Retinoic acid ameliorates blood–brain barrier disruption following ischemic stroke in rats

Human-induced pluripotent stem cell-derived neural stem cell exosomes improve blood-brain barrier function after intracerebral hemorrhage by activating astrocytes via PI3K/AKT/MCP-1 axis

JOURNAL/nrgr/04.03/01300535-202502000-00029/figure1/v/2024-05-28T214302Z/r/image-tiff Cerebral edema caused by blood-brain barrier injury after intracerebral hemorrhage is an important factor leading to poor prognosis. Human-induced pluripotent stem cell-derived neural stem cell exosomes (hiPSC-NSC-Exos) have shown potential for brain injury repair in central nervous system diseases. In this study, we explored the impact of hiPSC-NSC-Exos on blood-brain barrier preservation and the underlying mechanism. Our results indicated that intranasal delivery of hiPSC-NSC-Exos mitigated neurological deficits, enhanced blood-brain barrier integrity, and reduced leukocyte infiltration in a mouse model of intracerebral hemorrhage. Additionally, hiPSC-NSC-Exos decreased immune cell infiltration, activated astrocytes, and decreased the secretion of inflammatory cytokines like monocyte chemoattractant protein-1, macrophage inflammatory protein-1α, and tumor necrosis factor-α post-intracerebral hemorrhage, thereby improving the inflammatory microenvironment. RNA sequencing indicated that hiPSC-NSC-Exo activated the PI3K/AKT signaling pathway in astrocytes and decreased monocyte chemoattractant protein-1 secretion, thereby improving blood-brain barrier integrity. Treatment with the PI3K/AKT inhibitor LY294002 or the monocyte chemoattractant protein-1 neutralizing agent C1142 abolished these effects. In summary, our findings suggest that hiPSC-NSC-Exos maintains blood-brain barrier integrity, in part by downregulating monocyte chemoattractant protein-1 secretion through activation of the PI3K/AKT signaling pathway in astrocytes.

The Transcriptional Landscape of Pericytes in Acute Ischemic Stroke

The current treatment options for ischemic stroke aim to achieve reperfusion but are time critical. Novel therapeutic approaches that can be given beyond the limited time window of 3-4.5 h are still an unmet need to be addressed to improve stroke outcomes. The lack of oxygen and glucose in the area of ischemic injury initiates a pathological cascade leading to blood-brain barrier (BBB) breakdown, inflammation, and neuronal cell death, a process that may be intercepted to limit stroke progression. Pericytes located at the blood/brain interface are one of the first responders to hypoxia in stroke and therefore a potential target cell for early stroke interventions. Using single-cell RNA sequencing in a mouse model of permanent middle cerebral artery occlusion, we investigated the temporal differences in transcriptomic signatures in pericytes at 1, 12, and 24 h after stroke. Our results reveal a stroke-specific subcluster of pericytes that is present at 12 and 24 h and characterized by the upregulation of genes mainly related to cytokine signaling and immune response. This study identifies temporal transcriptional changes in the acute phase of ischemic stroke that reflect the early response of pericytes to the ischemic insult and its secondary consequences and may constitute potential future therapeutic targets.

Retinoic acid alleviates the reduction of Akt and Bad phosphorylation and regulates Bcl-2 family protein interactions in animal models of ischemic stroke

Ischemic stroke causes a lack of oxygen and glucose supply to brain, eventually leads to severe neurological disorders. Retinoic acid is a major metabolic product of vitamin A and has various biological effects. The PI3K-Akt signaling pathway is an important survival pathway in brain. Phosphorylated Akt is important in regulating survival and apoptosis. We examined whether retinoic acid has neuroprotective effects in stroke model by regulating Akt and its downstream protein, Bad. Moreover, we investigated the relationship between retinoic acid and Bcl-2 family protein interactions. Animals were intraperitoneally administered vehicle or retinoic acid (5 mg/kg) for four days before surgery and ischemic stroke was induced by middle cerebral artery occlusion (MCAO) surgery. Neurobehavioral tests were performed 24 h after MCAO and cerebral cortical tissues were collected. Cresyl violet staining and TUNEL histochemistry were performed, Western blot and immunoprecipitation analysis were performed to elucidate the expression of various proteins. Retinoic acid reduced neurological deficits and histopathological changes, decreased the number of TUNEL-positive cells, and alleviated reduction of phospho-PDK1, phospho-Akt, and phospho-Bad expression caused by MCAO damage. Immunoprecipitation analysis showed that MCAO damage reduced the interaction between phospho-Bad and 14-3-3, which was attenuated by retinoic acid. Furthermore, retinoic acid mitigated the increase in Bcl-2/Bad and Bcl-xL/Bad binding levels and the reduction in Bcl-2/Bax and Bcl-xL/Bax binding levels caused by MCAO damage. Retinoic acid alleviated MCAO-induced increase of caspase-3 and cleaved caspase-3 expression. We demonstrate that retinoic acid prevented apoptosis against cerebral ischemia through phosphorylation of Akt and Bad, maintenance of phospho-Bad and 14-3-3 binding, and regulation of Bcl-2 family protein interactions. .

Retinoic acid attenuates ischemic injury-induced activation of glial cells and inflammatory factors in a rat stroke model

Stroke is a leading cause of death and long-term disability which can cause oxidative damage and inflammation of the neuronal cells. Retinoic acid is an active metabolite of vitamin A that has various beneficial effects including antioxidant and anti-inflammatory effects. In this study, we investigated whether retinoic acid modulates oxidative stress and inflammatory factors in a stroke animal model. A middle cerebral artery occlusion (MCAO) was performed on adult male rats to induce focal cerebral ischemia. Retinoic acid (5 mg/kg) or vehicle was injected into the peritoneal cavity for four days before MCAO surgery. The neurobehavioral tests were carried out 24 h after MCAO and cerebral cortex tissues were collected. The cortical damage was assessed by hematoxylin-eosin staining and reactive oxygen species assay. In addition, Western blot and immunohistochemical staining were performed to investigate the activation of glial cells and inflammatory cytokines in MCAO animals. Ionized calcium-binding adapter molecule-1 (Iba-1) and glial fibrillary acidic protein (GFAP) were used as markers of microglial and astrocyte activation, respectively. Tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were used as representative pro-inflammatory cytokines. Results showed that MCAO damage caused neurobehavioral defects and histopathological changes in the ischemic region and increased oxidative stress. Retinoic acid treatment reduced these changes caused by MCAO damage. We detected increases in Iba-1 and GFAP in MCAO animals treated with vehicle. However, retinoic acid alleviated increases in Iba-1 and GFAP caused by MCAO damage. Moreover, MCAO increased levels of nuclear factor-κB and pro-inflammatory cytokines, including TNF-α and IL-1β. Retinoic acid alleviated the expression of these inflammatory proteins. These findings elucidate that retinoic acid regulates microglia and astrocyte activation and modulates pro-inflammatory cytokines. Therefore, this study suggests that retinoic acid exhibits strong antioxidant and anti-inflammatory properties by reducing oxidative stress, inhibiting neuroglia cell activation, and preventing the increase of pro-inflammatory cytokines in a cerebral ischemia.

Astrocyte Involvement in Blood-Brain Barrier Function: A Critical Update Highlighting Novel, Complex, Neurovascular Interactions

Neurological disorders have been linked to a defective blood-brain barrier (BBB), with dysfunctions triggered by stage-specific disease mechanisms, some of these being generated through interactions in the neurovascular unit (NVU). Advanced knowledge of molecular and signaling mechanisms in the NVU and the emergence of improved experimental models allow BBB permeability prediction and the development of new brain-targeted therapies. As NVU constituents, astrocytes are the most numerous glial cells, characterized by a heterogeneity that occurs as a result of developmental and context-based gene expression profiles and the differential expression of non-coding ribonucleic acids (RNAs). Due to their heterogeneity and dynamic responses to different signals, astrocytes may have a beneficial or detrimental role in the BBB's barrier function, with deep effects on the pathophysiology of (and on the progression of) central nervous system diseases. The implication of astrocytic-derived extracellular vesicles in pathological mechanisms, due to their ability to pass the BBB, must also be considered. The molecular mechanisms of astrocytes' interaction with endothelial cells at the BBB level are considered promising therapeutic targets in different neurological conditions. Nevertheless, a personalized and well-founded approach must be addressed, due to the temporal and spatial heterogeneity of reactive astrogliosis states during disease.

Protective effects of KLF4 on blood-brain barrier and oxidative stress after cerebral ischemia-reperfusion in rats through the Nrf2/Trx1 pathway

PURPOSE

To investigate the role of KLF4 in CI/R injury and whether Nrf2/Trx1 axis acted as a downstream pathway of KLF4 to exert the protective role in blood-brain barrier destruction after CI/R.

METHODS

The tMCAO rat model in vivo was constructed and received the intracerebroventricular injection of 5 μg/kg and 10 μg/kg rhKLF4 before operation. TTC, brain water content, neurological function, ELISA, behavioral tests, HE, TUNEL, and qRT-PCR were performed to detect the protective role of KLF4 on CIR. Double-fluorescence staining and western blot were performed to determine the localization and spatiotemporal expression in brain tissues. Furthermore, we also analyzed the effect of KLF4 on the blood-brain barrier (BBB) and related mechanisms in vivo and in vitro. Nrf2 inhibitor tretinoin was applied, which was intraperitoneally injected into CIR rat. Evans blue staining was conducted. In vitro OGD/R models of bEnd.3 cells were also established, and received KLF4 overexpressed transfection and 12.5 µM tretinoin incubation. The permeability of bEnd.3 cells was evaluated by TEER and FITC-dextran leakage. BBB-related factors and oxidative stress were also analyzed, respectively. The tubular ability of KLF4 on OGD/R bEnd3 cells was also evaluated.

RESULTS

In vivo study confirmed that KLF4 was expressed in astrocyte, and its content increased with time. KLF4 protected against brain injury caused by cerebral ischemia-reperfusion, reduced cerebral infarction area and oxidative stress levels, and promoted the recovery of behavioral ability in rats. Simultaneously, mechanism experiments confirmed that the repair effect of KLF4 on cerebral ischemia-reperfusion injury was closely related to the Nrf2/Trx1 pathway. KLF4 exerted the neuroprotective effect through upregulating Nrf2/Trx1 pathway. Consistent with in vivo animal study, in vitro study also confirmed the effect of KLF4 on the permeability of bEnd.3 cells after OGD/R injury through Nrf2/Trx1 pathway.

CONCLUSION

Collectively, KLF4 played neuroprotective role in CIR induced MCAO and OGD/R, and the beneficial effects of KLF4 was partly linked to Nrf2/Trx1 pathway.

