Detection of lysyl oxidase gene expression in rat skin during wound healing

Lysyl Oxidase Production by Murine C3H10T1/2 Mesenchymal Stem Cells Is Increased by TGFβs and Differentially Modulated by Mechanical Stimuli

Tendons are frequently injured and have limited regenerative capacity. This motivates tissue engineering efforts aimed at restoring tendon function through strategies to direct functional tendon formation. Generation of a crosslinked collagen matrix is paramount to forming mechanically functional tendon. However, it is unknown how lysyl oxidase (LOX), the primary mediator of enzymatic collagen crosslinking, is regulated by stem cells. This study investigates how multiple factors previously identified to promote tendon formation and healing (transforming growth factor [TGF]β1 and TGFβ2, mechanical stimuli, and hypoxia-inducible factor [HIF]-1α) regulate LOX production in the murine C3H10T1/2 mesenchymal stem cell (MSC) line. We hypothesized that TGFβ signaling promotes LOX activity in C3H10T1/2 MSCs, which is regulated by both mechanical stimuli and HIF-1α activation. TGFβ1 and TGFβ2 increased LOX levels as a function of concentration and time. Inhibiting the TGFβ type I receptor (TGFβRI) decreased TGFβ2-induced LOX production by C3H10T1/2 MSCs. Low (5 mPa) and high (150 mPa) magnitudes of fluid shear stress were applied to test impacts of mechanical stimuli, but without TGFβ2, loading alone did not alter LOX levels. Low loading (5 mPa) with TGFβ2 increased LOX at 7 days greater than TGFβ2 treatment alone. Neither HIF-1α knockdown (siRNA) nor activation (CoCl2) affected LOX levels. Ultimately, results suggest that TGFβ2 and appropriate loading magnitudes contribute to LOX production by C3H10T1/2 MSCs. Potential application of these findings includes treatment with TGFβ2 and appropriate mechanical stimuli to modulate LOX production by stem cells to ultimately control collagen matrix stiffening and support functional tendon formation.

LOXL2 inhibition ameliorates pulmonary artery remodeling in pulmonary hypertension

Background

Conduit pulmonary arterial stiffening and the resultant increase in pulmonary vascular impedance has emerged as an important underlying driver of pulmonary arterial hypertension (PAH). Given that matrix deposition is central to vascular remodeling, we evaluated the role of the collagen crosslinking enzyme lysyl oxidase like 2 (LOXL2) in this study.

Methods and Results

Human pulmonary artery smooth muscle cells (PASMCs) subjected to hypoxia showed increased LOXL2 secretion. LOXL2 activity and expression were markedly higher in primary PASMCs isolated from pulmonary arteries of the rat Sugen 5416 + hypoxia (SuHx) model of severe PH. Similarly, LOXL2 protein and mRNA levels were increased in pulmonary arteries (PA) and lungs of rats with PH (SuHx and monocrotaline (MCT) models). Pulmonary arteries (PAs) isolated from rats with PH exhibited hypercontractility to phenylephrine and attenuated vasorelaxation elicited by acetylcholine, indicating severe endothelial dysfunction. Tensile testing revealed a a significant increase in PA stiffness in PH. Treatment with PAT-1251, a novel small-molecule LOXL2 inhibitor, improved active and passive properties of the PA ex vivo. There was an improvement in right heart function as measured by right ventricular pressure volume loops in-vivo with PAT-1251. Importantly PAT-1251 treatment ameliorated PH, resulting in improved pulmonary artery pressures, right ventricular remodeling, and survival.

Conclusion

Hypoxia induced LOXL2 activation is a causal mechanism in pulmonary artery stiffening in PH, as well as pulmonary artery mechanical and functional decline. LOXL2 inhibition with PAT-1251 is a promising approach to improve pulmonary artery pressures, right ventricular elastance, cardiac relaxation, and survival in PAH.

New & Noteworthy

Pulmonary arterial stiffening contributes to the progression of PAH and the deterioration of right heart function. This study shows that LOXL2 is upregulated in rat models of PH. LOXL2 inhibition halts pulmonary vascular remodeling and improves PA contractility, endothelial function and improves PA pressure, resulting in prolonged survival. Thus, LOXL2 is an important mediator of PA remodeling and stiffening in PH and a promising target to improve PA pressures and survival in PH.

Head and Neck Region Dermatological Ultraviolet-Related Cancers are Associated with Exfoliation Syndrome in a Clinic-Based Population

OBJECTIVE

We assessed the relationship between ultraviolet (UV)-associated dermatological carcinomas (basal cell carcinoma [BCC] and squamous cell carcinoma [SCC]) and exfoliation syndrome (XFS) or exfoliation glaucoma (XFG).

DESIGN

Case-control study.

PARTICIPANTS

Between 2019 and 2021, 321 participants and control subjects (XFS or XFG = 98; primary open-angle glaucoma [POAG] = 117; controls = 106; ages 50-90 years) were recruited.

