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Exophers are a type of membrane-bound extracellular vesicle (EV) that are released by budding out of cells into the extracellular space. Exophers can be released by neurons [1] and muscle [2] in the nematode Caenorhabditis elegans and also from murine cardiomyocytes. [3] Exophers were first discovered in 2017 in the lab of Monica Driscoll at Rutgers University. [4]
Exophers are notable for their large size, averaging approximately four microns in diameter, and they are able to expel whole organelles, such as mitochondria and lysosomes as cargo. [1] An exopher can initially remain attached to the cell that produced it by a membranous filament that resembles a tunneling nanotube. Exophers share similarities with large oncosomes, but they differ in that they are produced by physiologically normal cells instead of aberrant cells associated with tumors. [5]
Exopher production is thought to be a mechanism cells use to preserve homeostasis. Exophers are produced in response to numerous stressors including intracellular protein aggregation, reactive oxygen species (ROS), [1] heat, osmotic hyertonicity, starvation, [6] and even space flight. [7] Extracellular signaling receptor MERTK, expressed by cardiac-resident macrophages, is necessary for exopher clearance by phagocytosis in mouse-derived cardiac tissue. [3]
Exophers may be relevant to disease. In mouse heart, eliminating macrophages or blocking their ability to engulf exophers lead to inflammation and ventricular dysregulation. [3] Exophers may also promote pathological protein spreading in neurodegenerative diseases due to their ability to carry aggregated proteins outside of neurons, including human huntingtin protein. [1]