Fibulin-5 in the pathogenesis of cutis laxa.

摘要

Fibulin-5 is a novel member of the fibulin family. Targeted inactivation of fibulin-5 in mice resulted in similar phenotypes to cutis laxa characterized by loose skin, tortuous arteries, and emphysema. To investigate the roles of fibulin-5 in extracellular matrix formation and in the pathomechanism of cutis laxa, we screened a cohort of probands with this condition. Three missense mutations were found in cutis laxa probands, and were not present in normal control panel. Allele frequencies of other variants were not significantly different in cutis laxa compared to controls. Abnormalities in the steady state level of fibulin-5 mRNA were not detected in fibroblasts from probands. Functional studies on three missense mutations demonstrated distinct in pathomechanisms for cutis laxa. Two missense mutations, S227P and C217R were identified in families with recessive cutis laxa. Both mutations resulted in reduced synthesis and secretion of fibulin-5 and significantly impaired ability of fibulin-5 to bind tropoelastin and elastic fibers suggesting that these were loss of function mutations. This was confirmed in vivo by the absence of fibulin-5 staining in patient skin samples. Electron microscopy indicated that loss of fibulin-5 function was associated with impaired polymerization of elastin and reduced elastin-microfibril interaction. In addition, mutation S227P resulted in severe misfolding of fibulin-5, triggering an endoplasmatic reticulum stress response and increased rates of apoptosis in fibroblasts, which was not observed in cells with the C217R mutation. Patients homozygous for S227P showed higher frequency of supravalvular aortic stenosis, emphysema and cardiopulmonary failure than patients with C217R, suggesting that toxicity associated with misfolded proteins may contribute to the pathogenesis of recessive cutis laxa. G202R showed increased affinity to elastin and promoted deposition of tropoelastin. It was found in a patient who also carried a disease-causing mutation in the elastin gene but only developed cutis laxa after skin inflammation. Thus, we concluded that acquired cutis laxa is a complex disease caused by the interaction of positive and negative genetic factors and inflammatory disease. These findings support a model of extracellular matrix formation, in which fibulin-5 facilitates the deposition of tropoelastin onto a microfibrillar scaffold via direct molecular interactions.