Eur J Cardiothorac Surg 2004;26:281-288
© 2004 Elsevier Science NL
Insulin potentiates expression of myocardial heat shock protein 70
Gefeng Lia,b,
R. William Currieb,
Imtiaz S. Alia,c*
a Division of Cardiac Surgery, Department of Surgery, Dalhousie University, Room 2263 NHI, 1796 Summer St, Halifax, NS, Canada B3H 3A7
b Department of Anatomy and Neurobiology, Dalhousie University, Halifax, NS, Canada B3H 1X5
c Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada B3H 1X5
Received 11 July 2003;
received in revised form 3 March 2004;
accepted 6 April 2004.
* Corresponding author. Address: Division of Cardiac Surgery, Department of Surgery, Dalhousie University, Room 2263 NHI, 1796 Summer St, Halifax, NS, Canada B3H 3A7. Tel.: +1-902-473-3808; fax: +1-902-473-4448
e-mail: imtiaz.ali{at}dal.ca
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Abstract
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Objective: Since insulin stimulates nitric oxide (NO) production and an increase in NO following heat shock is required for myocardial heat shock protein 70 (Hsp70) synthesis, we hypothesized that insulin would enhance myocardial Hsp70 synthesis by augmenting NO signaling. We examined whether a physiologic dose of insulin increased myocardial Hsp70 in unstressed and heat shock treated rats. Methods: Adult male Sprague–Dawley rats were assigned to groups: (1) control, (2) insulin injected (200 µU/gm body weight), (3) heat shock treated (core body temperature 42 °C for 15 min), (4) heat shock and insulin treated, (5) L-nitroarginine methyl ester (L-NAME) and heat shock and insulin treated, (6) sodium nitroprusside (SNP) and heat shock and insulin treated. Six hours later, myocardial Hsp70 content and localization was analyzed. Results: Hsp70 was increased in heat shock treated hearts (120.6±16.8 ng/mg protein, P<0.001) vs. control (12.9±2.0 ng/mg protein), or insulin treated hearts (15.5±0.83 ng/mg protein). In addition, Hsp70 was increased in the heat shock and insulin treated hearts (164.4±7.53 ng/mg protein) compared to control, insulin only (P=0.001), or heat shock only treated hearts (P=0.01). L-NAME did not abolish the insulin induced increase in Hsp70 in heat shocked hearts (195.2±13.4 ng/mg protein, P=0.21) and SNP did not further enhance Hsp70 in the insulin and heat shocked group (188.9±8.2 ng/mg protein, P=0.71). Western analysis and confocal microscopy revealed a lowlevel expression of myocardial Hsp70 in response to insulin. Hsp70 was localized primarily in blood vessels after insulin or heat shock treatments. Conclusions: Insulin caused a low-level expression of myocardial Hsp70 and potentiated Hsp70 synthesis in response to heat shock. The ability of insulin to potentiate Hsp70 after heat shock is independent of NO signaling as it was not altered by either L-NAME or SNP pretreatment. Blood vessels appear to be the primary site of Hsp70 after insulin or heat shock treatment.
Key Words: Insulin • Heat shock • Heat shock protein 70 • Blood vessels • Nitric oxide • L-Nitroarmginine methyl ester
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1. Introduction
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Induction of the heat shock response and subsequent synthesis of heat shock protein 70 (Hsp70) renders the heart resistant to ischemia-reperfusion injury [1]. The optimal synthesis of Hsp70 in the heart following heat shock treatment is dependent upon a transient up-regulation of the myocardial nitric oxide–cyclic guanosine monophosphate (NO–cGMP) signaling pathway [2]. Administration of the non-specific nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine to heat shock treated rats abrogated the transient increase in NO and significantly reduced myocardial Hsp70 synthesis [2]. Furthermore, administration of NO-donor compounds [3] to rats markedly enhanced myocardial Hsp70 synthesis and inhibition of NOS abolished the infarct-reducing effect of heat shock [4]. Thus, there is a relationship between heat shock and the myocardial NO–cGMP signaling system.
