoting inflammation of Krüppel-like factor 6 in acute kidney injury

Background

Krüppel-like factor 6 (KLF6) is a transcription factor that participate in various pathophysiological processes, but its contribution in ischemia acute kidney injury (AKI) is lacking so far. The study aimed to investigate the expression and the role of KLF6 in kidney ischemia–reperfusion (IR) injury.

Method

Microarray data were collected from GSE58438 and GSE52004. The rat IR model was established to evaluate the mRNA and protein expression of KLF6 and inflammatory cytokines in serum and kidney tissues. SiRNA-KLF6 was transfected with HK-2 cells, and then a cell-based hypoxia-reoxygenation (HR) model was established.

Results

Bioinformatics showed KLF6 mRNA in kidney tissue is up-regulated in 3 h after IR in rat kidney, which involved in cell activation, leukocyte activation, and response to hydrogen peroxide after IR. The rat IR model results showed that KLF6 expression was peaking at 6 h, and the expression of pro-inflammatory cytokines MCP-1 and TNF-α was increased both in serum and kidney tissues, while anti-inflammatory cytokine IL-10 was decreased after IR. Furthermore, in vitro results showed that KLF6 knock-down reduced the pro-inflammatory cytokines expression.

Conclusion

These results suggest that (1) KLF6 might be a novel biomarker for early diagnosis of AKI and (2) KLF6 may play a role in promoting inflammation in AKI.

Neuroimmune Communication in the Kidney

Recent studies have clarified the interaction between nervous systems and immunity regarding the manner in which local inflammation is regulated and systemic homeostasis is maintained. The cholinergic anti-inflammatory pathway (CAP) is a neuroimmune pathway activated by vagus nerve stimulation. Following afferent vagus nerve stimulation, signals are transmitted to immune cells in the spleen, including β2-adrenergic receptor-positive CD4-positive T cells and α7 nicotinic acetylcholine receptor-expressing macrophages. These immune cells release the neurotransmitters norepinephrine and acetylcholine, inducing a series of reactions that reduce proinflammatory cytokines, relieving inflammation. CAP contributes to various inflammatory diseases such as endotoxemia, rheumatoid arthritis, and inflammatory bowel disease. Moreover, emerging studies have revealed that vagus nerve stimulation ameliorates kidney damage in an animal model of acute kidney injury. These studies suggest that the link between the nervous system and kidneys is associated with the pathophysiology of kidney injury. Here, we review the current knowledge of the neuroimmune circuit and kidney disease, as well as potential for therapeutic strategies based on this knowledge for treating kidney disease in clinical settings.

Raw and salt-processed Achyranthes bidentata attenuate LPS-induced acute kidney injury by inhibiting ROS and apoptosis via an estrogen-like pathway

BACKGROUND

Traditional Chinese medicine suggests that Radix Achyranthis Bidentatae nourishes and protects the kidneys, the effect of which is enhanced following a salt treatment. Raw and salt-processed Achyranthes bidentata are produced via different processing techniques from the same crude Achyranthes root. The anti-inflammatory and immunomodulatory properties of this plant have been verified earlier. However, there is a scarcity of experimental evidence for the renal-protective effects.

AIM

The purpose of present study is to compare the protective effects of raw and salt-processed Achyranthes on lipopolysaccharide (LPS) - induced acute kidney injury in mice and chemically characterize their extracts.

METHOD

The monomer components of raw and salt-processed Achyranthes extracts were analyzed using high performance liquid chromatography (HPLC). The aggregation and distribution of 2-Deoxy-D-glucose (2-DG) near infrared fluorescence probe in mice was examined with a small animal imaging systems. The pathological and morphological changes of kidneys were observed by H&E staining, and the serum urea nitrogen (BUN) and serum creatinine (Scr) levels were used to evaluate the renal function. The levels of cytokines in serum were detected by cytometric bead array. Flow cytometry assay was performed to assess the apoptosis and reactive oxygen species (ROS) in the kidney cells, and cell surface marker expression including CD45⁺, F4/80⁺, and Ly-6G⁺. The estrogenic activities of the raw and salt-processed Achyranthes were observed by uterine weight gain test in sexually immature mice. Western blot was used to detect the protein expression levels in the kidney.

