肥胖是造成第二型糖尿病的危險因子，而青少年族群肥胖的盛行率日益增加，也提高了未來患有第二型糖尿病的風險。肥胖會導致胰島素的需求量上升，促使蘭氏小島分泌更多的胰島素以維持肥胖狀態下血糖的恆定，因此在肥胖患者會出現蘭氏小島增生的現象。蘭氏小島受到自主神精密集的支配以控制激素分泌，進而控制血糖。然而，當蘭氏小島因肥胖而增生時，神經網路會如何變化，以維持蘭氏小島的有效血糖調控目前仍有待探討。此外蘭氏小島所分泌的激素會進入小島內部的微血管網路輸送，而在肥胖的狀態下，微血管網路的變化也尚未被清楚的研究。
由於標準二維病理切片觀察的組織厚度在3-5 µm，無法針對蘭氏小島(50-200 µm)進行整體觀察。特別在增生之後的大型蘭氏小島(>250 µm)，病理切片觀察無法針對其微結構與血管神經組織進行整合分析。因此在本研究中，我們調整胰臟組織的光學性質，以組織透明溶液改變胰臟組織的折射率，並搭配共軛焦顯微鏡的三維影像擷取能力，觀察年輕肥胖db/db與ob/ob小鼠中蘭氏小島之三維組織顯微影像。我們的目標為釐清在年輕肥胖動物模型中，因蘭氏小島增生所誘發之微結構與血管神經組織的三維型態變化。
經由蒐集與分析三維胰臟組織影像，我們觀察到在db/db肥胖小鼠的蘭氏小島有微結構層面上的改變:原屬於外分泌組織的導管上皮組織，自發性的伸入屬於內分泌組織的蘭氏小島，形成在蘭氏小島外圍(peri-islet)與伸入蘭氏小島內部(intra-islet)的導管。在神經結構的層次上，我們發現了包圍蘭氏小島的導管會分泌神經生長因子招募交感神經聚集，使交感神經在肥胖小鼠的蘭氏小島中有較多的支配。我們更進一步地發現年輕肥胖小鼠的胰臟中有神經、蘭氏小島與導管所共同形成「神經-蘭氏小島-導管複合體(neuro-insular-ductal complex)」。在蘭氏小島之微血管變化的部分，我們觀察到年輕肥胖ob/ob小鼠有微血管內皮組織擴張的現象，此一內皮組織的病變伴隨著外被細胞(pericyte)密度的減少，並誘發外被細胞以鞘狀結構包覆微血管。而蘭氏小島也以此型變之後的血管結構，維持其內分泌組織之功能。
結論：在三維影像技術的輔助下，我們發現並確定蘭氏小島的微環境在年輕肥胖小鼠中的重塑現象。此一重塑現象包括蘭氏小島的增大、外分泌導管上皮組織伸入蘭氏小島、蘭氏小島交感神經增加、與微血管內皮組織與外被細胞的型變。這些胰臟導管與神經血管網絡在年輕肥胖動物模型所產生的變化，是傳統病理切片無法觀察到的現象，說明了以三維組織影像技術來研究蘭氏小島變化的價值。

Obesity and insulin resistance lead to islet hyperplasia. However, characterization of the associated remodeling of the islet microstructure and neurovascular networks remains a challenge task due to the difficulty of global visualization of the large islet (>200 m) and the neurovascular environment with high definition. Here, we adjusted the pancreatic optical property to examine the islets in the obese young db/db and ob/ob mice via penetrative 3-dimensional (3-D) microscopy. The 3-D images identify the unique “neuro-insular-ductal complex” in the pancreas, featuring the peri- and intra-islet ducts with prominent peri-ductal sympathetic innervation. In vascular characterization, we revealed a decreased population of the ob/ob islet pericytes, which adapt to ensheathing the dilated microvessels with hypertrophic processes. Based on the associated tissue remodeling, we propose a reactive islet microenvironment consisting of the endocrine cells, ductal epithelium, and neurovascular tissues in response to the metabolic challenge that experienced early in life.

1. Bray, G.A., et al., Relation of central adiposity and body mass index to the development of diabetes in the Diabetes Prevention Program. Am J Clin Nutr, 2008. 87(5): p. 1212-8.
