Dp. Witte et al., PLATELET ACTIVATION RELEASES MEGAKARYOCYTE-SYNTHESIZED APOLIPOPROTEIN-J, A HIGHLY ABUNDANT PROTEIN IN ATHEROMATOUS LESIONS, The American journal of pathology, 143(3), 1993, pp. 763-773
Apolipoprotein J (apoJ) is an abundant glycoprotein in many biological
fluids, and its constitutive high level synthesis is characteristic o
f many epithelial cells exposed to harsh fluids such as urine, bile, a
nd gastric secretions. In addition, dramatic induction of apoj occurs
in cells surrounding several kinds of pathological lesions. Because pl
atelets and circulating inflammatory cells represent critical elements
in numerous pathological processes, we evaluated bone marrow cells fo
r the presence of apoj. Based upon messenger RNA in situ hybridization
and immunofluorescent protein detection, high-level apoJ gene express
ion and protein accumulation occurred exclusively in mature megakaryoc
ytes. Our results indicate that apoj is stored in platelet granules an
d is released into extracellular fluid following platelet activation.
Because atheromatous plaque development involves platelet aggregation
and activation, we looked for and found abundant apoJ protein in advan
ced human atheromatous lesions. Thus, platelet sequestration and activ
ation may lead to the rapid deployment of apoj into sites of vascular
injury. We hypothesize that platelet-derived apoJ participates in both
short-term wound repair processes and chronic pathogenic processes at
vascular interfaces.