Abstract 154: Hierarchical Redundancy And Contextual Roles Of Vesicle-associated Membrane Proteins (VAMPs) In Platelet Function

Background: Platelet granule secretion, driven by the SNARE complex involving Vesicle-Associated Membrane Proteins (VAMPs) and t-SNAREs, is essential for vascular integrity. We dissected individual and combinatorial contributions of all four platelet VAMPs to granule secretion, hemostasis, and intracellular cargo trafficking. Research Questions: 1. Are specific VAMPs critical for granule fusion, or does total VAMP quantity (mass action) dictate secretion? 2. How do differential VAMP deficiencies impact hemostasis in arterial and venous microenvironments? 3. Do VAMPs influence platelet cargo loading and gene expression? Goals: Investigate individual and combinatorial roles of VAMPs in platelet biology and their context dependent contributions to hemostasis. Approach: We generated V7 -/- 8 -/- and V2 Δ 3 Δ 7 -/- 8 -/- mice, assessing granule secretion (dense, alpha, lysosomal) via ATP, PF4/P-selectin, and β-hexosaminidase/LAMP1 release assays, respectively. Hemostasis in arterial and venous models was evaluated with tail bleeding, FeCl3, and venous puncture injury assays. Cargo levels were analyzed using proteomic arrays, and platelet RNA sequencing identified transcriptional changes. Results: Global V7/V8 deletion modestly reduced secretion compared to isolated V8 deficiency. Surprisingly, while platelet-specific V2 Δ 3 Δ 7 -/- 8 -/- exhibited the most dramatic decrease, complete abolition was absent (p800 upregulated and >500 downregulated transcripts in V7 - /- 8 -/- and V2 Δ 3 Δ 8 -/- platelets, suggesting shared transcriptional control by V7 and secondary VAMPs (V2 and V3). Conclusions: VAMP functions exhibit hierarchical redundancy, with V8 presence minimally impacting dense granule secretion and arterial hemostasis. Alpha granule release is more sensitive to VAMP loss. The requirements for platelet granule secretion for hemostasis are context dependent. The deletion of VAMPs disrupts platelet cargo trafficking and transcription.