Insulin-like growth factors and neonatal cardiomyocyte development: ventricular gene expression and membrane receptor variations in normotensive and hypertensive rats

The Insulin-like Growth Factor Signalling Pathway in Cardiac Development and Regeneration

Insulin and Insulin-like growth factors (IGFs) perform key roles during embryonic development, regulating processes of cell proliferation and survival. The IGF signalling pathway comprises two IGFs (IGF1, IGF2), two IGF receptors (IGFR1, IGFR2), and six IGF binding proteins (IGFBPs) that regulate IGF transport and availability. The IGF signalling pathway is essential for cardiac development. IGF2 is the primary mitogen inducing ventricular cardiomyocyte proliferation and morphogenesis of the compact myocardial wall. Conditional deletion of the Igf1r and the insulin receptor (Insr) genes in the myocardium results in decreased cardiomyocyte proliferation and ventricular wall hypoplasia. The significance of the IGF signalling pathway during embryonic development has led to consider it as a candidate for adult cardiac repair and regeneration. In fact, paracrine IGF2 plays a key role in the transient regenerative ability of the newborn mouse heart. We aimed to review the current knowledge about the role played by the IGF signalling pathway during cardiac development and also the clinical potential of recapitulating this developmental axis in regeneration of the adult heart.

Leu27 IGF-II-induced hypertrophy in H9c2 cardiomyoblasts is ameliorated by saffron by regulation of calcineurin/NFAT and CaMKIIδ signaling

The insulin-like growth factor II receptor (IGF-IIR) induces myocardial hypertrophy under various pathological conditions like diabetes and hypertension via G protein receptors like Gαq or Gαs. Increased expression of the ligand IGF II and IGF-IIR induces pathological hypertrophy through downstream signaling mediators such as calcineurin, nuclear factor of activated T cells 3 and calcium-calmodulin (CaM)-dependent kinase II (CaMKII)-histone deacetylase 4 (HDAC4). The dried stigma of Crocus sativus L. (saffron) has a long repute as a traditional medicine against various disorders. In the present study, we have investigated whether C. sativus extract (CSE) canameliorate Leu²⁷ IGF-II triggered hypertrophy and have elucidated the underlying mechanism of protection. Additionally, the effects of oleic acid (OA), an activator of calcineurin and CaMKII was investigated thereof. The results demonstrate that CSE can ameliorate Leu²⁷ IGF-II-induced hypertrophy seemingly through regulation of calcineurin-NFAT3 and CaMKII-HDAC4 signaling cascade.

Small Molecule Compound Nerolidol attenuates Hypertension induced hypertrophy in spontaneously hypertensive rats through modulation of Mel-18-IGF-IIR signalling

BACKGROUND

Cardiovascular diseases are caused by multitudes of stress factors like hypertension and their outcomes are associated with high mortality and morbidity worldwide. Nerolidol, a naturally occurring sesquiterpene found in several plant species, embodies various pharmacological benefits against numerous health disorders. However, their effects on hypertension induced cardiac complications are not completely understood.

PURPOSE

The present study is to elucidate the efficacy of nerolidol against hypertension related cardiac hypertrophy in spontaneously hypertensive rats (SHRs).

STUDY DESIGN

For preliminary in vitro studies, H9c2 cardiomyoblasts cells were challenged with 200 nM Angiotensin-II (AngII) for 12 h and were then treated with nerolidol for 24 h. The hypertrophic effect in H9c2 cells were analyzed by actin staining and the modulations in hypertrophic protein markers and mediators were determined by Western blotting analysis. For in vivo experiments, sixteen week-old male Wistar Kyoto (WKY) and SHRs were segregated into five groups (n = 9): Control WKY, hypertensive SHRs, SHRs with low dose (75 mg/kg b.w/day) nerolidol, SHRs with high dose (150 mg/kg b.w/day) nerolidol and SHR rats treated with an anti-hypertensive drug captopril (50 mg/kg b.w/day). Nerolidol treatment was given orally for 8 weeks and were analysed through Echocardiography. After euthanasia, hematoxylin and eosin staining, Immunohistochemical analysis and Western blotting was performed on left ventricle tissue.

RESULTS

Western blotting analysis revealed that nerolidol significantly attenuates AngII induced expression of hypertrophic markers ANP and BNP in H9c2 cardiomyoblasts. In addition, actin staining further ascertained the potential of nerolidol to ameliorate AngII induced cardiac hypertrophy. Moreover, nerolidol administration suppressed the hypertrophic signalling mediators like calcineurin, GATA4, Mel-18, HSF-2 and IGFIIR in a dose-dependent fashion. In silico studies also ascertained the role of Mel-18 in the ameliorative effects of nerolidol. Further, these intriguing in vitro results were further confirmed in in vivo SHR model. Oral neraolidol in SHRs efficiently reduced blood pressure and ameliorated hypertension induced cardiac hypertrophic effects by effectively reducing the levels of proteins involved in cardiac MeL-18-HSF2-IGF-IIR signalling.

CONCLUSION

Collectively, the data reveals that the cardioprotective effect of nerolidol against hypertension induced hypertrophy involves reduction in blood pressure and regulation of the cardiac Mel-18-IGFIIR signalling cascade.

Tanshinone IIA Inhibits β-Catenin Nuclear Translocation and IGF-2R Activation via Estrogen Receptors to Suppress Angiotensin II-Induced H9c2 Cardiomyoblast Cell Apoptosis

Cardiomyopathy involves changes in the myocardial ultra-structure, hypertrophy, apoptosis, fibrosis and inflammation. Angiotensin II (AngII) stimulates the expression of insulin like-growth factors (IGF-2) and IGF-2 receptor (IGF-2R) in H9c2 cardiomyoblasts and subsequently leads to apoptosis. Estrogen receptors protect cardiomyocytes from apoptosis and fibrosis. Tanshinone IIA (TSN), a main active ingredient from Danshen, has been shown to protect cardiomyocytes from death caused by different stress signals. Estrogen receptor α (ER) is required for the rapid activation of the IGF-1R signaling cascade. This study aimed to investigate whether TSN protected H9c2 cardiomyocytes from AngII-induced activation of IGF-2R pathway and hypertrophy via ERs. We found that AngII caused the reduction in IGF-1R phosphorylation and the elevation of β-catenin and IGF-2R levels. This was reversed by increasing doses of TSN and of caspase-3 and ERK1/2 phosphorylation mediated by ERs. The phytoestrogen significantly attenuated AngII-induced apoptosis and suppressed the subsequent cardiac remodeling effect. Therefore, TSN reduced the AngII-induced activation of β-catenin and IGF-2R pathways, apoptosis and cardiac remodeling via ERs in H9c2 cardiomyoblasts.

Tanshinone IIA Prevents Leu27IGF-II-Induced Cardiomyocyte Hypertrophy Mediated by Estrogen Receptor and Subsequent Akt Activation

IGF-IIR plays important roles as a key regulator in myocardial pathological hypertrophy and apoptosis, which subsequently lead to heart failure. Salvia miltiorrhiza Bunge (Danshen) is a traditional Chinese medicinal herb used to treat cardiovascular diseases. Tanshinone IIA is an active compound in Danshen and is structurally similar to 17[Formula: see text]-estradiol (E[Formula: see text]. However, whether tanshinone IIA improves cardiomyocyte survival in pathological hypertrophy through estrogen receptor (ER) regulation remains unclear. This study investigates the role of ER signaling in mediating the protective effects of tanshinone IIA on IGF-IIR-induced myocardial hypertrophy. Leu27IGF-II (IGF-II analog) was shown in this study to specifically activate IGF-IIR expression and ICI 182,780 (ICI), an ER antagonist used to investigate tanshinone IIA estrogenic activity. We demonstrated that tanshinone IIA significantly enhanced Akt phosphorylation through ER activation to inhibit Leu27IGF-II-induced calcineurin expression and subsequent NFATc3 nuclear translocation to suppress myocardial hypertrophy. Tanshinone IIA reduced the cell size and suppressed ANP and BNP, inhibiting antihypertrophic effects induced by Leu27IGF-II. The cardioprotective properties of tanshinone IIA that inhibit Leu27IGF-II-induced cell hypertrophy and promote cell survival were reversed by ICI. Furthermore, ICI significantly reduced phospho-Akt, Ly294002 (PI3K inhibitor), and PI3K siRNA significantly reduced the tanshinone IIA-induced protective effect. The above results suggest that tanshinone IIA inhibited cardiomyocyte hypertrophy, which was mediated through ER, by activating the PI3K/Akt pathway and inhibiting Leu27IGF-II-induced calcineurin and NFATC3. Tanshinone IIA exerted strong estrogenic activity and therefore represented a novel selective ER modulator that inhibits IGF-IIR signaling to block cardiac hypertrophy.