METHODS

A cross-sectional survey assessing medical history, maximum known intraocular pressure, cup-to-disc ratio, Humphrey visual field 24-2, the propensity to tan or burn in early life, history of BCC or SCC, and XFS or XFG diagnosis. The multivariable models adjusted for age, sex, medical history, eye color, hair color, and likeliness of tanning versus burning at a young age.

MAIN OUTCOME MEASURES

History of diagnosed XFS or XFG.

RESULTS

Any history of BCC or SCC in the head and neck region was associated with a 2-fold higher risk of having XFS or XFG versus having POAG or being a control subject (odds ratio [OR], 2.01; 95% confidence interval [CI], 1.04-3.89) in a multivariable-adjusted analysis. We observed a dose-response association in which the chance of having XFS or XFG increased by 67% per head and neck BCC or SCC occurrence (OR, 1.67; 95% CI, 1.09-2.56). When we excluded POAG participants, head and neck BCC or SCC was associated with a 2.8-fold higher risk of XFS or XFG (OR, 2.80; 95% CI, 1.12-7.02), and each additional occurrence had a 2-fold higher risk of XFS or XFG (OR, 1.97; 95% CI, 1.09-3.58). The association between head and neck region BCC or SCC and POAG compared with the control subjects was null (OR, 1.42; 95% CI, 0.58-3.48). With BCC or SCC located anywhere on the body, there was a nonsignificantly higher risk of having XFS or XFG compared with having POAG or being a control subject (OR, 1.65; 95% CI, 0.88-3.09).

CONCLUSIONS

Head and neck region BCCs or SCCs are associated with a higher risk of having XFS or XFG. These findings support prior evidence that head and neck UV exposure may be a risk factor for XFS.

Wound healing in weaning, adult, and old rats with provoked incisional hernias. A comparative study

BACKGROUND

Incisional hernias are more frequent in adults than in children. It is hypothesized that a more efficient healing process in pediatric patients could explain this difference in incidence. Certain elements of healing such as neovascularization, degree of inflammation, percentage of mature and immature collagen, the proliferation of fibroblasts, and expression of certain genes could explain why healing in children is more efficient when compared to the adult and elderly populations.

MATERIALS AND METHODS

Seventy-one rats of 3 different age groups (weaning, adult, and old) underwent surgery with 3 different incisions (vertical, oblique, and horizontal). During the procedure, the skin and abdominal wall of the animal were sectioned and only the skin was sutured to mimic incisional hernia in the animals. Four weeks after surgery, the rats were euthanized, their skin was removed, and the extent of scar tissue formed in the muscle opening was measured. In addition, samples of the scar tissue were collected for histological, immunohistochemical, and molecular analyzes. Nine rats served as controls.

RESULTS

Shorter-length hernias were formed in weaning rats when compared to old ones when the surgical incision was horizontal (p = 0.03). There was a greater proliferation of fibroblasts in rats in the younger age groups, regardless of the type of incision. The Lox gene was more expressed in weaning rats with vertical and oblique incisions.

CONCLUSIONS

These differences could explain the better healing and lower incidence of hernias in the pediatric population, although this aspect requires further studies.

Enzymatic cross-linking of collagens in organ fibrosis - resolution and assessment

Introduction: Enzymatic cross-linking of the collagens within the extracellular matrix (ECM) catalyzed by enzymes such as lysyl oxidase (LOX) and lysyl oxidase like-enzymes 1-4 (LOXL), transglutaminase 2 (TG2), and peroxidasin (PXDN) contribute to fibrosis progression through extensive collagen cross-linking. Studies in recent years have begun elucidating the important role of collagen cross-linking in perpetuating progression of organ fibrosis independently of inflammation through an increasingly stiff and noncompliant ECM. Therefore, collagen cross-linking and the cross-linking enzymes have become new targets in anti-fibrotic therapy as well as targets of novel biomarkers to properly assess resolution of the fibrotic ECM.Areas covered: The enzymatic actions of enzymes catalyzing collagen cross-linking and their relevance in organ fibrosis. Potential biomarkers specifically quantifying proteolytic fragments of collagen cross-linking is discussed based on Pubmed search done in November 2020 as well as the authors knowledge.Expert opinion: Current methods for the assessment of fibrosis involve the use of invasive and/or cumbersome and expensive methods such as tissue biopsies. Thus, an unmet need exists for the development and validation of minimally invasive biomarkers of proteolytic fragments of cross-linked collagens. These biomarkers may aid in the development and proper assessment of fibrosis resolution in coming years.

Simultaneously targeting cancer-associated fibroblasts and angiogenic vessel as a treatment for TNBC

Fibrotic tumor stroma plays an important role in facilitating triple-negative breast cancer (TNBC) progression and chemotherapeutic resistance. We previously reported a rationally designed protein (ProAgio) that targets integrin αvβ3 at a novel site. ProAgio induces apoptosis via the integrin. Cancer-associated fibroblasts (CAFs) and angiogenic endothelial cells (aECs) in TNBC tumor express high levels of integrin αvβ3. ProAgio effectively induces apoptosis in CAFs and aECs. The depletion of CAFs by ProAgio reduces intratumoral collagen and decreases growth factors released from CAFs in the tumor, resulting in decreased cancer cell proliferation and apoptotic resistance. ProAgio also eliminates leaky tumor angiogenic vessels, which consequently reduces tumor hypoxia and improves drug delivery. The depletion of CAFs and reduction in hypoxia by ProAgio decreases lysyl oxidase (LOX) secretion, which may play a role in the reduction of metastasis. ProAgio stand-alone or in combination with a chemotherapeutic agent provides survival benefit in TNBC murine models, highlighting the therapeutic potential of ProAgio as a treatment strategy.

