FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W2029653522> ?p ?o ?g. }

• W2029653522 endingPage "360" @default.
• W2029653522 startingPage "353" @default.
• W2029653522 abstract "SummaryOur recent studies have demonstrated that PPARα activators stimulate differentiation and inhibit proliferation in cultured human keratinocytes and accelerate epidermal development and permeability barrier formation in fetal rat skin explants. As the role of PPARα activation in adult epidermis is not known, the aim of this study was to determine if topically applied PPARα ligands regulate keratinocyte differentiation in murine epidermis. Topical treatment with PPARα activators resulted in decreased epidermal thickness. Expression of structural proteins of the upper spinous/granular layers (involucrin, profilaggrin-filaggrin, loricrin) increased following topical treatment with PPARα activators. Furthermore, topically applied PPARα activators also increased apoptosis, decreased cell proliferation, and accelerated recovery of barrier function following acute barrier abrogation. Experiments with PPARα–/– knockout mice showed that these effects are specifically mediated via PPARα. Compared with the epidermis of PPARα+/+ mice, involucrin, profilaggrin-filaggrin, and loricrin expression were slightly decreased in PPARα–/– mice. Moreover, topical clofibrate treatment did not increase epidermal differentiation in PPARα–/– mice. Furthermore, in cultured human keratinocytes we have demonstrated that PPARα activators induce an increase in involucrin mRNA levels. We have also shown that this increase in gene expression requires an intact AP-1 response element at -2117 to -2111 bp. Thus, stimulation of PPARα stimulates keratinocyte/epidermal differentiation and inhibits proliferation. Our recent studies have demonstrated that PPARα activators stimulate differentiation and inhibit proliferation in cultured human keratinocytes and accelerate epidermal development and permeability barrier formation in fetal rat skin explants. As the role of PPARα activation in adult epidermis is not known, the aim of this study was to determine if topically applied PPARα ligands regulate keratinocyte differentiation in murine epidermis. Topical treatment with PPARα activators resulted in decreased epidermal thickness. Expression of structural proteins of the upper spinous/granular layers (involucrin, profilaggrin-filaggrin, loricrin) increased following topical treatment with PPARα activators. Furthermore, topically applied PPARα activators also increased apoptosis, decreased cell proliferation, and accelerated recovery of barrier function following acute barrier abrogation. Experiments with PPARα–/– knockout mice showed that these effects are specifically mediated via PPARα. Compared with the epidermis of PPARα+/+ mice, involucrin, profilaggrin-filaggrin, and loricrin expression were slightly decreased in PPARα–/– mice. Moreover, topical clofibrate treatment did not increase epidermal differentiation in PPARα–/– mice. Furthermore, in cultured human keratinocytes we have demonstrated that PPARα activators induce an increase in involucrin mRNA levels. We have also shown that this increase in gene expression requires an intact AP-1 response element at -2117 to -2111 bp. Thus, stimulation of PPARα stimulates keratinocyte/epidermal differentiation and inhibits proliferation. 5-bromo-2-deoxyuridine peroxisome-proliferator-activated receptor retinoic-acid-activated receptor retinoic-X-activated receptor transepidermal water loss TdT-mediated dUTP nick end-labeling Differentiation of keratinocytes is a multistep process (Fuchs, 1990Fuchs E. Epidermal differentiation. The bare essentials.J Cell Biol. 1990; 111: 2807-2814Crossref PubMed Scopus (568) Google Scholar; Eckert et al., 1997Eckert R.L. Crish J.F. Robinson N.A. The epidermal keratinocyte as a model for the study of gene regulation and function.Physiol Rev. 1997; 77: 397-424Crossref PubMed Scopus (331) Google Scholar) that is required for the formation of a functional stratum corneum that provides both the mechanical and permeability barrier between the external environment and the internal milieu (Elias and Menon, 1991Elias P.M. Menon G.M. Structural and biochemical correlates of the epidermal permeability barrier.Adv Lipid Res. 1991; 24: 1-26Crossref PubMed Google Scholar; Jackson et al., 1993Jackson S.M. Williams M.L. Feingold