IF a tri-engineered nuclear backup construct — combining (1) a synthetic "super-import" N-terminal MTS derived from the ATP5G1 presequence augmented with positively charged lysine/arginine residues to increase TOM20 affinity, (2) a hydrophobicity-reduced, codon-optimized MT-ND4 coding sequence in which transmembrane helix residues are minimally substituted with isosteric but less hydrophobic alternatives (e.g., leucine→valine swaps at non-critical packing positions, identified computationally), and (3) a 3'UTR cis-acting mitochondrial surface localization element (MSLE) derived from the yeast ATM1 or mammalian TOMM40 3'UTR to anchor ribosomal translation to the mitochondrial outer membrane — is packaged into a self-complementary AAV2 (scAAV2) vector and delivered intravitreally to aged (20–24 month) male C57BL/6 mice,

THEN the following measurable outcomes will be observed compared to aged controls injected with a standard scAAV2-ND4 construct (analogous to GS010/Lumevoq design with COX10-MTS and no 3'UTR localization element):

• ≥40% greater import efficiency of recombinant ND4 protein into the mitochondrial inner membrane fraction (quantified by proteinase K protection assay and western blot of fractionated retinal tissue),
• ≥25% restoration of retinal Complex I activity (NADH-ubiquinone oxidoreductase activity assay, rotenone-sensitive, in isolated retinal mitochondria),
• Statistically significant preservation of RGC layer thickness (≥15% more cells versus aged vehicle control, measured by optical coherence tomography [OCT] and RBPMS immunostaining),
• Reduced mitochondrial superoxide production in RGCs (≥30% decrease in MitoSOX fluorescence by confocal imaging of retinal flat mounts),

BECAUSE the following causal chain operates:

1. Age-accumulated somatic mtDNA mutations in RGCs, concentrated in Complex I subunit genes including MT-ND4, progressively impair electron transport and elevate ROS, driving RGC apoptosis — the damage is already present in aged tissue and cannot be reversed by prevention strategies alone. (Allotopic expression as a replacement strategy is supported by) (Codon optimization is an essential parameter for the efficient allotopic expression of mtDNA genes)[https://doi.org/10.1016/j.redox.2020.101429]

2. Standard post-translational import of cytoplasmic ND4 fails primarily because the naked hydrophobic polypeptide aggregates in the aqueous cytosol before engaging the TOM complex, a barrier explicitly identified as the rate-limiting step for Complex I allotopic expression. (Modifying the Mitochondrial Genome)[https://doi.org/10.1016/j.cmet.2016.04.004] The GS010 trials confirm partial but incomplete rescue, consistent with this bottleneck.

3. The 3'UTR MSLE element localizes ND4 mRNA to the mitochondrial outer membrane surface, enabling ribosomal docking at the TOM complex and initiating co-translational import — physically coupling synthesis to translocation and eliminatin...

SENS category: RepleniSENS

Key references: • doi.org/10.1016/j.redox.2020.101429] • doi.org/10.1016/j.cmet.2016.04.004] • doi.org/10.15252/emmm.201708084] • doi.org/10.1016/j.redox.2020.101429]. • doi.org/10.15252/emmm.201708084].