Figure 2.

TCDD elicited effects on the hepatic metabolism of homocysteine. (a) Schematic of pathway depicting enzymes and metabolites associated with homocysteine metabolism. Boxes represent enzymes and circles represent metabolites. (b) Hepatic gene expression associated with homocysteine metabolism was measured at 8 or 28 days by qRT-PCR and RNA-seq, respectively (n = 8). (c) Hepatic protein levels (mean ± s.e.m.) were determined by capillary electrophoresis for AHCY, BHMT, and CBS in male mice at 28 days (n = 4). (d) Metabolite fold change at 8 days (mean ± s.e.m., n = 3–6) or 28 days (mean ± s.e.m., n = 4–5) were determined by LC–MS/MS for betaine, N,N-dimethylglycine and (e) cystathionine (8 and 28 days), or methionine and homocysteic acid (28 days only). (f) Hepatic gene expression of methionine transporters at 28 days (n = 8). (g) Hepatic gene expression associated with homocysteine metabolism was determined by RNA-seq for a time-course after a bolus dose of 30 µg/kg TCDD (n = 5). For the heatmaps, the effective dose (ED₅₀), benchmark dose lower limit (BMDL), and relative transcript counts (rel. count) are denoted. The red/blue color scale represents the log₂(fold change) for differential gene expression. Orange represents the presence of putative dioxin response elements (pDREs). AhR enrichment peaks (FDR ≤ 0.05) are denoted by light green. pDREs found within AHR ChIP-seq enrichment peaks are denoted by garnet. Asterisks (*) denote p < 0.05 determined by one-way ANOVA with a Dunnett’s post-hoc test. Pound signs (#) denote posterior probabilities P1(t) ≥ 0.80 compared to vehicle. Official gene name and symbol: Ahcy adenosylhomocysteinase, Bhmt betaine homocysteine S-methyltransferase, Cbs cystathionine beta-synthetase.