Perturbation of lamellar granule secretion by sodium caprate implicates epidermal tight junctions in lamellar granule function.
BACKGROUND
Polarized secretion of lamellar granules (LGs) delivers various lipids, proteases, and protease inhibitors into the stratum corneum (SC) of the epithelium. Disruption of LGs is associated with severe cutaneous diseases, but the mechanism of their polarized secretion is not known. On the other hand, recent study shows epidermal tight junctions (TJs) localize in stratum granulosum (SG), and TJs are involved in polarized molecule secretion. Thus, we hypothesized epidermal TJs relate to polarized LGs secretion.


OBJECTIVE
To assess the possibility that epidermal TJs are involved in polarized LGs secretion.


METHODS
In order to examine LGs secretion, we used fluorescent ceramide (BODIPY FL C(5)-ceramide) and a natural LG cargo, lympho-epithelial Kazal-type-related inhibitor (LEKTI), in cultured normal human epidermal keratinocytes and a reconstructed human epidermis. We investigated their alteration using the medium-chain fatty acid sodium caprate (C10), TJs inhibitor. In addition, LG distribution was observed by electron microscopy.


RESULTS
C10 significantly inhibited secretion of both fluorescent ceramide and LEKTI in cultured normal human epidermal keratinocytes and a reconstructed human epidermis. C10 also disturbed the polarized localization of fluorescent ceramide and LEKTI in the reconstructed epidermis. Electron microscopy revealed that a large number of LGs remained in corneocytes in the C10-treated epidermis, rather than being secreted.


CONCLUSIONS
Our data indicate that C10 perturbs the polarized secretion of LGs. Our study therefore suggests that epidermal TJs are possibly involved in polarized LG secretion and provides new insights into potential of treatments for skin diseases caused by abnormal LG secretion.
Kuroda
Shohei
S
Pola Chemical Industries, Inc., 560 Kashio-cho, Totsuka-ku, Yokohama 244-0812, Japan.
Kurasawa
Masumi
M
Mizukoshi
Koji
K
Maeda
Tetsuo
T
Yamamoto
Takuya
T
Oba
Ai
A
Kishibe
Mari
M
Ishida-Yamamoto
Akemi
A
D002478:Cells, Cultured; D002518:Ceramides / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000187:drug effects* / Q000378:metabolism*; D003652:Decanoic Acids / Q000494:pharmacology*; D000078404:Epidermal Cells; D004817:Epidermis / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D053491:Proteinase Inhibitory Proteins, Secretory / Q000378:metabolism; D000074163:Serine Peptidase Inhibitor Kazal-Type 5; D019108:Tight Junctions / Q000187:drug effects / Q000502:physiology*
D002518:Ceramides; D003652:Decanoic Acids; D053491:Proteinase Inhibitory Proteins, Secretory; C120650:SPINK5 protein, human; D000074163:Serine Peptidase Inhibitor Kazal-Type 5; C031071:decanoic acid