MicroRNA cluster miR-17-92 Cluster in Exosomes Enhance Neuroplasticity and Functional Recovery After Stroke in Rats

Decoding epigenetic cell signaling in neuronal differentiation

Neurogenesis is the process by which new neurons are generated in the brain. Neural stem cells (NSCs) are differentiated into neurons, which are integrated into the neural network. Nowadays, pluripotent stem cells, multipotent stem cells, and induced pluripotent stem cells can be artificially differentiated into neurons utilizing several techniques. Specific transcriptional profiles from NSCs during differentiation are frequently used to approach and observe phenotype alteration and functional determination of neurons. In this context, the role of non-coding RNA, transcription factors and epigenetic changes in neuronal development and differentiation has gained importance. Epigenetic elucidation has become a field of intense research due to distinct patterns of normal conditions and different neurodegenerative disorders, which can be explored to develop new diagnostic methods or gene therapies. In this review, we discuss the complexity of transcription factors, non-coding RNAs, and extracellular vesicles that are responsible for guiding and coordinating neural development.

Mesenchymal stem cell-derived exosomes promote neurogenesis and cognitive function recovery in a mouse model of Alzheimer's disease

Studies have shown that mesenchymal stem cell-derived exosomes can enhance neural plasticity and improve cognitive impairment. The purpose of this study was to investigate the effects of mesenchymal stem cell-derived exosomes on neurogenesis and cognitive capacity in a mouse model of Alzheimer’s disease. Alzheimer’s disease mouse models were established by injection of beta amyloid 1−42 aggregates into dentate gyrus bilaterally. Morris water maze and novel object recognition tests were performed to evaluate mouse cognitive deficits at 14 and 28 days after administration. Afterwards, neurogenesis in the subventricular zone was determined by immunofluorescence using doublecortin and PSA-NCAM antibodies. Results showed that mesenchymal stem cells-derived exosomes stimulated neurogenesis in the subventricular zone and alleviated beta amyloid 1−42-induced cognitive impairment, and these effects are similar to those shown in the mesenchymal stem cells. These findings provide evidence to validate the possibility of developing cell-free therapeutic strategies for Alzheimer’s disease. All procedures and experiments were approved by Institutional Animal Care and Use Committee (CICUAL) (approval No. CICUAL 2016-011) on April 25, 2016.

Potential of Exosomes for the Treatment of Stroke

Stroke is the result of blockage or rupture of blood vessels in the brain and is the leading cause of death and disability in the world. Currently only a very limited number of therapeutic approaches are available for treatment of stroke patients, and the vast majority of neuroprotective agents that tested positively in pre-clinical studies failed in clinical trials. In recent years, the clinical value of the use of exosomes for stroke treatment has received widespread attention due their unique characteristics such as low immunogenicity, low toxicity and biodegradability, ability to cross the blood–brain barrier (BBB), and their important role in communication between cells. More and more evidence suggests that the secretion of exosomes is the mechanism underlying the protection induced by mesenchymal stromal cells (MSCs) after stroke. Exosomes are thought to support brain restoration and induce repairing effects, including neurovascular remodeling, and anti-apoptosis and anti-inflammatory effects. Recent reports have focused on the clinical application of exosomes as a potential drug delivery approach. This review focuses on the ability of exosomes to interrupt the stroke-induced pathologic processes of stroke, and on publications describing how to achieve more effective treatment of stroke with exosomes.

Exosome-mediated amplification of endogenous brain repair mechanisms and brain and systemic organ interaction in modulating neurological outcome after stroke

Ischemic stroke is caused by a regional interruption of cerebral blood flow to the brain. Rigorous pre-clinical and clinical research has made landmark progress in stroke treatment using thrombolytics and endovascular thrombectomy. Although numerous successful neuroprotective therapeutic agents for ischemic stroke have been reported in pre-clinical studies, most of them failed in clinical testing. Persistent pre-clinical research has demonstrated that the ischemic brain is not only passively dying but is also actively recovering. Within the neurovascular niche in the peri-infarct tissue, repair mechanisms thrive on the interactions between the neural and vascular compartments. In this review, we discuss exogenous therapy using mesenchymal stromal cell-derived exosomes to amplify endogenous brain repair mechanisms and to induce neurorestorative effects after stroke. Emerging evidence indicates that multiple communication axes between the various organs such as the brain, heart, kidney and gut, and whole body immune response mediated by the spleen can also affect stroke outcome. Therefore, in this review, we summarize this evidence and initiate a discussion on the potential to improve stroke outcome by amplifying multiple brain repair mechanisms after stroke, and by targeting peripheral organs and downstream events to enhance recovery in the injured brain and promote over all well being.

