The role of epithelium and mesenchyme in the production of a collagenolytic enzyme and a hyaluronidase in the anuran tadpole

Expression of matrix metalloproteinase genes in regressing or remodeling organs during amphibian metamorphosis

Several matrix metalloproteinases (MMP) are induced by thyroid hormone (TH) during the climax of amphibian metamorphosis and play a pivotal role in the remodeling of the intestine and the regressing tail and gills by degrading the extracellular matrix (ECM). We compared MMP gene expression levels precisely by quantitative real-time reverse transcription-polymerase chain reaction. The expression of MMP genes increases prominently at Nieuwkoop and Faber (NF) stages 60, 60-61 and 62 in the intestine, gills and tail, respectively, when the drastic morphological changes start in each organ. Gene expression analysis in the TH-treated tadpoles and cell line revealed that MMP mRNAs are upregulated in response to TH quickly within several hours to low levels and then increase in a day to high levels. All TH-induced MMP genes have TH response elements (TREs). The presence of high affinity TREs in MMP genes correlates with early TH-induction. Based on these results, we propose that TH stimulates the transcription of MMP genes through TREs within several hours to low levels and then brings about the main increase of mRNAs by TH-induced transcriptional factors, including TH receptor beta, in a cell type-specific transcriptional environment.

Tadpole skin dies autonomously in response to thyroid hormone at metamorphosis

Transgenic tadpoles that express a dominant negative thyroid hormone (TH) receptor specifically in their skin undergo normal metamorphosis, with one exception: they retain a larval epidermis over the developing adult epithelium. TH-induced death of the tadpole epidermis is inhibited by the dominant negative TH receptor whereas the TH-induced response of the neighboring fibroblasts and the cells that form the adult skin occur normally. Therefore death of the tadpole skin is a direct and cell autonomous target of TH, and its protection has no detectable influence on TH-induced changes of other cell types.

Matrix metalloproteinases mediate the dismantling of mesenchymal structures in the tadpole tail during thyroid hormone-induced tail resorption

It has been suggested that a family of tissue remodelling enzymes called matrix metalloproteinases (MMPs) play a causal role in the process of tail resorption during thyroid hormone-induced metamorphosis of the anuran tadpole; however, this hypothesis has never been directly substantiated. We cloned two new Xenopus MMPs, gelatinase A (MMP-2) and MT3-MMP (MMP-16), and the MMP inhibitor TIMP-2. These clones were used along with several others to perform a comprehensive expression study. We show that all MMPs and TIMP-2 are dramatically induced in the resorbing tail during spontaneous metamorphosis and are spatially coexpressed, primarily in the remodelling mesenchymal tissues. By Northern blotting, we show that all the examined MMPs/TIMP-2 are also induced by treatment of organ-cultured tails with thyroid hormone (T(3)). Using the organ culture model, we provide the first direct evidence that MMPs are required for T(3)-induced tail resorption by showing that a synthetic inhibitor of MMP activity/expression can specifically retard the resorption process. By gelatin zymography, we also show T(3) induction of a fifth MMP, preliminarily identified as gelatinase B (GelB; MMP-9). Moreover, T(3) not only induces MMP/TIMP expression but also MMP activation, and we provide evidence that TIMP-2 participates in the latter process. These findings suggest that MMPs and TIMPs act in concert to effect the dismantling of mesenchymal structures during T(3)-induced metamorphic tadpole tail resorption.

The expression pattern of thyroid hormone response genes in the tadpole tail identifies multiple resorption programs

Expression of genes up-regulated by thyroid hormone (TH) during amphibian tail resorption was localized by in situ hybridization. The constitutive thyroid hormone receptor (TRalpha) and its heterodimeric partners (RXRalpha and RXRbeta) are expressed ubiquitously in the resorbing tail. A group of early response genes, including those encoding transcription factors, are expressed at greatest levels within tissues whose cells attempt to grow and differentiate in the tail, but eventually succumb to the resorption program. The TH-inducible TR isoform, TRbeta, is expressed ubiquitously in the tail, but especially high in fibroblasts. Similarly, a group of delayed response genes including two proteolytic enzymes that appear to execute the tail resorption program, is expressed specifically in fibroblasts that line and surround the notochord and lie beneath the epidermal lamella (subepidermal fibroblasts). During active tail resorption these fibroblasts invade their neighboring epidermal and notochord lamellae as part of the resorption process. Expression analysis implicates the single layer of invasive subepidermal fibroblasts as crucial in tail resorption. Stromelysin-3 is up-regulated by TH with early kinetics, and is expressed most actively in fibroblasts within the tail fins. None of the proteases are expressed in the tadpole epidermis, which will be replaced entirely during metamorphosis. While very few TH response genes are expressed in tadpole muscle, many are activated in fibroblasts that surround muscle and could induce muscle cell death by proteolysis of the extracellular matrix. These distinct localization patterns suggest that the common fate of all cell types within the tail is the result of multiple genetic programs.

