Impaired elastic matrix development in the great arteries after ablation of the cardiac neural crest

Prevalence of Intracranial Aneurysm in Patients with Aortopathy: A Systematic Review with Meta-Analyses

BACKGROUND AND PURPOSE

Patients with aortic disease might have an increased risk of intracranial aneurysm (IA). We conducted this research to assess the prevalence of IA in patients with aortopathy, considering the impact of gender, age, and cardiovascular risk factors.

METHODS

We searched PubMed and Scopus from inception to August 2019 for epidemiological studies reporting the prevalence of IA in patients with aortopathy. Random-effect meta-analyses were performed to calculate the overall prevalence, and the effect of risk factors on the prevalence was also evaluated. Anatomical location of IAs in patients suffered from distinct aortic disease was extracted and further analyzed.

RESULTS

Thirteen cross-sectional studies involving 4,041 participants were included in this systematic review. We reported an estimated prevalence of 12% (95% confidence interval [CI], 9% to 14%) of IA in patients with aortopathy. The pooled prevalence of IA in patients with bicuspid aortic valve, coarctation of the aorta, aortic aneurysm, and aortic dissection was 8% (95% CI, 6% to 10%), 10% (95% CI, 7% to 14%), 12% (95% CI, 9% to 15%), and 23% (95% CI, 12% to 34%), respectively. Gender (female) and smoking are risk factors related to an increased risk of IA. The anatomical distribution of IAs was heterogeneously between participants with different aortic disease.

CONCLUSIONS

According to current epidemiological evidence, the prevalence of IA in patients with aortic disease is quadrupled compared to that in the general population, which suggests that an early IA screening should be considered among patients with aortic disease for timely diagnosis and treatment of IA.

New Pathophysiological Considerations on Cerebral Aneurysms

Cerebral aneurysm is a common cerebrovascular disease that is sometimes complicated by rupture or an enlarged mass. We are now aggressively evaluating and managing unruptured cerebral aneurysms based on a significant concern for the high morbidity and mortality related to its associated complications. However, the actual rupture rate is very low and the diagnostic and treatment modalities are expensive and invasive, which may lead to unnecessary costs and potential medical complications. This disproportionate situation is related to a poor understanding of the natural course and pathophysiology of cerebral aneurysms. In consideration of the concept that not all cerebral aneurysms must be removed, we need to examine their course and progression more accurately. Cerebral aneurysms may follow a variety of pathophysiological scenarios over their lifetime, from formation to growth and rupture. The disease course and the final outcome can differ depending on the timing and intensity of the pathological signals acting on the cerebral vessel wall. We should delineate a method of predicting the stability and risk of rupture of the lesion based on a comprehensive knowledge of the vessel wall integrity. This review deals with the basic knowledge and advanced concepts underlying the pathophysiology of cerebral aneurysms.

A Comparative Study of Histopathological Changes in the Ascending Aorta and the Risk Factors Related to Histopathological Conditions and Aortic Dilatation in Patients With Tetralogy of Fallot and a Functionally Univentricular Heart

BACKGROUND

The purposes of this study were to prospectively evaluate the histologic characteristics of the aortic wall of patients undergoing univentricular type of repair and compare the same with the findings observed in patients undergoing intracardiac repair of tetralogy of Fallot (TOF).

PATIENTS AND METHODS

Operatively excised full-thickness aortic wall tissue from 99 consecutive patients undergoing either intracardiac repair of TOF (group I; n=42) or univentricular repair (group II; n=57) were studied by light microscopy. Age at operation was 13 months to 28 years (mean 99.97±73.21months) for group I and 9 months to 25 years (mean 79.52±60.09) months for group II patients.

RESULTS

Dilatation of the ascending aorta was present in 85.7% patients with TOF and 91.2% patients with a univentricular heart. Seventeen (17.2%) aortic specimens were histologically normal and were used as normal controls (group I, n=5; group II, n=12). A lamellar count of less than 60 was associated with a sensitivity of 97.2% and a specificity of 66.7% in patients undergoing repair of TOF and a sensitivity of 84.6% and a specificity of 80% in patients undergoing univentricular type of repairs respectively. Patients undergoing intracardiac repair of TOF and those undergoing univentricular repair exhibited 23.67 times (15.91-147.40) and 8.48 times (3.62-15.84) increased risk of aortic dilatation respectively.

CONCLUSIONS

Our findings indicate the existence of significant elastic fragmentation, muscle disarray, medionecrosis and fibrosis involving the ascending aortic media in patients with a functionally univentricular heart and dilated aorta. These histopathological changes are similar to those encountered in patients with TOF and dilated aorta.

Heterogeneity in vascular smooth muscle cell embryonic origin in relation to adult structure, physiology, and disease

Regional differences in vascular physiology and disease response exist throughout the vascular tree. While these differences in physiology and disease correspond to regional vascular environmental conditions, there is also compelling evidence that the embryonic origins of the smooth muscle inherent to the vessels may play a role. Here, we review what is known regarding the role of embryonic origin of vascular smooth muscle cells during vascular development. The focus of this review is to highlight the heterogeneity in the origins of vascular smooth muscle cells and the resulting regional physiologies of the vessels. Our goal is to stimulate future investigation into this area and provide a better understanding of vascular organogenesis and disease. .

Unexpected death caused by rupture of a dilated aorta in an adult male with aortic coarctation

Aortic coarctation (AC) is a congenital aortic narrowing. We describe for the first time the findings obtained by unenhanced post mortem computed tomography (PMCT) in a case where the death was caused by cardiac tamponade from a ruptured aneurysmal dilatation of the ascending aorta and the aortic arch without dissection combined with aortic coarctation. The patient, a 46-year-old man, was found dead at home. PMCT showed haemopericardium and dilatation of the ascending aorta and the aortic arch. This appearance led to the mistaken interpretation that the images represented a dissecting aneurysm. The autopsy showed instead a thin-walled and floppy dilatation of the ascending aorta and aortic arch with a coarctation just proximal to the ligamentum arteriosum. A longitudinal tear was found in the posterior aortic wall just above the valves. Blood in the surrounding soft tissue intersected with a large haematoma (1000ml) in the pericardial sac. Cardiac hypertrophy (556g) was observed in the patient, though no other cardiovascular abnormalities were found. Histological analysis showed cystic medial necrosis of the ascending aortic wall. A ruptured aneurysmal dilatation of the ascending aorta and the aortic arch without aortic dissection associated with AC is an uncommon cause of haemopericardium that has only been described a few times before. The case is discussed in relation to other reported cases and in the context of the present understanding of this condition.

