Review of the innate immune response in acne vulgaris: activation of Toll-like receptor 2 in acne triggers inflammatory cytokine responses

Acne vulgaris is a common disorder that affects 40-50 million people in the USA alone. The pathogenesis of acne is multifactorial, including hormonal, microbiological and immunological mechanisms. One of the factors that contributes to the pathogenesis of acne is Propionibacterium acnes; yet, the molecular mechanism by which P. acnes induces inflammation is not known. Recent studies have demonstrated that microbial agents trigger cytokine responses via Toll-like receptors (TLRs). TLRs are pattern recognition receptors that recognize pathogen-associated molecular patterns conserved among microorganisms and elicit immune responses. We investigated whether TLR2 mediates P. acnes-induced cytokine production in acne. Using transfectant cells we found that TLR2 was sufficient for NF-kappaB activation in response to P. acnes. In addition, peritoneal macrophages from wild-type, TLR6 knockout and TLR1 knockout mice, but not TLR2 knockout mice, produced IL-6 in response to P. acnes.P. acnes induced activation of IL-12 and IL-8 production by primary human monocytes, and this cytokine production was inhibited by anti-TLR2-blocking antibody. Finally, in acne lesions, TLR2 was expressed on the cell surface of macrophages surrounding pilosebaceous follicles. These data suggest that P. acnes triggers inflammatory cytokine responses in acne by activation of TLR2. As such, TLR2 may provide a novel target for the treatment of this common skin disease.     

Zinc salts inhibit in vitro Toll-like receptor 2 surface expression by keratinocytes

Propionibacterium acnes (P. acnes) plays an important role in the induction and maintenance of the inflammatory phase of acne. At the therapeutic level, it has been shown that zinc salts could have a beneficial effect on mild and moderate inflammatory acne lesions. However, their mechanisms of action are still only partially known. Immediate early immune response is a crucial route in the development of inflammatory reaction and, specifically, activation of Toll-like Receptors (TLRs) leading to nuclear factor (NF)-kappaB translocation and production of inflammatory cytokines such as interleukin-8 (IL-8). The aim of this work was to determine if cytokine secretion and innate immunity could be targets of zinc salts. Normal Human Epidermal Keratinocytes (NHEK) and skin explants were stimulated by P. acnes extracts and incubated (3 h) with zinc salts (1 microg/mL). Then we successively studied TLR2 expression by immunohistochemistry and IL-8 production by ELISA. After incubation with zinc salts, the increase of TLR2 surface expression in skin upon membrane fraction (FM) of P. acnes challenge was decreased as compared to that in control samples. However, this inhibition does not modify IL-8 secretion by keratinocytes. In conclusion the inhibition of TLR2 surface expression by keratinocytes could be one of the anti-inflammatory mechanisms of zinc salts in acne.     

Distinct strains of Propionibacterium acnes induce selective human beta-defensin-2 and interleukin-8 expression in human keratinocytes through toll-like receptors

Acne is a chronic inflammatory disease of the pilosebaceous follicle. One of the main pathogenetic factors in acne is the increased proliferation of Propionibacterium acnes (P. acnes) in the pilosebaceous unit. We investigated whether direct interaction of P. acnes with keratinocytes might be involved in the inflammation and ductal hypercornification in acne. The capacities of different P. acnes strains to activate the innate immune response and the growth of cultured keratinocytes were investigated. We have found that two clinical isolates of P. acnes significantly induced human beta-defensin-2 (hBD2) messenger RNA (mRNA) expression; in contrast a third clinical isolate and the reference strain (ATCC11828) had no effect on hBD2 mRNA expression. In contrast, all four strains significantly induced the interleukin-8 (IL-8) mRNA expression. The P. acnes-induced increase in hBD2 and IL-8 gene expression could be inhibited by anti-Toll-like receptor 2 (TLR2) and anti-TLR4 neutralizing antibodies, suggesting that P. acnes-induced secretion of soluble factors in keratinocytes are both TLR2 and TLR4 dependent. In addition, the clinical isolate P. acnes (889) was capable of inducing keratinocyte cell growth in vitro. Our findings suggest that P. acnes modulates the antimicrobial peptide and chemokine expression of keratinocytes and thereby contributes to the recruitment of inflammatory cells to the sites of infections.     

