i think i'll save this.. maybe susan will comment further?
And i've not come to enough conclusions even though my last post
has a few:
Sun, Mar 31 2013 11:44 am
Subject: Re: Steroids produced in/by the skin as a cause of
inflammatory and autoimmune diseases
http://groups.google.com/group/alt.support.skin-diseases.psoriasis/msg/eea82dcbd8abccd6
>
> Another interesting one:
>
> Am J Physiol Endocrinol Metab. 2011 September; 301(3): E484–E493.
> Published online 2011 June 14. doi: 10.1152/ajpendo.00217.2011
> PMCID: PMC3174533
> Cutaneous hypothalamic-pituitary-adrenal axis homolog: regulation by
> ultraviolet radiation
> Cezary Skobowiat,1,5 John C. Dowdy,2 Robert M. Sayre,3 Robert C.
> Tuckey,4 and Andrzej Slominski1
> Departments of 1Pathology and Laboratory Medicine and
> 2Dermatology, University of Tennessee, Health Science Center, Memphis;
> 3Rapid Precision Testing Laboratories, Cordova, Tennessee;
> 4School of Biomedical, Biomolecular and Chemical Sciences, University of
> Western Australia, Crawley, Australia; and
> 5Department of Clinical Physiology, University of Warmia and Mazury,
> Olsztyn, Poland
> Corresponding author.
> Address for reprint requests and other correspondence: A. Slominski,
> Dept. of Pathology and Laboratory Medicine, Univ. of Tennessee Health
> Science Center, 930 Madison Ave. Rm. 525, Memphis, TN 38163 (e-mail:
>
aslom...@uthsc.edu).
> Received May 4, 2011; Accepted June 7, 2011.
> Copyright © 2011 the American Physiological Society
> Abstract
> The hypothalamic-pituitary-adrenal (HPA) axis maintains basal and
> stress-related homeostasis in vertebrates. Skin expresses all elements
> of the HPA axis including corticotropin-releasing hormone (CRH),
> proopiomelanocortin (POMC), ACTH, β-endorphin (β-END) with corresponding
> receptors, the glucocorticoidogenic pathway, and the glucocorticoid
> receptor (GR). To test the hypothesis that cutaneous responses to
> environmental stressors follow the organizational structure of the
> central response to stress, the activity of the “cutaneous HPA” axis
> homolog was investigated after exposure to ultraviolet radiation (UVR)
> wavelengths of UVA (320–400 nm), UVB (280–320 nm), and UVC (100–280 nm)
> in human skin organ culture and in co-cultured
> keratinocytes/melanocytes. The level of stimulation of CRH, POMC, MC1R,
> MC2R, CYP11A1, and CYP11B1 genes was dependent on UV wavelengths and
> doses, with the highest effects observed for highly energetic UVC and
> UVB. ELISA and Western assays showed significant production of CRH,
> POMC, ACTH, and CYP11A1 proteins and of cortisol, with a decrease in GR
> expression only after UVB and UVC. However, β-END expression was also
> stimulated by UVA. Immunocytochemistry localized the deposition of the
> aforesaid antigens predominantly to the epidermis with additional
> accumulation of CRH, β-END, and ACTH in the dermis. UVR-stimulated
> CYP11A1 expression was seen in the basal layer of the epidermis and
> cells of adjacent dermis. Thus, the capacity to activate or change the
> spatial distribution of the cutaneous HPA axis elements is dependent on
> highly energetic wavelengths (UVC and UVB), implying a dependence of a
> local stress response on their noxious activity with overlapping or
> alternative mechanisms activated by UVA.
>
> Keywords: corticotropin-releasing hormone, proopiomelanocortin, stress,
> cortisol, glucocorticoid receptor
> the hypothalamic-pituitary-adrenal (HPA) axis represents one of the main
> limbs of an adaptive system, which maintains the basal and
> stress-related homeostasis in vertebrates (6, 25, 28, 55). Thus, stress
> (psychological, physical, or biological) stimulates hypothalamic
> corticotropin-releasing hormone (CRH) production and release, which,
> after activation of CRH receptor type 1 (CRH-R1) in the anterior
> pituitary, stimulates production and release of proopiomelanocortin
> (POMC)-derived adrenocorticotropin ACTH (6, 25, 55). ACTH in the adrenal
> cortex activates MC2 receptors (MC2R, receptor for ACTH), stimulating
> secretion and production of glucorticoids (GC), mainly cortisol [COR,
> (6)]. COR counteracts the effects of stressors and exerts powerful
> immunosuppressive effects.
