Expression of type XVI collagen in human skin fibroblasts: enhanced expression in fibrotic skin diseases

Tissue mechanics coevolves with fibrillar matrisomes in healthy and fibrotic tissues

Fibrillar proteins are principal components of extracellular matrix (ECM) that confer mechanical properties to tissues. Fibrosis can result from wound repair in nearly every tissue in adults, and it associates with increased ECM density and crosslinking as well as increased tissue stiffness. Such fibrotic tissues are a major biomedical challenge, and an emerging view posits that the altered mechanical environment supports both synthetic and contractile myofibroblasts in a state of persistent activation. Here, we review the matrisome in several fibrotic diseases, as well as normal tissues, with a focus on physicochemical properties. Stiffness generally increases with the abundance of fibrillar collagens, the major constituent of ECM, with similar mathematical trends for fibrosis as well as adult tissues from soft brain to stiff bone and heart development. Changes in expression of other core matrisome and matrisome-associated proteins or proteoglycans contribute to tissue stiffening in fibrosis by organizing collagen, crosslinking ECM, and facilitating adhesion of myofibroblasts. Understanding how ECM composition and mechanics coevolve during fibrosis can lead to better models and help with antifibrotic therapies.

Dermal Fibroblast Heterogeneity and Its Contribution to the Skin Repair and Regeneration

Significance: Dermal fibroblasts are the major cell type in the skin's dermal layer. These cells originate from distinct locations of the embryo and reside in unique niches in the dermis. Different dermal fibroblasts exhibit distinct roles in skin development, homeostasis, and wound healing. Therefore, these cells are becoming attractive candidates for cell-based therapies in wound healing. Recent Advances: Human skin dermis comprises multiple fibroblast subtypes, including papillary, reticular, and hair follicle-associated fibroblasts, and myofibroblasts after wounding. Recent studies reveal that these cells play distinct roles in wound healing and contribute to diverse healing outcomes, including nonhealing chronic wound or excessive scar formation, such as hypertrophic scars (HTS) and keloids, with papillary fibroblasts having antiscarring and reticular fibroblast scar-forming properties. Critical Issues: The identities and functions of dermal fibroblast subpopulations in many respects remain unknown. In this review, we summarize the current understanding of dermal fibroblast heterogeneity, including their defined cell markers and dermal niches, dynamic changes, and contributions to skin wound healing, with the emphasis on scarless healing, healing with excessive scars (HTS and keloids), chronic wounds, and the potential application of this heterogeneity for developing cell-based therapies that allow wounds to heal faster with less scarring. Future Directions: Heterogeneous dermal fibroblast populations and their functions are poorly characterized. Refining and advancing our understanding of dermal fibroblast heterogeneity and their participation in skin homeostasis and wound healing may create potential therapeutic applications for nonhealing chronic wounds or wounds that heal with excessive scarring.

Fibroblast Heterogeneity in and Its Implications for Plastic and Reconstructive Surgery: A Basic Science Review

Fibroblasts’ integral role in tissue development, maintenance, and disease represents a fast-growing field of basic science research. Although fibroblasts were long thought to be a homogeneous cell population, recent research has illuminated the unforeseen complexity of these cells, giving rise to the rapidly expanding research field of “fibroblast heterogeneity.” Fibroblasts play a critical role in states of tissue fibrosis such as skin scarring, which affects hundreds of millions of patients annually and causes severe aesthetic, developmental, and functional morbidity. Beyond scarring, major organ fibrosis is an enormous public health concern responsible for nearly half of all deaths in the United States. Because fibrosis is a conserved response to tissue damage in all organs, the study of fibroblasts throughout the body may help us to understand their role in the conditions most relevant to plastic and reconstructive surgery—for instance, skin scarring (eg, from burns, traumatic lacerations, or surgical incisions), “pathological” scarring (hypertrophic scars, keloids), and capsular contracture. Here, we present a basic science review of fibroblast heterogeneity in wound healing, cancer, organ fibrosis, and human dermal architecture. The field of fibroblast heterogeneity is young, and many of the insights discussed have yet to be translated clinically. However, plastic surgeons stand in a unique position to bridge these discoveries into clinical realities. We hope this information can spur readers to consider both what questions in plastic surgery can be studied from the lens of fibroblast heterogeneity, and how these preclinical insights can be translated to improving care of our patients.

