Regulating stress response to promote postnatal beta-cell function and survival

工作负荷诱导的胰岛β-细胞功能障碍、身份丧失和细胞死亡，通常称为 β-细胞衰竭是2型糖尿病(T2D)的标志。这种疾病通常始于肥胖引起的胰岛素。 抵抗，当外周组织需要更高水平的循环胰岛素来储存和使用葡萄糖时。 胰岛β细胞通过扩大β细胞团和增加每个细胞的胰岛素产量来进行补偿，这需要 上调胰岛素生物合成和氧化葡萄糖代谢。它们在体内产生未折叠的胰岛素原 线粒体中的内质网和活性氧物种(ROS)，高水平可杀死β细胞。因此，β 细胞通过刺激几个早期SRG的活性来不断激活应激反应，包括Atf6， IRE1、PERK、HSF1和NURF2，导致：1)减弱整体蛋白质翻译；2)增强翻译 一些具有特殊功能的SRG mRNAs，如上游开放阅读框架(UORF) ORF；3)一些晚期SRGs表达上调。这些反应的总体效果是删除 蛋白质组动态平衡和可持续β细胞功能的未折叠蛋白质/ROS。然而，过度激活 一些晚期SRG，如ATF4和HSPs，通过激活一些促凋亡基因或诱导β细胞衰竭 通过极大地降低蛋白质翻译总量。因此，β细胞必须限制故障水平- 导致可持续的高水平胰岛素输出的SRG。我们最近出版的一种新兴模式 研究发现，含有MYT转录因子和SIN3的转录复合体可以选择性地抑制这些失败- 导致SRG。MYT转录因子是一个由三个髓鞘转录因子(Myt1、2和3)组成的家族，在 胰岛细胞。Sin3，包括sin3a和sin3b，是一种通过募集组蛋白来抑制转录的协同调节因子 脱乙酰酶(HDAC)来修饰组蛋白。我们发现MYT转录因子和SIN3可以形成转录复合体 在β细胞中。灭活小鼠和人β细胞中的这些基因会导致细胞功能障碍和/或死亡，而 过度激活导致β细胞故障的晚期SRG，但不激活早期SRG。耐人寻味的是，MYT TF， 尤其是Myt3，是由肥胖相关的应激源在小鼠和人类β细胞中诱导的，可能是由 Myt3基因5‘侧翼区的uORF。重要的是，myt3基因下调伴随着人类β细胞 T2D开发失败。我们的主要假设是，应激反应的MYT TF，特别是 Myt3通过SIN3介导组蛋白去乙酰化抑制晚期SRGs促进-细胞功能/存活 在正常生理和代谢压力下。目标1将确定MYT TF如何抑制SRG MYT-TF在人β细胞系中的表达及其对原代β细胞的影响 功能和生存。目标2将定义代谢应激源如何上调Myt3的产生以及如何 上调使代谢应激下的β细胞代偿。我们希望发现一种可调谐的机制 这可以用于预防/延迟β信元故障和T2D。

Workload-induced pancreatic islet β-cell dysfunction, loss-of identity, and cell death, commonly known as β-cell failure, is the hallmark of type 2 diabetes (T2D). This disease usually starts with obesity-induced insulin resistance, when peripheral tissues need higher levels of circulating insulin for glucose storage and usage. Islet β-cells compensate by expanding β-cell mass and increasing insulin output per cell, which requires upregulated insulin biosynthesis and oxidative glucose metabolism. These produce unfolded proinsulin in the ER and reactive oxygen species (ROS) in mitochondria, which at high levels can decimate β cells. Thus, β cells constantly activate stress response by stimulating the activity of several early-stage SRGs, including Atf6, IRE1, PERK, Hsf1, and Nurf2, to lead to: 1) attenuated overall protein translation; 2) enhanced translation of some SRG mRNAs that have special features such as upstream open reading frame (uORF) 5’ to the main ORF; 3) upregulated expression of some late-stage SRGs. The overall effect of these responses is to remove unfolded proteins/ROS for proteomic homeostasis and sustainable β-cell function. However, over-activating some late-stage SRGs such as Atf4 and Hsps induces β-cell failure by turning on some proapoptotic genes or by exceedingly lowering overall protein translation. Thus, it is imperative for β-cells to limit the levels of failure- causing SRGs for sustainable high-level of insulin output. An emerging model from our recent published findings is that a transcriptional complex containing Myt TFs and Sin3 can selectively repressing these failure- causing SRGs. Myt TFs are a family of three myelin transcription factors (Myt1, 2, and 3) highly expressed in islet cells. Sin3, including Sin3a and Sin3b, is a coregulator that represses transcription by recruiting histone deacetylases (HDACs) to modify histones. We showed that Myt TFs and Sin3 can form a transcription complex in β cells. Inactivating these genes in mouse and human β cells causes cell dysfunction and/or death while overactivating late-stage β-cell-failure-causing SRGs but not early stage SRGs. Intriguingly, Myt TFs, particularly Myt3, is induced by obesity-related stressors in mouse and human β cells, likely mediated by an uORF in 5’ flanking region of Myt3 mRNA. Importantly, MYT3 down-regulation accompanies human β-cell failure in T2D development. Our overarching hypothesis is that the stress-responsive Myt TFs, particularly Myt3, promote -cell function/survival by repressing late-stage SRGs via Sin3-mediated histone de-acetylation under both normal physiology and metabolic stress. Aim 1 will establish how MYT TFs repress SRG expression in a human β cell line and how manipulating MYT-TF levels will affect primary human β-cell function and survival. Aim 2 will define how metabolic stressors up-regulate Myt3 production and how this upregulation enable β-cell compensation under metabolic stress. We expect to uncover a tunable mechanism that can be explored for preventing/delaying β-cell failure and T2D.