The following research article on yet another aspect of tenascin was of
special interest to me, because I had quadruple bypass surgery after a near
fatal heart attack about three years ago.
Bypass grafts usually involve the use of one artery, the mammary artery, plus
sections of the saphenous veins of the legs to bypass the clogged arteries of
the heart. Now, as we know, arteries are high pressure conduits which
generally move blood away from the heart, while veins are low presssure
conduits which return blood to the heart, so that the wisdom of using veins
as bypasses is sometimes questioned. This article implies that the higher
pressures imposed on bypass veins which are being used to replace arteries
leads to expression of TN-C and seems to remodel these veins to become more
like arteries. Naturally, that makes me feel a lot happier about my own
bypass job!
Yet another interesting aspect to the tenascin family of proteins which I
wrote about earlier today!
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Wallner K, Li C, Fishbein MC, Shah PK & Sharifi BG Arterialization of human
vein grafts is associated with tenascin-C expression. J Am Coll Cardiol
1999 Sep; 34(3): 871-5
OBJECTIVES: This study was performed to test the hypothesis that tenascin-C
(TN-C), an extracellular matrix (ECM) protein with counteradhesive
chemotactic and vascular growth-promoting effects, is expressed in
"arterialized" human saphenous vein grafts (SVGs).
BACKGROUND: Tenascin-C is expressed in the vessel wall after vascular injury
in the experimental model, where it has been implicated in the formation of
neointima. Overexpression of TN-C has also been implicated in the development
and progression of pulmonary hypertension. Saphenous vein grafts are exposed
to hemodynamic stress when interposed in the arterial circulation and
mechanical stress upregulates expression of TN-C, whereas stress-relaxation
suppresses its synthesis. We hypothesized that the hemodynamic stress of
increased arterial pressure could also induce TN-C expression in SVG.
METHODS: We examined the expression of TN-C protein and mRNA in normal vein
and "arterialized" human SVG using immunohistochemistry and in situ
hybridization, respectively.
RESULTS: TN-C protein was not detected in control human saphenous veins;
however, it was uniformly and strongly expressed in the adventitia and media
of patent human vein grafts, with minimal or no expression in the neointima
(n = 27, 100%). In situ hybridization showed that TN-C mRNA was not detected
in the neointima, but was strongly upregulated in the adventitia and media,
corroborating immunostaining data (n = 10, 100%). Unlike patent SVG, TN-C was
not expressed in the adventitia of occluded grafts, except for a low level of
expression around the newly formed vessels in neointima (n = 5, 100%). Smooth
muscle cell-specific staining demonstrated that the lack of expression of
TN-C in occluded vein grafts is not due to the lack of presence of smooth
muscle cells in the graft.
CONCLUSIONS: These findings suggest that placement of a venous graft in the
arterial system leads to expression of TN-C, which may in turn facilitate
graft remodeling. Conversely, loss of flow and intravascular pressure,
associated with vein graft occlusion, is accompanied by disappearance of TN-C
expression.
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Dr Mel C Siff
Denver, USA
http://www.egroups.com/group/supertraining
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