The regenerative potential of the enteroblast in response to aging in Drosophila intestine

在衰老的动物中，肠遭受结构和功能损伤，并经历上皮发育不良。在正常组织稳态期间，肠干细胞（ISCs）缓慢分裂以取代受损细胞，但旧肠显示出增加的ISC分裂速率和错误分化细胞的积累。错误分化细胞的增殖和积累增加已被用作肠道发育不良的标志之一，以缩短寿命。果蝇中肠包括自我更新的ISCs，ISCs是果蝇中肠中唯一进行有丝分裂的细胞类型，即使在老化的中肠中，但它们的后代如EB、EC或EE是否可以在老化的中肠中去分化为ISCs仍然是未知的。考虑到果蝇和哺乳动物系统中用于调控ISC稳态和再生的保守遗传途径和调控机制，以及果蝇中丰富的遗传工具，迫切需要建立果蝇肠道模型来研究上皮发育异常对衰老的响应过程。 我们的初步研究表明，EGFR-Ras信号的激活可以诱导自主的肠母细胞（EB）有丝分裂。进一步的EBs谱系追踪分析显示，新的干细胞从EBs的后代产生，表明EBs可以去分化产生ISCs。此外，我们发现EB在50天龄的肠道中重新进入有丝分裂，这表明EB分化在衰老过程中受到损害。有趣的是，我们发现EGFR-Ras信号在老年肠道的EB中上调。基于这些初步的发现，我们推测，上调EGFR-Ras信号在老年肠道是至关重要的有丝分裂和EB的去分化的重新进入。为了检验这一假设，将追求以下两个具体目标。在目标1中，我们将确定EBs的去分化过程中激活EGFR-Ras信号。在目标2中，我们将确定EB如何促进ISC再生以应对衰老。在完成这项研究后，我们的预期结果将确定EB如何重新进入有丝分裂周期，以不对称地分裂，从而在果蝇肠道模型中产生功能性ISC以应对衰老。考虑到果蝇和哺乳动物中保守的遗传途径和调控机制，这些结果有望对揭示衰老相关肠道疾病调控的关键机制产生重要的积极影响，这可能适用于再生医学。

In aging animals, the intestine suffers structural and functional impairments and undergoes epithelial dysplasia. During normal tissue homeostasis, the intestinal stem cells (ISCs) divide slowly to replace the damaged cells, but old intestines show increased ISC division rate and accumulation of misdifferentiated cells. The increased proliferation and accumulation of misdifferentiated cells have been used as one of the hallmarks for the intestinal dysplasia to shorten lifespan. The Drosophila midgut includes self-renewed ISCs which is the only cell type to undergo mitosis in Drosophila midguts, even in the aged midguts, but whether their progeny such as EB, EC or EE can dedifferentiate to become ISCs in aged midguts has remained unexplored. Considering that the conserved genetic pathways and regulatory mechanisms employed to regulate ISC homeostasis and regeneration in both Drosophila and mammalian systems, and that the wealth of genetic tools are available in Drosophila, there is a critical need to establish a Drosophila intestinal model to investigate the process of epithelial dysplasia in response to the aging. Our preliminary studies have shown that activation of EGFR-Ras signaling can induce autonomous enteroblast (EB) mitosis. The further lineage-tracing analysis in EBs revealed that new stem cells are generated from the progeny of EBs, indicating that EBs can dedifferentiate to produce ISCs. Furthermore, we found that EBs re-entered mitosis in 50-day-old intestines, suggesting that EB differentiation is compromised during aging. Interestingly, we found that EGFR-Ras signaling was upregulated in EBs in aged intestines. Based on these preliminary findings, we hypothesize that upregulated EGFR-Ras signaling in aged intestines is crucial for the re-entry of mitosis and dedifferentiation of EBs. To test this hypothesis, the following two specific aims will be pursued. In Aim 1 we will determine the process of dedifferentiation in EBs upon the activation of EGFR-Ras signaling. In Aim 2 we will determine how EBs contribute to ISC regeneration in response to aging. At the completion of this proposed research, our expected outcomes will determine how EBs re-enter mitotic cycle to divide asymmetrically to produce functional ISCs in response to aging in the Drosophila intestine model. Considering the conserved genetic pathways and regulatory mechanisms in both Drosophila and mammals, these results are expected to have an important positive impact on uncovering the critical mechanisms by which the aging related intestinal disorders are regulated, which could be applied to the regenerative medicine.