Neuroprotective effects of insulin-like growth factor-2 in 6-hydroxydopamine-induced cellular and mouse models of Parkinson's disease

Skin-derived precursor Schwann cells have been reported to play a protective role in the central nervous system. The neuroprotective effects of skin-derived precursor Schwann cells may be attributable to the release of growth factors that nourish host cells. In this study, we first established a cellular model of Parkinson's disease using 6-hydroxydopamine. When SH-SY5Y cells were pretreated with conditioned medium from skin-derived precursor Schwann cells, their activity was greatly increased. The addition of insulin-like growth factor-2 neutralizing antibody markedly attenuated the neuroprotective effects of skin-derived precursor Schwann cells. We also found that insulin-like growth factor-2 levels in the peripheral blood were greatly increased in patients with Parkinson's disease and in a mouse model of Parkinson's disease. Next, we pretreated cell models of Parkinson's disease with insulin-like growth factor-2 and administered insulin-like growth factor-2 intranasally to a mouse model of Parkinson's disease induced by 6-hydroxydopamine and found that the level of tyrosine hydroxylase, a marker of dopamine neurons, was markedly restored, α-synuclein aggregation decreased, and insulin-like growth factor-2 receptor down-regulation was alleviated. Finally, in vitro experiments showed that insulin-like growth factor-2 activated the phosphatidylinositol 3 kinase (PI3K)/AKT pathway. These findings suggest that the neuroprotective effects of skin-derived precursor Schwann cells on the central nervous system were achieved through insulin-like growth factor-2, and that insulin-like growth factor-2 may play a neuroprotective role through the insulin-like growth factor-2 receptor/PI3K/AKT pathway. Therefore, insulin-like growth factor-2 may be an useful target for Parkinson's disease treatment.

Insulin-Like Growth Factor-2 Is Induced Following 5-Aminolevulinic Acid-Mediated Photodynamic Therapy in SW620 Human Colon Cancer Cell Line

The IGF system is a family of polypeptide growth factors, which plays a significant role in the development and growth of many cells. Dysregulation of insulin-like growth factors and their pathway components has been connected with essential tumor properties, such as tumor cell proliferation, antiapoptotic properties, invasive behavior and chemotherapy resistance. However, the effects of photodynamic therapy (PDT), one of the cancer treatment methods for the regulation of the IGF signaling pathway, are still unclear. The aim of this study was to investigate the expression of IGF-2 after 5-aminolevulinic acid (5-ALA)-mediated-PDT in SW620 human colorectal cancer cells with evaluation of cell proliferation and apoptosis and to determine the effects of PDT on the IGF-2 receptor (IGF-2R), IGF-2 binding protein-1 (IGF-2BP-1) and the proapoptotic protein, BAX. Cells were treated with 5-aminolevulinic acid and its methyl ester. Changes of the expression and concentration of IGF-2 before and after treatment were assayed by immunocytochemistry, Western blot and ELISA. We found that IGF-2 was significantly overexpressed in the SW620 cell line, while its receptor and binding protein-1 were not significantly changed. Within this study, we would like to suggest that IGF-2 contributes to the effects of PDT and that its expression will influence post-PDT efficacy.