IF AAV8-CYP27A1-F444A (gain-of-function variant; 1×10¹² vg, single tail-vein injection) is administered to 12-week-old male ApoE−/− mice on a Western diet,

THEN aortic plaque 7-KC burden will be reduced ≥50% by LC-MS/MS and aortic root lesion area ≥30% by Oil Red O at 24 weeks post-injection, and plasma HDL-associated 7-KC esters will be reduced ≥40% and aortic CYP7A1 activity (hepatic bile acid output) will be increased ≥2-fold, compared to AAV8-GFP controls,

BECAUSE the following causal chain operates across two anatomical compartments:

1. Macrophage lysosomal 7-KC is esterified by SOAT1 and exported selectively to HDL in peripheral/extra-hepatic cells, because those tissues lack robust oxidative machinery and rely on esterification as primary 7-KC handling. (7-KC esterification and HDL efflux as extra-hepatic clearance mechanism)[https://doi.org/10.1016/j.bbalip.2015.01.007] This makes HDL-7-KC esters a quantifiable biomarker of macrophage lysosomal 7-KC efflux.

2. Circulating HDL delivers 7-KC esters to the liver, where hepatic lipase and CETP activity release free 7-KC into hepatocytes — the primary site of sterol catabolism — making hepatic enzyme upregulation the ideal single intervention point for systemic 7-KC clearance. [SPECULATIVE: direct evidence that HDL-7-KC esters are preferentially hepatically catabolized is not yet in the evidence set.]

3. Recombinant CYP27A1 directly hydroxylates 7-KC to 7-KC-27OH and further oxidation products; the F444A mutation [SPECULATIVE: the specific F444A residue is inferred from structural analogy to CYP7A1 active site contacts] is proposed to enlarge the binding pocket to relieve steric clash with the C-7 keto group. (CYP27A1 converts 7-KC to sequential oxidation products; heat-inactivated controls show no product)[https://doi.org/10.1194/jlr.m014217]

4. 7-KC is a demonstrated inhibitor of CYP7A1 (cholesterol 7α-hydroxylase): crystal structures of human CYP7A1 reveal 7-KC occupying the active site as an inhibitory oxysterol rather than a substrate. (CYP7A1 crystal structure in complex with 7-KC as inhibitory ligand)[https://doi.org/10.1194/jlr.m050765] Therefore, hepatic 7-KC accumulation suppresses bile acid synthesis, trapping cholesterol in the enterohepatic circuit — a vicious cycle amplifying atherogenic cholesterol burden.

5. AAV8-CYP27A1-F444A-mediated hepatic 7-KC catabolism simultaneously derepresses CYP7A1, restoring bile acid synthesis flux. [SPECULATIVE: the magnitude of derepression in vivo is not yet quantified.] This creates a dual mechanism: (a) direct 7-KC hydroxylation to polar metabolites cleared in bile, and (b) allosteric derepression of CYP7A1 driving amplified cholesterol-to-bile-acid flux — predicting a greater lesion reduction than CYP27A1 wild-type overexpression alone.

6. Reduction of macrophage lysosomal 7-KC eliminates a driver of foam cell formation and pathological VSMC autophagy (via Nox4/Atg4B). (7-KC induces autophagy in vascula...

SENS category: LysoSENS

Key references: • doi.org/10.1016/j.bbalip.2015.01.007] • doi.org/10.1194/jlr.m014217] • doi.org/10.1194/jlr.m050765] • doi.org/10.1016/j.ajpath.2013.04.028] • doi.org/10.1016/j.bcp.2013.02.002]