Glucose metabolism is crucial for providing platelets with adequate ATP to do
their function properly. Little is known about platelet glucose uptake and the
role of the first rate-limiting glycolytic enzyme, hexokinase (HK), in the
regulation of platelet activation. Glucose uptake in response to platelet
agonists, thrombin and convulxin (CVX), increased in a dose and time�dependent manner. Focusing on signalling downstream of glycoprotein VI
(GPVI), it was found that inhibition of signalling enzymes SFKs, Syk, or PI3K
linked to this receptor significantly decreased platelet glucose uptake
combined with reduced P-selectin expression. Glucose uptake was found to
be independent to integrin activation, but interestingly required ADP signalling
and, to a lesser extent, TxA2 signalling. Using immunoblotting and
immunoprecipitation, we found that HK I and II are expressed in human and
murine platelets, with HK I equally localised in cytosol and mitochondria and
HK II was exclusively found in membrane fraction. Blocking HK activity with
three different HK inhibitors revealed that HK plays an important role in
glucose transport into platelets upon platelet activation with CVX. Functional
studies have shown that HK may play a role in GPVI-mediated platelet
aggregation and activation, αIIbβ3, and P-selectin expression. Platelet
activation with CVX caused an increase in HK activity, which required SFKs,
Syk, and PI3K/Akt pathways. These data suggest that HK plays a key, but
poorly defined, role in GPVI-mediated platelet activation. Next, the effect of
diabetes on platelet glucose uptake was examined. Type1 diabetes mellitus
was induced in mice using Streptozotocin (STZ) injection. C57BL/6J male
mice aged 8-12 weeks received STZ intraperitoneally (50 mg/kg body weight;
3 days). After confirming diabetes, glucose uptake studies demonstrated that
glucose uptake was basally high in diabetic mice compared to vehicle control.
Further, this increase in glucose uptake was also associated with increased
mitochondrial membrane potential in diabetic mice compared to vehicle group
(hyperpolarisation). Correlation analysis revealed a strong positive
association between fasting blood glucose levels and platelet glucose uptake
upon activation in STZ mice. These data suggest that glucose metabolism is
altered in diabetes. In conclusion, these studies suggest that platelets
activation regulates platelet glucose metabolism by regulating GLUT3
expression and HK activity.
