Are the behaviors of myogenic progenitors induced by mechanical stretch similar between the human quadriceps and diaphragm?

Introduction

The stretch-induced behaviors of myogenic progenitors from the human diaphragm during mechanical ventilation are poorly understood. In all muscles, following injury, quiescent satellite cells (SCs) become activated, proliferate into myoblasts, and then merge and differentiate to form myotubes. Until now, SC adaptation to injury has been considered similar across various muscles. However, in animal models, transcriptional factors involved in maintaining the quiescent state, such as PAX3 and PAX7, are expressed differently between the diaphragm and quadriceps. In humans, no data currently exist to determine whether differences in stretch-induced behavior of myogenic progenitors during mechanical ventilation exist between these two muscles.

Methods

To address this issue, we purified and characterized human satellite cells from quadriceps and diaphragm biopsies from 11 patients. We then plan to culture these cells on a stretchable PDMS support to develop an in vitro model involving mechanical stress applied to human primary muscle-derived cells. A stretch of 12% of the initial length was applied using a FlexCell apparatus at a frequency of 0.3 Hz to mimic mechanical ventilation in the ICU as showed in Fig. 1.

Results

Our preliminary results (n = 6) show that the Pax7/Pax3 ratio at the myoblast stage, the fusion index, and the surface area at the myotube stage were higher in quadriceps compared to the diaphragm, indicating a higher quality of differentiation (Fig. 2). In a preliminary exploratory experiment, human diaphragm muscle cells from one patient were subjected to different stretching protocols, varying between 2 and 6 days, initiated at different stages of development. Our first results as indicated in Fig. 3 show that the quadriceps and diaphragm cells tolerate the stretching protocol and can proliferate and differentiate under these conditions.

Conclusion

Our preliminary results show that a comparative study between diaphragmatic and quadriceps cells will allow us in the future to assess the sensitivity of these two cell populations to mechanical stress.