Epidermal growth factor preserves myelin and promotes astrogliosis after intraventricular hemorrhage

Reactive Gliosis in Neonatal Disorders: Friend or Foe for Neuroregeneration?

A developing nervous system is particularly vulnerable to the influence of pathophysiological clues and injuries in the perinatal period. Astrocytes are among the first cells that react to insults against the nervous tissue, the presence of pathogens, misbalance of local tissue homeostasis, and a lack of oxygen and trophic support. Under this background, it remains uncertain if induced astrocyte activation, recognized as astrogliosis, is a friend or foe for progressing neonatal neurodevelopment. Likewise, the state of astrocyte reactivity is considered one of the key factors discriminating between either the initiation of endogenous reparative mechanisms compensating for aberrations in the structures and functions of nervous tissue or the triggering of neurodegeneration. The responses of activated cells are modulated by neighboring neural cells, which exhibit broad immunomodulatory and pro-regenerative properties by secreting a plethora of active compounds (including interleukins and chemokines, neurotrophins, reactive oxygen species, nitric oxide synthase and complement components), which are engaged in cell crosstalk in a paracrine manner. As the developing nervous system is extremely sensitive to the influence of signaling molecules, even subtle changes in the composition or concentration of the cellular secretome can have significant effects on the developing neonatal brain. Thus, modulating the activity of other types of cells and their interactions with overreactive astrocytes might be a promising strategy for controlling neonatal astrogliosis.

c-Abl-induced Olig2 phosphorylation regulates the proliferation of oligodendrocyte precursor cells

Oligodendrocytes (OLs), the myelinating cells in the central nervous system (CNS), are differentiated from OL progenitor cells (OPCs). The proliferation of existing OPCs is indispensable for myelination during CNS development and remyelination in response to demyelination stimulation. The transcription factor Olig2 is required for the specification of OLs and is expressed in the OL lineage. However, the post-translational modification of Olig2 in the proliferation of OPCs is poorly understood. Herein, we identified that c-Abl directly phosphorylates Olig2 mainly at the Tyr137 site, and that Olig2 phosphorylation is essential for OPC proliferation. The expression levels of c-Abl gradually decreased with brain development; moreover, c-Abl was highly expressed in OPCs. OL-specific c-Abl knockout at the developmental stage led to an insufficient proliferation of OPCs, a decreased expression of myelin-related genes, and myelination retardation. Accordingly, a c-Abl-specific kinase inhibitor suppressed OPC proliferation in vitro. Furthermore, we observed that OL-specific c-Abl knockout reduced OPC proliferation and remyelination in a cuprizone model of demyelination. In addition, we found that nilotinib, a clinically used c-Abl inhibitor, decreased the expression of myelin basic protein (Mbp) and motor coordination in mice, indicating a neurological side effect of a long-term administration of the c-Abl inhibitor. Thus, we identified the important role of c-Abl in OLs during developmental myelination and remyelination in a disease model.

EGF-Coupled Gold Nanoparticles Increase the Expression of CNPase and the Myelin-Associated Proteins MAG, MOG, and MBP in the Septal Nucleus Demyelinated by Cuprizone

Current pharmacological therapies against demyelinating diseases are not quite satisfactory to promote remyelination. Epidermal growth factor (EGF) can expand the population of oligodendrocyte precursor cells (OPCs) that may help with the remyelination process, but its delivery into the injured tissue is still a biomedical challenge. Gold nanoparticles (GNPs) may be a useful tool for drug delivery into the brain. To evaluate remyelination in the septal nucleus, we administered intracerebral GNPs coupled with EGF (EGF–GNPs). C57BL6/J mice were demyelinated with 0.4% cuprizone (CPZ) and divided into several groups: Sham, Ctrl, GNPs, EGF, and EGF–GNPs. We evaluated the remyelination process at two time-points: 2 weeks and 3 weeks post-injection (WPI) of each treatment. We used the rotarod for evaluating motor coordination. Then, we did a Western blot analysis myelin-associated proteins: CNPase, MAG, MOG, and MBP. EGF–GNPs increase the expression of CNPase, MAG, and MOG at 2 WPI. At 3 WPI, we found that the EGF–GNPs treatment improves motor coordination and increases MAG, MOG, and MBP. EGF–GNPs enhance the expression of myelin-associated proteins and improve the motor coordination in mice. Thus, EGF-associated GNPs may be a promising pharmacological vehicle for delivering long-lasting drugs into the brain.