Mesenchymal Stem Cell Therapy in Stroke: A Systematic Review of Literature in Pre-Clinical and Clinical Research

Exogenous stem cell therapy (SCT) has been recognized recently as a promising neuroregenerative strategy to augment recovery in stroke survivors. Mesenchymal stem cells (MSCs) are the primary source of stem cells used in the majority of both pre-clinical and clinical studies in stroke. In the absence of evidence-based guidelines on the use of SCT in stroke patients, understanding the progress of MSC research across published studies will assist researchers and clinicians in better achieving success in translating research. We conducted a systematic review on published literature using MSCs in both pre-clinical studies and clinical trials between 2008 and 2017 using the public databases PubMed and Ovid Medline, and the clinical trial registry ( www.clinicaltrials.gov ). A total of 78 pre-clinical studies and eight clinical studies were identified. While majority of the pre-clinical and clinical studies demonstrated statistically significant effects, the clinical significance of these findings was still unclear. Effect sizes could not be measured mainly due to reporting issues in pre-clinical studies, thus limiting our ability to compare results across studies quantitatively. The overall quality of both pre-clinical and clinical studies was sub-optimal. By conducting a systematic review of both pre-clinical and clinical studies on MSCs therapy in stroke, we assessed the quality of current evidence and identified several issues and gaps in translating animal studies to human trials. Addressing these issues and incorporating changes into future animal studies and human trials may lead to better success of stem cells-based therapeutics in the near future.

Induced pluripotent stem cell-derived extracellular vesicles: A novel approach for cell-free regenerative medicine

In recent years, induced pluripotent stem cells (iPSCs) have been considered as a promising approach in the field of regenerative medicine. iPSCs can be generated from patients' somatic cells and possess the potential to differentiate, under proper conditions, into any cell type. However, the clinical application of iPS cells is restricted because of their tumorigenic potential. Recent studies have indicated that stem cells exert their therapeutic benefit via a paracrine mechanism, and extracellular vesicles have been demonstrated that play a critical role in this paracrine mechanism. Due to lower immunogenicity, easier management, and presenting no risk of tumor formation, in recent years, researchers turned attention to exosomes as potential alternatives to whole-cell therapy. Application of exosomes derived from iPSCs and their derived precursor provides a promising approach for personalized regenerative medicine. This study reviews the physiological functions of extracellular vesicles and discusses their potential therapeutic benefit in regenerative medicine.

Exosomes Derived From miR-133b-Modified Mesenchymal Stem Cells Promote Recovery After Spinal Cord Injury

Dysregulation of microRNAs (miRNAs) has been found in injured spinal cords after spinal cord injury (SCI). Previous studies have shown that miR-133b plays an important role in the differentiation of neurons and the outgrowth of neurites. Recently, exosomes have been used as novel biological vehicles to transfer miRNAs locally or systemically, but little is known about the effect of the delivery of exosome-mediated miRNAs on the treatment of SCI. In the present study, we observed that mesenchymal stem cells, the most common cell types known to produce exosomes, could package miR-133b into secreted exosomes. After SCI, tail vein injection of miR-133b exosomes into rats significantly improved the recovery of hindlimb function when compared to control groups. Additionally, treatment with miR-133b exosomes reduced the volume of the lesion, preserved neuronal cells, and promoted the regeneration of axons after SCI. We next observed that the expression of RhoA, a direct target of miR-133b, was decreased in the miR-133b exosome group. Moreover, we showed that miR-133b exosomes activated ERK1/2, STAT3, and CREB, which are signaling pathway proteins involved in the survival of neurons and the regeneration of axons. In summary, these findings demonstrated that systemically injecting miR-133b exosomes preserved neurons, promoted the regeneration of axons, and improved the recovery of hindlimb locomotor function following SCI, suggesting that the transfer of exosome-mediated miRNAs represents a novel therapeutic approach for the treatment of SCI.

Mesenchymal stem cell-derived extracellular vesicles affect disease outcomes via transfer of microRNAs

Mesenchymal stem cells (MSCs) are adult stromal cells with the capacity to differentiate into multiple types of cells. MSCs represent an attractive option in regenerative medicine due to their multifaceted abilities for tissue repair, immunosuppression, and anti-inflammation. Recent studies demonstrate that MSCs exert their effects via paracrine activity, which is at least partially mediated by extracellular vesicles (EVs). MSC-derived EVs (MSC-EVs) could mimic the function of parental MSCs by transferring their components such as DNA, proteins/peptides, mRNA, microRNA (miRNA), lipids, and organelles to recipient cells. In this review, we aim to summarize the mechanism and role of miRNA transfer in mediating the effects of MSC-EVs in the models of human diseases. The first three sections of the review discuss the sorting of miRNAs into EVs, uptake of EVs by target cells, and functional transfer of miRNAs via EVs. Then, we describe the composition of miRNAs in MSC-EVs. Next, we provide the existing evidence that MSC-EVs affect the outcomes of renal, liver, heart, and brain diseases by transferring their miRNA contents. In conclusion, EV-mediated miRNA transfer plays an important role in disease-modulating capacity of MSCs.

Cell Labeling with Cy3 through DNA Hybridization for Assessing Neural Stem Cells Survival and Differentiation

Neural stem cells (NSCs) have been attractive donor sources for cell therapy in traumatic brain injuries (TBI). Monitoring the fate of transplanted cells, including the survival and differentiation, will provide vital information to assess the outcome during the therapy time course. However, the current labeling methods are based on the principles of cell endocytosis, demanding relatively high fluorescent probes concentration and long incubation time, which may affect the proliferation and differentiation of transplanted cells. In our study, an efficient and relatively fast labeling strategy for NSCs with Cy3 based on DNA hybridization was proposed for monitoring the fate of transplanted cells. The oligo[dA]₂₀ conjugated with Cy3 was anchored on NSCs which had modified with oligo[dT]₂₀ via the oligo[dT]₂₀-oligo[dA]₂₀ hybridization. This labeling system did not affect the viability of labeled NSCs. After implantation of labeled NSCs into the brain, immunohistology demonstrated implanted cells were able to survive and differentiate into mature neural cells as long as one month. In conclusion, the DNA hybridization system can be used as an efficient cell labeling method in cell therapy.

