Implications for cumulative and prolonged clinical improvement induced by cross-linked hyaluronic acid: An in vivo biochemical/microscopic study in humans.

In photoaged human skin, type I collagen fragmentation impairs dermal extracellular matrix (ECM) integrity, resulting in collapsed/contracted fibroblasts with reduced type I procollagen synthesis. Injections of cross-linked hyaluronic acid (CL-HA) reverse these deleterious changes. To investigate the time course and effects of biochemical changes induced by injected CL-HA, particularly whether fibroblast activation leads to accumulation/deposition of dermal collagen, we injected CL-HA into photoaged skin of human participants over 60 years-old and performed biochemical/microscopic analyses of skin samples. Beginning 1 week post-injection and lasting 6-9 months, fibroblasts exhibited activation, including increased immunostaining and gene expression of markers of type I collagen synthesis, such as heat shock protein 47 and components of the transforming growth factor-ß pathway. At 1 week post-injection, multiphoton microscopy revealed elongation/stretching of fibroblasts, indicating enhanced dermal mechanical support. At 4 weeks, second-harmonic generation microscopy revealed thick collagen bundles densely packed around pools of injected CL-HA. At 12 months, accumulation of thick collagen bundles was observed and injected CL-HA remained present in substantial amounts. Thus, by occupying space in the dermal ECM, injected CL-HA rapidly and durably enhances mechanical support, stimulating fibroblast elongation and activation, which results in thick, densely packed type I collagen bundles accumulating as early as 4 weeks post-injection and continuing for at least a year. These observations indicate that early and prolonged clinical improvement following CL-HA injection results from space-filling and collagen deposition. As type I collagen has an estimated half-life of 15 years, our data provide the foundations for optimizing the timing/frequency of repeat CL-HA injections.

CCN proteins as potential actionable targets in scleroderma.

Systemic sclerosis (SSc) is a complex autoimmune connective tissue disease combining inflammatory, vasculopathic and fibrotic manifestations. Skin features, which give their name to the disease and are considered as diagnostic as well as prognostic markers, have not been thoroughly investigated in terms of therapeutic targets. CCN proteins (CYR61/CCN1, CTGF/CCN2, NOV/CCN3 and WISP1-2-3 as CCN4-5-6) are a family of secreted matricellular proteins implicated in major cellular processes such as cell growth, migration, differentiation. They have already been implicated in key pathophysiological processes of SSc, namely fibrosis, vasculopathy and inflammation. In this review, we discuss the possible implication of CCN proteins in SSc pathogenesis, with a special focus on skin features, and identify the potential actionable CCN targets.

Physical properties of the photodamaged human skin dermis: Rougher collagen surface and stiffer/harder mechanical properties.

Fragmentation of collagen fibrils and aberrant elastic material (solar elastosis) in the dermal extracellular matrix (ECM) is among the most prominent features of photodamaged human skin. These alterations impair the structural integrity and create a dermal microenvironment prone to skin disorders. The objective of this study was to determine the physical properties (surface roughness, stiffness and hardness) of the dermal ECM in photodamaged and subject-matched sun-protected human skin. Skin samples were sectioned and analysed by histology, atomic force microscopy and nanoindentation. Dermal ECM collagen fibrils were more disorganized (ie, rougher surface), and the dermal ECM was stiffer and harder, in photodamaged forearm, compared to sun-protected underarm skin. Cleavage of collagen fibrils in sun-protected underarm dermis by recombinant human matrix metalloproteinase-1 resulted in rougher collagen fibril surface and reduced dermal stiffness and hardness. Degradation of elastotic material in photodamaged skin by treatment with purified neutrophil elastase reduced stiffness and hardness, without altering collagen fibril surface roughness. Additionally, expression of two members of the lysyl oxidase gene family, which insert cross-links that stiffen and harden collagen fibrils, was elevated in photodamaged forearm dermis. These data elucidate the contributions of fragmented collagen fibrils, solar elastosis and elevated collagen cross-linking to the physical properties of the dermal ECM in photodamaged human skin. This new knowledge extends current understanding of the impact of photodamage on the dermal ECM microenvironment.

Atrophic and hypertrophic photoaging: Clinical, histologic, and molecular features of 2 distinct phenotypes of photoaged skin.

