Expressions Of TGFβ Receptors And TGFβ-related Smads In Dermatofibroma

Background: The transforming growth factorβs (TGFβs) regulate cell growth and differentiation, tissue remodeling, angiogenesis and immune response. TGFβs act through two types of transmembrane serine/threonine kinase receptors, the type I and II TGFβreceptors (TGFβRI and TGFβRII). The intracellular signaling of TGFβfrom the membrane receptors to nucleus is mediated and regulated by the Smad proteins, which have been divided into three distinct groups: the receptor-activated Smads (R-Smads), the common-partner Smad (Co-Smad) and the inhibitory Smads (I-Smads). Upon ligand binding, TGFβRI and TGFβRII form tetraheteromers, which phosphorylate the downstream R-Smads such as Smad2 and Smad3. Smad2 and Smad3 then form heteromeric complexes with Co-Smad——Smad4 and translocate to the nucleus to act as transcription factors for regulating the expresson of target genes. I-Smads, such as Smad6 or Smad7, can inhibit the TGFβsignaling cascade either by blocking phosphorylation and subsequent nuclear translocation of R-Smads or by an increase in TGFβR degradation via specific ubiquitin-proteasome pathways.The skin is a major target of the TGFβ. TGFβs can inhibit proliferation of epidermal keratinocytes and stimulate dermal fibroblasts to proliferate and synthesize extrocellular matrix components such as collagen and fibronectin. The contribution of TGFβhas been implicated in the progression of sclerosis in fibrotic diseases. TGFβsignaling plays a pivotal role in mechanism of fibroplasia or fibrosis occurring in cutaneous fibroproliferative diseases such as scleroderma, keoid, hypertrophic scar and Dupuytren's contracture. Dermatofibroma is a common benign tumor characterized by close whorls of fibrous tissue with abundant spindle-shaped fibroblastic cells. The expression of TGFβ1 and the elvated expression levels of TGFβRs in dermatofibromas were found in recent years. Based on the findings mentioned above, we suppose that altered expression of some important members in TGFβ/Smad signaling pathway family may also exist in dermatofibromas. Whether the expression levels of R-Smads, Co-Smad and I-Smads are altered in dermatofibromas remains unknownObjective: To investigate the expressions of TGFβRs (TGFβRI and TGFβRII), R-Smads (Smad2 and Smad3), Co-Smad (Smad4) and I-Smad (Smad7) in dermatofibroma, for further insights into the correlation between alterations in the TGFβsignaling pathway and pathological changes in dermatofibromas.Method: Reverse transcription (RT) and quantitative real-time polymerase chain reaction (real-time PCR) technique was utilized to assess the expressions of TGFβRI, TGFβRII, Smad2, Smad3, Smad4 and Smad7 mRNA in dermal compartment of dermatofibromas and normal skin specimens. The expresions of TGFβRI, TGFβRII, Smad1/2/3, p-Smad2/3, Smad4 and Smad7 proteins in dermatofibromas and normal skin specimens were detected using EliVisionTM plus immunohistochemical technique.Results: Up-regulated expressions of TGFβRI, TGFβRII, Smad2, Smad3 and Smad4 mRNA in dermal compartment of dermatofibromas were demonstrated by RT and real-time PCR, in comparison with those in dermis of normal skin specimens. Immunohistochemial analyses revealed that increased expressions of TGFβRI, TGFβRII, Smad1/2/3, pSmad2/3 and Smad4 proteins, and limited expression of Smad7 protein exist in abundant fibroblastic cells in dermatofibromas compared with those in dermis of normal skin specimens.However, a different expression pattern of TGFβRs and TGFβrelated Smad proteins in overlying epidermis of dermatofibromas was found by immunohistochemical staining, in comparison with that in dermal compartment of dermatofibromas. Immunohistochemial analyses displayed that decreased expressions of TGFβRI, TGFβRII, Smad1/2/3, pSmad2/3 and Smad4 proteins, and increased expression of Smad7 protein exist in overlying epidermis of dermatofibromas compared with those in epidermis of normal skin specimens.Conclusion: Dermatofibromas exhibit different regulation in TGFβ/Smad signaling pathway in dermal compartment and epidermal compartment. The up-regulated expressions of TGFβR, R-Smads, Co-Smad in TGFβ/Smad signaling pathway in abundant fibroblastic cells in dermatofibromas might promote and maintain fibroplasia. In contrast, the decreased expressions of TGFβR, R-Smads and Co-Smad, and increased expression of I-Smad in TGFβ/Smad signaling pathway occurring in overlying epidermis of dermatofibromas might contribute to formation and maintenance of epidermal hyperplasia.