Multicellular Crosstalk Between Exosomes and the Neurovascular Unit After Cerebral Ischemia. Therapeutic Implications

Restorative strategies after stroke are focused on the remodeling of cerebral endothelial cells and brain parenchymal cells. The latter, i.e., neurons, neural precursor cells and glial cells, synergistically interact with endothelial cells in the ischemic brain, providing a neurovascular unit (NVU) remodeling that can be used as target for stroke therapies. Intercellular communication and signaling within the NVU, the multicellular brain-vessel-blood interface, including its highly selective blood-brain barrier, are fundamental to the central nervous system homeostasis and function. Emerging research designates cell-derived extracellular vesicles and especially the nano-sized exosomes, as a complex mean of cell-to-cell communication, with potential use for clinical applications. Through their richness in active molecules and biological information (e.g., proteins, lipids, genetic material), exosomes contribute to intercellular signaling, a condition particularly required in the central nervous system. Cerebral endothelial cells, perivascular astrocytes, pericytes, microglia and neurons, all part of the NVU, have been shown to release and uptake exosomes. Also, exosomes cross the blood-brain and blood-cerebrospinal fluid barriers, allowing communication between periphery and brain, in normal and disease conditions. As such exosomes might be a powerful diagnostic tool and a promising therapeutic shuttle of natural nanoparticles, but also a means of disease spreading (e.g., immune system modulation, pro-inflammatory action, propagation of neurodegenerative factors). This review highlights the importance of exosomes in mediating the intercellular crosstalk within the NVU and reveals the restorative therapeutic potential of exosomes harvested from multipotent mesenchymal stem cells in ischemic stroke, a frequent neurologic condition lacking an efficient therapy.

Non-Coding RNA in Acute Ischemic Stroke: Mechanisms, Biomarkers and Therapeutic Targets

Non-coding RNAs (ncRNAs) are a class of functional RNAs that regulate gene expression in a post-transcriptional manner. NcRNAs include microRNAs, long non-coding RNAs and circular RNAs. They are highly expressed in the brain and are involved in the regulation of physiological and pathophysiological processes, including cerebral ischemic injury, neurodegeneration, neural development, and plasticity. Stroke is one of the leading causes of death and physical disability worldwide. Acute ischemic stroke (AIS) occurs when brain blood flow stops, and that stoppage results in reduced oxygen and glucose supply to cells in the brain. In this article, we review the latest progress on ncRNAs in relation to their implications in AIS, as well as their potential as diagnostic and prognostic biomarkers. We also review ncRNAs acting as possible therapeutic targets in future precision medicine. Finally, we conclude with a brief discussion of current challenges and future directions for ncRNAs studies in AIS, which may facilitate the translation of ncRNAs research into clinical practice to improve clinical outcome of AIS.

Applications of stem cell-derived exosomes in tissue engineering and neurological diseases

Exosomes are extracellular vesicles with diameters of 30-100 nm that are key for intercellular communication. Almost all types of cell, including dendritic cells, T cells, mast cells, epithelial cells, neuronal cells, adipocytes, mesenchymal stem cells, and platelets, can release exosomes. Exosomes are present in human body fluids, such as urine, amniotic fluid, malignant ascites, synovial fluid, breast milk, cerebrospinal fluid, semen, saliva, and blood. Exosomes have biological functions in immune response, antigen presentation, intercellular communication, and RNA and protein transfer. This review provides a brief overview of the origin, morphological characteristics, enrichment and identification methods, biological functions, and applications in tissue engineering and neurological diseases of exosomes.

Potential Effects of MSC-Derived Exosomes in Neuroplasticity in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common type of dementia affecting regions of the central nervous system that exhibit synaptic plasticity and are involved in higher brain functions such as learning and memory. AD is characterized by progressive cognitive dysfunction, memory loss and behavioral disturbances of synaptic plasticity and energy metabolism. Cell therapy has emerged as an alternative treatment of AD. The use of adult stem cells, such as neural stem cells and Mesenchymal Stem Cells (MSCs) from bone marrow and adipose tissue, have the potential to decrease cognitive deficits, possibly by reducing neuronal loss through blocking apoptosis, increasing neurogenesis, synaptogenesis and angiogenesis. These processes are mediated primarily by the secretion of many growth factors, anti-inflammatory proteins, membrane receptors, microRNAs (miRNA) and exosomes. Exosomes encapsulate and transfer several functional molecules like proteins, lipids and regulatory RNA which can modify cell metabolism. In the proteomic characterization of the content of MSC-derived exosomes, more than 730 proteins have been identified, some of which are specific cell type markers and others are involved in the regulation of binding and fusion of exosomes with adjacent cells. Furthermore, some factors were found that promote the recruitment, proliferation and differentiation of other cells like neural stem cells. Moreover, within exosomal cargo, a wide range of miRNAs were found, which can control functions related to neural remodeling as well as angiogenic and neurogenic processes. Taking this into consideration, the use of exosomes could be part of a strategy to promote neuroplasticity, improve cognitive impairment and neural replacement in AD. In this review, we describe how exosomes are involved in AD pathology and discuss the therapeutic potential of MSC-derived exosomes mediated by miRNA and protein cargo.

