The Activation of JAK/STAT3 Signaling and the Complement System Modulate Inflammation in the Primary Human Dermal Fibroblasts of PXE Patients.

Previous studies revealed a link between inflammation and overactivation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling in syndromes associated with aging. Pseudoxanthoma elasticum (PXE), a rare autosomal-recessive disorder, arises from mutations in ATP-binding cassette subfamily C member 6 (ABCC6). On a molecular level, PXE shares similarities with Hutchinson-Gilford progeria syndrome, such as increased activity of senescence-associated- beta-galactosidase or high expression of inflammatory factors. Thus, this study's aim was the evaluation of activated STAT3 and the influence of JAK1/2-inhibitor baricitinib (BA) on inflammatory processes such as the complement system in PXE. Analysis of activation of STAT3 was performed by immunofluorescence and Western blot, while inflammatory processes and complement system factors were determined based on mRNA expression and protein level. Our results assume overactivation of JAK/STAT3 signaling, increased expression levels of several complement factors and high C3 protein concentration in the sera of PXE patients. Supplementation with BA reduces JAK/STAT3 activation and partly reduces inflammation as well as the gene expression of complement factors belonging to the C1 complex and C3 convertase in PXE fibroblasts. Our results indicate a link between JAK/STAT3 signaling and complement activation contributing to the proinflammatory phenotype in PXE fibroblasts.

Understanding of arthrofibrosis: New explorative insights into extracellular matrix remodeling of synovial fibroblasts.

Arthrofibrosis following total knee arthroplasty is a fibroproliferative joint disorder marked by dysregulated biosynthesis of extracellular matrix proteins, such as collagens and proteoglycans. The underlying cellular events remain incompletely understood. Myofibroblasts are highly contractile matrix-producing cells characterized by increased alpha-smooth muscle actin expression and xylosyltransferase-I (XT-I) secretion. Human XT-I has been identified as a key mediator of arthrofibrotic remodeling. Primary fibroblasts from patients with arthrofibrosis provide a useful in vitro model to identify and characterize disease regulators and potential therapeutic targets. This study aims at characterizing primary synovial fibroblasts from arthrofibrotic tissues (AFib) regarding their molecular and cellular phenotype by utilizing myofibroblast cell culture models. Compared to synovial control fibroblasts (CF), AFib are marked by enhanced cell contractility and a higher XT secretion rate, demonstrating an increased fibroblast-to-myofibroblast transition rate during arthrofibrosis. Histochemical assays and quantitative gene expression analysis confirmed higher collagen and proteoglycan expression and accumulation in AFib compared to CF. Furthermore, fibrosis-based gene expression profiling identified novel modifier genes in the context of arthrofibrosis remodeling. In summary, this study revealed a unique profibrotic phenotype in AFib that resembles some traits of other fibroproliferative diseases and can be used for the future development of therapeutic interventions.

Matrix Metalloproteinases Contribute to the Calcification Phenotype in Pseudoxanthoma Elasticum.

Ectopic calcification and dysregulated extracellular matrix remodeling are prominent hallmarks of the complex heterogenous pathobiochemistry of pseudoxanthoma elasticum (PXE). The disease arises from mutations in ABCC6, an ATP-binding cassette transporter expressed predominantly in the liver. Neither its substrate nor the mechanisms by which it contributes to PXE are completely understood. The fibroblasts isolated from PXE patients and Abcc6-/- mice were subjected to RNA sequencing. A group of matrix metalloproteinases (MMPs) clustering on human chromosome 11q21-23, respectively, murine chromosome 9, was found to be overexpressed. A real-time quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and immunofluorescent staining confirmed these findings. The induction of calcification by CaCl2 resulted in the elevated expression of selected MMPs. On this basis, the influence of the MMP inhibitor Marimastat (BB-2516) on calcification was assessed. PXE fibroblasts (PXEFs) exhibited a pro-calcification phenotype basally. PXEF and normal human dermal fibroblasts responded with calcium deposit accumulation and the induced expression of osteopontin to the addition of Marimastat to the calcifying medium. The raised MMP expression in PXEFs and during cultivation with calcium indicates a correlation of ECM remodeling and ectopic calcification in PXE pathobiochemistry. We assume that MMPs make elastic fibers accessible to controlled, potentially osteopontin-dependent calcium deposition under calcifying conditions.

