Asymmetric cell-matrix and biomechanical abnormalities in elastin insufficiency induced aortopathy

Aortopathy is characterized by vascular smooth muscle cell (VSMC) abnormalities and elastic fiber fragmentation. Elastin insufficient (Eln (+/-)) mice demonstrate latent aortopathy similar to human disease. We hypothesized that aortopathy manifests primarily in the aorto-pulmonary septal (APS) side of the thoracic aorta due to asymmetric cardiac neural crest (CNC) distribution. Anatomic (aortic root vs. ascending aorta) and molecular (APS vs. non-APS) regions of proximal aorta tissue were examined in adult and aged wild type (WT) and mutant (Eln (+/-)) mice. CNC, VSMCs, elastic fiber architecture, proteoglycan expression, morphometrics and biomechanical properties were examined using histology, 3D reconstruction, micropipette aspiration and in vivo magnetic resonance imaging (MRI). In the APS side of Eln (+/-) aorta, Sonic Hedgehog (SHH) is decreased while SM22 is increased. Elastic fiber architecture abnormalities are present in the Eln (+/-) aortic root and APS ascending aorta, and biglycan is increased in the aortic root while aggrecan is increased in the APS aorta. The Eln (+/-) ascending aorta is stiffer than the aortic root, the APS side is thicker and stiffer than the non-APS side, and significant differences in the individual aortic root sinuses are observed. Asymmetric structure-function abnormalities implicate regional CNC dysregulation in the development and progression of aortopathy.

Defect in proline synthesis: pyrroline-5-carboxylate reductase 1 deficiency leads to a complex clinical phenotype with collagen and elastin abnormalities

Pyrroline-5-carboxylate reductase 1 (PYCR1) catalyzes the last step in proline synthesis. Deficiency of PYCR1, caused by a defect in PYCR1, was recently described in patients with cutis laxa, intrauterine growth retardation, developmental dysplasia of the hips and mental retardation. In this paper, we describe additional six patients (ages ranging from 4 months to 55 years) from four Iranian families with clinical manifestations of a wrinkly skin disorder. All patients have distinct facial features comprising triangular face, loss of adipose tissue and thin pointed nose. Additional features are short stature, wrinkling over dorsum of hand and feet, visible veins over the chest and hyperextensible joints. Three of the patients from a large consanguineous family do not have mental retardation, while the remaining three patients from three unrelated families have mental and developmental delay. Mutation analysis revealed the presence of disease-causing variants in PYCR1, including a novel deletion of the entire PYCR1 gene in one family, and in each of the other patients the homozygous missense mutations c.616G > A (p.Gly206Arg), c.89T > A (p.Ile30Lys) and c.572G > A (p.Gly191Glu) respectively, the latter two of which are novel. Light- and electron microscopy investigations of skin biopsies showed smaller and fragmented elastic fibres, abnormal morphology of the mitochondria and their cristae, and slightly abnormal collagen fibril diameters with irregular outline and variable size. In conclusion, this study adds information on the natural course of PYCR1 deficiency and sheds light on the pathophysiology of this disorder. However, the exact pathogenesis of this new disorder and the role of proline in the development of the clinical phenotype remain to be fully explained.

Discrete contributions of elastic fiber components to arterial development and mechanical compliance

OBJECTIVE

Even though elastin and fibrillin-1 are the major structural components of elastic fibers, mutations in elastin and fibrillin-1 lead to narrowing of large arteries in supravalvular aortic stenosis and dilation of the ascending aorta in Marfan syndrome, respectively. A genetic approach was therefore used here to distinguish the differential contributions of elastin and fibrillin-1 to arterial development and compliance.

METHODS AND RESULTS

Key parameters of cardiovascular function were compared among adult mice haploinsufficient for elastin (Eln(+/-)), fibrillin-1 (Fbn1(+/-)), or both proteins (dHet). Physiological and morphological comparisons correlate elastin haploinsufficiency with increased blood pressure and vessel length and tortuosity in dHet mice, and fibrillin-1 haploinsufficiency with increased aortic diameter in the same mutant animals. Mechanical tests confirm that elastin and fibrillin-1 impart elastic recoil and tensile strength to the aortic wall, respectively. Additional ex vivo analyses demonstrate additive and overlapping contributions of elastin and fibrillin-1 to the material properties of vascular tissues. Lastly, light and electron microscopy evidence implicates fibrillin-1 in the hypertension-promoted remodeling of the elastin-deficient aorta.

CONCLUSIONS

These results demonstrate that elastin and fibrillin-1 have both differential and complementary roles in arterial wall formation and function, and advance our knowledge of the structural determinants of vascular physiology and disease.

