Xiaoming Hu
University of Pittsburgh, USA
Title: Regulatory T cells ameliorate tissue plasminogen activator-induced brain hemorrhage after stroke
Biography
Biography: Xiaoming Hu
Abstract
Delayed thrombolytic treatment with recombinant tissue plasminogen activator (tPA) may exacerbate blood-brain barrier (BBB) breakdown after ischemic stroke and lead to lethal hemorrhagic transformation (HT). This study assessed the protective effect of regulatory T cell (Treg) transfer on tPA-induced HT and investigated the underlying mechanisms of protection. We used murine suture and embolic middle cerebral artery occlusion models of stroke to investigate the therapeutic potential of adoptive Treg transfer against tPA-induced HT. The results showed that delayed administration of tPA (10mg/kg) reproducibly resulted in hemorrhage in the ischemic territory 1d after MCAO. Intravenous administration of Tregs (2×106/mouse) immediately after tPA treatment almost completely abolished this hemorrhage and improved sensorimotor deficits after stroke. Tregs dramatically reduced BBB disruption in tPA-infused stroke mice, as measured by Evans blue or fluorescent tracer (cadaverine) leakage and IgG extravasation. Consistent with these observations, Treg treatment mitigated tight junction damage in tPA-treated stroke mice, as revealed by Western immunoblotting and electron microscopy. Mechanistic studies demonstrated that Tregs almost completely abolished the tPA-induced elevation of matrix metalloproteinase 9 (MMP9) and CCL2 after stroke. Using MMP9 and CCL2 knockout mice, we discovered that both molecules partially contributed to the protective actions of Tregs. In an in vitro endothelial cell-based model of the blood-brain barrier, we confirmed that Tregs inhibited tPA-induced endothelial expression of CCL2 and preserved blood-brain barrier integrity after an ischemic challenge. Lentivirus-mediated CCL2 knockdown in endothelial cells completely abolished the blood-brain barrier protective effect of Tregs. Altogether, our data suggest that Treg adoptive transfer after thrombolytic treatment alleviates hemorrhage in stroke victims. Treg-afforded protection in the tPA-treated stroke model may be mediated by two inhibitory mechanisms involving CCL2 and MMP9. Thus, Treg adoptive transfer may be useful as a cell-based therapy to improve the efficacy and safety of thrombolytic treatment for ischemic stroke