Related Experiment Video
Updated: May 24, 2026
An In Vitro Assay to Study Platelet Migration Using RGD-Functionalized Avidin-Biotin Tethers
Published on: November 8, 2024
Platelet activation by Streptococcus sanguinis is accompanied by MAP kinase phosphorylation
Ahmed Y Abdulrehman1, Elke C G Jackson, Archibald McNicol
1Departments of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada.
Abstract:
There is increasing interest in the role of infections in atherothrombotic conditions. In particular, bacteria, notably those of oral origin, have been shown to activate platelets using a variety of mechanisms. Previous studies have shown that S. sanguinis strain 2017-78 induces platelet aggregation which requires the presence of both vWF and IgG. This aggregation is accompanied by the consecutive phosphorylation/desphosphorylation/rephosphorylation of several signalling proteins. The first two phases are thromboxane-dependent whereas the rephosphorylation phase is mediated by engagement of the αIIbβ3 integrin. Here signalling events, specifically the potential role of MAP kinases, associated with S. sanguinis strain 2017-78-induced platelet activation have been further examined using an immunoblotting approach. The addition of S. sanguinis strain 2017-78 caused a similar triphasic phosphorylation profile of the platelet MAP kinase Erk2 to that seen with other phosphoproteins. Pretreatment with aspirin or RGDS did not affect 2017-78-induced Erk2 phosphorylation or desphosphorylation but both inhibited the rephosphorylation phase. In contrast the level of 2017-78-induced platelet MAP kinase p38 phosphorylation remained at an elevated level, and this was unaffected by aspirin. Similarly, 2017-78-induced cPLA(2) phosphorylation remained above basal levels during the aggregation process. The p38 inhibitor SB203580 inhibited S. sanguinis-induced aggregation with no effect on the phosphorylation of either p38 or cPLA(2). Thus the current study demonstrates the activation of both the Erk2 and p38 forms of MAP kinases, and of cPLA(2), in platelets stimulated with S. sanguinis strain 2017-78, and is consistent with a role for Erk2, but not for p38, in the cPLA(2) phosphorylation in response to S. sanguinis.
Insights
Oral bacteria like S. sanguinis activate platelets, triggering signaling pathways. This study reveals Erk2 MAP kinase involvement in S. sanguinis-induced platelet aggregation and phosphorylation, distinct from p38 MAP kinase.
Area of Science:
- Biochemistry
- Immunology
- Microbiology
Background:
- Infections, particularly oral bacteria, are increasingly linked to atherothrombotic conditions.
- Streptococcus sanguinis (S. sanguinis) strain 2017-78 is known to induce platelet aggregation.
- Platelet activation by S. sanguinis involves complex signaling, including protein phosphorylation and dependence on von Willebrand factor (vWF) and immunoglobulin G (IgG).
Purpose of the Study:
- To investigate the specific role of mitogen-activated protein (MAP) kinases in S. sanguinis strain 2017-78-induced platelet activation.
- To elucidate the signaling pathways downstream of S. sanguinis interaction with platelets, focusing on Erk2 and p38 MAP kinases and cPLA(2).
Main Methods:
- Immunoblotting was employed to analyze the phosphorylation status of MAP kinases (Erk2, p38) and cPLA(2) in platelets stimulated with S. sanguinis strain 2017-78.
- Platelets were pretreated with aspirin or RGDS peptide to assess their effects on signaling events.
- The p38 inhibitor SB203580 was used to evaluate the role of p38 in aggregation and phosphorylation.
Main Results:
- S. sanguinis strain 2017-78 induced a triphasic phosphorylation pattern of Erk2, similar to other signaling proteins, with rephosphorylation dependent on αIIbβ3 integrin engagement.
- Aspirin and RGDS inhibited the Erk2 rephosphorylation phase but not initial phosphorylation or dephosphorylation.
- p38 MAP kinase and cPLA(2) phosphorylation remained elevated upon S. sanguinis stimulation, unaffected by aspirin; however, the p38 inhibitor SB203580 inhibited aggregation without altering p38 or cPLA(2) phosphorylation.
Conclusions:
- The study confirms the activation of Erk2 and p38 MAP kinases, and cPLA(2) in platelets stimulated by S. sanguinis strain 2017-78.
- Erk2 appears to play a role in the cPLA(2) phosphorylation cascade during S. sanguinis-induced platelet activation.
- p38 MAP kinase is involved in S. sanguinis-induced platelet aggregation but not directly in the phosphorylation of p38 or cPLA(2).
Related Concept Videos
01:22Formation of the Platelet Plug
As the injured blood vessel contracts, endothelial cells undergo contraction, revealing collagen fibers in the basement membrane and underlying connective tissue. Furthermore, the plasma membrane of endothelial cells becomes adhesive, preparing the site for platelet adhesion. Platelets...
01:07MAPK Signaling Cascades
01:20Extrinsic and Intrinsic Pathways of Hemostasis
The Extrinsic Pathway
The extrinsic pathway of coagulation is typically initiated by tissue damage that exposes blood to tissue factor (TF), a protein released by the damaged tissue cells outside the blood vessels—this interaction with TF triggers biochemical reactions involving specific clotting factors. The key player here is Factor VII, which forms a...
01:18Structure and Function of Platelets
Platelets are continually replenished, circulating in the bloodstream for 9-12 days before being removed by phagocytes, primarily in the spleen. A microliter of circulating blood contains between 150,000 and 450,000 platelets, with...
01:20The JAK-STAT Signaling Pathway
01:17Intracellular Signaling Affects Focal Adhesions
Some...