Effect of antagomir-22-3p treatment on skeletal muscle growth in intrauterine growth-restricted lambs

Cell-free circulating miR-22-3p expression was more downregulated (P < 0.05) in NR-ANT22 lambs compared to that in CON-SHAM on d 14 after injection. On d 21 after injection, miR-22-3p expression in plasma tended to be more downregulated (P = 0.08) in NR-ANT22 compared to CON-SHAM. Lamb body weight and muscle weights at harvest were similar between the NR-ANT and CON- SHAM treatment groups. In the semitendinosus (ST) muscle, miR-22-3p expression was more downregulated (P < 0.05) in NR-ANT22_R ST (treated) lambs compared to that in NR-ANT22_L ST (non-treated) and CON-SHAM ST. In the heart and semimembranosus (SM) muscles, the expression of miR-22-3p was more downregulated (P < 0.05) in NR-ANT22 compared to that in CON-SHAM. In the gastrocnemius muscle, miR-22-3p expression remained unchanged (P > 0.05). The number of types I, IIa, and IIax muscle fibers were greater (P < 0.05) in NR-ANT22 lambs than those in CON-SHAM, whereas the number of type IIx fibers was greater (P < 0.05) in CON-SHAM lambs. NR-ANT22 treatment appears to promote a shift toward more oxidative muscle fiber metabolism. The systemic injection of antagomir-22-3p downregulated miR-22-3p expression in circulation and muscle tissues, which, in turn, altered the expression of HDAC/SIRT genes involved in muscle fiber type conversion and hypertrophy.