Cell Cycle Regulators in Pancreatic Development and Disease

在糖尿病中，产生胰岛素的胰岛β细胞被破坏、严重耗尽或功能受损。因此，更换功能性的β细胞团将促进临床糖尿病的治疗。我们以前已经证明了CDK4在调节β细胞质量中的重要性。CDK4基因缺陷的小鼠表现出β细胞发育不良并发展为糖尿病，而表达活性CDK4R24C激酶的小鼠则观察到β细胞增殖。虽然β细胞复制似乎是导致β细胞数量增加的主要机制，但相当多的证据也支持胰腺导管上皮在产生新的β细胞方面的贡献。我们的结论是，CDK4不仅促进了β细胞的复制，还促进了导管上皮中的β细胞前体细胞的激活。此外，我们还发现，CDK4通过招募静止细胞进入细胞周期来控制β细胞质量。我们发现CDK4及其下游转录因子E2F1在二次过渡之前和期间调节胰腺的发育。CDK4缺乏会导致胚胎胰腺体积缩小，这是由于间充质发育受损和Pdx1+胰祖细胞数量受限所致。有趣的是，活化的CDK4R24C激酶的表达导致Nkx2.2+和Nkx6.1+细胞的增加，以及Ngn3+内分泌前体细胞的数量和增殖增加，从而导致细胞谱系的扩大。此外，我们发现E2F1结合并激活了Ngn3启动子，从而以一种依赖于CDK4的方式调节胚胎胰腺中Ngn3的表达水平。这些结果证实CDK4是早期胰腺发育的重要调节因子，因为它能够调节胰腺前体细胞和内分泌前体细胞的增殖潜能。 我们已经开始对胰腺发育和功能中的其他细胞周期调节因子进行系统分析。我们最近发现了CDK2在β细胞功能和出生后β细胞增殖中的重要作用。CDK2的缺失导致了β细胞功能的丧失。此外，在CDK2缺乏的情况下，与年龄相关的β细胞质量减少。此外，我们还观察到，代谢应激进一步加剧了由于β细胞质量和功能进一步恶化而导致的CDK2丢失所致的排便障碍。我们目前正在调查这些发现背后的机制。

Insulin-producing pancreatic islet beta cells are destroyed, severely depleted or functionally impaired in diabetes. Therefore, replacing functional beta cell mass would advance clinical diabetes management. We have previously demonstrated the importance of Cdk4 in regulating beta cell mass. Cdk4-deficient mice display beta cell hypoplasia and develop diabetes, whereas beta cell hyperplasia is observed in mice expressing an active Cdk4R24C kinase. While beta cell replication appears to be the primary mechanism responsible for beta cell mass increase, considerable evidence also supports a contribution from the pancreatic ductal epithelium in generation of new beta cells. We conclude that Cdk4 not only promotes beta cell replication, but also facilitates the activation of beta cell progenitors in the ductal epithelium. In addition, we show that Cdk4 controls beta cell mass by recruiting quiescent cells to enter the cell cycle. We show that Cdk4 and its downstream transcription factor E2F1 regulate pancreas development prior to and during the secondary transition. Deficiency of Cdk4 results in reduced embryonic pancreas size due to impaired mesenchyme development and limitation of the number of Pdx1+ pancreatic progenitor cells. Interestingly, expression of activated Cdk4R24C kinase leads to increased Nkx2.2+ and Nkx6.1+ cells and a rise in the number and proliferation of Ngn3+ endocrine precursor cells resulting in expansion of the cell lineage. Further, we show that E2F1 binds and activates the Ngn3 promoter thereby modulating Ngn3 expression levels in the embryonic pancreas in a Cdk4-dependent manner. These results identify Cdk4 as an important regulator of early pancreas development by virtue of its ability to modulate the proliferation potential of pancreatic progenitors and endocrine precursors. We have begun a systematic analyses of other cell cycle regulators in pancreas development and function. We have recently uncovered an important role for CDK2 in beta cell function and post-natal beta cell proliferation. Cdk2 loss results in loss of beta cell function. Further, age associated reduction in beta cell mass is seen upon Cdk2 deficiency. Also, we observe that metabolic stress further accentuates the defecst due to loss of Cdk2 by further deterioration of beta cell mass and function. We are presently investigating the mechanisms that underlie these findings.