Angiotensin type 2 receptor activation limits kidney injury during the early phase and induces Treg cells during the late phase of renal ischemia

Role of local angiotensin II signaling in bladder function

Angiotensin II signaling plays a crucial role in many different diseases. Although it has been known for several decades that local angiotensin II signaling molecules are present in the bladder, the understanding of their functions there is still limited, especially compared with other organ systems such as cardiovascular and respiratory systems. This article reviews current literature regarding local angiotensin II signaling in the urinary bladder. By reviewing several decades of literature, the field has provided strong evidence to support the presence of local angiotensin II signaling in the bladder, including the expression of angiotensin type 1 receptor and angiotensin type 2 receptor in both human and animal tissues. In addition, evidence suggests a functional role of angiotensin type 1 receptor in mediating bladder contractions. In bladder disease models, angiotensin II signaling can be upregulated, and angiotensin type 1 receptor activity is associated with increases in inflammation, fibrosis, and oxidative stress. We also address the gaps in knowledge that remain in understanding local angiotensin II signaling in the bladder, including limitations on clinical translatability. Although there is a strong foundation regarding the local presence and role of angiotensin II signaling in the bladder, further research is needed to support translational applications.

Activation of angiotensin II type 2 receptor leads to preservation of primary cilia in tubular cells during renal ischaemia-reperfusion injury

Ischaemia-reperfusion (IR)-associated acute kidney injury (AKI) is a severe clinical condition that lacks effective pharmacological treatments. Our recent research revealed that pretreatment with the angiotensin II type 2 receptor (AT2R) agonist C21 alleviates kidney damage during IR. Primary cilia are organelles crucial for regulation of epithelial cell homeostasis, which are significantly affected by IR injury. This study aimed to evaluate the impact of AT2R activation on cilia integrity during IR and to identify pathways involved in the nephroprotective effect of C21. Rats were subjected to 40 min of unilateral ischaemia followed by 24 h of reperfusion. Immunofluorescence analysis of the kidneys showed that the nephroprotective effect of C21 was associated with preservation of cilia integrity in tubular cells. AT2R agonists increased α-tubulin acetylation in primary cilia in tubular cells in vivo and in a cell model. Analysis of ERK phosphorylation indicated that AT2R activation led to diminished activation of ERK1/2 in tubular cells. Similar to AT2R agonists, inhibitors of α-tubulin deacetylase HDAC6 or inhibitors of ERK activation ameliorated IR-induced cell death and preserved cilia integrity. Immunofluorescence analysis of tubular cells revealed significant ERK localization at primary cilia and demonstrated that ERK inhibition increased cilia levels of acetylated α-tubulin. Overall, our findings demonstrate that C21 elicits a preconditioning effect that enhances cilia stability in renal tubular cells, thereby preserving their integrity when exposed to IR injury. Furthermore, our results indicate that this effect might be mediated by AT2R-induced inhibition of ERK activation. These findings offer potential insights for the development of pharmacological interventions to mitigate IR-associated AKI. KEY POINTS: The AT2R agonist C21 prevents primary cilia shortening and tubular cell deciliation during renal ischaemia-reperfusion. AT2R activation inhibits ERK1/2 in renal tubular cells. Both AT2R agonists and ERK1/2 inhibitors increase alpha-tubulin acetylation at the primary cilium in tubular cells. AT2R activation, ERK1/2 inhibition or inhibition of alpha-tubulin deacetylation elicit protective effects in tubular cells subjected to ischaemia-reperfusion injury.

