Retinoid Induces the Degradation of Corneodesmosomes and Downregulation of Corneodesmosomal Cadherins: Implications on the Mechanism of Retinoid-induced Desquamation

Abstract

Background: Topical retinoids induce skin fragility. As corneodesmosomes are important adhesion structures in the epidermal cohesion, an effect of retinoids on corneodesmosomes has been suspected.

Objective: The aim of this study was to investigate the effect of retinoid on the expression of corneodesmosomal components including desmoglein (DSG) 1, desmocollin (DSC) 1, corneodesmosin (CDSN) and kallikrein (KLK)s.

Methods: 2% all-trans-retinol or ethanol was applied to the back of hairless mice for five days, and the structure of the stratum corneum was examined by transmission electron microscopy. The cultured human keratinocytes were treated with all-trans-retinoic acid (RA) in low or high calcium media for 24 hours.

Results: Topical retinol increased corneocyte detachment and degradation of corneodesmosomes. RA significantly decreased DSG1 and DSC1 expression at the mRNA and protein levels in keratinocytes that were cultured in both low- and high-calcium media. On the other hand, CDSN mRNA levels did not decrease in low-calcium media or increase in high-calcium media after RA treatment. KLK5 and KLK7 expression did not increase after RA treatment.

Conclusion: Our results indicate that DSG1 and DSC1 downregulation by RA could be related to the increased degradation of corneodesmosomes and consequent desquamation induced by retinoids.

Keywords: Corneodesmosome; Desmocollin 1; Desmoglein 1; Kallikrein; Retinoid.

Fig. 1

Electron microscopic findings in the stratum corneum of hairless mouse skin treated with all-trans retinol. Increased corneocyte detachment and consequent thinning of the stratum corneum is clearly apparent in the all-trans retinol-treated skin (B, ×20,000) compared to the vehicle-applied skin (A, ×20,000). Degradation of the corneodesmosomes was also prominently seen in the all-trans retinol-treated skin (D, ×30,000) compared to the vehicle-applied skin (C, ×30,000).

Fig. 2

Effects of RA on the mRNA expression of three corneodesmosomal components (DSG 1, DSC 1, CDSN) in keratinocytes cultured in different concentrations of calcium media. Keratinocytes were treated with RA at concentrations of 10^-6 M and 10^-7 M for 24 hours. Total RNA was extracted and RT-PCR was performed. (A) Agarose gel electrophoresis of amplified products of DSG1, DSC1, CDSN, and β-actin cDNA. The mRNA levels of DSG 1 significantly decreased after 10^-6 M or 10^-7 M RA treatment compared with those of untreated cells in low- (0.06 mM Ca²⁺) or high-calcium (1.5 mM Ca²⁺) media (B). DSC1 mRNA levels also significantly decreased after 10^-6 M or 10^-7 M RA treatment compared with those of untreated cells in low- or high-calcium media (C). mRNA levels of CDSN was not altered after RA treatment in low-calcium media, but significantly increased in high-calcium media (D). ^*p<0.05; ^†p<0.001 (Student's t-test). RA: retinoic acid, DSG: desmoglein, DSC: desmocollin, CDSN: corneodesmosin, RT-PCR: reverse transcriptase-polymerase chain reaction.

Fig. 3

Effect of RA on the protein levels of two corneodesmosomal components in keratinocytes (DSG1 and DSC1) cultured in different concentrations of calcium media. Keratinocytes were treated with RA at concentrations of 10^-6 M and 10^-7 M for 24 hours. Protein extraction and western blotting procedures were performed. (A) Protein expression levels of DSG1 and DSC1 were significantly decreased after 10^-6 M or 10^-7 M RA treatment compared with those of untreated cells in low- or high-calcium media (B, C). ^*p<0.001 (Student's t-test). RA: retinoic acid, DSG: desmoglein, DSC: desmocollin.

Fig. 4

Effect of RA on the mRNA levels of two serine proteases of the kallikrein family (KLK5 and KLK7) in keratinocytes cultured at different concentrations of calcium media. Keratinocytes were treated with RA at concentrations of 10^-6 M and 10^-7 M for 24 hours. Total RNA was extracted and RT-PCR was performed. (A) Agarose gel electrophoresis of amplified products of KLK5, KLK7, and β-actin cDNA. The mRNA levels of KLK5 and KLK7 did not significantly change after RA treatment in low- or high-calcium media (B, C). RA: retinoic acid, KLK: kallikrein, RT-PCR: reverse transcriptase-polymerase chain reaction.

Fig. 5

Effect of RA on the protein levels of two serine proteases in the kallikrein family (KLK5 and KLK7) in keratinocytes cultured in different concentrations of calcium media. Keratinocytes were treated with RA at concentrations of 10^-6 M and 10^-7 M for 24 hours. Protein extraction and western blotting procedures were performed. (A) Protein expression levels of KLK5 did not significantly change after RA treatment in low-calcium media, but significantly decreased in high-calcium media (B). Protein expression levels of KLK7 did not significantly change after RA treatment in low- or high-calcium media (C). ^*p<0.05; ^†p<0.001 (Student's t-test). RA: retinoic acid, KLK: kallikrein.