Pericellular plasmin induces smooth muscle cell anoikis

Abstract

Smooth muscle cell (SMC) rarefaction is involved in the development of several vascular pathologies. We suggest that the plasminogen activation system is a potential extracellular signal that can induce pericellular proteolysis and apoptosis of vascular SMCs. Using primary cultures of arterial SMCs, we show that plasmin generated from plasminogen on the cell surface induces cell retraction and fibronectin fragmentation, leading to detachment and morphological/biochemical changes characteristic of apoptosis (also called anoikis). The generation of cell-bound plasmin mediated by tissue-type plasminogen activator (t-PA), constitutively expressed by VSMCs, requires binding of plasminogen to the cell surface and is inhibited by epsilon-aminocaproic acid (IC50=0.9+/-0.2 mM), a competitor of plasminogen binding to membrane glycoproteins. Conversely, addition of alpha2-antiplasmin, which blocks free plasmin in the cell supernatant, could not fully prevent anoikis. Finally, an MMP inhibitor failed to prevent VSMC anoikis, arguing for a direct involvement of plasmin in this phenomenon. Indeed, similar changes are induced by plasmin directly added to VSMCs or to arterial rings, ex-vivo. We show for the first time that pathological anoikis can be triggered by a process that requires functional assembly of the plasminogen activation system on the surface of VSMCs.

Anoikis: an emerging hallmark in health and diseases

“…This is the case for the pericellular conversion of plasminogen to plasmin, which degrades fibronectin and induces anoikis of endothelial cells and smooth muscle cells. These pericellular proteolytic events are claimed to play a predominant role in the initiation of atherosclerosis and during the consequent athero-thrombotic complications [149,150]. A similar proteolytic cascade involving pericellular plasminogen activation and fibronectin degradation is instrumental in the disappearance of smooth muscle cells during aneurysm and varicose vein development [151,152].…”

Extracellular Proteases in Atherosclerosis and Restenosis

“…84 ECPs also promote apoptosis by cleaving cell-matrix interactions, a curious phenomenon known as "anoikis," as demonstrated for the plasminogen activation system in vascular smooth muscle cells. 85 Smooth muscle cell apoptosis in plaque shoulder regions may contribute to ACS by favoring plaque weakness because smooth muscle cells compete with proteases ECM degradation by secreting ECM and therefore increase fibrous capsule strength. Extracellular proteases, by releasing apoptotic cytokines such TNF-␣, also contribute to cell apoptosis.…”

Role of Leukocyte Elastase in Preventing Cellular Re-Colonization of the Mural Thrombus

“…DNA (10 g) was loaded on a 1.8% agarose gel containing 0.5 mg/ml ethidium bromide and separated by electrophoresis allowing detection of DNA fragmentation (DNA ladder). 34 Cell death detection was performed by photometric enzyme immunoassay for in vitro determination of cytoplasmic histone-associated DNA fragments according to the manufacturer's instructions (Roche).…”