Abstract
BackgroundMesenchymal stem cells (MSCs) are promising tools for the treatment of human lung disease and other pathologies relevant to newborn medicine. Recent studies have established MSC exosomes (EXO), as one of the main therapeutic vectors of MSCs in mouse models of multifactorial chronic lung disease of preterm infants, bronchopulmonary dysplasia (BPD). However, the mechanisms underlying MSC-EXO therapeutic action are not completely understood. Using a neonatal mouse model of human BPD, we evaluated the therapeutic efficiency of early gestational age (GA) human umbilical cord (hUC)-derived MSC EXO fraction and its exosomal factor, tumor necrosis factor alpha-stimulated gene-6 (TSG-6).MethodsConditioned media (CM) and EXO fractions were isolated from 25 and 30 weeks GA hUC-MSC cultures grown in serum-free media (SFM) for 24 h. Newborn mice were exposed to hyperoxia (> 95% oxygen) and were given intraperitoneal injections of MSC-CM or MSC-CM EXO fractions at postnatal (PN) day 2 and PN4. They were then returned to room air until PN14 (in a mouse model of severe BPD). The treatment regime was followed with (rh)TSG-6, TSG-6-neutralizing antibody (NAb), TSG-6 (si)RNA-transfected MSC-CM EXO and their appropriate controls. Echocardiography was done at PN14 followed by harvesting of lung, heart and brain for assessment of pathology parameters.ResultsSystemic administration of CM or EXO in the neonatal BPD mouse model resulted in robust improvement in lung, cardiac and brain pathology. Hyperoxia-exposed BPD mice exhibited pulmonary inflammation accompanied by alveolar-capillary leakage, increased chord length, and alveolar simplification, which was ameliorated by MSC CM/EXO treatment. Pulmonary hypertension and right ventricular hypertrophy was also corrected. Cell death in brain was decreased and the hypomyelination reversed. Importantly, we detected TSG-6, an immunomodulatory glycoprotein, in EXO. Administration of TSG-6 attenuated BPD and its associated pathologies, in lung, heart and brain. Knockdown of TSG-6 by NAb or by siRNA in EXO abrogated the therapeutic effects of EXO, suggesting TSG-6 as an important therapeutic molecule.ConclusionsPreterm hUC-derived MSC-CM EXO alleviates hyperoxia-induced BPD and its associated pathologies, in part, via exosomal factor TSG-6. The work indicates early systemic intervention with TSG-6 as a robust option for cell-free therapy, particularly for treating BPD.
Highlights
Mesenchymal stem cells (MSCs) are promising tools for the treatment of human lung disease and other pathologies relevant to newborn medicine
We demonstrate that EXO-depleted MSC-conditioned media (CM) 25 wks does not reverse hyperoxia-induced lung alterations and pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) associated with hyperoxia-induced bronchopulmonary dysplasia (BPD), suggesting that the therapeutic action of MSC-CM resides in the EXO fraction
Our results demonstrates that the therapeutic effects of the secretome of Umbilical cord (UC) MSCs resides in the EXO fraction, and tumor necrosis factor alpha-stimulated gene-6 (TSG-6) is one of the mediators in the 25 wks gestational age (GA) MSC-CM EXO, responsible for the attenuation of BPD pathology (Fig. 10)
Summary
Mesenchymal stem cells (MSCs) are promising tools for the treatment of human lung disease and other pathologies relevant to newborn medicine. Recent studies have established MSC exosomes (EXO), as one of the main therapeutic vectors of MSCs in mouse models of multifactorial chronic lung disease of preterm infants, bronchopulmonary dysplasia (BPD). Mesenchymal stromal cell (MSC) therapy has been demonstrated to exert therapeutic effects in animal models of injury in the developing lung [5, 6]; a better understanding of the most appropriate cell type, optimal transplantation conditions and importantly, mechanism of action of MSC transplantation is required [7]. Beneficial effects of MSCs have been reported even in the absence of significant engraftment of donor cells in the recipient lungs following MSC therapy, suggesting that the therapeutic mechanism of action are mainly paracrine [5, 8, 9]. The detailed mechanism of action or specific molecules involved in the action of MSC-CM EXO is yet to be reported
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