RESULTS

Chemical analysis showed that the salt-processed Achyranthes contained more ginsenoside Ro and chikusetsusaponin Ⅳa than the raw Achyranthes, but there was no difference in the contents of β-ecdysterone, 25R-inokosterone, and 25S-inokosterone.in vivo near-infrared fluorescence imaging showed a significant reduced inflammation in the AKI mice. Histological studies showed that the raw and salt-processed Achyranthes markedly decreased the inflammatory infiltration, swelling and vacuolar degeneration in renal tissues and the Scr and BUN. Importantly, the raw and salt-processed Achyranthes extracts demonstrated different degrees of inhibition on the LPS-induced AKI, with salt-processed Achyranthes showing better inhibition. Results of flow cytometry showed a significant inhibition of IFN-γ, TNF-α, and IL-2, and promoted IL-10, along with reduced macrophages (CD45 + F4/80+), neutrophils (CD45+ Ly-6G+) and phagocytes. Furthermore, the extracts reduced the accumulation of ROS and apoptosis in the kidney, and also regulated the expression of apoptosis marker proteins TLR4, Bcl-2, Bax, cleaved caspase 3 and cleaved caspase 9 levels. Notably, they increased ERα, ERβ, and GPR30 in the renal tissues of AKI mice and LPS non-treated mice. In the subsequent experiments, it was found that the raw and salt-processed Achyranthes extracts increased the uterine coefficient in sexually immature mice, improved the LPS-induced decrease in NRK52e cell viability, and reduced the apoptosis, which could be antagonized by ICI182, 780 (estrogen receptor-unspecific antagonist, Faslodex).

CONCLUSIONS

The renal-protective effect of raw and salt-processed Achyranthes was exhibited through antiapoptotic and antioxidant mechanisms via an estrogen-like pathway, along with a modulation of the inflammatory response by regulating immune cells. Ginsenoside Ro and Chikusetsu saponin IVa were found to be the key factors to enhance the protective effect of salt-processed Achyranthes.

Role of chemokines, innate and adaptive immunity

Polycystic Kidney Disease (PKD) triggers a robust immune system response including changes in both innate and adaptive immunity. These changes involve immune cells (e.g., macrophages and T cells) as well as cytokines and chemokines (e.g., MCP-1) that regulate the production, differentiation, homing, and various functions of these cells. This review is focused on the role of the immune system and its associated factors in the pathogenesis of PKDs as evidenced by data from cell-based systems, animal models, and PKD patients. It also highlights relevant pre-clinical and clinical studies that point to specific immune system components as promising candidates for the development of prognostic biomarkers and therapeutic strategies to improve PKD outcomes.

SerpinB2 Regulates Immune Response in Kidney Injury and Aging

BACKGROUND

Expression of SerpinB2, a regulator of inflammatory processes, has been described in the context of macrophage activation and cellular senescence. Given that mechanisms for these processes interact and can shape kidney disease, it seems plausible that SerpinB2 might play a role in renal aging, injury, and repair.

METHODS

We subjected SerpinB2 knockout mice to ischemia-reperfusion injury or unilateral ureteral obstruction. We performed phagocyte depletion to study SerpinB2's role beyond the effects of macrophages and transplanted bone marrow from knockout mice to wild-type mice and vice versa to dissect cell type-dependent effects. Primary tubular cells and macrophages from SerpinB2 knockout and wild-type mice were used for functional studies and transcriptional profiling.

