[Midkine in relation to development and pathological status of the nervous system]

Midkine (MK) is a novel heparin-binding growth factor whose expression is regulated by retinoic acid. Midkine is structurally unrelated to other growth factors, and together with pleiotrophin (PTN) subsequently cloned forms a new family of growth factors. Midkine enhances neurite outgrowth and survival of several embryonic neurons. Midkine mRNA is strongly expressed in the nervous system during the midgestation period, while the normal adult brain scarcely expresses it. Immunohistochemical studies revealed midkine localization beside radial glial processes along which neurons migrate. Upon experimental brain infarction in the rat, midkine expression in the ischemic region begins as early as 1 day after the operation. Senile plaques of patients with Alzheimer's disease invariability express midkine. These findings indicate that midkine plays significant roles both in the formation and repair of the central nervous system and processes leading to its diseases.