Cartilage-like composition of keloid scar extracellular matrix suggests fibroblast mis-differentiation in disease

Following wound damage to the skin, the scarring spectrum is wide-ranging, from a manageable normal scar through to pathological keloids. The question remains whether these fibrotic lesions represent simply a quantitative extreme, or alternatively, whether they are qualitatively distinct. A three-way comparison of the extracellular matrix (ECM) composition of normal skin, normal scar and keloids was performed using quantitative discovery-based proteomics. This approach identified 40 proteins that were significantly altered in keloids compared to normal scars, and strikingly, 23 keloid-unique proteins. The major alterations in keloids, when functionally grouped, showed many changes in proteins involved in ECM assembly and fibrillogenesis, but also a keloid-associated loss of proteases, and a unique cartilage-like composition, which was also evident histologically. The presence of Aggrecan and Collagen II in keloids suggest greater plasticity and mis-differentiation of the constituent cells. This study characterises the ECM of both scar types to a depth previously underappreciated. This thorough molecular description of keloid lesions relative to normal scars is an essential step towards our understanding of this debilitating clinical problem, and how best to treat it.

Lineage Identity and Location within the Dermis Determine the Function of Papillary and Reticular Fibroblasts in Human Skin

Human skin dermis is composed of the superficial papillary dermis and the reticular dermis in the lower layers, which can easily be distinguished histologically. In vitro analyses of fibroblasts from explant cultures from superficial and lower dermal layers suggest that human skin comprises at least two fibroblast lineages with distinct morphology, expression profiles, and functions. However, while for mouse skin cell surface markers have been identified, allowing the isolation of pure populations of one lineage or the other via FACS, this has not been achieved for human skin fibroblasts. We have now discovered two cell surface markers that discriminate between papillary and reticular fibroblasts. While FAP⁺CD90^- cells display increased proliferative potential, express PDPN and NTN1, and cannot be differentiated into adipocytes, FAP^-CD90⁺ fibroblasts express high levels of ACTA2, MGP, PPARγ, and CD36 and readily undergo adipogenic differentiation, a hallmark of reticular fibroblasts. Flow cytometric analysis of fibroblasts isolated from superficial and lower layers of human dermis showed that FAP⁺CD90^- cells are enriched in the papillary dermis. Altogether, functional analysis and expression profiling confirms that FAP⁺CD90^- cells represent papillary fibroblasts, whereas FAP^-CD90⁺ fibroblasts derive from the reticular lineage. Although papillary and reticular fibroblasts are enriched in the upper or lower dermis, respectively, they are not spatially restricted, and the microenvironment seems to affect their function.

Fibroblast heterogeneity: implications for human disease

Fibroblasts synthesize the extracellular matrix of connective tissue and play an essential role in maintaining the structural integrity of most tissues. Researchers have long suspected that fibroblasts exhibit functional specialization according to their organ of origin, body site, and spatial location. In recent years, a number of approaches have revealed the existence of fibroblast subtypes in mice. Here, we discuss fibroblast heterogeneity with a focus on the mammalian dermis, which has proven an accessible and tractable system for the dissection of these relationships. We begin by considering differences in fibroblast identity according to anatomical site of origin. Subsequently, we discuss new results relating to the existence of multiple fibroblast subtypes within the mouse dermis. We consider the developmental origin of fibroblasts and how this influences heterogeneity and lineage restriction. We discuss the mechanisms by which fibroblast heterogeneity arises, including intrinsic specification by transcriptional regulatory networks and epigenetic factors in combination with extrinsic effects of the spatial context within tissue. Finally, we discuss how fibroblast heterogeneity may provide insights into pathological states including wound healing, fibrotic diseases, and aging. Our evolving understanding suggests that ex vivo expansion or in vivo inhibition of specific fibroblast subtypes may have important therapeutic applications.

