Exosomes are small (~100nm) membrane bound vesicles excreted by cells as part of their normal biological processes. These extracellular vesicles are currently an area of intense research, since they were recently found to carry functional mRNA that allows transfer of proteins and other cellular instructions between cells. Exosomes have been implicated in a wide range of diseases, including cancer. Cancer cells are known to have increased exosome production, and may use those exosomes to prepare remote environments for metastasis. Therefore, there is a strong need to develop characterization methods to help understand the structure and function of these vesicles. However, current techniques, such as proteomics and genomics technologies, rely on aggregating a large amount of exosome material and reporting on chemical content that is averaged over many millions of exosomes. Here we report on the use of laser-tweezers Raman spectroscopy (LTRS) to probe individual vesicles, discovering distinct heterogeneity among exosomes both within a cell line, as well as between different cell lines. Through principal components analysis followed by hierarchical clustering, we have identified four “subpopulations” of exosomes shared across seven cell lines. The key chemical differences between these subpopulations, as determined by spectral analysis of the principal component loadings, are primarily related to membrane composition. Specifically, the differences can be ascribed to cholesterol content, cholesterol to phospholipid ratio, and surface protein expression. Thus, we have shown LTRS to be a powerful method to probe the chemical content of single extracellular vesicles.
Zachary J. Smith, Changwon Lee, Tatu Rojalin, Randy P. Carney, Sidhartha Hazari, Alisha Knudson, Kit S. Lam, Heikki Saari, Elisa Lazaro Ibañez, Tapani Viitala, Timo Laaksonen, Marjo Yliperttula, and Sebastian Wachsmann-Hogiu, "Raman spectroscopy of single extracellular vesicles reveals subpopulations with varying membrane content
(Conference Presentation)," Proc. SPIE 9704, Biomedical Vibrational Spectroscopy 2016: Advances in Research and Industry, 97040Q (Presented at SPIE BiOS: February 14, 2016; Published: 3 May 2016); https://doi.org/10.1117/12.2212914.4848581046001.
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