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.

Echocardiographic evidence of innate aortopathy in the human intracranial aneurysm

BACKGROUND

Intracranial aneurysm (IA) is significantly more prevalent in patients with coarctation of the aorta or bicuspid aortic valve than in the general population, suggesting a common pathophysiology connecting IA and aortopathy. Here, we analyzed echocardiographic aortic root dimension (ARD) in patients with IA to confirm this possibility.

METHODS

From January 2008 to December 2010, 260 consecutive patients with IA who were admitted to our institution for coil embolization or for acute stroke management and who also underwent echocardiography were enrolled. We hypothesized that patients with large, ruptured, or multiple IAs are more likely to harbor co-prevalent aortopathy as measured by ARD compared to patients with small, isolated, unruptured IAs. Eccentric group was defined as patients aged <55 years with at least one ruptured aneurysm, an aneurysm ≥7 mm in size, or multiple aneurysms; the remainder was classified into a non-eccentric group. Clinical, angiographic, and echocardiographic findings of the two groups were compared.

RESULTS

ARD was significantly larger in the eccentric group than in the non-eccentric group (P = 0.049), and the difference was confirmed by multivariable analysis (P = 0.02). Subgroup analysis of patients aged <55 years showed similar result for ARD (P = 0.03), whereas hypertension was more associated with the non-eccentric group (P = 0.01). In addition, height was inversely related to aneurysm size after adjustment for age, sex, weight, ARD, smoking status, and number of aneurysms (P = 0.004).

CONCLUSIONS

A certain group of IA patients share a common intrinsic wall defect with aortopathy. Shared neural crest cell origin may give rise to this phenomenon.

Pulmonary arterial wall stiffness and its impact on right ventricular afterload in patients with repaired tetralogy of Fallot

BACKGROUND

Recent histologic studies involving patients with tetralogy of Fallot (TOF) have revealed a reduction in normal elastic fibers in the pulmonary trunk. Such histologic changes may significantly alter the mechanical properties of the arterial wall and may thereby augment the pulsatile afterload on the right ventricle (RV) and propagate RV dilation and dysfunction.

METHODS

We studied 29 patients with repaired TOF (median age, 5.9 years) and 29 age-matched controls. Pulmonary arterial hemodynamics were investigated by measuring the pulmonary input impedance during cardiac catheterization.

RESULTS

Patients with TOF had higher characteristic impedance (p = 0.0002), lower total pulmonary vascular compliance (p < 0.0001), and enhanced wave reflection (p < 0.0001). Consistent with these changes, patients with TOF were subject to higher pulsatile load, measured by fundamental frequency impedance (p < 0.0001), which was significantly related to both reduced RV output and increased RV end-diastolic volume (p = 0.006 and 0.003, respectively). Moreover, pulmonary arterial compliance was strongly related to RV end-diastolic volume (r = -0.69, p = 0.0001). In multivariate analysis, pulmonary arterial compliance was a significant predictor of RV dilation independent of pulmonary regurgitation and pulmonary stenosis (p = 0.03).

CONCLUSIONS

In line with known histologic changes, pulmonary arterial stiffness is increased and is significantly related to reduced RV ejection and RV enlargement in patients with repaired TOF. These results suggest that not only pulmonary valvular function (pulmonary regurgitation/pulmonary stenosis) but also pulmonary vascular pulsatile properties can be an important therapeutic target to improve prognosis in this population.

Marked disparity in mechanical wall properties between ascending and descending aorta in patients with tetralogy of Fallot

OBJECTIVES

Recent studies have linked abnormal aortic medial pathology to progressive aortic root dilatation in patients with tetralogy of Fallot (TOF). To explore whether the aortic medial pathology in TOF is linked to aortic mechanical property, the present study tested the hypothesis that the distribution of impaired aortic elasticity corresponds to the known distribution of abnormal medial pathology (confined to the ascending aorta) in TOF.

METHODS

Pulse wave velocity (PWV) of the proximal and distal aortas was measured with a high-fidelity micromanometer in 98 TOF patients (64 with repaired TOF and 34 with unrepaired TOF) and 63 control subjects.

RESULTS

PWV of the proximal aorta was significantly higher in TOF than in the control, but similar in repaired and unrepaired TOF (repaired: 588 ± 205 cm/s, unrepaired: 680 ± 288 cm/s, control: 439 ± 101 cm/s, P < 0.001 for each TOF group vs. control, P = 0.07 for repaired vs. unrepaired TOF). In contrast, PWV of the distal aorta was almost identical among the three groups (repaired: 441 ± 189 cm/s, unrepaired: 430 ± 114 cm/s, control: 461 ± 164 cm/s, P = 0.73, analysis of variance), indicating that abnormal aortic mechanical property is confined to the proximal aorta regardless of the operative status of TOF. This was also confirmed by comparison within the group; PWV of the proximal aorta was significantly higher than that of the distal aorta in both TOF groups (P < 0.001, each), whereas there was no difference in PWV between the proximal and distal aortas in the control subjects (P = 0.61).

CONCLUSIONS

Consistent with the known histopathological disparity between the media of the ascending and descending aortas, aortic stiffness is markedly increased in the proximal but not in the distal aorta of TOF. These results suggest that aortic wall stiffness is a potentially useful clinical marker of aortic dilation in patients with TOF.

Review article: implications of vascular aging

Chronological age is a well-established risk factor for the development of cardiovascular diseases. The changes that accumulate in the vasculature with age, however, are highly variable. It is now increasingly recognized that indices of vascular health are more reliable than age per se in predicting adverse cardiovascular outcomes. The variation in the accrual of these age-related vascular changes is a function of multiple genetic and environmental factors. In this review, we highlight some of the pathophysiological mechanisms that characterize the vascular aging phenotype. Furthermore, we provide an overview of the key outcome studies that address the value of these vascular health indices in general and discuss potential effects on perioperative cardiovascular outcomes.

Screening for intracranial aneurysms in patients with bicuspid aortic valve

Objective: Bicuspid aortic valve (BAV) is a common congenital heart defect affecting half to 2% of the population. A generalized connective tissue disorder also involving the intracranial arteries has been suspected in this patient population. We therefore screened a group of patients with BAV for the presence of intracranial aneurysms.

Methods: Magnetic resonance angiography or CT angiography of the brain was used in 61 patients with BAV (age, 29–70 years [mean 48 years]) and in 291 controls (28–78 years [mean 56 years]).