BACKGROUND: Exposure to the sun causes premature skin aging, known as photoaging. Clinical features of photoaging vary widely among individuals. In one form, skin appears thin with telangiectasia, and in another form, skin appears thickened with coarse wrinkles. Etiologic, clinical, and therapeutic distinctions among different forms of photoaging remain largely unknown. OBJECTIVE: To characterize the clinical, histologic, and molecular features of hypertrophic and atrophic photoaging. METHODS: In total, 53 individuals were clinically classified as having primarily atrophic or hypertrophic photoaging or neither (controls). Participants' demographic and sun exposure-related lifestyle data were captured by questionnaire. Fifteen clinical features of participants were qualitatively or quantitively scored. Facial biopsies were analyzed for gene expression and histologic characteristics. RESULTS: Actinic and seborrheic keratosis, telangiectasia, and prior incidence of skin cancers were statistically significantly greater and photoaging scale severity, coarse wrinkles, thickness, and sallowness were significantly reduced in atrophic versus hypertrophic groups. Histology also revealed significantly less elastotic material in atrophic photoaging. Gene expression of matrix metalloproteinases and collagens did not differ between the 2 forms of photoaging. LIMITATIONS: The study was not designed to identify other possible subtypes of photoaging. CONCLUSION: Systematic, categorical, and quantitative clinical and histologic assessments distinguish atrophic and hypertrophic photoaging.

Actin cytoskeleton assembly regulates collagen production via TGF-ß type II receptor in human skin fibroblasts.

The dermal compartment of skin is primarily composed of collagen-rich extracellular matrix (ECM), which is produced by dermal fibroblasts. In Young skin, fibroblasts attach to the ECM through integrins. During ageing, fragmentation of the dermal ECM limits fibroblast attachment. This reduced attachment is associated with decreased collagen production, a major cause of skin thinning and fragility, in the elderly. Fibroblast attachment promotes assembly of the cellular actin cytoskeleton, which generates mechanical forces needed for structural support. The mechanism(s) linking reduced assembly of the actin cytoskeleton to decreased collagen production remains unclear. Here, we report that disassembly of the actin cytoskeleton results in impairment of TGF-ß pathway, which controls collagen production, in dermal fibroblasts. Cytoskeleton disassembly rapidly down-regulates TGF-ß type II receptor (TßRII) levels. This down-regulation leads to reduced activation of downstream effectors Smad2/Smad3 and CCN2, resulting in decreased collagen production. These responses are fully reversible; restoration of actin cytoskeleton assembly up-regulates TßRII, Smad2/Smad3, CCN2 and collagen expression. Finally, actin cytoskeleton-dependent reduction of TßRII is mediated by induction of microRNA 21, a potent inhibitor of TßRII protein expression. Our findings reveal a novel mechanism that links actin cytoskeleton assembly and collagen expression in dermal fibroblasts. This mechanism likely contributes to loss of TßRII and collagen production, which are observed in aged human skin.

YAP/TAZ regulates TGF-ß/Smad3 signaling by induction of Smad7 via AP-1 in human skin dermal fibroblasts.

BACKGROUND: Transcription factors YAP and TAZ function as the primary mediators of the Hippo pathway. Yet, crosstalk of YAP and TAZ with other signaling pathways remains relatively unexplored. We have explored the impact of YAP and TAZ levels on the TGF-ß/Smad signaling pathway in human skin dermal fibroblasts. METHODS: YAP and TAZ levels in dermal fibroblasts were reduced in dermal fibroblasts by siRNA-mediated knockdown. The effects of YAP and TAZ reduction on TGF-ß/Smad signaling were examined by quantitative real-time PCR, Western analysis, and immunostaining. Luciferase reporter assays and electrophoretic mobility shift assays were conducted to investigate the transcription factor DNA-binding and transcriptional activities. RESULTS: Knockdown of both YAP and TAZ (YAP/TAZ), but not either separately, impaired TGF-ß1-induced Smad3 phosphorylation and Smad3 transcriptional activity, thereby inhibiting the expression of TGF-ß target genes. This reduction by reduced levels of YAP/TAZ results from induction of inhibitory Smad7, which inhibits Smad3 phosphorylation and activity by TGF-ß1. Conversely, prevention of Smad7 induction restores Smad3 phosphorylation and Smad3 transcriptional activity in fibroblasts that have reduced YAP/TAZ. In agreement with these findings, inhibition of YAP/TAZ transcriptional activity, similar to the reduction of YAP/TAZ levels, also significantly induced Smad7 and impaired TGF-ß/Smad signaling. Further investigations revealed that reduced levels of YAP/TAZ led to induction of activator protein-1 (AP-1) activity, Activated AP-1 bound to DNA sequences in the Smad7 gene promoter, and deletion of these AP-1 binding sequences substantially reduced Smad7 promoter reporter activity. CONCLUSION: YAP/TAZ functions in concert with transcription factor AP-1 and Smad7 to regulate TGF-ß signaling, in human dermal fibroblasts. Reduction of YAP/TAZ levels leads to activation of AP-1 activity, which induces Smad7. Smad7 suppresses the TGF-ß pathway.

