Inhibition of ErbB2 mitigates secondary denervation after traumatic muscle injury

Abstract: Secondary denervation has recently been described as part of the sequela of volumetric muscle loss (VML) injury, occurring along with a significantly elevated neurotrophic response, specifically neuregulin-1 (NRG1). This may contribute to chronic functional impairments associated with the injury, representing an overlooked treatment target. Thus, though paradoxical, the goal of this study was to pharmacologically reduce neurotrophic signalling after VML using a monoclonal antibody (Herceptin) that inhibits ErbB2 receptors. We also assessed whether ErbB2 inhibition combined with a myogenic treatment (i.e. minced muscle graft) would have a synergistically beneficial effect on function. Adult male Lewis rats underwent surgical induction of tibialis anterior muscle VML injury and were randomized into one of four groups: VML untreated, VML Herceptin, VML muscle graft and VML muscle graft + Herceptin, with comparisons to the contralateral (uninjured) control muscle. Rats receiving Herceptin were administered the drug (8 mg/kg i.p.) at the time of surgery and thrice per week for the duration of the study (48 days). Terminally individual NMJs were quantitatively evaluated, and maximal in vivo torque was tested. ErbB2 inhibition fully restored the normal rates of NMJ innervation and morphology after VML injury, and improved innervation of de novo myofibres after a muscle-graft treatment. However ErbB2 inhibition did not improve skeletal muscle function alone or in combination with a muscle-graft treatment. We conclude that ErbB2 inhibition is a promising therapeutic option for treating VML injury, yet more work is needed to optimize the translation of improved NMJ characteristics to recover function. (Figure presented.). Key points: In cases of complex traumatic musculoskeletal injury, such as volumetric muscle loss (VML), the endogenous ability of skeletal muscle to regenerate and recover function is lost. Innervation, or the connection of a motor axon to each individual myofibre, is a necessary component of myofibre survival and contractile function, which is disrupted after VML. Paradoxically a monocolonal antibody inhibitor of neurotrophic signalling (receptor tyrosine kinase ErbB2; Herceptin) has been shown to improve regeneration in rodent models of nerve injury. Here we show that pharmaceutical ErbB2 inhibition following a rat model of VML improves muscle innervation; however it did not correspondingly recover muscle function. Although ErbB2 inhibition alone is an ineffective treatment for VML injury, its ability to improve innervation is noteworthy and should be considered as an adjunctive or combinatorial therapy option.