Differentiation-associated expression of ceramidase isoforms in cultured keratinocytes and epidermis

Abstract

Ceramides (Cers) accumulate within the interstices of the outermost epidermal layers, or stratum corneum (SC), where they represent critical components of the epidermal permeability barrier. Although the SC contains substantial sphingol, indicative of ceramidase (CDase) activity, which CDase isoforms are expressed in epidermis remains unresolved. We hypothesized here that CDase isoforms are expressed within specific epidermal compartments in relation to functions that localize to these layers. Keratinocytes/ epidermis express all five known CDase isoforms, of which acidic and alkaline CDase activities increase significantly with differentiation, persisting into the SC. Conversely, neutral and phytoalkaline CDase activities predominate in proliferating keratinocytes. These differentiation-associated changes in isoform activity/protein are attributed to corresponding, differentiation-associated changes in mRNA levels (by quantitative RT-PCR). Although four of the five known CDase isoforms are widely expressed in cutaneous and extracutaneous tissues, alkaline CDase-1 occurs almost exclusively in epidermis. These results demonstrate large, differentiationassociated, and tissue-specific variations in the expression and activities of all five CDase isoforms. Because alkaline CDase-1 and acidic CDase are selectively upregulated in the differentiated epidermal compartment, they could regulate functions that localize to the distal epidermis, such as permeability barrier homeostasis and antimicrobial defense.-Houben, E., W. M. Holleran, T. Yaginuma, C. Mao, L. M. Obeid, V. Rogiers, Y. Takagi, P. M. Elias, and Y. Uchida. Differentiation-associated expression of ceramidase isoforms in cultured keratinocytes and epidermis.

Lamellar Bodies of Human Epidermis

“…Until now, based on the physicochemical properties of these enzymes, the ceramidase activity has been considered to be restricted to the extracellular space. Moreover the strong increase in acidic ceramidase activity observed during keratinocyte differentiation is not paralleled by a similar change in acid ceramidase 1-encoding mRNA (69). Although this discrepancy has been tentatively explained by posttranscriptional modifications, it may also result from the expression of another acid ceramidase, i.e.…”

Ceramidases: regulators of cellular responses mediated by ceramide, sphingosine, and sphingosine-1-phosphate

“…In situ hybridization revealed that ACER1 mRNA is highly expressed in the upper nucleated layers of the epidermis, but it is undetectable in the basal cell layer. In cell culture, ACER2 mRNA is markedly upregulated in epidermal keratinocytes by 1.2 mM extracellular calcium [112] or the combination of fetal bovine serum, Ca 2+ , and ascorbic acid [132]. These observations indicate that ACER1 may have an important role in the differentiation of epidermal keratinocytes.…”

“…In addition to cell survival, we recently demonstrated that AC mediates the differentiation of epidermal keratinocytes [112,132]. We showed that AC expression is increased during calciuminduced differentiation of epidermal keratinocytes [112,132], and RNAi-mediated knockdown of AC significantly inhibited the calcium-induced expression of keratin 1 and involucrin, two important proteins highly expressed in differentiated keratinocytes [112].…”

“…ACER1 is mainly expressed in the skin [112,132]. In situ hybridization revealed that ACER1 mRNA is highly expressed in the upper nucleated layers of the epidermis, but it is undetectable in the basal cell layer.…”

Decreased Ceramide Transport Protein (CERT) Function Alters Sphingomyelin Production following UVB Irradiation

“…Cer hydrolysis, followed by sphingosine-to-sphingosine 1-phosphate generation. We previously reported that epidermal keratinocytes express all isoforms of ceramidase that have so far been characterized in mammalian species (46), suggesting that Cer can be hydrolyzed at/in ER/Golgi by alkaline ceramidase, in mitochondria and/or at the plasma membrane by neutral ceramidase, and in lysosomes by acidic ceramidase. We also recently demonstrated increases in Cer hydrolysis to sphingosine (followed by its conversion to sphingosine 1-phosphate) in keratinocytes in response to UV irradiation.…”