Innate Immune Pathways Promote Oligodendrocyte Progenitor Cell Recruitment to the Injury Site in Adult Zebrafish Brain

The oligodendrocyte progenitors (OPCs) are at the front of the glial reaction to the traumatic brain injury. However, regulatory pathways steering the OPC reaction as well as the role of reactive OPCs remain largely unknown. Here, we compared a long-lasting, exacerbated reaction of OPCs to the adult zebrafish brain injury with a timely restricted OPC activation to identify the specific molecular mechanisms regulating OPC reactivity and their contribution to regeneration. We demonstrated that the influx of the cerebrospinal fluid into the brain parenchyma after injury simultaneously activates the toll-like receptor 2 (Tlr2) and the chemokine receptor 3 (Cxcr3) innate immunity pathways, leading to increased OPC proliferation and thereby exacerbated glial reactivity. These pathways were critical for long-lasting OPC accumulation even after the ablation of microglia and infiltrating monocytes. Importantly, interference with the Tlr1/2 and Cxcr3 pathways after injury alleviated reactive gliosis, increased new neuron recruitment, and improved tissue restoration.

White matter injury in infants with intraventricular haemorrhage: mechanisms and therapies

Intraventricular haemorrhage (IVH) continues to be a major complication of prematurity that can result in cerebral palsy and cognitive impairment in survivors. No optimal therapy exists to prevent IVH or to treat its consequences. IVH varies in severity and can present as a bleed confined to the germinal matrix, small-to-large IVH or periventricular haemorrhagic infarction. Moderate-to-severe haemorrhage dilates the ventricle and damages the periventricular white matter. This white matter injury results from a constellation of blood-induced pathological reactions, including oxidative stress, glutamate excitotoxicity, inflammation, perturbed signalling pathways and remodelling of the extracellular matrix. Potential therapies for IVH are currently undergoing investigation in preclinical models and evidence from clinical trials suggests that stem cell treatment and/or endoscopic removal of clots from the cerebral ventricles could transform the outcome of infants with IVH. This Review presents an integrated view of new insights into the mechanisms underlying white matter injury in premature infants with IVH and highlights the importance of early detection of disability and immediate intervention in optimizing the outcomes of IVH survivors.

Exclusive human milk diet reduces incidence of severe intraventricular hemorrhage in extremely low birth weight infants

OBJECTIVE

Compare the incidence of severe (grade III/IV) intraventricular hemorrhage (IVH) and/or periventricular leukomalacia (PVL) between two groups of ELBW infants based on diet until 34 weeks corrected gestational age (CGA): (1) Exclusive human milk (EHM)-mother's own and/or pasteurized donor human milk, human milk-derived fortifier, and oral care with colostrum/human milk vs. (2) non-EHM-bovine formula or mother's own milk with bovine-derived fortifier.

STUDY DESIGN

Retrospective observational study of two groups of ELBW infants based on diet until 34 weeks CGA.

RESULT

There were n = 306 infants, 127 EHM and 179 non-EHM. Demographics and morbidities were similar except higher antenatal steroids and NEC in EHM group. The rate of severe IVH/PVL was lower in EHM compared to non-EHM group (7 vs. 18%, p < 0.006).

CONCLUSION

EHM diet had an independent neuroprotective effect and was associated with decreased incidence of severe IVH/PVL, supporting the need of EHM in ELBW infants.

