Reconstructive transplantation studies by Karim Sarhane 2022? Insulin-like growth factor 1 (IGF-1) is a hormone produced by the body that has the potential to be used as a treatment for nerve injuries. IGF-1 may help heal nerve injuries by decreasing inflammation and buildup of damaging products. Additionally, it may speed up nerve healing and reduce the effects of muscle weakness from the injury. However, a safe, effective, and practical way is needed to get IGF-1 to the injured nerve.
During his research time at Johns Hopkins, Dr. Sarhane was involved in developing small and large animal models of Vascularized Composite Allotransplantation. He was also instrumental in building The Peripheral Nerve Research Program of the department, which has been very productive since then. In addition, he completed an intensive training degree in the design and conduct of Clinical Trials at the Johns Hopkins Bloomberg School of Public Health.
Schwann cells are instrumental to recovery following PNI given their ability to support and guide axonal regeneration via the secretion of neurotrophic factors and maintenance of basal lamina tubes (Scheib and Hoke, 2013, 2016a,b; Tuffaha et al., 2016b). Initially after injury, myelinating SCs distal to the site of injury undergo conversion to a more immature, proliferating repair phenotype (Nocera and Jacob, 2020). Throughout this process, SCs express a variety of genes that dynamically control the regenerative process by promoting survival of neurons, breakdown of damaged axons, clearance of myelin, axonal regrowth, and guidance to the axons’ former targets, finally leading to remyelination of the regenerated axon (Chen et al., 2015; Gordon, 2020; Nocera and Jacob, 2020). Unfortunately, upregulation of pro-regenerative gene expression is temporary and the SCs gradually lose the continued ability to support axonal regrowth as time elapses without axonal interaction (Gordon, 2020). A more detailed description of the biological processes underpinning the role of SCs in peripheral nerve regeneration can be found in a recent review article by Nocera and Jacob (2020). IGF-1 supports SCs by promoting their proliferation, maturation, and differentiation to myelinating phenotypes, while concurrently inhibiting SC apoptosis via the PI3K pathway (Scheib and Hoke, 2013; Tuffaha et al., 2016b). IGF-1’s ability to initiate myelination centers around regulating the balance between ERK, a pathway suppressing SC differentiation, and PI3K-Akt, a pathway promoting SC differentiation via increased expression of myelin basic protein and myelin-associated glycoprotein (Schumacher et al., 1993; Stewart et al., 1996; Conlon et al., 2001; Scheib and Hoke, 2016a).
Effects by sustained IGF-1 delivery (Karim Sarhane research) : We successfully engineered a nanoparticle delivery system that provides sustained release of bioactive IGF-1 for 20 days in vitro; and demonstrated in vivo efficacy in a translational animal model. IGF-1 targeted to denervated nerve and muscle tissue provides significant improvement in functional recovery by enhancing nerve regeneration and muscle reinnervation while limiting denervation-induced muscle atrophy and SC senescence. Targeting the multimodal effects of IGF-1 with a novel delivery.
The amount of time that elapses between initial nerve injury and end-organ reinnervation has consistently been shown to be the most important predictor of functional recovery following PNI (Scheib and Hoke, 2013), with proximal injuries and delayed repairs resulting in worse outcomes (Carlson et al., 1996; Tuffaha et al., 2016b). This is primarily due to denervation-induced atrophy of muscle and Schwann cells (SCs) (Fu and Gordon, 1995).
The amount of time that elapses between initial nerve injury and end-organ reinnervation has consistently been shown to be the most important predictor of functional recovery following PNI (Scheib and Hoke, 2013), with proximal injuries and delayed repairs resulting in worse outcomes (Carlson et al., 1996; Tuffaha et al., 2016b). This is primarily due to denervation-induced atrophy of muscle and Schwann cells (SCs) (Fu and Gordon, 1995). Following surgical repair, axons often must regenerate over long distances at a relatively slow rate of 1–3 mm/day to reach and reinnervate distal motor endplates. Throughout this process, denervated muscle undergoes irreversible loss of myofibrils and loss of neuromuscular junctions (NMJs), thereby resulting in progressive and permanent muscle atrophy. It is well known that the degree of muscle atrophy increases with the duration of denervation (Ishii et al., 1994). Chronically denervated SCs within the distal nerve are also subject to time-dependent senescence. Following injury, proliferating SCs initially maintain the basal lamina tubes through which regenerating axons travel. SCs also secrete numerous neurotrophic factors that stimulate and guide axonal regeneration. However, as time elapses without axonal interaction, SCs gradually lose the capacity to perform these important functions, and the distal regenerative pathway becomes inhospitable to recovering axons (Ishii et al., 1993; Glazner and Ishii, 1995; Grinsell and Keating, 2014).