Age-Dependent Remodeling of the Sciatic Nerve Proteome in 5xFAD Mice Can Be Attenuated by Exercise or Donepezil Treatment to Maintain Neuromuscular Function

Abstract

Alzheimer's disease (AD) progresses along a continuum for years to possibly decades prior to cognitive decline. Although AD is primarily an age-related brain pathology, increasing evidence indicates dysfunction in peripheral nerves and skeletal muscle may manifest early in the disease progression. However, the underlying cause(s) for peripheral nerve dysfunction leading to impaired skeletal muscle torque production are not understood. Sciatic nerves from 5xFAD and wild-type (WT) mice were analyzed by tandem mass tag (TMT)-labeled proteomics at 3, 4, and 7 months, identifying proteome remodeling coincides with functional declines at 4 months particularly in pathways linked to mitochondrial turnover, calcium handling, and inflammation. We hypothesized either voluntary wheel running or donepezil treatment, begun prior to neuromuscular decline, would delay manifestation of neuromuscular impairment in 5xFAD mice. Separate cohorts, using 3-month-old 5xFAD mice and WT littermates, were given voluntary wheel access for 4 weeks or treated with the acetylcholinesterase inhibitor donepezil. We assessed tibial nerve stimulated plantar flexion torque and sciatic nerve compound (motor) neuron action potential (CNAP) in vivo at 4 months. Both exercise and donepezil attenuated in vivo nerve-stimulated muscle torque and CNAP dysfunction. Further, both exercise and donepezil attenuated the proteomic remodeling of the sciatic nerve through both shared and independent mechanisms that converged on mitochondria-centric pathways. Our findings in the 5xFAD model of AD support the notion that early phenotypes of AD are evident in the periphery that may have implications for timing of interventions.