Apoptosis inhibitor of macrophage as a biomarker for disease activity in Japanese children with IgA nephropathy and Henoch-Schönlein purpura nephritis

Potential role of liver-resident CD3+ macrophages in HBV clearance in a mouse hepatitis B model

Background & Aims

Chronic HBV infection usually causes cirrhosis and hepatocellular carcinoma. Comparative investigations of acute and chronic HBV cases would help determine the immune responses crucial for viral clearance.

Methods

A fast-cleared HBV mouse model was established in Alb-Cre mice via hydrodynamic injection of HBV plasmid, while persistent HBV model mice were generated via recombinant covalently closed circular DNA-adeno-associated virus 8 infection. The single-cell transcriptomes of CD45+ intrahepatic non-parenchymal cells from these mice were conducted. Multiplexed immunohistochemistry and flow cytometry were used to confirm the findings from single-cell transcriptomes. Transwell, coculture, and adoptive transfer experiments were performed to study the generation and functions of macrophages.

Results

Twenty-four clusters of immune cells were identified. Myeloid cells, including granulocytes, monocytes, and dendritic cells, are activated early in HBV fast-cleared mice. Significantly, a cluster of CD3+ macrophages was found in the viral clearance phase, which was confirmed in liver tissue from five acute patients with HBV. These cells highly expressed CXCL1, tumor necrosis factor alpha, and HBsAg-specific T cell receptors. The transwell assay revealed that CD3+ macrophages originate from macrophages (n = 6). T cells and anti-HBsAg antibodies are indispensable for their differentiation, which was further confirmed in T- and/or B-cell-deficient mice. Interestingly, these CD3+ macrophages capable of killing peptide-loaded hepatocytes and engulfing IgG-coated beads were persistently detectable in the mouse liver for 10 weeks after HBV clearance. The expression levels of CD5L and Bcl2, two classical antiapoptotic proteins, increased (p <0.001), suggesting that the CD3+ macrophages are long-term resident populations. Finally, adoptive transfer of CD3+ macrophages accelerated HBV clearance in mice (n = 5, p <0.01).

Conclusions

We identified long-term polyfunctional CD3+ macrophages residing in HBV fast-cleared livers that could help elucidate the immune responses involved in eliminating HBV.

Impact and implications

The liver is a special organ with unique immune characteristics and tolerance to foodborne antigens. Chronic infections can develop in newborns after exposure to HBV; however, acute infections usually occur in adults, indicating that immune cells in the liver tissue microenvironment can also effectively fight against the virus. Nevertheless, the mechanisms involved in acute HBV infection have rarely been studied. In this study, we identified a macrophage population with both T cell and macrophage characteristics in the livers of acute HBV model mice and revealed that these macrophages play important roles in HBV clearance. Moreover, we confirmed that this population is derived from macrophages in the presence of virus-specific T cells and antibodies. This finding highlights the complexity of antiviral immune responses in liver microenvironments.

The association between fractalkine/CX3CR1 axis with IgA vasculitis and nephritis

BACKGROUND

The study investigated whether the fractalkine/CX3CR1 axis is associated with the presence and severity of IgA vasculitis (IgAV) and IgA vasculitis nephritis (IgAVN) in children.

METHODS

We included 59 children with IgAV, 42 children with IgAVN (including 18 children with kidney biopsy), 26 plasma controls and 8 kidney controls. Clinical pathological data were collected, and the fractalkine/CX3CR1 axis and macrophage expression in the circulation and kidneys were detected.

RESULTS

Circulating fractalkine/CX3CR1 axis expression was significantly upregulated in children with IgAV and IgAVN compared to healthy controls. Plasma fractalkine levels and the proportion of CX3CR1+ monocytes were significantly higher in children with IgAVN than in those with IgAV, and the kidney expression of fractalkine/CX3CR1 axis and CD68 were significantly increased in the IgAVN group relative to normal controls, especially in children with IgAVN with more severe ISKDC pathological grading. Additionally, kidney levels of fractalkine, CX3CR1, and CD68 exhibited significant positive correlations with tubulointerstitial grading and serum creatinine levels.