Insulin, a metabolic modulator, is a potent cardioprotective agent. Insulin protects the ischemic-reperfused heart in animal models of myocardial infarction [5] and myocardial stunning [6]. Glucose–insulin–potassium solutions administered to humans evolving an acute myocardial infarction significantly reduce mortality [7]. In patients undergoing coronary artery bypass grafting, insulin-supplemented cardioplegia accelerated myocardial metabolic and functional recovery [8]. The cardioprotective effects of insulin have largely been attributed to its metabolic modulatory effects. More recently, however, insulin has been shown to modulate NO–cGMP signaling and increase NO production by endothelial cells via its ability to enhance endothelial NOS (eNOS) activity and expression [9]. Whether insulin modulates the myocardial heat shock response and alters myocardial Hsp70 synthesis is at present an open question.
Since a transient increase in NO following heat shock is required for optimal myocardial Hsp70 synthesis [2] and insulin stimulates NO production, we hypothesized that insulin would enhance myocardial Hsp70 synthesis by augmenting the NO signaling pathway. The purpose of our experiments was to determine the effect of a physiologic dose of insulin on myocardial Hsp70 content and localization in unstressed rats, and in rats following heat shock treatment. Our results suggest that insulin, at a physiologic dose, induces a low-level expression of Hsp70 in the naïve rat heart and also potentiates myocardial Hsp70 expression in heat shock treated rats independent of myocardial NO signaling.
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2. Materials and methods
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2.1. Animals
Male Sprague–Dawley rats (250–325 gm, Charles River Inc. St Constant, Québec, Canada) were cared for in accordance with the Guide to Care and Use of Experimental Animals of the Canadian Council on Animal Care.
2.2. Experimental protocol and groups
Rats were randomized into six groups, (1) control, CON; (2) insulin treated, INS; (3) heat shock treated, HS; (4) heat shock and insulin treated, HSINS, (5) L-NAME and heat shock and insulin treated, L-NA; and (6) SNP and heat shock and insulin treated, SNP. The experimental protocol and treatment groups are shown in Fig. 1
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Fig. 1. Schematic representation of the six experimental groups and their treatments. All animals were anesthetized with sodium pentobarbital at the times indicated. Insulin (200 µU/gm body weight) was injected in the insulin group and the heat shock and insulin group at the times indicated. Blood samples were taken for glucose analysis from all animals 10 min before insulin injection or heat shock treatment and approximately 60 min later. L-NAME, 10 µg/kg intravenously injected; SNP, 8 µg/kg/min, intravenously injected.
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For all groups, rats were anesthetized with sodium pentobarbital (50 mg/kg) i.p. Control rats received an injection of sodium pentobarbital, but were not heated or injected with insulin. For insulin treatment, rats were injected intramuscularly in the thigh with 200 µU/gm body weight. For heat shock treatment, rats were placed on a temperature-controlled heating pad (50 °C) until core body temperature reached 42 °C, monitored with a rectal thermometer. Core body temperature was maintained between 42 and 42.5 °C for 15 min. For heat shock and insulin treatment, rats were subjected to the heat shock treatment first and at 10 min after the heat shock treatment, were injected with insulin (200 µU/gm body weight) intramuscularly in the thigh (Fig. 1). L-NAME (10 mg/kg) was administered intravenously (penile vein) and SNP (8 µg/kg/min) was given as an intravenous infusion over 10 min via the tail vein. Both L-NAME and SNP were administered prior to heat shock and insulin.
2.3. Measurement of blood glucose
Blood samples were collected from the tail vein of all rats at the times indicated in Fig. 1 and glucose levels were determined with a glucose meter (Accusoft Advantage, Roche Diagnostics, Québec, Canada).
