Limits...
Intercellular calcium communication regulates platelet aggregation and thrombus growth.

Nesbitt WS, Giuliano S, Kulkarni S, Dopheide SM, Harper IS, Jackson SP - J. Cell Biol. (2003)

Bottom Line: In this study, we have examined the mechanisms regulating cytosolic calcium flux during the development of platelet-platelet adhesion contacts under the influence of flow.We demonstrate that ICC is primarily mediated by a signaling mechanism operating between integrin alpha IIb beta 3 and the recently cloned ADP purinergic receptor P2Y12.Furthermore, we demonstrate that the efficiency by which calcium signals are propagated within platelet aggregates plays an important role in dictating the rate and extent of thrombus growth.

View Article: PubMed Central - PubMed

Affiliation: Australian Centre for Blood Diseases, Department of Medicine, Monash University, Box Hill Hospital, Victoria 3128, Australia.

ABSTRACT
The ability of platelets to form stable adhesion contacts with other activated platelets (platelet cohesion or aggregation) at sites of vascular injury is essential for hemostasis and thrombosis. In this study, we have examined the mechanisms regulating cytosolic calcium flux during the development of platelet-platelet adhesion contacts under the influence of flow. An examination of platelet calcium flux during platelet aggregate formation in vitro demonstrated a key role for intercellular calcium communication (ICC) in regulating the recruitment of translocating platelets into developing aggregates. We demonstrate that ICC is primarily mediated by a signaling mechanism operating between integrin alpha IIb beta 3 and the recently cloned ADP purinergic receptor P2Y12. Furthermore, we demonstrate that the efficiency by which calcium signals are propagated within platelet aggregates plays an important role in dictating the rate and extent of thrombus growth.

Show MeSH

Related in: MedlinePlus

Proposed model of ICC and aggregation. (i) Primary adhesion. Initial outside-in signaling events mediated by GPIb/V/IX engagement of surface-immobilized vWf triggers the initiation of an elementary calcium event. Subsequent integrin αIIbβ3 engagement of the matrix initiates elevated and oscillatory calcium flux, driving further rounds of integrin activation and stationary adhesion at the vWf surface (Nesbitt et al., 2002). (ii) Platelet–platelet tethering. Platelets within the bulk flow interact with a primary adherent platelet via GPIb/V/IX binding to surface-expressed vWf. The nucleating (adherent) platelet presents a surface bearing active integrin αIIbβ3 and locally secretes ADP. (iii) Aggregation. Integrin αIIbβ3 engagement of platelet-expressed vWf and/or fibrinogen triggers further ADP release and stimulates platelet calcium signaling events throughout the local platelet population. ADP engagement of P2Y12 potentiates integrin αIIbβ3 activation and calcium signaling, thereby promoting platelet aggregation in the shear field. Ca2+, free cytosolic calcium; GP Ib/V/IX, glycoprotein Ib/V/IX vWF adhesion receptor; +, integrin activation.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172771&req=5

fig7: Proposed model of ICC and aggregation. (i) Primary adhesion. Initial outside-in signaling events mediated by GPIb/V/IX engagement of surface-immobilized vWf triggers the initiation of an elementary calcium event. Subsequent integrin αIIbβ3 engagement of the matrix initiates elevated and oscillatory calcium flux, driving further rounds of integrin activation and stationary adhesion at the vWf surface (Nesbitt et al., 2002). (ii) Platelet–platelet tethering. Platelets within the bulk flow interact with a primary adherent platelet via GPIb/V/IX binding to surface-expressed vWf. The nucleating (adherent) platelet presents a surface bearing active integrin αIIbβ3 and locally secretes ADP. (iii) Aggregation. Integrin αIIbβ3 engagement of platelet-expressed vWf and/or fibrinogen triggers further ADP release and stimulates platelet calcium signaling events throughout the local platelet population. ADP engagement of P2Y12 potentiates integrin αIIbβ3 activation and calcium signaling, thereby promoting platelet aggregation in the shear field. Ca2+, free cytosolic calcium; GP Ib/V/IX, glycoprotein Ib/V/IX vWF adhesion receptor; +, integrin activation.

Mentions: Our current working model to explain the synergy between ADP and integrin αIIbβ3 during platelet aggregate formation is described in Fig. 7. We propose that initial primary adhesion to immobilized vWf is dependent on a cooperative signaling mechanism operating between GPIb and integrin αIIbβ3, in which integrin αIIbβ3–derived signals sustain calcium oscillations and mediate stable adhesion (Nesbitt et al., 2002). This initial adhesion and calcium signaling can occur independent of soluble agonist stimulation (Yap et al., 2000; Nesbitt et al., 2002), although, as demonstrated here, it is greatly potentiated by such stimuli. In contrast to primary adhesion, our studies suggest that GPIb and integrin αIIbβ3 calcium signaling is insufficient to drive sustained calcium flux in subsequent layers of aggregating platelets, despite the fact that both receptors must engage platelet-expressed vWf for effective platelet aggregation under high shear flow conditions. The reason for this difference between primary adhesion and aggregating cells is not clear but may relate to a difference in the number of GPIb and integrin αIIbβ3 adhesive bonds. For example, under the experimental conditions employed in this study, primary adherent platelets are exposed to a purified vWf substrate, providing a relatively high concentration of binding sites for GPIb and integrin αIIbβ3. In aggregating platelets, the number of bonds formed between platelet-bound vWf, GPIb, and integrin αIIbβ3 may be limiting, thereby reducing platelet activation signals downstream of these receptors and explaining the requirement for soluble ADP.


