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

• DOI: 10.1111/jvim.13595
• Publication Date: 2015-08-20T05:12:24Z
• Authors: J.W. Norris; M. Pombo; E. Shirley; G. Blevins; F. Tablin
• Keywords: Veterinary sciences; Blood Platelets; 1.1 Normal biological development and functioning; Blotting, Western; 610; Veterinary and Food Sciences; Horse; 0403 veterinary science; Clinical Research; Underpinning research; 616; Animals; Veterinary Sciences; Horses; Agricultural; Blotting; AKT; Factor V; Fibrinogen; Hematology; 04 agricultural and veterinary sciences; Case-Control Studies; Horse Diseases; EQUID; Western; Proto-Oncogene Proteins c-akt; Bleeding Diathesis; Signal Transduction; Thrombasthenia

BackgroundTwo 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/ObjectivesPlatelet dysfunction in horses with this second thrombasthenia results from a secretory defect.AnimalsTwo affected and 6 clinically normal horses.MethodsEx 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).ResultsPlatelets 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 significanceDefects in fibrinogen binding, granule secretion, and signal transduction are unique to this thrombasthenia, which we designate as atypical equine thrombasthenia.