Hypothesis

Age‑dependent up‑regulation of the lncRNA NEAT1 promotes DRP1‑mediated mitochondrial fission in vascular smooth muscle cells (VSMCs), generating reactive oxygen species that simultaneously drive tropoelastin loss and VSMC osteogenic transdifferentiation, leading to arterial calcification that can be reversed by targeting NEAT1 or DRP1.

Mechanistic Model

1. NEAT1 scaffolds DRP1 to the outer mitochondrial membrane, increasing GTPase activity and fission.
2. Mitochondrial fission elevates ROS via electron‑transport chain leak, activating NF‑κB and MAPK pathways.
3. ROS‑dependent NF‑κB up‑regulates MMP‑2 and MMP‑9, which degrade elastin fibers; released elastin peptides act as DAMPs that suppress tropoelastin transcription through Hippo‑YAP/TAZ signaling.
4. ROS also stabilizes HIF‑1α, boosting BMP‑2 expression and SMAD1/5/8 signaling, while mtDNA released into the cytosol activates cGAS‑STING, inducing IRF3‑driven Runx2 expression.
5. Combined BMP‑2/SMAD and Runx2 pathways push VSMCs toward an osteogenic phenotype, evidenced by ↑ALP, ↓SM22α, and calcium deposition.
6. Inhibition of NEAT1 or DRP1 reduces fission, lowers ROS, restores tropoelastin synthesis, and blocks osteogenic shift, making calcification reversible.

Testable Predictions

• VSMCs from old mice show higher NEAT1, phospho‑DRP1 (Ser616), mitochondrial fragmentation, and ROS compared with young cells.
• NEAT1 knock‑down (ASO) or DRP1 inhibition (Mdivi‑1) decreases ROS, MMP activity, and elastin fragmentation while increasing tropoelastin mRNA and protein.
• Under osteogenic stress (β‑glycerophosphate), NEAT1/DRP1 suppression reduces ALP activity, Runx2 nuclear localization, and calcium staining.
• In vivo, aged ApoE‑/‑ mice treated with NEAT1 ASO or Mdivi‑1 exhibit reduced aortic pulse‑wave velocity, increased elastin integrity (SHG imaging), and lower calcium content (Alizarin Red) versus controls.
• Exogenous elastin peptides rescue tropoelastin expression in NEAT1‑high VSMCs, confirming a feedback loop.

Experimental Design

In vitro:

• Primary human aortic VSMCs cultured from donors <30 yr and >60 yr.
• Measure NEAT1 (qPCR), phospho‑DRP1 (Western blot), mitochondrial morphology (MitoTracker + confocal), ROS (DCFDA), MMP‑2/9 activity (gelatin zymography), tropoelastin (ELISA, immunostaining), osteogenic markers (ALP, Runx2, BMP‑2) and calcium (Alizarin Red).
• Interventions: NEAT1 ASO, scrambled ASO, Mdivi‑1 (50 µM), NAC (ROS scavenger).
• Rescue: add recombinant tropoelastin or elastin‑derived peptides.

In vivo:

• Aged (18‑month) ApoE‑/‑ mice receive tail‑vein NEAT1 ASO (20 mg/kg weekly) or oral Mdivi‑1 (30 mg/kg/day) for 8 weeks; controls get saline.
• Non‑invasive PWV measurement weekly.
• Terminal analysis: aortae harvested for SHG elastin imaging, Alizarin Red calcium quantification, histologic VSMC phenotype (SM22α, Runx2), and RNA‑seq for NEAT1‑driven pathways.

Expected Outcomes

If the hypothesis is correct, NEAT1 or DRP1 inhibition will:

• Decrease mitochondrial fission and ROS by ≥40 %.
• Lower MMP‑2/9 activity and increase tropoelastin levels by ≥30 %.
• Shift VSMC contractile‑to‑osteogenic ratio toward contractile (≥2‑fold increase in SM22α/Runx2).
• Improve arterial elasticity (↓PWV) and reduce calcification (≥35 % less Alizarin Red signal). Failure to observe these changes would falsify the proposed mechanistic link between NEAT1‑DRP1 mitochondrial dynamics, elastin loss, and VSMC osteogenic switching.