ROLE OF NF-kB IN STEM CELLS AGING

衰老被认为是随机的分子和细胞损伤累积的结果。 导致衰老相关退变的损伤的确切性质仍不清楚，但可能 包括线粒体损伤、端粒磨损、核畸形、遗传堆积 突变，或DNA、蛋白质和膜损伤。有几条证据支持这一观点 DNA损伤是导致衰老的一种分子损伤。首先，DNA损伤和 由DNA损伤引起的基因突变会在老年生物体的组织中积累。第二，窝藏老鼠 对基因毒性应激具有抵抗力的生殖系突变是长寿的。 早衰症(或加速衰老综合症)是由基因组所需基因的遗传突变引起的 维护^。例如，DNA修复内切酶ERCCI-XPF的缺失会导致早衰症。一个 该疾病的小鼠模型(Erccrl-小鼠)由合作者Laura Niedernhofer博士建立并使用 在此应用中，探讨vmDNA修复所致的早衰症与自然早衰症的相似性。 29岁。比较DNA修复缺陷小鼠和老年wdld型小鼠的转录组发现 高度显著的相关性。这是在暴露于基因毒性应激的年轻野生型(Wt)小鼠身上重述的。 许多类型的细胞损伤导致转录因子NF-kB的激活，包括氧化，物理， 和化学压力。核因子-kB在应激反应中的激活可能至少部分是通过DNA损伤来调节的。 紫外线、γ-射线和拓扑异构酶毒物引起的遗传毒性应激激活了核因子-kB。 此外，已证实DNA双链断裂可以激活ATM依赖的核因子-kB 举止。此外，相对于幼年动物，老年啮齿动物的多种组织中核因子-kB的表达上调，包括皮肤、肝脏、肾脏、小脑、心肌和胃粘膜等。最近，一项研究确定了核因子-kB是与哺乳动物衰老最相关的转录因子，随后研究表明，局部抑制皮肤中的核因子-kB在组织学上促进了皮肤的“年轻”，Ki67增加，pi6染色减少。这项研究还表明，在衰老过程中，核因子-kB调节基因的一个子集的表达增加。此外，C-Rel(一种核因子-kB亚基)的过度表达可诱导细胞的显著特征，包括增殖减少、抗凋亡和形态改变，如大的、多核的细胞，外观呈颗粒状。 许多年龄相关疾病的发病机制，包括动脉粥样硬化、骨关节炎、痴呆症、 骨质疏松症、癌症、S和心血管疾病。 核因子-kB传统上被认为是一种免疫转录因子，由致病因子激活 配体如内毒素和细胞因子，如肿瘤坏死因子-α和白介素B。核因子-kB的激活是刺激血管生成的关键 抗原提呈细胞(APC)，产生细胞因子、趋化因子和活性氧(ROS)； 从而激活适应性免疫系统以控制感染或病原性侮辱。然而， 核因子-kB也被其他类型的应激激活，包括遗传毒性、氧化、机械和其他 造成细胞损伤的环境侮辱。具体地说，DNA损害剂，如紫外线、γ-射线、 拓扑异构酶毒物和活性氧激活了核因子-kB，遗传毒性和氧化应激都是 与衰老的发病机制有关。因此，依赖于核因子-kB的信号机制调节 细胞对压力的反应可能会导致衰老。 核因子-kB是由p65、p50、c-rel、relB和p52的同源或异源二聚体组成的转录因子家族。 与免疫学相关的二聚体是炎症性p65/p50异源二聚体和抑制性p50同源二聚体。核因子-kB的激活有两条主要途径，但对于这一提议来说，重要的是通过IKK复合体发出信号的典型途径。IKK复合体由两个催化亚基Ikka和13以及一个调节亚基Ikky或Nemo组成。 一旦被Ikky激活，IKKJ3和一种磷酸化的IKB，核转录因子-kB的细胞质抑制因子^。之后 通过磷酸化，Ikba被泛素化，并经历蛋白酶体的降解。这释放了核因子-kB，使其能够移位到细胞核，在那里它促进了促炎症、抗凋亡和细胞生长基因的转录。IKK组装需要将Ikky/Nemo的N末端与IKKA和IKK13的C末端结合在这些亚基的C末端区域，称为Nemo结合结构域(NBD)。25 IKKB的NBD区域由从C末端设计的I I氨基酸组成，然后可以利用蛋白转导结构域(PTD)将其输送到细胞。26.27添加野生型，但不是突变的NBD肽被证明干扰IKK组装，并抑制细胞因子诱导的NF-kB的激活。值得注意的是，NBD肽并不阻断基础的IKK活性，而只是调节炎症信号诱导的IKK的激活。在体内，全身给予PTD-NBD多肽与任何已描述的小鼠或大鼠毒性无关，而抑制核因子-kB与不断生长的小鼠的治疗反应相关。 疾病清单。

Aging is thought to arise as a consequence of the accumulation of stochastic molecular and cellular damage^. The precise nature of the damage responsible for aging-related degeneration remains poorly-defined, but may consist of mitochondrial damage, telomere attrition, nuclear dysmorphology, accumulation of genetic mutations, or DNA, protein, and membrane damage. There are several lines of evidence to support the notion that DNA damage is one type of molecular damage that contributes to aging. First, both DNA lesions^ and genetic mutations caused by DNA damage accumulate in tissues of aged organisms. Second, mice harboring germ-line mutations that confer resistance to genotoxic stress are long-lived 1¿'". Third, the majority of human progerias (or syndromes of accelerated aging) are caused by inherited mutations in genes required for genome maintenance^. For example, deficiency of the DNA repair endonuclease ERCCi-XPF causes progeria^^. A mouse model of this disease (Erccrl- mice) was generated and used by Dr. Laura Niedernhofer, a collaborator on this application, to probe the similarity between progeria due to vmrepaired DNA damage and natural aging29. Comparison of the transcriptome of the DNA repair deficient mice and old wdld type mice revealed a highly significant correlation. This was recapitulated in young wild type (wt) mice exposed to genotoxic stress. Many types of cellular damage lead to activation of the transcription factor NF-kB including oxidative, physical, and chemical stress. NF-kB activation in response to stress may be mediated, at least in part, by DNA damage. Genotoxic stress caused by UV irradiation, y-irradiation, and topoisomerase poisons activate NF-kB^^'i^. Furthermore, DNA double strand breaks have been demonstrated to activate NF-kB in an ATM-dependent manner. In