K.R. et al.Pathobiology of the stratum corneum.Western J Med. 1993; 158: 279-285PubMed Google Scholar). The stratum corneum consists of corneocytes and extracellular lipid lamellar membranes that block water and solute movement (Elias and Menon, 1991Elias P.M. Menon G.M. Structural and biochemical correlates of the epidermal permeability barrier.Adv Lipid Res. 1991; 24: 1-26Crossref PubMed Google Scholar; Jackson et al., 1993Jackson S.M. Williams M.L. Feingold K.R. et al.Pathobiology of the stratum corneum.Western J Med. 1993; 158: 279-285PubMed Google Scholar). Corneocytes are terminally differentiated, anucleate keratinocytes, which have a rigid cornified envelope that provides strength and chemical resistance (Reichert et al., 1993Reichert U. Michel S. Schmidt R. The cornified cell envelope. A key structure of the terminally differentiated keratinocytes.in: Darmon M. Blumenberg M. Molecular Biology of the Skin: the Keratinocyte. Academic Press, San Diego1993: 107-150Crossref Google Scholar; Steinert, 1995Steinert P.M. A model for the hierarchical structure of the human epidermal cornified cell envelope.Cell Death Differ. 1995; 2: 23-31PubMed Google Scholar). The cornified envelope is characterized by extensively cross-linked involucrin, loricrin, and other structural proteins, which are catalyzed by the keratinocyte-specific enzyme, transglutaminase I (Steinert and Marenkov, 1995Steinert P.M. Marenkov L.N. The proteins elafin, filaggrin, keratin intermediate filaments, loricrin and SPRs are isopeptide crosslinked components of the human epidermal cornified cell envelope.J Biol Chem. 1995; 270: 17702-17711Crossref PubMed Scopus (464) Google Scholar,Steinert and Marenkov, 1997Steinert P.M. Marenkov L.N. Involucrin is an important early component in the assembly of the epidermal cornified cell envelope.J Biol Chem. 1997; 272: 2021-2030Crossref PubMed Scopus (193) Google Scholar). The immediate precursors of corneocytes are the terminally differentiating keratinocytes of the stratum granulosum. These keratinocytes are characterized by the presence of keratohyalin granules containing abundant quantities of filaggrin and loricrin, and numerous lamellar bodies. Despite its great importance, the regulation of terminal keratinocyte differentiation is still not well understood (Fuchs, 1990Fuchs E. Epidermal differentiation. The bare essentials.J Cell Biol. 1990; 111: 2807-2814Crossref PubMed Scopus (568) Google Scholar; Eckert et al., 1997Eckert R.L. Crish J.F. Robinson N.A. The epidermal keratinocyte as a model for the study of gene regulation and function.Physiol Rev. 1997; 77: 397-424Crossref PubMed Scopus (331) Google Scholar). Nuclear hormone receptors are transcription factors that regulate many cellular functions including cell differentiation (Mangelsdorf et al., 1995Mangelsdorf D.J. Thummel C. Beator M. et al.The nuclear receptor superfamily, the second decade.Cell. 1995; 83: 835-839Abstract Full Text PDF PubMed Scopus (5841) Google Scholar; Kliever et al., 1999Kliever S.A. Lehmann J.M. Willson T.M. Orphan nuclear receptors: shifting endocrinology into reverse.Science. 1999; 284: 757-760Crossref PubMed Scopus (414) Google Scholar). Some of these nuclear hormone receptors, including retinoic-acid-activated receptor (RAR), vitamin D receptor, and thyroid hormone receptor regulate transcription by forming heterodimers with retinoic-X-activated receptor (RXR). Ligands of these nuclear hormone receptors, including retinoic acid and vitamin D, have been shown to regulate keratinocyte proliferation and differentiation (Pillai and Bikle, 1991Pillai S. Bikle D.D. Role of intracellular free calcium in the cornified envelope formation of keratinocytes, differences in the mode of action of extracellular calcium and 1,25 dihydroxyvitamin D3.J Cell Physiol. 1991; 146: 94-100Crossref PubMed Scopus (119) Google Scholar; Bikle, 1996Bikle D.D. 1,25 OH2D3-modulated calcium induced keratinocyte differentiation.J Invest Dermatol Symp Proc The. 1996; 1: 22-27PubMed Google Scholar; Eichner et al., 1996Eichner R. Gendimenica G.J. Kahn M. et al.Effects of long-term retinoic acid treatment on epidermal differentiation in vivo, specific modification in the program of terminal differentiation.Br J Dermatol. 1996; 135: 687-695Crossref PubMed Scopus (24) Google Scholar; Fisher and Voorhees, 1996Fisher G.J. Voorhees J.J. Molecular mechanisms of retinoid actions in skin.FASEB J. 1996; 10: 1002-1013Crossref PubMed Scopus (327) Google Scholar; Kang et al., 1996Kang S. Li X.