An immunohistochemical analysis of regenerating cellular material in two distinct models of skeletal muscle injury
Tourniquet mediated Ischemia Reperfusion (I/R) injury causes damage to skeletal muscle, often resulting in prolonged functional impairment. The current study utilizes immunohistochemistry (IHC) to determine whether the controlled release of the anabolic factor, insulin-like growth factor-I (IGF-I), from the biodegradable PEGylated fibrin gel matrix can facilitate the recovery of skeletal muscle from I/R. Treatment groups following a 2-hour tourniquet applied to the limb of 6-9 month rats, included intramuscular injections of saline, PEGylated fibrin gel (PEG-Fib) only and IGF-I conjugated to PEGylated fibrin gel (PEG-Fib-IGF). Expression of the myogenic regulatory factors MyoD and myogenin detected via IHC in the PEG-Fib-IGF group was significantly lower compared to the saline group, showing a 1.4±0.8% nuclear co-localization for MyoD and a 2.0±0.8% nuclear co-localization for myogenin at 14 days of recovery. The saline group showed higher values, 31.4±4.4% and 44.1±7.3% for MyoD and myogenin nuclear co-localization respectively. A significantly greater percentage, 88.8±3.7% of Desmin positive myofibers was seen at 14 days of recovery, while a lower percentage of fibers expressing neonatal myosin, 7.7±2.7% was seen in the PEG-Fib-IGF group compared to the saline treatment group. These results indicate that IGF-I delivered intramuscularly via PEGylated fibrin gel, functions therapeutically in skeletal muscle recovery, from I/R mediated damage. In a separate injury model that deals with volumetric muscle loss, IHC analyses were performed to test the efficacy of a novel tissue engineering strategy utilizing extracellular matrix (ECM) as a scaffold. In this model, also called the defect model, a 1.0 X 1.0 cm piece of the lateral gastrocnemius was removed and replaced with a muscle-derived ECM. The constructs were then seeded with bone marrow derived cells (BMSCs), adipose derived stem cells (ADSCs) or the peroneal nerve was relocated to the area of the ECM implant. 42 days post recovery IHC analysis was performed on the ECM implants. The quantification of desmin-positive regenerating myofibers bearing centrally located nuclei, showed significantly greater values in the top, middle and bottom region of the ECM implants that received peroneal nerve relocation, when compared to the experimental group that received the ECM implant alone. Blood vessel density increases were seen within the middle region of the ECM implant groups that received BMSC+Nerve treatment and the bottom region of the ECM implant groups that received ADSC+Nerve treatment. Thus, these results corroborate the therapeutic effect of peroneal nerve relocation, which stimulated an increase in myofiber regeneration and vascular maintenance within the construct.