Form of dietary selenium affects mRNA encoding cholesterol biosynthesis and immune response elements in the early luteal phase bovine corpus luteum

Abstract

Widespread regions of the southeast United States have soils, and hence forages, deficient in selenium (Se), necessitating Se supplementation to grazing cattle for optimal immune function, growth, and fertility. We have reported that supplementation with an isomolar 1:1 mix (MIX) of inorganic (ISe) and organic (OSe) forms of Se increases early luteal phase (LP) progesterone (P4) above that in cows on ISe alone. Increased early LP P4 advances embryonic development. Our objective was to determine the effect of form of Se on the transcriptome of the early LP corpus luteum (CL) with the goal of elucidating form of Se-regulated processes affecting luteal steroidogenesis and function. Non-lactating, 3-yr-old Angus-cross cows underwent 45-d Se-depletion, then repletion periods, and then at least 90 d of supplementation (TRT) with 35 ppm Se/d as either ISe (n = 5) or MIX (n = 5). CL were then recovered on day 7 of the estrous cycle, total RNA isolated, and the effect of TRT on the luteal transcriptome evaluated using bovine gene 1.0 ST arrays (Affymetrix, Inc., Santa Clara, CA). The abundance of transcripts in each CL was subjected to one-way ANOVA using Partek Genomic Suite software to determine TRT effects. Microarray analysis indicated a total of 887 transcripts that were differentially expressed and functionally annotated, with 423 and 464 up- and down-regulated (P < 0.05) in MIX vs. ISe CL, respectively. Bioinformatic analysis (Ingenuity Pathway Analysis) revealed the top TRT-affected canonical pathways to include seven specific to cholesterol biosynthesis and two to inflammatory responses. Results from the microarray analysis were corroborated by targeted real-time PCR. MIX CL had increased (P < 0.05) abundance of transcripts regulating cholesterol biosynthesis including DHCR7, DHCR24, and CYP51A1 (fold changes of 1.65, 1.48, and 1.40, respectively), suggesting MIX-induced increases in P4 to be due, in part, to increased availability of substrate to luteal cells. In addition, MIX CL had increased (P < 0.05) abundance of immune-response transcripts including C1QC, FAS, ILR8B, and IL1R1 (fold changes of 2.30, 1.74, 1.66, and 1.63, respectively). SREBF1 mRNA was also increased (1.32-fold, P < 0.05) in the MIX CL, which increases cholesterol synthesis and stimulates IL1B, linking effects of form of supplemental Se (TRT) on cholesterol biosynthesis and immune function in the CL.

Keywords: cholesterol; corpus luteum; immune; progesterone; selenium; transcriptome.

Figure 1.

Microarray array-array intensity correlation plot.

Figure 2.

Score plot of principal component analysis of microarray transcriptome analysis of 10 samples of luteal tissue from cows supplemented with 3 mg Se/d in vitamin-mineral mixes as sodium selenite (ISe, n = 5, red spheres) or a 1:1 blend of ISe and OSe (MIX, n = 5, green spheres).

Figure 3.

Effect of form of Se on concentrations of total Se (ppm; LS Mean ± SEM) in whole blood of cows supplemented with either ISe (Sodium selenite, n = 5) or a 1:1 blend (MIX) of ISe and OSe (Sel-Plex, n = 5). Data were analyzed as an ANOVA with repeated measures. Total Se in whole blood was not affected by treatment (P = 0.24) but was affected by time (P < 0.01). Adapted from Carr et al. (2022).

Figure 4.

Hierarchical cluster analysis of the 887 transcripts identified as differentially expressed (one-way ANOVA P-values of < 0.05) in the CL of cows supplemented with 3 mg Se/d in vitamin-mineral mixes as sodium selenite (ISe, n = 5) or a 1:1 blend of ISe and OSe (MIX, n = 5).

Figure 5.

Overlapping canonical pathways associated with cholesterol biosynthesis and inflammatory responses from the bioinformatic analysis (Ingenuity Pathway Analysis).

Figure 6.

Mechanism of cholesterol availability and steroidogenesis with an emphasis on cholesterol biosynthesis. Blue arrows indicate increased abundance of mRNA transcripts identified by microarray analysis. Yellow arrows indicate confirmation of differences by qPCR.