Renin-angiotensin system-mediated nitric oxide signaling in podocytes

Nitric oxide (NO) is widely recognized for its role in regulating renal function and blood pressure. However, the precise mechanisms by which NO affects renal epithelial cells remain understudied. Our previous research has shown that NO signaling in glomerular podocytes can be initiated by Angiotensin II (ANG II) but not by ATP. This study aims to elucidate the crucial interplay between the renin-angiotensin system (RAS) and NO production in podocytes. To conduct our research, we used cultured human podocytes and freshly isolated rat glomeruli. A variety of RAS peptides were used, alongside confocal microscopy, to detect NO production and NO/Ca2+ cross talk. Dynamic changes in the podocyte cytoskeleton, mediated by RAS-NO intracellular signaling, were observed using fluorescent labeling for F-actin and scanning probe microscopy. The experiments demonstrated that ANG II and ANG III generated high levels of NO by activating the angiotensin II type 2 receptor (AT2R). We did not detect functional MAS receptor presence in podocytes, and the moderate NO response to ANG 1-7 was also mediated through AT2R. Furthermore, NO production impacted intracellular Ca2+ signaling and correlated with an increase in podocyte volume and growth. Scanning probe experiments revealed that AT2R activation and the corresponding NO generation are responsible for the protrusion of podocyte lamellipodia. Taken together, our data indicate that AT2R activation enhances NO production in podocytes and subsequently mediates changes in Ca2+ signaling and podocyte volume dynamics. These mechanisms may play a significant role in both physiological and pathophysiological interactions between the RAS and podocytes.NEW & NOTEWORTHY The renin-angiotensin system plays a crucial role in the production of intracellular nitric oxide within podocytes. This mechanism operates through the activation of the angiotensin II type 2 receptor, leading to dynamic modifications in intracellular calcium levels and the actin filament network. This intricate process is vital for linking the activity of angiotensin receptors to podocyte function.

The protective effect of 1400W against ischaemia and reperfusion injury is countered by transient medullary kidney endothelial dysregulation

Renal ischaemia and reperfusion (I/R) is caused by a sudden temporary impairment of the blood flow. I/R is a prevalent cause of acute kidney injury. As nitric oxide generated by inducible nitric oxide synthase (iNOS) has detrimental effects during I/R, the pharmacological blockade of iNOS has been proposed as a potential strategy to prevent I/R injury. The aim of this study was to improve the understanding of 1400W (an iNOS inhibitor) on renal I/R as a pharmacological strategy against kidney disease. BALB/c mice received 30 min of bilateral ischaemia, followed by 48 h or 28 days of reperfusion. Vehicle or 1400W (10 mg/kg) was administered 30 min before inducing ischaemia. We found that after 48 h of reperfusion 1400W decreased the serum creatinine, blood urea nitrogen, neutrophil gelatinase-associated lipocalin and proliferating cell nuclear antigen 3 in the I/R animals. Unexpectedly, we observed mRNA upregulation of genes involved in kidney injury, cell-cycle arrest, inflammation, mesenchymal transition and endothelial activation in the renal medulla of sham animals treated with 1400W. We also explored if 1400W promoted chronic kidney dysfunction 28 days after I/R and did not find significant alterations in renal function, fibrosis, blood pressure or mortality. The results provide evidence that 1400W may have adverse effects in the renal medulla. Importantly, our data point to 1400W-induced endothelial dysfunction, establishing therapeutic limitations for its use. KEY POINTS: Acute kidney injury is a global health problem associated with high morbidity and mortality. The pharmacological blockade of inducible nitric oxide synthase (iNOS) has been proposed as a potential strategy to prevent AKI induced by ischaemia and reperfusion (I/R). Our main finding is that 1400W, a selective and irreversible iNOS inhibitor with low toxicity that is proposed as a therapeutic strategy to prevent kidney I/R injury, produces aberrant gene expression in the medulla associated to tissue injury, cell cycle arrest, inflammation, mesenchymal transition and endothelial activation. The negative effect of 1400W observed in the renal medulla at 48 h from drug administration, is transient as it did not translate into a chronic kidney disease condition.

