Differential expression of heat shock protein genes associated with heat stress in Nelore and Caracu beef cattle

Abstract

High temperatures cause elevation of both blood cortisol concentrations and rectal temperature, which induce the action of heat shock proteins (HSPs) to regulate cell viability against heat stress. The aim of this study was to verify the effects of high temperatures on physiological parameters and to evaluate the level of relative expression of the HSPD1 (heat shock protein family D (Hsp60) member 1), HSPA1A (heat shock protein family A (Hsp70) member 1A), and HSP90AA1 (heat shock protein 90 alpha family class A member 1) genes in Nelore (Bos taurus indicus) and Caracu (Bos taurus taurus) beef cattle under high temperatures. A total of 40 Caracu and 37 Nelore steers were evaluated inside the pen in the morning, while in the afternoon the steers were evaluated in two different environments, shade and sun, for two hours to detect their rectal (RT) and skin (ST) temperatures. Blood samples were collected before (07:00 h) and after (15:00 h) the experiment to evaluate serum cortisol levels using ELISA and the relative expression of HSPD1, HSPA1A, and HSP90AA1 using qPCR. The data were analyzed using a MIXED model with least square means. Significant differences were observed between the Nelore and Caracu breeds in relation to RT (38.8 °C and 39.2 °C, respectively), cortisol concentration (18.5 and 23.7 ng/mL, respectively), and the relative expressions of HSPD1 (2.70 ± 0.12 and 3.05 ± 0.09, respectively) and HSP90AA1 (1.54 ± 0.10 and 1.25 ± 0.09, respectively). The lowest cortisol concentration (17.2 ng/mL) and RT (38.7 °C) were obtained in the morning treatment. Sun exposure did not influence the relative expression of the HSPs. Significant changes were observed during the months studied, indicating that environmental conditions (temperature and humidity) influenced RT, cortisol concentrations, and expression of the HSPs. The highest cortisol levels (24.3 ng/mL) and expression of HSPA1A (2.65 ± 0.15) were detected during the highest relative humidity. It is well known that an increase in RT is associated with the activation of HSPs in ruminants as observed herein, and the highest RT (39.1 °C) and relative expression of HSPD1 (3.35 ± 0.15) and HSP90AA1 (1.98 ± 0.13) were observed during the lower relative humidity and higher air temperature conditions. The physiological parameters and HSP expression pattern indicated that Caracu, despite being a tropically adapted taurine breed, is less adapted to thermal stress as compared to Nelore, a zebuine breed.