Ectopic odorant receptors responding to flavor compounds in skin health and disease: Current insights and future perspectives

A Food Odorant, α-Ionone, Inhibits Skin Cancer Tumorigenesis by Activation of OR10A6

SCOPE

This study aims to investigate the anticancer properties of α-ionone in squamous cell carcinoma (SCC).

METHODS AND RESULTS

The expression of OR10A6 together with olfactory receptor signaling components is demonstrated in A431 human SCC cells via RT-PCR and qRT-PCR analysis. OR10A6 activation in A431 cells using the ligand α-ionone inhibits proliferation and migration but induces apoptosis which is confirmed by proliferation assay, colony formation, and western blotting. The mechanism involves the core proteins of the Hippo pathway, where the phosphorylation of large tumor suppressor kinase (LATS), yes-associated protein (YAP), and transcriptional coactivator with PDZ-binding motif (TAZ) is confirmed by western blotting. However, the anticancer effects of α-ionone are abrogated in A431 cells with OR10A6 gene knockdown. In A431 xenograft mouse model, the injection of α-ionone suppresses tumor growth, induces apoptosis, and increases phosphorylation of the LATS-YAP-TAZ signaling axis in the Hippo pathway. None of these effects are observed in xenografted tumors with OR10A6 gene knockdown.

CONCLUSION

These findings collectively demonstrate that activation of ectopic OR OR10A6 by α-ionone in SCC cells stimulates the Hippo pathway and suppresses tumorigenesis both in vitro and in vivo, suggesting a novel therapeutic candidate for the treatment of SCC.

Fermented bamboo powder activates gut odorant receptors, and promotes intestinal health and growth performance of dwarf yellow-feathered broiler chickens

The present study investigated the effects of fermented bamboo powder (FPB) on gut odorant receptors (OR), intestinal health, and growth performance of dwarf yellow-feathered broiler chickens. Six hundred (600) healthy 1-day-old chicks were randomly assigned into 2 groups, with 10 replicates consisting of 30 chicks each. The control group was fed a basal diet. In contrast, the experimental group was fed the basal diet supplemented with 1.0, 2.0, 4.0, and 6.0 g/kg FBP for 4 different phases, namely phase I (1-22 d), phase II (23-45 d), phase III (46-60 d), and phase IV (61-77 d), respectively. The first 2 phases were considered pretreatment (0-45 d), and the remaining were experimental (46-77 d) periods. The tissue samples were collected from phase IV. The chickens in the FBP supplementation group exhibited a significant increment in body weight gain, evisceration yield, breast, thigh, and liver weight, while also experiencing a decrease in the FCR (P < 0.05). Furthermore, the villus height, crypt depth, and villus area exhibited significant increases in the FBP group (P < 0.01). Additionally, the secretion levels of gut hormones such as glucagon-like peptide-1, peptide YY, cholecystokinin, and 5-hydroxytryptamine were significantly elevated in the serum, duodenum, jejunum, and ileum tissues in the FBP group (P < 0.05). The results of qRT-PCR indicated that ORs had responsive expression in the gizzard, proventriculus, and small intestine of chickens when fed with the FBP diet (P < 0.05). Notably, the expression of the COR1, COR2, COR4, COR6, COR8, COR9, OR52R1, OR51M1, OR1F2P, OR5AP2, and OR14J1L112 genes was stronger in the small intestines compared to the gizzard and proventriculus. In conclusion, these results suggest that the FPB plays a crucial role in growth performance, activation of ORs, and gut health and development.

Dietary Isoeugenol Supplementation Attenuates Chronic UVB-Induced Skin Photoaging and Modulates Gut Microbiota in Mice

Photoaging, the primary cause of skin aging damage, results from chronic ultraviolet (UV) exposure, leading to dryness and wrinkle formation. Nutritional intervention has emerged as a practical approach for preventing and addressing the effect of skin photoaging. The primary aromatic compound isolated from clove oil, isoeugenol (IE), has antibacterial, anti-inflammatory, and antioxidant qualities that work to effectively restrict skin cancer cell proliferation. This investigation delved into the advantages of IE in alleviating skin photoaging using UVB-irradiated skin fibroblasts and female SKH-1 hairless mouse models. IE alleviated UVB-induced photodamage in Hs68 dermal fibroblasts by inhibiting matrix metalloproteinase secretion and promoting extracellular matrix synthesis. In photoaged mice, dietary IE reduced wrinkles, relieved skin dryness, inhibited epidermal thickening, and prevented collagen loss. Additionally, the intestinal dysbiosis caused by prolonged UVB exposure was reduced with an IE intervention. The results of Spearman's analysis showed a strong correlation between skin photoaging and gut microbiota. Given the almost unavoidable UVB exposure in contemporary living, this research demonstrated the efficacy of dietary IE in reversing skin photoaging, presenting a promising approach to tackle concerns related to extrinsic skin aging.

