Investigating the role of SIRT1 in hematopoetic stem cell maintenance

研究 SIRT1 在造血干细胞维持中的作用

• 批准号: 8553137
• 负责人: Philipp Oberdoerffer
• 金额: $ 40.31万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8553137
• 关键词: Ablation; Acute; Address; Adult; Affect; Age; Age Factors; Aging; Animal Model; Cell Maintenance; Cell Proliferation; Cell physiology; Cells; Chromatin; Chronic; Chronic Myeloid Leukemia; Complex; Cytotoxic agent; DNA Damage; DNA Repair; Data; Deacetylase; Defect; Development; Developmental Gene; Disease; Epigenetic Process; Future; Gene Expression Profiling; Gene Expression Regulation; Gene Targeting; Genes; Genome Stability; Genomic Instability; Genotoxic Stress; Goals; Growth; Hematopoietic; Hematopoietic System; Hematopoietic stem cells; Histone Deacetylase; Histone H4; Homeostasis; Investigation; Knockout Mice; Light; Link; Longevity; Maintenance; Malignant - descriptor; Malignant Neoplasms; Mediating; Modification; Molecular; Mus; Mutagens; Myeloproliferative disease; Natural regeneration; Orthologous Gene; Pathway interactions; Pattern; Physiological; Play; Polycomb; Process; Regulation; Role; Stem cells; Stress; Tissues; Transcriptional Activation; Transcriptional Regulation; Undifferentiated; Work; adult stem cell; biological adaptation to stress; chromatin immunoprecipitation; embryonic stem cell; exhaustion; functional decline; immune function; in vivo; mouse model; novel; overexpression; progenitor; response; response to injury; self-renewal; stem; stem cell fate

BACKGROUND:Stem cell homeostasis is a central aspect of tissue maintenance and regeneration in response to injury or stress, which is perhaps best exemplified in hematopoietic stem and progenitor cells (HSPCs). Adult HSPCs show extensive self-renewal capacity and allow for long-term multi-lineage differentiation in the hematopoietic system. If deregulated, this process can result in a variety of disorders including myeloproliferative diseases and loss of immune function. Recent evidence suggests that DNA damage accumulation or a defective response to genotoxic stress are key contributors to aberrant expansion and concomitant functional exhaustion of HSPCs, which is further associated with altered expression of hematopoietic differentiation factors and age-associated stem cell decline. Determining the factors that affect HSPC function with regard to both DNA damage accumulation and epigenetic deregulation is, thus, essential for our understanding of HSPC homeostasis in aging and disease. The (histone) deacetylase SIRT1 was shown to be critically involved in several aspects of the DNA damage response as well as in the transcriptional regulation of a variety of key developmental regulators, placing it at the crossroads of DNA damage and epigenetic gene regulation. Supporting a role for SIRT1 in the epigenetic (de)regulation of stem cell fate, SIRT1 was shown to be part of a novel polycomb repressive complex, PRC4, which has distinctive chromatin modifying activity and is expressed specifically in undifferentiated cells including embryonic stem cells. Notably, polycomb Group (PcG)-mediated gene regulation is known to play a critical role in HSPC maintenance. Together, these observations call for an in depth investigation of SIRT1 function in hematopoietic stem cells.RESULTS AND FUTURE DIRECTIONS:To unequivocally address the role of Sirt1 in HSPCs, we induced ablation of Sirt1 in adult mice, thereby avoiding possible developmental defects associated with conventional Sirt1 knock-out mice. In so doing, we found that Sirt1 ablation promotes aberrant expansion of HSPCs in vivo specifically in response to hematopoietic stress, as shown for cytotoxic and genotoxic agents. Sirt1 ablation in HSPCs further led to a reduced ability to repair DNA damage, resulting in genomic instability and a progressive loss of long-term progenitors following stress-induced proliferative expansion or DNA damage. Through gene expression profiling, we implicate inappropriate induction of the PcG target gene Hoxa9 as the mechanism that promotes HSPC expansion in the absence of Sirt1. Hoxa9 is a critical regulator of HSPC maintenance and Hoxa9 overexpression confers a growth advantage to HSPCs. Using chromatin immunoprecipitation (ChIP), we found Sirt1 is enriched at the Hoxa9 gene body. Notably, Sirt1 deletion caused a significant increase in Hoxa9-associated K16-acetylated histone H4 (H4K16Ac), which is a modification associated with transcriptional activation and a known preferred enzymatic target for Sirt1 deacetylase activity. Increased H4K16-Ac was previously shown to be inversely correlated with PcG-associated repressive marks, and consistent with this notion, H3K27 trimethylation was reduced in the absence of Sirt1. Moreover, we observed a strikingly similar pattern of enrichment for both H3K27me3 and Sirt1 across the Hoxa9 gene. While the physiological consequences of PcG-associated Sirt1 remained unexplored, our data now provide first in vivo evidence that Sirt1 can modulate the expression of PcG-target genes to promote the maintenance of hematopoietic stem cells. Together, our findings demonstrate a dual role for Sirt1 in HSPC homeostasis, both via epigenetic regulation of a key developmental gene and by promoting genome stability in adult stem cells.IMPLICATIONS: The tight regulation of HSPC proliferation is a central aspect of normal mammalian development and immune function. Moreover, perturbed quiescence and aberrant proliferation of HSPCs, as observed here, are key steps in malignant transformation of both acute and chronic myeloid leukemia, which have furthermore been linked to aberrant Hoxa9 expression. Our work suggest that (pharmacological) activation of Sirt1 may provide a means to interfere with HSPC expansion, concomitant exhaustion and possibly malignant transformation, particularly in situations of chronic hematopoietic stress. Taken together our data, thus, add to the understanding of stress-induced changes in HSPC homeostasis with implications for HSPC maintenance with age as well as during malignant transformation.