CONCLUSION

The expression of fractalkine/CX3CR1 axis is associated with the presence and severity of IgAV and IgAVN. Our findings support further investigation of fractalkine/CX3CR1 as a target for future therapies in IgAV and IgAN.

IMPACT

The expression of plasma fractalkine/CX3CR1 axis is associated with the presence and severity of IgAV and IgAVN. The expression of kidney fractalkine/CX3CR1 axis and macrophage are upregulated in IgAVN, which is closely associated with poorer kidney function and more severe kidney pathology. Our findings support further investigation of fractalkine/CX3CR1 as a target for future therapies in IgAV and IgAVN.

Administration of an antibody against apoptosis inhibitor of macrophage prevents aortic aneurysm progression in mice

Apoptosis inhibitor of macrophage (AIM) is known to induce apoptosis resistance in macrophages and to exacerbate chronic inflammation, leading to arteriosclerosis. The role of AIM in aortic aneurysm (AA) remains unknown. This study examined the effects of an anti-AIM antibody in preventing AA formation and progression. In apolipoprotein E-deficient mice, AA was induced by subcutaneous angiotensin II infusion. Mice were randomly divided into two groups: (i) AIM group; weekly anti-murine AIM monoclonal antibody injection (n = 10), and (ii) IgG group; anti-murine IgG antibody injection as control (n = 14). The AIM group, compared with the IgG group, exhibited reduced AA enlargement (aortic diameter at 4 weeks: 2.1 vs. 2.7 mm, respectively, p = 0.012); decreased loss of elastic lamellae construction; reduced expression levels of IL-6, TNF-α, and MCP-1; decreased numbers of AIM-positive cells and inflammatory M1 macrophages (AIM: 1.4 vs. 8.0%, respectively, p = 0.004; M1 macrophages: 24.5 vs. 55.7%, respectively, p = 0.017); and higher expression of caspase-3 in the aortic wall (22.8 vs. 10.5%, respectively, p = 0.019). Our results suggest that administration of an anti-AIM antibody mitigated AA progression by alleviating inflammation and promoting M1 macrophage apoptosis.

The role of mononuclear phagocyte system in IgA nephropathy: pathogenesis and prognosis

Although the "multiple hits" theory is a widely accepted pathogenesis in IgA nephropathy (IgAN), increasing evidence suggests that the mononuclear/macrophage system plays important roles in the progression of IgAN; however, the exact mechanism is unclear. In the present study, we explored 1,067 patients in 15 studies and found that the number of macrophages per glomerulus was positively related with the degree of hematuria, and the macrophages in the glomeruli were mainly related to mesangial proliferation (M) in renal biopsy. In the tubulointerstitium, macrophages were significantly paralleled to tubulointerstitial α-SMA and NF-kB expression, tubulointerstitial lesion, tubule atrophy/interstitial fibrosis (T), and segmental glomerulosclerosis (S). In the glomeruli and tubulointerstitium, M1 accounted for 85.41% in the M classification according to the Oxford MEST-C, while in the blood, M1 accounted for 100%, and the patients with low CD89⁺ monocyte mean fluorescence intensity displayed more severe pathological characteristics (S1 and T1-2) and clinical symptoms. M1 (CD80⁺) macrophages were associated with proinflammation in the acute phase; however, M2 (CD163⁺) macrophages participated in tissue repair and remodeling, which correlated with chronic inflammation. In the glomeruli, M2 macrophages activated glomerular matrix expansion by secreting cytokines such as IL-10 and tumor necrosis factor-β (TGF-β), and M0 (CD68⁺) macrophages stimulated glomerular hypercellularity. In the tubulointerstitium, M2 macrophages played pivotal roles in renal fibrosis and sclerosis. It is assumed that macrophages acted as antigen-presenting cells to activate T cells and released diverse cytokines to stimulate an inflammatory response. Macrophages infiltrating glomeruli destroy the integrity of podocytes through the mesangio-podocytic-tubular crosstalk as well as the injury of the tubule.

