Midkine (MK; gene name, Mdk), a
heparin-binding
growth factor, regulates cell growth, cell survival, migration and anti-apoptotic activity in nephrogenesis and development. In the kidney, MK is expressed mainly in proximal tubular epithelial cells and is induced by oxidative stress through the activation of
hypoxia-inducible factor-1α. The pathophysiological roles of MK are diverse, ranging from the occurrence of
acute kidney injury (AKI) to progression of
chronic kidney disease, often accompanied by
hypertension, renal ischemia and
diabetic nephropathy. In particular,
hypertension has indispensable implications for various
vascular diseases, including cardiovascular and renal disorders. Mdk(+/+) mice exhibited marked
hypertension in renal ablation model compared with Mdk(-/-) mice, eventually leading to more progressive
renal failure such as glomerular
sclerosis and tubulointerstitial
injuries in association with elevated plasma
angiotensin (Ang) II levels. MK is also induced in the lung endothelium by oxidative stress and subsequently up-regulated
angiotensin-converting enzyme (ACE) in the lung. Ang II is hydrolyzed by ACE to induce further oxidative stress, accelerating MK generation and leading to a vicious cycle of positive feedback on the MK-Ang II pathway. The kidney-lung interaction involving positive feedback between the renin-angiotensin system and MK may in part account for the pathogenesis of
hypertension and kidney injury. In addition to this pathway, MK is involved in the pathogenesis of
diabetic nephropathy and AKI through the recruitment of the inflammatory cells. Such multidisciplinary findings may open new avenues for targeting
therapies for
hypertension and various renal diseases, including AKI and
diabetic nephropathy.