| Cyanobacterial bloom has become an ecological disaster and causes huge health hazards to animals and human beings all over the world. Cyanobacterial bloom can produce many toxic derivative pollutants. Microcystin (MC) is a kind of secondary metabolic pollutant produced by cyanobacteria. MC-LR (L for leucine and R for arginine) has most occurrence amount, the highest toxicity and most wide distribution in environment. The toxicity of MC-LR has been extensively reported, however the exact molecular mechanisms of toxicity and health hazards remain unknown. Lake Taihu is undergoing a gradual eutrophication and an annual occurrence of cyanobacterial surface bloom in the warm seasons. Epidemiological investigation in Lake Taihu area indicated that hepatic disease in local region was associated with the contamination of drinking water by cyanobacterial bloom. Moreover, some public health problems, e.g. increase of liver cancer and digestive tract tumor incidence, have also arisen from the chronic exposure to cyanobacterial bloom in this area. However,the toxicity and toxic mechanisms of cyanobacterial bloom's water from Lake Taihu was not studied. Cyanobacterial bloom often happens in the environments with high level of nitrogen and ammonia nitrogen (NH4+-N) produces after cyanobacterial bloom. NH4+-N with high concentration can cause higher toxicity to aquatic animals,however, there is little information on toxicity and toxic mechanisms of NH4+-N in mammal animals and human beings.Endoplasmic reticulum stress (ERS) is a newly discovered pathway of medicating apoptosis and pathogenesis of many metabolic diseases. In this thesis,ERS in murine liver and kidney exposed to microcystin-LR and cyanobacterial bloom's water samples from Lake Taihu were studied. ERS in murine liver exposed to cyanobacterial bloom's water samples from Lake Taihu and genes expression related lipid metabolism were studied. This thesis also studied whether exposure to cyanobacterial bloom's pollutants MC-LR and NH4+-N increased risks of type 2 diabetes mellitus (T2DM). The main results and conclusions are listed as follows:1. Due to the organ specificity of toxic effects induced by MC-LR, exposure to 20 ?g/ kg/d MC-LR for 21 days induced damage and apoptosis in hepatic cells but not in renal cells. MC-LR exposure at 20 ?g/kg/d for 21 days induced ERS in hepatic cells but not in renal cells of mice and the involvement of ERS in induction of apoptosis in hepatic cells and anti-apoptosis in renal cells of mice exposed to MC-LR2. CHOP- and cleaved-caspase-12-mediated ERS pathway played important roles in MC-LR-induced and ERS-dependent apoptosis in hepatic cells but not in renal cells under exposure to 20 ?g/kg/d MC-LR for 21 days. The relevant special genes and proteins, such as CHOP and cleaved-caspase-12, could be considered as potentially new biomarkers used for detection of MC-LR toxicity in toxicological risk assessment.3. Cyanobacterial bloom's water samples from Meiliang Bay of Lake Taihu induced hepatic cell apoptosis via ERS but not renal cell. Meiliang Bay's water has lower toxicity to kidney than liver, but changed mRNA expression of molecules of ERS signaling in kidney, and the involvement of ERS in induction of anti-apoptosis in renal cells of mice exposed to cyanobacterial bloom's water samples.4. Water samples from Meiliang Bay caused hepatic lipid metabolism perturbations and abdominal obesity was found after the mice were chronically exposed to cyanobacrerial bloom's water samples from Lake Taihu. Sterol regulatory caccade response of ERS played an important role in hepatic lipid metabolism perturbations caused by cyanobacterial bloom's water samples. Water samples from Meiliang Bay's induced an obvious change of mRNA expressions of the lipid metabolism-related genes,including the up-regulation in the mRNA levels of LPL and Insig2, and down-regulation in mRNA expression level of PEPCK. Central lake's water sample markedly up-regulated mRNA levels of G6pc, LPL,Insig2 and PPAR-?.These results indicated that genes related lipid metabolism involved the lipid metabolic abnormality caused by cyanobacterial bloom's water.5. In addition, exposure to Meiliang Bay's water sample caused up-regulated mRNA expression of the pro-inflammatory cytokine TNF-a and the inflammation-related genes TLR-2 and TLR-4. Inflammatory reaction played an important role in lipid metabolism abnormality caused by Meiliang Bay's water sample. This study on toxicity of cyanobacterial bloom's water samples from Lake Taihu firstly demonstrated that exposure to cyanobacteria-blooming water might be involved the incidence of T2DM in mice.6. MC-LR and NH4+-N caused hyperinsulinemia and NH4+-N also caused hyperglycemia. In addition, MC-LR and NH4+-N changed triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and high-density lipoprotein cholesterol (HDL-C) contents. The results indicated MC-LR and NH4+-N increased the risk of T2DM.7. Exposure to cyanobacterial bloom's pollutants MC-LR and NH4+-N impaired insulin receptor signaling pathway, for example, MC-LR and NH4+-N down-regulated mRNA levels of IRS-1, IRS-2, Akt, and also down-regulated protein expression of PI3K, p-IRS-1 and p-IRS-2. Exposure to MC-LR and NH4+-N up-regulated the downstream molecules of PI3K, such as p-Akt level in liver. These results indicated that insulin receptor signaling pathway played an important role in potential public health risks of T2DM induced by cyanobacterial bloom.8. MC-LR and NH4+-N exposure had an obvious change in mRNA expressions of ERS signaling molecules, including the increase in the mRNA and protein levels of ATF6, eIF2a and PERK. Moreover, the effects of MC-LR and NH4+-N's exposure included the change of ERS downstream genes expression such as down-regulation of mRNA and protein levels of SREBP-1c, and up-regulation of ACACA, FASn and Gsk-3? by MC-LR as well as up-regulation of mRNA and protein levels of SREBP-1c,ACACA, FASn and Gsk-3? by NH4+-N These results showed that cyanobacterial bloom might induce potential public health risks of T2DM by ERS. |
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