The comprehensive role of apoptosis inhibitor of macrophage (AIM) in pathological conditions

CD5L/AIM (apoptosis inhibitor of macrophage), as an important component in maintaining tissue homeostasis and inflammation, is mainly produced and secreted by macrophages but partially dissociated and released from blood AIM-IgM. AIM plays a regulatory role in intracellular physiological mechanisms, including lipid metabolism and apoptosis. AIM not only increases in autoimmune diseases, directly targets liver cells in liver cancer and promotes cell clearance in acute kidney injury, but also causes arteriosclerosis and cardiovascular events, and aggravates inflammatory reactions in lung diseases and sepsis. Obviously, AIM plays a pleiotropic role in the body. However, to date, studies have failed to decipher the mechanisms behind its different roles (beneficial or harmful) in inflammatory regulation. The inflammatory response is a "double-edged sword," and maintaining balance is critical for effective host defense while minimizing the adverse side effects of acute inflammation. Enhancing the understanding of AIM function could provide the theoretical basis for new therapies in these pathological settings. In this review, we discuss recent studies on the roles of AIM in lipid metabolism, autoimmune diseases and organic tissues, such as liver cancer, myocardial infarction, and kidney disease.

Glomerular expression and urinary excretion of fatty acid-binding protein 4 in IgA nephropathy

BACKGROUND

Fatty acid-binding protein 4 (FABP4) is secreted from adipocytes and macrophages in adipose tissue and acts as an adipokine. It has recently been reported that FABP4, but not liver-type FABP (L-FABP/FABP1), is also expressed in injured glomerular endothelial cells and infiltrating macrophages in the glomerulus and that urinary FABP4 (U-FABP4) is associated with proteinuria and kidney function impairment in nephrotic patients. However, the link between glomerular FABP4 and U-FABP4 has not been fully addressed in IgA nephropathy (IgAN).

METHODS

We investigated the involvement of FABP4 in human and mouse IgAN.

RESULTS

In patients with IgAN (n = 23), the ratio of FABP4-positive area to total area within glomeruli (G-FABP4-Area) and U-FABP4 were positively correlated with proteinuria and were negatively correlated with eGFR. In 4-28-week-old male grouped ddY mice, a spontaneous IgAN-prone mouse model, FABP4 was detected in glomerular endothelial cells and macrophages, and G-FABP4-Area was positively correlated with urinary albumin-to-creatinine ratio (r = 0.957, P < 0.001). Endoplasmic reticulum stress markers were detected in glomeruli of human and mouse IgAN. In human renal glomerular endothelial cells, FABP4 was induced by treatment with vascular endothelial growth factor and was secreted from the cells. Treatment of human renal glomerular endothelial cells or mouse podocytes with palmitate-bound recombinant FABP4 significantly increased gene expression of inflammatory cytokines and endoplasmic reticulum stress markers, and the effects of FABP4 in podocytes were attenuated in the presence of an anti-FABP4 antibody.

CONCLUSION

FABP4 in the glomerulus contributes to proteinuria in IgAN, and U-FABP4 level is a useful surrogate biomarker for glomerular damage in IgAN.

Integrated analysis of immune- and apoptosis-related lncRNA-miRNA-mRNA regulatory network in children with Henoch Schönlein purpura nephritis

BACKGROUND

Long noncoding RNAs (lncRNAs) play important roles in the regulation of immunological and apoptotic function. This study aimed to explore the critical immune- and apoptosis-related lncRNAs in the occurrence and development of Henoch-Schönlein purpura nephritis (HSPN) in children.

METHODS

Differential analysis was employed to identify the differentially expressed lncRNAs, as well as the immune- and apoptosis-related mRNAs in children with HSPN. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to validate the immunological and apoptotic roles of the differentially expressed immune- and apoptosis-related lncRNAs and mRNAs. Spearman's correlation analysis was performed to analyze the differentially expressed lncRNAs and immune- and apoptosis-related messenger RNAs (mRNAs). Based on the competing endogenous RNA (ceRNA) mechanism, the immune- and apoptosis-related lncRNA-microRNA (miRNA)-mRNA regulatory network was then constructed in children with HSPN. The expression levels of the lncRNAs in the lncRNA-miRNA-mRNA regulatory network were further confirmed by quantitative real-time polymerase chain in the peripheral blood samples of children with HSPN.

