Acellular approaches for regenerative medicine: on the verge of clinical trials with extracellular membrane vesicles?

Biogenesis, Composition and Potential Therapeutic Applications of Mesenchymal Stem Cells Derived Exosomes in Various Diseases

Exosomes are nanovesicles with a wide range of chemical compositions used in many different applications. Mesenchymal stem cell-derived exosomes (MSCs-EXOs) are spherical vesicles that have been shown to mediate tissue regeneration in a variety of diseases, including neurological, autoimmune and inflammatory, cancer, ischemic heart disease, lung injury, and liver fibrosis. They can modulate the immune response by interacting with immune effector cells due to the presence of anti-inflammatory compounds and are involved in intercellular communication through various types of cargo. MSCs-EXOs exhibit cytokine storm-mitigating properties in response to COVID-19. This review discussed the potential function of MSCs-EXOs in a variety of diseases including neurological, notably epileptic encephalopathy and Parkinson's disease, cancer, angiogenesis, autoimmune and inflammatory diseases. We provided an overview of exosome biogenesis and factors that regulate exosome biogenesis. Additionally, we highlight the functions and potential use of MSCs-EXOs in the treatment of the inflammatory disease COVID-19. Finally, we covered a strategies and challenges of MSCs-EXOs. Finally, we discuss conclusion and future perspectives of MSCs-EXOs.

The evolving regulatory landscape in regenerative medicine

Regenerative medicine as a field has emerged as a new component of modern medicine and medical research that encompasses a wide range of products including cellular and acellular therapies. As this new field emerged, regulatory agencies like the Food and Drug Administration (FDA) rapidly adapted existing regulatory frameworks to address the transplantation, gene therapy, cell-based therapeutics, and acellular biologics that fall under the broader regenerative medicine umbrella. Where it has not been possible to modify existing regulation and processes, entirely new frameworks have been generated with the intention of providing flexible, forward-facing systems to regulate this rapidly growing field. This review discusses the current state of FDA regulatory affairs in the context of stem cells and extracellular vesicles by highlighting gaps in the current regulatory system and then discussing where regulatory science in regenerative medicine may be headed based on these gaps and the FDA's historical ability to deal with emerging fields. Lastly, we utilize case studies in stem cell and acellular based treatments to demonstrate how regulatory science has evolved in regenerative medicine and highlight the ongoing clinical efforts and challenges of these therapies.

Bioengineering Human Pluripotent Stem Cell-Derived Retinal Organoids and Optic Vesicle-Containing Brain Organoids for Ocular Diseases

Retinal organoids are three-dimensional (3D) structures derived from human pluripotent stem cells (hPSCs) that mimic the retina's spatial and temporal differentiation, making them useful as in vitro retinal development models. Retinal organoids can be assembled with brain organoids, the 3D self-assembled aggregates derived from hPSCs containing different cell types and cytoarchitectures that resemble the human embryonic brain. Recent studies have shown the development of optic cups in brain organoids. The cellular components of a developing optic vesicle-containing organoids include primitive corneal epithelial and lens-like cells, retinal pigment epithelia, retinal progenitor cells, axon-like projections, and electrically active neuronal networks. The importance of retinal organoids in ocular diseases such as age-related macular degeneration, Stargardt disease, retinitis pigmentosa, and diabetic retinopathy are described in this review. This review highlights current developments in retinal organoid techniques, and their applications in ocular conditions such as disease modeling, gene therapy, drug screening and development. In addition, recent advancements in utilizing extracellular vesicles secreted by retinal organoids for ocular disease treatments are summarized.

Small Extracellular Vesicles Secreted by Nigrostriatal Astrocytes Rescue Cell Death and Preserve Mitochondrial Function in Parkinson's Disease

Extracellular vesicles (EVs) are emerging as powerful players in cell-to-cell communication both in healthy and diseased brain. In Parkinson's disease (PD)-characterized by selective dopaminergic neuron death in ventral midbrain (VMB) and degeneration of their terminals in striatum (STR)-astrocytes exert dual harmful/protective functions, with mechanisms not fully elucidated. Here, this study shows that astrocytes from the VMB-, STR-, and VMB/STR-depleted brains release a population of small EVs  in a region-specific manner. Interestingly, VMB-astrocytes secreted the highest rate of EVs, which is further exclusively increased in response to CCL3, a chemokine that promotes robust dopaminergic neuroprotection in different PD models. The neuroprotective potential of nigrostriatal astrocyte-EVs is investigated in differentiated versus undifferentiated SH-SY5Y cells exposed to oxidative stress and mitochondrial toxicity. EVs from both VMB- and STR-astrocytes counteract H₂ O₂ -induced caspase-3 activation specifically in differentiated cells, with EVs from CCL3-treated astrocytes showing a higher protective effect. High resolution respirometry further reveals that nigrostriatal astrocyte-EVs rescue neuronal mitochondrial complex I function impaired by the neurotoxin MPP⁺ . Notably, only EVs from VMB-astrocyte fully restore ATP production, again specifically in differentiated SH-SY5Y. These results highlight a regional diversity in the nigrostriatal system for the secretion and activities of astrocyte-EVs, with neuroprotective implications for PD.

Novel insights into the role of circular RNAs in Parkinson disease: An emerging renaissance in the management of neurodegenerative diseases

Parkinson's disease (PD), as a debilitating neurodegenerative disease, particularly affects the elderly population, and is clinically identified by resting tremor, rigidity, and bradykinesia. Pathophysiologically, PD is characterized by an early loss of dopaminergic neurons in the Substantia nigra pars compacta, accompanied by the extensive aggregation of alpha-synuclein (α-Syn) in the form of Lewy bodies. The onset of PD has been reported to be influenced by multiple biological molecules. In this context, circular RNAs (circRNAs), as tissue-specific noncoding RNAs with closed structures, have been recently demonstrated to involve in a set of PD's pathogenic processes. These RNA molecules can either up- or downregulate the expression of α-Syn, as well as moderating its accumulation through different regulatory mechanisms, in which targeting microRNAs (miRNAs) is considered the most common pathway. Since circRNAs have prominent structural and biological characteristics, they could also be considered as promising candidates for PD diagnosis and treatment. Unfortunately, PD has become a global health concern, and a large number of its pathogenic processes are still unclear; thus, it is crucial to elucidate the ambiguous aspects of PD pathophysiology to improve the efficiency of diagnostic and therapeutic strategies. In line with this fact, the current review aims to highlight the interplay between circRNAs and PD pathogenesis, and then discusses the diagnostic and therapeutic potential of circRNAs in PD progression. This study will thus be the first of its kind reviewing the relationship between circRNAs and PD.

