Understanding the factors that regulate sebum production is important in identifying therapeutic targets for acne therapy. Insulin and IGF-1 stimulate sebaceous gland lipogenesis. IGF-1 increases expression of sterol response element-binding protein-1 (SREBP-1), a transcription factor that regulates numerous genes involved in lipid biosynthesis. SREBP-1 expression, in turn, stimulates lipogenesis in sebocytes. The goal of this study was to identify the intracellular signaling pathway(s) that transduces the lipogenic signal initiated by IGF-1. Sebocytes were treated with IGF-1 and assayed for activation of the phosphoinositide 3-kinase (PI3-K) pathway and of the three major arms of the mitogen-activated protein kinase (MAPK) pathway (MAPK/extracellular signal-regulated kinase (ERK), p38 MAPK, and stress-activated protein kinase/c-Jun-N terminal kinase). IGF-1 activated the MAPK/ERK and PI-3K pathways. Using specific inhibitors of each pathway, we found that the increase in expression of SREBP-1 induced by IGF-1 was blocked in the presence of the PI3-K inhibitor but not in the presence of the MAPK/ERK inhibitor. Furthermore, inhibition of the PI3-K pathway also blocked the IGF-1-induced transcription of SREBP target genes and sebocyte lipogenesis. These data indicate that IGF-1 transmits its lipogenic signal in sebocytes through activation of Akt. Specific targeted interruption of this pathway in the sebaceous gland could be a desirable approach to reducing sebum production and improving acne.

Sebum production is key in the pathophysiology of acne, an extremely common condition, which when severe, may require treatment with isotretinoin, a known teratogen. Apart from isotretinoin and hormonal therapy, no agents are available to reduce sebum. Increasing our understanding of the regulation of sebum production is a milestone in identifying alternative therapeutic targets. Studies in sebocytes and human sebaceous glands indicate that agonists of peroxisome proliferator-activated receptors (PPARs) alter sebaceous lipid production. The goal of this study is to verify the expression and activity of PPARs in human skin and SEB-1 sebocytes and to assess the effects of PPAR ligands on sebum production in patients. To investigate the contribution of each receptor subtype to sebum production, lipogenesis assays were performed in SEB-1 sebocytes that were treated with PPAR ligands and isotretinoin. Isotretinoin significantly decreased lipogenesis, while the PPARalpha agonist-GW7647, PPARdelta agonist-GW0742, PPARalpha/delta agonist-GW2433, PPARgamma agonist rosiglitazone, and the pan-agonist-GW4148, increased lipogenesis. Patients treated with thiazolidinediones or fibrates had significant increases in sebum production (37 and 77%, respectively) when compared to age-, disease-, and sex-matched controls. These data indicate that PPARs play a role in regulating sebum production and that selective modulation of their activity may represent a novel therapeutic strategy for the treatment of acne.

The pathogenesis of acne has been linked to multiple factors such as increased sebum production, inflammation, follicular hyperkeratinization, and the action of Propionibacterium acnes within the follicle. In an attempt to understand the specific genes involved in inflammatory acne, we performed gene expression profiling in acne patients. Skin biopsies were obtained from an inflammatory papule and from normal skin in six patients with acne. Biopsies were also taken from normal skin of six subjects without acne. Gene array expression profiling was conducted using Affymetrix HG-U133A 2.0 arrays comparing lesional to nonlesional skin in acne patients and comparing nonlesional skin from acne patients to skin from normal subjects. Within the acne patients, 211 genes are upregulated in lesional skin compared to nonlesional skin. A significant proportion of these genes are involved in pathways that regulate inflammation and extracellular matrix remodeling, and they include matrix metalloproteinases 1 and 3, IL-8, human beta-defensin 4, and granzyme B. These data indicate a prominent role of matrix metalloproteinases, inflammatory cytokines, and antimicrobial peptides in acne lesions. These studies are the first describing the comprehensive changes in gene expression in inflammatory acne lesions and are valuable in identifying potential therapeutic targets in inflammatory acne.