Plant-produced Asialo-erythropoietin and its Antiapoptotic Functions

In this project, we are taking the distinct advantage of plant expression systems, which is the lack of the capacity to add sialic acids, to genetically modify plants for asialo-rhuEPO - a special glycoprotein without sialic acids. Although nearly all human glycoproteins require sialic acid residues for their in vivo functions, the one exception we could find is rhuEPO, which has both hematopoietic and tissue protective functions. When rhuEPO is used as an antiapoptotic agent, its hematopoietic activity can cause bad side effects by leading to harmful increases in red blood cell mass. This activity can be disrupted by removing sialic acids. Asialo-rhuEPO generated by total enzymatic desialylation of rhuEPO has been demonstrated to retain the cell- and tissue-protective properties of EPO without hematopoietic activity. This type of EPO derivative can be explored as the antiapoptotic agent. However, there is no expression system that can produce asialo-rhuEPO directly. It is also unlikely to use commercially available rhuEPO, which is produced only in mammalian cells, to make asialo-rhuEPO because of its limited supply. Based on available knowledge and techniques, it is likely to genetically modify plants to produce human glycoproteins without sialic acids. We have co- expressed human GalT gene and EPO gene fusing with ER-signal peptides in tobacco plants, and try to inexpensively produce asialo-rhuEPO with the potential of large scale production. We expect plant-produced asialo-rhuEPO will have similar cytoprotective function as the enzymatically produced asialo-rhuEPO. The results of this project will also provide insights into the plant glycosylation mechanism and the antiapoptotic mechanism of the plant- produced asialo-rhuEPO. In addition, the protein purification methodologies that will be established and the glycoprotein analysis methods will be very valuable for future plant glycoengineering projects.