Relations of vascular calcium channels with blood pressure and endothelium in hypertension and with aging

Progressive aortic stiffness in aging C57Bl/6 mice displays altered contractile behaviour and extracellular matrix changes

Aortic stiffness is a hallmark of cardiovascular disease, but its pathophysiology remains incompletely understood. This study presents an in-dept characterization of aortic aging in male C57Bl/6 mice (2–24 months). Cardiovascular measurements include echocardiography, blood pressure measurement, and ex vivo organ chamber experiments. In vivo and ex vivo aortic stiffness increases with age, and precede the development of cardiac hypertrophy and peripheral blood pressure alterations. Contraction-independent stiffening (due to extracellular matrix changes) is pressure-dependent. Contraction-dependent aortic stiffening develops through heightened α₁-adrenergic contractility, aberrant voltage-gated calcium channel function, and altered vascular smooth muscle cell calcium handling. Endothelial dysfunction is limited to a modest decrease in sensitivity to acetylcholine-induced relaxation with age. Our findings demonstrate that progressive arterial stiffening in C57Bl/6 mice precedes associated cardiovascular disease. Aortic aging is due to changes in extracellular matrix and vascular smooth muscle cell signalling, and not to altered endothelial function.

A 24-month aging study in male C57Bl/6 mice reveals that aortic aging precedes cardiovascular disease and is due to changes in the extracellular matrix and vascular smooth muscle cell signaling.

Aortic Stiffness in L-NAME Treated C57Bl/6 Mice Displays a Shift From Early Endothelial Dysfunction to Late-Term Vascular Smooth Muscle Cell Dysfunction

Introduction and Aims: Endothelial dysfunction is recognized as a cardiovascular aging hallmark. Administration of nitric oxide synthase blocker N-Ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME) constitutes a well-known small animal model of cardiovascular aging. Despite extensive phenotypic characterization, the exact aortic function changes in L-NAME treated mice are largely unknown. Therefore, this study presents a longitudinal characterization of the aortic reactivity and biomechanical alterations in L-NAME treated C57Bl/6 mice.

Methods and Results: Male C57Bl/6 mice were treated with L-NAME (0.5 mg/ml drinking water) for 1, 2, 4, 8, or 16 weeks. Peripheral blood pressure measurement (tail-cuff) and transthoracic echocardiograms were recorded, showing progressive hypertension after 4 weeks of treatment and progressive cardiac hypertrophy after 8–16 weeks of treatment. Aortic stiffness was measured in vivo as aortic pulse wave velocity (aPWV, ultrasound) and ex vivo as Peterson modulus (E_p). Aortic reactivity and biomechanics were investigated ex vivo in thoracic aortic rings, mounted isometrically or dynamically-stretched in organ bath set-ups. Aortic stiffening was heightened in L-NAME treated mice after all treatment durations, thereby preceding the development of hypertension and cardiac aging. L-NAME treatment doubled the rate of arterial stiffening compared to control mice, and displayed an attenuation of the elevated aortic stiffness at high distending pressure, possibly due to late-term reduction of medial collagen types I, III, and IV content. Remarkably, endothelial dysfunction, measured by acetylcholine concentration-response stimulation in precontracted aortic rings, was only observed after short-term (1–4 weeks) treatment, followed by restoration of endothelial function which coincided with increased phosphorylation of endothelial nitric oxide synthase (S¹¹⁷⁷). In the late-disease phase (8–16 weeks), vascular smooth muscle cell (VSMC) dysfunction developed, including increased contribution of voltage-dependent calcium channels (assessed by inhibition with diltiazem), basal VSMC cytoplasmic calcium loading (assessed by removal of extracellular calcium), and heightened intracellular contractile calcium handling (assessed by measurement of sarcoplasmic reticulum-mediated transient contractions).

Conclusion: Arterial stiffness precedes peripheral hypertension and cardiac hypertrophy in chronic L-NAME treated male C57Bl/6 mice. The underlying aortic disease mechanisms underwent a distinct shift from early endothelial dysfunction to late-term VSMC dysfunction, with continued disease progression.