Glycobiology Research and Training Center (GRTC), Center for Academic Research and Training in Anthropogeny (CARTA), Departments of Medicine and Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, United States of America.
Department of Pediatrics, University of California San Diego, La Jolla, CA, United States of America.
PLoS Pathog. 2018 Jun 18;14(6):e1007133. doi: 10.1371/journal.ppat.1007133. eCollection 2018 Jun.
While infectious agents have typical host preferences, the noninvasive enteric bacterium Vibrio cholerae is remarkable for its ability to survive in many environments, yet cause diarrheal disease (cholera) only in humans. One key V. cholerae virulence factor is its neuraminidase (VcN), which releases host intestinal epithelial sialic acids as a nutrition source and simultaneously remodels intestinal polysialylated gangliosides into monosialoganglioside GM1. GM1 is the optimal binding target for the B subunit of a second virulence factor, the AB5 cholera toxin (Ctx). This coordinated process delivers the CtxA subunit into host epithelia, triggering fluid loss via cAMP-mediated activation of anion secretion and inhibition of electroneutral NaCl absorption. We hypothesized that human-specific and human-universal evolutionary loss of the sialic acid N-glycolylneuraminic acid (Neu5Gc) and the consequent excess of N-acetylneuraminic acid (Neu5Ac) contributes to specificity at one or more steps in pathogenesis. Indeed, VcN was less efficient in releasing Neu5Gc than Neu5Ac. We show enhanced binding of Ctx to sections of small intestine and isolated polysialogangliosides from human-like Neu5Gc-deficient Cmah-/- mice compared to wild-type, suggesting that Neu5Gc impeded generation of the GM1 target. Human epithelial cells artificially expressing Neu5Gc were also less susceptible to Ctx binding and CtxA intoxication following VcN treatment. Finally, we found increased fluid secretion into loops of Cmah-/- mouse small intestine injected with Ctx, indicating an additional direct effect on ion transport. Thus, V. cholerae evolved into a human-specific pathogen partly by adapting to the human evolutionary loss of Neu5Gc, optimizing multiple steps in cholera pathogenesis.
虽然传染性病原体通常具有特定的宿主偏好，但非侵入性肠道细菌霍乱弧菌的非凡之处在于它能够在许多环境中存活，但仅在人类中引起腹泻病（霍乱）。霍乱弧菌的一个关键毒力因子是其神经氨酸酶（VcN），它将宿主肠道上皮细胞的唾液酸作为营养源释放，并同时将肠道多唾液酸化神经节苷脂重塑为单唾液酸化神经节苷脂 GM1。GM1 是第二个毒力因子 AB5 霍乱毒素（Ctx）B 亚基的最佳结合靶标。这个协调的过程将 CtxA 亚基递送入宿主上皮细胞，通过 cAMP 介导的阴离子分泌激活和电中性 NaCl 吸收抑制触发液体流失。我们假设人类特异性和人类普遍性的唾液酸 N-羟乙酰神经氨酸（Neu5Gc）的进化丢失以及由此产生的 N-乙酰神经氨酸（Neu5Ac）过量导致在发病机制的一个或多个步骤中具有特异性。事实上，VcN 从 Neu5Gc 中释放的效率低于 Neu5Ac。我们显示出 Ctx 与类似于人类的 Neu5Gc 缺陷 Cmah-/- 小鼠的小肠段和分离的多唾液酸化神经节苷脂的结合增强，这表明 Neu5Gc 阻碍了 GM1 靶标的产生。与野生型相比，人工表达 Neu5Gc 的人上皮细胞在经过 VcN 处理后也对 Ctx 结合和 CtxA 中毒的敏感性降低。最后，我们发现 Cmah-/- 小鼠小肠环中注入 Ctx 后液体分泌增加，表明对离子转运有额外的直接影响。因此，霍乱弧菌进化成为一种人类特异性病原体，部分原因是适应了人类 Neu5Gc 的进化丢失，优化了霍乱发病机制的多个步骤。
