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


OBJECTIVE
Platelet dysfunction in horses with this second thrombasthenia results from a secretory defect.


METHODS
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
Defects in fibrinogen binding, granule secretion, and signal transduction are unique to this thrombasthenia, which we designate as atypical equine thrombasthenia.
5A60 Johns Hopkins Asthma and Allergy Center, Johns Hopkins Medical Institute - Sidney Kimmel Comprehensive Cancer Center, Baltimore, MD.
J W
JW
Norris
Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA.
M
M
Pombo
Hunters Glen Veterinary Hospital, Inc., Veterinary Acupuncture Services of Tulsa LLC, Tulsa, OK.
E
E
Shirley
19463 James Monroe HWY, Leesburg, VA.
G
G
Blevins
Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA.
F
F
Tablin
D000818:Animals; D001792:Blood Platelets / Q000502:physiology*; D015153:Blotting, Western; D016022:Case-Control Studies; D005165:Factor V / Q000032:analysis*; D005340:Fibrinogen / Q000502:physiology; D006734:Horse Diseases / Q000097:blood / Q000503:physiopathology*; D006736:Horses; D051057:Proto-Oncogene Proteins c-akt / Q000097:blood* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013915:Thrombasthenia / Q000097:blood / Q000503:physiopathology / Q000662:veterinary*
D005165:Factor V; D005340:Fibrinogen; D051057:Proto-Oncogene Proteins c-akt
AKT; Bleeding Diathesis; Factor V; Horse