Glucocorticoids enhance Toll-like receptor 2 expression in human keratinocytes stimulated with Propionibacterium acnes or proinflammatory cytokines

Toll-like receptors (TLRs) on keratinocytes are important cell surface receptors involved in the innate and acquired immune response to invading microorganisms. In acne vulgaris, TLR2 activation by Propionibacterium acnes (P. acnes) may induce skin inflammation via induction of various proinflammatory molecules that stimulate the invasion of inflammatory cells. Although corticosteroids themselves exert immunosuppressive or anti-inflammatory effects, it is well known clinically that systemic or topical glucocorticoid treatment provokes an acneiform reaction. Nevertheless, the effect of steroids on TLR2 expression in human keratinocytes remains unknown. Here, we found that the addition of glucocorticoids, such as dexamethasone and cortisol, to cultured human keratinocytes increased their TLR2 gene expression. Moreover, these glucocorticoids markedly enhanced TLR2 gene expression, which was further stimulated by P. acnes, tumor necrosis factor-alpha, and IL-1alpha. Gene expression of mitogen-activated protein kinase (MAPK) phosphatase-1 was also increased by the addition of dexamethasone. By using several inhibitors and activators, we found that TLR2 gene induction by glucocorticoids was mediated by the suppression of p38 MAPK activity following induction of MAPK phosphatase-1. These findings strongly suggest that steroid-induced TLR2 together with P. acnes existing as normal resident flora plays an important role in the exacerbation of acne vulgaris as well as in possible induction of corticosteroid-induced acne or in that of rosacea-like dermatitis.     

Induction of toll-like receptors by Propionibacterium acnes

BACKGROUND: The bacterium Propionibacterium acnes is involved in the induction and maintenance of the inflammatory phase of acne. Recent studies have found that keratinocytes express toll-like receptors (TLRs) implicated in immediate immunity. No studies have, to date, been carried out on the action of P. acnes upon TLR activation in keratinocytes. OBJECTIVES: Focusing on the inflammatory phase of acne, to clarify the role of P. acnes in immediate immunity by inducing expression of TLR-2 and TLR-4 by keratinocytes. We also studied how the secretion and expression of matrix metalloproteinase (MMP)-9 is induced by P. acnes. METHODS: The work was carried out on two levels: in vivo with the study of the expression of TLR-2 and TLR-4 proteins in biopsies of acne lesions and in vitro on cultured keratinocyte monolayers to study the modulating effects of P. acnes on the expression of TLR-2 and TLR-4 and also on the expression and secretion of MMP-9. RESULTS: Our findings reveal that in vivo TLR-2 and TLR-4 expression is increased in the epidermis of acne lesions. In vitro, an increase in TLR-2 and TLR-4 expression by human keratinocytes occurred in the first hours of incubation with bacterial fractions as well as an increase of the expression and secretion by the keratinocytes of MMP-9, which plays a role in inflammation. CONCLUSIONS: This work demonstrates that P. acnes induces TLR expression and that this mechanism could play an essential role in acne-linked inflammation. These receptors could be involved notably in acute acne.     

Propionibacterium acnes stimulates pro-matrix metalloproteinase-2 expression through tumor necrosis factor-alpha in human dermal fibroblasts

