Probiotics modulate intestinal expression of nuclear receptor and provide counter-regulatory signals to inflammation-driven adipose tissue activation

Abstract

Background: Adipocytes from mesenteric white adipose tissue amplify the inflammatory response and participate in inflammation-driven immune dysfunction in Crohn's disease by releasing proinflammatory mediators. Peroxisome proliferator-activated receptors (PPAR)-α and -γ, pregnane x receptor (PXR), farnesoid x receptor (FXR) and liver x-receptor (LXR) are ligand-activated nuclear receptor that provide counter-regulatory signals to dysregulated immunity and modulates adipose tissue.

Aims: To investigate the expression and function of nuclear receptors in intestinal and adipose tissues in a rodent model of colitis and mesenteric fat from Crohn's patients and to investigate their modulation by probiotics.

Methods: Colitis was induced by TNBS administration. Mice were administered vehicle or VSL#3, daily for 10 days. Abdominal fat explants obtained at surgery from five Crohn's disease patients and five patients with colon cancer were cultured with VSL#3 medium.

Results: Probiotic administration attenuated development of signs and symptoms of colitis, reduced colonic expression of TNFα, IL-6 and IFNγ and reserved colonic downregulation of PPARγ, PXR and FXR caused by TNBS. Mesenteric fat depots isolated from TNBS-treated animals had increased expression of inflammatory mediators along with PPARγ, FXR, leptin and adiponectin. These changes were prevented by VSL#3. Creeping fat and mesenteric adipose tissue from Crohn's patients showed a differential expression of PPARγ and FXR with both tissue expressing high levels of leptin. Exposure of these tissues to VSL#3 medium abrogates leptin release.

Conclusions: Mesenteric adipose tissue from rodent colitis and Crohn's disease is metabolically active and shows inflammation-driven regulation of PPARγ, FXR and leptin. Probiotics correct the inflammation-driven metabolic dysfunction.

Figure 1. Anti-inflammatory activity of VSL#3 in TNBS colitis.

Preteatment with VSL#3 (50×10⁹ colony-forming units (cfu)/kg/day) protects against the development of TNBS-induced colitis in mice. Colitis was induced by intrarectal instillation of 1.5 mg of TNBS per mouse. Mice were sacrificed 5 days after TNBS administration. (A and B) The severity of TNBS-induced inflammation (weight loss and fecal score) is reduced by VSL#3 administration. Data represent the mean ± SE of 8–10 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS). (C and D) VSL#3 reduces local signs of inflammation and inhibits the increase of macroscopic-score and neutrophil infiltration (MPO activity) induced by TNBS. Data represent the mean ± SE of 8–10 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS).

Figure 2. Histological analysis of colon and mesenteric adipose tissue of mice treated with TNBS alone or in combination with VSL#3.

(A, D and G) Histopathology analysis of colon samples, original magnification 10×; H&E staining. (A) naïve mice; (D) TNBS administration causes colon wall thickening and massive inflammatory infiltration in the lamina propria and mucosal erosions; (G) VSL#3 attenuates colon thickening and inflammatory infiltration of the mucosa and submucosa. (B,C,E,F,H and I) Histologic analysis of mesenteric adipose tissue, H&E staining. (B and C) Naïve mice, original magnification 10× and 20×; (E and F) TNBS group mice, original magnification 10× and 20×; (H and I) VSL#3 treated mice, original magnification 10× and 20x.

Figure 3. VSL#3 attenuates inflammatory changes in the colon and restores nuclear receptors expression in mice administered TNBS.

(Panel 1. A–F) RT-PCR analysis of the expression of inflammatory cytokines (IL-6, TNFα, IL-1β, and INFγ) and anti-inflammatory cytokines (IL-10 and TGF-β) in colons obtained 5 days after TNBS. Data represent the mean ± SE of 5 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS). (Panel 2 A–E) RT-PCR analysis of the expression of PPARα, PPARγ, FXR, LXR, PXR and CAR in colons removed 5 days after administration of TNBS alone or in combination with VSL#3. Data represent the mean ± SE of 5 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS).

Figure 4. VSL#3 attenuates inflammation-driven metabolic dysfunction in the mesenteric adipose tissue.

(Panel 1 A-E) RT-PCR analysis of expression of inflammatory cytokines (TNFα, IL-6, and MCP1) and adipokines (leptin and adiponectin) in mesenteric adipose tissues. Data represent the mean ± SE of 5 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS). (Panel 2 A-E) RT-PCR analysis of the expression of PPARα, PPARγ, LXR, PXR and FXR in mesenteric adipose tissues obtained 5 days after administration of TNBS alone or in combination with VSL#3. Data represent the mean ± SE of 5 mice per group. (#p<0.05 versus naïve; *p<0.05 versus TNBS).

Figure 5. Distinctive histologic features the creeping fat and mesenteric adipose tissue in Crohn's disease patients.

Rappresentative haematoxylin-eosin (H&E) staining of mesenteric adipose tissue of Crohn's patients. Creeping fat original magnification 10× and 20×, respectively (A) adipose tissue distal to intestinal mucosa of Crohn's disease patients, original magnification 20× (Bars: 100 µm) and 40×(Bars: 50 µm), respectively (B). Paired samples from three patients are shown.

Figure 6. Expression of inflammatory mediators, adipokines and selected nuclear receptors in mesenteric adipose tissues from Crohn's patients.

RT-PC analysis of expression of inflammatory TNFα, IL-6, MCP1, leptin and adiponectin (Panel 1 A-E) and nuclear receptors (PPARα, PPARγ, LXR, PXR and FXR) (Panel 2 A-E) in mesenteric adipose tissue (MAT) obtained from control subjects (N = 5) (colon carcinoma) and in Crohn's patients (creeping fat and distal MAT) (N = 5). Data represent the mean ± SE of 5 different subjects per group. (#p<0.05 versus MAT of control subjects ; *p<0.05 versus distal MAT obtained from Crohn's disease patients).

Figure 7. VSL#3 CM modulates the production of mesenteric adipose tissue factors.

Release of adiponectin, leptin, IL-6 and TNFα by adipose tissue explants. Release by proximal (creeping fat) and distal MAT explants from 5 Crhon's patients is shown. Creeping fat and MAT explants were cultured alone or in combination with different concentrations of VSL#3 CM for 48 h. (#p<0.05 basal production (Ctrl) creeping versus MAT; n = 25; * p<0.05 verus control group, n = 25).