Copper transporters and copper chaperones: roles in cardiovascular physiology and disease

Copper (Cu) is an essential micronutrient but excess Cu is potentially toxic. Its important propensity to cycle between two oxidation states accounts for its frequent presence as a cofactor in many physiological processes through Cu-containing enzymes, including mitochondrial energy production (via cytochrome c-oxidase), protection against oxidative stress (via superoxide dismutase), and extracellular matrix stability (via lysyl oxidase). Since free Cu is potentially toxic, the bioavailability of intracellular Cu is tightly controlled by Cu transporters and Cu chaperones. Recent evidence reveals that these Cu transport systems play an essential role in the physiological responses of cardiovascular cells, including cell growth, migration, angiogenesis and wound repair. In response to growth factors, cytokines, and hypoxia, their expression, subcellular localization, and function are tightly regulated. Cu transport systems and their regulators have also been linked to various cardiovascular pathophysiologies such as hypertension, inflammation, atherosclerosis, diabetes, cardiac hypertrophy, and cardiomyopathy. A greater appreciation of the central importance of Cu transporters and Cu chaperones in cell signaling and gene expression in cardiovascular biology offers the possibility of identifying new therapeutic targets for cardiovascular disease.

Regulation of fibrotic changes by the synergistic effects of cytokines, dimensionality and matrix: Towards the development of an in vitro human dermal hypertrophic scar model

Current therapeutic strategies to reduce scarring in full thickness skin defect offer limited success due to poor understanding of scar tissue formation and the underlying signaling pathways. There is an urgent need to develop human cell based in vitro scar tissue models as animal testing is associated with ethical and logistic complications and inter-species variations. Pro-inflammatory cytokines play critical role in regulating scar development through complex interplay and interaction with the ECM and corresponding signaling pathways. In this context, we assessed the responses of cultured fibroblasts with respect to their differentiation into myofibroblasts using optimised cytokines (TGF-β1, IL-6 and IL-8) for scar formation in 2D (tissue culture plate, collagen type I coated plate) vs 3D collagen type I gel based constructs. We attempted to deduce the role of dimensionality of cell culture matrix in modulating differentiation, function and phenotype of cultured fibroblasts. Validation of the developed model showed similarity to etiology and pathophysiology of in vivo hypertrophic scar with respect to several features: 1) transition of fibroblasts to myofibroblasts with convincing expression of α-SMA stress fibers; 2) contraction; 3) excessive collagen and fibronectin secretion; 4) expression of fibrotic ECM proteins (SPARC and Tenascin); 5) low MMP secretion. Most importantly, we elucidated the involvement of TGF-β/SMAD and Wnt/β-catenin pathways in developing in vitro dermal scar. Hence, this relatively simple in vitro human scar tissue equivalent may serve as an alternative for testing and designing of novel therapeutics and help in extending our understanding of the complex interplay of cytokines and related dermal scar specific signaling.

STATEMENT OF SIGNIFICANCE

Scarring of the skin affects almost millions of people per year in the developed world alone, nevertheless the complex pathophysiology and the precise signaling mechanisms responsible for this phenomenon of skin scarring are still unknown. A number of anti-scar drugs are being developed and being tested on animals and monolayer models. However, testing the efficacy of these drugs on lab based 3D in vitro models may prove extremely useful in recapitulating the 3D microenvironment of the native scar tissue. In that context in this study we have demonstrated the development of 3D in vitro dermal scar model, by optimizing a constellation of factors, such as combination of cytokines (TGF-β1,IL-6,IL-8) and cellular dimensionality in inducing the differentiation of dermal fibroblasts to myofibroblasts. This in vitro scar model was successful in replicating hallmark features of hypertrophic scar such as excessive synthesis of fibrotic extracellular matrix, perturbed matrix homeostasis, contraction, diminished MMP synthesis. The study also highlighted significant involvement of TGF-β/SMAD and Wnt/β-catenin signaling pathways in in vitro scar formation.

