Chromatin budding in laminopathy triggers a cGAS‑STING feedback that tunes nucleophagy, uncoupling protective rationing from inflammatory senescence

Hypothesis

In HGPS and physiological aging, progerin‑induced nuclear envelope budding exports chromatin fragments into the cytoplasm. These cytosolic nucleosomes are not merely waste; they act as endogenous DNA that activates the cGAS‑STING pathway. The resulting type‑I interferon response feeds back to modulate autophagy flux through TFEB nuclear translocation, thereby linking the magnitude of nucleophagy to the intensity of inflammatory signaling. This creates a self‑limiting loop: low‑level chromatin extrusion sustains protective nucleophagy without triggering chronic inflammation, whereas sustained high‑level extrusion drives maladaptive interferon signaling that converts a rationing system into a source of senescence‑associated secretory phenotype (SASP).

Novel mechanistic reasoning

1. Chromatin as a DAMP – Exported nucleosomal DNA binds cGAS with high affinity, generating 2′‑3′‑cGAMP and activating STING‑TBK1‑IRF3 signaling. This step has been shown to be essential for sensing cytosolic DNA in senescence models 7.
2. Feedback to autophagy – STING‑TBK1 phosphorylates and activates TFEB, promoting lysosomal biogenesis and autophagosome formation. Simultaneously, IRF3‑driven interferon transcription upregulates autophagy‑related genes (e.g., LC3, p62) but also induces p21‑mediated cell‑cycle arrest, shifting the balance from damage limitation to growth arrest.
3. Rheostat model – The rate of chromatin budding, dictated by lamin A/progerin ratio and membrane tension, sets the cytosolic DNA concentration. Below a threshold, TFEB activation enhances nucleophagy, preserving genome integrity. Above the threshold, chronic STING signaling sustains IFN‑β production, reinforcing SASP and suppressing proliferation, thus explaining why global autophagy activation can be beneficial in early stress but detrimental in chronic progeroid contexts.

Testable predictions

• Prediction 1: Knocking down cGAS in progerin‑expressing fibroblasts will reduce IFN‑β and ISG expression without decreasing LC3‑II turnover or p62‑mediated nucleophagy flux.
• Prediction 2: Overexpressing a non‑degradable, farnesylated lamin A mutant will increase cytosolic chromatin, elevate cGAS‑STING signaling, and shift autophagy from protective to senescence‑associated, measurable by increased SASP cytokines (IL‑6, IL‑8) and β‑galactosidase activity.
• Prediction 3: Pharmacological inhibition of STING (e.g., with C‑176) will rescue proliferation defects in HGPS iPSC‑derived mesenchymal stem cells while maintaining reduced γ‑H2AX foci, indicating uncoupled nucleophagy from inflammatory arrest.

Experimental approach

1. Cell models: Use HGPS fibroblasts and CRISPR‑engineered iPSC lines expressing inducible progerin or lamin A‑G608G.
2. Readouts: Measure cytosolic DNA by immunofluorescence for cGAS foci, quantify LC3‑II/p62 flux via bafilomycin A1 chase, assess IFN‑β mRNA (qPCR) and protein (ELISA), and evaluate senescence (SA‑β‑gal, p16, p21).
3. Interventions: siRNA against cGAS or STING, overexpression of TFEB‑S142A (non‑phosphorylatable) to block feedback, and treatment with STING inhibitor.
4. Controls: Rescue experiments with WT lamin A, and autophagy inhibition (ATG5 KO) to confirm that observed effects depend on nucleophagy flux.

If the data support these predictions, the hypothesis will redefine autophagy in laminopathies as a rationing system whose output is tuned by a DNA‑sensing inflammatory circuit, offering a precise target to decouple beneficial cleanup from deleterious senescence.