Role and new insights of microfibrillar-associated protein 4 in fibrotic diseases.

Fibrosis is one of the most worrisome complications of chronic inflammatory diseases, leading to tissue damage, organ failure, and ultimately, death. The most notable pathological characteristic of fibrosis is the excessive accumulation of extracellular matrix (ECM) components such as collagen and fibronectin adjacent to foci of inflammation or damage. The human microfibrillar-associated protein 4 (MFAP4), an important member of the superfamily of fibrinogen-related proteins, is considered to have an extremely important role in ECM transformation of fibrogenesis. This review summarizes the structure, characteristics, and physiological functions of MFAP4 and the importance of MFAP4 in various fibrotic diseases. Meanwhile, we elaborated the underlying actions and mechanisms of MFAP4 in the development of fibrosis, suggesting that a better understand of MFAP4 broadens novel perspective for early screening, diagnosis, prognostic risk assessment, and treatment of fibrotic diseases.

Microfibrillar-associated protein 4 as a potential marker of acute relapse in inflammatory demyelinating diseases of the central nervous system: Pathological and clinical aspects.

BACKGROUND: Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein not previously described in the human central nervous system (CNS). OBJECTIVES: We determined MFAP4 CNS expression and measured cerebrospinal fluid (CSF) and serum levels. METHODS: Tissue was sampled at autopsy from patients with acute multiple sclerosis (MS) (n = 3), progressive MS (n = 3), neuromyelitis optica spectrum disorder (NMOSD) (n = 2), and controls (n = 9), including 6 healthy controls (HC). MFAP4 levels were measured in 152 patients: 49 MS, 62 NMOSD, 22 myelin oligodendrocyte glycoprotein-associated disease (MOGAD), and 19 isolated optic neuritis (ION). RESULTS: MFAP4 localized to meninges and vascular/perivascular spaces, intense in the optic nerve. At sites of active inflammation, MFAP4 reactivity was reduced in NMOSD and acute MS and less in progressive MS. CSF MFAP4 levels were reduced during relapse and at the onset of diseases (mean U/mL: MS 14.3, MOGAD 9.7, and ION 14.6 relative to HC 17.9. (p = 0.013, p = 0.000, and p = 0.019, respectively). Patients with acute ON (n = 68) had reduced CSF MFAP4 (mean U/mL: 14.5, p = 0.006). CSF MFAP4 levels correlated negatively with relapse severity (rho = -0.41, p = 0.017). CONCLUSION: MFAP4 immunoreactivity was reduced at sites of active inflammation. CSF levels of MFAP4 were reduced following relapse and may reflect disease activity.

Declined plasma microfibrillar-associated protein 4 levels in acute coronary syndrome.

BACKGROUND: Microfibrillar-associated protein (MFAP4), initially identified as an extracellular matrix protein, has been demonstrated in multiple human disorders, but it is yet to be discovered following acute coronary syndrome (ACS) in clinical practice. Therefore, this study aimed to investigate the relationship between circulating MFAP4 levels and coronary stenosis in ACS. METHODS: We performed the study in 148 ACS subjects, including 75 ST-segment elevation myocardial infarction (STEMI), 27 non-ST-segment elevation myocardial infarction (non-STEMI) and 46 unstable angina (UA). Clinical variables were collected and Gensini and Syntax stenosis scoring systems were applied to assess the severity of coronary stenosis. Kaplan-Meier and logistic regression analysis were used to analyze the relationship between MFAP4 and the severity of coronary stenosis or ACS outcomes. Spearman analysis was used to describe the correlation between MFAP4 and clinical parameters. RESULTS: Circulating MFAP4 levels were significantly decreased in the STEMI group (0.008 ng/ml) compared with the non-STEMI group (0.014 ng/ml) and UA group (0.019 ng/ml) (p < 0.001). After adjusting for confounding factors, we found that MFAP4 was an independent risk factor for STEMI (odds ratio = 0.395, 95% CI 0.174-0.895, p = 0.026). MFAP4 level was negatively correlated with Gensini score and Syntax score (r = - 0.311 and - 0.211, p < 0.001 and 0.01, respectively). Based on the MFAP4 level of 0.117 ng/ml, ACS patients were divided into two groups: the low-MFAP4 group (< 0.117 ng/ml, n = 60) and the high-MFAP4 group (≥ 0.117 ng/ml, n = 88). After the median follow-up of 165 days, Kaplan-Meier survival analysis revealed that the MACE-free rate was significantly lower in ACS patients with lower MFAP4 levels (p = 0.009). CONCLUSIONS: MFAP4 has a potential as a biomarker for the degree of coronary stenosis in ACS. Confirmation of observations in larger cohorts and longer follow-up periods is warranted.