RESULTS

Cultured senescent tubular cells, kidneys of aged mice, and renal stress models exhibited upregulation of SerpinB2 expression. Functionally, lack of SerpinB2 in aged knockout mice had no effect on the magnitude of senescence markers but associated with enhanced kidney damage and fibrosis. In stress models, inflammatory cell infiltration was initially lower in knockout mice but later increased, leading to an accumulation of significantly more macrophages. SerpinB2 knockout tubular cells showed significantly reduced expression of the chemokine CCL2. Macrophages from knockout mice exhibited reduced phagocytosis and enhanced migration. Macrophage depletion and bone marrow transplantation experiments validated the functional relevance of these cell type-specific functions of SerpinB2.

CONCLUSIONS

SerpinB2 influences tubule-macrophage crosstalk by supporting tubular CCL2 expression and regulating macrophage phagocytosis and migration. In mice, SerpinB2 expression seems to be needed for coordination and timely resolution of inflammation, successful repair, and kidney homeostasis during aging. Implications of SerpinB2 in human kidney disease deserve further exploration.

Aquaporin 1 alleviates acute kidney injury via PI3K-mediated macrophage M2 polarization

BACKGROUND

Lipopolysaccharide (LPS)-induced acute kidney injury (AKI) is associated with an abnormal immune response. Accumulating evidence has demonstrated that aquaporin 1 (AQP1) prevents kidney tissue injury in LPS-induced AKI by mediating immune response. However, the underlying mechanisms remain obscure. Macrophages as immune cells with multiple phenotypes are important mediators in tissue homeostasis and host defense. We propose that macrophage polarization is implicated in AQP1-mediated immune response.

METHODS

Herein we established sepsis-induced AKI model rats through intraperitoneal injection of LPS into Wistar rats to reveal immune mechanism of damage. We also used LPS-induced mouse RAW264.7 cells to elucidate the molecular mechanism of macropage polarization.

RESULTS

Histopathology showed that renal tubular epithelial cells in the model group were swollen, inflammatory exudation was obvious and the inflammatory factors, interleukin-6 (IL-6) and tumor necrosis factor α (TNF-α) were increased. Western blotting showed PI3K was upregulated in the model group. Serum creatinine and urea nitrogen increased after LPS injection. Renal AQP1 mRNA is downregulated and serum AQP1 protein increased first and then decreased in LPS-induced AKI rats. M2 macrophage markers (Arg-1, CD206) were increased in repair stage. In addition, treatment of murine macrophages (RAW264.7) with AQP1 siRNA resulted in decreased PI3K activation and M2 polarization, but increased IL-6 and TNF-α. Moreover, inhibiting PI3K with wortmannin imitated the results of AQP1 silencing.

CONCLUSIONS

Macrophage M2 polarization is likely the cellular mechanism underlying the anti-AKI property of AQP1, and PI3K activation is involved in the AQP1-induced M2 phenotype switch.

Macrophage-secreted Lipocalin-2 Promotes Regeneration of Injured Primary Murine Renal Tubular Epithelial Cells

Lipocalin-2 (Lcn-2) is rapidly upregulated in macrophages after renal tubular injury and acts as renoprotective and pro-regenerative agent. Lcn-2 possesses the ability to bind and transport iron with high affinity. Therefore, the present study focuses on the decisive role of the Lcn-2 iron-load for its pro-regenerative function. Primary mouse tubular epithelial cells were isolated from kidney tissue of wildtype mice and incubated with 5μM Cisplatin for 24h to induce injury. Bone marrow-derived macrophages of wildtype and Lcn-2^-/- mice were isolated and polarized with IL-10 towards an anti-inflammatory, iron-release phenotype. Their supernatants as well as recombinant iron-loaded holo-Lcn-2 was used for stimulation of Cisplatin-injured tubular epithelial cells. Incubation of tubular epithelial cells with wildtype supernatants resulted in less damage and induced cellular proliferation, whereas in absence of Lcn-2 no protective effect was observed. Epithelial integrity as well as cellular proliferation showed a clear protection upon rescue experiments applying holo-Lcn-2. Notably, we detected a positive correlation between total iron amounts in tubular epithelial cells and cellular proliferation, which, in turn, reinforced the assumed link between availability of Lcn-2-bound iron and recovery. We hypothesize that macrophage-released Lcn-2-bound iron is provided to tubular epithelial cells during toxic cell damage, whereby injury is limited and recovery is favored.

