CRH stimulates POMC activity and corticosterone production in dermal fibroblasts

https://doi.org/10.1016/j.jneuroim.2005.01.014Get rights and content

Abstract

It has been previously documented that human skin cells including epidermal keratinocytes and dermal fibroblasts produce and process proopiomelanocortin (POMC), corticotropin releasing hormone (CRH), and express functional CRH receptors type-1 (CRH-R1). The skin also has corticosteroidogenic activity, suggesting a functional connection between these elements. In the current study, we found that human dermal fibroblasts (but not normal epidermal keratinocytes) respond to CRH with stimulation of cAMP, with POMC gene and protein expression, and ACTH production and release. Furthermore, CRH and ACTH stimulate production of corticosterone in fibroblasts, with ACTH being more potent. Although cortisol-immunoreactivity accumulation/production in fibroblasts has been detected by ELISA, it appears to be constitutive (not affected by CRH or ACTH). These effects are absent in keratinocytes. Therefore, we propose that fibroblasts but not keratinocytes display a functional CRH–POMC–corticosteroid axis organized similarly to the hypothalamus–pituitary–adrenal (HPA) axis. However, it diverges from the HPA organization in its distal step, where CRH and ACTH stimulate production of corticosterone, instead of cortisol.

Introduction

Evidence is accumulating that mediators known to be involved in the endocrine responses to systemic stress are also expressed or produced in the skin (Slominski and Wortsman, 2000, Slominski et al., 2000b, Slominski et al., 2001, Slominski et al., 2003). It is accepted that under systemic stress, the main adaptive response is mediated by the hypothalamic–pituitary–adrenal (HPA) axis (Chrousos, 1995). Activation of the HPA system starts with hypothalamic release of corticotropin-releasing hormone (CRH), which activates CRH receptor type 1 (CRH-R1) in the anterior pituitary to induce production/release of the POMC-derived peptide ACTH. In turn, ACTH stimulates production/secretion of corticosteroids by the adrenal cortex. We have demonstrated that the skin expresses the genes and functional proteins of this neuroendocrine axis and proposed that they are organized not randomly, but as a cutaneous equivalent of the central HPA (Slominski and Wortsman, 2000, Slominski et al., 2000b, Slominski et al., 2001, Slominski et al., 2004a). Such organization would function similarly to its systemic equivalent, although triggered by exposure to local stressors (solar, thermal, mechanical, chemical, biological, etc.).

Keratinocytes are the main cellular component of the epidermis, being responsible for the skin barrier function. In the dermis, the main cellular components are fibroblasts, responsible primarily for the organization and maintenance of the skin structure. Both cell types express functional CRH-R1, and produce and process POMC to its final products ACTH, MSH, and endorphin that can be secreted to the intra/extracellular milieu (Luger et al., 1999, Slominski and Wortsman, 2000, Slominski et al., 2000b, Slominski et al., 2001, Slominski et al., 2004a). We have further tested the extent of the central/peripheral homology in organization of the response to stress. We used as peripheral models normal epidermal keratinocytes and dermal fibroblasts and found that CRH does not modify POMC expression in keratinocytes, shifting our focus on dermal fibroblasts.

Section snippets

Cell culture

Cells, media, and supplements were purchased from Cascade Biologics, Inc., Portland, OR. Normal human dermal fibroblasts were maintained in 106 medium with Low Serum Growth Supplement and PSA (penicillin G (100 U/ml), streptomycin (100 μg/ml), amphotericin B (0.25 μg/ml)). Human epidermal keratinocytes were maintained in EpiLife medium with EpiLife Defined Growth Supplement (EDGS: bovine serum albumin (BSA), bovine transferrin, hydrocortisone, recombinant human insulin-like growth factor

Results and discussion

Addition of CRH stimulated POMC gene expression in fibroblasts (Fig. 1) but not in epidermal keratinocytes (not shown). Fibroblasts POMC mRNA stimulation was time dependent; maximal stimulation occurred at 1 h (24-fold), decreasing at 6 h (3-fold), and at 24 h it had returned to basal levels (Fig. 1A). The increase in POMC gene expression, albeit transient, resulted in increased expression of POMC protein after 24 h of incubation as detected by Western blot analysis; this was represented by the

Acknowledgement

Supported by NIH grant no. AR047079 to AS and Johnson and Johnson Skin Research Center Training Grant to BZ.

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