Ask1 regulates murine platelet granule secretion, thromboxane A2 generation, and thrombus formation

Blood. 2017 Mar 2;129(9):1197-1209. doi: 10.1182/blood-2016-07-729780. Epub 2016 Dec 27.

Abstract

Mitogen-activated protein kinases (MAPKs) are expressed in platelets and are activated downstream of physiological agonists. Pharmacological and genetic evidence indicate that MAPKs play a significant role in hemostasis and thrombosis, but it is not well understood how MAPKs are activated upon platelet stimulation. Here, we show that apoptosis signal-regulating kinase 1 (ASK1), a member of the MAP3K family, is expressed in both human and murine platelets. ASK1 is rapidly and robustly activated upon platelet stimulation by physiological agonists. Disruption of Ask1 (Ask1-/- ) resulted in a marked functional defect in platelets. Ask1-/- platelets showed an impaired agonist-induced integrin αIIbβ3 activation and platelet aggregation. Although there was no difference in Ca2+ rise, platelet granule secretion and thromboxane A2 (TxA2) generation were significantly attenuated in Ask1-/- platelets. The defective granule secretion observed in Ask1-/- platelets was a consequence of impaired TxA2 generation. Biochemical studies showed that platelet agonists failed to activate p38 MAPK in Ask1-/- platelets. On the contrary, activation of c-Jun N-terminal kinases and extracellular signal-regulated kinase 1/2 MAPKs was augmented in Ask1-/- platelets. The defect in p38 MAPK results in failed phosphorylation of cPLA2 in Ask1-/- platelets and impaired platelet aggregate formation under flow. The absence of Ask1 renders mice defective in hemostasis as assessed by prolonged tail-bleeding times. Deletion of Ask1 also reduces thrombosis as assessed by delayed vessel occlusion of carotid artery after FeCl3-induced injury and protects against collagen/epinephrine-induced pulmonary thromboembolism. These results suggest that the platelet Ask1 plays an important role in regulation of hemostasis and thrombosis.

MeSH terms

  • Animals
  • Blood Coagulation / physiology*
  • Blood Platelets / metabolism*
  • Cytoplasmic Granules / metabolism
  • Female
  • Flow Cytometry
  • Humans
  • Immunoblotting
  • MAP Kinase Kinase Kinase 5 / metabolism*
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Platelet Activation / physiology*
  • Thromboxane A2 / biosynthesis*

Substances

  • Thromboxane A2
  • MAP Kinase Kinase Kinase 5
  • Map3k5 protein, mouse