Blood, 15 March 2003, Vol. 101, No. 6, pp. 2078-2078
Platelet message and microarrays
Platelets are anucleate, and until the late 1980s it was
thought that circulating platelets have little residual RNA message. But in 1988 Newman et al (J Clin Invest. 1988;82:739-743) showed that one can use RT-PCR to amplify platelet-specific messages from
purified peripheral blood platelets. Since then, numerous laboratories
have taken advantage of this observation to clone and identify
mutations and determine relative levels of platelet-specific messages.
In time, it has been assumed that platelets are actually a rich source
of platelet message. With the more recent development of
microarrays and related approaches for widespread transcript analysis, one can envision an even greater use of circulating platelet
RNA. One might expect to more fully define the genes representative of
late megakaryocyte development. Perhaps these approaches would define
gene products whose expression levels correlate with an increased risk
of thrombotic or other clinical states.
The manuscript by Gnatenko and colleagues (page 2285) represents an
early use of such a strategy, and not only provides exciting new
information but also grounds expectation in reality. Platelets are not
a rich source of message. First, the vast majority of messages actually
are derived from the mitochondria. Second, even with taking extra steps
to ensure purity, the top 3 messages determined by microarray were
white cell or red cell messages. On the plus side, the study clearly
defined the relative abundance of a number of platelet-specific genes,
including the demonstration that chemokines such as PF4, PBP,
and RANTES are among the most abundant messages, pointing to the
importance of platelets in both thrombosis and inflammation. Also, 2 previously unrecognized messages for neurogranin, a protein kinase C
substrate, and clusterin, a complement lysis inhibitor, are present in
platelets. It is hoped that with further technical improvements,
additional insights and clinical usage can come from analysis
of this ready source of megakaryocyte/platelet message.
Mortimer Poncz
Children's Hospital of
Philadelphia
