This review will reconsider the current paradigm for understanding the critical, final steps in the progression of atherosclerotic lesions. That scheme, largely an outgrowth of observations of autopsy tissues by Davies and colleagues,1 2 asserts that the cause of death in atherosclerotic coronary artery disease is rupture of an advanced atherosclerotic lesion. Although this assumption may be partially true, recent autopsy studies suggest that it is incomplete.

To reconsider this paradigm, we reexamined the morphological classification scheme for lesions proposed by the American Heart Association (AHA).3 4 This scheme is difficult to use for 2 reasons. First, it uses a very long list of roman numerals modified by letter codes that are difficult to remember. Second, it implies an orderly, linear pattern of lesion progression. This tends to be ambiguous, because it is not clear whether there is a single sequence of events during the progression of all lesions. We have therefore tried to devise a simpler classification scheme that is consistent with the AHA categories but is easier to use, able to deal with a wide array of morphological variations, and not overly burdened by mechanistic implications.

The current paradigm is based on the belief that type IV lesions, or “atheromas,” described by the AHA are stable because the fatty, necrotic core is contained by a smooth muscle cell–rich fibrous cap. Virchow’s analysis5 in 1858 pointed out that historically, the term “atheroma” refers to a dermal cyst (“Grutzbalg”), a fatty …

Lessons From Sudden Coronary Death A Comprehensive Morphological Classification Scheme for Atherosclerotic Lesions

Sirius Red, a strong anionic dye, stains collagen by reacting, via its sulphonic acid groups, with basic groups present in the collagen molecule. The elongated dye molecules are attached to the collagen fibre in such a way that their long axes are parallel. This parallel relationship between dye and collagen results in an enhanced birefringency. Examination of tissue sections from 15 species of vertebrates suggests that staining with Sirius Red, when combined with enhancement of birefringency, may be considered specific for collagen. An improved and modified method of staining with Sirius Red is presented.

Picrosirius staining plus polarization microscopy, a specific method for collagen detection in tissue sections

Left ventricular hypertrophy (LVH) is the major risk factor associated with myocardial failure. An explanation for why a presumptive adaptation such as LVH would prove pathological has been elusive. Insights into the impairment in contractility of the hypertrophied myocardium have been sought in the biochemistry of cardiac myocyte contraction. Equally compelling is a consideration of abnormalities in myocardial structure that impair organ contractile function while preserving myocyte contractility. For example, in the LVH that accompanies hypertension, the extracellular space is frequently the site of an abnormal accumulation of fibrillar collagen. This reactive and progressive interstitial and perivascular fibrosis accounts for abnormal myocardial stiffness and ultimately ventricular dysfunction and is likely a result of cardiac fibroblast growth and enhanced collagen synthesis. The disproportionate involvement of this nonmyocyte cell, however, is not a uniform accompaniment to myocyte hypertrophy and LVH, suggesting that the growth of myocyte and nonmyocyte cells is independent of each other. This has now been demonstrated in in vivo studies of experimental hypertension in which the abnormal fibrous tissue response was found in the hypertensive, hypertrophied left ventricle as well as in the normotensive, nonhypertrophied right ventricle. These findings further suggest that a circulating substance that gained access to the common coronary circulation of the ventricles was involved. This hypothesis has been tested in various animal models in which plasma concentrations of angiotensin II and aldosterone were varied. Based on morphometric and morphological findings, it can be concluded that arterial hypertension (i.e., an elevation in coronary perfusion pressure) together with elevated circulating aldosterone are associated with cardiac fibroblast involvement and the resultant heterogeneity in tissue structure. Nonmyocyte cells of the cardiac interstitium represent an important determinant of pathological LVH. The mechanisms that invoke short- (e.g., collagen metabolism) and long-term (e.g., mitosis) responses of cardiac fibroblasts require further investigation and integration of in vitro with in vivo studies. The stage is set, however, to prevent pathological LVH resulting from myocardial fibrosis as well as to reverse it.