addition, NF-kB is up-regulated in a variety of tissues of aged rodents relative to young animals, including the skin, liver, kidney, cerebellum, cardiac muscle and gastric mucosa^s-is. Recently, a study determined that NF-kB was the transcription factor most associated with mammalian aging, and subsequently showed that local NF-kB inhibition in skin promoted "younger" skin histologically, with increased Ki67 and reduced pi6 staining'^. This study also demonstrated that expression of a subset of NF-kB regulated genes is increased during aging. Additionally, overexpression of C-rel (an NF-kB subimit) induces hallmark features of cellular scenescence including decreased proliferation, resistance to apoptosis, and morphologic changes, such as enlarged, multinucleated cells that are granular in appearance^o. NF-kB is also implicated in the pathogenesis of numerous age-associated diseases, including atherosclerosis, osteoarthritis^^, dementia^^, osteoporosis, cancer^s and cardiovascular disease. NF-kB is traditionally thought of as an immunologic transcription factor that is activated by pathogenic ligands such as LPS and cytokines such as TNF-a and IL-iB. NF-kB activation is critical for the stimulation of antigen presenting cells (APCs), which produce cytokines, chemokines and reactive oxygen species (ROS), leading to activation of the adaptive unmune system to control the infection or pathogenic insult. However, NF-kB is also activated by other types of stress including genotoxic, oxidative, mechanical and other environmental insults that cause cell damage3¿'3i. Specifically, DNA damaging agents such as UV, y-irradiation, topoisomerase poisons and reactive oxygen species activate NF-kB and both genotoxic and oxidative stress are implicated in the pathogenesis of aging. Therefore, NF-kB-dependent signaling mechanisms that regulate the cellular response to stress could contribute to aging. NF-kB is a family of transcription factors consisting of homo- or heterodimers of p65, p50, c-rel, relB and p52. The dimers of immunologic relevance are the inflammatory p65/p50 heterodimer and the repressor p50 homodimer. Two main pathways of NF-kB activation exist, but of importance for this proposal is the canonical pathway that signals via the IKK complex. The IKK complex is comprised of two catalytic subimits, IKKa and 13, and a reguatory subunit IKKy or NEMO. Once activated by IKKy, IKKJ3 and a phosphorylate IkB, the cytoplasmic inhibitor of NF-kB^^. After phosphorylation, IkBa is ubiquitinated and undergoes proteosomal degradation. This releases NF-kB, allowing it to translocate to the nucleus where it promotes transcription of mmierous pro-inflammatory, antiapoptotic and cellular growth genes. IKK assembly requires the binding of the N-terminus of IKKy/NEMO to the C-terminus of IKKa and IKK13 in a region of these subunits called the NEMO binding domain (NBD).25 The NBD region of IKKB consists of i i amino acids designed from the C-terminus, which can then be delivered to cells using a protein transduction domain (PTD).26.27 Addition of the wild type, but not mutant NBD peptide has been shown to interfere with IKK assembly and inhibits cytokine-induced activation of NF-kB. Notably, NBD peptide does not block basal IKK activity, but only modulates the induced activation of IKK in response to inflammatory signals. In vivo, systemic administration of a PTD-NBD peptide is not associated with any described toxicity in mice or rats and inhibition of NF-kB correlates with therapeutic responses in an evergrowing list of diseases.