Neural regeneration by regionally induced stem cells within post-stroke brains: Novel therapy perspectives for stroke patients

The role of small extracellular vesicles and microRNA as their cargo in the spinal cord injury pathophysiology and therapy

Spinal cord injury (SCI) is a devastating condition with a complex pathology that affects a significant portion of the population and causes long-term consequences. After primary injury, an inflammatory cascade of secondary injury occurs, followed by neuronal cell death and glial scar formation. Together with the limited regenerative capacity of the central nervous system, these are the main reasons for the poor prognosis after SCI. Despite recent advances, there is still no effective treatment. Promising therapeutic approaches include stem cells transplantation, which has demonstrated neuroprotective and immunomodulatory effects in SCI. This positive effect is thought to be mediated by small extracellular vesicles (sEVs); membrane-bound nanovesicles involved in intercellular communication through transport of functional proteins and RNA molecules. In this review, we summarize the current knowledge about sEVs and microRNA as their cargo as one of the most promising therapeutic approaches for the treatment of SCI. We provide a comprehensive overview of their role in SCI pathophysiology, neuroprotective potential and therapeutic effect.

The Role of Circular RNAs in Ischemic Stroke

Ischemic stroke (IS), a devastating condition characterized by intracranial artery stenosis and middle cerebral artery occlusion leading to insufficient oxygen supply to the brain, is a major cause of death and physical disability worldwide. Recent research has demonstrated the critical role of circular RNAs (circRNAs), a class of covalently enclosed noncoding RNAs that are widespread in eukaryotic cells, in regulating various physiological and pathophysiological cellular processes, including cell apoptosis, autophagy, synaptic plasticity, and neuroinflammation. In the past few years, circRNAs have attracted extensive attention in the field of IS research. This review summarizes the current understanding of the mechanisms underlying the involvement of circRNAs in IS development. A better understanding of circRNA-mediated pathogenic mechanisms in IS may pave the way for translating circRNA research into clinical practice, ultimately improving the clinical outcomes of IS patients.

Importance of Pericytes in the Pathophysiology of Cerebral Ischemia

Various cell types contribute to pathological changes observed in the brain following cerebral ischemia. Pericytes, as a component of neurovascular unit (NVU) and blood brain barrier (BBB), play a key role for cerebral blood flow control and regulation of vessel permeability. It was shown that pericytes can control cerebral blood flow at the level of capillaries, by their contractile property. Their role in BBB development and maintenance are crucial for guidance of brain vessel development, new vessel formation and stabilization of the newly formed vessels. Additionally, they can contribute to inflammation in response to inflammatory stimuli and can differentiate to various cell types by their multipotent differentiation properties. This cell type which is intimately associated with cerebral circulation also plays important roles during cerebral ischemia. Here, we review the properties and physiological functions of pericytes, how these functions change during ischemia to affect the pathophysiology of ischemic stroke and post stroke cognitive impairment. Pericytes are a neglected cell type and they are not unambiguously characterized which in turn led to contradictory findings in the literature. Clear characterization of pericytes by current methods will help better understanding of their role in the pathophysiology of stroke. With the information gained from these efforts it will be possible to develop pericyte specific therapeutic targets and achieve important breakthroughs in clinical recovery in ischemic stroke treatment.

Optimal therapeutic conditions for the neural stem cell-based management of ischemic stroke: a systematic review and network meta-analysis based on animal studies

BACKGROUND

In order to promote the clinical translation of preclinical findings, it is imperative to identify the most optimal therapeutic conditions and adopt them for further animal and human studies. This study aimed to fully explore the optimal conditions for neural stem cell (NSC)-based ischemic stroke treatment based on animal studies.

METHODS

The PubMed, Ovid-Embase, and Web of Science databases were searched in December 2021. The screening of search results, extraction of relevant data, and evaluation of study quality were performed independently by two reviewers.

RESULTS

In total, 52 studies were included for data analysis. Traditional meta-analysis showed that NSCs significantly reduced the modified neurological severity score (mNSS) and volume of cerebral infarct in animal models of ischemic stroke. Network meta-analysis showed that allogeneic embryonic tissue was the best source of NSCs. Further, intracerebral transplantation was the most optimal route of NSC transplantation, and the acute phase was the most suitable stage for intervention. The optimal number of NSCs for transplantation was 1-5×10⁵ in mouse models and 1×10⁶ or 1.8×10⁶ in rat models.

