Hypothesis\n\nWe propose that alternative splicing of the ANRIL long non‑coding RNA generates isoforms that either recruit PRC2 to silence CDKN2A/B or act as decoys that sequester PRC2, thereby permitting transcription. This isoform switch is modulated by cellular metabolite levels (e.g., acetyl‑CoA/SAM ratio) that influence splicing factor activity, linking metabolic state to senescence onset.\n\n## Mechanistic Model\n\n1. In proliferating, metabolically active cells, high acetyl‑CoA promotes inclusion of exon 2 in ANRIL, producing the ANRIL‑PRC2 isoform that binds EZH2 and deposits H3K27me3 at the CDKN2A/B promoter, keeping p16INK4a low (5).\n2. With age or caloric restriction, declining acetyl‑CoA and rising SAM shift splicing toward exclusion of exon 2, generating the ANRIL‑decoy isoform that lacks the PRC2‑binding domain but retains the chromatin‑interacting region. This decoy competes for promoter binding, displacing PRC2 and reducing H3K27me3, leading to CDKN2A/B transcription (6, 7).\n3. The resulting p16INK4a increase enforces G1 arrest via CDK4/6 inhibition (4), contributing to immunosenescence and stem‑cell exhaustion.\n\n## Predictions\n\n- P1: Manipulating the acetyl‑CoA/SAM ratio in primary fibroblasts will alter the ANRIL‑PRC2/ANRIL‑decoy isoform ratio, measurable by isoform‑specific RT‑qPCR.\n- P2: Overexpression of the ANRIL‑decoy isoform will decrease H3K27me3 at the CDKN2A/B promoter (ChIP‑seq) and increase p16INK4a expression, even in young cells.\n- P3: CRISPR‑mediated deletion of the exon 2 splice site will lock cells into the decoy phenotype, causing premature senescence that is rescued by EZH2 overexpression.\n- P4: In blood samples from older adults, the ANRIL‑decoy/ANRIL‑PRC2 ratio will correlate with circulating p16INK4a levels better than total ANRIL expression.\n\n## Experimental Design\n\n1. Isoform quantification – Design primers spanning the exon 2 junction; treat human dermal fibroblasts with acetyl‑CoA precursor (acetate) or SAM antagonist (cycloleucine) and measure isoform ratios.\n2. ChIP‑seq for H3K27me3 – Compare enrichment at the CDKN2A/B promoter after isoform overexpression or knock‑down.\n3. Senescence assays – SA‑β‑gal staining, EdU incorporation, and p16INK4a western blot following isoform manipulation.\n4. Clinical correlation – Obtain peripheral blood mononuclear cells from a cohort stratified by age; perform isoform‑specific RT‑qPCR and plasma p16INK4a ELISA; compute Spearman correlations.\n\nIf the predictions hold, this model provides a testable link between metabolic signaling, alternative splicing of a non‑coding RNA, and epigenetic control of the CDKN2A/B locus, offering a novel therapeutic avenue to modulate senescence without globally inhibiting EZH2 or Jmjd3.