>
> The skin, the largest organ of the body, is continuously exposed to
> environmental factors, of which ultraviolet (UV) wavelengths of solar
> radiation represent the most prevalent stressor to humans and diurnal
> animals (17, 39, 53). Therefore, it has been proposed that the homolog
> of the HPA axis has developed in the integument (skin) as an efficient
> way to deal with environmental stressors (30, 41, 43). This concept is
> strengthened by the evidence that vertebrate skin expresses CRH and
> related peptides, POMC, which its further processed to β-endorphin
> (β-END), ACTH, and melanocyte-stimulating hormone (MSH) (reviewed in
> Refs. 40, 42). In addition, skin cells express the corresponding
> functional CRH-R1 (reviewed in Ref. 48), melanocortin (MC), and opiate
> receptors (reviewed in Refs. 2, 53). Furthermore, CRH, POMC, and their
> corresponding receptors are coexpressed in cultured skin cells, with
> this coexpression also being demonstrated in skin biopsies by in situ
> hybridization or immunocytochemistry (18, 20, 22, 36, 42, 58). Finally,
> production of corticosterone (CORT) and COR has been clearly
> demonstrated in cultured normal human melanocytes and fibroblasts
> (45–47) and in human hair follicles (18, 29). In fact, skin expresses
> cytochrome P-450scc (P450scc or CYP11A1) and is capable of initiating
> steroidogenesis from cholesterol with pregnenolone as an intermediate
> product (49), which undergoes further sequential transformation to
> progesterone, deoxycorticosterone (DOC), 18(OH)-DOC, CORT, and COR (18,
> 33, 34, 45–47). The expression of these elements appears to be
> nonrandom, with organization into functional, cell type-specific
> regulatory loops with a structural hierarchy similar to that found at
> the central level (18, 43, 45, 46).
>
> Ultraviolet radiation (UVR) represents the electromagnetic energy
> covering wavelengths between 100 and 400 nm. It includes UVC (100–280
> nm), which is absorbed by the atmosphere but when generated by
> artificial light sources has profound mutagenic and lethal effects (1).
> UVB (280–320 nm), although representing only ∼5% of the UV spectrum of
> the solar radiation reaching the surface of the earth, is very efficient
> at stimulating cutaneous biological effects, including mutagenic and
> carcinogenic effects, induction of sunburns, stimulation of melanin
> pigmentation, and inducing transformation of 7-dehydrocholesterol to
> vitamin D3 (1, 10, 15, 17, 24, 38). It can penetrate to the level of the
> papillary dermis. UVA (320–400 nm), which has good cutaneous
> penetration, has lower ability to induce erythema and melanogenesis and
> is also less carcinogenic but having a profound effect on photoaging (1,
> 21). UV exerts many different biological actions on human and animal
> organisms utilizing different mechanisms of action including direct and
> indirect DNA damage, free radical production, and/or interaction with
> specific chromophores (1, 7, 10, 13, 35).
>
> Studies on cultured isolated skin cells have demonstrated that UVB can
> stimulate the expression of CRH, POMC, and POMC-peptides (4, 23, 27, 32,
> 57), implying its involvement in the regulation of local neuroendocrine
> activities (41). Since UVR is a prevalent environmental stressor, we
> decided to clarify the nature of cutaneous neuroendocrine responses to
> UVR by testing wavelength-dependent changes in the expression pattern of
> crucial elements of the HPA axis. We used co-cultured human
> keratinocytes and melanocytes, because of the bidirectional
> communication between these cells, and full-thickness histo-cultured
> skin biopsies as the reliable ex vivo models of human skin.
>
> MATERIALS AND METHODS
> Approval of human protocols.
> All procedures adhered to the principles of the Declaration of Helsinki
> and were approved by the local Institutional Review Board with Exempt
> Protocol no. 4.
>
> Co-cultures.
> Second passage of human neonatal epidermal keratinocytes (HEKn) and
> human neonatal epidermal melanocytes (HEMn) was used for co-cultures.
> Cells were seeded in a ratio 5:1; e.g., 5 × 105 HEKn and 1 × 105 HEMn
> per Petri dish (100 mm in diameter) in triplicate and maintained in 2 ml
> of serum-free medium (to remove all exogenous sources of POMC-derived
> peptides) composed of mixed KBM-2-MBM-4 (1:1) supplemented with insulin
> (5 μg/ml), human epidermal growth factor (2 μg/ml), human fibroblast
> growth factor (5 μg/ml), and 1% antibiotic antimycotic solution (AAS)
> (all from Lonza, Walkersville, MD). After 2 days of incubation time
> (37°C, 5% CO2), when the cells achieved 90% confluence, the media were
> discarded and cells washed 2× with PBS, and 3 ml of PBS was added to
> each flask. The cells were irradiated with the appropriate doses of UVA,
> UVB, or UVC (see Irradiation protocols below). The control cells were
> treated the same way, except that they were not exposed to UVR
> (sham-treated groups). During irradiation with UVA, both experimental
> and control (covered by aluminum foil) groups were placed on a cold
> (4°C) blanket to prevent UVA-induced temperature increases. After
> treatment, PBS was replaced with 2 ml of the same serum-free medium, and
> after 6, 12, 24, and 48 h, media from each conditions were collected and
> frozen (−80°C). The cells were rinsed with PBS and harvested by
> trypsinization, centrifuged into pellets as described previously (32,
> 37), and frozen separately at −80°C for RNA, Western blot (WB), and
> ELISA assays.
