Ultraviolet a induces endoplasmic reticulum stress response in human dermal fibroblasts.

The endoplasmic reticulum (ER) stress response is a cytoprotective mechanism against the accumulation of unfolded proteins in the ER (ER stress) that consists of three response pathways (the ATF6, IRE1 and PERK pathways) in mammals. These pathways regulate the transcription of ER-related genes through specific cis-acting elements, ERSE, UPRE and AARE, respectively. Because the mammalian ER stress response is markedly activated in professional secretory cells, its main function was thought to be to upregulate the capacity of protein folding in the ER in accordance with the increased synthesis of secretory proteins. Here, we found that ultraviolet A (UVA) irradiation induced the conversion of an ER-localized sensor pATF6α(P) to an active transcription factor pATF6α(N) in normal human dermal fibroblasts (NHDFs). UVA also induced IRE1-mediated splicing of XBP1 mRNA as well as PERK-mediated phosphorylation of an α subunit of eukaryotic initiation factor 2. Consistent with these observations, we found that UVA increased transcription from ERSE, UPRE and AARE elements. From these results, we concluded that UVA irradiation activates all branches of the mammalian ER stress response in NHDFs. This suggests that the mammalian ER stress response is activated by not only intrinsic stress but also environmental stress.

The epidermal stem cell factor is over-expressed in lentigo senilis: implication for the mechanism of hyperpigmentation.

We previously reported that accentuated expression of the endothelin-1 (ET-1)/endothelin B receptor (ET(B)R) cascade is involved in the mechanism of hyperpigmentation in lentigo senilis (LS) lesions. The paracrine mechanism underlying ultraviolet B (UVB)-induced hyperpigmentation in the skin may involve the stimulation of the ET-1/ET(B)R cascade as well as the stem cell factor (SCF)/SCF receptor cascade. Therefore, we used RT-PCR and immunohistochemistry to determine whether accentuated expression of the SCF/SCF receptor cascade is also associated with the mechanism of hyperpigmentation in epidermal LS lesions. RT-PCR analysis demonstrated the increased expression of mRNA transcripts for SCF (n=7), but not for SCF receptor (n=6) or growth-related oncogene alpha (GROalpha) (n=4) in LS lesions. Immunohistochemistry revealed markedly stronger staining for SCF but not for GROalpha or basic fibroblast growth factor (bFGF) in the lesional epidermis compared with the perilesional epidermis. This increased staining for SCF was corroborated by western blotting analysis for SCF expression in the lesional epidermis. These findings suggest that in addition to the stimulated expression of the ET-1/ET(B)R cascade, the accentuated expression of SCF in lesional skin plays an important role in the mechanism involved in the epidermal hyperpigmentation of LS.

Sphingosylphosphorylcholine is a Melanogenic Stimulator for Human Melanocytes.

As lysosphingolipids have multiple bio-modulator functions in various types of cells, we measured the biological effects of sphingosylphosphorylcholine (SPC) on cultured human melanocytes to determine whether these lysosphingolipids have the potential to activate these cells. The addition of SPC to cultured human melanocytes significantly stimulated DNA synthesis assessed by [3H]thymidine and melanogenesis assessed by the release of [3H]H2O (tyrosinase activity), the incorporation of [14C]thiouracil (melanin synthesis) and dopa-oxidase activity. Reverse transcription-polymerase chain reaction of RNA isolated from human melanocytes exposed to SPC revealed an upregulation of mRNA transcripts for tyrosinase, microphthalmia-associated transcription factor-M, endothelin B receptor and the stem cell factor receptor, c-kit. An increase in expression of tyrosinase and c-kit proteins was also demonstrated by Western blot analysis. This stimulation of melanogenesis by SPC was associated with a marked increase in the phosphorylation of extracellular signal-regulated kinase 1/2. These results suggest that SPC may be a melanogenic stimulator of human melanocytes inducing the coordinated upregulated expression of various melanogenic molecules, including c-kit.

Decreased levels of sphingosine, a natural antimicrobial agent, may be associated with vulnerability of the stratum corneum from patients with atopic dermatitis to colonization by Staphylococcus aureus.

The stratum corneum of the skin of patients with atopic dermatitis is highly susceptible to colonization by various bacteria, including Staphylococcus aureus. The defense system of the skin against bacterial invasion appears to be significantly disrupted in atopic dermatitis skin, but little is known about the defense mechanism(s) involved. As one sphingolipid metabolite, sphingosine is known to exert a potent antimicrobial effect on S. aureus at physiologic levels, and it may play a significant role in bacterial defense mechanisms of healthy normal skin. Because of the altered ceramide metabolism in atopic dermatitis, the possible alteration of sphingosine metabolism might be associated with the acquired vulnerability to colonization by S. aureus in patients with atopic dermatitis. In this study, we measured the levels of sphingosine in the upper stratum corneum from patients with atopic dermatitis, and then compared that with the colonization levels of bacteria in the same subjects. Levels of sphingosine were significantly downregulated in uninvolved and in involved stratum corneum of patients with atopic dermatitis compared with healthy controls. This decreased level of sphingosine was relevant to the increased numbers of bacteria including S. aureus present in the upper stratum corneum from the same subjects. This suggests the possibility that the increased colonization of bacteria found in patients with atopic dermatitis may result from a deficiency of sphingosine as a natural antimicrobial agent. As for the mechanism involved in the decreased production of sphingosine in atopic dermatitis, analysis of the activities of ceramidases, major sphingosine-producing enzymes, revealed that, whereas the activity of alkaline ceramidase did not differ between patients with atopic dermatitis and healthy controls, the activity of acid ceramidase was significantly reduced in patients with atopic dermatitis and this had obvious relevance to the increased colonization of bacteria in those subjects. Further, there was a close correlation between the level of sphingosines and acid ceramidase (r = 0.65, p < 0.01) or ceramides (r = 0.70, p < 0.01) in the upper stratum corneum from the same patients with atopic dermatitis. Collectively, our results suggest the possibility that vulnerability to bacterial colonization in the skin of patients with atopic dermatitis is associated with reduced levels of a natural antimicrobial agent, sphingosine, which results from decreased levels of ceramides as a substrate and from diminished activities of its metabolic enzyme, acid ceramidase.