Genomic copy number analysis of a spectrum of blue nevi identifies recurrent aberrations of entire chromosomal arms in melanoma ex blue nevus.

Blue nevi may display significant atypia or undergo malignant transformation. Morphologic diagnosis of this spectrum of lesions is notoriously difficult, and molecular tools are increasingly used to improve diagnostic accuracy. We studied copy number aberrations in a cohort of cellular blue nevi, atypical cellular blue nevi, and melanomas ex blue nevi using Affymetrix's OncoScan platform. Cases with sufficient DNA were analyzed for GNAQ, GNA11, and HRAS mutations. Copy number aberrations were detected in 0 of 5 (0%) cellular blue nevi, 3 of 12 (25%) atypical cellular blue nevi, and 6 of 9 (67%) melanomas ex blue nevi. None of the atypical cellular blue nevi displayed more than one aberration, whereas complex aberrations involving four or more regions were seen exclusively in melanomas ex blue nevi. Gains and losses of entire chromosomal arms were identified in four of five melanomas ex blue nevi with copy number aberrations. In particular, gains of 1q, 4p, 6p, and 8q, and losses of 1p and 4q were each found in at least two melanomas. Whole chromosome aberrations were also common, and represented the sole finding in one atypical cellular blue nevus. When seen in melanomas, however, whole chromosome aberrations were invariably accompanied by partial aberrations of other chromosomes. Three melanomas ex blue nevi harbored aberrations, which were absent or negligible in their precursor components, suggesting progression in tumor biology. Gene mutations involving GNAQ and GNA11 were each detected in two of eight melanomas ex blue nevi. In conclusion, copy number aberrations are more common and often complex in melanomas ex blue nevi compared with cellular and atypical cellular blue nevi. Identification of recurrent gains and losses of entire chromosomal arms in melanomas ex blue nevi suggests that development of new probes targeting these regions may improve detection and risk stratification of these lesions.

Elevated YAP and its downstream targets CCN1 and CCN2 in basal cell carcinoma: impact on keratinocyte proliferation and stromal cell activation.

Yes-associated protein (YAP) is a transcriptional co-activator of hippo signaling pathway, which plays an important role in organ size control and tumorigenesis. Here we report that YAP and its downstream transcriptional targets CCN1 and CCN2 are markedly elevated in keratinocytes in human skin basal cell carcinoma tumor islands. In human keratinocytes, knockdown of YAP significantly reduced expression of CCN1 and CCN2, and repressed proliferation and survival. This inhibition of proliferation and survival was rescued by restoration of CCN1 expression, but not by CCN2 expression. In basal cell carcinoma stroma, CCN2-regulated genes type I collagen, fibronectin, and α-smooth muscle actin were highly expressed. Furthermore, atomic force microscopy revealed increased tissue stiffness in basal cell carcinoma stroma compared to normal dermis. These data provide evidence that up-regulation of YAP in basal cell carcinoma impacts both aberrant keratinocyte proliferation, via CCN1, and tumor stroma cell activation and stroma remodeling, via CCN2. Targeting YAP and/or CCN1 and CCN2 may provide clinical benefit in basal cell carcinoma.

Role of Age-Associated Alterations of the Dermal Extracellular Matrix Microenvironment in Human Skin Aging: A Mini-Review.

