Examination of Wnt/β-catenin signaling in the blood-brain barrier: exploration in a human BBB culture model under normal and pathophysiological conditions
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Date
2020-12-22
Authors
Laksitorini, Marlyn
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Abstract
Introduction. Wnt/β-catenin plays an essential role in the development and maintenance of the blood-brain barrier (BBB). Dysregulation of Wnt/β-catenin signaling in brain microvessel endothelial cells have been linked to BBB dysfunction observed in various pathological conditions such as multiple sclerosis, Huntington’s disease and cerebral ischemia. However, the potential alteration in Wnt/β-catenin activity in brain endothelial cells upon chronic ethanol exposure has not been established.
Objectives. The studies examined Wnt/β-catenin activity using a culture model of the BBB to determine the impact on barrier properties under normal conditions and following exposure to ethanol. In addition, various pharmacological agents were screened for their ability to activate Wnt/β-catenin in the brain endothelial cells and improve barrier function.
Methods. Wnt/β-catenin signaling under normal monoculture conditions and following ethanol exposure was examined using the human cerebral microvessel endothelial cell line (hCMEC/D3). Studies correlated changes in downstream genes important for establishing the BBB phenotype as well as assessment of transporter activity and paracellular diffusion. Additionally, Wnt/β-catenin signaling was examined in both brain homogenate and isolated brain microvessels from C57B16 mice receiving daily i.p injections of ethanol (2.0 g/kg for 7 days).
Result. The hCMEC/D3 expressed an array of Wnt ligands, receptors/co-receptors and modulators. Inhibition of endogenous Wnt ligand had minimal impact on the maintanence of BBB phenotype in the hCMEC/D3 monolayers. However, external activation of Wnt/β-catenin signaling using lithium chloride 10 mM or Wnt3a 200 ng/ml significantly improved barrier properties. Mice treated with ethanol showed downregulation of Wnt/β-catenin signaling in both the brain homogenate and in isolated microvessels from brain cortex. Similar Wnt/β-catenin downregulation was also observed in hCMEC/D3 following ethanol exposure. While LiCl (10 mM) treatment improved the barrier restrictiveness of the monolayer, additional studies were conducted to explore clinically approved CNS drugs at therapeutically relevant concentrations to improve barrier function. Among the drugs examined, fluoxetine activated Wnt/β-catenin signaling and prevented barrier dysfunction following ethanol insult.
Conclusion. The studies suggest that Wnt/β-catenin signaling is downregulated at the BBB following exposure to ethanol and pharmacological interventions directed at activation of Wnt/β-catenin may counteract the negative effects of ethanol on the permeability of brain endothelial cells.
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Keywords
Wnt/beta catenin signaling, Blood-brain barrier, Chronic ethanol exposure
Citation
Laksitorini, M.D.; Yathindranath, V.; Xiong, W.; Hombach-Klonisch, S.; Miller, D.W. Modulation of Wnt/β-catenin signaling promotes blood-brain barrier phenotype in cultured brain endothelial cells. Sci. Rep. 2019, 9, 19718
Laksitorini MD, Yathindranath V, Xiong W, Parkinson FE, Thliveris JA, Miller DW. Impact of Wnt/β-catenin signaling on ethanol-induced changes in brain endothelial cell permeability. J Neurochem. 2020 Sep 30. doi: 10.1111/jnc.15203. Epub ahead of print. PMID: 32998179.
Laksitorini MD, Yathindranath V, Xiong W, Parkinson FE, Thliveris JA, Miller DW. Impact of Wnt/β-catenin signaling on ethanol-induced changes in brain endothelial cell permeability. J Neurochem. 2020 Sep 30. doi: 10.1111/jnc.15203. Epub ahead of print. PMID: 32998179.