Brimming with b's. Newfound cells in the pancreas give rise to neurons (red) and insulin-producing b cells (green).

每年的11月14日是世界糖尿病日，糖尿病在全世界發(fā)病率相當(dāng)高，現(xiàn)在全球糖尿病病人已超過1.7億，且每年都在快速增長(zhǎng),。糖尿病是繼心血管和腫瘤之后的第三大“健康殺手”,。

我們的血液中含有一定濃度的糖（血糖），為人體提供能量,。若血糖濃度過高或過低，就會(huì)引起疾病,。而保持血糖濃度的功臣就是胰島素,，它來源于胰腺，由胰島內(nèi)的一種叫β細(xì)胞產(chǎn)生,，并釋放入血液,。

近幾年,，1型糖尿病患者在逐年增加,，越來越年輕化,。1型糖尿病是一種自身免疫性疾病,，由于體內(nèi)多種T細(xì)胞（CD4＋細(xì)胞毒T淋巴細(xì)胞和CD8＋細(xì)胞毒T淋巴細(xì)胞）對(duì)胰島β細(xì)胞抗原發(fā)生反應(yīng)，引發(fā)白細(xì)胞浸潤(rùn)，從而產(chǎn)生炎性細(xì)胞因子和自由基,，導(dǎo)致胰島β細(xì)胞死亡,。胰島素水平降低，導(dǎo)致血糖濃度升高,。

因此,，對(duì)如何增加胰島β細(xì)胞數(shù)量的研究就成了研究者們致力的難題,。剛開始，研究者們就考慮到了利用胰腺干細(xì)胞可能會(huì)分化為β細(xì)胞,，但研究發(fā)現(xiàn)β細(xì)胞是由其他類型的β細(xì)胞產(chǎn)生的,，因此就停止了對(duì)胰腺干細(xì)胞的進(jìn)一步研究。

今年8月24日Nature說,，胰腺干細(xì)胞很有可能產(chǎn)生大量的β細(xì)胞,。一個(gè)研究小組在成年小鼠胰腺內(nèi)鑒定了一組細(xì)胞群可以分化產(chǎn)生大量的β細(xì)胞。多倫多大學(xué)的Derek試驗(yàn)小組用促進(jìn)神經(jīng)干細(xì)胞生長(zhǎng)的傳統(tǒng)培養(yǎng)基浸洗這一群細(xì)胞,，發(fā)現(xiàn)每5000個(gè)細(xì)胞中就由一個(gè)細(xì)胞能夠迅速地繁殖成一組細(xì)胞群,，且這群細(xì)胞具有不同于典型細(xì)胞的特性,。

這群細(xì)胞還有一個(gè)重要特點(diǎn):它們能夠很自然地發(fā)育成不同的組織。當(dāng)改變培養(yǎng)基且促進(jìn)細(xì)胞分化時(shí),，可以產(chǎn)生包括β細(xì)胞在內(nèi)的大量的多種類型的胰腺細(xì)胞,。若在培養(yǎng)基中加入糖，β細(xì)胞能夠釋放出高于平常兩倍的荷爾蒙,，這就是體內(nèi)β細(xì)胞通過釋放胰島素對(duì)糖作出反應(yīng)。

Derek試驗(yàn)小組在8月22日的Nature生物技術(shù)上發(fā)表了他們的研究?jī)?nèi)容,。但他們還沒有證明這一群細(xì)胞就是胰腺干細(xì)胞，不過這已經(jīng)在糖尿病長(zhǎng)期治療的路上又邁了一步,。不管怎樣,，這都是一個(gè)很大的突破,，具有重大的意義,。

Clonal identification of multipotent precursors from adult mouse pancreas that generate neural and pancreatic lineages
The clonal isolation of putative adult pancreatic precursors has been an elusive goal of researchers seeking to develop cell replacement strategies for diabetes. We report the clonal identification of multipotent precursor cells from the adult mouse pancreas. The application of a serum-free, colony-forming assay to pancreatic cells enabled the identification of precursors from pancreatic islet and ductal populations. These cells proliferate in vitro to form clonal colonies that coexpress neural and pancreatic precursor markers. Upon differentiation, individual clonal colonies produce distinct populations of neurons and glial cells, pancreatic endocrine -, - and -cells, and pancreatic exocrine and stellate cells. Moreover, the newly generated -like cells demonstrate glucose-dependent Ca2+ responsiveness and insulin release. Pancreas colonies do not express markers of embryonic stem cells, nor genes suggestive of mesodermal or neural crest origins. These cells represent a previously unidentified adult intrinsic pancreatic precursor population and are a promising candidate for cell-based therapeutic strategies.