Acute lysyl oxidase inhibition alters microvascular function in normotensive but not hypertensive men and women

The lysyl oxidase (LOX) family of enzymes regulates collagen cross-linking. LOX is upregulated in hypertension, increasing vascular stiffness. In vivo human research is sparse, as long-term LOX inhibition in animals causes vascular instability. Our aim was to evaluate the effects of LOX inhibition on cutaneous microvascular function to determine whether LOX function was upregulated in hypertensive humans. Four intradermal microdialysis fibers were placed in the forearm of 10 young [age: 24 ± 1 yr, mean arterial pressure (MAP): 87 ± 2 mmHg], 10 normotensive (age: 50 ± 2 yr, MAP: 84 ± 1 mmHg), and 10 hypertensive (age: 53 ± 2 yr, MAP: 112 ± 2 mmHg) subjects. Two sites were perfused with 10 mM β-aminopropionitrile (BAPN) to inhibit LOX. The remaining two sites were perfused with lactated Ringer solution (control). A norepinephrine dose response (10-12-10-2 M) was performed to examine receptor-mediated vasoconstrictor function. A sodium nitroprusside dose response (10-8-10-1.3 M) was performed to examine vascular smooth muscle vasodilator function. Red blood cell flux was measured via laser-Doppler flowmetry and normalized to cutaneous vascular conductance (flux/MAP). LogEC50 values were calculated to determine changes in vasosensitivity. Skin tissue samples were analyzed for both extracellular matrix-bound and soluble LOX. LOX inhibition augmented vasoconstrictor sensitivity in young (control: -6.0 and BAPN: -7.1, P = 0.03) and normotensive (control: -4.8 and BAPN: -7.0, P = 0.01) but not hypertensive (control: -6.0 and BAPN: -6.1, P = 0.79) men and women. Relative to young subjects, extracellular matrix-bound LOX expression was higher in hypertensive subjects (young: 100 ± 8 and hypertensive: 162 ± 8, P = 0.002). These results suggest that upregulated LOX may contribute to the vascular stiffness and microvascular dysfunction characteristic in hypertension. NEW & NOTEWORTHY Matrix-bound lysyl oxidase (LOX) and LOX-like 2 expression are upregulated in the microvasculature of hypertensive men and women. Microvascular responsiveness to exogenous stimuli is altered with localized LOX inhibition in healthy men and women but not hypertensive adults. The LOX family differentially affects microvascular function in hypertensive and normotensive men and women.

Scarless wound healing: Transitioning from fetal research to regenerative healing

Since the discovery of scarless fetal skin wound healing, research in the field has expanded significantly with the hopes of advancing the finding to adult human patients. There are several differences between fetal and adult skin that have been exploited to facilitate scarless healing in adults including growth factors, cytokines, and extracellular matrix substitutes. However, no one therapy, pathway, or cell subtype is sufficient to support scarless wound healing in adult skin. More recently, products that contain or mimic fetal and adult uninjured dermis were introduced to the wound healing market with promising clinical outcomes. Through our review of the major experimental targets of fetal wound healing, we hope to encourage research in areas that may have a significant clinical impact. Additionally, we will investigate therapies currently in clinical use and evaluate whether they represent a legitimate advance in regenerative medicine or a vulnerary agent. WIREs Dev Biol 2018, 7:e309. doi: 10.1002/wdev.309 This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Regeneration Plant Development > Cell Growth and Differentiation Adult Stem Cells, Tissue Renewal, and Regeneration > Environmental Control of Stem Cells.

Different properties of skin of different body sites: The root of keloid formation?

The purpose of this study was to examine extracellular matrix composition, vascularization, and immune cell population of skin sites prone to keloid formation. Keloids remain a complex problem, posing esthetical as well as functional difficulties for those affected. These scars tend to develop at anatomic sites of preference. Mechanical properties of skin vary with anatomic location and depend largely on extracellular matrix composition. These differences in extracellular matrix composition, but also vascularization and resident immune cell populations might play a role in the mechanism of keloid formation. To examine this hypothesis, skin samples of several anatomic locations were taken from 24 human donors within zero to 36 hours after they had deceased. Collagen content and cross-links were determined through high-performance liquid chromatography. The expression of several genes, involved in extracellular matrix production and degradation, was measured by means of real-time PCR. (Immuno)histochemistry was performed to detect fibroblasts, collagen, elastin, blood vessels, Langerhans cells, and macrophages. Properties of skin of keloid predilections sites were compared to properties of skin from other locations (nonpredilection sites [NPS]). The results indicated that there are site specific variations in extracellular matrix properties (collagen and cross-links) as well as macrophage numbers. Moreover, predilection sites (PS) for keloid formation contain larger amounts of collagen compared to NPS, but decreased numbers of macrophages, in particular classically activated CD40 positive macrophages. In conclusion, the altered (histological, protein, and genetic) properties of skin of keloid PS may cause a predisposition for and contribute to keloid formation.

The Role of the Lysyl Oxidases in Tissue Repair and Remodeling: A Concise Review

Tissue injury provokes a series of events containing inflammation, new tissue formation and tissue remodeling which are regulated by the spatially and temporally coordinated organization. It is an evolutionarily conserved, multi-cellular, multi-molecular process via complex signalling network. Tissue injury disorders present grievous clinical problems and are likely to increase since they are generally associated with the prevailing diseases such as diabetes, hypertension and obesity. Although these dynamic responses vary not only for the different types of trauma but also for the different organs, a balancing act between the tissue degradation and tissue synthesis is the same. In this process, the degradation of old extracellular matrix (ECM) elements and new ones' synthesis and deposition play an essential role, especially collagens. Lysyl oxidase (LOX) and four lysyl oxidase-like proteins are a group of enzymes capable of catalyzing cross-linking reaction of collagen and elastin, thus initiating the formation of covalent cross-links that insolubilize ECM proteins. In this way, LOX facilitates ECM stabilization through ECM formation, development, maturation and remodeling. This ability determines its potential role in tissue repair and regeneration. In this review, based on the current in vitro, animal and human in vivo studies which have shown the significant role of the LOXs in tissue repair, e.g., tendon regeneration, ligament healing, cutaneous wound healing, and cartilage remodeling, we focused on the role of the LOXs in inflammation phase, proliferation phase, and tissue remodeling phase of the repair process. By summarizing its healing role, we hope to shed light on the understanding of its potential in tissue repair and provide up to date therapeutic strategies towards related injuries.