Results: Intracranial aneurysms were detected in 6 of 61 patients with BAV (9.8%; 95% confidence interval [CI] 2.4%–17.3%). This was significantly higher than in the control population (3/291 [1.1%; 95% CI 0%–2.2%]) (p = 0.0012). Female sex (p = 0.02) and advanced age (p = 0.003), risk factors for intracranial aneurysm development, were more common in the control population than among the patients with a BAV. No significant differences were detected in age, sex, smoking, arterial hypertension, alcohol use, aortic diameter, or frequency of aortic coarctation between BAV patients with and without intracranial aneurysms.

Conclusion: In this case-control study, the frequency of intracranial aneurysms among our bicuspid aortic valve patient population was significantly higher than in the control population.

Cross-talk between macro- and microcirculation

Physiologically, macro- and microcirculation differ markedly as macrocirculation deals with pulsatile pressure and flow and microcirculation with steady pressure and flow. Various such haemodynamic aspects correspond to a large heterogeneity in the structure and function of the vascular tree. In the past, diseases such as hypertension and diabetes mellitus were classified on the basis of the structure and function of small and large arteries. The purpose of this paper is to review the cross-talk between the micro- and macrocirculation. We shall discuss this cross-talk from the perspective of the development, physiology and pathology of the entire arterial tree.

Evaluating arterial aging in the clinical setting: a tentative agenda for critical appraisal

Population aging is a worldwide phenomenon. However, the cultural attitude to older adults has not yet incorporated understanding of the effects of the aging process. The arterial system is affected by the aging process, which is responsible for the great majority of mortality, morbidity and disability in older people. We briefly describe how the aging process affects large arteries and their properties that are easily measurable noninvasively, and suggest a tentative agenda for solving the critical problems that have hampered the diffusion of routine assessment of arterial aging in the clinical setting.

Persistent truncus arteriosus with dissecting aneurysm and subsequent cardiac tamponade in a lamb

The present case report describes the necropsy and histopathology findings of a 3-week-old lamb with persistent truncus arteriosus (PTA). This rare cardiac malformation was characterized by the presence of a common arterial trunk arising from the right ventricle and overriding a ventricular septal defect. The pulmonary arteries originated from a short common trunk from this PTA, which subsequently continued as the thoracic aorta. The death of the lamb was attributed to a rupture of the PTA with subsequent cardiac tamponade. Histologically, a dissecting aneurysm with elastic fiber fragmentation in the wall of the PTA was identified as the underlying pathologic condition. Altered hemodynamic forces with subsequent secondary vasculopathy, as well as congenital primary vasculopathies, should be considered as an underlying pathogenetic mechanism.

Occurrence of an ascending aorta aneurysm 25 years after cure of a tetralogy of Fallot

The patient, who had undergone a complete cure of a tetralogy of Fallot 25 years previously, was discovered to have an ascending aorta aneurysm on echography. Bentall's procedure was carried-out, using a modified indirect coronary artery transplantation based on the Cabrol technique. As reported in the literature complications are mainly right sided and less frequently occur on the left side in this disease. Including the hypothesis of the overload volume which may provoke aortic root dilation, there is also an intrinsic pathology of the media which could often be related to embryogenesis abnormalities, i.e., abnormal migration of cardiac neural crest cells which may explain this condition.

Histopathologic changes in ascending aorta and risk factors related to histopathologic conditions and aortic dilatation in patients with tetralogy of Fallot

OBJECTIVE

The purposes of this study were to evaluate the histologic characteristics of the aortic wall and the risk factors related to histopathology and aortic dilatation in patients undergoing intracardiac repair of tetralogy of Fallot.

METHODS

Operatively excised full-thickness aortic wall tissue from 98 consecutive patients undergoing intracardiac repair of tetralogy of Fallot aged 6 months to 47 years (mean 104.5 +/- 102.8 months; median 72 months) were studied by light microscopy. The receiver operating characteristic curve analysis was done to quantify the diagnostic accuracy of loss of lamellar counts and multiple logistic regression models.

RESULTS

Twenty-five (25.5%) aortic tissue specimens were indicated as histologically normal and were used as normal controls. The incidence of elastic fragmentation, increased ground substance, medionecrosis, smooth muscle disarray, and fibrosis was 74.5%, 54%, 39.8%, 26.5%, and 57.1%, respectively. A lamellar count of less than 60 was associated with a sensitivity of 80% and a specificity of 87.67%. Area under the receiver operating characteristic curve indicated that 93.37% (standard error +/- 0.039) of the time the value of lamellar count was lower for the abnormal histopathology group than for the normal group (P < .001). The risk of aortic dilatation was 15.97 times higher in patients with histopathologically abnormal aorta.

CONCLUSIONS

The majority of aortic media of the ascending aorta in cyanotic tetralogy of Fallot indicates significant loss of lamellar units and pre-existing intrinsic aortopathy. The changes are present since infancy and are more pronounced in older patients subjected to long-standing cyanosis and volume overload and may account for or may coexist with the higher incidence of aortic dilatation encountered in these patients.

Genes, folate and homocysteine in embryonic development

Population-based studies of human pregnancies show that periconceptional folate supplementation has a significant protective effect for embryos during early development, resulting in a significant reduction in developmental defects of the face, the neural tube, and the cono-truncal region of the heart. These results have been supported by experiments with animal models. An obvious quality held in common by these three anatomical regions is that the normal development of each region depends on a set of multi-potent cells that originate in the mid-dorsal region of the neural epithelium. However, the reason for the sensitive dependence of these particular cells on folic acid for normal development has not been obvious, and there is no consensus about the biological basis of the dramatic rescue with periconceptional folate supplementation. There are two principal hypotheses for the impact of folate insufficiency on development; each of these hypotheses has a micronutrient component and a genetic component. In the first hypothesis the effect of low folate is direct, limiting the availability of folic acid to cells within the embryo itself; thus compromising normal function and limiting proliferation. The second hypothetical effect is indirect: low folate disrupts methionine metabolism; homocysteine increases in the maternal serum; homocysteine induces abnormal development by inhibiting the function of N-methyl-D-aspartate (NMDA) receptors in the neural epithelium. There are three general families of genes whose level of expression may need to be considered in the context of these two related hypotheses: folate-receptor genes; genes that regulate methionine– homocysteine metabolism; NMDA-receptor genes.

