Julia Reichelt

Newcastle University, Newcastle upon Tyne, ENG, United Kingdom

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Publications (22)127.38 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The five subunits of transcription factor NF-κB have distinct biological functions. NF-κB signaling is important for skin homeostasis and aging, but the contribution of individual subunits to normal skin biology and disease is unclear. Immunohistochemical analysis of the p50 and c-Rel subunits within lesional psoriatic and systemic sclerosis skin revealed abnormal epidermal expression patterns, compared with healthy skin, but RelA distribution was unaltered. The skin of Nfkb1(-/-) and c-Rel(-/-) mice is structurally normal, but epidermal thickness and proliferation are significantly reduced, compared with wild-type mice. We show that the primary defect in both Nfkb1(-/-) and c-Rel(-/-) mice is within keratinocytes that display reduced proliferation both in vitro and in vivo. However, both genotypes can respond to proliferative stress, with 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperproliferation and closure rates of full-thickness skin wounds being equivalent to those of wild-type controls. In a model of bleomycin-induced skin fibrosis, Nfkb1(-/-) and c-Rel(-/-) mice displayed opposite phenotypes, with c-Rel(-/-) mice being protected and Nfkb1(-/-) developing more fibrosis than wild-type mice. Taken together, our data reveal a role for p50 and c-Rel in regulating epidermal proliferation and homeostasis and a profibrogenic role for c-Rel in the skin, and identify a link between epidermal c-Rel expression and systemic sclerosis. Modulating the actions of these subunits could be beneficial for treating hyperproliferative or fibrogenic diseases of the skin.
    American Journal Of Pathology 04/2013; · 4.52 Impact Factor
  • Lee Wallace, Julia Reichelt
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    ABSTRACT: The ability to grow keratinocyte stem cells (KSCs) in 3D culture is an important step forward for investigating the physiological properties of these cells. In the epidermis, KSCs are subject to various types of mechanical stress. To study the effects of mechanical stress on KSCs, monolayer cultures are limited as the KSCs can only form cell-cell contacts in one plane and to prevent differentiation, KSCs are grown in low (0.05 mM) calcium, which impairs formation of calcium-dependent adhesion structures such as desmosomes. This is in contrast to how KSCs are found in the epidermis in vivo, where they are connected on all sides by other cells, allowing them to form a more organized cytoskeleton. The cytoskeleton is essential for transducing mechanical signals between cells, and this cannot be accurately reproduced in monolayer cultures, where the cells do not have the same level of organization or connections. We describe a technique which allows the generation of large numbers of uniformly sized cell aggregates using cultured murine KSCs. These aggregates are produced using physiological calcium concentrations (1.2 mM), allowing the cells within the aggregates to form calcium-dependent contacts with other cells on all sides, resulting in the reorganization of the cytoskeleton, integrating the cells within each aggregate. Within the aggregates, KSCs retain stem cell properties, such as p63 expression, despite the increased calcium concentration and show activation of the mitogen-activated protein kinase ERK upon stretch. KSC aggregates can be manipulated further and provide a more physiologically relevant model for studying mechanical signaling in KSCs.
    Methods in molecular biology (Clifton, N.J.) 01/2013; 989:153-164.
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    ABSTRACT: Aberrant signaling through the class I phosphatidylinositol 3-kinase (PI3K)–Akt axis is frequent in human cancer. Here, we show that Beclin 1, an essential autophagy and tumor suppressor protein, is a target of the protein kinase Akt. Expression of a Beclin 1 mutant resistant to Akt-mediated phosphorylation increased autophagy, reduced anchorage-independent growth, and inhibited Akt-driven tumorigenesis. Akt-mediated phosphorylation of Beclin 1 enhanced its interactions with 14-3-3 and vimentin intermediate filament proteins, and vimentin depletion increased autophagy and inhibited Akt-driven transformation. Thus, Akt-mediated phosphorylation of Beclin 1 functions in autophagy inhibition, oncogenesis, and the formation of an autophagy-inhibitory Beclin 1/14-3-3/vimentin intermediate filament complex. These findings have broad implications for understanding the role of Akt signaling and intermediate filament proteins in autophagy and cancer.