Increased insulin-like growth factor-1 in relation to cardiovascular function in polycystic ovary syndrome: friend or foe?

The incidence of cardiovascular disease (CVD) in patients with polycystic ovary syndrome (PCOS) is very high and conventional risk factors only partially explain excessive risk of developing CVD in patients of PCOS. The pathophysiology of PCOS is very unique, and several hormonal and metabolic changes occur. Several observations suggest that serum IGF-1 levels decrease in insulin resistance, which results in IGF-1 deficiency. In patient of PCOS, close relationships have been demonstrated between insulin resistance and serum IGF-1 levels. Hyperinsulinemic insulin resistance results in a general augmentation of steroidogenesis and LH release in PCOS. The action of IGF-1 varies in different tissues possibly via autocrine or paracrine mechanisms. The increase or decrease in IGF-1 in different tissues results in differential outcomes. Several studies suggest that lowered circulating IGF-1 levels play important role in the initiation of the cardiac hypertrophic response which results in the risk of cardiovascular disease. While recent results suggests that individual with elevated IGF-1 is protected against cardiovascular disease. Thus IGF-1 shows versatile pleiotropic actions. This review provides a current perspective on increased level of IGF-1 in PCOS and also adds to the current controversy regarding the roles of IGF-1 in cardiovascular disease.

Proliferation of murine c-kit(pos) cardiac stem cells stimulated with IGF-1 is associated with Akt-1 mediated phosphorylation and nuclear export of FoxO3a and its effect on downstream cell cycle regulators

Insulin-like growth factor-1 (IGF-1) is known to promote proliferation in many cell types including c-kit(pos) cardiac stem cells (CSCs). Downstream signaling pathways of IGF-1 induced CSC proliferation have not been investigated. An important downstream target of IGF-1/Akt-1 signaling is FoxO3a, a key negative regulator of cell-cycle progression. We studied the effect of IGF-1 on proliferation of c-kit(pos) murine CSCs and found that IGF-1-mediated cell proliferation is associated with FoxO3a phosphorylation and inactivation of its transcriptional activity. PI3 inhibitors LY294002 and Wortmannin abolished the effect of IGF-1 on FoxO3a phosphorylation indicating that FoxO3a phosphorylation is mediated by PI3/Akt-1 pathway. In cells with FoxO3a translocation to the cytoplasm, there is decreased expression of cell-cycle inhibitors such as p27(kip1) and p57(kip2) and increased expression of CyclinD1. Our study provides evidence that IGF-1 induced CSC proliferation could be the result of FoxO3a inactivation and its downstream effect on cell-cycle regulators.

Danshen mediates through estrogen receptors to activate Akt and inhibit apoptosis effect of Leu27IGF-II-induced IGF-II receptor signaling activation in cardiomyoblasts

Post-menopausal women show dramatically increased cardiovascular disease morbidity (CVD). Danshen is used widely in China for the treatment of cardiovascular disorders, including coronary heart disease. Danshen possesses lipid-soluble biologically active components with a structure similar to 17β-estrodiol (E2). This study assesses whether the cardio-protection exerted by Danshen is mediated through the ERs within H9c2 cardiomyoblast cells. Cardiomyoblast cells pretreated with Fulvestrant (ICI 182,780), an estrogen receptor antagonist was applied to investigate the estrogenic activity of Danshen. The Danshen extract preventive effects on Leu27IGF-II-induced IGF-IIR signaling activator and H9c2 cell apoptosis were identified using TUNEL assay, JC-1 staining and Western blot assay. We found that Danshen extract treatments significantly enhanced phosphorylated Akt through estrogen receptor activation to inhibit Leu27IGF-II-induced calcineurin activation and block H9c2 cell apoptosis. Danshen extracts suppressed the IGF-IIR signaling proteins, pro-apoptotic proteins and reversed the mitochondrial membrane instability induced by Leu27IGF-II. However, the cardioprotective properties of Danshen to inhibit Leu27IGF-II-induced cell apoptosis and promote cell survival were attenuated by applying ICI, which suggests that the Danshen cardioprotective effect is mediated through estrogen receptors. All our data indicated that Danshen exerts strong estrogenic activity which can be considered a novel selective estrogen receptor modulator (SERM) against IGF2R signaling that blocks cardiac apoptosis.

IGF-II and MMP9 as surgical repair indicators of ventricular septal defects

OBJECTIVE

The insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3) and human growth hormone (h-GH) have been recognized as therapeutic targets for the heart disease therapy. The bioavailability and actions of insulin-like growth factors-II (IGF-II) and matrix metalloproteinase-9 (MMP9) are important for embryonic development and cardiomyocyte differentiation as well. However, the clinical manifestations following the change in the serum IGF-II and MMP9 in infants with isolated ventricular septal defect (VSD) undergoing surgical repair have not been clearly defined.

STUDY DESIGN

Serum samples were collected from 72 infants: Twenty normal infants (group I) and 51 consecutive infants with echocardiography established isolated VSD (aged from 3 months to 1 year) were investigated. Among the 51 infants with VSD, 28 with shunt fraction, Qp/Qs < or = 1.5 were free of congestive heart failure symptoms (group II); 23 with shunt fraction, Qp/Qs > or = 2.0 were in congestive heart failure (group IIIa); and 23 of these 23 infants had undergone VSD repair 6 months before their second study (group IIIb). All insulin-like growth factors-II (IGF-II) and human growth hormone (h-GH), insulin like growth factor binding protein-3 (IGFBP-3) and its specific serum protease-MMP9 concentration were analyzed using ELISA and zymography, respectively.

RESULTS

Serum IGF-II and MMP9 exhibited significant decreasing trends among the three groups and significantly lower concentrations of IGF-II, IGF-II/IGFBP-3 ratio and MMP9, were found only in the severe group whereas h-GH/IGF-II ratio became significantly higher in this group. Moreover, there were no significant differences in these parameters between the infants after surgical correction and the normal ones.

CONCLUSIONS

The improvement in IGF-II and MMP9 serum concentration was identified in infants with VSD after surgical repair. These findings also indicate a significant relationship between IGF-II, MMP9 and VSD which might be used as diagnosis and prognosis indicators for this defect. Slight reductions in IGF-II/IGFBP3 ratio and slight increase in the h-GH/IGF-II ratio indicate mild VSD. The reductions in the MMP9, IGF-II, and IGF-II/IGFBP3 ratio plus high increase in the h-GH/IGF-II ratio indicate severe VSD.

Fun&Co: identification of key functional differences in transcriptomes

MOTIVATION

Microarray and other genome-wide technologies allow a global view of gene expression that can be used in several ways and whose potential has not been yet fully discovered. Functional insight into expression profiles is routinely obtained by using gene ontology terms associated to the cellular genes. In this article, we deal with functional data mining from expression profiles, proposing a novel approach that studies the correlations between genes and their relations to Gene Ontology (GO). We implemented this approach in a public web-based application named Fun&Co. By using Fun&Co, the user dissects in a pair-wise manner gene expression patterns and links correlated pairs to gene ontology terms. The proof of principle for our study was accomplished by dissecting molecular pathways in muscles. In particular, we identified specific cellular pathways by comparing the three different types of muscle in a pairwise fashion. In fact, we were interested in the specific molecular mechanisms regulating the cardiovascular system (cardiomyocytes and smooth muscle cells).

RESULTS

We applied here Fun&Co to the molecular study of cardiovascular system and the identification of the specific molecular pathways in heart, skeletal and smooth muscles (using 317 microarrays) and to reveal functional differences between the three different kinds of muscle cells.

