Heat-induced force suppression and HSP20 phosphorylation in swine carotid media

Hyperthermia as a trigger for Takotsubo syndrome in a rat model

Takotsubo syndrome is a well-characterized cause of acute yet reversible heart failure associated with periods of intense emotional stress, often mimicking on presentation an acute coronary syndrome. Animal models of Takotsubo syndrome have been developed, either through the application of a stressor, or administration of exogenous catecholamine. We found that in a model of isoproterenol-induced Takotsubo syndrome in anesthetized rats hyperthermia (40–41°C) would occur after the administration of isoproterenol. Maintenance of this hyperthermia would result in an apical hypocontractility typical of the syndrome, whereas prevention of hyperthermia with active cooling to maintain a euthermic core body temperature prevented (but did not subsequently reverse) apical hypocontractility. In vitro experimentation with isolated cardiomyocytes showed no effect of hyperthermia on either baseline contractility or contractility change after beta-adrenoceptor stimulation. We suggest that the rise in body temperature that is characteristic of catecholamine storm may be a component in the development of Takotsubo syndrome.

Small heat shock proteins in redox metabolism: implications for cardiovascular diseases

A timely review series on small heat shock proteins has to appropriately examine their fundamental properties and implications in the cardiovascular system since several members of this chaperone family exhibit robust expression in the myocardium and blood vessels. Due to energetic and metabolic demands, the cardiovascular system maintains a high mitochondrial activity but irreversible oxidative damage might ensue from increased production of reactive oxygen species. How equilibrium between their production and scavenging is achieved becomes paramount for physiological maintenance. For example, heat shock protein B1 (HSPB1) is implicated in maintaining this equilibrium or redox homeostasis by upholding the level of glutathione, a major redox mediator. Studies of gain or loss of function achieved by genetic manipulations have been highly informative for understanding the roles of those proteins. For example, genetic deficiency of several small heat shock proteins such as HSPB5 and HSPB2 is well-tolerated in heart cells whereas a single missense mutation causes human pathology. Such evidence highlights both the profound genetic redundancy observed among the multigene family of small heat shock proteins while underscoring the role proteotoxicity plays in driving disease pathogenesis. We will discuss the available data on small heat shock proteins in the cardiovascular system, redox metabolism and human diseases. From the medical perspective, we envision that such emerging knowledge of the multiple roles small heat shock proteins exert in the cardiovascular system will undoubtedly open new avenues for their identification and possible therapeutic targeting in humans. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

Large potentials of small heat shock proteins

Modern classification of the family of human small heat shock proteins (the so-called HSPB) is presented, and the structure and properties of three members of this family are analyzed in detail. Ubiquitously expressed HSPB1 (HSP27) is involved in the control of protein folding and, when mutated, plays a significant role in the development of certain neurodegenerative disorders. HSPB1 directly or indirectly participates in the regulation of apoptosis, protects the cell against oxidative stress, and is involved in the regulation of the cytoskeleton. HSPB6 (HSP20) also possesses chaperone-like activity, is involved in regulation of smooth muscle contraction, has pronounced cardioprotective activity, and seems to participate in insulin-dependent regulation of muscle metabolism. HSPB8 (HSP22) prevents accumulation of aggregated proteins in the cell and participates in the regulation of proteolysis of unfolded proteins. HSPB8 also seems to be directly or indirectly involved in regulation of apoptosis and carcinogenesis, contributes to cardiac cell hypertrophy and survival and, when mutated, might be involved in development of neurodegenerative diseases. All small heat shock proteins play important "housekeeping" roles and regulate many vital processes; therefore, they are considered as attractive therapeutic targets.

Differential effect of hyperthermia on nerves and smooth muscle of the mouse ileum

BACKGROUND AND OBJECTIVES

Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) gained wide acceptance as the treatment of choice for selected patients with peritoneal surface malignancies. Patients tend to suffer from prolonged ileus following CRS + HIPEC, complicating their recovery. We studied the effects of hyperthermia on the intestine to gain insight into mechanisms of ileus post-HIPEC.

METHODS

Segments of mouse ileum were incubated at 36°C. Electrical field stimulation (EFS) was applied, stimulating nerves, and the resultant muscle contraction was measured. The response was measured at varying temperatures (38-43°C) at exposure times of up to 120 min. We also stimulated the tissues with 10(-6) M carbachol, a muscarinic receptor agonist, which acts directly on smooth muscle.

