Vascular Protective Effects of Netrin-1 and Netrin-1 Pre-conditioned Endothelial Progenitor Cells
Many of the pathophysiological processes of vascular disease are attributed to endothelial dysfunction. Under normal conditions, nitric oxide (NO•) produced by endothelial NO• synthase (eNOS) plays a major role in maintaining vascular homeostasis. Due to a damage on endothelial cells (ECs), smooth muscle cells (SMCs) are proliferated and migrated to form neointimal cusion that can occlude blood vessels due to reduced NO• bioavailability. Platelets are also aggregated and activated to promote extracellular matrix production as well as additional inflammatory responses in the environment of disturbed NO• production. Therefore, one of the most effective approaches to protect the vasculature from these pathological circumstances would be to improve endothelial function. Cell-based therapies, such as approaches utilizing endothelial progenitor cells (EPCs), aim at accelerating revascularization. However, the challenge in cell isolation and acquisition of sufficient cell number of EPCs from circulation has limited its clinical application. Nonetheless, our studies have demonstrated pre-conditioning of EPCs with netrin-1 can markedly improve their functions as to improved proliferative activity and survival capacity, and that with this treatment much less number of EPCs is sufficient to induce robust vascular protection when delivered in vivo.
In our previous study, we demonstrated that NO• mediates mitogenic effects of netrin-1 on ECs via activation of DCC/ERK1/2 axis. The current study for the first time further revealed promoted functions of EPCs by netrin-1, which is also dependent on DCC and NO• production, resulting in protection against vascular endothelial damage. For these studies we employed two animal models; femoral artery wire injury model and apoE knockout mice fed high fat diet, for the development of neointima and atherosclerosis respectively. In addition to demonstration that netrin-1 protein infusion itself is robustly protective in these models, delivery of netrin-1 pre-conditioned EPCs proved to be markedly beneficial via augmented proliferation and resistance to oxidative stress. Moreover, the signaling pathway of NO•/cGMP/p38 MAPK was identified to mediate netrin-1 inhibition of SMC migration. The inhibitory effect of netrin-1 on monocytes adhesion to EC through UNC5B is also involved in the protection against atherogenesis. Although further studies are required, the present study indicates the strong potential of netrin-1 and netrin-1 pre-conditioned EPCs in vascular protection.