不同黑素细胞群在有色毛囊重建中作用的研究

目的观察不同种属小鼠的毛囊细胞能否嵌合重建有色毛囊, 探讨不同黑素细胞群在小鼠有色毛囊重建中的作用。方法选取C57BL/6J、BALB/C胎鼠或乳鼠皮肤, 分离出表皮细胞群、毛囊上皮细胞群和真皮细胞群, 培养、纯化从表皮细胞群获得的表皮黑素细胞。实验包含三部分, ①乳鼠C57BL/6J毛囊重建实验:分为表皮细胞+毛囊上皮细胞组、真皮细胞组;②嵌合毛囊重建实验:分为乳鼠C57BL/6J真皮细胞组、乳鼠BALB/C真皮细胞组、乳鼠BALB/C真皮+乳鼠C57BL/6J真皮细胞组、胎鼠BALB/C真皮细胞+胎鼠C57BL/6J真皮细胞组;③有色毛囊重建实验:分为乳鼠BALB/C真皮细胞+乳鼠C57BL/6J表皮细胞组、乳鼠BALB/C真皮细胞+乳鼠C57BL/6J毛囊上皮细胞组、乳鼠BALB/C真皮细胞+培养的C57BL/6J表皮黑素细胞组。采用小室移植法将不同细胞接种于裸鼠的背部, 每组4只。于移植后4周和8周, 通过大体观察、组织学及免疫荧光评估毛囊重建情况。结果移植后4周和8周, 乳鼠C57BL/6J毛囊重建实验中(本部分实验2组共8只BALB/C裸鼠, 7只存活, 1只因创面感染死亡...     

Irradiation of protoporphyric mice induces down-regulation of epidermal eicosanoid metabolism.

This study investigated the effect of radiation on clinical and histologic changes, and on cutaneous eicosanoid metabolism, in Skh:HR-1 hairless albino mice rendered protoporphyric by the administration of collidine. At 0.1-18 h after exposure to 12 kJ/m2 of 396-406 nm irradiation, thicknesses of back skin and ears were measured, and histologic changes were evaluated by using hematoxylin and eosin (H-E) and Giemsa's stains. Activities of eicosanoid-metabolizing enzymes in epidermal and dermal homogenates were assessed by incubating the tissue homogenates with 3H-AA, followed by quantitation of the eicosanoids generated by radio-TLC. In irradiated protoporphyric mice, an increase of back-skin thickness was noted at 0.1 h, reaching a peak at 18 h, whereas maximal increase in ear thickness was observed at 12 h. Histologic changes included dermal edema, increased mast cell degranulation, and mononuclear cells in the dermis. In these irradiated protoporphyric animals, generations of 6 keto-PGF1a, PGF2a, PGE2, PGD2, and HETE by epidermal eicosanoid-metabolizing enzymes were markedly suppressed at all the timepoints studied. Dermal eicosanoid-metabolizing enzymes of irradiated protoporphyric mice generated increased amounts of PGE2 and HETE at 18 h, probably reflecting the presence of dermal cellular infiltrates. The suppression of the activities of epidermal eicosanoid-metabolizing enzymes was prevented by intraperitoneal injection of WR-2721, a sulfhydryl group generator, prior to irradiation, suggesting that the suppression was secondary to photo-oxidative damage of the enzymes during the in vivo phototoxic response. These results suggest that the effect of protoporphyrin and radiation on cutaneous eicosanoid metabolism in this animal model in vivo is that of a down regulation of the activities of epidermal eicosanoid-metabolizing enzymes.     

