Evaluating the expression of microRNA miR-1 and miR-133 in the muscle of horses fed a docosahexaenoic acid -rich algae supplement after prolonged dexamethasone treatment
MicroRNAs (miRNAs) are small noncoding RNAs that bind to the 3’ untranslated (3’UTR) region of genes and are responsible for inhibiting translation or promoting mRNA degradation. Two well characterized muscle-specific miRNAs are miR-1, and miR-133. MiR-1 decreases myoblast proliferation and increases differentiation, whereas miR-133 has an opposing effect promoting myoblast proliferation while decreasing differentiation. It is known that skeletal muscle breakdown and an increase in circulating amino acids are associated with the decreased insulin sensitivity after prolonged dexamethasone (DEX) treatment. In horses there is an association between an increase in miR-1 and miR-133 levels and diseases involving muscle breakdown. Supplementing diets with DHA-rich algae (Algae SP-1, Alltech Inc., (ALG)) improves insulin sensitivity and decreases plasma amino acid levels in horses after prolonged DEX treatment. The objective of this study was to determine the effect of Algae SP-1 supplementation on miR-1 and miR-133 expression in healthy, mature horses (n = 5) before and after DEX treatment using a balanced, crossover design of two 56-d periods. In each period, horses were fed a basal diet (CON), or diet + 152 g/d of ALG for 28 d and muscle was sampled (pre-DEX). DEX was then administered (0.04 mg/kg BW/d, orally) for 21 d while dietary treatments continued. On d 49 of dietary treatments (post-DEX), muscle was sampled and microRNA was measured using TaqMan MicroRNA Assays (Applied Biosystems). The relative quantification (RQ) was expressed as a ratio of the target microRNA to control microRNA normalized to a pooled control (CON, pre-DEX) using the delta-delta Ct (ΔΔCt) method. There was no effect of diet, DEX or diet*DEX interaction on skeletal muscle miR-1 and miR-133 expression. Novel techniques used for miRNA evaluation could be useful to help relate changes in gene expression to physiological status, however further studies are needed.
Keywords: microRNA, horse, dexamethasone, docosahexaenoic acid