Hypertension, aging, and myocardial synthesis of heat-shock protein 72

Emerging role of heat shock proteins in cardiovascular diseases

Heat Shock Proteins (HSPs) are evolutionarily conserved proteins from prokaryotes to eukaryotes. They are ubiquitous proteins involved in key physiological and cellular pathways (viz. inflammation, immunity and apoptosis). Indeed, the survivability of the cells under various stressful conditions depends on appropriate levels of HSP expression. There is a growing line of evidence for the role of HSPs in regulating cardiovascular diseases (CVDs) (viz. hypertension, atherosclerosis, atrial fibrillation, cardiomyopathy and heart failure). Furthermore, studies indicate that a higher concentration of circulatory HSP antibodies correlate to CVDs; some are even potential markers for CVDs. The multifaceted roles of HSPs in regulating cellular signaling necessitate unraveling their links to pathophysiology of CVDs. This review aims to consolidate our understanding of transcriptional (via multiple transcription factors including HSF-1, NF-κB, CREB and STAT3) and post-transcriptional (via microRNAs including miR-1, miR-21 and miR-24) regulation of HSPs. The cytoprotective nature of HSPs catapults them to the limelight as modulators of cell survival. Yet another attractive prospect is the development of new therapeutic strategies against cardiovascular diseases (from hypertension to heart failure) by targeting the regulation of HSPs. Moreover, this review provides insights into how genetic variation of HSPs can contribute to the manifestation of CVDs. It would also offer a bird's eye view of the evolving role of different HSPs in the modulation and manifestation of cardiovascular disease.

PPAR-γ activator pioglitazone prevents age-related atrial fibrillation susceptibility by improving antioxidant capacity and reducing apoptosis in a rat model

INTRODUCTION

The in vivo role of peroxisome proliferator-activated receptor (PPAR)-γ, an essential transcriptional mediator of lipid and glucose metabolism, in atrial fibrillation (AF) remains to be fully elucidated. We investigated the effects of pioglitazone, a PPAR-γ activator, in an in vivo AF rat model.

METHODS AND RESULTS

We studied 3 groups of Wistar rats: young group, 3-month-old rats treated with vehicle; aged group, 9-month-old rats treated with vehicle; and aged+Pio group, 9-month-old rats treated with pioglitazone. After 4-week treatment, AF duration induced by 30-second burst pacing, gene and protein expressions, and atrial structural changes were compared between the 3 groups. Atrial oxidant reducing activity was measured by electron spin resonance method. AF duration was markedly prolonged in the aged group but significantly shortened in the aged+Pio group. Age-induced decrease in free radical reducing activity was reversed by pioglitazone. Gene and protein expression levels of antioxidant molecules Sod2 (MnSOD) and Hspa1a (heat shock 70 protein) were significantly enhanced, and p22(phox) and gp91(phox), two NADPH oxidase subunits, were significantly decreased in aged+Pio rats. Pioglitazone treatment significantly increased phosphorylated (p-) Akt but significantly reduced p-ERK1/2 and p-JNK. Pioglitazone significantly restored p-Bad and reduced cleaved caspase-3 and -9, indicating that pioglitazone prevented age-related enhancement of apoptotic signaling. Microscopic analysis revealed suppression of age-related histological changes (interstitial fibrosis and apoptosis) by pioglitazone.

CONCLUSIONS

Pioglitazone inhibited age-related arrhythmogenic atrial remodeling and AF perpetuation by improving antioxidant capacity and inhibiting the mitochondrial apoptotic signaling pathway. PPAR-γ activators could become a novel upstream therapy for age-related AF.

Estrogen, aging and the cardiovascular system

Estrogen is a powerful hormone with pleiotropic effects. Estrogens have potent antioxidant effects and are able to reduce inflammation, induce vasorelaxation and alter gene expression in both the vasculature and the heart. Estrogen treatment of cultured cardiac myocytes and endothelial cells rapidly activates NFkappaB, induces heat-shock protein (HSP)-72, a potent intracellular protective protein, and protects cells from simulated ischemia. In in vivo models, estrogens protect against ischemia and trauma/hemorrhage. Estrogens may decrease the expression of soluble epoxide hydrolase, which has deleterious effects on the cardiovascular system through metabolism of epoxyeicosatrienoic acids. Natural (endogenous) estrogens in premenopausal women appear to protect against cardiovascular disease and yet controlled clinical trials have not indicated a benefit from estrogen replacement postmenopause. Much remains to be understood in regards to the many properties of this powerful hormone and how changes in this hormone interact with aging-associated changes. The unexpected negative results of trials of estrogen replacement postmenopause probably arise from our lack of understanding of the many effects of this hormone.