The Consideration of Pseudoxanthoma Elasticum as a Progeria Syndrome.

BACKGROUND: Pseudoxanthoma elasticum (PXE) is a rare autosomal recessive disorder caused by mutations in the ATP-binding cassette sub-family C member 6 (ABCC6) gene. Patients with PXE show molecular and clinical characteristics of known premature aging syndromes, such as Hutchinson-Gilford progeria syndrome (HGPS). Nevertheless, PXE has only barely been discussed against the background of premature aging, although a detailed characterization of aging processes in PXE could contribute to a better understanding of its pathogenesis. Thus, this study was performed to evaluate whether relevant factors which are known to play a role in accelerated aging processes in HGPS pathogenesis are also dysregulated in PXE. METHODS: Primary human dermal fibroblasts from healthy donors (n = 3) and PXE patients (n = 3) and were cultivated under different culture conditions as our previous studies point towards effects of nutrient depletion on PXE phenotype. Gene expression of lamin A, lamin C, nucleolin, farnesyltransferase and zinc metallopeptidase STE24 were determined by quantitative real-time polymerase chain reaction. Additionally, protein levels of lamin A, C and nucleolin were evaluated by immunofluorescence and the telomere length was analyzed. RESULTS: We could show a significant decrease of lamin A and C gene expression in PXE fibroblasts under nutrient depletion compared to controls. The gene expression of progerin and farnesyltransferase showed a significant increase in PXE fibroblasts when cultivated in 10% fetal calf serum (FCS) compared to controls. Immunofluorescence microscopy of lamin A/C and nucleolin and mRNA expression of zinc metallopeptidase STE24 and nucleolin showed no significant changes in any case. The determination of the relative telomere length showed significantly longer telomeres for PXE fibroblasts compared to controls when cultivated in 10% FCS. CONCLUSIONS: These data indicate that PXE fibroblasts possibly undergo a kind of senescence which is independent of telomere damage and not triggered by defects of the nuclear envelope or nucleoli deformation.

The Human Myofibroblast Marker Xylosyltransferase-I: A New Indicator for Macrophage Polarization.

Chronic inflammation and excessive synthesis of extracellular matrix components, such as proteoglycans (PG), by fibroblast- or macrophage-derived myofibroblasts are the hallmarks of fibrotic diseases, including systemic sclerosis (SSc). Human xylosyltransferase-I (XT-I), which is encoded by the gene XYLT1, is the key enzyme that is involved in PG biosynthesis. Increased cellular XYLT1 expression and serum XT-I activity were measured in SSc. Nothing is known so far about the regulation of XT-I in immune cells, and their contribution to the increase in measurable serum XT-I activity. We utilized an in vitro model, with primary human CD14+CD16+ monocyte-derived macrophages (MΦ), in order to investigate the role of macrophage polarization on XT-I regulation. The MΦ generated were polarized towards two macrophage phenotypes that were associated with SSc, which were classified as classical pro-inflammatory (M1-like), and alternative pro-fibrotic (M2-like) MΦ. The fully characterized M1- and M2-like MΦ cultures showed differential XT-I gene and protein expressions. The fibrotic M2-like MΦ cultures exhibited higher XT-I secretion, as well as increased expression of myofibroblast marker α-smooth muscle actin, indicating the onset of macrophage-to-myofibroblast transition (MMT). Thus, we identified XT-I as a novel macrophage polarization marker for in vitro generated M1- and M2-like MΦ subtypes, and broadened the view of XT-I as a myofibroblast marker in the process of MMT.

Targeting ABCC6 in Mesenchymal Stem Cells: Impairment of Mature Adipocyte Lipid Homeostasis.

Mutations in ABCC6, an ATP-binding cassette transporter with a so far unknown substrate mainly expressed in the liver and kidney, cause pseudoxanthoma elasticum (PXE). Symptoms of PXE in patients originate from the calcification of elastic fibers in the skin, eye, and vessels. Previous studies suggested an involvement of ABCC6 in cholesterol and lipid homeostasis. The intention of this study was to examine the influence of ABCC6 deficiency during adipogenic differentiation of human bone marrow-derived stem cells (hMSCs). Induction of adipogenic differentiation goes along with significantly elevated ABCC6 gene expression in mature adipocytes. We generated an ABCC6-deficient cell culture model using clustered regulatory interspaced short palindromic repeat Cas9 (CRISPR-Cas9) system to clarify the role of ABCC6 in lipid homeostasis. The lack of ABCC6 in hMSCs does not influence gene expression of differentiation markers in adipogenesis but results in a decreased triglyceride content in cell culture medium. Protein and gene expression analysis of mature ABCC6-deficient adipocytes showed diminished intra- and extra-cellular lipolysis, release of lipids, and fatty acid neogenesis. Therefore, our results demonstrate impaired lipid trafficking in adipocytes due to ABCC6 deficiency, highlighting adipose tissue and peripheral lipid metabolism as a relevant target for uncovering systemic PXE pathogenesis.

