Local synthesis and effect of sex steroids in human skin and the hair follicle and hormonal effects on the wound healing response
Year: 2011
Type: dissertation
Abstract: Humans, as others mammals, are able to synthesize steroid hormones from endocrine organs, such as gonads, adrenal gland and placenta. The expression and activity of steroidogenic enzymes in peripheral tissues provide the intracrine production of active androgens and estrogens by transformation of adrenal precursor dehydroepiandrosterone (DHEA). Only human and primates are unique in having large amounts of the inactive adrenal DHEA and especially DHEA-sulfate (DHEA-S). However, adrenal secretion decreases from the age of 30 years in both sexes, thus potentially providing an explanation for part of the mechanisms involved in the pathogenesis of age-related conditions, such as skin aging. In this study, it was determined whether human skin expresses the enzymes required for the local biosynthesis of active sex steroid hormones. Specifically, biopsies of skin and hair follicles (HFs) were collected from female healthy donors, and cultured dermal fibroblasts (DFs) and cultured epidermal keratinocytes (EKs) were established from female and male healthy donors. The mRNA expression of seven key steroidogenic proteins (P450arom, P450scc, P450c17, STS, OATP2B1, 5α-reductase 1 and 5α-reductase 2), and the estrogen receptors (ERα and ERß) and the androgen receptor (AR) were investigated using RT-PCR and qRT-PCR. All samples produced PCR products of the expected size for P450scc, P450c17, STS and 5α-reductase 1. The mRNA expression of 5α-reductase 2 was detected only in HF. EK did not produce the transcript of P450arom and DF did not express OATP2B1. Both ERα and ERß were expressed in EK as well as in DF. In particular, EK showed to strongly express ERß compared to ERα. In contrast, ERα has been detected with higher expression than ERß in DF. Differences in estrogen receptors expression have been demonstrated also in human HFs that have showed strongly expressed ERß in comparison with ERα. On the other hand, all the samples showed AR expression. In order to the possibility of steroids metabolism, a gene array analysis was performed on whole transcriptome of human HFs and cultured EKs after steroid treatment. Three different hormones were used for 24h of incubation: DHEA-S (10μM), testosterone (TST) (50nM) and 17ß-estradiol (E2) (1nM). The global mRNA expression profiling revealed changes in the expression of a large number of genes. In particular, interesting up-regulation of genes involved in inflammation, cell proliferation and differentiation and structural functions. The analysis on EKs was focused on four genes up-regulated with all three steroids investigated: CXCL1, ANGPTL4, TXNIP, and LMNB1. In addition, the in vitro scratch wound assay was used to determine the direct effects of E2, DHEA, DHEA-S and TST on the migration of mechanically wounded human DFs and EKs. All steroids stimulated cell migration, although both DHEA and TST were blocked by an aromatase inhibitor (Arimidex) and DHEA-S by the STS inhibitor. These results indicate an important role for local synthesis of E2 in skin from the circulating precursor DHEAS and expression of its action in the wound healing process. To verify the hypothesis of the local synthesis of E2, the activity of the aromatase, which is the enzyme that catalyzes the conversion of androgen to estrogen, was assessed in EKs and DFs using the tritiated water (3H2O) assay. Specifically, it was investigated whether the aromatase activity and mRNA expression were modulated in cultured skin cells in response to either dexamethasone or mechanical wounding. The analysis revealed that dexamethasone increased the activity and mRNA expression in particular in DFs, in contrast, the mechanically wounded showed in EKs an increase of the aromatase activity at 24h compared to the non-wounded confluent monolayer cells. All data suggest that human skin and individual cells as target and source of active androgens and estrogens. Further studies are required to understand the role of steroids in inflammation, proliferation and differentiation which have implications for hair growth, skin cancer, aging and wound-healing. In particular, a greater understanding of DHEA signalling may help develop wound-healing therapies, without the risks of estrogen therapy, benefiting the elderly and patients with impaired wound-healing.
Author: Elena Pomari
Language: English
Topic: Hair Growth and Disorders
Subfield: Dermatology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W148395239