Targeted Disruption of Fibulin-4 Abolishes Elastogenesis and Causes Perinatal Lethality in Mice

Abstract

Elastic fibers provide tissues with elasticity which is critical to the function of arteries, lungs, skin, and other dynamic organs. Loss of elasticity is a major contributing factor in aging and diseases. However, the mechanism of elastic fiber development and assembly is poorly understood. Here, we show that lack of fibulin-4, an extracellular matrix molecule, abolishes elastogenesis. fibulin-4 ؊/؊ mice generated by gene targeting exhibited severe lung and vascular defects including emphysema, artery tortuosity, irregularity, aneurysm, rupture, and resulting hemorrhages. All the homozygous mice died perinatally. The earliest abnormality noted was a uniformly narrowing of the descending aorta in fibulin-4 ؊/؊ embryos at embryonic day 12.5 (E12.5). Aorta tortuosity and irregularity became noticeable at E15.5. Histological analysis demonstrated that fibulin-4 ؊/؊ mice do not develop intact elastic fibers but contain irregular elastin aggregates. Electron microscopy revealed that the elastin aggregates are highly unusual in that they contain evenly distributed rod-like filaments, in contrast to the amorphous appearance of normal elastic fibers. Desmosine analysis indicated that elastin cross-links in fibulin-4 ؊/؊ tissues were largely diminished. However, expression of tropoelastin or lysyl oxidase mRNA was unaffected in fibulin-4 ؊/؊ mice. In addition, fibulin-4 strongly interacts with tropoelastin and colocalizes with elastic fibers in culture. These results demonstrate that fibulin-4 plays an irreplaceable role in elastogenesis.Elastic fibers with morphologically distinct architectures are present in the extracellular matrix (ECM) to accommodate elastic requirements and mechanical stresses imposed on different tissues. They are particularly abundant in elastic tissues such as large blood vessels, lung, and skin. Loss of elasticity is a major contributing factor in aging and a myriad of pathological conditions including emphysema, artery diseases, and cutis laxa (39,41,44). Elastic fibers undergo irreversible structural and compositional changes with age and in some pathological conditions (41). Regardless of morphology, all elastic fibers consist of cross-linked elastin, fibrillin-rich microfibrils, and several associated molecules (23,37,38,46). Elastin endows the fiber with the characteristic property of elastic recoil. It is chemically inert, extremely hydrophobic, and insoluble under most conditions. Monomeric elastin, called tropoelastin, is secreted from the cell as a soluble protein. Isolated and purified tropoelastin has been shown to exhibit a great tendency to aggregate (coacervation) in physiological solution and at temperatures in the physiological range, giving rise to supramolecular structures very similar to those found in natural elastic fibers (4,5,11). This self-aggregation property of tropoelastin is thought to contribute to elastic fiber assembly in vivo. However, self-aggregation alone is insufficient to explain the efficiency of the assembly process and the variable form of elastic fibers ...

New insights into elastic fiber assembly

“…The elastic fibers contain irregular elastin aggregates with evenly distributed rod-like filaments visible within the usual amorphous globules. Elastin cross-links are greatly reduced, but the expression of tropoelastin and LOX is normal (McLaughlin et al, 2006). The rod-like filaments in the fbn42/2 elastic lamellae resemble those observed in the aorta of chicks fed b-aminopropionitrile (BAPN), an irreversible LOX inhibitor.…”

“…Fibulin-4 and/or -5 interact with these aggregates to facilitate cross-linking (McLaughlin et al, 2006) or to limit the aggregate size. The elastin aggregates remain on the cell surface long enough for new elastin to be secreted from the cell and added to the aggregates .…”

Fibulin-2 Is Dispensable for Mouse Development and Elastic Fiber Formation

“…A reduction in elastic fibers specifically in fascia connective tissues may explain the herniation phenotype. Mice lacking either fibulin-4 or fibulin-5 have highly disrupted and disorganized elastic fibers, leading to developmental defects in skin, arterial blood vessels, and lungs (13,14,27). Although the elastic fiber abnormalities are similar in these two mouse mutants, the fibulin-4 null mice are perinatally lethal, whereas the fibulin-5-deficient mice can survive until adulthood.…”

Overexpression of fibulin-4 is associated with tumor progression and poor prognosis in patients with cervical carcinoma

“…Our immunohistochemical studies showed an upregulation of fibulin-4 expression in cervical carcinoma tissues, compared with normal cervical tissues and CIN. Fibulin-4 is rich in elastic fiber tissue, and is mainly involved in the synthesis and arrangement of elastic fibers (39). In the present study, the expression of fibulin-4 in the extracellular matrix was found Figure 4.…”