Changes in lung hyaluronidase activity associated with lung growth, injury and repair

Hyaluronidase expression in human skin fibroblasts

Hyaluronidase activity has been detected for the first time in normal human dermal fibroblasts (HS27), as well as in fetal fibroblasts (FF24) and fibrosarcoma cells (HT1080). Enzymatic activity was secreted predominantly into the culture media, with minor amounts of activity associated with the cell layer. In both classes of fibroblasts, hyaluronidase expression was confluence-dependent, with highest levels of activity occurring in quiescent, post-confluent cells. However, in the fibrosarcoma cell cultures, expression was independent of cell density. The enzyme had a pH optimum of 3.7 and on hyaluronan substrate gel zymography, activity occurred as a single band corresponding to an approximate molecular size of 57 kDa. The enzyme could be immunoprecipitated in its entirety using monoclonal antibodies raised against Hyal-1, human plasma hyaluronidase. PCR confirmed that fibroblast hyaluronidase was identical to Hyal-1. The conclusion by previous investigators using earlier technologies that fibroblasts do not contain hyaluronidase activity should be reevaluated.

Lung hyaluronan and water content in preterm and term rabbit pups exposed to oxygen or air

Rabbit pups were delivered by cesarean section 1 or 2 d before term, or vaginally around term, and then reared in room air or exposed to intermittent or continuous hyperoxia (> 85%) for up to 9 d. Pups were killed at different ages, and lung hyaluronan (HA; microgram/g of dry lung weight) and lung water content, measured as wet/dry lung weight, were determined. Compared with the day of birth, the lung HA concentration did not change significantly on succeeding days in pups kept in air delivered 2 d (-2 d) or 1 d (-1 d) before term, whereas the water content decreased significantly. Continuous exposure to hyperoxia resulted in a significantly raised lung HA concentration 6 d postterm in both -2 d and -1 d pups, and intermittent exposure to hyperoxia resulted in a significantly raised HA concentration 6 d postterm in -1 d pups, compared with the groups exposed to room air. These increases were accompanied by significantly elevated wet/dry lung weight ratios. Microscopic examination revealed significantly increased HA staining scores in alveoli, arterioles, and bronchioli in both hyperoxia-exposed groups of -2 d pups 6 d postterm, and nonsignificantly higher scores in -1 d and vaginally delivered pups of comparable age, compared with the scores at birth. The results indicate that oxygen exposure neonatally may result in an increase in lung HA accompanied by an increase in lung water content. The increase in lung HA concentration in our study may be an effect of oxygen free radicals or of oxygen-induced stimulation of inflammatory mediators.

Expression of hyaluronan in normal and dysplastic bronchial epithelium and in squamous cell carcinoma of the lung

A series of 85 lung/bronchial tissue samples from 76 patients consisting of normal, metaplastic and dysplastic epithelium and different types of lung carcinomas were analyzed for the distribution of hyaluronan (HA), using a biotinylated hyaluronan binding complex as an HA-specific probe. The normal pseudo-stratified columnar bronchial epithelium was either negative for HA or displayed a weak staining around the basal cells. The epithelia of serous and mucous bronchial glands were HA negative whereas the submucosal connective tissue was strongly positive. In metaplastic, dysplastic and carcinoma in situ lesions the whole epithelium from basal to uppermost cells expressed HA on plasma membranes. Epithelial HA was also found in squamous cell carcinomas, but not in adenocarcinomas, carcinoid tumors or small cell carcinomas of the lung. Whereas epithelial HA was present in all lesions of the squamous cell type, the staining intensity displayed great local variability in 50% of the cases with severe dysplasia, carcinoma in situ and squamous cell carcinomas. In squamous cell carcinomas, such an irregular staining pattern was significantly associated with poor differentiation. Our results indicate that the expression of HA in different bronchial lesions and lung tumors is restricted to those showing squamous cell differentiation, being absent from other types of lung carcinomas. The increase of HA depleted areas in poorly differentiated squamous cell carcinomas emphasizes the important role of HA in tumor differentiation. HA on carcinoma cell surface may influence tumor growth and metastatic behavior.