Human skin is largely composed of a collagen-rich connective tissue, which provides structural and functional support. The collagen-rich connective tissue is produced, organized, and maintained by dermal fibroblasts. During aging, dermal collagen fibrils undergo progressive loss and fragmentation, leading to thin and structurally weakened skin. Age-related alterations of collagen fibrils impairs skin structure and function and creates a tissue microenvironment that promotes age-related skin diseases, such as delayed wound healing and skin cancer development. This mini-review describes cellular mechanisms that give rise to self-perpetuating, collagen fibril fragmentation that creates an age-associated dermal microenvironment, which contributes to decline of human skin function.

Contralateral breast dose from partial breast brachytherapy.

The purpose of this study was to determine the dose to the contralateral breast during accelerated partial breast irradiation (APBI) and to compare it to external beam-published values. Thermoluminescent dosimeter (TLD) packets were used to measure the dose to the most medial aspect of the contralateral breast during APBI simulation, daily quality assurance (QA), and treatment. All patients in this study were treated with a single-entry, multicatheter device for 10 fractions to a total dose of 34 Gy. A mark was placed on the patient's skin on the medial aspect of the opposite breast. Three TLD packets were taped to this mark during the pretreatment simulation. Simulations consisted of an AP and Lateral scout and a limited axial scan encompassing the lumpectomy cavity (miniscan), if rotation was a concern. After the simulation the TLD packets were removed and the patients were moved to the high-dose-rate (HDR) vault where three new TLD packets were taped onto the patients at the skin mark. Treatment was administered with a Nucletron HDR afterloader using Iridium-192 as the treatment source. Post-treatment, TLDs were read (along with the simulation and QA TLD and a set of standards exposed to a known dose of 6 MV photons). Measurements indicate an average total dose to the contralateral breast of 70 cGy for outer quadrant implants and 181 cGy for inner quadrant implants. Compared to external beam breast tangents, these results point to less dose being delivered to the contralateral breast when using APBI.

Cysteine-rich protein 61 (CCN1) domain-specific stimulation of matrix metalloproteinase-1 expression through αVß3 integrin in human skin fibroblasts.

Human skin largely comprises collagenous extracellular matrix. The hallmark of skin aging is fragmentation of collagen fibrils. Matrix metalloproteinases (MMPs) are largely responsible for collagen degradation. MMP-1, principally derived from dermal fibroblasts, is the major protease capable of initiating degradation of native fibrillar collagens. Presently, we report that CCN1, a secreted and extracellular matrix-associated protein, is elevated in aged human skin dermal fibroblasts in vivo and stimulates MMP-1 expression through functional interaction with αVß3 integrin in human dermal fibroblasts. CCN1 contains four conserved structural domains. Our results indicate that the three N-terminal domains (IGFBP, VWC, and TSP1), but not the C-terminal CT domain, are required for CCN1 to stimulate MMP-1 expression. This stimulation is dependent on interaction between the active structural domains and αVß3 integrin. The interaction of VWC domain with integrin αVß3 is necessary and requires functional cooperation with adjacent IGFBP and TSP1 domains to stimulate MMP-1 expression. Finally, induction of MMP-1 expression in dermal fibroblasts by CCN1 N-terminal domains resulted in fragmentation of type I collagen fibrils in a three-dimensional collagen lattice model. These data suggest that domain-specific interactions of CCN1 with αVß3 integrin contribute to human skin aging by stimulating MMP-1-mediated collagen fibril fragmentation.

Eccrine sweat glands are major contributors to reepithelialization of human wounds.

Eccrine sweat glands are skin-associated epithelial structures (appendages) that are unique to some primates including humans and are absent in the skin of most laboratory animals including rodents, rabbits, and pigs. On the basis of the known importance of other skin appendages (hair follicles, apocrine glands, and sebaceous glands) for wound repair in model animals, the present study was designed to assess the role of eccrine glands in the repair of wounded human skin. Partial-thickness wounds were generated on healthy human forearms, and epidermal repair was studied in skin biopsy samples obtained at precise times during the first week after wounding. Wound reepithelialization was assessed using immunohistochemistry and computer-assisted 3-dimensional reconstruction of in vivo wounded skin samples. Our data demonstrate a key role for eccrine sweat glands in reconstituting the epidermis after wounding in humans. More specifically, (i) eccrine sweat glands generate keratinocyte outgrowths that ultimately form new epidermis; (ii) eccrine sweat glands are the most abundant appendages in human skin, outnumbering hair follicles by a factor close to 3; and (iii) the rate of expansion of keratinocyte outgrowths from eccrine sweat glands parallels the rate of reepithelialization. This novel appreciation of the unique importance of eccrine sweat glands for epidermal repair may be exploited to improve our approaches to understanding and treating human wounds.

