Apoptosis of Human Vascular Smooth Muscle Cells Derived from Normal Vessels and Coronary Atherosclerotic Plaques
Before analysis of cell death, the rate of increase of cell number over time was analyzed in each cell type by cell counts. This indicated that plaque-derived cells showed a slower increase in cell number than cells derived from normal arterial conditions, as can be seen in the figure to the left, where the circles represent the plaque-derived VSMCs.
VSMCs indicated a marked difference in the frequency of cell death between the cell types. Cells from normal arteries underwent death only upon removal of serum growth factors, while plaque-derived cells died even in high serum conditions, and death increased after serum withdrawal. Death was characteristically by apoptosis in both normal and plaque-derived cells, as determined by time-lapse videomicroscopy (seen in the figure below), electron microscopy and DNA fragmentation patterns.
The addition of IGF-1, PDGF-BB and PDGF-AA markedly suppressed apoptosis of both plaque-derived and normal VSMCs in the absence of any other exogenous cytokines or nutrients. This is seen in the bar graph below for IGF-1 as compared to EGF, which had no noticeable effect on apoptosis rates.
Infection with bcl-2 also suppressed apoptosis of normal VSMCs in low serum conditions and partially suppressed apoptosis of plaque-derived cells in both low and high serum conditions, although these differences were unlikely to be caused by endogenous Bcl-2 expression as the gene was not detectable in Northern blots from any of the VSMC types.
As culture conditions of cells derived from plaques or normal vessels were identical and cells were separated from other components of the plaque, the higher death rate of plaque cells implied that these VSMCs possess an innate susceptibility to cell death. Cell loss via apoptosis may ultimately predispose to plaque fissuring or rupture, events associated with major cardiovascular disease conditions.
Significance/Critique
Bennet et al. take an effective initial approach to studying apoptosis factors within VSMCs under different conditions. Data collected shows an interesting contrast between VSMCs from atherosclerotic and healthy environments. Experimental conditions were highly regulated and controlled, making it easy to focus on the factors being tested for. Methods in determining the mode of cell death were very clearly stated to ensure that cell death due to other factors was not mistaken for apoptosis. More experiments involving protein analysis may have also been insightful into the inherent differences between the VSMCs being tested.
No true explanation is provides as to why these specific tests were performed as opposed to those testing for many of the other factors involved in apoptosis. Along the same lines, the implications of their findings are never really mentioned. The knowledge that cells infected with specific growth factors could lead to further information and future directions, but these are never brought up in the article.
9 comments:
How much of these differences could be chalked up to patient-to-patient variation as compared to healthy vs. atherosclerotic?
The authors provide a table outlining the age, sex, and clinical status of each patient from which cells were collected. These vary to some degree but the differences in cell doubling rates (fig 1) and apoptotic deaths are large enough that even with individual patient conditions taken into account, these are still significantly different.
Perhaps another good way to expand on this research would be to collect cultures from a larger sampling of patients and see if the same results remain apparent.
Seeing as the authors did not give a specific purpose for studying the death of VSMCs, they left the door wide open to speculation. Is it safe to assume that this research could be used to determine the longevity of coronary arterial stents? Because the cells composing vessels complicated by plaque tend to die off faster than those composing healthy vasculature, would this cause stents to become loosened?
It is interesting that the researchers studied the effects of Bcl-2 on the apoptosis of the cells. You said that the expression of Bcl-2 was not endogenous and weren't detected in northern blots but does the paper mention how they "infected" the cells with Bcl-2?
With regards to the implications of this study, do you think it is possible that this is a preliminary study in the development of a possible treatment for some of the problems that occur due to cell loss via apoptosis ("plaque fissuring or rupture")?
Also, a possible future works could be to see how these growth factors affect other cells in human blood vessels (if it has not already been done).
Are IGF-1, PDGF-BB and PDGF-AA normally present in the blood stream? It would be interesting to find out whether or not any of them also play a role in tumorigenesis.
Were the cells collected from patients then re-cultured before experiments were done? If they were, do you think the change in environment would affect the cells and their function?
As a point about future study, from the paper that they determined apoptosis via microscopy and factors such as Bcl-2.
I wondering, if you might know if levels of other types of cell death such as necrosis and autophagy were also higher in Coronary Atherosclerosis?
while they choose to use IGF-1, PDGF-BB and PDGF-AA, what are the significant effects they have?
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