Detection of MISEV recommended EV Protein-markers using Automated Western Blotting - Lisa Meyer

The limited amount of material and the diverse methods for isolation of extracellular vesicles (EV) pose unique challenges to proper characterization of experimental EV preparations. The “Minimal Information for Studies of Extracellular Vesicles” (MISEV) guidelines recommend characterizing preparations for both trans-membrane-, cytosolic- and contaminating non-EV proteins. However, compliance with these guidelines can be a considerable effort due to lack of easy and robust analytical protocols and the time consuming and user variable nature of standard western blotting protocols. Here we present a simple method for isolation of EVs and a simple western blotting platform for automated protein separation and immunodetection of MISEV-recommended proteins. The total EVs were isolated by affinity-membrane spin columns from pre-filtered 0.5-4 mL plasma or 2-20 mL urine, respectively. Intact vesicles were eluted and the EV-depleted biofluid fraction was collected from the flow-through. A small fraction (4 μL) was analyzed by a simple western blot workflow providing automated capillary electrophoresis-based protein separation and immunodetection, characterizing each fraction for presence or absence of MISEV-recommended proteins. A range of specific antibodies were identified and the EV fractions were shown to be enriched in EV-proteins, whereas contaminating non-EV proteins were significantly reduced. Isolation of EVs was necessary to allow detection of the low abundant EV protein markers, whereas non-EV proteins were readily detectable both in the neat biofluids and in the EV-depleted flow-through. We characterized the effect of washing on the purity of EV isolates and defined the dynamic range of the workflow using titrations of input volume of both plasma and urine EV isolations. In conclusion, Simple western blotting protocols were established for quality control of isolated EVs in accordance with MISEV-guidelines. EVs isolated using affinity-membrane spin columns were shown to be enriched in EV markers and depleted for non-EV proteins.