title: C1q induces a rapid up-regulation of P-selectin and modulates collagen- and collagen-related peptide-triggered activation in human platelets.
abstract: Blood platelets are emerging as important immunomodulatory cells, but complement interaction with platelets is not well understood. Several platelet structures have been described as complement protein 1q (C1q) binding receptors, such as C1qRp/CD93 and gC1qR. However, there are conflicting results whether these receptors are C1q binding structures, or even at all expressed on the cell surface. Recently, the collagen-binding integrin αIIβI was reported to bind C1q on mast cells, and this receptor is also present on platelets. The aim of this study was to further characterize the effects of C1q on platelets, by quantifying the platelet surface expression of P-selectin (CD62P) and monitoring the formation of platelet-neutrophil aggregates. Using flow cytometry, we found that C1q dose-dependently triggered a rapid but moderate and transient up-regulation of P-selectin already within 5s of C1q exposure. Pre-incubation with an antibody directed against gC1qR significantly inhibited (with 57% compared to control) the up-regulation, whereas an antibody towards the αIIβI-integrin showed no effect. Stimulation with C1q did not change the cytosolic calcium-levels, as measured with the fluorescent ratiometric probe Fura-2, however, a protein kinase C inhibitor (GF109203x) blocked the C1q-induced P-selectin expression. Furthermore, pre-incubation of platelets with C1q diminished both the collagen as well as the collagen-related peptide-induced up-regulation of P-selectin, most evident after 90s of stimulation. This indicates that C1q may regulate platelet activation via the GPVI receptor, which is a novel finding. Moreover, C1q antagonized the collagen-induced formation of platelet-neutrophil aggregates, indicating a reduced interaction between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1(PSGL-1/CD162). In summary, C1q induces a moderate rapid platelet P-selectin expression, modulates subsequent collagen and collagen-related peptide stimulation of platelets, and inhibits the formation of platelet-neutrophil aggregates. These immuno-regulatory effects of C1q may have a crucial role in innate immunity and inflammation.
authors.affiliation: Division of Drug Research, Department of Medical and Health Sciences, Linköping University, SE-58185 Linköping, Sweden. caroline.skoglund@liu.se
authors.forename: Caroline
authors.initials: C
authors.lastname: Skoglund
authors.forename: Jonas
authors.initials: J
authors.lastname: Wetterö
authors.forename: Pentti
authors.initials: P
authors.lastname: Tengvall
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Bengtsson
mesh_terms: D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D001792:Blood Platelets / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology*; D002448:Cell Adhesion / Q000187:drug effects; D002478:Cells, Cultured; D003094:Collagen / Q000494:pharmacology*; D015922:Complement C1q / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006801:Humans; D038982:Integrin alpha2beta1 / Q000276:immunology / Q000378:metabolism; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects; D019007:P-Selectin / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology*; D015539:Platelet Activation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D011951:Receptors, Complement / Q000276:immunology / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D000906:Antibodies; D002352:Carrier Proteins; D038982:Integrin alpha2beta1; D008562:Membrane Glycoproteins; D019007:P-Selectin; D010455:Peptides; D011951:Receptors, Complement; C435908:collagen-related peptide; C032402:complement 1q receptor; D015922:Complement C1q; D003094:Collagen; D011493:Protein Kinase C; D002118:Calcium