White matter injury in the neonatal hypoxic-ischemic brain and potential therapies targeting microglia

Neonatal hypoxic-ischemic (H-I) injury, which mainly causes neuronal damage and white matter injury (WMI), is among the predominant causes of infant morbidity (cerebral palsy, cognitive and persistent motor disabilities) and mortality. Disruptions to the oxygen and blood supply in the perinatal brain affect the cerebral microenvironment and may affect microglial activation, excitotoxicity, and oxidative stress. Microglia are significantly associated with axonal damage and myelinating oligodendrocytes, which are major pathological components of WMI. However, the effects of H-I injury on microglial functions and underlying transformation mechanisms remain poorly understood. The historical perception that these cells are major risk factors for ischemic stroke has been questioned due to our improved understanding of the diversity of microglial phenotypes and their alterable functions, which exacerbate or attenuate injuries in different regions in response to environmental instability. Unfortunately, although therapeutic hypothermia is an efficient treatment, death and disability remain the prognosis for a large proportion of neonates with H-I injury. Hence, novel neuroprotective therapies to treat WMI following H-I injury are urgently needed. Here, we review microglial mechanisms that might occur in the developing brain due to neonatal H-I injury and discuss whether microglia function as a double-edged sword in WMI. Then, we emphasize microglial heterogeneity, notably at the single-cell level, and sex-specific effects on the etiology of neurological diseases. Finally, we discuss current knowledge of strategies aiming to improve microglia modulation and remyelination following neonatal H-I injury. Overall, microglia-targeted therapy might provide novel and valuable insights into the treatment of neonatal H-I insult.

The impact of trophic and immunomodulatory factors on oligodendrocyte maturation: Potential treatments for encephalopathy of prematurity

Encephalopathy of prematurity (EoP) is a major cause of morbidity in preterm neonates, causing neurodevelopmental adversities that can lead to lifelong impairments. Preterm birth-related insults, such as cerebral oxygen fluctuations and perinatal inflammation, are believed to negatively impact brain development, leading to a range of brain abnormalities. Diffuse white matter injury is a major hallmark of EoP and characterized by widespread hypomyelination, the result of disturbances in oligodendrocyte lineage development. At present, there are no treatment options available, despite the enormous burden of EoP on patients, their families, and society. Over the years, research in the field of neonatal brain injury and other white matter pathologies has led to the identification of several promising trophic factors and cytokines that contribute to the survival and maturation of oligodendrocytes, and/or dampening neuroinflammation. In this review, we discuss the current literature on selected factors and their therapeutic potential to combat EoP, covering a wide range of in vitro, preclinical and clinical studies. Furthermore, we offer a future perspective on the translatability of these factors into clinical practice.

Interleukin-1β Drives Cellular Senescence of Rat Astrocytes Induced by Oligomerized Amyloid β Peptide and Oxidative Stress

Background: Alzheimer's disease (AD) is the leading cause of dementia. With no reliable treatment that delays or reverses the progress of AD, effective medical drugs, and interventions for AD treatment are in urgent need. Clinical success for patients thus relies on gaining a clearer understanding of AD pathogenesis to feed the development of novel and potent therapy strategies. It is well-established that inflammatory processes are involved in the pathology of AD, and recent studies implicated senescence of glial cells as an important player in the progression of AD.

Methods: We did a preliminary screen in rat astrocytes for the five most abundant inflammatory factors in neuroinflammation, namely IL-1β, IL-6, IL-8, TGF-β1, and TNF-α, and found that IL-1β could efficiently induce cellular senescence. After that, SA-β-gal staining, immunofluorescence, ELISA, qRT-PCR, and immunoblotting were used to explore the underlying mechanism through which IL-1β mediates cellular senescence of rat astrocytes.

Results: IL-1β-induced cellular senescence of rat astrocytes was accompanied by increased total and phosphorylated tau. Further experiments showed that both oligomerized amyloid β (Aβ) and H₂O₂ treatment can induce cellular senescence in rat astrocytes and increase the production and secretion of IL-1β from these cells. Subsequent mechanistic study revealed that activation of NLRP3 mediates Aβ and H₂O₂-induced maturation and secretion of IL-1β.

