Increased insulin-like growth factor-1 protein in human left ventricular hypertrophy

The intercalated disc: a mechanosensing signalling node in cardiomyopathy

Cardiomyocytes, the cells generating contractile force in the heart, are connected to each other through a highly specialised structure, the intercalated disc (ID), which ensures force transmission and transduction between neighbouring cells and allows the myocardium to function in synchrony. In addition, cardiomyocytes possess an intrinsic ability to sense mechanical changes and to regulate their own contractile output accordingly. To achieve this, some of the components responsible for force transmission have evolved to sense changes in tension and to trigger a biochemical response that results in molecular and cellular changes in cardiomyocytes. This becomes of particular importance in cardiomyopathies, where the heart is exposed to increased mechanical load and needs to adapt to sustain its contractile function. In this review, we will discuss key mechanosensing elements present at the intercalated disc and provide an overview of the signalling molecules involved in mediating the responses to changes in mechanical force.

Impact of ethnicity on cardiac adaptation to exercise

The increasing globalization of sport has resulted in athletes from a wide range of ethnicities emerging onto the world stage. Fuelled by the untimely death of a number of young professional athletes, data generated from the parallel increase in preparticipation cardiovascular evaluation has indicated that ethnicity has a substantial influence on cardiac adaptation to exercise. From this perspective, the group most intensively studied comprises athletes of African or Afro-Caribbean ethnicity (black athletes), an ever-increasing number of whom are competing at the highest levels of sport and who often exhibit profound electrical and structural cardiac changes in response to exercise. Data on other ethnic cohorts are emerging, but remain incomplete. This Review describes our current knowledge on the impact of ethnicity on cardiac adaptation to exercise, starting with white athletes in whom the physiological electrical and structural changes--collectively termed the 'athlete's heart'--were first described. Discussion of the differences in the cardiac changes between ethnicities, with a focus on black athletes, and of the challenges that these variations can produce for the evaluating physician is also provided. The impact of ethnically mediated changes on preparticipation cardiovascular evaluation is highlighted, particularly with respect to false positive results, and potential genetic mechanisms underlying racial differences in cardiac adaptation to exercise are described.

Ethnic differences in physiological cardiac adaptation to intense physical exercise in highly trained female athletes

BACKGROUND

Ethnicity is an important determinant of cardiovascular adaptation in athletes. Studies in black male athletes reveal a higher prevalence of electric repolarization and left ventricular hypertrophy than observed in white males; these frequently overlap with those observed in cardiomyopathy and have important implications in the preparticipation cardiac screening era. There are no reports on cardiac adaptation in highly trained black females, who comprise an increasing population of elite competitors.

METHODS AND RESULTS

Between 2004 and 2009, 240 nationally ranked black female athletes (mean age 21+/-4.6 years old) underwent 12-lead ECG and 2-dimensional echocardiography. The results were compared with 200 white female athletes of similar age and size participating in similar sports. Black athletes demonstrated greater left ventricular wall thickness (9.2+/-1.2 versus 8.6+/-1.2 mm, P<0.001) and left ventricular mass (187.2+/-42 versus 172.3+/-42 g, P=0.008) than white athletes. Eight black athletes (3%) exhibited a left ventricular wall thickness >11 mm (12 to 13 mm) compared with none of the white athletes. All athletes revealed normal indices of systolic and diastolic function. Black athletes exhibited a higher prevalence of T-wave inversions (14% versus 2%, P<0.001) and ST-segment elevation (11% versus 1%, P<0.001) than white athletes. Deep T-wave inversions (-0.2 mV) were observed only in black athletes and were confined to the anterior leads (V(1) through V(3)).

CONCLUSIONS

Systematic physical exercise in black female athletes is associated with greater left ventricular hypertrophy and higher prevalence of repolarization changes than in white female athletes of similar age and size participating in identical sporting disciplines. However, a maximal left ventricular wall thickness >13 mm or deep T-wave inversions in the inferior and lateral leads are rare and warrant further investigation.

Association of leukocyte telomere length with echocardiographic left ventricular mass: the Framingham heart study

BACKGROUND

Leukocyte telomere length (LTL) decreases over the adult life course owing to the cumulative burden of oxidative stress, inflammation, and exposure to vascular risk factors. Left ventricular (LV) mass is a biomarker of long-standing exposure to cardiovascular disease risk factors. We hypothesized that LTL is related inversely to LV mass.

METHODS AND RESULTS

We related LTL (measured by Southern blot analysis) to echocardiographic LV mass and its components (LV diastolic dimension and LV wall thickness) in 850 Framingham Heart Study participants (mean age 58 years, 58% women) using multivariable linear regression with adjustment for age, sex, height, weight, systolic blood pressure, hypertension treatment, and smoking. Overall, multivariable-adjusted LTL was positively related to LV mass (beta-coefficient per SD increase 0.072; P=0.001), LV wall thickness (beta=0.053; P=0.01), and LV diastolic dimension (beta=0.035; P=0.09). We observed effect modification by hypertension status (P for interaction=0.02 for LV mass); LTL was more strongly associated with LV mass and LV wall thickness in individuals with hypertension (beta-coefficient per SD increment of 0.10 and 0.08, respectively; P<0.01 for both). Participants with hypertension who were in the top quartile of LV mass had LTL that was 250 base pairs longer than those in the lowest quartile (P for trend across quartiles=0.009).