>
> Organ cultures.
> Skin samples were obtained from adult African American donors after
> breast reduction (The Med Hospital, Memphis, TN). The subcutaneous fat
> was removed, and skin was cut into 0.5 × 0.5-cm pieces. Skin fragments
> were placed dermis down onto humid (PBS) Waltham paper in a 60-mm Petri
> dish and irradiated with UVA, UVB, or UVC bulbs (see below). The UVB and
> UVC irradiation was performed at room temperature, while UVA and
> UVA-sham treated (as a control for UVA) were placed onto a cold (4°C)
> blanket to avoid heating. Eight skin fragments per dish (in duplicate
> cultures) were used for each condition. Next, the skin fragments were
> placed into six-well plates, eight per well, containing 1.5 ml of
> WILLIAM'S Medium E with l-glutamine and without phenol red (Sigma, St.
> Louis, MO) and supplemented with insulin (5 μg/ml) and AAS (1%) for 6,
> 12, 24, and 48 h of incubation at 37°C, 5% CO2. The fragments were used
> separately for RNA, WB, ELISA, and immunohistochemical (IHC) studies.
>
> Irradiation protocols.
> Doses of irradiations were as follows: UVA, sham control (C) = 0, 10,
> 20, 50 J/cm2; UVB, C 0, 50, 100, 200 mJ/cm2; and UVC, C = 0, 1, 5, 10
> mJ/cm2 (Table 1).
>
> Real-time RT-PCR (RT-PCR) assay.
> RNA from cell pellets was extracted using the Absolutely RNA Miniprep
> kit (Stratagene La Jolla, CA), and TRIzol reagents (Invitrogen,
> Carlsbad, CA) were used to isolate RNA from skin. The RNA concentration
> was quantified, and 3 μg of total RNA (either from cells or from the
> skin) was reverse-transcribed with SuperScript First-Strand Synthesis
> System (Applied Biosystems, Foster City, CA). Primers used for PCR
> amplification are listed in Table 2 and were designed with the Universal
> Probe Library (Roche,
https://www.roche-applied-science.com) and
> synthesized by Integrated DNA Technologies (Coralville, IA). The
> reaction was performed in triplicate with SYBR Green I Master Mix
> (Roche, Manheim, Germany). The data were collected on a Light Cycler 480
> (Roche). The amount of amplified product for each gene was compared with
> that for β-actin by using a comparative ΔΔCT method.
>
> ELISA assays.
> Cell pellets were lysed by vortexing while the skin fragments were
> homogenized with Brinkkmann homogenizer (Brinkkmann, Dallas, TX) with 2
> ml of ice-cold RIPA buffer [PBS containing 1% Nonidet P-40, 0.1% SDS
> supplemented with 1% proteinase inhibitor cocktail (PIC; 10 μl/1 ml,
> Sigma; St. Louis, MO)]. The homogenates were kept on ice for 20 min and
> then centrifuged for 25 min (13,000 g, 4°C). Supernatants were collected
> into fresh tubes and pellets discarded. Peptides and cortisol
> concentrations were measured with ELISA kits (Table 3) and normalized
> for total protein content in cell lysates (2.5 μg/μl, Bradford assay).
> The amount of peptides and cortisol was calculated from the standard
> curve (according to the manufacturer's instructions) and presented as
> nanograms or picograms per milliliter of cell/tissue extract from organ
> culture.
>
> Western blot analyses.
> Cell pellet was lysed in 100 μl of ice-cold RIPA buffer, while the skin
> scraps (2 per condition) were homogenized with 1 ml of the same lysis
> solution a using homogenizer. Next, homogenates were kept on ice for 20
> min and centrifuged for 20 min. Supernatants were collected into fresh
> tubes, and pellet or tissue was discarded; 2.5 μl of each sample was
> used for Bradford protein assay. Extracts (30 μg of protein per line)
> were suspended in the loading Laemmli buffer (4× concentrated),
> denatured, and separated by SDS-15% PAGE. Next, separated proteins were
> transferred to a 0.2-μm PVDF membrane (Millipore, Bedford, MA).