2.4. Tissue preparation and assays
At 6 h of recovery (Fig. 1), rats were injected with sodium pentobarbital (50 mg/kg) and decapitated. For biochemical analysis, hearts were removed and immediately freeze clamped. The frozen tissue was stored in liquid nitrogen for later analysis of Hsp70 and total protein.
2.5. Western analysis
Heart tissues were homogenized in 0.32 M sucrose. Protein concentration was determined by the method of Lowry et al. [10]. Samples containing 25 µg of protein were solubilized in sodium dodecyl sulfate (SDS) sample buffer, boiled for 10 min and loaded onto a polyacrylamide gel (2.5% upper gel, 7.5% running gel), according to previously described methods [1]. Proteins were separated by electrophoresis and then electrotransferred onto a Millipore-P membrane. Membranes were incubated in Blotto as previously described [11] at 37 °C for 1 h to block non-specific binding of primary antibody. Membranes were incubated at 4 °C overnight with primary mouse monoclonal anti-hsp70 antibody (1:500, SPA-810, StressGen, Vic., Canada) in fresh Blotto. Next day, following three 20 min washes, membranes were incubated in secondary horse anti-mouse horseradish peroxidase conjugated antibody (1:500, Vector Laboratories, Burlingame, CA). After six 10 min washes, membranes were incubated in ECLTM solution for 1 min, and then exposed on hyperfilm (Amersham, UK). Films were scanned on a HP6200 scanner to acquire digital imagines. Densitometric analysis was done with imaging software from Scion Co (Scion Imagine, Version 4.0.2).
2.6. Enzyme immunoassay for Hsp70
Hsp70 content of heart was determined by an enzyme immunoassay kit (StressGen, Vic., Canada). Frozen powdered ventricular tissue (200–250 mg) was placed in 1.0 ml 1xHsp70 Extraction Reagent at 4 °C. One protease inhibitor cocktail tablet (Sigma, St Louis, MO) was used in every 10 ml 1xExtraction Reagent. Tissue was homogenized with an electrical pestle at 3000 revolution/s at 4 °C for 30 s in a polypropylene tube. Homogenized samples were centrifuged at 21,000g for 10 min at 4 °C. Samples of supernatant (100 µl) and standards (100 µl) were added in duplicate to wells in the Hsp70 immunoassay plate, and then incubated at room temperature for 2 h. Wells were washed six times with 1xwash buffer. Anti-Hsp70:Biotin (100 µl) was added to each well and incubated at room temperature for 1 h. Wells were washed six times with 1x wash buffer. Avidin-HRP conjugate (100 µl) was added to each well, covered and incubated at room temperature for 1 h. Again, wells were washed six times with 1x wash buffer. TMB Substrate (100 µl) was added to each well and incubated at room temperature for 10 min. Acid stop solution (100 µl) was added to each well. The microplate was read at 450 nm with a microplate reader (Bio-Rad). Results were calculated and expressed as ng mg–1 protein.
2.7. Immunofluorescence microscopy
2.7.1. Tissue slicing and preparation
For immunofluorescence, fresh hearts were collected, rinsed of blood in saline, and then immersed and fixed in 2% paraformaldehyde at 4 °C overnight. Following fixation, tissues were cryoprotected in 30% sucrose at 4 °C. Tissues were cut into 20 µm thick sections with a freezing slicing microtome and sections were kept in Millonig's solution at 4 °C.
