IF an AI-engineered MMP-12 variant—designed via RFdiffusion motif-scaffolding to constrain a sterically restricted active site around desmosine/isodesmosine (DID) crosslinks, sequence-optimized by ProteinMPNN for solubility and fold fidelity, and refined through yeast surface display with dual negative selection against tropoelastin backbone cleavage and collagen type I/III—is delivered as nucleoside-modified LNP-encapsulated mRNA (0.5 mg/kg, intravenous, weekly × 8 weeks) engineered with a hepatocyte-optimized signal peptide for active secretion into systemic circulation, AND co-administered with N-acetyl-lactosamine (Lac-NAc, 10 mg/kg i.p.), a competitive antagonist of the elastin receptor complex (ERC/S-Gal), to suppress matrikine-driven inflammatory amplification following crosslink cleavage, to 24-month-old male C57BL/6J mice (n=15/group),

THEN the following measurable outcomes will be observed at week 8 relative to vehicle control:

• Aortic pulse wave velocity (Doppler ultrasound) will decrease by ≥15% from aged baseline (~450–520 cm/s)
• Dynamic lung compliance (FlexiVent forced oscillation, tissue elastance H) will improve by ≥20%
• Urinary DID by LC-MS/MS will display a biphasic profile: a transient spike of ≥30% above baseline at week 2 (confirming active DID crosslink cleavage and release), followed by a return to or below baseline by week 8 (indicating depletion of pathological crosslink burden)
• Verhoeff-Van Gieson and Hart's elastin stains will show ≤10% net increase in elastin fiber fragmentation (preserved architecture), and picrosirius red will show no significant increase in Type I/III collagen ratio

BECAUSE the following causal chain is operative:

1. In 24-month-old C57BL/6J mice, accumulated desmosine and isodesmosine crosslinks progressively stiffen the extracellular matrix of the aortic media and pulmonary alveolar walls; these crosslinks are chemically distinct from peptide bonds and are not cleaved by endogenous tissue remodeling at a rate sufficient to reverse accumulated stiffening (Evidence Set synthesis: Therapeutic Applications section — "Current literature regarding the enzymatic cleavage of DID crosslinks as a therapeutic strategy for arterial stiffness is virtually non-existent").

2. Standard ionizable LNP formulations (DLin-MC3-DMA class) administered intravenously are captured by hepatocytes via ApoE-mediated uptake at >90% efficiency (Evidence Set synthesis: LNP-mRNA Delivery section), meaning the engineered mRNA will be translated predominantly in the liver. By engineering the variant with a hepatocyte-compatible signal peptide and N-terminal pro-sequence cleaved in the secretory pathway, hepatocytes become a continuous biofactory releasing activated enzyme into the portal and systemic circulation — converting the delivery liability into a pharmacokinetic asset [SPECULATIVE: secretion efficiency of a pro-MMP-12 variant from hepatocytes has not been directly quantified].

3. RFdiffusion "mot...

SENS category: GlycoSENS