Inhibition of gelatinase activity reduces neural injury in an ex vivo model of hypoxia-ischemia

Ursolic Acid Ameliorated Neuronal Damage by Restoring Microglia-Activated MMP/TIMP Imbalance in vitro

Purpose

The oxygen and glucose deprivation-reoxygenation (OGDR) model is widely used to evaluate ischemic stroke and cerebral ischemia-reperfusion (I/R) injury in vitro. Excessively activated microglia produce pro-inflammatory mediators such as matrix metalloproteinases [MMPs] and their specific inhibitors, tissue inhibitors of metalloproteinases [TIMPs], causing neuronal damage. Ursolic acid (UA) acts as a neuroprotective agent in the rat middle cerebral artery occlusion/reperfusion (MCAO/R) model keeping the MMP/TIMP balance with underlying mechanisms unclear. Our study used OGDR model to determine whether and how UA reduces neuronal damage by reversing MMP/TIMP imbalance caused by microglia in I/R injury in vitro.

Methods

SH-SY5Y cells were first cultured with 95% N2 and 5% CO2 and then cultivated regularly for OGDR model. Cell viability was tested for a proper UA dose. We established a co-culture system with SH-SY5Y cells and microglia-conditioned medium (MCM) stimulated by lipopolysaccharide (LPS) and interferon-gamma (IFNγ). MMP9 and TIMP1 levels were measured with ELISA assay to confirm the UA effect. We added recombinant MMP9 (rMMP9) and TIMP1 neutralizing antibody (anti-TIMP1) for reconfirmation. Transmission electron microscopy was used to observe cell morphology, and flow cytometry and Annexin V-FITC and PI labeling for apoptotic conditions. We further measured the calcium fluorescence intensity in SH-SY5Y cells.

Results

The MCM significantly reduced cell viability of SH-SY5Y cells after OGDR (p<0.01), which was restored by UA (0.25 µM) (p<0.05), whereas lactate dehydrogenase activity, intraneuronal Ca2+ concentration, and apoptosis-related indexes were showed significant improvement after UA treatment (p<0.01). UA corrected the MMP/TIMP imbalance by decreasing MMP9 expression and increasing TIMP1 expression in the co-culture system (p<0.01) and the effects of UA on SH-SY5Y cells were mitigated by the administration of rMMP9 and anti-TIMP1 (p<0.01).

Conclusion

We demonstrated that UA inhibited microglia-induced neuronal cell death in an OGDR model of ischemic reperfusion injury by stabilizing the MMP9/TIMP1 imbalance.

Simvastatin Attenuates Hippocampal MMP-9 Expression in the Streptozotocin-Induced Cognitive Impairment

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) expression has been implicated in molecular mechanisms of neurodegenerative disorders, and its abnormal level has been reported in Alzheimer’s disease (AD). Some protective mechanisms of statins against neurodegeneration might be mediated by the inhibition of MMP-9 expression. Here, we investigated the effect of simvastatin on the hippocampal MMP-9 expression in the context of AD.

METHODS

We examined the influence of three-week simvastatin (5 mg/kg) administration on hippocampal MMP-9 expression in a rat model of cognitive decline induced by streptozotocin (STZ). Spatial long-term memory and MMP-9 expression were assessed by Morris water maze (MWM) test and quantitative polymerase chain reaction, respectively.

RESULTS

The results showed a decline in the learning and memory in STZ group when compared with the control group. The MMP-9 up-regulated (1.41 ± 0.2 vs. 0.980 ± 0.02, p < 0.05), and cresyl violet staining showed hippocampal cell damage in STZ group compared with the control group. Simvastatin prevented the up-regulation of MMP-9 (1.05 ± 0.05 vs. 1.41 ± 0.2, p < 0.05), improved spatial memory impairment and attenuated hippocampal cell damage. Furthermore, we found a negative correlation (r = 0.77) between MMP-9 expression and cognitive function.

CONCLUSION

Our findings suggest that the neuroprotective influence of simvastatin in battle to cognitive impairment is mediated in part by the modulation of MMP-9 expression. The reduction of MMP-9 expression in simvastatin-treated animals is in correlation with the improvement of cognitive functions. Understanding the protective mechanism of simvastatin will shed light on more efficient therapeutic modalities in AD.