2. Mokdad, A.H., et al., Prevalence of obesity, diabetes, and obesity-related health risk factors, 2001. JAMA, 2003. 289(1): p. 76-9.
3. Han, J.C., D.A. Lawlor, and S.Y. Kimm, Childhood obesity. Lancet, 2010. 375(9727): p. 1737-48.
4. Pulgaron, E.R. and A.M. Delamater, Obesity and type 2 diabetes in children: epidemiology and treatment. Curr Diab Rep, 2014. 14(8): p. 508.
5. Linnemann, A.K., M. Baan, and D.B. Davis, Pancreatic beta-cell proliferation in obesity. Adv Nutr, 2014. 5(3): p. 278-88.
6. Burris, R.E. and M. Hebrok, Pancreatic innervation in mouse development and beta-cell regeneration. Neuroscience, 2007. 150(3): p. 592-602.
7. Tang, S.C., et al., Plasticity of Schwann cells and pericytes in response to islet injury in mice. Diabetologia, 2013. 56(11): p. 2424-34.
8. Pagliuca, F.W. and D.A. Melton, How to make a functional beta-cell. Development, 2013. 140(12): p. 2472-83.
9. Butler, A.E., et al., Pancreatic duct replication is increased with obesity and type 2 diabetes in humans. Diabetologia, 2010. 53(1): p. 21-6.
10. Wardle, J., et al., Evidence for a strong genetic influence on childhood adiposity despite the force of the obesogenic environment. Am J Clin Nutr, 2008. 87(2): p. 398-404.
11. Guerre-Millo, M., B. Staels, and J. Auwerx, New insights into obesity genes. Diabetologia, 1996. 39(12): p. 1528-31.
12. Chagnon, Y.C. and C. Bouchard, Genetics of obesity: advances from rodent studies. Trends Genet, 1996. 12(11): p. 441-4.
13. Jequier, E., Leptin signaling, adiposity, and energy balance. Ann N Y Acad Sci, 2002. 967: p. 379-88.
14. Wang, B., P.C. Chandrasekera, and J.J. Pippin, Leptin- and leptin receptor-deficient rodent models: relevance for human type 2 diabetes. Curr Diabetes Rev, 2014. 10(2): p. 131-45.
15. Fu, Y.Y., et al., Three-dimensional optical method for integrated visualization of mouse islet microstructure and vascular network with subcellular-level resolution. J Biomed Opt, 2010. 15(4): p. 046018.
16. Lindstrom, P., beta-cell function in obese-hyperglycemic mice [ob/ob Mice]. Adv Exp Med Biol, 2010. 654: p. 463-77.
17. Fasshauer, M. and R. Paschke, Regulation of adipocytokines and insulin resistance. Diabetologia, 2003. 46(12): p. 1594-603.
18. Petersen, K.F. and G.I. Shulman, Etiology of insulin resistance. Am J Med, 2006. 119(5 Suppl 1): p. S10-6.
19. Kahn, B.B. and J.S. Flier, Obesity and insulin resistance. J Clin Invest, 2000. 106(4): p. 473-81.
20. Hull, R.L., et al., Dietary-fat-induced obesity in mice results in beta cell hyperplasia but not increased insulin release: evidence for specificity of impaired beta cell adaptation. Diabetologia, 2005. 48(7): p. 1350-8.
21. Bock, T., B. Pakkenberg, and K. Buschard, Increased islet volume but unchanged islet number in ob/ob mice. Diabetes, 2003. 52(7): p. 1716-22.
22. Rodriguez-Diaz, R., et al., Innervation patterns of autonomic axons in the human endocrine pancreas. Cell Metab, 2011. 14(1): p. 45-54.
23. Winkler, E.A., R.D. Bell, and B.V. Zlokovic, Central nervous system pericytes in health and disease. Nat Neurosci, 2011. 14(11): p. 1398-405.
24. Dai, C., et al., Pancreatic islet vasculature adapts to insulin resistance through dilation and not angiogenesis. Diabetes, 2013. 62(12): p. 4144-53.