CONCLUSIONS

We systematically explored the therapeutic strategy of NSCs in ischemic stroke, but additional research is required to develop optimal therapeutic strategies based on NSCs. Moreover, it is necessary to further improve and standardize the design, implementation, measuring standards, and reporting of animal-based studies to promote the development of better animal experiments and clinical research.

Natural recovery and regeneration of the central nervous system

The diagnosis and management of CNS injuries comprises a large portion of psychiatric practice. Many clinical and preclinical studies have demonstrated the benefit of treating CNS injuries using various regenerative techniques and materials such as stem cells, biomaterials and genetic modification. Therefore it is the goal of this review article to briefly summarize the pathogenesis of CNS injuries, including traumatic brain injuries, spinal cord injuries and cerebrovascular accidents. Next, we discuss the role of natural recovery and regeneration of the CNS, explore the relevance in clinical practice and discuss emerging and cutting-edge treatments and current barriers in the field of regenerative medicine.

Histone Methyltransferase Dot1L Contributes to RIPK1 Kinase-Dependent Apoptosis in Cerebral Ischemia/Reperfusion

Background

Neuron apoptosis is a pivotal process for brain damage in cerebral ischemia. Dot1L (disruptor of telomeric silencing 1‐like) is only known histone H3K79 methyltransferase. It is not clear whether the role and mechanism of Dot1L on cerebral ischemia is related to regulate neuron apoptosis.

Methods and Results

We use a combination of mice middle cerebral artery occlusion stroke and neurons exposed to oxygen‐glucose deprivation followed by reoxygenation to investigate the role and mechanism of Dot1L on cerebral ischemia. We find knockdown or inhibition of Dot1L reversed ischemia‐induced neuronal apoptosis and attenuated the neurons injury treated by oxygen‐glucose deprivation followed by reoxygenation. Further, blockade of Dot1L prevents RIPK1 (receptor‐interacting protein kinase 1)‐dependent apoptosis through increased RIPK1 K63‐ubiquitylation and decreased formation of RIPK1/Caspase 8 complexes. In line with this, H3K79me3 enrichment in the promoter region of deubiquitin‐modifying enzyme A20 and deubiquitinase cylindromatosis gene promotes the increasing expression in oxygen‐glucose deprivation followed by reoxygenation ‐induced neuronal cells, on the contrary, oxygen‐glucose deprivation followed by reoxygenation decreases H3K79me3 level in the promoter region of ubiquitin‐modifying enzyme cIAP1 (cellular inhibitors of apoptosis proteins), and both these factors ultimately cause K63‐deubiquitination of RIPK1. Importantly, knockdown or inhibition of Dot1L in vivo attenuates apoptosis in middle cerebral artery occlusion mice and reduces the extent of middle cerebral artery occlusion ‐induced brain injury.

Conclusions

These data support for the first time, to our knowledge, that Dot1L regulating RIPK1 to the apoptotic death trigger contributes to cerebral ischemia injury. Therefore, targeting Dot1L serves as a new therapeutic strategy for ischemia stroke.

Intracarotid Transplantation of Skin-Derived Precursor Schwann Cells Promotes Functional Recovery After Acute Ischemic Stroke in Rats

Purpose: Skin-derived Precursor Schwann cells (SKP-SCs) have been reported to provide neuroprotection for the injured and dysmyelinated nervous system. However, little is known about SKP-SCs on acute ischemic stroke (AIS). We aimed to explore the efficacy and the potential mechanism of action of SKP-SCs on AIS in a rat ischemic stroke model.

Methods: Adult male Sprague–Dawley rats were subjected to a middle cerebral artery occlusion (MCAO) for 1.5 h on Day 0 and subsequently received an intracarotid injection of 2 × 10⁶ green fluorescent protein (GFP) -labeled SKP-SCs or phosphate buffered saline (PBS) during reperfusion. Neurological function was assessed by behavioral tests on Days 1, 4, 7, 14, and 28. In a satellite cohort, rat brains were harvested and infarct volume was measured with 2,3,5-triphenyltetrazolium chloride (TTC) staining on Days 1 and 7, and migration and survival of SKP-SCs in the brain were traced by monitoring green fluorescence at 6 and12 h on Day 0, and on Days 1, 4, 7, 14, and 28. Histopathology and immunofluorescence staining were used to analyze the morphology, survival and apoptosis of neurons. Additionally, in an in vitro SKP-SC co-culture model using fetal rat primary cortical neurons underwent oxygen glucose deprivation/reoxygenation (OGD/R), Western blot was used to detect the expression of apoptosis indicators including activated caspase-3, Bax, and Bcl-2. TUNEL staining was used to count apoptotic cells.