Adipose-Derived Extracellular Vesicles: Systemic Messengers and Metabolic Regulators in Health and Disease

Adipose tissue is comprised of a heterogeneous population of cells that co-operate to perform diverse physiological roles including endocrine-related functions. The endocrine role of adipose tissue enables it to communicate nutritional and health cues to other organs, such as the liver, muscle, and brain, in order to regulate appetite and whole body metabolism. Adipose tissue dysfunction, which is often observed in obesity, is associated with changes in the adipose secretome, which can subsequently contribute to disease pathology. Indeed, secreted bioactive factors released from adipose tissue contribute to metabolic homeostasis and likely play a causal role in disease; however, what constitutes the entirety of the adipose tissue secretome is still poorly understood. Recent advances in nanotechnology have advanced this field substantially and have led to the identification of small, secreted particles known as extracellular vesicles (EVs). These small nano-sized lipid envelopes are released by most cell types and are capable of systemically delivering bioactive molecules, such as nucleic acids, proteins, and lipids. EVs interact with target cells to deliver specific cargo that can then elicit effects in various tissues throughout the body. Adipose tissue has recently been shown to secrete EVs that can communicate with the periphery to maintain metabolic homeostasis, or under certain pathological conditions, drive disease. In this review, we discuss the current landscape of adipose tissue-derived EVs, with a focus on their role in the regulation of metabolic homeostasis and disease pathology.

The Emerging Role of Exosomes in the Treatment of Human Disorders With a Special Focus on Mesenchymal Stem Cells-Derived Exosomes

Extracellular vesicles (EVs) are produced by diverse eukaryotic and prokaryotic cells. They have prominent roles in the modulation of cell-cell communication, inflammation versus immunomodulation, carcinogenic processes, cell proliferation and differentiation, and tissue regeneration. These acellular vesicles are more promising than cellular methods because of the lower risk of tumor formation, autoimmune responses and toxic effects compared with cell therapy. Moreover, the small size and lower complexity of these vesicles compared with cells have made their production and storage easier than cellular methods. Exosomes originated from mesenchymal stem cells has also been introduced as therapeutic option for a number of human diseases. The current review aims at summarization of the role of EVs in the regenerative medicine with a focus on their therapeutic impacts in liver fibrosis, lung disorders, osteoarthritis, colitis, myocardial injury, spinal cord injury and retinal injury.

Current status of myocardial restoration via the paracrine function of mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) have been studied for nearly two decades as a therapy for myocardial restoration. An emerging direction to repair myocardium is through their paracrine function, which includes the utilization of MSC-derived conditioned medium or extracellular vesicles. In this review, we go over the unique characteristics of MSCs that make it suitable for "off the shelf," cell-free regenerative therapy, current MSC-derived cell-free approaches including their advantages and disadvantages, and the known mechanisms of action of the paracrine effect of MSCs. With a summary of the clinical trials and preclinical studies of MSC-derived cell-free therapy, we classify the aforementioned mechanisms into angiogenesis, immunomodulation, extracellular matrix remodeling, antiapoptosis, and antioxidation. Particularly, we discuss on ways researchers have worked toward enhancing these desired properties to improve the therapeutic outcomes and the investigation of mechanobiology involved in MSC paracrine function. Lastly, we bring up the remaining challenges in this arising field and suggestions for future directions to improve our understanding and control over the potential of MSC paracrine function for myocardial restoration.

Nano-Neurotheranostics: Impact of Nanoparticles on Neural Dysfunctions and Strategies to Reduce Toxicity for Improved Efficacy

Nanotheranostics is one of the emerging research areas in the field of nanobiotechnology offering exciting promises for diagnosis, bio-separation, imaging mechanisms, hyperthermia, phototherapy, chemotherapy, drug delivery, gene delivery, among other uses. The major criteria for any nanotheranostic-materials is 1) to interact with proteins and cells without meddling with their basic activities, 2) to maintain their physical properties after surface modifications and 3) must be nontoxic. One of the challenging targets for nanotheranostics is the nervous system with major hindrances from the neurovascular units, the functional units of blood-brain barrier. As blood-brain barrier is crucial for protecting the CNS from toxins and metabolic fluctuations, most of the synthetic nanomaterials cannot pass through this barrier making it difficult for diagnosing or targeting the cells. Biodegradable nanoparticles show a promising role in this aspect. Certain neural pathologies have compromised barrier creating a path for most of the nanoparticles to enter into the cells. However, such carriers may pose a risk of side effects to non-neural tissues and their toxicity needs to be elucidated at preclinical levels. This article reviews about the different types of nanotheranostic strategies applied in nervous dysfunctions. Further, the side effects of these carriers are reviewed and appropriate methods to test the toxicity of such nano-carriers are suggested to improve the effectiveness of nano-carrier based diagnosis and treatments.

The Future of Regenerative Medicine: Cell Therapy Using Pluripotent Stem Cells and Acellular Therapies Based on Extracellular Vesicles

The rapid progress in the field of stem cell research has laid strong foundations for their use in regenerative medicine applications of injured or diseased tissues. Growing evidences indicate that some observed therapeutic outcomes of stem cell-based therapy are due to paracrine effects rather than long-term engraftment and survival of transplanted cells. Given their ability to cross biological barriers and mediate intercellular information transfer of bioactive molecules, extracellular vesicles are being explored as potential cell-free therapeutic agents. In this review, we first discuss the state of the art of regenerative medicine and its current limitations and challenges, with particular attention on pluripotent stem cell-derived products to repair organs like the eye, heart, skeletal muscle and skin. We then focus on emerging beneficial roles of extracellular vesicles to alleviate these pathological conditions and address hurdles and operational issues of this acellular strategy. Finally, we discuss future directions and examine how careful integration of different approaches presented in this review could help to potentiate therapeutic results in preclinical models and their good manufacturing practice (GMP) implementation for future clinical trials.

Local administration of stem cell-derived extracellular vesicles in a thermoresponsive hydrogel promotes a pro-healing effect in a rat model of colo-cutaneous post-surgical fistula

Extracellular vesicles (EVs), especially from stem/stromal cells (SCs), represent a cell-free alternative in regenerative medicine holding promises to promote tissue healing while providing safety and logistic advantages in comparison to cellular counterparts. Herein, we hypothesize that SC EVs, administered locally in a thermoresponsive gel, is a therapeutic strategy for managing post-surgical colo-cutaneous fistulas. This disease is a neglected and challenging condition associated to low remission rates and high refractoriness. Herein, EVs from a murine SC line were produced by a high-yield scalable method in bioreactors. The post-surgical intestinal fistula model was induced via a surgical cecostomy communicating the cecum and the skin in Wistar rats. Animals were treated just after cecostomy with PBS, thermoresponsive Pluronic F-127 hydrogel alone or containing SC EVs. A PET-monitored biodistribution investigation of SC EVs labelled with ⁸⁹Zr was performed. Fistula external orifice and output assessment, probe-based confocal laser endomicroscopy, MRI and histology were carried out for therapy follow-up. The relevance of percutaneous EV administration embedded in the hydrogel vehicle was indicated by the PET-biodistribution study. Local administration of SC EVs in the hydrogel reduced colo-cutaneous fistula diameter, output, fibrosis and inflammation while increasing the density of neo-vessels when compared to the PBS and gel groups. This multi-modal investigation pointed-out the therapeutic potential of SC EVs administered locally and in a thermoresponsive hydrogel for the management of challenging post-surgical colon fistulas in a minimally-invasive cell-free strategy.