AVAILABILITY

Application is online at http://tommy.unife.it.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Thyroid hormone receptor and IGF1/IGFR systems: Possible relations in the human heart

Thyroid hormone (TH) and insulin growth factor 1 (IGF1) systems both play crucial roles in the regulation of cardiac remodeling and hypertrophy processes. The mediation of this regulation is attributed to specific thyroid hormone receptors (TRs) and to the IGF1 receptor (IGF1R). In humans, two TR genes are expressed in the heart, TRalpha and TRbeta. Each gene generates two isoforms: TRalpha1, TRalpha2 and TRbeta1, TRbeta2. The aim of the present work was to study the local thyroid hormone and IGF1 signaling in human myocardium through the evaluation of the gene expression of TRalpha1, TRalpha2, TRbeta1 and IGF1R among atrial and ventricular biopsies obtained from patients undergoing cardiac surgery. Moreover, we evaluated possible correlations between TR and IGF1/IGF1R systems. Eighteen clinically and biochemically euthyroid patients (aged 68.3+/-3.2years, mean+/-SEM) without overt heart failure (Ejection Fraction (EF), 46.4+/-2.8%; Left Ventricular End Diastolic Diameter (LVEDD), 54.3+/-1.2mm, mean+/-SEM; NYHA I-II) were enrolled in the study: 13 undergoing aorto-coronary bypass and 5 undergoing valve replacement (aortic/mitral valve). The examination of total RNA, using real time PCR (LightCycler Technology) confirmed the expression of specific mRNAs encoding TRalpha1, TRalpha2, TRbeta1 and both IGF1 and IGF1R. We found that the three TR genes are co-expressed in the human atrium and ventricle. The finding of a strong correlation among IGF1R and the three TR genes expressed in the atrium (p<0.001) and among the three TRs in the atrium (p<0.001) suggests the interesting possibility that the two systems, TRs and IGF1R could also be functionally associated.

A case and review of acromegaly-induced cardiomyopathy and the relationship between growth hormone and heart failure: cause or cure or neither or both?

Growth hormone plays an integral role in the development and maintenance of structure and function of the heart. Specific involvement of the heart in acromegaly is termed acromegalic cardiomyopathy, manifested as concentric left ventricular hypertrophy and diastolic dys-function. Left untreated, it ultimately progresses to systolic heart failure. Heart failure from acromegalic cardiomyopathy is one of the most common causes of death in acromegaly. Current treatment options include different approaches to lower elevated growth hormone levels with improvement in symptoms, exercise tolerance, and echocardiographic improvement in regression of left ventricular hypertrophy and indices of diastolic dysfunction. On the other hand, growth hormone is essential for cardiac growth and function and exerts beneficial and protective effects on the cardiovascular system. Its potential role as adjunctive therapy in the treatment of heart failure as derived from experimental studies and clinical trials is discussed.

Insensitivity of cardiac delayed-rectifier I(Kr) to tyrosine phosphorylation inhibitors and stimulators

1. The rapidly activating delayed-rectifying K+ current (I(Kr)) in heart cells is an important determinant of repolarisation, and decreases in its density are implicated in acquired and inherited long QT syndromes. The objective of the present study on I(Kr) in guinea-pig ventricular myocytes was to evaluate whether the current is acutely regulated by tyrosine phosphorylation. 2. Myocytes configured for ruptured-patch or perforated-patch voltage-clamp were depolarised with 200-ms steps to 0 mV for measurement of I(Kr) tail amplitude on repolarisations to -40 mV. 3. I(Kr) in both ruptured-patch and perforated-patch myocytes was only moderately (14-20%) decreased by 100 microM concentrations of protein tyrosine kinase (PTK) inhibitors tyrphostin A23, tyrphostin A25, and genistein. However, similar-sized decreases were induced by PTK-inactive analogues tyrphostin A1 and daidzein, suggesting that they were unrelated to inhibition of PTK. 4. Ruptured-patch and perforated-patch myocytes were also treated with promoters of tyrosine phosphorylation, including phosphotyrosyl phosphatase (PTP) inhibitor orthovanadate, exogenous c-Src PTK, and four receptor PTK activators (insulin, insulin-like growth factor-1, epidermal growth factor, and basic fibroblast growth factor). None of these treatments had a significant effect on the amplitude of I(Kr). 5. We conclude that Kr channels in guinea-pig ventricular myocytes are unlikely to be regulated by PTK and PTP.

The total length of myocytes and capillaries, and total number of myocyte nuclei in the rat heart are time-dependently increased by growth hormone

Growth hormone (GH) can increase size and dimensions of rat hearts. The aim was to study how GH administration influences the growth of cardiac myocytes and capillaries in relation to time. Three-month-old female rats were divided into 10 groups (n=3), and injected with either GH (5mg/kg/day) or vehicle for 5, 10, 20, 40, or 80 days. From the left ventricle (LV) histological sections were made and stereological methods applied. Linear regression showed that GH time-dependently increased: LV volume (r=0.96, P<0.001), total volume of myocytes (r=0.96, P<0.001) and capillaries (r=0.64, P<0.05), total length of myocytes (r=0.90, P<0.001) and capillaries (r=0.78, P<0.001), and total number of myocyte nuclei (r=0.85, P<0.001). In conclusion, during 80 days of GH treatment the total volume and length of myocytes and capillaries, and total number of myocyte nuclei increased in a linear way. The results indicate that GH is a potent mediator of myocardial growth.

Disruption of growth hormone secretion alters Ca2+ current density and expression of Ca2+ channel and insulin-like growth factor genes in rat atria

The influence of the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis on expression of low-voltage-activated (LVA) Ca2+ current in atrial tissue was investigated using spontaneous dwarf (SpDwf) rats, a mutant strain that lacks GH. Atrial myocytes from SpDwf rats express LVA and high-voltage-activated (HVA) Ca2+ currents and the Ca2+ channel alpha1-subunit genes CaV1.2, CaV2.3, CaV3.1, and CaV3.2. LVA current density decreases significantly beginning at, or shortly after, birth in normal animals; however, its density is maintained in SpDwf rats at 1 pA/pF for > or =12 wk after birth. The abundance of mRNAs encoding CaV2.3 and CaV3.2 declines with advancing age in normal atrial development, yet expression of CaV2.3 mRNA remains significantly elevated in older SpDwf animals. Quantitation of local transcript levels for mRNAs encoding IGF-I and IGF-I receptor (IGF-IR) also reveals significant differences in expression of these transcripts in atrial tissue of SpDwf animals compared with controls. In SpDwf rats, the abundance of IGF-IR mRNA remains elevated at many postnatal ages, whereas mRNA encoding IGF-I is maintained only in older animals. Physiological concentrations of IGF-I cause two- to threefold increases in LVA current density in primary cultures of atrial myocytes, and this effect is blocked by an antisense oligonucleotide targeting the IGF-IR. Thus disruption of GH production in SpDwf animals alters expression of atrial LVA Ca2+ channel and IGF genes as well as postnatal regulation of LVA Ca2+ current density, most likely acting through compensatory mechanisms via the local IGF-IR.

Systemic complications of acromegaly: epidemiology, pathogenesis, and management

This review focuses on the systemic complications of acromegaly. Mortality in this disease is increased mostly because of cardiovascular and respiratory diseases, although currently neoplastic complications have been questioned as a relevant cause of increased risk of death. Biventricular hypertrophy, occurring independently of hypertension and metabolic complications, is the most frequent cardiac complication. Diastolic and systolic dysfunction develops along with disease duration; and other cardiac disorders, such as arrhythmias, valve disease, hypertension, atherosclerosis, and endothelial dysfunction, are also common in acromegaly. Control of acromegaly by surgery or pharmacotherapy, especially somatostatin analogs, improves cardiovascular morbidity. Respiratory disorders, sleep apnea, and ventilatory dysfunction are also important contributors in increasing mortality and are advantageously benefitted by controlling GH and IGF-I hypersecretion. An increased risk of colonic polyps, which more frequently recur in patients not controlled after treatment, has been reported by several independent investigations, although malignancies in other organs have also been described, but less convincingly than at the gastrointestinal level. Finally, the most important cause of morbidity and functional disability of the disease is arthropathy, which can be reversed at an initial stage, but not if the disease is left untreated for several years.