Myocardial hypoperfusion/reperfusion tolerance with exercise training in hypertension

The purpose of this study was to examine whether exercise training, superimposed on compensated-concentric hypertrophy, could increase myocardial hypoperfusion-reperfusion (H/R) tolerance. Female Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (age: 4 mo; N = 40) were placed into a sedentary (SED) or exercise training (TRD) group (treadmill running; 25 m/min, 1 h/day, 5 days/wk for 16 wk). Four groups were studied: WKY-SED ( n = 10), WKY-TRD ( n = 10), SHR-SED ( n = 10), and SHR-TRD ( n = 10). Blood pressure and heart rate were determined, and in vitro isolated heart performance was measured with a retrogradely perfused, Langendorff isovolumic preparation. The H/R protocol consisted of a 75% reduction in coronary flow for 17 min followed by 30 min of reperfusion. Although the rate-pressure product was significantly elevated in SHR relative to WKY, training-induced bradycardia reduced the rate-pressure product in SHR-TRD ( P < 0.05) without an attenuation in systolic blood pressure. Heart-to-body weight ratio was greater in both groups of SHR vs. WKY-SED ( P < 0.001). Absolute and relative myocardial tolerance to H/R was greater in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05). Endurance training superimposed on hypertension-induced compensated hypertrophy conferred no further cardioprotection to H/R. Postreperfusion 72-kDa heat shock protein abundance was enhanced in WKY-TRD and both groups of SHR relative to WKY-SED ( P < 0.05) and was highly correlated with absolute left ventricular functional recovery during reperfusion ( R2= 0.86, P < 0.0001). These data suggest that both compensated hypertrophy associated with short-term hypertension and endurance training individually improved H/R and that increased postreperfusion 72-kDa heat shock protein abundance was, in part, associated with the cardioprotective phenotype observed in this study.

Myocardial Heat Shock Protein 70 Expression in Young and Old Rats After Identical Exercise Programs

Synthesis of inducible heat shock protein 70 (HSP70) is impaired in aged animals following acute stresses including exercise. In this study we determined whether aging affects expression of this cytoprotective protein following chronic exercise participation. Male Fischer 344 rats, final ages 6 and 24 months, exercised identically for 10 weeks on a treadmill (15 degrees incline, 15 m/min for up to 60 minutes, 5 days/week). In 6-month-old animals, exercise increased HSP70 in heart (44%), liver (216%), and skeletal muscle (126%) (p <.05 vs sedentary). In 24-month-old animals, exercise increased HSP70 in muscle (69%), but not in heart or liver. In heart, antioxidant enzyme activities and HSP70 messenger RNA were measured and found to be unaffected by exercise at both ages. Our results indicate an age-related decrease in HSP70 production in heart and liver following chronic exercise. Furthermore, the aged heart does not increase its antioxidant enzyme defenses to compensate for the HSP70 deficit.

Age, cell signalling and cardioprotection

For many years investigators have been researching methods of preconditioning the myocardium against ischaemia-induced damage; however, a majority of this research has been carried out in young animals and cells. Normal ageing is accompanied by changes in the human myocardium that decrease its capacity to tolerate and respond to various forms of stress. Also, the likelihood of experiencing an ischaemic stress and other cardiovascular complications increases as an individual ages; therefore, an aged population would benefit most from cardioprotective treatments. Methods currently known to provide cardioprotection (or preconditioning) include exercise, heat stress, oxidative stress, brief ischaemia, stretch and certain pharmacological interventions. It is unclear whether the aged myocardium can adapt to a preconditioning stimulus; however, many researchers have observed age-related alterations in the expression and activation of proteins key to the cardioprotective process. These proteins include heat shock protein 70 (HSP70), nitric oxide synthase (NOS), the sodium-hydrogen exchanger (NHE), and the mitogen-activated protein (MAP) kinases c-Jun N-terminal Kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Therefore, the purpose of the current review will be to outline the current knowledge of these cardioprotective agents in an aged myocardium. Interactions among the cardioprotective agents outlined herein suggest that age-related changes in the myocardium will need to be better understood before cardioprotective interventions that have been proved effective in young animals can be applied to an aged human population.