RESULTS

Response to EFS decreased at high temperatures, especially above 41°C. This effect was irreversible for 120 min after decreasing temperature. When stimulating with carbachol, both transient and plateau responses decreased at 43°C (plateau more than transient) but the effect reversed on returning to 36°C.

CONCLUSION

The irreversible decline in responses to nerve stimulation when exposed to high temperatures was not seen with direct muscle stimulation. This indicates that smooth muscle is resilient and that the main effect of hyperthermia is on nerves. These results have significance for HIPEC.

Phosphorylated HSP20 modulates the association of thin-filament binding proteins: caldesmon with tropomyosin in colonic smooth muscle

Small heat shock proteins HSP27 and HSP20 have been implicated in regulation of contraction and relaxation in smooth muscle. Activation of PKC-α promotes contraction by phosphorylation of HSP27 whereas activation of PKA promotes relaxation by phosphorylation of HSP20 in colonic smooth muscle cells (CSMC). We propose that the balance between the phosphorylation states of HSP27 and HSP20 represents a molecular signaling switch for contraction and relaxation. This molecular signaling switch acts downstream on a molecular mechanical switch [tropomyosin (TM)] regulating thin-filament dynamics. We have examined the role of phosphorylation state(s) of HSP20 on HSP27-mediated thin-filament regulation in CSMC. CSMC were transfected with different HSP20 phosphomutants. These transfections had no effect on the integrity of actin cytoskeleton. Cells transfected with 16D-HSP20 (phosphomimic) exhibited inhibition of acetylcholine (ACh)-induced contraction whereas cells transfected with 16A-HSP20 (nonphosphorylatable) had no effect on ACh-induced contraction. CSMC transfected with 16D-HSP20 cDNA showed significant decreases in 1) phosphorylation of HSP27 (ser78); 2) phosphorylation of PKC-α (ser657); 3) phosphorylation of TM and CaD (ser789); 4) ACh-induced phosphorylation of myosin light chain; 5) ACh-induced association of TM with HSP27; and 6) ACh-induced dissociation of TM from caldesmon (CaD). We thus propose the crucial physiological relevance of molecular signaling switch (phosphorylation state of HSP27 and HSP20), which dictates 1) the phosphorylation states of TM and CaD and 2) their dissociations from each other.

Small heat shock protein 20 (HspB6) in cardiac hypertrophy and failure

Hsp20, referred to as HspB6, is constitutively expressed in various tissues. Specifically, HspB6 is most highly expressed in different types of muscle including vascular, airway, colonic, bladder, and uterine smooth muscle; cardiac muscle; and skeletal muscle. It can be phosphorylated at Ser-16 by both cAMP- and cGMP-dependent protein kinases (PKA/PKG). Recently, Hsp20 and its phosphorylation have been implicated in multiple physiological and pathophysiological processes including smooth muscle relaxation, platelet aggregation, exercise training, myocardial infarction, atherosclerosis, insulin resistance and Alzheimer's disease. In the heart, key advances have been made in elucidating the significance of Hsp20 in contractile function and cardioprotection over the last decade. This mini-review highlights exciting findings in animal models and human patients, with special emphasis on the potential salutary effects of Hsp20 in heart disease. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Structure, properties, and probable physiological role of small heat shock protein with molecular mass 20 kD (Hsp20, HspB6)

This review is devoted to critical analysis of data concerning the structure and functions of small heat shock proteins with apparent molecular mass 20 kD (Hsp20). We describe the structure of Hsp20, its phosphorylation by different protein kinases, interaction of Hsp20 with other small heat shock proteins, and chaperone activity of Hsp20. The distribution of Hsp20 in different animal tissues and the factors affecting expression of Hsp20 are also described. Data on the possible involvement of Hsp20 in regulation of platelet aggregation and glucose transport are presented and analyzed. Special attention is paid to literature data describing probable regulatory effect of Hsp20 on contraction of smooth muscle. Two hypotheses postulating direct effect of Hsp20 on actomyosin interaction or its effect on cytoskeleton are compared and analyzed. The most recent data on the effect of Hsp20 on apoptosis and contractile activity of cardiomyocytes are also presented.

