The Biological Role Of IL-22in Rat Pheochromocytoma Cell PC12

Interleukin-22(IL-22), an IL-10family cytokine, was produced by special immune cell populations including Th22, Thl, and Th17cells, classical and non-classical (NK-22) NK cells, NKT cells, and lymphoid tissue inducer cells. IL-22signals through a receptor complex composed of the ligand-binding chain IL-22R1and the accessory chain IL-10R2. This cytokine did not exert an effect on the hematopoietic function of cells. Instead, its target cells were tissue cells from the skin, liver, kidney, and from organs of the respiratory and gastrointestinal systems. IL-22mediated the crosstalk between leukocytes and epithelial cells. Previous studies reported that there was IL-22expression in mouse brain and the rat PC12pheochromocytoma cells are responsive to IL-22stimulation. However, the biological roles of IL-22in neuronal cells remained largely unknown. We detected the biological role of IL-22in PC12cells. The main results were as follows.1、In our preliminary experiment, IL-22R1mRNA expression was detected in PC12cells by RT-PCR analysis. We then investigated the signaling pathways mediated by IL-22in PCI2cells by western blot assay. IL-22induced tyrosine phosphorylation of Stat3. No activation of serine phosphorylation of Stat3was observed in IL-22-stimulated PC12cells. The increased phosphorylation of p38MAPK was detected during30-60min after IL-22stimulation whereas no significant activation of JNK was observed. Surprisingly, compared to basal levels of phosphorylation of Erkl/2in unstimulated PC12cells, phosphorylation of Erkl/2was signicicantly decreased in response to IL-22stimulation. Further the serine phosphorylation of Akt was detected. Taken together, the data indicated that IL-22activates STAT3, p38MAPK and Akt pathways and inhibits Erk/MAPK pathway in PCI2cells.2、To examine the effect of IL-22on PC12cell death by serum deprivation, PC12cells in DMEM deprived of serum were treated with various concentrations of IL-22or mock-treated for48h. Upon serum deprivation, approximately60-70%of the inoculated cells died. IL-22at concentrations of50and100ng/ml exerted significantly protective effect on PC12cell death. To elucidate the mechanism underlying the pro-survival effect of IL-22, we investigated the signaling pathways responsible for the effect. Therefore, PC12cells were treated with specific inhibitors of their respective pathways. These inhibitors at different concentrations were added to the PC12cell cultures1h before the addition of IL-22(100ng/ml). Taken together, the results indicated that the Jakl/Stat3and PI3K/Akt pathway were involved in IL-22-mediated PC12cells survival. We also found that IL-22induced autophagy of the undifferentiated serum-deprived PC12cells.3n IL-22had no effect on PC12cell proliferation and neurite outgrowth. In addition, our data suggested that IL-22might down-regulate NGF-primed effects on neurite outgrowth in PC12cells.4、Methyl-4-phenylpyridinium (MPP+), the active metabolite of1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), had been used extensively in various mammalian species to produce an experimental model of Parkinson’s disease (PD). MPP+induced cell death and/or apoptosis in PC12cells. The differentiated PC12cells were more sensitive to MPP+than undifferentiated cells. IL-22at the concentrations of50-500ng/ml had no protective effect on MPP+-induced cytotoxicity.100ng/ml IL-22treatment significantly reduced MPP+-induced neurodegeneration, indicating a protective effect by IL-22on MPP+-induced neurodegeneration of differentiated PC12cells.These results suggested that IL-22activated Stat3, p38MAPK and Akt pathways and inhibits Erk/MAPK pathway in PC12cells. We further demonstrated that IL-22protected PC12cells from serum starvation-induced cell death via the Jakl/Stat3and Akt pathways. IL-22also confered a neuroprotective function, which may provide a new therapeutic option for treatment of neurodegenerative diseases.