The distributions of type IV collagen alpha chains in basement membranes of human epidermis and skin appendages

Expression of extracellular matrix components in the meibomian gland

Purpose

Extracellular matrix (ECM) is a key component of the stem cell local microenvironment. Our study aims to explore the periglandular distribution of major components of ECM in the Meibomian gland (MG).

Methods

Human eyelids and mouse eyelids were collected and processed for immunofluorescence staining.

Results

Human MG tissues stained positive for collagen IV α1, collagen IV α2, collagen IV α5, and collagen IV α6 around the acini and duct, but negative for collagen IV α3 and collagen IV α4. The mouse MG were stained positive for the same collagen IV subunits as early as postnatal day 15. Laminin α2, laminin β1 and perlecan stained the regions surrounding the acini and the acinar/ductal junction in the human MG, but not the region around the duct. Tenascin-C was found specifically located at the junctions between the acini and the central ducts. Neither agrin nor endostatin was found in the human MG tissues.

Conclusion

The ECM expresses specific components in different regions around the MG, which may play a role in MG stem cell regulation, renewal, and regeneration.

Lack of collagen α6(IV) chain in mice does not cause severe-to-profound hearing loss or cochlear malformation, a distinct phenotype from nonsyndromic hearing loss with COL4A6 missense mutation

Congenital hearing loss affects 1 in every 1000 births, with genetic mutations contributing to more than 50% of all cases. X-linked nonsyndromic hereditary hearing loss is associated with six loci (DFNX1-6) and five genes. Recently, the missense mutation (c.1771G>A, p.Gly591Ser) in COL4A6, encoding the basement membrane (BM) collagen α6(IV) chain, was shown to be associated with X-linked congenital nonsyndromic hearing loss with cochlear malformation. However, the mechanism by which the COL4A6 mutation impacts hereditary hearing loss has not yet been elucidated. Herein, we investigated Col4a6 knockout (KO) effects on hearing function and cochlear formation in mice. Immunohistochemistry showed that the collagen α6(IV) chain was distributed throughout the mouse cochlea within subepithelial BMs underlying the interdental cells, inner sulcus cells, basilar membrane, outer sulcus cells, root cells, Reissner's membrane, and perivascular BMs in the spiral limbus, spiral ligament, and stria vascularis. However, the click-evoked auditory brainstem response analysis did not show significant changes in the hearing threshold of Col4a6 KO mice compared with wild-type (WT) mice with the same genetic background. In addition, the cochlear structures of Col4a6 KO mice did not exhibit morphological alterations, according to the results of high-resolution micro-computed tomography and histology. Hence, loss of Col4a6 gene expression in mice showed normal click ABR thresholds and normal cochlear formation, which differs from humans with the COL4A6 missense mutation c.1771G>A, p.Gly591Ser. Therefore, the deleterious effects in the auditory system caused by the missense mutation in COL4A6 are likely due to the dominant-negative effects of the α6(IV) chain and/or α5α6α5(IV) heterotrimer with an aberrant structure that would not occur in cases with loss of gene expression.

Laminins and interaction partners in the architecture of the basement membrane at the dermal-epidermal junction

The basement membrane at the dermal-epidermal junction keeps the epidermis attached to the dermis. This anatomical barrier is made up of four categories of extracellular matrix proteins: collagen IV, laminin, nidogen and perlecan. These proteins are precisely arranged in a well-defined architecture through specific interactions between the structural domains of the individual components. Some of the molecular constituents are provided by both fibroblasts and keratinocytes, while others are synthesized exclusively by fibroblasts or keratinocytes. It remains to be determined how the components from the fibroblasts are targeted to the dermal-epidermal junction and correctly organized and integrated with the proteins from the adjacent keratinocytes to form the basement membrane.

Unripe peach (Prunus persica) extract ameliorates damage from UV irradiation and improved collagen XVIII expression in 3D skin model

INTRODUCTION

Collagen type XVIII regulates cellular activities of adjacent cells at the dermal-epidermal junction (DEJ). To investigate its possible changes during aging, we compared its mRNA levels and protein localization in skin samples from female participants aged 20-70 years old. In addition, we evaluated the beneficial effects of unripe peach extracts in a 3D skin model.

