Microfibril-associated MAGP-2 Stimulates Elastic Fiber Assembly

Microfibril-Associated Glycoprotein-2 Promoted Fracture Healing via Integrin αvβ3/PTK2/AKT Signaling

Fracture healing is a complex physiological process in which angiogenesis plays an essential role. Microfibril-associated glycoprotein-2 (MAGP2) has been reported to possess a proangiogenic activity via integrin αvβ3, yet its role in bone repair is unexplored. In this study, a critical-sized femoral defect (2 mm) was created in mice, followed by the delivery of an adenovirus-based MAGP2 overexpression vector or its negative control at the fracture site. At days 7, 14, 21, and 28 postfracture, bone fracture healing was evaluated by radiography, micro-computed tomography, and histopathologic analysis. Adenovirus-based MAGP2 overexpression vector-treated mice exhibited increased bone mineral density and bone volume fraction. MAGP2 overexpression contributed to an advanced stage of endochondral ossification and induced cartilage callus into the bony callus. Further analysis indicated that MAGP2 was associated with enhanced angiogenesis, as evidenced by marked MAGP2 and integrin αvβ3 costaining and increased endothelial cell markers such as endomucin and CD31 levls, as well as elevated phosphorylation of protein tyrosine kinase 2 (PTK2) and AKT serine/threonine kinase 1 (AKT) in the callus. In vitro, recombinant human MAGP2 treatment enhanced the viability, migration, and tube formation ability of human microvascular endothelial cells, which was partially reversed by integrin αvβ3 inhibition or MK-2206, a specific AKT inhibitor. Inhibition of integrin αvβ3 abolished MAGP2-induced PTK2 and AKT activation. Taken together, our data provide the first evidence that MAGP2 promotes angiogenesis and bone formation by activating the integrin αvβ3/PTK2/AKT signaling pathway.

Specific Overexpression of YAP in Vascular Smooth Muscle Attenuated Abdominal Aortic Aneurysm Formation by Activating Elastic Fiber Assembly via LTBP4

Abdominal aortic aneurysm (AAA) is a fatal vascular disease. Vascular smooth muscle cells (VSMCs) play a crucial role in the pathogenesis of AAA. Increasing evidence has shown that Yes-associated protein (YAP) is involved in diverse vascular diseases. However, the role of YAP in AAA remains unclear. The current study aimed to determine the role of YAP in AAA formation and the underlying mechanism. We found that YAP expression in VSMCs was markedly decreased in human and experimental AAA samples. Furthermore, VSMC-specific YAP overexpression prevented several pathogenic factor-induced AAA. Mechanistically, YAP overexpression in VSMCs promoted latent transforming growth factor-β binding protein 4 (LTBP4) expression, an important factor in elastic fiber assembly. Finally, silencing of LTBP4 in VSMCs abolished the protective role of YAP in AAA formation in vivo. Our results suggest that YAP promotes LTBP4-mediated elastic fibril assembly in VSMCs, which mitigates elastin degradation and AAA formation.

MFAP4-Mediated Effects in Elastic Fiber Homeostasis, Integrin Signaling and Cancer, and Its Role in Teleost Fish

Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix (ECM) protein belonging to the fibrinogen-related domain superfamily. MFAP4 is highly expressed in elastin-rich tissues such as lung, blood vessels and skin. MFAP4 is involved in organization of the ECM, regulating proper elastic fiber assembly. On the other hand, during pathology MFAP4 actively contributes to disease development and progression due to its interactions with RGD-dependent integrin receptors. Both tissue expression and circulating MFAP4 levels are associated with various disorders, including liver fibrosis and cancer. In other experimental models, such as teleost fish, MFAP4 appears to participate in host defense as a macrophage-specific innate immune molecule. The aim of this review is to summarize the accumulating evidence that indicates the importance of MFAP4 in homeostasis as well as pathological conditions, discuss its known biological functions with special focus on elastic fiber assembly, integrin signaling and cancer, as well as describe the reported functions of non-mammalian MFAP4 in fish. Overall, our work provides a comprehensive overview on the role of MFAP4 in health and disease.

The "Elastic Perspective" of SARS-CoV-2 Infection and the Role of Intrinsic and Extrinsic Factors

Elastin represents the structural component of the extracellular matrix providing elastic recoil to tissues such as skin, blood vessels and lungs. Elastogenic cells secrete soluble tropoelastin monomers into the extracellular space where these monomers associate with other matrix proteins (e.g., microfibrils and glycoproteins) and are crosslinked by lysyl oxidase to form insoluble fibres. Once elastic fibres are formed, they are very stable, highly resistant to degradation and have an almost negligible turnover. However, there are circumstances, mainly related to inflammatory conditions, where increased proteolytic degradation of elastic fibres may lead to consequences of major clinical relevance. In severely affected COVID-19 patients, for instance, the massive recruitment and activation of neutrophils is responsible for the profuse release of elastases and other proteolytic enzymes which cause the irreversible degradation of elastic fibres. Within the lungs, destruction of the elastic network may lead to the permanent impairment of pulmonary function, thus suggesting that elastases can be a promising target to preserve the elastic component in COVID-19 patients. Moreover, intrinsic and extrinsic factors additionally contributing to damaging the elastic component and to increasing the spread and severity of SARS-CoV-2 infection are reviewed.

Development of a CAFs-related gene signature to predict survival and drug response in bladder cancer

As one of important components of tumor microenvironment, CAFs (cancer-associated fibroblasts) play a vital role in the development and metastasis of bladder cancer. The present study aimed to develop a CAFs-related gene signature to predict the prognosis of patients and the response to chemotherapy and immunotherapy based on research of multidatabase. Expression data and clinical information were obtained from TCGA and GEO databases. Different bioinformatic and statistical methods were combined to construct the robust CAFs-related gene signature for prognosis. The model was explored from four aspects: single-cell source, immune infiltration, correlation with cancer-related genes and pathways, and prediction of drug response. After screening, five genes (BNC2, LAMA2, MFAP5, NID1, and OLFML1) related to CAFs were used for constructing the signature to divide patients into high- and low-risk groups. Patients in low-risk group had better prognosis and multidatabase analysis confirmed the predictive value. The five genes were mainly expressed by fibroblasts and involved in regulation of pathways related with glycolysis, hypoxia, and epithelial-mesenchymal transition (EMT). BNC2, LAMA2, and NID1 were strongly associated with drug sensitivity. Moreover, the immunological status was different between high- and low-risk groups. High-risk patients had poor response to chemotherapy or immunotherapy. The CAFs-related gene signature might help to optimize risk stratification and provide a new insight in individual treatment for bladder cancer.

