Endocrine Abstracts

Cortisol-based therapy is still the most potent anti-inflammatory treatment available for skin conditions such as psoriasis and atopic dermatitis. Previous studies have demonstrated the presence of components of the steroidogenic pathway in keratinocytes, though surprisingly none have reported that these cells, which form up to 90% of the epidermis are able to synthesise cortisol^1,2. Here, we demonstrate that primary human keratinocytes (PHK) are capable of de novo cortisol synthesis and that keratinocyte steroid metabolism can be manipulated by calcium.

Immunofluorescence histochemistry shows that steroidogenic acute regulatory protein is predominantly expressed in the basal layer of normal epidermis. Cultured PHK isolated from redundant facelift skin (ethics approval T/01/034) transcribed steroid enzymes that are obligatory for de novo cortisol synthesis. The levels of StAR, CYP11A1 and CYP21 mRNA were greatest at low 0.09 mM Ca²⁺ that selects for proliferating keratinocytes but decreased with the addition of 1.2 mM Ca²⁺ that promotes keratinocyte differentiation. Radiometric assay showed PHK also metabolised [H³]-pregnenolone through each intermediate steroid to cortisol. The cortisol metabolite was detected at both 0.09 mM Ca²⁺ and 1.2 mM Ca²⁺ but more intermediate steroids for cortisol synthesis were identified with 0.09 mM Ca²⁺.

De novo steroid synthesis was confirmed by pregnenolone radioimmunoassay and cortisol ELISA. Over 24 h, the detected basal level of pregnenolone in spent keratinocyte culture media was 7.98±1.85 nmol/l, which was enhanced over threefold to 29.2±4.96 nmol/l (P<0.05) with the use of the pregnenolone metabolism inhibitors trilostane (100 μM) and ketoconazole (10 μM). The basal level of cortisol detected by ELISA was 1.02±0.22 nmol/l in spent keratinocyte medium after 24 h in culture.

Therefore we have mapped the endogenous cortisol synthesis pathway in PHK and shown that the greatest metabolism occurs in proliferating keratinocytes. Since cortisol is such a potent anti-inflammatory compound, this pathway could be essential for maintaining a healthy epidermis.

References

1. Rogoff D, Gomez-Sanchez CE, Foecking MF, Wortsman J & Slominski A. J Steroid Biochem Mol Biol 2001 78 77–81.

2. Milewich L, Shaw CB & Sontheimer RD. Ann N Y Acad Sci 1988 548 66–89.