Review papers with raw data transparency

Key claims made by the review (accurately cited)

• Host proteases (MMPs, serine proteases, cathepsins) and an imbalance with inhibitors are implicated in IBD pathology Host proteases in IBD (review)
• Faecal and mucosal proteolytic activity is increased in subsets of IBS and UC patients and can modulate neuronal sensitivity via PARs (PAR2 and PAR4 differences documented) Faecal proteases and PAR effects
• Commensal-derived proteases can disrupt epithelial junctions: Enterococcus faecalis GelE degrades occludin/E-cadherin and impairs barrier function in susceptible hosts (mouse models) GelE (E. faecalis) role

Strengths — what the review does well

• Comprehensive synthesis across host- and microbe-derived proteases, PAR biology, barrier biology and neuronal effects with extensive references (n≈97) Comprehensive review and references
• Clear identification of mechanistic hypotheses (PAR activation, junctional protein cleavage, mucolysis) and experimental gaps—helpful roadmap for follow-up mechanistic studies Mechanistic roadmap (review)

Limitations, blindspots and critical caveats

• Predominantly correlative human data available by 2012: increased faecal protease activity was measured, but precise bacterial protease species/enzymes were not systematically identified in patient samples—so causality in humans remained unproven Human data correlative (review)
• Heterogeneity: IBS and IBD are heterogeneous clinical syndromes; protease signatures likely vary by subtype and disease state; review acknowledges this but cannot resolve it with available data Heterogeneity of protease effects
• Therapeutic caution — protease inhibitors are non-specific and previous MMP inhibitor trials had adverse effects; the review correctly flags translational risks and need for specificity Therapeutic caution (review)

What new evidence (2025) changes/strengthens the picture?

Since 2012, targeted work has started to close the human-causality gap. Two representative advances from the supplied dataset:

• Bfp1 — a secreted protease from Bacteroides fragilis — was identified to cleave PAR2 and cause intestinal pain/inflammation in murine models; that is a concrete mechanistic example of a commensal protease acting through PARs, supporting the review's central hypothesis and validating the suggested experimental path (activity-resolved identification → PAR functional tests → in vivo perturbation) Bfp1 mechanistic study (2025)
• Environmental modulation of mucolysis: a 2025 study indicates bacterial proteases (not only glycanases) are primary drivers of mucus degradation under certain conditions, increasing plausibility that proteases can access epithelial targets if mucus is thinned (an IBD feature) Proteolytic mucus degradation (2025)

Critical synthesis and confidence-weighted conclusion

Conclusion: The 2012 review laid a robust conceptual and literature foundation that bacterial proteases can — plausibly and mechanistically — contribute to IBD/IBS pathophysiology by (1) degrading mucus and junctional proteins, (2) activating PARs on neurons/immune cells, and (3) dysbalancing host protease/antiprotease systems. Direct, enzyme‑level, causal proof in humans was limited in 2012; subsequent 2025 mechanistic studies (e.g., Bfp1) provide the first concrete commensal-to-host PAR cleavage demonstrations, increasing confidence in the review's main thesis while underscoring continued needs for patient-level, activity-resolved proteomics and careful safety assessment for protease-targeted therapies Steck et al. review conclusions Bfp1 causal evidence

What would disprove the review's central claims (falsification criteria)?

1. High-quality, large human studies showing elevated faecal/mucosal proteolytic activity is solely due to host proteases with no bacterial-derived protease signatures even after activity-resolved enrichment and proteomic identification.
2. Targeted knockout/inhibition of individual candidate bacterial proteases (in humanized microbiota animal models) failing to change barrier integrity, PAR signalling or symptomatology in replicated studies.
3. Therapeutic trials that modulate protease activity (or PAR signalling) with high specificity producing no clinical or mechanistic benefit despite adequate PD target engagement and safety.

Recommended next experiments (concise, specific, falsifiable)

1. Activity-resolved metaproteomics of stool/mucus from well-phenotyped IBD/IBS patients: use activity-based probes for serine/cysteine/metallo‑proteases, pull-down, LC‑MS/MS to identify and quantify active bacterial proteases vs host proteases (test: presence/abundance of bacterial proteases correlates with permeability/visceral sensitivity).
2. Human organoid + microbiota co-culture test: colon organoids with mucus layer exposed to isogenic bacterial strains (wild-type vs protease knockout) measuring TER, E-cadherin cleavage, PAR activation and neuronal co-culture responses (test: knockout abrogates barrier disruption and PAR signals).
3. Proof-of-concept precision inhibition: develop small-molecule or antibody inhibitors to a candidate bacterial protease (e.g., Bfp1 or GelE), test in humanized mouse models and evaluate barrier, inflammation and pain outcomes, plus off-target host protease effects.

Short methodological checklist for reproducible follow-up studies

• Pre-register sample collection, define clinical subtypes (IBD: UC vs CD; IBS: D vs C), control for diet/antibiotics.
• Use activity-based probes and parallel host/bacterial protease markers; deposit raw proteomics and metadata to public repositories.
• Use matched functional readouts (TER, E-cadherin immunoblot/cleavage products, PAR reporter assays, visceral pain assays) with blinded analysis.