Impacts of the apoptosis inhibitor of macrophage (AIM) on obesity-associated inflammatory diseases

Cryo-EM reveals structural basis for human AIM/CD5L recognition of polymeric immunoglobulin M

Cell surface scavenger receptors contribute to homoeostasis and the response to pathogens and products associated with damage by binding to common molecular features on a wide range of targets. Apoptosis inhibitor of macrophage (AIM/CD5L) is a soluble protein belonging to the scavenger receptor cysteine-rich (SRCR) superfamily that contributes to prevention of a wide range of diseases associated with infection, inflammation, and cancer. AIM forms complexes with IgM pentamers which helps maintain high-levels of circulating AIM in serum for subsequent activation on release from the complex. The structural basis for AIM recognition of IgM as well as other binding targets is unknown. Here we apply cryogenic electron microscopy imaging (cryo-EM) to show how interfaces on both of AIM's C-terminal SRCR domains interact with the Fcμ constant region and J chain components of the IgM core. Both SRCR interfaces are also shown to contribute interactions important for AIM binding to damage-associated molecular patterns (DAMPs).

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 effects of apoptosis inhibitor of macrophage in kidney diseases

Kidney disease is a progressive and irreversible condition in which immunity is a contributing factor that endangers human health. It is widely acknowledged that macrophages play a significant role in developing and causing numerous kidney diseases. The increasing focus on the mechanism by which macrophages express apoptosis inhibitor of macrophages (AIM) in renal diseases has been observed. AIM is an apoptosis inhibitor that stops different things that cause apoptosis from working. This keeps AIM-bound cell types alive. Notably, the maintenance of immune cell viability regulates immunity. As our investigation progressed, we concluded that AIM has two sides when it comes to renal diseases. AIM can modulate renal phagocytosis, expedite the elimination of renal tubular cell fragments, and mitigate tissue injury. AIM can additionally exacerbate the development of renal fibrosis and kidney disease by prolonging inflammation. IgA nephropathy (IgAN) may also worsen faster if more protein is in the urine. This is because IgA and immunoglobulin M are found together and expressed. In the review, we provide a comprehensive overview of prior research and concentrate on the impacts of AIM on diverse subcategories of nephropathies. We discovered that AIM is closely associated with renal diseases by playing a positive or negative role in the onset, progression, or cure of kidney disease. AIM is thus a potentially effective therapeutic target for kidney diseases.

Absolute Quantification of Pan-Cancer Plasma Proteomes Reveals Unique Signature in Multiple Myeloma

Mass spectrometry based on data-independent acquisition (DIA) has developed into a powerful quantitative tool with a variety of implications, including precision medicine. Combined with stable isotope recombinant protein standards, this strategy provides confident protein identification and precise quantification on an absolute scale. Here, we describe a comprehensive targeted proteomics approach to profile a pan-cancer cohort consisting of 1800 blood plasma samples representing 15 different cancer types. We successfully performed an absolute quantification of 253 proteins in multiplex. The assay had low intra-assay variability with a coefficient of variation below 20% (CV = 17.2%) for a total of 1013 peptides quantified across almost two thousand injections. This study identified a potential biomarker panel of seven protein targets for the diagnosis of multiple myeloma patients using differential expression analysis and machine learning. The combination of markers, including the complement C1 complex, JCHAIN, and CD5L, resulted in a prediction model with an AUC of 0.96 for the identification of multiple myeloma patients across various cancer patients. All these proteins are known to interact with immunoglobulins.

Relationship between polyautoimmunity and sarcopenic obesity in rheumatoid arthritis patients

OBJECTIVE

Sarcopenia is a major cause of morbidity in rheumatoid arthritis patients. Our purpose was to determine whether polyautoimmunity is associated with sarcopenia and alterations in whole body composition in patients with rheumatoid arthritis (RA).

METHODS

We performed a cross-sectional observational study of a series of cases of RA. All patients were recruited consecutively from a rheumatology clinic. Body composition by dual-energy x-ray absorptiometry (DEXA) was assessed. The variables of interest were polyautoimmunity (RA associated with other autoimmune diseases), sarcopenia, fat mass, and body mass index (BMI). Other variables included were clinical-analytical and inflammatory cytokines and adipokines. The relationship between sarcopenic obesity and the presence of polyautoimmunity was studied using multivariate analysis.

