NLRP3‑Caspase‑1 Cleavage of Beclin1 Drives Active Autophagy Suppression in Aged T Cells
Hypothesis
In aged T cells, chronic NLRP3 inflammasome activation leads to caspase‑1–dependent cleavage of the autophagy initiator Beclin1. The resulting C‑terminal fragment acts as a dominant‑negative inhibitor of the VPS34‑Beclin1 complex, directly blocking autophagosome nucleation. This proteolytic suppression of autophagy precedes and sustains T‑cell exhaustion, creating a feed‑forward loop where damaged mitochondria leak ROS that further fuels NLRP3 activity.
Rationale
- Autophagy decline in aging is not merely passive; NLRP3 deficiency preserves flux even in old mice (1, 4).
- NF‑κB drives NLRP3 transcription, and defective mitophagy from low autophagy raises ROS, reactivating NF‑κB→NLRP3 (2, 3).
- In lymphocytes, CD28 costimulation activates NF‑κB and mTOR, pathways known to suppress autophagy (6).
- Caspase‑1, the effector protease of NLRP3, routinely cleaves substrates beyond pro‑IL‑1β; emerging data show it can target Beclin1 in macrophages (5).
Novel Mechanistic Insight
We propose that caspase‑1 generates a Beclin1 C‑terminal fragment (≈150 aa) lacking the N‑terminal BH3 domain but retaining the coiled‑coil region. This fragment competitively binds VPS34, preventing formation of the active Beclin1‑VPS34‑ATG14L complex. Consequently, PI3P production drops, phagophore formation stalls, and LC3‑II lipidation fails despite normal upstream signaling. Unlike transcriptional repression, this post‑translational block operates rapidly and is reversible only by inhibiting caspase‑1 or removing the cleaved fragment.
Testable Predictions
- Biochemical – In sorted CD8⁺ T cells from aged (≥20 mo) mice or humans, immunoblotting will reveal a caspase‑1‑sized Beclin1 fragment that increases with age and correlates with NLRP3 activation. Immunoprecipitated VPS34 will show reduced Beclin1 binding in aged cells.
- Functional – Pharmacological inhibition of NLRP3 (MCC950) or caspase‑1 (VX‑765) in aged T‑cell cultures will decrease the Beclin1 fragment, restore LC3‑II/I ratio and lower p62, and enhance mitochondrial clearance (mito‑Keima assay).
- Phenotypic – Restored autophagy will concomitantly lower exhaustion markers (PD‑1, TIM‑3, TOX) and improve proliferative capacity after chronic antigen exposure (e.g., repeated OVA peptide stimulation).
- Genetic – T‑cell‑specific expression of a caspase‑1‑resistant Beclin1 mutant (D149A) in aged mice will preserve autophagy flux and delay exhaustion without altering NLRP3 levels.
Experimental Approach
- Isolate naïve CD8⁺ T cells from young (3 mo) and aged mice; activate with anti‑CD3/CD28 plus IL‑2 for 5 days to model chronic stimulation.
- Treat parallel cultures with MCC950, VX‑765, or anakinra (IL‑1R blocker) as controls.
- Measure: (a) Beclin1 cleavage by western blot; (b) autophagic flux using LC3‑II turnover with bafilomycin A1; (c) mitochondrial ROS (MitoSOX); (d) exhaustion markers by flow cytometry; (e) cytokine production (IFN‑γ, TNF‑α).
- Validate findings in human peripheral blood T cells from young vs. elderly donors using the same inhibitors.
Falsifiability
If aged T cells show no increase in the caspase‑1‑cleaved Beclin1 fragment, or if inhibiting caspase‑1/NLRP3 fails to rescue autophagy and exhaustion markers, the hypothesis would be refuted. Conversely, confirming the fragment’s inhibitory role and linking its removal to functional recovery would support the model of active, protease‑mediated autophagy suppression driving T‑cell aging.