Integrative analysis of single-cell and bulk RNA sequencing unveils the senescence landscape in ischemic stroke

Ischemic stroke (IS) is a fatal neurological disease that occurs when the blood flow to the brain is disrupted, leading to brain tissue damage and functional impairment. Cellular senescence, a vital characteristic of aging, is associated with a poor prognosis for IS. This study explores the potential role of cellular senescence in the pathological process following IS by analyzing transcriptome data from multiple datasets (GSE163654, GSE16561, GSE119121, and GSE174574). By using bioinformatics methods, we identified hub-senescence-related genes such as ANGPTL4, CCL3, CCL7, CXCL16, and TNF and verified them using quantitative reverse transcription polymerase chain reaction. Further analysis of single-cell RNA sequencing data suggests that MG4 microglial is highly correlated with cellular senescence in MCAO, and might play a crucial role in the pathological process after IS. Additionally, we identified retinoic acid as a potential drug for improving the prognosis of IS. This comprehensive investigation of cellular senescence in various brain tissues and peripheral blood cell types provides valuable insights into the underlying mechanisms of the pathology of IS and identifies potential therapeutic targets for improving patient outcomes.

Retinoic Acid Has Neuroprotective effects by Modulating Thioredoxin in Ischemic Brain Damage and Glutamate-exposed Neurons

Ischemic stroke is a neurological disorder that causes pathological changes by increasing oxidative stress. Retinoic acid is one of the metabolites of vitamin A. It regulates oxidative stress and exerts neuroprotective effects. Thioredoxin is a small redox protein with antioxidant activity. The aim of this study was to investigate whether retinoic acid modulates the expression of thioredoxin in ischemic brain injury. Cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) surgery and retinoic acid (5 mg/kg) or vehicle was administered to adult male rats for four days prior to surgery. MCAO induced neurological deficits and increased oxidative stress and retinoic acid attenuated these changes. Retinoic acid ameliorated the MCAO-induced decrease in thioredoxin expression. MCAO decreases the interaction between thioredoxin and apoptosis signal-regulating kinase 1 (ASK1), and retinoic acid treatment alleviates this decrease. Glutamate (5 mM) exposure induced cell death and decreased thioredoxin expression in cultured neurons. Retinoic acid treatment attenuated these changes in a dose-dependent manner. Retinoic acid prevented the decrease of bcl-2 expression and the increase of bax expression caused by glutamate exposure. Moreover, retinoic acid attenuated the increases in caspase-3, cleaved caspase-3, and cytochrome c in glutamate-exposed neurons. However, the mitigation effects of retinoic acid were lower in thioredoxin siRNA-transfected neurons than in non-transfected neurons. These results demonstrate that retinoic acid regulates oxidative stress and thioredoxin expression, maintains the interaction between thioredoxin and ASK1, and modulates apoptosis-associated proteins. Taken together, these results suggest that retinoic acid has neuroprotective effects by regulating thioredoxin expression and modulating apoptotic pathway.

Brain Trauma and the Secondary Cascade in Humans: Review of the Potential Role of Vitamins in Reparative Processes and Functional Outcome

An estimated sixty-nine million people sustain a traumatic brain injury each year. Trauma to the brain causes the primary insult and initiates a secondary biochemical cascade as part of the immune and reparative response to injury. The secondary cascade, although a normal physiological response, may also contribute to ongoing neuroinflammation, oxidative stress and axonal injury, continuing in some cases years after the initial insult. In this review, we explain some of the biochemical mechanisms of the secondary cascade and their potential deleterious effects on healthy neurons including secondary cell death. The second part of the review focuses on the role of micronutrients to neural mechanisms and their potential reparative effects with regards to the secondary cascade after brain injury. The biochemical response to injury, hypermetabolism and excessive renal clearance of nutrients after injury increases the demand for most vitamins. Currently, most research in the area has shown positive outcomes of vitamin supplementation after brain injury, although predominantly in animal (murine) models. There is a pressing need for more research in this area with human participants because vitamin supplementation post-trauma is a potential cost-effective adjunct to other clinical and therapeutic treatments. Importantly, traumatic brain injury should be considered a lifelong process and better evaluated across the lifespan of individuals who experience brain injury.

Impaired retinoic acid signaling in cerebral cavernous malformations

The capillary-venous pathology cerebral cavernous malformation (CCM) is caused by loss of CCM1/Krev interaction trapped protein 1 (KRIT1), CCM2/MGC4607, or CCM3/PDCD10 in some endothelial cells. Mutations of CCM genes within the brain vasculature can lead to recurrent cerebral hemorrhages. Pharmacological treatment options are urgently needed when lesions are located in deeply-seated and in-operable regions of the central nervous system. Previous pharmacological suppression screens in disease models of CCM led to the discovery that treatment with retinoic acid improved CCM phenotypes. This finding raised a need to investigate the involvement of retinoic acid in CCM and test whether it has a curative effect in preclinical mouse models. Here, we show that components of the retinoic acid synthesis and degradation pathway are transcriptionally misregulated across disease models of CCM. We complemented this analysis by pharmacologically modifying retinoic acid levels in zebrafish and human endothelial cell models of CCM, and in acute and chronic mouse models of CCM. Our pharmacological intervention studies in CCM2-depleted human umbilical vein endothelial cells (HUVECs) and krit1 mutant zebrafish showed positive effects when retinoic acid levels were increased. However, therapeutic approaches to prevent the development of vascular lesions in adult chronic murine models of CCM were drug regiment-sensitive, possibly due to adverse developmental effects of this hormone. A treatment with high doses of retinoic acid even worsened CCM lesions in an adult chronic murine model of CCM. This study provides evidence that retinoic acid signaling is impaired in the CCM pathophysiology and suggests that modification of retinoic acid levels can alleviate CCM phenotypes.

Retinoic Acid Prevents the Neuronal Damage Through the Regulation of Parvalbumin in an Ischemic Stroke Model

Ischemic stroke is a neurological disease that causes brain damage by increasing oxidative stress and ion imbalance. Retinoic acid is a major metabolite of vitamin A and regulates oxidative stress, calcium homeostasis, and cell death. Intracellular calcium is involved in neuronal growth and synaptic plasticity. Parvalbumin is a calcium-binding protein that is mainly expressed in brain. In this study, we investigated whether retinoic acid has neuroprotective effects by controlling intracellular calcium concentration and parvalbumin expression in ischemic brain damage. Middle cerebral artery occlusion (MCAO) was performed to induce cerebral ischemia. Retinoic acid (5 mg/kg) or vehicle was injected into the abdominal cavity for four days before surgery and cerebral cortices were collected 24 h after MCAO for further studies. MCAO damage induced neurological deficits and histopathological changes and decreased parvalbumin expression. However, retinoic acid treatment alleviated these changes. In cultured neurons, glutamate (5 mM) exposure induced neuronal cell death, increased intracellular calcium concentration, and decreased parvalbumin expression. Retinoic acid treatment attenuated these changes against glutamate toxicity in a dose-dependent manner. It also regulates glutamate induced change in bcl-2 and bax expression. The mitigation effects of retinoic acid were greater under non-transfection conditions than under parvalbumin siRNA transfection conditions. Our findings showed that retinoic acid modulates intracellular calcium concentration and parvalbumin expression and prevents apoptosis in ischemic brain injury. In conclusion, retinoic acid contributes to the preservation of neurons from ischemic stroke by controlling parvalbumin expression and apoptosis-related proteins.

Identification of changed proteins by retinoic acid in cerebral ischemic damage: a proteomic study

Ischemic stroke is a severe neurodegenerative disease with a high mortality rate. Retinoic acid is a representative metabolite of vitamin A. It has many beneficial effects including anti-inflammatory, anti-apoptotic, and neuroprotective effects. The purpose of this study is to identify specific proteins that are regulated by retinoic acid in ischemic stroke. Middle cerebral artery occlusion (MCAO) was performed to induce focal cerebral ischemia. Retinoic acid (5 mg/kg) or vehicle was injected intraperitoneally into male rats for four days prior to MCAO operation. Neurobehavioral tests were performed 24 hr after MCAO and the cerebral cortex was collected for proteomic study. Retinoic acid alleviates neurobehavioral deficits and histopathological changes caused by MCAO. Furthermore, we identified various proteins that were altered by retinoic acid in MCAO damage. Among these identified proteins, adenosylhomocysteinase, isocitrate dehydrogenase [NAD+] subunit α, glycerol-3-phosphate dehydrogenase, Rab GDP dissociation inhibitor β, and apolipoprotein A1 were down-regulated in MCAO animals with vehicle treatment, whereas retinoic acid treatment alleviated these reductions. However, heat shock protein 60 was up-regulated in MCAO animals with vehicle, while retinoic acid treatment attenuated this increase. The changes in these expressions were confirmed by reverse transcription-PCR. These proteins regulate cell metabolism and mediate stress responses. Our results demonstrated that retinoic acid attenuates the neuronal damage by MCAO and regulates the various protein expressions that are involved in the survival of cells. Thus, we can suggest that retinoic acid exerts neuroprotective effects on focal cerebral ischemia by modulation of specific proteins.

All-trans Retinoic Acid has Limited Therapeutic Effects on Cognition and Hippocampal Protein Expression After Controlled Cortical Impact

Traumatic brain injury (TBI) is known to impair synaptic function, and subsequently contribute to observed cognitive deficits. Retinoic Acid (RA) signaling modulates expression of synaptic plasticity proteins and is involved in hippocampal learning and memory. All trans-retinoic acid (ATRA), a metabolite of Vitamin A, has been identified as a potential pharmacotherapeutic for other neurological disorders due to this role. This study conducted an ATRA dose response to determine its therapeutic effects on cognitive behaviors and expression of hippocampal markers of synaptic plasticity and RA signaling proteins after experimental TBI. Under isoflurane anesthesia, adult male Sprague Dawley rats received either controlled cortical impact (CCI, 2.5 mm deformation, 4 m/s) or control surgery. Animals received daily intraperitoneal injection of 0.5, 1, 5, or 10 mg/kg of ATRA or vehicle for 2 weeks. Animals underwent motor and spatial learning and memory testing. Hippocampal expression of synaptic plasticity proteins neurogranin (Ng), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 sub-unit, as well as RA signaling proteins STRA6, ADLH1a1, CYP26A1 and CYP26B1 were evaluated by western blot at 2-weeks post-injury. ATRA treatment significantly recovered Ng synaptic protein expression, while having no effect on motor performance, spatial learning, and memory, and GluA1 expression after TBI. RA signaling protein expression is unchanged 2 weeks after TBI. Overall, ATRA administration after TBI showed limited therapeutic benefits compared to the vehicle.

Targeting Oxidative Stress and Inflammatory Response for Blood-Brain Barrier Protection in Intracerebral Hemorrhage

Significance: Blood-brain barrier (BBB) disruption is a major pathological change after intracerebral hemorrhage (ICH) and is both the cause and result of oxidative stress and of the immune response post-ICH. These processes contribute to ICH-induced brain injury. Recent Advances: After the breakdown of cerebral vessels, blood components, including erythrocytes and their metabolites, thrombin, and fibrinogen, can access the cerebral parenchyma through the compromised BBB, triggering oxidative stress and inflammatory cascades. These aggravate BBB disruption and contribute to further infiltration of blood components, resulting in a vicious cycle that exacerbates brain edema and neurological injury after ICH. Experimental and clinical studies have highlighted the role of BBB disruption in ICH-induced brain injury. Critical Issues: In this review, we focus on the strategies to protect the BBB in ICH. Specifically, we summarize the evidence and the underlying mechanisms, including the ICH-induced process of oxidative stress and inflammatory response, and we highlight the potential therapeutic targets to protect BBB integrity after ICH. Future Directions: Future studies should probe the mechanism of ferroptosis as well as oxidative stress-inflammation coupling in BBB disruption after ICH and investigate the effects of antioxidants and immunomodulatory agents in more ICH clinical trials. Antioxid. Redox Signal. 37, 115-134.