HSP20 phosphorylation and interstitial metabolites in hypoxia-induced dilation of swine coronary arteries

OBJECTIVE

Hypoxia induces coronary artery dilation, but the responsible mechanism is largely unknown. Many stimuli induce arterial smooth muscle relaxation by reducing ser19-myosin regulatory light chain (MLC) phosphorylation. Other stimuli can induce smooth muscle relaxation without reductions in ser19-MLC phosphorylation. This form of relaxation has been termed force suppression and appears to be associated with heat shock protein 20 (HSP20) phosphorylation on ser16. We investigated whether hypoxia-induced sustained dilation in swine coronary arteries was promoted without ser19-MLC dephosphorylation and associated with ser16-HSP20 phosphorylation. Nitroglycerin vasodilation served as control.

METHODS

In a pressure myograph, the tunica media of intact pre-contracted (PGF(2alpha); 10(-5) m) porcine coronary artery segments were cannulated using a microdialysis catheter. Diameter responses and interstitial lactate/pyruvate ratios were studied during 90 min hypoxia, hypoxia + reoxygenation (60 min), nitroglycerin (100 microm, 90 min), and nitroglycerin + wash-out (60 min). The arterial segments were snap-frozen and analysed for ser16-HSP20 phosphorylation and ser19-MLC phosphorylation.

RESULTS

The normalized diameter responses to hypoxia (6.1 +/- 4.3%) and nitroglycerin (12.6 +/- 1.6%) were both significantly greater than normoxic control arteries (-10.5 +/- 1.8%, anova, P < 0.05). Ser16-HSP20 phosphorylation was increased with hypoxia and nitroglycerin treatment and ser16-HSP20 phosphorylation correlated with changes in diameters (n = 29, r2 = 0.64, P < 0.001). Ser19-MLC phosphorylation was not significantly altered by hypoxia. The lactate/pyruvate ratio was significantly increased in hypoxic arteries but did not correlate with diameters or ser16-HSP20 phosphorylation.

CONCLUSION

Ser16-HSP20 phosphorylation is a potential regulator of hypoxia-induced dilation in coronary arteries.

Novel cardioprotective role of a small heat-shock protein, Hsp20, against ischemia/reperfusion injury

BACKGROUND

Heat-shock proteins (Hsps) have been shown to render cardioprotection from stress-induced injury; however, little is known about the role of another small heat-shock protein, Hsp20, which regulates activities of vasodilation and platelet aggregation, in cardioprotection against ischemia injury. We recently reported that increased expression of Hsp20 in cardiomyocytes was associated with improved contraction and protection against beta-agonist-induced apoptosis.

METHODS AND RESULTS

To investigate whether overexpression of Hsp20 exerts protective effects in both ex vivo and in vivo ischemia/reperfusion (I/R) injury, we generated a transgenic (TG) mouse model with cardiac-specific overexpression of Hsp20 (10-fold). TG and wild-type (WT) hearts were then subjected to global no-flow I/R (45 minutes/120 minutes) using the Langendorff preparation. TG hearts exhibited improved recovery of contractile performance over the whole reperfusion period. This improvement was accompanied by a 2-fold decrease in lactate dehydrogenase released from the TG hearts. The extent of infarction and apoptotic cell death was also significantly decreased, which was associated with increased protein ratio of Bcl-2/Bax and reduced caspase-3 activity in TG hearts. Furthermore, in vivo experiments of 30-minute myocardial ischemia, via coronary artery occlusion, followed by 24-hour reperfusion, showed that the infarct region-to-risk region ratio was 8.1+/-1.1% in TG hearts (n=7), compared with 19.5+/-2.1% in WT hearts (n=11, P<0.001).

CONCLUSIONS

Our data demonstrate that increased Hsp20 expression in the heart protects against I/R injury, resulting in improved recovery of cardiac function and reduced infarction. Thus, Hsp20 may constitute a new therapeutic target for ischemic heart diseases.

