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Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix (ECM) protein primarily located in elastic arteries. It can bind elastin and collagen, and furthermore activate vascular cells through cellular integrin binding and modulate matrix metalloprotinase (MMP) activity. We hypothesized that lack of MFAP4 would decrease vascular inflammation and abdominal aortic aneurysm (AAA) formation. AAA was induced in 9-11 week old mice using two experimental mouse models: 1) Male Mfap4 -/- /ApoE -/- double knock-out (dKO) and ApoE -/- littermate control mice were feed western diet and subjected to continuously angiotensin II (AngII, 1000 ng/kg/min) infusion for 9-28 days via subcutaneous osmotic mini-pumps. Arterial blood pressure was measured in the femoral artery. 2) 1.5 U/mL elastase was infused into the infrarenal aorta in Mfap4 -/- and littermate Mfap4 +/+ mice for 5 minutes. Aortic blood flow was restored and the mice recovered for 9-16 days. Aortic diameter was measured in mice subjected to AngII or elastase infusion at day 28 and 16 respectively. MMP activity was detected by zymography. No difference in AAA formation was observed between genotypes after elastase perfusion. In response to AngII infusion dKO mice showed a significantly decrease in AAA diameter and incidence rate compared to ApoE -/- mice. AngII-induced increase in blood pressure was not dependent of MFAP4. However, there was decreased aortic arch atherosclerotic plaque formation, MMP2 and MMP9 activity in aortic tissue from dKO mice compared to ApoE -/- mice. Furthermore there was a non-significant tendency of decreased elastin degradation score in the AngII infused dKO mice, however this was not observed in the elastase perfused mice. Activity of MMP12 and extent of infiltrating leukocytes in aneurysmal tissue from both models will be further investigated. In conclusion we observed a decreased AAA formation and MMP activity in Mfap4 -/- /ApoE -/- mice which was not explained by variation in blood pressure or altered elastin degradation. The data suggest that MFAP4 induces MMP2-activity and thus the propensity for AAA formation.

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Background and Purpose: Peptides derived from retroviral envelope proteins have been shown to possess a wide range of immunosuppressive and anti-inflammatory activities. We have previously reported identification of such a peptide derived from the envelope protein coded by a human endogenous retrovirus (HERV). In this study we assessed effects of this peptide treatment on inhibition of immune response in the DSS-induced mice model of colitis. Furthermore, we identified that in vitro the peptide inhibits the KCa3.1 potassium channel, a potential target for therapy of immune diseases. Experimental Approach: We characterized an immunosuppressive peptide ENV59, from a specific HERV envelope protein, in vivo effects on inflammation control in acute colitis mice model and in vitro on the production of pro-inflammatory cytokines. Furthermore, we described in vitro ENV59-GP3 effects with respect to potency of inhibition on KCa3.1 channels and calcium influx. Key Results: ENV59-GP3 peptide treatment showed reduction of the disease score in the DSS-induced acute colitis mice model, which was comparable to effects of the KCa3.1 channel blocker NS6180. Analysis of cytokine production from DSS-mice model treated animals revealed equipotent inhibitory effects of the ENV59-GP3 and NS6180 compounds on the production of IL-6, TNF-α, IL-1β. Patch clamp studies show that the peptide ENV59-GP3 is a blocker of the potassium channel KCa3.1. Conclusion and Implications: Env59-GP3 represents KCa3.1 channel inhibitor underlining the implications of using virus derived channel blockers for treatment of autoimmune diseases. There are no drugs with a similar mechanism of action currently on the market.

Arterial injury stimulates remodeling responses that, when overexuberant, leads to stenosis. This response is influenced by specific integrin signaling in vascular smooth muscle cells (VSMCs). Microfibrillar-associated protein 4 (MFAP4) is a matricellular integrin ligand localized to the vascular wall. We hypothesized that systemic MFAP4 (sMFAP4) associates to vascular remodeling processes and that MFAP4 enhances integrin dependent VSMC activation and vasculoproliferative disease-associated remodeling. We explored the hypotheses using a prospective human cohort with symptomatic obstructive peripheral arterial disease (PAD), VSMC culture studies, and produced MFAP4 deficient mice for studying neointima formation. We demonstrate that the highest tertile of sMFAP4 was significantly associated with primary patency after vascular reconstruction, and the overall need for vascular reconstruction and mortality in 343 PAD patients. MFAP4 mediated the adhesion, migration, and proliferation of VSMCs in an integrin αVβ3/5-dependent manner in vitro. These effects were inhibited by MFAP4-blocking antibodies. MFAP4-deficient mice displayed delayed neointimal formation when challenged with carotid artery ligation, but the compensatory outward remodeling of vessel diameter was reduced. In conclusion, sMFAP4 has the potential to serve as a systemic marker morbidity and mortality in PAD. MFAP4 regulates integrin αVβ3/5 signaling and pathological remodeling in vivo, and may have therapeutic implications in vasculoproliferative diseases.