Association of Factor V Secretion with Protein Kinase B Signaling in Platelets from Horses with Atypical Equine Thrombasthenia

J Vet Intern Med. 2015 Sep-Oct;29(5):1387-94. doi: 10.1111/jvim.13595. Epub 2015 Aug 19.

Abstract

Background: Two congenital bleeding diatheses have been identified in Thoroughbred horses: Glanzmann thrombasthenia (GT) and a second, novel diathesis associated with abnormal platelet function in response to collagen and thrombin stimulation.

Hypothesis/objectives: Platelet dysfunction in horses with this second thrombasthenia results from a secretory defect.

Animals: Two affected and 6 clinically normal horses.

Methods: Ex vivo study. Washed platelets were examined for (1) expression of the αIIb-β3 integrin; (2) fibrinogen binding capacity in response to ADP and thrombin; (3) secretion of dense and α-granules; (4) activation of the mammalian target of rapamycin (mTOR)-protein kinase B (AKT) signaling pathway; and (5) cellular distribution of phosphatidylinositol-4-phosphate-3-kinase, class 2B (PIK3C2B) and SH2 containing inositol-5'-phosphatase 1 (SHIP1).

Results: Platelets from affected horses expressed normal amounts of αIIb-β3 integrin and bound fibrinogen normally in response to ADP, but bound 80% less fibrinogen in response to thrombin. α-granules only released 50% as much Factor V as control platelets, but dense granules released their contents normally. Protein kinase B (AKT) phosphorylation was reduced after thrombin activation, but mTOR Complex 2 (mTORC2) and phosphoinositide-dependent kinase 1 (PDK1) signaling were normal. SH2-containing inositol-5'-phosphatase 1 (SHIP1) did not localize to the cytoskeleton of affected platelets and was decreased overall consistent with reduced AKT phosphorylation.

Conclusions and clinical significance: Defects in fibrinogen binding, granule secretion, and signal transduction are unique to this thrombasthenia, which we designate as atypical equine thrombasthenia.

Keywords: AKT; Bleeding Diathesis; Factor V; Horse.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Platelets / physiology*
  • Blotting, Western
  • Case-Control Studies
  • Factor V / analysis*
  • Fibrinogen / physiology
  • Horse Diseases / blood
  • Horse Diseases / physiopathology*
  • Horses
  • Proto-Oncogene Proteins c-akt / blood*
  • Proto-Oncogene Proteins c-akt / physiology
  • Signal Transduction / physiology
  • Thrombasthenia / blood
  • Thrombasthenia / physiopathology
  • Thrombasthenia / veterinary*

Substances

  • Factor V
  • Fibrinogen
  • Proto-Oncogene Proteins c-akt