Regulation of Alveolar Bone Marrow MSC Senescence in Skeletal Aging and Periodontitis

摘要 老年颅面骨骼严重影响创伤性骨缺损的修复和再生。 高龄是包括骨质疏松症在内的许多慢性和使人衰弱的骨骼疾病的关键危险因素 和牙周炎。牙周炎是牙槽骨和牙周结缔组织的炎性破坏， 导致牙齿失去支撑。疾病的易感性和严重性随着年龄的增长而急剧增加， 导致老龄化社会中的重大公共卫生问题。然而，驱动 颅面骨骼老化和与年龄相关的牙周炎恶化仍然是未知的。 细胞衰老，即衰老和受损细胞增殖的停止，在衰老过程中起着重要作用。 相关慢性疾病，包括糖尿病、骨质疏松症和牙周炎。骨髓间充质干细胞 具有自我更新能力和多谱系潜能。MSC池通过衰老耗尽 代表了骨骼老化的标志之一衰老的MSC失去增殖，自我更新的潜力 和成骨分化，导致骨量受损和长骨修复延迟。MSc 衰老还与年龄诱导的氧化应激累积、线粒体功能障碍和 DNA损伤。应激诱导的衰老可通过以下途径改变MSC介导的免疫调节： 衰老相关分泌表型（SASP）。直接证据表明，MSC 缺乏衰老和年龄相关的颅面骨丢失。值得注意的是，牙槽骨髓源性MSC 与长骨间充质干细胞相比，aBMSCs更适合于颅面修复，但表现出小生境特异性。 行为和对环境刺激的反应。 过氧化物酶体增殖物激活受体γ共激活因子1α（PGC-1α）是一种转录共激活因子， 在线粒体生物发生和各种富含维生素A的组织中调节氧化应激中起重要作用。 最近，我们发现PGC-1α直接调节MSCs的细胞命运决定，以防止骨骼衰老 和骨质疏松症。PGC-1α缺失还损害了MSC中的ROS防御，导致氧化应激增加。 然而，PGC-1α在MSC衰老和颅面骨骼组织中的作用尚不清楚。基于我们 在初步实验中，MSC特异性PGC-1α耗竭显著加剧了年龄诱导的骨小梁损伤。 下颌骨骨质流失PGC-1α的全面耗竭加剧了牙周炎和骨丢失， 小鼠牙周炎模型。有趣的是，体外实验表明，PGC-1α的缺乏促进了细胞的复制， aBMSCs的衰老。因此，我们假设PGC-1α通过调节细胞凋亡来调节aBMSC衰老。 氧化应激影响年龄相关的颅面和牙周骨丢失。为了验证我们的假设，我们建议 1）研究PGC-1α对aBMSCs衰老及颅面骨骼衰老的调控作用; 2)确定PGC-1α是否调节细胞衰老以影响年龄加重的牙周骨丢失; 3)阐明PGC-1α调控aBMSC衰老的分子机制。

ABSTRACT Aged craniofacial skeleton significantly impairs the repair and regeneration of trauma-induced bony defects. Advanced age is a critical risk factor for many chronic and debilitating skeletal diseases including osteoporosis and periodontitis. Periodontitis is the inflammatory destruction of alveolar bone and periodontal connective tissue, resulting in the loss of tooth support. The disease susceptibility and severity increase dramatically with age, leading to a significant public health concern in the aging society. However, the mechanisms that drive craniofacial skeletal aging and age-related exacerbation of periodontitis remain largely unknown. Cellular senescence, the halting of proliferation for aged and damaged cells, play an important role in age- related chronic diseases including diabetes, osteoporosis and periodontitis. Mesenchymal stem cells (MSCs) possess self-renewal ability and multiple lineage potentials. Exhaustion of the MSC pool through senescence represents one of the hall marks for skeletal aging. Senescent MSCs lose potential for proliferation, self-renewal and osteogenic differentiation, contributing to the impaired bone mass and delayed repair in long-bone. MSC senescence is also associated with age-induced acculumation of oxidative stress, mitochondrial dysfunction and DNA damage. The stress-induced senescence could alter MSC-mediated immunomodulation through senescence-associated secretory phenotype (SASP). The direct evidence on the molecular link between MSC senescence and age-related craniofacial bone loss is lacking. Notably, alveolar bone marrow derived MSCs (aBMSCs), compared to long-bone MSCs, are more suitable for craniofacial repair, but exhibit niche-specific behaviors and responses to environmental stimuli. Peroxisome proliferator-activated receptor γ coactivators 1α (PGC-1α) is a transcriptional coactivator with essential roles in mitochondrial biogenesis and regulation of oxidative stress in various mitochondria-rich tissues. Recently, we found that PGC-1α directly regulates cell fate decisions of MSCs to protect against skeletal aging and osteoporosis. PGC-1α depletion also impaired ROS defense in MSCs, resulting in increased oxidative stress. However, the role of PGC-1α in MSC senescence and craniofacial skeletal tissue is unknown. Based on our preliminary experiments, MSC-specific depletion of PGC-1α significantly exacerbated age-induced trabecular bone loss in the mandible. Global depletion of PGC-1α exacerbated periodontal inflammation and bone loss in murine periodontitis models. Intriguingly, in vitro assays revealed that lack of PGC-1α promoted replicative senescence of aBMSCs. Thus, we hypothesize that PGC-1α modulates aBMSC senescence via regulation of oxidative stress to impact age-related craniofacial and periodontal bone loss. To test our hypothesis, we propose the following aims:1) To determine if PGC-1α regulates senescence of aBMSCs and craniofacial skeletal aging; 2) To determine if PGC-1α regulates cellular senescence to influence age-exacerbated periodontal bone loss; 3) To elucidate the underlying molecular mechanism of how PGC-1α modulates aBMSC senescence.