Microglia in neurodegeneration

The neuroimmune system is involved in development, normal functioning, aging, and injury of the central nervous system. Microglia, first described a century ago, are the main neuroimmune cells and have three essential functions: a sentinel function involved in constant sensing of changes in their environment, a housekeeping function that promotes neuronal well-being and normal operation, and a defense function necessary for responding to such changes and providing neuroprotection. Microglia use a defined armamentarium of genes to perform these tasks. In response to specific stimuli, or with neuroinflammation, microglia also have the capacity to damage and kill neurons. Injury to neurons in Alzheimer's, Parkinson's, Huntington's, and prion diseases, as well as in amyotrophic lateral sclerosis, frontotemporal dementia, and chronic traumatic encephalopathy, results from disruption of the sentinel or housekeeping functions and dysregulation of the defense function and neuroinflammation. Pathways associated with such injury include several sensing and housekeeping pathways, such as the Trem2, Cx3cr1 and progranulin pathways, which act as immune checkpoints to keep the microglial inflammatory response under control, and the scavenger receptor pathways, which promote clearance of injurious stimuli. Peripheral interference from systemic inflammation or the gut microbiome can also alter progression of such injury. Initiation or exacerbation of neurodegeneration results from an imbalance between these microglial functions; correcting such imbalance may be a potential mode for therapy.

The multifaceted role of metalloproteinases in physiological and pathological conditions in embryonic and adult brains

Matrix metalloproteinases (MMPs) are a large family of ubiquitous extracellular endopeptidases, which play important roles in a variety of physiological and pathological conditions, from the embryonic stages throughout adult life. Their extraordinary physiological "success" is due to concomitant broad substrate specificities and strict regulation of their expression, activation and inhibition levels. In recent years, MMPs have gained increasing attention as significant effectors in various aspects of central nervous system (CNS) physiology. Most importantly, they have been recognized as main players in a variety of brain disorders having different etiologies and evolution. A common aspect of these pathologies is the development of acute or chronic neuroinflammation. MMPs play an integral part in determining the result of neuroinflammation, in some cases turning its beneficial outcome into a harmful one. This review summarizes the most relevant studies concerning the physiology of MMPs, highlighting their involvement in both the developing and mature CNS, in long-lasting and acute brain diseases and, finally, in nervous system repair. Recently, a concerted effort has been made in identifying therapeutic strategies for major brain diseases by targeting MMP activities. However, from this revision of the literature appears clear that MMPs have multifaceted functional characteristics, which modulate physiological processes in multiple ways and with multiple consequences. Therefore, when choosing MMPs as possible targets, great care must be taken to evaluate the delicate balance between their activation and inhibition and to determine at which stage of the disease and at what level they become active in order maximize chances of success.

How microglia kill neurons

Microglia are resident brain macrophages that become inflammatory activated in most brain pathologies. Microglia normally protect neurons, but may accidentally kill neurons when attempting to limit infections or damage, and this may be more common with degenerative disease as there was no significant selection pressure on the aged brain in the past. A number of mechanisms by which activated microglia kill neurons have been identified, including: (i) stimulation of the phagocyte NADPH oxidase (PHOX) to produce superoxide and derivative oxidants, (ii) expression of inducible nitric oxide synthase (iNOS) producing NO and derivative oxidants, (iii) release of glutamate and glutaminase, (iv) release of TNFα, (v) release of cathepsin B, (vi) phagocytosis of stressed neurons, and (vii) decreased release of nutritive BDNF and IGF-1. PHOX stimulation contributes to microglial activation, but is not directly neurotoxic unless NO is present. NO is normally neuroprotective, but can react with superoxide to produce neurotoxic peroxynitrite, or in the presence of hypoxia inhibit mitochondrial respiration. Glutamate can be released by glia or neurons, but is neurotoxic only if the neurons are depolarised, for example as a result of mitochondrial inhibition. TNFα is normally neuroprotective, but can become toxic if caspase-8 or NF-κB activation are inhibited. If the above mechanisms do not kill neurons, they may still stress the neurons sufficiently to make them susceptible to phagocytosis by activated microglia. We review here whether microglial killing of neurons is an artefact, makes evolutionary sense or contributes in common neuropathologies and by what mechanisms. This article is part of a Special Issue entitled SI: Neuroprotection.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

