Title: BMP/TGFbeta crosstalk in cartilage maintenance and osteoarthritis

标题：BMP/TGFbeta 串扰在软骨维护和骨关节炎中的作用

• 批准号: 10402239
• 负责人: Karen M. Lyons
• 金额: $ 33.98万
• 依托单位: UNIVERSITY OF CALIFORNIA LOS ANGELES
• 依托单位国家: 美国
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-19 至 2024-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10402239
• 关键词: Address; Adult; Affinity; Binding; Biochemical; Biological Assay; Birth; Blood Vessels; Cartilage; Chondrocytes; Chondrogenesis; Complex; Data; Defect; Degenerative polyarthritis; Development; Epiphysial cartilage; Exhibits; Genetic; Genetic Transcription; Goals; Growth Factor; Hypertrophy; Impairment; In Vitro; Knowledge; Lead; Ligands; Ligation; Maintenance; Mediating; Mus; Output; Pathologic; Pathology; Pathway interactions; Phenotype; Physiological; Prevention; Property; Reporter; Research Design; Role; Signal Transduction; Source; TGF-beta type I receptor; Testing; Therapeutic; Tissues; Transducers; Transforming Growth Factor beta; Work; articular cartilage; bone morphogenetic protein receptor type I; bone morphogenetic protein receptors; cartilage degradation; chondrodysplasia; chronic pain; crosslink; disability; early onset; in vivo; inhibitor; mutant; novel; prevent; receptor

PROJECT SUMMARY In the canonical pathway, TGFβs bind to their type I and II receptors TGFβRII and ALK5, respectively, to activate Smads 2 and 3. It has been shown that Smad3 is essential for articular cartilage maintenance, but the function of Smad2 in vivo is unknown. It has been shown that TGFβRII is not required for chondrogenesis during development, but the function of the type I receptor ALK5 is unknown. This is an important gap in knowledge because ALK5 can activate TGFβ pathways independently of TGFβRII. Moreover, ALK5 can interact with the type I BMP receptor ALK1, enabling TGFβs to activate BMP pathways. We found that loss of ALK5 leads to lethal chondrodysplasia, in contrast to the mild viable phenotype in mice lacking TGFβRII, demonstrating that ALK5 acts independently of TGFβRII in cartilage. Furthermore, we found that Smad2/3 mutants are viable, demonstrating that ALK5 does not act primarily as a transducer of canonical TGFβ signaling in cartilage. Unexpectedly, loss of ALK5 led to a significant increase in BMP output. Biochemical studies pointed to ALK1 as the source of elevated BMP signaling. This was confirmed by our finding that loss of Alk1 rescues the severe chondrodysplasia in Alk5 mutants. Our studies therefore uncover a new mechanism of action for ALK5 as a regulator of BMP output and a previously unknown pathological role for ALK1 in cartilage. We will investigate ALK1 and ALK5 action in growth plate cartilage in Aim 1. We also ablated Alk5 in adult articular cartilage (AC). Mutants develop early onset osteoarthritis (OA)-like pathologies. We will address whether ALK5 acts as a transducer of canonical TGFβ pathways and/or as an inhibitor of BMP signaling through ALK1 in AC in Aim 2. Finally, we performed crosslinking, reporter, proximity ligation, and other assays to investigate the basis for the genetic interaction between ALK1 and ALK5. These studies indicate that (a) loss of ALK5 triggers the de novo formation of ALK1/ActRIIB complexes, and (b) provide evidence for ligand- independent BMP signaling through ALK1 in cartilage. Prior in vitro studies have shown that ALK1 is unique among BMP receptors in its ability to activate ligand-independent signaling, but the underlying mechanisms and physiological relevance have never been investigated. We address these unknowns in Aim 3. In summary, these studies demonstrate that the primary role of ALK5 is not to transduce TGFβ signals, but rather is to prevent ligand-independent BMP signaling through ALK1 in cartilage. Completion of these studies could lead to a significant revision of our understanding of the role of ALK5 and its critical importance in regulating TGFβ/BMP crosstalk in cartilage.

项目摘要 在规范途径中，TGFβ分别与其I型和II受体TGFβRII和ALK5结合到 激活SMADS 2和3。已显示Smad3对于关节软骨维护至关重要，但是 Smad2在体内的功能尚不清楚。已经表明，软骨发生不需要TGFβRII 在开发过程中，但是I型受体ALK5的功能尚不清楚。这是一个重要的差距 知识，因为ALK5可以独立于TGFβRII激活TGFβ途径。而且，Alk5可以 与I型BMP受体ALK1相互作用，使TGFβ可以激活BMP途径。我们发现失去了 与缺乏TGFβRII的小鼠中的轻度活体表型相反，ALK5导致致命的软骨发育不良 证明ALK5在软骨中独立于TGFβRII起作用。此外，我们发现SMAD2/3 突变体是可行的，表明ALK5并非主要充当规范TGFβ的换能器 在软骨中发出信号。出乎意料的是，ALK5的损失导致BMP输出显着增加。生化 研究指出ALK1是BMP信号升高的来源。我们发现损失证实了这一点 ALK1的ALK5突变体中的严重软骨发育不全。因此，我们的研究发现了一种新机制 ALK5作为BMP输出的调节剂的作用和ALK1先前未知的病理作用 软骨。我们将在AIM 1中调查生长板软骨中的ALK1和ALK5作用。 成人关节软骨（AC）。突变体发生早期发作骨关节炎（OA）样病理。我们将解决 ALK5是否充当规范TGFβ途径的换能器和/或BMP信号传导的抑制剂 通过AC 2中的ALK1在AIM 2中进行。最后，我们进行了交联，记者，接近结扎和其他测定法 研究ALK1和ALK5之间的遗传相互作用的基础。这些研究表明（a） ALK5的损失会触发Alk1/actriib复合物的从头形成，并且（b）为配体提供了证据 通过ALK1在软骨中通过ALK1发出独立的BMP信号。先前的体外研究表明ALK1是独特的 在BMP受体中激活非配体的信号传导的能力，但潜在的机制 和身体相关性从未得到调查。我们在AIM 3中解决了这些未知数。总而言之， 这些研究表明，ALK5的主要作用不是翻译TGFβ信号，而是转化为 通过软骨中的ALK1防止与配体无关的BMP信号传导。这些研究的完成可能会导致 对我们对ALK5作用的理解及其在确定中的重要性进行了重大修改 软骨中的TGFβ/BMP串扰。