Cardiac hypertrophy is a well known response to increased hemodynamic load. Mechanical stress is considered to be the trigger inducing a growth response in the overloaded myocardium. Furthermore, mechanical stress induces the release of growth-promoting factors, such as angiotensin II, endothelin-1, and transforming growth factor-beta, which provide a second line of growth induction. In this review, we will focus on the primary effects of mechanical stress: how mechanical stress may be sensed, and which signal transduction pathways may couple mechanical stress to modulation of gene expression, and to increased protein synthesis. Mechanical stress may be coupled to intracellular signals that are responsible for the hypertrophic response via integrins and the cytoskeleton or via sarcolemmal proteins, such as phospholipases, ion channels and ion exchangers. The signal transduction pathways that may be involved belong to two groups: (1) the mitogen-activated protein kinases (MAPK) pathway; and (2) the janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway. The MAPK pathway can be subdivided into the extracellular-regulated kinase (ERK), the c-Jun N-terminal kinase (JNK), and the 38-kDa MAPK (p38 MAPK) pathway. Alternatively, the stress signal may be directly submitted to the nucleus via the cytoskeleton without the involvement of signal transduction pathways. Finally, by promoting an increase in intracellular Ca2+ concentration stretch may stimulate the calcium/calmodulin-dependent phosphatase calcineurin, a novel hypertrophic signalling pathway.

Epidemiologic studies have linked intrauterine growth restriction (IUGR) with an increased incidence of cardiovascular disease later in life; reduced cardiomyocyte number in IUGR hearts may underlie such prenatal programming. Our aim was to examine the effect of IUGR, as a result of maternal protein restriction, on the number of cardiomyocytes in the rat heart at birth. Rats were fed either a low-protein diet (LPD) or a normal-protein diet (NPD) during pregnancy. At birth, the offspring were killed and the hearts were immersion-fixed. The number of cardiomyocyte nuclei in the hearts were stereologically determined using an optical disector-fractionator approach. In some litters, cardiomyocytes were enzymatically isolated from freshly excised hearts and the proportion of binucleated cells was determined. Taking into account the number of binucleated cells, the nuclear counts were adjusted to estimate total cardiomyocyte number. Birth weight and heart weight were significantly reduced in the LPD offspring. This was accompanied by a significant reduction in the number of cardiomyocytes per heart in the LPD offspring compared with the NPD offspring (1.18 Ϯ 0.05 ϫ 10 7 and 1.41 Ϯ 0.06 ϫ 10 7 , respectively; p ϭ 0.001). The number of binucleated cardiomyocytes was low (~3%) and equal in both groups. In conclusion, IUGR as a result of maternal protein restriction leads to a reduction in the number of cardiomyocytes per heart. As cardiomyocyte proliferation is rare after birth, it is plausible that this reduction in cardiomyocytes may lead to compromised cardiac function later in life. Epidemiologic studies have shown a link between low birth weight, as a result of intrauterine growth restriction (IUGR), and an increased incidence of cardiovascular disease later in life (1), suggesting that maternal nutrition may affect the long-term disease profile of offspring. IUGR can result from a lack of nutrients, oxygen, or blood supply to the fetus (2). The link to cardiovascular disease later in life in IUGR infants may relate to underdevelopment of vital organs in utero. Indeed, early studies report that a reduced supply of nutrients during early life, prenatal and postnatal, interferes with the rate of cell multiplication in various organs (3) and that the effect is proportionally more deleterious in tissues with a faster rate of cell multiplication (4). Under these circumstances, growth of the brain is generally "spared" by preferential diversion of blood flow to the brain, whereas growth of other organs is usually proportional to body weight (5). For example, a reduced kidney weight in IUGR rats was shown to be associated with decreased nephron endowment (6,7). The effects of IUGR on the heart are less well defined. In IUGR rats that are exposed to maternal protein restriction, a reduced heart weight is often found (8,9). Alternatively, an increased heart weight as a result of a low-protein diet (LPD) has also been documented (10). Whether IUGR influences the number of cardiomyocytes in the heart is still unclear. If IUGR ...

