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Regulation of retinal glial cell proliferation by antiproliferative molecules
Abstract:
Glial cells normally do not proliferate in the adult retina despite the presence of glial mitogens. In this study, we examined the hypothesis that endogenous antiproliferative molecules inhibit the effects of glial mitogens. Using cultures of glial cells obtained from the adult human retina, we found that transforming growth factor beta 2 (TGF beta 2) and a metabotrophic glutamate agonist (t-ACPD) inhibit the mitogenic effects of basic fibroblast growth factor, platelet-derived growth factor, epidermal growth factor and insulin-like growth factor-1. These antiproliferative effects may involve activation of protein kinase C (PKC) since chelerythine, a specific PKC inhibitor, blocks the antiproliferative effects of TGF beta 2 and t-ACPD. Furthermore, exposure of the glia to a phorbol ester mimics the inhibitory effects of TGF beta 2 or t-ACPD. Although TGF beta 2 and t-ACPD markedly inhibit a number of mitogens, they do not alter the mitogenic response of retinal glia to thrombin and glutamate. A common characteristic of the mitogens sensitive to TGF beta 2 or t-ACPD is activation of tyrosine kinase-linked receptors. In contrast, thrombin acts at a G-protein-linked receptor, and glutamate stimulates retinal glial proliferation via activation of an NMDA receptor. It appears that TGF beta 2 and t-ACPD may selectively inhibit retinal glial mitogenesis mediated by activation of tyrosine kinase-linked receptors. Our experiments support the idea that endogenous antiproliferative molecules play a role in preventing glial proliferation in the retina.
Insights
Endogenous antiproliferative molecules like transforming growth factor beta 2 (TGF beta 2) prevent adult human retinal glial cell proliferation. These molecules selectively inhibit growth factors acting via tyrosine kinase-linked receptors.
Area of Science:
- Ophthalmology
- Neuroscience
- Cell Biology
Background:
- Glial cells in the adult retina typically do not proliferate.
- Glial mitogens are present in the adult retina, suggesting an inhibitory mechanism is at play.
Purpose of the Study:
- To investigate the hypothesis that endogenous antiproliferative molecules inhibit glial mitogens in the adult human retina.
- To identify specific molecules and signaling pathways involved in regulating retinal glial cell proliferation.
Main Methods:
- Culturing adult human retinal glial cells.
- Treating glial cells with various growth factors (mitogens) and potential inhibitors.
- Assessing antiproliferative effects using specific inhibitors (e.g., chelerythine) and activators (e.g., phorbol ester).
- Analyzing signaling pathways, including protein kinase C (PKC) and receptor types (tyrosine kinase-linked vs. G-protein-linked).
Main Results:
- Transforming growth factor beta 2 (TGF beta 2) and t-ACPD significantly inhibit the mitogenic effects of several growth factors (bFGF, PDGF, EGF, IGF-1).
- These inhibitory effects are blocked by a protein kinase C (PKC) inhibitor and mimicked by a PKC activator.
- TGF beta 2 and t-ACPD do not inhibit mitogenesis induced by thrombin or glutamate, which act via different receptor pathways.
- Sensitive mitogens activate tyrosine kinase-linked receptors, while insensitive mitogens activate G-protein-linked or NMDA receptors.
Conclusions:
- Endogenous molecules like TGF beta 2 and t-ACPD selectively inhibit retinal glial mitogenesis mediated by tyrosine kinase-linked receptors.
- Protein kinase C (PKC) signaling is involved in the antiproliferative effects of TGF beta 2 and t-ACPD.
- These findings support the role of endogenous antiproliferative factors in maintaining retinal glial quiescence.