Ultraviolet irradiation represses TGF-ß type II receptor transcription through a 38-bp sequence in the proximal promoter in human skin fibroblasts.

Transforming growth factor-ß (TGF-ß) is a major regulator of collagen gene expression in human skin fibroblasts. Cellular responses to TGF-ß are mediated primarily through its cell surface type I (TßRI) and type II (TßRII) receptors. Ultraviolet (UV) irradiation impairs TGF-ß signalling largely due to reduced TßRII gene expression, thereby decreasing type I procollagen synthesis, in human skin fibroblasts. UV irradiation does not alter either TßRII mRNA or protein stability, indicating that UV reduction in TßRII expression likely results from transcriptional or translational repression. To understand how UV irradiation regulates TßRII transcription, we used a series of TßRII promoter-luciferase 5'-deletion constructs (covering 2 kb of the TßRII proximal promoter) to determine transcriptional rate in response to UV irradiation. We identified a 137-bp region upstream of the transcriptional start site that exhibited high promoter activity and was repressed 60% by UV irradiation, whereas all other TßRII promoter reporter constructs exhibited either low promoter activities or no regulation by UV irradiation. Mutation of potential transcription factor binding sites within the promoter region revealed that an inverted CCAAT box (-81 bp from transcription start site) is required for promoter activity. Mutation of the CCAAT box completely abolished UV irradiation regulation of the TßRII promoter. Protein-binding assay, as determined by electrophoretic mobility-shift assays (EMSAs) using the inverted CCAAT box as probe (-100/-62), demonstrated significantly enhanced protein binding in response to UV irradiation. Super shift experiments indicated that nuclear factor Y (NFY) is able to binding to this sequence, but NFY binding was not altered in response to UV irradiation, indicating additional protein(s) are capable of binding this sequence in response to UV irradiation. Taken together, these data indicate that UV irradiation reduces TßRII expression, at least partially, through transcriptional repression. This repression is mediated by a 38-bp sequence in TßRII promoter, in human skin fibroblasts.

Age-related changes in dermal collagen physical properties in human skin.

Collagen is the major structural protein in the skin. Fragmentation and disorganization of the collagen fibrils are the hallmarks of the aged human skin dermis. These age-related alterations of collagen fibrils impair skin structural integrity and make the tissue microenvironment more prone to skin disorders. As the biological function of collagen lies predominantly in its physical properties, we applied atomic force microscopy (AFM) and nanoindentation to evaluate the physical properties (surface roughness, stiffness, and hardness) of dermal collagen in young (25±5 years, N = 6) and aged (75±6 years, N = 6) healthy sun-protected hip skin. We observed that in the aged dermis, the surface of collagen fibrils was rougher, and fiber bundles were stiffer and harder, compared to young dermal collagen. Mechanistically, the age-related elevation of matrix metalloproteinase-1 (MMP-1) and advanced glycation end products (AGEs) are responsible for rougher and stiffer/harder dermal collagen, respectively. Analyzing the physical properties of dermal collagen as a function of age revealed that alterations of the physical properties of collagen fibrils changed with age (22-89 years, N = 18). We also observed that the reticular dermis is rougher and mechanically stiffer and harder compared to the papillary dermis in human skin. These data extend the current understanding of collagen beyond biological entities to include biophysical properties.

Skin aging from the perspective of dermal fibroblasts: the interplay between the adaptation to the extracellular matrix microenvironment and cell autonomous processes.

