**Background:** High-fat diet (HFD)-induced obesity is associated with chronic low-grade inflammation, with the colon being an early site of pro-inflammatory changes linked to gut microbiota alterations. Sleeve gastrectomy (SG) is an effective obesity treatment that restores gut microbiota and reduces inflammation in liver and adipose tissue, but its effects on colonic inflammation and the role of gut microbiota in these effects were unknown.
**Methods:** Two cohorts of 4-week-old male C57BL/6J mice were fed 60% HFD for 12 weeks. In cohort 1, mice were randomized to SG (n=11) or sham surgery (SHAM, n=9) and maintained on HFD for 8 weeks post-surgery. One mouse died and three developed abdominal abscess after SG (final: SG n=7, SHAM n=9). In cohort 2, mice received broad-spectrum antibiotics (neomycin 1 g/L, metronidazole 0.25 g/L, vancomycin 0.5 g/L, ampicillin 1 g/L) in drinking water starting 2 days before surgery, then underwent SG (SG-ABX, n=11) or sham (SHAM-ABX, n=9). One mouse died and two developed abscess after SG (final: SG-ABX n=8, SHAM-ABX n=9). Outcomes included body weight, glucose tolerance (MMTT), serum lipids, colonic morphology, macrophage infiltration (CD68 immunohistochemistry, flow cytometry), cytokine and tight junction gene expression (qPCR), gut microbiota (16s rRNA sequencing), and colonic transcriptome (RNA-seq).
**Key Results:** SG led to significant weight loss, improved glucose tolerance, and decreased TC, LDL-C, and HDL-C. In the colon, SG did not alter length, cecum weight, or macrophage infiltration (comparable CD68+ cells, F4/80+CD11b+CD11c- cells, and macrophage-related chemokine/marker gene expression except CD11c). However, SG significantly decreased pro-inflammatory cytokine gene expression: IL-6, IL-1β, IL-18, and IL-23 were downregulated, while anti-inflammatory cytokines (IL-10, TNF-β, IL-33) were unchanged. SG increased tight junction protein gene expression (ZO-1, Occludin). Crypt depth was decreased in SG mice. Gut microbiota analysis showed increased richness (Chao1 index) and altered composition (unweighted UniFrac PCoA, PERMANOVA F=1.85, P=0.003) following SG, with increased Lactobacillus and decreased Desulfovibrio abundance. In the antibiotics-treated cohort, SG still produced weight loss, improved glucose tolerance, and decreased TC and LDL-C, but had no effect on colonic pro-inflammatory cytokine expression (IL-6, IL-1β, IL-18, IL-23 comparable between SG-ABX and SHAM-ABX), tight junction protein expression, or crypt depth. Colonic transcriptome analysis identified 179 DEGs between SG and SHAM (enriched in inflammatory response, leukocyte migration, PPAR signaling pathways), but only 73 DEGs between SG-ABX and SHAM-ABX with no enrichment of inflammation-associated pathways.
**Clinical Implications:** This study demonstrates that SG reduces HFD-induced colonic pro-inflammatory status through gut microbiota-dependent mechanisms, as antibiotic-mediated microbiota depletion abrogated these effects. The findings suggest that gut microbiota alterations—particularly increased anti-inflammatory Lactobacillus and decreased pro-inflammatory Desulfovibrio—are critical mediators of SG's anti-inflammatory effects in the colon. Improved tight junction protein expression further suggests enhanced gut barrier function. Notably, metabolic benefits (weight loss, glucose tolerance) were preserved despite microbiota depletion, indicating that different SG benefits are mediated through distinct mechanisms. These results highlight the gut microbiota as a potential therapeutic target for reducing intestinal inflammation in obesity, though further studies (e.g., metagenomic sequencing, bile acid analysis, fecal microbiota transfer) are needed to establish causality and mechanistic pathways.