Angiotensin II Type 2 Receptor Modulates Synovial Macrophage Polarization by Inhibiting GRK2 Membrane Translocation in a Rat Model of Collagen-Induced Arthritis

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.

Targeting different phenotypes of macrophages: A potential strategy for natural products to treat inflammatory bone and joint diseases

BACKGROUND

Macrophages, a key class of immune cells, have a dual role in inflammatory responses, switching between anti-inflammatory M2 and pro-inflammatory M1 subtypes depending on the specific environment. Greater numbers of M1 macrophages correlate with increased production of inflammatory chemicals, decreased osteogenic potential, and eventually bone and joint disorders. Therefore, reversing M1 macrophages polarization is advantageous for lowering inflammatory factors. To better treat inflammatory bone disorders in the future, it may be helpful to gain insight into the specific mechanisms and natural products that modulate macrophage polarization.

OBJECTIVE

This review examines the impact of programmed cell death and different cells in the bone microenvironment on macrophage polarization, as well as the effects of natural products on the various phenotypes of macrophages, in order to suggest some possibilities for the treatment of inflammatory osteoarthritic disorders.

METHODS

Using 'macrophage polarization,' 'M1 macrophage' 'M2 macrophage' 'osteoporosis,' 'osteonecrosis of femoral head,' 'osteolysis,' 'gouty arthritis,' 'collagen-induced arthritis,' 'freund's adjuvant-induced arthritis,' 'adjuvant arthritis,' and 'rheumatoid arthritis' as search terms, the relevant literature was searched using the PubMed, the Cochrane Library and Web of Science databases.

RESULTS

Targeting macrophages through different signaling pathways has become a key mechanism for the treatment of inflammatory bone and joint diseases, including HIF-1α, NF-κB, AKT/mTOR, JAK1/2-STAT1, NF-κB, JNK, ERK, p-38α/β, p38/MAPK, PI3K/AKT, AMPK, AMPK/Sirt1, STAT TLR4/NF-κB, TLR4/NLRP3, NAMPT pathway, as well as the programmed cell death autophagy, pyroptosis and ERS.

CONCLUSION

As a result of a search of databases, we have summarized the available experimental and clinical evidence supporting herbal products as potential treatment agents for inflammatory osteoarthropathy. In this paper, we outline the various modulatory effects of natural substances targeting macrophages in various diseases, which may provide insight into drug options and directions for future clinical trials. In spite of this, more mechanistic studies on natural substances, as well as pharmacological, toxicological, and clinical studies are required.

Macrophage: Key player in the pathogenesis of autoimmune diseases

The macrophage is an essential part of the innate immune system and also serves as the bridge between innate immunity and adaptive immune response. As the initiator and executor of the adaptive immune response, macrophage plays an important role in various physiological processes such as immune tolerance, fibrosis, inflammatory response, angiogenesis and phagocytosis of apoptotic cells. Consequently, macrophage dysfunction is a vital cause of the occurrence and development of autoimmune diseases. In this review, we mainly discuss the functions of macrophages in autoimmune diseases, especially in systemic lupus erythematosus (SLE), rheumatic arthritis (RA), systemic sclerosis (SSc) and type 1 diabetes (T1D), providing references for the treatment and prevention of autoimmune diseases.

Microglial angiotensin type 2 receptors mediate sex-specific expression of inflammatory cytokines independently of circulating estrogen

There are sex differences in microglia, which can maintain sex-related gene expression and functional differences in the absence of circulating sex steroids. The angiotensin type 2 (AT2) receptors mediate anti-inflammatory actions in different tissues, including brain. In mice, we performed RT-PCR analysis of microglia isolated from adult brains and RNA scope in situ hybridization from males, females, ovariectomized females, orchiectomized males and brain masculinized females. We also compared wild type and AT2 knockout mice. The expression of AT2 receptors in microglial cells showed sex differences with much higher AT2 mRNA expression in females than in males, and this was not dependent on circulating gonadal hormones, as observed using ovariectomized females, brain masculinized females and orchiectomized males. These results suggest genomic reasons, possibly related to sex chromosome complement, for sex differences in AT2 expression in microglia, as the AT2 receptor gene is located in the X chromosome. Furthermore, sex differences in expression of AT2 receptors were associated to sex differences in microglial expression of key anti-inflammatory cytokines such as interleukin-10 and pro-inflammatory cytokines such as interleukin-1β and interleukin-6. In conclusion, sex differences in microglial AT2 receptor expression appear as a major factor contributing to sex differences in the neuroinflammatory responses beyond the effects of circulating steroids.

