Regenerative Therapies to Restore Interneuron Disturbances in Experimental Models of Encephalopathy of Prematurity

Key roles of glial cells in the encephalopathy of prematurity

Across the globe, approximately one in 10 babies are born preterm, that is, before 37 weeks of a typical 40 weeks of gestation. Up to 50% of preterm born infants develop brain injury, encephalopathy of prematurity (EoP), that substantially increases their risk for developing lifelong defects in motor skills and domains of learning, memory, emotional regulation, and cognition. We are still severely limited in our abilities to prevent or predict preterm birth. No longer just the "support cells," we now clearly understand that during development glia are key for building a healthy brain. Glial dysfunction is a hallmark of EoP, notably, microgliosis, astrogliosis, and oligodendrocyte injury. Our knowledge of glial biology during development is exponentially expanding but hasn't developed sufficiently for development of effective neuroregenerative therapies. This review summarizes the current state of knowledge for the roles of glia in infants with EoP and its animal models, and a description of known glial-cell interactions in the context of EoP, such as the roles for border-associated macrophages. The field of perinatal medicine is relatively small but has worked passionately to improve our understanding of the etiology of EoP coupled with detailed mechanistic studies of pre-clinical and human cohorts. A primary finding from this review is that expanding our collaborations with computational biologists, working together to understand the complexity of glial subtypes, glial maturation, and the impacts of EoP in the short and long term will be key to the design of therapies that improve outcomes.

Stem cell-based interventions for the prevention and treatment of intraventricular haemorrhage and encephalopathy of prematurity in preterm infants

BACKGROUND

Germinal matrix-intraventricular haemorrhage (GMH-IVH) and encephalopathy of prematurity (EoP) remain substantial issues in neonatal intensive care units worldwide. Current therapies to prevent or treat these conditions are limited. Stem cell-based therapies offer a potential therapeutic approach to repair, restore, or regenerate injured brain tissue. These preclinical findings have now culminated in ongoing human neonatal studies. This is an update of the 2019 review, which did not include EoP.

OBJECTIVES

To evaluate the benefits and harms of stem cell-based interventions for prevention or treatment of GM-IVH and EoP in preterm infants.

SEARCH METHODS

We used standard, extensive Cochrane search methods. The latest search was April 2022.

SELECTION CRITERIA

We attempted to include randomised controlled trials, quasi-randomised controlled trials, and cluster trials comparing 1. stem cell-based interventions versus control; 2. mesenchymal stromal cells (MSCs) of type or source versus MSCs of other type or source; 3. stem cell-based interventions other than MSCs of type or source versus stem cell-based interventions other than MSCs of other type or source; or 4. MSCs versus stem cell-based interventions other than MSCs. For prevention studies, we included extremely preterm infants (less than 28 weeks' gestation), 24 hours of age or less, without ultrasound diagnosis of GM-IVH or EoP; for treatment studies, we included preterm infants (less than 37 weeks' gestation), of any postnatal age, with ultrasound diagnosis of GM-IVH or with EoP.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methods. Our primary outcomes were 1. all-cause neonatal mortality, 2. major neurodevelopmental disability, 3. GM-IVH, 4. EoP, and 5. extension of pre-existing non-severe GM-IVH or EoP. We planned to use GRADE to assess certainty of evidence for each outcome.

MAIN RESULTS

We identified no studies that met our inclusion criteria. Three studies are currently registered and ongoing. Phase 1 trials are described in the 'Excluded studies' section.

AUTHORS' CONCLUSIONS

No evidence is currently available to evaluate the benefits and harms of stem cell-based interventions for treatment or prevention of GM-IVH or EoP in preterm infants. We identified three ongoing studies, with a sample size range from 20 to 200. In two studies, autologous cord blood mononuclear cells will be administered to extremely preterm infants via the intravenous route; in one, intracerebroventricular injection of MSCs will be administered to preterm infants up to 34 weeks' gestational age.

Further Evidence of Neuroprotective Effects of Recombinant Human Erythropoietin and Growth Hormone in Hypoxic Brain Injury in Neonatal Mice

Experimental in vivo data have recently shown complementary neuroprotective actions of rhEPO and growth hormone (rhGH) in a neonatal murine model of hypoxic brain injury. Here, we hypothesized that rhGH and rhEPO mediate stabilization of the blood−brain barrier (BBB) and regenerative vascular effects in hypoxic injury to the developing brain. Using an established model of neonatal hypoxia, neonatal mice (P7) were treated i.p. with rhGH (4000 µg/kg) or rhEPO (5000 IU/kg) 0/12/24 h after hypoxic exposure. After a regeneration period of 48 h or 7 d, cerebral mRNA expression of Vegf-A, its receptors and co-receptors, and selected tight junction proteins were determined using qRT-PCR and ELISA. Vessel structures were assessed by Pecam-1 and occludin (Ocln) IHC. While Vegf-A expression increased significantly with rhGH treatment (p < 0.01), expression of the Vegfr and TEK receptor tyrosine kinase (Tie-2) system remained unchanged. RhEPO increased Vegf-A (p < 0.05) and Angpt-2 (p < 0.05) expression. While hypoxia reduced the mean vessel area in the parietal cortex compared to controls (p < 0.05), rhGH and rhEPO prevented this reduction after 48 h of regeneration. Hypoxia significantly reduced the Ocln+ fraction of cortical vascular endothelial cells. Ocln signal intensity increased in the cortex in response to rhGH (p < 0.05) and in the cortex and hippocampus in response to rhEPO (p < 0.05). Our data indicate that rhGH and rhEPO have protective effects on hypoxia-induced BBB disruption and regenerative vascular effects during the post-hypoxic period in the developing brain.