-Y. Voorhees J.J. Pharmacology and molecular action of retinoids and vitamin D in skin.J Invest Dermatol Symp Proc The. 1996; 1: 15-21Crossref PubMed Google Scholar). Furthermore, epidermal differentiation is abnormal in transgenic mice that overexpress RAR or RXR dominant negative mutants (Imakado et al., 1995Imakado S. Biackenbach J.R. Bundman D.J. et al.Targeting expression of a dominant-negative retinoic acid receptor mutant in the epidermis of transgenic mice results in loss of barrier function.Genes Dev. 1995; 9: 317-329Crossref PubMed Scopus (121) Google Scholar; Saitou et al., 1995Saitou M. Sugai S. Tawaka T. et al.Inhibition of skin development by targeted expression of a dominant-negative retinoic acid receptor.Nature. 1995; 374: 159-162Crossref PubMed Scopus (156) Google Scholar; Feng et al., 1997Feng X. Peng Z.H. Di W. et al.Suprabasal expression of a dominant-negative RXRα mutant in transgenic mouse epidermis impairs regulation of gene transcription and basal keratinocyte proliferation by RAR-selective retinoids.Genes Dev. 1997; 11: 59-71Crossref PubMed Scopus (57) Google Scholar). Peroxisome-proliferator-activated receptors (PPARs) also heterodimerize with RXR (Isseman and Green, 1990Isseman I. Green S. Activation of a member of the steroid hormone receptor superfamily by peroxisome proliferators.Nature. 1990; 347: 645-650Crossref PubMed Scopus (2951) Google Scholar; Schoonjans et al., 1996Schoonjans K. Staels B. Auwerx J. Role of the peroxisome proliferator-activated receptor in mediating the effects of fibrates and fatty acids on gene expression.J Lipid Res. 1996; 37: 907-925Abstract Full Text PDF PubMed Google Scholar). 1The current proposed designation of these nuclear receptors is NR1C1 for PPARα, NR1C2 for PPARδ, and NR1C3 for PPARγ (Nuclear Receptors Nomenclature Committee, 1999Nuclear Receptors Nomenclature Committee A unified nomenclature system for the nuclear receptor superfamily.Cell. 1999; 97: 161-163Abstract Full Text Full Text PDF PubMed Scopus (908) Google Scholar).1The current proposed designation of these nuclear receptors is NR1C1 for PPARα, NR1C2 for PPARδ, and NR1C3 for PPARγ (Nuclear Receptors Nomenclature Committee, 1999Nuclear Receptors Nomenclature Committee A unified nomenclature system for the nuclear receptor superfamily.Cell. 1999; 97: 161-163Abstract Full Text Full Text PDF PubMed Scopus (908) Google Scholar). The three PPAR isotypes, i.e., PPARα, PPARδ, and PPARγ, are all present in cultured keratinocytes (Rivier et al., 1998Rivier M. Safowoua I. Lebrun P. et al.Differential expression of peroxisome proliferator-activated receptor subtypes during the differentiation of human keratinocytes.J Invest Dermatol. 1998; 111: 1116-1121Crossref PubMed Scopus (143) Google Scholar) and PPARα and PPARδ are expressed both in fetal and adult rodent epidermis (Braissant et al., 1996Braissant O. Foutelle F. Scotto C. et al.Differential expression of peroxisome proliferator-activated receptors, PPA, Rs, tissue distribution of, PPAR- &, alpha;-β and-γ in the adult rat.Endocrinology. 1996; 137: 354-366Crossref PubMed Scopus (1733) Google Scholar; Braissant and Wahli, 1998Braissant O. Wahli W. Differential expression of peroxisome proliferator activated receptor-α -β and -γ during rat embryonic development.Endocrinology. 1998; 139: 2748-2754Crossref PubMed Scopus (377) Google Scholar). Recent studies by our laboratory have demonstrated that PPARα ligands stimulate differentiation and inhibit proliferation in cultured human keratinocytes (Hanley et al., 1998Hanley K. Jiang Y. He S.S. et al.Keratinocyte differentiation is stimulated by activators of the nuclear hormone receptor PPARα.J Invest Dermatol. 1998; 110: 368-375Crossref PubMed Scopus (160) Google Scholar). Additionally, we showed that PPARα ligands accelerated stratum corneum development and permeability barrier formation when added to fetal rat skin explants (Hanley et al., 1997Hanley K. Jiang Y. Crumerine D. et al.Activation of the nuclear hormone receptors PPARα and FXR accelerate the development of the fetal epidermal permeability barrier.J Clin Invest. 1997; 100: 705-712Crossref PubMed Scopus (136) Google Scholar; Kömüves et al., 1998Kömüves L.G. Hanley K. Jiang Y. et al.Ligands and activators of nuclear hormone receptors regulate epidermal differentiation during fetal rat skin development.J Invest Dermatol. 