Maloyan A, Palmon A, Horowitz M
Division of Physiology, Hadassah Schools of Dental Medicine and Medicine, The Hebrew University, Jerusalem 91120, Israel.
Am J Physiol. 1999 May;276(5):R1506-15. doi: 10.1152/ajpregu.1999.276.5.R1506.
It has been previously shown that heat acclimation leads to an elevated basal level of 72-kDa heat shock protein (HSP72). Augmented expression of HSP72 is considered as a cytoprotective response. This led us to hypothesize that alterations in the heat shock protein (HSP) defense pathway are an integral part of the heat acclimation repertoire. To investigate this, we studied the temporal profile of basal HSP expression upon acclimation and the dynamics of their accumulation subsequent to acute heat stress (HS). In parallel, HSP72 mRNA level before and after HS was measured. For comparison, HSC mRNA [the constitutive member of 70-kDa HSP (HSP70) family] was measured in similar conditions. Heat acclimation was attained by continuous exposure of rats to 34 degrees C for 0, 1, 2, and 30 days. HS was attained by exposure to 41 or 43 degrees C for 2 h. Thermoregulatory capacity of the rats was defined by rectal temperature, heating rate, and the cumulative heat strain invoked during HS. HSP72 and HSP70 gene transcripts were measured in the left ventricle of the heart by means of Western immunoblotting and semiquantitative RT-PCR, respectively. The resultant acclimatory change comprised a higher resting level of the encoded 72-kDa protein (Delta175%, P < 0.0001). After HS, peak HSP72 mRNA level was attained, 40 and 20 min post-HS at 41 and 43 degrees C, respectively, vs. 60 and 40 min in the nonacclimated group. The subsequent HSP synthesis, however, was dependent on the severity of the cumulative heat strain. At the initial phase of heat acclimation, augmented HSP72 transcription unaccompanied by HSP synthesis was observed. It is concluded that upon heat acclimation, the HSP defense pathway is predisposed to a faster response. At the initial phases of heat acclimation, inability to elevate the HSP cytosolic level rules out their direct cytoprotective role.
先前的研究表明，热适应会导致72-kDa热休克蛋白（HSP72）的基础水平升高。HSP72表达的增强被认为是一种细胞保护反应。这使我们推测，热休克蛋白（HSP）防御途径的改变是热适应机制的一个组成部分。为了对此进行研究，我们研究了适应过程中基础HSP表达的时间变化情况以及急性热应激（HS）后其积累的动态变化。同时，测量了热应激前后HSP72 mRNA水平。作为对照，在相似条件下测量了HSC mRNA[70-kDa HSP（HSP70）家族的组成成员]。通过将大鼠连续暴露于34℃ 0天、1天、2天和30天来实现热适应。通过将大鼠暴露于41或43℃ 2小时来实现热应激。大鼠的体温调节能力由直肠温度、升温速率以及热应激期间引发的累积热应激来定义。分别通过Western免疫印迹和半定量RT-PCR在心脏左心室中测量HSP72和HSP70基因转录本。由此产生的适应性变化包括编码的72-kDa蛋白的静息水平更高（Δ175%，P < 0.0001）。热应激后，在41℃和43℃热应激后分别在40分钟和20分钟达到HSP72 mRNA水平峰值，而非适应组分别为60分钟和40分钟。然而，随后的HSP合成取决于累积热应激的严重程度。在热适应的初始阶段，观察到HSP72转录增强但无HSP合成。结论是，热适应后，HSP防御途径倾向于更快的反应。在热适应的初始阶段，无法提高HSP胞质水平排除了它们直接的细胞保护作用。