> Membranes were blocked for 2 h at room temperature in skim milk (5%
> wt/vol) and Tris-buffered saline with Tween 20 (TBS-T). Membranes were
> then washed and incubated with primary antibody (Table 4) in 5% skim
> milk diluted (TBS-T) or nonimmune rabbit serum overnight (4°C).
> Membranes were then washed (TBS-T) and incubated with goat anti-rabbit
> IgG-conjugated HRP (0.1 μl/ml; Santa Cruz Biotechnology, Santa Cruz, CA)
> for 1 at room temperature. Blots were rinsed with TBS-T/TBS and exposed
> to the chemiluminescent substrate (SuperSignal West Pico, Thermo Sci,
> Rockford, PA). Bands were visualized by exposure to a classic blue
> autoradiography film BX (MidSci, St. Louis, MO) for 1–10 min. Membranes
> were stripped in Restore Plus Western Blot Stripping Buffer (Thermo
> Sci). The positive signals were standardized to the β-actin antibody
> (1:10,000, Sigma). Expression levels of proteins are the ratio of
> primary antibody to β-actin signal, respectively.
>
> Immunofluorescent staining of co-cultures in chambers.
> HEKn/HEMn were maintained and treated similarly as described earlier,
> except they were seeded at chamber slides (Thermo Sci). Following a 24-h
> incubation, cells were washed in PBS and fixed with 4% buffered PFA for
> 30 min. Afterward, cells were permeabilized and blocked in a solution
> comprising 0.2% Triton-X 100, 0.1% BSA, and 5% donkey serum for 30 min.
> Primary rabbit antibody directed against CRH, PC1, ACTH, β-END, and
> P450scc (details in Table 4) were mixed separately with mouse monoclonal
> MEL-5 antibody diluted in the same blocking solution and incubated for 3
> at room temperature. After an extensive washing in PBS, cells were
> incubated for 1 h in a mixture of species-specific secondary antibody
> conjugated with appropriate fluorophore, e.g., donkey anti-rabbit IgG
> conjugated-CY3 (red) and donkey anti-mouse IgG conjugated-FITC (green)
> (both from Jackson ImmunoResearch West Grove, PA). Cells were further
> washed, dried out, and mounted with mounting medium (Sigma). Negative
> controls were performed including omission of primary antibody,
> replacement with nonimmune rabbit serum, and exclusion of secondary
> antibodies. The positive control was performed on AtT-20 cell lines
> treated similarly. Stained cells were viewed with a fluorescent
> microscope equipped with a digital camera (Leica Digital DM4000B,
> Bannockburn, IL) and photographed under ×200 or ×400 magnifications. At
> least three chambers from each specimen were stained in each condition.
>
> Immunohistochemistry.
> Following a 24-h incubation with UV irradiation, the skin was fixed in
> 4% PFA (12 h, 4°C), rinsed several times in PBS, cryoprotected with 18%
> sucrose in PBS for 10 days (4°C), and cryosectioned (Leica, Bannockburn,
> IL). Ten-micrometer sections were mounted onto silanized slides (Dako,
> Carpinteria, CA), rinsed several times in PBS, and maintained for 1 h at
> room temperature in a blocking solution (5% donkey serum, 0.1% BSA, 0.2%
> Triton X-100 in PBS), rinsed in PBS and incubated for 16 h at room
> temperature with some rabbit polyclonals listed in Table 4. To visualize
> the immunocomplexes, the secondary donkey anti-rabbit biotinylated IgG
> (1:1,000) and then with CY3-conjugated streptavidin (0.2 μg/ml) as a
> fluorophore (both from Jackson ImmunoResearch, West Grove, PA) were
> applied. All slides were finally counterstained with DAPI. At least six
> slides from each specimen were stained and assessed. The immunoreactive
> (IR) signals were examined under fluorescent microscope (Leica Digital
> DM4000B) equipped with a digital camera. In addition, the intensity of
> fluorescent signals inside the epidermis layer was evaluated using
> ImageJ software (National Institutes of Health) and statistically
> compared between conditions with the controls. Positive-control staining
> was performed on human pituitary gland and uterus tissues, which were
> treated similarly to the skin. The negative controls consisted of
> tissues incubated without primary antibody or with nonimmune rabbit
> serum or with antibodies preabsorbed with 0.1 mmol/l concentrations of
> CRH (Sigma, St. Louis, MO), β-END, and ACTH (Peninsula Laboratory,
> Torrance, CA).
>
> Statistical evaluation.
> Data are presented as means ± SD and were analyzed with Student's t-test
> (for 2 groups) or (for more than 2 groups) with one-way ANOVA Dunnett's
> multiple comparison post hoc test using Prism 4.00 (GraphPad Software,
> San Diego, CA). Statistically significant differences are denoted by
> black (t-test) and white or gray (ANOVA) asterisks, where ***P ≤ 0.001,
> **P ≤ 0.005, and *P ≤ 0.05.
