Overexpression of TNF-α-converting enzyme in fibroblasts augments dermal fibrosis after inflammation

The basis of complications in the context of SARS-CoV-2 infection: Pathological activation of ADAM17

The virulence of SARS-CoV-2 decreases with increasing infectivity, the primary approaches for antiviral treatments will be preventing or minimizing the complications resulting from virus infection. ADAM metallopeptidase domain 17 (ADAM17) activation by SARS-CoV-2 infection has a dual effect on the development of the disease: increased release of inflammatory cytokines and dysregulation of Angiotensin converting enzyme II (ACE2) on cell surfaces, inflammatory cytokine infiltration and loss of ACE2 protective function lead to a significant increase in the incidence of related complications. Importantly, pathologically activated ADAM17 showed superior features than S protein in regulating ACE2 expression and participating in the intra cellular replication of SARS-CoV-2. In short, SARS-CoV-2 elicits only a limited immune response when it promotes its own replication and pathogenicity through ADAM17. Therefore, the pathological activation of ADAM17 may also represent a diminished innate antiviral defense and an altered strategy of SARS-CoV-2 infection. In this review, we summarized recent advances in our understanding of the pathophysiology of ADAM17, with a focus on the new findings that SARS-CoV-2 affects ADAM17 expression through Furin protein converting enzyme and Mitogen-activated protein kinase (MAPK) pathway, and raises the hypothesis that SARS-CoV-2 may mediates the pathological activation of ADAM17 by hijacking the actin regulatory pathway, and discussed the underlying biological principles.

Molecular pathogenicity of 1-nonadecene and L-lactic acid, unique metabolites in radicular cysts and periapical granulomas

Recently, 1-nonadecene and L-lactic acid were identified as unique metabolites in radicular cysts and periapical granuloma, respectively. However, the biological roles of these metabolites were unknown. Therefore, we aimed to investigate the inflammatory and mesenchymal-epithelial transition (MET) effects of 1-nonadecene, and the inflammatory and collagen precipitation effects of L-lactic acid on both periodontal ligament fibroblasts (PdLFs) and peripheral blood mononuclear cells (PBMCs). PdLFs and PBMCs were treated with 1-nonadecene and L-lactic acid. Cytokines' expression was measured using quantitative real-time polymerase chain reaction (qRT-PCR). E-cadherin, N-cadherin, and macrophage polarization markers were measured using flow cytometry. The collagen, matrix metalloproteinase (MMP)-1, and released cytokines were measured using collagen assay, western blot, and Luminex assay, respectively. In PdLFs, 1-nonadecene enhances inflammation through the upregulation of some inflammatory cytokines including IL-1β, IL-6, IL-12A, monocyte chemoattractant protein (MCP)-1, and platelet-derived growth factor (PDGF) α. 1-Nonadecene also induced MET through the upregulation of E-cadherin and the downregulation of N-cadherin in PdLFs. 1-Nonadecene polarized macrophages to a pro-inflammatory phenotype and suppressed their cytokines' release. L-lactic acid exerted a differential impact on the inflammation and proliferation markers. Intriguingly, L-lactic acid induced fibrosis-like effects by enhancing collagen synthesis, while inhibiting MMP-1 release in PdLFs. These results provide a deeper understanding of 1-nonadecene and L-lactic acid's roles in modulating the microenvironment of the periapical area. Consequently, further clinical investigation can be employed for target therapy.

The Effect of a Local Injection of Flurbiprofen Ester Microspheres on Systemic Inflammatory Model Rats With a Closed Femoral Shaft Fracture

Background: Periarticular injections with a combination of local anesthetics, non-steroidal anti-inflammatory analgesics (NSAIDs), and epinephrine are becoming increasingly popular in the perioperative analgesia of artificial joint replacement. However, data on the efficacy and safety of local injection NSAIDs are still scarce. The purpose of this study was to investigate the efficacy and safety of a local injection of Flurbiprofen Ester Lipid microspheres into the inflammatory model of femoral shaft closed fractures in rats.