METHODS

Sun-exposed or sun-protected female skin samples were compared by DNA array or by immunohistochemistry for basement membrane components. To evaluate protective effects of fresh unripe peach extract, UV-B irradiated human 3D skin models were incubated in the presence or absence of the extract, followed by measurements of mRNA levels by real-time PCR, or by immunohistochemistry.

RESULTS

In aged skin samples, COL18A1 mRNA levels were lower and the protein localization exhibited less intensive signal by anti-collagen type XVIII immunostaining. As observed in the skin tissues, collagen type XVIII exists at the DEJ in the 3D skin model. Fresh unripe peach extract significantly improved mRNA levels and partially localizations of collagen type XVIII, suggesting that fresh unripe peach extract ameliorates DEJ damages caused by UV-B irradiation.

CONCLUSION

Collagen type XVIII and fresh unripe peach extract can be promising protective cosmetic strategies against skin aging.

Cathepsin S degrades arresten and canstatin in infarcted area after myocardial infarction in rats

The basement membrane surrounding cardiomyocytes is mainly composed of α1 and α2 chain of type IV collagen. Arresten and canstatin are fragments of non-collagenous C-terminal domain of α1 and α2 chain, respectively. We previously reported that the expression of canstatin was decreased in infarcted area 2 weeks after myocardial infarction in rats. In the present study, we investigated the regulatory mechanism for expression of arresten and canstatin. Myocardial infarction model rats were produced by ligating left anterior descending artery. Western blotting and immunohistochemical staining were performed to determine the protein expression and distribution. Arresten and canstatin were highly expressed in the heart. One day and three days after myocardial infarction, the expression of arresten and canstatin in infarcted area was lower than that in non-infarcted area. The expression of cathepsin S, which is known to degrade arresten and canstatin, was increased in the infarcted area. A knockdown of cathepsin S gene using small interference RNA suppressed the decline of arresten and canstatin in the infarcted area 3 days after myocardial infarction. This study for the first time revealed that arresten and canstatin are immediately degraded by cathepsin S in the infarcted area after myocardial infarction. These findings present a novel fundamental insight into the pathogenesis of myocardial infarction through the turnover of basement membrane-derived endogenous factors.

Strategies for Optimizing the Soft Tissue Seal around Osseointegrated Implants

Percutaneous and permucosal devices such as catheters, infusion pumps, orthopedic, and dental implants are commonly used in medical treatments. However, these useful devices breach the soft tissue barrier that protects the body from the outer environment, and thus increase bacterial infections resulting in morbidity and mortality. Such associated infections can be prevented if these devices are effectively integrated with the surrounding soft tissue, and thus creating a strong seal from the surrounding environment. However, so far, there are no percutaneous/permucosal medical devices able to prevent infection by achieving strong integration at the soft tissue-device interface. This review gives an insight into the current status of research into soft tissue-implant interface and the challenges associated with these interfaces. Biological soft/hard tissue interfaces may provide insights toward engineering better soft tissue interfaces around percutaneous devices. In this review, focus is put on the history and current findings as well as recent progress of the strategies aiming to develop a strong soft tissue seal around osseointegrated implants, such as orthopedic and dental implants.

Investigating the race for the surface and skin integration in clinically retrieved abutments with two-photon microscopy

Bone conduction hearing implants can rehabilitate some types of hearing loss. A hydroxyapatite (HA)-coated skin-penetrating abutment was developed to allow for soft tissue preservation and increased skin-abutment adherence. Inflammation is thought to relate to bacterial infection of pockets around the abutment. Upon integration, the host's ability to cover the abutment surface ("race for the surface"), and thus control and prevent competitive bacteria from colonizing it, is improved. However, the attachment mechanisms behind it are not clear. In this study, we applied two-photon microscopy to visualize tissue attachment on abutments retrieved from patients. Skin integration markers were validated and applied to four HA-coated abutments. Evidence of skin integration was found, including the presence of hemidesmosomes, a basement membrane, dermal collagen and vascularization. Cases with clinical signs of severe inflammation and evident biofilm formation showed limited skin integration based on these indicators, confirming the applicability of the "race for the surface" model.

