Background: Rab GTPases serve as master regulators of vesicle biogenesis, traffic and fusion in eukaryotic cells. Platelets express over 40 different Rab proteins with potential roles in secretion, receptor trafficking and other cell physiological process critical to platelet function; however, roles for Rab proteins in platelet physiology remain minimally described.

Aims: We aim to determine the localization, distribution and regulation of Rab GTPase system proteins in platelets.

Methods: Through a combination of immunofluorescence microscopy and cell physiology methods, we determine the localization and regulation of >10 different Rab GTPases in resting platelets, as well as platelets stimulated with the platelet collagen receptor GPVI/ITAM agonist crosslinked collagen-related peptide (CRP-XL).

Results: Washed platelets were prepared from blood of healthy human donors for in vitro agonist stimulation. Conventional and super-resolution immunofluorescence microscopy found different Rab proteins localize to distinct vesicle populations in resting and activated human platelets. Rab7 and Rab10 show staining patterns consistent maturing endosomes/lysosomes; whereas Rab 8 and Rab10 appear to localize to multivesicular bodies. Other Rab proteins, including Rab9, Rab13, Rab30, Rab32 and Rab37 also exhibit distinct intracellular staining patterns that redistribute in platelets following activation with CRP-XL and other agonists.

Conclusions: Our work begins to systematically characterize Rab GTPase expression, localization, regulation and function in human platelets to better understand how Rab GTPase activities regulate platelet cellular homeostasis, as well as activation programs in health and disease.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/expression-and-localization-of-rab-gtpase-proteins-in-platelets/