Exosomes as new diagnostic tools in CNS diseases

•Exosomes have great potential as diagnostic tools and biomarkers for diseases affecting the central nervous system.•Exosomal contents are altered in disease.•Exosomal membrane markers can be potentially used to identify their cellular origin.•Exosomes enriched from bodily fluids can be used for detection of various proteins, lipids and nucleic acids.•Further studies are required to overcome technical issues to allow efficient routine screening of exosomes from patients.

Exosomes are small extracellular vesicles that modulate important functions in physiology and under pathological conditions of the central nervous system (CNS). Exosomal contents, proteins, lipids and various RNA species, are altered during disease. The fact that exosomes are released into the blood stream from blood cells and endothelial cells responding to CNS diseases as well as from the brain and spinal cord, and that they express markers which allow their tracking to the cell of origin, makes the use of exosomes for diagnostic purposes and biomarker discovery particularly appealing. While the utilization of exosomes for diagnostics in diseases affecting the CNS are still in the early stages of discovery and development, it is expected that through further research and fervent development of protocols relating to isolation and purification the true potential of exosomes derived from the CNS will be harnessed for more effective clinical disease diagnosis. In this review we begin with a short introduction to the origin, composition and function of exosomes in the CNS. Next we discuss the current status of methodologies related to isolation and detection of CNS exosomes. We end with an account of exosomes in diagnostics and biomarker discovery, which focuses on three diseases of the CNS: Alzheimer's disease, multiple sclerosis, and stroke. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.