Polyploid nuclei in human artery wall smooth muscle cells

Proliferation kinetics of aortic smooth muscle cell populations: comparison of normotensive and spontaneously hypertensive rats

An in vitro autoradiographic study of the proliferation of smooth muscle cells (SMC) from the aorta of normotensive and spontaneously hypertensive rats has been made. It was found, in primary culture, that SMC of spontaneously hypertensive rats entered proliferation at 2-2.5 days later than those from normotensive animals. As revealed by their very intensive labelling, a subpopulation of SMC with a high turnover rate was found in primary culture. In freshly isolated SMC from normotensive rat aorta, a subpopulation in S phase was detected, but we failed to detect it in aortae from spontaneously hypertensive rats. A difference in proliferative behaviour was also observed in subcultures of SMC from rats of both strains.

Induction of polyploidy in cultures of neonatal rat aortic smooth muscle cells

Arterial smooth muscle cells become tetraploid with age and hypertension. To further study this phenomenon, neonatal rat aortic smooth muscle cells were placed in cell culture and studied over time. Numerous cells with tetraploid and even octaploid DNA content appeared beginning in primary cultures. These increases in DNA content per cell were determined by quantitative fluorescence microscopy and flow cytometry, and true polyploidy was confirmed by chromosome counts. In contrast, cells from adult rat aortas failed to produce significant polyploid cells over time in culture. In vitro culture of neonatal aortic cells may therefore be a model system for studying the initiation of polyploidy in arterial smooth muscle.

Cytoskeletal features of normal and atheromatous human arterial smooth muscle cells

The distribution of actin, vimentin, desmin, and tropomyosin was studied in the media of the human aorta and femoral and coronary arteries, as well as in atheromatous plaques from the same arteries, by means of immunofluorescence, densitometric analysis of sodium dodecylsulfate-polyacrylamide gel electrophoresis, and bidimensional gel electrophoresis. The proportions of desmin-containing cells varied in the media of different arteries; 4 per cent of the cells in the aorta, 11 per cent in the coronary artery, and 37 per cent in the femoral artery contained desmin. In fibrous atheromatous plaques, independently of the artery, desmin-containing cells were almost absent, but they reappeared in complicated lesions. The content of vimentin per smooth muscle cell increased in fibrous atheromatous plaques, whereas the content of actin and tropomyosin was less than in normal media. Moreover, the alpha-actin predominance observed in the media was transformed to beta-actin predominance in the atheromatous plaques. These cytoskeletal changes provide new, possibly useful, biochemical markers for the characterization of smooth muscle cells during early and advanced phases of atheroma formation.

Strain and site dependence of polyploidization of cultured rat smooth muscle

Smooth muscle cell (SMC) growth may play an important role in the pathogenesis of vascular diseases such as atherosclerosis and hypertension. Recent studies have demonstrated that, under different growth stimuli in vivo, SMC may respond by proliferation of diploid cells, polyploidization to the tetraploid (or even octaploid) state, or both. In this study, we used flow cytometry to evaluate the intrinsic tendencies of aortic SMC and nonarterial cells from rats of different strains, ages, and blood pressures to polyploidize in response to in vitro growth stimulation. Significant strain-related differences in polyploidization of aortic SMC were found (P less than 0.001): highest in WKY (normotensive inbred rat related to SHR), intermediate in SHR (genetically hypertensive rat), and lowest in Sprague-Dawley and Fischer (normotensive outbred and inbred rats). Animal age had less or no effect on the degree of polyploidization. Nonarterial cells (venous SMC and lung cells) from WKY and SHR remained essentially diploid, suggesting tissue specificity of in vitro polyploidization. Studies of the growth kinetics of uncloned and clonal populations of aortic SMC revealed decreased proliferation as the ploidy increased in WKY, SHR, and Sprague-Dawley. These findings suggest that genetic strain factors as well as cell type/site of origin significantly influence in vitro polyploidization, whereas animal age and blood pressure do not. The findings also emphasize the need to consider ploidy changes when evaluating in vitro SMC growth kinetics. Further studies will improve understanding of SMC growth regulation and the functional significance of vascular polyploidy.

Replication of smooth muscle cells in vascular disease

Smooth muscle proliferation has been recognized as central to the pathology of both major forms of vascular disease: atherosclerosis and hypertension. Recent advances in our knowledge of mechanisms of control of proliferation suggest that events occurring in adult animals may recapitulate portions of the developmental biology of the smooth muscle cell. This review attempts to consider the current state of knowledge of the mechanisms controlling smooth muscle proliferation in these two diseases, to put that knowledge into the context of what is known about smooth muscle biology, and to offer two hypotheses on the possible roles of smooth muscle developmental biology in manifestations of atherosclerosis and hypertension in adult humans.