Proliferating oral epithelial cells in culture are capable of both extracellular and intracellular degradation of interstitial collagen

The potential of epithelial cells to degrade interstitial collagen was studied by culturing human masticatory mucosa on decalcified dentin matrix. Morphological changes were observed in the underlying collagen substratum and in the connective tissue of the explant. Degradation of the substratum was initiated two days after the first contact with epithelial cells exhibiting basal cell markers. Electron microscopic studies confirmed extensive collagen degradation in the vicinity of these cells. No collagen degradation was observed underneath the connective tissue portion of the explant. Experiments in which the explant was partially separated from the underlying substratum by a filter further showed that connective tissue was apparently not involved in the collagen degradation by the epithelial cells. Lysis of connective tissue of the explant was observed in association with epithelial cells that showed a disrupted basal lamina and release of vesicular material from the exposed cell membrane. Collagen fibers were visible inside some epithelial cells suggesting intracellular collagenolysis. Primary cultures of human gingival epithelial cells and porcine periodontal ligament epithelial cells (epithelial cell rests of Malassez) that expressed similar basal cell cytokeratins as the active cells of the mucosal explants secreted collagenase, gelatinase and TIMP to the culture medium. They also contained acid collagenolytic proteinases. When cultured on a porous polycarbonate membrane the epithelial cells secreted collagenolytic enzymes from the pores at cell membrane sites lacking basal lamina. These results provide evidence that proliferating basal epithelial cells have a strong capacity for collagen degradation. It seems that the absence of basement membrane is the signal for these cells to secrete matrix degrading enzymes.

Ability of various injuries to promote resorption of denervated, nerve independent regenerates of adult newts

Young blastemas of the newt resorb if the limb is denervated, and are thus called "nerve dependent". Late bud and later stage regenerates are termed "nerve independent" because, while denervation inhibits their growth, they proceed through differentiation to form a normally patterned regenerate. Schotté and Liversage ('59) found that reamputation of a denervated nerve independent regenerate causes it to resorb. The present study asked whether injuries of varying severity are equally effective at promoting resorption. Newt forelimbs were amputated through the mid-radius/ulna. At nerve independent stages, the regenerates were denervated and injured in one of a variety of ways, then monitored for signs of resorption. Reamputation of the tip or incisions which created large gaps in the wound epidermis promoted resorption in 77-90% of the cases. Histology showed that the tissue removed by tip reamputation was a small proportion of the entire regenerate, suggesting that blastema resorption is not determined simply by the number of cells directly affected by the injury. Pin prick injuries, which created small disruptions of the wound epidermis, never caused resorption. Devascularization, caused by severing the brachial artery, promoted resorption in 17% of cases. These results are not consistent with the hypothesis that avascularity is a major causative factor in nerve dependence.

An epidermal factor which induces thyroid hormone-dependent regression of mesenchymal tissues of the tadpole tail

Explants of tadpole tail skin secreted a factor which induces the thyroid hormone-dependent regression of the tail mesenchyme. The activity of the factor was not sensitive to digestion with trypsin or pronase. Heating at 120 degrees C but not at 100 degrees C for 20 min destroyed the activity. The factor came out gradually through a dialysis membrane. The factor was retarded on a Sephadex G-10 column and eluted with water after the salts fraction. We suggest that the active principle is a non-proteinaceous substance with a low molecular weight.

