A SMALL MOLECULE MODULATOR OF PRION PROTEIN INCREASES HUMAN MESENCHYMAL STEM CELL LIFESPAN, EX VIVO EXPANSION AND ENGRAFTMENT TO BONE MARROW IN NOD/SCID MICE

Human mesenchymal stem cells (hMSCs) have been shown to have potential in regenerative approaches in bone and blood. Most protocols rely on their in vitro expansion prior to clinical use. However, several groups including our own have shown that hMSC lose proliferation and differentiation ability with serial passage in culture, limiting their clinical applications. Cellular prion protein (PrP) has been shown to enhance proliferation and promote self-renewal of hematopoietic, mammary gland and neural stem cells. With this work I tested the hypothesis that PrP decreased with cellular ageing of hMSC and was, at least in part, responsible for the loss of proliferation and differentiation seen with expansion in culture. Here I showed, for the first time, that expression of PrP decreased in hMSC following ex vivo expansion. When PrP expression was knocked down, hMSC showed significant reduction in proliferation and differentiation. In contrast hMSC expanded in the presence of small molecule 3/689, which stabilized PrP expression, extended lifespan up to 10 population doublings. These cells showed a 10 fold increase in engraftment levels in bone marrow 5 weeks post-transplant suggesting they were of superior quality. This was due to enhanced protection from DNA damage and enhanced cell cycle progression through upregulation of superoxide dismutase-2 (SOD2). The increase in SOD2 was dependent on PrP expression and suggested increased scavenging of reactive oxygen species as mechanism of action. My data point to PrP as a good target for chemical intervention to delay stem cell ageing.