Microfibrillar-associated protein 4 in health and disease.

Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related domain family. It has been localized to elastic fiber-rich regions in several tissues including the arteries, lungs, heart and skin. MFAP4 binds collagen, fibrillins and tropoelastin and contributes to the process of microfibrillar assembly and maturation of elastic fibers. MFAP4 can also bind RGD-dependent integrins, predominantly αVß3 and αVß5 through its N-terminal RGD sequence, modulating cellular behavior. Circulating MFAP4 was suggested as a robust biomarker for hepatitis C virus- and alcoholic liver disease-related liver fibrosis, cardiovascular disorders and chronic obstructive pulmonary disease. In mice, MFAP4 seems to have a widely redundant role under homeostatic conditions, as global MFAP4 deficiency results in a mild pulmonary phenotype, causing emphysema-like airspace enlargement that progresses with age. However, emerging in vivo and in vitro data suggest that MFAP4 is actively involved in the pathogenesis of remodeling-associated diseases, including fibrosis, cardiovascular disorders, aging, asthma and cancer through activation of integrin-mediated signaling as well as by modulating TGF-ß pathway, thus supporting maladaptive matrix remodeling. This review summarizes the current knowledge about MFAP4 structure and localization, its mechanisms of action in disease-induced tissue remodeling as well as its potential role as a clinical biomarker.

Tumor-suppressive role of microfibrillar associated protein 4 and its clinical significance as prognostic factor and diagnostic biomarker in hepatocellular carcinoma.

Objective: Revealing microfibrillar-associated protein 4 (MFAP4)'s function and its clinical significance in hepatocellular carcinoma (HCC). Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were used to evaluate MFAP4 mRNA and protein expression in paired HCC and paracarcinoma tissues, respectively. MFAP4 serum concentration was detected using enzyme-linked immunosorbent assays in healthy people (n = 30), cirrhosis (n = 15) and HCC patients (n = 80). MFAP4 protein expression was detected in two tissue microarrays (n = 60 and n = 90). Plasmids were transfected into human HCC cell line Bel-7402, and MFAP4 function was determined in vitro in cell experiments. Furthermore, tumorigenicity studies in nude mice served to assess the function of MFAP4 for HCC. Results: Both MFAP4 mRNA and protein expression were significantly downregulated in HCC tissue compared with paracarcinoma tissue (P < 0.05). Decreased MFAP4 expression in paracarcinoma tissue was associated with poor postoperative survival in HCC patients (P = 0.027). MFAP4 was also downregulated in HCC sera compared with healthy people (P < 0.05). In vitro, MFAP4 upregulation in Bel-7402 cells induced S phase arrest, promoted apoptosis, and inhibited migration and invasion. Western blotting indicated MFAP4 overexpression increased CDK4, CDK6, pRB, P27, and BCL-XS expression. Tumorigenicity study showed that the upregulation of MFAP4 inhibited the proliferation of Bel-7402 cells in nude mice. Conclusions: MFAP4 expression was significantly lower both in sera and tissue of HCC patients. MFAP4 can serve as molecular marker for HCC diagnosis and prognosis. Additionally, MFAP4 acted as an important HCC tumor suppressor by inducing S phase arrest, and promoting apoptosis, cell migration, and invasion.

Pathological investigations and correlation research of microfibrillar-associated protein 4 and tropoelastin in oral submucous fibrosis.

