Ceramide Stimulates ABCA12 Expression via Peroxisome Proliferator-activated Receptor δ in Human Keratinocytes

doi:10.1074/jbc.M109.006973

Ceramide Stimulates ABCA12 Expression via Peroxisome Proliferator-activated Receptor δ in Human Keratinocytes*

From the ^‡Metabolism Section and
^§Dermatology Research Unit, Veterans Affairs Medical Center, Northern California Institute for Research and Education, University of California, San Francisco, California 94121,
the ^¶Department of Medicine, Medical University of South Carolina, Charleston, South Carolina 29425, and
the ^‖Department of Dermatology, Graduate School of Medicine, Hokkaido University, Sapporo 060-8638, Japan

¹ To whom correspondence should be addressed:
Metabolism Section (111F), Dept. of Veterans Affairs Medical Center, 4150 Clement St., San Francisco, CA 94121.
Tel.: 415-750-2005; Fax: 415-750-6927; E-mail: yan.jiang{at}med.va.gov.

Abstract

ABCA12 (ATP binding cassette transporter, family 12) is a cellular membrane transporter that facilitates the delivery of glucosylceramides to epidermal lamellar bodies in keratinocytes, a process that is critical for permeability barrier formation. Following secretion of lamellar bodies into the stratum corneum, glucosylceramides are metabolized to ceramides, which comprise ∼50% of the lipid in stratum corneum. Gene mutations of ABCA12 underlie harlequin ichthyosis, a devastating skin disorder characterized by abnormal lamellar bodies and a severe barrier abnormality. Recently we reported that peroxisome proliferator-activated receptor (PPAR) and liver X receptor activators increase ABCA12 expression in human keratinocytes. Here we demonstrate that ceramide (C₂-Cer and C₆-Cer), but not C₈-glucosylceramides, sphingosine, or ceramide 1-phosphate, increases ABCA12 mRNA expression in a dose- and time-dependent manner. Inhibitors of glucosylceramide synthase, sphingomyelin synthase, and ceramidase and small interfering RNA knockdown of human alkaline ceramidase, which all increase endogenous ceramide levels, also increased ABCA12 mRNA levels. Moreover, simultaneous treatment with C₆-Cer and each of these same inhibitors additively increased ABCA12 expression, indicating that ceramide is an important inducer of ABCA12 expression and that the conversion of ceramide to other sphingolipids or metabolites is not required. Finally, both exogenous and endogenous ceramides preferentially stimulate PPARδ expression (but not other PPARs or liver X receptors), whereas PPARδ knockdown by siRNA transfection specifically diminished the ceramide-induced increase in ABCA12 mRNA levels, indicating that PPARδ is a mediator of the ceramide effect. Together, these results show that ceramide, an important lipid component of epidermis, up-regulates ABCA12 expression via the PPARδ-mediated signaling pathway, providing a substrate-driven, feed-forward mechanism for regulating this key lipid transporter.

Footnotes

↵* This work was supported, in whole or in part, by National Institutes of Health Grants AR39448 and AR049932. This work was also supported by the Medical Research Service, Department of Veterans Affairs at San Francisco.
2 The abbreviations used are:

PPAR

peroxisome proliferator-activated receptor

LXR

liver X receptor

βCA

β-chloro-l-alanine hydrochloride

C₂-Cer

N-acetyl-d-erythro-sphingosine

C₆-Cer

N-hexanoyl-d-erythro-sphingosine

d-MAPP

d-erythro-2-tetradecanoylamino-1-phenyl-1-propanol

l-MAPP

l-erythro-2-tetradecanoylamino-1-phenyl-1-propanol

P4

d-threo-1-phenyl-2-palmitoyl-3-pyrrolidinopropanol

d-PPMP

d-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol·HCl

TUNEL

terminal dUTP nick-end labeling

siRNA

small interfering RNA.
- Received April 13, 2009.