Methods: A systemic inflammatory model was induced in SD rats (60) by closed femoral shaft fracture; 12 non-fractured rats were used as the blank control group (group A). The systemic inflammation model of 60 rats was divided into 5 groups (12 in each group); Group B: intramuscular injectionof the same amount of normal saline at different time points as a negative control; Group C: intravenous injection of Flurbiprofen Ester microspheres (4.5 mg/kg) at different time points; Group D: intramuscular injection of Flurbiprofen Ester microspheres (2.25 mg/kg) at different time points; Group E: intramuscular injection of Flurbiprofen Ester microspheres (4.5 mg/kg) at different time points; Group F: intramuscular injection of Flurbiprofen Ester microspheres (9 mg/kg) at different time points. The behavioral test observed the behavior of the rats. Then, the inflammation factors of CRP, IL-6, COX-1, COX-2 and TNF-αby ELISA were recorded.

Results: Through the behavioral test it could be found that the effect of the intramuscular and intravenous injections of Flurbiprofen Ester microspheres was similar. Fracture rats with a local injection of Flurbiprofen Ester microspheres showed lower inflammation levels measured by COX-1, CRP, and TNF-α compared with the control group. Pathological sections at 24, 48, and 96 h after surgery did not display any local muscle necrosis at the local injection site. These findings suggested that a Flurbiprofen Ester microsphere muscular injection exhibited a similar effect to an intravenous injection.

Conclusion: The local injection of Flurbiprofen Ester microspheres significantly reduced the inflammatory response in fracture rats and did not increase the risk of muscle necrosis, suggesting its feasibility in local injection analgesia.

Cardiac protection by pirfenidone after myocardial infarction: a bioinformatic analysis

Left ventricular (LV) remodeling after myocardial infarction (MI) is promoted by an intense fibrotic response, which could be targeted by the anti-fibrotic drug pirfenidone. We explored the relationship between protein modulation by pirfenidone and post-MI remodeling, based on molecular information and transcriptomic data from a swine model of MI. We identified 6 causative motives of post-MI remodeling (cardiomyocyte cell death, impaired myocyte contractility, extracellular matrix remodeling and fibrosis, hypertrophy, renin–angiotensin–aldosterone system activation, and inflammation), 4 pirfenidone targets and 21 bioflags (indirect effectors). Pirfenidone had a more widespread action than gold-standard drugs, encompassing all 6 motives, with prominent effects on p38γ-MAPK12, the TGFβ1-SMAD2/3 pathway and other effector proteins such as matrix metalloproteases 2 and 14, PDGFA/B, and IGF1. A bioinformatic approach allowed to identify several possible mechanisms of action of pirfenidone with beneficial effects in the post-MI LV remodeling, and suggests additional effects over guideline-recommended therapies.

Abnormal ADAM17 expression causes airway fibrosis in chronic obstructive asthma

Patients with chronic obstructive asthma (COA) develop airflow obstruction caused by subepithelial fibrosis. Although a disintegrin and metalloproteinase 17 (ADAM17) has been implicated in lung inflammation and tissue fibrosis, its role in airway fibrosis in COA has not been explored. Here, we found marked overexpression of ADAM17, phosphorylated ADAM17, and connective tissue growth factor (CTGF) in human airway fibroblasts from COA patients, compared with those of normal subjects. Similarly, levels of ADAM17, CTGF, α-smooth muscle actin (α-SMA), and collagen were increased in endobronchial biopsies from COA patients, but not in controls. In an ovalbumin-challenge asthma model, airway fibrosis was inhibited in ADAM17^f/f/Cre⁺ mice compared to control mice. TGF-β- and thrombin-induced fibrotic protein expression was reduced by ADAM17 small interfering (si)RNA, TAPI-0 (an ADAM17 inhibitor), and EGFR siRNA. In addition, exogenous HB-EGF reversed fibrotic response in ADAM17 knockdown human lung fibroblasts. ADAM17 causes subepithelial fibrosis through regulation of enhanced extracellular matrix production and fibroblast differentiation and is the common pathway for airway fibrosis mediated by TGF-β and thrombin through an aberrant ADAM17/EGFR signalling pathway.

