Neural trans-differentiation potential of hepatic oval cells in the neonatal mouse brain Jie Deng, a Dennis A. Steindler, b,c Eric D. Laywell, b,1 and Bryon E. Petersen a,c, * ,1 a Department of Pathology, Immunology and Laboratory Medicine, University of Florida, Gainesville, FL 32610, USA b Department of Neuroscience, College of Medicine, University of Florida, Gainesville, FL 32610, USA c Program in Adult Stem Cell Biology and Regenerative Medicine, University of Florida, Gainesville, FL 32610, USA Received 1 August 2002; revised 11 December 2002; accepted 16 December 2002 Abstract Although the existence of the hepatic oval cell (HOC), the liver stem cell has been known for almost 70 years, little is known about the potential for this adult stem cell to trans-differentiate into cells of other tissues. While their origin remains enigmatic, HOCs share many similarities with hematopoietic stem cells. Recent studies have revealed that a small percentage of HOCs can arise from a bone marrow-derived stem cell source. Here we report that, like bone marrow stem cells, HOCs can survive transplantation to the neonatal mouse brain and show signs of trans-differentiation by adopting the morphology and antigenic phenotype of both macro- and microglia cells. Trans-differentiated microglia cells were functional, showing active phagocytosis when cotransplanted with latex microbeads in vivo. In addition to glial markers, a small number of transplanted HOCs were immunopositive for neuronal markers, but displayed ambiguous phenotype, making their characterization difficult. © 2003 Elsevier Science (USA). All rights reserved. Keywords: Hepatic oval cell; Stem cell; Transplantation; Trans-differentiation; Neural phenotypic markers Introduction Stem cells have recently been characterized in a variety of tissues of adult animals, including liver, blood, skin, brain, and heart (Hughes, 2002; Johnes et al., 1995; Pe- tersen, 2001; Spangrude et al., 1988; Wetts and Fraser, 1988). Their plasticity, as demonstrated by the multipotency to differentiate into mature, tissue-specific cell types, may offer new therapeutic tools for a variety of diseases. Hepatic oval cells (HOCs) are considered to be the stem cells of the liver, having been shown to be capable of giving rise both to hepatocytes and to bile duct cells (Petersen et al., 1998). The majority of HOC studies have been conducted in var- ious rat models; however, a mouse model that allows for the isolation of large quantities of HOCs was recently devel- oped. This model incorporates the chemical 3,5-diethoxy- carbonyl-1,4-dihydrocollidin (DDC) at a 0.1% concentra- tion in the normal chow (Preisegger et al., 1999). Development of this mouse model also led to the charac- terization of an antibody, A6, that recognizes a specific epitope on mouse HOCs (Factor et al., 1990). In conjunction with this new mouse oval cell model and the two-step liver perfusion technique (Seglen, 1979), we have developed a enrichment protocol that allows us to isolate a greater than 90% pure Sca-1 + oval cell population from the DDC- treated mouse liver (Petersen et al., 2003). Trans-differentiation, the ability of stem cells from one tissue to generate cells characteristic of an entirely different tissue, is of interest not only because in it lies the true answer to the multipotent capabilities of the adult “stem” cells, but also because it may provide an easily accessible, noncontroversial source of cells for future autologous trans- plantation therapies. The use of stem cell therapy in treating neurodegenerative disorders has attracted considerable at- tention lately. The trans-differentiation of bone marrow- * Corresponding author. Department of Pathology, P.O. Box 100275, University of Florida, Gainesville, FL. Fax: +1-352-392-6249. E-mail address: Petersen@pathology.ufl.edu (B.E. Petersen). 1 Sharing senior authorship. R Available online at www.sciencedirect.com Experimental Neurology 182 (2003) 373–382 www.elsevier.com/locate/yexnr 0014-4886/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserved. doi:10.1016/S0014-4886(03)00058-X