Rationale: Pulmonary hypertension (PH) is characterized by progressive increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy, RV failure, and death. Current treatments only temporarily reduce severity of the disease, and an ideal therapy is still lacking. Objectives: Estrogen pretreatment has been shown to attenuate development of PH. Because PH is not often diagnosed early, we examined if estrogen can rescue preexisting advanced PH. Methods: PH was induced in male rats with monocrotaline (60 mg/kg). At Day 21, rats were either treated with 17-b estradiol or estrogen (E2, 42.5 mg/kg/d), estrogen receptor-b agonist (diarylpropionitrile, 850 mg/kg/d), or estrogen receptor a-agonist (4,4',4"-[4-Propyl-(1H)-pyrazole-1,3,5-triyl] trisphenol, 850 mg/kg/d) for 10 days or left untreated to develop RV failure. Serial echocardiography, cardiac catheterization, immunohistochemistry, Western blot, and real-time polymerase chain reaction were performed. Measurements and Main Results: Estrogen therapy prevented progression of PH to RV failure and restored lung and RV structure and function. This restoration was maintained even after removal of estrogen at Day 30, resulting in 100% survival at Day 42. Estradiol treatment restored the loss of blood vessels in the lungs and RV. In the presence of angiogenesis inhibitor TNP-470 (30 mg/kg) or estrogen receptor-b antagonist (PHTPP, 850 mg/kg/d), estrogen failed to rescue PH. Estrogen receptor-b selective agonist was as effective as estrogen in rescuing PH. Conclusions: Estrogen rescues preexisting severe PH in rats by restoring lung and RV structure and function that are maintained even after removal of estrogen. Estrogen-induced rescue of PH is associated with stimulation of cardiopulmonary neoangiogenesis, suppression of inflammation, fibrosis, and RV hypertrophy. Furthermore, estrogen rescue is likely mediated through estrogen receptor-b.Keywords: pulmonary hypertension; estrogen; neoangiogenesis; estrogen receptors; inflammation Pulmonary hypertension (PH) is a chronic lung disease characterized by pulmonary vascular remodeling and progressive increase in pulmonary artery pressure leading to right ventricular (RV) hypertrophy and RV failure (RVF). End-stage RVF has long been regarded as a terminal state of pathological cardiopulmonary remodeling, including fibrosis and chamber dilation, being unresponsive to available therapies. Advanced PH is most often treated with aggressive nonpharmacological therapies, such as lung transplantation, but this approach is only feasible for a fraction of patients. In the past decade, cell and gene therapies have shown great potential for treatment of PH in animal models (1, 2) and humans (3). However, effective pharmacological therapy for treatment of patients with advanced PH would be much more practical and much more cost effective. Several agents have been identified to attenuate the development of PH when the therapy is started before the initiating stimuli (4-6). Unfortunately, up to now, there has been no id...

