Amanda M. Nelson

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 that 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 P. acnes. Compared to normal subjects, peripheral blood monocytes from acne patients expressed significantly higher levels of 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 by one week of therapy. This effect was sustained six 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 in acne. The modulation of TLR-2 expression on monocytes has important implications in other inflammatory disorders characterized by TLR-2 dysregulation.

Prostaglandin D2 inhibits wound-induced hair follicle neogenesis through the receptor, Gpr44

Prostaglandins (PGs) are key inflammatory mediators involved in wound healing and regulating hair growth; however, their role in skin regeneration after injury is unknown. Using wound-induced hair follicle neogenesis (WIHN) as a marker of skin regeneration, we hypothesized that PGD2 decreases follicle neogenesis. PGE2 and PGD2 were elevated early and late respectively during wound healing. The levels of WIHN, lipocalin-type prostaglandin D2 synthase (Ptgds) and its product PGD2 each varied significantly among background strains of mice after wounding and all correlated such that the highest Ptgds and PGD2 levels were associated with the lowest amount of regeneration. Additionally, an alternatively spliced transcript variant of Ptgds missing exon 3 correlated with high regeneration in mice. Exogenous application of PGD2 decreased WIHN in wild type mice and PGD2 receptor Gpr44 null mice showed increased WIHN compared to strain-matched control mice. Furthermore, Gpr44 null mice were resistant to PGD2-induced inhibition of follicle neogenesis. In all, these findings demonstrate that PGD2 inhibits hair follicle regeneration through the Gpr44 receptor and imply that inhibition of PGD2 production or Gpr44 signaling will promote skin regeneration.

TRAIL contributes to the apoptotic effect of 13-cis retinoic acid in human sebaceous gland cells

Background  The full mechanism of action of isotretinoin [13‐cis retinoic acid (13‐cis RA)] in treating acne is unknown. 13‐cis RA induces key genes in sebocytes that are involved in apoptosis, including Tumor necrosis factor Related Apoptosis Inducing Ligand (TRAIL).

dsRNA Released by Tissue Damage Activates TLR3 to Drive Skin Regeneration

Regeneration of skin and hair follicles after wounding--a process known as wound-induced hair neogenesis (WIHN)--is a rare example of adult organogenesis in mammals. As such, WIHN provides a unique model system for deciphering mechanisms underlying mammalian regeneration. Here, we show that dsRNA, which is released from damaged skin, activates Toll-Like Receptor 3 (TLR3) and its downstream effectors IL-6 and STAT3 to promote hair follicle regeneration. Conversely, TLR3-deficient animals fail to initiate WIHN. TLR3 activation promotes expression of hair follicle stem cell markers and induces elements of the core hair morphogenetic program, including ectodysplasin A receptor (EDAR) and the Wnt and Shh pathways. Our results therefore show that dsRNA and TLR3 link the earliest events of mammalian skin wounding to regeneration and suggest potential therapeutic approaches for promoting hair neogenesis.

Temporal changes in gene expression in the skin of patients treated with isotretinoin provide insight into its mechanism of action

Isotretinoin (13-cis RA) is the most potent agent in the treatment of acne. Insights into its mechanism of action can lead to drug discovery of alternative compounds with comparable efficacy but improved safety. The goal of this study is to compare the temporal changes in gene expression in the skin of acne patients after 1 week and 8 weeks of treatment with isotretinoin. Microarray analysis was performed on skin biopsies taken from 8 acne patients prior to and at 8 weeks of treatment with isotretinoin. Results were compared with data obtained from 7 acne patients biopsied at one week of treatment in a prior study. Distinctly different patterns of gene expression were noted. At 8 weeks, genes encoding extracellular matrix proteins were up-regulated and numerous genes encoding lipid metabolizing enzymes were down-regulated. At one week, genes encoding differentiation markers, tumor suppressors and serine proteases were up-regulated. Only three genes were commonly down-regulated. The temporal changes in gene expression in patient skin noted with isotretinoin substantiate many previously reported effects of isotretinoin and other retinoids, suggesting a model wherein isotretinoin induces apoptosis leading to reduced sebaceous gland size, decreased expression of lipid metabolizing enzymes and increased matrix remodeling during acne resolution.