Microfibrillar-associated protein 5 regulates osteogenic differentiation by modulating the Wnt/β-catenin and AMPK signaling pathways

Background

Dysfunctional osteogenesis of bone marrow mesenchymal stem cells (BMSCs) plays an important role in osteoporosis occurrence and development. However, the molecular mechanisms of osteogenic differentiation remain unclear. This study explored whether microfibrillar-associated protein 5 (MFAP5) regulated BMSCs osteogenic differentiation.

Methods

We used shRNA or cDNA to knock down or overexpress MFAP5 in C3H10 and MC3T3-E1 cells. AR-S- and ALP-staining were performed to quantify cellular osteogenic differentiation. The mRNA levels of the classical osteogenic differentiation biomarkers Runx2, Col1α1, and OCN were quantified by qRT-PCR. Finally, we employed Western blotting to measure the levels of Wnt/β-catenin and AMPK signaling proteins.

Results

At days 0, 3, 7, and 14 after osteogenic induction, AR-S- and ALP-staining was lighter in MFAP5 knockdown compared to control cells, as were the levels of Runx2, Col1α1 and OCN. During osteogenesis, the levels of β-catenin, p-GSK-3β, AMPK, and p-AMPK were upregulated, while that of GSK-3β was downregulated, indicating that Wnt/β-catenin and AMPK signaling were activated. The relevant molecules were expressed at lower levels in the knockdown than control group; the opposite was seen for overexpressing cell lines.

Conclusions

MFAP5 regulates osteogenesis via Wnt/β‑catenin- and AMPK-signaling; MFAP5 may serve as a therapeutic target in patients with osteoporosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00413-0.

Structural studies of elastic fibre and microfibrillar proteins

Elastic tissues owe their functional properties to the composition of their extracellular matrices, particularly the range of extracellular, multidomain extensible elastic fibre and microfibrillar proteins. These proteins include elastin, fibrillin, latent TGFβ binding proteins (LTBPs) and collagens, where their biophysical and biochemical properties not only give the matrix structural integrity, but also play a vital role in the mechanisms that underlie tissue homeostasis. Thus far structural information regarding the structure and hierarchical assembly of these molecules has been challenging and the resolution has been limited due to post-translational modification and their multidomain nature leading to flexibility, which together result in conformational and structural heterogeneity. In this review, we describe some of the matrix proteins found in elastic fibres and the new emerging techniques that can shed light on their structure and dynamic properties.

Modulation of Photoaging-Induced Cutaneous Elastin: Evaluation of Gene and Protein Expression of Markers Related to Elastogenesis Under Different Photoexposure Conditions

INTRODUCTION

Photoaging is the process by which ultraviolet rays gradually induce clinical and histological changes in the skin through the production and organization of biological molecules, such as elastin, which is critical to skin strength and elasticity. After exposure to radiation, elastin may undergo alternative mRNA splicing, resulting in modified proteins that contribute to the formation of aging characteristics, such as solar elastosis. The present work aimed to study two different forms of elastin under these conditions: normal elastin and elastin that had been altered in exon 26A.

METHODS

These different forms of elastin were characterized for gene expression by quantitative real-time polymerase chain reaction (qPCR) and for protein expression by immunohistochemistry of ex vivo skins (from photoexposed and non-photoexposed areas) and in vitro reconstituted skin. In addition, up- and downstream molecules in the elastin signaling cascade were evaluated.

RESULTS

As a result, a significant increase in the gene expression of elastin 26A was observed in both ex vivo photoexposed skin tissues and the in vitro photoexposed reconstituted skins. Additionally, significant increases in the gene expression levels of matrix metalloproteinase-12 (MMP12) and lysyl oxidase (LOX) were observed in the ex vivo skin model. The evaluation of protein expression levels of some photoaging markers on the reconstituted skin revealed increased tropoelastin and fibrillin-1 expression after photoexposure.

CONCLUSION

This work contributes to a better understanding of the biological mechanisms involved in photoaging, making it possible to obtain new strategies for the development of dermocosmetic active ingredients to prevent and treat skin aging.

Primary angle closure glaucoma is characterized by altered extracellular matrix homeostasis in the iris

PURPOSE

To characterize the proteome of the iris in primary angle closure glaucoma (PACG).

EXPERIMENTAL DESIGN

In this cross-sectional study, iris samples were obtained from surgical iridectomy of 48 adults with PACG and five normal controls. Peptides from iris were analysed using liquid chromatography-tandem mass spectrometry on an Orbitrap Q Exactive Plus mass spectrometer. Verification of proteins of interest was conducted using selected reaction monitoring on a triple quadrupole mass spectrometer. The main outcome was proteins with a log₂ two-fold difference in expression in iris between PACG and controls.

RESULTS

There were 3,446 non-redundant proteins identified in human iris, of which 416 proteins were upregulated and 251 proteins were downregulated in PACG compared with controls. Thirty-two upregulated proteins were either components of the extracellular matrix (ECM) (fibrillar collagens, EMILIN-2, fibrinogen, fibronectin, matrilin-2), matricellular proteins (thrombospondin-1), proteins involved in cell-matrix interactions (integrins, laminin, histidine-rich glycoprotein, paxillin), or protease inhibitors known to modulate ECM turnover (α-2 macroglobulin, tissue factor pathway inhibitor 2, papilin). Two giant proteins, titin and obscurin, were up- and down-regulated, respectively, in the iris in PACG compared with controls.

CONCLUSIONS AND CLINICAL RELEVANCE

This proteomic study shows that ECM composition and homeostasis are altered in the iris in PACG.