2.7.2. Hsp70 with factor VIII and phalloidin immunofluorescence
To characterize the Hsp70 localization in heart and its relation to cardiomyocytes, sections were incubated with Hsp70 antibodies, and either factor VIII antibodies or phalloidin. For double labeling of Hsp70 and factor VIII, tissue sections were processed as previously described [12]. For double labeling of Hsp70 and actin with phalloidin, tissue sections were first reacted for Hsp70 immunofluorscence. Next, the tissue sections were washed with PBS three times, then fixed in 3.7% formaldehyde in PBS at room temperature for 10 min. Tissue sections were washed twice with PBS and extracted with –20 °C acetone for 3 min. Sections were washed in PBS and incubated in a solution of phalloidin (1:40 in PBS, Alexa green 488 conjugated, Molecular Probe Inc., USA) at 37 °C for 2 h. Finally, tissue sections were mounted onto gelatinized slides. In each batch of sections stained for fluorescence microscopy, some sections were incubated without primary antibody or phalloidin to serve as control for non-specific staining. A Zeiss LSM510 laser-scanning microscope was used to scan sections for confocal imaging. Images were captured with LASM 510 software (Version 2.01). Captured images were edited adjusting only brightness and contrast and composed with Photoshop (Version 6.0 ADOBE).
2.8. Statisticial analysis
Standard curves for Hsp70 EIA were transformed to log–log plot and calculated with a linear model. Data were analyzed with ANOVA (SPSS Version 11.5, Chicago, IL). If overall ANOVA was significant for a specific variable, Bonfferoni multi-comparison analysis was used to test the significance among the groups. For comparing the data of glucose levels before and after insulin injection or heat shock, the paired Student t-test was used. All data mentioned above were also confirmed with non-parametric statistical analysis after parametric analysis. The results are expressed as mean±SEM. Significance was set at P
0.05.
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3. Results
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3.1. Blood glucose determination
No significant differences were detected in blood glucose levels among the groups before and after insulin injection or heat shock treatment (Fig. 2)
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Fig. 2. Blood glucose levels before and after insulin treatment, heat shock treatment and heat shock and insulin treatment. There was no significant difference in glucose levels among the groups before and after insulin injection or heat shock treatment (P>0.05).
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3.2. Western analysis and densitometry
Hsp70 in the insulin treatment group was at a detectable level by Western analysis (Fig. 3A)
while in the control group Hsp70 was not detectable. However, this apparent difference in Hsp70 was not significant (P>0.05) following densitometric analysis (Fig. 3B). Hsp70 in the heat shock treated group and in the heat shock and insulin treatment group was abundant by Western analysis and following densitometric analysis was significantly different (P<0.001) compared to the control group (Fig. 3B). Pretreatment with L-NAME or SNP did not abolish or further enhance, respectively, the ability of insulin to potentiate Hsp70 after heat shock (Fig. 4A and B)
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Fig. 3. Hsp70 levels detected by Western analysis and densitometric analysis. (A) A representative membrane showing Hsp70 levels in two hearts in each of the four groups. (B) Relative densities (arbitrary units, mean±SEM) of Hsp70 in each group. Asterisks indicate statistical differences (p<0.05) versus control and insulin treated groups.
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Fig. 4. Hsp 70 levels detected by Western analysis and densitometric analysis. (A) A representative membrane showing Hsp70 levels in two hearts in each of the four groups. (B) Relative densities (arbitrary units, mean±SEM) of Hsp70 in each group. Asterisks indicate statistical differences (P<0.05) versus control and heat shock groups.
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3.3. Hsp70 immunoassay
Hsp70 in the insulin treatment group (15.5±0.8 ng/mg protein) was not significantly different (P>0.05) from that of the control group (12.9±2.0 ng/mg protein, Fig. 5)
. Hsp70 in the heat shock treated group (120.6±16.8 ng/mg protein) and in the heat shock and insulin treatment group (164.4±7.5 ng/mg protein) was significantly increased (P<0.001) compared to the control group. In addition, Hsp70 in the heat shock and insulin treatment group (164.4±7.5 ng/mg protein) was significantly greater (P<0.001) from that of the heat shock group (120.6±16.8 ng/mg protein, Fig. 5). Pretreatment with the NOS inhibitor L-NAME did not abolish the ability of insulin to potentiate Hsp70 in heat shocked animals (195.2±13.4 ng/mg protein, P=0.21, Fig. 5). Furthermore, pretreatment with the NO donor compound SNP did not further enhance Hsp70 synthesis in the heat shock and insulin treated group (188.9±8.2 ng/mg protein, P=0.71, Fig. 5).