This article summarizes important molecular mechanisms that drive aging in human skin from the perspective of dermal fibroblasts. The dermis comprises the bulk of the skin and is largely composed of a collagen-rich extracellular matrix (ECM). The dermal ECM provides mechanical strength, resiliency, and an environment that supports the functions of ibroblasts and other types of dermal cells. Fibroblasts produce the dermal ECM and maintain its homeostasis. Fibroblasts attach to the ECM and this attachment controls their morphology and function. During aging, the ECM undergoes gradual degradation that is nitiated by matrix metalloproteinases (MMPs). This degradation alters mechanical forces within the dermal ECM and disrupts he interactions between fibroblasts and the ECM thereby generating an aged fibroblast phenotype. This aged fibroblast phenotype is characterized by collapsed morphology, altered mechanosignaling, induction of CCN1, and activation of transcription factor AP-1, with consequent upregulation of target genes including MMPs and pro-inflammatory mediators. The TGF-beta pathway coordinately regulates ECM production and turnover. Altered mechanical forces, due to ECM fragmentation, down-regulate the type II TGF-beta receptor, thereby reducing ECM production and further increasing ECM breakdown. Thus, dermal aging involves a feed-forward process that reinforces the aged dermal fibroblast phenotype and promotes age-related dermal ECM deterioration. As discussed in the article, the expression of the aged dermal fibroblast phenotype involves both adaptive and cell-autonomous mechanisms.

Report on the 11th international workshop on the CCN family of genes, Nice, October 20-24, 2022.

In celebration of the twentieth anniversary of the inception of the CCN society, and of the first post-Covid-19 live meeting, the executive board of the ICCNS had chosen Nice as the venue for the 11th International workshop on the CCN family of genes. On this occasion participation in the meeting was extended to colleagues from other cell signaling fields who were invited to present both an overview of their work and the future directions of their laboratory. Also, for the first time, the members of the JCCS Editorial Board were invited to participate in a JCCS special session during which all aspects of the journal « life ¼ were addressed and opened to free critical discussion. The scientific presentations and the discussions that followed showed once more that an expansion of the session topics was beneficial to the quality of the meeting and confirmed that the ARBIOCOM project discussed last April in Nice was now on track to be launched in 2023. The participants unanimously welcomed Professor Attramadal's proposition to organize the 2024, 12th International CCN workshop in Oslo, Norway.

Matrix Metalloproteinase-1 Expression in Fibroblasts Accelerates Dermal Aging and Promotes Papilloma Development in Mouse Skin.

Fragmentation, disorganization, and depletion of the collagen-rich dermal extracellular matrix are hallmarks of aged human skin. These deleterious alterations are thought to critically mediate many of the prominent clinical attributes of aged skin, including thinning, fragility, impaired wound healing, and a propensity for carcinoma. Matrix metalloproteinase-1 (MMP1) initiates the cleavage of collagen fibrils and is significantly increased in dermal fibroblasts in aged human skin. To investigate the role of elevated MMP1 in skin aging, we generated a conditional bitransgenic mouse (type I collagen alpha chain 2; human MMP1 [Col1a2;hMMP1]) that expresses full-length, catalytically active hMMP1 in dermal fibroblasts. hMMP1 expression is activated by a tamoxifen-inducible Cre recombinase that is driven by the Col1a2 promoter and upstream enhancer. Tamoxifen induced hMMP1 expression and activity throughout the dermis Col1a2:hMMP1 mice. At 6 months of age, Col1a2;hMMP1 mice displayed loss and fragmentation of dermal collagen fibrils, which was accompanied by many of the features of aged human skin, such as contracted fibroblast morphology, reduced collagen production, increased expression of multiple endogenous MMPs, and proinflammatory mediators. Interestingly, Col1a2;hMMP1 mice displayed substantially increased susceptibility to skin papilloma development. These data demonstrate that fibroblast expression of hMMP1 is a critical mediator of dermal aging and creates a dermal microenvironment that promotes keratinocyte tumor development.

Receptor-type protein tyrosine phosphatase beta (RPTP-beta) directly dephosphorylates and regulates hepatocyte growth factor receptor (HGFR/Met) function.