Intercellular calcium communication regulates platelet aggregation and thrombus growth.

Nesbitt WS, Giuliano S, Kulkarni S, Dopheide SM, Harper IS, Jackson SP - J. Cell Biol. (2003)

Proposed model of ICC and aggregation. (i) Primary adhesion. Initial outside-in signaling events mediated by GPIb/V/IX engagement of surface-immobilized vWf triggers the initiation of an elementary calcium event. Subsequent integrin αIIbβ3 engagement of the matrix initiates elevated and oscillatory calcium flux, driving further rounds of integrin activation and stationary adhesion at the vWf surface (Nesbitt et al., 2002). (ii) Platelet–platelet tethering. Platelets within the bulk flow interact with a primary adherent platelet via GPIb/V/IX binding to surface-expressed vWf. The nucleating (adherent) platelet presents a surface bearing active integrin αIIbβ3 and locally secretes ADP. (iii) Aggregation. Integrin αIIbβ3 engagement of platelet-expressed vWf and/or fibrinogen triggers further ADP release and stimulates platelet calcium signaling events throughout the local platelet population. ADP engagement of P2Y12 potentiates integrin αIIbβ3 activation and calcium signaling, thereby promoting platelet aggregation in the shear field. Ca2+, free cytosolic calcium; GP Ib/V/IX, glycoprotein Ib/V/IX vWF adhesion receptor; +, integrin activation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172771&req=5

fig7: Proposed model of ICC and aggregation. (i) Primary adhesion. Initial outside-in signaling events mediated by GPIb/V/IX engagement of surface-immobilized vWf triggers the initiation of an elementary calcium event. Subsequent integrin αIIbβ3 engagement of the matrix initiates elevated and oscillatory calcium flux, driving further rounds of integrin activation and stationary adhesion at the vWf surface (Nesbitt et al., 2002). (ii) Platelet–platelet tethering. Platelets within the bulk flow interact with a primary adherent platelet via GPIb/V/IX binding to surface-expressed vWf. The nucleating (adherent) platelet presents a surface bearing active integrin αIIbβ3 and locally secretes ADP. (iii) Aggregation. Integrin αIIbβ3 engagement of platelet-expressed vWf and/or fibrinogen triggers further ADP release and stimulates platelet calcium signaling events throughout the local platelet population. ADP engagement of P2Y12 potentiates integrin αIIbβ3 activation and calcium signaling, thereby promoting platelet aggregation in the shear field. Ca2+, free cytosolic calcium; GP Ib/V/IX, glycoprotein Ib/V/IX vWF adhesion receptor; +, integrin activation.
Mentions: Our current working model to explain the synergy between ADP and integrin αIIbβ3 during platelet aggregate formation is described in Fig. 7. We propose that initial primary adhesion to immobilized vWf is dependent on a cooperative signaling mechanism operating between GPIb and integrin αIIbβ3, in which integrin αIIbβ3–derived signals sustain calcium oscillations and mediate stable adhesion (Nesbitt et al., 2002). This initial adhesion and calcium signaling can occur independent of soluble agonist stimulation (Yap et al., 2000; Nesbitt et al., 2002), although, as demonstrated here, it is greatly potentiated by such stimuli. In contrast to primary adhesion, our studies suggest that GPIb and integrin αIIbβ3 calcium signaling is insufficient to drive sustained calcium flux in subsequent layers of aggregating platelets, despite the fact that both receptors must engage platelet-expressed vWf for effective platelet aggregation under high shear flow conditions. The reason for this difference between primary adhesion and aggregating cells is not clear but may relate to a difference in the number of GPIb and integrin αIIbβ3 adhesive bonds. For example, under the experimental conditions employed in this study, primary adherent platelets are exposed to a purified vWf substrate, providing a relatively high concentration of binding sites for GPIb and integrin αIIbβ3. In aggregating platelets, the number of bonds formed between platelet-bound vWf, GPIb, and integrin αIIbβ3 may be limiting, thereby reducing platelet activation signals downstream of these receptors and explaining the requirement for soluble ADP.

Bottom Line: In this study, we have examined the mechanisms regulating cytosolic calcium flux during the development of platelet-platelet adhesion contacts under the influence of flow.We demonstrate that ICC is primarily mediated by a signaling mechanism operating between integrin alpha IIb beta 3 and the recently cloned ADP purinergic receptor P2Y12.Furthermore, we demonstrate that the efficiency by which calcium signals are propagated within platelet aggregates plays an important role in dictating the rate and extent of thrombus growth.

View Article: PubMed Central - PubMed

Affiliation: Australian Centre for Blood Diseases, Department of Medicine, Monash University, Box Hill Hospital, Victoria 3128, Australia.

ABSTRACT
The ability of platelets to form stable adhesion contacts with other activated platelets (platelet cohesion or aggregation) at sites of vascular injury is essential for hemostasis and thrombosis. In this study, we have examined the mechanisms regulating cytosolic calcium flux during the development of platelet-platelet adhesion contacts under the influence of flow. An examination of platelet calcium flux during platelet aggregate formation in vitro demonstrated a key role for intercellular calcium communication (ICC) in regulating the recruitment of translocating platelets into developing aggregates. We demonstrate that ICC is primarily mediated by a signaling mechanism operating between integrin alpha IIb beta 3 and the recently cloned ADP purinergic receptor P2Y12. Furthermore, we demonstrate that the efficiency by which calcium signals are propagated within platelet aggregates plays an important role in dictating the rate and extent of thrombus growth.

Show MeSH
Related in: MedlinePlus