Increased stiffness and cell-matrix interactions of abdominal aorta in two experimental nonhypertensive models: long-term chemically sympathectomized and sinoaortic denervated rats

Abstract

Rationale: Sinoaortic denervated (SAD) and chemically sympathectomized (SNX) rats are characterized by a decrease in arterial distensibility without hypertension and would, thus, be relevant for analyzing arterial wall stiffening independently of blood pressure level. The fibronectin network, which plays a pivotal role in cell-matrix interactions, is a major determinant of arterial stiffness. We hypothesized that in SAD and SNX rats, arterial stiffness is increased, due to alterations of cell-matrix anchoring leading to spatial reorganization of the extracellular matrix.

Methods: The intrinsic elastic properties of the arterial wall were evaluated in vivo by the relationship between incremental elastic modulus determined by echotracking and circumferential wall stress. The changes of cell-extracellular matrix links in the abdominal aorta were evaluated by studying fibronectin, vascular integrin receptors, and ultrastructural features of the aorta by immunochemistry.

Results: In both experimental conditions, wall stiffness increased, associated with different modifications of cell-extracellular matrix adhesion. In SAD rats, increased media cross-sectional area was coupled with an increase of muscle cell attachments to its extracellular matrix via fibronectin and its α5-β1 integrin. In SNX rats, reduced media cross-sectional area was associated with upregulation of αv-β3 integrin and more extensive connections between dense bands and elastic fibers despite the disruption of the elastic lamellae.

Conclusion: In aorta of SNX and SAD rats, a similar arterial stiffness is associated to different structural alterations. An increase in αvβ3 or α5β1 integrins together with the already reported increase in the proportion of less distensible (collagen) to more distensible (elastin) components in both models contributes to remodeling and stiffening of the abdominal aorta.

Figure 1

Mean aortic Einc-wall stress curves in chronic sinoaortic denervated (SAD) and chronic sympathectomized (SNX) rats and their respective control (Sham and CO). Each point is the mean ± SEM.

Figure 2

Aortic immunostaining of total fibronectin, EIIIA-fibronectin, α5 and α v integrins, smooth muscle alpha actin and vimentin of sinoaortic denervated (SAD) rats and their controls (Sham). Bottom panel presents the quantification of the immunostaning expressed in percent changes over Sham-operated rats. Each bar is the mean±SEM of 5–9 rats. * P<0.05 vs. SHAM.

Figure 3

Aortic immunostaining of total fibronectin, EIIIA-fibronectin, α5 and α v integrins, smooth muscle alpha actin and vimentin of sympathectomized (SNX) rats and their controls. Bottom panel presents the quantification of the immunostaning expressed in percent changes from controls. Each bar is the mean±SEM of 5–9 rats. * P<0.05 vs. controls.

Figure 4

Electronic microscopy of elastic lamellae (A) and smooth muscle cell (B) of the aorta of sinoaortic denervated (SAD), control (data pooled from sham-operated and control of SNX rats) and sympathectomized (SNX) rats. A- The elastic lamellae are bridged by elastic fibers and are separated by muscle cells and bundles of collagen fibrils. The interlamellar space, defined as the space between consecutive lamellae, is increased on average in SAD rats. The elastic lamellae are thinner and altered in SNX rats, in which some lamellae appear broken into large elastic bundles. B- Dense bands are a prominent feature in the media of the rat aorta. In SAD rats, the percentage of cell surface occupied by dense bands is increased compared with sham-operated rats. Dense bands connected to elastic lamellae remain unchanged. In SNX rats, cell surface occupied by dense bands is well conserved. Nevertheless, the percentage of cell surface connected to the elastic lamellae is twice as high in SNX rats compared with their controls. C- Characterization of Dense bands Representative images of dense bands associated with collagen (full arrows) and elastic fibers (dashed arrows)