Mechanical Strain Increases Expression of the Brain Natriuretic Peptide Gene in Rat Cardiac Myocytes

Abstract

Using a device that applies cyclical strain (1 Hz) to ventricular cardiocytes cultured on collagen-coated silicone elastomer surfaces, we have demonstrated straindependent increases in brain natriuretic peptide (BNP) secretion, BNP mRNA levels, and expression of a transiently transfected ؊1595 human BNP-luciferase reporter. When actinomycin D (10 M) was introduced concomitantly with the strain stimulus, the strain-induced increase in BNP mRNA was eliminated, and the decay of transcripts was identical in the control and strained cells, indicating the lack of independent effects on transcript stability. Strain-dependent ؊1595 human BNPluciferase activity was completely inhibited by chelerythrine, 2-aminopurine, genistein, and W-7 and only partially or not at all by KN-62, wortmannin, and H-89. The effects of these individual agents paralleled their effects on mitogen-activated protein kinase (MAPK) activity, but not c-Jun N-terminal kinase (JNK) activity, in the cells. Overexpression of wild-type MAPK and, to a lesser extent, JNK increased strain-dependent BNP promoter activity, whereas dominant-negative mutants of MAPK kinase, JNK kinase, or Ras completely blocked strain-dependent reporter activity. These findings provide the first demonstration that mechanical strain can increase myocardial gene expression through a transcriptional mechanism and suggest important roles for MAPK and JNK in mediating this effect.The natriuretic peptides comprise a family of vasoactive hormones that play an important role in the regulation of cardiovascular and renal homeostasis (1). Their natriuretic and vasodepressor properties suggest that they represent endogenous antagonists of the various systems (e.g. renin-angiotensin system and sympathetic nervous system) that support arterial blood pressure under basal conditions and, at times, contribute to the pathophysiology of cardiovascular disease.Atrial natriuretic peptide (ANP), 1 the prototype of the group, is produced primarily in the atria of the heart. ANP is expressed in the cardiac ventricle during development and early neonatal life (2, 3). Expression decays as the animal ages and remains quiescent in the adult unless the ventricle is subjected to hemodynamic overload (i.e. mechanical strain that leads to increased wall stress and subsequently to hypertrophy of the myocardium), as occurs with systemic arterial hypertension or congestive heart failure (4 -7).Brain natriuretic peptide (BNP) is also produced in the heart. Despite the nomenclature, relatively little BNP is expressed in the mammalian brain (the exception being the porcine brain, where the peptide was identified originally). Expression of BNP in the heart is lower than that of ANP under basal conditions, and the atrial/ventricular ratio of expression is considerably less than that seen with ANP (8). Ventricular expression of BNP is activated in a fashion similar to ANP in pathophysiological states associated with hemodynamic overload (9, 10). At some stages of advanced congestive heart failure, circulating BNP le...

Endothelin-Dependent and -Independent Components of Strain-Activated Brain Natriuretic Peptide Gene Transcription Require Extracellular Signal Regulated Kinase and p38 Mitogen-Activated Protein Kinase

“…The activation of both p38 MAPK 12 and ERK 7,8,10 has been demonstrated after the application of mechanical strain to cultured myocytes. The involvement of these pathways extends to both the ET-dependent and -independent components of the strain response (see earlier).…”

“…The nature of the signaling mechanism or mechanisms that account for this activity remains undefined, although the JNKs represent obvious candidates. Both ET 3 and mechanical strain 9,10 have been shown to stimulate JNK activity in cultured cardiac myocytes, and this stimulation has been linked to the hypertrophic phenotype. The levels of inhibition cited probably are low estimates of the true participation of this pathway (or pathways) in signaling the response to mechanical strain.…”

“…We have recently shown that mechanical strain stimulates the activity of a transfected human brain natriuretic peptide (hBNP) gene promoter in neonatal ventricular myocytes. 10 This stimulation appears to be derived in part from a direct effect on the cardiac myocyte and in part from an autocrine/paracrine pathway that involves the sequential generation of angiotensin II and endothelin (ET). 11 From a mechanotransduction standpoint, strain has been shown to activate ERKs, JNKs, and p38 MAPKs in these myocyte cultures, [7][8][9][10] with the latter (ie, p38 MAPK) accounting for Ϸ50% of the composite hBNP promoter response.…”

“…10 This stimulation appears to be derived in part from a direct effect on the cardiac myocyte and in part from an autocrine/paracrine pathway that involves the sequential generation of angiotensin II and endothelin (ET). 11 From a mechanotransduction standpoint, strain has been shown to activate ERKs, JNKs, and p38 MAPKs in these myocyte cultures, [7][8][9][10] with the latter (ie, p38 MAPK) accounting for Ϸ50% of the composite hBNP promoter response. 12 This activity depends on interaction of the transcription factor nuclear factor (NF)-B with 3 shear stress response element (SSRE)-like structures in the proximal hBNP promoter.…”

Successful Management of Enzyme Replacement Therapy in Related Fabry Disease Patients with Severe Adverse Events by Switching from Agalsidase Beta (Fabrazyme®) to Agalsidase Alfa (Replagal®)

“…A recent study showed that NT-proBNP was potentially useful as a biomarker in Fabry disease and correlated with changes in Mainz Severity Score Index (Torralba-Cabeza et al 2011). BNP gene expression is stimulated by both mechanical strain (Liang et al 1997;Liang and Gardner 1998) and autocrine/paracrine processes via angiotensin II (Liang and Gardner 1998). Renin-angiotensin system blockade reduces plasma NT-proBNP level and improves prognosis, which is most likely a reflection of improved cardiac function due to the treatment (Anand et al 2003).…”