Time course of skeletal muscle regeneration after severe trauma

Abstract

Background and purpose Animal models of skeletal muscle injury should be thoroughly described and should mimic the clinical situation. We established a model of a critical size crush injury of the soleus muscle in rats. The aim was to describe the time course of skeletal muscle regeneration using mechanical, histological, and magnetic resonance (MR) tomographic methods.

Methods Left soleus muscles of 36 Sprague-Dawley rats were crushed in situ in a standardized manner. We scanned the lower legs of 6 animals by 7-tesla MR one week, 4 weeks, and 8 weeks after trauma. Regeneration was evaluated at these times by in vivo measurement of muscle contraction forces after fast-twitch and tetanic stimulation (groups 1W, 4W, 8W; 6 per group). Histological and immunohistological analysis was performed and the amount of fibrosis within the injured muscles was determined histomorphologically.

Results MR signals of the traumatized soleus muscles showed a clear time course concerning microstructure and T1 and T2 signal intensity. Newly developed neural endplates and myotendinous junctions could be seen in the injured zones of the soleus. Tetanic force increased continuously, starting at 23% (SD 4) of the control side (p < 0.001) 1 week after trauma and recovering to 55% (SD 23) after 8 weeks. Fibrotic tissue occupied 40% (SD 4) of the traumatized muscles after the first week, decreased to approximately 25% after 4 weeks, and remained at this value until 8 weeks.

Interpretation At both the functional level and the morphological level, skeletal muscle regeneration follows a distinct time course. Our trauma model allows investigation of muscle regeneration after a standardized injury to muscle fibers.

TW: design of the study, animal surgery, and preparation of the manuscript. PvR and CP: MRI investigations. GM: muscle force measurements. MRS, SH, and GS: histological analysis. PS: animal surgery. GND: statistical analysis. ST: design of the study and preparation of manuscript.

The authors thank Susanne Mueller, Camilla Bergmann, and Gabriela Korus for providing excellent technical assistance. The study was supported by a kick-off grant from the Berlin-Brandenburg Center for Regenerative Therapies.

No competing interests declared.