Renin overexpression leads to increased titin-based stiffness contributing to diastolic dysfunction in hypertensive mRen2 rats

Abstract

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.

Anti-Atherogenic Properties of Allium ursinum Liophylisate: Impact on Lipoprotein Homeostasis and Cardiac Biomarkers in Hypercholesterolemic Rabbits

“…A 5-mm tissue sampling volume was obtained at the mitral annulus from both septal and lateral walls. From the acquired images, the following functional parameters were measured: S’, E’/A’ wave velocities, E/E’ (early diastolic mitral inflow velocity divided by average value of lateral and septal tissue Doppler early diastolic velocities) and E’/A’ (tissue Doppler early and late diastolic velocity ratio) [48]. …”

Tampering with springs: phosphorylation of titin affecting the mechanical function of cardiomyocytes

“…Thus, at least S12884 (mouse)/S12022 (human) can be phosphorylated by both CaMKIIδ and PKCα. The phospho-specific antibodies against p-S11878 and p-S12022 (p-S12742 and p-S12884 in mouse titin) have been used repeatedly to quantify PEVK phosphorylation by western blot in mouse, rat, dog, or human hearts (Hamdani et al 2013a, b, c; Hidalgo et al 2014; Hudson et al 2011; Hutchinson et al 2015; Kötter et al 2013, 2016; Kovács et al 2016; Mohamed et al 2016; Rain et al 2014; Tschöpe et al 2016; Zile et al 2015). …”

“…In a metabolic risk-induced animal model of HFpEF, the obese Zucker spontaneously hypertensive fatty-1 (ZSF1) rat, N2Bus phosphorylation at S4010 (S3991 in rat) was lower, but PEVK phosphorylation at S12022 (S12884 in rat) was higher than in healthy rat hearts, whereas PEVK phosphorylation at S11878 (S12742 in rat) was unaltered (Hamdani et al 2013b). The hearts of renin-overexpressing, hypertensive rats showed increased phosphorylation at PEVK site S12742 and unaltered phosphorylation at S12884, while N2Bus phosphosites were not studied (Kovács et al 2016). In mouse hearts stressed by pressure overload due to transverse aortic constriction surgery, PEVK site p-S11878 (PKCα) was hyper-phosphorylated and PEVK site p-S12022 (CaMKIIδ/PKCα) hypo-phosphorylated, whereas N2Bus phosphosites were again not studied (Hudson et al 2011).…”

Myosin heavy chain and cardiac troponin T damage is associated with impaired myofibrillar ATPase activity contributing to sarcomeric dysfunction in Ca2+-paradox rat hearts

“…For further analysis of the samples, titin was separated by SDS-PAGE on 2% agarose-strengthened gels as detailed elsewhere [25]. Protein bands with apparent molecular mass of 3000–3300 kDa were visualized using Coomassie brilliant blue (Reanal, Ltd., Budapest, Hungary).…”