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HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed on Heat Acclimation MICHAL HOROWITZ," ALINA MALOYAN, AND JUDITH SHLAIER Division of Physiology Hadassah Schools of Medicine and Dental Medicine The Hebrew University POB 12272 Jerusalem 91120, Israel At the cellular level, organisms respond to hyperthermic stress by synthesizing highly conserved families of proteins, the heat shock proteins (HSP). Among the HSPs, the 70 kDa family is the most responsive to heat stress. Upshift body temperature increases the transcription of the heat shock genes, which in turn, leads to augmentation of their concentration in the cell. This coincides with the development of rapid transient thermotolerance, which is due, at least in part, to HSP binding to denatured or nascent polypeptides in the different compartments of the cell.' There is a direct correlation between the magnitude, duration and rate of heating and HSP 70 kDa concentration. Therefore, their potential utilization as a biomarker of organltissue heat injury, particularly of tissues at risk during thermal stress, was recently examined.* The threshold temperatures for triggering increased expression of HSPs are several degrees above normal body temperature and range in various organisms from slightly above 0°C for antarctic fishes to approximately 100°C for hyperther- mophilic b a ~ t e r i a . ~ In mammalian species, a rise of approximately 4°C in body temperature is required to induce HSP accumulation. Acclimatization or acclima- tion may alter this threshold. So far, studies in this respect have been confined to HSP from the 90 kDa family, in poikilotherms. For example, in the eurythermal goby fish (Gilichthys mirabilis) the threshold for HSP 90 kDa induction in brain is changed (increased) by almost 14°C following the transition from cold acclima- tion to warm acclimation. This is accompanied by an increased HSP concen- trati~n.~ The effect of heat acclimation on HSP in mammalian species has not been studied. Based on our current knowledge, we hypothesize that their cytosolic level also rises. It is not known whether acclimation also affects the rate of production of newly synthesized HSP, induced upon stress. In our investigation the following questions were addressed: 1. Does long term heat acclimation lead to augmentation of the inducible HSP 70 kDa level? 2. Does heat acclimation affect the rate of HSP expression upon stress? The HSP 70 kDa profile was measured in the left ventricle of the rat heart at: 1. One to 48 hr following exposure to a heat stress of 41°C. 2. One hr following intermittent global ischemia. One month acclimation to an environmental tempera- a Fax: 972 2 439736; E-mail: [email protected]. 617

HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed on Heat Acclimation

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Page 1: HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed on Heat Acclimation

HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed

on Heat Acclimation MICHAL HOROWITZ," ALINA MALOYAN,

AND JUDITH SHLAIER Division of Physiology

Hadassah Schools of Medicine and Dental Medicine The Hebrew University

POB 12272 Jerusalem 91120, Israel

At the cellular level, organisms respond to hyperthermic stress by synthesizing highly conserved families of proteins, the heat shock proteins (HSP). Among the HSPs, the 70 kDa family is the most responsive to heat stress. Upshift body temperature increases the transcription of the heat shock genes, which in turn, leads to augmentation of their concentration in the cell. This coincides with the development of rapid transient thermotolerance, which is due, at least in part, to HSP binding to denatured or nascent polypeptides in the different compartments of the cell.' There is a direct correlation between the magnitude, duration and rate of heating and HSP 70 kDa concentration. Therefore, their potential utilization as a biomarker of organltissue heat injury, particularly of tissues at risk during thermal stress, was recently examined.*

The threshold temperatures for triggering increased expression of HSPs are several degrees above normal body temperature and range in various organisms from slightly above 0°C for antarctic fishes to approximately 100°C for hyperther- mophilic b a ~ t e r i a . ~ In mammalian species, a rise of approximately 4°C in body temperature is required to induce HSP accumulation. Acclimatization or acclima- tion may alter this threshold. So far, studies in this respect have been confined to HSP from the 90 kDa family, in poikilotherms. For example, in the eurythermal goby fish (Gilichthys mirabilis) the threshold for HSP 90 kDa induction in brain is changed (increased) by almost 14°C following the transition from cold acclima- tion to warm acclimation. This is accompanied by an increased HSP concen- t r a t i ~ n . ~

The effect of heat acclimation on HSP in mammalian species has not been studied. Based on our current knowledge, we hypothesize that their cytosolic level also rises. It is not known whether acclimation also affects the rate of production of newly synthesized HSP, induced upon stress. In our investigation the following questions were addressed: 1. Does long term heat acclimation lead to augmentation of the inducible HSP 70 kDa level? 2. Does heat acclimation affect the rate of HSP expression upon stress?