Elastic tissue disruption is a major pathogenic factor to human vascular disease

Elastic fibers are essential components of the arterial extracellular matrix. They consist of the protein elastin and an array of microfibrils that support the protein and connect it to the surrounding matrix. The elastin gene encodes tropoelastin, a protein that requires extensive cross-linking to become elastin. Tropoelastin is expressed throughout human life, but its expression levels decrease with age, suggesting that the potential to synthesize elastin persists during lifetime although declines with aging. The initial abnormality documented in human atherosclerosis is fragmentation and loss of the elastic network in the medial layer of the arterial wall, suggesting an imbalance between elastic fiber injury and restoration. Damaged elastic structures are not adequately repaired by synthesis of new elastic elements. Progressive collagen accumulation follows medial elastic fiber disruption and fibrous plaques are formed, but advanced atherosclerosis lesions do not develop in the absence of prior elastic injury. Aging is associated with arterial extracellular matrix anomalies that evoke those present in early atherosclerosis. The reduction of elastic fibers with subsequent collagen accumulation leads to arterial stiffening and intima-media thickening, which are independent predictors of incident hypertension in prospective community-based studies. Arterial stiffening precedes the development of hypertension. The fundamental role of the vascular elastic network to arterial structure and function is emphasized by congenital disorders caused by mutations that disrupt normal elastic fiber production. Molecular changes in the genes coding tropoelastin, lysyl oxidase (tropoelastin cross-linking), and elastin-associated microfibrils, including fibrillin-1, fibulin-4, and fibulin-5 produce severe vascular injury due to absence of functional elastin.

Hypoxia-induced MFAP5 Promotes Tumor Migration and Invasion via AKT Pathway in Head and Neck Squamous Cell Carcinoma

Objective: Microfibrillar-associated protein 5 (MFAP5) is highly expressed in many types of cancers. Our previous study has observed that overexpression of MFAP5 was correlated with lymph nodes metastasis and poor prognosis in head and neck squamous cell carcinoma (HNSCC), but the underlying mechanism is poorly understood.

Materials and methods: The MFAP5 expression is detected under hypoxia condition. HNSCC cell lines are transfected with MFAP5-expressing lentivirus vector to establish stable overexpression model. Wound-healing, migration and invasion assay are used to determine the effect of MFAP5 on HNSCC and metastasis-related proteins are examined by Western blot. In vivo lung metastasis assays are conducted by the tail vein injection. In addition, immunohistochemistry is applied to analyze the correlation of MFAP5, hypoxia-induced factor-1 α (HIF-1α), and vimentin in 84 HNSCC patients' tissue samples.

Results: Firstly, MFAP5 expression can be markedly induced under hypoxia condition in HNSCC cell lines. Cell lines with MFAP5 overexpression has a significant higher ability of migration and invasion. In addition, in vivo assay observes that overexpression of MFAP5 can promote tumor lung metastasis. Furthermore, MFAP5 facilitates this process by activating epithelial-mesenchymal transition (EMT) program via AKT pathway in HNSCC cell lines. The pro-metastatic effect of MFAP5 can be reversed by MK2206, an AKT phosphorylation inhibitor. Lastly, the positive correlation among HIF-1α, MFAP5 and vimentin from tissue samples and TCGA dataset are also observed in HNSCC.

Conclusion: Our study demonstrates MFAP5 plays a critical role in hypoxia-induced EMT program via AKT pathway in HNSCC, which would be a very promising therapeutic target.

Studies on sporadic non-syndromic thoracic aortic aneurysms: II. Alterations of extra-cellular matrix components and focal adhesion proteins

Background Sporadic non-syndromic thoracic aortic aneurysms (SNSTAAs) are less well understood than familial non-syndromic or syndromic ones. Here, we focused on morphologic and molecular changes of the extracellular matrix of the tunica media of SNSTAAs. Design Single centre design. Methods Surgical media samples from seven SNSTAAs and seven controls underwent quantitative polymerase chain reaction, proteomics-bioinformatics, immunoblotting, histology and immunohistochemistry analysis. Results A down-regulation of Decorin mRNA with unchanged protein levels associated with a remarkable increase of collagen fibres. A reduced and distorted network of elastic fibres partnered with an attenuated expression of microfibril-associated glycoprotein1 despite the rise of MFAP2 gene-encoded mRNA levels. An increasingly proteolysed paxillin (55 kDa PXN), a focal adhesion protein, combined with an upregulated 62 kDa PXN holoprotein, without changes in amount and phosphorylation of focal adhesion kinase (pp125^FAK). The upregulation of SPOCK2-encoded Testican2 proteoglycan and of ectodysplasin (EDA) protein was coupled with a down-regulation of EDA2 receptor (EDA2R). Conclusions Several tunica media extracellular matrix-related changes favour SNSTAA development. A steady level of decorin and a microfibril-associated glycoprotein1 protein shortage cause the assembly of structurally defective collagen and elastic fibres. Up-regulation of PXN holoproteins perturbs PXN/pp125^FAK interaction and focal adhesion functioning. Testican2 up-regulation suppresses the membrane-type matrix metalloproteinase inhibiting activities of other SPOCK family members thus enhancing extracellular matrix proteolysis. Finally, the altered EDA•EDA2R signalling would impact on the remodelling of SNSTAA tunica media. Altogether, our results pave the way to a deeper molecular understanding of SNSTAAs necessary to identify their early diagnostic biochemical markers.

MFAP5 promotes basal-like breast cancer progression by activating the EMT program

Purpose

Human basal-like breast cancer (BLBC) is an aggressive malignancy with poor prognosis. Since most current treatments are ineffective, there is an urgent need to identify therapeutic targets for BLBC. Microfibrillar-associated protein 5 (MFAP5) plays an important role in the integration of elastic microfibers and the regulation of endothelial cell behaviors. We previously demonstrated that MFAP5 was significantly overexpressed in BLBC tissues and associated with poor metastasis-free survival of patients with BLBC. However, the detailed role of MFAP5 in BLBC is unclear. Thereby, the current study aimed to investigate the underlying function of MFAP5 in BLBC.

Method

Functional analyses were conducted for the role of MFAP5 in BLBC in vitro and in vivo.

Results

Overexpression of MFAP5 resulted in a significant increase in the proliferation, migration, invasion and epithelial–mesenchymal transition (EMT) markers in BLBC in vitro and in vivo. In addition, other metastasis animal models by tail intravenous injection of BT20 cells further confirmed that MFAP5 overexpression promoted BLBC proliferation and BT20 cells metastasis. We found that the TGF-β or Notch inhibitor significantly reversed the tumorigenicity and metastasis of MFAP5-induced BLBC cells.

Conclusion

Our findings suggest that MFAP5 may promote EMT in BLBC metastasis via the TGF-β/Notch pathway.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0284-0) contains supplementary material, which is available to authorized users.