1998; 111: 429-433Crossref PubMed Scopus (91) Google Scholar). Thus in two different in vitro model systems PPARα ligands accelerate keratinocyte differentiation. The effect of PPARα ligands on intact epidermis following topical applications is not yet known, however. The purpose of this study was (i) to determine if PPARα ligands also induce differentiation and inhibit proliferation in the epidermis of intact skin in vivo; (ii) to determine which PPAR isotype is responsible for these effects; (iii) to determine if PPARα is required for normal epidermal differentiation; and finally, (iv) to determine the mechanism by which PPARα stimulates differentiation. Adult male hairless mice (Simonsen, Gilroy, CA, or Charles River, Wilmington, MA) or con-ventional hairy mice (B6129F1 and SV/129 strains, Jackson Laboratories, Bar Harbor, ME) were used in this study. C57BL/6 mice with targeted disruption of the PPARα gene (PPARα–/– knockout mice) and congenic C57BL/6 mice (PPARα+/+ wild-type mice) have been described earlier (Lee et al., 1995Lee S.S. Pineau T. Drago J. et al.Targeted disruption of the alpha isoform of the peroxisome-proliferator-activated receptor gene in mice results in abolishment of the pleiotropic effects of peroxisome proliferators.Molec Cell Biol. 1995; 15: 3012-3022Crossref PubMed Scopus (1465) Google Scholar). Adult male hairless mice and shaved areas of conventional hairy mice were treated on one side of the flank with 40 μl per cm2 1 mM (0.24% wt/vol) clofibrate, or with 0.5 mM (0.016% wt/vol) Wy-14,643, for 1, 2, 3, 4, and 6 d. Propylene glycol:ethanol, 7:3 ratio, absolute ethanol, or acetone was used as vehicle. Control animals were treated with vehicle only. At the indicated times following treatments the animals were killed. Tissue samples were fixed with 4% formaldehyde (freshly prepared from paraformaldehyde) in phosphate-buffered saline (PBS) at 4°C for 12 h, and embedded in paraffin. Sections were collected on Superfrost Plus microscope slides (Fisher Scientific, Pittsburgh, PA) and stained with hematoxylin and eosin or used for in situ hybridization or immuno-histochemistry (see below). Digoxigenin (DIG) labeled RNA probes to detect loricrin (3′ noncoding region, 200 bases) and profilaggrin (coding region, 300 bases) mRNAs were made from linearized cDNA sequences (a gift from S. Yuspa, NIH) using reagents supplied by Boehringer-Mannheim (Indianapolis, IN). In situ hybridization was performed as described previously (Kömüves et al., 1998Kömüves L.G. Hanley K. Jiang Y. et al.Ligands and activators of nuclear hormone receptors regulate epidermal differentiation during fetal rat skin development.J Invest Dermatol. 1998; 111: 429-433Crossref PubMed Scopus (91) Google Scholar). The sections were hybridized at 40°C and the hybridization of DIG-labeled probes to the endogenous mRNA was detected by anti-DIG-alkaline phosphatase (Boehringer-Mannheim). Alkaline phosphatase activity was revealed with 5-bromo-4-chloro-3-indolyl phosphate/nitrotetrazolium blue substrate (Chemicon, Temecula, CA), containing 2 mM levamisole (Sigma, St. Louis, MO). Hybridization with DIG-labeled sense control probes resulted in no signal, indicating the specificity of hybridization with the antisense probe. Omitting the DIG-labeled antisense probes from the hybridization cocktail resulted in no signal, which demonstrated that only DIG-containing RNA hybrids were detected. Moreover, incubation with the 5-bromo-4-chloro-3-indolyl phosphate/nitrotetrazolium blue substrate reagents alone resulted in no staining, showing that endogenous alkaline phosphatase activity within the tissues did not contribute to the signal obtained. Affinity-purified rabbit antibodies (BabCo, Berkeley, CA) specific for keratin 5 and keratin 10, involucrin, profilaggrin-filaggrin, and loricrin, and a monoclonal anti-proliferating cell nuclear antigen antibody (Dako, Carpinteria, CA) were used. The immunohistochemical localization of these proteins was performed as described earlier (Kömüves et al., 1998Kömüves L.G. Hanley K. Jiang Y. et al.Ligands and activators of nuclear hormone receptors regulate epidermal differentiation during fetal rat skin development.J Invest Dermatol. 