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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 inactivation in the brain leads to blunted neuroinflammatory response following traumatic brain injury (TBI). TBI were performed on 10–12 month old Ctrl and cKO mice. (A-C) IL6 (B), IL-1β (C) and TNFα (D) levels assayed by ELISA 3 hours and 3 days post-injury. N = 3/genotype. (D-G) Relative GFAP-positive (D and E) or Iba1-positive (F and G) cells in HPC (D and F) or CTX (E and G) in response to TBI at 14 days after TBI. All values were normalized to numbers of NT Ctrl mice. N = 6 mice/genotype. For each mouse, 3 evenly spaced sections were used for quantification. *p < 0.05; **p < 0.01; ***p < 0.001.
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Figure 4: IκBα inactivation in the brain leads to blunted neuroinflammatory response following traumatic brain injury (TBI). TBI were performed on 10–12 month old Ctrl and cKO mice. (A-C) IL6 (B), IL-1β (C) and TNFα (D) levels assayed by ELISA 3 hours and 3 days post-injury. N = 3/genotype. (D-G) Relative GFAP-positive (D and E) or Iba1-positive (F and G) cells in HPC (D and F) or CTX (E and G) in response to TBI at 14 days after TBI. All values were normalized to numbers of NT Ctrl mice. N = 6 mice/genotype. For each mouse, 3 evenly spaced sections were used for quantification. *p < 0.05; **p < 0.01; ***p < 0.001.

Mentions: Neuroinflammation is an invariable feature associated with TBI. This involves the activation of NFκB and the release of pro-inflammatory cytokines including TNFα, IL-1β and IL-6 by astrocytes and microglia. Having characterized the IκBα cKO mice under basal condition, we were interested in understanding how the basal activation of NFκB affects the brain damage following TBI. We performed controlled cortical impact (CCI), which is the most-widely used protocol and known to induce moderate to severe brain injury, to Ctrl and IκBα cKO mice, and measured cytokine levels without injury (NT) or 3 hours and 3 days after CCI (Figure 4A-C). As expected, levels of IL6, IL-1β and TNFα protein displayed time-dependent kinetic changes. All cytokines were strongly upregulated in response to the injury shortly after TBI (3 hour) but returned close to baseline 3 days post injury (Figure 4A-C). Noticeably, at 3 hour after injury, CCI-induced IL6 and IL-1β overexpression was significantly lower in the absence of IκBα (Figure 4A and B). This is also the case with TNFα although to a lesser degree (Figure 4C). No group differences were observed for cytokine expression either under basal condition or 3 days post injury. Combined together, these results indicate that the instant cytokine-associated inflammatory response to brain injury in IκBα cKO mice was blunted while later-phase cytokine expression was largely unaffected.


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 inactivation in the brain leads to blunted neuroinflammatory response following traumatic brain injury (TBI). TBI were performed on 10–12 month old Ctrl and cKO mice. (A-C) IL6 (B), IL-1β (C) and TNFα (D) levels assayed by ELISA 3 hours and 3 days post-injury. N = 3/genotype. (D-G) Relative GFAP-positive (D and E) or Iba1-positive (F and G) cells in HPC (D and F) or CTX (E and G) in response to TBI at 14 days after TBI. All values were normalized to numbers of NT Ctrl mice. N = 6 mice/genotype. For each mouse, 3 evenly spaced sections were used for quantification. *p < 0.05; **p < 0.01; ***p < 0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3473257&req=5

Figure 4: IκBα inactivation in the brain leads to blunted neuroinflammatory response following traumatic brain injury (TBI). TBI were performed on 10–12 month old Ctrl and cKO mice. (A-C) IL6 (B), IL-1β (C) and TNFα (D) levels assayed by ELISA 3 hours and 3 days post-injury. N = 3/genotype. (D-G) Relative GFAP-positive (D and E) or Iba1-positive (F and G) cells in HPC (D and F) or CTX (E and G) in response to TBI at 14 days after TBI. All values were normalized to numbers of NT Ctrl mice. N = 6 mice/genotype. For each mouse, 3 evenly spaced sections were used for quantification. *p < 0.05; **p < 0.01; ***p < 0.001.
Mentions: Neuroinflammation is an invariable feature associated with TBI. This involves the activation of NFκB and the release of pro-inflammatory cytokines including TNFα, IL-1β and IL-6 by astrocytes and microglia. Having characterized the IκBα cKO mice under basal condition, we were interested in understanding how the basal activation of NFκB affects the brain damage following TBI. We performed controlled cortical impact (CCI), which is the most-widely used protocol and known to induce moderate to severe brain injury, to Ctrl and IκBα cKO mice, and measured cytokine levels without injury (NT) or 3 hours and 3 days after CCI (Figure 4A-C). As expected, levels of IL6, IL-1β and TNFα protein displayed time-dependent kinetic changes. All cytokines were strongly upregulated in response to the injury shortly after TBI (3 hour) but returned close to baseline 3 days post injury (Figure 4A-C). Noticeably, at 3 hour after injury, CCI-induced IL6 and IL-1β overexpression was significantly lower in the absence of IκBα (Figure 4A and B). This is also the case with TNFα although to a lesser degree (Figure 4C). No group differences were observed for cytokine expression either under basal condition or 3 days post injury. Combined together, these results indicate that the instant cytokine-associated inflammatory response to brain injury in IκBα cKO mice was blunted while later-phase cytokine expression was largely unaffected.

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