Functional enrichment analysis
The DEGs were analyzed by DAVID database(https://david.ncfcrf.gov), an online tool providing a functional annotation of genes and discover enriched functional-related gene group [21]. The Gene Ontology (GO) constructs the annotation of genes, gene products and sequence [22]. KEGG pathway analysis was carried out to explore the gene linking functional and genomic information [23]. P<0.05 were considered significant.