Decreased lung fibroblast growth factor 18 and elastin in human congenital diaphragmatic hernia and animal models

RATIONALE

Lung hypoplasia in congenital diaphragmatic hernia (CDH) seems to involve impaired alveolar septation. We hypothesized that disturbed deposition of elastin and expression of fibroblast growth factor 18 (FGF18), an elastogenesis stimulus, occurs in CDH.

OBJECTIVES

To document FGF18 and elastin in human CDH and ovine surgical and rat nitrofen models and to use models to evaluate the benefit of treatments.

METHODS

Human CDH and control lungs were collected post mortem. Diaphragmatic hernia was created in sheep at 85 days; fetal lungs were collected at 139 days (term = 145 days). Pregnant rats received nitrofen at 12 days; fetal lungs were collected at 21 days (term = 22 days). Some of the sheep fetuses with hernia underwent tracheal occlusion (TO); some of the nitrofen-treated pregnant rats received vitamin A. Both treatments are known to promote lung growth.

MEASUREMENTS AND MAIN RESULTS

Coincidental with the onset of secondary septation, FGF18 protein increased threefold in control human lungs, which failed to occur in CDH. FGF18 labeling was found in interstitial cells of septa. Elastin staining demonstrated poor septation and markedly decreased elastin density in CDH lungs. Consistently, lung FGF18 transcripts were diminished 60 and 83% by CDH in sheep and rats, respectively, and elastin density and expression were diminished. TO and vitamin A restored FGF18 and elastin expression in sheep and rats, respectively. TO restored elastin density.

CONCLUSIONS

Impaired septation in CDH is associated with decreased FGF18 expression and elastic fiber deposition. Simultaneous correction of FGF18 and elastin defects by TO and vitamin A suggests that defective elastogenesis may result, at least partly, from FGF18 deficiency.

Bilateral semilunar valve disease in a child with partial deletion of the Williams-Beuren syndrome region is associated with elastin haploinsufficiency

Elastin is an extracellular matrix protein that is the primary component of elastic fibers, and is expressed in the great vessels as well as the semilunar and atrioventricular valves. Elastin haploinsufficiency, resulting from mutation or deletion of the elastin gene, is an important clinical problem that is typically characterized by arteriopathy. Herein is described a patient with elastin haploinsufficiency due to partial deletion of the Williams-Beuren syndrome region, resulting in bilateral semilunar valve disease and arteriopathy. Histochemical analysis of the aortic valve revealed decreased and disorganized elastin with loss of the normal trilaminar cusp organization. These findings suggest that elastin has a role in the pathogenesis of semilunar valve disease.

Effects of elastin haploinsufficiency on the mechanical behavior of mouse arteries

Supravalvular aortic stenosis (SVAS) is associated with decreased elastin and altered arterial mechanics. Mice with a single deletion in the elastin gene (ELN+/−) are models for SVAS. Previous studies have shown that elastin haploinsufficiency in these mice causes hypertension, decreased arterial compliance, and changes in arterial wall structure. Despite these differences, ELN+/− mice have a normal life span, suggesting that the arteries remodel and adapt to the decreased amount of elastin. To test this hypothesis, we performed in vitro mechanical tests on abdominal aorta, ascending aorta, and left common carotid artery from ELN+/− and wild-type (C57BL/6J) mice. We compared the circumferential and longitudinal stress-stretch relationships and residual strains. The circumferential stress-stretch relationship is similar between genotypes and changes <3% with longitudinal stretch at lengths within 10% of the in vivo value. At mean arterial pressure, the circumferential stress in the ascending aorta is higher in ELN+/− than in wild type. Although arterial pressures are higher, the increased number of elastic lamellae in ELN+/− arteries results in similar tension/lamellae compared with wild type. The longitudinal stress-stretch relationship is similar between genotypes for most arteries. Compared with wild type, the in vivo longitudinal stretch is lower in ELN+/− abdominal and carotid arteries and the circumferential residual strain is higher in ELN+/− ascending aorta. The increased circumferential residual strain brings the transmural strain distribution in ELN+/− ascending aorta close to wild-type values. The mechanical behavior of ELN+/− arteries is likely due to the reduced elastin content combined with adaptive remodeling during vascular development.

Genetic approaches to disease and regeneration

Cardiovascular disease is largely a consequence of coronary artery blockage through excessive proliferation of smooth muscle cells. It in turn leads to myocardial infarction and permanent and functionally devastating tissue damage to the heart wall. Our studies have revealed that elastin is a primary player in maintaining vascular smooth muscle cells in their dormant state and thus may be a useful therapeutic in vascular disease. By studying zebrafish, which unlike humans, can repair damage to heart muscle, we have begun to uncover some of the genes that seem necessary to undertake the de-differentiation steps that currently fail and prevent the formation of new proliferating cardiomyocytes at the site of damage in a mammalian heart.

