Reconciling molecular persistence and functional recovery: A hybrid four-layer computational model of botulinum neurotoxin A

Botulinum neurotoxin type A (BoNT/A) produces chemodenervation through receptor-associated uptake, light-chain translocation, and SNAP-25 cleavage, yet molecular persistence and clinical recovery may occur on different time scales. We built a literature-informed four-layer model linking ganglioside/SV2-associated binding, endocytosis with pH-dependent translocation, persistent light-chain activity with SNAP-25 cleavage, and calibrated reinnervation/remodeling. The model was verified numerically, evaluated against predefined time-scale targets, and tested with one-at-a-time and Morris global sensitivity analyses. At baseline, ternary-complex formation reached 90.09% of the effective local BoNT/A input and cytosolic light chain peaked at 0.07156 nM at 77.0 min. Force nadir occurred at day 4.2 with 26.1% residual force. Functional recovery reached 50%, 75%, and 90% at 61.6, 96.6, and 126.4 days, whereas the molecular 50% SNAP-25 cleavage threshold occurred at 329.5 days. All eight consistency targets were satisfied. Morris screening showed that functional recovery was driven primarily by reinnervation parameters and molecular persistence by toxin exposure, cleavage efficiency, and light-chain persistence. Re-anchoring the recovery layer to rodent observations returned functional recovery at day 27.9 while the unchanged molecular layers produced a larger molecular-to-functional time-scale ratio; varying sprouting latency shifted functional recovery by 30 days under imposed molecular invariance. Across three simulated injections the cleaved SNAP-25 burden rose to 85% and recovery lengthened, a prolongation whose sensitivity profile was dominated by toxin exposure and cleavage efficiency rather than baseline reinnervation parameters. These extensions test internal consistency rather than provide external validation. The framework supports reinnervation/remodeling as a plausible bridge between prolonged molecular blockade and earlier functional recovery, and indicates that the two become increasingly coupled under repeated dosing.