>
> RESULTS
> Changes in the expressions of CRH, POMC, MC1R, MC2R, CYP11A1 and CYP11B1
> genes.
> UVR significantly changed the expression of the HPA-related genes in
> both co-cultured human keratinocytes and melanocytes (the two main cell
> populations of the epidermis) and in full-thickness skin biopsies
> incubated ex vivo, in time-, dose-, and wavelength-dependent manners
> (Fig. 1). The most pronounced induction of the expression was observed
> at 12 and 24 h after irradiation. Of the doses tested, the one causing
> the highest stimulation was variable, particularly for UVA. For UVB the
> highest stimulation was at a dose of either 100 or 200 mJ/cm2 and for
> UVC was either 1 or 5 mJ/cm2. The highest increase of CRH mRNA
> expression was observed after 1 mJ/cm2 UVC [507 ± 2.15-fold change (fc)]
> and was also enhanced after UVA (10 J/cm2, 5.6 ± 0.19 fc) and UVB (100
> mJ/cm2, 3.5 ± 0.6 fc) for skin biopsies and 200 mJ/cm2, 8 ± 0.6 fc for
> co-cultures (Fig. 1). Stimulation of POMC followed the same trend, with
> the highest effect seen after UVC and UVB with the highest stimulation
> at 5 and 100 mJ/cm2, respectively. There was also a moderate effect
> after UVA, seen only at 10 J/cm2. The stimulation of MC1R expression was
> the greatest after UVC (all doses) and was nearly 100× higher than with
> the UVB (highest at 100 mJ/cm2), whereas UVA had no effect. Although
> MC2R expression was very low in untreated samples, its mRNA expression
> was induced by UVR, with the highest stimulation after UVB (200 mJ/cm2;
> 820 ± 0.24 fc) and a moderate stimulation after UVA (at 50 J/cm2), but
> only a minimal effect was seen after UVC (at 5 mJ/cm2). Expressions of
> the CYP11A1 and CYP11B1 genes encoding the GC synthesis pathway enzymes
> were noticeably increased after UVC exposure, especially with 1 mJ/cm2
> as well as after UVB. UVA stimulated the expression of CYP11A1 at 10 and
> 50 J/cm2, but it inhibited CYP11B1 gene expression (Fig. 1A). In
> co-cultured melanocytes and keratinocytes, the UVB-induced expression of
> HPA related genes expression consistently showed a dose-dependent
> stimulation, with the highest increases observed for either 100 or 200
> mJ/cm2 after 12 h of irradiation (Fig. 1B).
>
> Effect of UVR on CRH, ACTH, β-END, and COR production.
> The most remarkable effects were obtained after 24 h of irradiation. CRH
> production from the skin and co-cultures was stimulated in a
> dose-dependent manner by UVB and UVC (highest stimulation at 100 and 5
> mJ/cm2, respectively) but not by UVA (Fig. 2). Interestingly, the
> highest doses of UVC slightly but significantly decreased the CRH
> levels. The basal levels of ACTH were very low (below or at the border
> of detection). However, the ACTH concentration was significantly
> increased in a dose-dependent manner by UVB and UVC irradiation, which
> was highest at 100 and 5 mJ/cm2, respectively. Again, UVA had no effect
> on ACTH concentration (undetectable). β-END was endogenously produced
> both in skin and co-culture and its levels significantly increased after
> exposure to UVA, UVB and UVC in a dose-dependent manner with maximum
> stimulation at 20 J/cm2, 100 mJ/cm2 and 5 mJ/cm2, respectively. COR was
> also produced endogenously, and its levels increased after UVB and UVC
> irradiation in a dose-dependent manner, with UVA being without any effect.
>
> Changes in protein levels for CRH, POMC, P450scc (CYP11A1), and GR
> measured by western blotting.
> To complement gene expression and ELISA assays, we performed WB analyses
> on extracts from skin and co-cultures after UVB followed by 24 h of
> incubation (Fig. 3). The antibody against CRH recognized the 23-kDA
> pro-CRH protein, whose concentration was enhanced in a dose-dependent
> manner after UVB (Fig. 3A). Increased levels of POMC-derived 33-kDa
> protein were also seen after UVB by using an antibody directed against
> ACTH (Fig. 3B). In addition, a dose-dependent increase in the
> concentration of P450scc was evident after UVB irradiation (Fig. 3C).
> Remarkably, the same doses of UVB downregulated the levels of GR (Fig. 3D).
>
> Immunofluorescent in situ detection of CRH, proconvertase-1, ACTH,
> β-END, P450scc, and GR expressions followed by UVR.
