Molecular pathology of the elastic fibers

Mesopic and Scotopic Light Sensitivity and Its Microstructural Correlates in Pseudoxanthoma Elasticum

Importance

Correlates for Bruch membrane alterations are needed for interventional trials targeting the Bruch membrane in pseudoxanthoma elasticum (PXE).

Objectives

To quantify mesopic and scotopic light sensitivity and identify its microstructural correlates associated with a diseased Bruch membrane in patients with PXE.

Design, Setting, and Participants

A prospective, single-center, cross-sectional case-control study was conducted at a tertiary referral center from January 31, 2018, to February 20, 2020. Twenty-two eyes of 22 patients with PXE and 40 eyes of 40 healthy individuals were included. Data analysis was completed March 15, 2020.

Exposures

Mesopic and dark-adapted 2-color fundus-controlled perimetry (microperimetry) and multimodal retinal imaging including spectral-domain optical coherence tomography (SD-OCT) and OCT angiography were performed. Perimetry thresholds were analyzed using mixed models, and structure-function correlation with SD-OCT data was performed using machine learning.

Main Outcomes and Measures

Observed dark-adapted cyan sensitivity loss as measure of rod photoreceptor dysfunction, as well as mean absolute error between predicted and observed retinal sensitivity to assess the accuracy of structure-function correlation.

Results

Of the 22 patients with PXE included in this study, 15 were women (68%); median age was 56.5 years (interquartile range, 50.4-61.2). These patients exhibited mesopic (estimate, 5.13 dB; 95% CI, 2.89-7.38 dB), dark-adapted cyan (estimate, 9.08 dB; 95% CI, 6.34-11.82 dB), and dark-adapted red (estimate, 7.05 dB; 95% CI, 4.83-9.27 dB) sensitivity losses. This sensitivity loss was also evident in 9 eyes with nonneovascular PXE (mesopic: estimate, 3.21 dB; 95% CI, 1.28-5.14 dB; dark-adapted cyan: 5.93 dB; 95% CI, 3.59-8.27 dB; and dark-adapted red testing: 4.84 dB; 95% CI, 2.88-6.80 dB), showing a distinct centrifugal pattern of sensitivity loss with preserved function toward the periphery. Retinal function could be predicted from microstructure with high accuracy (mean absolute errors, of 4.91 dB for mesopic, 5.44 dB for dark-adapted cyan, and 4.99 dB for dark-adapted red). The machine learning-based analysis highlighted an association of a thinned inner retina and putative separation of the pigment-epithelium-photoreceptor complex with sensitivity loss.

Conclusions and Relevance

In this study, among 22 patients with PXE, those with and without choroidal neovascularization exhibited reductions of retinal sensitivity being most pronounced in dark-adapted cyan testing. This finding suggests that pathologic characteristics of this Bruch membrane disease may be dominated by rod photoreceptor degeneration and/or dysfunction. A putative pigment-epithelium-photoreceptor separation may further impair rod function, while inner retinal abnormalities appear to be correlated with overall dysfunction.

Modeling elastin-associated vasculopathy with patient induced pluripotent stem cells and tissue engineering

Elastin-associated vasculopathies are life-threatening conditions of blood vessel dysfunction. The extracellular matrix protein elastin endows the recoil and compliance required for physiologic arterial function, while disruption of function can lead to aberrant vascular smooth muscle cell proliferation manifesting through stenosis, aneurysm, or vessel dissection. Although research efforts have been informative, they remain incomplete as no viable therapies exist outside of a heart transplant. Induced pluripotent stem cell technology may be uniquely suited to address current obstacles as these present a replenishable supply of patient-specific material with which to study disease. The following review will cover the cutting edge in vascular smooth muscle cell modeling of elastin-associated vasculopathy, and aid in the development of human disease modeling and drug screening approaches to identify potential treatments. Vascular proliferative disease can affect up to 50% of the population throughout the world, making this a relevant and critical area of research for therapeutic development.