Functional assessment of a novel COL4A5 splice region variant and immunostaining of plucked hair follicles as an alternative method of diagnosis in X-linked Alport syndrome

BACKGROUND

Many COL4A5 splice region variants have been described in patients with X-linked Alport syndrome, but few have been confirmed by functional analysis to actually cause defective splicing. We sought to demonstrate that a novel COL4A5 splice region variant in a family with Alport syndrome is pathogenic using functional studies. We also describe an alternative method of diagnosis.

METHODS

Targeted next-generation sequencing results of an individual with Alport syndrome were analyzed and the results confirmed by Sanger sequencing in family members. A splicing reporter minigene assay was used to examine the variant's effect on splicing in transfected cells. Plucked hair follicles from patients and controls were examined for collagen IV proteins using immunofluorescence microscopy.

RESULTS

A novel splice region mutation in COL4A5, c.1780-6T>G, was identified and segregated with disease in this family. This variant caused frequent skipping of exon 25, resulting in a frameshift and truncation of collagen α5(IV) protein. We also developed and validated a new approach to characterize the expression of collagen α5(IV) protein in the basement membranes of plucked hair follicles. Using this approach we demonstrated reduced collagen α5(IV) protein in affected male and female individuals in this family, supporting frequent failure of normal splicing.

CONCLUSIONS

Differing normal to abnormal transcript ratios in affected individuals carrying splice region variants may contribute to variable disease severity observed in Alport families. Examination of plucked hair follicles in suspected X-linked Alport syndrome patients may offer a less invasive alternative method of diagnosis and serve as a pathogenicity test for COL4A5 variants of uncertain significance.

Epidermal Basement Membrane in Health and Disease

Skin, as the organ protecting the individual from environmental aggressions, constantly meets external insults and is dependent on mechanical toughness for its preserved function. Accordingly, the epidermal basement membrane (BM) zone has adapted to enforce tissue integrity. It harbors anchoring structures created through unique organization of common BM components and expression of proteins exclusive to the epidermal BM zone. Evidence for the importance of its correct assembly and the nonredundancy of its components for skin integrity is apparent from the multiple skin blistering disorders caused by mutations in genes coding for proteins associated with the epidermal BM and from autoimmune disorders in which autoantibodies target these molecules. However, it has become clear that these proteins not only provide mechanical support but are also critically involved in tissue homeostasis, repair, and regeneration. In this chapter, we provide an overview of the unique organization and components of the epidermal BM. A special focus will be given to its function during regeneration, and in inherited and acquired diseases.

Collagen IV in Normal Skin and in Pathological Processes

CONTEXT

Type IV collagen is a type of collagen found primarily in the skin within the basement membrane zone. The type IV collagen C4 domain at the C-terminus is not removed in post-translational processing, and the fibers are thus link head-to-head, rather than in a parallel fashion. Also, type IV collagen lacks a glycine in every third amino-acid residue necessary for the tight collagen helix. Thus, the overall collagen-IV conformation is structurally more pliable and kinked, relative to other collagen subtypes. These structural features allow collagen IV to form sheets, which is the primary structural form found in the cutaneous basal lamina. There are six human genes associated with collagen IV, specifically COL4A1, COL4A2, COL4A3, COL4A4, COL4A5 and COL4A6. The aim of this review is to highlight the significance of this protein in normal skin, and in selected diseases.

RESULTS

The alpha 3 protein constituent of type IV collagen is thought to be the antigen implicated in Goodpasture's syndrome, wherein the immune system attacks the basement membranes of the renal glomeruli and pulmonary alveoli. In addition, mutations to the genes coding for type IV collagen lead to the Alport syndrome. Furthermore, autoantibodies directed against denatured human type IV collagen have been described in rheumatoid arthritis, scleroderma, and SLE. Structural studies of collagen IV have been utilized to differentiate between subepidermal blistering diseases, including bullous pemphigoid, acquired epidermolysis bullosa, anti-epiligrin cicatricial pemphigoid, and bullous lupus erythematosus. Collagen IV is also of importance in wound healing and in embryogenesis.

CONCLUSIONS

Pathological studies have demonstrated that minor structural differences in collagen IV can lead to distinct, clinically different diseases.