Extracellular Vesicles as Drug Delivery Systems in Cancer

Within tumors, Cancer Stem Cell (CSC) subpopulation has an important role in maintaining growth and dissemination while preserving high resistance against current treatments. It has been shown that, when CSCs are eliminated, the surrounding Differentiated Cancer Cells (DCCs) may reverse their phenotype and gain CSC-like features to preserve tumor progression and ensure tumor survival. This strongly suggests the existence of paracrine communication within tumor cells. It is evidenced that the molecular crosstalk is at least partly mediated by Extracellular Vesicles (EVs), which are cell-derived membranous nanoparticles that contain and transport complex molecules that can affect and modify the biological behavior of distal cells and their molecular background. This ability of directional transport of small molecules prospects EVs as natural Drug Delivery Systems (DDS). EVs present inherent homing abilities and are less immunogenic than synthetic nanoparticles, in general. Currently, strong efforts are focused into the development and improvement of EV-based DDS. Even though EV-DDS have already reached early phases in clinical trials, their clinical application is still far from commercialization since protocols for EVs loading, modification and isolation need to be standardized for large-scale production. Here, we summarized recent knowledge regarding the use of EVs as natural DDS against CSCs and cancer resistance.

Extracellular vesicles as potential biomarkers and therapeutic approaches in autoimmune diseases

Extracellular vesicles are heterogeneous populations of naturally occurring secreted small vesicles. EVs function as signaling platforms to facilitate intracellular communication, which indicates the physiological or pathophysiological conditions of cells or tissues. Considering that EVs can be isolated from most body fluids and that molecular constituents could be reprogrammed according to the physiological status of the secreting cells, EVs are regarded as novel diagnostic and prognostic biomarkers for many diseases. The ability to protect encapsulated molecules from degradation in body fluids suggests the potential of EVs as biological medicines or drug delivery systems. This article focuses on the EV-associated biomarkers and therapeutic approaches in autoimmune diseases.

Extracellular vesicles from organoids and 3D culture systems

When discovered, extracellular vesicles (EVs) such as exosomes were thought of as junk carriers and a means by which the cell disposed of its waste material. Over the years, the role of EVs in cell communication has become apparent with the discovery that the nano-scale vesicles also transport RNA, DNA, and other bioactive components to and from the cells. These findings were originally made in EVs from body fluids of organisms and from in vitro two-dimensional (2D) cell culture models. Recently, organoids and other 3D multicellular in vitro models are being used to study EVs in the context of both physiologic and pathological states. However, standard, reproducible methods are lacking for EV analysis using these models. As a step toward understanding the implications of these platforms, this review provides a comprehensive picture of the progress using 3D in vitro culture models for EV analysis. Translational efforts and regulatory considerations for EV therapeutics are also briefly overviewed to understand what is needed for scale-up and, ultimately, commercialization.

Extracellular Vesicles as Nanotherapeutics for Parkinson's Disease

Extracellular vesicles (EVs) are naturally occurring membranous structures secreted by normal and diseased cells, and carrying a wide range of bioactive molecules. In the central nervous system (CNS), EVs are important in both homeostasis and pathology. Through receptor-ligand interactions, direct fusion, or endocytosis, EVs interact with their target cells. Accumulating evidence indicates that EVs play crucial roles in the pathogenesis of many neurodegenerative disorders (NDs), including Parkinson's disease (PD). PD is the second most common ND, characterized by the progressive loss of dopaminergic (DAergic) neurons within the Substantia Nigra pars compacta (SNpc). In PD, EVs are secreted by both neurons and glial cells, with either beneficial or detrimental effects, via a complex program of cell-to-cell communication. The functions of EVs in PD range from their etiopathogenetic relevance to their use as diagnostic tools and innovative carriers of therapeutics. Because they can cross the blood-brain barrier, EVs can be engineered to deliver bioactive molecules (e.g., small interfering RNAs, catalase) within the CNS. This review summarizes the latest findings regarding the role played by EVs in PD etiology, diagnosis, prognosis, and therapy, with a particular focus on their use as novel PD nanotherapeutics.

Extracellular Vesicles: New Endogenous Shuttles for miRNAs in Cancer Diagnosis and Therapy?

Extracellular Vesicles (EVs) represent a heterogeneous population of membranous cell-derived structures, including cargo-oriented exosomes and microvesicles. EVs are functionally associated with intercellular communication and play an essential role in multiple physiopathological conditions. Shedding of EVs is frequently increased in malignancies and their content, including proteins and nucleic acids, altered during carcinogenesis and cancer progression. EVs-mediated intercellular communication between tumor cells and between tumor and stromal cells can modulate, through cargo miRNA, the survival, progression, and drug resistance in cancer conditions. These consolidated suggestions and EVs’ stability in bodily fluids have led to extensive investigations on the potential employment of circulating EVs-derived miRNAs as tumor biomarkers and potential therapeutic vehicles. In this review, we highlight the current knowledge about circulating EVs-miRNAs in human cancer and the application limits of these tools, discussing their clinical utility and challenges in functions such as in biomarkers and instruments for diagnosis, prognosis, and therapy.

A scaffold laden with mesenchymal stem cell-derived exosomes for promoting endometrium regeneration and fertility restoration through macrophage immunomodulation

Endometrial traumas may cause intrauterine adhesions (IUAs), leading to infertility. Conventional methods in clinic have not solved the problem of endometrial regeneration in severe cases. Umbilical cord-derived mesenchymal stem cell (UC-MSC)-based therapies have shown some promising achievements in the treatment of IUAs. However, the limitations of potential tumorigenicity, low infusion and low retention are still controversial and restricted the clinical application of MSCs. In contrast, UC-MSC-derived exosomes exhibit a similar function to their source cells and are expected to overcome these limitations. Therefore, a novel and viable cell-free therapeutic strategy by UC-MSC-derived exosomes was proposed in this study. Here, we designed a construct of exosomes and collagen scaffold (CS/Exos) for endometrial regeneration in a rat endometrium-damage model, and investigated the regeneration mechanism through macrophage immunomodulation. The CS/Exos transplantation potently induced (i) endometrium regeneration, (ii) collagen remodeling, (iii) increased the expression of the estrogen receptor α/progesterone receptor, and (iv) restored fertility. Mechanistically, CS/Exos facilitated CD163⁺ M2 macrophage polarization, reduced inflammation, and increased anti-inflammatory responses in vivo and in vitro. By RNA-seq, miRNAs enriched in exosomes were the main mediator for exosomes-induced macrophage polarization. Overall, we demonstrated that CS/Exos treatment facilitated endometrium regeneration and fertility restoration by immunomodulatory functions of miRNAs. Our research highlights the therapeutic prospects of CS/Exos for the management of IUAs. STATEMENT OF SIGNIFICANCE: Severe endometrial traumas always result in intrauterine adhesions (IUAs) and infertility. The limited outcomes by conventional methods in the clinic make it very important to develop new strategies for endometrium regeneration and fertility restoration. In this study, an exosome-laden scaffold (CS/Exos) was designed and the transplantation of CS/Exos potently induced (i) endometrium regeneration, (ii) collagen remodeling, (iii) increased the expression of the estrogen receptor α/progesterone receptor, and (iv) restored fertility. In mechanism, the construct of CS/Exos facilitated M2 macrophage polarization, reduced inflammation, and increased anti-inflammatory responses. Furthermore, miRNAs enriched in exosomes were the main mediator for exosome-induced macrophage polarization. This study highlights the therapeutic prospects of CS/Exos and the translational application for the management of severe IUAs.