New in vivo model to analyse the expression of angiogenic genes in the borders of a cleft lip

Defects in the fusion of facial buds can result from an anomaly in tissue development or apoptosis, or both. Our working hypothesis was that anomalies in the development of tissues could be caused by a genetic angiogenic defect. Our main objective was to design a reproducible experimental model to study the expression of angiogenic genes in the borders of cleft lips with or without cleft palate. We therefore prospectively studied seven non-syndromic patients, three with a cleft lip (2 right, 1 left), and four with a cleft lip and palate (1 bilateral, 2 right, 1 left), with no CGH (comparative genomic hybridisation) array, who had primary operations to repair their clefts. We also used four controls (cultured fibroblasts from healthy skin samples). The mean (range) age at operation was 44 (13-77) days. We studied the lateral and medial borders histologically and did qPCR (quantitative real-time polymerase chain reaction) analysis for gene expression with 22 genes of interest (and two housekeeping genes) involved in cleft lip and angiogenesis. The qPCR analysis found significant (p<0.05) overexpression of eight genes in the medial border and seven in the lateral border, and underexpression of nine genes in the medial, and ten in the lateral border. The difference in expression between the two borders was not significant. This preliminary study has enabled us to develop a new method to analyse the expression of angiogenic genes in the borders of cleft lips.

Minor collagens of the skin with not so minor functions

The structure and function of the skin relies on the complex expression pattern and organisation of extracellular matrix macromolecules, of which collagens are a principal component. The fibrillar collagens, types I and III, constitute over 90% of the collagen content within the skin and are the major determinants of the strength and stiffness of the tissue. However, the minor collagens also play a crucial regulatory role in a variety of processes, including cell anchorage, matrix assembly, and growth factor signalling. In this article, we review the expression patterns, key functions and involvement in disease pathogenesis of the minor collagens found in the skin. While it is clear that the minor collagens are important mediators of normal tissue function, homeostasis and repair, further insight into the molecular level structure and activity of these proteins is required for translation into clinical therapies.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Epidermolysis bullosa - a group of skin diseases with different causes but commonalities in gene expression

Epidermolysis bullosa (EB) is a group of hereditary skin disorders. Although each subtype is caused by mutations in genes encoding differentially located components of the skin, the resulting phenotype is similar. In this study, we investigated similarities in the gene expression profiles of each subtype on mRNA level. Type XVI collagen (COL16A1), G0/G1 switch 2 (G0S2), fibronectin (FN1), ribosomal protein S27A (RPS27A) and low density lipoprotein receptor (LDLR) were shown to exhibit corresponding changes in gene expression in all three EB subtypes. While COL16A1, G0S2 and FN1 are up-regulated, LDLR and RPS27A mRNA levels are decreased. These data indicate that EB cells seem to take measures increasing their mechanical stability. Apoptosis is likely to be exacerbated, and migratory potential appears to be elevated. Protein degradation is hampered, and the release of fatty acids and glycerol is restricted, probably to save energy. These commonalities might benefit existing EB treatment strategies or could help to reveal new starting points for the treatment of EB in the future.

Collagen XVI in health and disease

Collagen XVI, by structural analogy a member of the FACIT- (fibril-associated collagens with interrupted triple helices) family of collagens, is described as a minor collagen component of connective tissues. Collagen XVI is expressed in various cells and tissues without known occurrence of splice variants or isoforms. For skin and cartilage tissues its suprastructure is known. Presumably, there it acts as an adaptor protein connecting and organizing large fibrillar networks and thus modulates integrity and stability of the extracellular matrix (ECM). Collagen XVI is produced by myofibroblasts in the normal intestine and its synthesis is increased in the inflamed bowel wall where myofibroblasts develop increased numbers of focal adhesion contacts on collagen XVI. Consequently, recruitment of α1 integrin into the focal adhesions at the tip of the cells is induced followed by increased cell spreading on collagen XVI. This presumably adds to the maintenance of myofibroblasts in the inflamed intestinal regions and thus promotes fibrotic responses of the tissue. Notably, α1/α2 integrins interact with collagen XVI through an α1/α2β1 integrin binding site located in the COL 1-3 domains. Collagen XVI may act as a substrate for adhesion and invasion of connective tissue tumor cells. In glioblastoma it induces tumor invasiveness by modification of the β1-integrin activation pattern. Thus, altering the cell-matrix interaction through collagen XVI might be a molecular mechanism to further augment the invasive phenotype of glioma cells. In this line, in oral squamous cell carcinoma collagen XVI expression is induced which results in an upregulation of Kindlin-1 followed by an increased interaction with beta1-integrin. Consequently, collagen XVI induces a proliferative tumor phenotype by promoting an early S-phase entry. In summary, collagen XVI plays a decisive role in the interaction of connective tissue cells with their ECM, which is impaired in pathological situations. Alteration of tissue location and expression level of collagen XVI appears to promote tumorigenesis and to perpetuate inflammatory reactions.

