INVESTIGATIVE REPORT

Expression of Filaggrin and its Degradation Products in Human Skin Following Erythemal Doses of Ultraviolet B Irradiation

Stine SIMONSEN 1, Jacob P. THYSSEN 1, Steffen HEEGAARD 2, 3, Sanja KEZIC 4 and Lone SKOV 1

1

Department of Dermatology and Allergy, Herlev and Gentofte Hospital, University of Copenhagen, Hellerup, 2 Department of Ophthalmology,

3

Eye Pathology Section, Department of Pathology, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark, and 4 Coronel Institute of Occupational Health, Academic Medical Center, University of Amsterdam, The Netherlands

Epidermal filaggrin level is affected by ultraviolet B irradiation in animal and experimental models. This study examined the effect of ultraviolet B irradiation on epidermal filaggrin and natural moisturizing factors in vivo in healthy adults( n = 22). Participants were irradiated with 2 minimal erythema doses of ultraviolet B on the skin. Biopsies and tape strips were collected from skin irradiated 24 and 72 h earlier and from nonirradiated skin( control). Real-time quantitative PCR on skin biopsies showed significantly reduced profilaggrin mRNA expression 24 h after irradiation( mean relative mRNA expression ± standard deviation: control, 3.86 ± 2.06 vs. 24 h, 1.52 ± 0.640; p = 0.02; n = 8). Immunohistochemistry showed aberrant spatial distribution of filaggrin protein 72 h after irradiation( n = 3). High-pressure liquid chromatography of tape extracts showed no change in mean total natural moisturizing factor levels after irradiation, but mean trans-urocanic acid was significantly reduced, as expected( n = 8). In conclusion, erythemal doses of ultraviolet B exert acute effects on profilaggrin mRNA and filaggrin protein in human skin in vivo.

Key words: filaggrin; ultraviolet B; acute inflammation; human. Accepted Mar 27, 2017; Epub ahead of print Mar 30, 2017 Acta Derm Venereol 2017; 97: 797 – 801.

Corr: Stine Simonsen, Department of Dermatology and Allergy, Herlev and Gentofte Hospital, Kildegårdsvej 28, DK-2900 Hellerup, Denmark. E-mail: stine. simonsen. 01 @ regionh. dk

Filaggrin is an important skin barrier protein. It is formed from processing of profilaggrin encoded by the filaggrin gene( FLG). Monomeric filaggrin emerges in the transition layer between stratum granulosum and stratum corneum( SC). In the SC, it is rapidly degraded to“ natural moisturizing factors”( NMFs) including trans-urocanic acid( trans-UCA), a major UVB photonabsorbing chromophore. Trans-UCA is converted to its cis-isomer upon absorption of UVB radiation. Cis-UCA may initiate immunosuppression( 7 – 9).

Approximately 10 % of white Europeans are carriers of loss-of-function mutations in FLG; this is a strong genetic risk factor for development of atopic dermatitis( AD).

UVB phototherapy is commonly used to treat inflammatory skin diseases, including AD. It has been shown to restore filaggrin levels in patients with AD after 12 weeks of treatment( 10), but little is known about the acute effects of erythemal UVB irradiation on filaggrin.

It is possible that erythemal doses of UVB irradiation suppress expression of profilaggrin mRNA expression and filaggrin protein. This has been investigated in animal models and in human in vitro models. To our knowledge, the present study is the first in vivo study in humans to investigate the acute effect of erythemal UVB irradiation on filaggrin homeostasis.

MATERIALS AND METHODS Participants

Twenty-two healthy volunteers of Northern European descent were recruited. Approval of the study was obtained from the local ethics committee( entry numbers H-4-2014-037 and H-4-2011- 136). Informed consent was obtained from all participants. All participants were 18 years old or over, and none of them had a history of skin disease or an atopic disposition. Blood samples were collected to determine the presence of the most common FLG mutations in Europe( R501X, 2282del4, and R2447X), and carriers of any of these mutations were excluded. All blood samples were analysed at the Department of Clinical Biochemistry, Herlev and Gentofte Hospital, Hellerup, Denmark. The age and sex of participants and number of participants in each sample group are shown in Table I.

Ultraviolet exposure

The sources of UVB radiation were 2 Philips TL 20W / 12 RS bulbs. These emitted a spectrum of 280 ‒ 365 nm with a peak emission at about 310 nm( and the main part of the energy having wavelengths

Table I. Demographics( age and sex) and number of participants in each sample group

Demographics mRNA Immunohistochemistry Tape strips

For each analysis the control samples and ultraviolet B irradiated samples were from the same volunteer.

This is an open access article under the CC BY-NC license. www. medicaljournals. se / acta Journal Compilation © 2017 Acta Dermato-Venereologica. doi: 10.2340 / 00015555-2662 Acta Derm Venereol 2017; 97: 797 – 801