    Science 11/2012; 338(6109):956-959. · 31.20 Impact Factor
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    ABSTRACT: Keratins K1 and K10 are the most abundant proteins in the upper epidermis where they polymerize to form intermediate filaments (IFs). In addition to their well-established function in providing epidermal stability, K1/K10 (i.e. the dimer between K1 and K10) IFs are supposed to be important for terminal epidermal differentiation and barrier formation. It was previously shown that the imbalanced deletion of one of the partner keratins, K10, disturbed epidermal homoeostasis, although stability was provided by compensatory upregulation of K5/K14, which formed IFs together with the remaining K1. Here, we show that deletion of both partner keratins, K1 and K10, results in lethal postnatal skin fragility in mice. Krt1(-/-);Krt10(-/-) mice revealed that K1/K10 IFs are unexpectedly dispensable for epidermal stratification. Although the stratum corneum was less compact and cornified envelope differentiation was impaired, a dye exclusion assay showed that the development of a functional water barrier was surprisingly independent from the presence of K1/K10 IFs. The deletion of K1/K10 was not compensated by any other keratin pair such as the basal epidermal keratins K5/K14, and electron microscopy revealed total absence of IFs in the suprabasal epidermis. Although plakoglobin was unchanged, the expression of the desmosomal proteins desmoplakin, desmocollin 1 and desmoglein 1 were altered and suprabasal desmosomes were smaller in Krt1(-/-);Krt10(-/-) than in wild-type epidermis suggesting an involvement of K1/K10 IFs in desmosome dynamics. Furthermore, Krt1(-/-);Krt10(-/-) mice showed premature loss of nuclei during epidermal differentiation and lower levels of emerin, lamin A/C and Sun1, revealing a previously unknown function for IFs in maintaining nuclear integrity in the upper epidermis.
    Journal of Cell Science 02/2012; 125(Pt 7):1750-8. · 5.88 Impact Factor
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    ABSTRACT: In the skin, multipotent keratinocyte stem cells (KSC) are localised in the hair follicle bulge region. Although, KSC can be cultivated and grown in two-dimensional (2D) culture they rapidly lose stem cell markers when isolated from their niche. Currently, there is no KSC culture method available which recapitulates an environment similar to the KSC niche in the hair follicle. Here we describe the successful establishment of an in vitro 3D stem cell culture model developed from clonally growing keratinocyte lines derived from neonatal mice using culture conditions previously established for human keratinocytes. After 20 passages, keratinocyte lines showed a stable ratio of holoclones (stem cells), meroclones (stem and precursor cells) and paraclones (differentiating cells), with approximately 29% holoclones, 54% meroclones and 17% paraclones, and were thus termed keratinocyte stem and precursor cell (KSPC) cultures. In high calcium medium, KSPC cultures grown at the air-liquid interphase differentiated and formed epidermal equivalents. Notably, and in contrast to primary keratinocytes, keratinocytes from KSPC cultures were able to aggregate and form spherical clusters in hanging drops, a characteristic hallmark shared with other stem cell types. Similar to the in vivo situation in the hair follicle bulge, KSPC aggregates also showed low proliferation, down-regulation of keratin 6, absence of keratin 1, and expression of the KSC markers keratin 15, Sox9, NFATc1 and Zfp145. KSPC aggregates therefore provide an optimal in vitro 3D environment for the further characterisation and study of normal and genetically modified KSPC.
    Stem cell reviews 09/2011; 8(2):402-13. · 5.08 Impact Factor
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    ABSTRACT: Zinc-finger nucleases (ZFNs) are sequence-specific genome engineering tools with great potential for the development of gene therapies. The achievement of permanent cures through gene therapy requires targeting of stem cells but the effects and/or side effects of ZFN treatment on adult stem cell potency are largely unknown. Keratinocyte stem cells (KSCs) are attractive candidates for the development of gene therapies as their isolation, culture and grafting are well established. We derived KSCs from eGFP-transgenic mice and knocked out eGFP expression by disrupting the open reading frame with specific ZFNs in cell culture. EGFP-negative KSCs were then used as a model system to study the impact of ZFN treatment on stem cell potential. We achieved high gene disruption efficiencies with up to 18% eGFP-negative KSCs. As expected, ZFN cytotoxicity increased with rising ZFN concentrations. However, the ratio of correctly targeted KSCs among total treated cells was similar at different ZFN doses. Most importantly, our in vitro assays showed that ZFN-treated KSCs maintained their stem cell potential. They retained the capacity to both self-renew and form fully differentiated epidermal equivalents in culture. Moreover, they were able to form spherical aggregates in suspension culture, a characteristic hallmark shared with other stem cell types, and they expressed the in vivo KSC markers K15, NFATc1 and Sox9. Our data suggest that the stem cell potential of KSCs is not impaired by highly efficient ZFN treatment.
