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Angiogenesis, the complex set of processes by which new blood vessels are produced, becomes less efficient with advancing age. One important consequence is a loss of capillary density, which has a range of detrimental effects on tissue function, particularly in energy-hungry tissues such as the brain and muscle. Regeneration from injury is also dependent on the quality and efficiency of angiogenesis. Researchers here take a narrow focus on the question of angiogenesis relevant to bone tissue maintenance and regeneration, and the use of exosome therapies to improve angiogenesis. To the degree that treatment with exosomes harvested from stem cells can improve angiogenesis throughout the body, this approach to therapy should produce broad benefits.
Bone is a metabolically dynamic structure that is generally remodeled throughout the lifetime of an individual but often causes problems with increasing age. A key player for bone development and homeostasis, but also under pathological conditions, is the bone vasculature. This complex system of arteries, veins, and capillaries forms distinct structures where each subset of endothelial cells has important functions. Starting with the basic process of angiogenesis and bone-specific blood vessel formation, coupled with initial bone formation, the importance of different vascular structures is highlighted with respect to how these structures are maintained or changed during homeostasis, aging, and pathological conditions.
After exemplifying the current knowledge on bone vasculature, this review will move on to exosomes, a novel hotspot of scientific research. Exosomes will be introduced starting from their discovery via current isolation procedures and state-of-the-art characterization to their role in bone vascular development, homeostasis, and bone regeneration and repair while summarizing the underlying signal transduction pathways. With respect to their role in these processes, especially mesenchymal stem cell-derived extracellular vesicles are of interest, which leads to a discussion on patented applications and an update on ongoing clinical trials. Taken together, this review provides an overview of bone vasculature and bone regeneration, with a major focus on how exosomes influence this intricate system, as they might be useful for therapeutic purposes in the near future.
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