Management of the human hair follicle microbiome by a synthetic odorant

BACKGROUND

Human scalp hair follicles (HFs) engage in olfactory receptor (OR)-dependent chemosensation. Activation of olfactory receptor family 2 subfamily AT member 4 (OR2AT4) by the synthetic, sandalwood-like odorant Sandalore® up-regulated HF antimicrobial peptide expression of dermcidin (DCD), which had previously been thought to be produced exclusively by sweat and sebaceous glands.

OBJECTIVES

To understand if intrafollicular DCD production can be stimulated by a commonly used cosmetic odorant, thus altering human HF microbiome composition in a clinically beneficial manner.

METHODS

DCD expression was compared between fresh-frozen scalp biopsies and microdissected, full-length scalp HFs, organ-cultured in the presence/absence of the OR2AT4 agonist, Sandalore® and/or antibiotics and/or the competitive OR2AT4 antagonist, Phenirat®. Amplicon-based sequencing and microbial growth assays were performed to assess how this treatment affected the HF microbiome.

RESULTS

Synthetic odorant treatment upregulated epithelial DCD expression and exerted antimicrobial activity in human HFs ex vivo. Combined antibiotic and odorant treatment, during an ex vivo dysbiosis event, prevented HF tissue damage and favoured a more physiological microbiome composition. Sandalore®-conditioned medium, containing higher DCD content, favoured Staphylococcus epidermidis and Malassezia restricta over S. aureus and M. globosa, while exhibiting antimicrobial activity against Cutibacterium acnes. These effects were reversed by co-administration of Phenirat®.

CONCLUSIONS

We provide the first proof-of-principle that a cosmetic odorant impacts the human HF microbiome by up-regulating antimicrobial peptide production in an olfactory receptor-dependent manner. Specifically, a synthetic sandalwood-like odorant stimulates intrafollicular DCD production, likely via OR2AT4, and thereby controls microbial overgrowth. Thus, deserving further exploration as an adjuvant therapeutic principle in the management of folliculitis and dysbiosis-associated hair diseases.

The gut odorant receptor and taste receptor make sense of dietary components: A focus on gut hormone secretion

Odorant receptors (ORs) and taste receptors (TRs) are expressed primarily in the nose and tongue in which they transduce electrical signals to the brain. Advances in deciphering the dietary component-sensing mechanisms in the nose and tongue prompted research on the role of gut chemosensory cells. Acting as the pivotal interface between the body and dietary cues, gut cells "smell" and "taste" dietary components and metabolites by taking advantage of chemoreceptors-ORs and TRs, to maintain physiological homeostasis. Here, we reviewed this novel field, highlighting the latest discoveries pertinent to gut ORs and TRs responding to dietary components, their impacts on gut hormone secretion, and the mechanisms involved. Recent studies indicate that gut cells sense dietary components including fatty acid, carbohydrate, and phytochemical by activating relevant ORs, thereby modulating GLP-1, PYY, CCK, and 5-HT secretion. Similarly, gut sweet, umami, and bitter receptors can regulate the gut hormone secretion and maintain homeostasis in response to dietary components. A deeper understanding of the favorable influence of dietary components on gut hormone secretion via gut ORs and TRs, coupled with the facts that gut hormones are involved in diverse physiological or pathophysiological phenomena, may ultimately lead to a promising treatment for various human diseases.