The role of NF-κB and Elk-1 in the regulation of mouse ADAM17 expression

ADAM17 is a cell membrane metalloproteinase responsible for the release of ectodomains of numerous proteins from the cell surface. Although ADAM17 is often overexpressed in tumours and at sites of inflammation, little is known about the regulation of its expression. Here we investigate the role of NF-κB and Elk-1 transcription factors and upstream signalling pathways, NF-κB and ERK1/2 in ADAM17 expression in mouse brain endothelial cells stimulated with pro-inflammatory factors (TNF, IL-1β, LPS) or a phorbol ester (PMA), a well-known stimulator of ADAM17 activity. Notably, NF-κB inhibitor, IKK VII, interfered with the IL-1β- and LPS-mediated stimulation of ADAM17 expression. Furthermore, Adam17 promoter contains an NF-κB binding site occupied by p65 subunit of NF-κB. The transient increase in Adam17 mRNA in response to PMA was strongly reduced by an inhibitor of ERK1/2 phosphorylation, U0126. Luciferase reporter assay with vectors encoding the ERK1/2 substrate, Elk-1, fused with constitutively activating or repressing domains, indicated Elk-1 involvement in Adam17 expression. The site-directed mutagenesis of potential Elk-1 binding sites pointed to four functional Elk-1 binding sites in Adam17 promoter. All in all, our results indicate that NF-κB and Elk-1 transcription factors via NF-κB and ERK1/2 signalling pathways contribute to the regulation of mouse Adam17 expression.

Summary: We show the involvement of ERK1/2 and NF-κB pathways in the stimulation of mouse Adam17 expression and determine functional Elk-1- and NF-κB binding sites in its promoter.

RHBDF2-Regulated Growth Factor Signaling in a Rare Human Disease, Tylosis With Esophageal Cancer: What Can We Learn From Murine Models?

Tylosis with esophageal cancer syndrome (TOC) is a rare autosomal dominant proliferative skin disease caused by missense mutations in the rhomboid 5 homolog 2 (RHBDF2) gene. TOC is characterized by thickening of the skin in the palms and feet and is strongly linked with the development of esophageal squamous cell carcinoma. Murine models of human diseases have been valuable tools for investigating the underlying genetic and molecular mechanisms of a broad range of diseases. Although current mouse models do not fully recapitulate all aspects of human TOC, and the molecular mechanisms underlying TOC are still emerging, the available mouse models exhibit several key aspects of the disease, including a proliferative skin phenotype, a rapid wound healing phenotype, susceptibility to epithelial cancer, and aberrant epidermal growth factor receptor (EGFR) signaling. Furthermore, we and other investigators have used these models to generate new insights into the causes and progression of TOC, including findings suggesting a tissue-specific role of the RHBDF2-EGFR pathway, rather than a role of the immune system, in mediating TOC; and indicating that amphiregulin, an EGFR ligand, is a functional driver of the disease. This review highlights the mouse models of TOC available to researchers for use in investigating the disease mechanisms and possible therapies, and the significance of genetic modifiers of the disease identified in these models in delineating the underlying molecular mechanisms.

ADAM17 regulates TNF-α expression upon lipopolysaccharide stimulation in oral keratinocytes

A disintegrin and metalloprotease 17 (ADAM17) is a tumor necrosis factor (TNF)-converting enzyme and was first identified as the enzyme that cleaves the prodomain of TNF-α, a proinflammatory cytokine that plays a central role in immune regulation and a variety of inflammatory responses in destructive periodontal disease. The aim of the present study was to verify the presence of ADAM17 in the gingival epithelium and elucidate its involvement in the release of TNF-αin oral keratinocytes. Immunohistochemical analyses of ADAM17 were performed in gingival tissues obtained from patients and in human oral keratinocytes (HOKs). Additionally, levels of TNF-α and ADAM17 in HOKs exposed to lipopolysaccharide (LPS) were assessed using enzyme-linked immunosorbent assays. Moreover, the effects of ADAM17 inhibitor, matrix metalloproteinase (MMP) inhibitor, and ADAM17 siRNA on TNF-α concentration were assessed. Strong immunoreactivity for ADAM17 was observed in the epithelium of the inflamed gingival tissues and in HOKs. Furthermore, treatment with either ADAM17 inhibitor or ADAM17 siRNA inhibited the generation of TNF-α induced by LPS in HOKs. The present study demonstrates that ADAM17 is strongly expressed in the epithelium of gingival tissues and suggests that ADAM17 may be a key enzyme that regulates the generation of TNF-α in oral keratinocytes.