Ferritins in Kidney Disease

Ferritins are evolutionarily conserved proteins that regulate cellular iron metabolism. It is the only intracellular protein that is capable of storing large quantities of iron. Although the ratio of different subunits determines the iron content of each ferritin molecule, the exact mechanism that dictates organization of these subunits still is unclear. In this review, we address renal ferritin expression and its implication in kidney disease. Specifically, we address the role of ferritin subunits in preventing kidney injury and also promoting tolerance against infection-associated kidney injury. We describe functions for ferritin that are independent of its ability to ferroxidize and store iron. We further discuss the implications of ferritin in body fluids, including blood and urine, during inflammation and kidney disease. Although there are several in-depth review articles on ferritin in the context of iron metabolism, we chose to focus on the role of ferritin particularly in kidney health and disease and highlight unanswered questions in the field.

IL-4 Receptor α Chain Protects the Kidney Against Tubule-Interstitial Injury Induced by Albumin Overload

Increasing evidence has highlighted the role of tubule-interstitial injury (TII) as a vital step in the pathogenesis of acute kidney injury (AKI). Incomplete repair of TII during AKI could lead to the development of chronic kidney disease. Changes in albumin endocytosis in proximal tubule epithelial cells (PTECs) is linked to the development of TII. In this context, interleukin (IL)-4 has been shown to be an important factor in modulating recovery of TII. We have studied the possible role of IL-4 in TII induced by albumin overload. A subclinical AKI model characterized by albumin overload in the proximal tubule was used, without changing glomerular function. Four groups were generated: (1) CONT, wild-type mice treated with saline; (2) BSA, wild-type mice treated with 10 g/kg/day bovine serum albumin (BSA); (3) KO, IL4Rα^–/– mice treated with saline; and (4) KO + BSA, IL4Rα^–/– mice treated with BSA. As reported previously, mice in the BSA group developed TII without changes in glomerular function. The following parameters were increased in the KO + BSA group compared with the BSA group: (1) tubular injury score; (2) urinary γ-glutamyltransferase; (3) CD4⁺ T cells, dendritic cells, macrophages, and neutrophils are associated with increases in renal IL-6, IL-17, and transforming growth factor β. A decrease in M2-subtype macrophages associated with a decrease in collagen deposition was observed. Using LLC-PK1 cells, a model of PTECs, we observed that (1) these cells express IL-4 receptor α chain associated with activation of the JAK3/STAT6 pathway; (2) IL-4 alone did not change albumin endocytosis but did reverse the inhibitory effect of higher albumin concentration. This effect was abolished by JAK3 inhibitor. A further increase in urinary protein and creatinine levels was observed in the KO + BSA group compared with the BSA group, but not compared with the CONT group. These observations indicate that IL-4 has a protective role in the development of TII induced by albumin overload that is correlated with modulation of the pro-inflammatory response. We propose that megalin-mediated albumin endocytosis in PTECs could work as a sensor, transducer, and target during the genesis of TII.

Identification and validation of biomarkers of persistent acute kidney injury: the RUBY study

Purpose

The aim of the RUBY study was to evaluate novel candidate biomarkers to enable prediction of persistence of renal dysfunction as well as further understand potential mechanisms of kidney tissue damage and repair in acute kidney injury (AKI).

Methods

The RUBY study was a multi-center international prospective observational study to identify biomarkers of the persistence of stage 3 AKI as defined by the KDIGO criteria. Patients in the intensive care unit (ICU) with moderate or severe AKI (KDIGO stage 2 or 3) were enrolled. Patients were to be enrolled within 36 h of meeting KDIGO stage 2 criteria. The primary study endpoint was the development of persistent severe AKI (KDIGO stage 3) lasting for 72 h or more (NCT01868724).