The De Barsy syndrome

BACKGROUND

In 1968, De Barsy reported on a girl exhibiting an aged aspect, 'dwarfism, oligophrenia, and degeneration of the elastic tissue in cornea and skin'. The disorder was recognized as a subgroup of cutis laxa syndrome and termed De Barsy-Moens-Dierckx syndrome. The pathogenesis of the disorder is unknown.

METHODS

To improve the comprehension of the pathogenetic mechanisms involved in the De Barsy syndrome, we performed an ultrastructural, morphometric, immunocytochemical study on a skin biopsy of a boy with the De Barsy phenotype, who has been clinically followed for 12 years from birth. Moreover, the lysyl oxidase activity was measured on skin fibroblasts cultured in vitro.

RESULTS

Light and electron microscopy, morphometry, and immunocytochemical observations showed a significant reduction of the elastic fibers in the papillary and in the reticular dermis of patient compared to an age-matched control (p < 0.05). By contrast, the collagen structure, content, and the distribution were normal, as well as lysyl oxidase activity in the medium of in vitro fibroblasts (12,323 DPM/10(6) cells). The immunoreaction for antibodies recognizing fibrillin-1, neutrophilic elastase, and tumor necrosis factor-alpha was stronger, whereas that for antibodies against transforming growth factor-beta was less pronounced in the dermis of the De Barsy boy compared to control.

CONCLUSIONS

Clinical, phenotypic, and structural data were consistent with the diagnosis of De Barsy syndrome. This is the first case described in Italy. Clinical and structural data confirm that the elastic component is mostly affected in this disorder. Moreover, ultrastructural and immunochemical findings suggest that both elastic fiber degradative and very likely synthetic processes are involved.

Developmental adaptation of the mouse cardiovascular system to elastin haploinsufficiency

Supravalvular aortic stenosis is an autosomal-dominant disease of elastin (Eln) insufficiency caused by loss-of-function mutations or gene deletion. Recently, we have modeled this disease in mice (Eln+/-) and found that Eln haploinsufficiency results in unexpected changes in cardiovascular hemodynamics and arterial wall structure. Eln+/- animals were found to be stably hypertensive from birth, with a mean arterial pressure 25-30 mmHg higher than their wild-type counterparts. The animals have only moderate cardiac hypertrophy and live a normal life span with no overt signs of degenerative vascular disease. Examination of arterial mechanical properties showed that the inner diameters of Eln+/- arteries were generally smaller than wild-type arteries at any given intravascular pressure. Because the Eln+/- mouse is hypertensive, however, the effective arterial working diameter is comparable to that of the normotensive wild-type animal. Physiological studies indicate a role for the renin-angiotensin system in maintaining the hypertensive state. The association of hypertension with elastin haploinsufficiency in humans and mice strongly suggests that elastin and other proteins of the elastic fiber should be considered as causal genes for essential hypertension.

Decreased elastin in vessel walls puts the pressure on

Mice haploinsufficient for elastin develop structural changes in vessel walls similar to those seen in patients with mutations in the elastin gene. A new study demonstrates that due to mechanical changes in the vessel wall, these animals exhibit increased mean arterial pressures. The results evoke the possibility that alterations in elastin may contribute to the development of essential hypertension in patients.

Vocal cord abnormalities in Williams syndrome: a further manifestation of elastin deficiency

Williams syndrome (WS) is due to a deletion in the WS critical region at 7q11.23 which includes the elastin gene (ELN). One of the most characteristic features of this disorder is a harsh, brassy, or hoarse voice but the etiology of the vocal characteristics are unknown. We report two patients with WS who had bilateral vocal cord abnormalities, bringing to four the number of children with WS in whom such defects have been documented. We suggest that vocal cord abnormalities may be a far more common feature of WS than has been previously suspected, and that mild vocal cord dysfunction caused by abnormal vocal cord elastin may be the cause of the hoarse voice in this condition.

Connection between elastin haploinsufficiency and increased cell proliferation in patients with supravalvular aortic stenosis and Williams-Beuren syndrome

