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TNFR1-JNK signaling is the shared pathway of neuroinflammation and neurovascular damage after LPS-sensitized hypoxic-ischemic injury in the immature brain.

Wang LW, Chang YC, Chen SJ, Tseng CH, Tu YF, Liao NS, Huang CC, Ho CJ - J Neuroinflammation (2014)

Bottom Line: Etanercept (a TNF-α inhibitor) and AS601245 (a JNK inhibitor) protected against LPS-sensitized HI brain injury.The TNFR1-knockout but not TNFR2-knockout pups had significant reduction in JNK activation, attenuation of microglial activation, BBB breakdown and cleaved caspase-3 expression, and showed markedly less cortical and white matter injury than the wild-type pups after LPS-sensitized HI.TNFR1-JNK signaling is the shared pathway leading to neuroinflammation and neurovascular damage after LPS-sensitized HI in the immature brain.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Chi Mei Medical Center, Tainan, 710, Taiwan. lanwan@ms67.url.com.tw.

ABSTRACT

Background: Hypoxic-ischemia (HI) and inflammation are the two major pathogenic mechanisms of brain injury in very preterm infants. The neurovascular unit is the major target of HI injury in the immature brain. Systemic inflammation may worsen HI by up-regulating neuroinflammation and disrupting the blood-brain barrier (BBB). Since neurons and oligodendrocytes, microvascular endothelial cells, and microglia may closely interact with each other, there may be a common signaling pathway leading to neuroinflammation and neurovascular damage after injury in the immature brain. TNF-α is a key pro-inflammatory cytokine that acts through the TNF receptor (TNFR), and c-Jun N-terminal kinases (JNK) are important stress-responsive kinases.

Objective: To determine if TNFR1-JNK signaling is a shared pathway underlying neuroinflammation and neurovascular injury after lipopolysaccharide (LPS)-sensitized HI in the immature brain.

Methods: Postpartum (P) day-5 mice received LPS or normal saline (NS) injection before HI. Immunohistochemistry, immunoblotting and TNFR1- and TNFR2-knockout mouse pups were used to determine neuroinflammation, BBB damage, TNF-α expression, JNK activation, and cell apoptosis. The cellular distribution of p-JNK, TNFR1/TNFR2 and cleaved caspase-3 were examined using immunofluorescent staining.

Results: The LPS + HI group had significantly greater up-regulation of activated microglia, TNF-α and TNFR1 expression, and increases of BBB disruption and cleaved caspase-3 levels at 24 hours post-insult, and showed more cortical and white matter injury on P17 than the control and NS + HI groups. Cleaved caspase-3 was highly expressed in microvascular endothelial cells, neurons, and oligodendroglial precursor cells. LPS-sensitized HI also induced JNK activation and up-regulation of TNFR1 but not TNFR2 expression in the microglia, endothelial cells, neurons, and oligodendrocyte progenitors, and most of the TNFR1-positive cells co-expressed p-JNK. Etanercept (a TNF-α inhibitor) and AS601245 (a JNK inhibitor) protected against LPS-sensitized HI brain injury. The TNFR1-knockout but not TNFR2-knockout pups had significant reduction in JNK activation, attenuation of microglial activation, BBB breakdown and cleaved caspase-3 expression, and showed markedly less cortical and white matter injury than the wild-type pups after LPS-sensitized HI.

Conclusion: TNFR1-JNK signaling is the shared pathway leading to neuroinflammation and neurovascular damage after LPS-sensitized HI in the immature brain.

