Amelioration of High Fat Diet-induced Glucose Intolerance by Blockade of Smad4 in Pancreatic Beta-Cells

Abstract

Background: In this study, we investigated whether Smad4 signaling is involved in the regulation of beta-cell function using a high fat diet (HFD)-induced obesity mouse model.

Methods: Beta-cell-specific Smad4-knockout mice (Smad4^-/-RIP-Cre⁺; β-Smad4KO) were generated by mating Smad4 (flox/flox) mice with rat insulin promoter (RIP)-Cre mice. Mice were fed a HFD beginning at 6 weeks of age for 16 weeks. Body weight, food intake, fasting and fed glucose levels, and glucose and insulin tolerance were measured.

Results: The expression of Smad4 mRNA was significantly decreased in the islets of β-Smad4KO mice. In wild-type mice, Smad4 mRNA was significantly decreased at 18 weeks of age as compared with 8 weeks of age. On a regular chow diet, β-Smad4KO mice showed no differences in body weight, fed and fasting blood glucose levels, and glucose tolerance compared with wild-type mice. When fed a HFD, body weight gain was significantly reduced in β-Smad4KO mice as compared with wild-type mice, although the amount of food intake was not different. During the HFD, fed and fasting blood glucose levels, glucose stimulated insulin secretion, disposition index and glucose tolerance were significantly improved in β-Smad4KO mice as compared with wild-type mice. However, insulin tolerance tests showed no differences between the 2 groups.

Conclusion: Inhibition of Smad4 in beta-cells conferred mild but significant improvements in glucose levels and glucose tolerance in HFD-induced obese mice. Therefore, regulation of Smad4 expression may be one of the mechanisms regulating physiological expansion of beta-cells during development of type 2 diabetes.

Key words

Type 2 diabetes - pancreatic beta-cell - high-fat diet-induced obesity - beta-cell-specific Smad4-knockout mice - transforming growth factor-β - smad4 - glucose tolerance

^* These authors contributed equally to this work.

