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

Abstract

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 hMSCs 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. Here we show, 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, a modulator of PrP expression, showed retention of PrP expression with ex vivo expansion and extended lifespan up to 10 population doublings. Moreover, cultures produced a 300-fold increase in the number of cells generated. These cells showed a 10-fold increase in engraftment levels in bone marrow 5 weeks post-transplant. hMSC treated with 3/689 showed enhanced protection from DNA damage and enhanced cell cycle progression, in line with data obtained by gene expression profiling. Moreover, upregulation of superoxide dismutase-2 (SOD2) was also observed in hMSC expanded in the presence of 3/689. The increase in SOD2 was dependent on PrP expression and suggests increased scavenging of reactive oxygen species as mechanism of action. These data point to PrP as a good target for chemical intervention in stem cell regenerative medicine.

Cellular prion protein controls stem cell-like properties of human glioblastoma tumor-initiating cells

“…showed a significant reduction in proliferation and clonogenic potential in human mesenchymal stem cells when PrP expression was down-regulated [74]. Similarly, PrP C was also shown to influence the proliferation of human CSCs in which a population of CD44 + /PrP C+ cells was isolated from primary colorectal tumors, showing an enhanced tumor-initiating and metastatic ability [37].…”

Activity of mesenchymal stem cells in therapies for chronic skin wound healing

“…110 Additionally, use of MSCs as therapeutic agents requires ex vivo expansion that, while somewhat more accessible than other stem cell types, can remain problematic due to the aforementioned heterogeneity as well as a very limited natural in vitro lifespan. 111 This all ultimately leads to issues in commercialization, where there remains no real set of guidelines for MSC expansion and general use in therapeutics for companies using the cells, despite their relatively common use in clinical trials and some marketed products. 112 Finally, the source of MSCs used can create a great deal of variation among therapeutic cells and also have an effect on harvesting methods.…”

The role of prion protein in stem cell regulation

“…Similarly, in the mammary gland, only those cells expressing PrP C were able to form mammospheres and regenerate the mammary gland when implanted into the mammary fat pad (Liao et al 2007). Indeed, small molecules that modulate PrP C expression can be used to enhance their proliferation and extend their life span in culture, while still retaining their ability to differentiate and engraft to BM (Mohanty et al 2012).…”