Insulin-like growth factor-1 induces an inositol 1,4,5-trisphosphate-dependent increase in nuclear and cytosolic calcium in cultured rat cardiac myocytes

In the heart, insulin-like growth factor-1 (IGF-1) is a pro-hypertrophic and anti-apoptotic peptide. In cultured rat cardiomyocytes, IGF-1 induced a fast and transient increase in Ca(2+)(i) levels apparent both in the nucleus and cytosol, releasing this ion from intracellular stores through an inositol 1,4,5-trisphosphate (IP(3))-dependent signaling pathway. Intracellular IP(3) levels increased after IGF-1 stimulation in both the presence and absence of extracellular Ca(2+). A different spatial distribution of IP(3) receptor isoforms in cardiomyocytes was found. Ryanodine did not prevent the IGF-1-induced increase of Ca(2+)(i) levels but inhibited the basal and spontaneous Ca(2+)(i) oscillations observed when cardiac myocytes were incubated in Ca(2+)-containing resting media. Spatial analysis of fluorescence images of IGF-1-stimulated cardiomyocytes incubated in Ca(2+)-containing resting media showed an early increase in Ca(2+)(i), initially localized in the nucleus. Calcium imaging suggested that part of the Ca(2+) released by stimulation with IGF-1 was initially contained in the perinuclear region. The IGF-1-induced increase on Ca(2+)(i) levels was prevented by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM, thapsigargin, xestospongin C, 2-aminoethoxy diphenyl borate, U-73122, pertussis toxin, and betaARKct (a peptide inhibitor of Gbetagamma signaling). Pertussis toxin also prevented the IGF-1-dependent IP(3) mass increase. Genistein treatment largely decreased the IGF-1-induced changes in both Ca(2+)(i) and IP(3). LY29402 (but not PD98059) also prevented the IGF-1-dependent Ca(2+)(i) increase. Both pertussis toxin and U73122 prevented the IGF-1-dependent induction of both ERKs and protein kinase B. We conclude that IGF-1 increases Ca(2+)(i) levels in cultured cardiac myocytes through a Gbetagamma subunit of a pertussis toxin-sensitive G protein-PI3K-phospholipase C signaling pathway that involves participation of IP(3).

Growth hormone increases the total number of cardiac myocyte nuclei in young rats but not in old rats

Previously we have shown that growth hormone (GH) increases the total number of myocyte nuclei of the left ventricle in adult rats (8 months old). In the present study, we investigated whether GH could increase the total number of myocyte nuclei of the left ventricle in young and old rats. Female rats, 3 months old and 20 months old, were injected with GH or vehicle for 80 days. Using immersion-fixed left ventricles, unbiased stereological methods were applied. The weight of the left ventricle was increased by 49% (P<0.001) in the GH-injected young rats and by 32% (P<0.01) in the GH-injected old rats compared with the controls. Compared with the control groups, there was a 31% increase in the total number of myocyte nuclei in the GH-injected young group (P<0.05), but no significant increase in the GH-injected old group. The total number of non-myocyte nuclei was increased by 59% in the young GH-injected group (P<0.001) and by 25% in the old GH-injected group (P<0.01). In conclusion, GH induced a substantial left ventricle growth in both young and old rats. GH increased the total number of myocyte nuclei in the left ventricle of young rats, but not in old rats. This study shows that the myocyte response to GH declines with ageing.

Growth hormone increases the total number of myocyte nuclei in the left ventricle of adult rats

Several studies have shown that growth hormone (GH) administration can increase size and dimensions of rat hearts. The aim of the present study was to evaluate the effect of GH on the growth of myocytes, myocyte nuclei, connective tissue, connective tissue nuclei and capillaries in the adult rat heart with special reference to total number, total length and total and relative volumes. Eight-month-old female rats were injected with either GH or vehicle for 80 days. Unbiased stereological methods were applied on immersion-fixed left ventricles. GH increased the total number of myocyte nuclei by 25% and the total number of non-myocyte nuclei by 46%. The total lengths of the myocytes and capillaries were increased by 24% and 25% respectively. Furthermore, GH increased the weight of the left ventricle by 58% without changing the relative volume fraction of myocytes, connective tissue or capillaries. In conclusion, GH seems to be a potent mediator of myocardial growth in the adult rat.

Supraphysiological doses of GH induce rapid changes in cardiac morphology and function

GH is an agent widely used in sport to improve physical performance and has been proposed as adjunctive therapy in several clinical conditions. However, its short-term effects on the normal human heart are poorly understood. Sixty young normal volunteers (30 males and 30 females) were enrolled in a multicenter, double-blind, placebo-controlled study. All subjects were randomized to receive GH (0.03 or 0.06 mg/kg.d) or placebo. A complete Doppler-echocardiographic examination was performed at baseline and after 4 wk of treatment. Low-dose GH did not significantly affect echocardiographic parameters. In contrast, high-dose GH increased left ventricular mass index by 12% (P < 0.05). The type of growth response was concentric, because left ventricular wall thickness but not diameter increased, leading to a 10% increase of relative wall thickness. These structural changes were associated with functional changes, including a significant increase in cardiac index and a decrease in peripheral vascular resistance; diastolic function was not altered. Fractional shortening and systemic blood pressure were unchanged in the two treatment groups. In conclusion, administration of GH for 4 wk at doses that simulate GH abuse in sport caused a high cardiac output state associated with concentric left ventricular remodeling.

Growth hormone and the heart

Impaired cardiovascular function has recently been demonstrated to potentially reduce life expectancy both in GH deficiency and excess. Experimental and clinical studies have supported the evidence that GH and IGF-I are implicated in cardiac development. In most patients with acromegaly a specific cardiomyopathy, characterized by myocardial hypertrophy with interstitial fibrosis, lympho-mononuclear infiltration and areas of monocyte necrosis, results in biventricular concentric hypertrophy. In contrast, patients with childhood or adulthood-onset GH deficiency (GHD) may suffer both from structural cardiac abnormalities, such as narrowing of cardiac walls, and functional impairment, that combine to reduce diastolic filling and impair left ventricular response to peak exercise. In addition, GHD patients may have an increase in vascular intima-media thickness and a higher occurrence of atheromatous plaques, that can further aggravate the haemodynamic conditions and contribute to increased cardiovascular and cerebrovascular risk. However, several lines of evidence have suggested that the cardiovascular abnormalities can be partially reversed by suppressing GH and IGF-I levels in acromegaly or after GH replacement therapy in GHD patients. Recently, much attention has been focussed on the ability of GH to increase cardiac mass suggesting its possible use in the treatment of chronic nonendocrine heart failure. In fact, GH administration can induce an improvement in haemodynamic and clinical status in some patients. Although these data need to be confirmed in more extensive studies, such promising results seem to open new perspectives for GH treatment in humans.

Synthesis of extracellular matrix and adhesion through beta(1) integrins are critical for fetal ventricular myocyte proliferation

Extracellular matrix (ECM) regulates vascular smooth muscle cell proliferation. The role of ECM in myocardial growth is unexplored. We sought to determine whether human fetal ventricular myocytes (HFVMs) produce ECM and whether synthesis and attachment to ECM are necessary for their epidermal growth factor (EGF)-dependent and -independent proliferation. Cultured HFVMs proliferate in the presence but not absence of serum and EGF, as determined by increase in cell number and [(3)H]thymidine and [(14)C]leucine incorporation (measures of DNA and protein synthesis, respectively). Using a cyanogen bromide digestion technique to measure collagen and elastin and using affinity chromatography for fibronectin, we found that HFVMs synthesized collagen and fibronectin but not elastin. HFVMs grown on exogenous ECM (including fibronectin and type I collagen and laminin) demonstrated no change in proliferation or DNA and protein synthesis with or without EGF. However, inhibition of collagen synthesis using cis-4-hydroxyproline resulted in a decrease in EGF-related HFVM proliferation and DNA and protein synthesis, which was reversed by exposure to L-proline but not by growth on type I collagen. Use of beta(1) but not beta(3) integrin antibody to inhibit cell interaction with ECM resulted in a decrease in HFVM proliferation and DNA and protein synthesis in response to EGF. Furthermore, EGF-dependent proliferation was enhanced by alpha(1)beta(1) and alpha(5)beta(1) antibodies that act as functional ligands, but not alpha(3)beta(1), the only beta(1) subtype expressed in adult myocytes. In conclusion, proliferating HFVMs synthesize collagen and fibronectin. The proliferative response of HFVMs to EGF requires the synthesis of collagen as well as attachment to specific alpha/beta(1) integrin heterodimers.

