From www.bloodjournal.org by guest on June 18, 2017. For personal use only.
4. Faderl S, Thomas DA, O’Brien S, et al. Augmented
hyper-CVAD based on dose-intensified vincristine,
dexamethasone, and asparaginase in adult acute
lymphoblastic leukemia salvage therapy. Clin Lymph
Myeloma Leuk. 2011;11(1):54-59.
better treatment of acute lymphoblastic leukaemia. Appl
Biochem Biotechnol. 2012;167(8):2144-2159.
5. Buaboonnam J, Cao X, Pauley JL, et al. Sequential
administration of methotrexate and asparaginase in
relapsed or refractory pediatric acute myeloid leukemia.
Pediatr Blood Cancer. 2013;60(7):1161-1164.
9. Nicklin P, Bergman P, Zhang B, et al. Bidirectional
transport of amino acids regulates mTOR and autophagy.
Cell. 2009;136(3):521-534.
8. Hensley CT, Wasti AT, Deberardinis RJ.
Glutamine and cancer: cell biology, physiology, and clinical
opportunities. J Clin Invest. 2013;123(9):3678-3684.
6. Avramis VI. Asparaginases: biochemical pharmacology
and modes of drug resistance. Anticancer Res. 2012;32(7):
2423-2437.
10. Ehsanipour EA, Sheng X, Behan JW, et al.
Adipocytes cause leukemia cell resistance to L-asparaginase
via release of glutamine. Cancer Res. 2013;73(10):
2998-3006.
7. Ramya LN, Doble M, Rekha VP, Pulicherla KK.
L-Asparaginase as potent anti-leukemic agent and its
significance of having reduced glutaminase side activity for
© 2013 by The American Society of Hematology
l l l PLATELETS & THROMBOPOIESIS
Comment on Hottz et al, page 3405
Dengue platelets meet
Sir
Arthur Conan Doyle
----------------------------------------------------------------------------------------------------Paul F. Bray1
1
THOMAS JEFFERSON UNIVERSITY
In this issue of Blood, Hottz et al provide compelling evidence that dengue
virus (DV) induces (1) platelet synthesis of interleukin-1b (IL-1b); (2)
platelet-derived IL-1b–containing microvesicles (MVs) that increase vascular
permeability; and (3) DV-triggered inflammasome activation in platelets.1
D
engue is a viral disease spread by
mosquitos. Although most commonly
occurring in the tropics, there has been a
worldwide increasing geographic expansion
and the World Health Organization considers
half the world at risk for infection (http://www.
Model of dengue-mediated platelet IL-1b synthesis and release. (A) Model proposes that platelets in healthy state have
relatively modest levels of the components of the inflammasome and caspase 1 activity, and limited messenger RNA
(mRNA) translation into protein. The low level of translation may be due to microRNA (miRNA) inhibition of translation
and/or low mRNA levels. (B) DV induces in vivo platelet translation of mRNA into IL-1b. DV mediates inflammasomemediated caspase 1 activation, enabling processing into active IL-1b with subsequent release into MVs for systemic
transport. Activated platelets also release RNA in vesicles. Because DV replication involves silencing host miRNA
production, megakaryocytes may deliver less miRNA for inhibiting platelet mRNA translation, or DV could compete with
endogenous miRNAs. In addition, DV may induce increased megakaryocyte delivery of IL-1b mRNA to the platelet.
Dashed lines indicate the uncertainty of the early events in the model.
3400
who.int/mediacentre/factsheets/fs117/en/).
Severe dengue (previously known as
dengue haemorrhagic fever) is relatively
common (;500 000 cases each year), and
is characterized by severe bleeding,
thrombocytopenia, vascular permeability with
plasma leakage and shock, and severe organ
impairment. It is the leading cause of death
among children in some Asian and Latin
American countries. The responsible
molecular mechanisms are not well
understood, but the proinflammatory cytokine
IL-1b is increased in the plasma of patients2
and levels are associated with disease
severity. The authors have previously shown
that DV causes platelet activation and
mitochondrial dysfunction. This manuscript
tests the hypothesis that DV-mediated
platelet activation induces platelet synthesis
and processing of IL-1b, which is capable
of disrupting the endothelial cell barrier function.
Using flow cytometry, the authors found
that compared with platelets from healthy
age- and gender-matched controls, a higher
percentage of platelets from patients with
dengue were positive for IL-1b. Importantly,
when leukocyte-depleted platelets from
normal individuals were incubated with DV
in vitro, IL-1b levels increased in both
platelets and the platelet supernatant. The
authors found DV also induced platelet
release of IL-1b-containing MVs. The
simplest interpretation of these data are that
DV induces both platelet translation of IL-1b
mRNA into protein and platelet release of
IL-1b. The authors collected 36 patients with
serologically/molecularly confirmed dengue.
Among these, the 16 with clinical signs of
vascular permeability had significantly higher
IL-1b levels in platelet-derived MVs. When
the authors exposed cultured human
microvascular endothelial cells to MVs
recovered from DV-exposed platelets, they
observed a significant increase in permeability
to albumin, and this increase was inhibited
by IL-1 receptor blockade.
IL-1b is synthesized as an inactive
precursor that is cleaved to an active form
by caspase 1, but little is known about caspase
1 in platelets. The authors show that
compared with control platelets, the platelets
from dengue patients have enhanced caspase
1 activation and DV induces caspase 1
processing and activation in normal platelets.
