Effects of fat deposition on the expression of insulin-signaling pathway and mTORC1 genes in Finnhorse mares

Obesity and insulin resistance (IR) are key factors lead to equine metabolic syndrome and laminitis. Diet may play an important role in eliciting obesity by affecting insulin dynamics. Insulin-pathway signaling and mTORC1 genes may contribute to incred IR. The first objective of this study was to find and validate internal control genes for quantitative PCR method for adipose tissues in Finnhorse mares. The second aim was to quantitate the expression of mTORC1 and insulin-pathway associated genes after pasture season in two different treatment groups of Finnhorse mares and compare gene expression differences between treatment groups. In addition, gene expression differences were compared between two different adipose tissues. Twenty-two mares were equally divided into eleven equal pairs, the two mares of each group were randomly grazed either on cultivated high-yielding pasture (CG) or on semi-natural grassland (NG) from the end of May to the beginning of September. Eight pairs of Finnhorse mares were selected for gene expression profiling. Subcutaneous adipose tissue (SAT) samples were collected from two groups of Finnhorse mares after pasture season. Gene expression of neck and tailhead SAT were determined with quantitative Real-Time PCR method (qPCR). The selected internal control genes were actin beta (ACTB), glucuronidase beta (GUSB) and mitochondrial ribosomal protein L39 (MRPL39). Candidate genes were mechanistic target of rapamycin (MTOR), sterol regulatory element binding transcription factor 1 (SREBF1), sterol regulatory element binding transcription factor 2 (SREBF2), TBC1 domain family member 7 (TBC1D7), leptin (LEP), glucose transporter type 4 (GLUT4), monocyte chemoattractant protein-1 (MCP-1), retinol binding protein 4 (RBP4), tuberous sclerosis 1 (TSC1), tuberous sclerosis 2 (TSC2). There were no distinct gene expression differences between NG and CG groups in both neck and tailhead SAT. However, RBP4 had significantly (P=0.035) higher and GLUT4 had a trend (P=0.064) to higher mRNA expression in CG group in neck SAT. TSC1 had a trend (P=0.071) of higher expression in CG group in tailhead SAT. Gene expression differences were observed between tailhead and neck SAT. SREBF1 and GLUT4 had significantly (P=0.007 and P=0.026, respectively) higher expression levels in tailhead SAT compared to neck SAT. RBP4 had a trend (P=0.066) to higher expression in neck SAT compared to tailhead SAT. Minor differences in gene expression between NG and CG groups indicate that pasture-associated fat depositionmaynotconsiderably affect expressionof insulin-pathway and mTORC1 genes associated to obesity and IR in studied subcutaneous adipose tissues. These results also provide additional evidence to our hypothesis that fattening resulting on unrestricted grazing on cultivated high-yielding pasture does not increase the risk of metabolic diseases in Finnhorse mares when they have normal body condition at the beginning of the grazing season