BACKGROUND: Oral submucous fibrosis (OSF), distinguished by abnormal collagen deposition, is a potentially malignant disorder with 4.2% (95% CI 2.7-5.6%) of malignant transformation and rising global prevalence. However, the precise pathogenesis and effective treatment remain elusive and controversial despite the abundance of literature on this topic. Therefore, it is crucial to explore the clinicopathological characteristics and potential markers for the diagnosis and prognosis of OSF. The objective of this study was to evaluate the influence and correlation of Microfibrillar-associated protein 4 (MFAP4) and tropoelastin (TE) in the development of OSF patients. MATERIAL AND METHODS: Clinicopathological factors, hematoxylin-eosin (HE) and Masson trichome staining, immunohistochemical characteristics and the correlation between MFAP4 and TE were recorded and compared among different stages of OSF progression among cases (n = 60) and controls (n = 10). Student's t test, ANOVA analysis, and the chi-square test were performed to compare the categorical variables for clinicopathological characteristics and the expression level of MFAP4 and TE between the fibrotic and normal tissues. Correlation analysis of MFAP4 and TE was performed using Pearson's correlation test and linear regression. RESULTS: MFAP4 and TE proteins are upregulated and increased gradually in patients with varying stages of OSF, relative to the control group. Furthermore, statistical analyses revealed that the expression level of MFAP4 was positively associated with TE, with a Pearson correlation coefficient of 0.3781 (p = 0.0048). Clinically, we found that OSF affected more males than females, with a ratio of 29:1. The age range was 16-60 years, and the mean age was 36.25 ± 10.25 years. In patients younger than 40 years, the positive expression rate of MFAP4 and TE was higher than in those over 40 years. All OSF cases had chewed areca nut, with 51.67% smoking tobacco. CONCLUSIONS: Our study elucidates that the accumulation of MFAP4 and TE proteins may play a vital role in the occurrence and development of OSF and may be promising candidate moleculars for prevention, diagnosis, and treatment strategies for OSF in the future.

Corrigendum to 'Level of MFAP4 in ascites independently predicts 1-year transplant-free survival in patients with cirrhosis' [JHEP Reports 3 (2021) 100287].

[This corrects the article DOI: 10.1016/j.jhepr.2021.100287.].

Level of MFAP4 in ascites independently predicts 1-year transplant-free survival in patients with cirrhosis.

BACKGROUND & AIMS: Prognostic models of cirrhosis underestimate disease severity for patients with cirrhosis and ascites. Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein linked to hepatic neoangiogenesis and fibrogenesis. We investigated ascites MFAP4 as a predictor of transplant-free survival in patients with cirrhosis and ascites. METHODS: A dual-centre observational study of patients with cirrhosis and ascites recruited consecutively in relation to a paracentesis was carried out. Patients were followed up for 1 year, until death or liver transplantation (LTx). Ascites MFAP4 was tested with the model for end-stage liver disease (MELD-Na), CLIF Consortium Acute Decompensation (CLIF-C AD), and Child-Pugh score in Cox regression models. RESULTS: Ninety-three patients requiring paracentesis were included. Median ascites MFAP4 was 29.7 U/L [22.3-41.3], and MELD-Na was 19 [16-23]. A low MELD-Na score (<20) was observed in 49 patients (53%). During follow-up, 20 patients died (22%), and 6 received LTx (6%). High ascites MFAP4 (>29.7 U/L) was associated with 1-year transplant-free survival (p = 0.002). In Cox regression, ascites MFAP4 and MELD-Na independently predicted 1-year transplant-free survival (hazard ratio [HR] = 0.97, p = 0.03, and HR = 1.08, p = 0.01, respectively). Ascites MFAP4 and CLIF-C AD also predicted survival independently (HR = 0.96, p = 0.02, and HR = 1.05, p = 0.03, respectively), whereas only ascites MFAP4 did, controlling for the Child-Pugh score (HR = 0.97, p = 0.03, and HR = 1.18, p = 0.16, respectively). For patients with MELD-Na <20, ascites MFAP4 but not ascites protein predicted 1-year transplant-free survival (HR 0.91, p = 0.02, and HR = 0.94, p = 0.17, respectively). CONCLUSIONS: Ascites MFAP4 predicts 1-year transplant-free survival in patients with cirrhosis and ascites. In patients with low MELD-Na scores, ascites MFAP4, but not total ascites protein, significantly predicted 1-year transplant-free survival. LAY SUMMARY: Patients with cirrhosis who have fluid in the abdomen, ascites, are at an increased risk of death and in need for liver transplantation. Our study identified patients with ascites and a poor prognosis by measuring microfibrillar associated protein 4 (MFAP4), a protein present in the abdominal fluid. Patients with low levels of the MFAP4 protein are at particularly increased risk of death or liver transplantation, suggesting that clinical care should be intensified in this group of patients.

