Necrotic Smooth Muscle Cells Research Articles

Uremia-Specific Effects in the Arterial Media During Development of Uremic Atherosclerosis in Apolipoprotein E–Deficient Mice

Uremia accelerates formation of atherosclerosis-like lesions in apolipoprotein E-deficient (apoE(-/-)) mice. In this study, we compared gene expression patterns in classical and uremic atherosclerosis. High-density oligonucleotide microarray analyses were performed with aortic RNA from 5/6 nephrectomized (NX) and sham-operated mice. After 12 weeks, NX apoE(-/-) mice had more atherosclerosis and 24 genes were differentially expressed as compared with sham apoE(-/-) mice. Nine genes expressed in muscle cells displayed reduced expression (3.3- to 142-fold, P<0.05), whereas osteopontin gene expression was increased 8.7-fold (P<0.05) in NX mice. Studies of NX wild-type mice suggested that the changes in NX apoE(-/-) mice were dependent on hypercholesterolemia. Nevertheless, lesioned versus nonlesioned areas of aortas from nonuremic apoE(-/-) mice with classical atherosclerosis displayed less pronounced reductions in expression of the muscle cell related genes than seen in NX apoE(-/-) mice even though the osteopontin gene expression was increased approximately 15-fold. Electron microscopy showed more vacuolized and necrotic smooth muscle cells within the media underneath both nonlesioned and lesioned intima in NX than in sham apoE(-/-) mice. The results suggest that uremic vasculopathy in apoE(-/-) mice, in addition to intimal atherosclerosis, is characterized by a uremia-specific medial smooth muscle cell degeneration, which appears to be accentuated by hypercholesterolemia.

Increased Expression of Protease Activated Receptor-2 (PAR-2) in Balloon-Injured Rat Carotid Artery

Protease-induced cell signaling is mediated by specific receptors such as the emerging family of protease activated receptors (PARs). Since proteases are involved in various aspects of vascular injury, we assessed expression of PAR-2, a protease-activated receptor closely related to the thrombin receptor (PAR-1) but activated by an unknown protease, in vascular injury. Rat carotids were subjected to balloon-catheter injury and perfusion fixed at 1, 3, 7 or 14 days after injury. Sections of injured and normal carotid arteries were immunohistochemically labeled with a polyclonal antibody raised against the N-terminal residues 37-53 of human PAR-2. Sections were also labeled with antibodies to factor VIII-related antigen, smooth muscle actin and a proliferating cell nuclear antigen (PCNA). In normal vessels, PAR-2 labeling was diffuse and patchy in medial smooth muscle and endothelium. At one and three days after injury, before appearance of neointima, PAR-2 labeling increased in cells adjacent to damaged or necrotic smooth muscle cells. In addition, proliferating adventitial myofibroblasts labeled strongly for PAR-2. At 7 and 14 days after injury, the media and neointima of injured vessels had increased PAR-2 labeling which was most intense at the luminal edge of the neointima. Double immunohistochemical labeling confirmed the greatest expression of PAR-2 in areas with the greatest density of PCNA-positive cells. In addition, PAR-2 mRNA localization using in situ hybridization paralleled PAR-2 expression. The data suggest an upregulation of PAR-2 in response to vascular injury which is associated with medial smooth muscle damage, proliferating adventitial myofibroblasts and smooth muscle cells of the neointima, particularly those at the proliferating luminal edge of the neointima. Possible functional consequences of this receptor upregulation and its role in the response to vascular injury remain to be determined.

Long period of balloon inflation and the implantation of stents potentiate smooth muscle cell death. Possible role of chronic vascular injury in restenosis.

BACKGROUND: It has been suggested that the severity of acute vascular injury immediately after percutaneous transluminal coronary angioplasty (PTCA) or stent implantation correlates with the extent of neointimal hyperplasia and restenosis. However, the influence of prolonged or chronic vessel injury on the pathogenesis of restenosis is unclear. METHODS: Rabbit iliac arteries were balloon dilated for a short (1 min) or prolonged (10 min) period of time, or were chronically dilated and received a Palmaz-Schatz stent (balloon inflation for 1 min). All arteries were overexpanded to a balloon:artery ratio of 1.2:1 as determined by angiography. The arteries were removed 30 min and 4 weeks after the angioplasty procedures. The sites of injury were evaluated by gross histology and transmission electron microscopy (TEM). Cell death of medial smooth muscle cells (SMCs) was specified by TEM images 30 min after the procedures. Computer-assisted quantification of the neointimal cross-sectional areas was performed after 4 weeks using a light microscope connected to a digital image analyser. RESULTS: The results show that prolonged balloon dilatation and stent implantation increased necrotic SMC death compared with balloon dilatation for 1 min. After 30 min, increased staining of SMC nuclei, enlarged intercellular spaces and changes in SMC shape in the media indicated cell death induced by prolonged balloon dilatation or chronic stent injury. Stent implantation markedly augmented vessel damage by persistent compression of the media, compared with a balloon dilatation for 1 or 10 min. Both prolonged balloon dilatation and stent implantation increased neointimal hyperplasia at 4 weeks compared with balloon dilatation for 1 min (0.6 3 0.2 and 1.0 3 0.2 mm(2) versus 0.2 3 0.1 mm(2), P < 0.001 versus dilatation for 1 min). CONCLUSION: Prolonged or chronic vascular expansion due to long balloon-inflation periods or the implantation of stents increases medial SMC death, which subsequently stimulates neointimal growth in this restenosis model. Chronic vascular injury may be an important stimulus for restenosis after angioplasty procedures.