Retinoic acid regulates the ubiquitin-proteasome system in a middle cerebral artery occlusion animal model

Background

Retinoic acid is a major metabolite of vitamin A and exerts beneficial effects including anti-oxidant and anti-inflammatory activities in neurons. The ubiquitin–proteasome system is an important biological system that regulates cell survival. Ubiquitination regulates protein degradation and plays an important role in oxidative stress. Deubiquitinating enzymes cleave ubiquitin from proteins and control ubiquitination-induced degradation. We detected decreases in ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in cerebral ischemic damage. In this study, we investigated whether retinoic acid regulates the expression of deubiquitinating enzymes ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in cerebral ischemic injury. Right middle cerebral artery occlusion (MCAO) was performed to induce cerebral ischemic damage in male rats. Retinoic acid (5 mg/kg) or vehicle was intraperitoneally injected every day from 4 days before surgery. Neurological behavioral tests were performed 24 h after MCAO, and right cerebral cortical tissues were collected.

Results

MCAO damage caused neurological behavioral dysfunction, and retinoic acid alleviated these deficits. The identified proteins decreased in MCAO animals with vehicle, while retinoic acid treatment attenuated these decreases. The results of proteomic study were confirmed by a reverse transcription-PCR technique. Expressions of ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 were decreased in MCAO animals treated with vehicle. Retinoic acid treatment alleviated these MCAO-induced reductions. The ubiquitin–proteasome system plays an essential role in maintaining cell function and preserving cell shape against ischemic damage.

Conclusions

These findings suggest that retinoic acid regulates ubiquitin- and proteasome-related proteins including ubiquitin carboxy-terminal hydrolase L1, ubiquitin thioesterase OTUB1, and proteasome subunit alpha types 1 and 3 in a brain ischemia model. Changes in these proteins are involved in the neuroprotective effects of retinoic acid.

Reactive Astrocytes in Central Nervous System Injury: Subgroup and Potential Therapy

Traumatic central nervous system (CNS) injury, which includes both traumatic brain injury (TBI) and spinal cord injury (SCI), is associated with irreversible loss of neurological function and high medical care costs. Currently, no effective treatment exists to improve the prognosis of patients. Astrocytes comprise the largest population of glial cells in the CNS and, with the advancements in the field of neurology, are increasingly recognized as having key functions in both the brain and the spinal cord. When stimulated by disease or injury, astrocytes become activated and undergo a series of changes, including alterations in gene expression, hypertrophy, the loss of inherent functions, and the acquisition of new ones. Studies have shown that astrocytes are highly heterogeneous with respect to their gene expression profiles, and this heterogeneity accounts for their observed context-dependent phenotypic diversity. In the inured CNS, activated astrocytes play a dual role both as regulators of neuroinflammation and in scar formation. Identifying the subpopulations of reactive astrocytes that exert beneficial or harmful effects will aid in deciphering the pathological mechanisms underlying CNS injuries and ultimately provide a theoretical basis for the development of effective strategies for the treatment of associated conditions. Following CNS injury, as the disease progresses, astrocyte phenotypes undergo continuous changes. Although current research methods do not allow a comprehensive and accurate classification of astrocyte subpopulations in complex pathological contexts, they can nonetheless aid in understanding the roles of astrocytes in disease. In this review, after a brief introduction to the pathology of CNS injury, we summarize current knowledge regarding astrocyte activation following CNS injury, including: (a) the regulatory factors involved in this process; (b) the functions of different astrocyte subgroups based on the existing classification of astrocytes; and (c) attempts at astrocyte-targeted therapy.

Astrocytes in the Traumatic Brain Injury: the Good and the Bad

Astrocytes control many processes of the nervous system in health and disease, and respond to injury quickly. Astrocytes produce neuroprotective factors in the injured brain to clear cellular debris and to orchestrate neurorestorative processes that are beneficial for neurological recovery after traumatic brain injury (TBI). However, astrocytes also become dysregulated and produce cytotoxic mediators that hinder CNS repair by induction of neuronal dysfunction and cell death. Hence, we discuss the potential role of astrocytes in neuropathological processes such as neuroinflammation, neurogenesis, synaptogenesis and blood-brain barrier repair after TBI. Thus, an improved understanding of the dual role of astrocytes may advance our knowledge of post-brain injury recovery, and provide opportunities for the development of novel therapeutic strategies for TBI.

Gangliosides combined with mild hypothermia provides neuroprotection in a rat model of traumatic brain injury

Traumatic brain injury (TBI) remains a major cause of disability and death in modern society. In this study, we explored the neuroprotection role of the combination of gangliosides (GM) and mild hypothermia (MH) and the potential effect on oxidative stress injuries in a rat model of TBI. All 50 rats were randomized to five groups: (1) NC group: undergoing surgery without hit; (2) TBI group: undergoing surgery with hit; (3) GM group: TBI treated with gangliosides; (4) MHT group: TBI treated with MH; (5) GM+MHT group: TBI treated with gangliosides and MH. Spatial learning impairments, neurological function injury, Evans Blue leakage, brain MRI and oxidative stress injuries were assessed. The protein levels of Cleaved-caspase 3 and CytC were also detected. Both GM and MHT could rescue TBI-induced spatial learning impairments, improve neurological function injury and brain edema. In addition, the combination of them has a better therapeutic effect. Through the MRI, we found that compared with the TBI group, the brain tissue edema area of GM group, MHT group, and GM+MHT group was smaller, the occupancy effect was weakened, and the midline was slightly shifted. Compared with the GM group and MHT group, these changes in the GM+MHT group were much smaller. GM combined with MH-alleviated TBI-induced oxidative stress injuries and apoptosis. Our study reveals that GM and MH potentially provide neuroprotection via the suppression of oxidative stress injuries and apoptosis after TBI in rats.

Vitamin A and Diabetes

Recently, research data have shown that vitamin A (VA, retinol) as a micronutrient participates in the regulation of glucose and lipid metabolism. Since diabetes is a metabolic disease, it is imperative to reveal the relationship of VA and diabetes. This review was aimed to summarize the current understanding of VA and its metabolites in diabetes. Since April of 2020, the authors have searched the PubMed using key words and retrieved articles that focused on diabetes and VA or its metabolites. Based on the published data, it appears that the development of type 1 diabetes leads to reduction of blood VA level in human and animals, and increase of hepatic VA store in experimental animals. On the other hand, the mutual impacts of type 2 diabetes and VA intake and blood VA level on each other appear to be uncertain. Retinoic acid, the active metabolite of VA, has been studied extensively for the treatment of diabetic complications. The current data appear to indicate that the development of diabetes is associated with changes of VA metabolism. More carefully designed clinical and laboratory experiments are needed to reveal the impacts of diabetes on VA metabolism and the role of VA in the development and treatment of diabetes.

Retinoic acid exerts neuroprotective effects against focal cerebral ischemia by preventing apoptotic cell death

Cerebral ischemia is a neurological disorder that leads to cognitive decline and high mortality. Retinoic acid is a metabolite of vitamin A that has anti-inflammatory and anti-apoptotic effects. This study investigated whether retinoic acid prevents neuronal cell damage on focal cerebral ischemia through modulating apoptosis signaling pathway. Middle cerebral artery occlusion (MCAO) was performed to induce focal cerebral ischemia in adult male rats. Retinoic acid (5 mg/kg) or vehicle was injected intraperitoneally for 4 days prior to MCAO. Neurological behavior deficit tests were performed 24 h after MCAO. Brain edema and infarct volume were measured, and TUNEL histochemistry was carried out. We also investigated the changes in apoptosis-related proteins including bcl-2 family proteins and caspases. MCAO injury induced severe neurological behavior deficits and brain edema. It also increased infarct volume, histopathological damages, and the number of TUNEL-positive cells in cerebral cortex. However, retinoic acid pretreatment attenuated MCAO-induced neurological behavior deficits, brain edema, and infarction. It also alleviated histopathological lesion and decreased the number of TUNEL-positive cells. Bcl-2 and bax proteins are representative bcl-2 family proteins. MCAO injury induced a decrease in bcl-2 expression and an increase in bax expression, and retinoic acid pretreatment alleviated these changes. MCAO injury caused a decrease in bcl-2/bax expression ratio in cerebral cortex, while retinoic acid restored this decrease by MCAO. Moreover, our result showed increases in caspase-9, caspase-3, PARP protein levels in MCAO-operated animals. Retinoic acid pretreatment prevented these increases. We identified the changes in cleaved forms of these proteins, similar to the changes in full-length protein. Activation of caspases and PARP proteins are considered to be representative apoptosis indicators. This study showed that retinoic acid regulates bcl-2 family proteins and caspase proteins in focal cerebral ischemia. Thus, our findings demonstrate that retinoic acid exhibits a neuroprotective effect against ischemic damage by modulating apoptosis signaling pathway.

Coding and non-coding nucleotides': The future of stroke gene therapeutics

Stroke is the foremost cause of death ranked after heart disease and cancer. It is the fatal life-threatening event that requires immediate medical admissions to overcome following morbidity and mortality. The therapeutic advances in stroke therapy have been manipulated with diverse paths for last 5 years. Recent research and clinical trials have investigated a variety of anti-stroke agents including anti-coagulants, cerebro-protective agents, antiplatelet therapy, stem-cell therapy, and specified gene therapy. In recent advanced studies, genetic therapies including noncoding RNAs (ncRNAs), long non-coding RNAs (LncRNAs), small interfering RNAs (siRNAs), microRNAs (miRNAs), Piwi interacting RNAs (PiWi RNAs) have shown better potential as targeted future therapeutics with a better outcome than conventional stroke therapeutics. The potential of targeted gene therapy is much more advanced in not only the induction of neuroprotection but also safer non-toxic targeted therapeutics. In the current state of the art review, we have focused on the recent advancements made towards the stroke with RNA modifications and targeted gene therapeutics.

Administration of all-trans retinoic acid after experimental traumatic brain injury is brain protective

BACKGROUND AND PURPOSE

All-trans retinoic acid (ATRA) is a vitamin A metabolite, important in the developing and mature brain. Pre-injury ATRA administration ameliorates ischaemic brain insults in rodents. This study examined the effects of post-traumatic ATRA treatment in experimental traumatic brain injury (TBI).

EXPERIMENTAL APPROACH

Male adult mice were subjected to the controlled cortical impact model of TBI or sham procedure and killed at 7 or 30 days post-injury (dpi). ATRA (10 mg kg-1, i.p.) was given immediately after the injury and 1, 2 and 3 dpi. Neurological function and sensorimotor coordination were evaluated. Brains were processed for (immuno-) histological, mRNA and protein analyses (qPCR and western blot).