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Fig. 5. Hsp70 levels measured by enzyme immunoassay in controls and at approximately 6 h in the six groups. P<0.001 for HS vs. CON and INS; P=0.01 for HSINS vs. HS; P<0.001 for HSINS, L-NA, SNP vs. CON and INS; P=0.21 for HSINS vs. L-NA; P=0.72 for HSINS vs. SNP.
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3.4. Hsp70 and factor VIII immunofluorscence microscopy
Confocal microscopy revealed little or no Hsp70 immunoreactivity (Hsp70-IR) in control hearts (Fig. 6A)
. Interestingly, low level Hsp70-IR was evident in hearts from the insulin treated group (Fig. 6B). Intense Hsp70-IR was evident in hearts from the heat shock treated group (Fig. 6C) and the heat shock and insulin-treated group (Fig. 6D). Factor VIII immunoreactivity (Factor VIII-IR) was evident in all hearts and was unaffected by the insulin or heat shock treatments (Fig. 6A–D). Co-localization of Hsp70-IR and factor VIII-IR appeared to be in blood vessels (Fig. 6B–D).
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Fig. 6. Confocal micrographs of ventricular sections double labeled with antibodies for Hsp70 and Factor VIII. Hsp70-IR (Cy3, red) and Factor VIII-IR (CY2, green). (A) Control, (B) insulin treated, (C) heat shock treated, (D) heat shock and insulin treated. Bar=50 µm.
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3.5. Hsp70 immunofluorscence and phalloidin fluorescence microscopy
Hsp70-IR was again not evident in control hearts (Fig. 7A)
and was evident at a low level in hearts from the insulin treated group (Fig. 7B). Intense Hsp70-IR was evident in hearts from the heat shock treated group (Fig. 7C) and the heat shock and insulin treated group (Fig. 7D). Phalloidin fluorescence was evident in all hearts and was unaffected by the insulin or heat shock treatments (Fig. 7A–D). No apparent co-localization of Hsp70-IR (in blood vessels) and phalloidin fluorescence (on actin in cardiomyocytes) was evident (Fig. 7B–D).
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Fig. 7. Confocal micrographs of ventricular sections double labeled with Hsp70 antibodies and phalloidin. Hsp70-IR (Cy3, red) and phalloidin (CY2, green). (A) Control, (B) insulin treated, (C) heat shock treated, (D) heat shock and insulin treated. Bar=20 µm.
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4. Discussion
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This study demonstrates that insulin induces an apparent low-level expression of Hsp70 primarily in microvessels, of the naïve, non-ischemic heart. Interestingly, after heat shock treatment, insulin potentiates myocardial Hsp70 synthesis and this effect is neither abrogated by the NOS inhibitor L-NAME or enhanced by the NO donor compound SNP. Thus, the insulin mediated potentiation of myocardial Hsp70 synthesis following heat shock appears to be independent of myocardial NO signaling.
4.1. Effect of insulin on Hsp70 in unstressed heart
Insulin is a cardioprotective agent in myocardial ischemia-reperfusion injury. For example, insulin treatment in the isolated perfused heart significantly improves functional recovery following ischemic injury [6]. Similarly, insulin treatment in vivo results in significant infarct size reduction and this protective effect appears to be dependent upon insulin-stimulated NO production [13]. The capacity of insulin to promote NO synthesis is considered paramount in its ability to mediate both metabolic and peripheral vascular actions.
In our study, the dose (200 µU/g body weight) and route (i.m.) of insulin administration was chosen based on this dose causing a nine-fold increase in basal plasma NO levels 30 min after injection in mice [14]. The insulin dose was physiologic and did not significantly alter blood glucose levels in any of the experimental groups (Fig. 2). This finding excludes the possibility that insulin altered myocardial Hsp70 expression secondary to a hypoglycemic effect.
