Kp. Dingemans et al., Extracellular matrix of the human aortic media: An ultrastructural histochemical and immunohistochemical study of the adult aortic media, ANAT REC, 258(1), 2000, pp. 1-14
Aortic distensability is the key to normal aortic function and relates to t
he lamellar unit in the media. However, the organization of the extracellul
ar matrix components in these lamellar units, which are largely responsible
for the distensability, is insufficiently known, especially in the human.
We therefore performed a detailed ultrastructural analysis of these compone
nts.
Thoracic aortas of 56 individuals (age 45-74 years), none of whom suffered
from aortic disease, were studied by immunoelectron microscopy of elastin,
collagen types I, III, IV, V, and VI, fibronectin, and fibrillin-1, and by
ultrastructural histochemistry of proteoglycans, which were further charact
erized by enzymatic digestion.
The elastic lamellae were closely associated with thick collagen fibers con
taining types I, III, and V collagen. Between these collagen fibers, numero
us complex, circumferentially oriented streaks of elastin protruded from th
e lamellae. In contrast to what is usually reported in the aortas of experi
mental animals, the smooth muscle cells preferentially adhered to these ill
-defined streaks rather than directly to the solid lamellae. Fibrillin-1- a
nd type VI collagen-containing bundles of micro fibrils (oxytalan fibers) w
ere also involved in the smooth muscle cell-elastin contact. The smooth mus
cle cells were invested by basal lamina-like layers connecting them to each
other as well as to the oxytalan fibers. Unexpectedly, these layers were a
bundantly labeled by anti-fibronectin, whereas type IV collagen, a specific
basement membrane component, was mainly found in larger, flocculent deposi
ts. The proteoglycans present were collagen-associated dermatan sulfate pro
teoglycan, cell-associated heparan sulfate proteoglycan, and interstitial c
hondroitin sulfate proteoglycan.
Our observations demonstrate that the extracellular matrix in the human aor
ta is extremely complex and therefore differs from most descriptions based
on experimental animals. They serve as reference for future studies on aort
ic diseases, such as aneurysmas and dissections. Anat Rec 258:1-14, 2000. (
C) 2000 Wiley-Liss, Inc.