背景：干细胞体内平衡是响应损伤或压力的组织维持和再生的中心方面，这在造血茎和祖细胞（HSPC）中也许可以最好地体现。成年HSPC显示出广泛的自我更新能力，并允许在造血系统中长期多轮差异化。如果放松管制，此过程可能会导致多种疾病，包括骨髓增生性疾病和免疫功能的丧失。最近的证据表明，DNA损伤的积累或对遗传毒性应激的有缺陷的反应是HSPC的异常膨胀和伴随的功能衰竭的关键因素，这与造血分化因子和年龄相关的干细胞下降的表达的改变进一步相关。因此，确定影响HSPC功能在DNA损伤积累和表观遗传失调方面的因素对于我们对HSPC稳态的理解至关重要。 （组蛋白）脱乙酰基酶SIRT1被证明与DNA损伤响应的多个方面以及各种关键发育调节剂的转录调控有关，将其置于DNA损伤和表观遗传基因调控的十字架上。 SIRT1支持SIRT1在干细胞命运表观遗传（DE）调节中的作用，SIRT1被证明是一种新型PolyComb抑制性复合物PRC4的一部分，该复合物具有独特的染色质修饰活性，并且在包括胚胎干细胞在内的未分化细胞中特异性表达。值得注意的是，已知PolyComb组（PCG）介导的基因调节在HSPC维持中起关键作用。总之，这些观察结果呼吁对造血干细胞中SIRT1功能进行深入研究。反应和未来方向：为了明确地解决SIRT1在HSPC中的作用，我们诱导了成年小鼠中SIRT1的消融，从而避免了与传统Sirt 1敲出1敲除鼠标相关的可能发育缺陷。这样，我们发现SIRT1消融促进了体内HSPC的异常膨胀，特别是针对造血应激的反应，如细胞毒性和遗传毒性剂所示。 HSPC中的SIRT1消融进一步导致修复DNA损伤的能力降低，导致基因组不稳定性和应力诱导的增殖性扩张或DNA损伤后长期祖细胞的逐渐丧失。通过基因表达分析，我们将PCG靶基因HOXA9的不当诱导视为在没有SIRT1的情况下促进HSPC扩展的机制。 HOXA9是HSPC维护和HOXA9过表达的关键调节剂，赋予HSPC的增长优势。使用染色质免疫沉淀（CHIP），我们发现SIRT1在HOXA9基因体上富集。值得注意的是，SIRT1缺失导致HOXA9相关的K16-乙酰化组蛋白H4（H4K16AC）显着增加，这是一种与转录激活相关的修饰和已知的SIRT1脱乙酰基酶活性的已知优选酶促靶标。先前显示出增加的H4K16-AC与PCG相关的抑制标记成反比，并且与该概念一致，在没有SIRT1的情况下，H3K27三甲基化降低了。此外，我们观察到了Hoxa9基因的H3K27me3和SIRT1的富集模式非常相似。尽管PCG相关的SIRT1的生理后果仍未探索，但我们的数据现在提供了首先在体内证据，表明SIRT1可以调节PCG-target基因的表达以促进造血干细胞的维持。总之，我们的发现表明了SIRT1在HSPC稳态中的双重作用，这是通过对关键发育基因的表观遗传调节以及促进成人干细胞中基因组稳定性的表观调节的。Implication：HSPC增殖的严格调节都是正常哺乳动物发育和免疫功能的核心方面。此外，如此处观察到的那样，HSPC的干扰和异常的增殖是急性和慢性髓样白血病的恶性转化的关键步骤，这些步骤与异常HOXA9表达有关。我们的工作表明，SIRT1的（药理）激活可能会提供一种干扰HSPC扩张，伴随精疲力尽和可能发生恶性转化的方法，尤其是在慢性造血应激的情况下。因此，我们的数据加在一起，增加了对HSPC稳态变化的理解，对HSPC维持年龄以及在恶性转化期间的维持有影响。