Endothelial Antioxidant-1: a Key Mediator of Copper-dependent Wound Healing in vivo

Copper (Cu), an essential nutrient, promotes wound healing, however, target of Cu action and underlying mechanisms remain elusive. Cu chaperone Antioxidant-1 (Atox1) in the cytosol supplies Cu to the secretory enzymes such as lysyl oxidase (LOX), while Atox1 in the nucleus functions as a Cu-dependent transcription factor. Using mouse cutaneous wound healing model, here we show that Cu content (by X-ray Fluorescence Microscopy) and nuclear Atox1 are increased after wounding, and that wound healing with and without Cu treatment is impaired in Atox1^-/- mice. Endothelial cell (EC)-specific Atox1^-/- mice and gene transfer of nuclear-target Atox1 in Atox1^-/- mice reveal that Atox1 in ECs as well as transcription factor function of Atox1 are required for wound healing. Mechanistically, Atox1^-/- mice show reduced Atox1 target proteins such as p47phox NADPH oxidase and cyclin D1 as well as extracellular matrix Cu enzyme LOX activity in wound tissues. This in turn results in reducing O₂^- production in ECs, NFkB activity, cell proliferation and collagen formation, thereby inhibiting angiogenesis, macrophage recruitment and extracellular matrix maturation. Our findings suggest that Cu-dependent transcription factor/Cu chaperone Atox1 in ECs plays an important role to sense Cu to accelerate wound angiogenesis and healing.

Fusaric acid induces a notochord malformation in zebrafish via copper chelation

Over a thousand extracts were tested for phenotypic effects in developing zebrafish embryos to identify bioactive molecules produced by endophytic fungi. One extract isolated from Fusarium sp., a widely distributed fungal genus found in soil and often associated with plants, induced an undulated notochord in developing zebrafish embryos. The active compound was isolated and identified as fusaric acid. Previous literature has shown this phenotype to be associated with copper chelation from the active site of lysyl oxidase, but the ability of fusaric acid to bind copper ions has not been well described. Isothermal titration calorimetry revealed that fusaric acid is a modest copper chelator with a binding constant of 4.4 × 10(5) M(-1). These results shed light on the toxicity of fusaric acid and the potential teratogenic effects of consuming plants infected with Fusarium sp.

Differential expressions of lysyl oxidase family in ACL and MCL fibroblasts after mechanical injury

Lysyl oxidase (LOX) family has the capacity to catalyse the cross-linking of collagen and elastin, implicating its important fundamental roles in tissue development and injury healing. However, the variations in expression of the LOX family in the normal and injured anterior cruciate ligament (ACL) are not fully known. To better understand the role of LOX family in the self-healing inability mechanism of injured ACL, this study is to measure the LOX family's differential expressions in ACL and medial collateral ligament (MCL) fibroblasts after mechanical injury induced by using an equi-biaxial stretching chamber. The cells received various degrees of mechanical stretch 0% (resting state), 6% (physiological state) and 12% (injurious state), respectively. The gene profile and protein expressions were analysed by semi-quantitative PCR, quantitative real-time PCR and Western blotting. At physiological state, gene expression showed LOX in ACL was 2.6-5.2 folds higher than that in MCL in all culture time periods, LOXL-4 1.2-3.6 folds, but LOXL-3 in MCL showed 1.1-4.8 folds higher than that in ACL. In injurious state, MCL gene expressions were 2.8-29.6 folds higher than ACL in LOX, LOXL-2, LOXL-3 and LOXL-4 at 2, 6 and 12h periods. These differential expression profiles of the LOX family in the two ligament tissues were further used to explain the intrinsic differences between ACL and MCL, and why injured ACL could not be amenable to repair itself, whereas MCL could.

Cellular distribution and gene expression profile during flexor tendon graft repair: A novel tissue engineering approach(*)

To understand scar and adhesion formation during postsurgical period of intrasynovial tendon graft healing, a murine model of flexor digitorum longus tendon graft repair was developed, by utilizing flexor digitorum longus tendon allograft from donor Rosa26/+ mouse, and the healing process at days 3, 7, 14, 21, 28, and 35 post surgery of host wild-type mouse was followed. Using X-gal staining, β-galactosidase positive cells of allograft origin were detectable in tissue sections of grafted tendon post surgery. Graft healing was assessed for the cellular density, scar and adhesion formation, and their interaction with surrounding tissue. From histological analysis, it was evident that the healing of intrasynovial flexor digitorum longus tendon graft takes place in an interactive environment of donor graft, host tendon, and host surrounding tissue. A total of 32 genes, analyzed by RNA analysis, expressed during healing process. Particularly, Alk1, Postn, Tnc, Tppp3, and Mkx will be further investigated for therapeutical value in reducing scars and adhesions.

