Fig 2: MMP13 deficiency protects mice from LPS-induced systemic inflammation and lethalityA–D. MMP13 gene expression analysis in ileum (A), liver (B) lung (C), and kidney (D) 0, 1, 4, 6, 8, and 12 h after LPS challenge (n = 5).E–F. Body temperature (E) and survival (F) of MMP13+/+ (black) and MMP13-/- (grey) mice after LPS injection (i.p.; 17.5 mg/kg) (n = 15).G. Survival of MMP13+/+ (black; n = 7) and MMP13-/- (grey; n = 12) mice after CLP.H–K. Serum cytokine and chemokine levels after injection of LPS in MMP13+/+ (black) and MMP13-/- (grey) mice: IL1ß (H), TNF (I), IL17 (J) and MCP1 (K) (n = 4–5).

Fig 3: Effect of MMP13 on intestinal barrier dysfunctionLPS-induced shock and DSS-induced colitis result in MMP13 up-regulation in the gut. This leads to MMP13-mediated shedding of transmembrane-bound TNF and release of bioactive, soluble TNF (1). Subsequently, sTNF induces goblet cell mucin expression and secretion and eventually results in ER-stress, which leads to mucus depletion and increased interaction of bacteria with IECs and Paneth cells (2). Additionally, TNF induces caveolin-dependent endocytosis, resulting in destabilization of tight junctions. This is associated with loss of tight junction functionality and increased intestinal permeability (3). Consequent leakage of intestinal components increases systemic inflammation, which leads to organ damage and eventually to death (4).

Fig 4: MMP13 deficiency results in reduced clinical signs of DSS-induced colitisClinical score of MMP13+/+ (black) and MMP13-/- (grey) mice after 5 days of treatment with 2% DSS (n = 12–14). Clinical scores are a composite of body weight loss, rectal bleeding and stool consistency scores.MMP13 gene expression before and 6 days after 2% DSS treatment.Colon length of MMP13+/+ (black) and MMP13-/- (grey) mice on day 6 after the start of the DSS treatment (n = 4).TNF bioactivity of colon lysates of MMP13+/+ (black) and MMP13-/- (grey) mice 6 days after 2% DSS treatment (n = 4; one-tailed t-test).

Fig 5: MMP13-dependent intestinal TNF activation results in mucus depletion, increased intestinal inflammation, systemic inflammation and organ damageA. TNF (2000 U/ml) induces upregulation of Muc2 gene expression in goblet cells in vitro (n = 6).B. Quantification of total goblet cell mucus before and 8 h after TNF injection in vivo by Alcian blue staining of isolated ileum samples, followed by laxative treatment and absorbance measurement of the supernatant (n = 8).C,D. Representative images of MUC2 (red) and DAPI (blue) immunostainings of ileal sections in the absence of TNF (C) and 8 h after TNF injection (D).E. Survival curve of non-sterile (black) and sterile, antibiotics treated (grey) mice after LPS injection (i.v.; 250 µg/20 g) (n = 12).F,G. Survival curve (F) and intestinal permeability (G) of LPS-injected MMP13+/+ mice pretreated with PBS (black; n = 10) or anti-TNF (grey; n = 3) (i.p.; 17.5 mg/kg).H,I. Representative mucin-2 (red) confocal images of ileal sections of LPS-injected mice pretreated with PBS (H) and anti-TNF (I).J,K. Gene expression analysis of IL6 and iNOS in ileum lysates of MMP13+/+ (black) and MMP13-/- (grey) mice 0 and 8 h after LPS injection (n = 4–5).L,M. Gene expression analysis of the Paneth-cell-specific genes MMP7 (H) and RegIII? (I) in ileum lysates of MMP13+/+ (black) and MMP13-/- (grey) mice 0 and 8 h after LPS injection (n = 4–5).N. IL-FABP levels in serum of MMP13+/+ (black) and MMP13-/- (grey) mice 8 h after LPS injection (n = 5–7).O. Relative serum LDH activity 8 h after LPS injection in MMP13+/+ (black) and MMP13-/- (grey) mice (n = 6–14).