Mastering the Tools: Natural versus Artificial Vesicles in Nanomedicine

Naturally occurring extracellular vesicles and artificially made vesicles represent important tools in nanomedicine for the efficient delivery of biomolecules and drugs. Since its first appearance in the literature 50 years ago, the research on vesicles is progressing at a fast pace, with the main goal of developing carriers able to protect cargoes from degradation, as well as to deliver them in a time- and space-controlled fashion. While natural occurring vesicles have the advantage of being fully compatible with their host, artificial vesicles can be easily synthetized and functionalized according to the target to reach. Research is striving to merge the advantages of natural and artificial vesicles, in order to provide a new generation of highly performing vesicles, which would improve the therapeutic index of transported molecules. This progress report summarizes current manufacturing techniques used to produce both natural and artificial vesicles, exploring the promises and pitfalls of the different production processes. Finally, pros and cons of natural versus artificial vesicles are discussed and compared, with special regard toward the current applications of both kinds of vesicles in the healthcare field.

HIV Associated Risk Factors for Ischemic Stroke and Future Perspectives

Although retroviral therapy (ART) has changed the HIV infection from a fatal event to a chronic disease, treated HIV patients demonstrate high prevalence of HIV associated comorbidities including cardio/cerebrovascular diseases. The incidence of stroke in HIV infected subjects is three times higher than that of uninfected controls. Several clinical and postmortem studies have documented the higher incidence of ischemic stroke in HIV infected patients. The etiology of stroke in HIV infected patients remains unknown; however, several factors such as coagulopathies, opportunistic infections, vascular abnormalities, atherosclerosis and diabetes can contribute to the pathogenesis of stroke. In addition, chronic administration of ART contributes to the increased risk of stroke in HIV infected patients. Concurrently, experimental studies in murine model of ischemic stroke demonstrated that HIV infection worsens stroke outcome, increases blood brain barrier permeability and increases neuroinflammation. Additionally, residual HIV viral proteins, such as Trans-Activator of Transcription, glycoprotein 120 and Negative regulatory factor, contribute to the pathogenesis. This review presents comprehensive information detailing the risk factors contributing to ischemic stroke in HIV infected patients. It also outlines experimental evidence demonstrating the impact of HIV infection on stroke outcomes, in addition to possible novel therapeutic approaches to improve these outcomes.

Small Extracellular Vesicles Have GST Activity and Ameliorate Senescence-Related Tissue Damage

Aging is a process of cellular and tissue dysfunction characterized by different hallmarks, including cellular senescence. However, there is proof that certain features of aging and senescence can be ameliorated. Here, we provide evidence that small extracellular vesicles (sEVs) isolated from primary fibroblasts of young human donors ameliorate certain biomarkers of senescence in cells derived from old and Hutchinson-Gilford progeria syndrome donors. Importantly, sEVs from young cells ameliorate senescence in a variety of tissues in old mice. Mechanistically, we identified sEVs to have intrinsic glutathione-S-transferase activity partially due to the high levels of expression of the glutathione-related protein (GSTM2). Transfection of recombinant GSTM2 into sEVs derived from old fibroblasts restores their antioxidant capacity. sEVs increase the levels of reduced glutathione and decrease oxidative stress and lipid peroxidation both in vivo and in vitro. Altogether, our data provide an indication of the potential of sEVs as regenerative therapy in aging.

Surface functionalization strategies of extracellular vesicles

Extracellular vesicles (EVs) are lipid-protein bilayer vesicular constructs secreted to the extracellular spaces by cells. All cells secrete EVs as a regular biological process that appears to be conserved throughout the evolution. Owing to the rich molecular cargo of EVs with specific lipid and protein content and documented role in cellular communication, EVs have been exploited as a versatile agent in the biomedical arena, including as diagnostic, drug delivery, immunomodulatory, and therapeutic agents. With these multifaceted applications in the biomedical field, the functionalization of EVs to add diverse functionality has garnered rapid attention. EVs can be functionalized with an exogenous imaging and targeting moiety that allows for the target specificity and the real-time tracking of EVs for diagnostic and therapeutic applications. Importantly, such added functionalities can be used to explore EVs' biogenesis pathway and their role in cellular communication, which can lead to a better understanding of EVs' cellular mechanisms and processes. In this report, we have reviewed the existing surface functionalization strategies of EVs and broadly classified them into three major approaches: physical, biological, and chemical approaches. The physical approach of EV functionalization includes methods like sonication, extrusion, and freeze-thaw that can change the surface properties of EVs via membrane rearrangements. The biological approach includes genetically and metabolically engineering cells to express protein or cargo molecules of interest in secreted EVs. The chemical approach includes different facile click type chemistries that can be used to covalently conjugate the EV lipid or protein construct with different linker groups for diverse functionality. Different chemistries like thiol-maleimide, EDC/NHS, azide-alkyne cycloaddition, and amidation chemistry have been discussed to functionalize EVs. Finally, a comparative discussion of all approaches has been done focusing on the significance of each approach. The collective knowledge of the major approach of surface functionalization can be used to improve the limitation of one technique by combining it with another. An optimized surface functionalization approach developed accordingly can efficiently add required functionality to EVs while maintaining their natural integrity.

MicroRNA Nanotherapeutics for Lung Targeting. Insights into Pulmonary Hypertension

In this review, the potential future role of microRNA-based therapies and their specific application in lung diseases is reported with special attention to pulmonary hypertension. Current limitations of these therapies will be pointed out in order to address the challenges that they need to face to reach clinical applications. In this context, the encapsulation of microRNA-based therapies in nanovectors has shown improvements as compared to chemically modified microRNAs toward enhanced stability, efficacy, reduced side effects, and local administration. All these concepts will contextualize in this review the recent achievements and expectations reported for the treatment of pulmonary hypertension.