真菌线粒体基因组计划的研究进展

线粒体基因组是真菌等生物的一个鉴定和分类的遗传标志,对系统发生分析有重要的意义。近年来加拿大学者提出了真菌线粒体基因组计划。真菌线粒体基因组均为闭合环形双链DNA,基因组的大小为10Kb～80kb,通常包括编码呼吸链亚基的基因、编码ATP合成酶复合物亚基的基因、编码核糖体RNA的基因和tRNA基因。真菌线粒体基因组具有丰富的多态性,可以作为真菌不同物种的DNA指纹用于鉴别,并且可对病原真菌进行科学的分类和亲缘分析。     

Mitochondrial inclusions in keratinocytes of hairless mouse skin exposed to UVB radiation

Mitochondrial inclusions were observed in keratinocytes during an ultrastructural investigation of the skin of hairless mice exposed to UVB radiation. Mice were irradiated 3 times a week for 5-6 months with sunlamps at individual doses seldom exceeding 0.06 J/cm2. Strips of dorsal skin were processed for electron microscopic examination; blocks were sectioned to include both epidermis and dermis. Mitochondrial inclusions were observed in keratinocytes of the basal, spinous and granular layers. They were spherical in shape and of moderate and homogeneous electron density. Mitochondria toward the upper regions of the epidermis were swollen and had fragmented cristae; mitochondria in the lower areas of the epidermis usually contained smaller and less dense inclusions and intact or partially disrupted cristae. Because mitochondria are essential in providing the energy for cellular function, keratinocyte mitochondrial damage induced by UVB radiation may have serious pathological consequences. Possible mechanisms involved in mitochondrial inclusion formation are suggested.     

Anatomical distribution analysis reveals lack of Langerin+ dermal dendritic cells in footpads and tail of C57BL/6 mice

Epidermal Langerhans cells (LCs) and dermal dendritic cells (dDCs) capture cutaneous antigens and present them to T‐cells in lymph nodes (LNs). The function of LCs and Langerin+ dDCs was extensively studied in the mouse, but their anatomical repartition is unknown. Here, we found LCs in back skin, footpads and tail skin of C57BL/6, BALB/c, 129/Sv and CBA/J mice. Langerin+ dDCs were readily observed in back skin of all strains, but only in footpads and tail of BALB/c and CBA/J mice. Similarly, while LCs were equally present in all LNs and strains, Langerin+ dDCs were found in popliteal LNs (draining footpads) only in BALB/c and CBA/J mice. The sciatic LNs, which we identified as the major tail‐draining lymphoid organ, were devoid of Langerin+ dDCs in all strains. Thus, functionally different DCs reside in different skin areas, with variations among mouse strains, implying a potential impact on the cutaneous immune reaction.     

Histamine metabolism in skin of MRL/I mice

Summary Of several murine autoimmune models, MRL/Mp-lpr/lpr (MRL/l) mice are the most attractive from a dermatopathological point of view, because their skin lesions resemble the erythematous lesions of systemic lupus erythematosus (SLE). In order to clarify the pathogenesis of lupus dermatoses, histamine and its metabolizing activities in the skin of MRL/l mice were investigated. The specific activities of histamine-N-methyltransferase (HMT) in the skin of MRL/l mice were significantly lower than those in the skin of control mice i.e., MRL/Mp-+/+ (MRL/n), C57BL/6J, and BALB/c mice. In the dorsal lesional skin of MRL/l mice, HMT activities were markedly lower than those in normal abdominal skin. In addition, age-related analysis of HMT levels in the dorsal skin of MRL/l mice revealed that HMT activities reached their maximum at the age of 2 or 3 months and then decreased at 4 or 5 months when skin manifestation appeared: however, HMT activities in the abdominal skin increased almost linearly with age. There were no significant differences in histamine content in these mice, and diamine-oxidase activities were not detected in any skin specimens. From these results, it is suggested that impaired histamine metabolism is a particular biochemical feature of the skin of MRL/l mice.This is the fifth part of a series of papers entitled Pathogenesis of Lupus Dermatoses in Autoimmune Mice     

Induction of eosinophil‐ and Th2‐attracting epidermal chemokines and cutaneous late‐phase reaction in tape‐stripped skin