KEY RESULTS

ATRA treatment reduced brain lesion size, reactive astrogliosis and axonal injury at 7 dpi, and hippocampal granule cell layer (GCL) integrity was protected at 7 and 30 dpi, independent of cell proliferation in neurogenic niches and blood-brain barrier damage. Neurological and motor deficits over time and the brain tissue loss at 30 dpi were not affected by ATRA treatment. ATRA decreased gene expression of markers for damage-associated molecular pattern (HMGB1), apoptosis (caspase-3 and Bax), activated microglia (TSPO), and reactive astrogliosis (GFAP, SerpinA3N) at 7 dpi and a subset of markers at 30 dpi (TSPO, GFAP).

CONCLUSION AND IMPLICATIONS

In experimental TBI, post-traumatic ATRA administration exerted brain protective effects, including long-term protection of GCL integrity, but did not affect neurological and motor deficits. Further investigations are required to optimize treatment regimens to enhance ATRA's brain protective effects and improve outcomes.

Astrocytes are necessary for blood-brain barrier maintenance in the adult mouse brain

In the adult brain, multiple cell types are known to produce factors that regulate blood-brain barrier (BBB) properties, including astrocytes. Yet several recent studies disputed a role for mature astrocytes at the BBB. To determine if astrocytes contribute a nonredundant and necessary function in maintaining the adult BBB, we used a mouse model of tamoxifen-inducible astrocyte ablation. In adult mice, tamoxifen induction caused sparse apoptotic astrocyte cell death within 2 hr. Indicative of BBB damage, leakage of the small molecule Cadaverine, and the large plasma protein fibrinogen into the brain parenchyma indicative of BBB damage was detected as early as astrocyte ablation was present. Vessels within and close to regions of astrocyte loss had lower expression of the tight junction protein zonula occludens-1 while endothelial glucose transporter 1 expression was undisturbed. Cadaverine leakage persisted for several weeks suggesting a lack of barrier repair. This is consistent with the finding that ablated astrocytes were not replaced. Adjacent astrocytes responded with partial nonproliferative astrogliosis, characterized by morphological changes and delayed phosphorylation of STAT3, which restricted dye leakage to the brain and vessel surface areas lacking coverage by astrocytes 1 month after ablation. In conclusion, astrocytes are necessary to maintain BBB integrity in the adult brain. BBB-regulating factors secreted by other cell types, such as pericytes, are not sufficient to compensate for astrocyte loss.

Retinoic Acid and the Gut Microbiota in Alzheimer's Disease: Fighting Back-to-Back?

BACKGROUND

There is growing evidence that the gut microbiota may play an important role in neurodegenerative diseases such as Alzheimer's disease. However, how these commensals influence disease risk and progression still has to be deciphered.

OBJECTIVE

The objective of this review was to summarize current knowledge on the interplay between gut microbiota and retinoic acid. The latter one represents one of the important micronutrients, which have been correlated to Alzheimer's disease and are used in initial therapeutic intervention studies.

METHODS

A selective overview of the literature is given with the focus on the function of retinoic acid in the healthy and diseased brain, its metabolism in the gut, and the potential influence that the bioactive ligand may have on microbiota, gut physiology and, Alzheimer's disease.

RESULTS

Retinoic acid can influence neuronal functionality by means of plasticity but also by neurogenesis and modulating proteostasis. Impaired retinoid-signaling, therefore, might contribute to the development of diseases in the brain. Despite its rather direct impact, retinoic acid also influences other organ systems such as gut by regulating the residing immune cells but also factors such as permeability or commensal microbiota. These in turn can also interfere with retinoid-metabolism and via the gutbrain- axis furthermore with Alzheimer's disease pathology within the brain.

CONCLUSION

Potentially, it is yet too early to conclude from the few reports on changed microbiota in Alzheimer's disease to a dysfunctional role in retinoid-signaling. However, there are several routes how microbial commensals might affect and might be affected by vitamin A and its derivatives.

Salidroside as a potential neuroprotective agent for ischemic stroke: a review of sources, pharmacokinetics, mechanism and safety

Salidroside (Sal) is a bioactive extract principally from traditional herbal medicine such as Rhodiola rosea L., which has been commonly used for hundreds of years in Asia countries. The excellent neuroprotective capacity of Sal has been illuminated in recent studies. This work focused on the source, pharmacokinetics, safety and anti-ischemic stroke (IS) effect of Sal, especially emphasizing its mechanism of action and BBB permeability. Extensive databases, including Pubmed, Web of science (WOS), Google Scholar and China National Knowledge Infrastructure (CNKI), were applied to obtain relevant online literatures. Sal exerts powerful therapeutic effects on IS in experimental models either in vitro or in vivo due to its neuroprotection, with significantly diminishing infarct size, preventing cerebral edema and improving neurological function. Also, the findings suggest the underlying mechanisms involve anti-oxidation, anti-inflammation and anti-apoptosis by regulating multiple signaling pathways and key molecules, such as NF-κB, TNF-α and PI3K/Akt pathway. In pharmacokinetics, although showing a rapid absorption and elimination, bioavailability of Sal is elevated under some non-physiological conditions. The component and its metabolite (tyrosol) are capable of distributing to brain tissue and the later keeps a higher level of concentration. Moreover, Sal scarcely has obvious toxicity or side effects in a variety of animal experiments and clinical trials, but combination of drugs and perinatal use of medicine should be taken more attentions. Finally, as an active ingredient, not only is Sal isolated from diverse plants with limited yield, but also large batches of the products can be harvested by biological and chemical synthesis. With higher efficacy and better safety profiles, Sal could sever as a promising neuroprotectant for preventing and treating IS. Nevertheless, further investigations are still required to explore the pharmacodynamic and pharmacokinetic properties of Sal in the treatment of IS.

Correlation between Serum Vitamin A and D Levels in Acute Phase Ischemic Stroke and Clinical Outcome

Background:

In the last decade, a number of studies have examined the relationship between serum vitamin D concentration and the risk of cerebrovascular events. Besides vitamin D, the latest evidence shows that vitamin A is also a risk factor for cerebrovascular disease. Vitamin A and its derivatives act biologically via specific nuclear receptors that regulate gene transcription. Vitamin A receptors can also interact with other nuclear receptors that have neuroprotective effects such as vitamin D, against stroke. Although many studies suggested the synergism of vitamin A and D, there is still no study that evaluates their levels simultaneously in acute phase ischemic stroke, and the relationship to outcome.

Objective:

The objective of this study was to analyze the correlation between serum vitamin A and D levels on admission in Acute Ischemic Stroke patients and clinical outcome by using the National Institutes of Health Stroke Scale (NIHSS).

Methods:

A prospective cohort study was conducted, and samples were followed since the diagnosis of acute-phase Ischemic Stroke was established until the clinical outcome of day 14 after stroke onset. A total of 50 subjects enrolled for this study would be examined for serum levels of vitamins A and D on admission, and on the 14th day were assessed for NIHSS as a clinical outcome.

Results:

From 50 research subjects, the mean of vitamin A and D level in the acute phase of Ischemic Stroke was 463.35 ± 116.97 µg/L and 21.65 ± 6.51 ng/mL, respectively. By using the Spearman’s correlation test, it was found that the acute phase vitamin A level and NIHSS on day 14 had a significant and strong correlation with p = 0.045 (r = -0.672). Along with it, vitamin D serum levels and NIHSS also had a significant and strong correlation with p = 0.026 (r = -0.754). Both of these results showed that vitamin A and D had an inverse association with NIHSS, meaning that the higher vitamin A and D serum levels, the better the clinical outcome would be.

Conclusion:

Both serum vitamin A and D levels in the acute phase of Ischemic Stroke was correlated strongly with short time clinical outcome. The higher vitamin A and D serum levels in the acute phase, the better the clinical outcome would be for Ischemic Stroke patients.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of fatality and disability worldwide. Despite its high prevalence, effective treatment strategies for TBI are limited. Traumatic brain injury induces structural and functional alterations of astrocytes, the most abundant cell type in the brain. As a way of coping with the trauma, astrocytes respond in diverse mechanisms that result in reactive astrogliosis. Astrocytes are involved in the physiopathologic mechanisms of TBI in an extensive and sophisticated manner. Notably, astrocytes have dual roles in TBI, and some astrocyte-derived factors have double and opposite properties. Thus, the suppression or promotion of reactive astrogliosis does not have a substantial curative effect. In contrast, selective stimulation of the beneficial astrocyte-derived molecules and simultaneous attenuation of the deleterious factors based on the spatiotemporal-environment can provide a promising astrocyte-targeting therapeutic strategy. In the current review, we describe for the first time the specific dual roles of astrocytes in neuronal plasticity and reconstruction, including neurogenesis, synaptogenesis, angiogenesis, repair of the blood-brain barrier, and glial scar formation after TBI. We have also classified astrocyte-derived factors depending on their neuroprotective and neurotoxic roles to design more appropriate targeted therapies.

Association of serum retinoic acid with depression in patients with acute ischemic stroke

Retinoic acid (RA), produced by the metabolism of vitamin A, makes effects on depression and stroke. This study was aimed to evaluate the relationship between RA levels in serum and post-stroke depression (PSD). A single-center (Chengdu, China) prospective cohort study was conducted on patients with acute ischemic stroke. The RA serum level was measured at admission. The PSD was assessed in the 3-month follow-up. The RA-PSD relationship was evaluated with conditional logistic regression. In total, 239 ischemic stroke cases and 100 healthy controls were included. The median RA serum level in patients with ischemic stroke was 2.45 ng/ml (interquartile range [IQR], 0.72-4.33), lower(P<0.001) than 3.89 ng/ml of those in control cases ([IQR]: 2.62-5.39). The crude and adjusted odds ratios [OR] (and 95% confidence intervals [CI]) of PSD associated with an IQR increase for RA were 0.54 (0.44, 0.67) and 0.66 (0.52, 0.79), respectively. Higher ORs of PSD associated with reduced RA levels ( Collapse

Key Words

• depression
• ischemic stroke
• retinoic acid
• stroke

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MESH Headings

• Aged
• Biomarkers/blood
• Cohort Studies
• Depression/blood
• Depression/etiology
• Female
• Humans
• Ischemic Stroke/blood
• Ischemic Stroke/complications
• Ischemic Stroke/psychology
• Male
• Middle Aged
• Prospective Studies
• Tretinoin/blood

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Affiliation(s)

Cai-Di Yang Department of Neurology, Eastern Hospital, Sichuan Academy of Medical Sciences and Sichuan Provincial People's Hospital, Chengdu 610101, China
Ming-Li Cheng Department of Neurology, People's Hospital of Jianyang, Jianyang 641400, China
Wen Liu The Clinical Laboratory Department, Affiliated Hospital of North Sichuan Medical College, Nanchong 637000, China
Ding-Hua Zeng Department of Neurology, Eastern Hospital, Sichuan Academy of Medical Sciences and Sichuan Provincial People's Hospital, Chengdu 610101, China

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Xu M, Xu L, Du H, Shan W, Feng J, Zhai G, Yang X. Decreased Serum Retinoic Acid May Predict Poor Outcome in Ischemic Stroke Patients. Neuropsychiatr Dis Treat 2020;16:1483-1491. [PMID: 32606701 PMCID: PMC7293911 DOI: 10.2147/ndt.s254591]

BACKGROUND AND AIMS

Decreased serum retinoic acid (RA) levels have been shown to be linked with increased mortality in cardiovascular diseases. This study aimed to investigate the relationship between serum RA and 3-month functional outcome after ischemic stroke.