Disease advocacy organizations catalyze translational research

Disease advocacy organizations have long played an important role in the continuum from basic science to therapy development in rare disease research. PXE International has led the field in innovative ways, venturing into specific activities that have traditionally been conducted by scientists. As lay founders, we have engaged in gene discovery, gene patenting, diagnostic test development, epidemiological studies, clinical trials, and therapy research and development. This article will describe the steps that we took, and the ways in which we have scaled these efforts for the larger community.

The complexity of elastic fibre biogenesis in the skin--a perspective to the clinical heterogeneity of cutis laxa

Elastic fibres are critical connective tissue components providing elasticity and resilience to skin and other tissues. These fibres are composed of elastin and a number of elastin-associated microfibrillar proteins that assemble in a complex fibre network in a multi-step process. Multiple cellular processes, including mitochondrial function, specific molecules in the secretory pathways and temporally and spatially ordered production of elastic fibre components, are required for the biogenesis of functional elastic fibres. Abnormalities in these processes can lead to loss of functional elastic fibres manifesting phenotypically as a skin disease. The paradigm of elastic fibre diseases affecting the skin is cutis laxa, a clinically and genetically heterogeneous group of disorders characterized by loose and sagging skin, frequently associated with extracutaneous manifestations in the lungs and the arterial blood vessels. The complexity of cutis laxa is emphasized by the fact that as many as 10 distinct genes can harbour mutations in this and related disorders. Understanding of the pathomechanistic pathways involved in perturbed elastic fibre assembly in cutis laxa provides information potentially helpful for the development of molecular strategies towards treatment of these, currently intractable, diseases.

Periodontal conditions in Williams Beuren syndrome: a series of 8 cases

BACKGROUND

Williams Beuren syndrome (WBS) is an unusual hereditary connective tissue disease caused by a microdeletion at position 7q11-23 and a haploinsufficiency at the elastin gene. The most frequent specific features are elf-like face, alteration of cognitive functions and cardiovascular diseases including isolated supravalvular aortic stenosis. A number of clinical findings have been reported, but none of the studies evaluating this syndrome consider the oral cavity. It is equally surprising that the gingival tissue, which carries a perfectly structured elastic fibre network, has not yet been investigated. It is important to verify whether subjects affected by WBS are more susceptible to periodontal disease than healthy subjects who are not that much affected, for periodontal disease may have deleterious effects on the cardiovascular system.

METHODS

In an attempt to address this issue, the oral manifestations of 8 patients (ages from 5 to 12 years) with WBS have been investigated: dental examination, periodontal examination (gingival phenotype, plaque control record, gingival index, bone quality).

RESULTS

All patients had oral parafunction, tooth number abnormalities and malocclusions. Average gingival height and width were greater than normal. Plaque index was always very high except for one patient, but the gingival inflammation was not linked to the quantity of clinical plaque index. There was no obvious loss of attachment.

CONCLUSION

As with collagen, elastin is a structural macromolecule of the gingiva. These components play an important role in gingival function and in the resistance of the periodontium to daily aggressions. Unlike genetic diseases characterized by impairment of collagen macrofibrils, it is suggested that the hemizygous gene encoding elastin does not result in periodontal disease. In addition there is an existence of a possible concordance between the elastin gene haploinsufficiency and the periodontal phenotype. There might be some adaptive process to this deficiency.

Growth factors upregulate deposition and remodeling of ECM by endothelial cells cultured for tissue-engineering applications

