| Abstract No.: | B-B2063 |
| Country: | Canada |
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| Title: | 9-CIS-RETINOIC ACID AT LOW CONCENTRATIONS ATTENUATES LIPOPOLYSACCHARIDE-MEDIATED ACTIVATION OF MICROGLIA THROUGH THE REDUCTION IN CELL NUMBER AND CHANGES IN MORPHOLOGY |
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| Authors/Affiliations: | 1 Mark Farso*; 1 Rémi Quirion;
1 Douglas Mental Health University Institute & Department of Psychiatry, McGill University, Montreal, QC, Canada
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| Content: | Microglial activation has been implicated in the pathogenesis of various neurodegenerative diseases. Therefore, modulating the activation profile of microglia may represent a therapeutic target for combating the inflammatory and immune processes that could participate in neurodegeneration. Recent reports indicate that the active metabolite of vitamin A, retinoic acid (RA), attenuates lipopolysaccharide (LPS)-induced microglial activation by suppressing the inflammatory responses – reduced production of nitrite (NO2-) and cytokines (e.g. TNF-α) (Dheen et al. Glia. 2005;50(1):21-31; Xu & Drew, J Neuroimmunol. 2006;171(1-2):135-44; Xu et al. J Neurosci Res. 2005;81(3):403-11). Objective: The current study sought to further elucidate the effects of 9-Cis-RA (RA) on microglial viability, number and morphology during LPS exposure. Methods: Microglia were isolated from cortical glial cultures of the brains of decapitated Sprague Dawley rats (postnatal days 1-2) at 10 days in vitro. After a 16h incubation in Dulbecco’s Modified Eagle’s Medium (+ 10% foetal bovine serum and 0.05µg/ml insulin) microglial cultures were maintained in Neurobasal™ medium (NBM) (+ 0.5mM glutamine and 2% B-27 supplements without anti-oxidants) for an additional 6-7h. The cells were then exposed to 1µg/ml LPS in the presence or absence of 1-10µM RA in NBM (without supplements) for 24h. Sample supernatant was collected for nitrite detection and the fixed cells were exposed to 1µg/ml of the Hoechst and Propidium Iodide (PI) dye for the assessment of cell number (Yahyavi-Firouz-Abadi et al. Neuroscience. 2007;144(3):1075-86) and cell death (Takano et al. Neuroscience. 2003;120(4):961-67), respectively. Results: A 24h exposure of LPS induced a marked change in microglial morphology and increased production of NO2- with minimal cell death when compared to the vehicle. However, RA at 1-10µM reduced LPS-mediated production of NO2- and the number of Hoechst positive cells compared to LPS alone. Furthermore, PI staining revealed that increasing concentrations of RA was toxic to these cells. Phase-contrast microscopy indicated that in the presence of LPS lower concentrations of RA may induce changes in microglial morphology that resembles a resting phenotype and higher concentrations which produce morphologies indicative of cell death. Conclusion: Cell death may contribute to the reduction in microglial activation observed at higher concentrations of RA. However, in addition to the diminished production of NO2- the concomitant reduction in microglial number may also play a role in the attenuation of LPS-mediated microglial activation at lower concentrations of RA. Overall, these results provide further evidence for the anti-inflammatory actions of RA in activated microglia. |
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