METHODS

Between January 2019 and September 2019, we prospectively recruited ischemic stroke patients within 24 hrs of symptom onset. Serum RA levels were measured for all patients at admission. The primary outcome was defined as poor functional outcome (modified Rankin Scale 3-6) at 90 days. The secondary outcome was defined as early neurological deterioration (END), which is considered as an increase of ≥1 point in motor power or total National Institutes of Health Stroke Scale score of ≥2 points within 7 days.

RESULTS

A total of 217 patients were included in the analysis. The median RA levels were 2.9 ng/mL. Ninety-four (43.3%) and 65 (30.0%) patients experienced 3-month poor outcome and END, respectively. After adjusted for potential confounders, decreased levels of serum RA were associated with a higher risk of poor outcome (P for trend = 0.001) and END (P for trend = 0.002). Adding RA quartile to the existing risk factors improved risk prediction for poor outcome [net reclassification improvement (NRI) = 42.6%, P = 0.001; integrated discrimination improvement (IDI) = 5.7%, P = 0.001] and END (NRI index = 45.4%, P = 0.001; IDI = 4.3%; P = 0.005).

CONCLUSION

Low serum RA levels at baseline were associated with poor prognosis at 90 days after ischemic stroke, suggesting that RA may be a potential prognostic biomarker for ischemic stroke.

Key Words

• acute ischemic stroke
• early neurological deterioration
• functional outcome
• retinoic acid

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Affiliation(s)

Mengshi Xu Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China
Liang Xu Department of Anesthesiology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215000, People's Republic of China
Huaping Du Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China
Wanying Shan Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China
Jie Feng Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China
Guojie Zhai Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China
Xiuyan Yang Department of Neurology, Suzhou Ninth People's Hospital, Suzhou, Jiangsu 215200, People's Republic of China

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Duan Z, Shan W, Du H, Xu M, Feng J, Qiu C, Ling Y. Association between serum retinoic acid levels and risk of post-stroke depression in patients with ischemic stroke. Asian J Psychiatr 2019;46:87-91. [PMID: 31639555 DOI: 10.1016/j.ajp.2019.09.038]

Previous studies suggest that retinoic acid (RA) can exert neuroprotective function in ischemic stroke. However, its role in post-stroke depression (PSD) has still been unclear. We sought to investigate the relationship between circulating RA levels and PSD in patients with ischemic stroke. From September 2018 to March 2019, we prospectively screened patients with ischemic stroke who were hospitalized within 7 days of symptoms onset. RA levels were measured after admission. All patients were followed up at 3 months after stroke. Diagnosis of PSD was made in line with the Chinese version of Structured Clinical Interview of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition criteria. PSD risk was estimated using multivariable regression models. In total, 352 ischemic stroke patients were enrolled for the final analysis. Up to 3 months after symptoms onset, 102 subjects experienced PSD. PSD patients showed significantly lower RA levels at baseline as compared to non-PSD patients. In univariate logistic analysis, reduced levels of RA was a significant predictor of PSD. These results were further confirmed in multivariate regression additionally controlled for possible relevant confounders. Our study shows that decreased serum RA levels at admission might be associated with 3-month PSD in ischemic stroke patients.

Key Words

• Hamilton depression scale
• Ischemic stroke
• Post-stroke depression
• Retinoic acid

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Affiliation(s)

Zhipei Duan Department of Oncology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Wanying Shan Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Huaping Du Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Mengshi Xu Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Jie Feng Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Chunfang Qiu Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China
Yunao Ling Department of Neurology, Suzhou Ninth People's Hospital, Suzhou 215200, Jiangsu, China.

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Spampinato SF, Bortolotto V, Canonico PL, Sortino MA, Grilli M. Astrocyte-Derived Paracrine Signals: Relevance for Neurogenic Niche Regulation and Blood-Brain Barrier Integrity. Front Pharmacol 2019;10:1346. [PMID: 31824311 PMCID: PMC6881379 DOI: 10.3389/fphar.2019.01346]

Astrocytes are essential for proper regulation of the central nervous system (CNS). Importantly, these cells are highly secretory in nature. Indeed they can release hundreds of molecules which play pivotal physiological roles in nervous tissues and whose abnormal regulation has been associated with several CNS disorders. In agreement with these findings, recent studies have provided exciting insights into the key contribution of astrocyte-derived signals in the pleiotropic functions of these cells in brain health and diseases. In the future, deeper analysis of the astrocyte secretome is likely to further increase our current knowledge on the full potential of these cells and their secreted molecules not only as active participants in pathophysiological events, but as pharmacological targets or even as therapeutics for neurological and psychiatric diseases. Herein we will highlight recent findings in our and other laboratories on selected molecules that are actively secreted by astrocytes and contribute in two distinct functions with pathophysiological relevance for the astroglial population: i) regulation of neural stem cells (NSCs) and their progeny within adult neurogenic niches; ii) modulation of the blood–brain barrier (BBB) integrity and function.

Key Words

• astrocytes
• blood–brain barrier
• neural stem cells
• neurogenesis
• niche
• paracrine signals
• secretome

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Affiliation(s)

Simona Federica Spampinato Section of Pharmacology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
Valeria Bortolotto Laboratory of Neuroplasticity, Department of Pharmaceutical Sciences, University of Piemonte Orientale, Novara, Italy
Pier Luigi Canonico Laboratory of Neuroplasticity, Department of Pharmaceutical Sciences, University of Piemonte Orientale, Novara, Italy
Maria Angela Sortino Section of Pharmacology, Department of Biomedical and Biotechnological Sciences, University of Catania, Catania, Italy
Mariagrazia Grilli Laboratory of Neuroplasticity, Department of Pharmaceutical Sciences, University of Piemonte Orientale, Novara, Italy

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Hou L, Ding C, Chen Z, Liu Y, Shi H, Zou C, Zhang H, Lu Z, Zheng D. Serum Retinoic Acid Level and The Risk of Poststroke Cognitive Impairment in Ischemic Stroke Patients. J Stroke Cerebrovasc Dis 2019;28:104352. [DOI: 10.1016/j.jstrokecerebrovasdis.2019.104352]

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Cai W, Wang J, Hu M, Chen X, Lu Z, Bellanti JA, Zheng SG. All trans-retinoic acid protects against acute ischemic stroke by modulating neutrophil functions through STAT1 signaling. J Neuroinflammation 2019;16:175. [PMID: 31472680 PMCID: PMC6717357 DOI: 10.1186/s12974-019-1557-6]

Background and purpose

Regulation of neural inflammation is considered as a vital therapeutic target in ischemic stroke. All-trans retinoic acid (atRA), a potent immune modulator, has raised interest in the field of stroke therapy. However, the immunological mechanisms for atRA-mediated neuroprotection remain elusive. The current study evaluated the impact of atRA on post-stroke neural inflammation and elucidated the mechanisms involved in the regulation of related neutrophil functions.

Methods

atRA was prophylactically administered to mice 1 day before transient middle cerebral artery occlusion (tMCAO, 1 h) and repeated daily immediately after reperfusion for 3 days. Stroke outcomes, neutrophil polarization, and formation of neutrophil extracellular traps (NETs) in the stroke lesion were assessed. Neutrophil depletion was induced with anti-Ly6G antibodies. Primary neutrophil cultures were used to explore the mechanisms of atRA treatment.

Results

Prophylactic atRA treatment reduced infarct volumes and neurological deficits at 1 day after tMCAO. Post-stroke neural inflammation was attenuated and neutrophil accumulation in lesion was downregulated. atRA treatment skewed neutrophil toward N2 phenotype which facilitated its clearance by macrophage and inhibited NETs formation. The functions of neutrophil were indispensable in the protective effects of atRA and were associated with suppression to STAT1 signaling by atRA. Administration of atRA after stroke still provided efficient protection to cerebral ischemia.

Conclusion

atRA displays potent therapeutic efficacy in ischemic stroke by attenuating neural inflammation. Treatment of atRA impeded neutrophil accumulation, favored N2 polarization, and forbade NETs formation in ischemic lesion. STAT1 signaling played a decisive role in the mechanisms of atRA-afforded regulation to neutrophil.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1557-6) contains supplementary material, which is available to authorized users.

Key Words

• All trans-retinoic acid
• Cerebral ischemia
• Neural inflammation
• Neuroprotection
• Neutrophil

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Affiliation(s)

Wei Cai Center of Clinical Immunology, Center for Mental and Neurological Disorders and Diseases, the Third Affiliated Hospital of Sun Yat-sen University, Guangzhou, People's Republic of China.,Department of Neurology, Center for Mental and Neurological Disorders and Diseases, the Third Affiliated Hospital of Sun Yat-sen University, 600 Tianhe Road, Guangzhou, 510630, Guangdong, China
Julie Wang Department of Internal Medicine, Ohio State University College of Medicine and Wexner Medical Center, Columbus, OH, 43201, USA
Mengyan Hu Department of Neurology, Center for Mental and Neurological Disorders and Diseases, the Third Affiliated Hospital of Sun Yat-sen University, 600 Tianhe Road, Guangzhou, 510630, Guangdong, China
Xiao Chen Division of Hematology and Oncology, Department of Medicine, Medical College of Wisconsin, Milwaukee, WI, USA
Zhengqi Lu Department of Neurology, Center for Mental and Neurological Disorders and Diseases, the Third Affiliated Hospital of Sun Yat-sen University, 600 Tianhe Road, Guangzhou, 510630, Guangdong, China.
Joseph A Bellanti Department of Pediatrics and Microbiology-Immunology, Georgetown University Medical Center, Washington, DC, 20057, USA
Song Guo Zheng Department of Internal Medicine, Ohio State University College of Medicine and Wexner Medical Center, Columbus, OH, 43201, USA.

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Inhibition of Drp1 after traumatic brain injury provides brain protection and improves behavioral performance in rats. Chem Biol Interact 2019;304:173-185. [DOI: 10.1016/j.cbi.2019.03.013]

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36

Pawlikowski B, Wragge J, Siegenthaler JA. Retinoic acid signaling in vascular development. Genesis 2019;57:e23287. [PMID: 30801891 DOI: 10.1002/dvg.23287]

Formation of the vasculature is an essential developmental process, delivering oxygen and nutrients to support cellular processes needed for tissue growth and maturation. Retinoic acid (RA) and its downstream signaling pathway is vital for normal pre- and post-natal development, playing key roles in the specification and formation of many organs and tissues. Here, we review the role of RA in blood and lymph vascular development, beginning with embryonic yolk sac vasculogenesis and remodeling and discussing RA's organ-specific roles in angiogenesis and vessel maturation. In particular, we highlight the multi-faceted role of RA signaling in CNS vascular development and acquisition of blood-brain barrier properties.

