Stimulation of fetal rat lung cell proliferation in vitro by mechanical stretch
It has been suggested in animal experiments that normal utero development of the lung requires normal fetal breathing movements. Abnormal growth of the fetal lung can be the result of restriction of normal intrathoracic volume by lesions or other thoracic abnormalities. The physical forces involved in the developmental pathways of the fetal lung have yet to be modeled. This group has developed a model which addresses the question of whether mechanical stretch or distortion directly stimulates in vitro fetal lung cell proliferation. By establishing organotypic fetal lung cell cultures subjected to controlled stretches, they have observed that the forces resulted in enhanced fetal lung cell growth and DNA synthesis.
Cells from fetal lungs of rats were obtained at 19 days gestation period and incubated and grown in culture. These cultures were then applied to gelatin sponges for mechanical testing using a mechanical stretch device. The device can be varied in amplitude, frequency, and periodicity. These cells were stretched for a 48-h period starting 48 h after cell inoculation. Cell growth was assessed by both using a cell counter and incorporation of thymidine into DNA synthesis. Stretch-induced cell damage was evaluated by the measurement of release of adenine.
A significant response to stretch was observed with a specific seeding density and concentration of fetal bovine serum (1-2% FBS). In addition, with a continuous cycle of cell stretch, cell proliferation was stimulated at frequencies of 6/min and 30/min, but cytotoxicity was evident at rate of 60/min. In preliminary studies, continuous thymidine incorporation took 48 h to demonstrate stretch-mediated enhancement. For the minimal duration of stretch, the group stretched intermittently at 6, 12, 24, and 48 h of 60 cycles/min. A stretch period of 6 h did not result in increased synthesis rate, but others exhibited rates of increase by 60-80% of the control.
The group did find significant results that mechanical forces are directly on lung cells stimulate cell proliferation in vitro and the response to stretch is dependent on amplitude, frequency, periodicity, and duration. This paper is significant because it shows that the in vitro experiments of cell cultures from live tissue cannot all account for the mechanical forces that exist in live bodies. I do not think, personally, there is any way to mimic the effects of mechanical forces in vitro while conducting an experiment. The cell cultures we used of course were prepared cell-lines that do not resemble any live tissue. However for future in vitro experiments using cells from live tissue, we need to keep these considerations in mind.
5 comments:
I definitely agree that this paper is very important for in vitro research. It's because sometimes experimenter may forget to take into account of some in vivo conditions. This paper not only can provide reference for other experimenters, it can also remind us to think of all the possible problems when designing experiment.
Isn't it also possible that this paper shows that in vivo conditions (which I agree would be impossible to replicate) do not need to be replicated in order to yield significant results? Maybe the mechanism behind the stimulation of proliferation of lung cells (amongst many other cellular actions and types) is simpler than people think.
i think that this is an example of how often in science research isnt about the huge discoveries but about the small steps you take - while the study isn't completely conclusive since it is so difficult to mimic in vivo conditions, it shows the effect of one mechanism on lung cell proliferation. in combination with future work that could look at lung cells under different conditions, this could provide valuable information for the engineering lung tissue one day.
Brian: Yes of course the in vitro results are significant. But you have to remember these results are significant within the limits of their experiment - meaning that they did not take into account other in vivo conditions and only mechanical stretch. I still believe the mechanism for proliferation depends strongly upon the environmental conditions as well as stretching.
Although it's true these experiments can't ever completely and accurately replicate in vivo conditions, they are still important because sometimes the only way to investigate issues is in vitro. Experiments like these can give you insight into the general trends of cell behavior and I'm sure the investigators know the limitations of their experiment.
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