The initiation of rheumatoid arthritis (RA) represents a silent prologue scripted by the exposome (14). Environmental “first hits” recalibrate cellular thresholds for inflammatory cell death, priming the transition from health to autoimmunity. Proteomic profiling has identified lysozyme (LYZ) as a pivotal orchestrator that, when overexpressed in early RA macrophages, exacerbates TNF-induced inflammatory death (21). Furthermore, chronic exposure to particulate matter precipitates the collapse of the Keap1-Nrf2 antioxidant axis, impairing cellular resistance to oxidative stress (13, 22).

A central enigma in RA pathogenesis is the translation of pulmonary insult into synovial destruction. We propose a systemic relay model—the Lung–Joint Axis—where lung-derived neutrophil extracellular traps (NETs) and exosomes facilitate the delivery of citrullinated damage-associated molecular patterns (DAMPs) to the joint (23, 24). Viral pathogens, notably Parvovirus B19, function as biological initiators; the B19-NS1 protein activates NRF2-mediated stress responses and mTOR signaling, recapitulating the synovial niche even in the absence of conventional autoantibodies (25). From a systems perspective, shared WNT/STAT3 signaling pathways within this axis may explain the epidemiological link between RA-associated interstitial lung disease and increased carcinogenesis risk (26). Additionally, senescent cells adopting a senescence-associated secretory phenotype (SASP) act as chronic inflammatory reservoirs that sustain this pathogenic state (27, 28). To interrupt this systemic relay, autophagy inhibitors have demonstrated high precision in blocking pathogenic NET release without compromising systemic host defense (24), offering a targeted strategy to decouple pulmonary triggers from synovial inflammation.

Gut dysbiosis in rheumatoid arthritis (RA) facilitates the systemic translocation of pro-inflammatory metabolites, effectively bridging intestinal imbalance with synovial inflammation. Functional metabolomics has identified palmitic acid (PA)—often elevated in the context of high-fat diets and dysbiosis—as a potent systemic trigger of synovial pathology (29). PA exacerbates the expression of pro-inflammatory mediators by activating the NLRP3/Caspase-1/GSDMD-N pyroptotic axis in fibroblast-like synoviocytes (FLSs), thereby “priming” the arthritogenic niche for clinical flares (29).

Conversely, commensal-derived metabolites function as endogenous inhibitors of the PANoptosome. Short-chain fatty acids (SCFAs), such as butyrate, modulate T-lymphocyte homeostasis by inducing apoptosis in activated T cells through histone deacetylase (HDAC) inhibition and Fas upregulation (20). This mechanism effectively prevents the intra-articular accumulation of senescent, senescence-associated secretory phenotype (SASP)-producing T cells. Furthermore, dietary polyphenols such as anthocyanins (e.g., PSPA) have been shown to remodel the gut microbiota by enriching beneficial taxa like *Akkermansia* and *Lactobacillus*. This microbial shift correlates with the attenuation of synovial pyroptosis and the restoration of PI3K/AKT signaling (30). A landmark study in 2025 identified Urolithin A (UA), a gut-derived metabolite of natural polyphenols, as a critical “molecular rheostat” in death-mode regulation. UA attenuates RA pathogenesis by suppressing the NF-κB pathway and concurrently activating AMPK signaling, thereby inhibiting GSDMD-mediated pyroptosis in synovial fibroblasts (31).

A transformative paradigm shift emerged in 2025 with the discovery that chronic arthritis pain—which often persists independently of local synovial disease activity—is underpinned by a failure of the death-resolution machinery within the dorsal root ganglia (DRG) (16). The neuro-immune interface further exerts direct regulatory control over synovial death modes via the cholinergic anti-inflammatory pathway. Specifically, the α7 nicotinic acetylcholine receptor (α7nAChR) has emerged as a pivotal checkpoint inhibiting the pyroptosis of RA synovial fibroblasts. By suppressing the NLRP3/GSDMD axis, α7nAChR activation effectively “reprograms” synoviocyte fate, thereby mitigating inflammatory flares and subsequent tissue destruction (32). Crucially, this operates as a bidirectional loop: the failure of efferocytosis in the DRG leads to the persistent release of neuropeptides (e.g., Substance P, CGRP), which are retrogradely transported to the joint to promote synovial vasodilation and maintain the inflammatory ‘fire’ even after local cytokines are suppressed. Pharmacological modulation of this axis, such as the inhibition of BDNF/TrkB signaling via ANA-12, significantly attenuates glial activation and pro-inflammatory cytokine secretion (17). Furthermore, reactive oxygen species (ROS)-scavenging hydrogen nanotherapy represents a dual-action approach, simultaneously alleviating synovial inflammation and central pain sensitization (33).

Investigation into Salvianolic acid B demonstrates that restoring the Keap1-Nrf2 axis via direct binding to the Keap1-Arg415 residue suppresses pyroptosis, identifying this residue as a pivotal gatekeeper of synovial death homeostasis (13). Furthermore, the systemic ramifications of redox collapse extend to extra-articular complications. Recent evidence indicates that silymarin, a natural flavonoid, attenuates cardiac injury and inflammation in rats with adjuvant-induced arthritis (AIA). This cardioprotective effect is mediated by the Nrf2/SLC7A11/GPX4 axis, which suppresses ferroptosis and inflammatory responses in cardiac tissues, suggesting that Nrf2-regulated death pathways are essential for managing RA as a multi-organ systemic pathology (34).

