Abstract
BackgroundNeural progenitor cells (NPCs) in the developing neuroepithelium are regulated by intrinsic and extrinsic factors. There is evidence that NPCs form a self-supporting niche for cell maintenance and proliferation. However, molecular interactions and cell-cell contacts and the microenvironment within the neuroepithelium are largely unknown. We hypothesized that cellular proteases especially those associated with the cell surface of NPCs play a role in regulation of progenitor cells in the brain.Methodology/Principal FindingsIn this work, we show that NPCs, isolated from striatal anlage of developing rat brain, express hepatocyte growth factor activator inhibitor-1 and -2 (HAI-1 and HAI-2) that are cell surface-linked serine protease inhibitors. In addition, radial glia cells derived from mouse embryonic stem cells also express HAI-1 and HAI-2. To study the functional significance of HAI-1 and HAI-2 in progenitor cells, we modulated their levels using expression plasmids or silencing RNA (siRNA) transfected into the NPCs. Data showed that overexpression of HAI-1 or HAI-2 decreased cell proliferation of cultured NPCs, whilst their siRNAs had opposite effects. HAI-1 also influenced NPC differentiation by increasing the number of glial fibrillary acidic protein (GFAP) expressing cells in the culture. Expression of HAI-1 in vivo decreased cell proliferation in developing neuroepithelium in E15 old animals and promoted astrocyte cell differentiation in neonatal animals. Studying the regulation of HAI-1, we observed that Bone morphogenetic protein-2 (BMP-2) and BMP-4 increased HAI-1 levels in the NPCs. Experiments using HAI-1-siRNA showed that these BMPs act on the NPCs partly in a HAI-1-dependent manner.ConclusionsThis study shows that the cell-surface serine protease inhibitors, HAI-1 and HAI-2 influence proliferation and cell fate of NPCs and their expression levels are linked to BMP signaling. Modulation of the levels and actions of HAI-1 in NPCs may be of a potential value in stem cell therapies in various brain diseases.
Highlights
Interactions between proteases and their inhibitors play an important role in development and post-injury tissue remodeling
This study shows that the cell-surface serine protease inhibitors, Hepatocyte growth factor activator inhibitor-1 (HAI-1) and HAI-2 influence proliferation and cell fate of Neural progenitor cells (NPCs) and their expression levels are linked to BMP signaling
NPCs Express the Cell-surface Proteins HAI-1 and HAI-2 In this study, we observed that HAI-1 and HAI-2 are expressed by nestin-positive NPCs in the embryonic (E17) and in the postnatal (P1) old rat neuroepithelium, as shown by immunostaining of dorsal cortex sections (Fig. 1A–D)
Summary
Interactions between proteases and their inhibitors play an important role in development and post-injury tissue remodeling. NPCs are present in the developing neuroepithelium in a local microenvironment and form a self-supporting niche that regulates cell maintenance and proliferation [3]. In this local tissue milieu the stem and progenitor cells can be in contact with other cell types such as endothelial cells and immature neuroblasts and glial cells [2,3]. Apart from cell adhesion molecules and integrins little is known about cell surfaceassociated proteins and how they influence NPCs. In this study, we have focused on the expression of cell-surface linked protease inhibitors in the NPCs and whether these putative molecules might influence cell proliferation or differentiation of the NPCs. Neural progenitor cells (NPCs) in the developing neuroepithelium are regulated by intrinsic and extrinsic factors. We hypothesized that cellular proteases especially those associated with the cell surface of NPCs play a role in regulation of progenitor cells in the brain
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