Morphological and biochemical investigations of mitral valve endocardiosis in pigs

Valvular and Mural Endocardiosis in Aging Zebrafish (Danio rerio)

Endocardiosis or myxomatous degeneration of the cardiac valves is a well-described age-related change in humans and dogs. Lesions consist of polypoid nodular proliferations of loose extracellular matrix and valvular interstitial cells, most commonly affecting the mitral valve. This entity has not been previously described in fish. Herein we report the appearance, location, and occurrence of valvular and mural endocardiosis in a retrospective survey of aging laboratory zebrafish. Endocardiosis was present in 59 of 777 fish (7.59%), most commonly affecting the sinoatrial (34 fish; 57.6%) and atrioventricular (33 fish; 55.9%) valves. Lesions were more common in fish raised in recirculating water systems and fed commercial diets (52/230 fish; 22.6%) versus flow-through systems with fish fed semi-purified diets (4/234; 1.71%). Lesions were overrepresented in fish heterozygous for a mutant smoothened allele (34/61 fish, 55.7% vs 17/168, 10.1% wild type). There was no association between endocardiosis and intestinal carcinoids. Valvular endocardiosis is a significant age- and husbandry-related background finding in zebrafish and should be considered in the design and interpretation of research studies.

Spontaneous Age-related Changes of Peripheral Nerves in Cattle: Morphological and Biochemical Studies

Peripheral nerve function is significantly affected by ageing. During ageing process, multiple changes occur on tissue cells and extracellular matrix. The aim of this work was to study the ageing-associated changes of peripheral nerves in adult and old regularly slaughtered cattle compared with young calves, and correlate them to the features reported in humans and laboratory animals. Samples of axial dorsal metacarpal nerves from 44 cows were collected immediately after slaughtering. Each nerve was dissected and divided into two fragments: one used for morphological evaluation (n = 43) and the other one for biochemical analysis (n = 31). Axonal degeneration, demyelination, thickness of perineurium and endoneurium and increase of mast cells were the most important features detected. The mean amount of glycosaminoglycan quantitative content recorded in the samples increased with the age. Axonal degeneration, demyelination and thickness of endoneurium were positively and significantly correlated with biochemistry. The presence of changes affecting the different elements of the peripheral nerves, similar to that reported in humans and in laboratory species, the easy availability of the nerve tissue in this species, the considerable size of the samples and the life conditions more similar to humans than to laboratory animals, allows the authors to consider cattle as a potential good model for the comparative study of spontaneous ageing nerve lesions.

Differentiating the aging of the mitral valve from human and canine myxomatous degeneration

During the course of both canine and human aging, the mitral valve remodels in generally predictable ways. The connection between these aging changes and the morbidity and mortality that accompany pathologic conditions has not been made clear. By exploring work that has investigated the specific valvular changes in both age and disease, with respect to the cells and the extracellular matrix found within the mitral valve, heretofore unexplored connections between age and myxomatous valve disease can be found. This review addresses several studies that have been conducted to explore such age and disease related changes in extracellular matrix, valvular endothelial and interstitial cells, and valve innervation, and also reviews attempts to correlate aging and myxomatous disease. Such connections can highlight avenues for future research and help provide insight as to when an individual diverts from an aging pattern into a diseased pathway. Recognizing these patterns and opportunities could result in earlier intervention and the hope of reduced morbidity and mortality for patients.

Valve proteoglycan content and glycosaminoglycan fine structure are unique to microstructure, mechanical load and age: Relevance to an age-specific tissue-engineered heart valve

This study characterized valve proteoglycan and glycosaminoglycan composition during development and aging. This knowledge is important for the development of age-specific tissue-engineered heart valves as well as treatments for age-specific valvulopathies. Aortic valves and mitral valves from first-third trimester, 6-week, 6-month and 6-year-old pigs were examined using immunohistochemistry for versican, biglycan, decorin and hyaluronan, as well as elastin and fibrillin. The fine structure of glycosaminoglycans was examined by fluorophore-assisted carbohydrate electrophoresis. Decorin expression was strongest in the 6-year-old valves, particularly in the aortic valve spongiosa. The quantity of iduronate was also highest in the 6-year-old valves. The central tensile-loading region of the anterior mitral leaflet demonstrated reduced glycosaminoglycan content, chain length and hydration and a larger fraction of 4-sulfated iduronate and lower fraction of 6-sulfation. With age, the anterior leaflet center showed a further increase in 4-sulfated iduronate and decrease in 6-sulfation. In contrast, the anterior leaflet free edge showed decreased iduronate and 4-sulfated glucuronate content with age. The young aortic valve was similar to the mitral valve free edge with a higher concentration of glycosaminoglycans and 6-rather than 4-sulfation, but aged to resemble the mitral anterior leaflet center, with an increase in 4-sulfated iduronate content and a decrease in the 6-sulfation fraction. Elastin and fibrillin often co-localized with the proteoglycans studied, but elastin co-localized most specifically with versican. In conclusion, composition and fine structure changes in valve proteoglycans and glycosaminoglycans with age are complex and distinct within valve type, histological layers and regions of different mechanical loading.