Key Words

• CNS
• angiogenesis
• blood vasculature
• embryonic development
• endothelial cell
• lymphatic vasculature
• vasculogenesis

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Affiliation(s)

Brad Pawlikowski Department of Molecular, Cell and Developmental Biology, University of Colorado-Boulder, Boulder, Colorado
Jacob Wragge Department of Pediatrics-Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus, Aurora, Colorado
Julie A Siegenthaler Department of Pediatrics-Section of Developmental Biology, University of Colorado, School of Medicine-Anschutz Medical Campus, Aurora, Colorado

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Tu WJ, Qiu HC, Zhang Y, Cao JL, Wang H, Zhao JZ, Liu Q, Zeng X. Lower serum retinoic acid level for prediction of higher risk of mortality in ischemic stroke. Neurology 2019;92:e1678-e1687. [PMID: 30850446 DOI: 10.1212/wnl.0000000000007261]

OBJECTIVE

To explore the association between serum retinoic acid (RA) level in patients with acute ischemic stroke (AIS) and mortality risk in the 6 months after admission.

METHODS

From January 2015 through December 2016, patients admitted to 3 stroke centers in China for first-ever AIS were screened. The primary endpoint was all-cause mortality or cardiovascular disease (CVD) mortality in the 6 months after admission. The significance of serum RA level, NIH Stroke Scale score, and established risk factors in predicting mortality were determined. The integrated discrimination improvement (IDI) and net reclassification improvement (NRI) statistics were applied in statistical analysis.

RESULTS

Of the 1,530 patients enrolled, 325 died within 6 months of admission, with an all-cause mortality of 21.2% and CVD-related mortality of 13.1%. In multivariable analysis, RA levels were expressed as quartiles with the clinical variables. The results of the second to fourth quartiles (Q2-Q4) were compared with the first quartile (Q1); RA levels showed prognostic significance, with decreased all-cause and CVD mortality of 55% and 63%, respectively. After RA was added to the existing risk factors, all-cause mortality could be better reclassified, in association with only the NRI statistic (p = 0.005); CVD mortality could be better reclassified with significance, in association with both the IDI and NRI statistics (p < 0.01).

CONCLUSIONS

Low circulating levels of RA were associated with increased risk of all-cause and CVD mortality in a cohort of patients with first-incidence AIS, indicating that RA level could be a predictor independent of established conventional risk factors.

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Affiliation(s)

Wen-Jun Tu From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China
Han-Cheng Qiu From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China
Yiqun Zhang From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China
Jian-Lei Cao From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China
Hong Wang From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China
Ji-Zong Zhao From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China.
Qiang Liu From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China.
Xianwei Zeng From the Institute of Radiation Medicine (W.-J.T., H.W., Q.L.), China Academy of Medical Science & Peking Union Medical College, Tianjin; Department of Neurosurgery (W.-J.T., H.-C.Q., J.-Z.Z.), Beijing Tiantan Hospital of Capital Medical University, Beijing; Department of Neurosurgery (W.-J.T., X.Z.), Qilu Hospital of Shandong University, Jinan, Shandong Province; Department of Vascular Neurosurgery (H.-C.Q., Y.Z.), New Era Stroke Care and Research Institute, the General Hospital of the PLA Rocket Force, Beijing; and Department of Cardiology (J.l.-C.), Zhongnan Hospital of Wuhan University, Wuhan, China.

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Dual Roles of Astrocyte-Derived Factors in Regulation of Blood-Brain Barrier Function after Brain Damage. Int J Mol Sci 2019;20:ijms20030571. [PMID: 30699952 PMCID: PMC6387062 DOI: 10.3390/ijms20030571]

The blood-brain barrier (BBB) is a major functional barrier in the central nervous system (CNS), and inhibits the extravasation of intravascular contents and transports various essential nutrients between the blood and the brain. After brain damage by traumatic brain injury, cerebral ischemia and several other CNS disorders, the functions of the BBB are disrupted, resulting in severe secondary damage including brain edema and inflammatory injury. Therefore, BBB protection and recovery are considered novel therapeutic strategies for reducing brain damage. Emerging evidence suggests key roles of astrocyte-derived factors in BBB disruption and recovery after brain damage. The astrocyte-derived vascular permeability factors include vascular endothelial growth factors, matrix metalloproteinases, nitric oxide, glutamate and endothelin-1, which enhance BBB permeability leading to BBB disruption. By contrast, the astrocyte-derived protective factors include angiopoietin-1, sonic hedgehog, glial-derived neurotrophic factor, retinoic acid and insulin-like growth factor-1 and apolipoprotein E which attenuate BBB permeability resulting in recovery of BBB function. In this review, the roles of these astrocyte-derived factors in BBB function are summarized, and their significance as therapeutic targets for BBB protection and recovery after brain damage are discussed.

Key Words

• astrocytes
• blood-brain barrier
• endothelial cells
• tight junction

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39

New progress in the approaches for blood–brain barrier protection in acute ischemic stroke. Brain Res Bull 2019;144:46-57. [DOI: 10.1016/j.brainresbull.2018.11.006]

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40

Yang Y, Dong B, Lu J, Wang G, Yu Y. Hemopexin reduces blood-brain barrier injury and protects synaptic plasticity in cerebral ischemic rats by promoting EPCs through the HO-1 pathway. Brain Res 2018;1699:177-185. [PMID: 30092232 DOI: 10.1016/j.brainres.2018.08.008]

Ischemic stroke causes endothelial dysfunction and blood-brain barrier dysfunction, thus damages synaptic plasticity such as learning and memory. In this study we aim to investigate the effect of hemopexin (HPX) in protecting synaptic plasticity and blood brain barrier integrity from toxic heme, and determine whether this effect is via the activation of endothelial progenitor cells (EPCs) through the heme oxygenase-1 (HO-1) pathway. Our data indicates HPX showed a significant effect in inducing the expression of HO-1, promoting the migration and differentiation of EPCs, facilitating new blood vessel formation thus protecting blood-brain barrier integrity. Also the magnitude of synaptic plasticity of rats recovered with HPX treatment. And in the presence of HO-1 blocker Zinc protoporphyrin-9 (ZnppIX), HPX lost its protective effect. This suggests that HPX protects endothelial and blood brain barrier integrity from toxic heme, thus protects neurologic function in cerebral ischemic rats in HO-1 pathway.

Key Words

• Blood brain barrier
• Cerebral ischemia
• Endothelial progenitor cells
• HO-1
• Hemopexin
• Synaptic plasticity

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MESH Headings

• Animals
• Blood-Brain Barrier/drug effects
• Blood-Brain Barrier/metabolism
• Blood-Brain Barrier/pathology
• Brain Ischemia/drug therapy
• Brain Ischemia/metabolism
• Brain Ischemia/pathology
• Capillary Permeability/drug effects
• Capillary Permeability/physiology
• Cells, Cultured
• Disease Models, Animal
• Endothelial Progenitor Cells/drug effects
• Endothelial Progenitor Cells/metabolism
• Endothelial Progenitor Cells/pathology
• Heme Oxygenase (Decyclizing)/metabolism
• Hemopexin/pharmacology
• Male
• Neuronal Plasticity/drug effects
• Neuronal Plasticity/physiology
• Neuroprotective Agents/pharmacology
• Random Allocation
• Rats, Sprague-Dawley
• Reperfusion Injury/drug therapy
• Reperfusion Injury/metabolism
• Reperfusion Injury/pathology
• Signal Transduction
• Stroke/drug therapy
• Stroke/metabolism
• Stroke/pathology
• Zonula Occludens-1 Protein/metabolism

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Affiliation(s)

Yongyan Yang Department of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China; Tianjin Institute of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China
Beibei Dong Department of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China
Jun Lu School of Biomedical Engineering, Tianjin Medical University, No. 22 Qixiangtai Road, Heping District, Tianjin 300070, China
Guolin Wang Department of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China; Tianjin Institute of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China
Yonghao Yu Department of Anesthesiology, Tianjin Medical University General Hospital, No. 154 Anshan Road, Heping District, Tianjin 300052, China.

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41

All-Trans Retinoic Acid Ameliorates the Early Experimental Cerebral Ischemia-Reperfusion Injury in Rats by Inhibiting the Loss of the Blood-Brain Barrier via the JNK/P38MAPK Signaling Pathway. Neurochem Res 2018;43:1283-1296. [PMID: 29802528 DOI: 10.1007/s11064-018-2545-4]

All-trans retinoic acid (ATRA) influences the outcomes of cerebral ischemic reperfusion (CIR) injury, but the mechanism remains unclear. The present study aimed to investigate the effects of ATRA on loss of the blood brain barrier (BBB) following CIR and to explore the possible mechanisms. Transient middle cerebral artery occlusion was performed on male SD rats to construct an in vivo CIR model. Neurological deficits, BBB permeability, brain edema, MRI and JNK/P38 MAPK proteins were detected at 24 h following CIR. We demonstrated that ATRA pretreatment could alleviate CIR-induced neurological deficits, increase of BBB permeability, infarct volume, degradation of tight junction proteins, inhibit MMP-9 protein expression and activity. ATRA treatment also reduced the p-P38 and p-JNK protein level. However the protective effect of ATRA on CIR could be reversed by administration of retinoic acid alpha receptor antagonist Ro41-5253. SP600125 and SB203580, which is the JNK/P38 pathway inhibitors has the same protective effect as ATRA. These results indicated that ATRA may inhibit the JNK/P38 MAPK pathway to alleviate BBB disruption and improve CIR outcomes.

Key Words

• All-trans retinoic acid
• Blood–brain barrier
• Cerebral ischemia–reperfusion
• JNK/P38 MAPK signaling pathway
• MMP-9

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42

Noumbissi ME, Galasso B, Stins MF. Brain vascular heterogeneity: implications for disease pathogenesis and design of in vitro blood-brain barrier models. Fluids Barriers CNS 2018;15:12. [PMID: 29688865 PMCID: PMC5911972 DOI: 10.1186/s12987-018-0097-2]

The vertebrate blood–brain barrier (BBB) is composed of cerebral microvascular endothelial cells (CEC). The BBB acts as a semi-permeable cellular interface that tightly regulates bidirectional molecular transport between blood and the brain parenchyma in order to maintain cerebral homeostasis. The CEC phenotype is regulated by a variety of factors, including cells in its immediate environment and within functional neurovascular units. The cellular composition of the brain parenchyma surrounding the CEC varies between different brain regions; this difference is clearly visible in grey versus white matter. In this review, we discuss evidence for the existence of brain vascular heterogeneity, focusing on differences between the vessels of the grey and white matter. The region-specific differences in the vasculature of the brain are reflective of specific functions of those particular brain areas. This BBB-endothelial heterogeneity may have implications for the course of pathogenesis of cerebrovascular diseases and neurological disorders involving vascular activation and dysfunction. This heterogeneity should be taken into account when developing BBB-neuro-disease models representative of specific brain areas.

Key Words

• Blood–brain barrier
• Cerebral vasculature
• Grey matter
• In vitro models
• Neurodegeneration
• Neurovascular unit
• White matter

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Affiliation(s)

Midrelle E Noumbissi Malaria Research Institute, Dept. Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, SPH East 4135, Baltimore, MD, 21205, USA
Bianca Galasso Malaria Research Institute, Dept. Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, SPH East 4135, Baltimore, MD, 21205, USA
Monique F Stins Malaria Research Institute, Dept. Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe Street, SPH East 4135, Baltimore, MD, 21205, USA.