    Stem cell reviews 08/2011; 8(2):426-34. · 5.08 Impact Factor
  • Julia Reichelt
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    ABSTRACT: The epidermis, like many other tissues, reacts to mechanical stress by increasing cell proliferation. Mechanically stressed skin regions often develop thicker skin and hyperkeratosis. Interestingly, a large number of skin diseases are accompanied by epidermal proliferation and hyperkeratosis even under normal mechanical stress conditions. Although, some of the molecular pathways of mechanical signaling involving integrins, the epidermal growth factor receptor and mitogen-activated protein kinases are known it is still unclear, how mechanical force is sensed and transformed into the molecular signals that induce cell proliferation. This review focuses on the molecules and pathways known to play a role in mechanotransduction in epidermal keratinocytes and discusses the pathways identified in other well-studied cell types.
    European Journal of Cell Biology 01/2008; 86(11-12):807-16. · 3.21 Impact Factor
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    ABSTRACT: Mutations in the valosin-containing protein (VCP, p97) gene on chromosome 9p13-p12 cause a late-onset form of autosomal dominant inclusion body myopathy associated with Paget disease of the bone and frontotemporal dementia (IBMPFD). We report on the pathological consequences of three heterozygous VCP (R93C, R155H, R155C) mutations on human striated muscle. IBMPFD skeletal muscle pathology is characterized by degenerative changes and filamentous VCP- and ubiquitin-positive cytoplasmic and nuclear protein aggregates. Furthermore, this is the first report demonstrating that mutant VCP leads to a novel form of dilatative cardiomyopathy with inclusion bodies. In contrast to post-mitotic striated muscle cells and neurons of IBMPFD patients, evidence of protein aggregate pathology was not detected in primary IBMPFD myoblasts or in transient and stable transfected cells using wild-type-VCP and R93C-, R155H-, R155C-VCP mutants. Glutathione S-transferase pull-down experiments showed that all three VCP mutations do not affect the binding to Ufd1, Npl4 and ataxin-3. Structural analysis demonstrated that R93 and R155 are both surface-accessible residues located in the centre of cavities that may enable ligand-binding. Mutations at R93 and R155 are predicted to induce changes in the tertiary structure of the VCP protein. The search for putative ligands to the R93 and R155 cavities resulted in the identification of cyclic sugar compounds with high binding scores. The latter findings provide a novel link to VCP carbohydrate interactions in the complex pathology of IBMPFD.
    Brain 03/2007; 130(Pt 2):381-93. · 9.92 Impact Factor
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    ABSTRACT: Mutations in the human myotilin gene may cause limb-girdle muscular dystrophy 1A and myofibrillar myopathy. Here, we describe a German patient with the clinically distinct disease phenotype of late adult onset distal anterior leg myopathy caused by a heterozygous S55F myotilin mutation. In addition to a thorough morphological and clinical analysis, we performed for the first time a protein chemical analysis and transient transfections. Morphological analysis revealed an inclusion body myopathy with myotilin- and desmin-positive aggregates. The clinical and pathological phenotype considerably overlaps with late onset distal anterior leg myopathy of the Markesbery-Griggs type. Interestingly, all three analyzed myotilin missense mutations (S55F, S60F and S60C) do not lead to gross changes in the total amount of myotilin or to aberrant posttranslational modifications in diseased muscle, as observed in a number of muscular dystrophies. Transiently transfected wild-type and S55F mutant myotilin similarly colocalised with actin-containing stress fibers in BHK-21 cells. Like the wild-type protein, mutated myotilin did not disrupt the endogenous desmin cytoskeleton or lead to pathological protein aggregation in these cells. This lack of an obvious dominant negative effect sharply contrasts to transfections with, for instance, the disease-causing A357P desmin mutant. In conclusion our data indicate that the disorganization of the extrasarcomeric cytoskeleton and the presence of desmin-positive aggregates are in fact late secondary events in the pathogenesis of primary myotilinopathies, rather than directly related. These findings suggest that unrelated molecular pathways may result in seemingly similar disease phenotypes at late disease stages.