1998; 111: 429-433Crossref PubMed Scopus (91) Google Scholar). For the detection of keratin 5, keratin 10, and proliferating cell nuclear antigen proteins, antigen retrieval was performed with microwave treatment in 10 mM citrate buffer, pH = 6.0. Affinity-purified biotinylated goat antirabbit IgG, affinity-purified biotinylated goat antimouse IgG, and avidin-biotin complex peroxidase were purchased from Vector (Burlingame, CA). Peroxidase activity was revealed with diaminobenzidine (QualTek Laboratories, Santa Barbara, CA), followed by counterstaining with methyl green. Omitting the first antibodies resulted in no signal and preabsorption of the antibodies resulted in the abolition of staining (not shown). These controls demonstrated that the antibodies used are specifically recognizing the antigens under the conditions employed. Omission of the first antibodies or incubation with the substrate solution resulted in no signal, showing that nonspecific binding of the second antibody and/or avidin-biotin complex peroxidase, or endogenous peroxidase activity, was not contributing to the signal obtained. Clofibrate- and vehicle-treated hairless mice were injected intraperitoneally with a 5 mg per ml solution (100 mg per g body weight) of 5-bromo-2-deoxyuridine (BrdU; Sigma) (Arbeit et al., 1994Arbeit J.M. Munger K. Howley P.M. et al.Progressive squamous epithelial neoplasia in K14-human papillomavirus type, 16 transgenic mice.J Virol. 1994; 68: 4358-4368PubMed Google Scholar). After 1 h the animals were sacrificed and skin and small intestinal samples were fixed, embedded in paraffin, and sectioned. A biotinylated mouse monoclonal anti-BrdU antibody (CalTag Laboratories, South San Francisco, CA), followed by avidin-Alexa (Molecular Probes, Eugene, OR) was used to detect BrdU-positive cells. The sections were counterstained with Sytox Orange (Molecular Probes) nuclear stain and coverslipped. The staining was analyzed using a laser-scanning confocal microscope (Leica, Deerfield, IL). Tissue samples from animals not injected with BrdU (negative control tissue) did not give a signal. Omitting the first antibody resulted in no signal. Incubation with avidin-Alexa alone resulted in no staining, showing that nonspecific binding of avidin or endogenous autofluorescence were not contributing to the signal obtained. A total of about 500 cells were counted from each sample and the proliferative index was calculated according to the following formula: proliferative index = (number of BrdU positive cells/number of cells in the basal layer) × 100. Deparaffinized sections were treated first with 0.5% sodium tetraborohydrate for 30 min. TUNEL assay was carried out using the in situ cell death detection kit from Boehringer-Mannheim, following the instructions of the manufacturer. Following the TUNEL reaction the sections were counterstained with Sytox Orange (Molecular Probes) nuclear stain. The incorporation of FITC-labeled dUTP was visualized with a Leica TCS laser-scanning confocal microscope. Male hairless mice were treated either with vehicle or with clofibrate, as described above, twice a day for 3 d. Next the animals were treated with 10% sodium dodecyl sulfate (SDS) solution or by repeated application of cellophane tape until the transepidermal water loss (TEWL) reached 6–8 mg per cm2 per h as measured with an electrolytic water analyzer (Meeco, Warrington, PA). TEWL was measured on four or five different spots on each site. The recovery of the epidermal permeability was monitored by hourly measurements of TEWL. Samples were fixed with a modified Karnovsky's fixative and embedded for transmission electron microscopy observations as described earlier (Hanley et al., 1996Hanley K. Rassner U. Jiang Y. et al.Hormonal basis for the gender difference in epidermal barrier formation in the fetal rat. Acceleration by estrogen and delay by testosterone.J Clin Invest. 