Extracellular regulated kinase, but not protein kinase C, is an antiapoptotic signal of insulin-like growth factor-1 on cultured cardiac myocytes

This study aims to elucidate the signaling pathway for insulin-like growth factor-1 (IGF-1) in cultured neonatal rat cardiomyocytes and particularly the role of IGF-1 in cardiac apoptosis. IGF-1 stimulated polyphosphoinositide turnover, translocation of protein kinase C (PKC) isoforms (alpha, epsilon, and delta) from the soluble to the particulate fraction, activation of phospholipid-dependent and Ca(2+)-, phospholipid-dependent PKC, and activation of the extracellular-regulated kinase (ERK). IGF-1 attenuated sorbitol-induced cardiomyocyte viability and nuclear DNA fragmentation. These antiapoptotic effects of IGF-1 were blocked by PD-098059 (an MEK inhibitor) but not by bisindolylmaleimide I (BIM, a specific PKC inhibitor). The ERK pathway may therefore be an important component in the mechanism whereby IGF-1 exerts its antiapoptotic effect on the cardiomyocyte.

IGF-1 regulates apoptosis of cardiac myocyte induced by osmotic-stress

Insulin-like growth factor-1 (IGF-1) is a natural protectant of cardiac myocytes that has been shown to improve cardiac function. The role of IGF-1 in attenuating apoptosis induced by osmotic stress (sorbitol, SOR) or by other known apoptotic stimuli (doxorubicin, angiotensin II, and serum withdrawal) was determined in cultured cardiac myocytes. After 6 h of exposure to SOR, apoptosis was initiated, concomitant with a decrease in cell survival and increases in poly-[ADP-ribose] polymerase (PARP) degradation and DNA fragmentation. These effects were maximal after 24 h. IGF-1 partially attenuated apoptosis induced by sorbitol but not that induced by angiotensin II, doxorubicin, or serum withdrawal. In cells preincubated with IGF-1 before the addition of SOR, we detected an increase in the number of viable cells, a decrease in the generation of DNA fragments on agarose gel electrophoresis and in the percentage of positive TUNEL cells, and a reduction on PARP levels. These results suggest that IGF-1 prevents apoptosis induced by osmotic stress in cardiac myocytes but not apoptosis induced by doxorubicin and angiotensin II.

Contribution of de novo protein synthesis to the hypertrophic effect of IGF-1 but not of thyroid hormones in adult ventricular cardiomyocytes

BACKGROUND

Enhanced expression of IGF-1 occurs in left ventricular hypertrophy (LVH) associated with systemic hypertension. Cardiac dysfunction accompanied by LVH is also observed in hyperthyroidism.

OBJECTIVE

to assess the relative contributions of de novo protein synthesis and attenuated protein degradation to increased protein mass associated with cardiomyocyte hypertrophy elicited by IGF-1 and thyroid hormones (tri-iodo thyronine T3, and l-thyroxine T4), respectively.

METHODS

total mass of protein, and both the incorporation, and removal of previously incorporated l-U-14C-phenylalanine, indices of protein synthesis and degradation, respectively, were assessed in quiescent adult rat ventricular cardiomyocytes maintained in short-term culture, and corrected for DNA content, as a index of cell number.

RESULTS

IGF-1 (1 pM-100 nM) increased cell protein significantly, maximally at 1 nM and by 38% above basal value after 24 h. T3 (10 pM-2 microM) and T4 (10 pM-2 microM) increased cell protein significantly maximally at 1 microM and by 33.2 and 30.5%, respectively, above basal value. IGF-1 (< or = 10 pM), T3 (10 pM-2 microM) and T4 (10 pM-2 microM) did not increase incorporation of l-U-14C-phenylalanine above basal values. IGF-1 (100 pM-100 nM) increased incorporation of radiolabel significantly maximally at 100 nM and by 56%. T4 (100 pM) and IGF-1 (10 pM), concentrations that did not stimulate de novo protein synthesis, attenuated the degradation of radiolabelled protein by 13.6 and 11.8%, respectively, compared to control values after 48 h.

CONCLUSION

These data indicate that the acute hypertrophic response to (i) thyroid hormones cannot be attributed to initiation of de novo protein synthesis; (ii) IGF- 1 comprises two components; the response elicited by IGF-1 (< 10 pM) is independent of, while the response elicited by IGF-1 (> 100 pM) is due to de novo protein synthesis.

Insulin-Like growth factor I: implications in aging

According to the somatomedin model, growth hormone (GH)-dependent hepatic synthesis is responsible for maintaining circulating insulin-like growth factor (IGF)-I levels. On the other hand, the local autocrine/paracrine IGF-I expression in peripheral tissue is generally GH-independent and reflects the effects of various and tissue-specific trophic hormones. Circulating IGF-I levels undergo important age-related variations increasing at puberty and decreasing, thereafter, to low levels in the elderly. Low IGF-I levels in the elderly mainly reflect impaired somatotroph secretion but the decline in gonadal sex steroid levels, some protein and micronutrients malnutrition as well as age-dependent variations in IGF-binding proteins may also play a role in the age-related decrease in IGF-I activity. This, in turn, partially accounts for age-related changes in bones, muscles, cardiovascular system, central nervous system and the immune system. However, it is currently unclear whether treatment with exogenous IGF-I can retard or reverse age-related changes in body structure and function.

Insulin-like growth factor I improves cardiovascular function and suppresses apoptosis of cardiomyocytes in dilated cardiomyopathy

To investigate how insulin-like growth factor I (IGF-I) modulates cardiovascular function and myocardial apoptosis in heart failure, the therapeutic effects of IGF-I were determined in a canine model of dilated cardiomyopathy. The animals were paced at 220 beats/min, and the left ventricular (LV) chamber became dilated after 2 weeks. A subset of paced dogs was treated with s.c. injections of IGF-I from week 3 to week 4. After 4 weeks of pacing, untreated paced dogs developed significant ventricular dysfunction. IGF-I-treated paced dogs showed better cardiac output, stroke volume, LV end-systolic pressure, and LV end-diastolic pressure. Moreover, pulmonary wedge pressure and systemic vascular resistance were increased in the untreated group and decreased in the IGF-I-treated group. IGF-I treatment was associated with less thinning of the ventricular wall. Compared with the controls, untreated paced dogs showed increased apoptosis of cardiac muscle cells, which was partially suppressed by IGF-I treatment. The myocardial apoptotic index was negatively related to the thickness of the ventricular wall and to cardiac output, suggesting that ventricular remodeling/dysfunction involves the occurrence of myocardial apoptosis. Due to the close resemblance between this experimental model of dilated cardiomyopathy and human heart failure, the results of this study provide evidence that IGF-I may be a potential therapeutic agent for the failing human heart.

Effects of antihypertensive treatment on cardiac IGF-1 during prevention of ventricular hypertrophy in the rat

There is some evidence that cardiac rather than circulating insulin-like growth factor-1 (IGF-1) levels contribute to the development of renovascular hypertensive left ventricular hypertrophy (LVH), remaining unknown the effects of antihypertensive drugs on IGF-1 levels. We have assessed here the preventive effects of enalapril, losartan, propanolol and alpha-methyldopa on left ventricle (LV) and circulating IGF-1 levels in a rat model of hypertension and LVH (Goldblatt, GB). Our results show that relative LV mass and the LV content of IGF-1 were significantly lower with all antihypertensive drugs in GB rats (p<0.001). Serum concentrations of IGF-1 were lower in GB rats treated with enalapril, alpha-methyldopa and propanolol (p<0.01), but not in those treated with losartan. These results support the hypothesis that local rather than seric IGF-1 contributes to the development of left ventricular hypertrophy induced by pressure overload in the rat.

Activity of GH/IGF-I axis in patients with dilated cardiomyopathy

OBJECTIVE

There is evidence showing that GH and IGF-I have specific receptors in the heart and that these hormones are able to promote cardiac remodelling and inotropism. It has been reported that patients with dilated cardiomyopathy (DCM) benefit from treatment with rhGH showing a striking increase in cardiac contractility. However, until now, the activity of GH/IGF-I axis in DCM has never been clearly assessed.