Alterations in nonhuman primate (M. nemestrina) lung proteoglycans during normal development and acute hyaline membrane disease

Proteoglycans (PGs) and lung hyaluronan (HA) are important components of the lung matrix both during normal development and in response to injury. We combined morphologic and biochemical techniques to study changes in PG and HA in a developmental series of Macaca nemestrina lungs ranging from 62% gestation to 3 mo post-term (n = 16), in adult lungs (n = 6), and from prematurely delivered, mechanically ventilated monkeys with hyaline membrane disease (HMD) (n = 7). Three groups of cuprolinic blue-positive (CuB) precipitates, identified by size, location, and susceptibility to enzyme digestion were found in lungs from all animals. Immature alveolar interstitium is characterized by loosely woven collagen bundles and an abundance of large (100 to 200 nm) stained filaments representing chondroitin sulfate proteoglycans (CSPGs). As maturation proceeds, the interstitial matrix appears increasingly organized, with large collagen bundles associated with 20 nm CuB-stained deposits (dermatan sulfate proteoglycans, DSPGs), and fewer large CSPGs. Fetal alveolar basement membrane contains CuB-stained heparin sulfate proteoglycans (HSPGs) (10 nm) scattered throughout. Lung matrix from animals with HMD appeared to have a disruption of the collagen-DSPG relationship, in addition to an enrichment in large CSPG. Complementary biochemical analysis of lung PGs and HA was done. Minced lung parenchyma was cultured with [3H]-glucosamine and [35S]-sulfate for 24 h; PGs and HA were extracted and analyzed. While PG synthesis during development tended to be highest at 80% gestation, animals with HMD showed greatly increased synthesis, approximately 2.5-fold higher than comparable fetal animals. In the developmental series, [3H]-glucosamine incorporation into HA was maximal at term, falling abruptly thereafter. HMD animals, however, showed a 2.3-fold increase over controls in net HA synthesis. Extracted PGs were separated according to buoyant density by dissociative cesium chloride density gradient ultracentrifugation. Two peaks of 35S-labeled PGs were separated from each density gradient fraction by chromatography on Sepharose CL-4B. A large CSPG was the principal PG eluting in the voiding volume, while the second broad peak (K(av) = 0.42) contained a mixed population of CSPG, DSPG, and HSPGs, the proportions of which varied with age. Both ultrastructural and biochemical analyses indicate that production of a large, high buoyant density CSPG predominates in fetal lung tissue, and diminishes with developmental age. Synthesis of large CSPG is greatly increased in lung explants from prematurely delivered animals with HMD.(ABSTRACT TRUNCATED AT 400 WORDS)

Pulmonary air-space enlargement induced by intratracheal instillment of hyaluronidase and concomitant exposure to 60% oxygen

Although emphysema is generally characterized by damage to pulmonary elastic fibers, the causes of such injury appear to be complex and are not entirely explained by a singular imbalance between elastases and their inhibitors. Other factors could compromise elastic fiber integrity. To test the validity of this argument, hamsters were instilled intratracheally with a nonelastolytic enzyme, hyaluronidase (which reduces lung hexuronic acid content by 21% after 24 h), then exposed to an otherwise nontoxic concentration of oxygen (60%) for 4 days. Additional groups were given (1) hyaluronidase and room air, (2) saline and 60% oxygen, and (3) saline and room air. Treatment with both hyaluronidase and 60% oxygen resulted in a significant increase in air-space enlargement at 4 days (67.1 vs. 57.9 microns for saline/room air controls; p < .05), which was accompanied by only minimal inflammatory changes, as determined by both light microscopy and lavage cytology. Animals receiving either hyaluronidase or 60% oxygen alone showed no significant increases in air-space size compared to those given saline and exposed to room air. While the mechanisms responsible for these results are unclear, the marked increase in radiolabeling of lung elastin cross-links (desmosine and isodesmosine) in animals receiving both hyaluronidase and 60% oxygen (429 vs. 168 cpm/g dry lung for saline/room air controls; p < .05), as well as a significant decrease in total lung desmosine and isodesmosine (32.5 vs. 37.7 micrograms/lung for saline/room air controls; p < .05), suggests that elastic fiber damage is a potential factor. Moreover, only those animals receiving both hyaluronidase and 60% oxygen showed a significant rise in cell-free elastase activity in lavage fluids compared to saline/room air controls (83.3 vs. 48.3 ng; p < .05). On the basis of these findings, it is concluded that while elastic fiber damage may be a common pathway in emphysema, the factors that initiate the disease may be more varied than previously suspected and not always related to the balance between elastases and their inhibitors.