Dietary Supplementation of Methyl Cedryl Ether Ameliorates Adiposity in High-Fat Diet-Fed Mice

Methyl cedryl ether (MCE) is a derivative of cedrol and is widely used as a fragrance compound. The aim of this study was to evaluate the preventative effects of MCE on obesity and related metabolic syndromes and to delineate the mechanisms from the perspective of gut microbiota and white adipose tissues (WAT) transcriptomic profiles. Five-week-old male C57BL/6J mice were randomly assigned into 3 groups and fed with chow diet, high-fat diet (HFD), or HFD supplemented with 0.2% (w/w) MCE for 13 weeks. We found that MCE significantly reduced body weight, inhibited adipocyte hypertrophy, and ameliorated hepatic steatosis under HFD conditions. MCE dietary supplementation downregulated the expression of adipogenesis genes (FAS and C/EBPα) and upregulated the mRNA levels of thermogenesis genes (PGC-1α, PRDM16, UCP1, Cidea, Cytc, and COX4) in epididymal WAT. 16S rRNA sequencing revealed that MCE improved gut microbiota dysbiosis in HFD-fed mice, as manifested by the alteration of strains associated with obesity. Further transcriptome analysis of WAT indicated that MCE dramatically changed the gene expression profiles. Our results demonstrate the anti-obesity effect of MCE under HFD conditions, highlighting the nutraceutical potential of MCE for preventing obesity.

α-Ionone protects against UVB-induced photoaging in epidermal keratinocytes

Objective

To evaluate whether α-ionone, an aromatic compound mainly found in raspberries, carrots, roasted almonds, fruits, and herbs, inhibits UVB-mediated photoaging and barrier dysfunction in a human epidermal keratinocyte cell line (HaCaT cells).

Methods

The anti-photoaging effect of α-ionone was evaluated by detecting the expression of barrier-related genes and matrix metalloproteinases (MMPs) in HaCaT cells. The levels of reactive oxygen species, oxidation product, antioxidant enzyme, and inflammatory factors were further analysed to underline the protective effect of α-ionone on epidermal photoaging.

Results

It was found that α-ionone attenuated UVB-induced barrier dysfunction by reversing keratin 1 and filaggrin in HaCaT cells. α-Ionone also reduced the protein amount of MMP-1 and mRNA expression of MMP-1 and MMP-3 in UVB-irradiated HaCaT cells, implying protective effects on extracellular matrix. Furthermore, HaCaT cells exposed to α-ionone showed significant decreases in interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α as compared to UVB-irradiated HaCaT cells. α-Ionone treatment significantly inhibited the UVB-induced intracellular reactive oxygen species increase and malondialdehyde accumulation. Therefore, the beneficial effects of α-ionone on inhibiting MMPs secretion and barrier damage may be related to attenuated inflammation and oxidative stress.

Conclusion

Our results highlight the protective effects of α-ionone on epidermal photoaging and promote its clinic application as a potential natural anti-photodamage agent in future.

OR2AT4, an Ectopic Olfactory Receptor, Suppresses Oxidative Stress-Induced Senescence in Human Keratinocytes

Olfactory receptors (ORs) are the largest protein superfamily in mammals. Certain ORs are ectopically expressed in extranasal tissues and regulate cell type-specific signal transduction pathways. OR2AT4 is ectopically expressed in skin cells and promotes wound healing and hair growth. As the capacities of wound healing and hair growth decline with aging, we investigated the role of OR2AT4 in the aging and senescence of human keratinocytes. OR2AT4 was functionally expressed in human keratinocytes (HaCaT) and exhibited co-expression with G-protein-coupled receptor signaling components, Golfα and adenylate cyclase 3. The OR2AT4 ligand sandalore modulates the intracellular calcium, inositol phosphate, and cyclic adenosine monophosphate (cAMP) levels. The increased calcium level induced by sandalore was attenuated in cells with OR2AT4 knockdown. OR2AT4 activation by sandalore inhibited the senescent cell phenotypes and restored cell proliferation and Ki-67 expression. Sandalore also inhibited the expression of senescence-associated β-galactosidase and increased p21 expression in senescent HaCaT cells in response to hydrogen peroxide. Additionally, sandalore activated the CaMKKβ/AMPK/mTORC1/autophagy signaling axis and promoted autophagy. OR2AT4 knockdown attenuated the increased in the intracellular calcium level, cell proliferation, and AMPK phosphorylation induced by sandalore. These findings demonstrate that the effects of sandalore are mediated by OR2AT4 activation. Our findings suggest that OR2AT4 may be a novel therapeutic target for anti-aging and anti-senescence in human keratinocytes.