Angiotensin II type 2 receptor prevents extracellular matrix accumulation in human peritoneal mesothelial cell by ameliorating lipid disorder via LOX-1 suppression

Evidence suggests that intracellular angiotensin II type 1 receptor (AT1) contributes to peritoneal fibrosis (PF) under high glucose (HG)-based dialysates. It is generally believed that AT2 antagonisticly affects AT1 function. The aim of this study was to explore whether AT2 activation is beneficial for attenuating human peritoneal mesothelial cell (HPMC) injury due to HG. We treated a HPMC line with HG to induce extracellular matrix (ECM) formation. AT2 was increased and blocked using CGP42112A and AT2 siRNA. Lipid deposition was detected, signaling molecules associated with lectin-like oxidized lipoprotein receptor-1 (LOX-1) and ECM proteins were evaluated by real-time PCR and western blot. The results showed that HG led to AT2 inhibition in HPMCs, inhibition of AT2 further aggravated the expression of ECM proteins, including α-smooth muscle actin, fibroblast specific protein-1 and collagen I, while AT2 decreased the expression of ECM proteins, even during HG stimulation. Interestingly, there was a parallel change in lipid accumulation and ECM formation when AT2 was increased or depressed. Moreover, AT2-mediated decreased ECM production was associated with reduced lipid accumulation in HPMCs and depended on the downregulation of LOX-1. Further analysis showed that HG increased oxidized low-density lipoprotein (ox-LDL) deposition in HPMCs concomitant with an enhanced expression of ECM components, whereas blocking LOX-1 reversed ox-LDL deposition even in the presence of HG. This effect was also accompanied by the remission of ECM accumulation. Our results suggested that AT2 prevented ECM formation in HG-stimulated HPMCs by ameliorating lipid via LOX‐1 suppression.

Angiotensin II type 2 receptor pharmacological agonist, C21, reduces the inflammation and pain hypersensitivity in mice with joint inflammatory pain

Primary and secondary hyperalgesia develop in response to chronic joint inflammation due to peripheral and central mechanisms. Synovial macrophage and spinal microglia are involved in pain sensitization in arthritis. The level of angiotensin II type 2 receptor (AT₂R) is related to the severity of arthritis. This study aimed to determine the role of AT₂R in primary and secondary hyperalgesia in joint inflammatory pain in mice. After intra-articular CFA injection, primary hyperalgesia in the ipsilateral knee joint was measured by pressure application meter and gait analysis, secondary hypersensitivity in ipsilateral hind-paw was measured by von-Frey and Hargreaves tests following a combination of global AT₂R-deficient (Agtr2^-/-) mice and AT₂R pharmacological agonist C21. Synovial macrophage and spinal microglia were collected for flow cytometry. Morphological reconstruction of microglia was detected by immunostaining. AT₂R expression was investigated by quantitative polymerase chain reaction and western blot. Neuronal hyperactivity was evaluated by c-Fos and CGRP immunostaining. We found that pain hypersensitivity and synovial inflammation in Agtr2^-/- mice were significantly exacerbated compared with wild-type mice; conversely, systemically administrated C21 attenuated both of the symptoms. Additionally, spinal microglia were activated, and an abundant increase of spinal AT₂R was expressed on activated microglia in response to peripheral joint inflammation. Intrathecally-administrated C21 reversed the secondary hypersensitivity, accompanied by alleviation of spinal microglial activation, spinal neuronal hyperactivity, and calcitonin gene-related peptide content. These findings revealed a beneficial role of AT₂R activating stimulation against pain hypersensitivity in joint inflammatory pain via direct modulation of synovial macrophage and spinal microglial activity.

Arsenic induces ferroptosis and acute lung injury through mtROS-mediated mitochondria-associated endoplasmic reticulum membrane dysfunction

The goal of this study was to analyze whether mitochondria-associated endoplasmic reticulum membrane (MAMs) dysfunction mediated arsenic (As)-evoked pulmonary ferroptosis and acute lung injury (ALI). As exposure led to alveolar structure damage, inflammatory cell infiltration and pulmonary function decline in mice. Ferritin, the marker of iron overload, was increased, GPX4, the index of lipid peroxidation, was decreased in As-exposed lungs and pulmonary epithelial cells (MLE-12). Pretreatment with ferrostatin-1 (Fer-1), the inhibitor of ferroptosis, alleviated As-evoked ALI. In addition, As-induced non-heme iron deposition was inhibited in Fer-1 pretreated-mice. Moreover, As-triggered mitochondria damage and ferroptosis were mitigated in Fer-1 pretreated-MLE-12 cells. Mechanistically, PERK phosphorylation and mitofusin-2 (Mfn-2) reduction was observed in As-exposed MLE-12 cells and mice lungs. Additionally, the interaction between PERK and Mfn-2 was downregulated and MAMs dysfunction was observed in As-exposed MLE-12 cells. Intriguingly, PERK inhibitor and Mfn-2-overexpression all mitigated As-induced ferroptosis in MLE-12 cells. Additionally, CLPP and mtHSP70, the markers of mitochondrial stress, were upregulated, mitochondrial ROS (mtROS) was elevated, mitochondrial membrane potential (MMP) and ATP were decreased in As-exposed MLE-12 cells. Mitoquinone mesylate (MitoQ), a novel mitochondrial-targeted antioxidant, alleviated As-induced excess mtROS, mitochondrial stress, MAMs dysfunction in pulmonary epithelial cells. Similarly, in vivo experiments indicated that MitoQ pretreatment countered As-induced pulmonary ferroptosis and ALI. These data indicated that mtROS-initiated MAMs dysfunction is, at least partially, implicated in As-evoked ferroptosis and ALI.