Propionibacterium acnes (P. acnes) is a commensal microorganism found in sebum-rich skin and plays a role in acne inflammation by stimulating keratinocyte to produce a number of proinflammatory cytokines. However, the role of P. acnes in the dermis of acne lesions, where tissue remodeling after inflammation eventually takes place, is not known. In this study, we investigated whether P. acnes induces matrix metalloproteinase (MMP), a key enzyme involved in matrix remodeling in human dermal fibroblasts (hDF). We found that P. acnes increased expression of pro-matrix metalloproteinase (proMMP)-2 mRNA/protein in hDF, but not that of proMMP-9. Concomitantly, P. acnes induced tumor necrosis factor-alpha (TNF-alpha) mRNA/protein expression in hDF, which in turn increases both proMMP-2 mRNA and protein expression. P. acnes induced such changes through the activated NF-kappaB pathway. Doxycycline was found to inhibit the expression of proMMP-2 induced either by P. acnes or TNF-alpha. These results suggest that P. acnes stimulates hDF to produce TNF-alpha, which mediates the expression of proMMP-2 through the NF-kappaB pathway. The secretion of proMMP-2 from hDF upon P. acnes stimulation may contribute to the pathogenesis of tissue remodeling in acne skin.     

Nadifloxacin, an antiacne quinolone antimicrobial, inhibits the production of proinflammatory cytokines by human peripheral blood mononuclear cells and normal human keratinocytes

BACKGROUND: Acne vulgaris is a chronic inflammatory disease involving colonization of Propionibacterium acnes (P. acnes), activation of neutrophils and lymphocytes. Circumstantial evidence suggests that antigen-independent and -dependent immune responses against P. acnes are involved in the pathogenesis of inflammatory acne. Epidermal keratinocytes are also suggested to be involved in initiation and progression of cutaneous inflammation. Nadifloxacin, a fluorinated quinolone, has potent antimicrobial activities against Gram-negative and -positive microbes and is used to treat multiple inflamed acne lesions. However, its effect on immune conferring cells such as mononuclear cells and keratinocytes has not been examined. OBJECTIVE: To evaluate the possible involvement of potential anti-inflammatory activity of nadifloxacin in its therapeutic effect on inflammatory acne, we examined the effects of nadifloxacin, in comparison with other antibiotics used to treat acne vulgaris, on cytokine production by human peripheral blood mononuclear cells (PBMC) and keratinocytes. METHODS: Cytokine production by PBMC was determined after treatment with heat-killed P. acnes in the presence or absence of antimicrobials using a real-time PCR and ELISA. Cultured human epidermal keratinocytes were stimulated by IFN-gamma plus IL-1beta and the effects of antimicrobials were examined by using ELISA. RESULTS: Nadifloxacin as well as macrolide antibiotics and clindamycin inhibited IL-12 and IFN-gamma production by PBMC stimulated by heat-killed P. acnes. The drug also inhibited the IL-1alpha, Il-6, IL-8 and GM-CMS production by keratinocytes treated with IFN-gamma plus IL-1beta. CONCLUSIONS: Inhibitory effects of nadifloxacin to activate T cells and keratinocytes may be involved at least in part in the mechanism of its therapeutic effect against inflammatory acne.     

Toll样受体2与痤疮相关性研究进展

痤疮是一种累及毛囊皮脂腺的慢性炎症性皮肤疾病。尽管痤疮的确切病因及发病机制尚不明确,但炎症反应是其发病的重要因素之一,其中痤疮丙酸杆菌是主要致病菌。痤疮丙酸杆菌可通过激活Toll样受体2(Toll-like receptors 2,TLR2)介导的信号传导通路诱导炎症级联反应,从而形成炎症性痤疮。一些药物可以通过调节TLR2受体的功能与表达,发挥抗炎及治疗痤疮的作用。该文就TLR2在痤疮发病中的作用及与之相关的治疗方法做一综述。     

In vitro modulation of TLR-2, CD1d and IL-10 by adapalene on normal human skin and acne inflammatory lesions