Human Microfibrillar-Associated Protein 4 (MFAP4) Gene Promoter: A TATA-Less Promoter That Is Regulated by Retinol and Coenzyme Q10 in Human Fibroblast Cells.

Elastic fibers are one of the major structural components of the extracellular matrix (ECM) in human connective tissues. Among these fibers, microfibrillar-associated protein 4 (MFAP4) is one of the most important microfibril-associated glycoproteins. MFAP4 has been found to bind with elastin microfibrils and interact directly with fibrillin-1, and then aid in elastic fiber formation. However, the regulations of the human MFAP4 gene are not so clear. Therefore, in this study, we firstly aimed to analyze and identify the promoter region of the human MFAP4 gene. The results indicate that the human MFAP4 promoter is a TATA-less promoter with tissue- and species-specific properties. Moreover, the promoter can be up-regulated by retinol and coenzyme Q10 (coQ10) in Detroit 551 cells.

Deletion of Microfibrillar-Associated Protein 4 Attenuates Left Ventricular Remodeling and Dysfunction in Heart Failure.

Background Cardiac remodeling predisposes individuals to heart failure if the burden is not solved, and heart failure is a growing cause of morbidity and mortality worldwide. The cardiac extracellular matrix not only provides structural support, but also is a core aspect of the myocardial response to various biomechanical stresses and heart failure. MFAP4 (microfibrillar-associated protein 4) is an integrin ligand located in the extracellular matrix, whose biological functions in the heart remain poorly understood. In the current study we aimed to test the role of MFAP4 in cardiac remodeling. Methods and Results MFAP4-deficient (MFAP4-/-) and wild-type mice were subjected to aortic banding surgery and isoproterenol to establish models of cardiac remodeling. We also evaluated the functional effects of MFAP4 on cardiac hypertrophy, fibrosis, and cardiac electrical remodeling. The expression of MFAP4 was increased in the animal cardiac remodeling models induced by pressure overload and isoproterenol. After challenge of 8 weeks of aortic banding or 2 weeks of intraperitoneal isoproterenol, MFAP4-/- mice exhibited lower levels of cardiac fibrosis and fewer ventricular arrhythmias than wild-type mice. However, there was no significant effect on cardiomyocyte hypertrophy. In addition, there was no significant difference in cardiac fibrosis severity, hypertrophy, or ventricular arrhythmia incidence between wild-type-sham and knockout-sham mice. Conclusions These findings are the first to demonstrate that MFAP4 deficiency inhibits cardiac fibrosis and ventricular arrhythmias after challenge with 8 weeks of aortic banding or 2 weeks of intraperitoneal isoproterenol but does not significantly affect the hypertrophy response. In addition, MFAP4 deficiency had no significant effect on cardiac fibrosis, hypertrophy, or ventricular arrhythmia in the sham group in this study.

Relationship between Microfibrillar-Associated Protein 4 Levels and Subclinical Myocardial Damage in Chronic Kidney Disease.

INTRODUCTION: Chronic kidney disease (CKD) is a widespread health problem, in which mortality is most frequently due to cardiovascular diseases. Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein. MFAP4 is involved in several biological processes, particularly the maintenance of vascular integrity and extracellular matrix remodeling. Our review of the literature revealed no data concerning MFAP4 levels in CKD and its relationship with myocardial functions. OBJECTIVE: The purpose of this study was therefore to investigate MFAP4 levels in CKD, parameters affecting these, and the relationship with myocardial functions. MATERIALS AND METHODS: Seventy-nine CKD patients and 30 healthy controls were included in the study. Routine biochemical tests and echocardiography were performed once demographic data had been recorded. Blood specimens were collected for MFAP4 analysis, and the results were subjected to statistical analysis. RESULTS: MFAP4 levels were significantly higher in the patient group than in the control group (p< 0.001). Doppler parameters revealed more frequent LV diastolic impairment in the patient group. Tissue Doppler systolic velocity and global longitudinal strain were significantly impaired, revealing the subclinical LV systolic dysfunction in CKD patients. MFAP4 elevation in the patient group was positively correlated with aortic root (AR), global circumferential strain (GCS), and GCS rate. CONCLUSION: Our results showed MFAP4 elevation in CKD for the first time in the literature, and that this elevation may be related to GCS and AR dilation. We think that, once supported by further studies, MFAP4 may constitute a marker in the evaluation of myocardial functions in CKD.

