Mesenchymal Stem Cells (MSCs) Treatment Alleviates Smoke Inhalation and BurnInduced Acute Respiratory Distress Syndrome (ARDS) by Inhibiting HMGB1-TLR4 Signal

Abstract ARDS is one of the leading causes of high morbidity and mortality in trauma patients. Previously our data demonstrated autologous MSCs treatment improved survival in a swine model of smoke inhalation and burn injury. However, the pathophysiological mechanisms are still largely unknown. Twenty anesthetized female swine underwent smoke inhalation injury and 40% TBSA burns, were then randomly assigned to either mock treatment (IC, n=10), or autologous MSCs treatment (MSCs, n=10), followed by ICU care up to 72 hours except in case of early death. Three doses of MSCs collected by bone marrow aspiration and concentrated using a bedside cell concentrator device were applied at 2, 24, and 48 hours of post-injury (PI). Blood and tissue samples were collected for ELISA and IHC analyses. In IC group, 10/10 injured pigs developed ARDS, but only 6/10 pigs in MSCs group developed ARDS. Serum analysis revealed that the HMGB1 level gradually increased after injury and reached a peak at 48h PI (5.7-fold increase vs. baseline). The SDC-1 and C3a levels also increased after injury but reached a peak at 24h (2.9-fold) and 72h PI (2.2-fold), respectively. The MSCs treatment significantly reduced the HMGB1 level in the serum, especially at 6h and 12h PI compared to the IC group but failed to inhibit the SDC-1 and C3a increases. IHC analyses showed that injury triggered a significantly higher expressions of HMGB1 and TLR4, as well as co-localization of HMGB1 and TLR4 in the lung; while MSCs treatment was able to disrupt the HMGB1-TLR4 interaction and significantly reduce their expressions. Our data indicate that the way MSCs treatment mitigates ARDS might be by reducing HMGB1 release and inhibiting the HMGB1-TLR4 signal pathway activation in pigs after smoke and burn injury. This work was supported by the US Army Medical Research and Development Command (USAMRDC) under Grant No. W81XWH-13-2-0005.