The anti-inflammatory mechanisms of adapalene, a synthetic retinoid used for the treatment of acne patients, are partially understood. They seem particularly related to the modulation of the non-specific immunity. Recent studies have shown that Toll-like receptor (TLR)-2 expression, a receptor of the innate immune system, was increased in acne lesions and could play an essential role in acne-linked inflammation. The aim of our study was to investigate the new mechanisms of the anti-inflammatory activity of adapalene in vitro, and more specifically the modulatory effect of adapalene on the expression of TLR-2, CD1d, a cell surface glycoprotein that plays a role as antigen-presenting molecules and is responsible for the development of cutaneous inflammation, and also on the expression and the secretion of the anti-inflammatory interleukin (IL)-10 cytokine. Both explants of normal human skin and explants of acne patients were incubated with adapalene (10(-7) or 10(-6) M) or the control medium for 24 h. Evaluation of epidermal expression by immunohistochemistry showed a decreased expression of TLR-2 and IL-10 in explants of normal skin and explants of acne with adapalene. On the contrary, adapalene increased CD1d expression in explants of acne patients. Thus, adapalene can modulate the epidermal immune system by increasing the CD1d expression and by decreasing the IL-10 expression by keratinocytes. Moreover, these modulations could increase the interactions between dendritic cells and T lymphocytes and could strengthen the antimicrobial activity against Propionibacterium acnes. The decreased expression of TLR-2 by the keratinocytes can contribute to explain the anti-inflammatory activity of adapalene observed in clinical practice.     

Systemic Isotretinoin Therapy Normalizes Exaggerated TLR-2-Mediated Innate Immune Responses in Acne Patients

Retinoids are used in the treatment of inflammatory skin diseases and malignancies, but studies characterizing the in vivo actions of these drugs in humans are lacking. Isotretinoin is a pro-drug for all-trans retinoic acid, which can induce long-term remissions of acne; however, its complete mechanism of action is unknown. We hypothesized that isotretinoin induces remission of acne by normalizing the innate immune response to the commensal bacterium Propionibacterium acnes. Compared with normal subjects, peripheral blood monocytes from acne patients expressed significantly higher levels of Toll-like receptor 2 (TLR-2) and exhibited significantly greater induction of TLR-2 expression following P. acnes stimulation. Treatment of patients with isotretinoin significantly decreased monocyte TLR-2 expression and subsequent inflammatory cytokine response to P. acnes after 1 week of therapy. This effect was sustained 6 months following cessation of therapy, indicating that TLR-2 modulation may be involved in the durable therapeutic response to isotretinoin. This study demonstrates that isotretinoin exerts immunomodulatory effects in patients and sheds light on a potential mechanism for its long-term effects on acne. The modulation of TLR-2 expression on monocytes has important implications in other inflammatory disorders characterized by TLR-2 dysregulation.     

Involvement of adenosine triphosphate‐binding cassette subfamily B member 1 in the augmentation of triacylglycerol excretion by Propionibacterium acnes in differentiated hamster sebocytes

An onset of acne, a common inflammatory skin disease, is associated with excess sebum production and secretion in sebaceous glands. Because Propionibacterium acnes has been reported to augment intracellular sebum accumulation in sebaceous glands in hamsters, it remains unclear whether P. acnes influences sebum secretion from differentiated sebocytes. Both P. acnes culture media (Acnes73‐CM ) and formalin‐killed P. acnes (F‐Acnes73) dose‐dependently increased the extracellular levels of triacylglycerol (TG ), a major sebum component, and Rhodamine 123, a substrate of adenosine triphosphate‐binding cassette (ABC ) transporter, from differentiated hamster sebocytes (DHS ). In addition, the gene expression of the ABC subfamily B member 1 (ABCB 1) was dose‐dependently augmented by adding Acnes73‐CM and F‐Acnes73 into DHS . Furthermore, the F‐Acnes73‐induced increase of TG excretion was suppressed by PSC 833, a selective ABCB 1 inhibitor. On the other hand, peptidoglycan (PGN ), which is a Toll‐like receptor 2 (TLR 2) ligand in P. acnes , increased extracellular TG levels, transporter activity and ABCB 1 mRNA expression in DHS . The PGN ‐augmented TG excretion was suppressed by PSC 833. Thus, these results provide novel evidence that P. acnes facilitates sebum secretion due to the activation of ABCB 1 concomitantly with the increased ABCB 1 expression, which may result from the activation of the TLR 2 pathway in DHS . Therefore, the ABCB 1 inhibitor is likely to become a candidate as a possible therapeutic for the treatment of acne.     