The HSP 70 kDa profile was measured in the left ventricle of the rat heart at: 1. One to 48 hr following exposure to a heat stress of 41°C. 2. One hr following intermittent global ischemia. One month acclimation to an environmental tempera-

a Fax: 972 2 439736; E-mail: [email protected]. 617

Page 2: HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed on Heat Acclimation

618 ANNALS NEW YORK ACADEMY OF SCIENCES

a

n Q) v) .- L

4-

3-

0 - - - - -_____ 2- .* __-__._....-. ------o------ ...._*._

1-

0 1 . I " I I

0 10 20 30 40 50

C AC

TIME (hour)

b

n I

NonAC AC Column 1

FIGURE 1. HSP (70 kDa family) level in hearts from nonacclimated and 30 days heat- acclimated rats at 34°C. The HSP level was measured by protein immunoblot (monoclonal antibodies, Stress Gene). (a) HSP level, 1-48 hr following heat stress of I hr at 41°C. Each point represents the mean of 5 hearts. (b) HSP level in nonacclimated and heat-acclimated hearts before and 1 hr after intermittent ischemia.

Page 3: HSP 70 kDa Dynamics in Animals Undergoing Heat Stress Superimposed on Heat Acclimation

HOROWITZ et al.: HSP 70 kDa DYNAMICS 619

ture of 34°C resulted in a 140% elevation in basal HSP content compared to that in the nonacclimated state. Following heat stress in the nonacclimated rats, 4 hr were required to attain a maximal HSP tissue level. In the heat-acclimated rats, the rise in HSP was markedly faster, and a plateau was attained 1 hr after stress. Interestingly, in nonacclimated hearts HSP increased by 220%, compared with 180% in the heat-acclimated ones (FIG. la). A similar response-difference between the two groups was obtained following ischemic insult (FIG. lb).

Our data show that in mammals, similarly to poikilotherms, heat acclimation leads to an elevated HSP level. Our novel finding is that heat acclimation acceler- ates the rate and alters the magnitude of HSP expression upon stress. Both features coincide with the improved heat endurance of the acclimated rat to heat stress4 as well as with the improved endurance of the heat-acclimated heart during ischemic i n ~ u l t . ~ Since during the acclimation period, the rectal temperature of the acclimat- ing animals is on the average only 1- 1 .YC higher than the nonacclimation tempera- ture, we believe that the augmented HSP level observed upon long-term heat acclimation is due to the cumulative effect of moderate heat and may involve a different pathway than that involved in heat stress. It is noteworthy that the initial phase of heat acclimation coincides with desensitization of HSP expression.

REFERENCES

1 . WELCH, W. 1992. Mammalian stress response: cell physiology, structure/function of stress proteins and implications for medicine and disease. Physiol. Rev. 72: 1063-1081.

2. FLANAGAN, S. W., A. J. RYAN, C. V. GISOLFI & P. L. MOSELEY. 1995. Tissue-specific HSP70 response in animals undergoing heat stress. Am. J. Physiol. 268: R28-R32.

3. Somero, G. N. 1995. Proteins and temperature. Annu. Rev. Physiol. 57: 43-68. 4. HOROWITZ, M. 1994. Heat stress and heat acclimation: the cellular response modifier

of autonomic control. in Integrative and Cellular Aspects of Autonomic Function. K. Pleschka & R. Gerstberger, Eds. 87-97. John Libby & Co. London.

5 . LEVI, E., A. VIVI, Y. HASIN, M. TASSIM, G . NAVON & M. HOROWITZ. 1993. Heat acclimation improves cardiac mechanics and metabolic performance during ischemia and reperfusion. J. Appl. Physiol. 75: 833-839.