Serum matrix metalloproteinase-9 levels and severity of symptoms in boys with attention deficit hyperactivity disorder ADHD/hyperkinetic disorder HKD

The serum levels of matrix metalloproteinase-9 (MMP-9) in neuropsychiatric disorders of adults have been widely investigated. So far, no studies have been conducted on the relationship of MMP-9 and cognitive domains in children with two phenotype models, attention deficit/hyperactivity disorder and hyperkinetic disorder (ADHD/HKD). The aim of this research was to evaluate and test the hypothesis that serum MMP-9 levels are associated with the severity of symptoms in children with ADHD/HKD and to compare the results in two models of this disorder. The study group comprised 37 Caucasian boys aged 7-12 years with HKD, being a subset of the combined ADHD subtype. Intellectual functions were measured using Wechsler Intelligence Scale for Children-Revised. The analysis of serum concentrations of MMP-9 was based on a quantitative sandwich ELISA. The statistical regression analysis revealed a correlation between increased serum MMP-9 levels and severity of symptoms in the ADHD (β = 0.33; p = 0.043) and HKD (β = 0.34, p = 0.037) model. According to the results, elevated levels of serum MMP-9 in boys with HKD may be associated with clinical impulsivity domain (β = 0.38; p = 0.019).

Splenic immune cells in experimental neonatal hypoxia-ischemia

Neuroimmune processes contribute to hypoxic-ischemic damage in the immature brain and may play a role in the progression of particular variants of neonatal encephalopathy. The present study was designed to elucidate molecular mediators of interactions between astrocytes, neurons and infiltrating peripheral immune cells after experimental neonatal hypoxia-ischemia (HI). Splenectomy was performed on postnatal day-7 Sprague-Dawley rats 3 days prior to HI surgery; in which the right common carotid artery was permanently ligated followed by 2 hours of hypoxia (8% O2). Quantitative analysis showed that natural killer (NK) and T cell expression was reduced in spleen but increased in the brain following HI. Elevations in cyclooxygenase-2 (COX-2) expression after HI by immune cells promoted interleukin-15 expression in astrocytes and infiltration of inflammatory cells to site of injury; additionally, down-regulated the pro-survival protein, phosphoinositide-3-kinase, resulting in caspase-3 mediated neuronal death. The removal of the largest pool of peripheral immune cells in the body by splenectomy, COX-2 inhibitors, as well as rendering NK cells inactive by CD161 knockdown, significantly ameliorated cerebral infarct volume at 72 hours, diminished body weight loss and brain and systemic organ atrophy, and reduced neurobehavioral deficits at 3 weeks. Herein we demonstrate with the use of surgical approach (splenectomy), with pharmacological loss-gain function approach using COX-2 inhibitors/agonists, as well as with NK cell-type specific siRNA that after neonatal HI, the infiltrating peripheral immune cells may modulate downstream targets of cell death and neuroinflammation by COX-2 regulated signals.

The history of the tetracyclines

The history of the tetracyclines involves the collective contributions of thousands of dedicated researchers, scientists, clinicians, and business executives over the course of more than 60 years. Discovered as natural products from actinomycetes soil bacteria, the tetracyclines were first reported in the scientific literature in 1948. They were noted for their broad spectrum antibacterial activity and were commercialized with clinical success beginning in the late 1940s to the early 1950s. The second-generation semisynthetic analogs and more recent third-generation compounds show the continued evolution of the tetracycline scaffold toward derivatives with increased potency as well as efficacy against tetracycline-resistant bacteria, with improved pharmacokinetic and chemical properties. Their biologic activity against a wide spectrum of microbial pathogens and their uses in mammalian models of inflammation, neurodegeneration, and other biological systems indicate that the tetracyclines will continue to be successful therapeutics in infectious diseases and as potential therapeutics against inflammation-based mammalian cell diseases.