寻常痤疮患者外周血单核细胞TLR2的表达及其与IL-8和TNF-α的相关性研究

目的 探讨Toll样受体2(TLR2)在寻常痤疮发病中的作用及意义.方法 选择轻、中、重度痤疮患者各30例,采用流式细胞仪检测其外周血CD14+单核细胞TLR2的表达,并采用双抗体夹心酶联免疫吸附法(ELISA)检测血清IL-8和TNF-α的水平.另取30例正常人作为对照组.结果 轻、中、重度组痤疮患者外周血单核细胞表面TLR2的表达均显著高于正常人对照组(P＜0.01).各组患者血清中IL-8和TNF-α的水平也显著高于正常人对照组(P＜0.01).直线相关分析显示,各组患者TLR2的表达与IL-8、TNF-α水平均呈正相关性(r分别为0.382、0.517、0.436、0.641、0.725、0.593,P＜0.05).痤疮严重程度与TLR2的表达呈正相关性(r=0.406,P＜0.01).结论 TLR2表达水平及相关细胞因子浓度与痤疮严重程度密切相关.

Abstract：

Objective To explore the role of Toll like receptor 2 (TLR2) in the pathogenesis of acne vulgaris. Methods Venous blood was collected from 30 normal human controls and 90 patients with acne vulgaris. The patients were equally divided into three groups, i.e., mild, moderate and severe groups, according to disease severity. Flow cytometry was performed to detect the expression of TLR2 in PBMCs, and double antibody sandwich ELISA to measure the levels of serum interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α). Results A significant increase was observed in the expression of TLR2 in PBMCs, serum level of IL-8and TNF-α in the three groups of patients with acne vulgaris compared with the normal human controls (all P ＜0.01). The expression of TLR2 was positively correlated with the expression of IL-8 (r=0.382, 0.517,0.436,respectively, all P＜0.05) and TNF-α(r=0.641, 0.725, 0.593, respectively, all P＜0.05) in the patients with mild, moderate and severe acne vulgaris, respectively, and with the severity of acne vulgaris (r = 0.406,P＜0.01 ). Conclusion The expression level of TLR2 and related cytokines seems closely correlated with the severity of acne vulgaris.     

白介素6在痤疮囊肿皮损中的表达及痤疮丙酸杆菌体外对THP-1细胞白介素6水平的影响

目的 检测寻常痤疮患者囊肿皮损中白介素6（IL?6）的表达,并观察痤疮丙酸杆菌体外对人急性单核细胞白血病细胞系THP?1信号分子p38MAPK及白介素6水平的影响。方法 实时荧光定量PCR检测6例痤疮患者囊肿皮损和6例健康人皮肤组织中IL?6 mRNA表达水平。用2 × 106、2 × 107、2 × 108 CFU/ml灭活痤疮丙酸杆菌菌悬液或脂多糖（100 μg/L）刺激THP?1细胞,同时设培养基对照组和p38MAPK抑制剂SB203580组（先用20 μmol/L SB203580处理,再用2 × 108 CFU/ml痤疮丙酸杆菌刺激）,作用不同时间（1 ~ 6 h）后,实时荧光定量PCR检测IL?6 mRNA表达水平,酶联免疫吸附试验检测上清液中IL?6含量。2 × 108 CFU/ml灭活痤疮丙酸杆菌菌悬液刺激THP?1细胞15、30、60 min或脂多糖（100 μg/L）刺激30 min后,Western印迹法检测p38MAPK和磷酸化p38MAPK表达水平。结果 痤疮囊肿皮损和健康对照皮肤IL?6 mRNA水平分别为3.680 ± 0.790、1.155 ± 0.250,两组比较差异有统计学意义（t = 3.047,P < 0.05）。双因素方差分析显示,不同浓度痤疮丙酸杆菌组、脂多糖组、培养基对照组IL?6 mRNA表达水平差异有统计学意义（F = 532.3,P < 0.001,ν = 4）,痤疮丙酸杆菌刺激1、3、6 h之间差异也有统计学意义（F = 526.6,P < 0.001,ν = 2）。2 × 108 CFU/ml痤疮丙酸杆菌组、脂多糖组、培养基对照组上清液中IL?6浓度分别为（1 618.22 ± 32.23）、（3 212.06 ± 353.00）、（147.10 ± 0.53） ng/L,3组间差异有统计学意义（ν = 2,F = 102.35,P < 0.01）。2 × 108 CFU/ml痤疮丙酸杆菌作用于THP?1细胞15、30、60 min后磷酸化p38MAPK蛋白水平升高。SB203580组THP?1细胞IL?6 mRNA水平与未抑制组比较明显降低（t = 15.91,P = 0.004）。结论 寻常痤疮患者囊肿中IL?6 mRNA水平显著升高。痤疮丙酸杆菌体外可激活人THP?1细胞信号分子p38MAPK,促进其分泌IL?6。     

