Hypothesis

Declining nitric oxide (NO) bioavailability initiates a self‑amplifying mechanotransduction loop in vascular smooth muscle cells (VSMCs) via activation of the Hippo pathway effectors YAP/TAZ, which suppresses eNOS transcription and promotes a synthetic, matrix‑producing phenotype. This loop accelerates arterial stiffening and elevates pulse wave velocity (PWV) even when systemic blood pressure remains normal, making PWV an early readout of YAP/TAZ‑mediated vascular aging.

Mechanistic Rationale

1. NO loss → ↑ RhoA/ROCK activity – Reduced NO diminishes cGMP‑PKG signaling, releasing inhibition of RhoA. Active ROCK phosphorylates LATS1/2, impairing Hippo kinase activity and allowing nuclear translocation of YAP/TAZ1.
2. YAP/TAZ nuclear signaling → ↓ eNOS, ↑ VSMC synthetic program – Nuclear YAP/TAZ binds TEAD transcription factors to repress NOS3 promoter activity and upregulate genes such as CTGF, FN1, and MMP9, fostering extracellular matrix deposition and VSMC dedifferentiation2.
3. Matrix stiffening → impaired endothelial shear sensing – Increased collagen cross‑linking and elastin fragmentation raise local tissue stiffness, attenuating endothelial mechanotransduction of shear stress and further lowering eNOS activation3.
4. Feedback to NO – YAP/TAZ also induces expression of asymmetric dimethylarginine (ADMA) via upregulated PRMT1, directly inhibiting eNOS and completing the cycle4.
5. Modulation by GLP‑1RA – GLP‑1 receptor activation raises cAMP, activating PKA which phosphorylates YAP at Ser127, promoting cytoplasmic retention and mitigating the loop5.

Testable Predictions

• Prediction 1: In asymptomatic adults aged 30‑50, baseline PWV will positively correlate with nuclear YAP/TAZ levels in circulating endothelial‑derived extracellular vesicles (EVs), independent of systolic blood pressure.
• Prediction 2: Acute pharmacologic inhibition of ROCK (e.g., fasudil) will reduce nuclear YAP/TAZ in EVs and increase plasma NO metabolites (nitrite/nitrate) within 2 h, preceding any change in BP.
• Prediction 3: Twelve‑week GLP‑1RA therapy will decrease EV‑YAP/TAZ nuclear ratio and PWV by ≥10 % in participants with PWV > 8 m/s, whereas a matched placebo group will show no change.
• Prediction 4: EVs isolated from high‑PWV individuals will carry higher ADMA and lower BH₄/BH₂ ratios; neutralizing ADMA with L‑arginine will restore eNOS coupling in cultured VSMCs only when YAP/TAZ is cytoplasmic.

Experimental Approach (Falsifiable)

1. Cohort (n = 120) stratified by PWV (<8, 8‑10, >10 m/s). Collect blood, isolate EVs, quantify YAP/TAZ (Western blot, immunofluorescence), ADMA, BH₄, and nitrite/nitrate.
2. Randomized, double‑blind crossover: fasudil (30 mg IV) vs saline; measure EV‑YAP/TAZ, NO metabolites, and carotid‑femoral PWV at 0, 30, 60, 120 min.
3. GLP‑1RA trial (liraglutide 1.8 mg daily) vs placebo for 12 weeks; primary outcome change in PWV; secondary outcomes EV‑YAP/TAZ, ADMA, BH₄.
4. In vitro: VSMCs treated with serum from high‑PWV donors; manipulate YAP/TAZ (siRNA, verteporfin) and assess eNOS uncoupling (DHE fluorescence) and collagen secretion.

Falsification: If PWV shows no correlation with EV‑YAP/TAZ, or if ROCK/GLP‑1RA interventions fail to alter YAP/TAZ localization and PWV despite robust NO changes, the hypothesis is refuted. Conversely, consistent directional changes across these layers would support a NO‑YAP/TAZ mechanostat as a central driver of vascular aging.

Implications

Targeting the YAP/TAZ node—either directly (verteporfin, TEAD inhibitors) or indirectly via ROCK/GLP‑1RA pathways—could decouple arterial stiffness from blood pressure, offering a preventative strategy for younger adults before clinical hypertension emerges.