The Impact of Inflammatory Stimuli on Xylosyltransferase-I Regulation in Primary Human Dermal Fibroblasts.

Inflammation plays a vital role in regulating fibrotic processes. Beside their classical role in extracellular matrix synthesis and remodeling, fibroblasts act as immune sentinel cells participating in regulating immune responses. The human xylosyltransferase-I (XT-I) catalyzes the initial step in proteoglycan biosynthesis and was shown to be upregulated in normal human dermal fibroblasts (NHDF) under fibrotic conditions. Regarding inflammation, the regulation of XT-I remains elusive. This study aims to investigate the effect of lipopolysaccharide (LPS), a prototypical pathogen-associated molecular pattern, and the damage-associated molecular pattern adenosine triphosphate (ATP) on the expression of XYLT1 and XT-I activity of NHDF. We used an in vitro cell culture model and mimicked the inflammatory tissue environment by exogenous LPS and ATP supplementation. Combining gene expression analyses, enzyme activity assays, and targeted gene silencing, we found a hitherto unknown mechanism involving the inflammasome pathway components cathepsin B (CTSB) and caspase-1 in XT-I regulation. The suppressive role of CTSB on the expression of XYLT1 was further validated by the quantification of CTSB expression in fibroblasts from patients with the inflammation-associated disease Pseudoxanthoma elasticum. Altogether, this study further improves the mechanistic understanding of inflammatory XT-I regulation and provides evidence for fibroblast-targeted therapies in inflammatory diseases.

Pulmonary affection of patients with Pseudoxanthoma elasticum: Long-term development and genotype-phenotype-correlation.

Pseudoxanthoma elasticum (PXE) is a rare, heritable disease caused by various, mainly recessively transmitted mutations in the ABCC6 gene. Due to calcification of soft connective tissue phenotypic hallmarks are progressive loss of vision, alternation of the skin and early onset atherosclerosis. Beside these main features patients also suffer from impaired alveolar diffusion. The present study focused on impaired lung functioning based on a large cohort of patients with PXE, its long-term development, and genotype-phenotype correlation. Retrospectively, 98 patients and 45 controls were enrolled. All patients underwent body plethysmography and carbon monoxide diffusion testing. Of 35 patients three or more body plethysmographic records were available for long-term analysis. For genotype-phenotype analysis ABCC6 genotypes were grouped as two missense, mixed, or two nonsense mutations. Patients with PXE showed significantly reduced vital capacity (p < 0.05), diffusion capacity (p < 0.01), and diffusion transfer coefficient (p < 0.05). Over a mean period of 38 months diffusion capacity (p < 0.05) and diffusion transfer coefficient (p < 0.01) dropped significantly whereas lung volumes remained unchanged. Genotype-phenotype correlation revealed no connection between gene variants and lung functioning. In conclusion, PXE is accompanied by progressive reduction of alveolar diffusion indicating progressive alterations of lung tissue. Genotype-phenotype correlation with genotypes sorted as missense and nonsense mutations do not explain impaired lung functioning.

Evidence of Long-Lasting Humoral and Cellular Immunity against SARS-CoV-2 Even in Elderly COVID-19 Convalescents Showing a Mild to Moderate Disease Progression.

