| Objectives:Stroke is the third and the first leading cause of death worldwide and in China, respectively. Stroke is a disease of heavy burden for family and society with about 30% of stoke survivors end up with disability. Unfortunately, therapeutic treatments available for stroke patients in clinic are limited. Recombinant tissue plasminogen activator (rt-PA) is the only approved treatment in acute ischemic stroke. Therefore, it is urgent to find novel therapeutic approaches for ischemic stroke victims. Microglia-mediated neurologic inflammation plays an important role in exacerbating ischemic brain injury, which makes it a promising target for therapeutic strategies in ischemic stroke. Meanwhile, it has been found that protect white matter injury against ischemic injury is essential for neurologic functions recovery since white matter injury is a main component of ischemic injury. To mitigate oligodendrocyte death and promote oligodendrocyte replacement has been shown to be critical in maintaining white matter integrity after cerebral ischemia. To find promising therapeutic strategies for ischemic stroke by targeting microglia and oligodendrocyte, in the present study, we investigated the effects and the underlying mechanisms of Dalesconols B (TL2) on modulating microglia-mediated inflammation in LPS-induced microglia. Secondly, we also investigated the effects of rosiglitazone, a PPARy agonist, on white matter injury following cerebral ischemia in a mice MCAO model. We further tested the effects of rosiglitazone on oligodendrocyte replacement and microglial polarization following cerebral ischemia in stroke mice.Methods:LPS-induced microglia-mediated inflammation was used as an in vitro model to test the effects of TL2 on modulating microglia mediated inflammation. Real-time PCR, Western blotting and ELISA was used to test the expression of pro-inflammatory mediators. Luciferase reporter gene assay was used to examine the activity of ARE promoter. Plasmid transfection was used to inhibit or over-express Nrf2 activity. To test the effects of rosglitazone on white matter injury following cerebral ischemia, mice MCAO model was established to mimic ischemic stroke and rosiglitazone was administrated initiating at 2 hours after reperfusion. Immunostaining was employed to assess white matter injury, oligodencrocyte replacement and microglial polarization at 21 days after cerebral ischemia. Behavior tests were used to test neurologic deficits of stroke mice.Results:1) Pretreatment with TL2 inhibited LPS-induced microglia-mediated inflammation, as evidenced by the decrease in production of NO and PGE2, the reduced expression of several pro-inflammatory mediators, including iNOS, COX2, TNF-α, IL-1β, IL-6, MCP-1 and MIP-1α.TL2 treatment also attenuated the activity of Akt/NF-κB, p38 and JNK in BV2 microglia cells. In addition, TL2 treatment activated Nrf2/HO-1 signaling in BV2 microglia. The inhibitory effects of TL2 on microglia-mediated inflammation were blocked when down-regulating the activity of Nrf2 or HO-1.2) Administration of rosiglitazone significantly improved the neurologic functions and white matter integrity after cerebral ischemia. Rosiglitazone treatment strongly increased the numbers of OPC in SVZ, SGZ and peri-infarct area and the numbers of oligodendrocyte in peri-infarct area of ipisilateral hemisphere. We further demonstrated that rosiglitazone treatment reduced the numbers of Iba1/CD16+ M1 microglia while increased the numbers of Iba1/CD206+ M2 microglia in peri-infarct area of ipisilateral hemisphere in stroke mice.Conclusions:1) TL2 treatment significantly inhibited LPS-induced microglia-mediated inflammation, which may be associated with the decreased activity of Akt/NF-κB, p38 and JNK and be contributed at least partially via activating Nrf2/HO-1 signaling in BV2 microglia cells.2) Post-stroke administration of rosiglitazone significantly improved long-term functional recovery and white matter integrity in stroke mice. Both direct (promoting endogenous oligodendrogenesis) and indirect (favored microglia polarization toward the M2 phenotype) mechanisms may underlie the white matter recovery properties of rosiglitazone. |
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