NRG/ErbB signaling regulates neonatal muscle growth but not neuromuscular contractures in neonatal brachial plexus injury

Abstract

Neonatal brachial plexus injury (NBPI) causes disabling and incurable muscle contractures that are driven by impaired growth of denervated muscles. A rare form of NBPI, which maintains afferent muscle innervation despite motor denervation, does not cause contractures. As afferent innervation regulates various aspects of skeletal muscle homeostasis through NRG/ErbB signaling, our current study investigated the role of this pathway in modulating contracture development. Through pharmacologic modification with an ErbB antagonist and NRG1 isoforms, we discovered that NRG/ErbB signaling does not modulate the development of contractures in neonatal mice. Instead, ErbB inhibition impeded growth in nondenervated skeletal muscles, whereas increased ErbB activation exacerbated denervation‐induced skeletal muscle atrophy. This potential regulatory effect of NRG/ErbB signaling on neonatal muscle growth warrants deeper investigation.

Characterization of small fiber neuropathy in hypermobile Ehlers Danlos Syndrome

“…Interestingly, unmyelinated small fibers (sympathetic and sensory axons) contribute to 80% of joint innervation and to other components of the musculoskeletal system such as the tendons [48] [49]. Afferent innervation also affects several aspects of muscle development, including muscle spindle formation and maintenance [50]. A loss of sensory innervation impairs healing of bone fractures and may contribute to chronic musculoskeletal diseases [51].…”

Sex-Specific Role of Myostatin Signaling in Neonatal Muscle Growth, Denervation Atrophy, and Neuromuscular Contractures

“…To assess the role of MSTN signaling in pediatric muscle contracture formation, we utilized our surgical mouse model of postganglionic NBPI where injury to the brachial plexus at postnatal day (P)5 induces contractures within 4 weeks after denervation. 12,13,61 Briefly, unilateral, global (C5-T1), post-ganglionic NBPIs were surgically created in P5 wildtype female and male mice (Charles River; CD-1® IGS mouse, strain code 022) by extraforaminal nerve root excision under isoflurane anesthesia. Following the surgery, mice were returned to their mums and housed in standard cages with bio-huts on a 12-hour light/12-hour dark cycle, with nutrition and activity ad libitum .…”

“…Elbow flexion and shoulder internal rotation contractures were subsequently calculated in AxioVision (Zeiss). 12,13,61 This previously validated method of assessing passive range of motion and contracture severity was performed with blinding to treatment groups. The forelimb images shown in Figures 3A and 3D are representative of their respective samples, and have been processed to reflect comparable levels of sharpness, brightness, and contrast for illustrative purposes.…”

“…Following 48 hours of fixation, bilateral brachialis muscles were dissected, soaked in 25% Lugol solution (Sigma-Aldrich #32922) overnight, and imaged by micro computed tomography for assessment of whole muscle cross-sectional area and volume. 12,13,61 Brachialis muscles were then recovered by soaking in PBS overnight at 4°C, digested in 15% sulfuric acid for 30 minutes to obtain muscle bundles, and imaged for sarcomere length.…”

“…Six images representing different muscle bundles of the same brachialis were acquired per muscle. Average sarcomere length of the brachialis was subsequently determined by measuring a series of 10 sarcomeres from each of the 6 representative DIC images with the AxioVision program as previously described, 12,13,61 with blinding to treatment groups. Representative sarcomere images in Figure 4A have been cropped to identical sizes, and processed to reflect comparable levels of sharpness, brightness, and contrast for illustrative purposes.…”