Smad7-induced -catenin degradation alters epidermal appendage development

Han, G. et al., 2006, Dev Cell.

Diagrammatic Depiction of the Hair Follicle Stem Cell Niche and the Cutaneous Lineages Deriving from the Bulge Stem Cells Adapted from Alonso and Fuchs, 2003

Schmidt-Ullrich, R. and Paus, R., 2005, BioEssays.

An overview of Hair Follicle development

Signaling for Hair Follicle development

Wnt signaling is essential for the initiation of hair follicle development.

Hedgehog signaling is required for the down growth of the hair follicle and for sebaceous gland development.

Recent studies have shown that expression of Smads and certain Smad target genes is preferentially enriched in the epidermal stem cell population.

Peter ten Dijke and Caroline S. Hill, 2004, TRENDS in Biochemical Sciences.

TGF signaling

Smad7 (Smad antagonist)

Smad7 blocks Smad signaling by inhibiting Smad phosphorylation and by recruiting a Smurf2 to degrade the type 1 receptors of TGF and/or Smads. Smad7 transgene expression in keratinocytes inhibits Smad signaling from TGFb/activin and bone morphogenetic protein (BMP), which results in multiple developmental defects in stratified epithelia, including decreased hair follicle size.

These mice die perinatally due to epithelial hyperkeratosis.

1, 2, 3, 5, 8

6, 7

Figure S1. Generation of Gene-switch Smad7 Transgenic Mice

Embedding procedure for obtaining longitudinal cryosections of mouse pelage HF

Paus, R. et al., 1999, J Inves Dermatol.

Figure 1. Smad7 Transgene Induction

epidermis, hair follicle placode

ORS : outer root sheath

RT

WB

Figure 2. Smad7 Induction Perturbed Hair Follicle Regeneration, but Accelerated Sebaceous Gland Morphogenesis

telogen

Adipophilin : an early sebaceous gland differentiation marker

We examined expression levels of sonic hedgehog (Shh) and indian hedgehog (Ihh), two molecules required for sebaceous gland development.

membrane -cat nucleus -cat

Figure 3. Smad7 Transgenic Skin Exhibited a Reduction in-catenin Staining and in -catenin-mediated Wnt Signaling

LacZ in placodes

Figure 4. Smad7 Transgene Expression Triggered -Catenin Degradation

Smad7 induces -catenin degradation via a ubiquitin proteasome pathway and coprecipitated with -catenin in the presence of MG132 in cultured keratinocytes.

Smurf2 is involved in Smad7-mediated bcatenin degradation through the ubiquitin proteasome pathway.

Figure 5. Low Level of Smad7 Overexpression Did Not Alter Smad Signaling, but Inhibited Wnt/-Catenin Signaling

Smad7-induced -catenin degradation and the subsequent Wnt signaling blockade appeared to be independent of its role in blocking TGF/BMP signaling.

Figure 6. Smurf2 Overexpression Exacerbated Smad7-Mediated Hair Follicle Abnormalities and -Catenin Degradation

(S3-S5) (S3-S5) (S2-S3) (S1-S2)

P25

telogen

The effect of Smurf2 on hair follicle/sebaceous gland morphogenesis is Smad7 dependent.

Figure 7. Endogenous Smad7 Is Involved in -Catenin Degradation

WT B6D2 mice

RT WB

Endogenous Smad7 inhibits Wnt signaling.