Environmental stressors accelerate the acquisition of a senescence-associated secretory phenotype (SASP) in immune cells, particularly CD4⁺ and CD8⁺ T cells (27). Functioning as intra-articular “inflammatory reservoirs,” these cells secrete TNF-α and IL-6, which provide the requisite “second hit” for the persistent assembly of synovial PANoptosomes (27, 28). This transition is molecularly governed by CCNE2; the inhibition of CCNE2 effectively triggers senescence-associated apoptosis in synoviocytes, representing a promising senolytic strategy (28). Furthermore, the epitranscriptomic regulation of cell fate is intrinsically coupled to the crosstalk between non-coding RNAs (ncRNAs) and programmed cell death (PCD) pathways (35). Dysregulated long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) within the RA synovial niche serve as master orchestrators, modulating the sensitivity of fibroblast-like synoviocytes (FLSs) to apoptotic and pyroptotic stimuli, thereby driving the progression from acute inflammation to chronic structural damage. This systemic failure of death-mode resolution across diverse anatomical sites—constituting the “synovial mosaic” of RA—is systematically summarized in Table 1.

In summary, these multi-organ relays do not operate in isolation; rather, they function as critical upstream priming signals (Figure 1). Whether via gut metabolite-induced NLRP3 activation or lung-derived damage-associated molecular pattern (DAMP)-mediated ZBP1 sensing, these systemic inputs lower the biophysical threshold for PANoptosome assembly. Consequently, the synovial niche serves as a molecular crucible where environmental “hits” are translated into the programmed execution of PANoptosis, a process ultimately governed by an underlying epitranscriptomic script.

Beyond its canonical role as the initiator of extrinsic apoptosis, Caspase-8 functions as the catalytic and structural rheostat of the PANoptosome in RA. In RA-FLSs, the overactivation of IAPs and the sequestration of Caspase-3 create a molecular bottleneck. Consequently, Caspase-8 undergoes a substrate-preference shift, engaging GSDME at the Asp270 site. This ‘backup plan’ transforms a suppressed apoptotic signal into an explosive pyroptotic flare. Recent evidence (49) reveals that Caspase-8 does not solely act as a protease but also as a scaffold for NLRP3 assembly. In RA-FLSs, Caspase-8 is redirected by c-FLIP_L, which forms a heterodimer that preferentially activates the ZBP1-RIPK3 axis, mirroring the molecular switch observed in pathogen-induced PANoptosis, switching the cell from a “silent” apoptotic exit to an explosive pyroptotic program (59). The pathogenic reach of this switch extends to rheumatoid sarcopenia. Recent evidence (44) underscores that TNF-α drives muscle atrophy by hijacking the Caspase-8/Caspase-3/GSDME-mediated pyroptotic axis. When primed by chronic TNF-α, Caspase-8 activation facilitates GSDME cleavage, triggering a lytic death that exacerbates tissue loss. This reinforces the necessity of targeting the Caspase-8 switch not only to preserve joint integrity but also to mitigate the systemic burden of the disease.

Joint destruction involves remote PANoptic relays. A failure of MerTK-mediated efferocytosis of apoptotic neutrophils in the DRG drives persistent mechanical hypersensitivity (16, 17). Remote chondrocyte demise is triggered by FLS-derived sEVs carrying miRNA-15–29148 targeting CIAPIN1 (36, 60). Subchondral bone survival is gated by the AMPK/HIF-1α axis in the hypoxic niche (39, 40). Pathological B-cell aggregates maintain the DAMP pool, which can be remodeled using bioactive glass IDPs (61).

The destruction of articular cartilage is increasingly recognized as a “remote PANoptic relay.” FLS-derived small extracellular vesicles (sEVs) act as long-range commands, transporting miRNA-15–29148 across the joint space (36). Once internalized by chondrocytes, this miRNA targets CIAPIN1 (Cytokine-Induced Apoptosis Inhibitor 1), effectively disabling the chondrocyte’s internal survival rheostat and triggering premature apoptosis even in paucimmune states (36, 60). This remote killing is amplified by the CXCL10/CXCR3 axis, which recruits further inflammatory precursors to the cartilage-pannus junction, creating a self-amplifying cycle of matrix degradation (60).

In the marginal zones of bone erosion, the survival of bone-resorbing osteoclasts is governed by a hypoxia-death checkpoint. The AMPK/HIF-1α axis prevents the PANoptic demise of osteoclast precursors in the hypoxic RA niche, converting synovial metabolic stress into a persistent bone-resorption signal (39, 40). This environment is further stabilized by pathological B-cell aggregates that maintain a localized DAMP pool. Recent evidence suggests that targeted B-cell depletion—utilizing bioactive glass ionic dissolution products (IDPs)—can remodel this osteoimmunological microenvironment, triggering osteoclast apoptosis and shifting the balance toward osteoblastic bone repair (61). Advanced nanozyme coatings can now reprogram this niche by converting H₂O₂ into O₂, thereby preventing macrophage apoptosis and shifting polarization toward the M2 phenotype. Classical agents like iguratimod also exert therapeutic effects by modulating this AMPK/HIF-1α axis to suppress osteoclast differentiation (39).