Small Heat-Shock Protein Hsp20 Phosphorylation Inhibits β-Agonist-Induced Cardiac Apoptosis

Activation of the sympathetic nervous system is a common compensatory feature in heart failure, but sustained β-adrenergic activation induces cardiomyocyte death, leading to cardiac remodeling and dysfunction. In mouse cardiomyocytes, we recently reported that prolonged exposure to β-agonists is associated with transient increases in expression and phosphorylation of a small heat-shock protein, Hsp20. To determine the functional significance of Hsp20, we overexpressed this protein and its constitutively phosphorylated (S16D) or nonphosphorylated (S16A) mutant in adult rat cardiomyocytes. Hsp20 protected cardiomyocytes from apoptosis triggered by activation of the cAMP-PKA pathway, as indicated by decreases in the number of pyknotic nuclei, terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling, and DNA laddering, which were associated with inhibition of caspase-3 activity. These protective effects were further increased by the constitutively phosphorylated Hsp20 mutant (S16D), which conferred full protection from apoptosis. In contrast, the nonphosphorylatable mutant (S16A) exhibited no antiapoptotic properties. Immunostaining studies and immunoprecipitations with Hsp20 or actin antibodies demonstrated that Hsp20 translocated to cytoskeleton and associated with actin on isoproterenol stimulation. These findings suggest that Hsp20 and its phosphorylation at Ser16 may provide cardioprotection against β-agonist-induced apoptosis. Thus, Hsp20 may represent a novel therapeutic target in the treatment of heart failure.

Some properties of human small heat shock protein Hsp20 (HspB6)

Human heat shock protein of apparent molecular mass 20 kDa (Hsp20) and its mutant, S16D, mimicking phosphorylation by cyclic nucleotide-dependent protein kinases, were cloned and expressed in Escherichia coli. The proteins were obtained in a homogeneous state without utilization of urea or detergents. On size exclusion chromatography at neutral pH, Hsp20 and its S16D mutant were eluted as symmetrical peaks with an apparent molecular mass of 55-60 kDa. Chemical crosslinking resulted in the formation of dimers with an apparent molecular mass of 42 kDa. At pH 6.0, Hsp20 and its S16D mutant dissociated, and were eluted in the form of two peaks with apparent molecular mass values of 45-50 and 28-30 kDa. At pH 7.0-7.5, the chaperone activity of Hsp20 (measured by its ability to prevent the reduction-induced aggregation of insulin or heat-induced aggregation of yeast alcohol dehydrogenase) was similar to or higher than that of commercial alpha-crystallin. Under these conditions, the S16D mutant of Hsp20 possessed lower chaperone activity than the wild-type protein. At pH 6.0, both alpha-crystallin and Hsp20 interacted with denatured alcohol dehydrogenase; however, alpha-crystallin prevented, whereas Hsp20 either did not affect or promoted, the heat-induced aggregation of alcohol dehydrogenase. The mixing of wild-type human Hsp27 and Hsp20 resulted in a slow, temperature-dependent formation of hetero-oligomeric complexes, with apparent molecular mass values of 100 and 300 kDa, which contained approximately equal amounts of Hsp27 and Hsp20 subunits. Phosphorylation of Hsp27 by mitogen activated protein kinase-activated protein kinase 2 was mimicked by replacing Ser15, 78 and 82 with Asp. A 3D mutant of Hsp27 mixed with Hsp20 rapidly formed a hetero-oligomeric complex with an apparent molecular mass of 100 kDa, containing approximately equal quantities of two small heat shock proteins.

Heat induced HSP20 phosphorylation without increased cyclic nucleotide levels in swine carotid media

BACKGROUND

Heat pretreatment of swine carotid artery has been shown to increase ser16-heat shock protein 20 (HSP20) phosphorylation and suppress force, i.e., reduce force with only minimal reduction in ser19-myosin regulatory light chain (MRLC) phosphorylation.

RESULTS

We further investigated this response in intact histamine stimulated swine carotid artery rings. There was a heat threshold such that increased ser16-HSP20 phosphorylation and force suppression were observed between 43 degrees C and 46 degrees C. The increased ser16-HSP20 phosphorylation persisted up to 16 hours after 44.5 degrees C heat treatment. Pretreatment of swine carotid media at 44.5 degrees C increased ser16-HSP20 phosphorylation without increases in [cAMP] or [cGMP], suggesting an alternate mechanism, perhaps phosphatase inhibition, for the increase in ser16-HSP20 phosphorylation. Heat pretreatment at 47.5 degrees C reduced force by decreasing MRLC phosphorylation rather than by large increases in ser16-HSP20 phosphorylation. HSP20 phosphorylation at the putative PKC site did not change with any treatment.

CONCLUSION

These results demonstrate that multiple mechanisms can induce force suppression that is correlated with ser16-HSP20 phosphorylation: 1) nitrovasodilators via cGMP, 2) forskolin via cAMP, and 2) thermal stress in a cyclic nucleotide independent manner.