Fibronectin lacking the ED-B domain is a major structural component of tracheal cartilage

A bovine acellular scaffold for vocal fold reconstruction in a rat model

With a rat model of vocal fold injury, this study examined the in vivo host response to an acellular xenogeneic scaffold derived from the bovine vocal fold lamina propria, and the potential of the scaffold for constructive tissue remodeling. Bilateral wounds were created in the posterior vocal folds of 20 rats, and bovine acellular scaffolds were implanted into the wounds unilaterally, with the contralateral vocal folds as control. The rats were humanely sacrificed after 3 days, 7 days, 1 month, and 3 months, and the coronal sections of their larynges were examined histologically. Expressions of key matrix proteins including collagen I, collagen III, elastin, fibronectin, hyaluronic acid, and glycosaminoglycans (GAGs) were quantified with digital image analysis. Significant infiltration of host inflammatory cells and host fibroblasts in the scaffold implant was observed in the acute stage of wound repair (3 days and 7 days postsurgery). The mean relative densities of collagen I, collagen III, and GAGs in the implanted vocal folds were significantly higher than those in the control after 3 days, followed by gradual decreases over 3 months. Histological results showed that the scaffolds were apparently degraded by 3 months, with no fibrotic tissue formation or calcification. These preliminary findings suggested that the bovine acellular scaffold could be a potential xenograft for vocal fold regeneration.

Nonlinear optical microscopy of the bronchus

Because of frequent exposure to carcinogens, the bronchus is prone to early pathologic alterations. The assessment of these early changes is of key significance in physiological studies and disease diagnosis of the bronchus. We utilize nonlinear optical microscopy (NLOM) to image mouse bronchial tissue based on intrinsic nonlinear optical contrast. Our results show that NLOM is effective for imaging the bronchial intact microstructural components, providing quantitative information about the biomorphology and biochemistry of tissue. Our findings also display that NLOM can provide a two-photon ratiometric redox fluorometry, based on mitochondrial signals and reduced pyridine nucleotide (NADH and NADPH) and oxidized flavoproteins (Fp) signals, to assess the metabolic state of the epithelial cells and chondrocytes. It was found that NLOM can offer a sensitive tool, based on the second-harmonic signal depth-dependent decay, to obtain quantitative information on the optical property of the stroma associated with normal and diseased tissue states. Our results suggest that with the advent of the clinical portability of typical nonlinear optical endoscopy, the NLOM technique has the potential to be applied in vivo to the clinical diagnosis and monitoring of bronchial disease.

Fibronectin and its fragments increase with degeneration in the human intervertebral disc

STUDY DESIGN

This laboratory-based experiment correlates fibronectin content of intervertebral disc with a morphologic grade of degeneration.

OBJECTIVES

To correlate the fibronectin content of the anulus fibrosus and nucleus pulposus with a gross morphologic grade of disc degeneration, and to determine the molecular size of the extractable fibronectin.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration increases with age and can lead to low back pain. Fibronectin helps to organize the extracellular matrix and provides environmental cues by interaction with cell surface integrins. In other tissues, its synthesis is elevated in response to injury. Fibronectin fragments can stimulate cells to produce metalloproteases and cytokines and inhibit matrix synthesis.

METHODS

In this study, 17 anuli fibrosis and 18 nuclei pulposus from 11 spines were graded by Thompson's gross morphologic scale. Fibronectin was sequentially extracted with 4 mol/L guanidine hydrochloride and trypsin, and then quantitated by enzyme-linked immunoassay. The size of extractable fibronectin was determined by Western blot analyses.

RESULTS

The fibronectin content of the disc increased with grade and was significantly elevated between Grades 3 and 4. The percentage of extractable fibronectin varied widely, but it was more extractable from the nucleus. In both the nucleus and anulus, 30% to 40% of the extractable fibronectin existed as fragments. Many of the fragments contained functional heparin or collagen-binding sites.

CONCLUSIONS

Fibronectin is elevated in degenerated discs and frequently present as fragments. Elevated levels of fibronectin suggest that disc cells are responding to the altered environment. Fibronectin fragments resulting from normal or enhanced proteolytic activity could be a mechanism that induces the cell to degrade the matrix further.

Expression of the (V+C)- fibronectin isoform is tightly linked to the presence of a cartilaginous matrix

Fibronectin is encoded by a single gene, but heterogeneity is introduced by alternative splicing of the pre-mRNA. An unique splice variant, designated (V+C)-, which deletes nucleotides encoding the V, III-15 and I-10 segments, has been identified in articular cartilage. In this study, a ribonuclease protection assay was used to quantitate expression of the (V+C)- isoform in eight canine cartilaginous tissues and in chondrocytes cultured as monolayers or in alginate beads. The (V+C)- fibronectin isoform was detected in all cartilaginous tissues examined, ranging from a low of 11% of steady-state fibronectin mRNA in the nucleus pulposus to 71% in the rib. An age dependent increase, from 18% in the epiphyseal cartilage of a newborn to 54% in the articular cartilage of dogs over 10 months of age, was observed. The ubiquitous presence of this isoform in cartilaginous tissues and its absence in all non-cartilaginous tissues examined to date is consistent with a very strong association of the (V+C)- fibronectin isoform with the cartilaginous phenotype. Results from a ribonuclease protection assay using a probe extending into the V region from III-14 were combined with the quantitative information about (V+C)- fibronection expression to develop an over-all profile of splicing within the V region in cartilage. Monolayer culture of articular chondrocytes altered fibronectin splicing patterns. The (V+C)- isoform was rapidly lost and ED-A(+) fibronectin was induced. Three-dimensional culture in alginate beads prevented induction of ED-A(+) fibronection, but failed to sustain expression of the (V+C)- isoform. Thus, some matrix component or structure, lost in cell culture, may be essential to maintain expression of the (V+C)- isoform. The possible relationship of changing patterns of fibronectin isoforms in cultured chondrocytes to maintenance of the differentiated phenotype is discussed.