Adult human keratinocytes migrating over nonviable dermal collagen produce collagenolytic enzymes that degrade type I and type IV collagen

Human adult keratinocytes migrating on a nonviable dermal substrate in cultures without fibroblasts induce thinning and degradation of the collagen substrate beneath the migrating epithelium. Further, unconcentrated conditioned medium from the cultures exhibit collagenolytic activity against both type I and type IV collagen which is inhibited by EDTA but not by phenylmethylsulfonyl fluoride or N-ethylmaleimide. Since the migrating epithelium and dermal substrate do not contain fibroblasts, this study shows that migratory keratinocytes in contact with interstitial collagen are capable of producing collagenases against type I and type IV collagen. Moreover, migratory keratinocytes appear to be similar to highly metastatic cells in their ability to degrade basement membrane collagen.

Retinoic acid stimulates degradation of interstitial collagen fibrils by rat mucosal keratinocytes in vitro

A large body of evidence suggests that retinoids modulate the phenotypic expression of epithelial cells of skin and mucous membranes. The purpose of this study was to investigate the effect of retinoic acid on keratinocyte-mediated collagen breakdown. Keratinocytes derived from the ventral surfaces of the tongues of 4-6 week-old male Wistar rats were established in culture under conditions which are restrictive to growth of fibroblasts, and they were eventually cloned by limiting dilution. The cells were seeded (100,000 cells/cm2) in dishes coated with 3H-labeled, reconstituted type I collagen fibrils and incubated in serum-free medium over a 3-5 day period. Dissolution of the collagen fibrils was monitored by the release of radioactivity to the culture medium. Unstimulated cells metabolized the collagen rather slowly, but addition of retinoic acid in concentrations from 10(-6)M to 10(-8)M resulted in marked acceleration of the degradative process, with complete solubilization of the collagen fibrils in four or five days. The effect of 10(-6)M retinoic acid was of the same order of magnitude as that obtained by addition of a proteolytic activating system either in the form of plasmin or of plasminogen, which is converted to catalytic plasmin by endogenous activators. The effects of retinoic acid and plasminogen/plasmin, however, were not additive. Keratinocytes rendered vitamin A-deficient by cultivation in sera from deficient rats were clearly less effective in degrading the collagen substrate than were "sufficient" cells. Addition of retinoic acid (10(-7)M) enhanced collagen breakdown in both sets of cultures and partially restored the collagenolytic activity of the deficient cells.

The wound healing process

A dramatic sequence of events accounts for the repair of cutaneous wounds, be they of a surgical or accidental nature. Although our understanding of this process is increasing at a rapid rate, unanswered questions remain. Undoubtedly, as time goes on and knowledge increases, we will gain further insight into the intricacies of the wound healing phenomenon. Physicians, particularly those who perform surgical procedures of the skin, should be familiar with the biologic precepts implicit in the wound healing process. The understanding of these principles will ultimately lead to a more rational approach to wound management, which does not run counter to a meticulously conceived script.

Applications and failure modes of percutaneous devices: a review

Percutaneous devices (PD) are designed to serve a variety of clinical and biomedical research purposes. Characteristically they are objects that permanently penetrate through a defect in the skin. The histological aspects of the implant skin interfacial reactions are reviewed in this article. A short description is presented of common applications of PDs. The five presently identified interfacial failure modes are described histologically with the aid of schematic drawings. These failure modes are marsupialization, permigration , avulsion, infection, alone or in combination. Single or multiple etiological factors may be responsible for these failure modes. These factors can be surgically created skin defects around the penetrating foreign implant, epidermal healing characteristics that prevent the formation of a suitable seal at the implant-skin interface and mechanical forces that may disrupt dermal attempts to seal the interface. Eventually the interface becomes infected necessitating removal of the device. Terminology recommended for use in percutaneous device research is indexed and defined.

Enhanced collagenase activity in diabetic rat gingiva: in vitro and in vivo evidence

Gingiva from alloxan and streptozotocin-diabetic rats exhibited markedly enhanced collagenolytic activity in tissue culture. This effect was eliminated by puromycin or by repeated freeze-thawing of the tissue prior to incubation. Soluble extracts of the diabetic gingiva in situ were found to contain breakdown products of collagen similar in size to the reaction products generated by tissue collagenase. These fragments were not detected in the control tissue. This study indicates that experimental diabetes stimulates the synthesis of gingival collagenase in culture and that a similar effect occurs in vivo.