Results: Intracarotid transplantation of SKP-SCs effectively migrated to the periinfarct area and survived for at least 4 weeks. Transplanted SKP-SCs inhibited neuronal apoptosis, reduced infarct volume, and improved neurological recovery in the MCAO rats. Moreover, in vitro data showed that SKP-SCs treatment inhibited OGD/R-induced neuronal apoptosis and promoted survival of the cultured primary cortical neurons.

Conclusions: Intracarotid transplantation of SKP-SCs promoted functional recovery in the rat AIS model and possesses the potential to be further developed as a novel therapy to treat ischemic stroke in humans.

Transcriptome Response and Spatial Pattern of Gene Expression in the Primate Subventricular Zone Neurogenic Niche After Cerebral Ischemia

The main stem cell niche for neurogenesis in the adult mammalian brain is the subventricular zone (SVZ) that extends along the cerebral lateral ventricles. We aimed at characterizing the initial molecular responses of the macaque monkey SVZ to transient, global cerebral ischemia. We microdissected tissue lining the anterior horn of the lateral ventricle (SVZa) from 7 day post-ischemic and sham-operated monkeys. Transcriptomics shows that in ischemic SVZa, 541 genes were upregulated and 488 genes were down-regulated. The transcription data encompassing the upregulated genes revealed a profile typical for quiescent stem cells and astrocytes. In the primate brain the SVZ is morphologically subdivided in distinct and separate ependymal and subependymal regions. The subependymal contains predominantly neural stem cells (NSC) and differentiated progenitors. To determine in which SVZa region ischemia had evoked transcriptional upregulation, sections through control and ischemic SVZa were analyzed by high-throughput in situ hybridization for a total of 150 upregulated genes shown in the www.monkey-niche.org image database. The majority of the differentially expressed genes mapped to the subependymal layers on the striatal or callosal aspect of the SVZa. Moreover, a substantial number of upregulated genes was expressed in the ependymal layer, implicating a contribution of the ependyma to stem cell biology. The transcriptome analysis yielded several novel gene markers for primate SVZa including the apelin receptor that is strongly expressed in the primate SVZa niche upon ischemic insult.

How Long Are Reperfusion Therapies Beneficial for Patients after Stroke Onset? Lessons from Lethal Ischemia Following Early Reperfusion in a Mouse Model of Stroke

Ischemic stroke caused by cerebral artery occlusion induces neurological deficits because of cell damage or death in the central nervous system. Given the recent therapeutic advances in reperfusion therapies, some patients can now recover from an ischemic stroke with no sequelae. Currently, reperfusion therapies focus on rescuing neural lineage cells that survive in spite of decreases in cerebral blood flow. However, vascular lineage cells are known to be more resistant to ischemia/hypoxia than neural lineage cells. This indicates that ischemic areas of the brain experience neural cell death but without vascular cell death. Emerging evidence suggests that if a vascular cell-mediated healing system is present within ischemic areas following reperfusion, the therapeutic time window can be extended for patients with stroke. In this review, we present our comments on this subject based upon recent findings from lethal ischemia following reperfusion in a mouse model of stroke.

Electro-Acupuncture Promotes the Differentiation of Endogenous Neural Stem Cells via Exosomal microRNA 146b After Ischemic Stroke

Background: Evidences indicate that exosomes-mediated delivery of microRNAs (miRNAs or miRs) is involved in the neurogenesis of stroke. This study was to investigate the role of exosomal miRNAs in non-drug therapy of electro-acupuncture (EA) regulating endogenous neural stem cells for stroke recovery.

Methods: The model of focal cerebral ischemia and reperfusion in rats were established by middle cerebral artery occlusion (MCAO) and treated by EA. The exosomes were extracted from peri-ischemic striatum and identified by exosomal biomarkers, and detected differentially expressed miRNAs with microarray chip. Primary stem cells were cultured, and oxygen–glucose deprivation and reperfusion (OGD/R) was used to mimic vitro ischemic injury.

