Ectopic expression of L1CAM ectodomain alters differentiation and motility, but not proliferation, of human neural progenitor cells

Authors: PUSEY, MICHELLE - University Of Delaware; PACE, KARMA - University Of Delaware; FASCELLI, MICHELE - University Of Delaware; LINSER, PAUL - University Of Florida; STEINDLER, DENNIS - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; GALILEO, DENI - University Of Delaware

Submitted to: International Journal of Developmental Neuroscience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2019
Publication Date: 8/14/2019
Citation: Pusey, M.A., Pace, K., Fascelli, M., Linser, P.J., Steindler, D.A., Galileo, D. 2019. Ectopic expression of L1CAM ectodomain alters differentiation and motility, but not proliferation, of human neural progenitor cells. International Journal of Developmental Neuroscience. 78:49-64. https://doi.org/10.1016/j.ijdevneu.2019.08.001.
DOI: https://doi.org/10.1016/j.ijdevneu.2019.08.001

Interpretive Summary: We originally discovered and characterized adult human neural progenitor cells ("AHNPs") involved in stem cell-related lifelong generation of brain cells in the adult brain. These cells also have been implicated as a potential source of brain cancer initiating-cells, but specific events that might cause cells to progress towards a transformed phenotype remain unclear. This study looked at a cell surface protein involved in cell recognition, motility, and proliferation during brain development: the L1CAM ("L1") cell adhesion/recognition molecule in human glioma cancer cells. Following the ectopic overexpression of the L1, it was found that there was reduced AHNP motility, altered expression of phenotypic cellular differentiation markers, and it did not increase cell proliferation in vitro, in stark contrast to the effects on glioma cancer cells. The results suggest that unlike for glioma cells, L1 does not increase AHNP cell motility, but rather it can influence the differentiation of normal brain progenitor cells; increasing motility and proliferation appears to be limited to already-transformed cells. These findings have implications for better understanding and in vitro modeling of aggressive human brain cancer-initiating and disease-propagating cells, implicating roles for cell surface adhesion proteins that are known to be involved in normal brain development.

Technical Abstract: Adult human neural progenitor and stem cells have been implicated as a potential source of brain cancer causing cells, but specific events that might cause these cells to progress towards a transformed phenotype remain unclear. The L1CAM (L1) cell adhesion/recognition molecule is expressed abnormally by human glioma cancer cells and is released as a large extracellular ectodomain fragment, which stimulates cell motility and proliferation. This study aims to identify the effects of ectopic overexpression of the L1 long ectodomain (L1LE; ~180 kDa) on the motility, proliferation, and differentiation of human neural progenitor cells (HNPs). L1LE was ectopically expressed in HNPs using a lentiviral vector. Surprisingly, overexpression of L1LE resulted in reduced HNP motility in vitro, which was in stark contrast to the effects on glioma and other cancer cell types. L1LE overexpression resulted in a variable degree of maintenance of HNP proliferation in media without added growth factors but did not increase proliferation. In monolayer culture, HNPs expressed a variety of differentiation markers. L1LE overexpression resulted in loss of GS and beta-III-tubulin expression in normal media, and reduced vimentin and increased GS expression in the absence of added growth factors. When co-cultured with chick embryonic brain cell aggregates, HNPs show increased differentiation potential. Some HNPs expressed phosphorylated neurofilaments and oligodendrocytic O4, indicating differentiation beyond that in monolayer culture. Most HNP-L1LE cells lost their vimentin and GFAP staining, and many cells were positive for astrocytic glutamine synthetase. However, these cells rarely were positive for neuronal markers beta-III-tubulin or phosphorylated neurofilaments, and few HNP oligodendrocyte progenitors were found. These results suggest that unlike for glioma cells, L1LE does not increase HNP cell motility, but rather can influence the differentiation of normal brain progenitor cells. Therefore, the effect of L1LE on increasing motility and proliferation appears to be limited to already transformed cells.