*2.2. Di*ff*erentially Expressed RNAs in Serum Exosomes with Age*

To determine whether aging affects the levels of serum exosomal RNAs, RNA profiles were determined by next-generation RNA Sequencing. After quality control and filtering, a total of 35117 RNAs, including mRNA, miRNAs and other type of RNAswere identified in exosomes from serum of young and old rats (Supplementary data). Following application of thresholds for significance, 2736 (17.9%) were down-regulated and 108 (7%) were up-regulated in serum exosomes from old rats (*p* < 0.05, >1.5-fold change; Figure 2A), among identified 15272 mRNA. In addition, 600 miRNAs were identified after quality control, among which 68 were relatively abundant in old rats, including 28 that were down-regulated and 40 that were up-regulated serum exosomes from old rats (*p* < 0.05, >1.5-fold change; Figure 2B). A volcano plot (Figure 2C) and cluster analysis (Figure 2D) revealed the overall distribution of differentially expressed mRNAs and miRNAs of serum exosomes with age after analysis with TargetScan.

**Figure 2.** Profiles for mRNAs and miRNAs of serum exosomes from young and old rats. (**A**,**B**) Venn diagram of all differentially expressed mRNAs (**A**) and miRNAs (**B**) identified in serum exosomes. (**C**) Volcano plot for comparing the differentially expressed exosomal mRNAs and miRNAs in serum from young and old rats after analysis with TargetScan (fold change > 1.5 and *p* < 0.05). (**D**) Heatmap of the differentially expressed mRNAs and miRNAs in serum exosomes from young and old rats (*n* = 6 each group) after TargetScan (fold change > 1.5 and *p* < 0.05). Young, serum exosomes from young rats; Old, serum exosomes from old rats.