Protein tyrosine phosphorylation is a ubiquitous, fundamental biochemical mechanism that regulates essential eukaryotic cellular functions. The level of tyrosine phosphorylation of specific proteins is finely tuned by the dynamic balance between protein tyrosine kinase and protein tyrosine phosphatase activities. Hepatocyte growth factor receptor (also known as Met), a receptor protein tyrosine kinase, is a major regulator of proliferation, migration, and survival for many epithelial cell types. We report here that receptor-type protein tyrosine phosphatase ß (RPTP-ß) specifically dephosphorylates Met and thereby regulates its function. Expression of RPTP-ß, but not other RPTP family members or catalytically inactive forms of RPTP-ß, reduces hepatocyte growth factor (HGF)-stimulated Met tyrosine phosphorylation in HEK293 cells. Expression of RPTP-ß in primary human keratinocytes reduces both basal and HGF-induced Met phosphorylation at tyrosine 1356 and inhibits downstream MEK1/2 and Erk activation. Furthermore, shRNA-mediated knockdown of endogenous RPTP-ß increases basal and HGF-stimulated Met phosphorylation at tyrosine 1356 in primary human keratinocytes. Purified RPTP-ß intracellular domain preferentially dephosphorylates purified Met at tyrosine 1356 in vitro. In addition, the substrate-trapping mutant of RPTP-ß specifically interacts with Met in intact cells. Expression of RPTP-ß in human primary keratinocytes reduces HGF induction of VEGF expression, proliferation, and motility. Taken together, the above data indicate that RPTP-ß is a key regulator of Met function.

Cysteine-rich protein 61 (CCN1) mediates replicative senescence-associated aberrant collagen homeostasis in human skin fibroblasts.

Dermal fibroblasts produce a collagen-rich extracellular matrix, which confers mechanical strength and resiliency to human skin. During aging, collagen production is reduced and collagen fragmentation is increased, which is initiated by matrix metalloproteinase-1 (MMP-1). This aberrant collagen homeostasis results in net collagen deficiency, which impairs the structural integrity and function of skin. Cysteine-rich protein 61 (CCN1), a member of the CCN family, negatively regulates collagen homeostasis, in primary human skin dermal fibroblasts. As replicative senescence is a form of cellular aging, we have utilized replicative senescent dermal fibroblasts to further investigate the connection between elevated CCN1 and aberrant collagen homeostasis. CCN1 mRNA and protein levels were significantly elevated in replicative senescent dermal fibroblasts. Replicative senescent dermal fibroblasts also expressed significantly reduced levels of type I procollagen and increased levels of MMP-1. Knockdown of elevated CCN1 in senescent dermal fibroblasts partially normalized both type I procollagen and MMP-1 expression. These data further support a key role of CCN1 in regulation of collagen homeostasis. Elevated expression of CCN1 substantially increased collagen lattice contraction and fragmentation caused by replicative senescent dermal fibroblasts. Atomic force microscopy (AFM) further revealed collagen fibril fragmentation and disorganization were largely prevented by knockdown of CCN1 in replicative senescent dermal fibroblasts, suggesting CCN1 mediates MMP-1-induced alterations of collagen fibrils by replicative senescent dermal fibroblasts. Given the ability of CCN1 to regulate both production and degradation of type I collagen, it is likely that elevated-CCN1 functions as an important mediator of collagen loss, which is observed in aged human skin.

Alteration in the gene encoding protein tyrosine phosphatase nonreceptor type 6 (PTPN6/SHP1) may contribute to neutrophilic dermatoses.

We have found a B2 repeat insertion in the gene encoding protein tyrosine phosphatase nonreceptor type 6 (PTPN6) in a mouse that developed a skin disorder with clinical and histopathological features resembling those seen in human neutrophilic dermatoses. Neutrophilic dermatoses are a group of complex heterogeneous autoinflammatory diseases that all demonstrate excessive neutrophil infiltration of the skin. Therefore, we tested the cDNA and genomic DNA sequences of PTPN6 from patients with Sweet's syndrome (SW) and pyoderma gangrenosum and found numerous novel splice variants in different combinations. Isoforms resulting from deletions of exons 2, 5, 11, and 15 and retention of intron 1 or 5 were the most common in a patients with a familial case of SW, who had a neonatal onset of an inflammatory disorder with skin lesions and a biopsy specimen consistent with SW. These isoforms were associated with a heterozygous E441G mutation and a heterozygous 1.7-kbp deletion in the promoter region of the PTPN6 gene. Although full-length PTPN6 was detected in all other patients with either pyoderma gangrenosum or SW, it was always associated with splice variants: a partial deletion of exon 4 with the complete deletion of exon 5, alterations that were not detected in healthy controls. The defect in transcriptional regulation of the hematopoietic PTPN6 appears to be involved in the pathogenesis of certain subsets of the heterogeneous group of neutrophilic dermatoses.