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43

Jiang W, Guo M, Gong M, Chen L, Bi Y, Zhang Y, Shi Y, Qu P, Liu Y, Chen J, Li T. Vitamin A bio-modulates apoptosis via the mitochondrial pathway after hypoxic-ischemic brain damage. Mol Brain 2018. [PMID: 29534734 PMCID: PMC5851324 DOI: 10.1186/s13041-018-0360-0]

Our previous studies demonstrated that vitamin A deficiency (VAD) can impair the postnatal cognitive function of rats by damaging the hippocampus. The present study examined the effects of retinoic acid (RA) on apoptosis induced by hypoxic-ischemic damage in vivo and in vitro, and investigated the possible signaling pathway involved in the neuroprotective anti-apoptotic effects of RA. Flow cytometry, immunofluorescence staining and behavioral tests were used to evaluate the neuroprotective and anti-apoptotic effects of RA. The protein and mRNA levels of RARα, PI3K, Akt, Bad, caspase-3, caspase-8, Bcl-2, Bax, and Bid were measured with western blotting and real-time PCR, respectively. We found impairments in learning and spatial memory in VAD group compared with vitamin A normal (VAN) and vitamin A supplemented (VAS) group. Additionally, we showed that hippocampal apoptosis was weaker in the VAN group than that in VAD group. Relative to the VAD group, the VAN group also had increased mRNA and protein levels of RARα and PI3K, and upregulated phosphorylated Akt/Bad levels in vivo. In vitro, excessively low or high RA signaling promoted apoptosis. Furthermore, the effects on apoptosis involved the mitochondrial membrane potential (MMP). These data support the idea that sustained VAD following hypoxic-ischemic brain damage (HIBD) inhibits RARα, which downregulates the PI3K/Akt/Bad and Bcl-2/Bax pathways and upregulates the caspase-8/Bid pathway to influence the MMP, ultimately producing deficits in learning and spatial memory in adolescence. This suggests that clinical interventions for HIBD should include suitable doses of VA.

Key Words

• Apoptosis
• Hypoxic-ischemic brain damage (HIBD)
• Mitochondrial membrane potential (MMP)
• PI3K/Akt
• Retinoic acid (RA)
• Vitamin A (VA)

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Affiliation(s)

Wei Jiang Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China.,Children Rehabilitation Center, Children's Hospital of Chongqing Medical University, Chongqing, China
Min Guo Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China.,Children Rehabilitation Center, Children's Hospital of Chongqing Medical University, Chongqing, China
Min Gong Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Li Chen Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Yang Bi Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Yun Zhang Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Yuan Shi Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Ping Qu Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Youxue Liu Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China.,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China.,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China.,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China
Jie Chen Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China. .,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China. .,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China. .,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China.
Tingyu Li Children Nutrition Research Center, Children's Hospital of Chongqing Medical University, Chongqing, 400014, China. .,Ministry of Education Key Laboratory of Child Development and Disorders, Chongqing, 400014, China. .,China International Science and Technology Cooperation Base of Child Development and Critical Disorders, Chongqing, 400014, China. .,Chongqing Key Laboratory of Translational Medical Research in Cognitive Development and Learning and Memory Disorders, Chongqing, 400014, China.

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44

Stem Cells as a Promising Tool for the Restoration of Brain Neurovascular Unit and Angiogenic Orientation. Mol Neurobiol 2016;54:7689-7705. [DOI: 10.1007/s12035-016-0286-4]

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45

Kelly KK, MacPherson AM, Grewal H, Strnad F, Jones JW, Yu J, Pierzchalski K, Kane MA, Herson PS, Siegenthaler JA. Col1a1+ perivascular cells in the brain are a source of retinoic acid following stroke. BMC Neurosci 2016;17:49. [PMID: 27422020 PMCID: PMC4947279 DOI: 10.1186/s12868-016-0284-5]

Background

Perivascular stromal cells (PSCs) are a recently identified cell type that comprises a small percentage of the platelet derived growth factor receptor-β+ cells within the CNS perivascular space. PSCs are activated following injury to the brain or spinal cord, expand in number and contribute to fibrotic scar formation within the injury site. Beyond fibrosis, their high density in the lesion core makes them a potential significant source of signals that act on neural cells adjacent to the lesion site.

Results

Our developmental analysis of PSCs, defined by expression of Collagen1a1 in the maturing brain, revealed that PSCs first appear postnatally and may originate from the meninges. PSCs express many of the same markers as meningeal fibroblasts, including expression of the retinoic acid (RA) synthesis proteins Raldh1 and Raldh2. Using a focal brain ischemia injury model to induce PSC activation and expansion, we show a substantial increase in Raldh1+/Raldh2+ PSCs and Raldh1+ activated macrophages in the lesion core. We find that RA levels are significantly elevated in the ischemic hemisphere and induce signaling in astrocytes and neurons in the peri-infarct region.

Conclusions

This study highlights a dual role for activated, non-neural cells where PSCs deposit fibrotic ECM proteins and, along with macrophages, act as a potentially important source of RA, a potent signaling molecule that could influence recovery events in a neuroprotective fashion following brain injury.

Key Words

• Brain fibrosis
• Meninges
• Pericyte
• Perivascular stromal cell
• Retinoic acid
• Stroke

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Affiliation(s)

Kathleen K Kelly Department of Pediatrics, Section of Developmental Biology, University of Colorado Denver-Anschutz Medical Campus, 12800 E. 19th Ave MS-8313, Aurora, CO, 80045, USA
Amber M MacPherson Department of Pediatrics, Section of Developmental Biology, University of Colorado Denver-Anschutz Medical Campus, 12800 E. 19th Ave MS-8313, Aurora, CO, 80045, USA
Himmat Grewal Department of Anesthesiology, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO, 80045, USA
Frank Strnad Department of Anesthesiology, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO, 80045, USA
Jace W Jones Department of Pharmaceutical Sciences, University of Maryland, Baltimore School of Pharmacy, Baltimore, MD, 21201, USA
Jianshi Yu Department of Pharmaceutical Sciences, University of Maryland, Baltimore School of Pharmacy, Baltimore, MD, 21201, USA
Keely Pierzchalski Department of Pharmaceutical Sciences, University of Maryland, Baltimore School of Pharmacy, Baltimore, MD, 21201, USA
Maureen A Kane Department of Pharmaceutical Sciences, University of Maryland, Baltimore School of Pharmacy, Baltimore, MD, 21201, USA
Paco S Herson Department of Anesthesiology, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO, 80045, USA.,Department of Pharmacology, University of Colorado Denver-Anschutz Medical Campus, Aurora, CO, 80045, USA.,Neuronal Injury Program, University of Colorado Denver-Anschutz Medical Campus, Aurora, USA
Julie A Siegenthaler Department of Pediatrics, Section of Developmental Biology, University of Colorado Denver-Anschutz Medical Campus, 12800 E. 19th Ave MS-8313, Aurora, CO, 80045, USA.

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46

Mfsd2a-based pharmacological strategies for drug delivery across the blood–brain barrier. Pharmacol Res 2016;104:124-31. [DOI: 10.1016/j.phrs.2015.12.024]

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Decreased Serum Retinoic Acid May Predict Poor Outcome in Ischemic Stroke Patients

BACKGROUND AND AIMS

Decreased serum retinoic acid (RA) levels have been shown to be linked with increased mortality in cardiovascular diseases. This study aimed to investigate the relationship between serum RA and 3-month functional outcome after ischemic stroke.

METHODS

Between January 2019 and September 2019, we prospectively recruited ischemic stroke patients within 24 hrs of symptom onset. Serum RA levels were measured for all patients at admission. The primary outcome was defined as poor functional outcome (modified Rankin Scale 3-6) at 90 days. The secondary outcome was defined as early neurological deterioration (END), which is considered as an increase of ≥1 point in motor power or total National Institutes of Health Stroke Scale score of ≥2 points within 7 days.

RESULTS

A total of 217 patients were included in the analysis. The median RA levels were 2.9 ng/mL. Ninety-four (43.3%) and 65 (30.0%) patients experienced 3-month poor outcome and END, respectively. After adjusted for potential confounders, decreased levels of serum RA were associated with a higher risk of poor outcome (P for trend = 0.001) and END (P for trend = 0.002). Adding RA quartile to the existing risk factors improved risk prediction for poor outcome [net reclassification improvement (NRI) = 42.6%, P = 0.001; integrated discrimination improvement (IDI) = 5.7%, P = 0.001] and END (NRI index = 45.4%, P = 0.001; IDI = 4.3%; P = 0.005).

CONCLUSION

Low serum RA levels at baseline were associated with poor prognosis at 90 days after ischemic stroke, suggesting that RA may be a potential prognostic biomarker for ischemic stroke.

Association between serum retinoic acid levels and risk of post-stroke depression in patients with ischemic stroke

Previous studies suggest that retinoic acid (RA) can exert neuroprotective function in ischemic stroke. However, its role in post-stroke depression (PSD) has still been unclear. We sought to investigate the relationship between circulating RA levels and PSD in patients with ischemic stroke. From September 2018 to March 2019, we prospectively screened patients with ischemic stroke who were hospitalized within 7 days of symptoms onset. RA levels were measured after admission. All patients were followed up at 3 months after stroke. Diagnosis of PSD was made in line with the Chinese version of Structured Clinical Interview of the Diagnostic and Statistical Manual of Mental Disorders, 4th edition criteria. PSD risk was estimated using multivariable regression models. In total, 352 ischemic stroke patients were enrolled for the final analysis. Up to 3 months after symptoms onset, 102 subjects experienced PSD. PSD patients showed significantly lower RA levels at baseline as compared to non-PSD patients. In univariate logistic analysis, reduced levels of RA was a significant predictor of PSD. These results were further confirmed in multivariate regression additionally controlled for possible relevant confounders. Our study shows that decreased serum RA levels at admission might be associated with 3-month PSD in ischemic stroke patients.

Astrocyte-Derived Paracrine Signals: Relevance for Neurogenic Niche Regulation and Blood-Brain Barrier Integrity

Astrocytes are essential for proper regulation of the central nervous system (CNS). Importantly, these cells are highly secretory in nature. Indeed they can release hundreds of molecules which play pivotal physiological roles in nervous tissues and whose abnormal regulation has been associated with several CNS disorders. In agreement with these findings, recent studies have provided exciting insights into the key contribution of astrocyte-derived signals in the pleiotropic functions of these cells in brain health and diseases. In the future, deeper analysis of the astrocyte secretome is likely to further increase our current knowledge on the full potential of these cells and their secreted molecules not only as active participants in pathophysiological events, but as pharmacological targets or even as therapeutics for neurological and psychiatric diseases. Herein we will highlight recent findings in our and other laboratories on selected molecules that are actively secreted by astrocytes and contribute in two distinct functions with pathophysiological relevance for the astroglial population: i) regulation of neural stem cells (NSCs) and their progeny within adult neurogenic niches; ii) modulation of the blood–brain barrier (BBB) integrity and function.

All trans-retinoic acid protects against acute ischemic stroke by modulating neutrophil functions through STAT1 signaling

Background and purpose

Regulation of neural inflammation is considered as a vital therapeutic target in ischemic stroke. All-trans retinoic acid (atRA), a potent immune modulator, has raised interest in the field of stroke therapy. However, the immunological mechanisms for atRA-mediated neuroprotection remain elusive. The current study evaluated the impact of atRA on post-stroke neural inflammation and elucidated the mechanisms involved in the regulation of related neutrophil functions.

