Abstract
BackgroundHeat induced by infrared (IR) radiation from sun exposure increases skin temperature and can lead to thermal and photo-aging. However, little is known about the relationship between heat induced by IR radiation and lipid biosynthesis in human sebocytes. This study investigated the expression of factors involved in lipid biosynthesis in human sebocytes exposed to heat. The effect of Cassia tora extract and chrysophanol, which is widely used as anti-inflammatory agent, on the heat shock effect in sebocytes was then examined.MethodsFor the treatment, cells were maintained in culture medium without FBS (i.e., serum starved) for 6 h and then moved for 30 min to incubators at 37 °C (control), 41 °C, or 44 °C (heat shock). Culture media were replaced with fresh media without FBS. To investigate expression of gene and signaling pathway, we performed western blotting. Lipid levels were assessed by Nile red staining. The cytokine levels were measured by cytokine array and ELISA kit.ResultsWe found that peroxisome proliferator-activated receptor (PPAR)γ and fatty acid synthase (FAS) were upregulated and the c-Jun N-terminal kinase (JNK)/p38 signaling pathways were activated in human sebocytes following heat exposure. Treatment with Cassia tora seed extract and chrysophanol suppressed this up-regulation of PPARγ and FAS and also suppressed the increase in IL-1β levels.ConclusionThese findings provide evidence that IR radiation can stimulate sebum production; Cassia tora seed extract and chrysophanol can reverse lipid stimulated inflammatory mediation, and may therefore be useful for treating skin disorders such as acne vulgaris.
Highlights
Heat induced by infrared (IR) radiation from sun exposure increases skin temperature and can lead to thermal and photo-aging
We examined whether Peroxisome proliferator-activated receptor γ (PPARγ) and fatty acid synthase (FAS) play a role in the increase in lipid production in human sebocytes caused by heat treatment
To investigate the effect of heat on lipid synthesis in human sebocytes, we examined lipid droplet formation using Nile Red staining and found that cells incubated at 44 °C showed higher lipid accumulation than those incubated at 41 °C (Fig. 1d)
Summary
Heat induced by infrared (IR) radiation from sun exposure increases skin temperature and can lead to thermal and photo-aging. Little is known about the relationship between heat induced by IR radiation and lipid biosynthesis in human sebocytes. This study investigated the expression of factors involved in lipid biosynthesis in human sebocytes exposed to heat. Human skin is composed of the epidermis, dermis, and a subcutaneous fat layer. Sebaceous glands produce and secrete sebum, which contains triglycerides, wax esters, squalene, cholesterol esters, cholesterol, and free fatty acids; excessive sebum production is associated with skin disorders such as acne [1, 2]. Heat from infrared (IR) radiation during sun exposure increases skin temperature. When exposed to sunlight in the summer, the skin temperature increases by more than 40 °C. When exposed to a temperature of 45 °C or more for 1 h or more, skin tissue is damaged by protein denaturation in the skin
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