Serine Protease Inhibitor Serp-1 Strongly Impairs Atherosclerotic Lesion Formation and Induces a Stable Plaque Phenotype in ApoE ^−/− Mice

Abstract

Abstract-The myxoma virus protein Serp-1 is a member of the serine protease inhibitor superfamily. Serp-1 potently inhibits human serum proteases including plasmin, urokinase-type plasminogen activator (uPA), and tissue-type plasminogen activator (tPA). Serp-1 also displays a high antiinflammatory activity, rendering it a promising candidate for antiatherosclerotic therapy. In this study, we have thus examined the effect of Serp-1 on de novo atherosclerotic plaque formation and on advanced lesions. Perivascular collars were placed around carotid arteries of ApoE Ϫ/Ϫ mice to induce atherosclerotic plaques and Serp-1 treatment started at week 1 and week 5 after collar placement. Effects of Serp-1 on de novo atherogenesis were characterized by a significantly lower plaque size than that of control mice (18Ϯ5ϫ10 3 versus 57Ϯ12ϫ10 3 m 2 , respectively; Pϭ0.007). Immunostaining showed a 50% (Pϭ0.004) decrease in the MOMA-2-stained lesion area of Serp-1-treated mice. Treatment of advanced lesions with Serp-1 resulted in a decrease in plaque size and lumen stenosis (Pϭ0.028). ␣-Actin staining of these lesions was significantly increased compared with the control (Pϭ0.017). In both studies, a higher cellularity of the plaque and increased collagen content was observed in Serp-1-treated mice. In vitro studies showed that Serp-1 induces proliferation and migration of vascular smooth muscle cells. In conclusion, Serp-1 inhibits carotid artery plaque growth and progression in ApoE Ϫ/Ϫ mice. Equally relevant, it enhances cellularity of the plaque core potentially leading to improved plaque stability.

FTY720, a Synthetic Sphingosine 1 Phosphate Analogue, Inhibits Development of Atherosclerosis in Low-Density Lipoprotein Receptor–Deficient Mice

“…Cross-sections with maximal stenosis were used for morphometric analysis on a DM-RE microscope with Leica Qwin image-analysis software (Leica Microsystems B.V., Rijswijk, the Netherlands), as described previously. 26,27 Corresponding sections were stained immunohistochemically with antibodies directed against mouse macrophages (monoclonal mouse IgG 2a , clone monocyte ϩ macrophage antibody-2 [MOMA-2], dilution 1:50; Sigma Diagnostics), vascular smooth muscle cells (monoclonal mouse IgG 2a , clone 1A4, dilution 1:50; Sigma), and lymphocytes (purified antimouse CD3 molecular complex, 17A2, dilution 1:50; BD Biosciences Pharmingen, San Diego, Calif). Sections were stained for collagen using Picrosirius Red (Sigma).…”

Extracellular Proteases in Atherosclerosis and Restenosis

“…In the advanced carotid atheromatous lesions of apolipoprotein E Ϫ/Ϫ mice, Serp-1 (a serine protease inhibitor) may improve plaque stability because it induces smooth muscle cell hypercellularity and increases the collagen content of the lesion core. 52 …”

The synergistic inhibition of atherogenesis in apoE−/− mice between pravastatin and the sPLA2 inhibitor varespladib (A-002)

“…sPLA 2 inhibition could be suppressing the formation of such oxidized adducts and result in increased SMC proliferation and larger fibrous caps. A 3-fold increase in lesional SMC content was observed in mice deficient in the serine protease Serp-1 gene, suggesting that altered protease activity may also have a role in the fibrous cap size increase (26). However, due to the fact that there was no change in the proteoglycan or collagen content of the lesion, it seems more likely that sPLA 2 inhibition has specifically altered SMC proliferation or survival and not changed the matrix degrading potential of macrophages or other cells within the lesion.…”