An electron microscopic study of cerebral vasospasm with resultant myonecrosis in cases of subarachnoid haemorrhage, meningitis and trans-sylvian surgery.

Electron microscopic data on the development of myonecrosis following cerebral vasospasm associated with subarachnoid haemorrhage, meningitis and trans-sylvian surgery are presented. The basic feature of myonecrosis was dissolution of myofilaments with resultant fine granular or filamentous material. The disintegrating cytoplasm often contained numerous glycogen granules, dense bodies, autophagic vacuoles and myelin-like membranous bodies. A well-developed sarcoplasmic reticulum was preserved despite myofilament dissolution, while mitochondria showed marked swelling. The nuclei showed either dilution of chromatin or pyknotic change. The basal lamina was remarkably thickened and maintained an irregular outline of the necrotic smooth muscle cells. Enlarged intercellular space contained abundant cellular debris, vesicular structures and connective tissue fibres. The pathogenesis of these changes is discussed.

Myonecrosis following Cerebral Arterial Spasm in Meningitis

Light and electron microscopic studies were conducted on myonecrosis following cerebral arterial spasm in meningitis. A 34-year-old female developed fever, headache and vomiting. Neurological examination revealed a drowsy state, nuchal stiffness and hemiparesis. Spinal puncture revealed a purulent fluid containing 1, 219/mm3 cells. She deteriorated steadily into semicoma 10 days after onset. Computerized tomography scan showed low density areas in bilateral basal ganglia and cerebellar hemispheres. Angiography showed vasospasm of the major cerebral arteries and vasodilatation of the left Sylvian arteries. Repeated angiography two months after onset showed a diffuse narrowing of these arteries. She died of uncal herniation 67 days after onset. Autopsy two hours after death disclosed softening in the territories of spastic arteries. Microscopically, the circle of Willis showed concentric stenosis due to an intimal proliferation. The media was remarkably atrophied and fibrotic with an infiltration of polymorphonuclear leucocytes. Electron-microscopically, the media disclosed numerous degenerating or necrotic smooth-muscle cells. The degenerating cells showed dissolution of myofilaments with resultant fine granular or filamentous material. The necrotic cells were abundant in vacuoles, lysosomes and dense bodies. The cytoplasm was eventually replaced by cellular debris and numerous collagen fibrils.

Ultrastructural observations on bifurcations in rat cerebral arteries. 2. Rats with long-term hypertension.

The bifurcation pads ("valve-like projections") in the anterior cerebral arteries of rats with long-term hypertension were studied electron microscopically. The rats ranging in age from 2 to 10 months were sacrificed after bilateral renal artery constriction at 5-week-old. In the bifurcation pads (intimal pads) of hypertensive rats, smooth muscle cell damage first appeared in the roots of the pads as well as underlying media in the form of granular, vesicular, and somewhat tubular structures (200-1500 A in diameter). Thereafter, with a lapse in time after the operation, these abnormal substances increased around the smooth muscle cells which were arranged in the marginal zones of the pads. Deeply arranged intimal smooth muscle cells which were embedded in an abundance of ground substances were only damaged in rats with very long-term hypertension. The medial smooth muscle cells beneath the pads manifested lesions which were more marked and diffuse than in the intima. These smooth muscle cells were bizarrely atrophied and abnormal substances which might be derived from necrotic smooth muscle cells were found around them. Basement membrane-like substances, either thick or multilaminated, were also present around them.

Ultrastructural Alterations in Gizzard Smooth Muscle of Selenium-Vitamin-E-Deficient Ducklings

Lesions of gizzard smooth muscle were studied by light and electron microscopy in newly hatched ducklings fed a selenium-vitamin-E-deficient diet for 13-21 days. Histopathologic alterations included initial hyaline change in damaged smooth-muscle cells, subsequent mineralization of sarcoplasmic debris in necrotic smooth-muscle cells, macrophagic invasion and phagocytosis of sarcoplasmic debris, and eventual fibroblastic proliferation and scarring of damaged areas in the gizzard wall. Ultrastructurally, mild damage in smooth-muscle cells was manifested by altered mitochondria with matrical densities and disrupted membranes and dilated elements of sarcoplasmic reticulum. In smooth-muscle cells with severe injury, the alterations of mitochondria and sarcoplasmic reticulum were accompanied by myofibrillar lysis and disruption of plasma membranes and external laminae. Expanding zones of mineralization of sarcoplasmic debris in necrotic smooth muscle cells were present at dense masses of lysed myofilaments that surrounded mineralized and disrupted mitochondria. Numerous macrophages infiltrated the areas of necrosis of smooth muscle and phagocytosed sarcoplasmic debris.