Inhibition of matrix metalloproteinases prevents the potentiation of nondeprived-eye responses after monocular deprivation in juvenile rats

The ocular dominance (OD) shift induced by monocular deprivation (MD) during the critical period is mediated by an initial depression of deprived-eye responses followed by an increased responsiveness to the nondeprived eye. It is not fully clear to what extent these 2 events are correlated and which are their physiological and molecular mediators. The extracellular synaptic environment plays an important role in regulating visual cortical plasticity. Matrix metalloproteinases (MMPs) are a family of activity-dependent zinc-dependent extracellular endopeptidases mediating extracellular matrix remodeling. We investigated the effects of MMP inhibition on OD plasticity in juvenile monocularly deprived rats. By using electrophysiological recordings, we found that MMP inhibition selectively prevented the potentiation of neuronal responses to nondeprived-eye stimulation occurring after 7 days of MD and potentiation of deprived-eye responses occurring after eye reopening. Three days of MD only resulted in a depression of deprived-eye responses insensitive to MMP inhibition. MMP inhibition did not influence homeostatic plasticity tested in the monocular cortex but significantly prevented an increase in dendritic spine density present after 7 days MD in layer II-III pyramids.

Central nervous system agents for ischemic stroke: neuroprotection mechanisms

Stroke is the third leading cause of mortality and disability in the United States. Ischemic stroke constitutes 85% of all stroke cases. However, no effective treatment has been found to prevent damage to the brain in such cases except tissue plasminogen activator with narrow therapeutic window, and there is an unmet need to develop therapeutics for neuroprotection from ischemic stroke. Studies have shown that mechanisms including apoptosis, necrosis, inflammation, immune modulation, and oxidative stress and mediators such as excitatory amino acids, nitric oxide, inflammatory mediators, neurotransmitters, reactive oxygen species, and withdrawal of trophic factors may lead to the development of the ischemic cascade. Hence, it is essential to develop neuroprotective agents targeting either the mechanisms or the mediators leading to development of ischemic stroke. This review focuses on central nervous system agents targeting these biochemical pathways and mediators of ischemic stroke, mainly those that counteract apoptosis, inflammation, and oxidation, and well as glutamate inhibitors which have been shown to provide neuroprotection in experimental animals. All these agents have been shown to improve neurological outcome after ischemic insult in experimental animals in vivo, organotypic brain slice/acute slice ex vivo, and cell cultures in vitro and may therefore aid in preventing long-term morbidity and mortality associated with ischemic stroke.

Primary culture of cellular subtypes from postnatal mouse for in vitro studies of oxygen glucose deprivation

One of the most widely utilized in vitro models of ischemia or oxygen glucose deprivation (OGD) is the hippocampal organotypical culture (HOTC). The HOTC is used not only for the study of the mechanisms of cell death, but also has been the cornerstone of synaptic physiology. Although the intact nature of the HOTC is one of its primary advantages, some studies require a dissociated preparation in order to distinguish cell type specific responses. Typically, primary dissociated neuronal cultures are prepared from embryonic tissue. Since the HOTC is prepared from postnatal pups, we wanted to establish a primary culture of hippocampus from postnatal pups to parallel our studies in the HOTC preparation. Mixed cultures were prepared by enzymatic dissociation of hippocampus from 7-day-old mouse pups. These cultures responded to OGD with a time course of delayed cell death that was similar to that reported in HOTC. Dual label immunocytochemical staining revealed that neurons, but not astrocytes, were dying from apoptosis following OGD. To examine this vulnerability further, we also prepared neuronal enriched cultures by treating mixed cultures with cytosine-β-d-arabinofuranoside (CBA). These neuronal cultures appear to be even more sensitive to OGD. In addition, we have established primary astrocyte-enriched cultures from the same age pups to examine the vulnerability of astrocytes to OGD. These three culture preparations are useful for comparison of the responses of the two major cell types in the same culture, and the enriched cultures will allow biochemical, electrophysiological and molecular studies of homogenous cell populations.