Matrix Metalloproteinases and Tissue Inhibitor of Metalloproteinases in Inflammation and Fibrosis of Skeletal Muscles

In skeletal muscles, levels and activity of Matrix MetalloProteinases (MMPs) and Tissue Inhibitors of MetalloProteinases (TIMPs) have been involved in myoblast migration, fusion and various physiological and pathological remodeling situations including neuromuscular diseases. This has opened perspectives for the use of MMPs' overexpression to improve the efficiency of cell therapy in muscular dystrophies and resolve fibrosis. Alternatively, inhibition of individual MMPs in animal models of muscular dystrophies has provided evidence of beneficial, dual or adverse effects on muscle morphology or function. We review here the role played by MMPs/TIMPs in skeletal muscle inflammation and fibrosis, two major hurdles that limit the success of cell and gene therapy. We report and analyze the consequences of genetic or pharmacological modulation of MMP levels on the inflammation of skeletal muscles and their repair in light of experimental findings. We further discuss how the interplay between MMPs/TIMPs levels, cytokines/chemokines, growth factors and permanent low-grade inflammation favor cellular and molecular modifications resulting in fibrosis.

Hypoxia-induced ADAM 17 expression is mediated by RSK1-dependent C/EBPβ activation in human lung fibroblasts

Hypoxia was identified as a mediator of lung fibrosis in patients with chronic obstructive asthma (COA). Overexpression of a disintegrin and metalloproteinase 17 (ADAM 17) and connective tissue growth factor (CTGF) leads to development of tissue fibrosis. However, the signaling pathway in hypoxia-induced ADAM 17 expression remains poorly defined. In this study, we investigated the roles that ribosomal S-6 kinase 1 (RSK1)/CCAAT/enhancer-binding protein β (C/EBPβ)-dependent ADAM 17 expression plays in hypoxia-induced CTGF expression in human lung fibroblasts. We observed that hypoxia caused increases in ADAM 17 expression and ADAM 17-luciferase activity in WI-38 cells. Hypoxia-induced CTGF-luciferase activity and CTGF expression were reduced in cells transfected with small interfering (si)RNA of ADAM 17 in WI-38 cells. Moreover, hypoxia-induced ADAM 17 expression was reduced by RSK1 siRNA and C/EBPβ siRNA. Hypoxia caused time-dependent increases in RSK1 phosphorylation at Thr359/Ser363. Exposure of cells to hypoxia resulted in increased C/EBPβ phosphorylation at Thr266 and C/EBPβ-luciferase activity in time-dependent manners, and these effects were suppressed by RSK1 siRNA. Hypoxia induced recruitment of C/EBPβ to the ADAM 17 promoter. Furthermore, CTGF-luciferase activity induced by hypoxia was attenuated by RSK1 siRNA and C/EBPβ siRNA. These results suggest that hypoxia instigates the RSK1-dependent C/EBPβ signaling pathway, which in turn initiates binding of C/EBPβ to the ADAM 17 promoter and ultimately induces ADAM 17 expression in human lung fibroblasts. Moreover, RSK1/C/EBPβ-dependent ADAM 17 expression is involved in hypoxia-induced CTGF expression. Our results suggest possible therapeutic approaches for treating hypoxia-mediated lung fibrosis in COA.

Autologous Graft Thickness Affects Scar Contraction and Quality in a Porcine Excisional Wound Model

BACKGROUND

Texture, color, and durability are important characteristics to consider for skin replacement in conspicuous and/or mobile regions of the body such as the face, neck, and hands. Although autograft thickness is a known determinant of skin quality, few studies have correlated the subjective and objective characters of skin graft healing with their associated morphologic and cellular profiles. Defining these relationships may help guide development and evaluation of future skin replacement strategies.

METHODS

Six-centimeter-diameter full-thickness wounds were created on the back of female Yorkshire pigs and covered by autografts of variable thicknesses. Skin quality was assessed on day 120 using an observer scar assessment score and objective determinations for scar contraction, erythema, pigmentation, and surface irregularities. Histological, histochemical, and immunohistochemical assessments were performed.

RESULTS

Thick grafts demonstrated lower observer scar assessment score (better quality) and decreased erythema, pigmentation, and surface irregularities. Histologically, thin grafts resulted in scar-like collagen proliferation while thick grafts preserves the dermal architecture. Increased vascularity and prolonged and increased cellular infiltration were observed among thin grafts. In addition, thin grafts contained predominately dense collagen fibers, whereas thick grafts had loosely arranged collagen. α-Smooth muscle actin staining for myofibroblasts was observed earlier and persisted longer among thinner grafts.

CONCLUSIONS

Graft thickness is an important determinant of skin quality. High-quality skin replacements are associated with preserved collagen architecture, decreased neovascularization, and decreased inflammatory cellular infiltration. This model, using autologous skin as a metric of quality, may give a more informative analysis of emerging skin replacement strategies.

