Diabetic connective tissues exhibit a deranged regulation of extracellular matrix biosynthesis. Fibronectin is shown to be increased in human dermal connective tissue by immunofluorescence, mainly at the dermoepidermal and capillary basement membranes. The rate of fibronectin biosynthesis, excretion, and incorporation in a pericellular polymeric form was investigated using genetically diabetic KK mouse skin and fibroblasts as compared to Swiss and C57BL mouse skin and fibroblasts. The rate of incorporation of [mS]methionine into proteins recovered in the culture medium or in deoxycholate and NaDodSO4 or urea extracts was investigated. The rate of incorporation in the medium and deoxycholate extracts was comparable. However, the relative rate of incorporation of the tracer in the NaDodSO4-extractable, pericellular polymeric form was increased in the diabetic KK fibroblasts both for total proteins and for fibronectin. In pulse-chase experiments, the deoxycholate-soluble and NaDodSO4-soluble fractions exhibited a precursor-product relationship. The rate of passage of fibronectin from the deoxycholate-soluble (cellular compartment) form to the NaDodSO4-soluble (pericellular polymeric) form was strongly accelerated in the diabetic fibroblast cultures. These results confirm the increased rate of synthesis of fibronectin in diabetic fibroblasts as well as its processing from the cellular compartment to the polymeric pericellular form. The increase of fibronectin in diabetic connective tissues, in the matrix as well as in the basement membranes, may play a role in the mechanism of micro-and macroangiopathies and in the perturbed permeability characteristics of the diabetic capillaries, and as a glycoprotein it may contribute to the increased periodic acid/Schiff reagent staining of diabetic capillary basement membranes.The diabetic state is accompanied by deranged regulation of the biosynthesis of extracellular matrix macromolecules (1-5). The increased thickness of capillary basement membranes is one of the histologically and electron-microscopically detectable manifestations of this perturbed matrix biosynthesis (6)(7)(8). It has been proposed that the deranged regulation of extracellular matrix biosynthesis concerns most if not all mesenchymal cells, not only those involved in basement membrane deposition (1-9). Biosynthetic experiments performed with biopsy specimens of diabetic human conjunctiva and skin, with biopsy specimens from diabetic (KK strain) mouse conjunctiva, and with diabetic (streptozotocin-induced) rat conjunctiva showed an increased rate of incorporation of [14C]proline into polymeric (insoluble) collagen (ref. 1, pp. 314-323; refs. 4-9). In these same experiments, an increased rate of incorporation of glucosamine into connective tissue glycoproteins was also seen (ref. 1, pp. 314-323; refs. 3-9). Experiments performed on genetically diabetic (KK strain) mouse skin explants showed an increased rate of incorporation of ["4C]proline into type III collagen, with no increase of total collagen...

Elastin was prepared from calf ligamentum nuchae with several methods using the following solvents for the extraction of extraneous (non-elastin) proteins : 0.1 N NaOH a t 100 "C, 88 formic acid a t 45 "C, 7001, trichloracetic acid at + 4 "C, 5 M guanidine HCl with a thiol reagent and autoclaving in water. All elastin samples contained small amounts of carbohydrate. Electron microscopy showed the presence in all samples of electron-translucent lamellae and osmiophilic uranyl-lead stainable "microfibrillar" eIements.The osmiophilic "microfibrils" decreased strongly in the elastin preparations after extractionThese solvents extracted a significant proportion of the hexose content of the elastin samples with only 6--7O/, o f their protein content. Similar results were obtained with chymotrypsin digestion although this enzyme acts less selectively than the above mentioned solvents and degrades elastin also.When 1Z5I-labelled elastin was used for extraction with 8 M urea-0.1 M mercaptoethanol the extracted glycopeptides had a significantly higher specific activity than the residual elastin. These results suggest that the microfibrillar elements are derived from or are identical with the structural glycoproteins which were extracted from elastin-rich tissues by identical proceduresThe presence of glycoprotein in varying proportions in purified elastin preparations can explain the variation of its amino acid content (ratio of polar to non-polar amino acids) with age or in certain pathological conditions (atheromatosis, emphysema) and some of its immsnochemical properties (cross reactions with structural glycoproteins). r121.Electron microscopic stiidies performed by several investigators on elastic fibers showed the presence of essentially two distinct types of structural elements : a homogenous, electron-transparent material, and a "microfibrillar" component, stainable with uranyl acetate and lead [I-51. Our recent studies indicated a chemical and immunological heterogeneity of purified elastin preparations [ 17,181 ; the structural glycoprotein fractions of aorta gave cross reactions with kappaelastin prepared from purified aorta elastin [18]. These results suggested the presence of common antigenic determinants in structural glycoprotein and elastin preparations. Therefore it appeared essential to

No abstract

No abstract