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

Abstract

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. 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. Controlled laboratory study. 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. 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; <i>P</i> = .026 vs 21.6 ± 5.1 N in control; <i>P</i> < .001 at 8 weeks), improved bone microarchitecture (higher bone mineral density at 8 weeks; <i>P</i> < .001), better histologic repair (Modified Histomorphometric Scoring System: 31.3 ± 2.1 vs 25 ± 1 in pEmpty@NP/GEL; <i>P</i> = .015 vs 22.67 ± 2.31 in control; <i>P</i> = .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. 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. The NGF has translational potential to improve clinical outcomes in RCTs.