Extracellular matrix incorporation of normal and nem-alkylated
plasma fibronectin: liver and spleen deposition.
Rebres, Robert A., Paula J. McKeown-Longo, Peter A. Vincent, Eshin
Cho, and Thomas M. Saba.
Department of Physiology and Cell Biology, Neil Hellman Medical
Research Building, Albany Medical College, Albany, New York 12208
APStracts 2:0121G, 1995.
The incorporation of plasma fibronectin (pFn) into the extracellular
matrix (ECM) is believed to influence tissue integrity, wound repair,
and vascular permeability. In vitro, matrix assembly of Fn requires
the binding of soluble Fn to cell-associated matrix assembly sites.
Alkylation of human pFn with N-ethyl-maleimide (NEM) prevents the
initial binding of Fn to matrix assembly sites as well as its in
vitro incorporation into the ECM as reflected by detergent insoluble
125I-Fn (Pool II-Fn). We determined the kinetics of Fn matrix
incorporation in tissue and if NEM treatment of rat pFn (NEM-RFn)
would limit its in vivo incorporation into ECM by analysis of Pool I
[deoxycholate (DOC) soluble] and Pool II (DOC insoluble) 125I-Fn in
tissues after its i.v. injection into rats. After i.v. injection, the
tissue incorporation of normal rat 125I-pFn was especially intense in
the liver and spleen, in agreement with the large amount of
endogenous Fn detected in the matrices of these organs. Tissue
deposition of the plasma-derived 125I-RFn in the liver and spleen
peaked by 4 h with significant (p<0.01) loss over 24 h,
indicating turnover of matrix Fn. Tissue localization of normal 125I
-RFn in the liver, lung, spleen, heart and intestine was greater
(p<0.05) than 125I-NEM-RFn at 4 h. Normal human Fn (HFn), but
not NEM-alkylated HFn, incorporated into tissues and co-localized
with endogenous Fn in the matrix. To identify the cells mediating the
intense incorpora tion of pFn into the liver ECM, we compared matrix
assembly of 125I-HFn by cultured fibroblasts, hepatocytes, and
hepatic Kupffer cells. With fibroblasts, 125I-HFn in Pool I reached
steady state by 3 h, while 125I-HFn in Pool II exceeded Pool I by 6 h
and continued to increase over 24 h. With hepatocytes, Pool I 125I
-HFn reached steady state by 1 h and a progressive increase
(p<0.05) of 125I-HFn in Pool II was observed over 24 h. Kupffer
cells were not able to incorporate significant amounts of 125I-HFn
into matrix. NEM-treated HFn displayed limited incorporation into ECM
by both fibroblast and hepatocyte cultures. These novel observations
suggest that the interaction of soluble pFn with matrix assembly
sites is necessary to its in vivo incorporation into the ECM.
Received 16 November 1994; accepted in final form 7 June 1995.
APS Manuscript Number G452-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.