Fibrillin microfibrils and elastic fibre proteins: Functional interactions and extracellular regulation of growth factors

Fibrillin microfibrils are extensible polymers that endow connective tissues with long-range elasticity and have widespread distributions in both elastic and non-elastic tissues. They act as a template for elastin deposition during elastic fibre formation and are essential for maintaining the integrity of tissues such as blood vessels, lung, skin and ocular ligaments. A reduction in fibrillin is seen in tissues in vascular ageing, chronic obstructive pulmonary disease, skin ageing and UV induced skin damage, and age-related vision deterioration. Most mutations in fibrillin cause Marfan syndrome, a genetic disease characterised by overgrowth of the long bones and other skeletal abnormalities with cardiovascular and eye defects. However, mutations in fibrillin and fibrillin-binding proteins can also cause short-stature pathologies. All of these diseases have been linked to dysregulated growth factor signalling which forms a major functional role for fibrillin.

Elastin-driven genetic diseases

Elastic fibers provide recoil to tissues that undergo repeated deformation, such as blood vessels, lungs and skin. Composed of elastin and its accessory proteins, the fibers are produced within a restricted developmental window and are stable for decades. Their eventual breakdown is associated with a loss of tissue resiliency and aging. Rare alteration of the elastin (ELN) gene produces disease by impacting protein dosage (supravalvar aortic stenosis, Williams Beuren syndrome and Williams Beuren region duplication syndrome) and protein function (autosomal dominant cutis laxa). This review highlights aspects of the elastin molecule and its assembly process that contribute to human disease and also discusses potential therapies aimed at treating diseases of elastin insufficiency.

FGF receptors control alveolar elastogenesis

Alveologenesis, the final step of lung development, is characterized by the formation of millions of alveolar septa that constitute the vast gas-exchange surface area. The genetic network driving alveologenesis is poorly understood compared with earlier steps in lung development. FGF signaling through receptors Fgfr3 and Fgfr4 is crucial for alveologenesis, but the mechanisms through which they mediate this process remain unclear. Here we show that in Fgfr3;Fgfr4 (Fgfr3;4) global mutant mice, alveolar simplification is first observed at the onset of alveologenesis at postnatal day 3. This is preceded by disorganization of elastin, indicating defects in the extracellular matrix (ECM). Although Fgfr3 and Fgfr4 are expressed in the mesenchyme and epithelium, inactivation in the mesenchyme, but not the epithelium, recapitulated the defects. Expression analysis of components of the elastogenesis machinery revealed that Mfap5 (also known as Magp2), which encodes an elastin-microfibril bridging factor, is upregulated in Fgfr3;4 mutants. Mfap5 mutation in the Fgfr3;4 mutant background partially attenuated the alveologenesis defects. These data demonstrate that, during normal lung maturation, FGF signaling restricts expression of the elastogenic machinery in the lung mesenchyme to control orderly formation of the elastin ECM, thereby driving alveolar septa formation to increase the gas-exchange surface.

Characterization of Microfibrillar-associated Protein 4 (MFAP4) as a Tropoelastin- and Fibrillin-binding Protein Involved in Elastic Fiber Formation

MFAP4 (microfibrillar-associated protein 4) is an extracellular glycoprotein found in elastic fibers without a clearly defined role in elastic fiber assembly. In the present study, we characterized molecular interactions between MFAP4 and elastic fiber components. We established that MFAP4 primarily assembles into trimeric and hexameric structures of homodimers. Binding analysis revealed that MFAP4 specifically binds tropoelastin and fibrillin-1 and -2, as well as the elastin cross-linking amino acid desmosine, and that it co-localizes with fibrillin-1-positive fibers in vivo. Site-directed mutagenesis disclosed residues Phe(241) and Ser(203) in MFAP4 as being crucial for type I collagen, elastin, and tropoelastin binding. Furthermore, we found that MFAP4 actively promotes tropoelastin self-assembly. In conclusion, our data identify MFAP4 as a new ligand of microfibrils and tropoelastin involved in proper elastic fiber organization.

MFAP5 is related to obesity-associated adipose tissue and extracellular matrix remodeling and inflammation

OBJECTIVE

Low-grade inflammation is involved in adipose tissue (AT) and extracellular matrix (ECM) remodeling and induces deposition of ECM proteins in AT. We have previously shown that MFAP5 (microfibrillar-associated protein 5) expression decreases in AT after weight loss. The aim of this study was to investigate MFAP5 localization in human AT and gene expression in adipocytes and the role of MFAP5 in adipocyte metabolism and inflammation.

METHODS

MFAP5 protein localization and gene expression were studied with immunohistochemistry and quantitative reverse transcriptase PCR (RT-qPCR) in human subcutaneous AT and cultured Simpson-Golabi-Behmel syndrome (SGBS) adipocytes, respectively. The effect of MFAP5 knock-down by siRNA on gene expression and insulin action was examined with RT-qPCR, western blot, and insulin-stimulated glucose uptake. The effect of different cytokines on MFAP5 gene and protein expression was investigated in cultured human SGBS preadipocytes.

RESULTS

MFAP5 protein was highly expressed in AT, and gene expression decreased during adipocyte differentiation in SGBS cells. Treatment of preadipocytes with TNFα and TGFβ1 increased MFAP5 gene and protein expression. Furthermore, MFAP5 knock-down decreased the expression of genes involved in inflammation.

CONCLUSIONS

Our results demonstrate that factors involving low-grade inflammation modulate MFAP5 expression and that the modified expression of MFAP5 may further regulate AT inflammation.

The microfibril-associated glycoproteins (MAGPs) and the microfibrillar niche

The microfibril-associated glycoproteins MAGP-1 and MAGP-2 are extracellular matrix proteins that interact with fibrillin to influence microfibril function. The two proteins are related through a 60 amino acid matrix-binding domain but their sequences differ outside of this region. A distinguishing feature of both proteins is their ability to interact with TGFβ family growth factors, Notch and Notch ligands, and multiple elastic fiber proteins. MAGP-2 can also interact with αvβ3 integrins via a RGD sequence that is not found in MAGP-1. Morpholino knockdown of MAGP-1 expression in zebrafish resulted in abnormal vessel wall architecture and altered vascular network formation. In the mouse, MAGP-1 deficiency had little effect on elastic fibers in blood vessels and lung but resulted in numerous unexpected phenotypes including bone abnormalities, hematopoietic changes, increased fat deposition, diabetes, impaired wound repair, and a bleeding diathesis. Inactivation of the gene for MAGP-2 in mice produced a neutropenia yet had minimal effects on bone or adipose homeostasis. Double knockouts had phenotypes characteristic of each individual knockout as well as several additional traits only seen when both genes are inactivated. A common mechanism underlying all of the traits associated with the knockout phenotypes is altered TGFβ signaling. This review summarizes our current understanding of the function of the MAGPs and discusses ideas related to their role in growth factor regulation.