Results

364 patients were enrolled of whom 331 (91%) were available for the primary analysis. One hundred ten (33%) of the analysis cohort met the primary endpoint of persistent stage 3 AKI. Of the biomarkers tested in this study, urinary C–C motif chemokine ligand 14 (CCL14) was the most predictive of persistent stage 3 AKI with an area under the receiver operating characteristic curve (AUC) (95% CI) of 0.83 (0.78–0.87). This AUC was significantly greater than values for other biomarkers associated with AKI including urinary KIM-1, plasma cystatin C, and urinary NGAL, none of which achieved an AUC > 0.75.

Conclusion

Elevated urinary CCL14 predicts persistent AKI in a large heterogeneous cohort of critically ill patients with severe AKI. The discovery of CCL14 as a predictor of persistent AKI and thus, renal non-recovery, is novel and could help identify new therapeutic approaches to AKI.

Electronic supplementary material

The online version of this article (10.1007/s00134-019-05919-0) contains supplementary material, which is available to authorized users.

Cordycepin protects renal ischemia/reperfusion injury through regulating inflammation, apoptosis, and oxidative stress

Cordycepin (3'-deoxyadenosine) is a naturally occurring adenosine analog and one of the bioactive constituents isolated from Cordyceps sinensis, species of the fungal genus Cordyceps. It has traditionally been a prized Chinese folk medicine for the human well-being. However, the actions of cordycepin against renal ischemia/reperfusion injury (I/R) are still unknown. In the present study, rats were subject to I/R and cordycepin was intragastrically administered for seven consecutive days before surgery to investigate the effects and mechanisms of cordycepin against renal I/R injury. The test results of kidney and peripheral blood samples of experimental animals showed that cordycepin significantly decreased serum blood urea nitrogen and creatinine levels and markedly attenuated cell injury. Mechanistic studies showed that cordycepin significantly regulated inflammation, apoptosis, and oxidative stress. These data provide new insights for investigating the natural product with the nephroprotective effect against I/R, which should be developed as a new therapeutic agent for the treatment of I/R in the future.

Involvement of hydrogen sulfide in the progression of renal fibrosis

OBJECTIVE

Renal fibrosis is the most common manifestation of chronic kidney disease (CKD). Noting that existing treatments of renal fibrosis only slow disease progression but do not cure it, there is an urgent need to identify novel therapies. Hydrogen sulfide (H2S) is a newly discovered endogenous small gas signaling molecule exerting a wide range of biologic actions in our body. This review illustrates recent experimental findings on the mechanisms underlying the therapeutic effects of H2S against renal fibrosis and highlights its potential in future clinical application.

DATA SOURCES

Literature was collected from PubMed until February 2019, using the search terms including "Hydrogen sulfide," "Chronic kidney disease," "Renal interstitial fibrosis," "Kidney disease," "Inflammation factor," "Oxidative stress," "Epithelial-to-mesenchymal transition," "H2S donor," "Hypertensive kidney dysfunction," "Myofibroblasts," "Vascular remodeling," "transforming growth factor (TGF)-beta/Smads signaling," and "Sulfate potassium channels."

STUDY SELECTION

Literature was mainly derived from English articles or articles that could be obtained with English abstracts. Article type was not limited. References were also identified from the bibliographies of identified articles and the authors' files.

RESULTS

The experimental data confirmed that H2S is widely involved in various renal pathologies by suppressing inflammation and oxidative stress, inhibiting the activation of fibrosis-related cells and their cytokine expression, ameliorating vascular remodeling and high blood pressure, stimulating tubular cell regeneration, as well as reducing apoptosis, autophagy, and hypertrophy. Therefore, H2S represents an alternative or additional therapeutic approach for renal fibrosis.

CONCLUSIONS

We postulate that H2S may delay the occurrence and progress of renal fibrosis, thus protecting renal function. Further experiments are required to explore the precise role of H2S in renal fibrosis and its application in clinical treatment.