Alzheimer's disease: phenotypic approaches using disease models and the targeting of tau protein

Introduction: Hyperphosphorylated and aggregated tau protein is the main hallmark of a class of neurodegenerative disorders known as tauopathies. Tau is a microtubule-binding protein which is important for microtubule assembly and stabilization, for proper axonal transport and overall neuronal integrity. However, in tauopathies, tau undergoes aberrant post-translational modifications that fundamentally affect its normal function. The etiology of these devastating diseases is unclear and there is no treatment for these disorders.Areas covered: This review examines the neurobiology of tau, tau post-translational modifications, and tau pathophysiology. Progress regarding the effort to identify and assess novel tau-targeted therapeutic strategies in preclinical studies is also discussed. We performed a search on PubMed of the relevant literature published between 1995 and 2020.Expert opinion: Tau diversity and the lack of clinically available test to diagnose and identify tauopathies are major obstacles; they represent a possible reason for the lack of success of clinical trials. However, given the encouraging advances in PET tau imaging and tau neurobiology, we believe that a more personalized approach could be on the horizon and that this will be key to addressing the heterogeneity of tau pathology.

Human Pluripotent Stem Cell-Derived Extracellular Vesicles: Characteristics and Applications

Extracellular vesicles (EVs), including exosomes and microvesicles, are found to play an important role in various biological processes and maintaining tissue homeostasis. Because of the protective effects, stem cell-derived EVs can be used to reduce oxidative stress and apoptosis in the recipient cells. In addition, EVs/exosomes have been used as directional communication tools between stem cells and parenchymal cells, giving them the ability to serve as biomarkers. Likewise, altered EVs/exosomes can be utilized for drug delivery by loading with proteins, small interfering RNAs, and viral vectors, in particular, because EVs/exosomes are able to cross the blood-brain barrier. In this review article, the properties of human induced pluripotent stem cell (iPSC)-derived EVs are discussed. The biogenesis, that is, how EVs originate in the endosomal compartment or from the cell layer of microvesicles, EV composition, the available methods of purification, and characterizations of EVs/exosomes are summarized. In particular, EVs/exosomes derived from iPSCs of different lineage specifications and the applications of these stem cell-derived exosomes in neurological diseases are discussed. Impact statement In this review, we summarized the work related to extracellular vesicles (EVs) derived from human pluripotent stem cells (hPSCs). In particular, EVs/exosomes derived from hPSCs of different lineage specifications and the applications of these stem cell-derived exosomes in neurological diseases are discussed. The results highlight the important role of cell-cell interactions in neural cellular phenotype and neurodegeneration. The findings reported in this article are significant for pluripotent stem cell-derived cell-free products toward applications in stem cell-based therapies.

The Role of Bone Marrow Mesenchymal Stem Cell Derived Extracellular Vesicles (MSC-EVs) in Normal and Abnormal Hematopoiesis and Their Therapeutic Potential

Mesenchymal stem cells (MSCs) represent a heterogeneous cellular population responsible for the support, maintenance, and regulation of normal hematopoietic stem cells (HSCs). In many hematological malignancies, however, MSCs are deregulated and may create an inhibitory microenvironment able to induce the disease initiation and/or progression. MSCs secrete soluble factors including extracellular vesicles (EVs), which may influence the bone marrow (BM) microenvironment via paracrine mechanisms. MSC-derived EVs (MSC-EVs) may even mimic the effects of MSCs from which they originate. Therefore, MSC-EVs contribute to the BM homeostasis but may also display multiple roles in the induction and maintenance of abnormal hematopoiesis. Compared to MSCs, MSC-EVs have been considered a more promising tool for therapeutic purposes including the prevention and treatment of Graft Versus Host Disease (GVHD) following allogenic HSC transplantation (HSCT). There are, however, still unanswered questions such as the molecular and cellular mechanisms associated with the supportive effect of MSC-EVs, the impact of the isolation, purification, large-scale production, storage conditions, MSC source, and donor characteristics on MSC-EV biological effects as well as the optimal dose and safety for clinical usage. This review summarizes the role of MSC-EVs in normal and malignant hematopoiesis and their potential contribution in treating GVHD.

Exosomes Could Offer New Options to Combat the Long-Term Complications Inflicted by Gestational Diabetes Mellitus

Gestational diabetes Mellitus (GDM) is a complex clinical condition that promotes pelvic floor myopathy, thus predisposing sufferers to urinary incontinence (UI). GDM usually regresses after birth. Nonetheless, a GDM history is associated with higher risk of subsequently developing type 2 diabetes, cardiovascular diseases (CVD) and UI. Some aspects of the pathophysiology of GDM remain unclear and the associated pathologies (outcomes) are poorly addressed, simultaneously raising public health costs and diminishing women's quality of life. Exosomes are small extracellular vesicles produced and actively secreted by cells as part of their intercellular communication system. Exosomes are heterogenous in their cargo and depending on the cell sources and environment, they can mediate both pathogenetic and therapeutic functions. With the advancement in knowledge of exosomes, new perspectives have emerged to support the mechanistic understanding, prediction/diagnosis and ultimately, treatment of the post-GMD outcomes. Here, we will review recent advances in knowledge of the role of exosomes in GDM and related areas and discuss the possibilities for translating exosomes as therapeutic agents in the GDM clinical setting.

Lipidomics and RNA sequencing reveal a novel subpopulation of nanovesicle within extracellular matrix biomaterials

Biomaterials composed of extracellular matrix (ECM) provide both mechanical support and a reservoir of constructive signaling molecules that promote functional tissue repair. Recently, matrix-bound nanovesicles (MBVs) have been reported as an integral component of ECM bioscaffolds. Although liquid-phase extracellular vesicles (EVs) have been the subject of intense investigation, their similarity to MBV is limited to size and shape. Liquid chromatography-mass spectrometry (LC-MS)-based lipidomics and redox lipidomics were used to conduct a detailed comparison of liquid-phase EV and MBV phospholipids. Combined with comprehensive RNA sequencing and bioinformatic analysis of the intravesicular cargo, we show that MBVs are a distinct and unique subpopulation of EV and a distinguishing feature of ECM-based biomaterials. The results begin to identify the differential biologic activities mediated by EV that are secreted by tissue-resident cells and deposited within the ECM.

Role of Non-Coding RNAs in the Development of Targeted Therapy and Immunotherapy Approaches for Chronic Lymphocytic Leukemia

In the past decade, novel targeted therapy approaches, such as BTK inhibitors and Bcl2 blockers, and innovative treatments that regulate the immune response against cancer cells, such as monoclonal antibodies, CAR-T cell therapy, and immunomodulatory molecules, have been established to provide support for the treatment of patients. However, drug resistance development and relapse are still major challenges in CLL treatment. Several studies revealed that non-coding RNAs have a main role in the development and progression of CLL. Specifically, microRNAs (miRs) and tRNA-derived small-RNAs (tsRNAs) were shown to be outstanding biomarkers that can be used to diagnose and monitor the disease and to possibly anticipate drug resistance and relapse, thus supporting physicians in the selection of treatment regimens tailored to the patient needs. In this review, we will summarize the most recent discoveries in the field of targeted therapy and immunotherapy for CLL and discuss the role of ncRNAs in the development of novel drugs and combination regimens for CLL patients.