Abstract: Skin barrier damage induces various harmful or even protective reactions in the skin, as represented by enhancement of keratinocyte cytokine production. To investigate whether acute removal of stratum corneum modulates the production of chemokines by epidermal cells, we treated ears of BALB/c and C57BL/6 mice by tape‐stripping, or acetone‐rubbing as a control of acute barrier disruption procedure. There was no difference between the tape‐stripped and acetone‐rubbed skin sites in the increased and recovered levels of transepidermal water loss. The mRNA expression levels of all the chemokines tested, including Th1 chemokines (CXCL10, CXCL9 and CXCL11), Th2 chemokines (CCL17 and CCL22) and eosinophil chemoattractant (CCL5), were higher in the epidermal cells from BALB/c than in those of C57BL/6 mice. In particular, CCL17, CCL22 and CCL5 were remarkably elevated in BALB/c mice and augmented by tape‐stripping more markedly than acetone‐rubbing, whereas Th1 chemokines were enhanced by acetone‐rubbing more remarkably. Tape‐stripping induced dermal infiltration of eosinophils in BALB/c but not C57BL/6 mice. In a contact hypersensitivity model, where BALB/c mice were sensitized on the abdomen and challenged on the ears with fluorescein isothiocyanate, mice exhibited higher ear swelling responses at the late‐phase as well as delayed‐type reactions, when challenged via the tape‐stripped skin. The challenge via tape‐stripped skin augmented the expression of IL‐4 and CCR4 in the skin homogenated samples, indicating infiltration of Th2 cells. These findings suggest that acute barrier removal induces the expression of Th2 and eosinophil chemokines by epidermal cells and easily evokes the late phase reaction upon challenge with antigen.     

Creatine supplementation normalizes mutagenesis of mitochondrial DNA as well as functional consequences

Mutations of mitochondrial (mt) DNA play a role in neurodegeneration, normal aging, premature aging of the skin (photoaging), and tumors. We and others could demonstrate that mtDNA mutations can be induced in skin cells in vitro and in normal human skin in vivo by repetitive, sublethal ultraviolet (UV)-A-irradiation. These mutations are mediated by singlet oxygen and persist in human skin as long-term biomarkers of UV exposure. Although mtDNA exclusively encodes for the respiratory chain, involvement of the energy metabolism in mtDNA mutagenesis and a protective role of the energy precursor creatine have thus far not been shown. We assessed the amount of a marker mutation of mtDNA, the so-called common deletion, by real-time PCR. Induction of the common deletion was paralleled by a measurable decrease of oxygen consumption, mitochondrial membrane potential, and ATP content, as well as an increase of matrix metalloproteinase-1. Mitochondrial mutagenesis as well as functional consequences could be normalized by increasing intracellular creatine levels. These data indicate that increase of the energy precursor creatine protects from functionally relevant, aging-associated mutations of mitochondrial DNA.     

Dermal dendritic cells,but not Langerhans cells,are critical in murine single epicutaneous sensitization

A murine repeated protein‐patch model has been established to study epicutaneous sensitization in atopic dermatitis. This model has shown a predominant Th2 and a weak Th1 response in both BALB/c and C57BL/6 mice. However, Th responses induced in the repeated model are not consistent with the generally accepted theory that BALB/c and C57BL/6 mice are Th2 and Th1 prone and are representatives of human atopy and non‐atopy, respectively. In this study, a single protein‐patch model was established, which showed in addition to the Th2 response, a remarkable Th1 response in C57BL/6 mice, but not in BALB/c mice. Moreover, using muLangerin‐DTR mice, we demonstrated that dermal dendritic cells, but not Langerhans cells, are critical in single epicutaneous sensitization in both strains of mice.     