    Neuromuscular Disorders 07/2006; 16(6):361-7. · 3.46 Impact Factor
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    ABSTRACT: Here, we present strong evidence that the targeted deletion of keratin 10 (K10) alters sebocyte differentiation in mice, mediated by an increased proliferation and differentiation of cells located in the periphery of the glands. This was not accompanied by the induction of the proliferation-associated keratins K6, K16 and K17. Sebaceous gland cells of K10-/- mice showed an accelerated turnover and secreted more sebum including wax esters, triglycerides, and cholesterol esters. The levels of the major epidermal lipids ceramides and cholesterol were also increased, whereas glycosylceramides and sphingomyelin were decreased which was not based on altered sphingolipid biosynthesis. The amount of Cer(OS), covalently bound to the cornified envelope, remained unchanged, as well as the amount of loricrin and involucrin. In agreement with the unaltered expression of beta-catenin and its targets cyclin D1 and c-Myc, we conclude that the altered composition of the suprabasal intermediate filament cytoskeleton in K10-/- mice increased the differentiation of epidermal stem cells towards the sebocyte lineage.
    European Journal of Cell Biology 01/2005; 83(11-12):747-59. · 3.21 Impact Factor
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    ABSTRACT: Keratin 10 (K10) is the major protein in the upper epidermis where it maintains keratinocyte integrity. Others have reported that K10 may act as a tumor suppressor upon ectopic expression in mice. Although K10(-/-) mice show significant epidermal hyperproliferation, accompanied by an activation of the mitogen-activated protein kinase (MAPK) pathway, they formed no spontaneous tumors. Here, we report that K10(-/-) mice treated with 7,12-dimethylbenz[a]anthracene (DMBA)/12-O-tetradecanoylphorbol-13-acetate (TPA) developed far less papillomas than wild-type mice. BrdU(5-bromo-2'-deoxyuridine)-labeling revealed a strongly accelerated keratinocyte turnover in K10(-/-) epidermis suggesting an increased elimination of initiated keratinocytes at early stages of developing tumors. This is further supported by the absence of label-retaining cells 18 d after the pulse whereas in wild-type mice label-retaining cells were still present. The concomitant increase in K6, K16, and K17 in K10 null epidermis and the increased motility of keratinocytes is in agreement with the pliability versus resilience hypothesis, stating that K10 and K1 render cells more stable and static. The K10(-/-) knockout represent the first mouse model showing that loss of a keratin, a cytoskeletal protein, reduces tumor formation. This is probably caused by an accelerated turnover of keratinocytes, possibly mediated by activation of MAPK pathways.
    Journal of Investigative Dermatology 12/2004; 123(5):973-81. · 6.19 Impact Factor
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    ABSTRACT: Intermediate filaments (IFs), desmosomes, and their associates are built from multidomain proteins that form cytoskeletal scaffolds in the cytoplasm and the nucleus of vertebrate tissues. Mutations in more than 80 genes cause monogenic disorders that include severe skin fragility, myopathies, neurodegeneration, and premature ageing, and contribute to polygenic disorders including liver and inflammatory bowel disease. First interpreted as "mechanical weakness" disorders resulting from a weakened cytoskeleton, emerging data support the concept that changes in cytoskeletal architecture profoundly alter signal transduction and cellular transcription patterns. This is in line with cell type-specific interactions between cytoskeletal and their associated proteins, and may involve both soluble and insoluble forms of intermediate filament proteins. Understanding how mutation-induced disruption of the cytoskeleton and its upstream regulators causes disease at the molecular level presents one of the major challenges in future research.