CONCLUSIONS

In contrast to our expectation, in the present community-based sample, LTL was positively associated with LV mass and wall thickness, especially so in participants with hypertension. These data are consistent with the hypothesis that longer LTL may be a marker of propensity to LV hypertrophy.

Intravenous IGF-I receptor antisense reduces IGF-IR expression and diminishes pressor responses to angiotensin II in conscious normotensive rats

Given the variety of cardiovascular effects of insulin-like growth factor-I (IGF-I), we investigated the effects of a functional deficit in IGF-I signalling in the conscious rat cardiovascular system using intravenous IGF-I receptor antisense (AS, 0.5 nmol) treatment.Insulin-like growth factor-I receptor (IGF-IR) immunoreactivity was reduced in IGF-IR AS-treated tail arteries. Western immunoblot analysis demonstrated a decrease in cardiac IGF-IR in IGF-IR AS-treated rats; treatment reduced the expression of IGF-IR to 83+/-6% of that in samples from vehicle-treated rats, compared to 99+/-3% for a control, full-mismatch oligonucleotide (MM-18) or 100% (vehicle).IGF-IR AS treatment had no effect on resting blood pressure during the 14-day treatment period. Pressor responses (as measured by increase in systolic arterial pressure) to angiotensin II (AngII) gradually decreased over 2 weeks treatment with IGF-IR AS (5 x 0.5 nmol per intravenous injection, 2 weeks), and were significantly reduced at treatment day 14 compared to day 7 (2.7-fold rightward shift). IGF-IR AS treatment caused a significant rightward shift in the angiotensin II (AngII) dose-response compared to both vehicle and full-mismatch treated rats (4.0-fold shift compared to vehicle, P<0.01, n=6-14). There was a significant decrease in cardiac angiotensin II type 1 receptor (AT(1)R) expression in AS-treated rats compared to vehicle-treated rats; cardiac AT(1)R was decreased to 80+/-6% in comparison to 100%. AT(1)R immunoreactivity was also reduced in IGF-IR AS-treated tail arteries.IGF-IR AS treatment resulted in structural changes in both the heart and aortae, with small but significant differences observed between left ventricle/bodyweight ratios of AS and both vehicle- and MM-18-treated rats (n=8, P<0.05). Aortic cross-sectional areas of AS-treated rats were significantly lower than MM-18- and vehicle-treated rats (27.4+/-5.7% reduction of vehicle-treated samples, n=8, P<0.01). The results of this study suggest that an induced loss of IGF-IR, while not affecting resting blood pressure, has a predominantly inhibitory effect on vascular response to vasoconstrictor agents including angiotensin II. This may occur through downstream effects on AT1R expression, via modulation of the expression of receptors for other vasoactive signalling molecules, or via changes in myocyte proliferation.

Regional overexpression of insulin-like growth factor-I and transforming growth factor-beta1 in the myocardium of patients with hypertrophic obstructive cardiomyopathy

OBJECTIVE

Hypertrophic obstructive cardiomyopathy has been proposed to be the result of gene mutations of contractile proteins. However, we have previously shown significant elevation of insulin-like growth factor-I (IGF-I) and transforming growth factor-beta1 (TGF-beta1) at the messenger RNA, protein, and receptor levels in patients with hypertrophic obstructive cardiomyopathy when compared with myocardium from patients without this disorder. We hypothesized that this growth factor overexpression is a regional phenomenon. To test this hypothesis, we compared levels of IGF-I and TGF-beta1 in hypertrophic and nonhypertrophic myocardium within the same group of patients with hypertrophic obstructive cardiomyopathy.

METHODS

Two biopsy specimens were obtained from each patient undergoing septal myectomy for severely symptomatic hypertrophic obstructive cardiomyopathy, from hypertrophied septum and from nonhypertrophied myocardium (8 patients in total). Clinical data were prospectively recorded. Messenger RNA levels for growth factor were quantified by means of multiplex reverse transcriptase-polymerase chain reaction, expressed as a densitometric ratio of growth factor/glyceraldehyde-3-phosphate dehydrogenase. Protein levels were quantified by means of chemiluminescent slot blot analysis. Growth factor proteins were used to generate a standard curve.

RESULTS

IGF-I messenger RNA and protein levels in hypertrophic myocardium were 2.6 and 2.9 times greater, respectively, than in nonhypertrophic myocardium of the same patients (both P <.01). TGF-beta 1 messenger RNA and protein levels in the hypertrophic myocardium were 2.5 and 2.8 times greater, respectively, than the levels in the nonhypertrophied myocardium (both P <.01). There was a significant correlation between the IGF-I protein ratio (hypertrophic/nonhypertrophic myocardium) and the inducible left ventricular outflow tract gradients measured at cardiac catheterization (r = 0.77, P =.025).

CONCLUSIONS

Myocardial overexpression of IGF-I and TGF-beta1 is a regional phenomenon in patients with hypertrophic obstructive cardiomyopathy and is likely involved in the pathogenesis of the disorder.