RESULTS

Of the 94 patients with RA included in the study, 15 (16%) had polyautoimmunity. A total of 23 patients with RA (24.5%) had sarcopenia, which was more prevalent in patients with polyautoimmunity than in patients without polyautoimmunity (46.7% vs 20.3%; p = .029). Sarcopenia was not associated with body fat content (p = .870) or with BMI (p = .998). The multivariate analysis showed the factors associated with polyautoimmunity in RA to be sarcopenia (odds ratio [95% CI], 4.80 [1.49-13.95]), BMI (1.18 [1.04-1.35]), and resistin (1.249 [1.01-1.53]).

CONCLUSION

Sarcopenia and obesity were more prevalent in patients with RA and polyautoimmunity. Resistin values were also higher in this group than in patients with RA without polyautoimmunity.

The Roles of Adipose Tissue Macrophages in Human Disease

Macrophages are a population of immune cells functioning in antigen presentation and inflammatory response. Research has demonstrated that macrophages belong to a cell lineage with strong plasticity and heterogeneity and can be polarized into different phenotypes under different microenvironments or stimuli. Many macrophages can be recruited by various cytokines secreted by adipose tissue. The recruited macrophages further secrete various inflammatory factors to act on adipocytes, and the interaction between the two leads to chronic inflammation. Previous studies have indicated that adipose tissue macrophages (ATMs) are closely related to metabolic diseases like obesity and diabetes. Here, we will not only conclude the current progress of factors affecting the polarization of adipose tissue macrophages but also elucidate the relationship between ATMs and human diseases. Furthermore, we will highlight its potential in preventing and treating metabolic diseases as immunotherapy targets.

Frequency of Polyautoimmunity in Patients With Rheumatoid Arthritis and Systemic Lupus Erythematosus

OBJECTIVE

To describe the frequency of polyautoimmunity and multiple autoimmune syndrome in patients with rheumatoid arthritis (RA) and patients with systemic lupus erythematosus (SLE).

PATIENTS AND METHODS

This was a cross-sectional observational study of patients with RA, SLE, and controls without autoimmune rheumatic disease. Cases were those with RA according to the 2010 American College of Rheumatology/European League Against Rheumatism criteria and SLE according to the 2019 American College of Rheumatology/European League Against Rheumatism criteria, consecutively recruited in a rheumatology clinic. Controls were subjects with no rheumatic autoimmune disease (AIDs) recruited in the same area. Patients filled out a questionnaire on polyautoimmunity. Variables of interest were polyautoimmunity (RA or SLE with other AIDs), whereas secondary variables were rheumatic, skin, endocrine, digestive, and neurological AIDs. Multiple autoimmune syndrome is defined as the presence of 3 or more AIDs and a family history of AIDs. Statistical analyses performed were descriptive, bivariate, and multivariate (dependent variable: polyautoimmunity).

RESULTS

The study population comprised 109 patients with RA, 105 patients with SLE, and 88 controls. Polyautoimmunity was recorded in 15 patients with RA (13.8%), 43 with SLE (41%), and 2 controls (2.2%). The most frequent AID in RA was Sjögren syndrome (53.3%), followed by Hashimoto thyroiditis and psoriasis; the most frequent AIDs in SLE were Sjögren syndrome (55.8%) and antiphospholipid syndrome (30.2%), followed by Hashimoto thyroiditis. Obesity was associated with polyautoimmunity in RA (odds ratio [OR], 3.362; p = 0.034). In SLE, joint damage (OR, 2.282; p = 0.038) and anti-RNP antibodies (OR, 5.095; p = 0.028) were risk factors for polyautoimmunity, and hydroxychloroquine was a protective factor (OR, 0.190; p = 0.004).

CONCLUSIONS

Polyautoimmunity is frequent in RA and even more frequent in SLE. It was associated with obesity in RA and with joint damage and anti-RNP in SLE. Hydroxychloroquine was a protector.