Altered temporal profile of heat shock factor 1 phosphorylation and heat shock protein 70 expression induced by heat shock in nucleus tractus solitarii of spontaneously hypertensive rats

BACKGROUND

We demonstrated recently that heat shock (HS)-induced heat shock protein 70 (HSP70) expression in bilateral nucleus tractus solitarii (NTS), the terminal site in the brain stem for primary baroreceptor afferents, confers cardiovascular protection against heatstroke by potentiating baroreceptor reflex (BRR) response. This study evaluated the hypothesis that altered regulation of HSP70 expression may be associated with the heightened susceptibility to heatstroke during hypertension.

METHODS AND RESULTS

Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats anesthetized with propofol were used. Compared with WKY rats, significant induction in HSP70 or phosphorylation of heat shock factor 1 (HSF1), but not HSF2, in the NTS and potentiation of BRR response in SHR occurred earlier (4 versus 8 hours), reaching peak magnitude sooner (16 versus 24 hours), and declined more rapidly after a brief hyperthermic HS (42+/-0.5 degrees C for 15 minutes). The protection conferred by HS against hypotension and bradycardia during the onset of heatstroke (45 degrees C for 60 minutes), although effective, was less effective in SHR. Microinjection bilaterally into the NTS of the selective protein kinase A (PKA) inhibitor H-89 (100 pmol) or the selective PKC inhibitor calphostin C (100 pmol) significantly attenuated all of the above events induced in SHR by HS. However, only H-89 was effective in WKY rats.

CONCLUSIONS

An altered temporal profile of HS-induced HSP70 expression or potentiation of BRR response by concurrent activation via both PKA and PKC pathways of phosphorylation of HSF1 in the NTS may be associated with greater susceptibility to heatstroke during hypertension.

The endothelium as physiological source of properdin: role of wall shear stress

Properdin is a positive regulator of the alternative pathway of complement activation. It can be released by peripheral blood cells but is not synthesized in the liver and the physiological source of properdin in plasma is unknown. The endothelium is an extra-hepatic source for several complement components and shear stress can modulate their expression. The aim of this study was to analyze shear stress-exposed endothelial cells (EC) as physiological source for plasma properdin. Human umbilical vein EC (HUVEC) and human cardiac microvascular EC (HCMEC) were exposed to shear stress using a cone-and-plate apparatus and properdin expression was analyzed by RT-PCR, Northern, and Western blot. mRNA for properdin is barely detectable in untreated EC but strongly induced by laminar shear stress exposure (6 dyn/cm(2); 24 h). Properdin is induced also at the protein level and is released in the extracellular compartment. Properdin up-regulation requires a shear stress of 2-3 dyn/cm(2), is not transient, and is reversible by restoration of static conditions. Turbulent flow exposure results in two times higher induction of properdin than laminar flow exposure. The ability of endothelial cells exposed to shear stress to synthesize properdin proposes the endothelium as physiological source for plasma properdin and suggests a link between flow conditions and the modulation of the alternative pathway. Furthermore, the stronger properdin induction by turbulent flow may suggest an involvement in the pathology of atherosclerosis.

Effect of long-term treatment with trandolapril on Hsp72 and Hsp73 induction of the failing heart following myocardial infarction

1. The effect of long-term treatment of rats with chronic heart failure (CHF) following acute myocardial infarction with trandolapril, an angiotensin I-converting enzyme (ACE) inhibitor, on heat shock-induced Hsp72 and Hsp73 production was examined. 2. Acute myocardial infarction was induced by coronary artery ligation (CAL). The animals with CAL showed symptoms of CHF at the 8th week after the operation. The hearts isolated from animals with CAL at the 2nd and 8th week after surgery were subjected to hyperthermia at 42 degrees C for 15 min followed by 6-h perfusion (hyperthermia/6-h perfusion). 3. In the hearts isolated from the animals at the 2nd week, an approximate 20% decline in the rate pressure product (RPP) was seen after hyperthermia/6-h perfusion, which was similar to that in non-operated controls. In contrast, a significant reduction in the RPP after hyperthermia/6-h perfusion was seen in the hearts of rats with CHF. These hearts did not increase Hsp72 and Hsp73 production after hyperthermia. The decline in RPP was associated with failure in the production of myocardial Hsp72 and Hsp73. 4. When rats with CAL were treated with 3 mg kg(-1) day(-1) trandolapril from the 2nd to 8th week after the operation, the decline in RPP of the failing heart after hyperthermia was similar to that of the sham-operated rats. The induction of myocardial Hsp72 and Hsp73 production of the coronary artery-ligated rats after hyperthermia was reversed by treatment with trandolapril. 5. These findings suggest that the preserved ability to induce Hsp72 and Hsp73 production in the heart with CAL by trandolapril treatment may be attributed to the increased tolerance against heat stress-induced deterioration of myocardial contractile function.