 
 
Figure 1. PMP colonies are formed from progenitors present in adult pancreatic islet and duct cell isolates, and express markers characteristic of both neural and pancreatic precursors.
(a) The frequency of PMP colonies from pancreatic islet and duct cell isolates is similar. The data are expressed as the mean number of colonies (+s.e.m.; n = 14 independent experiments) formed per 10,000 cells plated. Islet and ductal cell isolates do not contain significantly different numbers of PMPs (P > 0.05). (b) Light micrograph of a PMP colony. Scale bar, 50 m. (c) Light micrograph of a neurosphere. Scale bar, 50 m. (d) RT-PCR for neural and pancreatic precursor markers. The numbers on the left represent the number of individual PMP colonies that expressed the corresponding mRNA out of the total number of colonies tested by RT-PCR analysis. Only single colony RNA isolates that were found to express -actin were considered. Note that positive control (+) bands (see Supplementary Methods online for a complete list of tissue positive controls) appear brighter because of the greater amount of starting RNA in comparison to single PMP colonies. Ngn3 was not expressed at detectable levels in individual PMP colonies. However, Ngn3 mRNA was detected in a sample of five pooled (P) PMP colonies, suggesting that it is present in differentiated PMP colonies but perhaps at low levels. (e) Single cells from dissociated PMP colonies coexpress PDX-1 (red) and nestin (green) as seen by immunostaining. Note that the nucleus in this fluorescence micrograph is labeled with both DAPI (blue) and PDX-1, giving it a pink appearance. The white arrows indicate double-positive cells.
 

 
 
Figure 2. PMP colonies generate all three major neural cell lineages.
(a,b) When individual PMP colonies were differentiated, they were found to generate 3-tubulin+ neurons (red), occasionally forming large neuronal networks as shown in b. Scale bars: 50 m, a; 200 m, b. (c–e) 3-tubulin+ neurons that were generated by PMPs (c) coexpressed the more mature neuronal marker MAP2 (green) (d, and overlay e), thus confirming their neuronal identity. Scale bar, 50 m. (f,g) PMPs generated GFAP+ astrocytes (green). Scale bars, 20 m. (h) O4+ oligodendrocytes also were generated by PMP colonies (green). Scale bar, 20 m. All nuclei were counterstained with DAPI (blue) for purposes of quantification. Refer to Table 1 for relative proportions of each neural cell type produced by PMPs. (i) RT-PCR analyses confirm the presence of mRNA for neuronal and glial makers. Individual differentiated clonal PMP colonies all expressed detectable levels of 3-tubulin and MAP2, but not GFAP. However, GFAP mRNA was detected in a sample of five pooled (P) PMP colonies, suggesting that it is present in differentiated PMP colonies but at lower levels. This is in accordance with the relatively lower percentages of glial than neuronal progeny determined by immunocytochemistry (Table 1). Only single colony RNA isolates that were found to express -actin were considered. Note that positive control (+) bands appear brighter because of the greater amount of starting RNA in comparison to single PMP colonies.
 

 
 
Figure 3. Progeny from two distinct embryonic primary germ layers are generated by single, clonally derived PMPs that are present in islet and ductal cell isolates.
(a,b) Upon differentiation, single islet- (a) and ductal- (b) derived PMP colonies generated both 3-tubulin+ neurons (red) and insulin+ or C-peptide+ -cells (green). Note that although only one combination of 3-tubulin and insulin or C-peptide is shown for each of islet and ductal PMP colonies, both islet and ductal PMP colonies contained insulin+ and C-peptide+ cells in combination with 3-tubulin. The white arrows indicate insulin+ and C-peptide+ cells. Scale bars, 50 m. (c,d) To confirm that the insulin+ cells represented -cells and were generating insulin protein de novo, differentiated colonies were colabeled with antibodies against PDX-1 and C-peptide (c) or insulin (d). These micrographs illustrate single colonies with cells positive for both PDX-1 (red) and C-peptide or insulin (green). Scale bars, 25 m. (e,f) Insulin+ cells (red) all coexpress C-peptide (green) as illustrated by the merged field (yellow) (e) and C-peptide+ cells (green) all coexpress Glut2 (red) as shown in the merged field (yellow) (f). Scale bars, 50 m. Although only one example of each is illustrated, both islet- and ductal-derived PMP colony progeny exhibited these patterns. In all micrographs nuclei have been counterstained with DAPI for purposes of quantification. Note that in c and d, nuclei appear pink because of the colocalization of DAPI and PDX-1. Refer to Table 1 for the proportion of cells with -cell characteristics produced by single PMPs. (g) RT-PCR analyses confirm that single clonal differentiated PMP colonies express many characteristic islet/-cell markers. Only single-colony RNA isolates that were found to express -actin were considered. Note that positive control (+) bands appear brighter because of the greater amount of starting RNA in comparison to single PMP colonies.
 