> The basal expressions of CRH, proconvertase-1 (PC1), β-END, and P450scc
> antigens in control samples were low and limited mainly to basal or
> suprabasal epidermal layers, while only single ACTH-immunoreactive (IR)
> cells were seen (Fig. 4). However, there were significant and
> dose-dependent increases in CRH-, ACTH-, and β-END-IR signals after UVB,
> which were located in the cytoplasm of keratinocytes distributed through
> all layers of the epidermis (Fig. 4A). UVC also remarkably stimulated
> expression of all above with UVA having stimulatory effect mainly on
> CRH-IR and β-END-IR (Fig. 4B). The spatial distribution of these
> neuropeptides was similar to the that of the samples treated with UVB.
> The expression of GR-IR was high in nuclei of control epidermal
> keratinocytes, being seen in all layers of the epidermis. Exposure to a
> high dose of UVB (100 mJ/cm2) or UVC (5 mJ/cm2), but not to UVA,
> significantly decreased the immunopositive signal. The calculated values
> of immunopositive signal intensity for appropriate antigens expression
> are shown on inset graphs to Fig. 4, A and B. In contrast, P450scc-IR,
> while being low in control samples, significantly increased after UVB
> and UVC but only slightly after UVA. The antigen was localized in
> cytoplasm of basal keratinocytes, dermal fibroblasts, and other
> nonepithelial cells of the dermis (after UVC) (Fig. 4B).
>
> The chamber double staining of co-cultured melanocytes and keratinocytes
> showed that there were increases in immunofluorescence intensities for
> CRH, PC1, ACTH, β-END, and P450scc (localized to the cytoplasm),
> especially after UVB and UVC irradiation, with UVA lacking a visible
> effect on ACTH-IR (Fig. 4B). Double staining with melanocyte-specific
> MEL-5 antibody (FITC-green) demonstrated that not only keratinocytes but
> also melanocytes (yellow, as a result of digital overlapping of green
> and red fluorophors) expressed CRH, PC1, ACTH, β-END-IR, and P450scc
> after UVR (Fig. 4B).
>
> DISCUSSION
> This is the most comprehensive study yet on the effects of UVR on the
> cutaneous HPA axis. It shows wavelength-dependent changes in cutaneous
> expression of almost all of the main regulatory elements of the HPA axis
> at the levels of gene expression, protein, and final hormone (CRH, ACTH,
> β-END, and COR) concentrations. This indicates that UVR, a prevalent
> environmental stressor, can trigger local neuroendocrine stress
> responses, with CRH, POMC, and GC acting as coordinators of phenotypic
> responses aimed at stabilization or preservation of local homeostasis.
>
> These studies are in agreement with previous reports on UVB induction of
> CRH (32, 57), POMC, and MC1R (4, 5, 23, 27) expressions in cultured in
> vitro normal and malignant melanocytes and keratinocytes. There is also
> a striking resemblance between the range of biologically active UVB
> doses seen in this study with those demonstrated by Pawelek's group as
> the most effective for induction of melanin pigmentation (5, 24). The
> significance of our study is the demonstration of the
> wavelength-dependent capability of UVR to stimulate the expression of
> the crucial regulatory genes of the HPA axis. In general, the more
> energetic and shorter the wavelength, the stronger the effect, with UVC
> ≥ UVB > UVA. Nevertheless, there are some exceptions; for example, UVB
> was the most efficient in induction of the MC2R gene, whereas UVC had
> only a minor effect, and UVA inhibited CYP11B1 expression. Since UVC and
> UVB, but not UVA, show direct and prominent effects on DNA, which serves
> as a chromophore for both wavelengths (1), it is likely that the
> observed gene responses could occur via an SOS-like mechanism following
> DNA damage, similar to that which induces melanin pigmentation (13, 14).
> This conclusion is further substantiated by the protective role of the
> products of genes tested as in the following cases. First, CRH in
> addition to triggering the HPA axis, also has protective properties at
> tissue levels (16, 48). Second, POMC is processed to β-END, ACTH, and
> MSH peptides, which have respective, antinociceptive, anti-inflammatory,
> melanogenic, and protective activities in the skin (38, 40, 53). Third,
> the increased expression of steroidogenic genes leading to enhanced
> production of COR amplifies the above-mentioned protective properties to
> maintain the homeostasis in the skin. The above UV-induced,
> keratinocyte-derived growth factors can also regulate the activity of
> epidermal melanocytes in a context-dependent fashion as described above
> (38, 41). Finally, MC2R is crucial for ACTH-induced steroidogeneic
> activity (2, 6), while MC1R has antimutagenic and antiapoptotic
> activities, which are separate from melanin pigmentation (2, 19).