Strain-dependent effects of the histamine H₄ receptor antagonist JNJ7777120 in a murine model of acute skin inflammation

The effects of the histamine H(4) receptor antagonist JNJ7777120 were evaluated in a model of acute skin inflammation induced by local application of croton oil. The influence of strain on the effect of JNJ7777120 was investigated in four different mouse strains (CD-1, NMRI, BALB/c and C57BL/6J). In CD-1 mice, JNJ777720 (30-100 mg/kg subcutaneously, s.c.) exerted a dose-dependent inhibition of croton oil-induced ear inflammation and polymorphonuclear leucocyte infiltration, as confirmed by histological evaluation of ear tissues. JNJ7777120 (30-100 mg/kg) did not reduce ear oedema in NMRI, BALB/c or C57BL/6J mice. The positive control, dexamethasone (2 mg/kg s.c.) induced significant anti-inflammatory effects only in CD-1 and NMRI mice. In these strains, also the histamine H(1) -receptor blocker pyrilamine (30 mg/kg s.c.) significantly reduced ear oedema at 2 h after croton oil challenge, being as effective as JNJ7777120 in CD-1 mice. Taken together, these data demonstrate that the H(4) receptor antagonist JNJ7777120 may reduce acute croton oil-induced skin inflammation as effectively as H(1) receptor blockade. However, present experiments evidenced for the first time marked strain-related differences in the JNJ7777120 pharmacological activity, which have to be carefully considered when using this ligand to characterize histamine H(4) receptor functions in murine models and translating preclinical data to clinical human settings.     

Multifunctional analysis of the interaction of anthralin and its metabolites anthraquinone and anthralin dimer with the inner mitochondrial membrane

Summary We studied the interaction of the antipsoriatic compound anthralin (1.8-dihydroxy-9-anthrone), and its metabolites anthraquinone (1.8-dihydroxy-9.10-anthraquinone) and anthralin dimer (1.8.1.8.-tetrahydroxy-10.10-bis-9[10]-dianthrone) with the inner mitochondrial membrane. Mitochondrial membrane functions such as ubiquinone redox equilibria, redox status of iron sulfur clusters, cyanide-sensitive and cyanide-insensitive oxygen consumption, adenosine triphosphate (ATP) synthesis, ATP hydrolysis, and adenine nucleotide content of mitochondria were analyzed. Anthralin is an inhibitor of mitochondrial oxygen uptake in the presence of ADP and substrate (cyanide-sensitive respiration), inhibits ATP synthesis without affecting ATP hydrolysis, and depletes mitochondria of ATP. Anthralin dimer is a much weaker inhibitor of mitochondrial functions and anthraquinone is almost inactive. Anthralin, but not anthraquinone and anthralin dimer, reverses uncoupler stimulated oxygen consumption, stimulates cyanide-insensitive respiration, reduces mitochondrial ubiquinone-9 and -10 to the corresponding ubiquinols and reduces mitochondrial iron sulfur clusters. Anthralin may induce formation of reactive oxygen species by enhancing autoxidation of mitochondrial components and/or by catalyzed oxidation of anthralin. Taken together, anthralin acts as an electron donor to inner mitochondrial membrane associated redox components, inhibits the electron transport chain, and has an oligomycin-like effect. Anthralin dimer and anthraquinone do not function as electron donors and act by a different reaction mechanism. Respiratory measurements in human keratinocytes revealed similar results as obtained with isolated mitochondria. We suggest that modulation of membrane redox status may be a common concept of anthralin action in target cells such as keratinocytes and neutrophils.     

The antipsoriatic compound anthralin influences bioenergetic parameters and redox properties of energy transducing membranes