Angiotensin II type-2 receptor signaling facilitates liver injury repair and regeneration via inactivation of Hippo pathway

The angiotensin II type 2 receptor (AT2R) is a well-established component of the renin-angiotensin system and is known to counteract classical activation of this system and protect against organ damage. Pharmacological activation of the AT2R has significant therapeutic benefits, including vasodilation, natriuresis, anti-inflammatory activity, and improved insulin sensitivity. However, the precise biological functions of the AT2R in maintaining homeostasis in liver tissue remain largely unexplored. In this study, we found that the AT2R facilitates liver repair and regeneration following acute injury by deactivating Hippo signaling and that interleukin-6 transcriptionally upregulates expression of the AT2R in hepatocytes through STAT3 acting as a transcription activator binding to promoter regions of the AT2R. Subsequently, elevated AT2R levels activate downstream signaling via heterotrimeric G protein Gα12/13-coupled signals to induce Yap activity, thereby contributing to repair and regeneration processes in the liver. Conversely, a deficiency in the AT2R attenuates regeneration of the liver while increasing susceptibility to acetaminophen-induced liver injury. Administration of an AT2R agonist significantly enhances the repair and regeneration capacity of injured liver tissue. Our findings suggest that the AT2R acts as an upstream regulator in the Hippo pathway and is a potential target in the treatment of liver damage.

Angiotensin II Type 2 Receptor Antibodies in Glomerular Diseases

We evaluated the concentration of AT2R antibodies in 136 patients with primary and secondary glomerular diseases: membranous nephropathy (n = 18), focal and segmental glomerulosclerosis (n = 25), systemic lupus erythematosus (n = 17), immunoglobulin A (IgA) nephropathy (n = 14), mesangial (non-IgA) proliferative nephropathy (n = 6), c-ANCA vasculitis (n = 40), perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) vasculitis (n = 16), and compared it with a healthy control group (22 patients). Serum creatinine levels, proteinuria, serum albumin, and total protein concentrations were prospectively recorded for 2 years. The mean levels of AT2R antibodies in the lupus nephropathy group were significantly higher compared to the control group, 64.12 ± 26.95 units/mL and 9.72 ± 11.88 units/mL, respectively. There was no association between this level and the clinical course of the disease. The AT2R levels in other kinds of glomerular disease were no different from the control group. We found significant correlations between AT1R and AT2R in patients with membranous nephropathy (r = 0.66), IgA nephropathy (r = 0.61), and c-ANCA vasculitis (r = 0.63). Levels of AT2R antibodies in systemic lupus erythematosus are higher compared to other types of glomerulonephritis, vasculitis, and a healthy control group. Levels of AT2R antibodies correlate with AT1R antibodies in the groups of patients with membranous nephropathy, IgA nephropathy, and c-ANCA vasculitis. These kinds of AT2R antibodies have a stimulative effect on AT2R, but we have not found the influence of these antibodies on the clinical course of glomerular diseases.

Macrophage angiotensin AT2 receptor activation is protective against early phases of LPS-induced acute kidney injury

Lipopolysaccharide (LPS)-induced acute kidney injury (AKI) is characterized by inflammation and infiltration of immune cells, mainly neutrophils and macrophages, and results in sudden renal dysfunction. Previously, we have reported the anti-inflammatory and renoprotective role of the angiotensin II type 2 receptor (AT2R), expressed on kidney tubular cells and immune cells, in LPS-induced AKI. Moreover, in vitro studies revealed macrophage AT2R activation shifts the cells to the anti-inflammatory M2 subtype. However, the protective role of the macrophage AT2R in a model of AKI is unknown. The present study addressed this question by adoptive transfer of bone marrow-derived macrophages (BMDMs) in systemic macrophage-depleted mice. We acquired significant systemic macrophage depletion by two doses of liposomal clodronate (CLD), and the mice were repopulated with BMDMs (CD11b+F4/80+, double positive) primed with AT2R agonist C21 (CLD + MacC21 + LPS) or vehicle (CLD + Mac + LPS) in vitro for 60 min, followed by LPS (5 mg/kg body wt ip) challenge. We observed a gradual increase in the CD11b+ cells at 2 and 24 h after the LPS challenge. However, kidney CD11b+ cells in the CLD + Mac + LPS group were elevated compared with the CLD + MacC21 + LPS group at 2 h after the LPS challenge. The level of inflammatory cytokine (tumor necrosis factor-α) was elevated at 2 h, which was reduced significantly in CLD + MacC21 + LPS-treated animals. Also, CLD + MacC21 + LPS-treated animals had elevated plasma and renal IL-10, indicating an anti-inflammatory role of C21-treated BMDMs. Renal functional injury in CLD + MacC21 + LPS-treated animals was partially improved. Collectively, the data demonstrate that BMDM AT2R stimulation results in anti-inflammation and partial renoprotection against early stages of LPS-induced AKI.NEW & NOTEWORTHY Endotoxin such as lipopolysaccharide (LPS) induces acute kidney injury (AKI), which is a risk factor for and often leads to chronic kidney diseases. The present study revealed that bone marrow-derived macrophage activation of the angiotensin II type 2 receptor (AT2R) contributes to the anti-inflammation and partial renoprotection against early stages of LPS-induced AKI. Since AT2R is an emerging anti-inflammatory and organ-protective target, this study advances our understanding of AT2R's anti-inflammatory mechanisms associated with renoprotection.