Age-related changes in ploidy levels and biochemical parameters in cardiac myocytes isolated from spontaneously hypertensive rats

Postnatal growth of the mammalian ventricular myocyte is characterized by a brief period of hyperplasia followed by an extensive period of physiological hypertrophy. Using myocytes isolated from both Wistar-Kyoto and spontaneously hypertensive rats from fetus to 10 months old, we analyzed morphological, biochemical, and ploidy changes. Fetal myocytes from both spontaneously hypertensive and Wistar-Kyoto rats were mononuclear, diploid cells. By 4 weeks, adult binucleation levels (84% binuclear) were found, and myocytes pooled from both ventricles demonstrated nuclear ploidy shifts to tetraploid levels. However, analysis of myocytes isolated from left ventricle, right ventricle, and septum showed that nuclear polyploidation was confined to the right ventricle and septum, with few polyploid nuclei detected in the left ventricle. This pattern remained relatively constant through 10 months of age, although spontaneously hypertensive myocytes showed significantly more polyploidation than Wistar-Kyoto in all regions. Biochemical analysis of isolated myocytes substantiated the nuclear ploidy changes and demonstrated elevated protein and ribonucleic acid content in left ventricular myocytes without extensive polyploidation. Since cardiac hypertrophy, both physiological and pathological, is associated primarily with the left ventricle and occurs in the absence of significant ploidy changes, these findings suggest that a unique pattern of gene regulation may be ongoing in the left ventricle myocytes that is not present in the septum and right ventricle. These variations may be essential for cellular hypertrophy under normal and pathological conditions.

Growth kinetics as a function of ploidy in diploid, tetraploid, and octaploid smooth muscle cells derived from the normal rat aorta

The smooth muscle cell population in major arteries of humans and experimental animals is heterogeneous with regard to cellular DNA content. A proportion of cells has polyploid DNA content and this proportion increases with normal aging and with hypertension. We have isolated pure populations of rat aortic smooth muscle cells containing 2C, 4C, and 8C DNA content by cloning of cultures of cells previously subjected to flow cytometric cell sorting. Karyologic analysis of these clonal populations revealed them to be pure diploid, tetraploid, and octaploid populations, respectively, containing 2N (= 42), 4N, and 8N chromosomes. Cell attachment area and nuclear size appeared to increase with the level of ploidy. Studies of the proliferative characteristics of the cells revealed that the growth rate and ultimate cell densities achieved decreased as the ploidy level increased. The intrinsic cellular radiosensitivity of these clones did not vary with ploidy. Increased smooth muscle cell ploidy is, therefore, associated with a decreased rate of proliferation. The emergence of smooth muscle cells with polyploid DNA content under normal and pathologic conditions is probably due to mitotic polyploidization without net cell proliferation and may be related to the need for expression of differentiated functions.

Hyperplastic growth response of vascular smooth muscle cells following induction of acute hypertension in rats by aortic coarctation

This study examines the growth response of vascular smooth muscle cells following induction of acute hypertension in rats by partial ligation of the abdominal aorta between the renal arteries. Systolic blood pressures proximal to the ligature increased dramatically within 3 days (from 135 +/- 3 to 195 +/- 7 torr) of surgery while pressures distal to the ligature were reduced from control values. The frequency of smooth muscle cells undergoing DNA replication was increased 25-fold in thoracic aortas of coarctation rats compared to sham-operated controls 9 days post-coarctation, while no differences were observed in cells in abdominal aortic segments 1 cm distal to the ligature. A small but significant increase in the frequency of tetraploid smooth muscle cells was observed in thoracic aortas of coarctation rats, but this increase accounted for less than 2% of the increase in medial DNA content. By far, the major growth response was hyperplasia, as evidenced by a 25% increase in thoracic aortic medial smooth muscle cell number without a change in mean cellular volume (micron3/cell) or mass (ng/cell). Whereas no evidence of endothelial denudation was observed in thoracic aortas of coarctation rats by scanning electron microscopy, endothelial cell turnover rates were increased 23-fold compared to controls, indicating that some form of endothelial "injury" or dysfunction was present. Consistent with this, morphological changes indicative of endothelial injury (e.g., subendothelial edema) were observed by light and transmission electron microscopy. The marked contrast between results of this study and our previous studies showing that aortic medial hypertrophy in spontaneously hypertensive and Goldblatt hypertensive rats was due to cellular hypertrophy and hyperploidy without hyperplasia, clearly demonstrates that the growth response of smooth muscle cells within a given blood vessel can be quite different, depending on the model of hypertension. It is suggested that a non-denuding form of endothelial "injury" may play an important role in the proliferative growth response of smooth muscle cells following induction of coarctation hypertension.