Appropriate matrix formation, turnover and remodeling in tissue-engineered small diameter vascular conduits are crucial for their long-term function. The interaction between cells and extra-cellular components is indispensable in determining cellular behavior in tissues and on biomaterials. The fibrin that contains fibronectin shows promise in most aspects as a tissue engineering scaffold, whereas, deposition of elastin and collagen by endothelial cells grown in the lumen of the construct is desirable to improve post implant retention, mechanical stability and vaso-responsiveness. So far there is no report on production of extra-cellular matrix (ECM) proteins, elastin and collagen by endothelial cells (EC) in in vitro culture conditions. In this study, we have used a biomimetic approach of providing multiple growth factors (GF) in the fibronectin (FN)-containing fibrin matrix to induce production of elastin and collagen by the endothelial cells for application in vascular tissue engineering. Deposition of elastin and collagens with matrix remodeling is demonstrated through qualitative analysis of the matrices that were recovered after growing cells on the initial fibrin-FN-GF matrix. Expressions of mRNA for both proteins were assessed by real time polymerase chain reaction (RT-PCR) to estimate the effects of multiple growth factor compositions. Marked deposition of elastin and collagen was evidenced by staining the recovered matrix after different culture intervals. Obviously, the biomimetic environment created by adding angiogenic and platelet growth factors in the fibrin-fibronectin-gelatin matrix can induce deposition of collagens and elastin by EC.

Vascular Wall Remodeling in Patients with Supravalvular Aortic Stenosis and Williams Beuren Syndrome

Supravalvular aortic stenosis (SVAS) and Williams Beuren syndrome (WBS) can be considered as inherited diseases affecting the whole arterial tree and causing narrowing of the vessels. It has been reported that abnormal deposition of elastin in arterial walls of patients with SVAS and WBS leads to increased proliferation of arterial smooth muscle cells (SMC), which result in the formation of hyperplastic intimal lesions. In this work, we conducted morphological and morphometrical analysis with stenotic aortas from patients suffering from SVAS and WBS and from healthy control subjects and demonstrated that the amount of elastic fibers and the loss of integrity of vascular elastic fibers in the aortas reflect similar changes in the skin of patients with SVAS or WBS, as reported in our previous work conducted on skin in these pathological states. On the other hand, we conducted investigations on metalloproteinases (MMP2, MMP9, MMP7) and their specific tissue inhibitors TIMP1 and TIMP2 to verify their possible involvement in the etiopathogeny of SVAS and WBS. We particularly evidenced an altered MMP9/TIMP1 balance in favor of matrix degradation which could facilitate SMC migration and neointimal hyperplasia. Our findings suggest that elastinolytic enzymes secreted by arterial SMC, possibly including matrilysin 1, are critical for the development of arterial lesions in SVAS and WBS and contribute to perpetuate arterial stenosis in either SVAS or WBS.

Incorporation of intact elastin scaffolds in tissue-engineered collagen-based vascular grafts

Although collagen-based tissue-engineered blood vessels (TEBVs) have many interesting properties and have been utilized to study aspects of vascular biology, these constructs are too weak to be implanted as bypass grafts for in vivo investigations. This study presents a method to incorporate organized, intact elastin into collagen-based TEBVs to form hybrid constructs that better mimic arterial physiology and exhibit improved mechanical properties. Porcine carotids were digested with a series of autoclave and chemical treatments to elicit isolated elastin scaffolds. Elastin purity was verified via immunohistochemistry and amino acid analysis. Isolated scaffolds were combined with type I collagen and either human dermal fibroblasts (HDFs) or rat smooth muscle cells (RASMs) to form an elastin hybrid TEBV. Hybrid constructs exhibited increased tensile strengths (11-fold in HDFs; 7.5-fold in RASMs) and linear stiffness moduli (4-fold in HDFs; 1.8-fold in RASMs) compared with collagen control constructs with no exogenous elastin scaffold. Viscoelastic properties of the TEBVs also improved with the addition of an ancillary elastin scaffold as determined through stepwise stress relaxation analysis. Whereas the majority of resistance to deformation in collagen control constructs stemmed from viscous fluidlike effects, elastin hybrid constructs exhibited more ideal elastic solid mechanical behavior. Thus, elastin scaffolds can help recreate the elastic properties of native arteries. Future challenges include stimulating appropriate reorganization or synthesis of the collagen matrix to provide the necessary strength and viscoelastic properties for implantation.

