(160j) Development of a Plant-Made Therapeutic to Treat Spaceflight Osteopenia

Extended missions in a microgravity environment alter normal physiology in the human body. One critical issue in spaceflight is loss of bone mineral density. In the process of bone homeostasis, specialized cells facilitate bone remodeling with coupled bone resorption and formation. The reduced mechanical loading in microgravity causes resorption to outpace formation, which results in loss of bone mass. Medications such as parathyroid hormone (PTH) (1-34), a peptide fragment of naturally occurring human PTH, stimulates bone formation and may be able to restore bone mass in microgravity.. However, this requires a daily subcutaneous injection for a number of months, and in a limited resource environment, this is impractical. An alternative to transporting an injectable medication is to instead build capacity to produce it during the mission, which we propose to do in transgenic plants. We are producing transgenic lettuce which expresses a fusion protein consisting of PTH (1-34) linked with a fragment crystallizable (Fc) domain of human IgG1 via a flexible linker. The Fc region is intended to eliminate the injection requirement by increasing bioavailability via oral delivery. We constructed a binary vector for expression of this PTH-Fc protein and used it to produce two varieties of transgenic lettuce via Agrobacterium tumefaciens mediated transformation of wild type lettuce. From these T0 plants, we have grown T1 plants, and we are in the process of generating T2 plants. We have successfully developed a PCR protocol to detect our gene of interest and are in the process of optimizing it. In parallel, we are developing a protein purification method, along with quantitative and functional assays for lettuce-made PTH-Fc.