Effect of zinc gluconate on propionibacterium acnes resistance to erythromycin in patients with inflammatory acne: in vitro and in vivo study

Tetracyclines and macrolide antibiotics have been in use for acne treatment for more than 20 years. Since 1992 increasing resistance to these antibiotics, and especially to erythromycin, is reported with Propionibacterium acnes. Zinc salts have demonstrated their efficacy in inflammatory acne treatment as well as their bacteriostatic activity against Propionibacterium acnes. The objective of our work was firstly to determine whether the clinical anti-inflammatory efficacy of zinc salts was altered in the presence of erythromycin resistant strains in vivo, and secondly to study the in vitro and in vivo effect of zinc on the sensitivity of Propionibacterium acnes strains to erythromycin. Thirty patients with inflammatory acne were treated by zinc gluconate with a daily dose of 30 mg for two months and bacteriologic samples were taken at D0, D30 and D60. In vivo, this study displayed a reduction in the number of inflammatory lesions after a 2-month treatment whether or not Propionibacterium acnes carriage was present. Concurrently, in vitro addition of zinc salts in the culture media of Propionibacterium acnes reduced resistance of Propionibacterium acnes strains to erythromycin. Thus, association of zinc salts via a systemic route and topical erythromycin treatment seems an interesting option in the light of an increasing number of patients carrying erythromycin resistant Propionibacterium acnes strains.     

Inhibitory effect of catechin against the superantigen staphylococcal enterotoxin B (SEB)

Staphylococcal superantigens (SsAgs) have gained attention as one of the factors aggravating atopic dermatitis (AD) and several potential mechanisms of AD aggravation by SsAgs have been reported. Tea catechin has been found to have many unique antimicrobiological activities such as antibacterial, antiviral, antifungal and antitoxic effects. In the present study, we investigated the inhibitory effect of the green tea catechin extract, Polyphenon, and (–)-epigallocatechin gallate (EGCg) on staphylococcal enterotoxin B (SEB) and its mechanisms of action, and we also discuss the possibility of therapeutic benefits for AD patients of tea catechin. Polyphenon inhibited the lethal toxicity of SEB and the SEB-induced production of TNF-, IFN- and IL-4 following its intraperitoneal administration to BALB/c mice. Although Polyphenon is composed of several isomers among which EGCg is approximately 50% of the total, we considered that most of the inhibitory effect of Polyphenon in mice could be attributed to EGCg. EGCg was immediately bound to SEB molecules and neutralized SEB in a dose- and incubation time-dependent manner without molecular weight alteration of the SEB molecule. Furthermore, EGCg inhibited SEB-induced TNF- and IFN- production and IL-2, IFN- , IL-10 and IL-12 p40 mRNA expression in human PBMCs from normal donors in a dose-dependent manner. Inhibition of SsAg-induced T-cell activation by catechin was observed in both in vivo and in vitro studies, suggesting that catechin may be useful in the treatment of AD.     

