Transcriptomic analysis of skeletal muscle from beef cattle exposed to illicit schedules containing dexamethasone: identification of new candidate biomarkers and their validation using samples from a field monitoring trial.

Growth promoters (GPs) such as the glucocorticoid dexamethasone (DEX) and the β-adrenergic agonist clenbuterol (CLEN) are still used abusively in beef cattle production. Transcriptomic markers for indirect detection of such GPs have been discussed in either experimentally treated animals or commercial samples separately. In the present study we examine the transcriptomic signature of DEX alone or in combination with CLEN in skeletal muscle of experimentally treated beef cattle, and, furthermore, compare them with previously screened commercial samples from a field-monitoring study, as well as with proteomics data representing the same set of samples. Using DNA microarray technology, transcriptomic profiling was performed on 12 samples representing three groups of animals: DEX (0.75 mg/animal/day, n = 4), a combination of DEX (0.66 mg/animal/day) and CLEN (from 2 to 6 mg/animal/day, n = 4) and a control group (n = 4). Analyses showed the differential expression of 198 and 39 transcripts in DEX and DEX-CLEN groups, respectively. Both groups had no common modulated genes in between, neither with the proteomics data. Sixteen candidate genes were validated via qPCR. They showed high correlation with the corresponding microarray data. Principal component analysis (PCA) on both the qPCR and normalised microarray data resulted in the separation of treated animals from the untreated ones. Interestingly, all the PCA plots grouped the DEX-positive samples (experimental or commercial) apart from each other. In brief, this study provides some interesting glucocorticoid-responsive biomarkers whose expression was contradictory to what is reported in human studies. Additionally, this study points out the transcriptomic signature dissimilarity between commercial and experimentally treated animals.