An ELISA-like assay for hyaluronidase and hyaluronidase inhibitors

Hyaluronic acid (HA) is a prominent molecule in the extracellular matrix and is enriched whenever there is rapid tissue proliferation, regeneration and repair. HA is degraded in part by hyaluronidases (HA'ases) that are not well characterized. We have developed a novel ELISA-like rapid assay for HA'ases and their inhibitors. The assay is based on a high affinity biotinylated HA-binding peptide derived from tryptic digests of proteoglycan core protein of bovine nasal cartilage and the avidin-biotin reaction. HA-coated plates were incubated with serial dilutions of Streptomyces HA'ase, and the undegraded HA was measured. This established a standard curve for HA'ase activity against which all unknown enzyme samples were compared. The assay is easily modified to also serve a measure of HA'ase inhibitors. For detection of inhibitors, aliquots of sample were preincubated with a known activity of HA'ase and inhibition of HA degradation by the mixture was measured. We have used this assay to document the presence of potent HA'ase inhibitors in fetal calf sera. These techniques will aid in the purification and characterization of Ha'ases and their inhibitors.

Temporal and spatial differences in glycosaminoglycan synthesis by fetal lung fibroblasts

In studies of the ontogeny of fibroblast-epithelial interactions during late fetal lung rat lung development, we have identified two subpopulations of fibroblasts which differed in their ability to promote epithelial cell proliferation or differentiation. As glycosaminoglycans (GAGs) have been implicated in the regulation of these processes we have tested whether the two fibroblast populations synthesize different GAGs and whether the GAG pattern changes with development. Fibroblasts incorporate more [3H]glucosamine and Na2 35SO4 into GAGs than epithelial cells. Both cell types deposited a significant amount of newly synthesized GAGs in the cell-matrix layer. GAGs were lost faster from the cell-matrix layer of fibroblasts (t1/2 = 12 h) than from that of epithelial cells (t1/2 = 48 h). Total GAG synthesis by fibroblasts did not change with advancing gestation, but synthesis of sulfated GAGs by epithelial cells declined with advancing gestation. Independent of gestational age epithelial cells synthesized predominantly heparan sulfate. Depending on their proximity to the epithelium, fibroblasts differed in their production of GAGs. Fibroblasts in close proximity to the epithelium mainly produced and secreted hyaluronan. More distant fibroblasts, from the pseudoglandular stage of lung development synthesized primarily heparan sulfate and chondroitin sulfate. This same population of fibroblasts from the canalicular stage of lung development, produced more hyaluronan. As the shift to hyaluronan occurs with the thinning of the alveolar septal wall, this finding suggests that developmentally regulated GAG production by fibroblasts may facilitate epithelial-fibroblast interaction, thus influencing fetal lung growth and differentiation.

Hyaluronidase activity of rabbit skin wound granulation tissue fibroblasts

The objective of this work was to identify and compare hyaluronidase activities of normal dermal and dermal wound granulation tissue fibroblasts. Direct evidence of the fibroblast as a source of tissue hyaluronidase was obtained. Fourth passage rabbit dermal fibroblasts were harvested on culture days 4, 8, 14, 18, and 22. Hyaluronidase activity and [35S]-sulfate- or [3H]-glucosamine-labeled glycosaminoglycans (GAGs) were monitored. Hyaluronidase assays were performed on medium and cellular fractions at the designated intervals. Enzyme activity of cellular fractions for both normal dermal and 14-day post-wound granulation tissue fibroblasts increased progressively through culture day 8. Thereafter (days 14-22), an eight-fold drop in cellular activity was coupled with cell death and emergence of hyaluronidase activity in medium fractions. Marked increases in degradation of secreted matrix components were concurrent with lysis-induced release of hyaluronidase. In this culture system, hyaluronidase activity was confined exclusively to cellular fractions and was released into the medium only under non-physiological conditions conducive to cellular death and lysis. Accordingly, this work suggests that previously reported skin wound hyaluronidases may be of fibroblastic origin and that susceptible GAGs are not degraded extracellularly, but, rather, must be internalized as a prerequisite to depolymerization.

