Intermittent cyclic stretching and incrementally increasing strain amplitude cyclic stretching were explored to overcome the reported adaptation of fibroblasts in response to constant amplitude cyclic stretching, with the goals of accelerating collagen production and understanding the underlying cell signaling. The effects of constant amplitude, intermittent, and incremental cyclic stretching regimens were investigated for dermal fibroblasts entrapped in a fibrin gel by monitoring the extracellular signal-regulated kinase (ERK1/2) and p38 pathways, collagen transcription, and finally the deposited collagen protein. Activation of ERK1/2, which has been shown to be necessary for stretch-induced collagen transcription, was maximal at 15 min and decayed by 1 h. ERK1/2 was reactivated by an additional onset of stretching or by an increment in the strain amplitude 6 h after the initial stimulus, which was approximately the lifetime of activated p38, a known ERK1/2 inhibitor. While both intermittent and incremental regimens reactivated ERK1/2, only incremental stretching increased collagen production compared to samples stretched with constant amplitude, resulting in a 37% increase in collagen per cell after 2 weeks. This suggests that a regimen with small, frequent increments in strain amplitude is optimal for this system and should be used in bioreactors for engineered tissues requiring high collagen content.
Bibliographical noteFunding Information:
The authors thank Naomi Ferguson, Sandra Johnson, Jay Reimer, Dr. Colleen Witzenburg, and Dr. M. Cristine Charlesworth for technical assistance and Kiley Schmidt for providing illustrations. Nanoimmunoassay was performed in the Mayo Clinic Proteomics Core. This study was funded by a National Science Foundation Graduate Research Fellowship (to J.B.S) and National Institutes of Health/National Heart, Lung, and Blood Institute award HL107572 (to R.T.T.).
- Mechanical conditioning
- Mitogen activated protein kinase