A. Renin overexpression leads to increased titin-based stiffness contributing to diastolic dysfunction in hypertensive mRen2 rats. Am J Physiol Heart Circ Physiol 310: H1671-H1682, 2016. First published April 8, 2016; doi:10.1152/ajpheart.00842.2015.-Hypertension (HTN) is a major risk factor for heart failure. We investigated the influence of HTN on cardiac contraction and relaxation in transgenic renin overexpressing rats (carrying mouse Ren-2 renin gene, mRen2, n ϭ 6). Blood pressure (BP) was measured. Cardiac contractility was characterized by echocardiography, cellular force measurements, and biochemical assays were applied to reveal molecular mechanisms. Sprague-Dawley (SD) rats (n ϭ 6) were used as controls. Transgenic rats had higher circulating renin activity and lower cardiac angiotensin-converting enzyme two levels. Systolic BP was elevated in mRen2 rats (235.11 Ϯ 5.32 vs. 127.03 Ϯ 7.56 mmHg in SD, P Ͻ 0.05), resulting in increased left ventricular (LV) weight/body weight ratio (4.05 Ϯ 0.09 vs. 2.77 Ϯ 0.08 mg/g in SD, P Ͻ 0.05). Transgenic renin expression had no effect on the systolic parameters, such as LV ejection fraction, cardiomyocyte Ca 2ϩ -activated force, and Ca 2ϩ sensitivity of force production. In contrast, diastolic dysfunction was observed in mRen2 compared with SD rats: early and late LV diastolic filling ratio (E/A) was lower (1.14 Ϯ 0.04 vs. 1.87 Ϯ 0.08, P Ͻ 0.05), LV isovolumetric relaxation time was longer (43.85 Ϯ 0.89 vs. 28.55 Ϯ 1.33 ms, P Ͻ 0.05), cardiomyocyte passive tension was higher (1.74 Ϯ 0.06 vs. 1.28 Ϯ 0.18 kN/m 2 , P Ͻ 0.05), and lung weight/body weight ratio was increased (6.47 Ϯ 0.24 vs. 5.78 Ϯ 0.19 mg/g, P Ͻ 0.05), as was left atrial weight/body weight ratio (0.21 Ϯ 0.03 vs. 0.14 Ϯ 0.03 mg/g, P Ͻ 0.05). Hyperphosphorylation of titin at Ser-12742 within the PEVK domain and a twofold overexpression of protein kinase C-␣ in mRen2 rats were detected. Our data suggest a link between the activation of renin-angiotensin-aldosterone system and increased titin-based stiffness through phosphorylation of titin's PEVK element, contributing to diastolic dysfunction.Listen to this article's corresponding podcast at http://ajpheart. podbean.com/e/diastolic-dysfunction-in-the-hypertensive-mren2-rat/.renin-angiotensin-aldosterone system; RAAS; hypertension; diastolic dysfunction; passive stiffness; titin phosphorylation
NEW & NOTEWORTHYIt is shown that activation of the renin-angiotensin-aldosterone system leads to hypertension and impaired cardiac relaxation associated with increased cardiomyocyte stiffness and hyperphosphorylation of the PEVK region of titin. Moreover, diastolic dysfunction in mRen2 rats occurs without changes in systolic parameters, similarly to human heart failure with preserved ejection fraction.