The organization of cytoskeleton in the tegument of Schistosoma japonicum and its response to praziquantel

การจัดเรียงตัวของไซโตสเกเลตันในชั้นผิวของพยาธิใบไม้เลือด S.japonicum และการตอบสนองต่อยาพราซิควอนเทล

Name: Suwadee Chaunchaiyakul

MeSH: Cytoskeleton

MeSH: Praziquantel

MeSH: Schistosoma japonicum

Abstract: The organization of cytoskeleton in the tegument of various stages in the life cycle of Schistosoma japonicum was studied by conventional TEM and SEM methods together with the extraction by Triton X-100, and the mixture of Triton X-100 and DTT. The results show that cytoskeletal elements of the tegument in all stages are composed of two components: firstly, the network of knobby fibers which appear as dense dots or globular structures in cross sections. This network is designated as microtrabeculae which form the principal scaffold of the tegument cytoplasm; and secondly, the microtubules which concentrate in the tegument cells processes and the basal part of the tegument cytoplasm. Following extraction with Triton X-100 and DTT, microtrabecular network is unravelled to form thin and straight filaments, about 3 to 7 nm thick that may be the primary level organization. These filaments, in turn, may coil up to form knobby fibers, whose size at the knobby section is about 9 to 11 nm, which are highly cross-linked; and this structure may represent the secondary level of organization. At the tertiary level, these knobby fibers may be coiled up further to form closely aggregated and cross-linked globules, which appear as dense dots in cross sections; each globule is about 11 to 16 nm. Microtubules are confined within the tegument cells processes and spray out into the basal zone of the teguments cytoplasm. Microtrabecular network may help to maintain the structure and the characteristic shape of the tegument, while microtubules may be involved in the translocation of tegumental granules from the tegument cell bodies to the tegument. The packing of microtrabeculae is tightest and most uniform in cercarial tegument. In early schistosomula (3- to 6-hour) the microtrabeculae in the basal part of the tegument is loosened up such that two distinct layers could be visualized. The packing of microtrabeculae becomes progressively loosened, until in 15-day schistosomula and adult stages it starts to appear as three differentially packed layers, concurrently with the formation of ridges and pits in the tegument. The tightest packing of microtrabeculae is in the middle layer of the tegument, and it is moderately dense in the apical section, and becomes highly loosened in the basal cytoplasm where basal membrane infoldings and mitochondria are present. The result of the extraction by Triton X-100 and DTT in different stages support the above conclusion by showing differential unravelling of microtrabeculae in various stages of the life cycle, as well as in different layers of the tegument of the same stage.The survival of various developmental stages of S. japonicum (Chinese) and the changes in the ultrastructure of their tegument in response to PZQ were investigated by incubating parasites in MEM media containing 0.1, 1 and 10 ug/ml of the drug at 5,15,30,45,B0 min, 3, 6, 12, 24 hours. At the end of the experiments using the first 2 dosages,the two early stages(3- and 24-hour) schistosomula show 100 % survival, and this decreases to approximately 83 % at the dosage of 10 ug PZQ/ml, when compared to the control. Whereas 7-day schistosomula show lower survival rates,at approximately 97 %,85 X and 79 X at the end of experiments using the three dosages. In contrast 15-day schistosomula are the most affected and show only about 79 %,72 % and 68 % at the end of the experiments. In comparison,the adults are more affected and showed about 43 % survival at the first 5 min of incubation; and the percent survival decreases to 0 X at the end of 60 min at the concentration of 10 ug PZQ/ml (Ariyakunatorn, 1987; Sobhon and Upatham, 1990). The sequence of pathological changes occurring on the tegument surface during the period of incubation, when observed by SEM, consist of: (1) the contraction and shortening of body length; (2) the constriction of the body at the anterior and posterior ends; (3) the furrowing of the surface; (4) the disorganization of ridges; (5) the swelling of the surface and the flattening of ridges and pits; (6) the blebbing of the surface; and finally; (7) the forming of lesions and sloughing of the surface. When examined by TEM, the affected structures are the tegument, the muscle cells and the subte-gumental tissue. The sequence of histopathological changes in the tegument are: (l)the depolynerization of the microtrabecular network; (2) the formation of vacuoles; (3) the flattening of ridges and pits. And those occurring in muscle cells are:(l) the swelling and changing of the mitochondrias configuration; (2) the depolymerization of myofilaments; and (3) the disappearance of myofilaments. Various size vacuoles also form in the subtegumental tissue early in the incubation even at the low dosage. Generally changes are more pronounced in 15-day schistosomula than the three early stages even though the degree of severity is less than that occurring in the adult. In contrast to microtrabeculae, microtubules are not affected by PZQ. From these ultrastructural changes it is concluded that PZQ initially causes depolymerization of the microtrabecular network in the tegument which results in the weakening of the teguments cytoskeleton, that leads to the formation of vacuoles. The enlarging and swelling of the tegument follows due to the inflow of water, hence leading to the disorganization of the ridges and pits. Eventually, the blebs are formed at weakened spots that lead to bursting, lesions and sloughing of the tegument. Muscle cells are similarly affected though at a later time and higher dosage, by showing initially the depolymerization, and finally the dissolution of myofilaments. The depolymerization of the teguments microtrabeculae and the myofilaments could be due to the sudden influx of Ca(2)+into these structures that are induced by PZQ. Other ensuing changes may be the result of this influx and the subsequent impairment of the osmoregulatory mechanism in the tegument.

Mahidol University. Mahidol University Library and Knowledge Center

Address: NAKHONPATHOM

Email: liwww@mahidol.ac.th

Name: Prasert Sobhon

Role: Thesis Advisors

Name: Suchart Upatham

Role: Thesis Advisors

Name: Chaitip Wanichanon

Role: Thesis Advisors

Name: Jittipan Chavadej

Role: Thesis Advisors

Created: 1993

Modified: 2018-04-25

Issued: 2018-04-25

วิทยานิพนธ์/Thesis

application/pdf

eng

DegreeName: Doctor of Philosophy

Level: Doctoral Degree

Descipline: Anatomy

Grantor: Mahidol University

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