Exosomes and Their MicroRNA Cargo: New Players in Peripheral Nerve Regeneration

Peripheral nerve injury is a major clinical problem and often results in a poor functional recovery. Despite obvious clinical need, treatment strategies have been largely suboptimal. In the nervous system, exosomes, which are nanosized extracellular vesicles, play a critical role in mediating intercellular communication. More specifically, microRNA carried by exosomes are involved in various key processes such as nerve and vascular regeneration, and exosomes originating from Schwann cells, macrophages, and mesenchymal stem cells can promote peripheral nerve regeneration. In this review, the current knowledge of exosomes' and their miRNA cargo's role in peripheral nerve regeneration are summarized. The possible future roles of exosomes in therapy and the potential for microRNA-containing exosomes to treat peripheral nerve injuries are also discussed.

Directed glial differentiation and transdifferentiation for neural tissue regeneration

Glial cells which are indispensable for the central nervous system development and functioning, are proven to be vulnerable to a harmful influence of pathological cues and tissue misbalance. However, they are also highly sensitive to both in vitro and in vivo modulation of their commitment, differentiation, activity and even the fate-switch by different types of bioactive molecules. Since glial cells (comprising macroglia and microglia) are an abundant and heterogeneous population of neural cells, which are almost uniformly distributed in the brain and the spinal cord parenchyma, they all create a natural endogenous reservoir of cells for potential neurogenerative processes required to be initiated in response to pathophysiological cues present in the local tissue microenvironment. The past decade of intensive investigation on a spontaneous and enforced conversion of glial fate into either alternative glial (for instance from oligodendrocytes to astrocytes) or neuronal phenotypes, has considerably extended our appreciation of glial involvement in restoring the nervous tissue cytoarchitecture and its proper functions. The most effective modulators of reprogramming processes have been identified and tested in a series of pre-clinical experiments. A list of bioactive compounds which are potent in guiding in vivo cell fate conversion and driving cell differentiation includes a selection of transcription factors, microRNAs, small molecules, exosomes, morphogens and trophic factors, which are helpful in boosting the enforced neuro-or gliogenesis and promoting the subsequent cell maturation into desired phenotypes. Herein, an issue of their utility for a directed glial differentiation and transdifferentiation is discussed in the context of elaborating future therapeutic options aimed at restoring the diseased nervous tissue.

Role of Exosomes as a Treatment and Potential Biomarker for Stroke

Approximately, 16 million strokes occur worldwide each year, causing 6 million deaths and considerable disability, implying an enormous social, individual health, and economic burden. Due to this high incidence, strategies to promote stroke recovery are urgently needed. Research into new therapeutic approaches for stroke has determined that intravenous administration of mesenchymal stem cells (MSCs) is a good strategy to improve recovery by amplifying mechanisms implicated in brain plasticity. Recent studies have demonstrated the efficacy of MSCs in stroke, with no need for them to reach the area of brain injury. Although the mechanisms by which they mediate restorative effects are still unknown, the evidence suggests that MSCs might use specialised communication by sending and receiving biological information included in elements called exosomes. Exosomes are nanosized extracellular vesicles released into physical environments, and they have recently been suggested to mediate restorative stem cell effects. Moreover, after stroke, exosomes can also be synthesised and released from brain cells, passing through the blood-brain barrier (BBB), and can be detected in peripheral blood or in cerebrospinal fluid. Thus, exosomes could possibly be biomarkers that reflect pathological progress and promote stroke recovery. This review discusses the translational aspects of MSC-derived exosomes and their various roles in brain repair and as circulating biomarkers in stroke.

MicroRNA Profiling and Bioinformatics Target Analysis in Dorsal Hippocampus of Chronically Stressed Rats: Relevance to Depression Pathophysiology

Studies conducted in rodents subjected to chronic stress and some observations in humans after psychosocial stress, have allowed to establish a link between stress and the susceptibility to many complex diseases, including mood disorders. The studies in rodents have revealed that chronic exposure to stress negatively affects synaptic plasticity by triggering changes in the production of trophic factors, subunit levels of glutamate ionotropic receptors, neuron morphology, and neurogenesis in the adult hippocampus. These modifications may account for the impairment in learning and memory processes observed in chronically stressed animals. It is plausible then, that stress modifies the interplay between signal transduction cascades and gene expression regulation in the hippocampus, therefore leading to altered neuroplasticity and functioning of neural circuits. Considering that miRNAs play an important role in post-transcriptional-regulation of gene expression and participate in several hippocampus-dependent functions; we evaluated the consequences of chronic stress on the expression of miRNAs in dorsal (anterior) portion of the hippocampus, which participates in memory formation in rodents. Here, we show that male rats exposed to daily restraint stress (2.5 h/day) during 7 and 14 days display a differential profile of miRNA levels in dorsal hippocampus and remarkably, we found that some of these miRNAs belong to the miR-379-410 cluster. We confirmed a rise in miR-92a and miR-485 levels after 14 days of stress by qPCR, an effect that was not mimicked by chronic administration of corticosterone (14 days). Our in silico study identified the top-10 biological functions influenced by miR-92a, nine of which were shared with miR-485: Nervous system development and function, Tissue development, Behavior, Embryonic development, Organ development, Organismal development, Organismal survival, Tissue morphology, and Organ morphology. Furthermore, our in silico study provided a landscape of potential miRNA-92a and miR-485 targets, along with relevant canonical pathways related to axonal guidance signaling and cAMP signaling, which may influence the functioning of several neuroplastic substrates in dorsal hippocampus. Additionally, the combined effect of miR-92a and miR-485 on transcription factors, along with histone-modifying enzymes, may have a functional relevance by producing changes in gene regulatory networks that modify the neuroplastic capacity of the adult dorsal hippocampus under stress.