Microfibrillar-associated protein 4 in serum is associated with asthma in Danish adolescents and young adults.

BACKGROUND: Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein belonging to the fibrinogen-related protein superfamily, which plays multifaceted roles in innate immunity and normal endothelial function. It has been proposed that MFAP4 promotes the development of asthma in vivo and proasthmatic pathways of bronchial smooth muscle cells in vitro. The aim of this study was to investigate the significance of serum MFAP4 in adolescents and young adolescents with persistent asthma. METHODS: Prospective, observational study including adolescents and young adults (age 11-27 years) previously diagnosed with asthma during childhood 2003 to 2005 (0-15 years) at the four pediatric outpatient clinics in the Region of Southern Denmark (n = 449). Healthy controls were recruited at follow-up (n = 314). Detection of serum MFAP4 was performed by AlphaLISA technique. RESULTS: Current asthma was associated to a 14% higher mean level of serum MFAP4 compared with controls (expß 1.14, 95% confidence intervals [CI], 1.05-1.23) and a 6% higher mean level compared with subjects with no current asthma (expß 1.06, 95% CI, 0.99-1.13). No association was found at follow-up between serum MFAP4 and self-reported atopic symptoms (other than asthma), Asthma Control Test-score, fractional exhaled nitric oxide (FeNO), nor to flow rate at 1 second, forced vital capacity, and forced expiratory flow 25% to 75%, response to short-acting beta 2 agonist or mannitol. CONCLUSIONS: We found a significantly higher mean level of serum MFAP4 in adolescent and young adults with mild to moderate asthma compared with healthy controls but no association to FeNO and lung function nor to the response to short-acting beta 2 agonist or mannitol. The result supports the hypothesis that MFAP4 plays a role in the pathogenesis of asthma although the marker did not demonstrate any obvious potential as an asthma biomarker in adolescents and young adults with asthma. To understand the possible proasthmatic functions of MFAP4, further investigation in specific asthma phenotypes and the underlying molecular mechanisms is warranted.

Site-specific absence of microfibrillar-associated protein 4 (MFAP4) from the internal elastic membrane of arterioles in the rheumatoid arthritis synovial membrane: an immunohistochemical study in patients with advanced rheumatoid arthritis versus osteoarthritis.

Microfibrillar-associated protein 4 (MFAP4) is a non-structural matrix protein with cell regulatory activities and a potential as seromarker for fibrosis. We aimed to study the occurrence of MFAP4 in the synovial membrane from patients with rheumatoid arthritis (RA) vs osteoarthritis (OA). Formaldehyde-fixed synovial tissue sections, from patients with RA (N = 6) and OA (N = 6) undergoing total hip arthroplasty, were deparaffinized and immunostained with monoclonal antibodies against MFAP4. Elastin was detected using ElastiKit. MFAP4 in serum (sMFAP4) and synovial fluid was measured by an immunoassay. MFAP4 was present in synovial biopsies from both RA and OA patients, particularly prominent in deep arterioles where it colocalized with elastin. Notably however, MFAP4 was absent from the internal elastic lamina in RA arterioles irrespective of disease duration and synovitis activity, while present although with irregular staining patterns in OA specimens. sMFAP4 was increased in RA and OA serum vs healthy controls: median (interquartile range) 29.8 (25.3-39.1) and 25.5 U/L (18.1-43.3) vs 17.7 U/L (13.7-21.2), p = 0.006 and p = 0.02, respectively The concentration of synovial fluid was lower than in serum in both RA and OA. These findings may suggest that MFAP4 is involved in adaptive vessel wall remodeling associated with chronic joint disease.

Increased plasma microfibrillar-associated protein 4 is associated with atrial fibrillation and more advanced left atrial remodelling.