To elucidate the pathomechanism leading to obstructive vascular disease in patients with elastin deficiency, we compared both elastogenesis and proliferation rate of cultured aortic smooth-muscle cells (SMCs) and skin fibroblasts from five healthy control subjects, four patients with isolated supravalvular aortic stenosis (SVAS), and five patients with Williams-Beuren syndrome (WBS). Mutations were determined in each patient with SVAS and in each patient with WBS. Three mutations found in patients with SVAS were shown to result in null alleles. RNA blot hybridization, immunostaining, and metabolic labeling experiments demonstrated that SVAS cells and WBS cells have reduced elastin mRNA levels and that they consequently deposit low amounts of insoluble elastin. Although SVAS cells laid down approximately 50% of the elastin made by normal cells, WBS cells deposited only 15% of the elastin made by normal cells. The observed difference in elastin-gene expression was not caused by a difference in the stability of elastin mRNA in SVAS cells compared with WBS cells, but it did indicate that gene-interaction effects may contribute to the complex phenotype observed in patients with WBS. Abnormally low levels of elastin deposition in SVAS cells and in WBS cells were found to coincide with an increase in proliferation rate, which could be reversed by addition of exogenous insoluble elastin. We conclude that insoluble elastin is an important regulator of cellular proliferation. Thus, the reduced net deposition of insoluble elastin in arterial walls of patients with either SVAS or WBS leads to the increased proliferation of arterial SMCs. This results in the formation of multilayer thickening of the tunica media of large arteries and, consequently, in the development of hyperplastic intimal lesions leading to segmental arterial occlusion.

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.

Skin elastic fibers in Williams syndrome

The elastin gene is consistently deleted in Williams syndrome and as this protein represents the major component of the elastic fibers of the dermis, we sought to investigate skin elastic fibers in Williams syndrome as a key to unraveling extracellular matrix disorganization in this condition. Both morphometric parameters analyzed by using automated image analysis and immunofluorescence labeling with monoclonal antibodies against elastin and fibrillin 1 showed a disorganized pre-elastic (oxytalan and elaunin) and mature elastic fibers in the dermis of 10 Williams syndrome patients compared with five healthy children and one patient with isolated supravalvular aortic stenosis. Skin biopsies in Williams syndrome patients provide a simple mean to elucidate extracellular matrix anomalies. Hopefully, this method could give clues to the understanding of the elastic network anomalies in this condition and even to the consequences of these latter on elasticity and resilience of other tissues such as the arterial tree.

Reduced capacity to inhibit elastase in abdominal aortic aneurysm

BACKGROUND

Loss of elastin in the aortic wall is an early event in abdominal aortic aneurysm (AAA). An imbalance in the protease-antiprotease system is proposed to be one of the factors that promote connective tissue destruction. We hypothesize that plasma from AAA patients will have a reduced inhibitory capacity in comparison to normal controls.

MATERIALS AND METHODS

Using an assay we developed, plasma (10 microliters), collected from AAA patients (n = 14) and normal controls (n = 13), was added to the elastase inhibition assay containing succinylated elastin substrate. The reaction was initiated with 13.9 units porcine pancreatic elastase (PPE). Elastase activity in the presence and absence of plasma was compared. Plasma elastase was also determined using the Merck PMN-elastase kit.

RESULTS

The relative activity of exogenous elastase (%) in the presence of AAA plasma (n = 14, mean age 73.4 years +/- 1.7 SEM) was 42.59% +/- 4.3 SEM, while that in the presence of control plasma (n = 13, mean age 73.9 years +/- 2.1 SEM) was 10.23% +/- 2.1 SEM (P < 0.0001). Analysis of plasma elastase (microgram/L) indicated that there was no significant difference between normal (n = 9, 207.33 microgram/L +/- 58.67 SEM) and AAA (n = 9, 145.34 microgram/L +/- 29.54 SEM) (P = 0.359).

CONCLUSION

There is a significant reduction in the plasma inhibitory capacity of elastase in AAA patients in comparison to normal controls, though plasma elastase level was not significantly different. The data presented here give experimental evidence to the protease-antiprotease imbalance in AAA patient plasma and may lead to the development of a measurable parameter to monitor AAA.

Elastin is an essential determinant of arterial morphogenesis

Elastin, the main component of the extracellular matrix of arteries, was thought to have a purely structural role. Disruption of elastin was believed to lead to dissection of arteries, but we showed that mutations in one allele encoding elastin cause a human disease in which arteries are blocked, namely, supravalvular aortic stenosis. Here we define the role of elastin in arterial development and disease by generating mice that lack elastin. These mice die of an obstructive arterial disease, which results from subendothelial cell proliferation and reorganization of smooth muscle. These cellular changes are similar to those seen in atherosclerosis. However, lack of elastin is not associated with endothelial damage, thrombosis or inflammation, which occur in models of atherosclerosis. Haemodynamic stress is not associated with arterial obstruction in these mice either, as the disease still occurred in arteries that were isolated in organ culture and therefore not subject to haemodynamic stress. Disruption of elastin is enough to induce subendothelial proliferation of smooth muscle and may contribute to obstructive arterial disease. Thus, elastin has an unanticipated regulatory function during arterial development, controlling proliferation of smooth muscle and stabilizing arterial structure.