 
 
Figure 4. Insulin+ cells generated de novo from PMPs demonstrate glucose-stimulated Ca2+ responses and glucose-stimulated insulin release.
(a,b) Bright-field and fluorescence micrographs demonstrating YFP+ cells from AdRIP2EYFP-infected islet- (a) and ductal- (b) derived differentiated PMP colonies. Scale bars, 50 m. (c,d) Calcium traces for islet- (c) and ductal- (d) derived PMP colonies demonstrating glucose-stimulated [Ca2+]i responses, which were augmented by the addition of either GLP-1 or TEA, respectively. The addition of the voltage-dependent Ca2+ channel blocker verapamil (VER) returned the [Ca2+]i to basal levels. Shown above the Ca2+ trace are fluorescence micrographs of YFP+ cells and the ratiometric Fura images (pseudocolored according to the scale shown to the right) corresponding to the numbered time points on the trace. Note that in (c), the YFP- cell does not demonstrate a glucose response. These Ca2+ traces are representative of at least five independent experiments. Note that GLP-1 and TEA produced similar responses in both islet- and ductal-derived PMP progeny, although only one example is depicted for each in the [Ca2+]i traces shown. (e,f) Demonstration of increased insulin release by islet- (e) and ductal- (f) derived PMP colonies in response to high glucose (HG) alone or with the addition of GLP-1, TEA or to Carbachol (Carb) alone. The addition of verapamil (VER) abolished the glucose-stimulated insulin release. These data were generated from three to four independent experiments.
 
 

 
 
Figure 5. PMP colonies generate multiple islet endocrine subtypes and exocrine cells.
(a) When individual PMP colonies were differentiated, they were found to generate glucagon+ -cells (green) and somatostatin+ -cells (red). Cells coexpressing these hormones were never observed. Note that this field depicts only a portion of a larger differentiated PMP colony. The arrangement of endocrine cells in these colonies is suggestive of either multiple divisions of one local progenitor cell within the colony, or that there may be a type of 'community effect' whereby endocrine cells of similar phenotype tend to differentiate in close contact with each other. (b) PMP colonies generated cells characteristic of the exocrine compartment of the pancreas, amylase+ acinar cells. (c-d) A large proportion of the cells generated by individual clonal PMP colonies were large, flat cells with characteristic morphology and arrangement that expressed SMA (c) and nestin (d), typical of pancreatic stellate cells. All nuclei were counterstained with DAPI (blue) for purposes of quantification. Refer to Table 1 for relative proportions of each pancreatic cell type produced by PMPs. Scale bars, 25 m.
 

 
 
Figure 6. PMPs are not general endodermal or mesodermal precursors, nor are they ES cell–like stem cells or neural crest precursors.
(a) Individual PMP colonies were assayed by RT-PCR for the presence of the early endoderm markers GATA-4 and HNF3. None of the colonies tested expressed either marker, suggesting that PMPs are not generalized endodermal precursors. (b) mRNA for Oct4 and Nanog, proteins encoded by genes characteristic of ES cells, was not detected in any of the single clonal PMP colonies assayed, suggesting that PMPs are not ES cell–like pluripotent stem cells. (c) Brachyury and GATA-1, markers of mesodermal tissue, were not detected by RT-PCR in PMP colonies, suggesting that PMPs are not of mesodermal origin. (d) Clonal PMP colonies do not exhibit a characteristic neural crest progenitor profile. Although PMP colonies do express Slug and Snail, and a proportion of them express detectable levels of p75, they do not express many other characteristic neural crest markers including Pax3, Twist, Sox10 or Wnt1 by RT-PCR analysis. Only single colony RNA isolates that were found to express -actin were considered. Note that positive control (+) bands appear brighter because of the greater amount of starting RNA in comparison to single PMP colonies.