Cholesterol regulates melanogenesis in human epidermal melanocytes and melanoma cells

Abstract

Cholesterol is important for membrane stability and is the key substrate for the synthesis of steroid hormones and vitamin D. Furthermore, it is a major component of the lipid barrier in the stratum corneum of the human epidermis. Considering that steroid hormone synthesis is taking place in epidermal melanocytes, we tested whether downstream oestrogen receptor/cAMP signalling via MITF/tyrosine hydroxylase/tyrosinase/pigmentation could be possibly modulated by cholesterol. For this purpose, we utilized human primary melanocyte cell cultures and human melanoma cells with different pigmentation capacity applying immunofluorescence, RT-PCR, Western blotting and determination of melanin content. Our in situ and in vitro results demonstrated that melanocytes can synthesize cholesterol via HMG-CoA reductase and transport cholesterol via LDL/Apo-B100/LDLR. Moreover, we show that cholesterol increases melanogenesis in these cells and in human melanoma cells of intermediate pigmentation (FM55) in a time- and dose-dependent manner. Cellular cholesterol levels in melanoma cells with different pigmentation patterns, epidermal melanocytes and keratinocytes do not differ except in the amelanotic (FM3) melanoma cell line. This result is in agreement with decreasing cholesterol content versus increasing pigmentation in melanosomes. Cholesterol induces cAMP in a biphasic manner i.e. after 30 min and later after 6 and 24 h, meanwhile protein expression of oestrogen receptor beta, CREB, MITF, tyrosine hydroxylase and tyrosinase is induced after 72 h. Taken together, we show that human epidermal melanocytes have the capacity of cholesterol signalling via LDL/Apo-B100/LDL receptor and that cholesterol under in vitro conditions increases melanogenesis.

Identifying melanogenesis inhibitors from Cinnamomum subavenium with in vitro and in vivo screening systems by targeting the human tyrosinase

“…Cell pellets were dissolved in 1.0 N NaOH containing 10% DMSO and heated at 80°C for 1 h and suspensions were clarified by centrifugation for 10 min at 10 000 g. The amount of melanin was determined spectrophotometrically based on the absorbance at 475 nm (21)(22)(23).…”

Inhibition of UVA-mediated melanogenesis by ascorbic acid through modulation of antioxidant defense and nitric oxide system

“…Various melanoma cell lines have been previously used as models to study the regulation of melanogenesis and the mechanisms of action of promising antimelanogenic agents (Nawarak et al, 2008;Chung et al, 2009;Schallreuter et al, 2009). Moreover, poorlypigmented cells have been previously shown to be more susceptible to UVA-induced oxidative stress (Kvam and Dahle, 2003).…”

Mevastatin suppresses melanogenesis by lowering the levels of cyclic adenosine monophosphate and cholesterol

“…Of these hormones, steroids and vitamin D play important roles in cellular and biochemical signalling pathways. Interestingly, a recent study has reported that cholesterol has pro-melanogenic effects in both human epidermal melanocytes and FM55 melanoma cells (1). Cholesterol was reported to initially stimulate cyclic adenosine monophosphate (cAMP) release and activate the transcription of related genes via oestrogen receptor b, with consequent stimulation of cAMP response element-binding protein (CREB)/microphthalmia-associated transcription factor (MITF)/tyrosinase pathways.…”

“…This is currently a major issue in the treatment of melanoma by immunotherapy with monoclonal antibodies (anti-CTLA4/PD1 antibody), vaccines and tumor-infiltrating lymphocytes (TILs) (1).…”