Conservation of glucagon like peptide-1 level with liraglutide and linagilptin protects the kidney against angiotensin II-induced tissue fibrosis in rats

This study tested the hypothesis that the enhancement of glucagon-like peptide-1 (GLP-1) level through either exogenous supply of GLP-1 agonist, liraglutide or prevention of endogenous GLP-1 degradation with dipeptidyl peptidease-4 inhibitor, lingaliptin ameliorates angiotensin II (Ang II)-induced renal fibrosis. Sprague-Dawley rats were randomly divided into four groups: 0.9% saline or Ang II (500 ng/kg/min) was infused with osmotic minipumps for 4 weeks, defined as sham and Ang II groups. In drug treated groups, liraglutide (0.3 mg/kg) was injected subcutaneously twice daily or linagliptin (8 mg/kg) was administered daily via oral gavage during Ang II infusion. Compared with Ang II stimulation, liraglutide or linagliptin comparatively down-regulated the protein level of the AT₁ receptor, and up-regulated the AT₂ receptor, as identified by a reduced AT₁/AT₂ ratio (all p < 0.05), consistent with less locally-expressed AT₁ receptor and enhanced AT₂ receptor in the glomerular capillaries and proximal tubules of the renal cortex. Furthermore, both drugs significantly increased the expression of GLP-1 receptor and attenuated the protein levels of TLR4, NOX4 and IL-6. The populations of macrophages and α-SMA expressing myofibroblasts decreased with treatment of liraglutide and linagliptin, in coincidence with the reduced expression of phosphor-Smad2/3, Smad4, TGFβ1, and up-regulated Smad7. Along with these modulations, renal morphology was preserved and synthesis of fibronectin/collagen I was down-regulated, as identified by small collagen-rich area in the renal cortex. These results suggest that the preservation of GLP-1 level using liraglutide or linagliptin might be considered as an add-on therapeutic option for inhibiting Ang II induced renal fibrosis and failure.

The pathobiology of polycystic kidney disease from a metabolic viewpoint

Autosomal dominant polycystic kidney disease (ADPKD) affects an estimated 1 in 1,000 people and slowly progresses to end-stage renal disease (ESRD) in about half of these individuals. Tolvaptan, a vasopressin 2 receptor blocker, has been approved by regulatory authorities in many countries as a therapy to slow cyst growth, but additional treatments that target dysregulated signalling pathways in cystic kidney and liver are needed. Metabolic reprogramming is a prominent feature of cystic cells and a potentially important contributor to the pathophysiology of ADPKD. A number of pathways previously implicated in the pathogenesis of the disease, such as dysregulated mTOR and primary ciliary signalling, have roles in metabolic regulation and may exert their effects through this mechanism. Some of these pathways are amenable to manipulation through dietary modifications or drug therapies. Studies suggest that polycystin-1 and polycystin-2, which are encoded by PKD1 and PKD2, respectively (the genes that are mutated in >99% of patients with ADPKD), may in part affect cellular metabolism through direct effects on mitochondrial function. Mitochondrial dysfunction could alter the redox state and cellular levels of acetyl-CoA, resulting in altered histone acetylation, gene expression, cytoskeletal architecture and response to cellular stress, and in an immunological response that further promotes cyst growth and fibrosis.

Perivascular CD73+ cells attenuate inflammation and interstitial fibrosis in the kidney microenvironment

Progressive tubulointerstitial fibrosis may occur after acute kidney injury due to persistent inflammation. Purinergic signaling by 5'-ectonucleotidase, CD73, an enzyme that converts AMP to adenosine on the extracellular surface, can suppress inflammation. The role of CD73 in progressive kidney fibrosis has not been elucidated. We evaluated the effect of deletion of CD73 from kidney perivascular cells (including pericytes and/or fibroblasts of the Foxd1+ lineage) on fibrosis. Perivascular cell expression of CD73 was necessary to suppress inflammation and prevent kidney fibrosis in Foxd1CreCD73fl/fl mice evaluated 14 days after unilateral ischemia-reperfusion injury or folic acid treatment (250 mg/kg). Kidneys of Foxd1CreCD73fl/fl mice had greater collagen deposition, expression of proinflammatory markers (including various macrophage markers), and platelet-derived growth factor recepetor-β immunoreactivity than CD73fl/fl mice. Kidney dysfunction and fibrosis were rescued by administration of soluble CD73 or by macrophage deletion. Isolated CD73-/- kidney pericytes displayed an activated phenotype (increased proliferation and α-smooth muscle actin mRNA expression) compared with wild-type controls. In conclusion, CD73 in perivascular cells may act to suppress myofibroblast transformation and influence macrophages to promote a wound healing response. These results suggest that the purinergic signaling pathway in the kidney interstitial microenvironment orchestrates perivascular cells and macrophages to suppress inflammation and prevent progressive fibrosis.