We here evaluate the humoral and cellular immune response against SARS-CoV-2 in 41 COVID-19 convalescents. As previous studies mostly included younger individuals, one advantage of our study is the comparatively high mean age of the convalescents included in the cohort considered (54 ± 8.4 years). While anti-SARS-CoV-2 antibodies were still detectable in 95% of convalescents up to 8 months post infection, an antibody-decay over time was generally observed in most donors. Using a multiplex assay, our data additionally reveal that most convalescents exhibit a broad humoral immunity against different viral epitopes. We demonstrate by flow cytometry that convalescent donors show a significantly elevated number of natural killer cells when compared to healthy controls, while no differences were found concerning other leucocyte subpopulations. We detected a specific long-lasting cellular immune response in convalescents by stimulating immune cells with SARS-CoV-2-specific peptides, covering domains of the viral spike, membrane and nucleocapsid protein, and measuring interferon-γ (IFN-γ) release thereafter. We modified a commercially available ELISA assay for IFN-γ determination in whole-blood specimens of COVID-19 convalescents. One advantage of this assay is that it does not require special equipment and can, thus, be performed in any standard laboratory. In conclusion, our study adds knowledge regarding the persistence of immunity of convalescents suffering from mild to moderate COVID-19. Moreover, our study provides a set of simple methods to characterize and confirm experienced COVID-19.

Cytokine-mediated induction of human xylosyltransferase-I in systemic sclerosis skin fibroblasts.

Systemic sclerosis (SSc) is an inflammatory fibrotic disease characterized by an excessive extracellular matrix deposition in the skin and internal organs. One fibrotic key event remains the fibroblast-to-myofibroblast differentiation that is controlled by a combination of mechanical and soluble factors, such as transforming growth factor-ß1 (TGF-ß1) and interleukin-1ß (IL-1ß). One important myofibroblast biomarker is human xylosyltransferase-I (XT-I), the initial enzyme in proteoglycan biosynthesis. Increased serum XT activity was quantified in SSc, but the underlying cellular mechanisms remain elusive. This study aims to determine the cellular basis of XT-I induction in SSc by using a myofibroblast cell culture model with SSc fibroblasts (SScF) and healthy control fibroblasts. We found that SScF exhibit a higher extracellular XT-I activity compared to control fibroblasts. This increased XT-I activity in SScF was demonstrated to be mediated by an enhanced autocrine TGF-ß signaling. Upon IL-1ß treatment, SScF showed an increased mRNA expression level of XT-I and TGF-ß receptor II (TGFBR2), while healthy control fibroblasts did not, pointing towards an involvement of IL-1ß in the cytokine-mediated XT-I induction. Performing microRNA (miRNA) inhibition experiments in the presence of TGF-ß1, we showed that the pro-fibrotic effect of IL-1ß may be mediated by a miRNA-21/TGF-ß receptor II axis, enhancing the autocrine TGF-ß signaling in SScF. Taken together, this study improves the mechanistic understanding of fibrotic XT-I induction in SSc by identifying a hitherto unknown IL-1ß-mediated miRNA-21/TGFBR2 regulation contributing to the enhanced XYLT1 expression and XT-I activity in SScF.

Statins as a Therapeutic Approach for the Treatment of Pseudoxanthoma Elasticum Patients: Evaluation of the Spectrum Efficacy of Atorvastatin In Vitro.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disorder caused by mutations in the ATP-binding cassette sub-family C member 6 gene. Our previous studies revealed that PXE might be associated with premature aging. Treatment with statins showed positive effects not only for PXE but also for other diseases associated with premature aging like Hutchinson-Gilford progeria syndrome. Nevertheless, the molecular mechanisms in the case of PXE remain unclear. Thus, this study was performed to evaluate the efficiency of atorvastatin by analyzing key characteristics of the PXE phenotype in primary human dermal fibroblasts of PXE patients. Our data indicate that an atorvastatin treatment has a positive effect, especially on factors associated with cholesterol biosynthesis and prenylation processes, whereas the effect on age- and calcification-related factors was less pronounced.

Development of a xylosyltransferase-I-selective UPLC MS/MS activity assay using a specific acceptor peptide.

Xylosyltransferases-I and -II (XT-I and -II) play an important role regarding the homeostasis of the extracellular matrix. Both enzymes catalyze the initial step of the proteoglycan (PG) biosynthesis by the transfer of xylose from their natural substrate uridine diphosphate (UDP) -xylose to a PG-core protein. The subsequent addition of further sugars, catalyzed by different glycosyltransferases, leads to the formation of a tetrasaccharide linker, which connects the PG-core protein and glycosaminoglycans. The reason for the appearance of two XT isoforms in all higher organisms is not known and remarkable, as both enzymes are able to initiate PG biosynthesis. The determination of the XT-I activity is of clinical importance because it can be used as a biomarker of several PG-associated fibrotic diseases. Since previous assays did not adequately differentiate between both XT-isoforms, the aim of this study was to develop an XT-I selective mass spectrometric (MS) assay. For this purpose, we initially used isoform-specific supernatants to successfully identify a synthetic acceptor peptide which was xylosylated much more selectively by the XT-I when compared to the XT-II isoform. The assay was further optimized concerning methodical parameters such as the injection volume and the incubation time of the reaction-mixture. By using samples covering a broad XT-activity spectrum, we successfully validated the assay to be used not only for the quantification of cell culture samples but also human serum specimens. Compared to previously used XT-activity assays, our newly developed test is more selective and sensitive, less expensive and easier to perform in high throughput.

