Microfibril-associated MAGP-2 Stimulates Elastic Fiber Assembly

Abstract

Elastic fibers are complex structures composed of a tropoelastin inner core and microfibril outer mantle guiding tropoelastin deposition. Microfibrillar proteins mainly include fibrillins and microfibril-associated glycoproteins (MAGPs). MAGP-2 exhibits developmental expression peaking at elastic fiber onset, suggesting that MAGP-2 mediates elastic fiber assembly. To determine whether MAGP-2 regulates elastic fiber assembly, we used an in vitro model featuring doxycycline-regulated cells conditionally overexpressing exogenous MAGP-2 and constitutively expressing enhanced green fluorescent protein-tagged tropoelastin. Analysis by immunofluorescent staining showed that MAGP-2 overexpression dramatically increased elastic fibers levels, independently of extracellular levels of soluble tropoelastin, indicating that MAGP-2 stimulates elastic fiber assembly. This was associated with increased levels of matrix-associated MAGP-2. Electron microscopy showed that MAGP-2 specifically associates with microfibrils and that elastin globules primarily colocalize with MAGP-2-associated microfibrils, suggesting that microfibril-associated MAGP-2 facilitates elastic fiber assembly. MAGP-2 overexpression did not change levels of matrix-associated fibrillin-1, MAGP-1, fibulin-2, fibulin-5, or emilin-1, suggesting that microfibrils and other elastic fiberassociated proteins known to regulate elastogenesis do not mediate MAGP-2-induced elastic fiber assembly. Moreover, mutation analysis showed that MAGP-2 does not stimulate elastic fiber assembly through its RGD motif, suggesting that integrin receptor binding does not mediate MAGP-2-induced elastic fiber assembly. Because MAGP-2 interacts with Jagged-1 that controls cell-matrix interaction and cell motility, two key factors in elastic fiber macroassembly, microfibril-associated MAGP-2 may stimulate elastic fiber macroassembly by targeting the release of elastin globules from the cell membrane onto developing elastic fibers.

Microfibril-associated Glycoprotein 2 (MAGP2) Loss of Function Has Pleiotropic Effects in Vivo

“…studies suggest MAGP2 expression may be necessary for normal elastic fiber assembly (30). This idea is supported by the expression pattern of MAGP2 in elastin-rich structures such as the aorta, aortic root, atrialis of the mitral valve, bronchioles of the lung, large vessels of the heart, lung, and kidney, as well as skin (Figs.…”

Effects of tamoxifen and ethynylestradiol cotreatment on uterine gene expression in immature, ovariectomized mice

“…Cytoskeletal reorganization is integral to estrogenmediated restructuring of proliferating tissue (Moggs et al 2004). Several genes associated with the cytoskeleton including Bicd2 (Hoogenraad et al 2003), Dctn2 (Uetake et al 2004), and Mfap5 (Lemaire et al 2007) were induced by EE and repressed after TAM cotreatment (category A). Although these genes have not been identified to be ER regulated, their differential expression serves to prepare the tissue for proliferation, and therefore, their inhibition is consistent with a compromised uterotrophic response.…”

Tissue elasticity and the ageing elastic fibre

“…Subsequent microfibril assembly, which occurs pericellularly, is critically dependent on interactions with heparin, heparan sulphate and fibronectin (Kinsey et al 2008;Tiedemann et al 2001). Elastin, which is secreted as the soluble precursor, tropoelastin, aggregates at the cell surface prior to transfer onto the microfibril scaffold and enzymatic conversion to the mature cross-linked form via lysyl oxidase (LOX) or LOX-like proteins (Lemaire et al 2007;Mithieux and Weiss 2005). In the mature elastic fibre, the elastin core comprises over 90% of the volume whilst the fibrillin microfibrils are largely to confined to an outer mantle (Mecham and Davis 1994).…”

“…The elastic modulus of fibrillin microfibrils, however, remains controversial with estimates ranging from 1.0 MPa (Aaron and Gosline 1981) to 96 MPa (Sherratt et al 2003) Gallagher et al 2005;Hubmacher et al 2006;Kielty et al 2002). The MAGPs are small proteins which, in the case of MAGP-1, appear to be essential for the maintenance of microfibril structure (Lemaire et al 2007). The carboxy-termini of MAGP-1 and -2 are thought to bind to the amino-terminal regions of fibrillin via disulphide bonds (Penner et al 2002).…”