Aortic correlates of clinical markers of large artery structure and function. Effects of aging and hypertension

BACKGROUND AND AIMS

Non-invasive measures of large artery structure and function--such as aorto-femoral pulse wave velocity (PWV), arterial compliance (AC) and common carotid intima-media thickness (CCA IMT)--can predict new CV events, independently of traditional CV risk factors. However, neither their relations with aorta properties nor the effects of aging and hypertension on those relations are yet clear.

METHODS AND RESULTS

40 subjects (18 M, 22 F; mean age 60+/-16 yrs, range 21-83 yrs) free of any acute CV event, valve disease or atrial fibrillation, were studied. Aortic IMT, diastolic diameter (D) and distensibility (Dist) were measured by transesophageal echocardiography at three different levels: ascending aorta (AA), distal aortic arch (Aarc) and descending aorta (DA). PWV was measured by Complior. AC was measured as the ratio of stroke volume to pulse pressure. CCA IMT was measured by ultrasonography in diastole. The Dist, IMT, and D of each aortic segment were introduced alternatively into the regression models. After controlling for age, sex, traditional risk factors and prevalent CV disease, AC showed a significant positive association with the distensibility of proximal aortic segments, but no significant association with properties of distal aorta; PWV showed a significant positive association with proximal aorta wall thickness and a negative association with distal aorta distensibility; CCA IMT was positively associated with distal aorta wall thickness, but not with any explored property of the proximal aorta. None of these relationships differed between younger or older, normotensive or hypertensive subjects.

CONCLUSIONS

Non-invasive measures of large artery structure and function are not equivalent with respect to their relations with aortic properties, so that AC seems to reflect proximal aorta function, PWV proximal aorta structure and distal aorta function, and CCA IMT distal aorta structure. Future studies are needed to confirm whether these relations identify a common pathogenetic mechanism, which may be the target for new therapeutic strategies.

Respective contribution of age, mean arterial pressure, and body weight on central arterial distensibility in SHR

In spontaneously hypertensive rats (SHR), carotid and aortic distensibilities measured at operational blood pressure (BP) are reduced. Increased body weight and mean arterial pressure (MAP) are both known to reduce distensibility independently. However, whether, after adjustment to body weight and mean BP, distensibility remains reduced in SHR has never been investigated. Carotid and abdominal aorta distensibilities were measured under anesthesia in SHR at 5, 12, 52, and 78 wk of age, and measurements were compared with age-matched normotensive Wistar rats. Each age group was composed of 9 or 10 animals. We determined distensibility using echo-tracking techniques of high resolution. Compared with Wistar rats, carotid and aortic distensibilities measured at operational MAP are reduced in SHR. This reduction is accentuated with age, particularly for the carotid artery. After adjustment to body weight and MAP, carotid and aortic distensibilities become identical in Wistar and SHR (or even slightly increased in SHR) but continue to be reduced with age, mainly for the carotid artery. In conclusion, in SHR, age and high BP do not have a parallel and similar influence on the reduction of arterial distensibility. Aging constantly reduces arterial distensibility, whereas MAP levels contribute to maintenance of arterial function.

Vascular development, pulse pressure, and the mechanisms of hypertension

For a given cardiac function, the cyclic blood pressure (BP) curve results from 2 different phenotypes: the mean arterial pressure (MAP), a steady component reflecting the resistance of the microvascular network, and pulse pressure (PP), another component corresponding to large artery stiffness and wave reflections. Around birth, cardiovascular (CV) survival is critically influenced by the coupling between the heart and thoracic aorta, and hence, the adequacy of the Windkessel function, the magnitude of aortic elastin accumulation and the PP level. The maturation of the aortic trunk and its branches results from adaptative mechanisms involving shear and tensile stress, with major potential consequences on heart rate control, transit of wave reflections, and coronary perfusion. An adequate optimization of the Windkessel function, and hence PP, diastolic coronary perfusion and CV survival needs a critical MAP level to be reached in each individual during the postnatal period. The achievement of this MAP level requires the development of multiple resistance segments of the microvascular network, particularly within the kidney. Translated in adult populations, this pathophysiological process gives rise to a Gaussian BP distribution, with individuals remaining in the same BP percentile from birth onward (BP tracking). We suggest that hypertension results from early developmental vascular mechanisms that direct BP toward the higher percentiles of the Gaussian distribution curve.

Cardiac neural crest ablation alters aortic smooth muscle force and voltage-sensitive Ca2+ responses

Ablation of the premigratory cardiac neural crest (CNC) from the chick embryo results in a malformed outflow tract vasculature termed persistent truncus arteriosus (PTA). In addition, loss of the CNC disrupts myocardial excitation-contraction (EC) coupling, decreases intracellular Ca2+ transients, and depresses force generation. We examined if similar defects occurred in the neural crest-derived smooth muscle of the aortic arch in a test of the hypothesis that loss of elements from the CNC disrupts EC coupling and force production in the smooth muscle of the tunica media of the aortic arch. Aortic arch segments from chicks (embryonic day 15) displaying PTA generated approximately 43% of stress generated by the aortic arch from sham-operated control embryos during potassium depolarization. The depressed force response was associated with a twofold lower Fura-2 transient. In contrast, force and steady-state Fura-2 signals during endothelin-1 stimulation were unchanged. The differences seen in stress generation with potassium depolarization between sham and PTA displaying embryos were not seen in the descending aorta, a tissue not derived from the neural crest. Protein content and immunostaining revealed no differences in the content of actin, myosin, or dihydropyridine receptor from sham or PTA aortic arch. Our results suggest that the CNC is required for normal aortic arch smooth muscle function and support the hypothesis that the loss of CNC impacts the force generating ability, in part by disruption of the EC-coupling processes and altering Ca(2+)-handling.

