circular rna (circrna) molecules are noncoding rnas with unique circular covalently closed structures that contribute to gene expression regulation, protein translation and act as microrna sponges. circrnas also have important roles in human disease, particularly tumorigenesis and antitumor processes. Methylation is an epigenetic modification that regulates the expression and roles of dna and coding rna and their interactions, as well as of noncoding rna molecules. Previous studies have focused on the effects of methylation modification on circRNA expression, transport, stability, translation and degradation of circrnas, as well as how circrna methylation occurs and the influence of circRNAs on methylation modification processes. circRNA and methylation can also regulate disease pathogenesis via these interactions. In the present study, we define the relationship between circrnas and methylation, as well as the functions and mechanisms of their interactions during disease progression. Contents1. introduction 2. literature search strategy 3. dna methylation 4. rna methylation 5. effects of methylation on circrna biological function 6. Study of methylation-modified circRNAs in disease 7. circRNAs influence disease progression via methylation regulation 8. databases related to circrna methylation research 9. conclusion

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The plateau environment impacts male reproductive function, causing decreased sperm quality and testosterone levels. l-carnitine can improve the semen microenvironment. However, the role of l-carnitine in a high-altitude environment remains unclear. In our study, we investigated the effects of l-carnitine administration in a male Wistar rat reproductive system injury model in the context of a simulated high-altitude environment. Rats were randomly divided into a normal control group (group A1, A2-low dose and A3-high dose) and high-altitude model groups (group B, C-low dose and D-high dose) with 20 rats in each group. With the exception of the normal control group exposed to normoxic conditions, the other groups were maintained in a hypobaric oxygen chamber that simulated an altitude of 6000 m for 28 days. In the experimental period, the low-dose groups (A2 and C) were administered 50 mg/kg l-carnitine via intraperitoneal injection once a day, and the high-dose groups (A3 and D) were given 100 mg/kg. After the feeding period, blood samples were collected to assess blood gas, serum hormone levels and oxidative stress. Sperm from the epididymis were collected to analyse various sperm parameters. After obtaining the testicular tissue, the morphological and pathological changes were observed under a light microscope and transmission electron microscopy (TEM). The impact of the simulated high-altitude environment on the rat testis tissue is obvious. Specifically, a decreased testicular organ index and altered indices of arterial blood gas and serum sex hormone levels caused testicular tissue morphological damage, reduced sperm quality, increased sperm deformity rate and altered malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) concentrations. The results demonstrate that l-carnitine can be administered as a preventive intervention to reduce the reproductive damage caused by high-altitude hypobaric and hypoxic environments and improve semen quality in a rat model.