Molecular mechanisms of inherited thoracic aortic disease - from gene variant to surgical aneurysm

Aortic dissection is a catastrophic event that has a high mortality rate. Thoracic aortic aneurysms are the clinically silent precursor that confers an increased risk of acute aortic dissection. There are several gene mutations that have been identified in key structural and regulatory proteins within the aortic wall that predispose to thoracic aneurysm formation. The most common and well characterised of these is the FBN1 gene mutation that is known to cause Marfan syndrome. Others less well-known mutations include TGF-β1 and TGF-β2 receptor mutations that cause Loeys-Dietz syndrome, Col3A1 mutations causing Ehlers-Danlos Type 4 syndrome and Smad3 and-4, ACTA2 and MYHII mutations that cause familial thoracic aortic aneurysm and dissection. Despite the variation in the proteins affected by these genetic mutations, there is a unifying pathological end point of medial degeneration within the wall of the aorta characterised by vascular smooth muscle cell loss, fragmentation and loss of elastic fibers, and accumulation of proteoglycans and glycosaminoglycans within vascular smooth muscle cell-depleted areas of the aortic media. Our understanding of these mutations and their post-translational effects has led to a greater understanding of the pathophysiology that underlies thoracic aortic aneurysm formation. Despite this, there are still many unanswered questions regarding the molecular mechanisms. Further elucidation of the signalling pathways will help us identify targets that may be suitable modifiers to enhance treatment of this often fatal condition.

MFAP5 loss-of-function mutations underscore the involvement of matrix alteration in the pathogenesis of familial thoracic aortic aneurysms and dissections

Thoracic aortic aneurysm and dissection (TAAD) is an autosomal-dominant disorder with major life-threatening complications. The disease displays great genetic heterogeneity with some forms allelic to Marfan and Loeys-Dietz syndrome, and an important number of cases still remain unexplained at the molecular level. Through whole-exome sequencing of affected members in a large TAAD-affected family, we identified the c.472C>T (p.Arg158(∗)) nonsense mutation in MFAP5 encoding the extracellular matrix component MAGP-2. This protein interacts with elastin fibers and the microfibrillar network. Mutation screening of 403 additional probands identified an additional missense mutation of MFAP5 (c.62G>T [p.Trp21Leu]) segregating with the disease in a second family. Functional analyses performed on both affected individual's cells and in vitro models showed that these two mutations caused pure or partial haploinsufficiency. Thus, alteration of MAGP-2, a component of microfibrils and elastic fibers, appears as an initiating mechanism of inherited TAAD.

Microfibril-associated glycoprotein 2 (MAGP2) loss of function has pleiotropic effects in vivo

Microfibril-associated glycoprotein (MAGP) 1 and 2 are evolutionarily related but structurally divergent proteins that are components of microfibrils of the extracellular matrix. Using mice with a targeted inactivation of Mfap5, the gene for MAGP2 protein, we demonstrate that MAGPs have shared as well as unique functions in vivo. Mfap5(-/-) mice appear grossly normal, are fertile, and have no reduction in life span. Cardiopulmonary development is typical. The animals are normotensive and have vascular compliance comparable with age-matched wild-type mice, which is indicative of normal, functional elastic fibers. Loss of MAGP2 alone does not significantly alter bone mass or architecture, and loss of MAGP2 in tandem with loss of MAGP1 does not exacerbate MAGP1-dependent osteopenia. MAGP2-deficient mice are neutropenic, which contrasts with monocytopenia described in MAGP1-deficient animals. This suggests that MAGP1 and MAGP2 have discrete functions in hematopoiesis. In the cardiovascular system, MAGP1;MAGP2 double knockout mice (Mfap2(-/-);Mfap5(-/-)) show age-dependent aortic dilation. These findings indicate that MAGPs have shared primary functions in maintaining large vessel integrity. In solid phase binding assays, MAGP2 binds active TGFβ1, TGFβ2, and BMP2. Together, these data demonstrate that loss of MAGP2 expression in vivo has pleiotropic effects potentially related to the ability of MAGP2 to regulate growth factors or participate in cell signaling.

Elastic fibres in health and disease

Elastic fibres are insoluble components of the extracellular matrix of dynamic connective tissues such as skin, arteries, lungs and ligaments. They are laid down during development, and comprise a cross-linked elastin core within a template of fibrillin-based microfibrils. Their function is to endow tissues with the property of elastic recoil, and they also regulate the bioavailability of transforming growth factor β. Severe heritable elastic fibre diseases are caused by mutations in elastic fibre components; for example, mutations in elastin cause supravalvular aortic stenosis and autosomal dominant cutis laxa, mutations in fibrillin-1 cause Marfan syndrome and Weill–Marchesani syndrome, and mutations in fibulins-4 and -5 cause autosomal recessive cutis laxa. Acquired elastic fibre defects include dermal elastosis, whereas inflammatory damage to fibres contributes to pathologies such as pulmonary emphysema and vascular disease. This review outlines the latest understanding of the composition and assembly of elastic fibres, and describes elastic fibre diseases and current therapeutic approaches.

Identification of a functional proprotein convertase cleavage site in microfibril-associated glycoprotein 2

Microfibril-associated glycoprotein 2 (MAGP2) is a secreted protein associated with multiple cellular activities including the organization of elastic fibers in the extracellular matrix (ECM), angiogenesis, as well as regulating Notch and integrin signaling. Importantly, increases in MAGP2 positively correlate with poor prognosis for some ovarian cancers. It has been assumed that full-length MAGP2 is responsible for all reported effects; however, here we show MAGP2 is a substrate for the proprotein convertase (PC) family of endoproteases. Proteolytic processing of MAGP2 by PC cleavage could serve to regulate secretion and thus, activity and function as reported for other extracellular and cell-surface proteins. In support of this idea, MAGP2 contains an evolutionarily conserved PC consensus cleavage site, and amino acid sequencing of a newly identified MAGP2 C-terminal cleavage product confirmed functional PC cleavage. Additionally, mutagenesis of the MAGP2 PC consensus cleavage site or treatment with PC inhibitors prevented MAGP2 proteolytic processing. Finally, both cleaved and uncleaved MAGP2 were detected extracellularly and MAGP2 secretion appeared independent of PC cleavage, suggesting that PC processing occurs mainly outside the cell. Our characterization of alternative forms of MAGP2 present in the extracellular space not only enhances diversity of this ECM protein but also provides a previously unrecognized molecular mechanism for regulation of MAGP2 biological activity.