The therapeutic potential of the mesenchymal stem cell secretome in ischaemic stroke

Mesenchymal stem cells (MSCs) hold great potential as a regenerative therapy for stroke, leading to increased repair and functional recovery in animal models of cerebral ischaemia. While it was initially hypothesised that cell replacement was an important mechanism of action of MSCs, focus has shifted to their paracrine actions or the so called "bystander" effect. MSCs secrete a wide array of growth factors, chemokines, cytokines and extracellular vesicles, commonly referred to as the MSC secretome. There is evidence suggesting the MSC secretome can promote repair through a number of mechanisms including preventing cell apoptosis, modulating the inflammatory response and promoting endogenous repair mechanisms such as angiogenesis and neurogenesis. In this review, we will discuss the in vitro approaches currently being employed to drive the MSC secretome towards a more anti-inflammatory and regenerative phenotype. We will then examine the role of the secretome in promoting repair and improving recovery in preclinical models of cerebral ischaemia.

Immunological and non-immunological effects of stem cell-derived extracellular vesicles on the ischaemic brain

Following the implementation of thrombolysis and endovascular recanalization strategies, stroke therapy has profoundly changed in recent years. In spite of these advancements, a considerable proportion of stroke patients still exhibit functional impairment in the long run, increasing the need for adjuvant therapies that promote neurological recovery. Stem cell therapies have initially attracted great interest in the stroke field, since there were hopes that transplanted cells may allow for the replacement of lost cells. After the recognition that transplanted cells integrate poorly into existing neural networks and that they induce brain remodelling in a paracrine way by secreting a heterogeneous group of nanovesicles, these extracellular vesicles (EVs) have been identified as key players that mediate restorative effects of stem and progenitor cells in ischaemic brain tissue. We herein review restorative effects of EVs in stroke models and discuss immunological and non-immunological mechanisms that may underlie recovery of function.

Distinct function of miR-17-92 cluster in the dorsal and ventral adult hippocampal neurogenesis

It has been known that the dorsal and ventral areas of the dentate gyrus in the hippocampus have distinct roles in memory and mood behaviors. We previously reported that microRNA miR-17-92 regulates adult hippocampal neurogenesis and mood disorders. Here, we suggest that the miR-17-92 cluster is highly expressed in the ventral than the dorsal dentate gyrus in the adult mouse hippocampus. Deletion of miR-17-92 in the adult hippocampus only affects development of neural progenitors in the ventral dentate gyrus, and miR-17-92 knockout mice have no defects in memory functions. Our results suggest that regional expression of miR-17-92 in the dentate gyrus is associated with their distinct functions in hippocampal neurogenesis and related behaviors.

Deciphering Non-coding RNAs in Cardiovascular Health and Disease

After being long considered as “junk” in the human genome, non-coding RNAs (ncRNAs) currently represent one of the newest frontiers in cardiovascular disease (CVD) since they have emerged in recent years as potential therapeutic targets. Different types of ncRNAs exist, including small ncRNAs that have fewer than 200 nucleotides, which are mostly known as microRNAs (miRNAs), and long ncRNAs that have more than 200 nucleotides. Recent discoveries on the role of ncRNAs in epigenetic and transcriptional regulation, atherosclerosis, myocardial ischemia/reperfusion (I/R) injury and infarction (MI), adverse cardiac remodeling and hypertrophy, insulin resistance, and diabetic cardiomyopathy prompted vast interest in exploring candidate ncRNAs for utilization as potential therapeutic targets and/or diagnostic/prognostic biomarkers in CVDs. This review will discuss our current knowledge concerning the roles of different types of ncRNAs in cardiovascular health and disease and provide some insight on the cardioprotective signaling pathways elicited by the non-coding genome. We will highlight important basic and clinical breakthroughs that support employing ncRNAs for treatment or early diagnosis of a variety of CVDs, and also depict the most relevant limitations that challenge this novel therapeutic approach.

Cellular mechanisms responsible for cell-to-cell spreading of prions

Prions are infectious agents that cause fatal neurodegenerative diseases. Current evidence indicates that they are essentially composed of an abnormally folded protein (PrPSc). These abnormal aggregated PrPSc species multiply in infected cells by recruiting and converting the host PrPC protein into new PrPSc. How prions move from cell to cell and progressively spread across the infected tissue is of crucial importance and may provide experimental opportunity to delay the progression of the disease. In infected cells, different mechanisms have been identified, including release of infectious extracellular vesicles and intercellular transfer of PrPSc-containing organelles through tunneling nanotubes. These findings should allow manipulation of the intracellular trafficking events targeting PrPSc in these particular subcellular compartments to experimentally address the relative contribution of these mechanisms to in vivo prion pathogenesis. In addition, such information may prompt further experimental strategies to decipher the causal roles of protein misfolding and aggregation in other human neurodegenerative diseases.