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TNF-α up-regulation, and apoptosis of endothelial cells, neurons, and oligodendrocyte progenitors after lipopolysaccharide (LPS)-sensitized hypoxic-ischemia (HI). Immunofluorescence in the LPS + HI group 24 hours post-insult showed that many Iba1-positive activated microglia co-expressed TNF-α, whereas IB4-positive endothelial cells, NeuN-positive neurons, and O4-postive oligodendrocytes precursor cells co-expressed cleaved caspase-3. Scale bar = 50 μm for IB4 and 25 μm for others. Inset scale bar = 5 μm.
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Fig3: TNF-α up-regulation, and apoptosis of endothelial cells, neurons, and oligodendrocyte progenitors after lipopolysaccharide (LPS)-sensitized hypoxic-ischemia (HI). Immunofluorescence in the LPS + HI group 24 hours post-insult showed that many Iba1-positive activated microglia co-expressed TNF-α, whereas IB4-positive endothelial cells, NeuN-positive neurons, and O4-postive oligodendrocytes precursor cells co-expressed cleaved caspase-3. Scale bar = 50 μm for IB4 and 25 μm for others. Inset scale bar = 5 μm.

Mentions: At 24 hours post-insult, the LPS + HI group, rather than the NS + HI group, had significantly increased Iba1-positive activated microglia and BBB damage (IgG extravasation) (Figure 2B). The effects of LPS and LPS + HI on TNF-α expression were examined using immunoblotting. Compared to NS, LPS injection before HI did not increase TNF-α levels (Figure 2C, upper panel). In contrast, after LPS-sensitized HI, the TNF-α levels were significantly increased at 3 hours, and especially at 24 hours after HI (Figure 2C, lower panel). The LPS + HI pups also had significantly more up-regulation of TNF-α (Figure 2D, upper panel) and cleaved caspase-3 levels (Figure 2D, lower panel) at 24 hours post-insult compared to the NS + HI pups. Further immunofluorescence study in the LPS + HI group showed that Iba1-positive microglia highly expressed TNF-α (Figure 3). Cleaved caspase-3 was highly expressed in the IB4-positive microvascular endothelial cells, NeuN-positive neurons, and O4-positive oligodendroglial precursor cells, indicating that these cells were undergoing apoptosis (Figure 3).Figure 3


TNFR1-JNK signaling is the shared pathway of neuroinflammation and neurovascular damage after LPS-sensitized hypoxic-ischemic injury in the immature brain.

Wang LW, Chang YC, Chen SJ, Tseng CH, Tu YF, Liao NS, Huang CC, Ho CJ - J Neuroinflammation (2014)

TNF-α up-regulation, and apoptosis of endothelial cells, neurons, and oligodendrocyte progenitors after lipopolysaccharide (LPS)-sensitized hypoxic-ischemia (HI). Immunofluorescence in the LPS + HI group 24 hours post-insult showed that many Iba1-positive activated microglia co-expressed TNF-α, whereas IB4-positive endothelial cells, NeuN-positive neurons, and O4-postive oligodendrocytes precursor cells co-expressed cleaved caspase-3. Scale bar = 50 μm for IB4 and 25 μm for others. Inset scale bar = 5 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4300587&req=5

Fig3: TNF-α up-regulation, and apoptosis of endothelial cells, neurons, and oligodendrocyte progenitors after lipopolysaccharide (LPS)-sensitized hypoxic-ischemia (HI). Immunofluorescence in the LPS + HI group 24 hours post-insult showed that many Iba1-positive activated microglia co-expressed TNF-α, whereas IB4-positive endothelial cells, NeuN-positive neurons, and O4-postive oligodendrocytes precursor cells co-expressed cleaved caspase-3. Scale bar = 50 μm for IB4 and 25 μm for others. Inset scale bar = 5 μm.
Mentions: At 24 hours post-insult, the LPS + HI group, rather than the NS + HI group, had significantly increased Iba1-positive activated microglia and BBB damage (IgG extravasation) (Figure 2B). The effects of LPS and LPS + HI on TNF-α expression were examined using immunoblotting. Compared to NS, LPS injection before HI did not increase TNF-α levels (Figure 2C, upper panel). In contrast, after LPS-sensitized HI, the TNF-α levels were significantly increased at 3 hours, and especially at 24 hours after HI (Figure 2C, lower panel). The LPS + HI pups also had significantly more up-regulation of TNF-α (Figure 2D, upper panel) and cleaved caspase-3 levels (Figure 2D, lower panel) at 24 hours post-insult compared to the NS + HI pups. Further immunofluorescence study in the LPS + HI group showed that Iba1-positive microglia highly expressed TNF-α (Figure 3). Cleaved caspase-3 was highly expressed in the IB4-positive microvascular endothelial cells, NeuN-positive neurons, and O4-positive oligodendroglial precursor cells, indicating that these cells were undergoing apoptosis (Figure 3).Figure 3