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

BACKGROUND

To evaluate the apoptosis inhibitor of macrophage (AIM) deposition patterns on the kidneys of children with IgA nephropathy (IgAN) and Henoch-Schönlein purpura nephritis (HSPN) and to investigate the clinical usefulness of serum and/or urinary AIM levels as biomarkers for the disease activity.

METHODS

Immunohistochemical study was performed in the kidneys of 37 patients with IgAN and 10 patients with HSPN. Serum and urinary AIM levels in the patients and 20 healthy controls (HCs) were quantified by enzyme-linked immunosorbent assay. The results were compared with clinical features.

RESULTS

In patients with IgAN and HSPN, AIM expression was observed in various areas, including the glomerular mesangial and capillary areas, the proximal and distal tubular epithelial cells, and on infiltrating macrophages in the glomeruli and interstitial areas. Serum and urinary AIM levels were significantly elevated in these patients compared with the HCs. Urinary AIM levels were positively correlated with the histological severity and degree of proteinuria and hematuria as well as urinary β2 microglobulin and urinary N-acetyl-β-D-glucosaminidase levels.

CONCLUSIONS

AIM plays an important role in the pathogenesis of IgAN and HSPN. Urinary AIM levels can potentially reflect active renal inflammation in these diseases and may represent a useful biomarker for disease activity.

IMPACT

Urinary AIM levels may represent a useful biomarker for disease activity of IgAN and HSPN. AIM expression was observed in the glomeruli, tubular epithelial cells, and infiltrating macrophages in glomeruli and interstitial area. U-AIM/Cr were significantly correlated not only with proteinuria, hematuria, and u-β2MG and u-NAG levels but also with the activity index of histological findings in kidney biopsy specimens. Our results can emphasize the important role of AIM in the pathogenesis of IgAN and HSPN.

Does Proteomic Mirror Reflect Clinical Characteristics of Obesity?

Obesity is a frightening chronic disease, which has tripled since 1975. It is not expected to slow down staying one of the leading cases of preventable death and resulting in an increased clinical and economic burden. Poor lifestyle choices and excessive intake of “cheap calories” are major contributors to obesity, triggering type 2 diabetes, cardiovascular diseases, and other comorbidities. Understanding the molecular mechanisms responsible for development of obesity is essential as it might result in the introducing of anti-obesity targets and early-stage obesity biomarkers, allowing the distinction between metabolic syndromes. The complex nature of this disease, coupled with the phenomenon of metabolically healthy obesity, inspired us to perform data-centric, hypothesis-generating pilot research, aimed to find correlations between parameters of classic clinical blood tests and proteomic profiles of 104 lean and obese subjects. As the result, we assembled patterns of proteins, which presence or absence allows predicting the weight of the patient fairly well. We believe that such proteomic patterns with high prediction power should facilitate the translation of potential candidates into biomarkers of clinical use for early-stage stratification of obesity therapy.

Association between apoptosis inhibitor of macrophage and microsatellite instability status in colorectal cancer

BACKGROUND

The microsatellite instability (MSI) in colorectal cancer (CRC) has a more favorable clinical outcome and is characterized by highly upregulated expression of various immunological checkpoints than microsatellite stable (MSS) tumors. Apoptosis inhibitor of macrophage (AIM) is a circulating protein and circulates throughout the body to remove cellular debris. The aim of this study was to evaluate the association between MSI status and AIM levels in CRC patients.

METHODS

In this study, we evaluated the levels of AIM by Enzyme Linked Immuno-Sorbent Assay (ELISA) in serum of 430 CRC patients. All patients' clinical and laboratory characteristics at initial diagnosis were collected. The relationship between AIM levels and MSI status was examined.

RESULTS

64 patients (14.9%) were identified as having MSI-H (high-frequency MSI) and 366 casess (85.1%) having MSS. Patients with an MSI-H phenotype had lower AIM levels compared with MSS patients. Moreover, AIM levels were correlated with histological type and MSI status. Logistic regression analysis revealed that decreased AIM levels were independently associated with MSI-H phenotype after adjusting confounding factors.

CONCLUSION

Reduced AIM levels are associated with MSI-H subtyping of CRC. Further research on the involvement of AIM in MSI-H CRC is needed.