Exosome and Biomimetic Nanoparticle Therapies for Cardiac Regenerative Medicine

Exosomes and biomimetic nanoparticles have great potential to develop into a wide-scale therapeutic platform within the regenerative medicine industry. Exosomes, a subgroup of EVs with diameter ranging from 30-100 nm, have recently gained attention as an innovative approach for the treatment of various diseases, including heart disease. Their beneficial factors and regenerative properties can be contrasted with various cell types. Various biomimetic nanoparticles have also emerged as a unique platform in regenerative medicine. Biomimetic nanoparticles are a drug delivery platform, which have the ability to contain both biological and fabricated components to improve therapeutic efficiency and targeting. The novelty of these platforms holds promise for future clinical translation upon further investigation. In order for both exosome therapeutics and biomimetic nanoparticles to translate into large-scale clinical treatment, numerous factors must first be considered and improved. Standardization of different protocols, from exosome isolation to storage conditions, must be optimized to ensure batches are pure. Standardization is also important to ensure no variability in this process across studies, thus making it easier to interpret data across different disease models and treatments. Expansion of clinical trials incorporating both biomimetic nanoparticles and exosomes will require a standardization of fabrication and isolation techniques, as well as stricter regulations to ensure reproducibility across various studies and disease models. This review will summarize current research on exosome therapeutics and the application of biomimetic nanoparticles in cardiac regenerative medicine, as well as applications for exosome expansion and delivery on a large clinical scale.

Advances in imaging strategies for in vivo tracking of exosomes

Exosomes have many biological functions as short- and long distance nanocarriers for cell-to-cell communication. They allow the exchange of complex information between cells, and thereby modulate various processes such as homeostasis, immune response and angiogenesis, in both physiological and pathological conditions. In addition, due to their unique abilities of migration, targeting, and selective internalization into specific cells, they are promising delivery vectors. As such, they provide a potentially new field in diagnostics and treatment, and may serve as an alternative to cell-based therapeutic approaches. However, a major drawback for translating exosome treatment to the clinic is that current understanding of these endogenous vesicles is insufficient, especially in regards to their in vivo behavior. Tracking exosomes in vivo can provide important knowledge regarding their biodistribution, migration abilities, toxicity, biological role, communication capabilities, and mechanism of action. Therefore, the development of efficient, sensitive and biocompatible exosome labeling and imaging techniques is highly desired. Recent studies have developed different methods for exosome labeling and imaging, which have allowed for in vivo investigation of their bio-distribution, physiological functions, migration, and targeting mechanisms. These improved imaging capabilities are expected to greatly advance exosome-based nanomedicine applications. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Mesenchymal stromal cell secretome as a therapeutic strategy for traumatic brain injury

Traumatic brain injury (TBI) is a global health problem that is a common cause of disability and mortality. Despite the availability of many treatment options, none is capable of restoring functional and structural recovery of the damaged brain. Both the results of preclinical and clinical studies suggest the use of mesenchymal stromal cells (MSCs) as a therapeutic strategy for structural and functional recovery in TBI. However, recent evidence shows that the neuroprotective potential of MSCs is due to multiple secretions of bioactive molecules that modulate tissue microenvironment for tissue repair and regeneration. The results of preclinical studies indicate the therapeutic benefits of MSC secretome in TBI. Soluble bioactive molecules and extracellular vesicles are the various factors secreted by MSCs that can induce neurogenesis, angiogenesis, neovascularization, and anti-inflammatory activities. This review highlights the neuroprotective effect of MSC secretome for the treatment of TBI. In addition, the possible challenges of secretome as biotherapeutics are identified and how some of the issues raised could be overcome for effective clinical application are also discussed.

Differential Effects of Extracellular Vesicles of Lineage-Specific Human Pluripotent Stem Cells on the Cellular Behaviors of Isogenic Cortical Spheroids

Extracellular vesicles (EVs) contribute to a variety of signaling processes and the overall physiological and pathological states of stem cells and tissues. Human induced pluripotent stem cells (hiPSCs) have unique characteristics that can mimic embryonic tissue development. There is growing interest in the use of EVs derived from hiPSCs as therapeutics, biomarkers, and drug delivery vehicles. However, little is known about the characteristics of EVs secreted by hiPSCs and paracrine signaling during tissue morphogenesis and lineage specification. Methods: In this study, the physical and biological properties of EVs isolated from hiPSC-derived neural progenitors (ectoderm), hiPSC-derived cardiac cells (mesoderm), and the undifferentiated hiPSCs (healthy iPSK3 and Alzheimer’s-associated SY-UBH lines) were analyzed. Results: Nanoparticle tracking analysis and electron microscopy results indicate that hiPSC-derived EVs have an average size of 100–250 nm. Immunoblot analyses confirmed the enrichment of exosomal markers Alix, CD63, TSG101, and Hsc70 in the purified EV preparations. MicroRNAs including miR-133, miR-155, miR-221, and miR-34a were differently expressed in the EVs isolated from distinct hiPSC lineages. Treatment of cortical spheroids with hiPSC-EVs in vitro resulted in enhanced cell proliferation (indicated by BrdU+ cells) and axonal growth (indicated by β-tubulin III staining). Furthermore, hiPSC-derived EVs exhibited neural protective abilities in Aβ42 oligomer-treated cultures, enhancing cell viability and reducing oxidative stress. Our results demonstrate that the paracrine signaling provided by tissue context-dependent EVs derived from hiPSCs elicit distinct responses to impact the physiological state of cortical spheroids. Overall, this study advances our understanding of cell‒cell communication in the stem cell microenvironment and provides possible therapeutic options for treating neural degeneration.

Propagation of Tau via Extracellular Vesicles

Extracellular vesicles (EVs), like exosomes, play a critical role in physiological processes, including synaptic transmission and nerve regeneration. However, exosomes in particular can also contribute to the development of neurodegenerative conditions such as Alzheimer's disease (AD), Parkinson's disease, and prion diseases. All of these disorders are characterized by protein aggregation and deposition in specific regions of the brain. Several lines of evidence indicate that protein in exosomes is released from affected neurons and propagated along neuroanatomically connected regions of the brain, thus spreading the neurodegenerative disease. Also, different cell types contribute to the progression of tauopathy, such as microglia. Several groups have reported tau release via exosomes by cultured neurons or cells overexpressing human tau. Although the exact mechanisms underlying the propagation of protein aggregates are not fully understood, recent findings have implicated EVs in this process. The AD brain has two hallmarks, namely the presence of amyloid-β-containing plaques and neurofibrillary tangles, the latter formed by hyperphosphorylated tau protein. Both amyloid peptide and tau protein are present in specific exosomes. This review summarizes recent advances in our understanding of exosomes in the pathology of AD, with a special focus on tau protein.