Transcription levels of endothelin-1 and endothelin receptors are associated with age and leaflet location in porcine mitral valves

The aim of the study was to investigate the expression levels of endothelin-1 (ET-1) and ET(A) and ET(B) receptors (ET(A)-R and ET(B)-R) in porcine mitral valves and associate the transcription levels to age, leaflet location and deposition of mucopolysaccharides (MPS). Tissue samples from the chordal and inter-chordal insertion area of the anterior mitral valve leaflet from 11 sows (> or = 2 years of age) and 10 slaughter pigs (approximately 6 months old) were obtained and the relative gene expression levels of ET-1, ET(A)-R and ET(B)-R measured by semi-quantitative real-time PCR. A separate tissue sample was taken for histopathological grading of MPS deposition. The transcription levels of ET-1 (P < 0.0001) and ET(A)-R (P < 0.0004) were significantly higher in leaflets from the sows compared with slaughter pigs. The gene expression of ET(B)-R was not associated to age (P = 0.38), but increased in chordal insertion areas compared with inter-chordal areas (P = 0.01). The expression of ET-1 and ET(A)-R mRNA did not differ significantly between the two leaflet locations. The valve leaflets from sows had a significantly increased degree of MPS deposition compared with slaughter pigs upon histological examination (P = 0.04). In conclusion, an age-related valvular degeneration is observed in porcine mitral valve leaflets and ET-1 is suggested to be involved through action of both ET(A) and ET(B) receptors.

Increased expression of endothelin B receptor in static stretch exposed porcine mitral valve leaflets

The aim of this study was to evaluate the effect of mechanical stretch on the expression of ET-1 and ET(A)- and ET(B)-receptors in porcine mitral valve leaflets. Leaflet segments from 10 porcine mitral valves were exposed to a static stretch load of 1.5 N for 3.5h in buffer at 37 degrees C together with matching control segments. Subsequently, the mRNA expression of ET-1, ET(A)-R and ET(B)-R was measured by real-time RT-PCR in the chordal insertion areas. The analyses showed an increased transcription of ET(B)-receptors in stretch-exposed leaflet segments compared to unstretched segments median 2.23 (quartiles 1.37 and 2.70) vs. median 1.56 (quartiles 1.38 and 2.17, P=0.03) whereas the mRNA expression of ET(A)-receptors (P=0.90) and ET-1 (P=0.51) remained unchanged. Stretch increased the expression of ET(B)-receptors in porcine mitral valve leaflets. The finding could lead to a better understanding of the pathogenesis of myxomatous mitral valve disease.

Angiogenic modulators in valve development and disease: does valvular disease recapitulate developmental signaling pathways?

PURPOSE OF REVIEW

Neovascularization is a recognized feature of many valvular diseases and is established by numerous angiogenic modulators. Less known is that angiogenic modulators are multifunctional and have additional roles in valve development and disease. Recent advancements in this area are described.

RECENT FINDINGS

Initiation of epithelial to mesenchymal transformation, a developmental induction that specifies primordial interstitial cells (mesenchymal cells), requires vascular endothelial growth factor A, which stimulates matrix metalloproteinase 2 production and the invasive migration of mesenchymal cells. Epithelial to mesenchymal transformation also requires the matrix component hyaluronan to facilitate signaling through ErbB2/ErbB3 receptors and then is terminated by an increase in vascular endothelial growth factor A expression. Fibroblast growth factor 4 has been implicated in stimulating the following stage of proliferative expansion. Subsequently, in the remodeling phase, heparin-binding epidermal growth factor-like growth factor limits mesenchymal cell proliferation by signaling through the EGFR/ErbB1 receptor. Many adult valvular lesions appear similar to the embryonic proliferative expansion phase as they exhibit accumulations of extracellular matrix and myofibroblasts (a mesenchyme-like interstitial cell). The origins of such lesions may involve transforming growth factor beta 1. Similar to epithelial to mesenchymal transformation, tumor growth factor beta1 can induce cultured valvular endothelial cells to transdifferentiate to a myofibroblast-like phenotype. This scenario may occur in carcinoid valve disease because serotonin can induce interstitial cell expression of tumor growth factor beta1. Additionally, prolonged tumor growth factor beta1 activity may predispose to calcific degeneration. Calcific leaflets also exhibit tenascin-C, which may facilitate inflammatory cell migration through upregulation of pro-matrix metalloproteinase 2.

SUMMARY

Numerous angiogenic modulators control multiple stages of valvulogenesis and in the context of adult valvular disease may recapitulate their embryonic roles. Thus, lessons learned from valvulogenesis may provide insights into the molecular basis of adult valvular disease.