Methylation of 2-hydroxyestradiol in isolated organs

Vascular smooth muscle and glomerular mesangial cells in culture express a biochemical pathway that methylates 2-hydroxyestradiol (17beta-estradiol metabolite) to produce 2-methoxyestradiol, a cell growth inhibitor that may mediate the cardiorenal protective effects of 17beta-estradiol. Whether this pathway exists in intact organ systems is currently unclear. Accordingly, the purpose of the present investigation was to characterize the methylation of 2-hydroxestradiol in intact organs from both male and female rats. No significant differences were detected in the ability of male and female tissues to methylate 2-hydroxyestradiol. In isolated hearts, kidneys, and mesenteries perfused with Tyrode's solution, Km values for 2-hydroxyestradiol methylation were 0.175+/-0.021, 0.387+/-0.054, and 0.495+/-0.089 micromol/L, respectively, and Vmax values were 21.0+/-1.58, 24.9+/-1.49, and 1.01+/-0.148 pmol 2-methoxyestradiol x min(-1) x ml(-1) per gram, respectively. The catalytic efficiency (Vmax/Km) was greatest in the heart compared with the kidney and mesentery (132+/-14.3, 78.4+/-15.1, and 2.30+/-0.263 pmol 2-methoxyestradiol x min(-1) x mL(-1) x micromol/L(-1) per gram, respectively). In the kidney, the catechol-O-methyltransferase inhibitor quercetin and norepinephrine (10 micromol/L) reduced methylation of 2-hydroxyestradiol by approximately 90% and 41%, respectively. Importantly, methylation in the kidney was inhibited by an average of 16.6+/-1.80% by endogenous norepinephrine released by renal artery nerve stimulation. Our results indicate that a robust 2-hydroxyestradiol methylation pathway exists in the kidney and heart, but not in the mesentery, and that this pathway is mediated by catechol-O-methyltransferase. Our findings also suggest that catecholamines may interfere with 2-hydroxyestradiol methylation and thereby attenuate the cardiorenal protective effects of 17beta-estradiol.

A syndrome of spontaneous cerebral and cervical artery dissections with angiolipomatosis. Report of two cases

A primary or systemic arteriopathy is frequently suspected in patients with spontaneous cerebral or cervical artery dissections. The authors report on two patients with such dissections accompanied by angiolipomatosis, a previously unreported association, and propose a common developmental defect in these patients. A 50-year-old man with subcutaneous angiolipomatosis developed painful monocular blindness. Angiography studies revealed a spontaneous extracranial internal carotid artery (ICA) dissection and an ipsilateral fusiform intracranial ICA aneurysm. The ICA dissection was treated with aspirin, and after 6 months a craniotomy was performed. The aneurysm was found to be fusiform; it involved the entire supraclinoid portion of the ICA, and was wrapped with cotton. A 49-year-old man with a congenitally bicuspid aortic valve and subcutaneous angiolipomatosis developed posterior neck pain. Magnetic resonance imaging and angiography demonstrated a fusiform distal vertebral artery aneurysm. A craniotomy was performed and the aneurysm was found to incorporate the posterior inferior cerebellar artery as well as a perforating artery: the lesion was wrapped cotton. The tunica media of the arteries of the head and neck as well as the aortic valvular cusps are derived from neural crest cells, and angiolipomatosis has been associated with tumors of neural crest derivation. These associations indicate that a neural crest disorder may be the underlying abnormality in these patients.

Bicuspid aortic valve associated with aortic dilatation: a community-based study

OBJECTIVE

This study was undertaken to examine the association between bicuspid aortic valve (BAV) and aortic dilatation in the community. The association between BAV and aortic dilatation has been reported predominantly in retrospective studies in patients mostly with valvular dysfunction or selected surgical patients from tertiary referral centers. An independent association of BAV and aortic dilatation in a community-based study has not been demonstrated.

METHODS AND RESULTS

In a geographically defined population of Olmsted County, Minnesota, residents with BAV (n=44, age 35+/-13 years) without hemodynamically significant obstruction or regurgitation and matched controls with normal tricuspid aortic valves were identified by transthoracic echocardiography. The two groups were compared with respect to measurements of the aorta. The BAV and control groups differed with respect to size of the aortic anulus (23.2+/-2.4 versus 21.6+/-2.4 mm; P=0.002), aortic sinus (33.5+/-4.6 versus 30.3+/-4.1 mm; P=0.0001), and proximal ascending aorta (33.3+/-6.5 versus 27.9+/-3.6 mm; P=0.0001). There was no difference in the size of the aortic arch (24.2+/-3.6 versus 25.3+/-3.4 mm; P=0.16). These differences were maintained when the groups were stratified by sex and blood pressure. The relationship between bicuspid aortic valve and aortic dilatation was maintained when adjusting for factors related to fluid mechanics and hemodynamics such as systolic blood pressure, diastolic blood pressure, left ventricular ejection time, and peak aortic valve velocity.

CONCLUSIONS

In a community-based study, BAV is associated with an alteration of aortic dimensions even in the absence of hemodynamically significant aortic valve stenosis or regurgitation.

Regional differentiation of desmin, connexin43, and connexin45 expression patterns in rat aortic smooth muscle

The gap-junctional protein, connexin43, is differentially expressed in vascular smooth muscle cells (SMCs) according to phenotype. Previous studies suggest that desmin-negative SMCs are characterized by high levels of connexin43, whereas desmin-positive SMCs (of a more contractile phenotype) typically have low connexin43 levels. In this study, we examine systematically the inverse relationship between connexin43 and desmin in SMCs of defined regions of the rat aortic media and determine whether additional connexin isotypes are expressed and contribute to this relationship. Immunoconfocal microscopy demonstrated that (1) the inverse relationship between connexin43 and desmin expression holds true for the media of sequential aortic zones, with 1 exception, the ascending aorta, and (2) an additional vascular connexin, connexin45, is expressed by aortic SMCs. Examination of connexin43, connexin45, and desmin expression in sequential aortic zones reveals 3 SMC subpopulations. The first, predominating in the aortic arch and thoracic aorta, is desmin negative and contains high connexin43 levels; the second, predominating in the abdominal aorta and iliac artery, is desmin positive and contains low connexin43 levels; and the third, which is restricted to the ascending aorta, is desmin positive and expresses high connexin43 levels. Connexin45 levels are high in the ascending aorta but low in the other aortic segments. In para-aortic veins, a fourth SMC subpopulation appears, one that is desmin positive and contains connexin45 but not connexin43. These results demonstrate that a diversity of connexin expression patterns characterizes distinctive subpopulations of medial SMCs in situ with a potential to contribute to regional differentiation of vascular function.

