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IκBα deficiency in brain leads to elevated basal neuroinflammation and attenuated response following traumatic brain injury: implications for functional recovery.

Lian H, Shim DJ, Gaddam SS, Rodriguez-Rivera J, Bitner BR, Pautler RG, Robertson CS, Zheng H - Mol Neurodegener (2012)

Bottom Line: By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development.However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated.We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Huffington Center on Aging Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT

Background: The transcription factor NFκB is an important mediator of cell survival and inflammation in the immune system. In the central nervous system (CNS), NFκB signaling has been implicated in regulating neuronal survival following acute pathologic damage such as traumatic brain injury (TBI) and stroke. NFκB is normally bound by the principal inhibitory protein, IκBα, and sequestered in the cytoplasm. Activation of NFκB requires the degradation of IκBα, thereby freeing NFκB to translocate to the nucleus and activate the target genes. Mice deficient in IκBα display deregulated and sustained NFκB activation and early postnatal lethality, highlighting a critical role of IκBα in NFκB regulation.

Results: We investigated the role of IκBα in regulating NFκB activity in the brain and the effects of the NFκB/IκBα pathway in mediating neuroinflammation under both physiological and brain injury conditions. We report that astrocytes, but not neurons, exhibit prominent NFκB activity, and that basal NFκB activity in astrocytes is elevated in the absence of IκBα. By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development. However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated. This leads to impaired inflammatory responses following TBI and worsened brain damage including higher blood brain barrier permeability, increased injury volumes and enlarged ventricle volumes.

Conclusions: We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation. We further demonstrate that IκBα plays an important role in regulating NFκB activity in the brain and a robust NFκB/IκBα-mediated neuroinflammatory response immediately following TBI is beneficial.

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IκBα cKO mice display increased BBB permeability and tissue damage after TBI. (A) Representative T1-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI. Water droplets (separate circles in upper left) serve as the background control and uninjured areas (marked in yellow) are used as the internal control. Injured areas were marked in red. (B) Representative T2-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI with the injured brain tissue marked in red. (C) Representative images of Nissl stained brain sections from mice survived 14 days after TBI. Scale bar: 1 mm. (D) Quantification of relative BBB permeability (normalized intensity) based on T1-weighted MRI images shown in (A). N = 3 for each group. (E) Quantification of total injury volume based on T2-weighted MRI images shown in (B). N = 3 for each group/time point. (F) Relative ventricular sizes were calculated as pixel numbers taken by ventricles divided by that of whole brain substances based on Nissl staining results. L-LV: left lateral ventricle, D-3 V: dorsal third ventricle, V-3 V: ventral third ventricle. N = 5-6 mice/genotype. *p < 0.05; **p < 0.01.
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Figure 5: IκBα cKO mice display increased BBB permeability and tissue damage after TBI. (A) Representative T1-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI. Water droplets (separate circles in upper left) serve as the background control and uninjured areas (marked in yellow) are used as the internal control. Injured areas were marked in red. (B) Representative T2-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI with the injured brain tissue marked in red. (C) Representative images of Nissl stained brain sections from mice survived 14 days after TBI. Scale bar: 1 mm. (D) Quantification of relative BBB permeability (normalized intensity) based on T1-weighted MRI images shown in (A). N = 3 for each group. (E) Quantification of total injury volume based on T2-weighted MRI images shown in (B). N = 3 for each group/time point. (F) Relative ventricular sizes were calculated as pixel numbers taken by ventricles divided by that of whole brain substances based on Nissl staining results. L-LV: left lateral ventricle, D-3 V: dorsal third ventricle, V-3 V: ventral third ventricle. N = 5-6 mice/genotype. *p < 0.05; **p < 0.01.

Mentions: To test the functional effect of attenuated cytokine release resulting from brain IκBα deficiency, we performed MRI scans to measure blood brain barrier (BBB) permeability (Figure 5A) and tissue damage (Figure 5B) in control and IκBα cKO mice at 3 hours and 3 days post-TBI. Quantification of MRI images showed that both the BBB permeability (Figure 5D) and the volume of injured tissue (Figure 5E) exhibited similar time-dependent differences as the cytokine profiles, i.e., significantly higher BBB permeability and brain injury can be detected in IκBα cKO mutant at 3 hours but not 3 days after TBI. Altered cytokine expression and BBB permeability in IκBα cKO mice immediately following TBI is associated with their impaired long-term recovery. Assessment of morphological changes by Nissl staining of comparable sections and quantification of the sizes of left lateral ventricle (L-LV), dorsal third ventricle (D-LV) and ventral third ventricle (V-3 V) 14 days after TBI showed that, while L-LV and D-LV did not show statistical difference, V-3 V was significantly enlarged in IκBα cKO mice (Figure 5C and quantified in F).


IκBα deficiency in brain leads to elevated basal neuroinflammation and attenuated response following traumatic brain injury: implications for functional recovery.