Monoclonal antibodies that distinguish between human aorta smooth muscle and endothelial cells

A monoclonal antibody has been generated that interacts with the surface of cultured human aorta smooth muscle cells and does not bind to the endothelial cells from aorta and umbilical vein. An antigen recognized by the antibody has a molecular mass of 330 kDa as determined by electrophoresis of immunoprecipitate in SDS-polyacrylamide gel. The same antigen appeared to be present on the fibroblast surface while neither immunofluorescence, flow cytofluorimetry nor immunoprecipitation reveal it on the endothelial cell surface or in the Triton X-100 extract.

Differential effects of antihypertensive drug therapy on vascular smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the spontaneously hypertensive rat

The present report extends our previous studies of smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the 5-month-old spontaneously hypertensive and Wistar-Kyoto rats to include analyses of 3- and 7-month-old rats and explores the effects of antihypertensive drug treatment on the accelerated growth of vascular smooth muscle in aortas of spontaneously hypertensive vs. Wistar-Kyoto rats. Drug-treated rats were administered a combination of reserpine, hydralazine, and chlorathiazide in their drinking water, either between 3 and 5 months or between 5 and 7 months of age. Drug treatment decreased the blood pressure of spontaneously hypertensive rats to values at or below those of Wistar-Kyoto rats for both age-treatment groups. Smooth muscle growth was evaluated by morphometric analyses of aortic smooth muscle content, flow cytometric and microdensitometric measurements of the frequency of polyploid smooth muscle cells, biochemical estimates of aortic medial smooth muscle cell number, and microdensitometric measurements of individual smooth muscle cell protein content. The following results were obtained. Aortic medial smooth muscle content was not significantly increased in 3-month spontaneously hypertensive compared to Wistar-Kyoto rats, indicating that aortic smooth muscle hypertrophy occurred post-3 months, as well as after blood pressure was elevated. In 5-month-old spontaneously hypertensive and Wistar-Kyoto rats, medial smooth muscle hypertrophy could be accounted for by cellular hypertrophy without hyperplasia; in contrast, medial hypertrophy in 7-month-old spontaneously hypertensive rats involved both cellular hypertrophy and hyperplasia. Antihypertensive treatment prevented the accelerated growth of vascular smooth muscle that occurred in spontaneously hypertensive rats via cellular hypertrophy and hyperploidy, but it did not prevent an increase in smooth muscle cell number in spontaneously hypertensive rats between 5 and 7 months of age. Furthermore, it had no effect on the parallel increases in aortic medial smooth muscle cell number that occurred in both spontaneously hypertensive and Wistar-Kyoto rats between 3 and 5 months of age. Whereas drug treatment prevented accelerated development of smooth muscle cell polyploidism in spontaneously hypertensive rats, in no case (spontaneously hypertensive or Wistar-Kyoto rats) did it reverse changes in ploidy that existed at the time of initiation of drug treatment, although it did cause cellular atrophy in smooth muscle cells of each ploidy class.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth and aging in the rat: changes in total protein, cellularity, and polyploidy in various organs

The objectives of this study were to determine the influence of growth and aging on ploidy, cell number, and protein content of various organs. Tissue homogenates were prepared at 3, 8, 25, 50, and 100 weeks of age. Samples were analyzed for DNA per nucleus (by flow cytofluorometry), nuclei number, and protein content. Livers of 8- and 100-week-old animals were also perfused with collagenase and the released cells separated into parenchymal and nonparenchymal populations by unit gravity sedimentation. Nuclei of these cells were also analyzed for DNA. In all four zones of the kidney and in thyroid, 4n nuclei diminished in percentage between 3 and 50 weeks and increased at 100 weeks. In the growth phase these probably are cycling cells and after 50 weeks represent an increasing population of nuclei arrested after synthesis of DNA. Constant levels of ploidy were found in brain, heart, rectus abdominis, and adrenal throughout the 3-100 weeks. A dramatic increase in 4n nuclei occurred between 3 and 8 weeks in liver with little change occurring thereafter. Ploidy is a property of only parenchymal cells in liver and this probably is also true in other organs. The 4n nuclei that remain in constant proportion to the total population are established early in life and are not related to aging. They are probably tetraploid and replicate into 4n daughter cells during growth. Cerebrum shows no changes in nuclei number but exhibits a 70% increase in protein between 3 and 100 weeks. Although kidney, liver and adrenal show large increases in number of nuclei (approximately equal to fourfold) with growth, these are not as great as increases in body weight (approximately equal to 11-fold). With regard to organ protein, only liver shows increases approximating those in body weight. Increases in organ nuclei appear to occur in concert for adrenal, kidney, and liver whereas increases in organ protein bear no relationship to each other. Protein content remains at stable levels in organs of 100-week-old animals and little (adrenal, liver) or no (brain, kidney) diminution occurs in nuclei numbers.