Microfibrillar-associated protein 5 is linked with markers of obesity-related extracellular matrix remodeling and inflammation

Objective:

Microfibrillar-associated protein 5 (MFAP5) is an extracellular matrix (ECM) glycoprotein, which is colocalized with microfibrils in elastin networks. Its function in adipose tissue (AT) is not known. We have recently shown that the expression of MFAP5 is downregulated in AT along with weight reduction (WR) in persons with metabolic syndrome (MetS). The aim of this work was to study whether the change of MFAP5 mRNA expression in response to WR is associated with markers of adiposity, glucose metabolism and insulin resistance in human AT.

Design:

Weight reduction intervention study in parallel study design (The Genobin study). Altogether 46 obese subjects with impaired glucose tolerance and features of MetS were randomized to a WR (n=28) or a control group (n=18) lasting for 33 weeks.

Measurements:

Circulating glucose and insulin concentrations were measured and subcutaneous AT biopsies were performed before and after the intervention. The mRNA expression was studied by quantitative real-time PCR (QPCR).

Results:

QPCR of human AT biopsy samples confirmed that MFAP5 is highly expressed in AT and its expression is decreased during WR. The mRNA expression of MFAP5 correlated positively with body mass index, and the change in MFAP5 mRNA expression during WR correlated positively with the change of body fat mass. Furthermore, the MFAP5 mRNA expression correlated negatively with circulating fasting concentrations of adiponectin and interleukin (IL)-1β and positively with leptin, insulin and IL-1Ra levels. In addition, the MFAP5 mRNA expression correlated positively with the mRNA expressions of peroxisome proliferator-activated receptor gamma, cyclin D2 and A disintegrin and metalloproteinase domain 12, genes involved in AT remodeling.

Conclusion:

This study demonstrates that MFAP5 is highly expressed in human AT and is correlated with markers of insulin resistance. Furthermore, it is possible that MFAP5 is related to ECM remodeling during development of obesity.

Human microvascular lymphatic and blood endothelial cells produce fibrillin: deposition patterns and quantitative analysis

Fibrillin microfibrils constitute a scaffold for elastin deposition in the wall of arteries and form the anchoring filaments that connect the lymphatic endothelium to surrounding elastic fibers. We previously reported that fibrillin is deposited in a honeycomb pattern in bovine arterial endothelial cells, which also deposit microfibril-associated glycoprotein (MAGP)-1, whereas thoracic duct endothelial cells form an irregular web. The present immunohistochemical study was designed to verify whether lymphatic and blood human dermal microvascular endothelial cells (HDMECs) isolated from human foreskin by the sequential use of a pan-endothelial marker, CD31, and the lymphatic specific marker, D2-40, deposit fibrillin and MAGP-1. In both cell types, fibrillin and MAGP-1 co-localized and were deposited with different patterns of increasing complexity co-existing in the same culture. Fibrillin microfibrils formed a wide-mesh honeycomb leaving fibrillin-free spaces that were gradually filled. This modality of fibrillin deposition, similar to that of bovine large artery endothelial cells, was basically the same in blood and lymphatic HDMECs. In some lymphatic HDMECs, fibrillin was initially deposited as uniformly scattered short fibrillin strands probably as a result of anchoring filaments carried over from the vessels of origin. Our findings show that blood and lymphatic endothelial cells participate in fibrillin deposition in human skin.

A prognostic gene signature in advanced ovarian cancer reveals a microfibril-associated protein (MAGP2) as a promoter of tumor cell survival and angiogenesis

Ovarian cancer is the most lethal gynecologic cancer, and this is largely related to its late diagnosis. High grade serous cancers often initially respond to chemotherapy, resulting in a better survival rate, compared to other ovarian carcinoma subtypes. We review recent work identifying a survival-associated gene expression profile for advanced serous ovarian cancer. Within this signature, the authors identified MAGP2, also known as microfibrillar associated protein 5 (MFAP5), as a highly significant indicator of survival and chemosensitivity. MAGP2 is a multifunctional secreted protein--important for elastic microfibril assembly and modulating endothelial cell behavior--with a newly identified role in cell survival. Through alpha(V)beta(3) integrin-mediated signaling, MAGP2 promotes tumor and endothelial cell survival and endothelial cell motility, providing a potential mechanistic link between MAGP2 and angiogenesis as well as patient survival.

Unraveling the mechanism of elastic fiber assembly: The roles of short fibulins

Evolution of elastic fibers is associated with establishment of the closed circulation system. Primary roles of elastic fibers are to provide elasticity and recoiling to tissues and organs and to maintain the structural integrity against mechanical strain over a lifetime. Elastic fibers are comprised of an insoluble elastin core and surrounding mantle of microfibrils. Elastic fibers are formed in a regulated, stepwise manner, which includes the formation of a microfibrillar scaffold, deposition and integration of tropoelastin monomers into the scaffold, and cross-linking of the monomers to form an insoluble, functional polymer. In recent years, an increasing number of glycoproteins have been identified and shown to be located on or surrounding elastic fibers. Among them, the short fibulins-3, -4 and -5 particularly drew attention because of their potent elastogenic activity. Fibulins-3, -4 and -5 are characterized by tandem repeats of calcium binding EGF-like motifs and a C-terminal fibulin module, which is conserved throughout fibulin family members. Initial biochemical characterization and gene expression studies predicted that fibulins might be involved in structural support and/or matrix-cell interactions. Recent analyses of short fibulin knockout mice have revealed their critical roles in elastic fiber development in vivo. We review recent findings on the elastogenic functions of short fibulins and discuss the molecular mechanism underlying their activity in vitro and in vivo.