Bottom Line: Etanercept (a TNF-α inhibitor) and AS601245 (a JNK inhibitor) protected against LPS-sensitized HI brain injury.The TNFR1-knockout but not TNFR2-knockout pups had significant reduction in JNK activation, attenuation of microglial activation, BBB breakdown and cleaved caspase-3 expression, and showed markedly less cortical and white matter injury than the wild-type pups after LPS-sensitized HI.TNFR1-JNK signaling is the shared pathway leading to neuroinflammation and neurovascular damage after LPS-sensitized HI in the immature brain.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatrics, Chi Mei Medical Center, Tainan, 710, Taiwan. lanwan@ms67.url.com.tw.

ABSTRACT

Background: Hypoxic-ischemia (HI) and inflammation are the two major pathogenic mechanisms of brain injury in very preterm infants. The neurovascular unit is the major target of HI injury in the immature brain. Systemic inflammation may worsen HI by up-regulating neuroinflammation and disrupting the blood-brain barrier (BBB). Since neurons and oligodendrocytes, microvascular endothelial cells, and microglia may closely interact with each other, there may be a common signaling pathway leading to neuroinflammation and neurovascular damage after injury in the immature brain. TNF-α is a key pro-inflammatory cytokine that acts through the TNF receptor (TNFR), and c-Jun N-terminal kinases (JNK) are important stress-responsive kinases.

Objective: To determine if TNFR1-JNK signaling is a shared pathway underlying neuroinflammation and neurovascular injury after lipopolysaccharide (LPS)-sensitized HI in the immature brain.

Methods: Postpartum (P) day-5 mice received LPS or normal saline (NS) injection before HI. Immunohistochemistry, immunoblotting and TNFR1- and TNFR2-knockout mouse pups were used to determine neuroinflammation, BBB damage, TNF-α expression, JNK activation, and cell apoptosis. The cellular distribution of p-JNK, TNFR1/TNFR2 and cleaved caspase-3 were examined using immunofluorescent staining.

Results: The LPS + HI group had significantly greater up-regulation of activated microglia, TNF-α and TNFR1 expression, and increases of BBB disruption and cleaved caspase-3 levels at 24 hours post-insult, and showed more cortical and white matter injury on P17 than the control and NS + HI groups. Cleaved caspase-3 was highly expressed in microvascular endothelial cells, neurons, and oligodendroglial precursor cells. LPS-sensitized HI also induced JNK activation and up-regulation of TNFR1 but not TNFR2 expression in the microglia, endothelial cells, neurons, and oligodendrocyte progenitors, and most of the TNFR1-positive cells co-expressed p-JNK. Etanercept (a TNF-α inhibitor) and AS601245 (a JNK inhibitor) protected against LPS-sensitized HI brain injury. The TNFR1-knockout but not TNFR2-knockout pups had significant reduction in JNK activation, attenuation of microglial activation, BBB breakdown and cleaved caspase-3 expression, and showed markedly less cortical and white matter injury than the wild-type pups after LPS-sensitized HI.

Conclusion: TNFR1-JNK signaling is the shared pathway leading to neuroinflammation and neurovascular damage after LPS-sensitized HI in the immature brain.

Show MeSH
Related in: MedlinePlus