Renal Inflammation and Fibrosis: A Double-edged Sword

Renal tissue injury initiates inflammatory and fibrotic processes that occur to promote regeneration and repair. After renal injury, damaged tissue releases cytokines and chemokines, which stimulate activation and infiltration of inflammatory cells to the kidney. Normal tissue repair processes occur simultaneously with activation of myofibroblasts, collagen deposition, and wound healing responses; however, prolonged activation of pro-inflammatory and pro-fibrotic cell types causes excess extracellular matrix deposition. This review focuses on the physiological and pathophysiological roles of specialized cell types, cytokines/chemokines, and growth factors, and their implications in recovery or exacerbation of acute kidney injury.

The transcription factor Twist1 in the distal nephron but not in macrophages propagates aristolochic acid nephropathy

Tubulointerstitial disease in the kidney culminates in renal fibrosis that portents organ failure. Twist1, a basic helix-loop-helix protein 38 transcription factor, regulates several essential biological functions, but inappropriate Twist1 activity in the kidney epithelium can trigger kidney fibrogenesis and chronic kidney disease. By contrast, Twist1 in circulating myeloid cells may constrain inflammatory injury by attenuating cytokine generation. To dissect the effects of Twist1 in kidney tubular versus immune cells on renal inflammation following toxin-induced renal injury, we subjected mice with selective deletion of Twist1 in renal epithelial cells or macrophages to aristolochic acid-induced chronic kidney disease. Ablation of Twist1 in the distal nephron attenuated kidney damage, interstitial fibrosis, and renal inflammation after aristolochic acid exposure. However, macrophage-specific deletion of Twist1 did not impact the development of aristolochic acid-induced nephropathy. In vitro studies confirmed that Twist1 in renal tubular cells underpins their susceptibility to apoptosis and propensity to generate pro-fibrotic mediators in response to aristolochic acid. Moreover, co-culture studies revealed that Twist1 in renal epithelia augmented the recruitment and activation of pro-inflammatory CD64⁺ macrophages. Thus, Twist1 in the distal nephron rather than in infiltrating macrophages propagates chronic inflammation and fibrogenesis during aristolochic acid-induced nephropathy.

Effect of M2 Macrophages on Injury and Apoptosis of Renal Tubular Epithelial Cells Induced by Calcium Oxalate Crystals

