Induction of Astrocyte Differentiation by Endothelial Cells

Abstract

Here we have investigated the mechanisms that control astrocyte differentiation within the developing rat optic nerve. Astrocytes are normally generated by astrocyte precursor cells within the embryonic optic nerve. We show that there is a close temporal and spatial correlation between endothelial and astrocyte differentiation. We tested the potential role of endothelial cells in inducing astrocyte differentiation by developing an immunopanning method to highly purify endothelial cells from developing optic nerves. We show that the purified endothelial cells, but not other embryonic optic nerve cell types, strongly induce the differentiation of purified astrocyte precursor cells into astrocytes in vitro. Leukemia inhibitory factor (LIF) and LIF receptors have been implicated previously in astrocyte differentiation in vivo. We show that purified endothelial cells express LIF mRNA and that their ability to induce astrocyte differentiation is prevented by a neutralizing anti-LIF, but not anti-ciliary neurotrophic factor, antiserum. These findings demonstrate a role for endothelial cells in inducing astrocyte differentiation. The induction of astrocyte differentiation by endothelial cells makes sense phylogenetically, anatomically, and functionally, because astrocytes evolved concurrently with brain vasculature and ensheathe capillaries throughout the brain. The ability to purify and culture astrocytes and endothelial cells should provide an excellent model system for future studies of bloodbrain barrier development. Key words: glial development; vasculature; capillaries; astrocyte precursor cells; leukemia inhibitory factor (LIF); endothelial cells; blood-brain barrierTo better understand the cell-cell interactions that control astrocyte development, we have been focusing on the development of glial cells within the rat optic nerve. The optic nerve is part of central white matter and, in addition to the axons of retinal ganglion cells, contains the same glial cell types found in white matter throughout the CNS. Previous studies have found that two different glial lineages develop within the nerve Miller et al., 1985Miller et al., , 1989. Type-1 astrocytes develop in the embryonic optic nerve from astrocyte precursor cells (APCs) Miller et al., 1985Miller et al., , 1989Mi and Barres, 1999), whereas oligodendrocytes develop in the postnatal optic nerve from oligodendrocyte precursor cells (Raff et al., 1983;Miller et al., 1985).In the developing brain, it has been found previously that astrocytes are generated by neural stem cells located in the ventricular zone and subventricular zone (Levison and Goldman, 1993;Goldman, 1996;Barres, 1999). The generation of astrocytes from multipotent neural stem cells in culture is induced by bone morphogenetic factors, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), basic FGF (bFGF), and Notch signaling Lillien et al., 1988;Yoshida et al., 1993;Nakagaito et al., 1995;Gross et al., 1996;Johe et al., 1996;Richards et al., 1996;Bonni et al., 1997;Qian et al., 19...

Vascular Endothelial Cells Promote Acute Plasticity in Ependymoglial Cells of the Neuroendocrine Brain

“…Endothelial cells of the median eminence (ECME) were isolated from 10-d-old rats using a procedure adapted from a protocol kindly provided by Dr. Ben Barres (Stanford, CA) (Mi et al, 2001). In brief, minced median eminence explants were enzymatically dissociated at 37°C for 90 min by using a papain solution (33 U/ml) (Worthington/ Cooper, Lakewood, NJ) in MEM/HEPES (Invitrogen) containing L-cysteine (0.4 mg/ml) (Sigma) and DNase (125 U/ml) (Sigma).…”

“…To purify ECME, we incubated enzymatically dissociated P10 median eminence cells first on a panning dish coated with a monoclonal anti-Thy1.1 antibody to deplete microglia and meningeal fibroblasts (Mi and Barres, 1999) and second on a dish coated with a monoclonal anti-RAN-2 antibody to retain astrocytes and ependymal cells (Bartlett et al, 1981). The remaining floating cells were incubated on a third dish coated with BSLII, which selects endothelial cells (Mi et al, 2001). ECME were then removed from the BSLII-coated dish by trypsinization, seeded onto 12-well plates, and grown to confluence.…”

A potential role for β‐ and γ‐crystallins in the vascular remodeling of the eye

“…While oligodendrocytes of the glial cell family have been shown to express crystallins, there has not been a report indicating expression of ␤ and ␥-crystallins by astrocytes (Dabir et al, 2004). The glial cells of the optic nerve contain the same cell types found in the white matter throughout the Central Nervous System (CNS) (Mi et al, 2001). Type-1 astrocytes develop in the embryonic optic nerve from astrocyte precursor cells (APC) (Raff et al, 1984;Miller et al, 1985Miller et al, , 1989Mi and Barres, 1999).…”

The Role of Astrocytes in Epileptogenesis

“…There is some evidence of cross-talk with astrocytes. Indeed, endothelial cells seem to be the primary source of leukemia inhibitory factor (LIF), which helps induce astrocyte differentiation (Mi et al;2001 (Ballabh et al;2004). Pericytes can also help to stabilize capillaries that are recently formed by endothelial cells, thereby regulating angiogenesis (Balabanov & Dore-Duffy, 1998).…”