Prostacyclin (PGI2) controls platelet activation and
thrombosis through a cyclic
adenosine monophosphate (cAMP) signaling cascade. However, in patients with
cardiovascular diseases this protective mechanism fails for reasons that are unclear. Using both pharmacological and genetic approaches we describe a mechanism by which oxidized
low density lipoproteins (
oxLDL) associated with
dyslipidemia promote platelet activation through impaired PGI2 sensitivity and diminished cAMP signaling. In functional assays using human platelets,
oxLDL modulated the inhibitory effects of PGI2, but not a
phosphodiesterase (PDE)-insensitive cAMP analog, on platelet aggregation, granule secretion and in vitro
thrombosis. Examination of the mechanism revealed that
oxLDL promoted the hydrolysis of cAMP through the phosphorylation and activation of PDE3A, leading to diminished cAMP signaling. PDE3A activation by
oxLDL required
Src family kinases, Syk and
protein kinase C. The effects of
oxLDL on platelet function and cAMP signaling were blocked by pharmacological inhibition of CD36, mimicked by CD36-specific oxidized
phospholipids and ablated in CD36-/- murine platelets. The injection of
oxLDL into wild-type mice strongly promoted FeCl3-induced
carotid thrombosis in vivo, which was prevented by pharmacological inhibition of PDE3A. Furthermore, blood from dyslipidemic mice was associated with increased oxidative
lipid stress, reduced platelet sensitivity to PGI2 ex vivo and diminished PKA signaling. In contrast, platelet sensitivity to a PDE-resistant cAMP analog remained normal. Genetic deletion of CD36 protected dyslipidemic animals from PGI2 hyposensitivity and restored PKA signaling. These data suggest that CD36 can translate atherogenic
lipid stress into platelet hyperactivity through modulation of inhibitory cAMP signaling.