Acute-phase proteins (APPs) are key effectors of the immune response and are routinely used as biomarkers in cerebrovascular diseases, but their role during brain inflammation remains largely unknown. Elevated circulating levels of the acute-phase protein pentraxin-3 (PTX3) are associated with worse outcome in stroke patients. Here we show that PTX3 is expressed in neurons and glia in response to cerebral ischemia, and that the proinflammatory cytokine interleukin-1 (IL-1) is a key driver of PTX3 expression in the brain after experimental stroke. Gene deletion of PTX3 had no significant effects on acute ischemic brain injury. In contrast, the absence of PTX3 strongly compromised blood-brain barrier integrity and resolution of brain edema during recovery after ischemic injury. Compromised resolution of brain edema in PTX3-deficient mice was associated with impaired glial scar formation and alterations in scar-associated extracellular matrix production. Our results suggest that PTX3 expression induced by proinflammatory signals after ischemic brain injury is a critical effector of edema resolution and glial scar formation. This highlights the potential role for inflammatory molecules in brain recovery after injury and identifies APPs, in particular PTX3, as important targets in ischemic stroke and possibly other brain inflammatory disorders.

BackgroundThe acute phase protein pentraxin 3 (PTX3) is a new biomarker of stroke severity and is a key regulator of oedema resolution and glial responses after cerebral ischaemia, emerging as a possible target for brain repair after stroke. Neurogenesis and angiogenesis are essential events in post-stroke recovery. Here, we investigated for the first time the role of PTX3 in neurogenesis and angiogenesis after stroke.MethodsPTX3 knockout (KO) or wild-type (WT) mice were subjected to experimental cerebral ischaemia (induced by middle cerebral artery occlusion (MCAo)). Poststroke neurogenesis was assessed by nestin, doublecortin (DCX) and bromodeoxyuridine (BrdU) immunostaining, whereas angiogenesis was assessed by BrdU, vascular endothelial growth factor receptor 2 (VEGFR2) and PECAM-1 immunostaining. In vitro neurogenesis and angiogenesis assays were carried out on neurospheres derived from WT or interleukin-1β (IL-1β) KO mice, and mouse endothelial cell line bEnd.5 respectively. Behavioural function was assessed in WT and PTX3 KO mice using open-field, motor and Y-maze tests.ResultsNeurogenesis was significantly reduced in the dentate gyrus (DG) of the hippocampus of PTX3 KO mice, compared to WT mice, 6 days after MCAo. In addition, recombinant PTX3 was neurogenic in vitro when added to neurospheres, which was mediated by IL-1β. In vivo poststroke angiogenesis was significantly reduced in PTX3 KO mice compared to WT mice 14 days after MCAo, as revealed by reduced vascular density, less newly formed blood vessels and decreased expression of VEGFR2. In vitro, recombinant PTX3 induced marked endothelial cellular proliferation and promoted formation of tube-like structures of endothelial cell line bEnd.5. Finally, a lack of PTX3 potentiated motor deficits 14 days after MCAo.ConclusionsThese results indicate that PTX3 mediates neurogenesis and angiogenesis and contributes to functional recovery after stroke, highlighting a key role of PTX3 as a mediator of brain repair and suggesting that PTX3 could be used as a new target for stroke therapy.

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Traumatic brain injury (TBI) is a leading cause of hospital visits in pediatric patients and often leads to long-term disorders even in cases of mild severity. White matter (WM) alterations are commonly observed in patients months or years after the injury assessed by magnetic resonance imaging (MRI), but little is known about WM pathophysiology early after mild pediatric TBI. To evaluate the status of the gliovascular unit in this context, mild TBI was induced in postnatal-day 17 mice using a closed head injury model with two grades of severity (G1, G2). G2 resulted in significant WM edema (increased T2-signal) and BBB damage (IgG-extravasation immunostaining) whereas decreased T2 and the increased levels of astrocytic water-channel AQP4 were observed in G1 mice 1 day post-injury. Both severities induced astrogliosis (GFAP immunolabeling). No changes in myelin and neurofilament were detected at this acute time point. One month after injury G2 mice exhibited diffusion tensor imaging MRI alterations (decreased fractional anisotropy) accompanied by decreased neurofilament staining in the WM. Both severities induced behavioral impairments at this time point. In conclusion, long-term deficits and WM changes similar to those found after clinical TBI are preceded by distinct early gliovascular phenotype alterations after juvenile mild TBI, revealing AQP4 as a potential candidate for severity-based treatments.