Conclusion: Our results suggest that IL-1β mediates senescence in rat astrocytes induced by several common adverse stimuli in AD, implicating IL-1β and NLRP3 as valuable diagnostic biomarkers and therapeutic targets for AD.

Serum epidermal growth factor, clinical illness course, and limbic brain volumes in early-stage bipolar disorder

BACKGROUND

Epidermal growth factor (EGF) belongs to a family of growth factors implicated in the etiology of psychiatric illnesses. We conducted this cross-sectional case-control study to determine whether (1) serum EGF levels differ between bipolar disorder (BD) patients and non-BD comparison subjects, (2) EGF levels in patients are influenced by mood illness related factors (number of past mood episodes, medication treatment) and non-mood illness related factors (body mass index), and (3) lower EGF levels predict lower limbic brain volumes in BD.

METHODS

We measured serum EGF in 51 early-stage BD patients and 22 healthy comparison subjects (HS). A subset of 25 patients underwent cerebral magnetic resonance imaging (MRI). Participants were assessed at the University of British Columbia Mood Disorders Centre between June 2004 and June 2012.

RESULTS

A general linear model with diagnosis and BMI category (overweight/obese vs normal weight) as factors showed that patients had lower mean log(e)-transformed EGF (LnEGF) than HS (4.99 vs 5.47, p = .011). There was no effect of BMI and no diagnosis x BMI interaction. Multiple linear regression models showed that in patients, more past mood episodes predicted lower LnEGF (β = -0.358, t = -2.585, p = .013) and lower LnEGF predicted lower bilateral temporal lobe volumes (left: β = 0.560, p = .011; right: β = 0.543, p = .009).

LIMITATIONS

Our cross-sectional study design limits our ability to make inferences about the causal directions of the relationships between EGF, diagnosis, mood episodes, and brain volumes.

CONCLUSIONS

These findings provide preliminary evidence that EGF is a novel biomarker that may play a role in the pathophysiology of BD.

EGFR806-CAR T cells selectively target a tumor-restricted EGFR epitope in glioblastoma

Targeting solid tumor antigens with chimeric antigen receptor (CAR) T cell therapy requires tumor specificity and tolerance toward variability in antigen expression levels. Given the relative paucity of unique cell surface proteins on tumor cells for CAR targeting, we have focused on identifying tumor-specific epitopes that arise as a consequence of target protein posttranslational modification. We designed a CAR using a mAb806-based binder, which recognizes tumor-specific untethered EGFR. The mAb806 epitope is also exposed in the EGFRvIII variant transcript. By varying spacer domain elements of the CAR, we structurally tuned the CAR to recognize low densities of EGFR representative of non-gene amplified expression levels in solid tumors. The appropriately tuned short-spacer 2nd generation EGFR806-CAR T cells showed efficient in vitro cytokine secretion and glioma cell lysis, which was competitively blocked by a short peptide encompassing the mAb806 binding site. Unlike the nonselective Erbitux-based CAR, EGFR806-CAR T cells did not target primary human fetal brain astrocytes expressing wild-type EGFR, but showed a similar level of activity compared to Erbitux-CAR when the tumor-specific EGFRvIII transcript variant was overexpressed in astrocytes. EGFR806-CAR T cells successfully treated orthotopic U87 glioma implants in NSG mice, with 50% of animals surviving to 90 days. With additional IL-2 support, all tumors were eradicate without recurrence after 90 days. In a novel human induced pluripotent stem cell (iPSC)-derived teratoma xenograft model, EGFR806-CAR T cells infiltrated but were not activated in EGFR+ epidermal cell nests as assessed by Granzyme B expression. These results indicate that EGFR806-CAR T cells effectively and selectively target EGFR-expressing tumor cells.