Extracellular Vesicles in the Oviduct: Progress, Challenges and Implications for the Reproductive Success

The oviduct is the anatomical part of the female reproductive tract where the early reproductive events take place, from gamete transport, fertilization and early embryo development to the delivery of a competent embryo to the uterus, which can implant and develop to term. The success of all these events rely upon a two-way dialogue between the oviduct (lining epithelium and secretions) and the gametes/embryo(s). Recently, extracellular vesicles (EVs) have been identified as major components of oviductal secretions and pointed to as mediators of the gamete/embryo-maternal interactions. EVs, comprising exosomes and microvesicles, have emerged as important agents of cell-to-cell communication by the transfer of biomolecules (i.e., mRNAs, miRNAs, proteins) that can modulate the activities of recipient cells. Here, we provide the current knowledge of EVs in the oviductal environment, from isolation to characterization, and a description of the EVs molecular content and associated functional aspects in different species. The potential role of oviductal EVs (oEVs) as modulators of gamete/embryo-oviduct interactions and their implications in the success of early reproductive events is addressed. Lastly, we discuss current challenges and future directions towards the potential application of oEVs as therapeutic vectors to improve pregnancy disorders, infertility problems and increase the success of assisted reproductive technologies.

Mesenchymal Stem Cell-Derived Extracellular Vesicle Therapy for Stroke: Challenges and Progress

Stroke is the leading cause of physical disability among adults. Stem cells such as mesenchymal stem cells (MSCs) secrete a variety of bioactive substances, including trophic factors and extracellular vesicles (EVs), into the injured brain, which may be associated with enhanced neurogenesis, angiogenesis, and neuroprotection. EVs are circular membrane fragments (30 nm−1 μm) that are shed from the cell surface and harbor proteins, microRNAs, etc. Since 2013 when it was first reported that intravenous application of MSC-derived EVs in a stroke rat model improved neurological outcomes and increased angiogenesis and neurogenesis, many preclinical studies have shown that stem cell-derived EVs can be used in stroke therapy, as an alternative approach to stem cell infusion. Although scientific research regarding MSC-derived EV therapeutics is still at an early stage, research is rapidly increasing and is demonstrating a promising approach for patients with severe stroke. MSC therapies have already been tested in preclinical studies and clinical trials, and EV-mediated therapy has unique advantages over cell therapies in stroke patients, in terms of biodistribution (overcoming the first pass effect and crossing the blood-brain-barrier), cell-free paradigm (avoidance of cell-related problems such as tumor formation and infarcts caused by vascular occlusion), whilst offering an off-the-shelf approach for acute ischemic stroke. Recently, advances have been made in the understanding of the function and biogenesis of EVs and EVs therapeutics for various diseases. This review presents the most recent advances in MSC-derived EV therapy for stroke, focusing on the application of this strategy for stroke patients.

THE EFFECT OF MESENCHYMAL STEM CELL DERIVED MICROVESICLES IN REPAIR OF FEMORAL CHONDRAL DEFECTS IN DOGS

Mesenchymal stem cells (MSCs) releases in culture extracellular vesicles called microvesicles (MVs). MVs have beneficial cytokines that prevent progression of the disease and help in the regeneration process. This study is aimed to evaluate the effect of MSCs derived MVs in repair of induced chondral defect in a dog model. Methods: Chondral defects were created surgically ([Formula: see text][Formula: see text]mm) in both femoral condyles of nine dogs, autologous MSCs were isolated and MVs were prepared and injected intraarticularly in the right joint. The left joint was injected with normal saline as control negative. Evaluation of the treatment after first injection was carried out by physical examination and histopathology at different time periods ([Formula: see text]½, 3 and 6 months). Results: Treated joints showed marked degree of cartilage regeneration and restoration of chondral histomorphological picture on the contrary of the control joints that showed deterioration over time and defect filling with only fibrous tissue forming a fibrocartilage at the end of six months period. Conclusion: We demonstrated in this study that administration of MVs was effective on the functional and morphological recovery of the injured cartilage and could be exploited as a cell free therapeutic approach in regenerative medicine.

Thermoresponsive Gel Embedded with Adipose Stem-Cell-Derived Extracellular Vesicles Promotes Esophageal Fistula Healing in a Thermo-Actuated Delivery Strategy

Extracellular vesicles (EVs) are increasingly envisioned as the next generation of biological pro-regenerative nanotherapeutic agents, as has already been demonstrated for heart, kidney, liver, and brain tissues; lung injury repair; and skin regeneration. Herein, we explore another potential EV therapeutic application, fistula healing, together with a local minimally invasive delivery strategy. Allogenic extracellular vesicles (EVs) from adipose tissue-derived stromal cells (ASCs) are administered in a porcine fistula model through a thermoresponsive Pluronic F-127 (PF-127) gel, injected locally at 4 °C and gelling at body temperature to retain EVs in the entire fistula tract. Complete fistula healing is reported to be 100% for the gel plus EVs group, 67% for the gel group, and 0% for the control, supporting the therapeutic use of Pluronic F-127 gel alone or combined with EVs. However, only the combination of gel and EVs results in a statistically significant (i) reduction of fibrosis, (ii) decline of inflammatory response, (iii) decrease in the density of myofibroblasts, and (iv) increase of angiogenesis. Overall, we demonstrate that ASC-EV delivery into a PF-127 gel represents a successful local minimally invasive strategy to induce a therapeutic effect in a swine fistula model. Our study presents prospects for EV administration strategies and for the management of post-operative fistulas.

The extracellular vesicles-derived from mesenchymal stromal cells: A new therapeutic option in regenerative medicine

Mesenchymal stem cells (MSCs) are adult multipotent cells that due to their ability to homing to damaged tissues and differentiate into specialized cells, are remarkable cells in the field of regenerative medicine. It's suggested that the predominant mechanism of MSCs in tissue repair might be related to their paracrine activity. The utilization of MSCs for tissue repair is initially based on the differentiation ability of these cells; however now it has been revealed that only a small fraction of the transplanted MSCs actually fuse and survive in host tissues. Indeed, MSCs supply the microenvironment with the secretion of soluble trophic factors, survival signals and the release of extracellular vesicles (EVs) such as exosome. Also, the paracrine activity of EVs could mediate the cellular communication to induce cell-differentiation/self-renewal. Recent findings suggest that EVs released by MSCs may also be critical in the physiological function of these cells. This review provides an overview of MSC-derived extracellular vesicles as a hopeful opportunity to advance novel cell-free therapy strategies that might prevail over the obstacles and risks associated with the use of native or engineered stem cells. EVs are very stable; they can pass the biological barriers without rejection and can shuttle bioactive molecules from one cell to another, causing the exchange of genetic information and reprogramming of the recipient cells. Moreover, extracellular vesicles may provide therapeutic cargo for a wide range of diseases and cancer therapy.

