Nerve Growth Factor Gene Delivery via Nanosphere-Hydrogel Composites and Tendon-Bone Interface Healing in a Rat Rotator Cuff Tear Model

Background: Rotator cuff repair (RCR) often fails because of poor tendon-bone interface (TBI) healing. Nerve growth factor (NGF) has been shown to regulate tenocyte function and promote regeneration, but it lacks sufficient systematic research, limiting its clinical translation. Purpose: To evaluate the therapeutic efficacy of NGF-encoding plasmid (pNGF) for TBI healing in a rat acute rotator cuff tear (RCT) model, delivered via nanosphere-hydrogel (NP-GEL) composites. Study Design: Controlled laboratory study. Methods: We performed physicochemical characterization of pNGF-loaded NP-GEL (morphology, particle size/zeta potential, and in vitro pNGF release) and assessed rat tenocyte responses (proliferation, migration, and protein expression) in vitro. For in vivo studies, 42 Sprague-Dawley rats were randomized into 3 groups after bilateral acute RCT model establishment: RCR alone (control group), RCR combined with local empty plasmid-loaded NP-GEL composites (pEmpty@NP/GEL group), and RCR combined with local pNGF-loaded NP-GEL composites (pNGF@NP/GEL group). Rats were euthanized at 4 and 8 weeks postoperatively (n = 7 rats per time point, 14 shoulders/group). At 4 weeks, 8 shoulders/group were allocated to biomechanical testing, and 6 shoulders/group to histologic analysis. At 8 weeks, 8 shoulders/group underwent pain threshold and gait analysis before biomechanical testing, while 6 shoulders/group underwent micro-computed tomography imaging before histologic analysis. Results: In vitro, pNGF@NP/GEL exhibited pH-responsive sustained release (88% at pH 5, 76% at pH 7 over 28 days), and pNGF maximized primary tenocyte proliferation/migration (peak effect at 2.5 μg pNGF). In vivo, the pNGF@NP/GEL group showed superior TBI healing: higher biomechanical strength (maximum load: 32.7 ± 4.9 N vs 25.5 ± 5.2 N in pEmpty@NP/GEL; P = .026 vs 21.6 ± 5.1 N in control; P < .001 at 8 weeks), improved bone microarchitecture (higher bone mineral density at 8 weeks; P < .001), better histologic repair (Modified Histomorphometric Scoring System: 31.3 ± 2.1 vs 25 ± 1 in pEmpty@NP/GEL; P = .015 vs 22.67 ± 2.31 in control; P = .003 at 8 weeks), optimized collagen I/III ratio, and enhanced functional recovery, with only mild neurotrophin-3 upregulation and increased heterotopic ossification (HO) although not in clinically concerning regions. Conclusion: NGF gene delivery effectively enhances TBI healing in a rat model of acute RCT histologically, structurally, and functionally via NP-GEL composites, accompanied by mild upregulation of NT-3 and increased HO, although not in clinically concerning regions. Thus, this strategy holds translational potential to improve the clinical outcomes of RCTs. Clinical Relevance: The NGF has translational potential to improve clinical outcomes in RCTs.