Acquired disorders of elastic tissue: part I. Increased elastic tissue and solar elastotic syndromes

Elastic fibers in the extracellular matrix are an integral component of dermal connective tissue. The resilience and elasticity required for normal structure and function of the skin may be attributed to the network of elastic tissue. Advances in our understanding of elastic tissue physiology provide a foundation for studying the pathogenesis of elastic tissue disorders. Many acquired disorders are nevertheless poorly understood due to the paucity of reported cases. Several acquired disorders in which accumulation or elastotic degeneration of dermal elastic fibers produces prominent clinical and histopathologic features have recently been described. They include elastoderma, linear focal elastosis, and late-onset focal dermal elastosis and must be differentiated from better-known disorders, among them acquired pseudoxanthoma elasticum, elastosis perforans serpiginosa, and Favré-Racouchot syndrome. Learning objective At the conclusion of this learning activity, participants should understand the similarities and differences between acquired disorders of elastic tissue that are characterized by an increase in elastic tissue, as well as the spectrum of solar elastotic dermatoses.

The viscoelastic basis for the tensile strength of elastin

Purified aortic elastin displays failure behaviour characteristic of an amorphous, noncrystalizing elastomer with failure properties showing a strong dependence on viscoelastic behaviour. Tensile breaking stresses and breaking strains measured over a range of temperatures, hydration levels, and strain rates are reducible to single curves by the application of shift factors obtained from dynamic mechanical tests. The breaking stress of rubbery elastin is similar to that found in other elastomers, but glassy elastin is about an order of magnitude less strong than expected. We suggest elastin's ability to be strengthened through viscous dissipation of strain energy and crack tip blunting is limited by its fibrillar structure.

Impaired elastic-fiber assembly by fibroblasts from patients with either Morquio B disease or infantile GM1-gangliosidosis is linked to deficiency in the 67-kD spliced variant of beta-galactosidase

We have previously shown that intracellular trafficking and extracellular assembly of tropoelastin into elastic fibers is facilitated by the 67-kD elastin-binding protein identical to an enzymatically inactive, alternatively spliced variant of beta-galactosidase (S-Gal). In the present study, we investigated elastic-fiber assembly in cultures of dermal fibroblasts from patients with either Morquio B disease or GM1-gangliosidosis who bore different mutations of the beta-galactosidase gene. We found that fibroblasts taken from patients with an adult form of GM1-gangliosidosis and from patients with an infantile form, carrying a missense mutations in the beta-galactosidase gene-mutations that caused deficiency in lysosomal beta-galactosidase but not in S-Gal-assembled normal elastic fibers. In contrast, fibroblasts from two cases of infantile GM1-gangliosidosis that bear nonsense mutations of the beta-galactosidase gene, as well as fibroblasts from four patients with Morquio B who had mutations causing deficiency in both forms of beta-galactosidase, did not assemble elastic fibers. We also demonstrated that S-Gal-deficient fibroblasts from patients with either GM1-gangliosidosis or Morquio B can acquire the S-Gal protein, produced by coculturing of Chinese hamster ovary cells permanently transected with S-Gal cDNA, resulting in improved deposition of elastic fibers. The present study provides a novel and natural model validating functional roles of S-Gal in elastogenesis and elucidates an association between impaired elastogenesis and the development of connective-tissue disorders in patients with Morquio B disease and in patients with an infantile form of GM1-gangliosidosis.

Impaired elastogenesis in Hurler disease: dermatan sulfate accumulation linked to deficiency in elastin-binding protein and elastic fiber assembly

Hurler disease resulting from a deficiency in alpha-L-iduronidase, which causes an accumulation of dermatan sulfate and heparan sulfate glycosaminoglycans, is characterized by connective tissue and skeletal deformations, cardiomyopathy, cardiac valve defects, and progressive coronary artery stenosis. In this report, we present evidence that accumulation of dermatan sulfate but not heparan sulfate moieties is linked to impaired elastic fiber assembly that, in turn, contributes substantially to the development of the clinical phenotype in Hurler disease. Our data suggest that dermatan sulfate-bearing moieties bind to and cause functional inactivation of the 67-kd elastin-binding protein, a molecular chaperone for tropoelastin, which normally facilitates its secretion and assembly into elastic fibers. We demonstrate that, in contrast to normal skin fibroblasts and cells from Sanfilippo disease, which accumulate heparan sulfate, Hurler fibroblasts show reduced expression of elastin-binding protein and do not assemble elastic fibers, despite an adequate synthesis of tropoelastin and sufficient production of a microfibrillar scaffold of elastic fibers. Because cultured Hurler fibroblasts proliferate more quickly than their normal counterparts and the addition of exogenous insoluble elastin reduces their proliferation, we suggest that cell contacts with insoluble elastin play an important role in controlling their proliferation.