PATIENTS

To clarify this point, we enrolled 39 patients with idiopathic or post-ischaemic DCM (36 M/3 F; age (mean +/- S.D.) 55.3 +/- 9.0 years; BMI: 25.3 +/- 3.2 kg/m2; New York Heart Association class (NYHA) I/2, II/19, III/15, IV/3) and 42 age-matched controls (CS, 38 M/4 F; age 56.0 +/- 7.8 years; BMI: 24.9 +/- 1.5 kg/m2). DCM patients were characterized by a left-ventricular diastolic diameter of 73.8 +/- 8.3 mm, a shortening fraction of 15.9 +/- 6.4% and a left ventricular ejection fraction of 25.1 +/- 8.7%. In all subjects clinical and biochemical indices of renal and hepatic function as well as nutritional parameters were in the normal range.

MEASUREMENTS

In both groups we studied: a) IGF-I levels in basal conditions and after administration of low rhGH doses for 4 days (5.0 or 10.0 mu/kg/day x 4 days); b) the acute GH-response to GHRH (1.0 mu/kg i.v.) or hexarelin (HEX, 2.0 mu/kg i.v.), a peptidyl GH secretagogue (GHRP); c) mean GH concentration (mGHc) over 10 h sampling (every 20 min) from 2200 h to 0800 h.

RESULTS

Basal IGF-I levels in DCM were lower (P = 0.000039) than in CS (135.2 +/- 46.8 vs. 193.7 +/- 63.7 mu/l), whereas, basal IGFBP-3 and GHBP2 levels in DCM and CS were similar (2.5 +/- 1.3 vs. 2.6 +/- 0.5 mg/l and 25.3 +/- 3.6 vs. 28.3 +/- 5.0%; P = 0.95 and P = 0.085, respectively). After 4 days of 5.0 mu/kg/day rhGH administration, IGF-I levels in DCM (215.4 +/- 82.0 mu/l; P = 0.0023 vs. baseline) remained lower (P = 0.027) than those in CS (280.0 +/- 80.7 mu/l; P = 0.000080 vs. baseline). After 10.0 mu/kg/day for 4 days, IGF-I levels in DCM (297.2 +/- 109.2 mu/l; P = 0.0033 vs. baseline) were similar (P = 0.76) to those in CS (310.9 +/- 81.7 mu/l; P = 0.000060 vs. baseline). The GH response to GHRH in DCM was lower (P = 0.0022) than that in CS (hAUC0-120: 192.0 +/- 177.3 vs. 345.3 +/- 191.1 mu/l/h) whereas that to HEX in DCM and CS was similar (611.0 +/- 437.5 vs. 535.4 +/- 302.8 mu/l/h; P = 0.95). Within the DCM group, basal and rhGH-stimulated IGF-levels as wel as the GH response to GHRH or HEX were not different among NYHA classes and did not show any correlation with ECHO parameters. The mGHc in DCM (1.0 +/- 0.5 mu/l) was similar (P = 0.57) to that in CS (0.9 = 0.7 mu/l).

CONCLUSIONS

Our present data demonstrate that in dilated cardiomyopathy patients with severe left ventricular dysfunction basal IGF-I levels are reduced whereas the IGF-I response to low rhGH doses is preserved. These findings suggest a normal peripheral GH sensitivity in dilated cardiomyopathy. On the other hand, though nocturnal mean GH concentration in dilated cardiomyopathy patients is similar to that in normal subjects, the somatotroph responsiveness to GHRH, but not that to hexarelin, is reduced. Thus, subtle alterations in the activity of GH/IGF-I axis are present in dilated cardiomyopathy.

Growth hormone and the heart

Until a few years ago, growth hormone (GH) and insulin-like growth factor-1 (IGF-1) were considered essential only to the control of linear growth, glucose homeostasis, and for the maintenance of skeletal muscle mass. A large body of evidence recently coming from animal and human studies has unequivocally proven that the heart is a target organ for the GH/IGF-1 axis. Specifically GH exerts both direct and indirect cardiovascular actions. Among the direct effects, the ability of GH to trigger cardiac tissue growth plays a pivotal role. Another direct effect is to augment cardiac contractility, independent of myocardial growth. Direct effects of GH also include the improvement of myocardial energetics and mechanical efficiency. Indirect effects of GH on the heart include decreased peripheral vascular resistance (PVR), expansion of blood volume, increased glomerular filtration rate, enhanced respiratory activity, increased skeletal muscle performance, and psychological well-being. Among them, the most consistently found is the decrease of PVR. GH may also raise preload through its sodium-retaining action and its interference with the hormonal system that regulates water and electrolyte metabolism. Particularly important is the effect of GH on skeletal muscle mass and performance. Taking into account that heart failure is characterized by left ventricular dilation, reduced cardiac contractility, and increase of wall stress and peripheral vascular resistance, GH may be beneficial for treatment of heart failure. Animal studies and preliminary human trials have confirmed the validity of the GH approach to the treatment of heart failure. Larger placebo-controlled human studies represent the main focus of future investigations.

Alterations in insulin-like growth factor-1 gene and protein expression and type 1 insulin-like growth factor receptors in the brains of ageing rats

Ageing in mammals is characterized by a decline in plasma levels of insulin-like growth factor-1 that appears to contribute to both structural and functional changes in a number of tissues. Although insulin-like growth factor-1 has been shown to provide trophic support for neurons and administration of insulin-like growth factor-1 to ageing animals reverses some aspects of brain ageing, age-related changes in insulin-like growth factor-1 or type 1 insulin-like growth factor receptors in brain have not been well documented. In this series of studies, insulin-like growth factor-1 messenger RNA and protein concentrations, and type 1 insulin-like growth factor receptor levels were analysed in young (three to four- and 10-12-month-old), middle-aged (19-20-month-old) and old (29-32-month-old) Fisher 344 x Brown Norway rats. Localization of insulin-like growth factor-1 messenger RNA throughout the lifespan revealed that expression was greatest in arteries, arterioles, and arteriolar anastomoses with greater than 80% of these vessels producing insulin-like growth factor-1 messenger RNA. High levels of expression were also noted in the meninges. No age-related changes were detected by either in situ hybridization or quantitative dot blot analysis of cortical tissue. However, analysis of insulin-like growth factor-1 protein levels in cortex analysed after saline perfusion indicated a 36.5% decrease between 11 and 32 months-of-age (P<0.05). Similarly, analysis of type 1 insulin-like growth factor receptor messenger RNA revealed no changes with age but levels of type 1 insulin-like growth factor receptors indicated a substantial decrease with age (31% in hippocampus and 20.8 and 27.3% in cortical layers II/III and V/VI, respectively). Our results indicate that (i) vasculature and meninges are an important source of insulin-like growth factor-1 for the brain and that expression continues throughout life, (ii) there are no changes in insulin-like growth factor-1 gene expression with age but insulin-like growth factor-1 protein levels decrease suggesting that translational deficiencies or deficits in the transport of insulin-like growth factor-1 through the blood-brain barrier contribute to the decline in brain insulin-like growth factor-1 with age, and (iii) type 1 insulin-like growth factor receptor messenger RNA is unchanged with age but type 1 insulin-like growth factor receptors decrease in several brain regions. We conclude that significant perturbations occur in the insulin-like growth factor-1 axis with age. Since other studies suggest that i.c.v. administration of insulin-like growth factor-1 reverses functional and cognitive deficiencies with age, alterations within the insulin-like growth factor-1 axis may be an important contributing factor in brain ageing.

