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    Inhibition of fatty acid synthesis aggravates brain injury, reduces blood-brain barrier integrity and impairs neurological recovery in a murine stroke model
    (Frontiers Media SA, 2021) Janssen, Lisa; Ai, Xiaoyu; Zheng, Xuan; Wei, Wei; Çağlayan, Ahmet Burak; Kılıç, Ertuğrul; Wang, Ya-chao; Hermann, Dirk M.; Venkataramani, Vivek; Baehr, Mathias; Doeppner, Thorsten R.
    Inhibition of fatty acid synthesis (FAS) stimulates tumor cell death and reduces angiogenesis. When SH-SY5Y cells or primary neurons are exposed to hypoxia only, inhibition of FAS yields significantly enhanced cell injury. The pathophysiology of stroke, however, is not only restricted to hypoxia but also includes reoxygenation injury. Hence, an oxygen-glucose-deprivation (OGD) model with subsequent reoxygenation in both SH-SY5Y cells and primary neurons as well as a murine stroke model were used herein in order to study the role of FAS inhibition and its underlying mechanisms. SH-SY5Y cells and cortical neurons exposed to 10 h of OGD and 24 h of reoxygenation displayed prominent cell death when treated with the Acetyl-CoA carboxylase inhibitor TOFA or the fatty acid synthase inhibitor cerulenin. Such FAS inhibition reduced the reduction potential of these cells, as indicated by increased NADH(2)(+)/NAD(+) ratios under both in vitro and in vivo stroke conditions. As observed in the OGD model, FAS inhibition also resulted in increased cell death in the stroke model. Stroke mice treated with cerulenin did not only display increased brain injury but also showed reduced neurological recovery during the observation period of 4 weeks. Interestingly, cerulenin treatment enhanced endothelial cell leakage, reduced transcellular electrical resistance (TER) of the endothelium and contributed to poststroke blood-brain barrier (BBB) breakdown. The latter was a consequence of the activated NF-kappa B pathway, stimulating MMP-9 and ABCB1 transporter activity on the luminal side of the endothelium. In conclusion, FAS inhibition aggravated poststroke brain injury as consequence of BBB breakdown and NF-kappa B-dependent inflammation.
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    Lithium modulates miR-1906 levels of mesenchymal stem cell-derived extracellular vesicles contributing to poststroke neuroprotection by toll-like receptor 4 regulation
    (Wiley, 2021) Haupt, Matteo; Zheng, Xuan; Kuang, Yaoyun; Lieschke, Simone; Janssen, Lisa; Bosche, Bert; Jin, Fengyan; Hein, Katharina; Kılıç, Ertuğrul; Venkataramani, Vivek; Hermann, Dirk M.; Bahr, Mathias; Doeppner, Thorsten R.
    Lithium is neuroprotective in preclinical stroke models. In addition to that, poststroke neuroregeneration is stimulated upon transplantation of mesenchymal stem cells (MSCs). Preconditioning of MSCs with lithium further enhances the neuroregenerative potential of MSCs, which act by secreting extracellular vesicles (EVs). The present work analyzed, whether MSC preconditioning with lithium modifies EV secretion patterns, enhancing the therapeutic potential of such derived EVs (Li-EVs) in comparison with EVs enriched from native MSCs. Indeed, Li-EVs significantly enhanced the resistance of cultured astrocytes, microglia, and neurons against hypoxic injury when compared with controls and to native EV-treated cells. Using a stroke mouse model, intravenous delivery of Li-EVs increased neurological recovery and neuroregeneration for as long as 3 months in comparison with controls and EV-treated mice, albeit the latter also showed significantly better behavioral test performance compared with controls. Preconditioning of MSCs with lithium also changed the secretion patterns for such EVs, modifying the contents of various miRNAs within these vesicles. As such, Li-EVs displayed significantly increased levels of miR-1906, which has been shown to be a new regulator of toll-like receptor 4 (TLR4) signaling. Li-EVs reduced posthypoxic and postischemic TLR4 abundance, resulting in an inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B) signaling pathway, decreased proteasomal activity, and declined both inducible NO synthase and cyclooxygenase-2 expression, all of which culminating in reduced levels of poststroke cerebral inflammation. Conclusively, the present study for the first time demonstrates an enhanced therapeutic potential of Li-EVs compared with native EVs, interfering with a novel signaling pathway that yields both acute neuroprotection an enhanced neurological recovery.