1996; 97: 2576-2584Crossref PubMed Scopus (85) Google Scholar). Ultrathin sections were examined in a Zeiss 10E electron microscope. Epidermal thickness was measured on hematoxylin and eosin stained sections photographed using a 40× planapochromate objective (final magnification 125×) and projected on a screen. Epidermal thickness (defined as the distance between the basement lamina and the apical surface of the uppermost nucleated keratinocytes, i.e., the border between the stratum granulosum and stratum corneum) was measured on projected images (magnification factor 10×) of the microphotographs. From each animal 10 randomly selected areas of the skin were photographed and the epidermal thickness was measured at five randomly selected spots within each microphotograph. Photographs were taken with a Nikon Microphot FX microscope on Kodak (Rochester, NY) Ektachrome 64T film, and the 35 mm slides were digitized with a slide scanner (Polaroid, Cambridge, MA). The digitized images were cropped and assembled using Photoshop 3.0 (Adobe Systems, Mountain View, CA) on a Macintosh G3 platform (Apple, Cupertino, CA). Apart from adjusting the background intensities (using the Level feature in Photoshop), no other digital tools were applied to the images. The figures were printed with a Kodak XLS 8600 PS digital printer. The 3.7 kb INV promoter was a gift from Dr. J. Carroll (State University of New York, Stony Brook, NY). Deletional INV constructs were generated as described previously (Ng et al., 1996Ng D.C. Su M.-J. Kim R. Bikle D.D. Regulation of involucrin gene expression by calcium in normal human keratinocytes.Frontiers in Bioscience. 1996; 1: a16-24PubMed Google Scholar). The INV construct containing the mutant AP-1 site was prepared by PCR, using oligonucleotides 5′-tcga-tatgccg-tgagtca-gagggc-3′ and 5′-tcga-tatgccg-tgagCca-gagggc-3′. The AP-1 site is underlined and the single bp mutation is in upper case. Keratinocytes were transfected as described byNg et al., 1996Ng D.C. Su M.-J. Kim R. Bikle D.D. Regulation of involucrin gene expression by calcium in normal human keratinocytes.Frontiers in Bioscience. 1996; 1: a16-24PubMed Google Scholar with minor modifications. Briefly, keratinocytes were transiently transfected 1 d after plating (at a confluence of approximately 20%-40%). Ten milligrams per milliliter final concentration of polybrene dihexabromide (Aldrich, Milwaukee, WI), RSV-β-galactosidase (0.2 μg), and involucrin promoter-luciferase construct (2 μg) were added in 0.65 ml media (KGM containing 0.03 mM Ca2+). Keratinocytes were incubated at 37°C for 5 h with gentle shaking at each hour. Cells were then rinsed with calcium, magnesium free (CMF)-PBS, and incubated at room temperature for 3 min with 10% glycerol in media. Cells were again rinsed with CMF-PBS, incubated overnight with fresh KGM containing 0.03 m M Ca2+, and then treated for 24 h as indicated for each experiment. Cells were rinsed and harvested in 250 μl reporter lysis buffer (Promega, Madison, WI). The lysate was centrifuged at 10,000g (4°C) for 2 min, and 10–20 μl of supernatant was assayed with luciferase substrate (Promega) and β-galactosidase substrate Galacto-Light (Tropix, Bedford, MA) following the manufacturer's instructions. β-galactosidase activity was used to normalize data and correct for variations in transfection efficiencies. Data are presented as mean ± SEM. Differences were analyzed using Student's t test. Adult hairless mice were treated twice a day topically with clofibrate for 1, 2, 3, 4, or 6 d. Separate vehicle-treated animals served as controls. Propylene glycol:ethanol (7:3 ratio), absolute ethanol, or acetone was used as vehicle. The use of propylene glycol-ethanol as vehicle resulted in an increase in epidermal thickness in vehicle-treated animals (probably a result of mild irritation) following treatments for 6 d (Table 1, Figure 1a vs 1d). In contrast, no such effect was seen in ethanol- or acetone-treated animals Table 1. Following prolonged topical clofibrate treatment there was a significant decrease in epidermal thickness compared with untreated controls (Table 1, Figure 1c, d vs 1g, h), regardless of which vehicle system was employed. Treatment with another PPARα activator (Wy-14,643) resulted in similar changes (Figure 1e). It should be noted that, even with vehicles that did not induce hyperproliferation, clofibrate treatment resulted in decreased epidermal thickness. Despite the decrease in epidermal thickness in PPAR-activator-treated animals (compared with untreated controls), the organization of the epidermis remained intact; the basal, suprabasal, granular layers, and stratum corneum were present. The stratum corneum was often separated from the epidermis, however, and was less compact than in control, untreated skin (Figure 1).Table 1Effect of topical application of a PPARα activator (clofibrate) on epidermal thicknessTreatmentEpidermal thickness (μm)aData are presented as mean ± SEM.