Protectant activity of hexarelin or growth hormone against postischemic ventricular dysfunction in hearts from aged rats

The ability of hexarelin, a recently synthesized hexapeptide with a strong growth hormone (GH)-releasing activity, or of GH itself to display a protectant activity against postischemic ventricular dysfunction in senescent hearts was studied in 24-month-old male rats. Heart preparations from control (saline-treated) senescent rats, subjected to moderate ischemia, showed at reperfusion: (a) a low recovery of postischemic left ventricular developed pressure (LVDP; 37% of the preischemic values; from 90 +/- 5.7 to 33.5 +/- 3.8 mm Hg; p < 0.01; n = 10) coupled to a substantial increase in coronary perfusion pressure (CPP; 71% over baseline; from 68.3 +/- 5.2 to 116.8 +/- 4.6 mm Hg; p < 0.01; n = 10); (b) a marked increase of creatine kinase (CK) released in the perfusates (6.6-fold increase over preischemic values; from 45 +/- 4 to 298 +/- 25 mU/min/g wet tissue; p < 0.001; n = 10). In vivo administration of hexarelin (80 microg/kg, b.i.d., s.c.) for 21 days resulted in a striking heart protection against reperfusion stunning. In fact, the recovery of LVDP at reperfusion was almost complete (90% of the preischemic values; from 93 +/- 5.8 to 83.7 +/- 5.9 mm Hg; p > 0.05; n = 9), and the increase in coronary resistance was minimal (from 67 +/- 5.8 to 79.7 +/- 6.9 mm Hg; p > 0.05; n = 9). Furthermore, the concentration of CK in the perfusates was increased only twofold (from 45.8 +/- 5.5 to 90 +/- 7.2 mU/min/g wet tissue; p < 0.05; n = 9), with a gradual return toward basal values at the end of reperfusion. The protectant activity of hexarelin was divorced from any detectable alteration of the somatotropic function, as assessed by pituitary GH messenger RNA (mRNA) and plasma insulin-like growth factor I levels. In vivo administration of GH (400 microg/kg b.i.d., s.c.) for the same time lapse resulted in only a partial protectant activity: 55% of LVDP recovery (from 91.5 +/- 6.2 to 50 +/- 3.5 mm Hg; p < 0.01; n = 6); 65% increase of coronary resistance (from 68 +/- 4.3 to 112.2 +/- 5.2 mm Hg; p < 0.01; n = 6); 5.3-fold increase of CK concentrations in heart perfusates on reperfusion (from 43.8 +/- 3.8 to 232 +/- 16 mU/min/g wet tissue; p < 0.001; n = 6). Evaluation of the rate of release of 6-keto-prostaglandin F1alpha (PGF1alpha), the stable metabolite of prostacyclin, in heart perfusates, and assessment of the vasopressor activity of angiotensin II on the coronary vasculature, did not show any change in these parameters among the three experimental groups. Collectively these data indicate that hexarelin displays a strong heart-protectant activity against myocardial stunning in senescent rats. The protection afforded by the peptide is likely due to a direct cardiotropic action and is far greater than that of GH. Neither compound appears able to interfere with the endothelium-dependent relaxant mechanism.

Insulin-like growth factor-1 but not growth hormone augments mammalian myocardial contractility by sensitizing the myofilament to Ca2+ through a wortmannin-sensitive pathway: studies in rat and ferret isolated muscles

A growing body of evidence has been accumulated recently suggesting that growth hormone (GH) and insulin-like growth factor-1 (IGF-1) affect cardiac function, but their mechanism(s) of action is unclear. In the present study, GH and IGF-1 were administered to isolated isovolumic aequorin-loaded rat whole hearts and ferret papillary muscles. Although GH had no effect on the indices of cardiac function, IGF-1 increased isovolumic developed pressure by 24% above baseline. The aequorin transients were abbreviated and demonstrated decreased amplitude. The positive inotropic effects of IGF-1 were not associated with increased intracellular Ca2+ availability to the contractile machinery but to a significant increase of myofilament Ca2+ sensitivity. Accordingly, the Ca2+-force relationship obtained under steady-state conditions in tetanized muscle was shifted significantly to the left (EC50, 0.44+/-0.02 versus 0.52+/-0.03 micromol/L with and without IGF-1 in the perfusate, respectively; P<0.05); maximal Ca2+-activated tetanic pressure was increased significantly by 12% (211+/-3 versus 235+/-2 mm Hg in controls and IGF-1-treated hearts, respectively; P<0.01). The positive inotropic actions of IGF-1 were not associated with changes in either pHi or high-energy phosphate content, as assessed by 31P nuclear magnetic resonance spectroscopy, and were blocked by the phosphatidylinositol 3-kinase inhibitor wortmannin. Concomitant administration of IGF binding protein-3 blocked IGF-1-positive inotropic action in ferret papillary muscles. In conclusion, IGF-1 is an endogenous peptide that through a wortmannin-sensitive pathway displays distinct positive inotropic properties by sensitizing the myofilaments to Ca2+ without increasing myocyte [Ca2+]i.

Cell cycle regulators during human atrial development

OBJECTIVES

The molecular mechanisms that regulate cardiomyocyte cell cycle and terminal differentiation in humans remain largely unknown. To determine which cyclins, cyclin dependent kinases (CDKs) and cyclin kinase inhibitors (CKIs) are important for cardiomyocyte proliferation, we have examined protein levels of cyclins, CDKs and CKIs during normal atrial development in humans.

METHODS

Atrial tissues were obtained in the fetus from inevitable abortion and in the adult during surgery. Cyclin and CDK proteins were determined by Western blot analysis. CDK activities were determined by phosphorylation amount using specific substrate.

RESULTS

Most cyclins and CDKs were high during the fetal period and their levels decreased at different rates during the adult period. While the protein levels of cyclin D1, cyclin D3, CDK4, CDK6 and CDK2 were still detectable in adult atria, the protein levels of cyclin E, cyclin A, cyclin B, cdc2 and PCNA were not detectable. Interestingly, p27KIP1 protein increased markedly in the adult period, while p21CIP1 protein in atria was detectable only in the fetal period. While the activities of CDK6, CDK2 and cdc2 decreased markedly, the activity of CDK4 did not change from the fetal period to the adult period.

CONCLUSION

These findings indicate that marked reduction of protein levels and activities of cyclins and CDKs, and marked induction of p27KIP1 in atria, are associated with the withdrawal of cardiac cell cycle in adult humans.

IGF I induction of p53 requires activation of MAP kinase in cardiac muscle cells

The aim of this study was to investigate whether IGF I induction of p53 expression and p21 promoter require activation of MAP kinase in cardiac muscle cells. Compared to cardiomyocytes transfected with control vector, activation of MAP kinase by IGF I was decreased by approximately 60-70% in the cells transfected with dominant negative MAP kinase Y185. Transfection with Y185 also resulted in decreased induction of p53 mRNA by IGF I (70% reduction). In the cells transfected with a wildtype p21WAF1/CIP1 promoter construct, activation of luciferase reporter gene by IGF I was decreased in the cells co-transfected with Y185. To further confirm these findings, cells were preincubated with PD98059, a specific MAP kinase kinase inhibitor. As expected, PD98059 inhibited induction of p53 mRNA and p21WAF1/CIP1 promoter by IGF I. These data indicate that transcriptional activation of p53 and p21WAF1/CIP1 by IGF I involves MAP kinase pathway in cardiomyocytes, and thus link MAP kinase to negative modulation of the cell cycle in cardiac muscle cells.

Selective increase in cardiac IGF-1 in a rat model of ventricular hypertrophy

There is evidence that insulin-like growth factor-1 (IGF-1) plays a role in the development of left ventricular hypertrophy, but it is uncertain whether cardiac IGF-1 changes before or after hypertension is established, and whether circulating IGF-1 are involved in cardiac hypertrophy. We have investigated changes in circulating and left ventricular IGF-1 and in the expression of the IGF-1 gene in the left ventricles of rats during the development of hypertensive left ventricular hypertrophy (Goldblatt model; 2 kidney-1 clamped). Our results show that the left ventricular contents of IGF-1 and its mRNA were increased at one and four weeks of hypertension and hypertrophy, and that both returned to control values after nine weeks. These changes were unrelated to the seric concentration of IGF-1 in the blood. These results show that local rather than circulating IGF-1 levels contributed to the development of renovascular hypertensive left ventricular hypertrophy.

Effect of inhibitors of signal transduction on IGF-1-induced protein synthesis associated with hypertrophy in cultured neonatal rat ventricular myocytes

IGF-1 increased 2-fold protein synthesis in cardiac myocytes. Genistein, whether added during preincubation or with IGF-1 at the start of incubation, significantly inhibited the IGF-1-induced stimulation of protein synthesis, autophosphorylation of the beta-subunit of IGF-1 receptor and inhibition of ERK. When added 1 or 6 h after IGF-1, however, genistein was without effect. IGF-1-stimulated protein synthesis was also significantly inhibited by PD-098059, staurosporine, and rapamycin, but not by wortmannin, in cardiac myocytes. Some inhibitors produced a reduction in cell size. Activation of the ERK cascade by IGF-1 may be responsible for some of the features associated with cardiac myocyte hypertrophy.