The epidermal basement membrane is a composite of separate laminin- or collagen IV-containing networks connected by aggregated perlecan, but not by nidogens

The basement membrane between the epidermis and the dermis is indispensable for normal skin functions. It connects, and functionally separates, the epidermis and the dermis. To understand the suprastructural and functional basis of these connections, heterotypic supramolecular aggregates were isolated from the dermal-epidermal junction zone of human skin. Individual suprastructures were separated and purified by immunomagnetic beads, each recognizing a specific, molecular component of the aggregates. The molecular compositions of the suprastructures were determined by immunogold electron microscopy and immunoblotting. A composite of two networks was obtained from fibril-free suspensions by immunobeads recognizing either laminin 332 or collagen IV. After removal of perlecan-containing suprastructures or after enzyme digestion of heparan sulfate chains, a distinct network with a diffuse electron-optical appearance was isolated with magnetic beads coated with antibodies to collagen IV. The second network was more finely grained and comprised laminin 332 and laminins with α5-chains. The core protein of perlecan was an exclusive component of this network whereas its heparan sulfate chains were integrated into the collagen IV-containing network. Nidogens 1 and 2 occurred in both networks but did not form strong molecular cross-bridges. Their incorporation into one network appeared to be masked after their incorporation into the other one. We conclude that the epidermal basement membrane is a composite of two structurally independent networks that are tightly connected in a spot-welding-like manner by perlecan-containing aggregates.

Skin regeneration in adult axolotls: a blueprint for scar-free healing in vertebrates

While considerable progress has been made towards understanding the complex processes and pathways that regulate human wound healing, regenerative medicine has been unable to develop therapies that coax the natural wound environment to heal scar-free. The inability to induce perfect skin regeneration stems partly from our limited understanding of how scar-free healing occurs in a natural setting. Here we have investigated the wound repair process in adult axolotls and demonstrate that they are capable of perfectly repairing full thickness excisional wounds made on the flank. In the context of mammalian wound repair, our findings reveal a substantial reduction in hemostasis, reduced neutrophil infiltration and a relatively long delay in production of new extracellular matrix (ECM) during scar-free healing. Additionally, we test the hypothesis that metamorphosis leads to scarring and instead show that terrestrial axolotls also heal scar-free, albeit at a slower rate. Analysis of newly forming dermal ECM suggests that low levels of fibronectin and high levels of tenascin-C promote regeneration in lieu of scarring. Lastly, a genetic analysis during wound healing comparing epidermis between aquatic and terrestrial axolotls suggests that matrix metalloproteinases may regulate the fibrotic response. Our findings outline a blueprint to understand the cellular and molecular mechanisms coordinating scar-free healing that will be useful towards elucidating new regenerative therapies targeting fibrosis and wound repair.

Distribution of α(IV) collagen chains in the ocular anterior segments of adult mice

The distribution of the collagen chains from α1(IV) to α6(IV) could serve as a basis for the characterization of type IV collagen. In this study, immunohistochemistry of the ocular anterior segment of adult mice was performed using specific monoclonal antibodies against each chain in the series from α1(IV) to α6(IV). The results show that the components of type IV collagen in vascular basement membranes are α1(IV) and α2(IV) with or without α5(IV) and α6(IV) chains and those in epithelium and muscle basement membranes are α1(IV), α2(IV), α5(IV), and α6(IV) chains. In corneal endothelium, pigmented epithelium of iris and ciliary body, and trabecular meshwork, α3(IV) and α4(IV) chains are also expressed in addition to α1(IV), α2(IV), α5(IV), and α6(IV) chains. Moreover, we investigated the change in molecular composition in ciliary body during postnatal development. α3(IV) and α4(IV) chains were also expressed in addition to α1(IV), α2(IV), α5(IV), and α6(IV) chains in ciliary pigmented epithelium basement membrane from 7 days after birth. This result suggests that the basement membranes gradually change their biochemical features owing to temporal regulation. Taken together, these findings suggest that the different distribution and the developmental expression of α1(IV) to α6(IV) chains are associated with the tissue-specific function of type IV collagen in basement membranes.

