By Releasing ADP, Acanthamoeba castellanii Causes an Increase in the Cytosolic Free Calcium Concentration and Apoptosis in Wish Cells

The role played by soluble molecules that may participate in acanthamoebal cytopathogenicity has yet to be fully characterized. We demonstrate here that Acanthamoeba castellanii trophozoites constitutively release ADP in the medium. Cell-free supernatants prepared from A. castellanii, by interaction with specific P(2y2) purinoceptors expressed on the Wish cell membrane, caused a biphasic rise in [Ca(2+)](i), extensive cell membrane blebbing, cytoskeletal disorganization, and the breakdown of nuclei. Cell damage induced by amoebic supernatants was blocked by the P(2y2) inhibitor Suramin. The same results were found in Wish cells exposed to purified ADP. These findings suggest that pathogenic free-living A. castellanii may have a cytopathic effect on human epithelial cells through ADP release, by a process that begins with a rise of cytosolic free-calcium concentration, and culminates in apoptosis.

目前，可能参与棘阿米巴细胞致病作用的可溶性分子的功能尚未得到完全阐明。本研究证实，卡氏棘阿米巴（Acanthamoeba castellanii）滋养体可在培养基中组成型释放腺苷二磷酸（ADP）。从卡氏棘阿米巴中制备的无细胞上清液，可通过与Wish细胞膜上表达的特异性P(2y2)嘌呤能受体（P(2y2) purinoceptors）结合，引发细胞内游离钙离子浓度[Ca(2+)](i)出现双相升高、广泛的细胞膜起泡、细胞骨架紊乱以及核裂解。P(2y2)受体抑制剂苏拉明（Suramin）可阻断棘阿米巴上清液诱导的细胞损伤。用纯化的腺苷二磷酸处理Wish细胞，可得到相同的实验结果。上述研究结果表明，致病性自由生活的卡氏棘阿米巴可通过释放腺苷二磷酸，经以胞质游离钙离子浓度升高为起始、最终诱导细胞凋亡的过程，对人类上皮细胞产生细胞致病作用。