Surveillance of Hepatocellular Carcinoma in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is becoming the leading cause of hepatocellular carcinoma (HCC), liver-related mortality, and liver transplantation. There is sufficient epidemiological cohort data to recommend the surveillance of patients with NAFLD based upon the incidence of HCC. The American Gastroenterology Association (AGA) expert review published in 2020 recommends that NAFLD patients with cirrhosis or advanced fibrosis estimated by non-invasive tests (NITs) consider HCC surveillance. NITs include the fibrosis-4 (FIB-4) index, the enhanced liver fibrosis (ELF) test, FibroScan, and MR elastography. The recommended surveillance modality is abdominal ultrasound (US), which is cost effective and noninvasive with good sensitivity. However, US is limited in obese patients and those with NAFLD. In NAFLD patients with a high likelihood of having an inadequate US, or if an US is attempted but inadequate, CT or MRI may be utilized. The GALAD score, consisting of age, gender, AFP, the lens culinaris-agglutinin-reactive fraction of AFP (AFP-L3), and the protein induced by the absence of vitamin K or antagonist-II (PIVKA-II), can help identify a high risk of HCC in NAFLD patients. Innovative parameters, including a Mac-2 binding protein glycated isomer, type IV collagen 7S, free apoptosis inhibitor of the macrophage, and a combination of single nucleoside polymorphisms, are expected to be established. Considering the large size of the NAFLD population, optimal screening tests must meet several criteria, including high sensitivity, cost effectiveness, and availability.

Apoptosis Inhibitor of Macrophage, Monocyte Chemotactic Protein-1, and C-Reactive Protein Levels Are Increased in Patients with Metabolic Syndrome: A Pilot Study

Background: Apoptosis inhibitor of macrophage (AIM) and monocyte chemotactic protein-1 (MCP-1) are molecules that cause migration of M1 macrophages to visceral adipocytes, which is the first step in development of metabolic syndrome. The aim of this study is to evaluate the status of AIM and MCP-1 in metabolic syndrome and to investigate their use as biomarkers. Methods: Forty metabolic syndrome patients and 40 healthy individuals were enrolled in the study. Serum AIM, MCP-1, and C-reactive protein (CRP) levels were measured by enzyme-linked immunosorbent assay. Results: AIM, MCP-1, and CRP levels were significantly higher in the metabolic syndrome group (P < 0.01, P < 0.01, and P < 0.05, respectively). There was a positive correlation of serum AIM, MCP-1, and CRP levels with waist circumference (r = 0.480, r = 0.663, and r = 0.418, respectively; P < 0.01). Receiver operating characteristic (ROC) curve analyses revealed AIM, MCP-1, and CRP cutoff points as 2383.7 ng/mL, 172.8 pg/mL, and 0.366 mg/dL, which could be used in the diagnosis of metabolic syndrome with highest sensitivity and specificity. In the logistic regression model, including age, AIM, CRP, and MCP-1 as covariates, having serum AIM and CRP levels above cutoffs were significant independent predictors for metabolic syndrome (odds ratios 13.8 and 21.3), whereas the serum MCP-1 level was not a significant independent predictor, although the odds ratio was 2.6 (P = 0.193). Conclusions: These results suggest that AIM and MCP-1 may play a role in the pathogenesis of metabolic syndrome. AIM and CRP levels may be used as biomarkers in the diagnosis of metabolic syndrome. Although MCP-1 is not an independent predictor, its elevation in metabolic syndrome is noteworthy, which warrants further analyses in larger groups.

AIM-deficient mouse fed a high-trans fat, high-cholesterol diet: a new animal model for nonalcoholic fatty liver disease

