Proceedings of The Physiological Society
King's College London (2011) Proc Physiol Soc 22, PC19
The role of the orphan nuclear receptor TLX in IL-1+
S. Ryan1, Y. M. Nolan1
1. Anatomy and Neuroscience, University College Cork, Cork, Ireland.
The orphan nuclear receptor TLX is a key regulator of neurogenesis, which occurs throughout the embryonic brain, and in the dentate gyrus of the adult hippocampus. It is required to maintain neural precursor cells (NPCs) in an undifferentiated state (Shi et al, 2003). Neurogenesis is impaired in Alzheimer’s disease, major depression and bipolar disorder. Inflammation is also implicated in these disorders due to increased levels of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus. IL-1β has also been shown to negatively influence neurogenesis. Although data is emerging on the role of TLX in neural development, the effect of inflammatory modulators on TLX has not yet been explored. The aims of this study were to 1) assess the effect of IL-1β on the expression of TLX within proliferating NPCs prepared from adult rat dentate gyrus, and 2) determine if pharmacological inhibition of the IL-1 type 1 receptor (IL-1R1) prevents IL-1β-induced changes in TLX expression within proliferating cells. Neurosphere cultures were established from dentate gyri pooled from two 2-3 month old male Sprague Dawley rats and were allowed to proliferate for 7 days in vitro (DIV) as previously described (Nolan et al., 2010). Cells were treated with IL-1β (10ng/ml or 100ng/ml) and/or IL-1 receptor antagonist (IL-1RA) (1μg/ml) for the final 24h of culture. Cells were also treated during this period with 5-bromo-2-deoxyuridine (BrdU) (0.2μM) for detection of proliferating cells. Dissociated neurosphere cells were immunocytochemically stained for IL-1R1 and co-stained for TLX and BrdU. The intensity of TLX expression in proliferating cells was measured by densitometry. IL-1β did not affect the percentage of BrdU+ cells within the culture. Analysis of TLX expression by densitometry showed that IL-1β (100ng/ml) significantly decreased TLX expression in proliferating cells compared to control (10.4±0.4 vs. 7.9±0.3; p<0.001; ANOVA; n=3), while no change was observed in TLX expression within proliferating cells after treatment with IL-1β (10ng/ml). Co-treatment of NPCs with IL-1RA and IL-1β (100ng/ml) blocked the IL-1β-induced decrease in the intensity of TLX within proliferating cells (9.5±0.3 vs 7.9±0.3; p<0.05; ANOVA; n=3). Treatment with IL-1RA alone resulted in a significant increase in the fluorescence intensity of TLX within proliferating cells (11.8±0.3 vs 10.4±0.4; p<0.05; ANOVA; n=3). An IL-1β-induced decrease in expression of TLX in adult hippocampal NPCs suggests that IL-1β prevents these cells from remaining in an undifferentiated state. These results indicate that TLX is susceptible to inflammatory insult and may act as a regulator of adult hippocampal NPC fate in an inflammatory environment.
Where applicable, experiments conform with Society ethical requirements