Aortic microcalcification is associated with elastin fragmentation in Marfan syndrome

Marfan syndrome (MFS) is a connective tissue disorder in which aortic rupture is the major cause of death. MFS patients with an aortic diameter below the advised limit for prophylactic surgery (<5 cm) may unexpectedly experience an aortic dissection or rupture, despite yearly monitoring. Hence, there is a clear need for improved prognostic markers to predict such aortic events. We hypothesize that elastin fragments play a causal role in aortic calcification in MFS, and that microcalcification serves as a marker for aortic disease severity. To address this hypothesis, we analysed MFS patient and mouse aortas. MFS patient aortic tissue showed enhanced microcalcification in areas with extensive elastic lamina fragmentation in the media. A causal relationship between medial injury and microcalcification was revealed by studies in vascular smooth muscle cells (SMCs); elastin peptides were shown to increase the activity of the calcification marker alkaline phosphatase (ALP) and reduce the expression of the calcification inhibitor matrix GLA protein in human SMCs. In murine Fbn1C1039G/+ MFS aortic SMCs, Alpl mRNA and activity were upregulated as compared with wild-type SMCs. The elastin peptide-induced ALP activity was prevented by incubation with lactose or a neuraminidase inhibitor, which inhibit the elastin receptor complex, and a mitogen-activated protein kinase kinase-1/2 inhibitor, indicating downstream involvement of extracellular signal-regulated kinase-1/2 (ERK1/2) phosphorylation. Histological analyses in MFS mice revealed macrocalcification in the aortic root, whereas the ascending aorta contained microcalcification, as identified with the near-infrared fluorescent bisphosphonate probe OsteoSense-800. Significantly, microcalcification correlated strongly with aortic diameter, distensibility, elastin breaks, and phosphorylated ERK1/2. In conclusion, microcalcification co-localizes with aortic elastin degradation in MFS aortas of humans and mice, where elastin-derived peptides induce a calcification process in SMCs via the elastin receptor complex and ERK1/2 activation. We propose microcalcification as a novel imaging marker to monitor local elastin degradation a

Glycoproteomic Analysis of the Aortic Extracellular Matrix in Marfan Patients.

OBJECTIVE: Marfan syndrome (MFS) is caused by mutations in FBN1 (fibrillin-1), an extracellular matrix (ECM) component, which is modified post-translationally by glycosylation. This study aimed to characterize the glycoproteome of the aortic ECM from patients with MFS and relate it to aortopathy. Approach and Results: ECM extracts of aneurysmal ascending aortic tissue from patients with and without MFS were enriched for glycopeptides. Direct N-glycopeptide analysis by mass spectrometry identified 141 glycoforms from 47 glycosites within 35 glycoproteins in the human aortic ECM. Notably, MFAP4 (microfibril-associated glycoprotein 4) showed increased and more diverse N-glycosylation in patients with MFS compared with control patients. MFAP4 mRNA levels were markedly higher in MFS aortic tissue. MFAP4 protein levels were also increased at the predilection (convexity) site for ascending aorta aneurysm in bicuspid aortic valve patients, preceding aortic dilatation. In human aortic smooth muscle cells, MFAP4 mRNA expression was induced by TGF (transforming growth factor)-β1 whereas siRNA knockdown of MFAP4 decreased FBN1 but increased elastin expression. These ECM changes were accompanied by differential gene expression and protein abundance of proteases from ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family and their proteoglycan substrates, respectively. Finally, high plasma MFAP4 concentrations in patients with MFS were associated with a lower thoracic descending aorta distensibility and greater incidence of type B aortic dissection during 68 months follow-up. CONCLUSIONS: Our glycoproteomics analysis revealed that MFAP4 glycosylation is enhanced, as well as its expression during the advanced, aneurysmal stages of MFS compared with control aneurysms from patients without MFS

Pregnancy and Thoracic Aortic Disease: Managing the Risks

The most common aortopathies in women of childbearing age are bicuspid aortic valve, coarctation of the aorta, Marfan syndrome, Ehlers-Danlos syndrome, Loeys-Dietz syndrome, SMAD3 aortopathy, Turner syndrome, and familial thoracic aneurysm and dissection. The hemodynamic and hormonal changes of pregnancy increase the risk of progressive dilatation or dissection of the aorta in these women. The presence of hypertension increases the risk further. Therefore, appropriate preconception counselling is advised. For women who become pregnant, serial follow-up by a specialized multidisciplinary team throughout pregnancy and postpartum period is required. In this review we discuss risk assessment and management strategies for women with aortopathie

Microfibril-associated glycoprotein 4 forms octamers that mediate interactions with elastogenic proteins and cells