Human Cord Blood-Derived Unrestricted Somatic Stem Cell Infusion Improves Neurobehavioral Outcome in a Rabbit Model of Intraventricular Hemorrhage

Intraventricular hemorrhage (IVH) is a severe complication of preterm birth, which leads to hydrocephalus, cerebral palsy, and mental retardation. There are no available therapies to cure IVH, and standard treatment is supportive care. Unrestricted somatic stem cells (USSCs) from human cord blood have reparative effects in animal models of brain and spinal cord injuries. USSCs were administered to premature rabbit pups with IVH and their effects on white matter integrity and neurobehavioral performance were evaluated. USSCs were injected either via intracerebroventricular (ICV) or via intravenous (IV) routes in 3 days premature (term 32d) rabbit pups, 24 hours after glycerol‐induced IVH. The pups were sacrificed at postnatal days 3, 7, and 14 and effects were compared to glycerol‐treated but unaffected or nontreated control. Using in vivo live bioluminescence imaging and immunohistochemical analysis, injected cells were found in the injured parenchyma on day 3 when using the IV route compared to ICV where cells were found adjacent to the ventricle wall forming aggregates; we did not observe any adverse events from either route of administration. The injected USSCs were functionally associated with attenuated microglial infiltration, less apoptotic cell death, fewer reactive astrocytes, and diminished levels of key inflammatory cytokines (TNFα and IL1β). In addition, we observed better preservation of myelin fibers, increased myelin gene expression, and altered reactive astrocyte distribution in treated animals, and this was associated with improved locomotor function. Overall, our findings support the possibility that USSCs exert anti‐inflammatory effects in the injured brain mitigating many detrimental consequences associated with IVH. stem cells translational medicine2019;8:1157–1169

Autologous cord blood in children with cerebral palsy: a review

The aim of this narrative review is to report on the current knowledge regarding the clinical use of umbilical cord blood (CB) based on articles from PubMed and clinical trials registered on ClinicalTrials.gov. An increasing amount of evidence suggests that CB may be used for both early diagnostics and treatment of cerebral palsy. The acidity of CB and its biochemical parameters, including dozens of cytokines, growth factors, and other metabolites (such as amino acids, acylcarnitines, phosphatidylcholines, succinate, glycerol, 3-hydroxybutyrate, and O-phosphocholine) are predictors of future neurodevelopment. In addition, several clinical studies confirmed the safety and efficacy of CB administration in both autologous and allogeneic models, including a meta-analysis of five clinical trials involving a total of 328 participants. Currently, nine clinical trials assessing the use of autologous umbilical CB in children diagnosed with hypoxic-ischemic encephalopathy or cerebral palsy are in progress. The total population assessed in these trials exceeds 2500 patients.

Emergent Prophylactic, Reparative and Restorative Brain Interventions for Infants Born Preterm With Cerebral Palsy

Worldwide, an estimated 15 million babies are born preterm (<37 weeks' gestation) every year. Despite significant improvements in survival rates, preterm infants often face a lifetime of neurodevelopmental disability including cognitive, behavioral, and motor impairments. Indeed, prematurity remains the largest risk factor for the development of cerebral palsy. The developing brain of the preterm infant is particularly fragile; preterm babies exhibit varying severities of cerebral palsy arising from reductions in both cerebral white and gray matter volumes, as well as altered brain microstructure and connectivity. Current intensive care therapies aim to optimize cardiovascular and respiratory function to protect the brain from injury by preserving oxygenation and blood flow. If a brain injury does occur, definitive diagnosis of cerebral palsy in the first few hours and weeks of life is difficult, especially when the lesions are subtle and not apparent on cranial ultrasound. However, early diagnosis of mildly affected infants is critical, because these are the patients most likely to respond to emergent treatments inducing neuroplasticity via high-intensity motor training programs and regenerative therapies involving stem cells. A current controversy is whether to test universal treatment in all infants at risk of brain injury, accepting that some patients never required treatment, because the perceived potential benefits outweigh the risk of harm. Versus, waiting for a diagnosis before commencing targeted treatment for infants with a brain injury, and potentially missing the therapeutic window. In this review, we discuss the emerging prophylactic, reparative, and restorative brain interventions for infants born preterm, who are at high risk of developing cerebral palsy. We examine the current evidence, considering the timing of the intervention with relation to the proposed mechanism/s of action. Finally, we consider the development of novel markers of preterm brain injury, which will undoubtedly lead to improved diagnostic and prognostic capability, and more accurate instruments to assess the efficacy of emerging interventions for this most vulnerable group of infants.