All-trans retinoic acid shifts Propionibacterium acnes-induced matrix degradation expression profile toward matrix preservation in human monocytes

Propionibacterium acnes is a critical component in the pathogenesis of acne vulgaris, stimulating the production of various inflammatory mediators, such as cytokines and chemokines, important in the local inflammatory response found in acne. This study explored the role of P. acnes and its ability to induce matrix metalloproteinases (MMPs) in primary human monocytes and how this induction is regulated by retinoids. MMP-1- and MMP-9-expressing cells were present in perifollicular and dermal inflammatory infiltrates within acne lesions, suggesting their role in acne pathogenesis. In vitro, we found that P. acnes induced MMP-9 and MMP-1 mRNA, and the expression of MMP-9, but not of MMP-1, was found to be Toll-like receptor 2-dependent. P. acnes induced the mRNA expression of tissue inhibitors of metalloproteinase (TIMP)-1, the main regulator of MMP-9 and MMP-1. Treatment of monocytes with all-trans retinoic acid (ATRA) significantly decreased baseline MMP-9 expression. Furthermore, co-treatment of monocytes with ATRA and P. acnes inhibited MMP-9 and MMP-1 induction, while augmenting TIMP-1 expression. These data indicate that P. acnes-induced MMPs and TIMPs may be involved in acne pathogenesis and that retinoic acid modulates MMP and TIMP expression, shifting from a matrix-degradative phenotype to a matrix-preserving phenotype.     

Propionibacterium acnes activates the IGF-1/IGF-1R system in the epidermis and induces keratinocyte proliferation

Propionibacterium acnes has a major role in the development of acne lesions. IGF-1 stimulates the proliferation of keratinocytes via an activation of the IGF-1 receptor (IGF-1R). Zinc has been proven to work efficiently against inflammatory acne and to modulate the IGF-1 system. Our objectives were to study the modulation of IGF-1 and IGF-1R expression by P. acnes extracts and to determine their modulation by zinc gluconate. In vivo, we analyzed biopsies of acne lesions and healthy skin, and in vitro we used skin explants incubated with two P. acnes extracts--membrane fraction (MF) and cytosolic proteins--with or without zinc. IGF-1 and IGF-1R expression was evaluated using immunohistochemistry, and the IGF-1 production in supernatants was measured by ELISA. Then, IGF-1 and IGF-1R mRNA levels were analyzed using quantitative PCR on normal human epidermal keratinocytes (NHEKs). IGF-1 and IGF-1R were overexpressed in acne lesions. MF increased IGF-1 and IGF-1R expression in the epidermis of explants and was associated with an overexpression of both Ki-67 and filaggrin. Zinc had the effect of downregulating IGF-1 and IGF-1R levels. These observations were confirmed at the mRNA level for IGF-1R in NHEKs. These results demonstrate that P. acnes can induce the formation of comedones by stimulating the IGF/IGF-1R system. Moreover, zinc downregulates this pathway.     

Effects of Propionibacterium acnes on various mRNA expression levels in normal human epidermal keratinocytes in vitro

Propionibacterium acnes is one of the most significant pathogenic factors of acne vulgaris. This bacteria relates to acne by various pathways. It has also been reported that P. acnes influences pro-inflammatory cytokine production in keratinocytes in vitro . However, the influence on the differentiation of keratinocytes by P. acnes has not been studied extensively. We analyzed the expression of keratinocyte differentiation-specific markers, keratins, and pro-inflammatory cytokines in normal human epidermal keratinocytes (NHEK) exposed to P. acnes in vitro . All P. acnes strains used in this study increased transglutaminase (TGase), keratin 17 (K17) and interleukin (IL) mRNA expression levels in NHEK, and decreased K1 and K10 expression levels. Some P. acnes strains increased involucrin and K6 mRNA expression levels in NHEK and decreased filaggrin, K6 and K16 expression levels in vitro . This experiment clarified that P. acnes influences the differentiation of NHEK in vitro . As a result, P. acnes influenced the expression of not only pro-inflammatory cytokines but also some keratinocyte differentiation-specific markers and keratins in NHEK. Our results suggest that P. acnes relates to acne pathogenesis by not only the induction of inflammation but also in the differentiation of keratinocytes. Moreover, it was considered that the reaction of NHEK to P. acnes may be different depending on the type of bacteria.