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Objective: This study aimed to explore the mechanism by which noise contributes to the development of Alzheimer's disease (AD)–like lesions. Method: Male Wistar rats (24 months) were allocated into two groups (n = 6 per groups): a noise group exposed to 98 dB sound pressure–level white noise for 4 hours daily from 8:00 to 12:00 for 30 days, and a control group without noise exposure. The cognitive functions of the rats were assessed using new-object recognition and Morris water maze tests. Then, hippocampal tissues were collected, and the levels of amyloid β 1-42 (Aβ1-42), Aβ1-40, brain-derived neurotrophic factor (BDNF), and tropomyosin receptor kinase B (TrkB) were measured using enzyme-linked immunosorbent assay (ELISA). Protein expression was evaluated through Western blot. Results: Noise exposure significantly impaired cognitive and recognition abilities, increased the escape latency, and decreased the number of crossings through the platform quadrant intersection and the time spent in the target quadrant (P < 0.01). The new-object exploration and recognition index of the rats in the noise group markedly decreased (P < 0.01). ELISA results indicated increases in Aβ1-40 and Aβ1-42 levels and decreases in BDNF and TrkB levels in the rat hippocampus in the noise group (P < 0.01). Western blot analyses revealed that beta-site amyloid precursor protein (APP) cleaving enzyme 1, phosphorylated tau protein, gamma-H2A histone family, member X, checkpoint kinase 2, p53, and p21 were remarkably elevated in the noise group (P < 0.01). Conclusion: Chronic noise exposure can cause hippocampal genetic damage in aged rats, leading to cognitive disorders and the development of lesions similar to those observed in AD. Thus, noise is a potential risk factor for neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

The signal peptide-encoding sequence, which was included in the gene (GenBank No. DQ782954) encoding for endoglucanase, was removed by PCR. The gene without the signal peptide was then ligated with the expression plasmid pHIS1525. The recombination plasmid pHIS1525 was transformed into Escherichia coli DH5a and the transformant was designated DH5a-pHIS1525-G7. The plasmid from the recombinant DH5a-pHIS1525-G7 was transformed into the proto-plasts of Bacillus megaterium strains WH320, and the genetically engineered bacterium, known as WH320-pHIS1525-G7, was acquired. The effective expression of the gene in the recombinant was confirmed by Congo-red dyeing and SDS poly-acrylamide gel electrophoresis (SDS-PAGE). WH320-pHIS1525-G7 was cultured in optimum condition. The activity of the endoglucanase was 899U, which was 11.22-fold higher than that of B.subtilis C-36. The properties of enzyme were deter-mined. The optimum temperature and pH value were 65 and pH 6.0, respectively. The enzyme maintained over 80% of the original enzyme activity between pH 4.5 and pH 10.0 after incubated at 50 for 30 min.