Thrombospondin-1 promotes hemostasis through modulation of cAMP signaling in blood platelets

Abstract

Thrombospondin-1 (TSP-1) is released by platelets upon activation and can promote platelet activation, but its role in haemostasis in vivo is unclear. We show that TSP-1 is a critical mediator of haemostasis that promotes platelet activation by modulating inhibitory cAMP signaling. Genetic deletion of TSP-1 did not affect platelet activation in vitro, but in vivo models of haemostasis and thrombosis demonstrated that TSP-1 deficient mice had prolonged bleeding, defective thrombosis and increased sensitivity to the prostacyclin mimetic iloprost. Adoptive transfer of wild type (WT), but not TSP-1-/- platelets, ameliorated the thrombotic phenotype, suggesting a key role for platelet-derived TSP-1. In functional assays, TSP-1-deficient platelets showed an increased sensitivity to cAMP signaling, inhibition of platelet aggregation and arrest under flow by PGI2. Plasma swap experiments showed that plasma TSP-1 did not correct PGI2 hypersensitivity in TSP-1-/- platelets. By contrast, incubation of TSP-1-/- platelets with releasates from WT platelets or purified TSP-1, but not releasates from TSP-1-/- platelets, reduced the inhibitory effects of PGI2. Activation of WT platelets resulted in diminished cAMP accumulation and downstream signaling, which was associated with increased activity of the cAMP hydrolyzing enzyme phosphodiesterase 3A (PDE3A). PDE3A activity and cAMP accumulation were unaffected in platelets from TSP-1-/- mice. Platelets deficient in CD36, a TSP-1 receptor, showed increased sensitivity to PGI2/cAMP signaling and diminished PDE3A activity, which was unaffected by platelet-derived or purified TSP-1. This suggests that the release of TSP-1 regulates haemostasis in vivo through modulation of platelet cAMP signaling at sites of vascular injury.

Thrombospondin-1 CD47 Signalling: From Mechanisms to Medicine

“…TSP1-mediated platelet activation is also associated with a reduced cAMP signalling in platelets and haemostasis at the site of vascular injury. A genetic deletion of TSP1 in vitro did not have any impact on platelet activation, however, in vivo studies of TSP1-null mice demonstrated prolonged bleeding and defective thrombosis [ 74 ].…”

A Novel Volume-Stable Collagen Matrix Induces Changes in the Behavior of Primary Human Oral Fibroblasts, Periodontal Ligament, and Endothelial Cells

“…In this respect, our results of strongly induced SERPINE1 gene expression in primary hPDLCs, hOFs, and HUVECs grown on native as well as TGF-β1-, PDGF-BB- or FGF-2-coated vCMs strongly support the favorable effect of vCM on the regenerative process. The three growth factors TGF-β1, PDGF-BB, and FGF-2 as well as the investigated by us thrombospondin 1, encoded by the THBS1 gene in humans, are released by activated platelets at wounded sites [ 46 , 47 , 58 ]. All four factors are known to efficiently bind extracellular matrix proteins such as collagen [ 7 , 59 ] and thus, they may coat the vCM in situ after its placement at the defect site.…”

Thrombospondin 1 in Metabolic Diseases

“…There is evidence of TSP1 as a promoter of platelet aggregation and activation ( 58 ). Interestingly, only TSP1 released from alpha granules of activated platelets will suppress cAMP signaling and increase phosphodiesterase 3 (PDE3A) favoring hemostasis ( 59 ). CD36 seems to be required, in part, for these processes as platelet-secreted TSP1 can increase the expression of phosphatidylserine by interacting with CD36, enhancing the stabilization of the thrombus ( 60 ).…”