% of controlControl, untreated (n = 5)25.2 ± 1.9bNot significantly different.100%Propylene glycol/ethanol vehicle, day 3 (n = 3)24.8 ± 2.6bNot significantly different.Clofibrate in propylene glycol/ethanol, day 3 (n = 3)20.5 ± 1.2cp < 0.001 compared with untreated control.,ep < 0.001 compared with the vehicle-treated samples.81%Propylene glycol/ethanol vehicle, day 6 (n = 3)32.2 ± 2.6dp < 0.0005 compared with the untreated control samples.128%Clofibrate, day 6 (n = 3)19.52 ± 1.5cp < 0.001 compared with untreated control.,ep < 0.001 compared with the vehicle-treated samples.78%Ethanol vehicle, day 6 (n = 3)26.1 ± 0.8bNot significantly different.Clofibrate, day 6 (n = 3)18.7 ± 1.2cp < 0.001 compared with untreated control.,ep < 0.001 compared with the vehicle-treated samples.74%Acetone vehicle, day 6 (n = 3)25.7 ± 2.1bNot significantly different.Clofibrate in acetone, day 6 (n = 3)20.7 ± 0.0.9cp < 0.001 compared with untreated control.,ep < 0.001 compared with the vehicle-treated samples.82%a Data are presented as mean ± SEM.b Not significantly different.c p < 0.001 compared with untreated control.d p < 0.0005 compared with the untreated control samples.e p < 0.001 compared with the vehicle-treated samples. Open table in a new tab We next compared the changes in the expression of several structural proteins following topical treatment with PPARα activators. These proteins are localized to the basal (keratin 5), suprabasal (keratin 10), and spinous/granular layers (involucrin, profilaggrin-filaggrin, loricrin) in the epidermis. Staining for keratin 5 (a protein whose expression is restricted to the basal layer in murine epidermis) did not change after the treatments (not shown). Although the number of cell layers expressing keratin 10 (which is expressed in the nucleated suprabasal layers) decreased (as the epidermis thinned), the intensity of the staining in individual cells did not change (not shown). The staining for later markers of keratinocyte differentiation, such as involucrin (not shown), profilaggrin-filaggrin (Figure 2a, b and c), and loricrin (Figure 2d, e and f), was markedly increased in the epidermis following PPARα activator treatment, regardless of the vehicle used. Analysis by in situ hybridization revealed that, despite the decrease in epidermal thickness in Wy-14,643- or clofibrate-treated animals, the outer nucleated cells of the epidermis contained increased profilaggrin (Figure 2g, h and i) and loricrin mRNA (Figure 2j, k and l). Furthermore, we also found that even a single application of clofibrate resulted in upregulation of the profilaggrin and loricrin mRNAs and proteins (not shown). Finally, we assessed whether PPARα activators regulated differentiation not only in adult hairless mice but also in other strains. Adult hairy mice (B6129F1 and SV/129 males) were carefully but thoroughly trimmed with a hair clipper and then treated with vehicle (control) or clofibrate twice a day for 3 d. Histologic, in situ hybridization, and immunohistochemical analysis revealed that clofibrate treatment resulted in epidermal thinning and an increased staining for profilaggrin and loricrin mRNA and proteins (not shown). These observations indicate that topically applied PPARα activators promote terminal differentiation of the epidermis. Previous in vitro studies in cultured keratinocytes demonstrated that clofibrate inhibited cell proliferation (Hanley et al., 1998Hanley K. Jiang Y. He S.S. et al.Keratinocyte differentiation is stimulated by activators of the nuclear hormone receptor PPARα.J Invest Dermatol. 1998; 110: 368-375Crossref PubMed Scopus (160) Google Scholar). Therefore, we next determined if topical" @default.
• W2029653522 created "2016-06-24" @default.
• W2029653522 creator A5003154600 @default.
• W2029653522 creator A5032781101 @default.
• W2029653522 creator A5047081897 @default.
• W2029653522 creator A5049938896 @default.
• W2029653522 creator A5050608918 @default.
• W2029653522 creator A5051847291 @default.
• W2029653522 creator A5055263060 @default.
• W2029653522 creator A5082650655 @default.
• W2029653522 creator A5083628557 @default.
• W2029653522 creator A5087736818 @default.
• W2029653522 date "2000-09-01" @default.
• W2029653522 modified "2023-10-17" @default.
• W2029653522 title "Stimulation of PPARα Promotes Epidermal Keratinocyte Differentiation In Vivo" @default.
• W2029653522 cites W128536076 @default.
• W2029653522 cites W1453703257 @default.
• W2029653522 cites W1551998217 @default.
