ZSCAN4-Mediated Stem Cell Potency in Adult and Cancer Stem Cells

Abstract

The replication and differentiation capacity of stem cells (stem cell potency) are important determinants in a variety of human diseases. Impaired potency of endogenous stem cells is a contributing factor to aging-related diseases, including neurodegenerative disease. Cell therapies, aimed at treating neurodegenerative disease, use exogenous stem cells, whose efficacy varies based on their potency. Previous reports have demonstrated that mesenchymal stem cells (MSCs), are a promising source for stem cell therapies in neurodegenerative disease. Our laboratory has previously reported the generation of fully defined MSCs from palatine tonsil (T-MSC) biopsies of less than 1g of tissue, with extremely high efficiency compared to extraction protocols from other sources. However, clinical applications of MSCs are still limited by low replication potential and telomere shortening in cells derived from elderly individuals. Furthermore, after expansion in culture, T-MSCs show a reduced ability to differentiate due to accelerated aging in vitro. Therefore, methods to control survival and enhance the differentiation capacity of aged MSCs are urgently needed for the scale-up needs of regenerative medicine. This is a key obstacle to the engineering of cell therapies for neurodegenerative diseases, as cells not only need to be able to self-renew, but also to efficiently differentiate for clinical applications. In these studies, we first developed a procedure to generate neuron-like cells from T-MSCs and defined their neurogenic potential. Our results demonstrate that T-MSCs extracted from pediatric donors have high neurogenic potency for 6-10 passages, compared to bone-marrow derived MSCs. Next, we assessed the potential of ZSCAN4, an early embryonic gene associated with developmental potency, to increase the differentiation potential of aged MSCs with the future goal of enhancing their efficacy for the treatment of neurodegenerative diseases. Our data indicate that expression of ZSCAN4 in these cells increases stem cell characteristics and their ability to differentiate to neural stem-like cells. In the next part of our work we studied the mechanism of ZSCAN4, the effect of its interaction with another factor, RNF20, and their mutual significance to pluripotency gene expression in cancer cell lines. Aberrant increases in stem cell potency factors in a small number of transformed tumor cells, creates a sub-population of Cancer Stem Cells (CSCs). Such cells are responsible for seeding metastases and driving tumor aggressiveness, while being comparatively slower growing and more resistant to radiation and common chemotherapies, versus bulk tumor cells. Thus, methods to reduce stem cell potency in cancers may be beneficial. Previous findings in our lab show that ZSCAN4, while not normally expressed in post-embryonic human cells, is expressed in human cancers and cancer cell lines, leading us to theorize that ZSCAN4 may be mediating the cancer stem cell phenotype in the same manner it has been reported to regulate stem cell potency in pluripotent stem cells. Our results indicate that ZSCAN4 expression is associated with cancer stem cells, and enhances pluripotency gene expression in cancer stem cells. We further found that while ZSCAN4 can exert epigenetic effects independently of RNF20, both proteins need to be present for ZSCAN4’s effects on telomere length and expression of pluripotency genes. Altering stem cell potency is important in regenerative medicine, where increased stem cell potency is desirable, and for oncology, where reduced stem cell potency is sought. Our results indicate that ZSCAN4, whose expression is otherwise restricted to early development, positively regulates stem cell potency when expressed in either T-MSCs or in cancer cell lines. Thus, ZSCAN4 is a promising target for use in regenerative medicine and inhibition in cancers.