Limits...
Chronic intermittent hypoxia exerts CNS region-specific effects on rat microglial inflammatory and TLR4 gene expression.

Smith SM, Friedle SA, Watters JJ - PLoS ONE (2013)

Bottom Line: In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally.Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia.We found that microglia from different CNS regions responded to IH differently.

View Article: PubMed Central - PubMed

Affiliation: Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin, United States of America.

ABSTRACT
Intermittent hypoxia (IH) during sleep is a hallmark of sleep apnea, causing significant neuronal apoptosis, and cognitive and behavioral deficits in CNS regions underlying memory processing and executive functions. IH-induced neuroinflammation is thought to contribute to cognitive deficits after IH. In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally. To test this hypothesis, adult rats were exposed to intermittent hypoxia (2 min intervals of 10.5% O2) for 8 hours/day during their respective sleep cycles for 1, 3 or 14 days. Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia. Inflammatory gene expression was also assessed in tissue homogenates (containing all CNS cells). We found that microglia from different CNS regions responded to IH differently. Cortical microglia had longer lasting inflammatory gene expression whereas spinal microglial gene expression was rapid and transient. We also observed that inflammatory gene expression in microglia frequently differed from that in tissue homogenates from the same region, indicating that cells other than microglia also contribute to IH-induced neuroinflammation. Lastly, microglial TLR4 mRNA levels were strongly upregulated by IH in a region- and time-dependent manner, and the increase in TLR4 expression appeared to coincide with timing of peak inflammatory gene expression, suggesting that TLR4 may play a role in IH-induced neuroinflammation. Together, these data indicate that microglial-specific neuroinflammation may play distinct roles in the effects of intermittent hypoxia in different CNS regions.

Show MeSH

Related in: MedlinePlus

Intermittent hypoxia-induced TLR4 gene expression in microglia differs by time and CNS region.TLR4 gene expression was analyzed by qRT-PCR in immunomagnetically-separated microglia from the cortex, brainstem and spinal cord of healthy male rats exposed either to normoxia or IH for 1, 3 or 14 days. Means +/− 1 SEM are presented relative to expression in normoxic controls. **p<0.01; ***p<0.001; #p = 0.085.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3852519&req=5

pone-0081584-g004: Intermittent hypoxia-induced TLR4 gene expression in microglia differs by time and CNS region.TLR4 gene expression was analyzed by qRT-PCR in immunomagnetically-separated microglia from the cortex, brainstem and spinal cord of healthy male rats exposed either to normoxia or IH for 1, 3 or 14 days. Means +/− 1 SEM are presented relative to expression in normoxic controls. **p<0.01; ***p<0.001; #p = 0.085.

Mentions: Because TLR4 plays an important role in mediating inflammatory gene induction in microglia, and endogenous TLR4 ligands are increased in IH-susceptible CNS regions, we evaluated the expression of TLR4 over time following IH exposure (Fig. 4). Very interestingly, the largest increase in TLR4 mRNA levels occurred in microglia from the cortex where expression was increased by approximately 12-fold at 14 days of IH (p = 0.001). The apparent 2-fold increase at 1 day of IH was not significant (p = 0.398 by ANOVA). TLR4 expression in microglia from the medulla was increased by 7-fold at 3 days of IH (p = <0.001), and remained elevated (by 4-fold at 14 days (p = 0.001). In spinal microglia, TLR4 expression was not significantly increased at any time point tested, although an approximate 3-fold increase at 3 days of IH was observed (p =  0.085 by ANOVA).


Chronic intermittent hypoxia exerts CNS region-specific effects on rat microglial inflammatory and TLR4 gene expression.

Smith SM, Friedle SA, Watters JJ - PLoS ONE (2013)

Intermittent hypoxia-induced TLR4 gene expression in microglia differs by time and CNS region.TLR4 gene expression was analyzed by qRT-PCR in immunomagnetically-separated microglia from the cortex, brainstem and spinal cord of healthy male rats exposed either to normoxia or IH for 1, 3 or 14 days. Means +/− 1 SEM are presented relative to expression in normoxic controls. **p<0.01; ***p<0.001; #p = 0.085.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3852519&req=5

pone-0081584-g004: Intermittent hypoxia-induced TLR4 gene expression in microglia differs by time and CNS region.TLR4 gene expression was analyzed by qRT-PCR in immunomagnetically-separated microglia from the cortex, brainstem and spinal cord of healthy male rats exposed either to normoxia or IH for 1, 3 or 14 days. Means +/− 1 SEM are presented relative to expression in normoxic controls. **p<0.01; ***p<0.001; #p = 0.085.
Mentions: Because TLR4 plays an important role in mediating inflammatory gene induction in microglia, and endogenous TLR4 ligands are increased in IH-susceptible CNS regions, we evaluated the expression of TLR4 over time following IH exposure (Fig. 4). Very interestingly, the largest increase in TLR4 mRNA levels occurred in microglia from the cortex where expression was increased by approximately 12-fold at 14 days of IH (p = 0.001). The apparent 2-fold increase at 1 day of IH was not significant (p = 0.398 by ANOVA). TLR4 expression in microglia from the medulla was increased by 7-fold at 3 days of IH (p = <0.001), and remained elevated (by 4-fold at 14 days (p = 0.001). In spinal microglia, TLR4 expression was not significantly increased at any time point tested, although an approximate 3-fold increase at 3 days of IH was observed (p =  0.085 by ANOVA).

Bottom Line: In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally.Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia.We found that microglia from different CNS regions responded to IH differently.

View Article: PubMed Central - PubMed

Affiliation: Department of Comparative Biosciences, University of Wisconsin, Madison, Wisconsin, United States of America.

ABSTRACT
Intermittent hypoxia (IH) during sleep is a hallmark of sleep apnea, causing significant neuronal apoptosis, and cognitive and behavioral deficits in CNS regions underlying memory processing and executive functions. IH-induced neuroinflammation is thought to contribute to cognitive deficits after IH. In the present studies, we tested the hypothesis that IH would differentially induce inflammatory factor gene expression in microglia in a CNS region-dependent manner, and that the effects of IH would differ temporally. To test this hypothesis, adult rats were exposed to intermittent hypoxia (2 min intervals of 10.5% O2) for 8 hours/day during their respective sleep cycles for 1, 3 or 14 days. Cortex, medulla and spinal cord tissues were dissected, microglia were immunomagnetically isolated and mRNA levels of the inflammatory genes iNOS, COX-2, TNFα, IL-1β and IL-6 and the innate immune receptor TLR4 were compared to levels in normoxia. Inflammatory gene expression was also assessed in tissue homogenates (containing all CNS cells). We found that microglia from different CNS regions responded to IH differently. Cortical microglia had longer lasting inflammatory gene expression whereas spinal microglial gene expression was rapid and transient. We also observed that inflammatory gene expression in microglia frequently differed from that in tissue homogenates from the same region, indicating that cells other than microglia also contribute to IH-induced neuroinflammation. Lastly, microglial TLR4 mRNA levels were strongly upregulated by IH in a region- and time-dependent manner, and the increase in TLR4 expression appeared to coincide with timing of peak inflammatory gene expression, suggesting that TLR4 may play a role in IH-induced neuroinflammation. Together, these data indicate that microglial-specific neuroinflammation may play distinct roles in the effects of intermittent hypoxia in different CNS regions.

Show MeSH
Related in: MedlinePlus