Mouse transient receptor potential channel type 6 selectively regulates agonist-induced platelet function

Abstract

While changes in intracellular calcium levels is a central step in platelet activation and thrombus formation, the contribution and mechanism of receptor-operated calcium entry (ROCE) via transient receptor potential channels (TRPCs) in platelets remains poorly defined. In previous studies, we have shown that TRPC6 regulates hemostasis and thrombosis, in mice. In the present studies, we employed a knockout mouse model system to characterize the role of TRPC6 in ROCE and platelet activation. It was observed that the TRPC6 deletion ( Trpc6 −/− ) platelets displayed impaired elevation of intracellular calcium, i.e., defective ROCE. Moreover, these platelets also exhibited defects in a host of functional responses, namely aggregation, granule secretion, and integrin αIIbβ3. Interestingly, the aforementioned defects were specific to the thromboxane receptor (TPR), as no impaired responses were observed in response to ADP or the thrombin receptor-activating peptide 4 (TRAP4). The defect in ROCE in the Trpc6 −/− was also observed with 1-oleoyl-2-acetyl-sn-glycerol (OAG). Finally, our studies also revealed that TRPC6 regulates clot retraction. Taken together, our findings demonstrate that TRPC6 directly regulates TPR-dependent ROCE and platelet function. Thus, TRPC6 may serve as a novel target for the therapeutic management of thrombotic diseases.

Trpc6 gain-of-function disease mutation enhances phosphatidylserine exposure in murine platelets

“…Previous studies report that Trpc6 deficiency does not affect these responses to various stimuli, including ADP and thrombin, though there is disagreement as to whether thromboxane A2 receptor agonist response is blunted. [17, 20] The effect of Trpc6 genotype on integrin αIIbβ3 activation and P-selectin surface expression was assessed by flow cytometry (Fig 3A-B). In line with the lack of effect on ADP and U46619 induced calcium transients (Fig 2), Trpc6 genotype did not affect αIIbβ3 activation or P-selectin surface expression in response to these stimuli (Fig 3A-B).…”

“…These results are consistent with prior studies reporting that loss of Trpc6 does not influence these aspects of platelet activation. [17, 20] However, stimulating TRPC6 using GSK does augment the modest platelet activation induced by ADP. This suggests that as yet unidentified physiological activators of TRPC6 could enhance platelet activation synergistically with other weak platelet agonsists.…”

Mechanisms Underlying Dichotomous Procoagulant COAT Platelet Generation—A Conceptual Review Summarizing Current Knowledge

“…Two depletion-independent mechanisms (ROCE) mobilize Ca 2+ to form the primary wave of Ca 2+ with the Ca 2+ released from internal storages. DAG-mediated entry of extracellular Ca 2+ is operated through the transient receptor potential cation channel subfamily C member 6 (TRPC6) opening [ 97 , 98 ]. TRPC6 is an unselective Ca 2+ -permeable cation channel, which also imports Na + during platelet activation [ 43 ].…”

Novel Mechanistic Insights and Potential Therapeutic Impact of TRPC6 in Neurovascular Coupling and Ischemic Stroke

“…Thus, this agent may have the potential to modulate platelet function before or after ischemic stroke. There is some evidence indicating that TRPC6 plays a critical role in platelet function via receptor-operated calcium (ROC) [ 119 , 120 ] or store-operated calcium (SOC) entry [ 121 ]. On the contrary, one report suggests Ca 2+ influx via TRPC6 may not have functional relevance in platelet hemostasis [ 122 ].…”