Owing to changes in lifestyle, nonalcoholic fatty liver disease (NAFLD) is becoming a common form of chronic liver injury. NAFLD comprises a wide variety of disease stages, from simple steatosis to nonalcoholic steatohepatitis, which is a risk factor for the development of hepatocellular carcinoma (HCC). Because animal models for NAFLD are needed to investigate the precise pathogenesis, we aimed to establish a new mouse model employing mice deficient for apoptosis inhibitor of macrophage (AIM^−/−), which exhibit accelerated lipid storage in the liver and high susceptibility to developing HCC in response to a high-fat diet (HFD). AIM^−/− mice were fed the D09100301 diet, which contains 40 kcal% fat (trans fat 30 kcal%), high cholesterol (2%), and 40 kcal% carbohydrates (20 kcal% fructose), and then features of obesity and NAFLD including steatosis, inflammation, fibrosis, and HCC development were analyzed. Although a comparable grade of liver steatosis was promoted in AIM^−/− mice by the D09100301 diet and the standard HFD (60 kcal% largely lard fat), significantly less lipid storage in visceral fat was observed when the mice were fed the D09100301 diet. Accelerated liver inflammation was promoted by the D09100301 diet compared with the HFD, but interestingly, HCC development was decreased in mice fed the D09100301 diet. Our findings suggest that AIM^−/− mice fed the D09100301 diet exhibited a phenotype that resembled nonobese NAFLD patients and thus could be an appropriate tool to study the pathophysiology by which obesity increases the risk of HCC.

Verification of B-lymphocyte activating factor's involvement in the exacerbation of insulin resistance as well as an autoimmune response in patients with nonalcoholic steatohepatitis and patients with HCV-related chronic liver disease

BACKGROUND

Ten to forty percent of nonalcoholic steatohepatitis (NASH) and HCV-related chronic liver disease (CLD-C) patients have antinuclear antibodies (ANAs). However, the relationship between autoimmune response and insulin resistance remains uncertain among those patients. The primary purpose of this study was to investigate whether or not ANA status was associated with the development of insulin resistance and obesity in NASH and CLD-C patients.

METHODS

Degrees of hepatic fibrosis and steatosis were evaluated by the classification proposed by Brunt et al. Obesity and insulin resistance were estimated by calculating body mass index and the value of homeostasis model of for assessment of insulin resistance (HOMA-IR), respectively. A revised scoring system was applied to the diagnosis of autoimmune hepatitis (AIH). Serum B-lymphocyte activating factor (BAFF) levels were determined, using an ELISA technique.

RESULTS

Ten of 25 (40%) NASH patients and 9 of 22 (41%) CLD-C patients had ANAs, though the titers were weak in most patients. Only one NASH patient met the category of "definite" AIH among the enrolled patients. Serum IgG levels were significantly higher in NASH and CLD-C patients with ANAs than in those without ANAs, and NASH and CLD-C patients with ANAs had significantly higher HOMA-IR values than those without ANAs (6.81 ± 3.36 vs. 4.00 ± 2.57, p = 0.0305, 3.01 ± 1.31 vs. 1.28 ± 0.50, p = 0.0011). CLD-C patients with ANAs had more advanced hepatic fibrosis and steatosis than those without ANAs, while ANA status was not associated with hepatic fibrosis or steatosis in NASH patients. Obesity was independent of ANA status in both subjects. Serum BAFF levels were significantly higher in CLD-C patients with ANAs than those in CLD-C patients without ANAs (1303 ± 268 vs. 714 ± 143 pg/ml, p = 0.0036). A close correlation between serum BAFF level and the HOMA-IR value was observed in CLD-C patients (r = 0.467, p = 0.0485).

CONCLUSION

Our data suggest that NASH and CLD-C patients with ANAs have more severe insulin resistance than those without ANAs. More advanced insulin resistance deriving from excessive BAFF production may result in severe hepatic fibrosis and steatosis in CLD-C patients with ANAs.

The utility of apoptosis inhibitor of macrophages as a possible diagnostic marker in patients with Crohn's disease

Background

Apoptosis inhibitor of macrophages (AIM) was initially identified as an apoptosis inhibitor that supports the survival of macrophages against various apoptosis-inducing stimuli, and AIM produced by macrophages may contribute to the pathogenesis of inflammatory bowel diseases (IBDs). However, there have been no reports on the kinetics of AIM in IBD and the impact of AIM on the pathogenesis of IBD. In this study, we aimed to investigate the diagnostic utility of levels of AIM and their correlation with the activity of Crohn’s disease (CD) and IBD.

Methods

We used an enzyme-linked immunosorbent assay (ELISA) to examine AIM serum levels in 16 healthy subjects and 90 patients with inflammatory bowel diseases, namely 39 with CD and 51 with ulcerative colitis (UC), as well as 17 patients with Behcet’s disease (BD) as intestinal disease controls. We compared serum AIM levels among groups and examined whether there were correlations between serum AIM levels and disease activity and type. We also performed immunohistochemical staining of AIM in intestinal tissues of patients with CD.