Bioenergetic parameters and redox properties of energy transducing membranes in rat liver mitochondria and cyanobacteria were investigated in the presence of the antipsoriatic compound anthralin (1,8-dihydroxy-9-anthrone). Transmembrane pH and electrical gradients were determined using electron paramagnetic resonance spectroscopy. In mitochondria, ubiquinones 9,10 and other redox components of the electron transport chain are reduced by anthralin; the proton motive force is increased. In the absence of ADP, anthralin slightly stimulates mitochondrial cyanide-insensitive oxygen consumption. It is suggested that increased cyanide-insensitive respiration is due to enhanced autoxidation of mitochondrial components and/or catalyzed oxidation of anthralin. In the presence of ADP mitochondrial respiration is decreased, and ATP synthesis is inhibited. Uncoupler-induced mitochondrial respiration is also decreased by anthralin, indicating inhibition of the electron transport chain. In the cyanobacterium Synechococcus PCC 6311 anthralin increases the pH gradient and decreases ATP levels. Thus, anthralin acts as an electron donor to membrane associated redox components and inhibits ATP synthesis in two different biologic systems. In human keratinocytes oxygen metabolism is influenced by anthralin in a similar pattern as in isolated mitochondria, and ATP content is decreased. Because anthralin reacts with redox components in different biologic membranes, alterations of subcellular/cellular redox status and energy metabolism might contribute significantly to its antiproliferative activity.     

T helper type 1 cytokines and keratinocyte growth factor play a critical role in pseudoepitheliomatous hyperplasia initiation during cutaneous leishmaniasis

Pseudoepitheliomatous hyperplasia (PEH) is an exuberant proliferation of the epidermis. The underlying mechanism(s) that lead to PEH have not been completely elucidated. Here, we characterize PEH during the healing stages of cutaneous leishmanial ulcers in mice. During experimental cutaneous leishmaniasis (CL) C57BL/6 mice produce PEH, and BALB/c do not. A series of immunohistochemical and immunological studies were performed to identify the secretory products of PEH regulation. We observed that the distribution of TNF-α and IFN-γ under PEH had a stripe-like diffuse pattern and localized in the upper part of the papillary dermis directly under the proliferating epidermis. Macrophages were identified as the major source of TNF-α (56.3%). The importance of IFN-γ and TNF-α in PEH development was proven by the initiation of PEH after three intralesional injections of TNF-α and IFN-γ every three days in infected BALB/c mice. In C57BL/6 mice, keratinocyte growth factor (KGF) expressing cells were found immediately under the basal membrane of the hyperplastic epidermis in comparison with sporadic KGF positive cells deep in the dermis of BALB/c mice. Quantitative RT-PCR analysis demonstrated increased KGF and KGF receptor expression in uninfected C57BL/6 mice as compared to BALB/c mice. These data indicate that Th1 cytokines and KGF play a critical role in PEH initiation during CL.     

Cell-density-dependent changes in mitochondrial membrane potential and reactive oxygen species production in human skin cells post sunlight exposure

Background: Solar ultraviolet radiation (UVR) is the principal etiological factor in skin carcinogenesis. In vivo and in vitro studies have demonstrated previously that oxidative DNA damage, mitochondrial mass and mitochondrial membrane potential (MMP) changes are associated with skin cell response to UVR stress. Methods: Spontaneously immortalized human skin keratinocytes were irradiated with increasing sub‐lethal doses of simulated sunlight irradiation (SSI) using a Q‐Sun solar simulator. The effects of SSI on reactive oxygen species (ROS) formation, mitochondrial mass and MMP were then determined. Results: SSI induced mitochondrial mass increase post low SSI (0.25–2.5 J/cm²), whereas higher SSI doses (5.0 and 7.5 J/cm²) decreased mitochondrial mass. Mitochondrial mass increased with time post 5.0 J/cm² irradiation and all changes in mass were independent of cell density status. Changes in ROS and MMP were cell density dependent. Additionally, an inverted dose‐dependent decrease in ROS formation was observed 3 h post SSI with the lower SSI dose (0.25 J/cm²). Conclusions: Observations from the present study suggest that changes in the cell's microenvironment (modeled through varying cell density) influence changes in MMP and ROS detoxifying responses in sun‐exposed skin cells.     

