β-Ionone Attenuates Dexamethasone-Induced Suppression of Collagen and Hyaluronic Acid Synthesis in Human Dermal Fibroblasts

Abstract

Stress is a major contributing factor of skin aging, which is clinically characterized by wrinkles, loss of elasticity, and dryness. In particular, glucocorticoids are generally considered key hormones for promoting stress-induced skin aging through binding to glucocorticoid receptors (GRs). In this work, we aimed to investigate whether β-ionone (a compound occurring in various foods such as carrots and almonds) attenuates dexamethasone-induced suppression of collagen and hyaluronic acid synthesis in human dermal fibroblasts, and to explore the mechanisms involved. We found that β-ionone promoted collagen production dose-dependently and increased mRNA expression levels, including collagen type I α 1 chain (COL1A1) and COL1A2 in dexamethasone-treated human dermal fibroblasts. It also raised hyaluronic acid synthase mRNA expression and hyaluronic acid levels. Notably, β-ionone inhibited cortisol binding to GR, subsequent dexamethasone-induced GR signaling, and the expression of several GR target genes. Our results reveal the strong potential of β-ionone for preventing stress-induced skin aging and suggest that its effects are related to the inhibition of GR signaling in human dermal fibroblasts.

Keywords: collagen; glucocorticoid; hyaluronic acid; stress; β-ionone.

Figure 1

(a,b) Effects of β-ionone on the viability of dexamethasone-untreated and dexamethasone-treated human dermal fibroblasts. The cells were treated for 72 h with either vehicle (dimethyl sulfoxide (DMSO); shown as “-“) or different doses of β-ionone (12.5, 25, 50, 100, or 200 µM) with or without dexamethasone (1 µM). Cell viability was assessed by the WST-1 assay. Values are shown as mean ± standard error of the mean (SEM) of three experiments.

Figure 2

Impact of β-ionone on collagen synthesis in human dermal fibroblasts. The cells were treated with either vehicle (shown as “-”) or three doses of β-ionone (12.5, 25, or 50 µM (shown as “+”)) and dexamethasone (1 µM) for 24 h. (a) The procollagen type I C-peptide content was measured in the culture supernatants of the dermal fibroblasts, and (b,c) the gene expression levels of collagen type I α 1 chain (COL1A1) and COL1A2 were quantitated in the cells. Values are shown as mean ± standard error of the mean (SEM) of three experiments. Statistical significance is expressed as follows: * p < 0.05, ** p < 0.01.

Figure 3

Effect of β-ionone on hyaluronic acid synthesis in human dermal fibroblasts. The cells were cultured with either vehicle (shown as “-”) or three concentrations of β-ionone (12.5, 25, or 50 µM (shown as “+”)) and dexamethasone (1 µM) for 24 h. (a) Hyaluronic acid content was measured in the culture medium of dermal fibroblasts, and (b) mRNA expression levels of hyaluronic acid synthase 2 (HAS2) were determined in the cells. Values are shown as mean ± standard error of the mean (SEM) of three experiments. Statistical significance is expressed as follows: * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 4

The inhibitory influence of β-ionone on glucocorticoid binding to glucocorticoid receptors (GRs). The human-GR–fluormone complex was incubated with either vehicle or various concentrations of β-ionone (10⁻⁸–10⁻² M) for 2 h, and fluorescence polarization was measured. Values are shown as mean ± standard error of the mean (SEM) of three experiments.

Figure 5

Effect of β-ionone on GR signaling. Human dermal fibroblasts were treated with either vehicle (shown as “-”) or β-ionone (shown as “+”) as well as dexamethasone for 30 min. Whole-cell protein extracts were prepared and analyzed by Western blotting. The levels of phosphorylated GR and total GR were normalized to the level of GAPDH, and then the ratio of phosphorylated/total GR was calculated. The ratio of phosphorylated GR to total GR is presented (p-GR/t-GR). Values are shown as mean ± standard error of the mean (SEM) of three experiments. Statistical significance is expressed as follows: * p < 0.05.

Figure 6

β-ionone suppresses dexamethasone-induced GR target genes in human dermal fibroblasts. Human dermal fibroblasts were treated with either vehicle (shown as “-”) or β-ionone (shown as “+”) as well as dexamethasone for 12 h. Total RNA samples were prepared and analyzed by quantitative RT-PCR. (a,b) The mRNA expression of well-known glucocorticoid-responsive genes (ErbB receptor feedback inhibitor 1, ERRFI1; solute carrier family 19 member 2, SLC19A2; nuclear factor kappa B inhibitor alpha, NFKBIA; phosphoinositide-3-kinase regulatory subunit 1, PIK3R1; glutamate-ammonia ligase, GLUL; zinc fingers and homeoboxes 3, ZHX3; metallothionein 2A, MT2A; metallothionein 1E, MT1E; AT-rich interaction domain 5b, ARID5B; annexin A4. ANXA4; kruppel-like factor 13, KLF13; B-cell lymphoma 6, BCL6; glucocorticoid-induced leucine zipper, GILZ; dual specificity phosphatase 1, DUSP1; FK506 binding protein 5, FKBP5; DNA damage inducible transcript 4, DDIT4; and serum deprivation-response protein, SDPR) was evaluated. Values are shown as mean ± standard error of the mean (SEM) of three experiments. Statistical significance is expressed as follows: * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 7

A suggested mechanism by which β-ionone attenuates glucocorticoid-induced suppression of collagen and hyaluronic acid synthesis in human dermal fibroblasts. As shown in a schematic illustration, the inhibition of glucocorticoid binding to its receptor by β-ionone suppresses the glucocorticoid-induced GR signaling and subsequent collagen and hyaluronic acid degradation. The detailed molecular mechanism of how GR transcription factor regulates collagen and hyaluronic acid needs further investigation.