Nonmyocardial production of ST2 protein in human hypertrophy and failure is related to diastolic load

Abstract

Objectives: This study was designed to investigate: 1) relationships between serum ST2 levels and hemodynamic/neurohormonal variables; 2) myocardial ST2 production; and the 3) expression of ST2, membrane-anchored ST2L, and its ligand, interleukin (IL)-33, in myocardium, endothelium, and leukocytes from patients with left ventricular (LV) pressure overload and congestive cardiomyopathy.

Background: Serum levels of ST2 are elevated in heart failure. The relationship of ST2 to hemodynamic variables, source of ST2, and expression of ST2L and IL-33 in the cardiovascular system are unknown.

Methods: Serum ST2 (pg/ml; median [25th, 75th percentile]) was measured in patients with LV hypertrophy (aortic stenosis) (n = 45), congestive cardiomyopathy (n = 53), and controls (n = 23). ST2 was correlated to N-terminal pro-brain natriuretic peptide, C-reactive protein, and hemodynamic variables. Coronary sinus and arterial blood sampling determined myocardial gradient (production) of ST2. The levels of ST2, ST2L, and IL-33 were measured (reverse transcriptase-polymerase chain reaction) in myocardial biopsies and leukocytes. The ST2 protein production was evaluated in human endothelial cells. The IL-33 protein expression was determined (immunohistochemistry) in coronary artery endothelium.

Results: The ST2 protein was elevated in aortic stenosis (103 [65, 165] pg/ml, p < 0.05) and congestive cardiomyopathy (194 [69, 551] pg/ml, p < 0.01) versus controls (49 [4, 89] pg/ml) and correlated with B-type natriuretic peptide (r = 0.5, p < 0.05), C-reactive protein (r = 0.6, p < 0.01), and LV end-diastolic pressure (r = 0.38, p < 0.03). The LV ST2 messenger ribonucleic acid was similar in aortic stenosis and congestive cardiomyopathy versus control (p = NS). No myocardial ST2 protein gradient was observed. Endothelial cells secreted ST2. The IL-33 protein was expressed in coronary artery endothelium. Leukocyte ST2L and IL-33 levels were highly correlated (r = 0.97, p < 0.001).

Conclusions: In human hypertrophy and failure, serum ST2 correlates with the diastolic load. Though the heart, endothelium, and leukocytes express components of ST2/ST2L/IL-33 pathway, the source of circulating serum ST2 is extra-myocardial.

Figure 1. Serum levels of humoral markers

A. Serum levels of ST2, CRP and BNP in AS, CCM and control patients. Box-plots show median [25^th-75^th]. B. Scatterplot between NT-pro-BNP and ST2 (left) and CRP and ST2 (right) in all patients.

Figure 2. Relationship between serum ST2 levels and extent of diastolic load as assessed from left ventricular end diastolic pressure (LVEDP)

Serum ST2 levels according to LVEDP in all study subjects(left panel), and in Controls and in CCM patients(right panel). Box-plots show median [25^th-75^th].

Figure 3. Serum ST2 and BNP in patients with isolated diastolic heart failure

A. Serum ST2 (left) and BNP (right) levels in patients with isolated diastolic failure. Data were transformed due to heterogeneity of variance into the log scale. B. LVEDP (left) and LV ejection fraction in patients with diastolic failure compared to control patients.

Figure 4. Transmyocardial gradient of and myocardial RNA levels of BNP and ST2

A. Transmyocardial production of BNP (left) and ST2 (right) in individual patients (N=24) with heart failure. Mean±SD are also shown in addition to individual values. B. LV BNP mRNA levels (left) in Control, AS and CCM cardiac biopsies. LV ST2 mRNA levels (right) are not significantly different in all groups. AU: arbitrary units.

Figure 5. ST2 protein secretion by human venous and arterial endothelial cells

Phorbol ester, IL-1β and tumor necrosis factor-1 induced ST2 secretion in venous endothelial cells (left). IL-1β induced secretion while H₂O₂ blocked secretion in arterial endothelial cells (middle). Time course shows ST2 is rapidly synthesized and secreted with significantly elevated levels at 3 hours and reaches peak values at 6 hours (right). Brefeldin A blocked ST2 secretion (right).

Figure 6. IL33 and ST2 mRNA levels in myocardial biopsies

A. IL-33 mRNA levels were decreased in AS hearts compared to CCM hearts. ST2L mRNA levels were significantly decreased in AS hearts compared to Control. ST2L levels were similar in CCM hearts compared to Control (middle). B. IL-33 protein was expressed in human coronary artery endothelium (brown staining).

Figure 7. Correlation between ST2L and IL-33 in leukocytes

Relationship between ST2L vs. IL-33 mRNA levels in leukocytes from Control, AS and CCM patients.