Hyperactive behavior in female rats in utero-exposed to group B Streptococcus-induced inflammation.

Group B Streptococcus (GBS) is one the most common bacterium responsible of maternal infections during pregnancy. Offspring in utero-exposed to GBS-induced placental inflammation displayed sex-specific forebrain injuries. Sex differences have been reported in several neuropsychiatric disorders. Hence, we hypothesized that female rats in utero-exposed to GBS may present sex-specific neurobehavioral impairments. Lewis rats were injected intraperitoneally every 12 h from gestational day (G) 19 to G22 with either saline (controls) or inactivated serotype Ia GBS (109 CFU). Before puberty, no difference in terms of spontaneous motor activity, exploratory or anxiety-related behaviors was noticed between experimental conditions. During puberty, GBS-exposed females - but not males - performed worse than same-sex controls in a forced motor task. During adulthood, GBS-exposed females - but not males - displayed increased spontaneous locomotor activity and decreased inhibition. In conclusion, our findings show for the first time that adult females - but not males - in utero-exposed to GBS-induced inflammation presented a hyperactive and disinhibited phenotype emerging after puberty.

Neuronal self-injury mediated by IL-1ß and MMP-9 in a cerebral palsy model of severe neonatal encephalopathy induced by immune activation plus hypoxia-ischemia.

BACKGROUND: Inflammation due to remote pathogen exposure combined to hypoxia/ischemia (HI) is one of the most common causes of neonatal encephalopathy affecting at-term or near-term human newborn, which will consequently develop cerebral palsy. Within term-equivalent rat brains exposed to systemic lipopolysaccharide (LPS) plus HI, it was previously showed that neurons produce IL-1ß earlier than do glial cells, and that blocking IL-1 was neuroprotective. To further define the mechanisms whereby IL-1 exerts its neurotoxic effect, we hypothesize that IL-1ß plays a pivotal role in a direct and/or indirect mechanistic loop of neuronal self-injury through matrix metalloproteinase (MMP)-9. METHODS: An established preclinical rat model of LPS+HI-induced neonatal encephalopathy was used. In situ hybridization, ELISA, and immunolabeling techniques were employed. Selective blocking compounds allowed addressing the respective roles of IL-1 and MMP-9. RESULTS: In LPS+HI-exposed forebrains, neuronal IL-1ß was first detected in infarcted neocortical and striatal areas and later in glial cells of the adjacent white matter. Neuronal IL-1ß played a key role: (i) in the early post-HI exacerbation of neuroinflammation and (ii) in generating both core and penumbral infarcted cerebral areas. Systemically administered IL-1 receptor antagonist (IL-1Ra) reached the brain and bound to the neocortical and deep gray neuronal membranes. Then, IL-1Ra down-regulated IL-1ß mRNA and MMP-9 neuronal synthesis. Immediately post-HI, neuronal IL-1ß up-regulated cytokine-induced neutrophil chemoattractant (CINC-1), monocyte chemoattractant protein-1 (MCP-1), and inducible nitric oxide synthase. MMP-9 would disrupt the blood-brain barrier, which, combined to CINC-1 up-regulation, would play a role in polymorphonuclear cell (PMN) infiltration into the LPS+HI-exposed brain. IL-1ß blockade prevented PMN infiltration and oriented the phenotype of macrophagic/microglial cells towards anti-inflammatory and neurotrophic M2 profile. IL-1ß increased the expression of activated caspase-3 and of receptor-interacting-protein (RIP)-3 within infarcted forebrain area. Such apoptotic and necroptotic pathway activations were prevented by IL-1Ra, as well as ensuing cerebral palsy-like brain damage and motor impairment. CONCLUSIONS: This work uncovered a new paradigm of neuronal self-injury orchestrated by neuronal synthesis of IL-1ß and MMP-9. In addition, it reinforced the translational neuroprotective potential of IL-1 blockers to alleviate human perinatal brain injuries.

Involvement of neuronal IL-1ß in acquired brain lesions in a rat model of neonatal encephalopathy.

BACKGROUND: Infection-inflammation combined with hypoxia-ischemia (HI) is the most prevalent pathological scenario involved in perinatal brain damage leading to life-long neurological disabilities. Following lipopolysaccharide (LPS) and/or HI aggression, different patterns of inflammatory responses have been uncovered according to the brain differentiation stage. In fact, LPS pre-exposure has been reported to aggravate HI brain lesions in post-natal day 1 (P1) and P7 rat models that are respectively equivalent - in terms of brain development - to early and late human preterm newborns. However, little is known about the innate immune response in LPS plus HI-induced lesions of the full-term newborn forebrain and the associated neuropathological and neurobehavioral outcomes. METHODS: An original preclinical rat model has been previously documented for the innate neuroimmune response at different post-natal ages. It was used in the present study to investigate the neuroinflammatory mechanisms that underline neurological impairments after pathogen-induced inflammation and HI in term newborns. RESULTS: LPS and HI exerted a synergistic detrimental effect on rat brain. Their effect led to a peculiar pattern of parasagittal cortical-subcortical infarcts mimicking those in the human full-term newborn with subsequent severe neurodevelopmental impairments. An increased IL-1ß response in neocortical and basal gray neurons was demonstrated at 4 h after LPS + HI-exposure and preceded other neuroinflammatory responses such as microglial and astroglial cell activation. Neurological deficits were observed during the acute phase of injury followed by a recovery, then by a delayed onset of profound motor behavior impairment, reminiscent of the delayed clinical onset of motor system impairments observed in humans. Interleukin-1 receptor antagonist (IL-1ra) reduced the extent of brain lesions confirming the involvement of IL-1ß response in their pathophysiology. CONCLUSION: In rat pups at a neurodevelopmental age corresponding to full-term human newborns, a systemic pre-exposure to a pathogen component amplified HI-induced mortality and morbidities that are relevant to human pathology. Neuronal cells were the first cells to produce IL-1ß in LPS + HI-exposed full-term brains. Such IL-1ß production might be responsible for neuronal self-injuries via well-described neurotoxic mechanisms such as IL-1ß-induced nitric oxide production, or IL-1ß-dependent exacerbation of excitotoxic damage.