A low-level expression of Hsp70 was observed by Western analysis (Fig. 3) and immunofluorescence (Figs. 6 and 7) in hearts in response to insulin treatment. However, this apparent low-level expression of Hsp70 in insulin treated hearts did not reach statistical significance when semi-quantitated by optical densitometry (Fig. 3B) or immunoassay techniques (Fig. 5). Although we could not quantitatively demonstrate a statistically significant increase in Hsp70 in insulin treated hearts (Fig. 3B and 5), we are confident that insulin is capable of modulating Hsp70 expression in the unstressed heart as evidenced by the mild but definite bands evident in the Western analysis (Fig. 3A) and the immunoflourescence evident in Figs. 6 and 7. Insulin is capable of inducing Hsp70 mRNA in the human hepatoma cell line Hep3B/T2 and this effect is mediated by the insulin receptor [15]. Similarly, insulin is known to induce a transient synthesis of Hsp70 in cultured fibroblasts and epithelial cells [16].
4.2. Effect of heat shock on myocardial Hsp70
Induction of the heat shock response in rats is associated with a transient increase of NO synthesis in the heart, lung and liver [2]. Administration of the NOS inhibitor N(omega)-nitro-L-arginine to heat shock treated rats abolishes the transient increase in NO and significantly attenuates myocardial Hsp70 synthesis [2]. Administration of NOS inhibitors also abolishes the infarct-reducing effect of heat shock [4]. These studies suggest that a transient stimulation of NOS and NO synthesis is crucial for expression of Hsp70 and the myocardial protection that results following heat shock.
Heat shock treatment of rats induces expression of Hsp70 and significantly improves contractile recovery of hearts following ischemic injury [1]. Hearts of transgenic mice overexpressing the human Hsp70 [11] show a significant resistance to ischemic injury and provide direct evidence for a protective role for Hsp70 in myocardial ischemia-reperfusion injury. As expected, heat shock treatment significantly increased myocardial Hsp70 content (Figs. 3 and 5).
4.3. Effect of insulin on myocardial Hsp70 in the heat shock treated rat
Insulin potentiated the expression of Hsp70 in the heart following heat-shock treatment. By the semi-quantitative Western analysis technique of optical densitometry, there was no apparent increase in Hsp70 when insulin was administered with heat shock treatment (Fig. 3B), compared to the heat shock alone treatment group. However, by enzyme immunoassay, a more sensitive quantitative method, myocardial Hsp70 was significantly increased in the group administered insulin following heat shock treatment, as compared to the heat shock only treated group (Fig. 5).
The potentiation of Hsp70 by insulin in the heat shock treated hearts was not abolished by pretreatment with the NOS inhibitor L-NAME and was not further amplified by pretreatment with the NO donor compound SNP (Fig. 5). This suggests that insulin potentiates Hsp70 in heat shocked myocardium by mechanisms independent of its ability to stimulate NO signaling. The mechanism(s) responsible for the potentiation of Hsp70 synthesis by insulin following heat shock are at best speculative. The downstream signaling events occurring in response to insulin occupying its receptor are numerous and complex. In addition, the intracellular signaling cascades activated by heat shock are poorly understood. However, it is interesting to note that both insulin and heat shock may share common down-stream signaling pathways. For example, both insulin [17] and heat shock [18] have been shown to activate the phosphatidyl-inositol 3-kinase (PI3-kinase)/Akt signaling pathway. This signaling pathway appears to be critical for inhibiting apoptosis [19] and is known to result in eNOS stimulation and NO production [20]. Apoptosis in the heart following reperfusion is inhibited by heat shock and this may contribute to its infarct-reducing effect [21]. It is interesting to note that the infarct-reducing effect of insulin in vivo is also related to an inhibition of apoptosis that is dependent upon NO production [13]. Whether the stimulation of Hsp70 synthesis by insulin contributes to the latter's anti-apoptotic effect in the heart remains to be determined. The potentiation of Hsp70 synthesis by insulin with heat shock treatment observed in our study may be indicative of similar signaling pathways being activated by insulin and heat shock treatments.
