Pressure-overload magnitude-dependence of the anti-hypertrophic efficacy of PDE5A inhibition

Abstract

Increased myocardial cGMP, achieved by enhancing cyclase activity or impeding cGMP hydrolysis by phosphodiesterase type-5 (PDE5A), suppresses cellular and whole organ hypertrophy. The efficacy of the latter also requires cyclase stimulation and may depend upon co-activation of maladaptive signaling suppressible by cGMP-stimulated kinase (cGK-1). Thus, PDE5A inhibitors could paradoxically be more effective against higher than lower magnitudes of pressure-overload stress. To test this, mice were subjected to severe or moderate trans-aortic constriction (sTAC, mTAC) for 6 wks +/-co-treatment with oral sildenafil (SIL 200 mg/kg/d). LV mass (LVM) rose 130% after 3-wks sTAC and SIL blunted this by 50%. With mTAC, LVM rose 56% at 3 wks but was unaffected by SIL, whereas a 90% increase in LVM after 6 wks was suppressed by SIL. SIL minimally altered LV function and remodeling with mTAC until later stages that stimulated more hypertrophy and remodeling. SIL stimulated cGK-1 activity similarly at 3 and 6 wks of mTAC. However, pathologic stress signaling (e.g. calcineurin, ERK-MAPkinase) was little activated after 3-wk mTAC, unlike sTAC or later stage mTAC when activity increased and SIL suppressed it. With modest hypertrophy (3-wk mTAC), GSK3beta and Akt phosphorylation were unaltered but SIL enhanced it. However, with more severe hypertrophy (6-wk mTAC and 3-wk sTAC), both kinases were highly phosphorylated and SIL treatment reduced it. Thus, PDE5A-inhibition counters cardiac pressure-overload stress remodeling more effectively at higher than lower magnitude stress, coupled to pathologic signaling activation targetable by cGK-1 stimulation. Such regulation could impact responses of varying disease models to PDE5A inhibitors.

Figure 1

A) Example M-mode echocardiographic images at baseline (sham operated), and vehicle versus sildenafil treated animals for 3-wks severe TAC, and 3-wks, 6-wks moderate TAC models. Chamber end-diastolic dimension is highlighted (arrows) and shows reduction at 3-wks sTAC, but no change until 6-wks mTAC. B) Summary echocardiographic data for LV diastolic dimension (LVDd), LV systolic dimension (LVDs), fractional shortening (FS), and LV mass (N=5–10). After 3-wks sTAC, SIL reduced chamber dilation and dysfunction, and suppressed hypertrophy. With mTAC, SIL did not alter heart function at 3-wks where there was moderate LVH (about half the extent with sTAC), but did blunt hypertrophy and remodeling at a later stage (6-wks).

Figure 2

A) Example pressure-volume loops for sham control, and moderate TAC ±SIL treatment at 3 and 6-wks timepoints. Increased cardiac loading is demonstrated by the higher systolic pressures, but at 3-wks there was negligible functional impact of SIL, whereas at 6-wks, untreated hearts dilated and had reduced function compared with SIL treated hearts. B) Summary results from PV analysis for LV end-diastolic and end-systolic volumes (LV-EDV, LV-ESV), maximal LV pressure (LVPmx), end-systolic elastance (Ees), and maximal rate of pressure rise normalized to instantaneous developed pressure (dP/dt_max/IP) (N=5–7).

Figure 3

A) cGK-1 activity measured in sham and after 3 or 6-wks mTAC±SIL (N=4). Rest (vehicle treated) activity increased at each time point, but was further and similarly enhanced (~4-fold over sham) with SIL treatment. Augmentation of activity after 3-wks sTAC ±SIL co-treatment is shown for comparison. * p<0.02 versus sham control; †p<0.01 versus vehicle treated at same time point. B) Influence of mTAC±SIL on ERK1/2 phosphorylation and calcineurin (Cn) protein expression (N=3). SIL had minimal impact at 3 wks, but significantly depressed expression levels when treated out to 6-wks of mTAC. Comparison expression levels after 3-wks of sTAC (previously shown to be blunted by SIL treatment [8]) were similar to those observed after 6-wks mTAC. C) Gene expression for RCAN-1, ANP, and β-MHC (N=4). * p<0.05 versus sham control; † p<0.05 versus 6-wks mTAC vehicle treated.

Figure 4

Influence of mTAC±SIL on phosphorylation of Akt and GSK3β varies depending upon the time course of moderate hypertrophic stimulation (N=3). At 3-wks, phosphorylation was little altered from sham controls in vehicle treated hearts, but was significantly enhanced by SIL. However, at 6-wks, with more sustained overload and hypertrophic response, phosphorylation of both kinases was increased over control, and now SIL depressed this response. * p<0.05 versus sham control. † p<0.05 versus vehicle treated at corresponding time point. Basal (non-SIL treated) phosphorylation levels for 3-wks sTAC are shown for comparison. As previously reported, SIL depresses this activation [8].