MicroRNA-based therapeutics in central nervous system injuries

Central nervous system (CNS) injuries, such as stroke, traumatic brain injury (TBI) and spinal cord injury (SCI), are important causes of death and long-term disability worldwide. MicroRNA (miRNA), small non-coding RNA molecules that negatively regulate gene expression, can serve as diagnostic biomarkers and are emerging as novel therapeutic targets for CNS injuries. MiRNA-based therapeutics include miRNA mimics and inhibitors (antagomiRs) to respectively decrease and increase the expression of target genes. In this review, we summarize current miRNA-based therapeutic applications in stroke, TBI and SCI. Administration methods, time windows and dosage for effective delivery of miRNA-based drugs into CNS are discussed. The underlying mechanisms of miRNA-based therapeutics are reviewed including oxidative stress, inflammation, apoptosis, blood-brain barrier protection, angiogenesis and neurogenesis. Pharmacological agents that protect against CNS injuries by targeting specific miRNAs are presented along with the challenges and therapeutic potential of miRNA-based therapies.

Mesenchymal stromal cell-derived extracellular vesicles: regenerative and immunomodulatory effects and potential applications in sepsis

Mesenchymal stromal (stem) cells (MSCs) have multipotent differentiation capacity and exist in nearly all forms of post-natal organs and tissues. The immunosuppressive and anti-inflammatory properties of MSCs have made them an ideal candidate in the treatment of diseases, such as sepsis, in which inflammation plays a critical role. One of the key mechanisms of MSCs appears to derive from their paracrine activity. Recent studies have demonstrated that MSC-derived extracellular vesicles (MSC-EVs) are at least partially responsible for the paracrine effect. MSC-EVs transfer molecules (such as proteins/peptides, mRNA, microRNA and lipids) with immunoregulatory properties to recipient cells. MSC-EVs have been shown to mimic MSCs in alleviating sepsis and may serve as an alternative to whole cell therapy. Compared with MSCs, MSC-EVs may offer specific advantages due to lower immunogenicity and higher safety profile. The first two sections of the review discuss the preclinical and clinical findings of MSCs in sepsis. Next, we review the characteristics of EVs and MSC-EVs. Then, we summarize the mechanisms of MSC-EVs, including tissue regeneration and immunomodulation. Finally, our review presents the evidences that MSC-EVs are effective in treating models of sepsis. In conclusion, MSC-EVs may have the potential to become a novel therapeutic strategy for sepsis.

Current understanding of neuroinflammation after traumatic brain injury and cell-based therapeutic opportunities

Traumatic brain injury (TBI) remains a major cause of death and disability worldwide. Increasing evidence indicates that TBI is an important risk factor for neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, and chronic traumatic encephalopathy. Despite improved supportive and rehabilitative care of TBI patients, unfortunately, all late phase clinical trials in TBI have yet to yield a safe and effective neuroprotective treatment. The disappointing clinical trials may be attributed to variability in treatment approaches and heterogeneity of the population of TBI patients as well as a race against time to prevent or reduce inexorable cell death. TBI is not just an acute event but a chronic disease. Among many mechanisms involved in secondary injury after TBI, emerging preclinical studies indicate that posttraumatic prolonged and progressive neuroinflammation is associated with neurodegeneration which may be treatable long after the initiating brain injury. This review provides an overview of recent understanding of neuroinflammation in TBI and preclinical cell-based therapies that target neuroinflammation and promote functional recovery after TBI.

Clustered miRNAs and their role in biological functions and diseases

MicroRNAs (miRNAs) are endogenous, small non-coding RNAs known to regulate expression of protein-coding genes. A large proportion of miRNAs are highly conserved, localized as clusters in the genome, transcribed together from physically adjacent miRNAs and show similar expression profiles. Since a single miRNA can target multiple genes and miRNA clusters contain multiple miRNAs, it is important to understand their regulation, effects and various biological functions. Like protein-coding genes, miRNA clusters are also regulated by genetic and epigenetic events. These clusters can potentially regulate every aspect of cellular function including growth, proliferation, differentiation, development, metabolism, infection, immunity, cell death, organellar biogenesis, messenger signalling, DNA repair and self-renewal, among others. Dysregulation of miRNA clusters leading to altered biological functions is key to the pathogenesis of many diseases including carcinogenesis. Here, we review recent advances in miRNA cluster research and discuss their regulation and biological functions in pathological conditions.

Neural stem cell therapies and hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury is a significant cause of morbidity and mortality in the adult as well as in the neonate. Extensive pre-clinical studies have shown promising therapeutic effects of neural stem cell-based treatments for hypoxic-ischemic brain injury. There are two major strategies of neural stem cell-based therapies: transplanting exogenous neural stem cells and boosting self-repair of endogenous neural stem cells. Neural stem cell transplantation has been proved to improve functional recovery after brain injury through multiple by-stander mechanisms (e.g., neuroprotection, immunomodulation), rather than simple cell-replacement. Endogenous neural stem cells reside in certain neurogenic niches of the brain and response to brain injury. Many molecules (e.g., neurotrophic factors) can stimulate or enhance proliferation and differentiation of endogenous neural stem cells after injury. In this review, we first present an overview of neural stem cells during normal brain development and the effect of hypoxic-ischemic injury on the activation and function of endogenous neural stem cells in the brain. We then summarize and discuss the current knowledge of strategies and mechanisms for neural stem cell-based therapies on brain hypoxic-ischemic injury, including neonatal hypoxic-ischemic brain injury and adult ischemic stroke.

