Renal protective effects of extracellular vesicle-encapsulated tumor necrosis factor-α-induced protein 6 derived from mesenchymal stem cells

Acute kidney injury (AKI) is involved in subsequent chronic kidney disease (CKD) development, and effective treatments to prevent AKI to CKD progression are lacking. Mesenchymal stem cells (MSCs) are emerging as a promising cellular therapy to impede such progression through the secretion of various humoral factors. Among these factors, tumor necrosis factor-α-induced protein 6 (TSG-6) has a central role in the anti-inflammatory effects of MSCs. However, the mechanisms by which MSCs secrete TSG-6 and exert anti-inflammatory effects are not fully clarified. Here, we investigated these mechanisms using TSG-6-overexpressing MSCs (TSG-6 MSCs) with an adeno-associated virus. Extracellular vesicles (EVs) were isolated from MSC culture supernatants by ultracentrifugation. MSCs were injected through the abdominal aorta into rats with ischemia-reperfusion injury (IRI) to evaluate their anti-inflammatory and anti-fibrotic effects. Additionally, we explored natural compounds that increased TSG-6 expression in MSCs. Most TSG-6 was immediately secreted in EVs and was not stored intracellularly. Administration of TSG-6 MSCs strongly suppressed renal fibrosis and inflammation in IRI rats. Although EVs and conditioned medium from TSG-6 MSCs (TSG-6 MSC-CM) strongly promoted polarization of M2 macrophages, TSG-6 MSC-CM after EV depletion promoted it only slightly. Moreover, TSG-6 MSC-CM enhanced regulatory T-cell induction. MSCs treated with indole-3-carbinol had enhanced TSG-6 expression and markedly suppressed IRI-induced renal fibrosis. Taken together, TSG-6 is secreted in EVs from MSCs and exerts potent anti-inflammatory effects by promoting M2 macrophage polarization and regulatory T-cell induction. Administration of MSCs with enhanced TSG-6 secretion is a promising therapeutic strategy to impede AKI to CKD progression.