Fibronectins (FNs) comprise a family of adhesive extracellular matrix proteins that arise by alternative splicing in three regions: V (IIICS), EIIIA (ED-A), and EIIIB (ED-B). FNs bearing the EIIIA and EIIIB segments are prevalent during embryogenesis, expressed to lesser degrees in normal adult tissues, and may be locally reexpressed at adult tissue injury. RNase mapping shows that normal rat arteries express low levels of FNs that are predominantly EIIIA- and EIIIB-. Following balloon injury, arterial walls produce increased total levels of FN transcripts that preferentially include both the EIIIA and EIIIB segments. However, despite inducing increased total FN mRNA, balloon injury does not alter the relative composition of V120+, V95+, AND V0 spliced forms. In situ hybridization reveals that as early as 4 days after injury medial cells express increased total FN mRNA, and by 7 days substantial neointimal and focal medial synthesis of EIIIA+, EIIIB+, and V120+ FNs occurs; macrophages do not significantly contribute to this observed vascular FN synthesis. Consistent with the mRNA data, immunofluorescence microscopic analysis reveals increased deposition of EIIIB+ and V+ FN protein forms in injured arterial walls, particularly within the neointima. Our results suggest that local synthesis of specific FN isoforms is important to the neointimal formation that ensues after balloon injury.
Proteases from human neutrophils can generate angiotensin II directly from angiotensin I or angiotensinogen. We examined whether neutrophil protease also influences angiotensin formation by activating human prorenin (also called inactive renin). When incubated with partially purified plasma and amniotic prorenin, sonicates from 10 6 neutrophils resulted in 120 ± 30% and 1,240 ± 290% increase in renin activity, respectively. The pH optimum of neutrophil prorenin-activating enzyme(s) is 6.5-7.0, and the activity of the enzyme(s) is inhibited by a mixture of serine protease inhibitors but not by inhibitors of other proteases, suggesting that prorenin-activating enzyme(s) is a neutral serine pro-tease^). Stimulation of neutrophils by f-met-leu-phe in the presence of cytochalasin B resulted in release of prorenin-activating enzyme(s) in a dose-dependent fashion. We attempted to isolate prorenin-activating enzyme(s) from neutrophil granules using aprotinin-affinity and carboxymethyl cellulose chromatographies. Prorenin-activating enzyme(s) coeluted with cathepsin G and elastase activities. Prorenin activation was greatly inhibited by anticathepsin G antiserum. Purified cathepsin G activated prorenin in a dose-dependent fashion. Elastase probably also contributes to prorenin activation since purified elastase also activated human prorenin. We speculate that this neutrophilic angiotensin-generating system may play a role in the local generation and concentration of angiotensins by influencing multiple steps of the renin-angiotensin system. (Circulation Research 1987;60:595-601)
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