Intestinal Epithelial Chemokine (C-C Motif) Ligand 7 Overexpression Protects Against High Fat Diet-Induced Obesity and Hepatic Steatosis in Mice
Obesity and its associated metabolic complications, including non-alcoholic fatty liver disease (NAFLD), insulin resistance, and dysregulated glucose metabolism, represent significant global health challenges. The intestinal epithelium, a critical interface between dietary components and systemic metabolism, has emerged as a key player in modulating metabolic health through immune regulation and interactions with gut microbiota. Chemokine (C-C motif) ligand 7 (CCL7), a chemotactic factor expressed in the intestinal lamina propria, is known to regulate immune cell recruitment and inflammatory responses. Previous work by the authors demonstrated that intestinal epithelial CCL7 influences acute liver injury. Building on this foundation, the current study investigates the role of intestinal epithelial CCL7 overexpression in mitigating chronic metabolic disorders induced by a high-fat diet (HFD), focusing on obesity, hepatic steatosis, and gut microbiota dysbiosis.
Experimental Design and Animal Model
The study utilized intestinal epithelial CCL7-overexpressing transgenic mice (CCL7tgIEC) and their wild-type (WT) littermates (C57BL/6J background). Female mice aged 5–6 weeks were divided into four groups: WT and CCL7tgIEC mice fed either a normal chow (NC, 10% kcal fat) or an HFD (60% kcal fat) for 16 weeks. Body weight, adipose tissue accumulation, glucose tolerance, insulin sensitivity, hepatic lipid content, and inflammatory markers were systematically evaluated. Fecal samples were collected for 16S rRNA gene sequencing to analyze gut microbial composition.
CCL7 Overexpression Attenuates HFD-Induced Weight Gain and Adiposity
CCL7tgIEC mice exhibited significant resistance to HFD-induced obesity. After 16 weeks, HFD-fed CCL7tgIEC mice gained 8.9 g in body weight compared to 17.0 g in HFD-fed WT mice (P < 0.05). Adipose tissue indices, measured as percentages of total body weight, were markedly lower in CCL7tgIEC mice: mesenteric fat (1.0% vs. 1.76%), gonadal fat (2.1% vs. 6.1%), and subcutaneous fat (1.0% vs. 2.8%) (P < 0.05 for all comparisons). Food intake did not differ between groups, ruling out reduced caloric intake as a contributing factor. These results highlight the protective role of intestinal CCL7 in limiting fat deposition despite sustained HFD consumption.
Improved Glucose Metabolism and Insulin Sensitivity
HFD-induced metabolic dysfunction was ameliorated in CCL7tgIEC mice. Intraperitoneal glucose tolerance tests (GTT) revealed lower plasma glucose levels in CCL7tgIEC mice at all time points (0–120 minutes post-injection), with a 25% reduction in the area under the curve (AUC) compared to WT (P < 0.05). Similarly, insulin tolerance tests (ITT) demonstrated enhanced insulin sensitivity in CCL7tgIEC mice, with a 20% decrease in AUC values (P < 0.05). These findings suggest that intestinal CCL7 overexpression preserves systemic glucose homeostasis and mitigates insulin resistance under obesogenic conditions.
Protection Against Hepatic Steatosis and Inflammation
HFD-fed CCL7tgIEC mice displayed reduced hepatic lipid accumulation and inflammatory markers. Liver triglyceride levels were 30% lower in CCL7tgIEC mice compared to WT (25.2 vs. 36.1 mg/g tissue; P < 0.05), while plasma cholesterol decreased by 18% (3.8 vs. 4.6 mmol/L; P < 0.05). Histological analysis via hematoxylin and eosin (H&E) and Oil Red O staining confirmed diminished steatosis and lobular inflammation in CCL7tgIEC livers. The non-alcoholic fatty liver disease activity score (NAS), which evaluates steatosis, inflammation, and ballooning, was significantly lower in CCL7tgIEC mice (2.1 vs. 4.3 in WT; P < 0.05).
Pro-inflammatory cytokine expression in the liver was suppressed in CCL7tgIEC mice. Quantitative PCR revealed reductions in IL-1β (40%), IL-6 (35%), CXCL2 (50%), CCL2 (45%), and CCL4 (55%) compared to WT (P < 0.05). Conversely, anti-inflammatory cytokines IL-10 and IL-13 were upregulated by 30% and 25%, respectively. These data indicate that intestinal CCL7 overexpression attenuates hepatic inflammation, a key driver of NAFLD progression.
Modulation of Gut Microbial Composition
16S rRNA sequencing revealed that CCL7tgIEC mice exhibited distinct gut microbiota profiles compared to WT under HFD conditions. Principal coordinate analysis (PCoA) based on Bray-Curtis distances showed clear separation between HFD-fed CCL7tgIEC and WT mice, whereas NC-fed groups clustered together. Linear discriminant analysis (LDA) identified Lactococcus as a genus enriched in HFD-fed CCL7tgIEC mice.
At the phylum level, HFD-fed WT mice had a 2.5-fold increase in Proteobacteria compared to NC-fed WT (P < 0.05), a shift linked to metabolic dysfunction. This increase was blunted in CCL7tgIEC mice, with Proteobacteria abundance 1.8-fold lower than in WT (P < 0.05). Similarly, the family Desulfovibrionaceae, associated with sulfate reduction and intestinal inflammation, was 3-fold higher in HFD-fed WT mice but reduced by 50% in CCL7tgIEC mice. These findings suggest that CCL7 overexpression restores microbial homeostasis, potentially through immune-mediated mechanisms that limit dysbiosis.
Mechanistic Insights and Implications
The study posits that intestinal CCL7 overexpression exerts protective effects through dual mechanisms: (1) direct modulation of immune cell recruitment and inflammatory signaling, and (2) indirect reshaping of gut microbiota composition. By attenuating HFD-induced dysbiosis, CCL7tgIEC mice likely experience reduced endotoxin translocation and systemic inflammation, contributing to improved metabolic parameters. The enrichment of Lactococcus, a genus with probiotic potential, further supports the hypothesis that CCL7 fosters a microbiota profile conducive to metabolic health.
Limitations and Future Directions
While the study establishes a clear link between intestinal CCL7 and metabolic protection, several questions remain. The precise mechanisms by which CCL7 influences gut microbiota remain undefined. Additionally, the role of CCL7 receptor signaling in peripheral tissues, such as adipose or liver, warrants investigation. Future studies using conditional knockout models or microbiota transplantation could elucidate causal relationships between CCL7, microbial communities, and metabolic outcomes.
Conclusion
This work demonstrates that intestinal epithelial CCL7 overexpression protects against HFD-induced obesity, hepatic steatosis, and insulin resistance in mice. The benefits are mediated through reduced adipose accumulation, improved glucose homeostasis, attenuated hepatic inflammation, and restoration of gut microbial balance. These findings highlight the intestine as a therapeutic target for metabolic disorders and underscore the potential of chemokine modulation in combating obesity-related pathologies.
doi.org/10.1097/CM9.0000000000000915
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