Increased 2-methoxyestradiol production in human coronary versus aortic vascular cells

Estradiol may be cardioprotective; however, the mechanisms involved remain unclear. Recent findings that estradiol attenuates neointima formation in estrogen receptor knockout mice suggest that the cardioprotective effects of estradiol may be mediated through estrogen receptor-independent mechanisms. Because 2-methoxyestradiol, an endogenous metabolite of estradiol with no affinity for estrogen receptors, is more potent than estradiol in inhibiting vascular smooth muscle cell growth, it is feasible that 2-methoxyestradiol mediates in part the cardioprotective effects of estradiol. To address this hypothesis, we examined the kinetics of 2-methoxyestradiol synthesis in vascular smooth muscle cells and endothelial cells. In human aortic smooth muscle cells, the V(max), K(m), and V(max)/K(m) ratio values for conversion of 2-hydroxyestradiol to 2-methoxyestradiol were 19+/-0.69 pmol. min(-1) per 10(6) cells, 0.52+/-0.085 micromol/L, and 44+/-4.9 pmol. min(-1). micromol/L per 10(6) cells, respectively. In human coronary artery vascular smooth muscle cells, the V(max), K(m), and V(max)/K(m) ratio values for conversion of 2-hydroxyestradiol to 2-methoxyestradiol were 16+/-0.59 pmol. min(-1) per 10(6) cells, 0.23+/-0.011 micromol/L, and 69+/-3.6 pmol. min(-1). micromol/L per 10(6) cells, respectively (all values significantly different compared with human aortic smooth muscle cells). Also, in human aortic versus coronary artery endothelial cells, the V(max) (33+/-0.24 versus 22+/-0.33 pmol. min(-1) per 10(6) cells, respectively), K(m) (0.20+/-0.010 versus 0.099+/-0.014 micromol/L, respectively), and V(max)/K:(m) (163+/-7.7 versus 243+/-41 pmol. min(-1). micromol/L per 10(6) cells, respectively) values were significantly different. Our results indicate that vascular smooth muscle and endothelial cells effectively metabolize 2-hydroxyestradiol to 2-methoxyestradiol. The lower K(m) and higher V(max)/K(m) ratio of human coronary versus aortic cells indicate a faster rate of local metabolism of 2-hydroxyestradiol to 2-methoxyestradiol in the coronary circulation at low levels of 2-hydroxyestradiol.

Structural abnormalities of great arterial walls in congenital heart disease: light and electron microscopic analyses

BACKGROUND

Great arteries in congenital heart disease (CHD) may dilate, become aneurysmal, or rupture. Little is known about medial abnormalities in these arterial walls. Accordingly, we studied 18 types of CHD in patients from neonates to older adults.

METHODS AND RESULTS

Intraoperative biopsies from ascending aorta, paracoarctation aorta, truncus arteriosus, and pulmonary trunk in 86 patients were supplemented by 16 necropsy specimens. The 102 patients were 3 weeks to 81 years old (average, 32+/-6 years). Biopsies were examined by light (LM) and electron (EM) microscopy; necropsy specimens by LM. Positive aortic controls were from 15 Marfan patients. Negative aortic controls were from 11 coronary artery disease patients and 1 transplant donor. Nine biopsies from acquired trileaflet aortic stenosis were compared with biopsies from bicuspid aortic stenosis. Negative pulmonary trunk controls were from 7 coronary artery disease patients. A grading system consisted of negative controls and grades 1, 2, and 3 (positive controls) based on LM and EM examination of medial constituents.

CONCLUSIONS

Medial abnormalities in ascending aorta, paracoarctation aorta, truncus arteriosus, and pulmonary trunk were prevalent in patients with a variety of forms of CHD encompassing a wide age range. Aortic abnormalities may predispose to dilatation, aneurysm, and rupture. Pulmonary trunk abnormalities may predispose to dilatation and aneurysm; hypertensive aneurysms may rupture. Pivotal questions are whether these abnormalities are inherent or acquired, whether CHD plays a causal or facilitating role, and whether genetic determinants are operative.

Connexin 43 expression reflects neural crest patterns during cardiovascular development

We used transgenic mice in which the promoter sequence for connexin 43 linked to a lacZ reporter was expressed in neural crest but not myocardial cells to document the pattern of cardiac neural crest cells in the caudal pharyngeal arches and cardiac outflow tract. Expression of lacZ was strikingly similar to that of cardiac neural crest cells in quail-chick chimeras. By using this transgenic mouse line to compare cardiac neural crest involvement in cardiac outflow septation and aortic arch artery development in mouse and chick, we were able to note differences and similarities in their cardiovascular development. Similar to neural crest cells in the chick, lacZ-positive cells formed a sheath around the persisting aortic arch arteries, comprised the aorticopulmonary septation complex, were located at the site of final fusion of the conal cushions, and populated the cardiac ganglia. In quail-chick chimeras generated for this study, neural crest cells entered the outflow tract by two pathways, submyocardially and subendocardially. In the mouse only the subendocardial population of lacZ-positive cells could be seen as the cells entered the outflow tract. In addition lacZ-positive cells completely surrounded the aortic sac prior to septation, while in the chick, neural crest cells were scattered around the aortic sac with the bulk of cells distributed in the bridging portion of the aorticopulmonary septation complex. In the chick, submyocardial populations of neural crest cells assembled on opposite sides of the aortic sac and entered the conotruncal ridges. Even though the aortic sac in the mouse was initially surrounded by lacZ-positive cells, the two outflow vessels that resulted from its septation showed differential lacZ expression. The ascending aorta was invested by lacZ-positive cells while the pulmonary trunk was devoid of lacZ staining. In the chick, both of these vessels were invested by neural crest cells, but the cells arrived secondarily by displacement from the aortic arch arteries during vessel elongation. This may indicate a difference in derivation of the pulmonary trunk in the mouse or a difference in distribution of cardiac neural crest cells. An independent mouse neural crest marker is needed to confirm whether the differences are indeed due to species differences in cardiovascular and/or neural crest development. Nevertheless, with the differences noted, we believe that this mouse model faithfully represents the location of cardiac neural crest cells. The similarities in location of lacZ-expressing cells in the mouse to that of cardiac neural crest cells in the chick suggest that this mouse is a good model for studying mammalian cardiac neural crest and that the mammalian cardiac neural crest performs functions similar to those shown for chick.

Cervical artery dissection is associated with widened aortic root diameter

OBJECTIVE

Dissection of the internal carotid and vertebral arteries is a well recognized cause of stroke, especially in the middle-aged. The exact etiology of this condition is controversial. According to one theory there is an underlying vasculopathy originating from disturbed development of the neural crest. The neural crest gives rise to several tissues, including the tunica media of large cervical arteries and the outflow tract of the heart. We attempted to test the theory that developmental abnormality at the level of the neural crest may play a role in dissection of the large cervical arteries.

METHODS

We designed a retrospective case control study. By means of transthoracic echocardiography we measured the aortic root diameter in a group of patients with radiographically determined dissection of at least one large artery in the neck. The results were compared to a control group.