Methods

atRA was prophylactically administered to mice 1 day before transient middle cerebral artery occlusion (tMCAO, 1 h) and repeated daily immediately after reperfusion for 3 days. Stroke outcomes, neutrophil polarization, and formation of neutrophil extracellular traps (NETs) in the stroke lesion were assessed. Neutrophil depletion was induced with anti-Ly6G antibodies. Primary neutrophil cultures were used to explore the mechanisms of atRA treatment.

Results

Prophylactic atRA treatment reduced infarct volumes and neurological deficits at 1 day after tMCAO. Post-stroke neural inflammation was attenuated and neutrophil accumulation in lesion was downregulated. atRA treatment skewed neutrophil toward N2 phenotype which facilitated its clearance by macrophage and inhibited NETs formation. The functions of neutrophil were indispensable in the protective effects of atRA and were associated with suppression to STAT1 signaling by atRA. Administration of atRA after stroke still provided efficient protection to cerebral ischemia.

Conclusion

atRA displays potent therapeutic efficacy in ischemic stroke by attenuating neural inflammation. Treatment of atRA impeded neutrophil accumulation, favored N2 polarization, and forbade NETs formation in ischemic lesion. STAT1 signaling played a decisive role in the mechanisms of atRA-afforded regulation to neutrophil.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1557-6) contains supplementary material, which is available to authorized users.

Retinoic acid signaling in vascular development

Formation of the vasculature is an essential developmental process, delivering oxygen and nutrients to support cellular processes needed for tissue growth and maturation. Retinoic acid (RA) and its downstream signaling pathway is vital for normal pre- and post-natal development, playing key roles in the specification and formation of many organs and tissues. Here, we review the role of RA in blood and lymph vascular development, beginning with embryonic yolk sac vasculogenesis and remodeling and discussing RA's organ-specific roles in angiogenesis and vessel maturation. In particular, we highlight the multi-faceted role of RA signaling in CNS vascular development and acquisition of blood-brain barrier properties.

Lower serum retinoic acid level for prediction of higher risk of mortality in ischemic stroke

OBJECTIVE

To explore the association between serum retinoic acid (RA) level in patients with acute ischemic stroke (AIS) and mortality risk in the 6 months after admission.

METHODS

From January 2015 through December 2016, patients admitted to 3 stroke centers in China for first-ever AIS were screened. The primary endpoint was all-cause mortality or cardiovascular disease (CVD) mortality in the 6 months after admission. The significance of serum RA level, NIH Stroke Scale score, and established risk factors in predicting mortality were determined. The integrated discrimination improvement (IDI) and net reclassification improvement (NRI) statistics were applied in statistical analysis.

RESULTS

Of the 1,530 patients enrolled, 325 died within 6 months of admission, with an all-cause mortality of 21.2% and CVD-related mortality of 13.1%. In multivariable analysis, RA levels were expressed as quartiles with the clinical variables. The results of the second to fourth quartiles (Q2-Q4) were compared with the first quartile (Q1); RA levels showed prognostic significance, with decreased all-cause and CVD mortality of 55% and 63%, respectively. After RA was added to the existing risk factors, all-cause mortality could be better reclassified, in association with only the NRI statistic (p = 0.005); CVD mortality could be better reclassified with significance, in association with both the IDI and NRI statistics (p < 0.01).

CONCLUSIONS

Low circulating levels of RA were associated with increased risk of all-cause and CVD mortality in a cohort of patients with first-incidence AIS, indicating that RA level could be a predictor independent of established conventional risk factors.

Dual Roles of Astrocyte-Derived Factors in Regulation of Blood-Brain Barrier Function after Brain Damage

The blood-brain barrier (BBB) is a major functional barrier in the central nervous system (CNS), and inhibits the extravasation of intravascular contents and transports various essential nutrients between the blood and the brain. After brain damage by traumatic brain injury, cerebral ischemia and several other CNS disorders, the functions of the BBB are disrupted, resulting in severe secondary damage including brain edema and inflammatory injury. Therefore, BBB protection and recovery are considered novel therapeutic strategies for reducing brain damage. Emerging evidence suggests key roles of astrocyte-derived factors in BBB disruption and recovery after brain damage. The astrocyte-derived vascular permeability factors include vascular endothelial growth factors, matrix metalloproteinases, nitric oxide, glutamate and endothelin-1, which enhance BBB permeability leading to BBB disruption. By contrast, the astrocyte-derived protective factors include angiopoietin-1, sonic hedgehog, glial-derived neurotrophic factor, retinoic acid and insulin-like growth factor-1 and apolipoprotein E which attenuate BBB permeability resulting in recovery of BBB function. In this review, the roles of these astrocyte-derived factors in BBB function are summarized, and their significance as therapeutic targets for BBB protection and recovery after brain damage are discussed.

Hemopexin reduces blood-brain barrier injury and protects synaptic plasticity in cerebral ischemic rats by promoting EPCs through the HO-1 pathway

Ischemic stroke causes endothelial dysfunction and blood-brain barrier dysfunction, thus damages synaptic plasticity such as learning and memory. In this study we aim to investigate the effect of hemopexin (HPX) in protecting synaptic plasticity and blood brain barrier integrity from toxic heme, and determine whether this effect is via the activation of endothelial progenitor cells (EPCs) through the heme oxygenase-1 (HO-1) pathway. Our data indicates HPX showed a significant effect in inducing the expression of HO-1, promoting the migration and differentiation of EPCs, facilitating new blood vessel formation thus protecting blood-brain barrier integrity. Also the magnitude of synaptic plasticity of rats recovered with HPX treatment. And in the presence of HO-1 blocker Zinc protoporphyrin-9 (ZnppIX), HPX lost its protective effect. This suggests that HPX protects endothelial and blood brain barrier integrity from toxic heme, thus protects neurologic function in cerebral ischemic rats in HO-1 pathway.

All-Trans Retinoic Acid Ameliorates the Early Experimental Cerebral Ischemia-Reperfusion Injury in Rats by Inhibiting the Loss of the Blood-Brain Barrier via the JNK/P38MAPK Signaling Pathway

All-trans retinoic acid (ATRA) influences the outcomes of cerebral ischemic reperfusion (CIR) injury, but the mechanism remains unclear. The present study aimed to investigate the effects of ATRA on loss of the blood brain barrier (BBB) following CIR and to explore the possible mechanisms. Transient middle cerebral artery occlusion was performed on male SD rats to construct an in vivo CIR model. Neurological deficits, BBB permeability, brain edema, MRI and JNK/P38 MAPK proteins were detected at 24 h following CIR. We demonstrated that ATRA pretreatment could alleviate CIR-induced neurological deficits, increase of BBB permeability, infarct volume, degradation of tight junction proteins, inhibit MMP-9 protein expression and activity. ATRA treatment also reduced the p-P38 and p-JNK protein level. However the protective effect of ATRA on CIR could be reversed by administration of retinoic acid alpha receptor antagonist Ro41-5253. SP600125 and SB203580, which is the JNK/P38 pathway inhibitors has the same protective effect as ATRA. These results indicated that ATRA may inhibit the JNK/P38 MAPK pathway to alleviate BBB disruption and improve CIR outcomes.

Brain vascular heterogeneity: implications for disease pathogenesis and design of in vitro blood-brain barrier models

The vertebrate blood–brain barrier (BBB) is composed of cerebral microvascular endothelial cells (CEC). The BBB acts as a semi-permeable cellular interface that tightly regulates bidirectional molecular transport between blood and the brain parenchyma in order to maintain cerebral homeostasis. The CEC phenotype is regulated by a variety of factors, including cells in its immediate environment and within functional neurovascular units. The cellular composition of the brain parenchyma surrounding the CEC varies between different brain regions; this difference is clearly visible in grey versus white matter. In this review, we discuss evidence for the existence of brain vascular heterogeneity, focusing on differences between the vessels of the grey and white matter. The region-specific differences in the vasculature of the brain are reflective of specific functions of those particular brain areas. This BBB-endothelial heterogeneity may have implications for the course of pathogenesis of cerebrovascular diseases and neurological disorders involving vascular activation and dysfunction. This heterogeneity should be taken into account when developing BBB-neuro-disease models representative of specific brain areas.

Vitamin A bio-modulates apoptosis via the mitochondrial pathway after hypoxic-ischemic brain damage

Our previous studies demonstrated that vitamin A deficiency (VAD) can impair the postnatal cognitive function of rats by damaging the hippocampus. The present study examined the effects of retinoic acid (RA) on apoptosis induced by hypoxic-ischemic damage in vivo and in vitro, and investigated the possible signaling pathway involved in the neuroprotective anti-apoptotic effects of RA. Flow cytometry, immunofluorescence staining and behavioral tests were used to evaluate the neuroprotective and anti-apoptotic effects of RA. The protein and mRNA levels of RARα, PI3K, Akt, Bad, caspase-3, caspase-8, Bcl-2, Bax, and Bid were measured with western blotting and real-time PCR, respectively. We found impairments in learning and spatial memory in VAD group compared with vitamin A normal (VAN) and vitamin A supplemented (VAS) group. Additionally, we showed that hippocampal apoptosis was weaker in the VAN group than that in VAD group. Relative to the VAD group, the VAN group also had increased mRNA and protein levels of RARα and PI3K, and upregulated phosphorylated Akt/Bad levels in vivo. In vitro, excessively low or high RA signaling promoted apoptosis. Furthermore, the effects on apoptosis involved the mitochondrial membrane potential (MMP). These data support the idea that sustained VAD following hypoxic-ischemic brain damage (HIBD) inhibits RARα, which downregulates the PI3K/Akt/Bad and Bcl-2/Bax pathways and upregulates the caspase-8/Bid pathway to influence the MMP, ultimately producing deficits in learning and spatial memory in adolescence. This suggests that clinical interventions for HIBD should include suitable doses of VA.

Col1a1+ perivascular cells in the brain are a source of retinoic acid following stroke

Background

Perivascular stromal cells (PSCs) are a recently identified cell type that comprises a small percentage of the platelet derived growth factor receptor-β+ cells within the CNS perivascular space. PSCs are activated following injury to the brain or spinal cord, expand in number and contribute to fibrotic scar formation within the injury site. Beyond fibrosis, their high density in the lesion core makes them a potential significant source of signals that act on neural cells adjacent to the lesion site.

Results

Our developmental analysis of PSCs, defined by expression of Collagen1a1 in the maturing brain, revealed that PSCs first appear postnatally and may originate from the meninges. PSCs express many of the same markers as meningeal fibroblasts, including expression of the retinoic acid (RA) synthesis proteins Raldh1 and Raldh2. Using a focal brain ischemia injury model to induce PSC activation and expansion, we show a substantial increase in Raldh1+/Raldh2+ PSCs and Raldh1+ activated macrophages in the lesion core. We find that RA levels are significantly elevated in the ischemic hemisphere and induce signaling in astrocytes and neurons in the peri-infarct region.

Conclusions

This study highlights a dual role for activated, non-neural cells where PSCs deposit fibrotic ECM proteins and, along with macrophages, act as a potentially important source of RA, a potent signaling molecule that could influence recovery events in a neuroprotective fashion following brain injury.