Brain edema is a common feature of brain injuries, which leads to increased intracranial pressure (ICP) and ischemia that worsen outcome. Current management of edema focuses on reduction of ICP, but there are no treatments targeting the molecular players directly involved in edema process. The perivascular astrocyte endfeet are critical in maintaining brain homeostasis with ionic and water exchange; in this context, aquaporins (AQPs), astrocyte water channels, have emerged as privileged targets for edema modulation. However, AQPs can facilitate either accumulation or drainage of water, depending on the osmotic gradients between extra‐intracellular space; and thus inhibition of AQPs leads to different outcomes depending on specific tissue characteristics and time post‐injury. Most of this knowledge has been gathered from the study of AQP4, the best characterized AQP and the one that has the biggest impact on water movement. In addition to the level of expression, the ratio of AQP4 isoforms (m1, m23 or mz), the spatial distribution of AQP4 into orthogonal arrays of particles, and the interaction of AQP4 with neighboring ionic channels and gap junctions could directly impact edema formation. Although there are no specific AQP4 pharmacological blockers, the development of AQP4 siRNA offers a promising therapeutic tool. Given the complex dynamics of AQP4, therapies targeting AQP4 should carefully take into account the particular features of the injury (e.g., hemorrhagic vs. non‐hemorrhagic) and different times after injury (e.g., phase of edema formation vs. resolution).

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Stroke represents an unresolved challenge for both developed and developing countries and has a huge socio-economic impact. Although considerable effort has been made to limit stroke incidence and improve outcome, strategies aimed at protecting injured neurons in the brain have all failed. This failure is likely to be due to both the incompleteness of modelling the disease and its causes in experimental research, and also the lack of understanding of how systemic mechanisms lead to an acute cerebrovascular event or contribute to outcome.Inflammation has been implicated in all forms of brain injury and it is now clear that immune mechanisms profoundly influence (and are responsible for the development of) risk and causation of stroke, and the outcome following the onset of cerebral ischemia. Until very recently, systemic inflammatory mechanisms, with respect to common comorbidities in stroke, have largely been ignored in experimental studies. The main aim is therefore to understand interactions between the immune system and brain injury in order to develop novel therapeutic approaches. Recent data from clinical and experimental research clearly show that systemic inflammatory diseases -such as atherosclerosis, obesity, diabetes or infectionsimilar to stress and advanced age, are associated with dysregulated immune responses which can profoundly contribute to cerebrovascular inflammation and injury in the central nervous system. In this review, we summarize recent advances in the field of inflammation and stroke, focusing on the challenges of translation between pre-clinical and clinical studies, and potential anti-inflammatory/immunomodulatory therapeutic approaches.

Mild‐traumatic brain injury (mTBI) represents ~80% of all emergency room visits and increases the probability of developing long‐term cognitive disorders in children. To date, molecular and cellular mechanisms underlying post‐mTBI cognitive dysfunction are unknown. Astrogliosis has been shown to significantly alter astrocytes' properties following brain injury, potentially leading to significant brain dysfunction. However, such alterations have never been investigated in the context of juvenile mTBI (jmTBI). A closed‐head injury model was used to study jmTBI on postnatal‐day 17 mice. Astrogliosis was evaluated using glial fibrillary acidic protein (GFAP), vimentin, and nestin immunolabeling in somatosensory cortex (SSC), dentate gyrus (DG), amygdala (AMY), and infralimbic area (ILA) of prefrontal cortex in both hemispheres from 1 to 30 days postinjury (dpi). In vivo T2‐weighted‐imaging (T2WI) and diffusion tensor imaging (DTI) were performed at 7 and 30 dpi to examine tissue level structural alterations. Increased GFAP‐labeling was observed up to 30 dpi in the ipsilateral SSC, the initial site of the impact. However, vimentin and nestin expression was not perturbed by jmTBI. The morphology of GFAP positive cells was significantly altered in the SSC, DG, AMY, and ILA up to 7 dpi that some correlated with magnetic resonance imaging changes. T2WI and DTI values were significantly altered at 30 dpi within these brain regions most prominently in regions distant from the impact site. Our data show that jmTBI triggers changes in astrocytic phenotype with a distinct spatiotemporal pattern. We speculate that the presence and time course of astrogliosis may contribute to pathophysiological processes and long‐term structural alterations following jmTBI.