INTRODUCTION: This study aimed to evaluate the relationship of plasma microfibrillar-associated protein 4 (MFAP4) to atrial fibrillation (AF) and atrial structural remodelling. MATERIAL AND METHODS: Plasma MFAP4 levels were measured in 92 patients with AF (61 paroxysmal AF (PAF) patients and 31 persistent AF (PersAF) patients) and 71 control subjects without AF. Linear and logistic multivariate regression analyses were performed to determine the potential value of MFAP4 for predicting the incidence of AF and left atrial size. Then, plasma and atrial protein levels of MFAP4 and its association with atrial fibrosis ratio were analysed in an atrial-specific fibrosis rat model. RESULTS: There were significant differences in MFAP4 levels based on clinical group, with a gradient from control (1.71 ±0.53 ng/ml) to PAF (1.98 ±0.53 ng/ml) to PersAF (2.09 ±0.76 ng/ml) (p < 0.01). With multivariate analyses, plasma MFAP4 was found to be an independent determinant of left atrial diameter in AF patients. In atrial fibrosis rats, both plasma MFAP4 and atrial MFAP4 protein levels increased in atrial fibrosis rats and positively correlated with atrial fibrosis severity. CONCLUSIONS: Plasma MFAP4 was increased in patients with AF and was highest in those with PersAF; both plasma MFAP4 and atrial MFAP4 protein expression were directly associated with the extent of LA structural remodelling.

Integrated analysis of microfibrillar-associated proteins reveals MFAP4 as a novel biomarker in human cancers.

AIM: The potential functions and underlying mechanism of microfibrillar-associated proteins (MFAPs) are explored in human cancers. MATERIALS & METHODS: Here, we examined the expression profiles, prognostic values, epigenetic and genetic alterations of MFAPs in human cancers from public omics repository. RESULTS: Among MFAPs family, MFAP4 was frequently downregulated in the most human cancers and high mRNA expression of MFAP4 significantly correlated with better overall survival in breast cancer. DNA hypermethylation in the promoter of MFAP4 decreased its mRNA expression. MFAP4 strongly associated with pathway in impairment and alteration of the elastic fibers. CONCLUSION: This integrated analysis provides new insights into MFAPs in human cancers and indicates that MFAP4 could be used as novel biomarker for developing therapies against human cancers.

Association between microfibrillar-associated protein 4 (MFAP4) and micro- and macrovascular complications in long-term type 1 diabetes mellitus.

AIMS: To evaluate microfibrillar-associated protein 4 (MFAP4) as a marker of micro- and macrovascular complications in patients with type 1 diabetes. METHODS: This cross-sectional study included 203 persons with a long duration of type 1 diabetes from a population-based cohort ascertained in the former Funen County, Denmark. Detection of plasma-MFAP4 (pMFAP4) was performed by the AlphaLISA Technique. Diabetic retinopathy (DR) was graded in accordance with the Early Treatment Diabetic Retinopathy Study adaptation of the modified Airlie House classification. A monofilament test was used to test for neuropathy, and nephropathy was evaluated in a single spot urine sample. Data describing macrovascular disease were obtained from the Danish National Patient Register. RESULTS: Median age and duration of diabetes were 58.7 and 43 years, respectively, and 61% were males. High levels of pMFAP4 were found in participants of old age, in women and in non-smokers (p < 0.05). In a multiple logistic regression model, patients with high levels of pMFAP4 were more likely to have diabetic neuropathy (OR 2.47 for quartile 4 versus quartile 1, 95% CI 1.01-6.03). No association was found between pMFAP4 and proliferative diabetic retinopathy, nephropathy or macrovascular disease. CONCLUSIONS: No association between pMFAP4 and macrovascular vascular complications was found. However, high levels of pMFAP4 correlated independently with diabetic neuropathy. Further studies on the predictive value of increased circulating MFAP4 in diabetic neuropathy are warranted.

Evaluation of the biomarker candidate MFAP4 for non-invasive assessment of hepatic fibrosis in hepatitis C patients.