Postnatal administration of IL-1Ra exerts neuroprotective effects following perinatal inflammation and/or hypoxic-ischemic injuries.

New therapeutic strategies are needed to protect neonates, especially premature newborns, against brain injury and associated neurobehavioral deficits. The role of pro-inflammatory cytokines, especially IL-1ß, in the pathophysiological pathway leading to neonatal brain damage is increasingly recognized and represents an attractive therapeutic target. We investigated the therapeutic potential of postnatal systemic administration of the interleukin (IL)-1 receptor antagonist (IL-1Ra) in an animal model of perinatal brain injury using the insults most common to human neonates, i.e. prenatal exposure to inflammation and/or postnatal hypoxia-ischaemia (HI). We found that postnatal administration of IL-1Ra preserved motor function and exploratory behavior after either prenatal exposure to inflammatory agent lipopolysaccharide (LPS) or postnatal HI insult. The deleterious effect of combined prenatal LPS and postnatal HI on brain development was also alleviated by administration of IL-1Ra, as seen by the protected neural stem cell population, prevention of myelin loss in the internal capsule, decreased gliosis, and decreased neurobehavioral impairment. This study showed the distinct pattern of functional deficits induced by prenatal inflammation as compared to postnatal HI and the therapeutic potential of IL-1Ra administration against neonatal brain injury. Furthermore, our results highlight the potential for postnatal treatment of prenatal inflammatory stressors.

Developmental regulation of the neuroinflammatory responses to LPS and/or hypoxia-ischemia between preterm and term neonates: An experimental study.

BACKGROUND: Preterm and term newborns are at high risk of brain damage as well as subsequent cerebral palsy and learning disabilities. Indeed, hypoxia-ischemia (HI), pathogen exposures, and associated intracerebral increase of pro-inflammatory cytokines have all been linked to perinatal brain damage. However, the developmental effects of potential variations of pro- and anti-inflammatory cytokine ratios remain unknown. METHODS: Using rat models of perinatal brain damage induced by exposures to lipopolysaccharide (LPS) and/or HI at distinct levels of maturity, we compared cytokine expression at stages of cerebral development equivalent to either preterm (postnatal day 1, P1) or term (P12) newborns. RESULTS: At P1, expression of anti-inflammatory cytokine within the brain was either not modulated (IL-6, IL-10) or down-regulated (IL-1ra, TGF-ß1) by HI, LPS or LPS+HI. In contrast, there was at P12 an up-regulation of all anti-inflammatory cytokines studied in HI or LPS+HI condition, but not after LPS exposure. Interestingly, IL-1ß was the main pro-inflammatory cytokine up-regulated moderately at P1, and strongly at P12, with a weak co-expression of TNF-α observed mainly at P12. These age-dependant inflammatory reactions were also accompanied, under HI and LPS+HI conditions, at P12 only, by combined: (i) expression of chemokines CINC-1 and MCP-1, (ii) blood-brain barrier (BBB) leakage, and (iii) intracerebral recruitment of systemic immune cells such as neutrophils. In contrast, sole LPS induced IL-1ß responses mainly within white matter at P1 and mainly within gray matter at P12, that were only associated with early MCP-1 (but no CINC-1) induction at both ages, without any recruitment of neutrophils and CD68+ cells. CONCLUSION: HI and LPS+HI induce pro-inflammatory oriented immune responses in both preterm and term like brains, with a maximal inflammatory response triggered by the combination of LPS+HI. The profile of these neuroinflammatory responses presented striking variations according to age: no or down-regulated anti-inflammatory responses associated with mainly IL-1ß release in preterm-like brains (P1), in sharp contrast to term-like brains (P12) presenting stronger anti-and pro-inflammatory responses, including both IL-1ß and TNF-α releases, and BBB leakage. These developmental-dependant variations of neuroinflammatory response could contribute to the differential pattern of brain lesions observed across gestational ages in humans. This also highlights the necessity to take into consideration the maturation stage, of both brain and immune systems, in order to develop new anti-inflammatory neuroprotective strategies.

Role of perinatal inflammation in cerebral palsy.

Inflammatory molecules are promptly upregulated in the fetal environment and postnatally in brain-damaged subjects. Intrauterine infections and inflammation are often associated with asphyxia. This double-hit effect by combined infection or inflammation and hypoxia is therefore a frequent concomitant in neonatal brain damage. Animal models combining hypoxia and infection were recently designed to explore the mechanisms underlying brain damage in such circumstances and to look for possible neuroprotective strategies. Proinflammatory cytokines are thought to be major mediators in brain injury in neonates with perinatal asphyxia, bacterial infection, or both. Cytokines, however, could also have neuroprotective properties. The critical point in the balance between neurodamaging and neuroprotective effects of cytokines has yet to be unraveled. This understanding might help to develop new therapeutic approaches to counteract the inflammatory disequilibrium observed in the pathophysiologic mechanisms associated with brain injury.