Background: M2 macrophages have important roles in diseases such as tumours, cardiovascular diseases and renal diseases. This study aimed to determine the effects and protective mechanism of M2 macrophages against oxidative stress injury and apoptosis induced by calcium oxalate crystals (CaOx) in renal tubular epithelial cells (HK-2) under coculture conditions. Methods: THP-1 cells were induced to differentiate into M2 macrophages by using phorbol-12-myristate-13-acetate, IL-4 and IL-13. Morphological features were observed by microscopy. Phenotypic markers were identified by reverse transcription-polymerase chain reaction, Western blot and enzyme-linked immunosorbent assay (ELISA). HK-2 cells were treated with 0.5 mg/mL CaOx crystals and co-cultured with M2 macrophages or apocynin. The viability of HK-2 cells was detected by CCK-8 assay. The lactate dehydrogenase (LDH) activity of HK-2 cells was analysed using a microplate reader. The apoptosis of HK-2 cells was examined by flow cytometry and Hoechst 33258 staining. Reactive oxygen species (ROS) expression and mitochondrial membrane potential in HK-2 cells were detected by a fluorescence microplate reader. Western blot analysis was conducted to detect the expression of p47phox, Bcl-2, cleaved caspase-3, cytochrome c, p38 MAPK, phospho-p38 MAPK, Akt and phospho-Akt. Results: The results of morphology, reverse transcription-polymerase chain reaction, Western blot and ELISA showed that THP-1 cells were successfully polarised to M2 macrophages. The results of co-culture suggested that M2 macrophages or apocynin significantly increased the cell viability and decreased the LDH activity and apoptosis rate after HK-2 cells were challenged with CaOx crystals. The expression of the p47phox protein and the concentration of ROS were reduced, the release of mitochondrial membrane potential and the expression of the Bcl-2 protein were upregulated and the protein expression of cleaved caspase-3 and cytochrome c was downregulated. The expression of the phosphorylated form of p38 MAPK increased. Under coculture conditions with M2 macrophages, the Akt protein of HK-2 cells treated with CaOx crystals was dephosphorylated, but the phosphorylated form of Akt was not reduced by apocynin. Conclusions: M2 macrophages reduced the oxidative stress injury and apoptosis of HK-2 cells by downregulating the activation of NADPH oxidase, reducing the production of ROS, inhibiting the phosphorylation of p38 MAPK and enhancing the phosphorylation of Akt. We have revealed one of the possible mechanisms by which M2 macrophages reduce the formation of kidney stones.

The Impact of Versatile Macrophage Functions on Acute Kidney Injury and Its Outcomes

Acute kidney injury (AKI) is a common and devastating clinical condition with a high morbidity and mortality rate and is associated with a rapid decline of kidney function mostly resulting from the injury of proximal tubules. AKI is typically accompanied by inflammation and immune activation and involves macrophages (Mϕ) from the beginning: The inflamed kidney recruits “classically” activated (M1) Mϕ, which are initially poised to destroy potential pathogens, exacerbating inflammation. Of note, they soon turn into “alternatively” activated (M2) Mϕ and promote immunosuppression and tissue regeneration. Based on their roles in kidney recovery, there is a growing interest to use M2 Mϕ and Mϕ-modulating agents therapeutically against AKI. However, it is pertinent to note that the clinical translation of Mϕ-based therapies needs to be critically reviewed and questioned since Mϕ are functionally plastic with versatile roles in AKI and some Mϕ functions are detrimental to the kidney during AKI. In this review, we discuss the current state of knowledge on the biology of different Mϕ subtypes during AKI and, especially, on their role in AKI and assess the impact of versatile Mϕ functions on AKI based on the findings from translational AKI studies.

The Anti-Inflammatory, Anti-Oxidative, and Anti-Apoptotic Benefits of Stem Cells in Acute Ischemic Kidney Injury

Ischemia-reperfusion injury (IRI) plays a significant role in the pathogenesis of acute kidney injury (AKI). The complicated interaction between injured tubular cells, activated endothelial cells, and the immune system leads to oxidative stress and systemic inflammation, thereby exacerbating the apoptosis of renal tubular cells and impeding the process of tissue repair. Stem cell therapy is an innovative approach to ameliorate IRI due to its antioxidative, immunomodulatory, and anti-apoptotic properties. Therefore, it is crucial to understand the biological effects and mechanisms of action of stem cell therapy in the context of acute ischemic AKI to improve its therapeutic benefits. The recent finding that treatment with conditioned medium (CM) derived from stem cells is likely an effective alternative to conventional stem cell transplantation increases the potential for future therapeutic uses of stem cell therapy. In this review, we discuss the recent findings regarding stem cell-mediated cytoprotection, with a focus on the anti-inflammatory effects via suppression of oxidative stress and uncompromised immune responses following AKI. Stem cell-derived CM represents a favorable approach to stem cell-based therapy and may serve as a potential therapeutic strategy against acute ischemic AKI.

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.