    Experimental Cell Research 12/2004; 301(1):91-102. · 3.56 Impact Factor
  • Methods in cell biology 02/2004; 78:65-94. · 1.44 Impact Factor
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    J Kirfel, T M Magin, J Reichelt
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    ABSTRACT: Intermediate filament proteins form an essential part of the cytoskeleton and provide topological order to cells and tissues. These features result from their intrinsic property of self-organization and their response to extrinsic cues. Keratins represent the largest subgroup among all intermediate filament proteins and are differentially expressed as pairs of type I and type II intermediate filament proteins in epithelia. Their primary function is to impart mechanical strength to cells. This function is illustrated by patients with keratin mutations and by gene-deficient mice. Additional functions include their participation in the response to stress, cell signalling and apoptosis, and thus the keratin cytoskeleton appears far more dynamic than previously anticipated. This may result from hyperphosphorylation and possibly from interaction with associated proteins. How signalling networks affect keratin organization, turnover and function and vice versa will be a major challenge for future investigations.
    Cellular and Molecular Life Sciences CMLS 02/2003; 60(1):56-71. · 5.62 Impact Factor
  • Journal of Anatomy 12/2002; 201(5):424. · 2.36 Impact Factor
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    ABSTRACT: Defolliculated is a novel spontaneous mouse mutation that maps to chromosome 11 close to the type I keratin locus. Histology shows abnormal differentiation of the sebaceous gland, with the sebocytes producing little or no sebum and undergoing abnormal cornification. The hair follicles fail to regress during catagen leading to abnormally long follicles. In contrast the hair shafts are shorter than normal, suggesting altered differentiation or proliferation of matrix cells during anagen. The shafts emerge from the follicle with cornified material still attached. The dermis contains increased numbers of immune cells, including T cells (CD4-positive), macrophages, and mast cells, at all time points examined. Complete elimination of all pelage and tail follicles occurs after two to three hair cycles, apparently by necrosis. Defolliculated may be a useful model for determining further functions of the sebaceous gland, and for understanding the regulation of catagen and hair follicle immunology.
    Journal of Investigative Dermatology 08/2002; 119(1):32-7. · 6.19 Impact Factor
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    Julia Reichelt, Thomas M Magin
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    ABSTRACT: In the past, keratins have been established as structural proteins. Indeed, mutations in keratin 10 (K10) and other epidermal keratins lead to severe skin fragility syndromes. Here, we present adult K10-/- mice, which reveal a novel connection between the regulation of cell proliferation and K10. Unlike most keratin mutant mice, the epidermis of adult K10-/- mice showed no cytolysis but displayed hyperproliferation of basal keratinocytes and an increased cell size. BrdU labelling revealed a shortened transition time for keratinocytes migrating outwards and DAPI staining of epidermal sheets uncovered an impaired organization of epidermal proliferation units. These remarkable changes were accompanied by the induction of c-Myc, cyclin D1, 14-3-3sigma and of wound healing keratins K6 and K16. The phosphorylation of Rb remained unaltered. In line with the downregulation of K10 in squamous cell carcinomas and its absence in proliferating cells in vivo, our data suggest that the tissue-restricted expression of some members of the keratin gene family not only serves structural functions. Our results imply that the altered composition of the suprabasal cytoskeleton is able to alter the proliferation state of basal cells through the induction of c-Myc. A previous model based on transfection of K10 in immortalized human keratinocytes suggested a direct involvement of K10 in cell cycle control. While those experiments were performed in human cultured keratinocytes, our data establish, that in vivo, K10 acts by an indirect control mechanism in trans.
