探討幽門螺旋桿菌感染胃上皮細胞時半乳糖凝集素-3與-8在細胞自嗜所扮演的角色

Abstract

半乳糖凝集素，是會接上beta-galactoside的凝集素，已知會行使許多功能，包含影響細胞活化、生長與凋亡。近年來半乳糖凝集素也被發現在偵測到細菌引起的液泡破裂後會調控細胞自嗜。幽門螺旋桿菌是一種主要存在於胃中的細菌，一旦感染細胞後能夠活化細胞自嗜。在本篇論文中，我們意欲研究半乳糖凝集素-3和-8在胃上皮細胞受幽門螺旋桿菌感染時扮演的角色。我們發現當AGS胃上皮細胞株受此細菌感染後，細胞內的半乳糖凝集素-3和-8會有凝聚現象。特別的是這些凝聚的半乳糖凝集素在細胞中的定位在溶酶體，而且當抑制細胞O-聚醣合成時，它們的凝聚會明顯減少。這暗示幽門螺旋桿菌感染會造成溶酶體破損，以致於細胞質的半乳糖凝集素-3和-8辨識到暴露出來的O-聚醣而聚集在破損的溶酶體。而感染引發的半乳糖凝集素-8的凝聚可促進細胞自嗜。雖然感染引發的半乳糖凝集素-3的凝聚可能也有促進細胞自嗜的功能，我們發現只有在細胞沒有表現半乳糖凝集素-8時，這樣的功能性才會比較明顯。另外vacuolating cytotoxin A (VacA)是一種會對細胞造成孔洞的幽門螺旋桿菌細胞毒素。我們發現這個細胞毒素對感染造成的半乳糖凝集素-8的凝聚與增強的細胞自嗜反應有所貢獻。整體來說，我們的研究結果顯示半乳糖凝集素-3和-8在辨識到幽門螺旋桿菌造成的溶酶體破損後，會促進細胞自嗜反應，而VacA可能是感染引發溶酶體破損的一個重要因子。

Galectins, beta-galactoside-binding lectins, are known to exert various functions, including cell activation, growth, and apoptosis. In recent years, galectins were shown to regulate cellular autophagy response after sensing bacteria-induced vacuole lysis. Helicobacter (H.) pylori is a bacterium majorly found in the stomach and capable of activating autophagy in infected cells. In this thesis, we investigated the role of galectin-3 and -8 in gastric epithelial cells upon exposure to H. pylori. We found that H. pylori coculture increases intracellular aggregation of galectin-3 and -8 in human-derived AGS gastric epithelial cells. Notably, both galectin aggregates colocalize with lysosomes, and their aggregation is markedly reduced following the attenuation of host O-glycan processing. This indicates that H. pylori infection induces lysosomal damage, which in turn results in the accumulation of cytosolic galectin-3 and -8 around damaged lysosomes through the recognition of exposed vacuolar host O-glycans. H. pylori-induced galectin-8 aggregates may enhance autophagy activity in infected cells. While H. pylori-elicited galectin-3 aggregates may also execute a function on potentiating autophagy response, this functional effect is apparent only when cells are devoid of galectin-8 expression. We also found autophagy plays a part in facilitating H. pylori-mediated galectin-8 aggregation. Additionally, vacuolating cytotoxin A (VacA), a pore-forming H. pylori cytotoxin, contributes to the increased galectin-8 aggregation and elevated autophagy response in infected cells. Collectively, our results suggest that both galectin-3 and -8 promote host autophagy response following recognizing lysosomal injury induced by H. pylori, and that VacA may be a critical factor to destabilize lysosomal membrane during infection.