transforming-growth-factor-beta and Pseudoxanthoma-Elasticum

Pseudoxanthoma elasticum is an autosomal recessive genodermatosis with variable expression, due to mutations in the ABCC6 or ENPP1 gene. It is characterized by elastic fiber mineralization and fragmentation, resulting in skin, eye and cardiovascular symptoms. Significant advances have been made in the last 20 years with respect to the phenotypic characterization and pathophysiological mechanisms leading to elastic fiber mineralization. Nonetheless, the substrates of the ABCC6 transporter - the main cause of PXE - remain currently unknown. Though the precise mechanisms linking the ABCC6 transporter to mineralization of the extracellular matrix are unclear, several studies have looked into the cellular consequences of ABCC6 deficiency in PXE patients and/or animal models. In this paper, we compile the evidence on cellular signaling in PXE, which seems to revolve mainly around TGF-βs, BMPs and inorganic pyrophosphate signaling cascades. Where conflicting results or fragmented data are present, we address these with novel signaling data. This way, we aim to better understand the up- and down-stream signaling of TGF-βs and BMPs in PXE and we demonstrate that ANKH deficiency can be an additional mechanism contributing to decreased serum PPi levels in PXE patients.

Topics: Bone Morphogenetic Proteins; Humans; Multidrug Resistance-Associated Proteins; Phosphate Transport Proteins; Phosphates; Pseudoxanthoma Elasticum; Skin; Transforming Growth Factor beta

Latent transforming growth factor-beta 1 (TGF-beta 1) and its binding protein-1 (LTBP-1) are components of the extracellular matrix microfibrils of cultured human fibroblasts. Using immunohistochemistry we have studied the localization of TGF-beta 1 and LTBP-1 and compared their distribution with that of elastic fibres in the interstitial connective tissue matrix of the human dermis. Prominent LTBP-1 specific fibrillar staining co-localized with the elastic fibres in normal human skin. Co-distribution was also observed in a number of pathological states of the elastic fibres such as solar elastosis, solar keratosis and pseudoxanthoma elasticum. TGF-beta 1 had a staining pattern similar to that of LTBP-1 in solar elastosis and solar keratosis. No staining for LTBP-1 or TGF-beta 1 was found in dermis devoid of elastic fibres, as in anetoderma. LTBP-1 is released from the extracellular matrix of cultured human fibroblasts, epithelial and endothelial cells by proteases. Analogously, the immunoreactivity for LTBP-1 and TGF-beta 1 were also lost from the skin sections by elastase, and by trypsin, a protease pretreatment commonly used in immunohistochemistry. These results indicate that LTBP-1 is a component of the elastin-associated microfibrils of the interstitial connective tissue matrix of human skin. Furthermore, the small latent form of TGF-beta 1 is likely to associate with the extracellular matrix of human dermis via LTBP-1. The release of latent TGF-beta 1 from the matrix, as a consequence of proteolytic cleavage of LTBP-1, is a plausible extracellular mechanism for the regulation of TGF-beta 1 activation.

Topics: Adolescent; Adult; Aged; Atrophy; Biomarkers; Carrier Proteins; Child; Child, Preschool; Elastic Tissue; Humans; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; Latent TGF-beta Binding Proteins; Middle Aged; Nevus; Photosensitivity Disorders; Pseudoxanthoma Elasticum; Skin; Skin Diseases; Skin Neoplasms; Transforming Growth Factor beta