Olfactory ensheathing glia

Olfactory ensheathing glia (OEG), also known as olfactory ensheathing cells (OECs) or olfactory ensheathing glial cells, are a type of macroglia (radial glia) found in the nervous system. They are also known as olfactory Schwann cells because they ensheath the non-myelinated axons of olfactory neurons in a similar way to which Schwann cells ensheath non-myelinated peripheral neurons. They also share the property of assisting axonal regeneration. OEG are capable of phagocytosing axonal debris in vivo, and in vitro they phagocytose bacteria. Olfactory glia that express LYZ are thought to play an important role in immunoprotection in the mucosa, where neurons are directly exposed to the external environment. OEG have been tested successfully in experimental axonal regeneration in adult rats with traumatic spinal cord damage, and clinical trials are currently being conducted to obtain more information on spinal cord injuries and other neurodegenerative diseases. Olfactory ensheathing glia (OEG), also known as olfactory ensheathing cells (OECs) or olfactory ensheathing glial cells, are a type of macroglia (radial glia) found in the nervous system. They are also known as olfactory Schwann cells because they ensheath the non-myelinated axons of olfactory neurons in a similar way to which Schwann cells ensheath non-myelinated peripheral neurons. They also share the property of assisting axonal regeneration. OEG are capable of phagocytosing axonal debris in vivo, and in vitro they phagocytose bacteria. Olfactory glia that express LYZ are thought to play an important role in immunoprotection in the mucosa, where neurons are directly exposed to the external environment. OEG have been tested successfully in experimental axonal regeneration in adult rats with traumatic spinal cord damage, and clinical trials are currently being conducted to obtain more information on spinal cord injuries and other neurodegenerative diseases. In the peripheral nervous system OEG are dispersed within the olfactory epithelium and the olfactory nerve. In the central nervous system, OEG are found within the outer two layers of the olfactory bulb. During development, primitive olfactory neurons extend their axons from the olfactory placode, through the mesenchyme, towards the telencephalic vesicle. After reaching the telencephalic vesicle, a small layer of cells and axons cover the vesicle. Olfactory axons invade the basal lamina of the glia limitans and the olfactory bulb to create the olfactory nerve and glomerular layers. A fraction of the epithelial migrating precursors give rise to olfactory ensheathing glia that inhabit the olfactory nerve and glomerular layers. OEG and astrocytes interact with each other to form a new glia limitans. OEG are distinct from other glia in their developmental origin for they are present in the peripheral nervous system as well as the central nervous system. They also form on bundles of olfactory sensory neuron axons in a manner distinct from myelination. OEG are radial glia that perform a variety of functions. Within the olfactory system they phagocytose axonal debris and dead cells. When cultured in a petri dish (in vitro), they phagocytose bacteria. Multiple studies have shown that OEG may assist in treating spinal cord injury (SCI) due to their regenerate properties in the peripheral nervous system and their presence in the central nervous system. OEG are also known to support and guide olfactory axons, grow through glial scars, and secrete many neurotrophic factors. OEG express glial markers such as glial fibrillary acidic protein, s100, and p75, and radial glial markers such as nestin and vimentin, which may further assist researchers with understanding the labeling characteristics of these specialized glia. The mammalian olfactory system is unusual in that it has the ability to continuously regenerate its neurons during adulthood. This ability is associated with olfactory ensheathing glia. New olfactory receptor neurons must project their axons through the central nervous system to an olfactory bulb in order to be functional. The growth and regeneration of olfactory axons can be attributable to OEG, as they form the fascicles through which axons grow from the peripheral nervous system into the central nervous system. Olfactory receptor neurons have an average lifespan of 6–8 weeks and therefore must be replaced by cells differentiated from the stem cells that are within a layer at the nearby epithelium's base. Axonal growth is guided by the glial composition and cytoarchitecture of the olfactory bulb in addition to the presence of OEG. OEG are thought to be in part responsible for the neurogenesis of primary olfactory neurons through the processes of fasciculation, cell sorting, and axonal targeting. Traumatic spinal cord damage causes a permanent loss of motor and sensory functions in the central nervous system, termed paraplegia or tetraplegia based on the site of the injury. Other detrimental effects may take place in the respiratory system and renal system as a result of the injury. Unlike the peripheral nervous system, the central nervous system is unable to regenerate damaged axons, so its synaptic connections are lost forever. Current treatment is limited and the primary potential methods are either controversial or noneffective. Studies dating back to the 1990s have begun researching the olfactory system of mammals, rats in particular, to gain a greater understanding of axonal regeneration and neurogenesis, and the possible implementation of these cells at the site of the spinal cord injury. Transplantation of OEG into the spinal cord has become a possible therapy for spinal cord damage and other neural diseases in animal models. Several recent studies have reported that preventing OEG inhibition will present a uniform population of cells in the spinal cord, creating an environment in which damaged axons can be repaired. In October 2014, the Polish firefighter Darek Fidyka became the first paraplegic patient to regain mobility after OEG transplantation. OEG are similar to Schwann cells in that they provide an upregulation of low-affinity NGF receptor p75 following injury; however, unlike Schwann cells they produce lower levels of neurotrophins. Several studies have shown evidence of OEG being able to support regeneration of lesioned axons, but these results are often unable to be reproduced. Regardless, OEG have been investigated thoroughly in relation to spinal cord injuries, amyotrophic lateral sclerosis, and other neurodegenerative diseases. Researchers suggest that these cells possess a unique ability to remyelinate injured neurons.