UVB irradiation down-regulates type XVI collagen expression in mouse and human skin

BACKGROUND

Type XVI collagen is a member of the fibril-associated collagens with interrupted triple helices; however, its function or regulation remain unclear.

AIMS

This study is to examine the effect of ultraviolet B (UVB) or photoaging on type XVI collagen expression in various cultured cells, mouse, and human skin.

METHODS

The level of α1 (XVI) collagen mRNA was determined by quantitative real-time reverse transcriptase-polymerase chain reaction and the localization of type XVI collagen in normal human skins was detected by theα1 (XVI) collagen polypeptide antibody.

RESULTS

Exposure of keratinocytes resulted in suppression of mRNA level in a dose- and time-dependent manner and in normal fibroblasts or organotypic cocultures was also inhibited. Expression level in hairless mouse skin was decreased by UVB exposure. Messenger RNA level of human skins in the sun-protected area appeared to be greater than that in the sun-exposed area. Sun-protected and sun-exposed normal skin taken from young subjects showed positive immunoreactivities with the anti-α1 (XVI) collagen antibody in the subepidermal region, whereas sun-exposed skin from elderly subjects exhibited negative immunoreaction.

CONCLUSIONS

Reduction of type XVI collagen by UVB irradiation in vitro and in vivo may be related to the alteration of extracellular matrix in the photodamaged skin.

Fibroblasts-a diverse population at the center of it all

The capacity of fibroblasts to produce and organize the extracellular matrix and to communicate with other cells makes them a central component of tissue biology. Even so, fibroblasts remain a somewhat enigmatic population. Our inability to fully comprehend these cells is in large part due to the paucity of unique cellular markers and to their pervasive diversity. Much of our understanding of fibroblast diversity has evolved from studies where subpopulations of these cells have been produced without resorting to cell surface markers. In this regard, cloning and mechanical separation of tissues prior to establishing cultures has provided multiple subpopulations. Nonetheless, in isolated situations, the expression or lack of expression of Thy-1/CD90 has been used to separate fibroblast subsets. The role of fibroblasts in intercellular communication is emerging through the implementation of organotypic studies in which three-dimensional fibroblast culture are combined with other populations of cells. Such studies have revealed critical paracrine loops that are essential for organ development and for wound repair. These studies also provide a backdrop for the emerging field of tissue engineering. The participation of fibroblasts in the regulation of tissue homeostasis and their contribution to the aging process are emerging issues that require better understanding. In short, fibroblasts represent a multifaceted, complex group of cells.

Collagen XVI expression is upregulated in glioblastomas and promotes tumor cell adhesion

The poor prognosis of glioblastoma patients is related to diffuse brain invasion and interaction of tumor cells with extracellular matrices (ECM). We describe expression and function of the FACIT-collagen XVI in glioblastomas. We found upregulation of collagen XVI mRNA as well as protein in glioblastomas as compared to normal cortex. SiRNA knockdown resulted in decreased cell adhesion whereas increased adhesion was observed on surfaces coated with collagen XVI. The migration of glioblastoma cells on this substrate remained unchanged. Our results demonstrate de-novo expression of collagen XVI in glioblastomas as part of the tumor specific remodeling of the ECM.