Preterm brain injury: Germinal matrix-intraventricular hemorrhage and post-hemorrhagic ventricular dilatation

Germinal matrix hemorrhage and intraventricular hemorrhages (GMH-IVH) remain a common and clinically significant problem in preterm infants, particularly extremely preterm infants. A large GMH-IVH is often complicated by posthemorrhagic ventricular dilation (PHVD) or parenchymal hemorrhagic infarction and is associated with an increased risk of adverse neurologic sequelae. The widespread use of cranial ultrasonography since the early 1980s has shown a gradual decrease in the incidence of GMH-IVH and has helped with the identification of antenatal and perinatal risk factors and timing of the lesion. The increased use of magnetic resonance imaging (MRI) has contributed to more detailed visualization of the site and extent of the GMH-IVH. In addition, MRI has contributed to the awareness of associated white matter changes as well as associated cerebellar hemorrhages. Although GMH-IVH and PHVD still cannot be prevented, cerebrospinal fluid drainage initiated in the early stage of PHVD development seems to be associated with a better neurodevelopmental outcome. Further studies are underway to improve treatment strategies for PHVD and to potentially prevent and repair GMH-IVH and PHVD and associated brain injury. This chapter discusses the pathogenesis, incidence, risk factors, and management, including preventive measures, of GHM-IVH and PHVD.

Estrogen Treatment Reverses Prematurity-Induced Disruption in Cortical Interneuron Population

Development of cortical interneurons continues until the end of human pregnancy. Premature birth deprives the newborns from the supply of maternal estrogen and a secure intrauterine environment. Indeed, preterm infants suffer from neurobehavioral disorders. This can result from both preterm birth and associated postnatal complications, which might disrupt recruitment and maturation of cortical interneurons. We hypothesized that interneuron subtypes, including parvalbumin-positive (PV⁺), somatostatin-positive (SST⁺), calretinin-positive (CalR⁺), and neuropeptide Y-positive (NPY⁺) interneurons, were recruited in the upper and lower cortical layers in a distinct manner with advancing gestational age. In addition, preterm birth would disrupt the heterogeneity of cortical interneurons, which might be reversed by estrogen treatment. These hypotheses were tested by analyzing autopsy samples from premature infants and evaluating the effect of estrogen supplementation in prematurely delivered rabbits. The PV⁺ and CalR⁺ neurons were abundant, whereas SST⁺ and NPY⁺ neurons were few in cortical layers of preterm human infants. Premature birth of infants reduced the density of PV⁺ or GAD67⁺ neurons and increased SST⁺ interneurons in the upper cortical layers. Importantly, 17 β-estradiol treatment in preterm rabbits increased the number of PV⁺ neurons in the upper cortical layers relative to controls at postnatal day 14 (P14) and P21 and transiently reduced SST population at P14. Moreover, protein and mRNA levels of Arx, a key regulator of cortical interneuron maturation and migration, were higher in estrogen-treated rabbits relative to controls. Therefore, deficits in PV⁺ and excess of SST⁺ neurons in premature newborns are ameliorated by estrogen replacement, which can be attributed to elevated Arx levels. Estrogen replacement might enhance neurodevelopmental outcomes in extremely preterm infants.SIGNIFICANCE STATEMENT Premature birth often leads to neurodevelopmental delays and behavioral disorders, which may be ascribed to disturbances in the development and maturation of cortical interneurons. Here, we show that preterm birth in humans is associated with reduced population of parvalbumin-positive (PV⁺) neurons and an excess of somatostatin-expressing interneurons in the cerebral cortex. More importantly, 17 β-estradiol treatment increased the number of PV⁺ neurons in preterm-born rabbits, which appears to be mediated by an elevation in the expression of Arx transcription factor. Hence the present study highlights prematurity-induced reduction in PV⁺ neurons in human infants and reversal in their population by estrogen replacement in preterm rabbits. Because preterm birth drops plasma estrogen level 100-fold, estrogen replacement in extremely preterm infants might improve their developmental outcome and minimize neurobehavioral disorders.