RESULTS

By intersecting the differentially expressed immune-related and apoptosis-related genes through GO and KEGG analyses, a total of 43 genes were identified in children with HSPN, and 100 lncRNAs highly correlated with the above genes were identified by correlation analysis. The immune- and apoptosis-related lncRNA-miRNA-mRNA regulatory network was then established based on ceRNA mechanism. Dysregulation of a total of 11 lncRNAs were discovered, including upregulated SNHG3, LINC00152, TUG1, GAS5, FGD5-AS1, DLEU2, and SCARNA9; and downregulated SNHG1, NEAT1, DISC1-IT1, and PVT1. The validation conducted in the clinical samples also suggested that the above lncRNAs in the specific regulatory network may act as potential biomarkers with prognosis in children with HSPN.

CONCLUSIONS

LncRNAs may play essential regulatory roles in the occurrence and development of HSPN in children, and the immune- and apoptosis-related lncRNA-miRNA-mRNA regulatory network might be the underlying molecular mechanism that dissects the disease pathogenesis. In addition, the dysregulated lncRNAs in the regulatory network may be novel biomarkers for the diagnosis and therapy of HSPN in children.

IgA glycosylation and immune complex formation in IgAN

IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide. This disease, discovered in 1968, is characterized by IgA-IgG glomerular immunodeposits with a mesangial pattern. It is thought that these immunodeposits originate from the immune complexes formed in the circulation. It is hypothesized that the pathogenesis of IgAN is driven by aberrant glycoforms of IgA1 (galactose-deficient IgA1, Gd-IgA1). Gd-IgA1, in genetically susceptible individuals, represents the initiating factor for the formation of circulating immune complexes due to its recognition by IgG autoantibodies and the subsequent formation of pathogenic IgA1-IgG immune complexes. Complement activation through alternative and/or lectin pathways is likely playing an important role in the pathogenic properties of these complexes and may further upregulate local inflammatory responses and glomerular injury.

Decreased glycolysis induced dysfunction of NK cells in Henoch-Schonlein purpura patients

BACKGROUND

Henoch-Schonlein purpura (HSP) is the most common systemic vasculitis of the childhood. However, its mechanisms and pathogenesis still need more exploration. Natural killer (NK) cells are innate lymphocytes, and there is a growing appreciation that cellular metabolism is important in determining the immune responsiveness of lymphocytes. Thus, we aimed to analyze the NK cells phenotype and explore the association between glucose metabolism and NK cells function in HSP patients.

RESULTS

A total number of 64 HSP patients and 34 healthy children were included. The HSP patients were divided into two groups according to whether accompanied with nephritis or not. NK cells in HSP patients without nephritis showed a reduced frequency in peripheral blood, a down-regulated expression of activating receptors both NKp30 and NKp46, and an attenuated cytotoxic function against tumor cells. In addition, the function impairment of NK cells was shown to exacerbate in HSPN. Our data further revealed an aberrant metabolic reprogramming of NK cells in HSP patients. Upon stimulation with cytokines (IL-15, IL-12 and IL-2), NK cells from healthy controls switched to an elevated glycolysis rate to support their effector function. By contrast, the glycolysis rate of activated NK cells in HSP group was not significantly up-regulated from the resting level possibly owing to the inhibition of mTORC1.

CONCLUSIONS

Our study found that HSP patients were accompanied with dysfunction of NK cells. We concluded that the dysfunction of NK cells in HSP patients was induced with a decreased glycolysis rate and suggested that metabolic reprogramming of NK cells might be a player in the pathogenesis of HSP.

Perspectives on how mucosal immune responses, infections and gut microbiome shape IgA nephropathy and future therapies

Infections have been considered to play a critical role in the pathogenesis of IgA nephropathy (IgAN) because synpharyngitic hematuria is a common feature in IgAN. However, how infections participate in this process is still debated. More recent studies have also revealed that the alteration of the gut microbiome exerts a profound effect on host immune responses, contributing to the etiology or progression of autoimmunity. Considering IgA as the first line of defense against bacterial and viral antigens, this review evaluates the relationships among intestinal infections, gut microbiome, and IgA for a better understanding of the pathogenesis of IgAN. Moreover, as a prototype of IgA immunity, we provide detailed clarification of IgAN pathogenesis to shed light on other diseases in which IgA plays a role. Finally, we discuss potential therapies focusing on microbes and mucosal immune responses in IgAN.