Results

Serum AIM levels were significantly higher in patients with CD than in patients with UC, BD, and controls (3.27 ± 2.14, 1.88 ± 1.43, 2.34 ± 1.37, and 2.13 ± 0.64 μg/ml, respectively; P < 0.01). There was no difference in serum AIM levels before and after treatment in patients with CD. However, in these patients the diagnostic rate using AIM was better than that based on anti-Saccharomyces cerevisiae antibodies. AIM was expressed in macrophages that were positive for CD14, CD16, or both in the intestinal tissues of patients with CD.

Conclusions

AIM is a novel biomarker of CD that can distinguish CD from UC or BD. It is suggested that AIM may contribute to intestinal inflammation by inhibiting the apoptosis of macrophages.

Impact of feline AIM on the susceptibility of cats to renal disease

Renal failure is one of the most important social problems for its incurability and high costs for patients’ health care. Through clarification of the underlying mechanism for the high susceptibility of cats to renal disease, we here demonstrates that the effective dissociation of serum AIM protein from IgM is necessary for the recovery from acute kidney injury (AKI). In cats, the AIM-IgM binding affinity is 1000-fold higher than that in mice, which is caused by the unique positively-charged amino-acid cluster present in feline AIM. Hence, feline AIM does not dissociate from IgM during AKI, abolishing its translocation into urine. This results in inefficient clearance of lumen-obstructing necrotic cell debris at proximal tubules, thereby impairing AKI recovery. Accordingly, mice whose AIM is replaced by feline AIM exhibit higher mortality by AKI than in wild-type mice. Recombinant AIM administration into the mice improves their renal function and survival. As insufficient recovery from AKI predisposes patients to chronic, end-stage renal disease, feline AIM may be involved crucially in the high mortality of cats due to renal disease. Our findings could be the basis of the development of novel AKI therapies targeting AIM-IgM dissociation, and may support renal function in cats and prolong their lives.

Effect of Lipopolysaccharide on the Progression of Non-Alcoholic Fatty Liver Disease in High Caloric Diet-Fed Mice

The incidence of non-alcoholic steatohepatitis (NASH) is increasing. Because gut microbiota have been highlighted as one of the key factors in the pathogenesis of metabolic syndrome, we investigated the involvement of the bacterial component in the progression of non-alcoholic fatty liver (NAFL) to NASH. C57BL/6 mice were fed with maintenance food (MF, groups A and B) or a high caloric diet (HCD, groups C and D) for 1 month. Mice were then divided into four groups: Groups A and C were inoculated with PBS, while groups B and D were inoculated with lipopolysaccharide (LPS) plus complete Freund's adjuvant (CFA). The inoculations were performed a total of 3 times over 3 months. At 6 months, while hepatic steatosis was observed in groups C and D, cellular infiltration and fibrosis were less evident in group C than in group D. Inflammatory cytokines were upregulated in groups B and D. 16S rRNA pyrosequencing of whole colon homogenates containing faeces showed that certain bacterial groups, such as Bacteroidaceae, Peptostreptococcaceae and Erysipelotrichaceae, were increased in groups C and D. Although loading of bacterial components (LPS) resulted in hepatic inflammation in both MF- and HCD-fed mice, HCD feeding was more crucial in the progression of NAFL during the triggering phase.

MafB deficiency accelerates the development of obesity in mice

MafB, a transcription factor expressed selectively in macrophages, has important roles in some macrophage-related diseases, especially in atherosclerosis. In this study, we investigated the mechanism by which hematopoietic-specific MafB deficiency induces the development of obesity. Wild-type and hematopoietic cell-specific Mafb-deficient mice were fed a high-fat diet for 10 weeks. The Mafb-deficient mice exhibited higher body weights and faster rates of body weight increase than control mice. The Mafb-deficient mice also had a higher percentage of body fat than the wild-type mice, due to increased adipocyte size and serum cholesterol levels. Reverse transcription-PCR analysis showed a reduction in apoptosis inhibitor of macrophage (AIM) in Mafb-deficient adipose tissue. AIM is known as an inhibitor of lipogenesis in adipocytes and is expressed in adipose tissue macrophages. Collectively, our data suggest that Mafb deficiency in hematopoietic cells accelerates the development of obesity.