STEM CELLS 2007;25:271-278

Background-Hypertension is an important clinical problem and is often accompanied by left ventricular (LV) hypertrophy and dysfunction. Whether the myocardial high-energy phosphate (HEP) metabolism is altered in human hypertensive heart disease and whether this is associated with LV dysfunction is not known. Methods and Results-Eleven patients with hypertension and 13 age-matched healthy subjects were studied with magnetic resonance imaging at rest and with phosphorus-31 magnetic resonance spectroscopy at rest and during high-dose atropine-dobutamine stress. Hypertensive patients showed higher LV mass (98Ϯ28 g/m 2 ) than healthy control subjects (73Ϯ13 g/m 2 , PϽ0.01). LV filling was impaired in patients, reflected by a decreased peak rate of wall thinning (PRWThn), E/A ratio, early peak filling rate, and early deceleration peak (all PϽ0.05), whereas systolic function was still normal. The myocardial phosphocreatine (PCr)/ATP ratio determined in patients at rest (1.20Ϯ0.18) and during stress (0.95Ϯ0.25) was lower than corresponding values obtained from healthy control subjects at rest (1.39Ϯ0.17, PϽ0.05) and during stress (1.16Ϯ0.18, PϽ0.05). The PCr/ATP ratio correlated significantly with PRWThn (rϭϪ0.55, PϽ0.01), early deceleration peak (rϭϪ0.56, PϽ0.01), and with the rate-pressure product (rϭϪ0.53, PϽ0.001). Conclusions-Myocardial HEP metabolism is altered in patients with hypertensive heart disease. In addition, there is an association between impaired LV diastolic function and altered myocardial HEP metabolism in humans.

Nitric oxide (NO) produced in the heart by nitric oxide synthase (NOS) is a highly reactive signaling molecule and an important modulator of myocardial function. NOS catalyzes the conversion of L: -arginine to L: -citrulline and NO but under particular circumstances reactive oxygen species (ROS) can be formed instead of NO (uncoupling). In the heart, three NOS isoforms are present: neuronal NOS (nNOS, NOS1) and endothelial NOS (eNOS, NOS3) are constitutively present enzymes in distinct subcellular locations within cardiomyocytes, whereas inducible NOS (iNOS, NOS2) is absent in the healthy heart, but its expression is induced by pro-inflammatory mediators. In the tissue, NO has two main effects: (i) NO stimulates the activity of guanylate cyclase, leading to cGMP generation and activation of protein kinase G, and (ii) NO nitrosylates tyrosine and thiol-groups of cysteine in proteins. Upon nitrosylation, proteins may change their properties. Changes in (i) NOS expression and activity, (ii) subcellular compartmentation of NOS activity, and (iii) the occurrence of uncoupling may lead to multiple NO-induced effects, some of which being particularly evident during myocardial overload as occurs during aortic constriction and myocardial infarction. Many of these NO-induced effects are considered to be cardioprotective but particularly if NOS becomes uncoupled, formation of ROS in combination with a low NO bioavailability predisposes for cardiac damage.

Elevated cardiac troponin-I (cTnI) levels have been demonstrated in serum of patients without acute coronary syndromes, potentially via a stretch-related process. We hypothesize that this cTnI release from viable cardiomyocytes is mediated by stimulation of stretchresponsive integrins. Cultured cardiomyocytes were treated with (1) Gly-Arg-Gly-Asp-Ser (GRGDS, n=22) to stimulate integrins, (2) Ser-Asp-Gly-Arg-Gly (SDGRG, n=8) that does not stimulate integrins, or (3) phosphate-buffered saline (control, n=38). Cells and media were analyzed for intact cTnI, cTnI degradation products, and matrix metalloproteinase (MMP)-2. Cell viability was examined by assay of lactate dehydrogenase (LDH) activity and by nuclear staining with propidium iodide. GRGDS-induced integrin stimulation caused increased release of intact cTnI (9.6±3.0%) as compared to SDGRG-treated cardiomyocytes (4.5 ± 0.8%, p < 0.001) and control (3.0 ± 3.4%, p<0.001). LDH release from GRGDS-treated cardiomyocytes (15.9±3.8%) equalled that from controls (15.2±2.3%, p=n.s.), indicating that the GRGDS-induced release of cTnI is not due to cell necrosis. This result was confirmed by nuclear staining with propidium iodide. Integrin stimulation increased the intracellular and extracellular MMP2 activity as compared to controls (both p<0.05). However, despite the ability of active MMP2 to degrade cTnI in vitro, integrin stimulation in cardiomyocytes was not associated with cTnI degradation. The present study demonstrates that intact cTnI can be released from viable cardiomyocytes by stimulation of stretch-responsive integrins.

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