RESULTS

In comparison to age matched controls, male patients were found to have a significantly larger aortic root. Although a similar trend was apparent in females, the difference between the patient and control group of females was not statistically significant.

CONCLUSIONS

Patients with cervical artery dissections may have other abnormalities in other organs arising from the neural crest. A larger prospective clinical study and further research are needed to establish a firm link between dissection of the cervical arteries and abnormalities in other organs.

Neural crest cells in outflow tract septation of the embryonic chicken heart: differentiation and apoptosis

The heart consists of cells deriving from the cardiogenic plate and also from extracardiac sources. One of the major extracardiac contributions is given by the neural crest. The differentiation pathway and fate of the neural crest cells in the outflow tract have been followed over a prolonged period during outflow tract septation. We studied the role of the neural crest in remodeling the outflow tract by long-term cell tracing, differentiation markers and apoptosis. The pattern of neural crest cells migrating to the heart was investigated by heterospecific chicken quail chimeras and by retroviral infection of the reporter gene LacZ to the stem cells. The tagged neural crest cells move to areas that are morphogenetically active, such as the outflow tract, the semilunar valves, the wall of the arteries and the cardiac ganglia. Two differentiated subpopulations are discerned on the basis of immunohistochemical characterization with antibodies against smooth muscle cells in the arterial vessel wall and against ganglionic cells that were scattered around the vessels of the arterial pole and the heart. A third subpopulation did not stain with these antibodies, but presented locally with the phenomenon of apoptosis as shown with the TUNEL approach. In a developmental series of chicken embryos the populations were followed until stage 40. It was evident that the outflow tract septum in the early phase of development consisted mainly of mesenchymal neural crest cells. In a later phase neural crest cells were still detected at semilunar valve level, but nearly absent in the outflow tract septum below valve level. The septum at that time had become myocardialized. It is evident that neural crest cells are actually removed from this part of the heart by apoptosis. We are pursuing the hypothesis that an important function of apoptotic cells in heart development might be to activate the cardiomyocytes to muscularize the outflow tract septum through mobilizing or delivering growth factors at the time and place that septum formation is initiated.

Onset of elastogenesis and downregulation of smooth muscle actin as distinguishing phenomena in artery differentiation in the chick embryo

During development, the arterial system is grossly divided into elastic and muscular vessel types. Apart from local environmental factors, it has been suggested that vascular smooth muscle cell origin (mesoderm or neural crest) is involved in this, as yet poorly understood, arterial differentiation. We describe differentiation of the thoracic arterial system in the chick embryo, using immunohistochemical techniques staining for muscle-specific actin, vinculin and desmin and histological staining to visualise elastin. The initial developmental stages of the vessel wall in all arteries appeared to be highly similar, with all arteries showing peri-endothelial actin and vinculin staining. Major alterations did not occur until the start of elastogenesis, which coincided with complete loss of actin staining from the proximal part of the great arteries. Later in development, however, actin was re-expressed in a subpopulation of medial cells, which also expressed vinculin and desmin. Concomitantly another, nonmuscular, cell type became evident in the great arteries. Transient loss of actin expression and segregation of very distinct cell populations occurred only in vessels prone to elastic development and known to receive a neural crest contribution. In contrast, arteries that developed a muscular phenotype never lost the initially acquired peri-endothelial actin expression. We also show a significant difference in the organisation of elastic fibres between elastic vessels that contain neural crest derivatives and those that do not. The ductus arteriosus still presents as an enigma in the sense that it is the only part of the pharyngeal arch complex that develops a muscular phenotype.

Intracranial aneurysms and cervicocephalic arterial dissections associated with congenital heart disease

OBJECTIVE

The number of patients with congenital heart disease who survive to adolescence and adulthood continues to increase. We review our experience with noninfectious intracranial aneurysms and cervicocephalic arterial dissections in patients with congenital heart disease, expanding the clinical spectrum of the cerebrovascular abnormalities that may be encountered in this group of patients.

METHODS

All patients with congenital heart disease and intracranial aneurysms of cervicocephalic arterial dissections, who were evaluated at the Mayo Clinic between 1969 and 1992, were identified.

RESULTS

Congenital heart disease was diagnosed in 3 (8%) of 36 children with intracranial aneurysms, in 5 (0.3%) of 1994 adults with intracranial aneurysms, in 1 (4%) of 25 children with cervicocephalic arterial dissections, and in 5 (2%) of 250 adults with cervicocephalic arterial dissections. The mean age of the 14 patients was 32 years (range, 13-58 yr). The congenital heart disorders consisted of complex cardiac anomalies in three patients (truncus arteriosus, transposition of the great arteries, and tricuspid atresia in one patient each), pulmonic valve or arterial stenosis in two patients, aortic coarctation in four patients, and bicuspid aortic valve in five patients. Only one patient had an intracranial aneurysm and coarctation of the aorta.

CONCLUSION

Individuals with a variety of congenital heart disorders may be at an increased risk of intracranial aneurysm development and cervicocephalic arterial dissection, particularly in adolescence. The muscular arteries of the head and neck are derived from neural crest cells and the neural crest is also of major importance in early cardiac development, suggesting that an abnormality of the neural crest may be the common pathogenetic factor explaining this association.

Progressive intracranial aneurysmal disease in a child with progressive hemifacial atrophy (Parry-Romberg disease): case report

Intracranial aneurysms are uncommon in children, and their presence often leads to suspicion of a systemic connective tissue disorder. We describe the case of a young male patient with progressive hemifacial atrophy (Parry-Romberg disease) and multiple intracranial aneurysms, a previously undescribed association, and propose that a neural crest defect may be the underlying abnormality in this patient. At age 5 years, the patient was treated for a giant aneurysm of the left cavernous carotid artery with carotid ligation in the neck and a superficial temporal artery-middle cerebral artery bypass. At age 12 years, the patient was similarly treated for a giant aneurysm of the right cavernous carotid artery, which had progressed from a previously noted minute dilatation at age 5 years, with carotid ligation and a superficial temporal artery-middle cerebral artery bypass. At age 21 years, the patient was endovascularly treated for a de novo saccular aneurysm of the left posterior cerebral artery at the P1-P2 junction and a fusiform aneurysm of the distal left posterior cerebral artery. Various studies have suggested that the facial dermis, the subcutaneous tissues, and the skeleton, as well as the tunica media of the cervicocephalic arteries, all arise from neural crest cells, and a disorder of neural crest migration might explain the constellation of findings in this patient.

