Host autophagy combating S. aureus: α-toxin will be tolerated

Cosmosiin Increases ADAM10 Expression via Mechanisms Involving 5'UTR and PI3K Signaling

The α-secretase “a disintegrin and metalloproteinase domain-containing protein” (ADAM10) is involved in the processing of amyloid precursor protein (APP). Upregulation of ADAM10 precludes the generation of neurotoxic β-amyloid protein (Aβ) and represents a plausible therapeutic strategy for Alzheimer’s disease (AD). In this study, we explored compounds that can potentially promote the expression of ADAM10. Therefore, we performed high-throughput small-molecule screening in SH-SY5Y (human neuroblastoma) cells that stably express a luciferase reporter gene driven by the ADAM10 promoter, including a portion of its 5’-untranslated region (5’UTR). This has led to the discovery of cosmosiin (apigenin 7-O-β-glucoside). Here, we report that in human cell lines (SH-SY5Y and HEK293), cosmosiin proportionally increased the levels of the immature and mature forms of the ADAM10 protein without altering its mRNA level. This effect was attenuated by translation inhibitors or by deleting the 5’UTR of ADAM10, suggesting that a translational mechanism was responsible for the increased levels of ADAM10. Luciferase deletion assays revealed that the first 144 nucleotides of the 5’UTR were necessary for mediating the cosmosiin-induced enhancement of ADAM10 expression in SH-SY5Y cells. Cosmosiin failed to increase the levels of the ADAM10 protein in murine cells, which lack native expression of the ADAM10 transcript containing the identified 5’UTR element. The potential signaling pathway may involve phosphatidylinositide 3-kinase (PI3K) because pharmacological inhibition of PI3K attenuated the effect of cosmosiin on the expression of the ADAM10 protein. Finally, cosmosiin attenuated Aβ generation because the levels of Aβ40/42 in HEK-APP cells were significantly reduced after cosmosiin treatment. Collectively, we found that the first 144 nucleotides of the ADAM10 5’UTR, and PI3K signaling, are involved in cosmosiin-induced enhancement of the expression of ADAM10 protein. These results suggest that cosmosiin may be a potential therapeutic agent in the treatment of AD.

Interactions between Autophagy and Bacterial Toxins: Targets for Therapy?

Autophagy is a physiological process involved in defense mechanisms for clearing intracellular bacteria. The autophagic pathway is finely regulated and bacterial toxins interact with this process in a complex manner. Bacterial toxins also interact significantly with many biochemical processes. Evaluations of the effects of bacterial toxins, such as endotoxins, pore-forming toxins and adenylate cyclases, on autophagy could support the development of new strategies for counteracting bacterial pathogenicity. Treatment strategies could focus on drugs that enhance autophagic processes to improve the clearance of intracellular bacteria. However, further in vivo studies are required to decipher the upregulation of autophagy and potential side effects limiting such approaches. The capacity of autophagy activation strategies to improve the outcome of antibiotic treatment should be investigated in the future.