On the role of pleiotrophin and its receptors in development and angiogenesis.

The secreted growth factor pleiotrophin (PTN) is expressed in all species and is evolutionarily highly conserved, suggesting that it plays a significant role in the regulation of important processes. The observation that it is highly expressed at early stages during development and in embryonic progenitor cells highlights a potentially important contribution to development. There is ample evidence of the role of PTN in the development of the nervous system and hematopoiesis, some, albeit inconclusive, evidence of its role in the skeletomuscular system, and limited evidence of its role in the development of other organs. Studies on its role in the cardiovascular system and angiogenesis suggest that PTN has a significant regulatory effect by acting on endothelial cells, while its role in the functions of smooth or cardiac muscle cells has not been studied. This review highlights what is known to date regarding the role of PTN in the development of various organs and in angiogenesis. Wherever possible, evidence on the crosstalk between the receptors that mediate PTN's functions is also quoted, highlighting the complex regulatory pathways that affect development and angiogenesis.