EIF4A3 Promotes Muscle Atrophy and Aging by Inhibiting the FAK Pathway Through NEDD9 mRNA Destabilization

Muscle atrophy has a poor prognosis, caused by various factors. Identifying a shared treatment target could address an unmet clinical need. The exon junction complex (EJC), a protein complex assembly that binds to RNA, facilitates post-transcriptional regulation by participating in mRNA splicing, mRNA export, translation and nonsense-mediated mRNA decay. This study aims to investigate the role of the EJC in muscle atrophy.

Single-cell transcriptome analysis and western blot were employed to analyse EJC expression in muscle atrophy. Overexpression of EJC helicase EIF4A3, as well as counteracting endogenous EIF4A3, was manipulated using lentiviral and adeno-associated virus 8 (AAV8) at both in vitro and in vivo levels. Imaging, RT-qPCR and immunoblot were utilized to identify phenotypes associated with muscle atrophy and aging. RNA-seq, RIP-seq, RT-qPCR and RIP-PCR were conducted to determine the targets of EIF4A3. A pharmacological approach that activates the downstream pathways in EIF4A3 knockdown muscle was employed to elucidate the molecular mechanisms of EIF4A3 in muscle atrophy.

The core RNA helicase of the EJC, EIF4A3, showed increased expression in atrophied muscles and aging human muscle (+150.43%, n = 5 in young and aged human, age: 26.20 ± 6.760 vs. 73.60 ± 5.030, p < 0.001) and aged mice muscle (+74.54% in male, +61.28% in female: n = 6 in young and aged mice in male/female, age: 3 months vs. 20 months, p < 0.001). In vitro studies demonstrated that EIF4A3 overexpression promoted muscle atrophy and aging in myotubes (n = 6, p < 0.05), while EIF4A3 inhibition mitigated these effects (p < 0.05). In vivo phenotypic analysis indicated that overexpression of EIF4A3 in skeletal muscle promoted muscle atrophy (n = 10, p < 0.05) including reduced grip strength (-42.36%, p < 0.001), running capacity (-21.24%, p < 0.001), contraction force (-19.62%, p < 0.001), muscle weight (gastrocnemius muscle: -15.75%; p < 0.001; tibialis anterior muscle: -9.50%, p < 0.01), myofiber size (-11.59%, p < 0.001) and worsened molecular phenotypes (all p < 0.05). Knockdown of EIF4A3 protected against muscle atrophy induced by various stimuli, including denervation (n = 10, p < 0.05), immobilization (n = 10, p < 0.05) and angiotensin II (n = 6-10, p < 0.05) in mice. Mechanistically, Neural Precursor Cell Expressed, Developmentally Down-Regulated 9 (NEDD9) mRNA was identified as a direct target of EIF4A3. EIF4A3 promoted the decay of NEDD9 mRNA and inhibited the downstream focal adhesion kinase (FAK) and PI3K-Akt pathway, promoting muscle atrophy. Pharmacological activation of the NEDD9-FAK pathway abolished the pro-atrophy effects of EIF4A3.

Our findings shed significant light on the pivotal function of the EJC in muscle atrophy, revealing novel mechanisms that contribute to EJC-related disorders. Providing a target for therapeutic interventions aimed at combating muscle atrophy.