Association of plasma antibodies against the inducible Hsp70 with hypertension and harsh working conditions

Autoantibodies against certain stress or heat shock proteins (Hsps) may play a role in the pathogenesis and/ or prognosis of some diseases. Using immunoblotting with human recombinant Hsps and univariate and multivariate logistic regression models, we have investigated the presence of antibodies against Hsp70, the inducible member of the 70-kDa family of heat shock proteins, and analyzed its possible association with hypertension and working conditions. Plasma and serum were collected from 764 steel mill workers from 6 work sites exposed to (1) severe noise; (2) severe noise and dust; (3) noise, dust, and heat; (4) noise and heat; (5) severe noise and heat; and (6) office conditions (control). Workers with prolonged exposure to stresses such as noise, dust, and high temperature and a combination of these in the workplace had a high incidence (26.6% to 40.2%) of antibodies to Hsp70 compared to the lowest incidence (18.6%) of antibodies to Hsp70 in the control group of office workers. Moreover, there was a statistical association of antibodies against Hsp70 with hypertension. The statistical correlation between the presence of antibodies to Hsp70 and hypertension is higher in the group of workers with blood pressure of 160/95 mmHg than in the 140/90-mmHg group after excluding possible effects of the workplace stresses. These results suggest that harsh workplace conditions can increase the production of antibodies against Hsp70 and that the presence of antibodies to this stress protein may be associated with hypertension. The precise mechanism for the elevation of antibodies against Hsps by environmental and workplace stresses and their relation to hypertension remains to be established.

Heat shock proteins and cardiovascular pathophysiology

In the eukaryotic cell an intrinsic mechanism is present providing the ability to defend itself against external stressors from various sources. This defense mechanism probably evolved from the presence of a group of chaperones, playing a crucial role in governing proper protein assembly, folding, and transport. Upregulation of the synthesis of a number of these proteins upon environmental stress establishes a unique defense system to maintain cellular protein homeostasis and to ensure survival of the cell. In the cardiovascular system this enhanced protein synthesis leads to a transient but powerful increase in tolerance to such endangering situations as ischemia, hypoxia, oxidative injury, and endotoxemia. These so-called heat shock proteins interfere with several physiological processes within several cell organelles and, for proper functioning, are translocated to different compartments following stress-induced synthesis. In this review we describe the physiological role of heat shock proteins and discuss their protective potential against various stress agents in the cardiovascular system.

Effect of aging on the ability of preconditioning to protect rat hearts from ischemia-reperfusion injury

Ischemic preconditioning (IP) reduces infarct size in young animals; however, its impact on aging is underinvestigated. The effect of variations in IP stimuli was studied in young, middle-aged, and aged rat hearts. Isolated hearts underwent 35 min of regional ischemia and 120 min of reperfusion. Hearts with IP were subjected to either one ischemia-reperfusion cycle (5 min of ischemia and 5 min of reperfusion per cycle) or three successive cycles before 35 min of regional ischemia. Additional studies investigated the effects of pharmacological preconditioning in aged hearts using the adenosine A(1) receptor agonist 2-chloro-N(6)-cyclopentyladenosine, the protein kinase C analog 1,2-dioctanoyl-sn-glycerol, and the mitochondrial ATP-sensitive potassium (K(ATP))-channel opener diazoxide. Infarct sizes indicated that the aged rat heart could not be preconditioned via ischemic or pharmacological means. The middle-aged rat heart had a blunted IP response compared with the young adult (only an increased IP stimulus caused a significant reduction in infarct size). These results suggest that there are defects within the IP signaling cascade of the aged heart. Clinical relevance is important if we are to use any IP-like mimetics to the benefit of an aging population.