Antagonistic effect of the matricellular signaling protein CCN3 on TGF-beta- and Wnt-mediated fibrillinogenesis in systemic sclerosis and Marfan syndrome

Abnormal fibrillinogenesis is associated with connective tissue disorders (CTDs), including Marfan syndrome (MFS), systemic sclerosis (SSc) and Tight-skin (Tsk) mice. We have previously shown that TGF-beta and Wnt stimulate fibrillin-1 assembly and that fibrillin-1 and the developmental regulator CCN3 are both highly increased in Tsk skin. We investigated the role of CCN3 in abnormal fibrillinogenesis in Tsk mice, MFS, and SSc. Smad3 deletion in Tsk mice decreased CCN3 overexpression, suggesting that TGF-beta mediates at least part of the effect of Tsk fibrillin on CCN3 which is consistent with a synergistic effect of TGF-beta and Wnt in vitro on CCN3 expression. Disruption of fibrillin-1 assembly by MFS fibrillin decreased CCN3 expression and skin from patients with early diffuse SSc showed a strong correlation between increased CCN3 and fibrillin-1 expression, suggesting that CCN3 regulation by fibrillin-1 extends to these CTDs. Diffuse SSc skin and sera also showed evidence of increased Wnt activity, implicating a Wnt stimulus behind this correlation. CCN3 overexpression markedly repressed fibrillin-1 assembly and also blocked other TGFbeta- and Wnt-regulated profibrotic gene expression. Together, these data indicate that CCN3 counter-regulates positive signals from TGF-beta and Wnt for fibrillin fibrillogenesis and profibrotic gene expression.

Tissue elasticity and the ageing elastic fibre

The ability of elastic tissues to deform under physiological forces and to subsequently release stored energy to drive passive recoil is vital to the function of many dynamic tissues. Within vertebrates, elastic fibres allow arteries and lungs to expand and contract, thus controlling variations in blood pressure and returning the pulmonary system to a resting state. Elastic fibres are composite structures composed of a cross-linked elastin core and an outer layer of fibrillin microfibrils. These two components perform distinct roles; elastin stores energy and drives passive recoil, whilst fibrillin microfibrils direct elastogenesis, mediate cell signalling, maintain tissue homeostasis via TGFβ sequestration and potentially act to reinforce the elastic fibre. In many tissues reduced elasticity, as a result of compromised elastic fibre function, becomes increasingly prevalent with age and contributes significantly to the burden of human morbidity and mortality. This review considers how the unique molecular structure, tissue distribution and longevity of elastic fibres pre-disposes these abundant extracellular matrix structures to the accumulation of damage in ageing dermal, pulmonary and vascular tissues. As compromised elasticity is a common feature of ageing dynamic tissues, the development of strategies to prevent, limit or reverse this loss of function will play a key role in reducing age-related morbidity and mortality.

Vascular extracellular matrix and arterial mechanics

An important factor in the transition from an open to a closed circulatory system was a change in vessel wall structure and composition that enabled the large arteries to store and release energy during the cardiac cycle. The component of the arterial wall in vertebrates that accounts for these properties is the elastic fiber network organized by medial smooth muscle. Beginning with the onset of pulsatile blood flow in the developing aorta, smooth muscle cells in the vessel wall produce a complex extracellular matrix (ECM) that will ultimately define the mechanical properties that are critical for proper function of the adult vascular system. This review discusses the structural ECM proteins in the vertebrate aortic wall and will explore how the choice of ECM components has changed through evolution as the cardiovascular system became more advanced and pulse pressure increased. By correlating vessel mechanics with physiological blood pressure across animal species and in mice with altered vessel compliance, we show that cardiac and vascular development are physiologically coupled, and we provide evidence for a universal elastic modulus that controls the parameters of ECM deposition in vessel wall development. We also discuss mechanical models that can be used to design better tissue-engineered vessels and to test the efficacy of clinical treatments.

Cell adhesion to tropoelastin is mediated via the C-terminal GRKRK motif and integrin alphaVbeta3

Elastin fibers are predominantly composed of the secreted monomer tropoelastin. This protein assembly confers elasticity to all vertebrate elastic tissues including arteries, lung, skin, vocal folds, and elastic cartilage. In this study we examined the mechanism of cell interactions with recombinant human tropoelastin. Cell adhesion to human tropoelastin was divalent cation-dependent, and the inhibitory anti-integrin alpha(V)beta(3) antibody LM609 inhibited cell spreading on tropoelastin, identifying integrin alpha(V)beta(3) as the major fibroblast cell surface receptor for human tropoelastin. Cell adhesion was unaffected by lactose and heparin sulfate, indicating that the elastin-binding protein and cell surface glycosaminoglycans are not involved. The C-terminal GRKRK motif of tropoelastin can bind to cells in a divalent cation-dependent manner, identifying this as an integrin binding motif required for cell adhesion.

The topography of microstructured surfaces differently affects fibrillin deposition by blood and lymphatic endothelial cells in culture

While tissue-engineered blood vessels have already been successfully used in surgical practice, artificially restoring lymphatic circulation when needed is still far to be realized. Stability of arterial vessel wall depends on proper fibrillin deposition; fibrillin in fact is the scaffold for elastic fiber formation. In lymphatic vessels fibrillin is probably implied in lymph formation in response to interstitial requirements. This study was designed to verify whether fibrillin deposition is influenced by the topography of the substrate on which blood and lymphatic endothelial cells grow. Blood and lymphatic endothelial cells were cultured on microstructured surfaces with different topography: stripes of different widths (25, 50, and 100 microm), squares and rectangles, and spiral geometry, obtained by the photoimmobilization of Hyaluronan (Hyal) on aminosilanized glass. Cell orientation and fibrillin deposition were influenced by the topography of the microstructure. Blood endothelial cells deposited fibrillin as a bundle running parallel to the major axis of stripes and spirals, whereas the irregular network of fibrillin deposited by lymphatic endothelial cells was affected by the topography of the substrate only in the smallest stripes. These data bring a contribution to the basic knowledge required to design tissue-engineered blood and lymphatic vessels capable of adapting to the functional requirements of the surrounding environment.

Functional evolution of the microfibril-associated glycoproteins

The microfibril-associated glycoproteins (MAGPs) are cysteine-rich low molecular weight components of the fibrillin-based microfibrillar complex. MAGPs are evolutionarily conserved in vertebrates and have important roles in microfibril and elastic fiber structure, homeostasis, and vascular development. Two MAGPs, designated MAGP1 and MAGP2, are encoded in the mammalian genome. Although MAGP sequences have been identified in several vertebrate species, the extent of conservation and evolutionary history of the MAGPs in vertebrates is unknown. Sequence similarity searches of nucleotide and protein databases identified the first homologs of MAGP1 in monotremes, birds, elasmobranchs and agnathans, and the first MAGP2 genes in marsupials, birds and teleosts. A model for MAGP evolution is presented. Phylogenetic analysis identified the ancient origin of MAGP1 and the evolution of MAGP2 from a gene duplication event early in vertebrate evolution. Phylogenomic analysis shows conservation of synteny between teleosts and tetrapods and suggests a multigene duplication event. The MAGP2 gene has evolved rapidly as an innovation in the bony vertebrate lineage. Estimates of functional divergence and complex nucleotide substitution models suggest that the divergence of MAGP2 took place by relaxation of selective constraints; and that MAGP1 has consistently been constrained by strong purifying selection. Correlated evolution between MAGP1 and the developmental regulator, Notch1, may explain some of the selective forces acting on MAGP2.