Overexpression of transforming growth factor-beta1 and insulin-like growth factor-I in patients with idiopathic hypertrophic cardiomyopathy

BACKGROUND

Idiopathic hypertrophic cardiomyopathy (HCM) is characterized by regional myocardial hypertrophy. To investigate involvement of growth factors on myocardial hypertrophy in HCM patients, we evaluated gene expression and cellular localization of transforming growth factor-beta1 (TGF-beta1), insulin-like growth factors (IGF-I and IGF-II), and platelet-derived growth factor-B (PDGF-B) in ventricular biopsies obtained from patients with HCM (n=8), aortic stenosis (AS) (n=8), or stable angina (SA) (n=8) and from explanted hearts with ischemic cardiomyopathy (TM) (n=7).

METHODS AND RESULTS

Levels of TGF-beta1, IGF-I, IGF-II, and PDGF-B transcripts were quantified with the use of multiplex RT-PCR. Glyceraldehyde 3-phosphate dehydrogenase was used as an internal standard. Antibodies against TGF-beta and IGF-I were used to localize their peptides within the myocardium. Antisense and sense (control) cRNA probes of TGF-beta1 and IGF-I, labeled with digoxigenin, were used to localize the growth factor transcripts by in situ hybridization. mRNA levels (densitometric ratio of growth factor/glyceraldehyde-3-phosphate dehydrogenase) of TGF-beta1 and IGF-I in HCM (0.75+/-0.05 and 0.85+/-0.15, respectively; mean+/-1 SEM) were significantly (P<.01 for all groups) elevated in comparison with non-HCM myocardium (AS: 0.38+/-0.07, 0.29+/-0.06; SA: 0.32+/-0.04, 0.18+/-0.05; TM: 0.25+/-0.03, 0.15+/-0.03). mRNA levels of TGF-beta1 and IGF-I in the hypertrophic AS myocardium were greater (P=.02, P=.05) than those in the explanted myocardium (TM). Immunohistochemical and in situ hybridization studies showed increased expression of TGF-beta1 and IGF-I in the HCM cardiomyocytes.

CONCLUSIONS

Gene expression of TGF-beta1 and IGF-I was enhanced in idiopathic hypertrophic cardiomyopathy and may be associated with its development.

Insulin-like growth factor-I rapidly activates multiple signal transduction pathways in cultured rat cardiac myocytes

In response to insulin-like growth factor-I (IGF-I), neonatal rat cardiac myocytes exhibit a hypertrophic response. The elucidation of the IGF-I signal transduction system in these cells remains unknown. We show here that cardiac myocytes present a single class of high affinity receptors (12,446 +/- 3,669 binding sites/cell) with a dissociation constant of 0.36 +/- 0.10 nM. Two different beta-subunits of IGF-I receptor were detected, and their autophosphorylation was followed by increases in the phosphotyrosine content of extracellular signal-regulated kinases (ERKs), insulin receptor substrate 1, phospholipase C-gamma1, and phosphatidylinositol 3-kinase. IGF-I transiently activates c-Raf in cultured neonatal cardiac myocytes, whereas A-raf is activated much less than c-Raf. Two peaks of ERK activity (ERK1 and ERK2) were resolved in cardiac myocytes treated with IGF-I by fast protein liquid chromatography, both being stimulated by IGF-I (with EC50 values for the stimulation of ERK1 and ERK2 by IGF-I of 0.10 and 0. 12 nM, respectively). Maximal activation of ERK2 (12-fold) and ERK1 (8.3-fold) activities was attained after a 5-min exposure to IGF-I. Maximal activation of p90 S6 kinase by IGF-I was achieved after 10 min, and then the activity decreased slowly. Interestingly, IGF-I stimulates incorporation of [3H]phenylalanine (1.6-fold) without any effect on [3H]thymidine incorporation. These data suggest that IGF-I activates multiple signal transduction pathways in cardiac myocytes some of which may be relevant to the hypertrophic response of the heart.

Is growth hormone good for the heart?

Growth hormone (GH), probably acting indirectly through locally produced insulin-like growth factor I, stimulates myocardial hypertrophy and increases myocyte contractility. In experimental models insulin-like growth factor I appears to be a key regulator of ventricular hypertrophy. Many adults with growth hormone deficiency (GHD) have reduced left ventricular mass, a lower ejection fraction, and reduced exercise tolerance. Elevated serum lipid levels, increased visceral fat, and early atheroma formation may contribute to an increased mortality rate from cardiovascular disease in these persons, but GH replacement therapy appears to correct many of these abnormalities. GH excess (acromegaly) results in cardiac hypertrophy that can progress to cardiac failure. Treatment with octreotide at least partially reverses cardiac hypertrophy and dysfunction. GH treatment may induce beneficial cardiac hypertrophy in adults without GHD who have dilated cardiomyopathy. Significant cardiac dysfunction has not been reported in children with GHD who are treated with GH, nor have adverse cardiac effects been reported with GH in short children without GHD, including those with Turner syndrome. We now have extensive experience with the therapeutic use of GH in children with cardiac structural abnormalities (e.g., Turner and Noonan syndromes, congenital heart disease), and such use appears to be safe. Furthermore, cardiac complications of GH in children without cardiac disease are rare. Continued observation to ensure that GH therapy has no long-term effects on cardiac anatomy or function in children is necessary.

Thyroid hormone controls the expression of insulin-like growth factor I receptor gene at different levels in lung and heart of developing and adult rats

Thyroid hormone exerts profound effects on the insulin-like growth factors (IGFs)/IGF factor I receptor (IGF-IR) system through its action on the production of IGF-I peptide and IGF-binding proteins. Most of these actions are mediated by the direct control of pituitary GH gene by thyroid hormone. In this work, we have analyzed the possible effect of hypothyroidism on the expression of IGF-IR gene, both in adult and developing animals. Our results show that in the lung and heart, thyroid hormone exerts a negative effect on IGF-IR gene expression in the adult animals and during perinatal life (from day 15 onwards). This negative effect is exerted at different levels. In the heart, this regulation occurs at a pretranslational level, indicated by the fact that parallel changes in the number of membrane IGF-I receptors and IGF-IR transcripts were observed, whereas in lung, no effect of thyroid hormone was noted in the amount of IGF-IR transcripts, suggesting a translational or posttranslational control. GH does not seem to mediate T3 effects on this gene. In contrast, retinoic acid increases the expression of IGF-IR gene at a transcriptional or posttranscriptional level in adult lung and heart. Because the IGFE/ IGF-IR system is depressed in hypothyroid animals, the specific increase in the number of IGF-IRs in the lung and heart of these animals could represent a mechanism to ameliorate the negative effects of hypothyroidism on these important organs.

Worsening of ischemic damage in hearts from rats with selective growth hormone deficiency

The effects of growth hormone (GH) deficiency on cardiac function were studied in young male rats administered an anti-GH-releasing hormone (GHRH) serum from postnatal day 20 to 40. Dependence of heart abnormalities on GH deficiency was ascertained by giving a group of anti-GHRH serum-treated rats GH replacement therapy. Heart preparations from anti-GHRH serum-treated rats, undergoing low-flow ischemia, showed a progressive increase in left ventricular end-diastolic pressure with poor recovery of mechanical activity and increased coronary perfusion pressure upon reperfusion. Hearts from anti-GHRH serum + GH-treated rats, undergoing global reduction to the flow, showed only a minimal increase of left ventricular end-diastolic pressure and, upon reperfusion, cardiac mechanical activity recovered almost completely. Similar findings were also observed in heart preparations from control (normal rabbit serum-treated) rats. Infusion of acetylcholine (10(-6) M) into heart preparations in the preischemic period increased coronary perfusion pressure values more markedly in hearts from normal rabbit serum- and anti-GHRH serum + GH-treated rats than in those from anti-GHRH serum-treated rats. These results indicate that selective GH deficiency in young male rats renders the heart more sensitive to ischemic damage and leads to an impairment of cardiac muscarinic receptor function.