Induction of MMP-9 release from human dermal fibroblasts by thrombin: involvement of JAK/STAT3 signaling pathway in MMP-9 release

Background

It has been recognized that dermal fibroblasts and matrix metalloproteases (MMP) play crucial roles in wound healing process in skin. Thrombin was found to stimulate IL-8 release from human dermal fibroblasts (HDFs). However, little is known of the effect of thrombin on secretion of MMPs from dermal fibroblasts. In the present study, the influence of thrombin on proMMP-2 and proMMP-9 activity release from primary cultured HDFs, and its potential signaling pathways were investigated.

Results

The results showed that thrombin induced proMMP-9, but not proMMP-2 release from HDFs in a dose dependent manner at 6 h following incubation. Thrombin also upregulated expression of proMMP-9 mRNA in HDFs. Hirudin completely abolished the action of thrombin on HDFs. An agonist peptide of protease-activated receptor-1, SFLLR-NH₂ stimulated an enhanced release of proMMP-9 from HDFs. AG490, an inhibitor of STAT3 inhibited basal and thrombin-provoked proMMP-9 release and phosphorylation of STAT3. PD98059, an inhibitor of MAPK and LY294002, an inhibitor PI3K failed to significantly inhibit thrombin induced proMMP-9 release.

Conclusion

Thrombin is a potent stimulus of proMMP-9 release from HDFs. Thrombin induced proMMP-9 release is most likely through activation of PAR-1. JAK/STAT3 signaling pathway is involved in proMMP-9 release from HDFs.

Clonal characterization of fibroblasts in the superficial layer of the adult human dermis

The dermis of adult human skin contains a physiologically heterogeneous population of fibroblasts that interact to produce its unique architecture and that participate in inflammatory and wound repair functions in vivo. This heterogeneity has been well documented for fibroblasts located in the superficial papillary dermis and the deep reticular dermis. However, the existence of diverse fibroblast subpopulations within a given region of the dermis has not been explored. In this study, fibroblast cultures have been established from the superficial dermis following enzymatic dissociation of the tissue. These fibroblasts have been cloned by limiting dilution and initially selected on the basis of morphology and proliferation kinetics. Fibroblasts in some of the clones selected for study express alpha-smooth muscle actin, a myofibroblast characteristic. Significant differences for fibroblast clones obtained from the same piece of skin have been observed with regard to their rate of collagen lattice contraction, their ability to organize a fibronectin matrix, their release of specific growth factors/cytokines into culture medium, and their response to interleukin-1alpha. These differences in both morphological and physiological characteristics indicate that the superficial papillary dermis contains a heterogeneous population of fibroblasts. This heterogeneity might indicate that diverse subpopulations of fibroblasts are required to interact in both homeostatic and pathological situations in skin.

Fibrillin-1 and elastin are differentially expressed in hypertrophic scars and keloids

Hypertrophic scars and keloids are two forms of excessive cutaneous scarring. Considering the importance of extracellular matrix elements in tissue repair, a morphological and quantitative analysis of the elastic system components (fibrillin-1 and elastin) was performed in normal skin, normal scars, hypertrophic scars, and keloids. In superficial and deep dermis, fibrillin-1 volume density was significantly higher in normal skin compared with normal scars, hypertrophic scars, and keloids. The fibrillin-1 volume density did not show differences between hypertrophic scars and keloids in superficial or deep dermis. In superficial dermis, elastin volume density was higher in normal skin compared with normal scars, hypertrophic scars, and keloids. In deep dermis, the elastin volume density was higher in keloids compared with normal skins, normal scars, and hypertrophic scars. We showed that the distribution of fibrillin-1 and elastin is disrupted in all kinds of scars analyzed, but there are two patterns: one for normal scars and another for excessive scars.

Fibroblast heterogeneity: more than skin deep

Dermal fibroblasts are a dynamic and diverse population of cells whose functions in skin in many respects remain unknown. Normal adult human skin contains at least three distinct subpopulations of fibroblasts, which occupy unique niches in the dermis. Fibroblasts from each of these niches exhibit distinctive differences when cultured separately. Specific differences in fibroblast physiology are evident in papillary dermal fibroblasts, which reside in the superficial dermis, and reticular fibroblasts, which reside in the deep dermis. Both of these subpopulations of fibroblasts differ from the fibroblasts that are associated with hair follicles. Fibroblasts engage in fibroblast-epidermal interactions during hair development and in interfollicular regions of skin. They also play an important role in cutaneous wound repair and an ever-increasing role in bioengineering of skin. Bioengineered skin currently performs important roles in providing (1) a basic understanding of skin biology, (2) a vehicle for testing topically applied products and (3) a resource for skin replacement.