How might DV do this? Caspase 1 is activated
by inflammasomes, which are multimolecular
BLOOD, 14 NOVEMBER 2013 x VOLUME 122, NUMBER 20
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complexes involved in innate immunity.3
The nucleotide-binding domain, leucine-rich
repeat-containing (NLR) proteins define
one class of inflammasomes that are activated
by diverse agonists, including pathogen,
environmental, and self-derived activators.
The NRLP3 (also known as cryopyrin)
inflammasome requires the adaptor apoptosisassociated speck-like protein containing
a caspase recruitment domain to recruit
procaspase-1. Although DV is known to
activate NLR protein-3 inflammasome in
macrophages,4 there had been no information
regarding inflammasomes in platelets. The
authors not only provide evidence for an
NLR protein-3 inflammasome in platelets,
but also show DV induces caspase 1 activation
and IL-1b activation in a caspase 1-dependent
manner. In addition, the DV-induced caspase
1 activation requires functional mitochondria,
consistent with reactive oxygen speciesmediated NLR protein-3 inflammasome
activation in monocytes.5
This interesting study has at least 3
potentially important findings as summarized
in the figure. First, these results provide
insights into the mechanisms of the most
serious complication of a globally important
disease, and the data suggest systemic delivery
of IL-1b via platelet MVs may contribute, in
part, to the abnormal vascular permeability
in dengue. Second, these are the first data
suggesting the inflammasome is present and
functional in human platelets. The authors
have just scratched the surface in this regard,
and it will be important to advance these
findings using additional experimental
approaches, since most of the authors’
conclusions are based on the use of small
molecule inhibitors and probes. Numerous
questions remain, including the following:
What is the significance of delivering IL-1b in
vesicles as opposed to free in the plasma? How
does the IL-1 receptor participate in this
process? Does DV induce megakaryocytes
to transcribe more mRNA or to repress
microRNA biogenesis? Regarding the latter,
DV replication involves silencing microRNA
biogenesis pathways6 and it may be of interest
that platelets express high levels of miR-495,
which is predicted to target IL-1b mRNA.
The third important finding pertains
to platelet mRNA translation. It is wellestablished that platelets synthesize IL-1b
and release it into MVs when stimulated by
LPS in vitro.7 Nevertheless, it has been
challenging to show platelet translation occurs
in in vivo situations, in part because it is
difficult to uncouple translation occurring
in a platelet from that occurring in
a megakaryocyte. Furthermore, a traditional
and conservative view of platelet physiology
focuses primarily on hemostasis and
pathologic thrombosis – processes in which
the major function is over in minutes. This
limited view has difficulty integrating in vitro
translation experiments that appear to require
1 or more hours. However, infections or other
causes of inflammation subject the in vivo
platelet to potentially activating stimuli for
days on end – ample time for the platelet
translation machinery to synthesize proteins.
This notion is further supported by the recent
demonstration that platelets have increased
IL-1b content and appear to be a major
source of plasma IL-1b in mice infected with
Plasmodium berghei.8 Thus, when considering
that platelets from patients with dengue have
increased IL-1b content and that DV induces
accumulation of IL-1b when incubated with
BLOOD, 14 NOVEMBER 2013 x VOLUME 122, NUMBER 20
pure platelets, then the most logical
explanation is that platelets translate IL-1b
mRNA into protein in vivo. Because
megakaryocytes and leukocytes were
eliminated from the experiments of Hottz
et al1 and other potential explanations are far
less straightforward, one is reminded of
a quote from Sir Arthur Conan Doyle’s
greatest creation: “Eliminate all other factors,
and the one which remains must be the
truth.” Sherlock Holmes, The Sign of the Four.
Conflict-of-interest disclosure: The author declares
no competing financial interests. n
REFERENCES
1. Hottz ED, Lopes JF, Freitas C, et al. Platelets mediate
increased endothelium permeability in dengue through
NLRP3-inflammasome activation. Blood. 2013;122(20):
3405-3414.
2. Suharti C, van Gorp EC, Setiati TE, et al. The role of
cytokines in activation of coagulation and fibrinolysis in
dengue shock syndrome. Thromb Haemost. 2002;87(1):42-46.
3. Davis BK, Wen H, Ting JP. The inflammasome NLRs
in immunity, inflammation, and associated diseases. Annu
Rev Immunol. 2011;29:707-735.
4. Wu MF, Chen ST, Yang AH, et al. CLEC5A is critical
for dengue virus-induced inflammasome activation in
human macrophages. Blood. 2013;121(1):95-106.
5. Zhou R, Yazdi AS, Menu P, Tschopp J. A role for
mitochondria in NLRP3 inflammasome activation. Nature.
2011;469(7329):221-225.
6. Kakumani PK, Ponia SS, S RK, et al. Role of RNA
interference (RNAi) in dengue virus replication and
identification of NS4B as an RNAi suppressor. J Virol.
2013;87(16):8870-8883.
7. Brown GT, McIntyre TM. Lipopolysaccharide
signaling without a nucleus: kinase cascades stimulate
platelet shedding of proinflammatory IL-1b-rich
microparticles. J Immunol. 2011;186(9):5489-5496.
8. Aggrey AA, Srivastava K, Ture S, Field DJ, Morrell
CN. Platelet induction of the acute-phase response is
protective in murine experimental cerebral malaria.
J Immunol. 2013;190(9):4685-4691.
© 2013 by The American Society of Hematology
3401
From www.bloodjournal.org by guest on June 18, 2017. For personal use only.
2013 122: 3400-3401
doi:10.1182/blood-2013-09-526418
Dengue platelets meet Sir Arthur Conan Doyle
Paul F. Bray
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