Results: The levels of exosomal biomarkers TSG101 and CD81 were increased in peri-ischemic striatum after EA treatment, and we revealed 25 differentially expressed miRNAs in isolated exosomes, of which miR-146b was selected for further analysis, and demonstrated that EA increased miR-146b expression and its inhibitors could block the effects. Subsequently, we confirmed that EA upregulated miR-146b expression to promote neural stem cells differentiation into neurons in peri-ischemic striatum. In vitro, it was verified that OGD/R hindered neural stem cells differentiation, and miR-146b inhibitors furtherly suppressed its differentiation, simultaneously NeuroD1 was involved in neural stem cells differentiation into neurons. Moreover, in vivo we found EA promoted NeuroD1-mediated neural stem cells differentiation via miR-146b. In addition, EA also could improve neurological deficits through miR-146b after ischemic stroke.

Conclusion: EA promotes the differentiation of endogenous neural stem cells via exosomal miR-146b to improve neurological injury after ischemic stroke.

Adult mesenchymal stem cells: is there a role for purine receptors in their osteogenic differentiation?

The role played by mesenchymal stem cells (MSCs) in contributing to adult tissue homeostasis and damage repair thanks to their differentiation capabilities has raised a great interest, mainly in bone regenerative medicine. The growth/function of these undifferentiated cells of mesodermal origin, located in specialized structures (niches) of differentiated organs is influenced by substances present in this microenvironment. Among them, ancestral and ubiquitous molecules such as adenine-based purines, i.e., ATP and adenosine, may be included. Notably, extracellular purine concentrations greatly increase during tissue injury; thus, MSCs are exposed to effects mediated by these agents interacting with their own receptors when they act/migrate in vivo or are transplanted into a damaged tissue. Here, we reported that ATP modulates MSC osteogenic differentiation via different P2Y and P2X receptors, but data are often inconclusive/contradictory so that the ATP receptor importance for MSC physiology/differentiation into osteoblasts is yet undetermined. An exception is represented by P2X7 receptors, whose expression was shown at various differentiation stages of bone cells resulting essential for differentiation/survival of both osteoclasts and osteoblasts. As well, adenosine, usually derived from extracellular ATP metabolism, can promote osteogenesis, likely via A2B receptors, even though findings from human MSCs should be implemented and confirmed in preclinical models. Therefore, although many data have revealed possible effects caused by extracellular purines in bone healing/remodeling, further studies, hopefully performed in in vivo models, are necessary to identify defined roles for these compounds in favoring/increasing the pro-osteogenic properties of MSCs and thereby their usefulness in bone regenerative medicine.

Therapeutic mechanism of human neural stem cell-derived extracellular vesicles against hypoxia-reperfusion injury in vitro

AIMS

This study aimed to explore that the human neural stem cell derived extracellular vesicles (hNSC-EVs) have therapeutic effect on neuronal hypoxia-reperfusion (H/R) injured neurons in vitro by mediating the nuclear translocation of NF-E2-related factor 2 (Nrf2) to regulate the expression of downstream oxidative kinases.

MAIN METHODS

The neuroprotective effects of hNSC-EVs were evaluated in an in vitro neuronal H/R model. Three parameters of hNSC-EVs, structure, phenotype and particle size, were characterized. At the cellular level, a human neuron cerebral ischemic reperfusion (CIR) injury model was constructed. Cell viability, apoptosis, and the amount of reactive oxygen species (ROS) were detected using real-time cell analysis (RTCA), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and dichloro-dihydro-fluorescein diacetate (DCFH-DA), respectively. The neuronal axonal elongation was assessed by Opera Phenix™ screening system. The angiogenesis of human umbilical vein endothelial cells (HUVECs) was evaluated by co-culturing HUVECs with hNSC-EVs in Matrigel. The expression of apoptosis and oxidative stress-related proteins in cells and the nuclear transfer of Nrf2 following hypoxia-reperfusion (H/R) was verified by Western-blotting.

KEY FINDINGS

We found that the hNSC-EVs can promote the survival of post-H/R injury neurons, inhibit neuronal apoptosis, and enhance nuclear transfer of Nrf2, in response to oxidative stress. We also found the hNSC-EVs can promote the elongation of neuronal axons and the angiogenesis of HUVECs.

SIGNIFICANCE

At present, there is no effective therapy for CIR injury. We suggest that the hNSC-EVs could be considered a new strategy to achieve nerve repair for the treatment of neurological diseases, especially stroke.