Intravenously transplanted mesenchymal stromal cells: a new endocrine reservoir for cardioprotection

Intravenous administration of mesenchymal stromal cells (MSCs) has an acknowledged competence of cardiac repair, despite a lack of systematic description of the underlying biological mechanisms. The lung, but not the heart, is the main trapped site for intravenously transplanted MSCs, which leaves a spatial gap between intravenously transplanted MSCs and the injured myocardium. How lung-trapped MSCs after intravenous transplantation rejuvenate the injured myocardium remains unknown.

MSCs were isolated from human placenta tissue, and DF-MSCs or Gluc-MSCs were generated by transduced with firefly luciferase (Fluc)/enhanced green fluorescence protein (eGFP) or Gaussia luciferase (Gluc) lactadherin fusion protein. The therapeutic efficiency of intravenously transplanted MSCs was investigated in a murine model of doxorubicin (Dox)-induced cardiotoxicity. Trans-organ communication from the lung to the heart with the delivery of blood was investigated by testing the release of MSC-derived extracellular vesicles (MSC-EVs), and the potential miRNA inner MSC-EVs were screened out and verified. The potential therapeutic miRNA inner MSC-EVs were then upregulated or downregulated to assess the further therapeutic efficiency RESULTS: Dox-induced cardiotoxicity, characterized by cardiac atrophy, left ventricular dysfunction, and injured myocardium, was alleviated by consecutive doses of MSCs. These cardioprotective effects might be attributed to suppressing GRP78 triggering endoplasmic reticulum (ER) stress-induced apoptosis in cardiomyocytes. Our results confirmed that miR-181a-5p from MSCs-derived EVs (MSC-EVs) inhibited GRP78. Intravenous DF-MSCs were trapped in lung vasculature, secreted a certain number of EVs into serum, which could be confirmed by the detection of eGFP⁺ EVs. GLuc activity was increased in serum EVs from mice administrated with GLuc-MSCs. MiR-181a-5p, inhibiting GRP78 with high efficacy, was highly expressed in serum EVs and myocardium after injecting consecutive doses of MSCs into mice treated with Dox. Finally, upregulation or downregulation of miR-181a-5p levels in MSC-EVs enhanced or weakened therapeutic effects on Dox-induced cardiotoxicity through modulating ER stress-induced apoptosis.

This study identifies intravenously transplanted MSCs, as an endocrine reservoir, to secrete cardioprotective EVs into blood continuously and gradually to confer the trans-organ communication that relieves Dox-induced cardiotoxicity.