Proteolytic Potential of the MSC Exosome Proteome : Implications for an Exosome-Mediated Delivery of Therapeutic Proteasome

Abstract EN

Mesenchymal stem cells (MSCs) are used in many of the current stem cell-based clinical trials and their therapeutic efficacy has increasingly been attributed to secretion of paracrine factors.

We have previously demonstrated that a therapeutic constituent of this secretion is exosome, a secreted bilipid membrane vesicle of ~50–100 nm with a complex cargo that is readily internalized by H9C2 cardiomyocytes.

It reduces infarct size in a mouse model of myocardial ischemia/reperfusion (MI/R) injury.

We postulate that this therapeutic efficacy is derived from the synergy of a select permutation of individual exosome components.

To identify protein candidates in this permutation, the proteome was profiled and here we identified 20S proteasome as a protein candidate.

Mass spectrometry analysis detected all seven α and seven β chains of the 20S proteasome, and also the three beta subunits of “immunoproteasome” with a very high confidence level.

We demonstrated that a functional proteasome copurified with MSC exosomes with a density of 1.10–1.18 g/mL, and its presence correlated with a modest but significant reduction in oligomerized protein in a mouse model of myocardial infarction.

Circulating proteasomes in human blood also copurified with exosomes.

Therefore, 20S proteasome is a candidate exosome protein that could synergize with other constituents to ameliorate tissue damage.