Background

Evidence shows that aging is accompanied by a global decline in vitamin K–dependent carboxylation, exemplified by elevated undercarboxylated osteocalcin in elderly women [1] and a positive correlation between the carboxylated/total osteocalcin ratio and bone quality [2]. Vitamin K–dependent proteins extend beyond bone to include regulators of vascular calcification, inflammation, and cellular signaling. Moreover, age‑associated changes in stromal stem cells persist in vitro, indicating an epigenetic “memory” rather than a transient metabolic defect [3]. Osteocalcin also acts as a hormone linking bone to glucose metabolism and adiponectin signaling, creating bidirectional feedback loops [4].

Hypothesis

We hypothesize that age‑related impairment of vitamin K epoxide reductase (VKOR) activity reduces the carboxylation status of a broad substrate pool, generating undercarboxylated proteins that act as endogenous ligands for nuclear receptors (e.g., LXR, PPARγ) and histone deacetylase complexes. This altered ligand/receptor balance drives a coordinated epigenetic reprogramming that simultaneously manifests as the canonical hallmarks of aging (genomic instability, epigenetic alteration, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem‑cell exhaustion, altered intercellular communication, chronic inflammation, and dysbiotic microbiome). In this model, vitamin K–dependent carboxylation is not merely a downstream biomarker but an upstream metabolic‑epigenetic hub that synchronizes multiple aging pathways.

Mechanistic Model

1. VKOR decline → increased pool of γ‑glutamyl‑under‑carboxylated proteins (UCPs).
2. UCPs bind nuclear receptors with altered affinity, shifting co‑activator/co‑repressor recruitment.
3. Receptor complexes recruit HDACs/SIRT1 to specific chromatin regions, leading to localized histone deacetylation and DNA methylation changes.
4. Epigenetic remodeling represses youthful gene networks (e.g., WNT/β‑catenin, TGF‑β) and activates senescence‑associated secretory phenotype (SASP) genes.
5. Feedback loops: SASP factors further suppress VKOR expression via inflammatory cytokines (IL‑6, TNF‑α), amplifying the defect.
6. Systemic effects: Undercarboxylated osteocalcin and other UCPs circulate, modulating glucose metabolism, adiponectin signaling, and vascular calcification, thereby linking bone, metabolic, and cardiovascular hallmarks.

Testable Predictions

• Prediction 1: Pharmacologic or genetic restoration of VKOR activity in aged mice will increase global protein carboxylation, reduce UCPs, and reverse age‑associated DNA methylation signatures (e.g., Horvath clock) to youthful levels.
• Prediction 2: VKOR restoration will concurrently improve multiple hallmarks: increased bone mineral density, decreased vascular calcification, reduced systemic inflammation (lower IL‑6, TNF‑α), enhanced stem‑cell colony‑forming units, and improved glucose tolerance.
• Prediction 3: Adding exogenous UCPs (e.g., recombinant undercarboxylated osteocalcin) to young mice will accelerate epigenetic aging and induce hallmarks even when VKOR activity is intact.

Experimental Design

• Model: C57BL/6 mice aged 20 months; groups: (a) VKOR overexpression via AAV8‑VKORC1, (b) vitamin K2 (menaquinone‑7) supplementation (200 µg/kg/day), (c) control (AAV‑GFP or vehicle).
• Readouts (at baseline, 8 weeks, 16 weeks):
  • Global carboxylation status assessed by anti‑γ‑carboxyglutamate immunoblotting of plasma proteins.
  • Epigenetic age measured by reduced representation bisulfite sequencing (RRBS) and epigenetic clocks.
  • Hallmark panels: bone micro‑CT, aortic calcification (Alizarin Red), serum cytokines, glucose tolerance test, colony‑forming unit‑fibroblast (CFU‑F) assay, SASP profiling.
  • Rescue experiment: administer recombinant undercarboxylated osteocalcin to young VKOR‑overexpressing mice to test sufficiency.
• Statistical plan: Power analysis (n=10/group) to detect 15% change in epigenetic age acceleration with α=0.05, power=0.8.

Potential Outcomes and Falsifiability

If VKOR restoration normalizes epigenetic age and ameliorates ≥3 hallmarks, the hypothesis gains strong support. If carboxylation improves but epigenetic age and hallmarks remain unchanged, the model is falsified, suggesting vitamin K–dependent carboxylation is a downstream effector rather than an upstream controller. Conversely, if UCPs alone induce hallmarks in young animals, it confirms their signaling capacity.

Implications

Positioning vitamin K–dependent carboxylation at the nexus of metabolism and epigenetics reframes aging as a coordinated program amenable to nutritional or genetic intervention, shifting focus from treating individual hallmarks to targeting a single, measurable upstream node.