IL-1 signalling is dispensable for protective immunity in Leishmania-resistant mice

Leishmaniasis is a parasitic disease affecting ～12 million people. Control of infection (e.g. in C57BL/6 mice) results from IL-12-dependent production of IFNγ by Th1/Tc1 cells. In contrast, BALB/c mice succumb to infection because of preferential Th2-type cytokine induction. Infected dendritic cells (DC) represent important sources of IL-12. Genetically determined differences in DC IL-1α/β production contribute to disease outcome. Whereas the course of disease was not dramatically altered in IL-1RI(-/-) mice, local administration of IL-1α to infected C57BL/6 mice improved disease outcome. To definitively elucidate the involvement of IL-1 in immunity against leishmaniasis, we now utilized IL-1α/β-double-deficient C57BL/6 mice. C57BL/6 mice are believed to be a good surrogate model for human, self limited cutaneous leishmaniasis (CL). Leishmania major-infected IL-1α/β(-/-) mice were resistant to experimental CL comparable to controls. In addition, DC-based vaccination against leishmaniasis in C57BL/6 mice was independent of IL-1. Thus, in Leishmania-resistant C57BL/6 mice, IL-1 signalling is dispensable for protection.     

Optimization of tetrachlorosalicylanilide and ultraviolet A doses a sensitization and challenge for contact photosensitivity in the mouse

Summary We studied contact photosensitivity (CPS) to tetrachlorosalicylanilide (TCSA) in BALB/cJ mice with various doses of TCSA and UVA at sensitization and challenge. From these studies we recommend the following protocol: sensitization on days 0 and 1 with 50 l of 1% TCSA followed by 3 J/cm² of UVA, and challenge on day 7 with 10 l of 3% TCSA followed by 6 J/cm² of UVA. This gave an ear swelling response of 27.4±0.6×10^-3 (mean±standard error). We also demonstrated that there is reciprocity between volume and concentration of TCSA at sensitization but not between TCSA and UVA doses at sensitization.This study was supported by the Medical Research Council of Canada and the Ontario Ministry of Health. This work was presented in part at the 1988 annual meeting of the Society for Investigative Dermatology, Washington, D.C.     

Insufficient generation of Th17 cells in IL‐23p19‐deficient BALB/c mice protects against progressive cutaneous leishmaniasis

Healing of leishmaniasis—a parasitic skin disease—is associated with high levels of secreted interferon (IFN)γ and IL‐12 in resistant C57BL/6 mice and humans. Susceptible BALB/c mice predominantly react with a Th17/Th2/Treg‐related immune response and finally succumb to infection. Previously, we showed that BALB/c IL‐17A^?/? mice are protected against Leishmania (L.) major infections, indicating that IL‐17A—predominantly produced by Th17 cells—plays an important role for disease outcome. We now investigated DC‐derived cytokines and finally identified IL‐23p19 as key cytokine responsible for induction of Leishmania‐specific Th17 cells that play an important role for progressive disease in susceptible BALB/c mice.     

Effect of ultraviolet irradiation on mast cell-deficient W/Wv mice

The effect of UV irradiation on the skin was investigated in (WB-W/+) X (C57BL/6J-Wv/+)F1-W/Wv mice, which are genetically deficient in tissue mast cells. Their congenic littermates (+/+) and normal albino mice (ICR or BALB/c) were used as controls. Mice were irradiated with 500 mJ/cm2 of UVB and the increment of ear thickness was measured before and 6, 12, and 24 h after irradiation. Ear swelling in W/Wv mice at 12 and 24 h after irradiation was significantly smaller than that in +/+ and ICR mice. In contrast, the number of sunburn cells formed 24 h after UVB irradiation (200 or 500 mJ/cm2) was similar in W/Wv, +/+ and ICR mice. On the other hand, when mice were treated with 8-methoxy-psoralen (0.5%) plus UVA irradiation (4 J/cm2) (topical PUVA), ears of W/Wv and BALB/c mice, which were both white in color, were thickened similarly 72 h after treatment, but less swelling was observed in +/+ mice, which were black in skin color. The amount of prostaglandin D2 (PGD2) in ears, determined by radioimmunoassay specific for PGD2, was elevated 3-fold in +/+ and ICR mice at 3 h after irradiation with 500 mJ/cm2 of UVB in comparison with basal level without irradiation. However, such elevation was not observed in W/Wv mice. These results suggest that mast cells play an important role in UVB-induced inflammation, and PGs from mast cells are responsible at least in part for the development of this reaction. However, neither mast cells nor PGs contribute to the sunburn cell formation and ear swelling response by PUVA treatment.     