Glycogen synthase kinase-3β inhibition enhances myelination in preterm newborns with intraventricular hemorrhage, but not recombinant Wnt3A

Intraventricular hemorrhage (IVH) in preterm infants results in reduced proliferation and maturation of oligodendrocyte progenitor cells (OPCs), and survivors exhibit reduced myelination and neurological deficits. Wnt signaling regulates OPC maturation and myelination in a context dependent manner. Herein, we hypothesized that the occurrence of IVH would downregulate Wnt signaling, and that activating Wnt signaling by GSK-3β inhibition or Wnt3A recombinant human protein (rh-Wnt3A) treatment might promote maturation of OPCs, myelination of the white matter, and neurological recovery in premature rabbits with IVH. These hypotheses were tested in autopsy samples from preterm infants and in a rabbit model of IVH. Induction of IVH reduced expressions of activated β-catenin, TCF-4, and Axin2 transcription factors in preterm newborns. Both AR-A014418 (ARA) and Wnt-3A treatment activated Wnt signaling. GSK-3β inhibition by intramuscular ARA treatment accelerated maturation of OPCs, myelination, and neurological recovery in preterm rabbits with IVH compared to vehicle controls. In contrast, intracerebroventricular rh-Wnt3A treatment failed to enhance myelination and neurological function in rabbits with IVH. ARA treatment reduced microglia infiltration and IL1β expression in rabbits with IVH relative to controls, whereas Wnt3A treatment elevated TNFα, IL1β, and IL6 expression without affecting microglia density. GSK-3β inhibition downregulated, while rh-Wnt3A treatment upregulated Notch signaling; and none of the two treatments affected the Sonic-Hedgehog pathway. The administration of ARA or rh-Wnt3A did not affect gliosis. The data suggest that GSK-3β inhibition promoted myelination by suppressing inflammation and Notch signaling; and Wnt3A treatment failed to enhance myelination because of its pro-inflammatory activity and synergy with Notch signaling. GSK-3β inhibitors might improve the neurological outcome of preterm infants with IVH.

Nexilin Regulates Oligodendrocyte Progenitor Cell Migration and Remyelination and Is Negatively Regulated by Protease-Activated Receptor 1/Ras-Proximate-1 Signaling Following Subarachnoid Hemorrhage

Progressive white matter (WM) impairments caused by subarachnoid hemorrhage (SAH) contribute to cognitive deficits and poor clinical prognoses; however, their pathogenetic mechanisms are poorly understood. We investigated the role of nexilin and oligodendrocyte progenitor cell (OPC)-mediated repair in a mouse model of experimental SAH generated via left endovascular perforation. Nexilin expression was enhanced by the elevated migration of OPCs after SAH. Knocking down nexilin by siRNA reduced OPC migration both in vitro and in vivo and abridged WM repair. In contrast, the protease-activated receptor 1 (PAR1), Ras-proximate-1 (RAP1) and phosphorylated RAP1 (pRAP1) levels in WM were elevated after SAH. The genetic inhibition of PAR1 reduced RAP1 and pRAP1 expression, further enhancing nexilin expression. When delivered at an early stage at a concentration of 25 µg/kg, thrombin receptor antagonist peptide along with PAR1 knockdown rescued the down-regulation of myelin basic protein and improved remyelination at the later stage of SAH. Our results suggest that nexilin is required for OPC migration and remyelination following SAH, as it negatively regulates PAR1/RAP1 signaling, thus providing a promising therapeutic target in WM repair and functional recovery.