A model for the role of hyaluronic acid and fibrin in the early events during the inflammatory response and wound healing

A model is presented outlining the molecular and cellular events that occur during the early stages of the wound healing process. The underlying theme is that there is a specific binding interaction between fibrin, the major clot protein, and hyaluronic acid (HA), a constituent of the wound extracellular matrix. This binding interaction, which could also be stabilized by other cross-linking components, provides the driving force to organize a three-dimensional HA matrix attached to and interdigitated with the initial fibrin matrix. The HA-fibrin matrix plays a major role in the subsequent tissue reconstruction processes. We suggest that HA and fibrin have both structural and regulatory functions at different times during the wound healing process. The concentration of HA in blood and in the initial clot is very low. This is consistent with the proposed interaction between HA and fibrin(ogen), which could interfere with either fibrinogen activation or fibrin assembly and cross-linking. We propose that an activator (e.g. derived from a plasma precursor, platelets or surrounding cells) is produced during the clotting reaction and then stimulates one or more blood cell types to synthesize and secrete HA into the fibrin matrix of the clot. We predict that HA controls the stability of the matrix by regulating the degradation of fibrin. The new HA-fibrin matrix increases or stabilizes the volume and porosity of the clot and then serves as a physical support, a scaffold through which cells trapped in the clot or cells infiltrating from the peripheral edge of the wound can migrate. The HA-fibrin matrix also actively stimulates or induces cell motility and activates and regulates many functions of blood cells, which are involved in the inflammatory response, including phagocytosis and chemotaxis. The secondary HA-fibrin matrix itself is then modified as cells continue to migrate into the wound, secreting hyaluronidase and plasminogen activator to degrade the HA and fibrin. At the same time these cells secrete collagen and glycosaminoglycans to make a more differentiated matrix. The degradation products derived from both fibrin and HA are, in turn, important regulatory molecules which control cellular functions involved in the inflammatory response and new blood vessel formation in the healing wound. The proposed model generates a number of testable experimental predictions.

Cytochemical visualization of anions in collagenous and elastic fiber-associated connective tissue matrix in neonatal and adult rat lungs using iron-containing stains

The cytochemical reactivity of pulmonary connective tissue matrix component in neonatal and adult rat was evaluated using high iron diamine (HID) to detect sulfate ester end groups and dialyzed iron (DI) to detect sulfated and carboxylated end groups of complex carbohydrates, including glycoproteins and glycosaminoglycans at the ultrastructural level. The HID reaction product, in the form of discrete 5-12 nm silver particles following appropriate intensification with thiocarbohydrazide-silver proteinate, was found associated with cell surfaces, the elastin component of elastic fibers, and at regular intervals along the length of collagen fibers in large airways and deep lung interstitium. Staining was similar in adult and neonatal rats, except in areas where connective tissues were presumably still rapidly developing in the neonatal animals. Here large gaps or spaces containing filamentous structures were observed between collagen and elastic fibers. The distribution of DI-reactive sites was similar to that seen with HID with the exception of elastic fibers in which only the microfibrillar portion stained. The collagen-associated reaction was not regularly disposed like that stained with HID, but rather it formed a tight continuous density around the fiber. These results indicated the presence and location of glycoproteins and glycosaminoglycans in connective tissue ground substance regions prior to the full development of elastic and collagenous elements in neonatal pulmonary airways and parenchyma. They also demonstrate cytochemically the presence of a sulfate ester-containing complex sugar found associated with the elastin component of elastic fibers in the lung.