Fibrillins, fibulins, and matrix-associated glycoprotein modulate the kinetics and morphology of in vitro self-assembly of a recombinant elastin-like polypeptide

Elastin is the polymeric protein responsible for the properties of extensibility and elastic recoil of the extracellular matrix in a variety of tissues. Although proper assembly of the elastic matrix is crucial for its durability, the process by which this assembly takes place is not well-understood. Recent data suggest the complex interaction of tropoelastin, the monomeric form of elastin, with a number of other elastic matrix-associated proteins, including fibrillins, fibulins, and matrix-associated glycoprotein (MAGP), is important to achieve the proper architecture of the elastic matrix. At the same time, it is becoming clear that self-assembly properties intrinsic to tropoelastin itself, reflected in a temperature-induced phase separation known as coacervation, are also important in this assembly process. In this study, using a well-characterized elastin-like polypeptide that mimics the self-assembly properties of full-length tropoelastin, the process of self-assembly is deconstructed into "coacervation" and "maturation" stages that can be distinguished kinetically by different parameters. Members of the fibrillin, fibulin, and MAGP families of proteins are shown to profoundly affect both the kinetics of self-assembly and the morphology of the maturing coacervate, restricting the growth of coacervate droplets and, in some cases, causing clustering of droplets into fibrillar structures.

Microfibril-associate glycoprotein-2 (MAGP-2) promotes angiogenic cell sprouting by blocking notch signaling in endothelial cells

Angiogenesis is highly sensitive to the composition of the vascular microenvironment, however, our understanding of the structural and matricellular components of the vascular microenvironment that regulate angiogenesis and the molecular mechanisms by which these molecules function remains incomplete. Our previous results described a novel pro-angiogenic activity for Microfibril-Associated Glycoprotein-2 (MAGP-2), but did not address the molecular mechanism(s) by which this is accomplished. We now demonstrate that MAGP-2 promotes angiogenic cell sprouting by antagonizing Notch signaling pathways in endothelial cells. MAGP-2 decreased basal and Jagged1 induced expression from the Notch sensitive Hes-1 promoter in ECs, and blocked Jagged1 stimulated Notch1 receptor processing in transiently transfected 293T cells. Interestingly, inhibition of Notch signaling by MAGP-2 seems to be restricted to ECs since MAGP-2 increased Hes-1 promoter activity and Notch1 receptor processing in heterologous cell types. Importantly, constitutive activation of the Notch signaling pathway blocked the ability of MAGP-2 to promote angiogenic cell sprouting, as well as morphological changes associated with angiogenesis. Collectively, these observations indicate that MAGP-2 promotes angiogenic cell spouting in vitro by antagonizing Notch signaling pathways in ECs.

Arg-Gly-Asp-containing domains of fibrillins-1 and -2 distinctly regulate lung fibroblast migration

Development of the extracellular matrix is a critical feature of alveolar formation and actively involves pulmonary interstitial fibroblasts. The elastic fiber network is an interconnected system of load-bearing fibers that also influences the behavior of adjacent cells, particularly the interstitial lung fibroblasts (LF). We hypothesized that discrete domains of fibrillins-1 and -2 interact with LF integrins and direct their migration in the presence of platelet-derived growth factor (PDGF)-A. Surfaces coated with recombinant peptides lacking or including an arginine-glycine-aspartic acid (RGD) motif were used to study LF migration across porous filters and on protein-coated glass. Exon 24 of fibrillin-2 (Fib2 24), which encodes for an RGD-containing transforming growth factor-beta-binding (TB) domain, stimulated migration with greater directional persistence and more effectively stimulated trans-filter migration at low concentrations. Exons 36-44 of fibrillin-1 (Fib1 36-44), which include epidermal growth factor-like domains and an RGD-containing TB domain, induce more lamlellipodia and more widespread remodeling of the leading edge, resulting in greater migration velocity than did Fib2 24. Distinct structural features in regions that surround the RGD motifs may differentially regulate how the PDGF receptor-alpha promotes integrin distribution and actin filament remodeling at the cell's leading edge. Understanding how fibrillins regulate LF migration may help elucidate how the elastic fiber system could be restored as an interconnected unit, which fails to occur in emphysematous lungs.

Transcriptome analysis of endothelial cell gene expression induced by growth on matrigel matrices: identification and characterization of MAGP-2 and lumican as novel regulators of angiogenesis

Remodeling of vascular microenvironments during normal and tumor-induced angiogenesis is an important, yet poorly understood mechanism by which endothelial cells (ECs) contribute to the activation or resolution of angiogenesis. We used microarray analyses to monitor changes in the transcriptome of ECs undergoing angiogenesis when cultured onto Matrigel matrices. This strategy identified 308 genes whose expression in ECs was altered at least 3-fold by angiogenesis, of which 63 genes were found to encode for secretory proteins. In vitro assays that modeled key steps in the angiogenic process showed that several identified genes possessed pro- or anti-angiogenic activities (e.g., SMOC-2, secreted modular calcium-binding protein-2; CRELD-2, cysteine-rich with EGF-like domains-1; MAGP-2, microfibril-associated glycoprotein-2; lumican; and ECM-1, extracellular matrix protein-1). In particular, MAGP-2 expression potentiated EC proliferation and p38 MAPK activation stimulated by the pro-angiogenic factors, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), and vascular endothelial growth factor (VEGF); it also stimulated EC invasion and angiogenic sprouting, and more importantly, promoted the development and infiltration of vessels into Matrigel plugs implanted into genetically normal mice. Conversely, lumican inhibited EC activation of p38 MAPK, as well as their invasion, angiogenic sprouting, and vessel formation in mice. Collectively, our findings provide new insights into how EC stromal remodeling regulates angiogenesis activation and resolution, as well as identify two novel EC-secreted stromal proteins that modulate angiogenesis both in vitro and in vivo.