Potential nephroprotective effects of angiotensin II type 2 receptor agonist Compound 21 in renal ischemia-reperfusion injury

This study examined the reno-protective potential of Compound 21 during renal ischemia-reperfusion injury by regulating the PI3K expression. 20 adult male Swiss-albino mice, aged 8-12 weeks and weighing 20-30g, were randomly assigned to four equal groups: sham, control, vehicle, and Compound 21. Serum urea, creatinine, inflammatory mediators, tissue 8-isoprostane, and myeloperoxidase were quantified using ELISA. Compared to the sham group, blood levels of urea, creatinine, TNF-α, IL-6, and IL-10 were significantly higher in the ischemia-reperfusion group than in the sham group (p<0.05). However, these indicators were significantly lower in the Compound 21 group (p<0.05). Histological analysis revealed significant renal tissue damage in the ischemia-reperfusion group (p<0.05), which was significantly reduced in the Compound 21 group (p<0.05). PCR results showed that PI3K expression was significantly lower (p<0.05) in the control group compared to the sham group but significantly higher in the Compound 21 group (p<0.05). Furthermore, P-AKT expression levels in the control group were considerably lower than in the sham group (p<0.05). On the other hand, the level of P-AKT expression in the Compound 21 group was significantly upregulated compared to the control group (p<0.05). The findings revealed that Compound 21 could mitigate renal dysfunction induced by ischemia-reperfusion injury in male mice through modulation of the PI3K/AKT signaling pathway, resulting in decreased levels of pro-inflammatory cytokines and renal oxidative stress markers.

Renal vascular responses to angiotensin II infusion in two kidneys-one clip hypertensive rats under partial ischemia/reperfusion with and without ischemia preconditioning: the roles of AT1R blockade and co-blockades of AT1R and MasR

Background and purpose

The renin-angiotensin system activation, partial ischemia/reperfusion (IR) injury, and hypertension contribute to the development of acute kidney injury. The study aims to look at the vascular responses of angiotensin II (Ang II) during Ang II type 1 receptor (AT1R) blockade (losartan) or co-blockades of AT1R and Mas receptor (A779) in two kidneys one clip (2K1C) hypertensive rats which subjected to partial IR injury with and without ischemia preconditioning (IPC).

Experimental approach

Thirty-three 2K1C male Wistar rats with systolic blood pressure ≥ 150 mmHg were divided into three groups of sham, IR, and IPC + IR divided into two sub-groups receiving losartan or losartan + A779. The IR group had 45 min partial kidney ischemia, while the IPC + IR group had two 5 min cycles of partial ischemia followed by 10 min of reperfusion and then 45 min of partial kidney ischemia followed by reperfusion. The sham group was subjected to similar surgical procedures except for IR or IPC.

Findings/Results

Ang II increased mean arterial pressure in all the groups, but there were no significant differences between the sub-groups. A significant difference was observed in the renal blood flow response to Ang II between two sub-groups of sham and IR groups treated with AT1R blockade alone or co-blockades of AT1R + A779.