Fibroblast function and wound breaking strength is impaired by acute ethanol intoxication

BACKGROUND

Alcohol intoxication occurs in nearly half of all trauma patients and increases the morbidity, mortality, and healing complications of these patients. Prior studies in our laboratory and elsewhere have demonstrated impairments in re-epithelialization, angiogenesis, and inflammation in wounds following acute ethanol exposure. Clinically, acute ethanol exposure has been shown to cause an increased breakdown of wounds. To date, the mechanisms by which acute ethanol exposure modifies wound strength have received little experimental attention.

METHODS

To examine how ethanol influences functions critical to the development of wound strength, the effect of ethanol exposure on fibroblast proliferation and extracellular matrix production was examined. Normal human dermal fibroblasts (NHDF) were exposed to ethanol (100 mg/dl) and then examined for proliferative capacity and mRNA production of collagen I, collagen III, and lysyl oxidase (LOX). In in vivo studies, the wound breaking strength, LOX activity, collagen, and hyaluronic acid (HA) contents of wounds of ethanol-exposed (100 mg/dl) mice were examined.

RESULTS

At 24, 48, and 72 hours after acute ethanol exposure (8 hours duration), NHDF displayed a significant impairment in proliferative capacity (up to 50% at 24 hours p < 0.001). After ethanol exposure, NHDF produced less collagen I and LOX mRNA, but more collagen III mRNA than control fibroblasts (p < 0.05). Ethanol exposure in vivo caused a reduction in wound breaking strength of up to 40% when compared to control mice (p < 0.01). LOX activity, collagen, and HA contents in the wounds of ethanol-exposed mice were significantly reduced (p < 0.01).

CONCLUSIONS

These studies reveal that a single exposure to ethanol prior to injury can cause a significant decrease in wound breaking strength. Our studies suggest that ethanol directly impairs fibroblast function, leading to decreased collagen production. The results provide a possible explanation for how acute ethanol exposure might increase in wound complications and wound failure.

Functional consequences of mitochondrial DNA deletions in human skin fibroblasts: increased contractile strength in collagen lattices is due to oxidative stress-induced lysyl oxidase activity

Deletions within the mitochondrial DNA (mtDNA) are thought to contribute to extrinsic skin aging. To study the translation of mtDNA deletions into functional and structural changes in the skin, we seeded human skin fibroblasts into collagen gels to generate dermal equivalents. These cells were either derived from Kearns-Sayre syndrome (KSS) patients, who constitutively carry large amounts of the UV-inducible mitochondrial common deletion, or normal human volunteers. We found that KSS fibroblasts, in comparison with normal human fibroblasts, contracted the gels faster and more strongly, an effect that was dependent on reactive oxygen species. Gene expression and Western blot analysis revealed significant upregulation of lysyl oxidase (LOX) in KSS fibroblasts. Treatment with the specific LOX inhibitor beta-aminopropionitrile decreased the contraction difference between KSS and normal human fibroblast equivalents. Also, addition of the antioxidant N-tert-butyl-alpha-phenylnitrone reduced the contraction difference by inhibiting collagen gel contraction in KSS fibroblasts, and both beta-aminopropionitrile and N-tert-butyl-alpha-phenylnitrone diminished LOX activity. These data suggest a causal relationship between mtDNA deletions, reactive oxygen species production, and increased LOX activity that leads to increased contraction of collagen gels. Accordingly, increased LOX expression was also observed in vivo in photoaged human and mouse skin. Therefore, mtDNA deletions in human fibroblasts may lead to functional and structural alterations of the skin.

Early-gestation fetal scarless wounds have less lysyl oxidase expression

BACKGROUND

Lysyl oxidase cross-links collagen and elastin. Because cross-linking likely influences collagen architecture, the authors compared lysyl oxidase expression during scarless and scarring fetal dermal wound repair.

METHODS

Excisional dermal wounds were made on E17 (gestational day 16.5) and E19 (gestational day 18.5) mouse fetuses. Skin and wound RNA was collected at 8, 12, and 24 hours. Quantitative real-time polymerase chain reaction was performed for lysyl oxidase. The effect of transforming growth factor (TGF)-beta1 on lysyl oxidase expression in fetal fibroblasts was tested. Confluent primary fetal and postnatal fibroblast cultures were stimulated with TGF-beta1 for 24 hours, and lysyl oxidase expression was quantitated by performing real-time polymerase chain reaction. Lysyl oxidase expression was also quantitated in unwounded fetal skin to determine its expression profile during development.

