Alamer, Maryam Adel H; (2024) Identifying platelet vesicles in osteoblast cells. Doctoral thesis (Ph.D), UCL (University College London).

Text Thesis 2024 Identifying platelet vesicles in osteoblast cells .pdf - Other Access restricted to UCL open access staff until 1 July 2026. Download (6MB)

Abstract

During bone formation, osteoblasts play a significant role in controlling calcium and phosphate ions. Researchers studying bone formation have studied invertebrates like sea urchins as a model. These organisms initiate mineralization using amorphous mineral precursors that subsequently undergo crystallization. This discovery has prompted investigations in vertebrates, suggesting that intracellular vesicles transport amorphous calcium phosphate from osteoblasts to the extracellular space, contributing to the formation of bone apatite. Although we understand the involvement of amorphous mineral precursors in mineralization, the source of these precursors is still not completely clear. Numerous studies have shown that extracellular vesicles (EVs), particularly those from platelets, play a key role in intercellular communication and the transfer of bioactive molecules. Such as EVs can transport proteins between platelets and cells which has a role in the functional state of recipient cells by delivering enzymes, growth factors, or other bioactive proteins. Intriguingly, studies have shown a link between platelets and bone cells, particularly osteoblasts, as both originate from megakaryocytes (MKs) and secrete proteins crucial for the bone formation process. Platelets significantly contribute to bone formation by releasing growth factors from alpha granules. The intricate connections between osteoblasts and platelets have led us to hypothesize that dense granules found in platelets might be present in osteoblasts, potentially serving as a source for bone formation. Although earlier studies have explored the role of platelets in bone regeneration, the presence of dense granules from platelets in osteoblasts remains undiscovered.. This project aims to detect platelet-derived dense granules, characterized by their spherical shape and a diameter range between 40-300 nm, within osteoblast cells using transmission electron microscopy (TEM). It also seeks to analyse the chemical composition 5 (calcium ca2+ , phosphate PO₄³⁻) of these spherical structures using transmission electron microscopy/energy-dispersive X-ray spectroscopy (TEM/EDX). Additionally, we aim to utilize dual scanning electron microscopy/focused ion beam (SEM/FIB) to investigate the possibility of detecting vesicles components. In addition to structural and compositional analysis, the study employs immunofluorescence techniques to observe the presence of dense granule-specific markers (CD41) that overlap with polyphosphate (polyP) and serotonin transporters (SERT) in platelet-derived dense granules. These observations suggest that dense granules are present in osteoblasts, potentially serving as a source of ions for bone formation

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