The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice

<p>Abstract</p> <p>Background</p> <p>Obesity and insulin resistance are two major risk factors underlying the metabolic syndrome. The development of these metabolic disorders is frequently studied, but mainly in liver, skeletal muscle, and adipose tissue. To gain more insight in the role of the small intestine in development of obesity and insulin resistance, dietary fat-induced differential gene expression was determined along the longitudinal axis of small intestines of C57BL/6J mice.</p> <p>Methods</p> <p>Male C57BL/6J mice were fed a low-fat or a high-fat diet that mimicked the fatty acid composition of a Western-style human diet. After 2, 4 and 8 weeks of diet intervention small intestines were isolated and divided in three equal parts. Differential gene expression was determined in mucosal scrapings using Mouse genome 430 2.0 arrays.</p> <p>Results</p> <p>The high-fat diet significantly increased body weight and decreased oral glucose tolerance, indicating insulin resistance. Microarray analysis showed that dietary fat had the most pronounced effect on differential gene expression in the middle part of the small intestine. By overrepresentation analysis we found that the most modulated biological processes on a high-fat diet were related to lipid metabolism, cell cycle and inflammation. Our results further indicated that the nuclear receptors Ppars, Lxrs and Fxr play an important regulatory role in the response of the small intestine to the high-fat diet. Next to these more local dietary fat effects, a secretome analysis revealed differential gene expression of secreted proteins, such as Il18, Fgf15, Mif, Igfbp3 and Angptl4. Finally, we linked the fat-induced molecular changes in the small intestine to development of obesity and insulin resistance.</p> <p>Conclusion</p> <p>During dietary fat-induced development of obesity and insulin resistance, we found substantial changes in gene expression in the small intestine, indicating modulations of biological processes, especially related to lipid metabolism. Moreover, we found differential expression of potential signaling molecules that can provoke systemic effects in peripheral organs by influencing their metabolic homeostasis. Many of these fat-modulated genes could be linked to obesity and/or insulin resistance. Together, our data provided various leads for a causal role of the small intestine in the etiology of obesity and/or insulin resistance.</p

Muscarinic M3-receptors mediate cholinergic synergism of mitogenesis in airway smooth muscle

Muscarinic receptor agonists have been considered to act syner- and cytoskeletal reorganization has been proposed (4–6). gistically in combination with growth facors on airway smooth Furthermore, M2-receptors may stimulate nonselective catmuscle growth. Characterization of the proliferative responses ion channels through Gi/G(o) proteins, resulting in a rise in and of the receptor subtype(s) involved has not yet been stud- [Ca2�]i (7). ied. Therefore, we investigated mitogenesis induced by stimula- Muscarinic receptor agonists have been reported to be tion of muscarinic receptors, alone and in combination with mitogenic for human ASM cells, though at most modestly, stimulation by platelet-derived growth factor (PDGF). For this and to respond synergistically in combination with growth purpose, [ 3H]thymidine-incorporation was measured at differfactors (8, 9). Although carbachol-induced mitogenesis has ent culture stages in bovine tracheal smooth muscle cells. Funcbeen reported to be pertussis toxin (PTX)-sensitive (8, 10), tional muscarinic M3-receptors, as measured by formation of suggesting a role for the Gi-protein–coupled muscarinic M2inositol phosphates, were present in unpassaged cells, but were receptor, measurements were performed using human AS

Bradykinin augments EGF-induced airway smooth muscle proliferation by activation of conventional protein kinase C isoenzymes

This study aims to investigate the effects of bradykinin, alone and in combination with growth factors on proliferation of cultured bovine tracheal smooth muscle cells. Bradykinin did not induce mitogenic responses by itself, but concentration-dependently augmented growth factor-induced [H-3]thymidine incorporation and cell proliferation. The bradykinin effect was mediated by bradykinin B? receptors, and not dependent on cyclo-oxygenase. Bradykinin-induced synergism with epidermal growth factor (EGF) could be suppressed by the protein kinase C (PKC) inhibitors GF 109203X (Bisindolylmaleimide 1; specific for conventional and novel PKCs) and Go 6976 (12-(2-Cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo(2,3-a)pyrrolo(3,4-c)-carbazole; specific for conventional PKCs). In addition, sole activation of PKC using Phorbol 12-myristate 13-acetate (PMA) was sufficient for a synergistic interaction with EGF. In contrast to bradykinin however, PMA was mitogenic by itself which was not at all affected by Go 6976, but abolished by GF 109203X. Bradykinin transiently activated the p42/p44 MAP kinase pathway, whereas PMA-induced activation of p42/p44 mitogen activated protein (MAP) kinase was sustained. Neither the combination of bradykinin and EGF nor that of PMA and EGF induced synergistic activation of p42/p44 MAP kinase, however. These results show that bradykinin B, receptor-stimulation augments growth factor-induced mitogenic responses of airway smooth muscle cells through activation of conventional PKC isozymes. In addition, the results show that PKC isozyme-specificity underlies stimulus-specific differences in mitogenic capacity for bradykinin and PMA. Published by Elsevier B.V

The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice-1

N at least one week of diet intervention are plotted (grey bars). Among those are genes that were consistently up- (I) or down-regulated (D) on a high-fat diet (white and black bars, respectively).<p><b>Copyright information:</b></p><p>Taken from "The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice"</p><p>http://www.biomedcentral.com/1755-8794/1/14</p><p>BMC Medical Genomics 2008;1():14-14.</p><p>Published online 6 May 2008</p><p>PMCID:PMC2396659.</p><p></p

The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice-4

Ng Ki67-specific antibodies. Besides the villus length (A) and total number of villus cells (B), also the number of Ki67-positive cells per villus (C) were determined. Per mouse, 15 villi were counted and the mean values were calculated. * p < 0.05, # p = 0.07. LF = low-fat diet, HF = high-fat diet.<p><b>Copyright information:</b></p><p>Taken from "The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice"</p><p>http://www.biomedcentral.com/1755-8794/1/14</p><p>BMC Medical Genomics 2008;1():14-14.</p><p>Published online 6 May 2008</p><p>PMCID:PMC2396659.</p><p></p

The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice-7

Ly expressed genes with fold changes < -1.5 and > +1.5 in at least one week of diet intervention. Red and green boxes indicate a significant up- and down-regulation, respectively. NC = no change, A = absent.<p><b>Copyright information:</b></p><p>Taken from "The role of the small intestine in the development of dietary fat-induced obesity and insulin resistance in C57BL/6J mice"</p><p>http://www.biomedcentral.com/1755-8794/1/14</p><p>BMC Medical Genomics 2008;1():14-14.</p><p>Published online 6 May 2008</p><p>PMCID:PMC2396659.</p><p></p