Inflammatory Mediator TAK1 Regulates Hair Follicle Morphogenesis and Anagen Induction Shown by Using Keratinocyte-Specific TAK1-Deficient Mice

Transforming growth factor-β-activated kinase 1 (TAK1) is a member of the NF-κB pathway and regulates inflammatory responses. We previously showed that TAK1 also regulates keratinocyte growth, differentiation, and apoptosis. However, it is unknown whether TAK1 has any role in epithelial–mesenchymal interactions. To examine this possibility, we studied the role of TAK1 in mouse hair follicle development and cycling as an instructive model system. By comparing keratinocyte-specific TAK1-deficient mice (Map3k7fl/flK5-Cre) with control mice, we found that the number of hair germs (hair follicles precursors) in Map3k7fl/flK5-Cre mice was significantly reduced at E15.5, and that subsequent hair follicle morphogenesis was retarded. Next, we analyzed the role of TAK1 in the cyclic remodeling in follicles by analyzing hair cycle progression in mice with a tamoxifen-inducible keratinocyte-specific TAK1 deficiency (Map3k7fl/flK14-Cre-ERT2). After active hair growth (anagen) was induced by depilation, TAK1 was deleted by topical tamoxifen application. This resulted in significantly retarded anagen development in TAK1-deficient mice. Deletion of TAK1 in hair follicles that were already in anagen induced premature, apoptosis-driven hair follicle regression, along with hair follicle damage. These studies provide the first evidence that the inflammatory mediator TAK1 regulates hair follicle induction and morphogenesis, and is required for anagen induction and anagen maintenance

Gene Expression Profiling of the Intact Dermal Sheath Cup of Human Hair Follicles

Cells that constitute the dermal papillae of hair follicles might be derived from the dermal sheath, the peribulbar component of which is the dermal sheath cup. The dermal sheath cup is thought to include the progenitor cells of the dermal papillae and possesses hair inductive potential; however, it has not yet been well characterized. This study investigated the gene expression profile of the intact dermal sheath cup, and identified dermal sheath cup signature genes, including extracellular matrix components and bone morphogenetic protein-binding molecules, as well as transforming frowth factor beta 1 as an upstream regulator. Among these, gremilin-2, a member of the bone morphogenetic protein antagonists, was found by in situ hybridization to be highly specific to the dermal sheath cup, implying that gremlin-2 is a key molecule contributing to maintenance of the properties of the dermal sheath cup

Keratinocyte-specific TAK1 deletion delays hair cycle progression in adolescent mice.

<p>(A) Schedule of tamoxifen application. The hair cycle was synchronized to anagen phase by wax depilation, and tamoxifen was topically applied to the dorsal skin of <i>Map3k7</i>^fl/flK14-Cre-ER^T2mice to delete TAK1. As controls, <i>Map3k7</i>^fl/fl mice or <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice were treated with tamoxifen or ethanol, respectively. (B) Clinical appearance at the indicated time point after the depilation. At 2 weeks, hair shaft formation was noted in the control mice, while hair shaft growth was not seen in the tamoxifen-treated <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice. (C) Histological analysis at the indicated time point after the depilation. Anagen progression was severely delayed in TAK1-deleted mice at 1–3 weeks. Scale bar, 100 µm.</p

Keratinocyte-specific TAK1 deletion causes a transition from anagen to dystrophic catagen in adolescent mice.

<p>(A) Schedule of tamoxifen application. The hair cycle was synchronized to anagen phase by wax depilation. At 7 days after depilation, tamoxifen was applied for 5 days. (B) Clinical appearance of the mice 2 weeks after depilation. (C) Histological analysis of the mice 2 weeks after depilation. (D) Higher magnification of the tamoxifen-treated <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice in (C). Scale bar, 100 µm. (E) Dystrophic catagen was defined according to a previous report <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011275#pone.0011275-Hendrix1" target="_blank">[28]</a>. Then, the rate (%) of a certain hair follicle stage per total hair follicles was calculated. Quantitative analyses confirmed that most of the hair follicles in tamoxifen-treated <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice were in late dystrophic catagen, while those of controls were in anagen.</p

Keratinocyte-specific TAK1 deletion results in hair loss in adolescent mice.

<p>Tamoxifen was topically applied to the dorsal skin of the <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice for 5 consecutive days to delete TAK1. The clinical appearance of the mice 4 weeks after the application is shown. As controls, <i>Map3k7</i>^fl/fl mice or <i>Map3k7</i>^fl/flK14-Cre-ER^T2 mice were treated with tamoxifen or ethanol, respectively.</p

Model for the signaling pathways involved in hair follicle development.

<p>In the development of primary hair placodes, TAK1 is involved in the Edar/NF-κB pathway. In secondary hair placodes, NF-κB (TAK1)-independent pathways regulate hair placode development.</p

Southern blot analysis.

<p>Genomic DNA prepared from the ear skin of mice treated with tamoxifen solution (15 µL/ear) or ethanol for 5 consecutive days was digested with <i>Xba</i>I and <i>Eco</i>RI. Southern blot analysis for the deletion of the floxed <i>Tak1</i> allele was performed as described previously <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0011275#pone.0011275-Sato1" target="_blank">[1]</a>. Cre expression resulted in excision of the floxed allele (<i>flox</i>) and generated the deleted allele (Δ) of <i>Map3k7</i>.</p