Genetic deletion of Abcc6 disturbs cholesterol homeostasis in mice.

Genetic studies link adenosine triphosphate-binding cassette transporter C6 (ABCC6) mutations to pseudoxanthoma elasticum (PXE). ABCC6 sequence variations are correlated with altered HDL cholesterol levels and an elevated risk of coronary artery diseases. However, the role of ABCC6 in cholesterol homeostasis is not widely known. Here, we report reduced serum cholesterol and phytosterol levels in Abcc6-deficient mice, indicating an impaired sterol absorption. Ratios of cholesterol precursors to cholesterol were increased, confirmed by upregulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmgcr) expression, suggesting activation of cholesterol biosynthesis in Abcc6-/- mice. We found that cholesterol depletion was accompanied by a substantial decrease in HDL cholesterol mediated by lowered ApoA-I and ApoA-II protein levels and not by inhibited lecithin-cholesterol transferase activity. Additionally, higher proprotein convertase subtilisin/kexin type 9 (Pcsk9) serum levels in Abcc6-/- mice and PXE patients and elevated ApoB level in knockout mice were observed, suggesting a potentially altered very low-density lipoprotein synthesis. Our results underline the role of Abcc6 in cholesterol homeostasis and indicate impaired cholesterol metabolism as an important pathomechanism involved in PXE manifestation.

Linking ABCC6 Deficiency in Primary Human Dermal Fibroblasts of PXE Patients to p21-Mediated Premature Cellular Senescence and the Development of a Proinflammatory Secretory Phenotype.

Pseudoxanthoma elasticum (PXE) is a rare autosomal-recessive disorder that is mainly caused by mutations in the ATP-binding cassette sub-family C member 6 (ABCC6) gene. Clinically PXE is characterized by a loss of skin elasticity, arteriosclerosis or visual impairments. It also shares some molecular characteristics with known premature aging syndromes like the Hutchinson-Gilford progeria syndrome (HGPS). However, little is known about accelerated aging processes, especially on a cellular level for PXE now. Therefore, this study was performed to reveal a potential connection between premature cellular aging and PXE pathogenesis by analyzing cellular senescence, a corresponding secretory phenotype and relevant factors of the cell cycle control in primary human dermal fibroblasts of PXE patients. Here, we could show an increased senescence-associated ß-galactosidase (SA-ß-Gal) activity as well as an increased expression of proinflammatory factors of a senescence-associated secretory phenotype (SASP) like interleukin 6 (IL6) and monocyte chemoattractant protein-1 (MCP1). We further observed an increased gene expression of the cyclin-dependent kinase inhibitor (CDKI) p21, but no simultaneous induction of p53 gene expression. These data indicate that PXE is associated with premature cellular senescence, which is possibly triggered by a p53-independent p21-mediated mechanism leading to a proinflammatory secretory phenotype.

Identification of Putative Non-Substrate-Based XT-I Inhibitors by Natural Product Library Screening.

Fibroproliferative diseases are characterized by excessive accumulation of extracellular matrix (ECM) components leading to organ dysfunction. This process is characterized by an increase in myofibroblast content and enzyme activity of xylosyltransferase-I (XT-I), the initial enzyme in proteoglycan (PG) biosynthesis. Therefore, the inhibition of XT-I could be a promising treatment for fibrosis. We used a natural product-inspired compound library to identify non-substrate-based inhibitors of human XT-I by UPLC-MS/MS. We combined this cell-free approach with virtual and molecular biological analyses to confirm and prioritize the inhibitory potential of the compounds identified. The characterization for compound potency in TGF-ß1-driven XYLT1 transcription regulation in primary dermal human fibroblasts (key cells in ECM remodeling) was addressed by gene expression analysis. Consequently, we identified amphotericin B and celastrol as new non-substrate-based XT-I protein inhibitors. Their XT-I inhibitory effects were mediated by an uncompetitive or a competitive inhibition mode, respectively. Both compounds reduced the cellular XYLT1 expression level and XT-I activity. We showed that these cellular inhibitor-mediated changes involve the TGF-ß and microRNA-21 signaling pathway. The results of our study provide a strong rationale for the further optimization and future usage of the XT-I inhibitors identified as promising therapeutic agents of fibroproliferative diseases.