>
> The striking UVB- and UVC-restricted effects are best illustrated when
> one analyzes the levels of the final products. For both wavelengths, but
> not UVA, the boosted production of CRH, ACTH, and COR, with UVA being
> able to increase only β-END, was shown in whole skin extracts and in
> situ in the epidermis by IHC. The spatial pattern of UV-induced CRH,
> ACTH, and β-END expression in epidermis is consistent with previous
> studies on increased expression of POMC in the upper layers of the
> epidermis (3) and prodifferentiation effects of CRH (44, 48, 56). This
> could contribute to building the biological barrier in the outermost
> layer of skin to protect against environmental or biological insults (9,
> 31, 36, 41, 52). Increased expression of CYP11A1 in basal layers of the
> epidermis suggests strategic production of pregnenolone that could be
> used for steroid synthesis in either epidermal or superficial dermal
> compartments with multiple biological implications (49–51).
> Colocalization of those antigens in co-cultured melanocytes and
> keratinocytes indicates that both cell types play a role in building
> this barrier. In contrast, expression of GR was inhibited by UVB and
> UVC, which may indicate an epidermal mechanism designed to attenuate the
> long-term immunosuppression caused by cortisol throughout the
> downregulation of its receptor. At the present stage of our knowledge, a
> possible molecular mechanism regulating this process is speculative;
> however, it indicates a linkage to pathways activated by UVB and UVC but
> not UVA. Also, in many autoimmune skin disorders, the glucocorticoid
> resistance appears to be associated with a qualitative or quantitative
> deficiency in GR activity (11, 26). Thus, further careful studies
> including defining a role for GRα and GRβ isoforms and a mechanism
> regulating their expression and activity are required to uncover a
> biological and clinical significance of the above findings.
>
> POMC-derived peptides will also generate an immunosuppressive
> environment (2, 23) weakening the epidermal barrier, which however is
> compensated for by their induction of melanin (a factor protecting skin
> from environmental stress) production (38). The UV-induced stimulation
> of the expression of P450scc (CYP11A1), which is localized predominantly
> in the basal layer of epidermis and dermal fibroblasts, is consistent
> with the skin cell expression of this enzyme previously described by us
> (49). Furthermore, increased cleavage of cholesterol or its precursor by
> this enzyme in the upper layer of the epidermis would disrupt proper
> barrier formation, which requires cholesterol and its derivatives (8).
> The noticeable stimulation of β-END by all wavelengths of UV tested is
> consistent with the nociceptive action of this peptide and perhaps may
> explain the phenomenon of UV-induced “opioid-like” effects described in
> the literature (12, 54). Thus, the described differential expression of
> HPA axis elements induced by diverse UV wavelengths offers distinct but
> overlapping mechanisms by which local neuroendocrine pathways maintain
> the protection of cutaneous homeostasis. This extends far beyond the
> visionary concept that proposed a critical role of MSH receptor activity
> for UV-induced melanin pigmentation (24), a recognized protector against
> environmental stress. These mechanisms include different layers of local
> HPA axis activities, which could have developed in the integument (30)
> and which are independent of regulation of melanin pigmentation or
> represent reaction to sub- or lethal insults, for which the testing
> model has been UVC.
>
> Conclusion
>
> In summary, we have shown differential susceptibility of the cutaneous
> HPA axis following UV irradiation at diverse wavelengths. The most
> remarkable effects were mediated by highly energetic UVC and UVB,
> implying a dependence on a local stress response for their noxious
> activity. Stimulation of CRH and β-END within the epidermis by UVA
> indicates an overlapping (with the equivalent hypothalamic-pituitary
> axis) or alternative mechanisms induced by this wavelength. These
> differential responses of “cutaneous HPA” axis elements are consistent
> with differences in the mechanism of action of different UV wavelengths
> and their pathological consequences.
>
> GRANTS
> This study was supported by grants from National Science Foundation
> (IOS-0918934) and National Institutes of Health (AR-052190) to A. Slominski.
>
> DISCLOSURES
> No conflicts of interest, financial or otherwise, are declared by the
> author(s).
>
> ACKNOWLEDGMENTS
> We thank Dr. Zorica Janjetovic and Tae-Kang Kim for technical assistance.
>
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> Figures and Tables
> Table 1.
>
> Specification of UV lamps used in this study
>
> Bulb Name Destination Total Energy 100% (W/cm2) UVA, % UVB, % UVC, %
> Spectroline BLE-1500B UVA 6.26 × 10−3 98.8 0.016 0.0002
> USHIO G15T8E UVB 7.71 × 10−3 37.8 55 1.1
> Plusrite G15T8 Germ UVC 1.78 × 10−2 1.59 1.82 88.7
> Table 2.
