IF a recombinant Heterocephalus glaber lysosomal acid lipase (NMR-LAL), engineered with an appended mannose-6-phosphate (M6P) glycosylation signal for lysosomal routing and packaged in a hepatotropic AAV9 vector under a CMV/CBA promoter driving secreted expression, is administered via tail-vein injection (1×10¹¹ vg/mouse) to aged (22-month-old) male C57BL/6J mice carrying an established hepatic and neuronal lipofuscin burden,

THEN a ≥35–45% reduction in autofluorescent lipofuscin granule area density (measured by quantitative confocal microscopy of liver sections and cortical neurons), accompanied by a ≥30% reduction in lysosomal oxidized cholesteryl ester content (measured by lysosomal fractionation + lipidomics) and partial rescue of lysosomal lumen acidification (LysoSensor ratiometric imaging), will be observed within 16–20 weeks post-injection,

BECAUSE the following mechanistic chain is supported:

1. NMR tissues resist age-associated lipofuscin accumulation through constitutively superior lysosomal hydrolytic activity — specifically elevated Cathepsin B, Cathepsin L, and, by inference, lysosomal lipid-processing enzymes including LAL — maintained across their 30+ year lifespan in contrast to the progressive lysosomal deterioration observed in Mus musculus (as synthesized in the task output citing Zhao et al., 2014, Autophagy; Rodriguez et al., 2012, PNAS).

2. Lysosomal acid lipase (LAL) is the rate-limiting gatekeeper for intracellular neutral lipid clearance: LAL hydrolyzes cholesteryl esters and triglycerides delivered to the lysosome via endocytosis and autophagy, and its deficiency leads to progressive lysosomal lipid entrapment that feeds lipofuscin core formation through oxidative cross-linking of lipid peroxidation products. (Lysosomal lipid accumulation as a driver of later, indigestible lesions)[https://doi.org/10.3389/fcell.2015.00003]

3. Oxidized lipid species within lysosomal lumen are central to lipofuscin pathology: The progressive shift from cytosolic lipid droplet accumulation to mixed lysosomal lipid sequestration in aging is driven by insufficiently active lysosomal lipases that cannot process oxidatively modified esterified cholesterol — precisely the substrate class implicated in lipofuscin ceroid cores. (Time-dependent shift to lysosomal lipid sequestration)[https://doi.org/10.3389/fcell.2015.00003] [SPECULATIVE: NMR-LAL is predicted to have evolved superior Vmax or altered substrate-binding cleft geometry accommodating oxidized lipid substrates compared to murine LAL — this requires direct enzymatic characterization.]

4. The mannose-6-phosphate receptor pathway is a validated, scalable route for delivering exogenous enzymes into the lysosomal lumen of target cells: Myeloperoxidase — a peroxidase not canonically expressed in lysosomes — when M6P-tagged and delivered extracellularly, is internalized by retinal pigment epithelial cells via M6PR and retains full enzymatic activity within the ly...

SENS category: LysoSENS

Key references: • doi.org/10.3389/fcell.2015.00003] • doi.org/10.1074/jbc.m116.739441] • doi.org/10.1074/jbc.m115.695825] • doi.org/10.1074/jbc.m114.555300] • doi.org/10.1101/2023.03.27.534444]