Suppression of inflammatory damage to the brain after global cerebral ischemia by transplanted mesenchymal stem cells via secretion of TSG-6

Objective: Numerous studies have shown that bone marrow-derived mesenchymal stem cells (MSCs) enhance neurological recovery after cerebral ischemia. However, the mechanisms are still not clear. The present study aimed to investigate the beneficial effects of MSCs on global cerebral ischemia induced by cardiac arrest (CA) and the underlying mechanisms. Methods: Rats subjected to asphyxial CA were injected intravenously with MSCs (5×106) at 2 hours after resuscitation. Whole brain histopathologic damage scores (HDS) were assessed by histopathology at 3 and 7 days after resuscitation. The distribution of donor MSCs in the brain was evaluated. The expression of tumor necrosis factor-α-induced protein 6 (TSG-6) and pro-inflammatory cytokines in cerebral cortex was assayed. After intravenous infusion of TSG-6 siRNA-MSCs, HDS and pro-inflammatory cytokines were reevaluated at 7 days after resuscitation. Results: Intravenously administered MSCs significantly reduced whole brain HDS after global cerebral ischemia. Immunofluorescence microscopy revealed that donor MSCs were primarily found in cerebral cortex and expressed TSG-6. MSCs treatment significantly increased the expression of TSG-6 and reduced the expression of pro-inflammatory cytokines in cerebral cortex. In addition, intravenous infusion of TSG-6 siRNA-MSCs failed to attenuate brain inflammation. Conclusion: Systemically administered MSCs reduced inflammatory damage to brain in rats with global cerebral ischemia via secretion of TSG-6. Neurology Asia 2016; 21(2) : 113 – 122 Address correspondence to: Dr Zitong Huang, Department of Emergency, Sun Yat-sen Memorial Hospital, Sun Yat-sen University, 107 Yanjiang W Rd, Yuexiu, Guangzhou, Guangdong, 510120, China. Tel: +86 020 8133 2410, E-mail: [email protected] INTRODUCTION Cardiac arrest (CA) is the critically ill condition, and the mortality rate of those who gain return of spontaneous circulation (ROSC) remains high. Despite advances in cardiopulmonary resuscitation (CPR), the overall survival rate for out-of-hospital CA is reported to be as low as 5%. Therefore, even small incremental improvements in outcomes would be likely to translate into thousands of lives saved every year. Brain damage caused by CA and CPR is initially triggered by complete temporary global cerebral ischemia and then exacerbated by reperfusion. Reperfusion can trigger a cascade of inflammation which can lead to dysfunction of the blood brain barrier, cerebral edema, and neuronal cell death. A number of cytokines related to inflammation such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) have been reported to exacerbate brain damage. Taken together, anti-inflammation therapy may benefit the neurological outcome after CA. Mesenchymal stem cells (MSCs) have been shown to display a significant capacity of decreasing inflammation and protecting tissue from injuries, mostly by paracrine mechanisms. Increasing evidence suggests that administration of MSCs can produce beneficial therapeutic effects in experimental models of cerebral ischemia. Our previous study demonstrated that intravenous delivery of MSCs improved neurological function after global cerebral ischemia induced by CA ORIGINAL ARTICLES Neurology Asia June 2016 114 in rats. However, the mechanisms of action of MSCs require further investigation. TNF-αinduced protein 6 (TSG-6), a 35 kDa secreted protein produced by MSCs in response to signals from injured tissues, can inhibit the amplification of the pro-inflammatory signals to limit lesions of tissues. Recent research finds that administration of TSG-6 decreases the lesion size in models of traumatic brain injury at 2 weeks. This was a rat model study of global cerebral ischemia to provide the evidence in support of the hypothesis that administration of MSCs reduced post-ischemic inflammation in the brain via secretion of TSG-6. To test this hypothesis, we have assessed whole brain histopathologic alterations, the changes in pro-inflammatory cytokines levels, and the changes of TSG-6 expression in global ischemic rats following intravenously injected MSCs or TSG-6 siRNAMSCs.