Horse ceramide accentuates glucosylceramide synthase and ceramide synthase 3 by activating PPAR β/δ and/or γ to stimulate ceramide synthesis

〇Tami Igarashi¹, Hiroki Yanagi¹, Masayuki Yagi¹, Masamitsu Ichihashi² , Genji Imokawa³,
¹Rosette Co., LTD., Tokyo, Japan, ²Arts Ginza Clinic, Tokyo, Japan. ³Center for Bioscience Research and Education, Utsunomiya University, Tochigi, Japan.

　We previously reported that horse ceramide (HC), which contains galactosyl ceramides as its main component, significantly improves skin symptoms by topical application at 0.8% to patients with mild-to-moderate atopic dermatitis. We speculated that efficacy resulted from the amelioration of epidermal ceramide metabolism and we characterized those effects using reconstructed human epidermal equivalents (RHEEs). Analyses of lipids and by RT-PCR and Western blotting revealed that HC significantly increased the total ceramide content of the stratum corneum (SC), accompanied by significantly increased gene and/or protein expression levels of ceramide synthesis-related (CSR) enzymes (ceramide synthase 3 (CerS3)/fatty acid elongase 4 (Elovl4)/glucosylceramide synthase (GCS)/β-glucocerebrosidase/sphingomyelin synthase/acid sphingomyelinase) and of keratinization-related proteins (involucrin/transglutaminase1). Mechanistic analyses using monolayer cultures of primary human keratinocytes revealed that the marked stimulatory effects of HC on the expression levels of CSR genes encoding CerS3, Elovl4 and GCS as well as peroxisome proliferator activated receptors (PPAR)β/δ occur predominantly under high calcium-derived differentiation (HCDD) conditions. Analyses using antagonists of PPARs under HCDD conditions demonstrated that an antagonist of PPAR β/δ significantly abrogated the HC-stimulated mRNA expression levels of GCS, CerS3 and Elovl4. Further, GW9662, an antagonist of PPARγ, significantly abolished the HC-up-regulated mRNA expression levels of GCS and Elovl4, but not of CerS3. These findings suggest that HC has a distinct potential to accentuate the expression of GCS, CerS3 and Elovl4 via the activation of PPAR β/δ and/or PPAR γ to accelerate ceramide synthesis in the SC.