Discrete integration of collagen XVI into tissue-specific collagen fibrils or beaded microfibrils

The structural and functional diversity of extracellular matrices is determined, not only by individual macromolecules, but even more decisively, by the alloyed aggregates they form. Although quantitatively major matrix molecules can occur ubiquitously, their organization varies from one tissue to another due to their amalgamation with specific sets of minor components. Here, we show that the fibril-associated collagen with interrupted triple helices collagen XVI is unique in that, depending on the tissue context, it can be incorporated into distinct suprastructural aggregates. In papillary dermis, the protein unexpectedly does not occur in banded collagen fibrils, but rather, is a component of specialized fibrillin-1-containing microfibrils. In territorial cartilage matrix, however, collagen XVI is not a component of aggregates containing fibrillin-1. Instead, the protein resides in a discrete population of thin, weakly banded collagen fibrils also containing collagens II and XI. Collagen IX also occurs in this population of fibrils, but at longitudinal locations discrete from those of collagen XVI. This suprastructural versatility of a collagen is without precedent and highlights pivotal differences in the tissue-specific organization of matrix aggregate structures.

Expression of keratin K2e in cutaneous and oral lesions: association with keratinocyte activation, proliferation, and keratinization

The cytoskeleton in keratinocytes is a complex of highly homologous structural proteins derived from two families of type I and type II polypeptides. Keratin K2e is a type II polypeptide that is expressed in epidermis late in differentiation. Here we report the influence of keratinocyte activation, proliferation, and keratinization on K2e expression in samples of cutaneous and oral lesions. The normal expression of K2e in the upper spinous and granular layers of interfollicular epidermis is increased in keloid scars but showed distinct down-regulation in psoriasis and hypertrophic scars where keratinocytes are known to undergo activation. Unlike normal and psoriatic skin, K2e expression in hypertrophic and keloid scars began in the deepest suprabasal layer. In cutaneous basal and squamous cell carcinomas, K2e was absent in most tumor islands but the overlying epidermis showed strong expression. No significant K2e expression in nonkeratinized or keratinized oral epithelia, including buccal mucosa, lateral border of tongue and gingiva was detected. In oral lichen planus K2e expression was undetectable, but in benign keratoses of lingual mucosa induction of K2e along with K1 and K10 was observed. In mild-to-moderate oral dysplasia with orthokeratinization, K2e was highly expressed compared with parakeratinized areas but in severe dysplasia as well as in oral squamous cell carcinoma, K2e expression was undetectable. Taken together, the data suggest that K2e expression in skin is sensitive to keratinocyte activation but its up-regulation in oral lesions is a reflection of the degree of orthokeratinization.

Type XVI collagen is expressed in factor XIIIa+ monocyte-derived dermal dendrocytes and constitutes a potential substrate for factor XIIIa

We have previously reported that connective tissue cells in the superficial dermis preferentially express alpha1(XVI) collagen rather than those in the lower dermis. Double immunofluorescence labeling using the antibodies for alpha1(XVI) collagen and factor XIIIa (plasma transglutaminase), which is a marker of dermal dendrocytes, demonstrated that both antibodies reacted with the same cells in the superficial dermis of normal skin as well as the lesional skins of dermal dendrocyte-related disorders, dermatofibroma, and psoriasis. Dermal dendrocytes are considered to be established by a culture of peripheral blood monocytes in the presence of granulocyte macrophage-colony stimulating factor and interleukin-4. Reverse transcription--polymerase chain reaction, metabolic labeling, and immunofluorescence studies demonstrated that treatment of CD14+ peripheral blood monocytes with granulocyte macrophage-colony stimulating factor/interleukin-4 over a period of 8 d resulted in the induction of alpha1(XVI) collagen as well as factor XIIIa. The physiologic significance of colocalization of alpha1(XVI) collagen and factor XIIIa in the tissue and their coordinate induction in CD14+ monocyte-derived dendritic cells in vitro was studied. Considerable incorporation of [3H]putrescine by factor XIIIa into recombinant noncollagenous domain (NC) 11 but not into collagenous domain (COL) 1.NC1 domain of the alpha1(XVI) polypeptide was found. Incubation of recombinant NC11 of alpha1(XVI) polypeptide with factor XIIIa in vitro produced a covalent cross-linking complex on sodium dodecylsulfate-polyacrylamide gel electrophoresis. The results indicate that alpha1(XVI) collagen is constitutively expressed by most dermal dendrocytes in the skin and dendritic cells differentiated from peripheral blood monocytes in vitro. Type XVI collagen is expressed in factor XIIIa+ dermal dendrocytes and may form an intermolecular cross-linking through NC11 domain by the reaction catalyzed by factor XIIIa contributing to the structural integrity of factor XIIIa+ dendritic cell-rich tissues.