4.4. Localization of Hsp70 following insulin and heat shock
The confocal microscopy demonstrates that Hsp70 appears to localize predominantly in blood vessels following both insulin and heat shock treatments (Figs. 6 and 7). This finding supports our previous results [12] and those of other investigators [22] and highlights the importance of blood vessels and endothelium in myocardial protection. It is known that coronary endothelial damage contributes to the poor contractile recovery of the isolated ischemic reperfused heart. Interestingly, heat shock treatment completely prevents the endothelial dysfunction in coronary arteries isolated from rats subjected to myocardial ischemia-reperfusion injury and restores NO-mediated coronary artery vasorelaxation [23]. The critical importance of the coronary endothelium in heat-shock mediated cardioprotection is also demonstrated by the lack of a protective effect of heat-shock on functional recovery following ischemia-reperfusion injury in rat hearts which have had endothelium removed [22]. These findings suggest an association between Hsp70 in myocardial blood vessels and functional recovery during reperfusion after an ischemic injury. Furthermore, showing that insulin can induce an apparent low-level expression of Hsp70 in blood vessels of the heart and potentiate Hsp70 expression following heat shock raises the interesting possibility that insulin may augment Hsp70 synthesis following other pathophysiological stimuli such as ischemia. If insulin is indeed capable of enhancing Hsp70 expression, some of the infarct-reducing capacity of insulin may be attributable to mechanisms quite independent of its metabolic modulatory effects.
4.5. Limitations
Our interpretation that insulin potentiates heat shock mediated myocardial Hsp70 synthesis independently of its ability to augment NO signaling is based on the fact that pretreatment with a NOS inhibitor (L-NAME) or NO donor (SNP) had no effect, respectively, in either abolishing or enhancing myocardial Hsp70 levels in animals treated with heat shock and insulin. However, this interpretation is limited by the fact that we have not actually measured NO. We could not demonstrate quantitatively a statistically significant increase in Hsp70 content of control hearts after insulin treatment alone, although an effect was clearly evident by the Western blot and immunohistochemistry. Only one dose of insulin was tested.
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5. Conclusions
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In summary, we have shown that a physiologic dose of insulin induces a low-level expression of Hsp70 in the naïve, unstressed rat heart and significantly potentiates myocardial Hsp70 synthesis following heat-shock treatment. The latter effect is not altered by pretreatment with either L-NAME or SNP, suggesting that it is independent of insulin's known ability to stimulate NO signaling. Hsp70 localization appears to be in blood vessels predominantly following insulin treatment and heat shock. These findings suggest intriguing possibilities regarding the cardioprotective effects of insulin and heat shock.
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Acknowledgments
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We thank Ms Brenda Ross for excellent technical assistance. This work was funded by the Queen Elizabeth II Hospital Research Foundation (ISA) and the Heart and Stroke Foundation of New Brunswick (RWC).
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G. Li, I. S. Ali, and R. W. Currie
Insulin-induced myocardial protection in isolated ischemic rat hearts requires p38 MAPK phosphorylation of Hsp27
Am J Physiol Heart Circ Physiol,
January 1, 2008;
294(1):
H74 - H87.
[Abstract]
[Full Text]
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G. Li, I. S. Ali, and R. W. Currie
Insulin induces myocardial protection and Hsp70 localization to plasma membranes in rat hearts
Am J Physiol Heart Circ Physiol,
October 1, 2006;
291(4):
H1709 - H1721.
[Abstract]
[Full Text]
[PDF]
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Top
Abstract
1. Introduction
