Muscular microRNA expressions in healthy and myopathic horses suffering from polysaccharide storage myopathy or recurrent exertional rhabdomyolysis

Reasons for performing study: MicroRNAs (miRNA) are small endogenous noncoding interfering RNA molecules (18–25 nucleotides) regarded as major regulators in eukaryotic gene expression. They play a role in developmental timing, cellular differentiation, signalling and apoptosis pathways. Because of the central function of miRNAs in the proliferation and differentiation of the myoblasts demonstrated in mouse and man, it is assumed that they could be present in equine muscles and their expression profile may be related to the muscle status. Objective: To identify miRNA candidates in the muscles of control and affected horses suffering from polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER). Methods: Muscle biopsies were collected in the gluteus medius of horses allocated into 4 groups: French Trotters (3 control‐TF vs. 3 RER‐TF) and Norman Cob (5 control‐Cob vs. 9 PSSM‐Cob). Blood samples were collected for miRNA analysis. Total RNA were extracted and real time quantitative RT‐QPCR analysis were conducted using 10 miRNA assays (mir‐1‐23‐30‐133‐181‐188‐195‐206‐339‐375). Results: All the miRNA candidates were significantly detected in the muscles and some in blood samples. Variance analysis revealed highly significant (P<0.0001) effects of the miRNA type, breed and pathology on the miRNA expression. A specific miRNA profile was related to each myopathy: a higher expression of mir‐1, 133, 23a, 30b, 195 and 339 in RER‐TF vs. control‐TF (P<0.05); a higher expression of mir‐195 in PSSM‐Cob vs. control‐Cob (P<0.05). The miRNA profile was different between breeds for mir‐181, 188 and 206 (P<0.05). The mir‐1, 133, 181, 195 and 206 were detected in blood of control‐Cob and PSSM‐Cob horses. Conclusions: This first study about muscular miRNA profile in equine myopathies indicated that it is possible to discriminate pathological from control horses according to their miRNA profile. The RER miRNA profile was more specific and contrasted than the PSSM profile.