Conclusion and implications

These findings demonstrated the significance of AT1R and Mas receptor following partial renal IR in the renal blood flow responses to Ang II in 2K1C hypertensive rats.

Investigating the renoprotective effect of C21 in male mice with sepsis via modulation of p-AKT/PI3K expression

This study aimed to investigate if C21 could prevent acute renal injury induced by sepsis by regulating the expression of p-AKT/PI3K. Five equal groups of 25 adult male Swiss-albino mice were randomly divided (n=5): sham (laparotomy without CLP), CLP, vehicle (equivalent amount of DMSO one hour before CLP), and C21 (0.03 mg/kg, one hour before CLP). ELISA was used to measure serum inflammatory mediators, and the expression of PI3K and P-AKT was determined using PCR and immunohistochemistry (IHC), respectively. TNF, TNF receptor, F8-isoprostane, urea, creatinine, and IL-6 blood levels were considerably lower in the CLP group (p<0.05) compared to the sham group, whereas the C21 treated group had significantly (p<0.05) greater levels of these inflammatory mediators. The IHC analysis revealed that P-AKT expression was significantly lower (p<0.05) in the CLP group compared to the sham group, while the C21 pretreatment group had significantly higher levels of P-AKT expression compared to the CLP group (p<0.05). The PI3K expression in the CLP group was significantly lower than in the sham group (p<0.05), according to PCR results, whereas the PI3K expression in the C21 pretreatment group was significantly greater than in the CLP group (p<0.05). This study showed that C21 might reduce levels of pro-inflammatory cytokines, including TNF-, IL-6, and TNF receptor, by modulating the PI3K/AKT signaling pathways, which can, in turn, reduce renal dysfunction during CLP-induced sepsis in male mice.

View of the Renin-Angiotensin System in Acute Kidney Injury Induced by Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury (RIRI) is a sequence of complicated events that is defined as a reduction of the blood supply followed by reperfusion. RIRI is the leading cause of acute kidney injury (AKI). Among the diverse mediators that take part in RIRI-induced AKI, the renin-angiotensin system (RAS) plays an important role via conventional (angiotensinogen, renin, angiotensin-converting enzyme (ACE), angiotensin (Ang) II, and Ang II type 1 receptor (AT1R)) and nonconventional (ACE2, Ang 1-7, Ang 1-9, AT2 receptor (AT2R), and Mas receptor (MasR)) axes. RIRI alters the balance of both axes so that RAS can affect RIRI-induced AKI. In overall, the alteration of Ang II/AT1R and AKI by RIRI is important to consider. This review has looked for the effects and interactions of RAS activities during RIRI conditions.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Probenecid induces the recovery of renal ischemia/reperfusion injury via the blockade of Pannexin 1/P2X7 receptor axis

Renal ischemia/reperfusion injury (RI/RI) is one of the main driving causes of acute kidney injury. However, effective treatment to limit injury and promote recovery and/or survival is still unavailable. Probenecid (PBN), a drug indicated for refractory gout, exhibits protective activities against several preclinical diseases including cerebral and myocardial I/RI via Pannexin 1 (Panx1) and P2X7 receptors' (P2X7R) inhibition. However, its protective role against RI/RI has not been previously addressed. Accordingly, we subjected rats to bilateral RI/RI with/or without PBN treatment. Twenty-four hours post-reperfusion, PBN showed mild tubular injury and reduced serum nephrotoxicity indices, gene and protein expression levels of Panx 1 and P2X7R, and ATP and pro-inflammatory cytokines' levels. The nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome signaling was also downregulated, as demonstrated by reduced gene and protein expression of NLRP3 and caspase-1, along with suppressed IL-1β maturation. Furthermore, PBN enhanced Tregs activity as indicated by elevated FoxP3 gene expression, IL-10, and TGF-β renal levels. On day 5 post-reperfusion, PBN noticeably enhanced renal recovery, as demonstrated by intact tubular epithelium and restored nephrotoxicity indices, Panx 1 and P2X7R gene and protein expression levels, ATP and pro-inflammatory cytokine levels, and NLRP3 inflammasome signaling. Besides, renal Tregs activity was also significantly increased. Our study elaborates for the first time the effectiveness of PBN in recovering post-ischemic renal injury through synergistic inhibition in Panx1/P2X7R axis leading to inactivation of NLRP3 inflammasome signaling and activation of Tregs in ischemic renal tissues. Therefore, PBN can be considered a promising drug for RI/RI treatment.