Association of apoptosis inhibitor of macrophage (AIM) expression with urinary protein and kidney dysfunction

BACKGROUND

Apoptosis inhibitor of macrophage (AIM) expressed on macrophages prolongs inflammation by protecting macrophages from apoptosis. Most circulating AIM co-exists with immunoglobulin M (IgM). AIM's pathophysiological role in relation to IgM remains unclear. Here we evaluated the glomerular expression/deposition of AIM and IgM in the kidney using immunohistochemistry and its associations with clinical manifestations in 43 patients with biopsy-confirmed kidney diseases.

METHODS

Kidney biopsy tissue from all patients was immunostained for AIM and IgM. Staining patterns and percent stained areas within the glomeruli were determined. Cells expressing AIM were identified by co-staining with macrophage and endothelial cell surface markers. Correlations between staining results and clinical parameters were evaluated using univariate and multivariate analyses.

RESULTS

AIM was deposited in various areas, such as mesangial and capillary area. A part of AIM expression was localized to CD68-positive macrophages in the glomerulus. Amount of glomerular expression was positively correlated with urinary protein in patients with severe proteinuria (urinary protein ≥0.5 g/day) and kidney dysfunction [estimated glomerular filtration ratio (eGFR) <60 ml/min/1.73 m²]. Urinary protein was higher in patients exhibiting overlapping glomerular expression of AIM and IgM. Annual eGFR decline rate negatively correlated with AIM-positive area. AIM-positive area and initial serum creatinine were independently associated with decreased kidney function.

CONCLUSION

AIM expression in the kidney was associated with urinary protein and decline in kidney function. Co-expression with IgM appeared to exacerbate AIM's deleterious effects on kidney function. Combined glomerular AIM and IgM expression is a candidate prognostic index for kidney disease.

Apoptosis inhibitor of macrophage protein enhances intraluminal debris clearance and ameliorates acute kidney injury in mice

Acute kidney injury (AKI) is associated with prolonged hospitalization and high mortality, and it predisposes individuals to chronic kidney disease. To date, no effective AKI treatments have been established. Here we show that the apoptosis inhibitor of macrophage (AIM) protein on intraluminal debris interacts with kidney injury molecule (KIM)-1 and promotes recovery from AKI. During AKI, the concentration of AIM increases in the urine, and AIM accumulates on necrotic cell debris within the kidney proximal tubules. The AIM present in this cellular debris binds to KIM-1, which is expressed on injured tubular epithelial cells, and enhances the phagocytic removal of the debris by the epithelial cells, thus contributing to kidney tissue repair. When subjected to ischemia-reperfusion (IR)-induced AKI, AIM-deficient mice exhibited abrogated debris clearance and persistent renal inflammation, resulting in higher mortality than wild-type (WT) mice due to progressive renal dysfunction. Treatment of mice with IR-induced AKI using recombinant AIM resulted in the removal of the debris, thereby ameliorating renal pathology. We observed this effect in both AIM-deficient and WT mice, but not in KIM-1-deficient mice. Our findings provide a basis for the development of potentially novel therapies for AKI.

Interaction of AIM with insulin-like growth factor-binding protein-4

Apoptosis inhibitor of macrophages (AIM/cluster of differentiation 5 antigen-like/soluble protein α) has been shown to inhibit cellular apoptosis; however, the underlying molecular mechanism has not been elucidated. Using yeast two-hybrid screening, the present study uncovered that AIM binds to insulin-like growth factor binding protein-4 (IGFBP-4). AIM interaction with IGFBP-4, as well as IGFBP-2 and -3, but not with IGFBP-1, -5 and -6, was further confirmed by co-immunoprecipitation (co-IP) using 293 cells. The binding activity and affinity between AIM and IGFBP-4 in vitro were analyzed by co-IP and biolayer interferometry. Serum depletion-induced cellular apoptosis was attenuated by insulin-like growth factor-I (IGF-I), and this effect was abrogated by IGFBP-4. Of note, in the presence of AIM, the inhibitory effect of IGFBP-4 on the anti-apoptosis function of IGF-I was attenuated, possibly through binding of AIM with IGFBP-4. In conclusion, to the best of our knowledge, the present study provides the first evidence that AIM binds to IGFBP-2, -3 and -4. The data suggest that this interaction may contribute to the mechanism of AIM-mediated anti-apoptosis function.