Type IV collagen alpha chains of the basement membrane in the rat bronchioalveolar transitional segment

In the present study, we have analyzed the alpha(IV) chain distribution in the subepithelial basement membrane (BM) of the rat pulmonary airway from the bronchi to alveoli. We have furthermore analyzed the alpha(IV) chain distribution in the subepithelial BM of the bronchioalveolar duct junction (BADJ) using alpha(IV) chain specific monoclonal antibodies. Our results show that the BM of the bronchial and bronchiolar epithelium contains [alpha1(IV)]2alpha2(IV) and [alpha5(IV)]2alpha6(IV) molecules and confirmed that the alveolar BM consists of [alpha1(IV)]2alpha2(IV) and alpha3(IV) alpha4(IV)alpha5(IV) molecules. There are also small regions in BADJ consisting of only [alpha1(IV)]2alpha2(IV) molecules without alpha3(IV)alpha4(IV)alpha5(IV) and [alpha5(IV)]2alpha6(IV) molecules. Moreover, the bronchioalveolar stem cells (BASCs)-primordial cells for bronchiolar Clara cells and alveolar type II (AT2) cells - lie adjacent to such small regions. These findings suggest that [alpha1(IV)]2 alpha2(IV) may be important for the BASCs to self-renew or to self-maintain themselves and that microenvironments produced by alpha(IV) chains may be important for cell differentiation.

Developmental distribution of collagen IV isoforms and relevance to ocular diseases

Type IV collagens are the most abundant proteins in basement membranes. Distinct genes encode each of six isoforms, alpha1(IV) through alpha6(IV), which assemble into one of three characteristic heterotrimers. Disease-causing mutations in each of the six genes are identified in humans or mice and frequently include diverse ocular pathogenesis that encompass common congenital and progressive blinding diseases, such as optic nerve hypoplasia, glaucoma, and retinal degeneration. Understanding where and when collagen IV molecules are expressed is important because it defines limits for the location and timing of primary pathogenesis. Although localization of collagen IV isoforms in developed human eyes is known, the spatial and temporal distribution of type IV collagens throughout ocular development has not been determined in humans or in mice. Here, we use isoform-specific monoclonal antibodies to systematically reveal the localization of all six collagen IV isoforms in developing mouse eyes. We found that alpha1(IV) and alpha2(IV) always co-localized and were ubiquitously expressed throughout development. alpha3(IV) and alpha4(IV) also always co-localized but in a much more spatially and temporally specific manner than alpha1(IV) and alpha2(IV). alpha5(IV) co-localized both with alpha3(IV)/alpha4(IV), and with alpha6(IV), consistent with alpha5(IV) involvement in two distinct heterotrimers. alpha5(IV) was present in all basement membranes except those of the vasculature. alpha6(IV) was not detected in vasculature or in Bruch's membrane, indicating that alpha5(IV) in Bruch's membrane is part of the alpha3alpha4alpha5 heterotrimer. This comprehensive analysis defines the spatial and temporal distribution of type IV collagen isoforms in the developing eye, and will contribute to understanding the mechanisms underlying collagen IV-related ocular diseases that collectively lead to blindness in millions of people worldwide.

The distribution of type IV collagen alpha chains in the mouse ovary and its correlation with follicular development

The present study aims to identify alpha chains of type IV collagen in the basement membrane of the mouse ovarian follicle and examine their changes during follicular development using immunofluorescence microscopy with specific monoclonal antibodies. The basement membrane of the serous mesothelium enveloping the ovary contained all alpha chains of type IV collagen, alpha1(IV) through alpha6(IV) chains. Primordial follicles showed a distinct immunoreactivity against all six alpha chains in their basement membranes. Immunolabeling for alpha3(IV) and alpha4(IV) chains was almost eliminated in the primary follicles. In basement membranes of secondary and Graafian follicles, the immunofluorescent reaction of alpha3(IV) and alpha4(IV) chains disappeared in Graafian follicles, a partial reduction in fluorescent immunostaining intensity to alpha5(IV) and alpha6(IV) chains was observed; only alpha1(IV) and alpha2(IV) chains were not degraded throughout follicular development. On atretic follicles, in addition to alpha1(IV) and alpha2(IV) chains, alpha3(IV), alpha4(IV), alpha5(IV) and alpha6(IV) chains frequently persisted. A basement membrane-like matrix within the follicular granulosa cell layer, such as the focimatrix (focal intraepithelial matrix) and/or Call-Exner body, was also recognized in mouse secondary and Graafian follicles and contained alpha1(IV), alpha2(IV), alpha5(IV) and alpha6(IV) chains but not alpha3(IV) and alpha4(IV) chains. We expect that the decrease in alpha(IV) chains prompts follicular development and is a prerequisite condition for follicular maturation.