Protective effect of heat shock protein 72 on contractile function of perfused failing heart

The contribution of heat shock protein 72 (HSP72) to the protection of cardiac function was examined in rats with chronic heat failure (CHF) following coronary artery ligation (CAL). The CAL animals revealed functional deterioration without low cardiac output 2 wk after CAL and with low cardiac output 8 wk after CAL, suggesting that CHF had developed by 8 wk after CAL. The hearts isolated from animals 2 and 8 wk after CAL (2-wk CAL heart and 8-wk CAL heart, respectively) were subjected to hyperthermia (at 42 degrees C) for 15 min, followed by 6-h perfusion (hyperthermia/6-h perfusion). The 2-wk CAL heart showed a 19.0 +/- 3.9% decline in the rate- pressure product (RPP) after hyperthermia/6-h perfusion, similar to the nonoperated control (19.8 +/- 2.9% decline). The production of myocardial HSP72 increased in the 2-wk CAL heart in response to hyperthermia (412.7 +/- 29.5% of each prehyperthermia value). The 8-wk CAL heart showed a reduction in the RPP (45.2 +/- 4.3% decline) after hyperthermia/6-h perfusion, associated with blunting of the production of HSP72 (68.9 +/- 22.6% increase, respectively). The results suggest that functional deterioration of the isolated failing heart may be attributed to a reduction in the production of myocardial HSP72.

Heat stress response and myocardial protection

Prior whole-body hyperthermia is able to protect the myocardium against ischaemia-reperfusion injury by reducing cellular necrosis, preserving the ventricular function and preventing the occurrence of arrhythmias. These cardioprotective effects are associated with reduction of oxidative stress, preservation of the high-energy phosphate levels and synthesis of heat stress proteins. A better understanding of this powerful protective adaptation of the myocytes would be of interest for potential clinical application, and rational design of specific agents that activate this mechanism will hopefully follow soon.

Heat shock protein expression in hearts hypertrophied by genetic and nongenetic hypertension

Genetically hypertensive animals are characterized by greater thermosensitivity and overexpression of heat shock proteins (HSP) upon thermal stimulation. We examined HSP72 expression under conditions of brief coronary occlusion or thermal stimulation, and the effects of the severity of these stimuli and of myocardial hypertrophy on the expression in hearts of spontaneously hypertensive rat (SHR) and Wistar Kyoto rat (WKY) groups, A snare was created around the left coronary artery in the SHR (n = 16) and WKY (n = 19) groups. In 7 WKY rats, the ascending aorta was banded and a snare was created simultaneously (WKY-AoB). By tying the snare, 4 weeks later, we applied 5- or 10-min coronary occlusion without opening the chest. For thermal stimulation, the SHR (n = 13) and WKY (n = 11) rats were placed in a 42 degrees C chamber for 15 or 40 min. The mRNA or protein level was estimated 1 or 24h after stimulation. In the SHR vs WKY groups, the mRNA and protein levels were higher after 5-min occlusion or 15-min thermal stimulation. After 10-min occlusion or 40-min thermal stimulation the difference was no longer observed. The overexpression was not observed in the WKY-AoB group despite the presence of hypertrophy similar to that seen in the SHR group (3.11+/-0.11 vs 3.20+/-0.06 mg/g in left ventricular weight/body weight). The HSP72 was overexpressed in hearts of genetically hypertensive animals after brief ischemia. Differential expression between the two groups was observed after mild stimuli, but not after more severe stimuli. Cardiac hypertrophy was not a major factor for determining the overexpression of HSP72.

Developmental and afterload stress regulation of heat shock proteins in the ovine myocardium

Heat shock proteins (hsps) are produced in the myocardium in response to stresses such as ischemia, hyperthermia, and increased afterload. The role of these stress proteins in the developing myocardium is unknown. Expression of the inducible (hsp 72) and cognate (hsc 73) hsps was determined in the immature ovine myocardium during the perinatal transition, and their role in subsequent myocardial growth was examined. hsp synthesis was also studied during acute afterload stress in newborns by aortic banding to a gradient of 50 torr for 4 h. Expression of the inducible (hsp 72) isoform is developmentally regulated in both right and left ventricles: low levels in the fetus, increasing throughout development, and peaking in the 14-25-d newborn and adult. The cognate (hsc 73) isoform remains unchanged during development in the left ventricle but decreases with age in the right ventricle. The inducible (hsp 72) isoform is also developmentally regulated in the lung, increasing postnatally to a peak in the 14-25-d-old and adult sheep. Finally, newborn myocardium demonstrated a rapid increase in hsp expression in response to afterload stress, similar to that seen in the adult.

