Effects of Maternal Nutrient Restriction during Either the First or Second Trimester on Bovine Fetal Adipose Tissue microRNA at the End of Mid-Gestation

The objective of this study was to determine the effects of early or mid-gestation maternal nutrient restriction on adipose tissue development and expression of microRNAs. Primiparous Angus-cross cows (n = 22) were synchronized and inseminated with sexed semen (time of AI= d0) from a single Angus sire. Animals were fed at 1.2 x (Control [CON]) or 0.55 x (Nutrient Restricted [NR]) of maintenance energy and protein requirements based on BW (NRC 1996). Animals were blocked into groups by BCS and BW then fed CON (n = 8) from d 30-190 of gestation, NR (n = 7) from d 30-110 followed by CON from d 110-190, or CON (n = 7) from d 30-110 followed by NR from d 110-190. Cows were harvested and fetuses collected on d 190 of gestation. Isolation of total RNA was performed using flash frozen fetal perirenal adipose tissue samples (3 subsamples/treatment) using the mirVana microRNA isolation kit and analyzed using a previously validated bovine miRNA microarray containing 1636 probes. Fetal weights tended to be reduced (P = 0.07) in NR/CON and CON/NR vs. CON fetuses (9.05 ± 0.48, 8.91 ± 0.48 vs. 10.34 ± 0.45 kg, respectively). Perirenal adipose weight tended to be increased (P = 0.09) in CON fetuses compared to NR/CON and CON/NR fetuses (34.3 ± 1.7 vs 28.3 ± 1.9, and 30.8 ± 1.9 g, respectively). Fetal perirenal adipose tissue from the CON group had bta-miR-376b and PC-5p-8838_20 unregulated (P < 0.05) and fourteen down regulated miRNAs (P < 0.05) vs NR/CON and CON/NR adipose tissue. The miRNA, mmu-miR-6236-p3 was upregulated (P < 0.05) in NR/CON group and no other microRNAs independently down regulated (P > 0.05) vs CON/NR and CON animals. Animals in the CON/NR group exhibited 3 upregulated (P < 0.05) miRNAs, with bta-miR-361 and bta-miR-2904-3-p5 down regulated (P < 0.05) vs. CON and NR/CON fetal perirenal adipose. Nine miRNA were similarly upregulated (P < 0.05) in the NR/CON and CON/NR tissues compared to the CON fetuses. Five microRNAs were upregulated (P < 0.05) in the CON and NR/CON fetal adipose tissue compared to the CON/NR fetal adipose tissue. Hence, maternal nutrient restriction during early or mid-gestation tends to cause alterations in fetal growth and affects miRNA regulation differently depending on the time of gestation in which the restriction occurs. Interestingly, a majority of miRNA expression patterns are similarly upregulated between the two NR treatments compared to the CON fetuses.