Extracellular vesicles: Critical bilateral communicators in periphery-brain crosstalk in central nervous system disorders

Brain-Periphery Axes: The Potential Role of Extracellular Vesicles-Delivered miRNAs

Bidirectional communication between the central nervous system (CNS) and peripheral organs and tissue has been widely documented in physiological and pathological conditions. This communication relies on the bilateral transmission of signaling molecules and substances that circulate throughout the body and reach their target site(s) via the blood and other biological fluids (e.g., the cerebrospinal fluid, the lymph). One of the mechanisms by which these molecular messengers are exchanged is through the secretion of extracellular vesicles (EVs). EVs are known to mediate cell-to-cell communication by delivering biological molecules, including nucleic acids, proteins, lipids, and various other bioactive regulators. Moreover, EVs can cross the blood-brain barrier (BBB), enabling direct communication between the periphery and the brain. In particular, the delivery of microRNAs (miRNAs) can modulate the expression profiles of recipient cells, thereby influencing their functions. This review synthesizes current findings about the brain-periphery cross-talk mediated by EVs-delivered miRNAs. Although this mechanism has been definitively shown in a few cases, much evidence indirectly indicates that it could mediate brain-peripherical organs/tissue communication, especially in pathological conditions. Therefore, understanding this process could provide valuable insights for the treatment and management of neurological and systemic diseases.

Role of Redox Homeostasis in the Communication Between Brain and Liver Through Extracellular Vesicles

Extracellular vesicles (EVs) are small, membrane-bound particles secreted by cells into the extracellular environment, playing an increasingly recognized role in inter-organ communication and the regulation of various physiological processes. Regarding the redox homeostasis context, EVs play a pivotal role in propagating and mitigating oxidative stress signals across different organs. Cells under oxidative stress release EVs containing signaling molecules that can influence the redox status of distant cells and tissues. EVs are starting to be recognized as contributors to brain-liver communication. Therefore, in this review, we show how redox imbalance can affect the release of EVs in the brain and liver. We propose EVs as mediators of redox homeostasis in the brain-liver axis.

Extracellular Vesicles in the Central Nervous System: A Novel Mechanism of Neuronal Cell Communication

Cell-to-cell communication is essential for the appropriate development and maintenance of homeostatic conditions in the central nervous system. Extracellular vesicles have recently come to the forefront of neuroscience as novel vehicles for the transfer of complex signals between neuronal cells. Extracellular vesicles are membrane-bound carriers packed with proteins, metabolites, and nucleic acids (including DNA, mRNA, and microRNAs) that contain the elements present in the cell they originate from. Since their discovery, extracellular vesicles have been studied extensively and have opened up new understanding of cell-cell communication; they may cross the blood-brain barrier in a bidirectional way from the bloodstream to the brain parenchyma and vice versa, and play a key role in brain-periphery communication in physiology as well as pathology. Neurons and glial cells in the central nervous system release extracellular vesicles to the interstitial fluid of the brain and spinal cord parenchyma. Extracellular vesicles contain proteins, nucleic acids, lipids, carbohydrates, and primary and secondary metabolites. that can be taken up by and modulate the behaviour of neighbouring recipient cells. The functions of extracellular vesicles have been extensively studied in the context of neurodegenerative diseases. The purpose of this review is to analyse the role extracellular vesicles extracellular vesicles in central nervous system cell communication, with particular emphasis on the contribution of extracellular vesicles from different central nervous system cell types in maintaining or altering central nervous system homeostasis.

Involvement of Astrocytes in the Formation, Maintenance, and Function of the Blood-Brain Barrier

The blood-brain barrier (BBB) is a fundamental structure that protects the composition of the brain by determining which ions, metabolites, and nutrients are allowed to enter the brain from the blood or to leave it towards the circulation. The BBB is structurally composed of a layer of brain capillary endothelial cells (BCECs) bound to each other through tight junctions (TJs). However, its development as well as maintenance and properties are controlled by the other brain cells that contact the BCECs: pericytes, glial cells, and even neurons themselves. Astrocytes seem, in particular, to have a very important role in determining and controlling most properties of the BBB. Here, we will focus on these latter cells, since the comprehension of their roles in brain physiology has been continuously expanding, even including the ability to participate in neurotransmission and in complex functions such as learning and memory. Accordingly, pathological conditions that alter astrocytic functions can alter the BBB's integrity, thus compromising many brain activities. In this review, we will also refer to different kinds of in vitro BBB models used to study the BBB's properties, evidencing its modifications under pathological conditions.

Unraveling the Emerging Niche Role of Extracellular Vesicles (EVs) in Traumatic Brain Injury (TBI)

Extracellular vesicles or exosomes, often known as EVs, have acquired significant attention in the investigations of traumatic brain injury (TBI) and have a distinct advantage in actively researching the fundamental mechanisms underlying various clinical symptoms and diagnosing the wide range of traumatic brain injury cases. The mesenchymal stem cells (MSCs) can produce and release exosomes, which offer therapeutic benefits. Exosomes are tiny membranous vesicles produced by various cellular entities originating from endosomes. Several studies have reported that administering MSC-derived exosomes through intravenous infusions improves neurological recovery and promotes neuroplasticity in rats with traumatic brain damage. The therapeutic advantages of exosomes can be attributed to the microRNAs (miRNAs), which are small non-coding regulatory RNAs that significantly impact the regulation of posttranscriptional genes. Exosome-based therapies, which do not involve cells, have lately gained interest as a potential breakthrough in enhancing neuroplasticity and accelerating neurological recovery for various brain injuries and neurodegenerative diseases. This article explores the benefits and drawbacks of exosome treatment for traumatic brain injury while emphasizing the latest advancements in this field with clinical significance.

Microbial Extracellular Vesicles in Host-Microbiota Interactions

Extracellular vesicles have emerged as key players in cellular communication, influencing various physiological processes and pathophysiological progression, including digestion, immune response, and tissue repairs. Recently, a class of EVs derived from microbial communities has gained significant attention due to their pivotal role in intercellular communication and their potential as biomarkers and biotherapeutic agents. Microbial EVs are membrane-bound molecules encapsulating bioactive metabolites that modulate host physiological and pathological processes. This chapter discusses the evolving history of microbiota-produced EVs, including their discovery, characterization, current research status, and their diverse mechanisms of interaction with other microbes and hosts. This review also highlights the importance of EVs in health and disease and discusses recent research that shows promising results for the therapeutic potential of EVs.