25. Winer, S., et al., Autoimmune islet destruction in spontaneous type 1 diabetes is not beta-cell exclusive. Nat Med, 2003. 9(2): p. 198-205.
26. Teitelman, G., et al., Islet injury induces neurotrophin expression in pancreatic cells and reactive gliosis of peri-islet Schwann cells. J Neurobiol, 1998. 34(4): p. 304-18.
27. Vetere, A., et al., Targeting the pancreatic beta-cell to treat diabetes. Nat Rev Drug Discov, 2014. 13(4): p. 278-89.
28. Chen, H., et al., Evidence that the diabetes gene encodes the leptin receptor: identification of a mutation in the leptin receptor gene in db/db mice. Cell, 1996. 84(3): p. 491-5.
29. Ingalls, A.M., M.M. Dickie, and G.D. Snell, Obese, a new mutation in the house mouse. J Hered, 1950. 41(12): p. 317-8.
30. Lindstrom, P., The physiology of obese-hyperglycemic mice [ob/ob mice]. ScientificWorldJournal, 2007. 7: p. 666-85.
31. Fekete, C., et al., alpha-Melanocyte-stimulating hormone is contained in nerve terminals innervating thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus and prevents fasting-induced suppression of prothyrotropin-releasing hormone gene expression. J Neurosci, 2000. 20(4): p. 1550-8.
32. Elias, C.F., et al., Leptin differentially regulates NPY and POMC neurons projecting to the lateral hypothalamic area. Neuron, 1999. 23(4): p. 775-86.
33. Yeh, V.V.T.R.K.W.A.T., Optical Clearing of Tissues and Cells. Journal of Biomedical Optics, 2008. 13(2).
34. Tuchin, V.V., R.K. Wang, and A.T. Yeh, Optical clearing of tissues and cells. J Biomed Opt, 2008. 13(2): p. 021101.
35. Xu, X. and R.K. Wang, Synergistic effect of hyperosmotic agents of dimethyl sulfoxide and glycerol on optical clearing of gastric tissue studied with near infrared spectroscopy. Phys Med Biol, 2004. 49(3): p. 457-68.
36. Parra, S.G., et al., Multiphoton microscopy of cleared mouse brain expressing YFP. J Vis Exp, 2012(67): p. e3848.
37. Oldham, M., et al., Optical clearing of unsectioned specimens for three-dimensional imaging via optical transmission and emission tomography. J Biomed Opt, 2008. 13(2): p. 021113.
38. Hama, H., et al., Scale: a chemical approach for fluorescence imaging and reconstruction of transparent mouse brain. Nat Neurosci, 2011. 14(11): p. 1481-8.
39. Conchello, J.A. and J.W. Lichtman, Optical sectioning microscopy. Nat Methods, 2005. 2(12): p. 920-31.
40. Tang, S.C., S.J. Peng, and H.J. Chien, Imaging of the islet neural network. Diabetes Obes Metab, 2014. 16 Suppl 1: p. 77-86.
41. Toma, H., et al., Nerve growth factor expression is up-regulated in the rat model of L-arginine-induced acute pancreatitis. Gastroenterology, 2000. 119(5): p. 1373-81.
42. Street, C.N., et al., Islet graft assessment in the Edmonton Protocol: implications for predicting long-term clinical outcome. Diabetes, 2004. 53(12): p. 3107-14.
43. Reichert, M. and A.K. Rustgi, Pancreatic ductal cells in development, regeneration, and neoplasia. J Clin Invest, 2011. 121(12): p. 4572-8.
44. Talchai, C., et al., Genetic and biochemical pathways of beta-cell failure in type 2 diabetes. Diabetes Obes Metab, 2009. 11 Suppl 4: p. 38-45.
45. Hellstrom, M., et al., Lack of pericytes leads to endothelial hyperplasia and abnormal vascular morphogenesis. J Cell Biol, 2001. 153(3): p. 543-53.
46. Xiao, X., et al., Pancreatic duct cells as a source of VEGF in mice. Diabetologia, 2014. 57(5): p. 991-1000.
47. Borden, P., et al., Sympathetic innervation during development is necessary for pancreatic islet architecture and functional maturation. Cell Rep, 2013. 4(2): p. 287-301.