Stress proteins and atherosclerosis

Several cytotoxic stimuli of a different nature are involved in the complex etiology of atherosclerosis. Cells of the vasculature may potentially cope with the presence of these stressors through the increased synthesis of stress proteins (or heat shock proteins, hsps), an ubiquitous and conserved defense response. Evidence exists that the expression of two stress proteins of intermediate molecular weight, hsp60 and hsp70, is higher at sites of atherosclerotic lesions than it is in normal tissue. The role of hsps in atherosclerosis is controversial. While hsp70 is likely to be involved in cytoprotection, hsp60 is probably acting as an autoantigen, and may trigger both cell-mediated and antibody-mediated immune responses.

Delayed protection of the ischemic heart--from pathophysiology to therapeutic applications

Preconditioning the heart with brief episodes of ischemia paradoxically increases its resistance to subsequent ischemic episodes, and markedly limits infarct size. Although preconditioning is now considered as the most powerful antiischemic intervention known, its beneficial effects are short-lived since they are lost if the reperfusion period after preconditioning is extended past 2-3 h. There is, however, some evidence of a delayed phase of protection, manifest 24 h after the initial preconditioning stimulus, associated with a decrease in infarct size, a prevention of postischemic contractile dysfunction (stunning) and a reduction in endothelial injury. The delayed beneficial effects of preconditioning resemble those induced by prior heat stress, and might be related to the expression of stress proteins (heat shock proteins or HSP). Evidence for a role of HSP derives from observations showing that brief ischemia is a potent stimulus for HSP expression. Moreover, transfection of isolated cells with HSP or overexpression of HSP in transgenic mice renders the myocytes more resistant to ischemia. Once produced, HSP are believed to facilitate protein synthesis, stabilize newly formed proteins and repair denatured ones. Alternatively, delayed preconditioning may be mediated by antioxidant enzymes such as superoxide dismutase or catalase, which are also upregulated by ischemia and this could lead to a lesser production of oxygen-derived free radicals during reperfusion. Indeed, in isolated myocytes, prevention of hypoxia-induced expression of superoxide dismutase (using an antisense oligonucleotide) abolished the delayed protective effect of preconditioning. Importantly, recent in vivo evidence suggests that the delayed protection may be mediated by adenosine, through activation of A1-receptors, and by stimulation of protein kinase C. Finally, although the exact mechanisms by which preconditioning induces delayed protection are still mostly unknown, the fact that the expression of protective proteins such as HSP can be induced by many other means than ischemia suggests that it is possible to pharmacologically stimulate this expression and thus possibly mimic the endogenous protective pathway. This could lead to the development of new pharmacological interventions which induce delayed myocardial protection in clinical situations such as angioplasty, coronary bypass surgery or even in patients at high risk of infarction.

Age-related changes before and after imposition of hemodynamic stress in the mammalian heart

This review focusses on the following issues: how the mammalian heart grows and ages; age-related changes in the mammalian heart before and after imposition of hemodynamic stress; and antiaging modulation in the mammalian heart. The heart and other organs grow and age together in the whole body, and interactions occur between these organs. Therefore, the age-related changes at the molecular and cellular level in the in vivo heart are the summation of the changes of the heart per se and the effects of other organs or tissues on the heart. Furthermore, myocytes grow and age under the influence of age-related changes in other myocytes and other types of cells in the myocardial tissue through autocrine or paracrine mechanisms, because myocytes are exposed to many biologically active substances which are released from those cells. Since hypertension and ischemia are very common hemodynamic events in aged hearts, the characteristics in aged hearts are discussed in terms of responses to hypertension or ischemia. The induction of proto-oncogenes and heat shock protein genes in response to milder hemodynamic stress such as pressure-overload and ischemia is diminished in aged hearts. However, the aged heart can respond to more severe stress to a level similar to that of young-adult hearts. Therefore, the senescent heart is characterized by its attenuated adaptation to hemodynamic stress and by its ability to adapt to limited environmental changes. Several interventions have antiaging effects on the heart at the molecular and cellular level.

Environmentally-regulated genes of hypertension

Several monogenetic causes of hypertension have recently been identified, but for the most part, the disease is of polygenic and possibly heterogenous character. The environmental impact, representing about 2/3 of blood pressure variance, is usually thought to be exerted at the level of phenotypic modification, additive to the effect of genetic loci determining blood pressure. The concept presented here is that for a significant part, the environment interacts with genes, influencing their expression. Of particular interest are stress genes expressed differentially in human and experimental hypertension. They may constitute candidate genes of blood pressure and heart weight, influenced by environmental stressors at the level of gene expression.