The roles of extracellular vesicle microRNAs in the central nervous system

MicroRNAs (miRNAs) are small, highly conserved non-coding RNA molecules that post-transcriptionally regulate protein expression and most biological processes. Mature miRNAs are recruited to the RNA-induced silencing complex (RISC) and target mRNAs via complementary base-pairing, thus resulting in translational inhibition and/or transcript degradation. Here, we present evidence implicating miRNAs within extracellular vesicles (EVs), including microvesicles and exosomes, as mediators of central nervous system (CNS) development, homeostasis, and injury. EVs are extracellular vesicles that are secreted by all cells and represent a novel method of intercellular communication. In glial cells, the transfer of miRNAs via EVs can alter the function of recipient cells and significantly impacts cellular mechanisms involved in both injury and repair. This review discusses the value of information to be gained by studying miRNAs within EVs in the context of CNS diseases and their potential use in the development of novel disease biomarkers and therapeutic strategies.

Behavioral outcomes of a novel, pelvic nerve damage rat model of fecal incontinence

BACKGROUND

Fecal incontinence (FI) has a multifactorial pathophysiology with a severe social impact. The most common cause for FI is pudendal nerve damage, which mostly occurs in women during or after labor. A better understanding of the pathophysiology is required to optimize treatment of FI. In this study, we evaluate the use of a novel pelvic nerve damage rat model of FI.

METHODS

This new model simulates the forces on the pelvic floor during labor by prolonged transvaginal, retro-uterine intrapelvic balloon distention in female rats. Number of fecal pellets produced per day and defecation pattern was compared between the experimental and control group for 2 weeks. The cages of the rats were divided in food, nesting and latrine areas to evaluate changes in defecation pattern. The FI Index (FII) was calculated to assess the ratio of fecal pellets between the non-latrine areas and the total number of pellets. A higher score represents more random distribution of feces outside the latrine area.

RESULTS

Total number of fecal pellets was higher in the experimental group as compared with the controls. In both groups most fecal pellets were deposited in the nesting area, which is closest to the food area. The experimental group deposited more fecal pellets in the latrine area and had a lower FII indicating less random distribution of feces outside the latrine area.

CONCLUSION

Transvaginal, retro-uterine intrapelvic balloon distention is a safe and feasible animal model simulating the human physiologic impact of labor by downwards pressure on the pelvic floor.

Mesenchymal stem cell-derived extracellular vesicles: novel frontiers in regenerative medicine

Mesenchymal stem cells (MSCs) are multipotent stem cells that have gained significant attention in the field of regenerative medicine. The differentiation potential along with paracrine properties of MSCs have made them a key option for tissue repair. The paracrine functions of MSCs are applied through secreting soluble factors and releasing extracellular vesicles like exosomes and microvesicles. Extracellular vesicles are predominantly endosomal in origin and contain a cargo of miRNA, mRNA, and proteins that are transferred from their original cells to target cells. Recently it has emerged that extracellular vesicles alone are responsible for the therapeutic effect of MSCs in plenty of animal diseases models. Hence, MSC-derived extracellular vesicles may be used as an alternative MSC-based therapy in regenerative medicine. In this review we discuss MSC-derived extracellular vesicles and their therapeutic potential in various diseases.

Cell-Based and Exosome Therapy in Diabetic Stroke

Stroke is a global health concern and it is imperative that therapeutic strategies with wide treatment time frames be developed to improve neurological outcome in patients. Patients with diabetes mellitus who suffer a stroke have worse neurological outcomes and long‐term functional recovery than nondiabetic stroke patients. Diabetes induced vascular damage and enhanced inflammatory milieu likely contributes to worse post stroke outcomes. Diabetic stroke patients have an aggravated pathological cascade, and treatments that benefit nondiabetic stroke patients do not necessarily translate to diabetic stroke patients. Therefore, there is a critical need to develop therapeutics for stroke specifically in the diabetic population. Stem cell based therapy for stroke is an emerging treatment option with wide therapeutic time window. Cell‐based therapies for stroke promote endogenous central nervous system repair and neurorestorative mechanisms such as angiogenesis, neurogenesis, vascular remodeling, white matter remodeling, and also modulate inflammatory and immune responses at the local and systemic level. Emerging evidence suggests that exosomes and their cargo microRNA mediate cell therapy derived neurorestorative effects. Exosomes are small vesicles containing protein and RNA characteristic of its parent cell. Exosomes are transported by biological fluids and facilitate communication between neighboring and remote cells. MicroRNAs, a class of naturally occurring, small noncoding RNA sequences, contained within exosomes can regulate recipient cell's signaling pathways and alter protein expression either acting alone or in concert with other microRNAs. In this perspective article, we summarize current knowledge and highlight the promising future of cell based and exosome therapy for stroke and specifically for diabetic stroke. stemcellstranslationalmedicine2018;7:451–455

MicroRNAs participate in the regulation of oligodendrocytes development in white matter injury

White matter injury (WMI) often results in cognitive impairment, behavioral disorders, and cerebral palsy and thus imposes a tremendous burden on society. The cells in brain white matter mainly comprise oligodendrocytes (OLs), astrocytes, and microglia. The dysregulation of OLs development is the pathological hallmark of WMI. Recent studies have demonstrated that microRNAs (miRNAs or miRs) participate in the regulation of OLs development, and the dysregulation of this process represents the pathogenesis of WMI. This review summarizes the progress made in this field that will help clinicians and researchers understand the molecular etiology of WMI and develop miRNAs as new agents for the prevention and treatment of WMI.