Cognitive performance during adulthood in a rat model of neonatal diffuse white matter injury

RATIONALE

Infants born prematurely risk developing diffuse white matter injury (WMI), which is associated with impaired cognitive functioning and an increased risk of autism spectrum disorder. Recently, our rat model of preterm diffuse WMI induced by combined fetal inflammation and postnatal hypoxia showed impaired motor performance, anxiety-like behaviour and autism-like behaviour in juvenile rats, especially males. Immunohistochemistry showed delayed myelination in the sensory cortex and impaired oligodendrocyte differentiation.

OBJECTIVE

To assess long-term cognitive deficits in this double-hit rat model of diffuse WMI, animals were screened on impulsivity, attention and cognitive flexibility in adulthood using the 5-choice serial reaction time task (5CSRTT) and a probabilistic reversal learning task, tests that require a proper functioning prefrontal cortex. Thereafter, myelination deficits were evaluated by immunofluorescent staining in adulthood.

RESULTS

Overall, little effect of WMI or sex was found in the cognitive tasks. WMI animals showed subtle differences in performance in the 5CSRTT. Manipulating 5CSRTT parameters resulted in performance patterns previously seen in the literature. Sex differences were found in perseverative responses and omitted trials: female WMI rats seem to be less flexible in the 5CSRTT but not in the reversal learning task. Males collected rewards faster in the probabilistic reversal learning task. These findings are explained by temporally rather than permanently affected myelination and by the absence of extensive injury to prefrontal cortical subregions, confirmed by immunofluorescent staining in both adolescence and adulthood.

CONCLUSION

This rat model of preterm WMI does not lead to long-term cognitive deficits as observed in prematurely born human infants.

Research progress of IGF-1 and cerebral ischemia

Cerebral ischemic disease is a group of diseases that cause insufficient blood supply to the cerebrum, cerebellum or brain stem for different reasons, resulting in corresponding nervous system symptoms. Cardiovascular disease is the leading cause of death in the world. Among them, the death caused by cerebral ischemia accounts for the vast majority, and it is one of the fatal diseases in the middle-aged and elderly at present. Epidemiologic studies have projected increasing mortality due to cardiovascular disease worldwide (about 23.3 million people by 2030) because of the aging population. However, related studies have shown that insulin-like growth factor I (IGF-1) is a multifunctional cell proliferation regulator. It plays an important role in cerebral ischemia. It is effective in promoting cell differentiation, proliferation and individual development. Studies have shown that IGF-1 signaling pathway is a key pathway controlling cell growth and survival. There may be five mechanisms in cerebral ischemia: prevention of intracellular calcium overload, inhibition of the upregulation of nNOS, IGF-1upregulations activating HIF-1α, regulation of Bcl-2 to resist apoptosis, and enhancement of vascular endothelial function. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3)/Ca2+. IGF-1 plays an important role in cerebral ischemia and myocardial ischemia, mainly by activating downstream of IGF-1, controlling cell death and differentiation or transcription work, improving the function of heart muscle cells, reducing the myocardial cell apoptosis induced by myocardial infarction, regulating endogenous protection and restoration of cerebral ischemia injury, thus protecting cerebral and myocardial injury. Related studies have shown that bcl-2 exerts great influence on both cerebral ischemia and myocardial ischemia. Therefore, the relevant pathways and targets of cerebral ischemia and myocardial ischemia and the role of IGF-1 in protecting the heart are reviewed in this paper.

Microglia-Mediated Neurodegeneration in Perinatal Brain Injuries

Perinatal brain injuries, including encephalopathy related to fetal growth restriction, encephalopathy of prematurity, neonatal encephalopathy of the term neonate, and neonatal stroke, are a major cause of neurodevelopmental disorders. They trigger cellular and molecular cascades that lead in many cases to permanent motor, cognitive, and/or behavioral deficits. Damage includes neuronal degeneration, selective loss of subclasses of interneurons, blocked maturation of oligodendrocyte progenitor cells leading to dysmyelination, axonopathy and very likely synaptopathy, leading to impaired connectivity. The nature and severity of changes vary according to the type and severity of insult and maturation stage of the brain. Microglial activation has been demonstrated almost ubiquitously in perinatal brain injuries and these responses are key cell orchestrators of brain pathology but also attempts at repair. These divergent roles are facilitated by a diverse suite of transcriptional profiles and through a complex dialogue with other brain cell types. Adding to the complexity of understanding microglia and how to modulate them to protect the brain is that these cells have their own developmental stages, enabling them to be key participants in brain building. Of note, not only do microglia help build the brain and respond to brain injury, but they are a key cell in the transduction of systemic inflammation into neuroinflammation. Systemic inflammatory exposure is a key risk factor for poor neurodevelopmental outcomes in preterm born infants. Based on these observations, microglia appear as a key cell target for neuroprotection in perinatal brain injuries. Numerous strategies have been developed experimentally to modulate microglia and attenuate brain injury based on these strong supporting data and we will summarize these.