Cellular and Molecular Biomarkers Indicate Premature Aging in Pseudoxanthoma Elasticum Patients.

The molecular processes of aging are very heterogenic and not fully understood. Studies on rare progeria syndromes, which display an accelerated progression of physiological aging, can help to get a better understanding. Pseudoxanthoma elasticum (PXE) caused by mutations in the ATP-binding cassette sub-family C member 6 (ABCC6) gene shares some molecular characteristics with such premature aging diseases. Thus, this is the first study trying to broaden the knowledge of aging processes in PXE patients. In this study, we investigated aging associated biomarkers in primary human dermal fibroblasts and sera from PXE patients compared to healthy controls. Determination of serum concentrations of the aging biomarkers eotaxin-1 (CCL11), growth differentiation factor 11 (GDF11) and insulin-like growth factor 1 (IGF1) showed no significant differences between PXE patients and healthy controls. Insulin-like growth factor binding protein 3 (IGFBP3) showed a significant increase in serum concentrations of PXE patients older than 45 years compared to the appropriate control group. Tissue specific gene expression of GDF11 and IGFBP3 were significantly decreased in fibroblasts from PXE patients compared to normal human dermal fibroblasts (NHDF). IGFBP3 protein concentration in supernatants of fibroblasts from PXE patients were decreased compared to NHDF but did not reach statistical significance due to potential gender specific variations. The minor changes in concentration of circulating aging biomarkers in sera of PXE patients and the significant aberrant tissue specific expression seen for selected factors in PXE fibroblasts, suggests a link between ABCC6 deficiency and accelerated aging processes in affected peripheral tissues of PXE patients.

Activin A-Mediated Regulation of XT-I in Human Skin Fibroblasts.

Fibrosis is a fundamental feature of systemic sclerosis (SSc) and is characterized by excessive accumulation of extracellular matrix components like proteoglycans (PG) or collagens in skin and internal organs. Serum analysis from SSc patients showed an increase in the enzyme activity of xylosyltransferase (XT), the initial enzyme in PG biosynthesis. There are two distinct XT isoforms-XT-I and XT-II-in humans, but until now only XT-I is associated with fibrotic remodelling for an unknown reason. The aim of this study was to identify new XT mediators and clarify the underlying mechanisms, in view of developing putative therapeutic anti-fibrotic interventions in the future. Therefore, we used different cytokines and growth factors, small molecule inhibitors as well as small interfering RNAs, and assessed the cellular XT activity and XYLT1 expression in primary human dermal fibroblasts by radiochemical activity assays and qRT-PCR. We identified a new function of activin A as a regulator of XYLT1 mRNA expression and XT activity. While the activin A-induced XT-I increase was found to be mediated by activin A receptor type 1B, MAPK and Smad pathways, the activin A treatment did not alter the XYLT2 expression. Furthermore, we observed a reciprocal regulation of XYLT1 and XYLT2 transcription after inhibition of the activin A pathway components. These results improve the understanding of the differential expression regulation of XYLT isoforms under pathological fibroproliferative conditions.

microRNA-145 mediates xylosyltransferase-I induction in myofibroblasts via suppression of transcription factor KLF4.

