Angiogenesis and its Importance in Health and Disease
The formation of new blood vessels, commonly called ‘angiogenesis’, comprises several processes that include vasculogenesis, where stem cells or angioblasts differentiate into blood vessels and which occurs in developing, initially avascular embryos and to a certain extent in adults;1 and angiogenesis per se, where new blood vessels (especially capillaries) grow from pre-existing vessels by sprouting or branching2 and which is the prevailing mechanism in adults.3
Angiogenesis is necessary to supply tissues with nutrients and oxygen, and is an integral mechanism in many physiological processes, such as wound healing and tissue growth and repair,4 muscle development5 and ovulation.6 At the same time, disruption of the fine balance between factors that induce blood vessel formation and those that inhibit or halt the process can result in pathological angiogenesis, or neovascularisation, leading to increased formation of blood vessels that may be excessive or occur in normally avascular tissue. For example, rapid and persistent growth of new blood vessels is a hallmark of cancer, while excessive angiogenesis can provide a route of entry for inflammatory cells into sites of chronic injury (e.g. Crohn’s disease), contributes to the increased epithelial cell turnover and skin plaques in psoriasis and causes ocular diseases that can lead to blindess.7 Neovascularisation is implicated in a multitude of malignant, ischaemic, inflammatory, infectious and immune disorders.3
As angiogenesis is so vital for health, any therapeutic strategy aimed at treating angiogenic-mediated disease must discriminate between physiological and pathological angiogenesis to ensure that only neovascularisation is affected. It is also important to recognise that all angiogenic mechanisms may participate in neovascularisation to various extents in different diseases. A thorough understanding of the processes controlling angiogenesis and gaining access to as many molecular targets in the relevant regulatory pathways as possible is essential in developing an appropriate therapy.
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