    Journal of Cell Science 08/2002; 115(Pt 13):2639-50. · 5.88 Impact Factor
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    J Reichelt, H Büssow, C Grund, T M Magin
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    ABSTRACT: The expression of distinct keratin pairs during epidermal differentiation is assumed to fulfill specific and essential cytoskeletal functions. This is supported by a great variety of genodermatoses exhibiting tissue fragility because of keratin mutations. Here, we show that the loss of K10, the most prominent epidermal protein, allowed the formation of a normal epidermis in neonatal mice without signs of fragility or wound-healing response. However, there were profound changes in the composition of suprabasal keratin filaments. K5/14 persisted suprabasally at elevated protein levels, whereas their mRNAs remained restricted to the basal keratinocytes. This indicated a novel mechanism regulating keratin turnover. Moreover, the amount of K1 was reduced. In the absence of its natural partner we observed the formation of a minor amount of novel K1/14/15 filaments as revealed by immunogold electron microscopy. We suggest that these changes maintained epidermal integrity. Furthermore, suprabasal keratinocytes contained larger keratohyalin granules similar to our previous K10T mice. A comparison of profilaggrin processing in K10T and K10(-/-) mice revealed an accumulation of filaggrin precursors in the former but not in the latter, suggesting a requirement of intact keratin filaments for the processing. The mild phenotype of K10(-/-) mice suggests that there is a considerable redundancy in the keratin gene family.
    Molecular Biology of the Cell 07/2001; 12(6):1557-68. · 4.60 Impact Factor
  • J Reichelt, D O Schachtschabel
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    ABSTRACT: Oxidative phosphorylation is the main endogenous source for the generation of reactive oxygen species (ROS). In order to investigate the influence of enhanced ROS production on the in vitro senescence of Wi-38 fibroblasts, cells were cultivated in medium with elevated (hypertonic) NaCl concentrations. The number of active Na(+)/K(+)-ATPase molecules per cell was found to be increased. A rise in both respiration and glycolysis as evidenced by the increases in oxygen and glucose consumption and lactate production was revealed. Cells stayed alive in medium with NaCl concentrations of up to 0.30 M and could be adapted to growth under these hypertonic conditions (high-NaCl tolerant cells). These cells exhibited an increased cell size and protein content. A growing number of cells showed stress fibers and granulation. The proliferation rate and the maximum number of cumulative population doublings of these high-NaCl tolerant cultures were reduced and saturation density was decreased. Thus, these cells under energetic stress due to increased energy requirements for active ion transport expressed features typical for aging in vitro. We conclude therefore that energetic stress induces premature aging in human diploid fibroblasts.
    Archives of Gerontology and Geriatrics 07/2001; 32(3):219-31. · 1.70 Impact Factor
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    ABSTRACT: Recently, we established keratin 10-deficient mice, serving as a model for the hyperkeratotic skin disorder epidermolytic hyperkeratosis. The considerable ichthyosis in these mice suggested alterations in terminal differentiation and in the formation of a functional epidermal barrier. Here, we report on the ultrastructural organization and composition of the stratum corneum lipids and on the expression of two major cornified envelope proteins. Electron microscopy of ruthenium tetroxide postfixed skin samples demonstrated a normal extrusion and morphology of lamellar bodies as well as the formation of bona fide lamellar layers in neonatal keratin 10-deficient mice. When we studied the composition of the major stratum corneum lipids, however, we found significant changes. Most importantly, the analysis of ceramide subpopulations revealed that the total amount of ceramide 2 was elevated in keratin 10-deficient mice, whereas ceramides 1, 3, 4, and 5 were decreased among total stratum corneum lipids. The amount of the ceramide precursors sphingomyelin and glucosylceramide was reduced in the stratum corneum without accompanying changes in the mRNA coding for acid sphingomyelinase. Notably, we found an increased mRNA and protein content for involucrin in neonatal keratin 10-deficient mice, whereas the expression of loricrin was not changed. Our data demonstrate that, although the formation of lipid layers in the stratum corneum appeared to be normal, its lipid composition is significantly altered in keratin 10-deficient mice.
    Journal of Investigative Dermatology 10/1999; 113(3):329-34. · 6.19 Impact Factor

Publication Stats

518 Citations
127.38 Total Impact Points


  • 2008–2013
    • Newcastle University
      • • Institute of Cellular Medicine
      • • North East England Stem Cell Institute
      Newcastle upon Tyne, ENG, United Kingdom
  • 2006
    • University of Cologne
      • Institute for Biochemistry I
      Köln, North Rhine-Westphalia, Germany
  • 1997–2005
    • University of Bonn
      • • Institut für Physiologie I
      • • Institut für Pathologie
      • • Institute of Genetics
      Bonn, North Rhine-Westphalia, Germany