The metabolic pathways of the identified proteins were analyzed according to the KEGG pathway database (http://www.genome.jp/kegg/pathway.html). Gene Ontology (GO) analyses (http://www.geneontology.org) were conducted according to a previously reported method26. For the differential protein expression, GO functional enrichment and KEGG pathway analyses were performed using the Cytoscape software version 2.6.2 (http://www.cytoscape.org/).