Pathological Damage And Immunomodulatory Effects In Zebrafish Exposed To Microcystin-LR

With the development of human civilization, much more sanitary sewage and agriculture fertilizers are poured into water, which results in the increasingly serious eutrophication of lakes, and triggers the widespread occurrence of cyanobacterial blooms. This has been regarded as a serious environmental issue and received increasing attention. A potentially hazardous consequence of cyanobacterial blooms is the production of several kinds of cyanotoxins. The microcystins(MCs) are the most commonly identified toxins in freshwater blooms, and microcystin-LR(MC-LR) is recognized as the most toxic and is distributed worldwide. Fish are easily exposed to MCs either by ingestion or absorption through the skin and gills. Some studies revealed that MCs have adverse impacts on development, growth and immune system of fish, and induced the oxidative damage in fish.The study was conducted to investigate the toxic effects of mycrocystin-LR on fish from perspectives of histopathological lesion and immune response. Adult zebrafish were exposed to 0, 1, 5 and 20 μg/L of MC-LR for 30 d, respectively; Optical microscope and electron microscope were used to observe the tissue pathological changes of spleen, intestines and gill in zebrafish;The expression of immune-related genes Interferon 1(IFN-1),Interleukin 1β(IL-1β),Interleukin 8(IL-8),Transforming growth factor-β(TGFβ) and(Tumor necrosis factor α) TNFα in spleen, intestine and gill was examined by real-time PCR. Results and conclusions: 1. Pathological damage effects of spleen, intestine and gill in zebrafish exposed to MC-LRAfter 30 d exposure to 0, 1, 5 and 20 μg/L of MC-LR, varying degrees of pathological damages were observed in spleen, intestine and gill of zebrafish. In zebrafish exposed to 5 and 20 μg/L MC-LR, edematous mitochondria, deformation of the nucleus and compaction of chromatin were observed in lymphocyte of spleen; frayed gut villi, exfoliation of epithelial cells and widespread cell lyses were observed in intestines; hyperemia in gill lamellae, epithelial tissue edema and uplift and lamellar fusion were observed in gill. After the measure of villus height of foregut and hindgut, we found that the length of intestinal villi markedly reduced in treatment group due to serious damage. The higher concentration of MC-LR in treated groups, the more seriously the intestinal tissue of zebrafish injured. In light of the results above, we inferred that MC-LR induced serious tissue damage in zebrafish, and the higher concentration of MC-LR in treated groups, the more seriously the tissue of zebrafish injured. 2. Immune related gene expression effects of zebrafish exposed to microcystin-LRFive immune-related genes IFN-1, IL-1β, IL-8, TGFβ and TNFα of spleen, intestine and gill of zabrafish were examined by real-time PCR after exposure to 0, 1, 5 and 20 μg/L MC-LR. The transcriptional levels of IFN-1 and IL-8 in spleen significantly were up-regulated in 20 μg/L group, and the transcription of IL-1β and TNFα in spleen increased in 1 μg/L MC-LR treated fish. In addition, the m RNA levels of IFN-1, IL-8, TGFβ and TNFα dramatically increased in intestine and gill of all MC-LR treated groups. The present study indicated that MC-LR exposure caused marked pathological damage. However, fish could positively adjust the expression of innate immune-related genes to resist the tissue damage. Our findings provide strong evidence of the recovery potential of fish exposed to microcystins.