• References

• 1 Kaiser N, Leibowitz G. Failure of beta-cell adaptation in type 2 diabetes: Lessons from animal models. Front Biosci (Landmark Ed) 2009; 14: 1099-1115
• 2 Prentki M, Nolan CJ. Islet beta cell failure in type 2 diabetes. The Journal of clinical investigation 2006; 116: 1802-1812
• 3 Goulley J, Dahl U, Baeza N et al. BMP4-BMPR1A signaling in beta cells is required for and augments glucose-stimulated insulin secretion. Cell metabolism 2007; 5: 207-219.
• 4 Florio P, Luisi S, Marchetti P et al. Activin A stimulates insulin secretion in cultured human pancreatic islets. Journal of endocrinological investigation 2000; 23: 231-234
• 5 Xu X, Browning VL, Odorico JS. Activin, BMP and FGF pathways cooperate to promote endoderm and pancreatic lineage cell differentiation from human embryonic stem cells. Mechanisms of development 2011; 128: 412-427
• 6 Brown ML, Schneyer AL. Emerging roles for the TGFbeta family in pancreatic beta-cell homeostasis. Trends in endocrinology and metabolism: TEM 2010; 21: 441-448
• 7 Lin HM, Lee JH, Yadav H et al. Transforming growth factor-beta/Smad3 signaling regulates insulin gene transcription and pancreatic islet beta-cell function. The Journal of biological chemistry 2009; 284: 12246-12257
• 8 Gordon KJ, Blobe GC. Role of transforming growth factor-beta superfamily signaling pathways in human disease. Biochimica et biophysica acta 2008; 1782: 197-228
• 9 Sekine N, Yamashita N, Kojima I et al. Bimodal effect of transforming growth factor-beta on insulin secretion in MIN6 cells. Diabetes research and clinical practice 1994; 26: 7-14
• 10 Suzuki T, Dai P, Hatakeyama T et al. TGF-beta Signaling Regulates Pancreatic beta-Cell Proliferation through Control of Cell Cycle Regulator p27 Expression. Acta histochemica et cytochemica 2013; 46: 51-58
• 11 Miralles F, Battelino T, Czernichow P et al. TGF-beta plays a key role in morphogenesis of the pancreatic islets of Langerhans by controlling the activity of the matrix metalloproteinase MMP-2. The Journal of cell biology 1998; 143: 827-836
• 12 Brorson M, Hougaard DM, Nielsen JH et al. Expression of SMAD signal transduction molecules in the pancreas. Histochemistry and cell biology 2001; 116: 263-267
• 13 Cui Y, Huang L, Elefteriou F et al. Essential role of STAT3 in body weight and glucose homeostasis. Molecular and cellular biology 2004; 24: 258-269
• 14 Gannon M, Shiota C, Postic C et al. Analysis of the Cre-mediated recombination driven by rat insulin promoter in embryonic and adult mouse pancreas. Genesis 2000; 26: 139-142
• 15 Bergman RN, Ader M, Huecking K et al. Accurate assessment of beta-cell function: the hyperbolic correction. Diabetes 2002; 51 (Suppl. 01) S212-220
• 16 Roberts AB, Flanders KC, Heine UI et al. Transforming growth factor-beta: multifunctional regulator of differentiation and development. Philosophical transactions of the Royal Society of London Series B, Biological sciences 1990; 327: 145-154
• 17 Massague J, Blain SW, Lo RS. TGFbeta signaling in growth control, cancer, and heritable disorders. Cell 2000; 103: 295-309
• 18 Shi Y, Massague J. Mechanisms of TGF-beta signaling from cell membrane to the nucleus. Cell 2003; 113: 685-700
• 19 Nomura M, Zhu HL, Wang L et al. SMAD2 disruption in mouse pancreatic beta cells leads to islet hyperplasia and impaired insulin secretion due to the attenuation of ATP-sensitive K+ channel activity. Diabetologia 2014; 57: 157-166 DOI:
• 20 Tan CK, Leuenberger N, Tan MJ et al. Smad3 deficiency in mice protects against insulin resistance and obesity induced by a high-fat diet. Diabetes 2011; 60: 464-476
• 21 Tan CK, Chong HC, Tan EH et al. Getting ‘Smad’ about obesity and diabetes. Nutrition & diabetes 2012; 2: e29 2012; 2: e29
• 22 Yadav H, Quijano C, Kamaraju AK et al. Protection from obesity and diabetes by blockade of TGF-beta/Smad3 signaling. Cell metabolism 2011; 14: 67-79
• 23 Tsurutani Y, Fujimoto M, Takemoto M et al. The roles of transforming growth factor-beta and Smad3 signaling in adipocyte differentiation and obesity. Biochemical and biophysical research communications 2011; 407: 68-73
• 24 Yang X, Li C, Xu X et al. The tumor suppressor SMAD4/DPC4 is essential for epiblast proliferation and mesoderm induction in mice. Proceedings of the National Academy of Sciences of the United States of America 1998; 95: 3667-3672
• 25 Gong Z, Muzumdar RH. Pancreatic function, type 2 diabetes, and metabolism in aging. International journal of endocrinology 2012; 2012 320482
• 26 Drott CJ, Olerud J, Emanuelsson H et al. Sustained beta-cell dysfunction but normalized islet mass in aged thrombospondin-1 deficient mice. PloS one 2012; 7: e47451
• 27 Dalboge LS, Almholt DL, Neerup TS et al. Characterisation of age-dependent beta cell dynamics in the male db/db mice. PloS one 2013; 8: e82813
• 28 Araujo EP, De Souza CT, Ueno M et al. Infliximab restores glucose homeostasis in an animal model of diet-induced obesity and diabetes. Endocrinology 2007; 148: 5991-5997
• 29 Tsuboyama-Kasaoka N, Shozawa C, Sano K et al. Taurine (2-aminoethanesulfonic acid) deficiency creates a vicious circle promoting obesity. Endocrinology 2006; 147: 3276-3284
• 30 Winzell MS, Magnusson C, Ahren B. Temporal and dietary fat content-dependent islet adaptation to high-fat feeding-induced glucose intolerance in mice. Metabolism: clinical and experimental 2007; 56: 122-128
• 31 Choudhury AI, Heffron H, Smith MA et al. The role of insulin receptor substrate 2 in hypothalamic and beta cell function. The Journal of clinical investigation 2005; 115: 940-950
• 32 Cocolakis E, Dai M, Drevet L et al. Smad signaling antagonizes STAT5-mediated gene transcription and mammary epithelial cell differentiation. The Journal of biological chemistry 2008; 283: 1293-1307
• 33 Zhou YX, Zhao M, Li D et al. Cerebellar deficits and hyperactivity in mice lacking Smad4. The Journal of biological chemistry 2003; 278: 42313-42320
• 34 Lee JY, Ristow M, Lin X et al. RIP-Cre revisited, evidence for impairments of pancreatic beta-cell function. The Journal of biological chemistry 2006; 281: 2649-2653