Co‐ordination between localized wound‐induced Ca²⁺ signals and pre‐wound serum signals is required for proliferation after mechanical injury

Abstract

The signals which initiate proliferation of endothelial cells after injury are important for selective blood vessel growth during wound healing or tumour growth. Upon mechanically wounding quiescent cells, a transient [Ca2+]i increase was induced in cells at the wound edge. These same cells proliferated 18-24 h post wounding, as measured by bromodeoxyuridine incorporation. The localized Ca2+ signal was required specifically during wounding since blocking Ca2+ influx reduced proliferation by 40-50%. Proliferation also required serum since starvation reduced proliferation by 80%. Serum-starved cells proliferated if briefly primed with serum prior to wounding. The signals derived from serum and [Ca2+]i combined at least additively to induce proliferation. Therefore, serum priming followed by a single, transient Ca2+ signal induced by mechanical injury must occur in a temporally and spatially regulated manner for normal proliferation. Co-ordination between signalling cascades induced by growth factors and release from contact inhibition might be obligatory for localized re-endothelialization after injury.

Ca2+ Signalling in Damaged Endothelium: Do Connexin Hemichannels Aid in Filling the Gap?

“…Importantly, they showed that ECs located within the first row, which are primarily involved in the regeneration process, manifested a minor Ca 2+ transient in absence of extracellular Ca 2+ [20]. Injury-induced Ca 2+ inflow was in turn the main trigger of ECs motility and proliferation during the subsequent wound repair [19][20], as demonstrated by the higher mitotic rate at the lesion edge [19]. Spreading of the Ca 2+ signal through adjoining CPAE required the release of an identified soluble factor from ruptured cells, while it did not involve the direct transfer of the Ca 2+ wave through gap junctions [35].…”

“…The involvement of intracellular Ca 2+ signals in endothelial regeneration was postulated based on the increasing evidence that such an ion could control cellular proliferation and motility [73]. Subsequent investigations demonstrated that, in calf pulmonary artery ECs (CPAE), relatively gross de-endothelization elicited an increase in [Ca 2+ ] i [35], which was in turn responsible for proliferation and migration into the denuded area of the cells adjacent to the lesion site [19][20][21]. Quite notably, there were no further reports of Ca 2+ signals in injured endothelium until a few years ago, when two separate groups described the Ca 2+ response in rat aortic ECs [33] and human umbilical vein ECs (HUVECs) [22].…”

“…Despite its recognized role in controlling endothelial repair, the molecular machinery underpinning injuryinduced Ca 2+ signalling in vascular ECs is still poorly understood. Such uncertainty arose from the employment of endothelial monolayers in vitro to study the Ca 2+ signals elicited by mechanical denudation [19][20][21][22]34]. Indeed, cultured ECs have been shown to express a different blend of ion channels, receptors and transporters as compared to in situ ECs [40,41].…”

“…It has long been known that endothelial proliferation and migration are tightly regulated by an increase in intracellular Ca 2+ concentration ([Ca 2+ ] i ) [3,20,22,[24][25][26][27][28][29][30][31][32]. Consistent with a role in wound repair, endothelial scraping may induce an elevation in [Ca 2+ ] i in nearby survivors, which has been associated to the subsequent covering of the lesioned area [19][20][21][22][33][34][35]. As a further support that subcellular Ca 2+ signals may drive the regeneration process, injury-induced Ca 2+ waves have been observed in several cell types, such as rat alveolar type II cells [36], human urothelial cells [37], human corneal epithelial cells [38], and polarized hepatic cells [39].…”

“…Endothelial regeneration requires spreading, migration and proliferation of mature ECs adjacent to the lesion site and release from contact inhibition [18][19][20][21][22]. According to such a model, stimulated ECs move into the lesion site from the wound edge and re-seal the inner vessel wall, thus dampening or even stopping neointima hyperplasia in the lesioned arterial segment [9][10].…”