ADAM17 Promotes Motility, Invasion, and Sprouting of Lymphatic Endothelial Cells

Tumor-associated lymphatic vessels actively participate in tumor progression and dissemination. ADAM17, a sheddase for numerous growth factors, cytokines, receptors, and cell adhesion molecules, is believed to promote tumor development, facilitating both tumor cell proliferation and migration, as well as tumor angiogenesis. In this work we addressed the issue of whether ADAM17 may also promote tumor lymphangiogenesis. First, we found that ADAM17 is important for the migratory potential of immortalized human dermal lymphatic endothelial cells (LEC). When ADAM17 was stably silenced in LEC, their proliferation was not affected, but: (i) single-cell motility, (ii) cell migration through a 3D Matrigel/collagen type I matrix, and (iii) their ability to form sprouts in a 3D matrix were significantly diminished. The differences in the cell motility between ADAM17-proficient and ADAM17-silenced cells were eliminated by inhibitors of EGFR and HER2, indicating that ADAM17-mediated shedding of growth factors accounts for LEC migratory potential. Interestingly, ADAM17 depletion affected the integrin surface expression/functionality in LEC. ADAM17-silenced cells adhered to plastic, type I collagen, and fibronectin faster than their ADAM17-proficient counterparts. The difference in adhesion to fibronectin was abolished by a cyclic RGD peptide, emphasizing the involvement of integrins in the process. Using a soluble receptor array, we identified BIG-H3 among several candidate proteins involved in the phenotypic and behavioral changes of LEC upon ADAM17 silencing. In additional assays, we confirmed the increased expression of BIG-H3, as well as TGFβ2 in ADAM17-silenced LEC. The antilymphangiogenic effects of ADAM17 silencing in lymphatic endothelial cells suggest further relevance of ADAM17 as a potential target in cancer therapy.

Overexpression of TNF-α converting enzyme promotes adipose tissue inflammation and fibrosis induced by high fat diet

Obesity is a state in which chronic low-grade inflammation persists in adipose tissues. Pro-inflammatory cytokines, including TNF-α, produced by adipose tissues have been implicated as active participants in the development of obesity-related diseases. Since TNF-α converting enzyme (TACE) is the major factor that induces soluble TNF-α, TACE has been noted as a pivotal regulator in this field. To reveal the role of TACE in adipose tissue inflammation, TACE-transgenic (TACE-Tg) and wild type (WT) mice were fed with high fat diet (HFD) or control diet for 16 weeks. At 13 weeks after the beginning of the diet, serum TNF-α and macrophage-related cytokine/chemokine levels were elevated in TACE-Tg mice fed with HFD (Tg-HFD mice), and the number of the so-called crown-like adipocyte was significantly increased in adipose tissues of Tg-HFD mice at the end of the experiment. Although macrophage infiltration was not detected in the adipose tissues at this time, fibrosis was observed around the crown-like adipocytes. These findings suggested that TACE overexpression induced macrophage infiltration and subsequent fibrosis in adipose tissues under HFD regimen. The collective evidence suggested that TACE could be a therapeutic target of HFD-induced obesity-related adipose tissue inflammation.

Chemopreventive effect of a novel, selective TACE inhibitor on DMBA- and TPA-induced skin carcinogenesis

Abstract Context: Tumor necrosis factor (TNF)-α, a potent proinflammatory cytokine, plays a major role in the pathogenesis of cancer. TNF-α converting enzyme (TACE) mediates processing and release of biologically active TNF-α.

OBJECTIVE

We aimed to investigate the effect of a novel, selective TACE inhibitor (compound 11p) on skin inflammation and associated tumorigenesis in mice.

METHODS

Skin edema was induced in mice by dermal application 12-O-tetradecanoylphorbol-13-acetate (TPA) solution in acetone on to the ear and the effect of post-treatment of compound 11p (topical application) was evaluated. Edema and inflammation was assessed by measuring ear thickness, weight of skin punch and cytokine levels. Skin cancer in mice was initiated by single topical application of 7,12-dimethylbenz[a]anthracene (DMBA) and promoted by repeated TPA application for 20 weeks. The effect of compound 11p on papilloma incidence and multiplicity was evaluated.

