Thymosin 4 reverses phenotypic polarization of glial cells and cognitive impairment via negative regulation of NF-B signaling axis in APP/PS1 mice

Background: Thymosin beta 4 (T beta 4) is the most abundant member of the beta-thymosins and plays an important role in the control of actin polymerization in eukaryotic cells. While its effects in multiple organs and diseases are being widely investigated, the safety profile has been established in animals and humans, currently, little is known about its influence on Alzheimer's disease (AD) and the possible mechanisms. Thus, we aimed to evaluate the effects and mechanisms of T beta 4 on glial polarization and cognitive performance in APP/PS1 transgenic mice. Methods: Behavior tests were conducted to assess the learning and memory, anxiety and depression in APP/PS1 mice. Thioflavin S staining, Nissl staining, immunohistochemistry/immunofluorescence, ELISA, qRT-PCR, and immunoblotting were performed to explore A beta accumulation, phenotypic polarization of glial cells, neuronal loss and function, and TLR4/NF-kappa B axis in APP/PS1 mice. Results: We demonstrated that T beta 4 protein level elevated in all APP/PS1 mice. Over-expression of T beta 4 alone alleviated AD-like phenotypes of APP/PS1 mice, showed less brain A beta accumulation and more Insulin-degrading enzyme (IDE), reversed phenotypic polarization of microglia and astrocyte to a healthy state, improved neuronal function and cognitive behavior performance, and accidentally displayed antidepressant-like effect. Besides, T beta 4 could downregulate both TLR4/MyD88/NF-kappa B p65 and p52-dependent inflammatory pathways in the APP/PS1 mice. While combination drug of TLR4 antagonist TAK242 or NF-kappa B p65 inhibitor PDTC exerted no further effects. Conclusions: These results suggest that T beta 4 may exert its function by regulating both classical and non-canonical NF-kappa B signaling and is restoring its function as a potential therapeutic target against AD.