Lian H, Shim DJ, Gaddam SS, Rodriguez-Rivera J, Bitner BR, Pautler RG, Robertson CS, Zheng H - Mol Neurodegener (2012)

IκBα cKO mice display increased BBB permeability and tissue damage after TBI. (A) Representative T1-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI. Water droplets (separate circles in upper left) serve as the background control and uninjured areas (marked in yellow) are used as the internal control. Injured areas were marked in red. (B) Representative T2-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI with the injured brain tissue marked in red. (C) Representative images of Nissl stained brain sections from mice survived 14 days after TBI. Scale bar: 1 mm. (D) Quantification of relative BBB permeability (normalized intensity) based on T1-weighted MRI images shown in (A). N = 3 for each group. (E) Quantification of total injury volume based on T2-weighted MRI images shown in (B). N = 3 for each group/time point. (F) Relative ventricular sizes were calculated as pixel numbers taken by ventricles divided by that of whole brain substances based on Nissl staining results. L-LV: left lateral ventricle, D-3 V: dorsal third ventricle, V-3 V: ventral third ventricle. N = 5-6 mice/genotype. *p < 0.05; **p < 0.01.
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Figure 5: IκBα cKO mice display increased BBB permeability and tissue damage after TBI. (A) Representative T1-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI. Water droplets (separate circles in upper left) serve as the background control and uninjured areas (marked in yellow) are used as the internal control. Injured areas were marked in red. (B) Representative T2-weighted MRI images of Ctrl and cKO mice 3 hour and 3 day after TBI with the injured brain tissue marked in red. (C) Representative images of Nissl stained brain sections from mice survived 14 days after TBI. Scale bar: 1 mm. (D) Quantification of relative BBB permeability (normalized intensity) based on T1-weighted MRI images shown in (A). N = 3 for each group. (E) Quantification of total injury volume based on T2-weighted MRI images shown in (B). N = 3 for each group/time point. (F) Relative ventricular sizes were calculated as pixel numbers taken by ventricles divided by that of whole brain substances based on Nissl staining results. L-LV: left lateral ventricle, D-3 V: dorsal third ventricle, V-3 V: ventral third ventricle. N = 5-6 mice/genotype. *p < 0.05; **p < 0.01.
Mentions: To test the functional effect of attenuated cytokine release resulting from brain IκBα deficiency, we performed MRI scans to measure blood brain barrier (BBB) permeability (Figure 5A) and tissue damage (Figure 5B) in control and IκBα cKO mice at 3 hours and 3 days post-TBI. Quantification of MRI images showed that both the BBB permeability (Figure 5D) and the volume of injured tissue (Figure 5E) exhibited similar time-dependent differences as the cytokine profiles, i.e., significantly higher BBB permeability and brain injury can be detected in IκBα cKO mutant at 3 hours but not 3 days after TBI. Altered cytokine expression and BBB permeability in IκBα cKO mice immediately following TBI is associated with their impaired long-term recovery. Assessment of morphological changes by Nissl staining of comparable sections and quantification of the sizes of left lateral ventricle (L-LV), dorsal third ventricle (D-LV) and ventral third ventricle (V-3 V) 14 days after TBI showed that, while L-LV and D-LV did not show statistical difference, V-3 V was significantly enlarged in IκBα cKO mice (Figure 5C and quantified in F).

Bottom Line: By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development.However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated.We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Huffington Center on Aging Baylor College of Medicine, Houston, TX 77030, USA.

ABSTRACT

Background: The transcription factor NFκB is an important mediator of cell survival and inflammation in the immune system. In the central nervous system (CNS), NFκB signaling has been implicated in regulating neuronal survival following acute pathologic damage such as traumatic brain injury (TBI) and stroke. NFκB is normally bound by the principal inhibitory protein, IκBα, and sequestered in the cytoplasm. Activation of NFκB requires the degradation of IκBα, thereby freeing NFκB to translocate to the nucleus and activate the target genes. Mice deficient in IκBα display deregulated and sustained NFκB activation and early postnatal lethality, highlighting a critical role of IκBα in NFκB regulation.

Results: We investigated the role of IκBα in regulating NFκB activity in the brain and the effects of the NFκB/IκBα pathway in mediating neuroinflammation under both physiological and brain injury conditions. We report that astrocytes, but not neurons, exhibit prominent NFκB activity, and that basal NFκB activity in astrocytes is elevated in the absence of IκBα. By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development. However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated. This leads to impaired inflammatory responses following TBI and worsened brain damage including higher blood brain barrier permeability, increased injury volumes and enlarged ventricle volumes.

Conclusions: We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation. We further demonstrate that IκBα plays an important role in regulating NFκB activity in the brain and a robust NFκB/IκBα-mediated neuroinflammatory response immediately following TBI is beneficial.

Show MeSH
Related in: MedlinePlus