Emerging role of exosome-mediated intercellular communication in vascular remodeling

Vascular remodeling refers to the alternations of function and structure in vasculature. A complex autocrine/paracrine set of cellular interaction is involved in vascular remodeling. Exosome, a newly identified natural nanocarrier and intercellular messenger, plays a pivotal role in regulating cell-to-cell communication. Exosome emerges as an important mediator in the process of vascular remodeling, showing the most prognostic and therapeutic potent in vascular diseases. Benefiting from exosomal trafficking, the vasculature can not only maintain its function and structure in physiological condition, but also adapt itself in pathological status. In this review, we will represent the roles of exosomes in angiogenesis, endothelial function and cardiac regeneration. In addition, greatly depending on the pathophysiological status of donor cells and peripheral micro-circumstance, the exosomal content could alter, which makes exosomes exhibit pleiotropic effects in vascular diseases. Hence, the diverse effects of exosomes in vascular diseases including atherosclerosis, neointima formation and vascular repair, primary hypertension, pulmonary artery hypertension, and aortic aneurysm will be discussed. Finally, the translational appliances targeting exosomes will be concluded by providing updated applications of engineered exosomes in clinic.

Tau Spreading Mechanisms; Implications for Dysfunctional Tauopathies

Tauopathies comprise a group of progressive age-associated neurodegenerative diseases where tau protein deposits are found as the predominant pathological signature (primary tauopathies) or in combination with the presence of other toxic aggregates (secondary tauopathies). In recent years, emerging evidence suggests that abnormal tau accumulation is mediated through spreading of seeds of the protein from cell to cell, favouring the hypothesis of a prion-like transmission of tau to explain the propagation of the pathology. This would also support the concept that the pathology initiates in a very small part of the brain before becoming symptomatic and spreads across the brain over time. To date, many key questions still remain unclear, such as the nature of the tau species involved in the spreading, the precise seeding/template and uptaking mechanisms or the selectivity explaining why certain neurons are affected and some others are not. A better understanding of the tau spreading machinery will contribute to the development of new therapeutic approaches focused on halting the abnormal propagation, offering also new perspectives for early diagnosis and preventive therapies. In this review, we will cover the most recent advances in tau spreading mechanisms as well as the implications of these findings for dysfunctional tauopathies.

Potential Role of Exosomes in Mending a Broken Heart: Nanoshuttles Propelling Future Clinical Therapeutics Forward

Stem cell transplantation therapy is a promising adjunct for regenerating damaged heart tissue; however, only modest improvements in cardiac function have been observed due to poor survival of transplanted cells in the ischemic heart. Therefore, there remains an unmet need for therapies that can aid in attenuating cardiac damage. Recent studies have demonstrated that exosomes released by stem cells could serve as a potential cell-free therapeutic for cardiac repair. These exosomes/nanoshuttles, once thought to be merely a method of waste disposal, have been shown to play a crucial role in physiological functions including short- and long-distance intercellular communication. In this review, we have summarized studies demonstrating the potential role of exosomes in improving cardiac function, attenuating cardiac fibrosis, stimulating angiogenesis, and modulating miRNA expression. Furthermore, exosomes carry an important cargo of miRNAs and proteins that could play an important role as a diagnostic marker for cardiovascular disease post-myocardial infarction. Although there is promising evidence from preclinical studies that exosomes released by stem cells could serve as a potential cell-free therapeutic for myocardial repair, there are several challenges that need to be addressed before exosomes could be fully utilized as off-the-shelf therapeutics for cardiac repair.

A Systematic Evaluation of Factors Affecting Extracellular Vesicle Uptake by Breast Cancer Cells

Extracellular vesicles (EVs) are nanometer-scale particles that are secreted by cells and mediate intercellular communication by transferring biomolecules between cells. Harnessing this mechanism for therapeutic biomolecule delivery represents a promising frontier for regenerative medicine and other clinical applications. One challenge to realizing this goal is that to date, our understanding of which factors affect EV uptake by recipient cells remains incomplete. In this study, we systematically investigated such delivery questions in the context of breast cancer cells, which are one of the most well-studied cell types with respect to EV delivery and therefore comprise a facile model system for this investigation. By displaying various targeting peptides on the EV surface, we observed that although displaying GE11 on EVs modestly increased uptake by MCF-7 cells, neuropeptide Y (NPY) display had no effect on uptake by the same cells. In contrast, neurotensin (NTS) and urokinase plasminogen activator (uPA) display reduced EV uptake by MDA-MB-231 cells. Interestingly, EV uptake rate did not depend on the source of the EVs; breast cancer cells demonstrated no increase in uptake on administration of breast cancer-derived EVs in comparison to HEK293FT-derived EVs. Moreover, EV uptake was greatly enhanced by delivery in the presence of polybrene and spinoculation, suggesting that maximal EV uptake rates are much greater than those observed under basal conditions in cell culture. By investigating how the cell's environment might provide cues that impact EV uptake, we also observed that culturing cells on soft matrices significantly enhanced EV uptake, compared to culturing on stiff tissue culture polystyrene. Each of these observations provides insights into the factors impacting EV uptake by breast cancer cells, while also providing a basis of comparison for systematically evaluating and perhaps enhancing EV uptake by various cell types.

Towards Therapeutic Delivery of Extracellular Vesicles: Strategies for In Vivo Tracking and Biodistribution Analysis

Extracellular vesicles (EVs), such as microvesicles and exosomes, are membranous structures containing bioactive material released by several cells types, including mesenchymal stem/stromal cells (MSCs). Increasing lines of evidences point to EVs as paracrine mediators of the beneficial effects on tissue remodeling associated with cell therapy. Administration of MSCs-derived EVs has therefore the potential to open new and safer therapeutic avenues, alternative to cell-based approaches, for degenerative diseases. However, an enhanced knowledge about in vivo EVs trafficking upon delivery is required before effective clinical translation. Only a few studies have focused on the biodistribution analysis of exogenously administered MSCs-derived EVs. Nevertheless, current strategies for in vivo tracking in animal models have provided valuable insights on the biodistribution upon systemic delivery of EVs isolated from several cellular sources, indicating in liver, spleen, and lungs the preferential target organs. Different strategies for targeting EVs to specific tissues to enhance their therapeutic efficacy and reduce possible off-target effects have been investigated. Here, in the context of a possible clinical application of MSC-derived EVs for tissue regeneration, we review the existing strategies for in vivo tracking and targeting of EVs isolated from different cellular sources and the studies elucidating the biodistribution of exogenously administered EVs.