RESULTS

Treatment with compound 11p strongly suppressed TPA-induced elevation in skin thickness and weight. A dose-dependent suppression in TPA-mediated TNF-α, IL-6, IFN-γ, IL-17 and PGE2 levels which was associated with a decrease in infiltration of inflammatory cells was also observed with the treatment. Moreover, compound 11p treatment delayed the onset, markedly reduced the papilloma incidence and multiplicity persuaded by DMBA and TPA.

DISCUSSION AND CONCLUSION

These findings suggest that selective blockade of TACE suppresses TPA-induced epidermal hyperplasia, inflammatory cell infiltration and cytokine level. Inhibition of inflammatory events related to tumor growth might have led to the anti-tumor effect in mouse skin cancer model induced by DMBA and TPA.

EGFR controls IQGAP basolateral membrane localization and mitotic spindle orientation during epithelial morphogenesis

Establishing the correct orientation of the mitotic spindle is an essential step in epithelial cell division in order to ensure that epithelial tubules form correctly during organ development and regeneration. While recent findings have identified some of the molecular mechanisms that underlie spindle orientation, many aspects of this process remain poorly understood. Here, we have used the 3D-MDCK model system to demonstrate a key role for a newly identified protein complex formed by IQGAP1 and the epithelial growth factor receptor (EGFR) in controlling the orientation of the mitotic spindle. IQGAP1 is a scaffolding protein that regulates many cellular pathways, from cell-cell adhesion to microtubule organization, and its localization in the basolateral membrane ensures correct spindle orientation. Through its IQ motifs, IQGAP1 binds to EGFR, which is responsible for maintaining IQGAP1 in the basolateral membrane domain. Silencing IQGAP1, or disrupting the basolateral localization of either IQGAP1 or EGFR, results in a non-polarized distribution of NuMA, mitotic spindle misorientation and defects in single lumen formation.

In vivo imaging method to distinguish acute and chronic inflammation

Inflammation is a fundamental aspect of many human diseases. In this video report, we demonstrate non-invasive bioluminescence imaging techniques that distinguish acute and chronic inflammation in mouse models. With tissue damage or pathogen invasion, neutrophils are the first line of defense, playing a major role in mediating the acute inflammatory response. As the inflammatory reaction progresses, circulating monocytes gradually migrate into the site of injury and differentiate into mature macrophages, which mediate chronic inflammation and promote tissue repair by removing tissue debris and producing anti-inflammatory cytokines. Intraperitoneal injection of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione, sodium salt) enables detection of acute inflammation largely mediated by tissue-infiltrating neutrophils. Luminol specifically reacts with the superoxide generated within the phagosomes of neutrophils since bioluminescence results from a myeloperoxidase (MPO) mediated reaction. Lucigenin (bis-N-methylacridinium nitrate) also reacts with superoxide in order to generate bioluminescence. However, lucigenin bioluminescence is independent of MPO and it solely relies on phagocyte NADPH oxidase (Phox) in macrophages during chronic inflammation. Together, luminol and lucigenin allow non-invasive visualization and longitudinal assessment of different phagocyte populations across both acute and chronic inflammatory phases. Given the important role of inflammation in a variety of human diseases, we believe this non-invasive imaging method can help investigate the differential roles of neutrophils and macrophages in a variety of pathological conditions.

Systemic overexpression of TNFα-converting enzyme does not lead to enhanced shedding activity in vivo

TNFα-converting enzyme (TACE/ADAM17) is a membrane-bound proteolytic enzyme with a diverse set of target molecules. Most importantly, TACE is indispensable for the release and activation of pro-TNFα and the ligands for epidermal growth factor receptor in vivo. Previous studies suggested that the overproduction of TACE is causally related to the pathogenesis of inflammatory diseases and cancers. To test this hypothesis, we generated a transgenic line in which the transcription of exogenous Tace is driven by a CAG promoter. The Tace-transgenic mice were viable and exhibited no overt defects, and the quantitative RT-PCR and Western blot analyses confirmed that the transgenically introduced Tace gene was highly expressed in all of the tissues examined. The Tace-transgenic mice were further crossed with Tace⁻/⁺ mice to abrogate the endogenous TACE expression, and the Tace-transgenic mice lacking endogenous Tace gene were also viable without any apparent defects. Furthermore, there was no difference in the serum TNFα levels after lipopolysaccharide injection between the transgenic mice and control littermates. These observations indicate that TACE activity is not necessarily dependent on transcriptional regulation and that excess TACE does not necessarily result in aberrant proteolytic activity in vivo.