Luteolin induces caspase-14-mediated terminal differentiation in human epidermal keratinocytes

Experimental study on the effect of luteolin on the proliferation, apoptosis and expression of inflammation-related mediators in lipopolysaccharide-induced keratinocytes

OBJECTIVE

This study aimed at exploring the effects of luteolin on psoriasis-like cell model proliferation, apoptosis regulation and the expression of inflammation-related mediators.

METHODS

A Cell Counting Kit-8 (CCK-8) assay was used to determine the survival rate of human immortalized keratinocytes (HaCaT cells) and normal human epidermal keratinocytes (NHEK cells) following stimulation with luteolin and lipopolysaccharide (LPS). Western blot and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis were used to detect the protein and mRNA expressions of nuclear factor (NF)-κB p65 and interleukin (IL)-6 after LPS stimulation. Then a luteolin stimulation protocol (10 μmol/L, 24 h) was determined and a reasonable LPS stimulation concentration (20 μg/mL, 24 h) was chosen to establish the psoriasis cell model. Keratinocytes in luteolin pre-treatment and control groups were stimulated with 20 μg/mL LPS for 24 h, and the expressions of NF-κB p65 and IL-6 were detected by western blot and RT-qPCR. The apoptosis of HaCaT cells was detected by flow cytometry, and the enzyme-linked immunosorbent assay (ELISA) was used to detect the expression of psoriasis-related inflammatory factors.

RESULTS

CCK-8 assay indicated that luteolin inhibited the proliferation of keratinocytes. LPS stimulated the proliferation of keratinocytes and upregulated the expression of NF-κB p65 and IL-6 in a concentration-dependent manner, and induced psoriasis-like changes. Furthermore, the protein and mRNA expression levels of NF-κB p65 and IL-6 were decreased in the luteolin pre-stimulation group (p < 0.05). Treatment with luteolin downregulated the expression of the LPS-induced inflammatory mediators in keratinocytes (p < 0.05). The flow cytometry results showed that luteolin induced HaCaT cells apoptosis. Finally, ELISA results demonstrated that luteolin inhibited the release of the IL-17, IL-23 and tumor necrosis factor α (TNF-α) in the pre-stimulation group (p < 0.05).

CONCLUSION

This study confirmed that luteolin can effectively relieve inflammatory mediators in LPS-induced keratinocyte models of psoriasis, which suggested the potential of luteolin in treating psoriasis.

The Role of FABP5 in Radiation-Induced Human Skin Fibrosis

Radiation-induced skin fibrosis is a detrimental and chronic disorder that occurs after radiation exposure. The molecular changes underlying the pathogenesis of radiation-induced fibrosis of human skin have not been extensively reported. Technical advances in proteomics have enabled exploration of the biomarkers and molecular pathogenesis of radiation-induced skin fibrosis, with the potential to broaden our understanding of this disease. In this study, we compared protein expression in radiation-induced fibrotic human skin and adjacent normal tissues using iTRAQ-based proteomics technology. We identified 186 preferentially expressed proteins (53 upregulated and 133 downregulated) between radiogenic fibrotic and normal skin tissues. The differentially expressed proteins included keratins (KRT5, KRT6A, KRT16 and KRT17), caspase-14, fatty acid-binding protein 5 (FABP5), SLC2A14 and resistin. Through bioinformatic analysis of the proximal promoters, common motifs and corresponding transcriptional factors were identified that associate with the dysregulated proteins, including PAX5, TBX1, CLOCK and AP2D. In particular, FABP5 (2.15-fold increase in fibrotic skin tissues), a transporter of hydrophobic fatty acids, was investigated in greater detail. Immunohistochemistry confirmed that the protein level of FABP5 was increased in fibrotic human skin tissues, especially in the epidermis. Overexpression of FABP5 resulted in nuclear translocation of SMAD2 and significant activation of the profibrotic TGF-β signaling pathway in human fibroblast WS1 cells. Moreover, exogenous FABP5 (FABP5-EGFP) could be incorporated by skin cells and intensify TGF-β signaling, indicating a communication between the microenvironment and skin fibrosis. Taken together, our findings illustrate the molecular changes during radiation-induced human skin fibrosis and the critical role of FABP5 in activating the TGF-β signaling pathway.

Luteolin and apigenin activate the Oct-4/Sox2 signal via NFATc1 in human periodontal ligament cells

Identifying small molecules to activate the Oct-4/Sox2-derived pluripotency network represents a hopeful and safe method to pluripotency without genetic manipulation. Luteolin and apigenin, two major bioactive flavonoids, enhance reprogramming efficiency and increase expression of Oct-4/Sox2/c-Myc, albeit the detailed mechanism regulating pluripotency in dental-derived cells remains unknown. In the present study, to elucidate the effect of luteolin/apigenin on pluripotency of periodontal ligament cells (PDLCs) through interaction with downstream signals, we examined cell cycle, proliferation, apoptosis, expression of Oct-4/Sox2/c-Myc, and multilineage differentiation of PDLCs with luteolin/apigenin treatment. Moreover, we profiled the differentially expressed pluripotency genes by PCR arrays. Our results demonstrated that luteolin/apigenin restrained cell proliferation, increased apoptosis, and arrested PDLCs in G2/M and S phase. Luteolin and apigenin activated expression of Oct-4, Sox2, and c-Myc in a time- and dose-dependent pattern, and repressed lineage-specific differentiation. PCR arrays profiled multiple signals in PDLCs with luteolin/apigenin treatment, among which NFATc1 was the major upregulated gene. Notably, blocking of the NFATc1 signal with INCA-6 significantly decreased mRNA and protein expression of Oct-4, Sox2, and c-Myc in PDLCs with luteolin/apigenin treatment, indicating that NFATc1 may act as an upstream modulator of Oct-4/Sox2 signal. Taken together, this study showed that luteolin and apigenin effectively maintain pluripotency of PDLCs through activation of Oct-4/Sox2 signal via NFATc1.