Hypothesis

In vascular smooth muscle cells (VSMCs), age‑related decline of ZMPSTE24 causes prelamin A to accumulate at the nuclear lamina, where it sequesters CK2 and concurrently alters the phosphorylation state of replication‑fork proteins. This shifts DNA double‑strand break repair in lamina‑associated domains (LADs) from homologous recombination (HR) toward error‑prone non‑homologous end joining (NHEJ). Simultaneously, age‑dependent deterioration of nuclear pore complexes (NPCs) permits cytoplasmic phosphatases to leak into the nucleus, further dephosphorylating CK2 substrates and reinforcing the repair bias. Together, these lamina‑NPC defects create a VSMC‑specific vulnerability that drives genomic instability in both physiological aging and progeria.

Mechanistic Model

1. Prelamin A–CK2 sequestration – Prelamin A binds CK2 via its C‑terminal tail, reducing CK2’s ability to phosphorylate PCNA (Tyr211) and RFC1. Loss of these phosphorylations weakens fork protection and stalls replication, generating single‑ended DSBs that are channeled into NHEJ when LADs detach from the periphery (2).
2. LAD detachment signaling – DNA damage within LADs triggers ATM‑dependent nuclear envelope remodeling, reducing lamin B1/LBR and mobilizing LINC complexes to release the damaged domain (3). In the prelamin A‑rich environment, CK2 is not available to phosphorylate downstream effectors (e.g., KAP1) that would favor HR, so the detached LAD is repaired predominantly by NHEJ.
3. NPC leak amplifies the bias – Age‑linked NPC deterioration increases nucleocytoplasmic permeability, allowing cytoplasmic PP2A phosphatase to enter the nucleus (4; 5). PP2A dephosphorylates CK2‑phosphorylated sites on PCNA/RFC1 and on HR factors (BRCA1, RAD51), further suppressing HR and favoring NHEJ.
4. VSMC specificity – VSMCs exhibit high basal lamin A turnover and rely on precise fork progression for contractile protein synthesis; thus, the combined CK2 sequestration and NPC leak disproportionately generate chromosomal breaks in these cells (6).

Testable Predictions

• Prediction 1: In primary human VSMCs from donors >65 yr, phospho‑PCNA (Tyr211) and phospho‑RFC1 levels will be significantly lower than in donors <30 yr. Overexpressing ZMPSTE24 or treating with spermidine will restore these phosphorylations to youthful levels.
• Prediction 2: Acute induction of NPC leak via siRNA‑mediated knockdown of Nup93 in young VSMCs will decrease phospho‑PCNA/RFC1 and increase NHEJ markers (Ku70, Ku80, DNA‑PKcs autophosphorylation) specifically within LADs, as measured by chromatin‑immunoprecipitation followed by sequencing (ChIP‑seq) for γH2AX.
• Prediction 3: Expressing a cell‑permeable peptide that blocks the prelamin A‑CK2 interaction will rescue phospho‑PCNA levels and reduce chromosomal breaks (metaphase spread analysis) even when NPCs are leaky, demonstrating that CK2 sequestration is epistatic to NPC‑mediated phosphatase influx.

Falsifiability

If any of the three predictions fail—for example, if phospho‑PCNA remains unchanged with ZMPSTE24 overexpression, or if NPC leak does not alter NHEJ usage in LADs, or if the blocking peptide fails to reduce breaks—then the proposed mechanistic link between prelamin A‑CK2 sequestration, NPC permeability, and repair‑pathway bias in VSMCs is not supported, and the hypothesis would be falsified.

Potential Impact

Confirming this model would identify a dual‑target strategy: boosting ZMPSTE24 activity to clear prelamin A and fortifying NPCs (e.g., with Nup93 stabilizers) to preserve nuclear‑cytoplasmic compartmentalization, thereby shifting DSB repair back toward high‑fidelity HR and mitigating vascular genomic instability in aging and progeroid conditions.