RESULTS

E17 and E19 fetal skin had approximately 2-fold greater lysyl oxidase expression than postnatal skin (p < 0.01), and fetal fibroblasts had greater baseline lysyl oxidase expression than postnatal fibroblasts. After TGF-beta1 stimulation, fetal and postnatal fibroblasts responded with increases in lysyl oxidase expression. In E17 early-gestation scarless fetal wounds, lysyl oxidase had small increases (<1.5-fold) in expression from 1 to 12 hours. In late-gestation E19 scarring fetal wounds, lysyl oxidase increased 1.8-fold at 8 hours and 2-fold at 12 hours, which was significantly greater than the changes observed in E17 scarless wounds (p < 0.01 for each).

CONCLUSIONS

Lysyl oxidase has greater expression in E19 late-gestation wounds that heal with scar compared with E17 early-gestation scarless wounds. This suggests a role for lysyl oxidase in scar formation.

Lysyl oxidase in development, aging and pathologies of the skin

Lysyl oxidase (LOX) is a copper- and lysyl-tyrosyl cofactor containing amine oxidase that has been known to play a critical role in the catalysis of lysine-derived crosslinks in extracellular matrix (ECM) proteins in the dermis. Changes in the composition and crosslinked state of the ECM and alterations in LOX synthesis and activity are known to be associated with aging and a range of acquired and heritable skin disorders. It has been assumed until recently that the LOX-related changes in the skin are mediated through the catalytic activity of LOX. However, work by several laboratories over the last few years has shown that LOX is a multifunctional protein. In this review we discuss the regulation of expression, localization and activation of LOX in the normal developing and adult skin, and alterations in LOX expression and activity associated with skin aging and senescence, and in pathological conditions, including wound healing, fibrosis, hypertrophic scarring, keloids, scleroderma, and diabetic skin. We further evaluate the role of LOX in skin ECM changes associated with the normal aging process and with these pathological states. In addition to collagen and elastin cross-linkages, regulatory and activation mechanisms and cell type specific LOX interactions may contribute to a range of novel intra- and extracellular LOX functions that appear critical determinants of the cellular microenvironment in the normal skin and in these skin disorders.

Cellular fibronectin binds to lysyl oxidase with high affinity and is critical for its proteolytic activation

Lysyl oxidase (LOX) is a copper-containing amine oxidase known to catalyze the covalent cross-linking of fibrillar collagens and elastin at peptidyl lysine residues. In addition, its involvement in cancer, wound healing, cell motility, chemotaxis, and differentiation reflect a remarkable functional diversity of LOX. To investigate novel mechanisms of LOX regulation and function, we performed a yeast two-hybrid screen to identify LOX-interacting proteins. Three overlapping positive clones were identified as C-terminal fragments of fibronectin (FN). Glutathione S-transferase pull-downs and solid phase binding assays confirmed this interaction. LOX binds to the cellular form of FN (cFN) with a dissociation constant (K(d)) of 2.5 nm. This was comparable with our measured K(d) of LOX binding to tropoelastin (1.9 nm) and type I collagen (5.2 nm), but LOX demonstrated a much lower binding affinity for the plasma form of FN (pFN). Immunofluorescent microscopy revealed co-localization of FN and LOX in normal human tissues, where these proteins may interact in vivo. LOX enzymatic activity assays showed that cFN does not seem to be a substrate of LOX. However, cFN can act as a scaffold for enzymatically active 30-kDa LOX. Furthermore, in FN-null mouse embryonic fibroblasts, we observed dramatically decreased proteolytic processing of the 45-kDa LOX proenzyme to the 30-kDa active form, with a corresponding decrease in LOX enzyme activity. Our results suggest that the FN matrix may provide specific microenvironments to regulate LOX catalytic activity.

Lysyl oxidase expression in a rat model of arterial balloon injury

OBJECTIVE

Traditional therapies for arteriosclerotic disease often fail as a result of an exaggerated fibroproliferative response (recurrent stenosis) at the site of the intervention. Lysyl oxidase, secreted by activated vascular smooth muscle cells and fibroblasts, catalyzes a key step in the cross-linking and stabilization of collagen and elastin in the vascular wall. We hypothesized that lysyl oxidase messenger RNA (mRNA) and protein expression are time-dependent and precede collagen accumulation and luminal narrowing after arterial balloon injury in the rat.

METHODS

A 2F balloon-tipped catheter was used to injure the right common carotid artery in male Sprague-Dawley rats. Injured right and control (uninjured) left common carotid arteries were harvested at 0, 0.25, 1, 3, 7, 14, 21, 28, and 60 days for mRNA quantitation and immunohistochemical analysis. Steady-state lysyl oxidase mRNA levels were quantitated with real-time reverse transcription polymerase chain reaction (TaqMan). Immunohistochemical staining with antibodies to alpha-smooth muscle cell actin and lysyl oxidase, and Movat pentachrome staining were performed for qualitative assessment of changes in the cellular and extracellular matrix components of the vessel wall. Post-injury intimal area was measured from hematoxylin and eosin-stained specimens at each time point.

RESULTS

When compared with sham-operated control arteries, lysyl oxidase expression in balloon-injured arteries increased significantly to 212% by day 3 after injury, and remained elevated through day 21, with a decrease toward baseline levels by day 28. Lysyl oxidase protein expression did not peak until day 14, and persisted through day 28. Collagen accumulation peaked at day 28, corresponding to the maximal increase in intimal area, with later accumulation of proteoglycans and ground substance in the intimal lesion.