Fibroblast-matrix interactions in wound healing and fibrosis

The regulation of matrix deposition is a key event in many physiological and pathological situations. It involves the activity of mediators in autocrine and paracrine fashions and the contact of cells with the surrounding extracellular matrix as well. The tightly regulated balance of both mechanisms guarantees rapid and adaptive cellular responses to meet changes in the biological requirements of the environment. Disturbances lead to wound healing defects or the development of fibrosis. The molecular mechanisms for these regulatory events are only partially understood, but involve the activity of integrins and a structural continuum of extracellular matrix-receptor-cytoskeleton-nucleus for transfer of information and the regulation of activated genes.

Expression of type XVI collagen in cultured skin fibroblasts is related to cell growth arrest

The expression of type XVI collagen in various phases of cell growth in cultured skin fibroblasts was studied. A marked increase in type XVI collagen mRNA level was found in stationary phases of cell growth (non-adherent and confluent phases), whereas the expression of type I and III collagens was undetectable in the non-adherent phase but became greater in the confluent phase. When suspended cells were further cultured over 72 h (suspension arrest), mRNA level and gene transcription of type XVI collagen were time-dependently increased whereas those of type I collagen remained undetectable. When the confluent cells were further cultured for 72 h under the condition of serum deprivation (serum deprivation arrest), mRNA levels of both type XVI collagen and type I collagen were elevated. The level of type XVI collagen polypeptide in the culture media of suspension-arrested and serum deprivation-arrested cells paralleled the mRNA level of type XVI collagen. The results indicate that expression of type XVI collagen (a member of the fibril-associated collagens with interrupted triple helices), unlike interstitial collagens (type I collagen), is related to cell growth arrest brought about by two different growth inhibiting systems, suspension arrest and serum deprivation arrest.

Interactions of fibroblasts with the extracellular matrix: implications for the understanding of fibrosis

The cellular organization and the compartmentalization in multicellular organisms is mediated by the extracellular matrix (ECM). This structure is composed by a wide variety of different macromolecules which carry distinct domains with defined structural and/or biological activities. Cells are known to interact with these molecules via specific receptors. Following activation, these receptors transduce signals either directly to the intracellular cytoskeleton or via different signalling cascades. Cell-matrix interactions, therefore, not only control the shape and orientation of cells but can also directly regulate cellular functions, including migration, differentiation, proliferation, and the expression of different genes. These cell-matrix interactions have been elucidated in detail for several biological processes, especially morphogenesis and differentiation, but also play an important role during pathological situations, e.g. wound healing and tumor progression. Although much less investigated, similar mechanisms are thought to regulate the biological behavior of fibroblastic cells, the final target cells in fibrosis. The activity of these cells depends in various ways on the presence of ECM molecules. First, some of the molecules are known to bind to and modulate the activity of those growth factors and cytokines, which lead to the activation of fibroblasts during the early phases of fibrosis. Second, deposition of large amounts of ECM molecules alters the environment and the mechanical load on the cells which are embedded in this matrix. Third, ECM molecules directly modulate fibroblast metabolism via certain integrin receptors. This review summarizes recent developments in all three domains. It mainly focuses on the direct role of ECM molecules in the biosynthetic activity of fibroblasts.