# Molecular Mechanisms of Platelet Alpha Granule Biogenesis

> **NIH NIH R01** · COLORADO STATE UNIVERSITY · 2022 · $380,000

## Abstract

PROJECT SUMMARY
 Platelets play central roles in hemostasis and thrombosis. Platelet activation triggers secretion and release of contents
from α-granules, δ-granules and lysosomes that in turn leads to the recruitment and aggregation of additional platelets and
a myriad of physiological responses. While impaired platelet function is associated with disorders that manifest with
moderate to severe bleeding, excessive platelet aggregation is a major cause of morbidity and mortality due to its effect in
cardiovascular disease and stroke. Alpha-granules are crucial to these platelet functions both in health and disease. However,
in spite of the relevance of platelet α-granules for human health, remarkably little is known about their biogenesis. Therefore,
our goal is to understand the pathways and molecular mechanism responsible for the biogenesis of platelet α-granules.
 Mutations in VPS33B, VPS16B and NBEAL2 cause the α-granule deficiency and bleeding manifestations observed in
patients suffering Arthrogryposis, Renal Dysfunction and Cholestasis (ARC) syndrome and Gray Platelet syndrome (GPS).
However, the mechanism of action of these proteins in α-granule biogenesis is a mystery. Consequently, a major objective
of this proposal is to address the function of VPS33B, VPS16B and NBEAL2 at the cellular and molecular level.
 Platelet α-granules are produced in the megakaryocyte, the platelet precursor cell. In addition to soluble proteins taken
up by endocytosis, α-granules contain hundreds of proteins synthesized by the megakaryocyte. The pathways taken by
megakaryocyte-synthesized proteins to reach the α-granule are unknown. In this proposal, we show that the sorting
endosome is a fundamental precursor organelle in α-granule formation that is used by megakaryocyte-synthesized proteins.
This implies a more complex biogenesis mechanism than previously anticipated. In this application we build on our novel
findings, hypothesizing that fundamental components of the α-granule biogenesis machinery work at the megakaryocyte
sorting endosome by regulating vesicular trafficking. We propose two specific aims. Aim 1 will determine the transport
pathways followed by newly synthesized α-granule soluble and membrane proteins using an innovative method to
synchronize and evaluate transport of proteins to α-granules in real time. We will test the hypothesis that there are multiple,
separate pathways followed by megakaryocyte-synthesized α-granule proteins and test whether α-granules segregate into
distinct populations. Aim 2 will define the molecular mechanism of platelet α-granule biogenesis by: (i) testing the
hypothesis that VPS33B and VPS16B regulate the SNARE-mediated fusion of Golgi-derived vesicles containing α-granule
cargo with sorting endosomes; (ii) addressing the function of novel components of the transport machinery identified here,
including a new complex that coordinates α-granule cargo traffic through sorting endosomes; (iii) testing the hypothesis
...

## Key facts

- **NIH application ID:** 10319019
- **Project number:** 5R01HL151988-02
- **Recipient organization:** COLORADO STATE UNIVERSITY
- **Principal Investigator:** Santiago Mauro Di Pietro
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $380,000
- **Award type:** 5
- **Project period:** 2020-12-15 → 2024-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10319019

## Citation

> US National Institutes of Health, RePORTER application 10319019, Molecular Mechanisms of Platelet Alpha Granule Biogenesis (5R01HL151988-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10319019. Licensed CC0.

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