Double-Negative T Cells Attenuate Cisplatin-Induced Acute Kidney Injury via Upregulating IL-10/AT2R Axis

Objective

Our previous research showed that TCR+CD4-CD8-double-negative (DN) T cells protect renal epithelial cells from cisplatin-induced acute kidney injury (AKI). Therefore, this study is aimed at investigating the mechanism underlying the effect of DN T cells against Cis-induced AKI.

Methods

HK-2 cells cultured alone or with DN T cells were treated with or without Cis. After treatment, the cell viability and death were analyzed by a CCK-8 kit and flow cytometric assay with Annexin V/PI staining, respectively. The expressions of inflammatory factors in HK-2 and DN T cells were analyzed using qPCR. The expression levels of nephrotoxicity-associated biomarkers (KIM, calbindin, and TIMP-1), Bcl-2, and angiotensin AT2 receptor (AT2R) were determined by Western blot and qPCR.

Results

The administration of cisplatin significantly decreased the cell viability and AT2R expression, and increased cell death, inflammatory factors, and nephrotoxicity-associated biomarkers of HK-2 cells, while these effects were partly attenuated when cocultured with DN T cells. IL-10 expression was significantly increased in DN T cells after coculture, and cisplatin treatment aggravated this elevation. IL-10 supplementation exhibited a similar effect to coculture, whereas anti-IL-10 antibody reversed the effect of coculture on cisplatin-treated HK-2 cells. Finally, PD123319, an AT2R antagonist, also reversed the effect of IL-10 and coculture on the cell viability, death, and the expression of KIM, calbindin, TIMP-1, and Bcl-2 of cisplatin-treated HK-2 cells.

Conclusions

DN T cells protected HK-2 cells from cisplatin-induced injury through IL-10/AT2R axis, which may act as a potential target for the treatment of cisplatin-induced AKI.

Angiotensin AT2 Receptor Stimulation Alleviates Collagen-Induced Arthritis by Upregulation of Regulatory T Cell Numbers

The angiotensin AT₂ receptor (AT₂R) is a main receptor of the protective arm of the renin-angiotensin system and exerts for instance anti-inflammatory effects. The impact of AT₂R stimulation on autoimmune diseases such as rheumatoid arthritis (RA) is not yet known. We investigated the therapeutic potential of AT₂R-stimulation with the selective non-peptide AT₂R agonist Compound 21 (C21) in collagen-induced arthritis (CIA), an animal model for inflammatory arthritis. Arthritis was induced by immunization of DBA/1J mice with collagen type II (CII). Prophylactic and therapeutic C21 treatment alleviates arthritis severity and incidence in CIA. Joint histology revealed significantly less infiltrates of IL-1 beta and IL-17A expressing cells and a well-preserved articular cartilage in C21- treated mice. In CIA, the number of CD4⁺CD25⁺FoxP3⁺ regulatory T (Treg) cells significantly increased upon C21 treatment compared to vehicle. T cell differentiation experiments demonstrated increased expression of FoxP3 mRNA, whereas IL-17A, STAT3 and IFN-gamma mRNA expression were reduced upon C21 treatment. In accordance with the mRNA data, C21 upregulated the percentage of CD4⁺FoxP3⁺ cells in Treg polarizing cultures compared to medium-treated controls, whereas the percentage of CD4⁺IL-17A⁺ and CD4⁺IFN-gamma⁺ T cells was suppressed. To conclude, C21 exerts beneficial effects on T cell-mediated experimental arthritis. We found that C21-induced AT₂R-stimulation promotes the expansion of CD4⁺ regulatory T cells and suppresses IL-17A production. Thus, AT₂R-stimulation may represent an attractive treatment strategy for arthritis.

