The morphology of matrix vesicles produced in experimental arterial aneurysms of rabbits

Cellular Crosstalk in the Vascular Wall Microenvironment: The Role of Exosomes in Vascular Calcification

Vascular calcification is prevalent in aging, diabetes, chronic kidney disease, cardiovascular disease, and certain genetic disorders. However, the pathogenesis of vascular calcification is not well-understood. It has been progressively recognized that vascular calcification depends on the bidirectional interactions between vascular cells and their microenvironment. Exosomes are an essential bridge to mediate crosstalk between cells and organisms, and thus they have attracted increased research attention in recent years. Accumulating evidence has indicated that exosomes play an important role in cardiovascular disease, especially in vascular calcification. In this review, we introduce vascular biology and focus on the crosstalk between the different vessel layers and how their interplay controls the process of vascular calcification.

Systemic injection of planktonic forms of mammalian-derived nanoparticles alters arterial response to injury in rabbits

Experiments were designed to test the hypothesis that the systemic delivery of planktonic forms of nanoparticles (NPs) derived from calcified, diseased human tissue or bovine blood are transmissible particles that exacerbate arterial response to injury. New Zealand White rabbits in which the endothelium was mechanically removed from one carotid artery were injected intravenously with either saline (control), lipopolysaccharide (LPS; surrogate for subclinical infection), hydroxyapatite crystals (HA; surrogate for NP shell), HA crystals exposed to culture media, or planktonic forms of bovine- or human-derived NPs. Carotid arteries were monitored by ultrasonography for 5 wk and then removed for histological examination. Uninjured arteries from all animals in each group remained patent with a normal anatomy. Injured arteries from 6 of 11 animals injected with human-derived NPs occluded and/or calcified; none of the injured arteries from animals in the other groups occluded (n = 28; P < or = 0.05). Injured arteries of rabbits injected with LPS or HA crystals developed eccentric hyperplasia. Discontinuous internal elastic laminae and thinning media characterized arteries from animals injected with bovine-derived NPs or cultured HA crystals. In conclusion, the systemic administration of planktonic forms of human-derived NPs exacerbated arterial response to injury distinct from that of bovine-derived NPs and other inflammatory agents.

Mechanism of pi-induced vascular calcification

Vascular calcification is clinically important in the development of cardiovascular disease. It has been suggested that apoptosis is one of the processes regulating calcification in vascular smooth muscle cells (VSMC). In this review, we discuss the role of apoptosis in inorganic phosphate (Pi)- induced calcification, focusing on regulation of the survival pathway mediated by growth arrest- specific gene 6 (Gas6). Further, we mention the beneficial effect of statins mediated by inhibition of apoptosis which is accompanied by restoration of the Gas6-mediated survival pathway. These findings indicate that Gas6 is a novel target of statins' effects to prevent vascular calcification.

Vascular smooth muscle cell phenotypic plasticity and the regulation of vascular calcification

Vascular smooth muscle cells (VSMCs) exhibit an extraordinary capacity to undergo phenotypic change during development, in vitro and in association with disease. Unlike other muscle cells they do not terminally differentiate. Development and maintenance of the mature contractile phenotype is regulated by a number of interacting transcription factors. In response to injury contractile VSMCs can be induced to change phenotype, proliferate and migrate to effect repair. On completion of the repair process VSMCs return to a nonproliferating contractile phenotype. In this way, in the context of atherosclerosis, a protective fibrous cap is formed and maintained at sites of injury. However in disease, when modulatory signals are perturbed, this phenotypic transition is dysregulated and VSMCs are induced to undergo inappropriate differentiation into cells with features of other mesenchymal lineages such as osteoblasts, chondrocytes and adipocytes. Moreover, evidence is accumulating that these aberrant phenotypic transitions contribute to the pathogenesis of vascular diseases such as atherosclerosis and Monckeberg's Sclerosis. Indeed, the osteo/chondrocytic conversion of VSMCs and the association of this phenotype with vascular calcification is a paradigm for how inappropriate differentiation can influence disease processes. Understanding of the mechanisms and signalling pathways involved in this particular phenotype change is well advanced offering the possibility for the design of successful therapeutic interventions in the future.

Histopathology and ultrastructure of human umbilical blood vessels

To resolve controversy over umbilical vessels structure, a morphological review was undertaken of the histology of blood vessels in 130 fetal umbilical cords varying in gestational age and the ultrastructure of blood vessels in 6 umbilical cords. Arteries and veins were lined by endothelium. The internal elastic lamina was frequently interrupted when associated with intimal thickening of longitudinally orientated smooth muscle cells. Fragments of elastic laminae developed in the intima and inner media both of which were thicker in arteries than in vein. No external elastic laminae or distinct adventitia were found. Most notable was the accumulation of cell debris developed from blebs derived from polypoid cytoplasmic protrusions of smooth muscle cells of both arteries and veins. They underwent hydropic change and became detached and fragmented particularly after 20 weeks' gestation. Similar hydropic degeneration occurred in endothelial cells of arteries and veins, such changes being consistent with the destructive pattern of hemodynamic stresses.

The elusive local factor in atherosclerosis

Recent evidence confirms that local haemodynamic stresses account for the initiation, topographical localization and complications of atherosclerosis. These causative stresses are vibratory and associated with pulse pressure and the lesser vibrations of greater frequency generated by blood flow at predilection sites. This bioengineering fatigue hypothesis is further substantiated by analogous effects of repetitive stresses on erythrocytes and in the musculoskeletal system. The mechanism underlying fatigue is cumulative molecular scissions of the mural constituents which ultimately result in failure of the wall as a whole. Free radicals and oxidation products are by-products of this molecular scission in atherogenesis. This theory which explains the progressive inexorable loss of mural cohesion, its pathogenesis and complications is completely substantiated by the iatrogenic and experimental reproduction of the disease by haemodynamic means.

Isolation and purification of extracellular matrix vesicles from blood vessels

Extracellular membrane-bound vesicles (called matrix vesicles) which occur in abundance in atherosclerotic blood vessels are believed to be associated with lipid accumulation and calcification. A technique has been developed to isolate them from experimental aneurysms in sheep in which they are known to be plentiful. The matrix vesicles were isolated by differential centrifugation following extraction by hypotonic salt solution. Most of the vesicles were pelleted at 30,000g and fell within the size range of matrix vesicles in situ in the aneurysmal wall. Preliminary characterization of the enzymatic activities indicates that many of these vesicles are formed from cell membranes rather than being derived from lysosomes, mitochondria or endoplasmic reticulum. Morphologically they are similar to matrix vesicles of other mineralizing tissues.

The vascular pathology of familial hypercholesterolemia

Homozygous familial hypercholesterolemia is so rare there is a dearth of illustrated detail of the vascular pathology. Autopsy material from an 11 year old homozygote was used to confirm and illustrate essential pathological differences between the arterial lesions and conventional atherosclerosis. These previously overlooked differences provide crucial data in the current controversy over the role of cholesterol in atherogenesis.