Familial aorto-cervicocephalic arterial dissections and congenitally bicuspid aortic valve

BACKGROUND

A primary arteriopathy is often implicated in the etiology of spontaneous cervicocephalic arterial dissections, but its exact nature usually remains unknown. We describe the familial occurrence of spontaneous arterial dissections and congenitally bicuspid aortic valve (BAV) and propose a common developmental defect in these families.

SUMMARY OF REPORT

In the first family, a 63-year-old man suffered an extracranial internal carotid artery (ICA) dissection, and his 43-year-old cousin with BAV suffered an intracranial vertebral artery (VA) dissection. Two other family members had pathologically proven BAV. In the second family, a 31-year-old woman suffered bilateral extracranial ICA and VA dissections. Her father, at age 46, suffered an aortic dissection associated with cystic medial necrosis and BAV. Her paternal uncle died from an aortic dissection at age 59. In the third family, a 39-year-old woman suffered extracranial ICA and VA dissections, and her brother died at age 48 from an aortic dissection associated with a BAV.

CONCLUSIONS

The familial occurrence of spontaneous arterial dissections and BAV suggests a common developmental defect. The aortic valvular cusps and the arterial media of the aortic arch and its branches are derived from neural crest cells, suggesting that a neural crest defect may be the underlying abnormality in these families.

Expression of collagens and decorin during aortic arch artery development: implications for matrix pattern formation

The elastic matrix of the large arteries shows a high level of spatial order. However, the mechanisms by which such order is established and maintained are largely unknown. The embryonic development of the avian heart and great vessels provides an appropriate model to investigate these mechanisms. In control embryos, an elastic matrix with a high level of spatial order develops in the nascent great vessels. But after the normal vascular smooth muscle (VSM) progenitor cells in the great vessels are experimentally replaced by other VSM progenitor cells, the elastic extracellular matrix is congenitally disordered. The present study used this model to test the hypothesis that the proteoglycan decorin was involved in the establishment and maintenance of the normal three-dimensional spatial order of the vascular elastic matrix. The temporospatial expression of decorin was analysed during development of normal vessels and in experimental vessels with surrogate VSM. The results showed the following: (1) the expression of decorin was related in time and space to the establishment of large helical collagen type III fibers that are characteristic of the normal elastic extracellular matrix; (2) in the experimental extracellular matrix there were few helical fibers of collagen type III, but those that were present remained positive for decorin; and (3) in both control and experimental vessels, decorin associated with neither fibers of collagen type I nor fibers of collagen type III in any conformation other than the large helical fibers. These data indicate a previously unrecognized relationship between decorin and the spatial order of the physiologically significant helical fibers of collagen type III.

Developmentally regulated neural protein EAP-300 is expressed by myocardium and cardiac neural crest during chick embryogenesis

The spatiotemporal distribution of EAP-300 (embryonic avian polypeptide of 300 kDa) was analyzed in embryonic chick heart using immunohistochemistry and confocal microscopy. EAP-300 is a developmentally regulated protein initially characterized in neural cells from chick retina. Myocardial cells all along the early tubular heart were ubiquitously immunolabeled for EAP-300 by embryonic day 2 (E2, Stage 13)). At E5 (Stage 24), myocardial EAP-300 expression levels remained significant in both atrial and ventricular myocardium. At E6 (Stage 28), distinct populations of EAP-300 immunolabeled cells were also observed external to the heart, in septal mesenchymal tissue and neural ganglia adjacent to the outflow tract; these cell populations were confirmed as neural crest-derived by co-localization of EAP-300 and HNK-1. At E13 (Stage 39), myocardial immunolabeling for EAP-300 was no longer ubiquitous, but increasingly restricted to conduction tissues, including the atrioventricular bundle and subendocardial Purkinje cells. This restriction of immunolabeling could be demonstrated definitively at E15 (stage 41), by which stage subendocardial and periarterial Purkinje fibers were clearly immunoreactive for EAP-300 and several known markers of chick conduction tissue, including specific myosin heavy chain isoforms and connexin42, a gap junctional protein preferentially expressed by Purkinje fibers. Just prior to hatching at E21 (Stage 46), immunolabeling of conduction tissues was reduced, although still above that of non-conductile myocardium. This spatiotemporal map of cardiac EAP-300 expression indicates that it is independently and transiently expressed in early myocardium, cardiac conduction tissue, and neural crest derivatives during development.

Elastic extracellular matrix of the embryonic chick heart: an immunohistological study using laser confocal microscopy

The "elastic matrix" constitutes a specialized component of the extracellular matrix which confers resiliency to tissues and organs subjected to repeated deformations. The role of the elastic matrix in living organisms appears to be of key importance since diseases characterized by expression of defective inherited genes which encode components of the elastic matrix lead to premature death. While the elastic matrix of adult organs has received a great deal of attention, little is known about when it first appears in embryonic tissues or its possible role in developing organs. In the present study we have performed an immunohistochemical study of the distribution of elastin and three additional components often associated with elastic matrices in adult tissues (i.e., fibrillin, emilin, and type VI collagen) during the development of the chicken embryonic heart. The three-dimensional arrangement of these components was established through the observation of whole-amount specimens with scanning laser confocal microscopy. Our results revealed three different periods of heart development regarding the composition of the elastic matrix. Prior to stage 21 the embryonic heart lacks elastin but exhibits a matrix scaffold of fibrillin and emilin associated with the endocardium and the developing cardiac jelly. Between stages 22 and 29 the heart shows a transient elastic scaffold in the outflow tract which contains elastin, fibrillin, and emilin. Elastin-positive fibrillar material is also observed during these stages in the base of the atrioventricular cushion adjacent to the myocardial wall. In addition, emilin-positive material appears to be associated with the zones of formation of ventricular trabeculae. Collagen type VI was not detected during these early stages. From stage 30 to stage 40 a progressive modification of the pattern of distribution of elastin, fibrillin, emilin, and collagen type VI is observed in association with the formation of the definitive four-chambered heart. The distribution of the elastic scaffold in the outflow tract appears to be rearranged and becomes restricted to the roots of the main arteries. Each of the components studied here is also deposited at increasing levels in the developing valvular apparatus including the valve leaflets and the chordae tendinea. The components are also present in the subendocardial space where they form aligned fibrillar tracts, an arrangement suggestive of a role in ventricular contractile function. The epicardium constitutes an additional region of elastic matrix deposition during these later stages and contains elastic, fibrillin, and collagen type VI.(ABSTRACT TRUNCATED AT 400 WORDS)