Isotretinoin Temporally Regulates Distinct Sets of Genes in Patient Skin

TO THE EDITOR The goal of this study is to gain insight into putative pathways by which 13-cis retinoic acid (13-cisRA) improves acne by comparing the temporal changes in gene expression in the skin of acne patients. Gene array analysis and immunohistochemistry were performed on skin biopsies from patients at baseline and after 8 weeks of isotretinoin therapy and compared to data obtained at 1 week (Nelson et al., 2008). As 13-cisRA drastically decreases sebaceous gland size after 16 weeks (Goldstein et al., 1982); we chose an 8week time point to examine changes in skin histology and gene expression. All protocols were approved by the Institutional Review Board of The Pennsylvania State University College of Medicine and were conducted according to the principles outlined in the Declaration of Helsinki. Eight patients who were prescribed isotretinoin for their severe acne enrolled in the study after giving informed consent and 5-mm punch biopsies of uninvolved skin were taken from their upper backs at baseline and 8 weeks of treatment. Demographic data are presented in Figure 1a. After 8 weeks, sebaceous gland size was reduced by 76% (4.17fold) compared to baseline (P1⁄40.009) (Figure 1b and d). At 1 week, glands were decreased by approximately 49% (not significant; Figure 1c and d). Gene array expression analysis was performed on biopsies at baseline and after 8 weeks of therapy. Using a false discovery rate of 0.05 corresponding to Abbreviation: 13-cisRA, 13-cis retinoic acid

Isotretinoin Increases Skin Surface Levels of Neutrophil Gelatinase-Associated Lipocalin in Patients Treated for Severe Acne

Background  A clear‐cut need exists for safe and effective alternatives to the use of isotretinoin in severe acne. Lack of data regarding the specifics of isotretinoin’s mechanism of action has hampered progress in this area. Recently, the protein neutrophil gelatinase‐associated lipocalin (NGAL) has been identified as a mediator of the apoptotic effect of isotretinoin on sebocytes.

Improving acne keloidalis nuchae with targeted ultraviolet B treatment: a prospective, randomized, split-scalp comparison study

Acne keloidalis nuchae (AKN) is a chronic scarring folliculitis with fibrotic papules on the occipital scalp. Its treatment is limited and unsatisfactory.

Early gene changes induced by isotretinoin in the skin provide clues to its mechanism of action

Gene expression analysis of patient skin at one-week of oral isotretinoin therapy for severe acne illustrates the initial changes caused by 13-cis RA. Focus on the function of these significantly changed genes provides clues to its mechanism of action in skin. Significant gene changes included the up-regulation of lipocalin 2, which encodes the protein neutrophil gelatinase associated lipocalin (NGAL). Detailed studies of NGAL’s localization and function within the sebaceous gland demonstrated that NGAL mediates the apoptotic action of 13-cis RA on sebaceous glands, thereby suggesting that agents which selectively induce NGAL expression in sebaceous glands might represent therapeutic alternatives to the use of 13-cis RA for the treatment of acne

Interleukin 6 and STAT3 regulate p63 isoform expression in keratinocytes during regeneration.

Department of Dermatology, Johns Hopkins School of Medicine, Baltimore, MD, USA Correspondence: Luis Garza, MD-PhD, Department of Dermatology, Johns Hopkins School of Medicine, Room 204, Koch CRBII, 1551 Orleans Street, Baltimore, MD 21287, USA. Tel.: +410 955 8662, Fax +410 955 8645, e-mail: LAG@jhmi.edu * Present Address: Department of Dermatology, Penn State Hershey College of Medicine, Hershey, PA, USA