Experimental Murine Protoporphyria Induced by Griseofulvin (GF): The Relationship between Hepatic Porphyrin Levels and Liver Function Test Values in Mice Treated with GF

To investigate the hepatic abnormalities accompanying experimental protoporphyria due to griseofulvin (GF), liver function test values and porphyrin levels in mice were assayed at days 2, 4, 8, and 16 after starting the administration of 0.5% GF feed. Furthermore, in an attempt to elucidate the harmful effects of GF on liver functions, the above mentioned assay was also performed after the feed was discontinued in mice given 0.5% GF feed for 16 days. The hepatic protoporphyrin (PP) level had already risen by day 2, but the erythrocytic PP level was within normal limits at that time. Hepatic PP levels increased gradually, followed by an increase in erythrocytic PP levels. The variation in liver function test values roughly paralleled the porphyrin levels. Over the time span of the response to GF, the variations in the serum glutamate oxaloacetate transaminase (S-GOT) levels, serum glutamate pyruvate transaminase (S-GPT) levels, and leucine amino peptidase (LAP) levels resembled those in hepatic PP. On the other hand, the changes in alkaline phosphatase (ALP) levels paralleled those of the erythrocytic PP levels. Erythrocytic and fecal protoporphyrin levels decreased to the normal level one month after the discontinuation of GF administration, but the hepatic protoporphyrin level still was 53.6 times higher than the normal level two months after switching to normal feed. The values of liver function tests had returned to within the normal range after one month. By the fourth day after the administration of GF, a brown pigmented material could be observed around the hepatocytes and the Glisson sheath; the amount of this material increased day by day. Its amount gradually decreased after cessation of GF. These results suggested that the hepatic abnormalities were not induced by the deposition of PP in the liver, but by the direct toxicity of GF. This means that GF-induced protoporphyria mice are not suitable for investigating porphyric damage to the liver because of the strong hepatic intoxication by GF. However, they may be useful for studies of the removal of deposits of porphyrin granules from the liver.     

Bleomycin‐induced fibrosis in MC1 signalling‐deficient C57BL/6J‐Mc1re/e mice further supports a modulating role for melanocortins in collagen synthesis of the skin

The melanocortin‐1 receptor (MC₁) binds α‐melanocyte‐stimulating hormone (α‐MSH) with high affinity and has a physiological role in cutaneous melanin pigmentation. Previously, we reported that human dermal fibroblasts also express functional MC₁. α‐MSH suppressed transforming growth factor‐β₁‐ and bleomycin (BLM)‐induced collagen synthesis in vitro and in vivo. Using MC₁ signalling‐deficient C57BL/6J‐Mc1r^e/e mice, we tested as to whether MC₁ has a regulatory role on dermal collagen synthesis in the BLM model of scleroderma. Notably, mice with a C57BL/6J genetic background were previously shown to be BLM‐non‐susceptible. Interestingly, treatment of C57BL/6J‐Mc1r^e/e but not of C57BL/6J‐wild‐type mice with BLM increased cutaneous collagen type I content at RNA and protein level along with development of skin fibrosis. Cutaneous levels of connective tissue growth factor and monocyte chemotactic protein‐1 were also increased in BLM‐treated C57BL/6J‐Mc1r^e/e mice. Primary dermal fibroblasts from C57BL/6J‐wt mice further expressed MC₁, suggesting that these cells are directly targeted by melanocortins to affect collagen production of the skin. Our findings support the concept that MC₁ has an endogenous regulatory function in collagen synthesis and controls the extent of fibrotic stress responses of the skin.