CONCLUSION

Our results indicate that lysyl oxidase mRNA and protein expression is time-dependent after balloon injury of the rat carotid artery and that expression appears to precede maximal collagen accumulation and corresponding increases in intimal area. This suggests that lysyl oxidase may have an important role in stabilization of collagen and elastin at sites of vascular injury and that modulation of lysyl oxidase activity may be a viable method to prevent or reduce recurrent stenosis.

CLINICAL RELEVANCE

Failure of traditional therapies for ischemic arteriosclerotic disease is often due to an exaggerated fibroproliferative response (recurrent stenosis) at the site of intervention. Recurrent stenosis can be viewed as an injury-repair process, with an initial stage characterized by cellular proliferation followed by deposition of extracellular matrix. This study focuses on lysyl oxidase, a key enzyme involved in stabilization of collagen and elastin. This study demonstrates that lysyl oxidase messenger RNA and protein expression are time-dependent, preceding collagen accumulation and corresponding increases in intimal area. Accumulation of extracellular matrix is a major factor in growth of the restenotic lesion, and modulation of lysyl oxidase activity may offer a therapeutic method for decreasing or preventing recurrent stenosis.

Lysyl oxidases: a novel multifunctional amine oxidase family

Lysyl oxidase (LOX), a copper-containing amine oxidase, belongs to a heterogeneous family of enzymes that oxidize primary amine substrates to reactive aldehydes. LOX has been traditionally known for one function, the extracellular catalysis of lysine-derived cross-links in fibrillar collagens and elastin. More recently, diverse roles have been attributed to lysyl oxidase and these novel activities cover a spectrum of diverse biological functions such as developmental regulation, tumor suppression, cell motility, and cellular senescence. Lysyl oxidase has also been shown to have both intracellular and intranuclear locations. The multifunctional properties of lysyl oxidase (LOX) and our recent discovery of three novel members of this amine oxidase family, LOX-like (LOXL), LOXL2, and LOXL3, indicate the possibility that these varied functions are performed in both intracellular and extracellular environments by individual novel members of the LOX amine-oxidase family. Structural similarities of the highly conserved copper-binding and lysyl-tyrosylquinone cofactor sites among the LOX and LOX-like proteins may result in similar amine oxidase activities. However, specific novel functions, such as a potential role in cell adhesion and cell growth control, will be determined by other, conserved domains such as the cytokine receptor-like domain that is shared by all LOXs and by multiple scavenger receptor cysteine-rich (SRCR) domains present in LOXL2 and LOXL3. Furthermore, these functions may be carried out in a temporally and spatially regulated fashion.

Enhancement of fibroblast collagen synthesis by nitric oxide

Fibroblasts can be stimulated by cytokines to synthesize nitric oxide (NO, nitrogen monoxide), while wound-derived fibroblasts synthesize NO spontaneously. Since wound fibroblasts are phenotypically characterized by greater collagen synthesis when compared to fibroblasts derived from noninjured tissue, we hypothesized that there may be a correlation between wound-induced NO synthesis and enhanced collagen production. To study the role of NO on collagen metabolism, normal dermal fibroblasts were cultured in the presence or absence of the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) and their collagen metabolism was studied on the transcriptional as well as translational level. Fibroblast collagen synthesis was enhanced by 74.3 +/- 18.2 and 87.5 +/- 28.2% in the presence of 100 and 400 microM SNAP, respectively. This effect was not due to increased collagen type I or type III gene transcription. Cellular proliferation measured by thymidine incorporation was significantly decreased in the presence of SNAP, indicating that the increased collagen production was due to a net increase of collagen synthesis by the cells. Investigation of the collagen breakdown pathway showed that neither collagenase gene expression nor collagenase protein expression was affected by SNAP. The results of this study demonstrate for the first time that NO enhances collagen synthesis, most likely at a posttranslational level.

Cross-linked telopeptides of type I and III collagens in malignant ovarian tumours in vivo

Malignant tumours often induce a fibroproliferative response in the adjacent stroma, characterized by increased expression of type I and type III procollagens. In normal tissues, fibrillar collagens normally undergo extensive intermolecular cross-linking that provides tensile strength to the tissue. Here we set out to characterize collagen cross-linking in human ovarian carcinoma tissue in vivo. Biochemical and immunochemical methods were used for cross-linked telopeptides of type I and III collagens in samples of benign and malignant serous tumours. The locations and staining patterns of these proteins were visualized immunohistochemically. The contents of both total collagen and the cross-linked type I and type III collagens in the malignant samples were only about 20% of those in the benign tumours. The cross-linked telopeptide antigens derived from the collagens were smaller and more heterogeneous in size in the malignant than in the benign tumours, indicating a defective cross-linking process scarcely leading to the formation of mature cross-links in the collagen fibres in malignancy. Immunostaining revealed disorganized type I and type III collagen bundles in carcinomas. These findings suggest that the collagen cross-linking process is aberrant in malignant tumours, possibly resulting in increased susceptibility of tumour collagens for the proteolysis often associated with tumour invasion.