A high throughput screen identifies chemical modulators of the laminin-induced clustering of dystroglycan and aquaporin-4 in primary astrocytes

BACKGROUND

Aquaporin-4 (AQP4) constitutes the principal water channel in the brain and is clustered at the perivascular astrocyte endfeet. This specific distribution of AQP4 plays a major role in maintaining water homeostasis in the brain. A growing body of evidence points to a role of the dystroglycan complex and its interaction with perivascular laminin in the clustering of AQP4 at perivascular astrocyte endfeet. Indeed, mice lacking components of this complex or in which laminin-dystroglycan interaction is disrupted show a delayed onset of brain edema due to a redistribution of AQP4 away from astrocyte endfeet. It is therefore important to identify inhibitory drugs of laminin-dependent AQP4 clustering which may prevent or reduce brain edema.

METHODOLOGY/PRINCIPAL FINDINGS

In the present study we used primary rat astrocyte cultures to screen a library of >3,500 chemicals and identified 6 drugs that inhibit the laminin-induced clustering of dystroglycan and AQP4. Detailed analysis of the inhibitory drug, chloranil, revealed that its inhibition of the clustering is due to the metalloproteinase-2-mediated ß-dystroglycan shedding and subsequent loss of laminin interaction with dystroglycan. Furthermore, chemical variants of chloranil induced a similar effect on ß-dystroglycan and this was prevented by the antioxidant N-acetylcysteine.

CONCLUSION/SIGNIFICANCE

These findings reveal the mechanism of action of chloranil in preventing the laminin-induced clustering of dystroglycan and AQP4 and validate the use of high-throughput screening as a tool to identify drugs that modulate AQP4 clustering and that could be tested in models of brain edema.

Minocycline may be useful to prevent/treat postoperative cognitive decline in elderly patients

Postoperative cognitive dysfunction (POCD) is reported to occur frequently after all types especially cardiac surgery in elderly patients. It can be short-term or long-term and some cases even develop into Alzheimer's disease (AD). Although multi-risk factors associated with POCD have been identified, the etiology and pathophysiological mechanisms of this surgical complication remain elusive. Therefore, developing strategies for preventing or treating POCD is still challenging. However, increasing evidence suggests that central and systemic inflammation triggered by surgery likely plays a fundamental role in POCD developing and progression. Minocycline, a tetracycline derivative with anti-inflammatory properties, has been shown to be effective in treating neuroinflammatory related conditions or neurodegenerative diseases such as AD, Parkinson's disease, Huntington's disease. Considering that inflammation may be a potential factor of POCD and minocycline is effective in improving cognitive dysfunction induced by inflammation, we hypothesize that minocycline may be useful to treat/prevent the POCD development after surgery in elderly patients.

Amelioration of inflammation and cytotoxicity by dipyridamole in brain endothelial cells

BACKGROUND

Increasing evidence suggests that beyond its antiplatelet properties, dipyridamole may have pleiotropic effects on other cells within the neurovascular elements of the brain. In this experimental cellular study, we asked whether dipyridamole can ameliorate brain endothelial injury after exposure to inflammatory and metabolic insults.

METHODS

Human brain endothelial cells were grown in culture, and exposed to TNFalpha (continuously for 20 h) or subjected to oxygen-glucose deprivation (OGD; 6 h of insult followed by 18 h recovery). Expression of ICAM-1, VCAM-1 and PECAM-1 were measured by immunoblotting. Matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in the conditioned media were quantified via zymography. MTT mitochondrial activity was measured to assess endothelial cell viability.

RESULTS

Exposure of human brain endothelial cells to TNFalpha (12.5-50 ng/ml) induced a clear increase in protein levels of ICAM-1, VCAM-1 and MMP-9. TNFalpha did not alter PECAM-1. Dipyridamole (1-5 muM) significantly attenuated ICAM-1 and MMP-9 levels after this inflammatory insult. No significant effects of dipyridamole were noted for VCAM-1. Six-hour OGD induced moderate endothelial cell death accompanied by a release of MMP-9. Dipyridamole significantly decreased MMP-9 levels and cell death after this metabolic insult.

CONCLUSIONS

These results suggest that dipyridamole may ameliorate brain endothelial injury after inflammation and/or metabolic insults. How these putative cellular mechanisms may relate to clinical outcomes and conditions in stroke patients remains to be elucidated.