Remodelling of the extracellular matrix by myofibroblasts is crucial for wound repair, but if deregulated, it might contribute to the development of fibrosis. Fibroblast-to-myofibroblast differentiation is promoted by aberrant microRNA-145-5p (miR-145) expression in response to transforming growth factor ß1 (TGFß1). One of several myofibroblast markers is human xylosyltransferase-I (XT-I), which is the initial and rate-limiting enzyme of proteoglycan biosynthesis. Increased serum XT activity was quantified in patients with systemic sclerosis (SSc), but the underlying cellular mechanism of this disease remains unknown. This study aims to determine the underlying molecular basis of XT-I induction by considering the miR-mediated regulation of XT-I. We found that miR-145 is upregulated in TGFß1-treated dermal fibroblasts and correlates with an increased cellular XYLT1 expression and XT activity. Overexpression of miR-145 in dermal fibroblasts induced XYLT1 expression and XT activity and enhanced TGFß1-promoted XT activity increase. Since direct XYLT1 3'-UTR targeting by miR-145 could be experimentally excluded, an indirect effect of miR-145 on XT-I regulation was indicated. We identified six transcription factor-binding sites for Krueppel-like factor 4 (KLF4), a zinc-finger transcription regulator and putative miR-145 target, in the XYLT1 promoter in silico. A suppressive role of KLF4 on XYLT1 expression was confirmed by targeted gene silencing in dermal fibroblasts and the quantification of KLF4 expression in SSc fibroblasts. Taken together, this study improves the mechanistic understanding of fibrotic remodelling in SSc by identifying a hitherto unknown miR-145/KLF4 pathway mediating the fibrogenic XT-I induction. This knowledge on XYLT1 may lead to the development of novel approaches in the therapy of fibrosis.

Retinal findings in carriers of monoallelic ABCC6 mutations.

AIM: Biallelic ABCC6 mutations cause pseudoxanthoma elasticum, a systemic disease characterised by calcification of elastic tissue and a specific retinal phenotype. In this study, we investigated if monoallelic ABCC6 mutations are also associated with retinal alterations. METHODS: In this prospective, cross-sectional, monocentre case-control study, carriers of monoallelic ABCC6 mutations were investigated and compared with age-matched controls. The retinal phenotype was characterised using fundus photography, fundus autofluorescence, confocal near-infrared reflectance imaging, spectral domain optical coherence tomography and in selected cases late-phase indocyanine green angiography. RESULTS: Thirty-eight subjects carrying monoallelic ABCC6 mutations (mean age 70.2 years, range 50-90, 26 female) were examined and compared with 77 age-matched controls (mean age 69.9 years, range 50-93, 43 female). Retinal alterations were more frequently found in carriers of monoallelic ABCC6 mutations compared with controls (50% vs 33.8%, p=0.107) with increasing prevalence at older age. Typical findings were peripapillary atrophy (37% vs 23%, p=0.184), pattern dystrophy-like changes (24% vs 12%, p=0.109), reticular pseudodrusen (21% vs 5%, p=0.019), small angioid streaks (8% vs 1%, p=0.105), choroidal neovascularisations and atrophic lesions (both 8% vs 0%, p=0.034). Late-phase indocyanine green angiography showed a reduced cyanescence centred to the posterior pole in 11 of 14 examined subjects with monoallelic ABCC6 mutations. CONCLUSION: The findings of this study indicate a possible ocular ABCC6 haploinsufficiency phenotype. Due to its late-onset and phenotypic similarities, misinterpretation as age-related macular degeneration is possible.

Xylosyltransferase-deficient human HEK293 cells show a strongly reduced proliferation capacity and viability.

Human xylosyltransferases-I and -II (XT-I and XT-II) catalyze the initial and rate-limiting step in proteoglycan (PG)-biosynthesis. Because PG are major components of the extracellular matrix (ECM), an alternated XT expression is associated with the manifestation of ECM-related diseases. While Drosophila melanogaster and Caenorhabditis elegans only harbor one XT-isoform, all higher organisms contain two isoforms, which are expressed in a tissue-specific manner. The reason for the appearance of two isoenzymes remains unexplained and remarkable, as all other enzymes involved in the synthesis of the tetrasaccharid linker, which connects the PG core protein with attached glycosaminoglycans, only show one isoform. In human, mutations in the XYLT genes cause diseases affecting the homeostasis of the ECM, such as skeletal dysplasias. We investigated for the first time whether already XT-I-deficient human embryonic kidney (HEK293) cells can compensate for decreased expression levels of both XT-isoforms. A siRNA-mediated XYLT2 mRNA knockdown led to reduced cellular proliferation rates and a partially increased cellular senescence of treated HEK293 cells. These results were verified by conducting a stable CRISPR/Cas9-mediated XYLT2 knockout, which revealed that only cells expressing at least partially functional XT-II proteins remain proliferative. Our study, therefore, shows for the first time that cells lacking both XT-isoforms are not viable and clearly indicates the importance of the XT concerning the cellular metabolism.