Angiotensin II type-2-receptor stimulation ameliorates focal and segmental glomerulosclerosis in mice

Podocyte damage and loss are the early event in the development of focal segmental glomerulosclerosis (FSGS). Podocytes express angiotensin II type-2-receptor (AT2R), which may play a key role in maintaining kidney integrity and function. Here, we examined the effects of AT2R deletion and AT2R agonist compound 21 (C21) on the evolution of FSGS. FSGS was induced by adriamycin (ADR) injection in both male wild-type (WT) and AT2R knockout (KO) mice. C21 was administered to WT-FSGS mice either one day before or 7 days after ADR (Pre-C21 or Post-C21), using two doses of C21 at either 0.3 (low dose, LD) or 1.0 (high dose, HD) mg/kg/day. ADR-induced FSGS was more severe in AT2RKO mice compared with WT-FSGS mice, and included profound podocyte loss, glomerular fibrosis, and albuminuria. Glomerular cathepsin L expression increased more in AT2RKO-FSGS than in WT-FSGS mice. C21 treatment ameliorated podocyte injury, most significantly in the Pre C21-HD group, and inhibited glomerular cathepsin L expression. In vitro, Agtr2 knock-down in mouse podocyte cell line given ADR confirmed the in vivo data. Mechanistically, C21 inhibited cathepsin L expression, which protected synaptopodin from destruction and stabilized actin cytoskeleton. C21 also prevented podocyte apoptosis. In conclusion, AT2R activation by C21 ameliorated ADR-induced podocyte injury in mice by the inhibition of glomerular cathepsin L leading to the maintenance of podocyte integrity and prevention of podocyte apoptosis.

Splenocyte transfer from hypertensive donors eliminates premenopausal female protection from ANG II-induced hypertension

Premenopausal females are protected from angiotensin II (ANG II)-induced hypertension following the adoptive transfer of T cells from normotensive donors. For the present study, we hypothesized that the transfer of hypertensive T cells (HT) or splenocytes (HS) from hypertensive donors would eliminate premenopausal protection from hypertension. Premenopausal recombination-activating gene-1 (Rag-1)-/- females received either normotensive (NT) or hypertensive cells 3 wk before ANG II infusion (14 days, 490 ng/kg/min). Contrary to our hypothesis, no increase in ANG II-induced blood pressure was observed in the NT/ANG or HT/ANG groups. Flow cytometry demonstrated that renal FoxP3+ T regulatory cells were significantly decreased, and immunohistochemistry showed an increase in renal F4/80+ macrophages in the HT/ANG group, suggesting a shift in the renal inflammatory environment despite no change in blood pressure. Renal mRNA expression of macrophage chemoattractant protein-1 (MCP-1), endothelin-1 (ET-1), and G protein-coupled estrogen receptor-1 (GPER-1) was significantly decreased in the HT/ANG group. The adoptive transfer of hypertensive splenocytes before ANG II infusion (HS/ANG) eliminated premenopausal protection from hypertension and significantly decreased splenic FoxP3+ T regulatory cells compared with females that received normotensive splenocytes (NS/ANG). Expression of macrophage inflammatory protein 1α/chemokine (C-C motif) ligand 3 (MCP-1/CCL3), a potent macrophage chemokine, was elevated in the HS/ANG group; however, no increase in renal macrophage infiltration occurred. Together, these data show that in premenopausal females, T cells from hypertensive donors are not sufficient to induce robust ANG II-mediated hypertension; in contrast, transfer of hypertensive splenocytes (consisting of T/B lymphocytes, dendritic cells, and macrophages) is sufficient. Further work is needed to understand how innate and adaptive immune cells and estrogen signaling coordinate to cause differential hypertensive outcomes in premenopausal females.NEW & NOTEWORTHY Our study is the first to explore the role of hypertensive T cells versus hypertensive splenocytes in premenopausal protection from ANG II-induced hypertension. We show that the hypertensive status of T cell donors does not impact blood pressure in the recipient female. However, splenocytes, when transferred from hypertensive donors, significantly increased premenopausal recipient blood pressure following ANG II infusion, highlighting the importance of further investigation into estrogen signaling and immune cell activation in females.

