Abnormal tissue repair in Glanzmann's thrombasthenia

Comparative studies of collagen lattice contraction utilizing a normal and a transformed cell line

Differences between the behavior of cultured rat skin fibroblasts and that of a line of transformed rat sarcoma cells incorporated into a polymerized collagen lattice were examined. Fibroblast-populated collagen lattices (FPCL) were manufactured. Within 24 to 48 hr after manufacture, both cell lines reduced lattice size by a process known as lattice contraction. Contraction occurred more rapidly in both cell lines when the media were supplemented with 25% serum rather than the usual concentration of 10% serum. Similar growth patterns were observed with transformed cells within collagen lattices and on plastic surfaces. Normal rat fibroblasts were found to contract lattices faster than transformed cells. At the end of a 2-week period, the final contracted size of the transformed cell lattice was the same as that of normal cell lattices. The cellular density of transformed cells within the FPCL was eight times greater than that of FPCL made with normal rat cells. Normal rat fibroblasts elongated and flattened more, and organized the collagen matrix to a greater degree, than did transformed cells. In this instance, therefore, lattice contraction was shown to be linked more to the process of fibroblast elongation and collagen fiber organization than to cell number or density.

Reduced surface expression and binding of fibronectin by thrombin-stimulated thrombasthenic platelets

Thrombin stimulation results in increased surface expression of endogeneous fibronectin and binding of plasma fibronectin to human platelets. Platelets of patients with Glanzmann's thrombasthenia, a bleeding disorder, exhibit reduced thrombin-induced platelet aggregation, little or no clot retraction, and abnormal platelet spreading on glass surfaces. Thrombin stimulation of patient platelets from four thrombasthenic kindreds resulted in little fibronectin binding. Nevertheless, thrombin did induce serotonin secretion from these cells, indicating that stimulation was occurring. Thrombasthenic platelets did not inhibit thrombin-stimulated fibronectin binding to coincubated normal cells, suggesting that their defect was not due to the presence of a soluble inhibitor of fibronectin binding. Thrombin-stimulated afibrinogenemic platelets bound similar quantities of fibronectin to normal cells, indicating that the thrombasthenic deficit is not secondary to reduced fibrinogen content or binding. The thrombasthenic cells had an endogenous fibronectin content of 2.9 +/- 0.7 micrograms/10(9) platelets, whereas cells simultaneously prepared from five normal individuals contained 1.8 +/- 0.7 micrograms/10(9) platelets, a statistically insignificant difference. Nevertheless, thrombin stimulation did not increase expression of endogeneous fibronectin antigen on the surface of the thrombasthenic platelets as judged by immunofluorescence. These defects in platelet fibronectin binding and surface expression may account for some of the manifestations of Glanzmann's thrombasthenia.

Demonstration of fibronectin in normal and injured aorta by an indirect immunoperoxidase technique

The presence and localization of fibronectin in normal and mechanically injured aorta in rabbits was studied using an indirect immunoperoxidase technique on tissue specimens fixed in formaldehyde, embedded in paraffin and pretreated with pepsin. The effect on staining quality of treatment with testicular hyaluronidase prior to immunoperoxidase staining was also examined. In the intima from normal aorta fibronectin was present in the subendothelial basal layer, along the internal and external elastic laminae, around and between the smooth muscle cells of the media and along the collagen and elastic fibres in the adventitia. Sixteen days after a single mechanical dilatation of the descending thoracic aorta all animals developed gross atherosclerotic-like changes. Microscopic examination revealed prominent neo-intimal hyperplasia with subendothelial, cushion-like thickenings but no medial or adventitial alterations. Fibronectin, in increased amounts, was found between and around the endothelial cells and in the subendothelial thickenings between the proliferating smooth muscle cells in relation to the fine, thin elastic and argyrophilic fibres. In the media and adventitia the amount and distribution of fibronectin was indistinguishable from uninjured control aortas. Treatment with testicular hyaluronidase before immunoperoxidase staining resulted in a higher staining resolution in normal and injured aorta. The conspicuous observation in the present study is that fibronectin exclusively accumulates in areas of tissue repair. The origins and functions of fibronectin during tissue injury and repair are discussed.