Enzyme CTSL Triggers Rogue Notch1 Signaling That Drives Artery-Aging and Plaque
A novel CTSL–Notch1–CUX1 pathway drives endothelial senescence and atherosclerotic plaque buildup, revealing fresh drug targets.
Summary
Scientists at the University of Pittsburgh discovered a previously unknown chain of molecular events that accelerates artery aging and plaque formation. An enzyme called cathepsin L (CTSL) directly cuts and activates the Notch1 protein without the usual cellular signal — releasing a fragment that travels to the nucleus and switches on genes that push blood vessel cells into senescence, a state of permanent growth arrest. This senescence drives atherosclerosis. In mice engineered to develop artery disease, blocking any step in this pathway — CTSL, Notch1, or the downstream gene CUX1 — dramatically reduced plaque size, protected elastic fibers in artery walls, and lowered inflammatory immune cell infiltration. Human plaque samples confirmed elevated levels of CTSL and active Notch1. The findings open a new therapeutic window for targeting cellular senescence to slow or prevent heart disease.
Detailed Summary
Atherosclerosis, the hardening and narrowing of arteries that underlies most heart attacks and strokes, is increasingly understood as a disease driven not just by cholesterol but by the biology of aging itself. Cellular senescence — a state in which cells stop dividing but remain metabolically active and inflammatory — accumulates in arterial plaques and is thought to accelerate disease progression. Despite this, the specific molecular mechanisms linking aging pathways to plaque formation remain incompletely mapped.
Researchers at the University of Pittsburgh set out to identify the transcriptional regulator connecting cathepsin L (CTSL), a lysosomal protease, to the gene CUX1 and its downstream effector p16INK4a, a well-known inducer of cellular senescence. Prior genome-wide association study functional analyses had implicated this axis in atherosclerosis, but the linking molecule was unknown.
The team discovered that Notch1 is a direct substrate of CTSL. Crucially, CTSL can cleave and activate Notch1 without any ligand binding — bypassing the normal receptor-ligand mechanism entirely. This releases the Notch1 intracellular domain (NICD), which complexes with the transcription factor RBPJ in the nucleus to drive CUX1 expression and, subsequently, p16INK4a-dependent senescence. Human atherosclerotic plaque samples showed elevated CTSL and NICD alongside increased senescence markers, validating the pathway clinically.
In atherosclerosis-prone ApoE-knockout mice, endothelial deletion of CUX1 blocked high-fat diet-induced senescence throughout plaques and mimicked the protective phenotype seen when CTSL or Notch1/RBPJ is inactivated: significantly attenuated lesions, intact elastin fibers, and reduced macrophage infiltration.
These findings identify a non-canonical, ligand-independent Notch1 activation route as a central driver of vascular aging and atherosclerosis. The CTSL–Notch1–CUX1–p16INK4a axis represents a potentially druggable senescence pathway. Senolytics or targeted inhibitors of CTSL or Notch1 cleavage may one day complement lipid-lowering therapies to reduce cardiovascular risk in aging populations.
Key Findings
- CTSL cleaves and activates Notch1 without a ligand, releasing NICD to drive vascular cell senescence.
- NICD–RBPJ nuclear complex upregulates CUX1 and p16INK4a, pushing endothelial cells into senescence.
- Human atherosclerotic plaques show elevated CTSL and NICD co-localized with senescence markers.
- Endothelial CUX1 deletion in ApoE-/- mice reduced plaque size, macrophage content, and elastin damage.
- Blocking CTSL or Notch1/RBPJ phenocopied CUX1 deletion, validating the pathway as a drug target.
Methodology
The study combined post-GWAS functional analysis, human atherosclerotic plaque sampling, and mechanistic cell biology experiments. In vivo validation used endothelial-specific CUX1 knockout in ApoE-/- mice fed a high-fat diet, with lesion area, elastin integrity, and macrophage infiltration as endpoints. Biochemical assays confirmed direct CTSL-mediated proteolytic cleavage of Notch1.
Study Limitations
This summary is based on the abstract only; full methodology, statistical details, and supplementary data were not accessible. Mouse models of atherosclerosis do not perfectly replicate human disease, and translational applicability requires further clinical validation. The ligand-independent Notch1 activation mechanism needs confirmation in additional human vascular tissue models.
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