P 5.7. Substance P promotes viability in human mesenteric preadipocytes through proliferative and anti-apoptotic pathways

Background and aims. It is becoming increasingly clear that white adipose tissue (WAT) is actively involved in the regulation of immunity and inflammation and in the pathogenesis of Inflammatory Bowel Disease (IBD), where fat hypertrophy, proliferation and wrapping of the bowel correlates with the extent of transmural inflammation. We recently reported that human mesenteric preadipocytes express a functional neurokinin-1 receptor (NK-1R) for substance P (SP). We also reported increased expression of cytokines and NK-1R in the mesenteric fat during experimental colitis, indicating that mesenteric depots may participate in intestinal inflammatory responses via SP-NK-1R related inflammatory pathways. Here we examined the hypothesis that SP directly enhances proliferation of human mesenteric preadipocytes and examined the mechanism(s) of this response. Methods. Preadipocytes were isolated from mesenteric fat (colonic epiploices) biopsied during gastric bypass surgery using methods to assure culture purity. MTS, BrdU, and TUNEL assays, as well as Western blot analyses were used to delineate proliferative and anti-apoptotic SP responses. Results. SP (10 super(-7) M) increased mesenteric preadipo-cyte cell viability (MTS assay), and proliferation (BrdU assay) (by similar to 20%), and, time-dependently (15-30 min), induced Akt, EGFR, alpha5-beta3 integrin and PKC theta phosphorylation (Western blot). Inhibition of Akt and PKC-theta activation with pharmacologic antagonists significantly decreased SP-induced prea-dipocyte proliferation (BrdU assay) (by similar to 20%). Fas is a well-known initiator of apoptotic pathways when occupied by its ligand (FasL). We found that exposure of FasL (100 mu M) to preadipocytes induced nuclear DNA fragmentation (TUNEL assay), while co-treatment with SP reduced the number of apoptotic cells (by 30-40%). Further, SP (10 super(-7) M) time-dependently stimulated expression of cyclin D1, a major cell cycle inducer. SP also induced 4E-BP expression, and phosphorylation of S6kinase, molecules that increase the efficiency of protein translation. Conclusions. SP increases viability, reduces apoptosis, stimulates proliferation through cell cycle upregulation and increases the efficiency of protein translation in human mesenteric preadipocytes. We speculate that SP-induced proliferative and anti-apoptotic pathways in fat depots may contribute to the creeping fat pheno-type, and thus the inflammation, characteristic of Cro-hn's Disease.