• W2029653522 cites W1687775674 @default.
• W2029653522 cites W1882211948 @default.
• W2029653522 cites W1964795669 @default.
• W2029653522 cites W1965756947 @default.
• W2029653522 cites W1967190331 @default.
• W2029653522 cites W1999613725 @default.
• W2029653522 cites W2017609866 @default.
• W2029653522 cites W2028753942 @default.
• W2029653522 cites W2032918258 @default.
• W2029653522 cites W2036915597 @default.
• W2029653522 cites W2039663743 @default.
• W2029653522 cites W2041460044 @default.
• W2029653522 cites W2046576762 @default.
• W2029653522 cites W2047982128 @default.
• W2029653522 cites W2051503115 @default.
• W2029653522 cites W2052579722 @default.
• W2029653522 cites W2053147796 @default.
• W2029653522 cites W2061843934 @default.
• W2029653522 cites W2066092624 @default.
• W2029653522 cites W2072062048 @default.
• W2029653522 cites W2076452736 @default.
• W2029653522 cites W2081501399 @default.
• W2029653522 cites W2082492482 @default.
• W2029653522 cites W2097060373 @default.
• W2029653522 cites W2101041635 @default.
• W2029653522 cites W2106511392 @default.
• W2029653522 cites W2119725374 @default.
• W2029653522 cites W2121914083 @default.
• W2029653522 cites W2126394796 @default.
• W2029653522 cites W2140038597 @default.
• W2029653522 cites W2166021357 @default.
• W2029653522 cites W2172256092 @default.
• W2029653522 cites W2184835492 @default.
• W2029653522 cites W2342083870 @default.
• W2029653522 cites W2605614532 @default.
• W2029653522 cites W4235718886 @default.
• W2029653522 doi "https://doi.org/10.1046/j.1523-1747.2000.00073.x" @default.
• W2029653522 hasPubMedId "https://pubmed.ncbi.nlm.nih.gov/10951268" @default.
• W2029653522 hasPublicationYear "2000" @default.
• W2029653522 type Work @default.
• W2029653522 sameAs 2029653522 @default.
• W2029653522 citedByCount "149" @default.
• W2029653522 countsByYear W20296535222012 @default.
• W2029653522 countsByYear W20296535222013 @default.
• W2029653522 countsByYear W20296535222014 @default.
• W2029653522 countsByYear W20296535222015 @default.
• W2029653522 countsByYear W20296535222016 @default.
• W2029653522 countsByYear W20296535222018 @default.
• W2029653522 countsByYear W20296535222019 @default.
• W2029653522 countsByYear W20296535222020 @default.
• W2029653522 countsByYear W20296535222021 @default.
• W2029653522 countsByYear W20296535222022 @default.
• W2029653522 countsByYear W20296535222023 @default.
• W2029653522 crossrefType "journal-article" @default.
• W2029653522 hasAuthorship W2029653522A5003154600 @default.
• W2029653522 hasAuthorship W2029653522A5032781101 @default.
• W2029653522 hasAuthorship W2029653522A5047081897 @default.
• W2029653522 hasAuthorship W2029653522A5049938896 @default.
• W2029653522 hasAuthorship W2029653522A5050608918 @default.
• W2029653522 hasAuthorship W2029653522A5051847291 @default.
• W2029653522 hasAuthorship W2029653522A5055263060 @default.
• W2029653522 hasAuthorship W2029653522A5082650655 @default.
• W2029653522 hasAuthorship W2029653522A5083628557 @default.
• W2029653522 hasAuthorship W2029653522A5087736818 @default.
• W2029653522 hasBestOaLocation W20296535221 @default.
• W2029653522 hasConcept C169760540 @default.
• W2029653522 hasConcept C185592680 @default.
• W2029653522 hasConcept C202751555 @default.
• W2029653522 hasConcept C207001950 @default.
• W2029653522 hasConcept C24998067 @default.
• W2029653522 hasConcept C2777074287 @default.
• W2029653522 hasConcept C54355233 @default.
• W2029653522 hasConcept C55493867 @default.
• W2029653522 hasConcept C86803240 @default.
• W2029653522 hasConcept C95444343 @default.
• W2029653522 hasConceptScore W2029653522C169760540 @default.
• W2029653522 hasConceptScore W2029653522C185592680 @default.
• W2029653522 hasConceptScore W2029653522C202751555 @default.
• W2029653522 hasConceptScore W2029653522C207001950 @default.
• W2029653522 hasConceptScore W2029653522C24998067 @default.

• next