elastin and Telangiectasia--Hereditary-Hemorrhagic

TMEM100 was previously identified as a downstream target of activin receptor-like kinase 1 (ALK1; ACVRL1) signalling. Mutations on ALK1 cause hereditary haemorrhagic telangiectasia (HHT), a vascular disorder characterized by mucocutaneous telangiectases and visceral arteriovenous malformations (AVMs). The aims of this study are to investigate the in vivo role of TMEM100 at various developmental and adult stages and to determine the extent to which TMEM100 contributed to the development of AVMs as a key downstream effector of ALK1.. Blood vasculature in Tmem100-null embryos and inducible Tmem100-null neonatal and adult mice was examined. We found that TMEM100 deficiency resulted in cardiovascular defects at embryonic stage; dilated vessels, hyperbranching, and increased number of filopodia in the retinal vasculature at neonatal stage; and various vascular abnormalities, including internal haemorrhage, arteriovenous shunts, and weakening of vasculature with abnormal elastin layers at adult stage. However, arteriovenous shunts in adult mutant mice appeared to be underdeveloped without typical tortuosity of vessels associated with AVMs. We uncovered that the expression of genes encoding cell adhesion and extracellular matrix proteins was significantly affected in lungs of adult mutant mice. Especially Mfap4, which is associated with elastin fibre formation, was mostly down-regulated.. These results demonstrate that TMEM100 has essential functions for the maintenance of vascular integrity as well as the formation of blood vessels. Our results also indicate that down-regulation of Tmem100 is not the central mechanism of HHT pathogenesis, but it may contribute to the development of vascular pathology of HHT by weakening vascular integrity.

Topics: Activin Receptors, Type I; Activin Receptors, Type II; Age Factors; Animals; Arteriovenous Malformations; Carrier Proteins; Disease Models, Animal; Elastin; Extracellular Matrix Proteins; Gene Expression Regulation, Developmental; Genotype; Gestational Age; Glycoproteins; Lung; Membrane Proteins; Mice, 129 Strain; Mice, Inbred C57BL; Mice, Knockout; Morphogenesis; Phenotype; Retinal Vessels; Signal Transduction; Telangiectasia, Hereditary Hemorrhagic

Cutis marmorata telangiectatica congenita (CMTC) is a rare cutaneous vascular disease presenting at birth with levido reticularis, phlebectasia, and telangiectasia, often accompanied by skin ulcerations. Extra-dermal vascular anomalies can be also detected in 30-70% of described cases. The pathomechanism responsible for development of these phenotypic changes is not well understood. Here, we report on a 16-month-old boy with CMTC, generalized vascular abnormalities and severe, nitric oxide sensitive, pulmonary hypertension associating with markedly elevated level of blood copper. Results of laboratory investigations indicated that primary cultures (passage one) of dermal fibroblasts derived from this patient were capable of normal synthesis of tropoelastin, but their net deposition of mature elastic fibers was significantly diminished as compared with cultures of normal fibroblasts. Because the low net deposition of elastin was reversed when 1 mg/ml of alpha1-antitrypsin was added to the media, we conclude that heightened elastolysis by endogenous serine proteinase's is responsible for the low net elastogenesis by CMTC fibroblasts. Since simultaneous addition of 30 microM CuSO(4) and 1 mg/ml alpha1-antitrypsin abolished the beneficial effect of this serine proteinase's inhibitor, we concluded that this may be due to copper-dependent inactivation of alpha1-antitrypsin. Our data suggest that a high level of free copper may constitute a major triggering factor contributing to the development of the CMTC phenotype.

Topics: Autoradiography; Case-Control Studies; Cells, Cultured; Copper; Elastin; Fibroblasts; Humans; Immunohistochemistry; Infant; Male; Models, Biological; Reference Standards; Skin; Skin Diseases, Vascular; Skin Ulcer; Telangiectasia, Hereditary Hemorrhagic; Tropoelastin