Novel Compound Q-1 Alleviates Type II Collagen-Induced Arthritis in Rats through the NF-κB Pathway

Background

Q-1 is a novel compound extracted from the Miao medicine Tiekuaizi. Although Q-1 is known to be a coumarin derivative, its structure has not been deposited in the ACX library. Our previous study showed that Q-1 inhibits the activity of inflammatory cells. This study explores the efficacy of Q-1 in regulating rheumatoid arthritis (RA). The findings show that Q-1 acts through the NF-κB signaling pathway.

Methods

The effects of Q-1 were explored using a bovine type II collagen-induced arthritis (CIA) rat model. The CIA rats were intragastrically administered with high (30 mg·kg⁻¹) or low (15 mg·kg⁻¹) doses of Q-1. The control group was administered with an equal volume of drinking water, while the positive control group was administered with Tripterygium glycoside (9.45 mg·kg⁻¹) for 28 consecutive days. The arthritis indices and ankle joint swelling rates were determined. The levels of IL-1β, IL-6, monocyte chemoattractant protein-1 (MCP-1) in serum and sialic acid (SA) in liver homogenate were determined by enzyme-linked immunosorbent assay (ELISA). The pathological features of the ankle joint were analyzed by hematoxylin and eosin (HE) staining. The IκB, P-IκB, P65, and P-P65 protein levels in synovial tissue were assayed by western blotting.

Results

The arthritis index, ankle joint swelling rate, IL-1β, IL-6, and MCP-1 levels in serum, SA level in liver tissue, and IκB, P-IκB, P65, and P-P65 protein levels in synovial tissues were significantly higher (P < 0.01) in the CIA model compared to the control group. RA was successfully replicated by the CIA model, as shown by the joint swelling results and histopathological sections of the ankle. Notably, all the above indicators decreased significantly (P < 0.01) after treatment with Q-1 compared to the model. In addition, animals treated with Q-1 showed lower inflammation in the ankle joints than the model rats.

Conclusion

The findings indicate that Q-1 effectively inhibited RA in rats by downregulating IκB, P-IκB, P65, and P-P65, inhibiting the excessive release of inflammatory factors, and inhibiting the overactivation of the NF-κB signaling pathway.

Preoperative angiotensin II type 2 receptor is a predictor for developing chronic post-surgical pain after total knee arthroplasty surgery

OBJECTIVE

This study aimed to explore whether preoperative angiotensin II type 2 receptor (AT₂R) level in knee osteoarthritis (OA) patients was an independent risk factor for chronic post-surgical pain (CPSP) after total knee arthroplasty (TKA).

METHODS

A total of 220 patients who had undergone unilateral TKA were enrolled from October 2019 to January 2020. Quantitative sensory testing (QST), PainDETECT questionnaires (PD-Q), the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), the hospital anxiety and depression (HAD) and serum AT₂R were collected preoperatively. The primary outcome was the incidence of CPSP, which was defined as the visual analogue scale (VAS) score ≥ 4 in the ipsilateral knee joint six months after operation.

RESULTS

The prevalence of CPSP was 13.6% (n = 30). Multiple logistic regression analysis showed that patients with higher AT₂R level (OR: 1.007, 95% CI: 1.003-1.011) and PD-Q score (OR: 1.146, 95% CI: 1.008-1.298) before surgery had an increased risk of CPSP after surgery, and a combination of preoperative AT₂R and PD-Q (Akaike information criterion: 147.2; area under receiver operating characteristic (ROC) curve: 0.890) was able to correctly classify 90.16% of patients into CPSP positive or negative groups.

CONCLUSION

Our findings suggest that patients with higher preoperative AT₂R level are at increased risk of developing CPSP following TKA. AT₂R may serve as a candidate predictor for phenotyping CPSP in OA patients.

Update on Angiotensin II Subtype 2 Receptor: Focus on Peptide and Nonpeptide Agonists

Angiotensin II (Ang II) is the most dominant effector component of the renin-angiotensin system (RAS) that generally acts through binding to two main classes of G protein-coupled receptors, namely Ang II subtype 1 receptor (AT1R) and angiotensin II subtype 2 receptor (AT2R). Despite some controversial reports, the activation of AT2R generally antagonizes the effects of Ang II binding on AT1R. Studying AT2R signaling, function, and its specific ligands in cell culture or animal studies has confirmed its beneficial effects throughout the body. These characteristics classify AT2R as part of the protective arm of the RAS that, along with functions of Ang (1-7) through Mas receptor signaling, modulates the harmful effects of Ang II on AT1R in the activated classic arm of the RAS. Although Ang II is the primary ligand for AT2R, we have summarized other natural or synthetic peptide and nonpeptide agonists with critical evaluation of their structure, mechanism of action, and biologic activity. SIGNIFICANCE STATEMENT: AT2R is one of the main components of the RAS and has a significant prospective for mediating the beneficial action of the RAS through its protective arm on the body's homeostasis. Targeting AT2R offers substantial clinical application possibilities for modulating various pathological conditions. This review provided concise information regarding the AT2R peptide and nonpeptide agonists and their potential clinical applications for various diseases.