Disruption of Interneuron Neurogenesis in Premature Newborns and Reversal with Estrogen Treatment

Many Preterm-born children suffer from neurobehavioral disorders. Premature birth terminates the hypoxic in utero environment and supply of maternal hormones. As the production of interneurons continues until the end of pregnancy, we hypothesized that premature birth would disrupt interneuron production and that restoration of the hypoxic milieu or estrogen treatment might reverse interneuron generation. To test these hypotheses, we compared interneuronal progenitors in the medial ganglionic eminences (MGEs), lateral ganglionic eminences (LGEs), and caudal ganglionic eminences (CGEs) between preterm-born [born on embryonic day (E) 29; examined on postnatal day (D) 3 and D7] and term-born (born on E32; examined on D0 and D4) rabbits at equivalent postconceptional ages. We found that both total and cycling Nkx2.1⁺, Dlx2⁺, and Sox2⁺ cells were more abundant in the MGEs of preterm rabbits at D3 compared with term rabbits at D0, but not in D7 preterm relative to D4 term pups. Total Nkx2.1⁺ progenitors were also more numerous in the LGEs of preterm pups at D3 compared with term rabbits at D0. Dlx2⁺ cells in CGEs were comparable between preterm and term pups. Simulation of hypoxia by dimethyloxalylglycine treatment did not affect the number of interneuronal progenitors. However, estrogen treatment reduced the density of total and proliferating Nkx2.1⁺ and Dlx2⁺ cells in the MGEs and enhanced Ascl1 transcription factor. Estrogen treatment also reduced Ki67, c-Myc, and phosphorylation of retinoblastoma protein, suggesting inhibition of the G1-to-S phase transition. Hence, preterm birth disrupts interneuron neurogenesis in the MGE and estrogen treatment reverses interneuron neurogenesis in preterm newborns by cell-cycle inhibition and elevation of Ascl1. We speculate that estrogen replacement might partially restore neurogenesis in human premature infants.SIGNIFICANCE STATEMENT Prematurity results in developmental delays and neurobehavioral disorders, which might be ascribed to disturbances in the development of cortical interneurons. Here, we show that preterm birth disrupts interneuron neurogenesis in the medial ganglionic eminence (MGE) and, more importantly, that estrogen treatment reverses this perturbation in the population of interneuron progenitors in the MGE. The estrogen seems to restore neurogenesis by inhibiting the cell cycle and elevating Ascl1 expression. As preterm birth causes plasma estrogen level to drop 100-fold, the estrogen replacement in preterm infants is physiological. We speculate that estrogen replacement might ameliorate disruption in production of interneurons in human premature infants.

Severe Convulsions and Dysmyelination in Both Jimpy and Cx32/47 -/- Mice may Associate Astrocytic L-Channel Function with Myelination and Oligodendrocytic Connexins with Internodal Kv Channels

The Jimpy mouse illustrates the importance of interactions between astrocytes and oligodendrocytes. It has a mutation in Plp coding for proteolipid protein and DM20. Its behavior is normal at birth but from the age of ~2 weeks it shows severe convulsions associated with oligodendrocyte/myelination deficits and early death. A normally occurring increase in oxygen consumption by highly elevated K+ concentrations is absent in Jimpy brain slices and cultured astrocytes, reflecting that Plp at early embryonic stages affects common precursors as also shown by the ability of conditioned medium from normal astrocytes to counteract histological abnormalities. This metabolic response is now known to reflect opening of L-channels for Ca2+. The resulting deficiency in Ca2+ entry has many consequences, including lack of K+-stimulated glycogenolysis and release of gliotransmitter ATP. Lack of purinergic stimulation compromises oligodendrocyte survival and myelination and affects connexins and K+ channels. Mice lacking the oligodendrocytic connexins Cx32 and 47 show similar neurological dysfunction as Jimpy. This possibly reflects that K+ released by intermodal axonal Kv channels is transported underneath a loosened myelin sheath instead of reaching the extracellular space via connexin-mediated transport to oligodendrocytes, followed by release and astrocytic Na+,K+-ATPase-driven uptake with subsequent Kir4.1-facilitated release and neuronal uptake.