BACKGROUND: The human microfibrillar-associated protein 4 (MFAP4) is located to extracellular matrix fibers and plays a role in disease-related tissue remodeling. Previously, we identified MFAP4 as a serum biomarker candidate for hepatic fibrosis and cirrhosis in hepatitis C patients. The aim of the present study was to elucidate the potential of MFAP4 as biomarker for hepatic fibrosis with a focus on the differentiation of no to moderate (F0-F2) and severe fibrosis stages and cirrhosis (F3 and F4, Desmet-Scheuer scoring system). METHODS: MFAP4 levels were measured using an AlphaLISA immunoassay in a retrospective study including n = 542 hepatitis C patients. We applied a univariate logistic regression model based on MFAP4 serum levels and furthermore derived a multivariate model including also age and gender. Youden-optimal cutoffs for binary classification were determined for both models without restrictions and considering a lower limit of 80 % sensitivity (correct classification of F3 and F4), respectively. To assess the generalization error, leave-one-out cross validation (LOOCV) was performed. RESULTS: MFAP4 levels were shown to differ between no to moderate fibrosis stages F0-F2 and severe stages (F3 and F4) with high statistical significance (t test on log scale, p value <2.2·10(-16)). In the LOOCV, the univariate classification resulted in 85.8 % sensitivity and 54.9 % specificity while the multivariate model yielded 81.3 % sensitivity and 61.5 % specificity (restricted approaches). CONCLUSIONS: We confirmed the applicability of MFAP4 as a novel serum biomarker for assessment of hepatic fibrosis and identification of high-risk patients with severe fibrosis stages in hepatitis C. The combination of MFAP4 with existing tests might lead to a more accurate non-invasive diagnosis of hepatic fibrosis and allow a cost-effective disease management in the era of new direct acting antivirals.

Characterization of Microfibrillar-associated Protein 4 (MFAP4) as a Tropoelastin- and Fibrillin-binding Protein Involved in Elastic Fiber Formation.

MFAP4 (microfibrillar-associated protein 4) is an extracellular glycoprotein found in elastic fibers without a clearly defined role in elastic fiber assembly. In the present study, we characterized molecular interactions between MFAP4 and elastic fiber components. We established that MFAP4 primarily assembles into trimeric and hexameric structures of homodimers. Binding analysis revealed that MFAP4 specifically binds tropoelastin and fibrillin-1 and -2, as well as the elastin cross-linking amino acid desmosine, and that it co-localizes with fibrillin-1-positive fibers in vivo. Site-directed mutagenesis disclosed residues Phe(241) and Ser(203) in MFAP4 as being crucial for type I collagen, elastin, and tropoelastin binding. Furthermore, we found that MFAP4 actively promotes tropoelastin self-assembly. In conclusion, our data identify MFAP4 as a new ligand of microfibrils and tropoelastin involved in proper elastic fiber organization.

Microfibrillar-associated protein 4: a potential biomarker of chronic obstructive pulmonary disease.

BACKGROUND: Microfibrillar-associated protein 4 (MFAP4) is a matricellular glycoprotein that co-localises with elastic fibres and is highly expressed in the lungs. The aim of this study was to test the hypothesis that plasma MFAP4 (pMFAP4) reflects clinical outcomes in chronic obstructive pulmonary disease (COPD). METHODS: pMFAP4 was measured by an AlphaLISA immunoassay in stable COPD (n = 69) at baseline and at follow-up until 24 months after inclusion and in acute exacerbations of COPD (AECOPD) (n = 14) at baseline and until 6 months after inclusion. RESULTS: The majority of patients (89%) were in GOLD II and III. Multiple linear regressions showed positive associations between pMFAP4 and the Global initiative for Obstructive Lung Disease (GOLD) grade (p = 0.01), modified Medical Research Council score (p < 0.0001) and BODE index (p = 0.04). Negative associations were found with 6-min walking distance (p = 0.04) and bronchodilator-induced reversibility (p = 0.02). The pMFAP4 levels varied less than 25% between the baseline and a 3 month follow-up in 83% of the patients. The pMFAP4 levels appeared unaffected in the acute phase of severe AECOPD but rose to an increased stable level within one month after hospitalization. CONCLUSION: Increased pMFAP4 was associated to the severity in COPD and has the potential to serve as a stable disease biomarker. This observation warrants confirmation in a larger longitudinal COPD population.