Ferulic Acid Inhibits UVA-induced Photoaging In Human Skin Fibroblasts Through Telomere Pathway

Background:Skin is the largest organ of the human body and like all other organs, skin also undergoes aging. Skin aging is a complex, multifactorial, cumulative, and progressive process resulting in several functional and aesthetic changes in the skin. It includes intrinsic (or natural) aging, an unpreventable process, and extrinsic aging that is caused by exposure to environmental factors. The primary environmental factor that leads to human skin aging is ultraviolet (UV) irradiation from the sun and therefore is termed photoaging. Photoaging is characterized by clinical and histologic changes of the skin which is induced by continuous and long-term exposure to UVA and UVB irradiation. UVA irradiation (320-400 nm) of sunlight is the most effective wavelength in causing photoaging since UVA rays are able to penetrate deeper into the matrix-rich dermal layer of the skin, whose major cellular components are resting fibroblasts, as compared to UVB rays that can only penetrate through the epidermal layer of the skin. Clinically, photoaged skin is coarsely wrinkled, lost of skin tone and resilience, and associated with dyspigmentation, telangiectasia, and cutaneous malignancies. The increased number of aging population and higher exposure to UV light as well as the changes of facial appearance affected by photoaging lead people to seek treatment for prevention of UV-induced photoaging in skin for delaying their effects.Recent work has elucidated the molecular mechanisms of skin aging, in which telomere-based signaling plays a crucial role. Telomeres are the specialized structures located at each ends of chromosomes to protect the chromosome against deterioration, degradation, fusion events and as being recognized as broken or damaged DNA. Telomere length is a molecular marker of cell aging, and genomic instability due to telomere shortening has been linked to aging-related diseases. It has been assumed that telomere shortening played an essential role in both of the skin aging process. Chronological skin aging is controlled by progressive telomere shortening, while in photoaging UV irradiation not only damages DNA but also accelerates telomere shortening. Moreover, telomerase, an enzyme encoded by hTERT gene, can counteract this telomere shortening by its reverse transcriptase activity and therefore thought to prevent a telomere-dependent aging process and delay the skin changes associated with skin aging.Ferulic acid is a phenolic compound of low toxicity present in several plants, that is considered to be a potential therapeutic agent against various human diseases including skin aging-related diseases. This anti-aging effect is associated with the antioxidant properties of ferulic acid due to its ability to scavenge free radicals and suppress UV-induced oxidative reactions. Preliminary studies have reported that ferulic acid provides photo-protective effects and inhibits the proliferation reduction induced by UVA and UVB irradiation to skin cells, including keratinocytes and fibroblasts, by restoring and strengthening antioxidation defense system and decreasing oxidation damaged of oxygen radicals at cellular and molecular levels. This mechanism together with decreasing the collagen degradation might also be related to the protective effect of ferulic acid on human fibroblasts against UVA-induced photoaging.Objective:In this study, we aimed to observe the effects of UVA irradiation and ferulic acid intervention in human skin fibroblasts and investigate whether ferulic acid could protect cultured human skin fibroblasts from UVA irradiation induced photoaging through telomere pathway, in order to explore the possible mechanisms of photoaging delay.Methods:Subconfluent fibroblasts were divided into normal control group, ferulic acid group, UVA irradiation group, and UVA plus ferulic acid group. Fibroblasts were shammed or irradiated with 10 J/cm2 of UVA irradiation and treated with 200μg/mL of ferulic acid. In our laboratory setting, telomere length was measured by real-time quantitative PCR, while telomerase activity and expression were measured by two different methodologies. For the purposes of quantifying telomerase activity and expression in the context of clinical research, the most common nonradioactive techniques used include the highly sensitive photometric enzyme immunoassay, TRAP-ELISA assay, and real-time quantitative PCR analysis for expression of telomerase activity and mRNA levels of hTERT genes, respectively. These methods are largely sufficient for assessing overall telomerase function within a tissue of interest.1. The telomere lengths were measured by real-time quantitative PCR.2. The telomerase activities were assayed by TRAP-ELISA.3. The mRNA levels of human telomerase reverse transcriptase (hTERT) were also measured by real-time quantitative PCR.Results:The present findings potentially provides the basis for better understanding of the molecular mechanism of UVA-induced photoaging and the protective effect of ferulic acid against it through telomere signaling pathway.1. The fibroblasts telomere length in ferulic acid group was significantly increased, while significantly decreased in UVA group compared to control group. When performed irradiation simultaneously with ferulic acid treatment, the shorter telomere length return to normal, indicating ferulic acid treatment inhibit UVA-accelerated telomere shortening.2. All ΔA value of each sample groups were lower than the two-fold background activity, indicating that the expression of telomerase activity were negative in all groups.3. UVA irradiation down-regulated the mRNA levels of hTERT genes, while ferulic acid treatment could reduce these changes more significantly.The intervention of ferulic acid could restore the telomere length compared with UVA group (p<0.5), while the expression of telomerase activity was undetectable and hTERT mRNA expression was decreased. These results have important implications for further research of ferulic acid role and mechanism in photoaging.Conclusion:The results indicated that the telomeres were shown to be adversely affected by UVA irradiation and the damage caused was related to cell aging, confirmed that telomeres rather than telomerase are more involved in cellular senescence, and hence ferulic acid can significantly delay the shortening of telomere length of skin fibroblast either under physiological state or post-UVA irradiation, and postpone cellular senescence, but it is not through telomeric-dependent pathway of telomerase activity. Future advances in this field need to be taken up for the development of more anti-aging agents.