Neuroinflammation, myelin and behavior: Temporal patterns following mild traumatic brain injury in mice.

Traumatic brain injury (TBI) results in white matter injury (WMI) that is associated with neurological deficits. Neuroinflammation originating from microglial activation may participate in WMI and associated disorders. To date, there is little information on the time courses of these events after mild TBI. Therefore we investigated (i) neuroinflammation, (ii) WMI and (iii) behavioral disorders between 6 hours and 3 months after mild TBI. For that purpose, we used experimental mild TBI in mice induced by a controlled cortical impact. (i) For neuroinflammation, IL-1b protein as well as microglial phenotypes, by gene expression for 12 microglial activation markers on isolated CD11b+ cells from brains, were studied after TBI. IL-1b protein was increased at 6 hours and 1 day. TBI induced a mixed population of microglial phenotypes with both pro-inflammatory, anti-inflammatory and immunomodulatory markers from 6 hours to 3 days post-injury. At 7 days, microglial activation was completely resolved. (ii) Three myelin proteins were assessed after TBI on ipsi- and contralateral corpus callosum, as this structure is enriched in white matter. TBI led to an increase in 2',3'-cyclic-nucleotide 3'-phosphodiesterase, a marker of immature and mature oligodendrocyte, at 2 days post-injury; a bilateral demyelination, evaluated by myelin basic protein, from 7 days to 3 months post-injury; and an increase in myelin oligodendrocyte glycoprotein at 6 hours and 3 days post-injury. Transmission electron microscopy study revealed various myelin sheath abnormalities within the corpus callosum at 3 months post-TBI. (iii) TBI led to sensorimotor deficits at 3 days post-TBI, and late cognitive flexibility disorder evidenced by the reversal learning task of the Barnes maze 3 months after injury. These data give an overall invaluable overview of time course of neuroinflammation that could be involved in demyelination and late cognitive disorder over a time-scale of 3 months in a model of mild TBI. This model could help to validate a pharmacological strategy to prevent post-traumatic WMI and behavioral disorders following mild TBI.

Etazolate, an α-secretase activator, reduces neuroinflammation and offers persistent neuroprotection following traumatic brain injury in mice.

Traumatic brain injury (TBI) evokes an intense neuroinflammatory reaction that is essentially mediated by activated microglia and that has been reported to act as a secondary injury mechanism that further promotes neuronal death. It involves the excessive production of inflammatory cytokines and the diminution of neuroprotective and neurotrophic factors, such as the soluble form alpha of the amyloid precursor protein (sAPPα), generated by the activity of α-secretases. Hence, the aim of this study was to examine the effects of etazolate, an α-secretase activator, on acute and belated post-TBI consequences. The mouse model of TBI by mechanical percussion was used and injured mice received either the vehicle or etazolate at the dose of 1, 3 or 10 mg/kg at 2 h post-TBI. Neurological score, cerebral œdema, IL-1ß and sAPPα levels, microglial activation and lesion size were evaluated from 6 to 24 h post-TBI. Spontaneous locomotor activity was evaluated from 48 h to 12 weeks post-TBI, memory function at 5 weeks and olfactory bulb lesions at 13 weeks post-TBI. A single administration of etazolate exerted a dose-dependent anti-inflammatory and anti-œdematous effect accompanied by lasting memory improvement, reduction of locomotor hyperactivity and olfactory bulb tissue protection, with a therapeutic window of at least 2 h. These effects were associated with the restoration of the levels of the sAPPα protein post-TBI. Taken together, these results highlight for the first time the therapeutic interest of an α-secretase activator in TBI.

Minocycline restores sAPPα levels and reduces the late histopathological consequences of traumatic brain injury in mice.

Traumatic brain injury (TBI) induces both focal and diffuse lesions that are concurrently responsible for the ensuing morbidity and mortality and for which no established treatment is available. It has been recently reported that an endogenous neuroprotector, the soluble form α of the amyloid precursor protein (sAPPα), exerts neuroprotective effects following TBI. However, the emergent post-traumatic neuroinflammatory environment compromises sAPPα production and may promote neuronal degeneration and consequent brain atrophy. Hence, the aim of this study was to examine the effects of the anti-inflammatory drug minocycline on sAPPα levels, as well as on long-term histological consequences post-TBI. The weight-drop model was used to induce TBI in mice. Minocycline or its vehicle were administered three times: at 5 min (90 mg/kg, i.p.) and at 3 and 9 h (45 mg/kg, i.p.) post-TBI. The levels of sAPPα, the extent of brain atrophy, and reactive gliosis were evaluated by ELISA, cresyl violet, and immunolabeling of GFAP and CD11b, respectively. Our results revealed a post-TBI sAPPα decrease that was significantly attenuated by minocycline. Additionally, corpus callosum and striatal atrophy, ventriculomegaly, astrogliosis, and microglial activation were observed at 3 months post-TBI. All the above consequences were significantly reduced by minocycline. In conclusion, inhibition of the acute phase of post-TBI neuroinflammation was associated with the sparing of sAPPα and the protection of brain tissue in the long-term, emphasizing the potential role of minocycline as an effective treatment for TBI.