Differences In Mesenteric Adipose Tissue Attached To Different Intestinal Segments

Mesenteric adipose tissue(MAT)is a contiguous set of visceral adipose tissue that attaches around the different segments of the intestines including duodenum,jejunum,ileum and colon.In recent years,researchers have gradually recongnized the key role of MAT in maintaining intestinal homeostasis,and there were a dramatic growing number of studies delve into the MAT.As we known,the function of adipose tissue is usually adapted to that of its adjacent organs,and a single subcutaneous fat depot has heterogeneity in different regions.However,whether there exist any mesenteric differences adjacent to the small and large intestines(SMAT and LMAT)has not been properly characterized,though the small and large intestines have evidently intrinsic and distinct characteristics,and MAT associated with them is a long,contiguous and widely distributed tissue have been well established.In the more than 2,000 published research reports focusing on human or mouse MAT,MAT is regarded as an inherently undifferentiated tissue.Our study committed to elucidate the differences between SMAT and LMAT,thereby confirming the heterogeneity of MAT.Recognizing the heterogeneity of MAT will bring unprecedented development to the related research of MAT,and provide a theoretical basis for the in-depth precise research on the specific functions of MAT in different intestinal segments.First,we investigated the heterogeneity of mouse MAT under physiological conditions.SMAT and LMAT were obtained from 10-12weeks old C57BL/6J mice for HE staining,immunofluorescence and toluidine blue staining.The morphological results showed that SMAT not only has smaller adipocytes but also contains more fat-associated lymphoid clusters than LMAT.Analysis paired mesenteric RNA-sequencing(RNA-seq)data indicated that the development related genes and B cell marker gene expression profiles have distinct differences.The enrichment pathway of different expression genes were concentrated in development,immune and inflammatory related pathways.Sn RNA-seq showed that significant differences in the proportions of cell types between SMAT and LMAT.And there are also differences in gene expression in various types of cells.Then,Adipocytes,stromal vascular fraction(SVF),and adipose-derived stem cell(ASC)were isolated from SMAT and LMAT for RT-q PCR analysis to verifying RNA-seq results.In addition,adipose-derived stem cells of LMAT exhibited higher adipogenic potential and lower proliferation rates than those of SMAT,flow cytometry analysis further confirmed that SMAT contains much more B cells than LMAT.To investigate the functional differences between SMAT and LMAT,we constructed MAT partial excision models by microsurgery and a transgenic mouse model of adipocyte specific ablation in LMAT.The results showed that MAT pruning would increase intestinal permeability,affect the immune system,and affect the intestinal ecological environment.What’s more,LMAT had a greater effect than SMAT,moreover,adipocytes in LMAT may play a critical role in maintaining local intestinal tight junction gene expression.Second,High fat diet(HFD)induced obese mice were constructed to investigate the heterogeneity of MAT in the pathological state of obesity and the influence of MATs by obesity.SMAT and LMAT were obtained from HFD mice or age-matched mice on normal diet(ND)mice for HE staining and flow cytometry.The results showed that the adipocyte volume in SMAT was always smaller than that in LMAT.And in obese state,the proportion of macrophages accumulated specifically in SMAT.Whereas,the proportion of B cells was significantly increased merely in LMAT.The proportion of CD4~+T cells increased in SMAT after obesity,but decreased in LMAT.Moreover,significantly enrichment of CD8~+T cells occurs only in LMAT of HFD mice compared to control mice.But there was little change in the small intestine after obesity.Furthermore,the proportion of CD8~+T cells in obese LMAT was significantly higher than that in obese SMAT.Bioinformatic analysis of MATs’RNA-seq data damastrated that the gene expression profile is also discrepant between obese SMAT and obese LMAT,and inflammatory and immune-related signaling pathways are significantly activated in obese MATs compared with physiological MATs.Third,SMAT and LMAT were obtained from relative healthy human for HE staining to observe the morphological structure.Paired mesenteric samples and adipocytes,SVF,ASC of SMAT and LMAT were analyzed by RT-q PCR.Flow cytometry and adipogenic differentiation also used to investigate the immunological characteristics and ASC function of SMAT and LMAT.Our data suggest that the differences between human SMAT and LMAT are similar to the heterogeneity of mouse MAT.We further performed HE staining and RT-q PCR detection of lipid metabolism-related gene expression in SMAT and LMAT from bariatric surgery patients,and found that the smaller adipocytes were more enriched in SMAT of these two MATs,and lipid decomposition and anabolism were more active in SMAT.Taken together,our studies uncovered that there is heterogeneity in the MAT of mice in both physiological and obese pathological states.LMAT has more obvious effects on the immune system and intestinal ecological environment.Obesity had different effects on SMAT and LMAT,and LMAT was more affected by obesity in terms of immune characteristics.In humans,MAT is also heterogeneous and comparable to mice,whether in a relatively normal physiological state or a pathological state of obesity.