Hypertension I: Structure of Small Arteries in Hypertension

Re: 0704 Lehoux Static and pulsatile stretch

On Fri Dec 11, Russell L. Prewitt wrote
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>Dr. Lehoux:
> This is a very nice study showing a difference in signal pathways for a steady increase in pressure and pulsatile stretch. I would like to ask why 20% FCS is added to your medium as this may induce phenotypic changes in the SMC and alter the responses to the mechanical forces? FCS contains many growth factors, cytokines and unknown elements that would never be seen by a normal vessel. In resistance size arteries FCS leads to SMC migration and DNA synthesis, a clearly abnormal situation.
> Why do you use pressures outside the physiological range, i.e. 10 and 150 mmHg?
> You are careful to prevent damage to the endothelium. Do you have any evidence that the endothelial cells participate in the response to pressure or cyclic stretch?

Thank you for your questions Dr Prewitt

First, it is true that in cell culture experiments, 20% FCS will result in changes in cell phenotype (contractile to synthetic) and cell hyperplasia. Nevertheless, in our organ culture system, FCS alone does not induce any obvious phenotypic changes and certainly does not promote DNA synthesis; we found that changes in phenotype (in the form of loss of smooth muscle cell marker proteins) could be attributed to loss of stretch stimuli (ie in vessels maintained without pressure, compared to vessels maintained at 80 mmHg) rather to the presence of serum. These discrepancies between cell and organ culture systems may reflect on the importance of the environment (3-D structure, complex extracellular matrix) in determining the phenotypic or synthetic outcome of specific treatments used in culture.

Second, I'm afraid that 10 mmHg should rather be labeled as 50 mmHg. Nonetheless, there are no observed differences in MAP kinase activity between vessels maintained at 10, 50 or 80 mmHg in our organ culture system. 150 mmHg is used as an in vitro model of vessel stretch which may be encountered during hypertension.

Third, there does not appear to be a significant role for endothelial cells in conveying mechanical stress, at least not in the case of pulsatile stretch. Indeed, in vessels where the endothelium was stripped (using a Fogarty catheter) without overstretching, the MAP kinase activation in response to pulsatility was identical to that seen in non-denuded vessels. The equivalent experiment was not done for steady stretch, however, and it will be interesting to investigate a potential role for endothelial cells in that situation. Nevertheless, one must keep in mind the possibility that endothelial cells may contribute to MAP kinase activation, but that this response be masked by that of the more abundant vascular smooth muscle cells.

Tue Dec 15