Potential Role of Extracellular Vesicles in the Pathophysiology of Drug Addiction

Extracellular vesicles (EVs) are small vesicles secreted by cells and are known to carry sub-cellular components including microRNA, proteins, and lipids. Due to their ability to transport cargo between cells, EVs have been identified as important regulators of various pathophysiological conditions and can therefore influence treatment outcomes. In particular, the significance of microRNAs in EV-mediated cell-cell communication is well-documented. While the influence of EVs and the cargo delivered by EVs has been extensively reviewed in other neurological disorders, the available literature on the potential role of EVs in the pathophysiology of drug addiction has not been reviewed. Hence, in this article, the known effects of commonly abused drugs (ethanol, nicotine, opiates, cocaine, and cannabinoids) on EV secretion have been reviewed. In addition, the potential role of drugs of abuse in affecting the delivery of EV-packaged microRNAs, and the subsequent impact on neuronal health and continued drug dependence, has been discussed.

"Good things come in small packages": application of exosome-based therapeutics in neonatal lung injury

Infants born at very low gestational age contribute disproportionately to neonatal morbidity and mortality. Advancements in antenatal steroid therapies and surfactant replacement have favored the survival of infants with ever-more immature lungs. Despite such advances in medical care, cardiopulmonary and neurological impairment prevail in constituting the major adverse outcomes for neonatal intensive care unit survivors. With no single effective therapy for either the prevention or treatment of such neonatal disorders, the need for new tools to treat and reduce risk of further complications associated with extreme preterm birth is urgent. Mesenchymal stem/stromal cell (MSC)-based approaches have shown promise in numerous experimental models of lung injury relevant to neonatology. Recent studies have highlighted that the therapeutic potential of MSCs is harnessed in their secretome, and that the therapeutic vector therein is represented by the exosomes released by MSCs. In this review, we summarize the development and significance of stem cell-based therapies for neonatal diseases, focusing on preclinical models of neonatal lung injury. We emphasize the development of MSC exosome-based therapeutics and comment on the challenges in bringing these promising interventions to clinic.

[Research advances in mesenchymal stem cell-derived exosomes in treatment of brain injury]

Mesenchymal stem cell (MSC) transplantation is considered one of the most promising therapeutic strategies for the repair of brain injuries and plays an important role in various links of nerve repair. Recent studies have shown that MSC-derived exosomes may dominate the repair of brain injuries and help to promote angiogenesis, regulate immunity, inhibit apoptosis, and repair the nerves, and therefore, they have a great potential in the treatment of brain injuries in neonates. With reference to these studies, this article reviews the mechanism of action of exosomes in the repair of brain injuries and related prospects and challenges, in order to provide new directions for the treatment of brain injuries in neonates with stem cells.

Concise Review: Extracellular Vesicles Overcoming Limitations of Cell Therapies in Ischemic Stroke

Despite recent advances in stroke therapy, current therapeutic concepts are still limited. Thus, additional therapeutic strategies are in order. In this sense, the transplantation of stem cells has appeared to be an attractive adjuvant tool to help boost the endogenous regenerative capacities of the brain. Although transplantation of stem cells is known to induce beneficial outcome in (preclinical) stroke research, grafted cells do not replace lost tissue directly. Rather, these transplanted cells like neural progenitor cells or mesenchymal stem cells act in an indirect manner, among which the secretion of extracellular vesicles (EVs) appears to be one key factor. Indeed, the application of EVs in preclinical stroke studies suggests a therapeutic role, which appears to be noninferior in comparison to the transplantation of stem cells themselves. In this short review, we highlight some of the recent advances in the field of EVs as a therapeutic means to counter stroke. Stem Cells Translational Medicine2017;6:2044–2052

Mesenchymal Stem/Stromal Cell-Derived Extracellular Vesicles and Their Potential as Novel Immunomodulatory Therapeutic Agents

Extracellular vesicles (EVs), such as exosomes and microvesicles, have been identified as mediators of a newly-discovered intercellular communication system. They are essential signaling mediators in various physiological and pathophysiological processes. Depending on their origin, they fulfill different functions. EVs of mesenchymal stem/stromal cells (MSCs) have been found to promote comparable therapeutic activities as MSCs themselves. In a variety of in vivo models, it has been observed that they suppress pro-inflammatory processes and reduce oxidative stress and fibrosis. By switching pro-inflammatory into tolerogenic immune responses, MSC-EVs very likely promote tissue regeneration by creating a pro-regenerative environment allowing endogenous stem and progenitor cells to successfully repair affected tissues. Accordingly, MSC-EVs provide a novel, very promising therapeutic agent, which has already been successfully applied to humans. However, the MSC-EV production process has not been standardized, yet. Indeed, a collection of different protocols has been used for the MSC-EV production, characterization and application. By focusing on kidney, heart, liver and brain injuries, we have reviewed the major outcomes of published MSC-EV in vivo studies.