Pleiotrophin (PTN) is a secreted, strongly heparinbinding, developmentally regulated cytokine. PTN is a highly conserved protein，Human, mouse, rat, canine, porcine, equine and bovine PTN share 98% aa sequence identity or greater. PTN and midkine share 50% amino acid (aa) sequence identity, share some functions, and constitute a family. During development, PTN is involved in development of brain, bone, and organs undergoing branching morphogenesis. PTN causes PTPRB dimerization and inactivates its phosphatase activity, which allows increased tyrosine phosphorylation of its substrates. Increased expression of PTN is correlated with neuronal development or stresses such as brain ischemia and Parkinson’s disease.