Suppression of VAMP2 Alters Morphology of the Tegument and Affects Glucose uptake, Development and Reproduction of Schistosoma japonicum

Abstract

Schistosomiasis caused by schsitosomes is a serious global public health concern. The tegument that surrounds the worm is critical to the schistosomes survival. The tegument apical membrane undergoes a continuous process of rupture and repair owing to membranous vacuoles fusing with the plasma membrane. Vesicle-associated membrane protein 2 (VAMP2), a member of soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNAREs) is required for membrane fusion. Here, we used RNA interference (RNAi) to knock down the expression of VAMP2 of Schistosoma japonicum (SjVAMP2), and both real-time PCR and western blot analysis confirmed the suppression of this molecule, as well as the suppression of the transcript levels of schistosome glucose transporters (SGTP1 and SGTP4), and insulin receptors (SjIR1 and SjIR2). SjVAMP2-suppressed worms exhibited a lower viability, and phenotypic alterations were also observed in the tegument. Moreover, the glucose consumption of SjVAMP2-suppressed worms decreased significantly in 4 and 6 days, respectively, as well as a significant reduction in egg production. We also observed a significant reduction in worm burden and hepatic eggs burden in two independent RNAi experiment in vivo, and minor pathological changes in mice treated with SjVAMP2 specific small interfering (si)RNA. These findings reveal that SjVAMP2 may play important roles in the maintenance of tegument, glucose uptake, worm development and egg production in schistosomes.Schistosomiasis is a tropical parasitic disease that infects approximately 200 million people, and approximately 700 million people are at risk in 74 countries; it is caused by blood-dwelling fluke worms of the genus Schistosoma. Schistosomes have a complex life cycle that involves snails as intermediate hosts, and mammals (including humans) as definitive hosts 1, 2 . After cercariae penetrate the skin, they transform into young worms known as schistosomula, move into the bloodstream, and mature. After sexual maturation, adult schistosomes mate and lay eggs, and the eggs are primarily responsible for the pathological damage and disease transmission 3, 4 . Paired male and female schistosomes reside in the mesenteric veins of mammalian hosts and can survive for decades surrounded by the components of the immune system. Therefore, these organisms must have sophisticated mechanisms to evade host immune effectors and use host nutrients for metabolic processes and growth 5 .The entire worm is surrounded by a continuous cytoplasmic membrane, or syncytium, known as the tegument which is the direct interface between the parasite and its host 6 . The tegument is believed to be pivotal in evading hostile immune responses via antigenic mimicry 7,8 , proteolytic degradation of "attacking" host proteins 9 , rigid biophysical membrane properties 10 and a rapid tegumental membrane turnover 11,12 . Besides, the tegument is an important site of nutrient uptake from the host, such as glucose 13,14 , amino acids and cholesterol 15,16 , and also an ideal target sit...

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“…Interestingly, three phosphorylated proteins identified in Cluster 10 are involved in SNARE interactions during vesicular transport and thus might play an important part in the successful delivery of vesicles to the schistosome surface to replenish/modify the host-interactive surface layer of the parasite which turns over in vivo. In this context, the SNARE family member vesicle associated membrane protein 2 (VAMP2) was recently found to play a likely role in tegument maintenance, glucose uptake and egg production in S. japonicum [81]. Moreover, because the contents of schistosomederived extracellular vesicles [82,83] have recently been found to modulate host immune cells to support parasite survival [84,85], developing an understanding of vesicle trafficking mechanisms in these worms is a priority.…”

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“…It should be noted that, in addition to host insulin, schistosome IRs can also bind to the schistosome insulin-like peptide, thereby activating the worm’s insulin pathway [ 68 ]. Further studies confirmed that vesicle-associated membrane protein 2 (VAMP2) knockdown significantly affected the transcript levels of SGTP1 , SGTP4 , and insulin receptors ( IR1 and IR2 ) [ 69 ]. In female worms, vamp2 RNAi mainly caused a reduction in egg production [ 69 ], which may be influenced by impaired energy access in males [ 70 ].…”

“…Further studies confirmed that vesicle-associated membrane protein 2 (VAMP2) knockdown significantly affected the transcript levels of SGTP1 , SGTP4 , and insulin receptors ( IR1 and IR2 ) [ 69 ]. In female worms, vamp2 RNAi mainly caused a reduction in egg production [ 69 ], which may be influenced by impaired energy access in males [ 70 ].…”

“…The Vamp2 gene is mainly expressed in the tegument and its transcript is abundantly expressed in schistosomula and adult worms [ 97 ]. Suppression of Vamp2 revealed that 67% of the treated worms had significant changes in their tegument and underlying tissues, manifested as partial tegument shedding, and the formation of oversized bulb-like structures [ 69 ] ( Fig 3A ).…”