In summary, PANoptosis in RA represents a ‘messy death’ that fundamentally sabotages the resolution of inflammation. Unlike homeostatic apoptosis, which is ‘silent’ and facilitates clearance, the lytic nature of PANoptotic FLSs releases a massive pool of DAMPs (e.g., HMGB1) that overwhelms the efferocytic capacity of local MerTK+ macrophages. This combination of explosive cell death and ‘cleaning failure’ (impaired efferocytosis) creates a feed-forward loop that perpetuates the autoimmune response within the synovial mosaic.

Collectively, these multi-organ relays converge on the synovial niche to prime PANoptosome assembly. A critical unresolved question is whether RA subtypes differentially engage these pathways.

Emerging evidence suggests distinct “trigger fingerprints” across RA subtypes:

Therapeutic implication: Subtype-tailored strategies may be required—ACPA blockade plus NLRP3 inhibition for seropositive disease versus microbiome modulation or Piezo1 antagonism for seronegative cases.

A primary obstacle in RA management is the lack of tools to visualize the intra-articular death landscape. A 2025 breakthrough identifies [¹¹C]CMP1 PET as a high-affinity radiotracer for RIPK1, enabling the first-ever spatial mapping of necroinflammatory “hot-spots” in vivo a technique adapted from RIPK1 neuroimaging (8, 18). This “molecular compass” allows clinicians to identify patients with active PANoptic flares, facilitating the selection of individuals for targeted death-mode interventions rather than broad-spectrum biological therapy (8, 18). Critically, RIPK1+ synovial burden may differ between subtypes: seropositive patients with chronic lung–joint axis activation (ACPA/ionic flux) (12, 23, 24) may exhibit sustained, diffuse signals, whereas seronegative cases reliant on intermittent triggers (gut-metabolic/mechanical) (29, 50) may show spatially restricted patterns. Longitudinal [¹¹C]CMP1 PET studies correlating uptake with autoantibody titers and systemic relay biomarkers are urgently needed to validate the subtype-specific models proposed in Section 4.4. Additionally, circulating AIM2 methylation levels have emerged as a novel epigenetic biomarker to predict therapeutic response in difficult-to-treat (D2T) RA (9, 64), while near-infrared fluorescent probes (e.g., BHD) enable real-time monitoring of microenvironmental alterations associated with synovial demise (15). Integrating [¹¹C]CMP1 PET with circulating m6A signatures (9) and relay-specific markers would operationalize the three-tier stratification algorithm detailed in Section 5.4, ensuring the right therapy reaches the right patient phenotype.

While JAK inhibitors act as inadvertent top-down ‘PANoptotic silencers’ by downregulating ZBP1 and RIPK1, future strategies aim for direct enzymatic and metabolic “editing” of the death script.

The transition from “killing” to “niche-resetting” requires restoring efferocytic capacity. Engineered vesicles (D@ApoEVFasL) promote macrophage efferocytosis (62), established as a critical resolution mechanism. This is complemented by systemic rheostats like New Bitongling (NBTL), which suppresses Mapt expression to restore mitochondrial function (66, 74), and pH-responsive hybrid nanoparticles (Pae-PPNPs-DS) that modulate the STAT axis to promote the resolution of inflammation (52, 79). Achieving antigen-specific, drug-free remission remains the ultimate goal of PANoptic niche eradication (80). The diverse array of precision platforms enabling this transition—from spatiotemporal mapping of ‘hotspots’ to the sophisticated bio-responsive editing of death modes—is comprehensively integrated in Table 5.

i. Off-target toxicity: Systemic nanoparticle exposure risks hepatorenal accumulation. Mitigation strategies include:

Tissue-specific targeting: Conjugating collagen II-binding peptides or folate receptor-α ligands to target activated FLS (62).

Dual-gating release: Requiring both inflammatory cues (ROS, acidic pH) and external triggers (e.g., focused ultrasound) to prevent premature cargo release.

Biodegradable scaffolds: Utilizing FDA-approved polymers (PLGA, chitosan) to streamline regulatory approval.

ii. Patient stratification: We propose a three-tier biomarker algorithm to identify responders:

Tier 1 (Imaging): [¹¹C]CMP1 PET positivity identifies RIPK1+ “hotspots” suitable for death-mode interventions.

Tier 2 (Molecular): Circulating m6A-modified NLRP3/GSDMD transcripts (liquid biopsy) (9) confirm active PANoptotic signaling.

Tier 3 (Clinical): Relay profiling distinguishes seropositive cases (lung-joint axis markers) from seronegative cases (gut-metabolic signatures), as detailed in Section 4.4.

iii. Regulatory and Manufacturing: Clinical translation requires overcoming batch-to-batch variability via microfluidic synthesis for GMP compliance, and mitigating immunogenicity through PEGylation or zwitterionic coatings.