>
> List of primers used for real-time RT-PCR
>
> Gene Name Primer Location Accession no. Forward Sequence, 5′-3′ Reverse
> Sequence, 5′-3′
> CRH Exon 2 NM_000756 ACTCAGAGACCAAGTCCA CTTCCCAGGCGCTTCGCAGGT
> POMC Exon 3 NM_000939 CTACGGCGGTTTCATGACCT CCCTCACTCGCCCTTCTTG
> MC1R Exon 1 NM_002386.3 ACTCCGTCTGCTCCAATGAC AGAGCTGGCAGCAAAGATG
> MC2R Exon 2 NM_000529 TCTTCAGCCTGTCTGTGATTG GGCACAGGATGAAGACCAG
> CYP11A1 Exon 4 NM_001099773 CCAGACCTGTTCCGTCTGTT AAAATCACGTCCCATGCAG
> CYP11B1 Exons 2/3 NM_000497.3 AGGTGGACAGCCTGCATC CCATTCAGGCCCATTCAG
> β-Actin NM_001101.3 CCAACCGCGAGAAGATGA CCAGAGGCGTACAGGGATAG
> Table 3.
>
> List of ELISA kits used
>
> Name Cat. No. Vendor
> CRH EK-019-06 Phoenix Pharmac., USA
> ACTH 21-ACTH-E01 Alpco Immuno., USA
> β-END S-1170 Peninsula Lab., USA
> CORTISOL KGE008 R&D Systems, UK
> Table 4.
>
> List of primary antibody used for Western blotting or immunohistochemistry
>
> Antigen Host Titer Source
> Corticotropin-releasing hormone, CRH* (PBL rC70) Rabbit 1:2,000 Prof.
> Wylie Vale, Salk Inst., USA
> Proconvertase-1, PC1 Rabbit 1:1,000 Dr. Iris Lindberg, USA
> Adrenocorticotropic hormone, ACTH*,# Rabbit 1:500 Dr. Allen, USA
> Adrenocorticotropic hormone, ACTH (AFP-6328031) Rabbit 1:1,000 Dr.
> Parlow, NIDDKD, USA
> β-Endorphins, β-END* Rabbit 1:2,000 Dr. Allen, USA
> Cytochrome P-450 side-chain-cleavage, P450scc Rabbit 1:1,000 Prof.
> Robert Tuckey, Univ. of Western Australia
> Glucocorticoid receptor, GR (sc-8992) Rabbit 1:500 Santa Cruz Biotech., USA
> MEL-5 (MA02026) Mouse 1:300 Signet, USA
> β-Actin-HRP, β-actin# (A3854) Mouse 1:10,000 Sigma, USA
> *In general, cross-reactivity of antibodies against β-END and ACTH with
> noncorresponding POMC peptides has been reported to be <1% (1, 33, 40).
> Anti CRH antibody had very low cross-reactivity to other hypothalamic
> peptides (25).
> #Antibody used exclusively for Western blot.
> Fig. 1.
>
> Comparison of the expression level of selected HPA axis genes (CRH,
> POMC, MC1R, MC2R, CYP11A1, CYP11B1) after UVA, UVB, or UVC irradiation
> followed by 12 h of cultured human skin (A), and co-cultured HEKn/HEMn
> after UVB (B). See text for definitions. Values on the x-axis are doses
> of irradiation: mJ/cm2 for UVB and UVC and J/cm2 for UVA. On the y-axis
> are provided the mRNA expression levels as a fold change using a
> comparative ΔΔCT method with β-actin. Real-time RT-PCR presented as
> means ± SD.
>
> Fig. 2.
>
> UVB irradiation enhances CRH, ACTH, β-END, and cortisol (COR) production
> in the skin (A) and in HEKn/HEMn co-culture (B) followed by 24 h of
> culture. ELISA study presented as means ± SD.
>
> Fig. 3.
>
> Quantitative comparison of selected HPA axis protein concentrations,
> measured by Western blotting, relative to β-actin. Primary antibodies,
> listed in Table 4, were directed against CRH (A), ACTH (B), P450scc (C),
> GR (D).
>
> Fig. 4.
>
> Immunofluorescent examples of in situ localization of CRH-, PC1-, ACTH-,
> β-END-, P450scc-, and GR-immunoreactive (IR) signals (CY3-red) in human
> skin. A: dose-dependent increase in CRH-, ACTH-, and β-END-IR signals
> after UVB irradiation. B: wavelength-dependent changes in selected
> antigen expression shown as single (skin) and double (co-culture)
> staining with the use of melanocyte-specific markers [mouse MEL-5
> antibody (FITC-green)]. Graphs show quantitative (means ± SD) comparison
> of immunoreactive signal intensity for appropriate antigens as a
> function of dose and/or wavelength. All viable nuclei were
> counterstained with DAPI (blue). Magnification ×200 (skin) and ×400
> (co-culture).
>
> Articles from American Journal of Physiology - Endocrinology and
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