Heat shock response in PBMCs of Nellore cows after in vitro thermal stress

Adaptation is an important feature to be studied in animals when thinking about maintenance and raise of productivity<i>.</i> Although Nellore breed is widely disseminated in Brazil, the knowledge related to its thermotolerance in tropical climate conditions remains unknown. Hence, the aim of this study was to understand the Nellore breed cellular adaptation when exposed to heat shock in vitro, using peripheral blood mononuclear cells (PBMCs). The comprehension of the most expressed and sensible heat shock proteins in <i>Bos taurus indicus</i> may elucidate a molecular marker for genetic improvement related to thermotolerance. Previous to blood sampling, the physiological parameters of 16 cows were measured in order to classify them in efficient and non-efficient on heat loss. For this experiment, the blood was collected in three different heparin tubes by jugular venipuncture only in 10 cows, 5 efficient and 5 non-efficient, at morning. The molecular analyzes were performed in Physiology and Molecular Endocrinology Laboratory, Faculty of Veterinary Medicine and Animal Science, University of São Paulo. After sampling, each blood tube were placed in three different water bath devices calibrated for: 38°C, 40°C and 42°C for two consecutive hours. The PBMCs were separated, washed with hemolysis solution, the RNA extracted, the cDNA synthetized and performed the qPCR for the genes HSP60, HSP70 and HSP90. There was a maintenance on HSPs transcripts on 38°C and 40°C and a decrease on all HSPs transcripts at 42°C. Among all, the HSP70 was the most expressed at 38°C and 40°C, elucidating its protective importance. No difference was observed between gene expression and heat loss efficiency. In conclusion, the Nellore cell adaptability was confirmed by the maintenance of heat shock proteins 60, 70 and 90 kDa. The pathway for understanding responses involving thermotolerance is still long and requires more knowledge of cell signaling, either <i>in vitro</i> or <i>in vivo </i>conditions<i>.</i> Taken together, these informations may contribute in future keys for genetic selection of adapted animals.