Mildly oxidized low density lipoprotein rapidly stimulates via activation of the lysophosphatidic acid receptor Src family and Syk tyrosine kinases and Ca2+ influx in human platelets

In contrast to native low density lipoprotein (LDL), mildly oxidized LDL (mox-LDL) induced platelet shape change and stimulated during shape change the tyrosine phosphorylation of specific proteins including Syk; the translocation of Src, Fyn, and Syk to the cytoskeleton; and the increase of cytosolic Ca2+ due to mainly Ca2+ entry. The stimulation of these early signal pathways by mox-LDL was inhibited by desensitization of the lysophosphatidic acid (LPA) receptor and specific LPA receptor antagonists, was independent of the alpha(IIb)beta(3)-integrin, and was mimicked by LPA. Stimulation of tyrosine phosphorylation and Syk activation were independent of the increase of cytosolic Ca2+ and were suppressed by genistein and two specific inhibitors of the Src family tyrosine kinases, PP1 and PD173956. In contrast to PP1 and PD 173956, genistein prevented shape change by mox-LDL. The results indicate that mox-LDL, through activation of the LPA receptor, stimulates two separate early signal pathways, (a) Src family and Syk tyrosine kinases, and (b) Ca2+ entry. The activation of these early signaling pathways by mox-LDL probably plays a role in platelet responses subsequent to shape change. The inhibition of mox-LDL-induced platelet activation by LPA receptor antagonists or dietary isoflavonoids such as genistein could have implications in the prevention and therapy of cardiovascular diseases.