Rapid remote conditioning mediates modulation of blood cell paracrine activity and leads to the production of a secretome with neuroprotective features.

The indirect use of the protective potential of stem cells in the form of cell secretomes has become an attractive strategy in regenerative medicine. In the present work, we studied the paracrine activity of blood cells that could be modulated towards a neuroprotective nature using in vivo remote conditioning (i.e. tolerant blood cells). The increased neuronal survival mediated by the tolerant secretome was clearly confirmed in vitro in a model of glutamate toxicity in a primary culture of rat cortical neurons and in vivo in a pre- and post-treatment of rats that were subjected to transient occlusion of the middle cerebral artery. Bioinformatic-based analysis of the protein profile revealed higher amounts of proteins released by the tolerant blood cells; 29 proteins were recognised as secreted. More than half of these secreted proteins were involved in the biological processes of the response to the stimulus (GO:0050896) and the response to chemicals (GO:0042221). The protective phenotype was most likely mediated by the synergistic effect of multiple identified proteins, including unique to the tolerant secretome (ceruloplasmin, D-3-phosphoglycerate dehydrogenase) and was promoted by the co-participation of several reaction pathways. The most probably of these pathways were post-translation protein modification, MAP2K and MAPK activation and platelet activation. Taken together, our results demonstrate that properly stimulated blood cells could serve as a source for cell-free-based therapies of regenerative medicine.