Pathological hypertrophy and cardiac interstitium. Fibrosis and renin-angiotensin-aldosterone system.

https://www.oarsijournal.com/article/S1063-4584(05)00197-4/pdf

Osteoarthritis cartilage histopathology: grading and staging

Macrophages perform both injury-inducing and repair-promoting tasks in different models of inflammation, leading to a model of macrophage function in which distinct patterns of activation have been proposed. We investigated macrophage function mechanistically in a reversible model of liver injury in which the injury and recovery phases are distinct. Carbon tetrachloride--–induced liver fibrosis revealed scar-associated macrophages that persisted throughout recovery. A transgenic mouse (CD11b-DTR) was generated in which macrophages could be selectively depleted. Macrophage depletion when liver fibrosis was advanced resulted in reduced scarring and fewer myofibroblasts. Macrophage depletion during recovery, by contrast, led to a failure of matrix degradation. These data provide the first clear evidence that functionally distinct subpopulations of macrophages exist in the same tissue and that these macrophages play critical roles in both the injury and recovery phases of inflammatory scarring.

/pdf/selective-depletion-of-macrophages-reveals-distinct-opposing-1ofujnx7y1.pdf

Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair

/pdf/the-use-of-the-picrosirius-polarization-method-for-the-study-1vuhyzh908.pdf

The use of the Picrosirius-polarization method for the study of the biopathology of collagen

The influence of tissue section thickness on the color and intensity of birefringence displayed by collagen in tissue sections studied by means of the Picrosirius-polarization method, is reported in this paper. When dermal collagen sections of different thicknesses (ranging from 0.25 to 11 micrometers) were studied by this method, it became evident that not only did the intensity of birefringence increase proportionally to tissue section thickness, as was to be expected, but also a gradual shift in color from green through a yellow to red could be observed as tissue section thickness increased. The limitations of the Picrosirius-polarization method for the localization of collagen types I, II, and III in routinely used histological slides is discussed, showing that this method is useful for the study of the distribution of the different types of interstitial collagen in normal adult vertebrate organs.

The influence of tissue section thickness on the study of collagen by the Picrosirius-polarization method.

A simple and sensitive method for the quantitative estimation of collagen

The purpose of this article is to review our knowledge to date of collagen-proteoglycan interaction. Many topics have been taken into account in order to provide a reasonably complete picture of this highly complex subject. Basic information about collagen biology, and an overview of the current concepts and advances regarding proteoglycans, have served as a basis to elucidate collagen-proteoglycan interaction. The bases of some methods of study have been reviewed in order to provide a fuller understanding of the results that are cited in this article. The experimental models and biological examples discussed herein demonstrate that collagen-proteoglycan interaction is essential to the extracellular matrix resiliency. The organization of these macromolecules is critical: collagen molecules become assembled into fibrils, fibrils aggregate to form fibers, fibers associate into bundles of fibers, and proteoglycans in the ground substance play a major role in the ordering process; on the other hand, glycosaminoglycans (GAGs) are composed of repeating monomers--GAGs linked to a same protein core form a proteoglycan--which, in turn, may bind to a hyaluronic acid molecule to form a proteoglycan aggregate together with other proteoglycans. Further growth of these complex macromolecules at higher hierarchical levels occurs by interaction of collagen with proteoglycans. A striking correlation between the tissue distribution of the genetically-distinct types of interstitial collagen and the occurrence of the different GAGs (which argues strongly in favour of a specific interaction) is demonstrated comprehensively in this review. Tissues composed of collagen type I possess small amounts of proteoglycans which contain almost exclusively dermatan sulfate; while tissues containing only collagen type II have high amounts of chondroitin sulfates. Collagen type III is the major fibrillary constituent of tissues that possess intermediate levels of proteoglycans, which contain great amounts of heparan sulfate. The histochemical and ultrastructural equivalents of these interactions have been emphasized in order to permit an interpretation of the morphologic aspects that can contribute to distinguishing these macromolecular components when studying tissue sections either under the light microscope or by aid of electron microscopy.

L. C. U. Junqueira

Papers

Picrosirius staining plus polarization microscopy, a specific method for collagen detection in tissue sections

The use of the Picrosirius-polarization method for the study of the biopathology of collagen

The influence of tissue section thickness on the study of collagen by the Picrosirius-polarization method.

A simple and sensitive method for the quantitative estimation of collagen

Biology of Collagen-Proteoglycan Interaction