Localization of collagenase in human middle ear cholesteatoma

The process of connective tissue breakdown in chronic otitis media is described in the context of recent advances in our understanding of collagen degradation and bone resorption. The significance of the initial step in collagen breakdown, brought about by the action of a specific collagen dissolving enzyme is emphasized in terms of recent studies in other chronic inflammatory diseases characterized by connective tissue breakdown. Bone resorption, a characteristic feature of chronic otitis media, requires the breakdown of collagen, which comprises over 90 percent of bone protein. Evidence in support of collagenase in bone resorption from adjacent tissue (in this case, inflammatory connective tissue) would require identification of the enzyme in cells involved in the inflammatory process adjacent to the resorbing bone. Collagenase was found localized in frozen sections of canal wall skin, middle ear granulation and in cholesteatoma by a specific binding of the enzyme with an antiserum produced against purified human skin collagenase. The antigen antibody complex was labelled with fluorescein. Collagenase appeared in the subepithelial connective tissue of cholesteatoma, granulation tissue from the middle ear and the dermis of canal skin; but was not seen in the keratin layer, epithelium or the epidermal appendages. The enzyme appeared within certain fibroblasts, macrophages and endothelial cells of capillary buds. Collagenase enhanced by chronic inflammation attacks the intact collagen molecule, making it susceptible to further digestion by other proteases that are also products of inflammation. This process brings about resorption of connective tissue and bone.

Growth and differentiation of skin

During the past 25 years, attention has turned from the morphologic aspects of skin development which are well known, to the mechanisms that control this development. Although our knowledge of these mechanisms is still limited, some avenues of investigation appear promising, e.g., epithelial-mesenchymal interactions, cell communication and other cell surface phenomena, and certain aspects of the proliferative process. In the analysis of what controls growth and differentiation, skin, as the experimental system, has played a major role.

Cellular mechanisms involved in cyclic stroma renewal of the uterus. III. Cells of the immune response

The principal cell types associated with the humoral immune response (monocyte-macrophages, lymphocytes, and plasma cells) are numerous in the endometrial stroma of the uterus during the first four postpartum days in two types of mammals, the marsupial North America opossum and the eutherian albino rat. This transietn cellular differentiation coincides with the physiologic period of rapid uterine regression which includes massive reduction in the amount of extracellular stromal material. In addition, heterophils and eosinophils, cell types also known to be associated with phagocytic and immunologic activity, appear in the stroma during the first two postpartum days; their presence may, however, be associated more directly with the postpartum estrus that occurs on day 1 postpartum than with endometrial regression. Thus, the five cell types, which are known in pathologic conditions to be components present in the inflammatory response to a foreign antigen, are conspicuously present in the normal regressing endometrium. Furthermore, there is ample ultrastructural evidence of frequent macrophagic-lymphocytic interaction, transformation of lymphocytes, and active secretion by plasma cells during this early postpartum period. An hypothesis has been derived by uniting this new description of endometrial stromal cell differentiation with the existing literature on uterine collagenase activity, an important feature of postpartum regression (reviews of Gross, '74; Harris and Krane, '74). It is based on the assumption that during regression the extracellular action of neutral collagenase (and possibly other extracellular proteases) release new antigenic sites in proteins located in the ground substance. In the case of collagenase, these transient antigenic sites would arise at the locus of enzymic cleavage as well as from the subsequent denaturation of the fragments of the collagen molecule. This endogenous antigenic stimulus would be strong and temporary, and would lead to the cellular manifestations of the transient humoral immunologic response which are evident in the regressing stroma of these two mammals. This humoral immune reaction may be one of the regulatory mechanisms involved in the cyclic renewal of the extracellular compartment of the uterine stroma.

The effect of prolactin and thyroxine on tail resorption in R. pipiens: in vivo and in vitro

Thyroxine induces tail resorption in anurans both in vivo and in vitro. This event is accompanied by an increase in the activity of the hydrolytic enzymes acid phosphtase and B-N-acetylglucosaminidase. Prolactin treatment promotes tail growth and directly antagonizes the action of thyroxine on tail tissues. This is evident at the gross morphological level as well as at the biochemical level where prolactin inhibits the increase in activity on the hydrolytic enzymes that occurs during thyroid hormone induced resorption.