RNA sequencing and proteomic profiling reveal different alterations by dietary methylmercury in the hippocampal transcriptome and proteome in BALB/c mice

Abstract

Methylmercury (MeHg) is a highly neurotoxic form of mercury (Hg) present in seafood. Here, we recorded and compared proteomic and transcriptomic changes in hippocampus of male BALB/c mice exposed to two doses of MeHg. Mice were fed diets spiked with 0.28 mg MeHg kg-1, 5 mg MeHg kg-1, or an unspiked control diet for 77 days. Total mercury content was significantly (P < 0.05) increased in brain tissue of both MeHg-exposed groups (18 ± 2 mg Hg kg-1 and 0.56 ± 0.06 mg Hg kg-1). Hippocampal protein and ribonucleic acid (RNA) expression levels were significantly altered both in tissues from mice receiving a low dose MeHg (20 proteins/294 RNA transcripts) and a high dose MeHg (61 proteins/876 RNA transcripts). The majority but not all the differentially expressed features in hippocampus were dose dependent. The combined use of transcriptomic and proteomic profiling data provided insight on the influence of MeHg on neurotoxicity, energy metabolism, and oxidative stress through several regulated features and pathways, including RXR function and superoxide radical degradation.

Keywords: RNA sequencing; hippocampus; methylmercury; mice; proteomic.

Graphical Abstract

Juvenile mice, exposed to low (0.04 mg kg^–1 bw^–1 day^–1) and high dose (0.67 mg kg^–1 bw^–1 day^–1) MeHg, revealed differential expression of brain proteome and transcriptome.

Fig. 1

Hg concentration (mg Hg kg^–1, ww) in cortex collected during the last week of the experiment. Data are presented as means with 95% confidence interval spread (n = 6). Different letters indicate statistical significance between groups. Statistics are performed using one-way ANOVA and Tukey's multiple comparison test on Box-Cox transformed data; raw data are presented in figure. Abbreviations: Ctr, control; LD, low dose; HD, high dose; ww, wet weight.

Fig. 2

PCA of proteins (A, n = 4) and RNA transcripts (B, n = 5). Multigroup comparisons (ANOVA) were performed using QOE, P < 0.05. Abbreviations: Ctr, control; LD, low dose; HD, high dose.

Fig. 3

Overview of differentially expressed proteins and RNA overlapping between the two exposure groups. The differentially expressed features displayed are initially compared with the control group. Table of overlapping RNA and proteins is found in Table S5. Abbreviations: LD, low dose; HD, high dose; prot, proteins.

Fig. 4

Comparison of differentially expressed proteins and RNA by MeHg exposure (LD and HD related to Ctr) detected through proteomics and RNA sequencing, respectively (one-way ANOVA, P < 0.05). Features are matched and overlapped independent of MeHg exposure dose. The overlapping features are presented in Table 2.

Fig. 5

Overlapping canonical pathways and upstream regulators between RNA sequencing and proteomics, and LD and HD. (a) Overlapping significant canonical pathways (P < 0.05); “a” denotes overlap between HD RNA and HD protein; “b” denotes overlap for LD protein and HD RNA; and “c” denotes overlap for HD both for RNA and proteins and LD RNA. (b) Overlapping significant upstream regulators (P < 0.05); “a” denotes overlap between HD RNA and HD protein; “b” denotes overlap for LD protein and HD RNA; “c” denotes overlap for HD both for RNA and proteins and LD protein; “d” denotes overlap for all groups; “e” denotes overlap for LD and HD for proteins and LD for RNA; “f” denotes overlap for LD and HD for RNA and HD protein; and “g” denotes overlap for HD protein and LD RNA.