Retinol-binding protein 4 and its potential roles in hypercholesterolemia revealed by proteomics

Effects of hypercholesterolemia on alterations of serum proteins have not been fully elucidated. Herein, using two-dimensional gel electrophoresis (2-DE) in conjunction with LC-MS searching has successfully been carried out to investigate the change of protein expression profiles as consequences of raised blood cholesterol at different levels (normal group: total cholesterol 200 mg/dL; borderline high group: total cholesterol 200-239 mg/dL; and high group: total cholesterol ≥ 240 mg/dL) (n = 45). Results revealed that down-regulation of retinol-binding protein 4 (RBP4) (-2.26 fold), transthyretin (-1.25 fold) and gelsolin (-1.47 fold) was observed in the high group. Meanwhile, the other proteins such as haptoglobin, complement factor B and CD5 antigen-like protein were up-regulated upto +3.24, +1.96 and +2.04 fold, respectively. Confirmation by Western blotting revealed a significant reduction of RBP4 (approximately 50 %) in individual samples derived from the high group. Presumptive conclusion can be drawn that down-regulation of RBP4 might be attributable to the inflammation of adipocytes caused by the release of proinflammatory cytokines (e.g. tumor necrosis factor α and interleukin-1β) from adipose tissues. Moreover, the decrease of transthyretin might also be taken into accounts since it is known that the transthyretin usually forms complex with RBP4 to prevent glomerular filtration and excretion through the kidney. The suppressing effect on RBP4 should be potentiated by the increase of complement factor B and CD5 antigen-like protein, which rendered the adipose tissues to overwhelm the liberation of RBP4 to blood circulation by metabolic and inflammatory processes. Such inflammation could further modulate the induction of cytokine release (e.g. IL-6 and IL-1β), resulting in the synthesis of acute phase protein, in particular, haptoglobin and C-reactive proteins from hepatocytes. However, the mechanism of gelsolin reduction remains unclear. Among these differentially expressed proteins, the RBP4 has been proposed as a major linkage between hypercholesterolemia, adipose tissues, liver and kidney, which is believed to be a potential biomarker for metabolic and cardiovascular disorders associated with dyslipidemia in the future.

Circulating AIM as an indicator of liver damage and hepatocellular carcinoma in humans

Background

Hepatocellular carcinoma (HCC), the fifth most common cancer type and the third highest cause of cancer death worldwide, develops in different types of liver injuries, and is mostly associated with cirrhosis. However, non-alcoholic fatty liver disease often causes HCC with less fibrosis, and the number of patients with this disease is rapidly increasing. The high mortality rate and the pathological complexity of liver diseases and HCC require blood biomarkers that accurately reflect the state of liver damage and presence of HCC.

Methods and Findings

Here we demonstrate that a circulating protein, apoptosis inhibitor of macrophage (AIM) may meet this requirement. A large-scale analysis of healthy individuals across a wide age range revealed a mean blood AIM of 4.99±1.8 µg/ml in men and 6.06±2.1 µg/ml in women. AIM levels were significantly augmented in the younger generation (20s–40s), particularly in women. Interestingly, AIM levels were markedly higher in patients with advanced liver damage, regardless of disease type, and correlated significantly with multiple parameters representing liver function. In mice, AIM levels increased in response to carbon tetrachloride, confirming that the high AIM observed in humans is the result of liver damage. In addition, carbon tetrachloride caused comparable states of liver damage in AIM-deficient and wild-type mice, indicating no influence of AIM levels on liver injury progression. Intriguingly, certain combinations of AIM indexes normalized to liver marker score significantly distinguished HCC patients from non-HCC patients and thus could be applicable for HCC diagnosis.

Conclusion

AIM potently reveals both liver damage and HCC. Thus, our results may provide the basis for novel diagnostic strategies for this widespread and fatal disease.