Decreased elastin deposition and high proliferation of fibroblasts from Costello syndrome are related to functional deficiency in the 67-kD elastin-binding protein

Costello syndrome is characterized by mental retardation, loose skin, coarse face, skeletal deformations, cardiomyopathy, and predisposition to numerous malignancies. The genetic origin of Costello syndrome has not yet been defined. Using immunohistochemistry and metabolic labeling with [3H]-valine, we have established that cultured skin fibroblasts obtained from patients with Costello syndrome did not assemble elastic fibers, despite an adequate synthesis of tropoelastin and normal deposition of the microfibrillar scaffold. We found that impaired production of elastic fibers by these fibroblasts is associated with a functional deficiency of the 67-kD elastin-binding protein (EBP), which is normally required to chaperone tropoelastin through the secretory pathways and to its extracellular assembly. Metabolic pulse labeling of the 67-kD EBP with radioactive serine and further chase of this tracer indicated that both normal fibroblasts and fibroblasts from patients with Costello syndrome initially synthesized comparable amounts of this protein; however, the fibroblasts from Costello syndrome patients quickly lost it into the conditioned media. Because the normal association between EBP and tropoelastin can be disrupted on contact with galactosugar-bearing moieties, and the fibroblasts from patients with Costello syndrome revealed an unusual accumulation of chondroitin sulfate-bearing proteoglycans (CD44 and biglycan), we postulate that a chondroitin sulfate may be responsible for shedding EBP from Costello cells and in turn for their impaired elastogenesis. This was further supported by the fact that exposure to chondroitinase ABC, an enzyme capable of chondroitin sulfate degradation, restored normal production of elastic fibers by fibroblasts from patients with Costello syndrome. We also present evidence that loss of EBP from fibroblasts of Costello syndrome patients is associated with an unusually high rate of cellular proliferation.

Elastin: molecular description and function

Elastin, the protein responsible for the elastic properties of vertebrate tissues, has been thought to be solely restricted to that role. As a consequence, elastin was conventionally described as an amorphous polymer. Recent results in the biomedical, biochemical and biophysical fields have lead to the conclusion that the presence of elastin in the extracellular space has very complex implications involving many other molecules. The present review describes the current state of knowledge concerning elastin as an elastic macromolecule. First, the genetic, biological, biochemical and biophysical processes leading to a functional polymer are described. Second, the elastic function of elastin is discussed. The controversy on elastin structure and elasticity is discussed and a novel dynamic mechanism of elasticity proposed. Finally, pathologies where the elastin molecule is involved are considered. This updated description of functional elastin provides the required background for the understanding of its pathologies and defines clearly the properties a substance should possess to be qualified as a good elastic biomaterial.

Biochemistry and molecular regulation of matrix macromolecules in abdominal aortic aneurysms

Past concepts of aneurysmal dilatation as a passive process of attenuation are oversimplified and inaccurate. Aneurysm formation is a complex remodeling process that involves both synthesis and degradation of matrix proteins. Interstitial procollagen gene expression is increased in AAA compared to AOD or normal aorta, whereas tropoelastin gene expression is decreased in both AOD and AAA. The medial elastin network is disrupted and discontinuous in small AAA. Thus, the growth rate of an established AAA may well relate to the balance between collagen synthesis and degradation. Although the increased procollagen expression found in AAA may represent a compensatory response, understanding the factors that modulate matrix metabolism in AAA may allow for development of pharmacologic strategies which effectively inhibit the growth of small aneurysms.