Abstract Microfibril-associated glycoprotein 4 (MFAP4) is a 36-kDa extracellular matrix glycoprotein with critical roles in organ fibrosis, chronic obstructive pulmonary disease, and cardiovascular disorders, including aortic aneurysms. MFAP4 multimerises and interacts with elastogenic proteins, including fibrillin-1 and tropoelastin, and with cells via integrins. Structural details of MFAP4 and its potential interfaces for these interactions are unknown. Here, we present a cryo-electron microscopy structure of human MFAP4. In the presence of calcium, MFAP4 assembles as an octamer, where two sets of homodimers constitute the top and bottom halves of each octamer. Each homodimer is linked together by an intermolecular disulphide bond. A C34S missense mutation prevents disulphide-bond formation between monomers but does not prevent octamer assembly. The atomic model, built into the 3.55 Å cryo-EM map, suggests that salt-bridge interactions mediate homodimer assembly, while non-polar residues form the interface between octamer halves. In the absence of calcium, an MFAP4 octamer dissociates into two tetramers. Binding studies with fibrillin-1, tropoelastin, LTBP4, and small fibulins show that MFAP4 has multiple surfaces for protein-protein interactions, most of which depend upon MFAP4 octamer assembly. The C34S mutation does not affect these protein interactions or cell interactions. MFAP4 assemblies with fibrillin-1 abrogate MFAP4 interactions with cells

Renal cystic disease in the Fbn1C1039G/+ Marfan mouse is associated with enhanced aortic aneurysm formation

Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in the fibrillin-1 gene (FBN1), resulting in aortic aneurysm formation and dissections. Interestingly, variable aortopathy is observed even within MFS families with the same mutation. Thus, additional risk factors determine disease severity. Here, we describe a case of a 2-month-old Fbn1C1039G/+ MFS mouse with extreme aortic dilatation and increased vascular inflammation, when compared to MFS siblings, which coincided with unilateral renal cystic disease. In addition, this mouse presented with increased serum levels of creatinine, angiotensin-converting enzyme, corticosterone, macrophage chemoattractant protein-1, and interleukin-6, which may have contributed to the vascular pathology. Possibly, cystic kidney disease is associated with aneurysm progression in MFS patients. Therefore, we propose that close monitoring of the presence of renal cysts in MFS patients, during regular vascular imaging of the whole aorta trajectory, may provide insight in the frequency of cystic kidney disease and its potential as a novel indicator of aneurysm progression in MFS patients

qPCR measurement of FL-MMP-2 and NTT-MMP-2 transcript abundance in control protocol biopsies and DGF biopsies.

<p>mRNA was extracted from paraffin-embedded formalin-fixed renal biopsy specimens and FL-MMP-2 and NTT-MMP-2 transcript abundance was determined by qPCR as detailed in Materials and Methods. Both isoforms were normalized to a ribosomal protein, 36B4. There was a low, but detectable level of FL-MMP-2 transcript in the control protocol biopsies, consistent with the level of FL-MMP-2 immunohistochemical staining shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136276#pone.0136276.g002" target="_blank">Fig 2</a>. FL-MMP-2 transcript abundance was increased approximately twelve-fold in the DGF samples. NTT-MMP-2 transcript abundance was nearly undetectable in the control protocol biopsies, consistent with the absence of NTT-MMP-2 immunohistochemical staining in controls (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0136276#pone.0136276.g002" target="_blank">Fig 2</a>). In contrast, NTT-MMP-2 transcripts were readily detectable in the DGF biopsies (* p<0.01).</p

FL-MMP-2 and NTT-MMP-2 are found within discrete tubular epithelial cellular compartments.

<p>Images of DGF biopsies were acquired using Nomarksi optics and processed with pseudocolor to enhance contrast as detailed in Materials and Methods. Panel A: Immunohistochemical staining for FL-MMP-2 is confined to the cytoplasmic compartment (N, nucleus). Panel B: Immunohistochemical staining for NTT-MMP-2 is concentrated at the basolateral surfaces of the proximal tubular epithelial cells adjacent to the tubular basement membrane. The insert demonstrates NTT-MMP-2 staining within extended filamentous structures contained within basolateral infoldings characteristic of mitochondria. (Final magnification Panels A, B: X600, insert X1200).</p

FL-MMP-2 and NTT-MMP-2 expression in control protocol renal biopsies.

<p>Panel A: Control protocol biopsy stained for FL-MMP-2. There is trace, focal immunohistochemical staining for FL-MMP-2 in proximal tubules (arrows) Panel B: Control protocol biopsy stained for NTT-MMP-2. There is no detectable immunohistochemical staining. (Final magnification X 200).</p

Tubular Injury Scoring Scale.

<p>Tubular Injury Scoring Scale.</p

Characteristics of Study Population by Transplant Type.

<p>Characteristics of Study Population by Transplant Type.</p