Mesenchymal Stem Cell Protects Injured Renal Tubular Epithelial Cells by Regulating mTOR-Mediated Th17/Treg Axis

The increase in T helper 17 cell (Th17)-mediated pro-inflammatory response and decrease in regulatory T cell (Treg)-mediated anti-inflammatory effect aggravate renal tubular epithelial cell (RTEC) injury. However, increasing evidence indicated that mesenchymal stem cell (MSC) possessed the ability to control the imbalance between Th17 and Treg. Given that Th17 and Treg are derived from a common CD4⁺ T cell precursor, we summarize the current knowledge of MSC-mediated inhibition of the mammalian target of rapamycin (mTOR), which is a master regulator of CD4⁺ T cell polarization. During CD4⁺ T cell differentiation, mTOR signaling mediates Th17 and Treg differentiation via hypoxia-inducible factor-1α (HIF-1α)-dependent metabolic regulation and signaling pathway, as well as mTOR-mediated phosphorylation of signal transducer and activator of transcription (STAT) 3 and 5. Through interfering with mTOR signaling, MSC restrains CD4⁺ T cell differentiation into Th17, but in turn promotes Treg generation. Thus, this review indicates that MSC-mediated Th17-to-Treg polarization is expected to act as new immunotherapy for kidney injury.

Angiotensin AT2 Receptor is Anti-inflammatory and Reno-Protective in Lipopolysaccharide Mice Model: Role of IL-10

Acute kidney injury (AKI) due to endotoxemic insult is predicted by the infiltration of neutrophils, monocytes and macrophages, and the release of pro-and anti-inflammatory cytokines to the site of injury. Earlier, we have demonstrated the role of angiotensin-II type 2 receptor (AT2R) stimulation in reno-protection in lipopolysaccharide (LPS)-induced inflammation and AKI in C57BL6/NHsd mice. Moreover, AT2R activation has been shown to increase the anti-inflammatory cytokine interleukin-10 (IL-10), its role in AT2R-mediated anti-inflammation and reno-protection is unknown. To address this question, in the present study mice were treated with the AT2R agonist C21 (0.3 mg/kg, intraperitoneally), LPS (5 mg/kg, intraperitoneally), or LPS with C21 pre-treatment with or without neutralizing IL-10 antibody. Treatment with C21 alone caused an increase in the plasma and kidney IL-10 levels, which peaks at 2-h, and returned to baseline at 6-h. The C21-induced IL-10 increase was blocked by the AT2R antagonist PD123319 suggesting AT2R's involvement. LPS treatment caused a profound increase in tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) and the LPS-induced increase in these cytokines was attenuated by the C21 pre-treatment (1-h prior LPS) both in the plasma and kidney. Neutralizing IL-10 antibody treatment abrogated the C21-lowering of TNF-α and IL-6 in the kidney but not in the plasma. Similar results as related to the cytokines profiles in all the groups were also observed in the heart and spleen. The alteration in early cytokine profile prompted us to measure the markers of renal function (blood urea nitogen and urinary creatinine) in order to analyze the effect of IL-10 neutralization. However, it was too early to observe changes in renal function. Therefore, the renal function and injury markers were again measured at 24 h. Treatment with neutralizing IL-10 antibody attenuated the C21-mediated improvement in indices of the kidney function, but not the biomarkers of renal injury (kidney injury molecule-1 and neutrophil-gelatinase associated lipocalin). Collectively, our data suggest that the involvement of IL-10 in AT2R-mediated anti-inflammation and reno-protection against LPS is complex, mediating the renal cytokine profile and kidney filtration function, but not the plasma cytokine profile and renal injury markers.