Identification of surface morphologic changes in the mitral valve leaflets and chordae tendineae of dogs with myxomatous degeneration

OBJECTIVE

To describe structural changes in the left atrioventricular (mitral) valve complex of dogs with endocardiosis by use of scanning electron microscopy.

ANIMALS

5 clinically normal dogs and 4 dogs with mitral valve endocardiosis.

PROCEDURE

The mitral valve complex from each dog was fixed and prepared for examination via scanning electron microscopy. Findings in valves from clinically normal and affected dogs were compared to identify surface changes associated with endocardiosis.

RESULTS

Compared with findings in valves from clinically normal dogs, endocardiosis-affected mitral valve complexes had several morphologic abnormalities. Tissue swelling on the edge of valve leaflets, chordae tendineae, and the chordal-papillary muscle junction was evident. Damage to the valve complex endothelium was unevenly distributed; in some areas, denudation of endothelial cells had exposed the basement membrane or subendothelial valve collagen matrix. This damage was most noticeable on the leaflet edges and extended more to the ventricular aspect of the valve than the atrial side. Cell loss also extended to the chordae tendineae but was less apparent at the chordal-papillary muscle junction. The remaining endothelial cells on affected valves were arranged in less-ordered rows and had more plasmalemmal microappendages, compared with cells on unaffected valves.

CONCLUSIONS AND CLINICAL RELEVANCE

Morphologic changes associated with mitral valve endocardiosis in dogs were similar to those observed in humans with mitral valve prolapse. In dogs with mitral valve endocardiosis, gross changes in the valve complex may affect hemodynamics in the heart; alterations in the leaflet and chordal endothelium may contribute to pathogenesis of this disease.

Glycosaminoglycan profiles of myxomatous mitral leaflets and chordae parallel the severity of mechanical alterations

OBJECTIVES

This biochemical study compared the extracellular matrix of normal mitral valves and myxomatous mitral valves with either unileaflet prolapse (ULP) or bileaflet prolapse (BLP).

BACKGROUND

Myxomatous mitral valves are weaker and more extensible than normal valves, and myxomatous chordae are more mechanically compromised than leaflets. Despite histological evidence that glycosaminoglycans (GAGs) accumulate in myxomatous valves, previous biochemical analyses have not adequately examined the different GAG classes.

METHODS

Leaflets and chordae from myxomatous valves (n = 41 ULP, 31 BLP) and normal valves (n = 27) were dried, dissolved, and assayed for deoxyribonucleic acid, collagen, and total GAGs. Specific GAG classes were analyzed with selective enzyme digestions and fluorophore-assisted carbohydrate electrophoresis.

RESULTS

Biochemical changes were more pronounced in chordae than in leaflets. Myxomatous leaflets and chordae had 3% to 9% more water content and 30% to 150% higher GAG concentrations than normal. Collagen concentration was slightly elevated in the myxomatous valves. Chordae from ULP had 62% more GAGs than those from BLP, primarily from elevated levels of hyaluronan and chondroitin-6-sulfate.

CONCLUSIONS

The GAG classes elevated in the myxomatous chordae are associated with matrix microstructure and elastic fiber deficiencies and may influence the hydration-related "floppy" nature of these tissues. These abnormalities may be related to the reported mechanical weakness of myxomatous chordae. The biochemical differences between ULP and BLP confirm previous mechanical and echocardiographic distinctions.

Pathology of mitral valve in regularly slaughtered pigs: an abattoir survey on the occurrence of myxoid degeneration (endocardiosis), fibrosis and valvulitis

The aim of this study was to report the prevalence of degenerative and early inflammatory lesions and to discuss some histological aspects of normal and pathological mitral valve leaflets in healthy, normally slaughtered pigs. Mitral valves were collected from 112, 6 month-old, pigs reared under different conditions. Histological examination revealed the presence of myxoid degeneration in 29.5% of the valves with no significantly different prevalence according to rearing conditions; fibrosis was present in 12.5%; inflammation (non-vegetative valvulitis) occurred in 20 (17.9%) macroscopically normal valves. No vegetative endocarditis could be observed. A significantly higher degree of inflammation was observed in valves affected by myxoid degeneration (P < 0.05) and Anitschkow cells were prevalent in all the pathological valves (P < 0.01). Capillaries were observed in a wide majority of the valves (86.5%), but small arterioles were related to fibrotic thickening of the leaflets (P < 0.01). The following conclusions are discussed: (1) environmental factors seem not to influence the prevalence of endocardiosis; (2) inflammatory foci in myxoid valves are a reaction to both abnormal friction and products of degraded collagen and extracellular matrix; (3) the authors consider the presence of capillaries in pig valves a normal finding whereas proliferation of the vessels occurs under pathological conditions; (4) non vegetative valvulitis can be related to the presence of vessels in the valve and may have a role in both infectious endocarditis and fibrosis; (5) Anitschkow cells are normally observed in pig valves and are not specifically related to pathological lesions.