Human umbilical cord blood cell therapy blocks the morphological change and recruitment of CD11b-expressing, isolectin-binding proinflammatory cells after middle cerebral artery occlusion

Secondary neurodegeneration resulting from stroke is mediated by delayed proinflammatory signaling and immune cell activation. Although it remains unknown which cell surface markers signify a proinflammatory phenotype, increased isolectin binding occurs on CD11b-expressing immune cells within injured brain tissue. Several reports have confirmed the efficacy of human umbilical cord blood (HUCB) cell therapy in reducing ischemic injury in rat after middle cerebral artery occlusion (MCAO), and these effects were attributed in part to dampened neuroinflammation. The present study examined the time course of lectin binding to cells of microglia/macrophage lineage within 96 hr after MCAO and whether delayed HUCB cell treatment alters the migration and/or morphological characteristics of these cells throughout the period of infarct expansion. Isolectin binding was up-regulated in response to injury, was maximal at 96 hr, and colocalized with cells that expressed the putative proinflammatory markers MMP-9 and nitric oxide. Isolectin-tagged fluorescence was also significantly increased at 72 hr and localized to greater numbers of amoeboid, CD11b-expressing cells relative to 51 hr. Treatment with 1 x 10(6) HUCB cells significantly reduced total lectin binding at 72 hr, as well as the total area occupied by lectin-tagged fluorescence at both 51 and 72 hr, relative to vehicle-treated controls. This effect was accompanied by a shift in the morphology of CD11b-positive cells from amoeboid to ramified shape. These data indicate that HUCB cell therapy suppressed the recruitment of proinflammatory, isolectin-binding cells during the period of infarct expansion, thus offering a potential mechanism for the protective effects of HUCB cell therapy.

Delayed treatments for stroke influence neuronal death in rat organotypic slice cultures subjected to oxygen glucose deprivation

A major limitation of current stroke therapies is the need to treat candidate patients within 3 h of stroke onset. Human umbilical cord blood cell (HUCBC) and the sigma receptor agonist 1,3, di-o-tolylguanidine (DTG) administration both caused significant reductions in brain damage in the rat middle cerebral artery occlusion model of stroke when administered at delayed timepoints. In vivo, these treatments suppress the infiltration of peripheral lymphocytes into the brain in addition to decreasing neurodegeneration. An ex vivo organotypic slice culture (OTC) model was utilized to characterize the efficacy of these treatments in mitigating neurodegeneration in ischemic brain tissue in the absence of the peripheral immune system. Slice cultures subjected to oxygen glucose deprivation (OGD) had significantly elevated levels of degenerating neurons and microglial nitric oxide production when compared to their normoxic counterparts. In cultures subjected to OGD, HUCBC but not DTG treatment reduced the number of degenerating neurons and the production of microglial derived nitric oxide back to levels detected in normoxic controls. These data show that HUCBC treatment can mediate direct neuroprotection and suppress innate inflammation in ischemic brain tissue in the absence of the peripheral immune system, whereas DTG requires peripheral effects to mediate neuroprotection. These experiments yield insight into the mechanisms by which these neuroprotective treatments function at delayed timepoints following stroke.

Neuroinflammation and MMPs: potential therapeutic targets in neonatal hypoxic-ischemic injury

Exposure to hypoxic-ischemic insults during the neonatal or perinatal developmental periods produces various forms of pathology. Injuries that occur in response to these events often manifest as severe cognitive and/or motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of hypoxic-ischemic injury, there is a growing need for effective therapies that can be delivered at delayed time points. Much of the research into mechanisms of neural injury has focused on molecular targets associated with excitotoxicity and free oxygen radicals. Despite repeated success in animal models, these compounds have failed to show efficacy in clinical trials. Increasing evidence indicates that hypoxic-ischemic injury in the neonate is progressive, and the resulting neuropathies are linked to the activation of neuroinflammatory processes that occur in response to the initial wave of cell death. Understanding this latter response, therefore, will be critical in the development of novel therapies to block the progression of the injury. In this review, we summarize emerging concepts from rodent models concerning the regulation of various cytokines, chemokines, and matrix metalloproteinases in response to ischemia, and the various ways in which the delayed neuroinflammatory response may contribute to the progressive nature of neonatal hypoxic-ischemic injury in rat. Finally, we discuss data that supports the potential to target these neuroinflammatory signals at clinically relevant time points.