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