Diastolic dysfunction is associated with cardiac fibrosis in the senescence-accelerated mouse

Abstract

Diastolic heart failure is a major cause of mortality in the elderly population. It is often preceded by diastolic dysfunction, which is characterized by impaired active relaxation and increased stiffness. We tested the hypothesis that senescence-prone (SAMP8) mice would develop diastolic dysfunction compared with senescence-resistant controls (SAMR1). Pulsed-wave Doppler imaging of the ratio of blood flow velocity through the mitral valve during early (E) vs. late (A) diastole was reduced from 1.3 ± 0.03 in SAMR1 mice to 1.2 ± 0.03 in SAMP8 mice (P < 0.05). Tissue Doppler imaging of the early (E') and late (A') diastolic mitral annulus velocities found E' reduced from 25.7 ± 0.9 mm/s in SAMR1 to 21.1 ± 0.8 mm/s in SAMP8 mice and E'/A' similarly reduced from 1.1 ± 0.02 to 0.8 ± 0.03 in SAMR1 vs. SAMP8 mice, respectively (P < 0.05). Invasive hemodynamics revealed an increased slope of the end-diastolic pressure-volume relationship (0.5 ± 0.05 vs. 0.8 ± 0.14; P < 0.05), indicating increased left ventricular chamber stiffness. There were no differences in systolic function or mean arterial pressure; however, diastolic dysfunction was accompanied by increased fibrosis in the hearts of SAMP8 mice. In SAMR1 vs. SAMP8 mice, interstitial collagen area increased from 0.3 ± 0.04 to 0.8 ± 0.09% and perivascular collagen area increased from 1.0 ± 0.11 to 1.6 ± 0.14%. Transforming growth factor-β and connective tissue growth factor gene expression were increased in the hearts of SAMP8 mice (P < 0.05 for all data). In summary, SAMP8 mice show increased fibrosis and diastolic dysfunction similar to those seen in humans with aging and may represent a suitable model for future mechanistic studies.

Fig. 1.

Mean arterial pressure was unchanged in senescence-resistant controls (SAMR1) and senescence-prone (SAMP8) mice from 3 to 6 mo of age (n = 5; P = NS).

Fig. 2.

Functional analysis of isolated cardiomyocytes. A: mean of diastolic sarcomere length was significantly shorter in cardiomyocytes from SAMP8 compared with SAMR1 at 6 mo of age (n = 53, 59; *P < 0.05). B: fractional shortening of isolated cardiomyocytes paced at 1.0 Hz at 37°C represented as the peak shortening divided by the baseline sarcomere length (n = 53, 59; P = NS). C: time to 90% peak contraction in isolated cardiomyocytes (n = 47, 51; P = NS). D: isolated cardiomyocytes from SAMP8 mice have a prolonged relaxation constant (τ) compared with SAMP1 mice (n = 53, 59; P = NS).

Fig. 3.

SAMP8 mice show greater collagen deposition and hence increased cardiac fibrosis in both the interstitial areas and perivascular areas compared with SAMR1 controls at 6 mo of age. A: picrosirius red staining to evaluate collagen deposition. With the use of bright-field microscopy, SAMP8 mice show a more intense red stain than SAMR1 mice, indicating greater collagen accumulation. When polarized light is used, larger collagen fibers appear as bright yellow or orange, and thinner fibers are green. Both modalities show increased collagen accumulation in SAMP8 mice at 6 mo of age. B: Masson's trichrome staining to evaluate collagen deposition (n = 4; *P < 0.01).

Fig. 4.

Expression of extracellular matrix proteins. SAMP8 mice show increased gene expression of collagens 1A1 (A) and 3A (B) and as well as fibronectin 1 (C) compared with SAMR1 controls at 6 mo of age (n = 7; *P < 0.05).

Fig. 5.

Expression of profibrotic cytokines. A: transforming growth factor-β (TGF-β). B: connective tissue growth factor (CTGF). C: α-smooth muscle actin (α-SMA). SAMP8 mice show increased gene expression of TGF-β compared with SAMR1 controls at 6 mo of age (n = 7; *P < 0.05).