Proteoglycan Metabolism During Cardiac Valve Development and Disease

总结：大约1.5%的人患有二叶式主动脉瓣（BAV），这可能导致 血流和器官损伤（1，2）。BAV也是升主动脉壁的独立危险因素 可能导致破裂和猝死的并发症。然而，BAV的细胞和分子基础是 未知由于多种细胞谱系的贡献，甚至BAV形成的基本方面也不确定 以及缺乏高度渗透的存活BAV小鼠模型。功能障碍的主动脉瓣 细胞外基质（ECM）蛋白聚糖多功能蛋白聚糖（Vcan）和聚集蛋白聚糖（Acan）的积累（3-7），但 过量蛋白聚糖的起源和后果在很大程度上是未知的。由于蛋白聚糖是高度稳定的， 蛋白多糖的丰度主要受蛋白水解降解的调节，这使我们研究了蛋白多糖 乳沟我们发现单一ECM蛋白聚糖酶Adamts 5的缺失导致主动脉瓣扩大 上升性脊髓炎（100%）。这些缺陷与Vcan和Acan的显著增加共定位， 反映人体状况的受影响组织（8-10）。从机制上讲，在Adamts 5-/-主动脉瓣原基中 当Vcan过量时，pSmad 2减少，当Smad 2通过产生Adamts 5-/- 在Smad 2 +/-小鼠中，存在高BAV检出率（75%），远高于在其它小鼠BAV模型中所见。 本提案的目的是利用表现出高百分比的Adamts 5-/-; Smad 2 +/-小鼠。 BAV，以定义形态学事件、细胞行为和当被破坏时有助于BAV形成的因素。 由于过量Vcan是功能障碍和患病瓣膜的标志，因此使用具有影响 Vcan含量的控制，可以揭示蛋白多糖代谢在发育中是如何调节的， 也能让我们了解疾病实验验证了ECM Vcan切割协调 间充质细胞的行为和心肌细胞的贡献是三尖瓣形态所需的， 主动脉瓣在两个目标中测试该假设：目标1测试改变的Vcan切割对Vcan细胞的影响。 间充质细胞谱系的行为所需的主动脉瓣形成。初步数据显示， Vcan切割片段的丢失和过量的完整Vcan，破坏了发育中的谱系特异性模式， BAV Adamts 5-/-; Smad 2 +/-小鼠的主动脉瓣。体外和体内方法的结合将破译 谱系特异性细胞行为，以及依赖于Vcan切割和阻止Vcan切割的指导因子。 BAV。尽管教条指出瓣膜尖来自间充质细胞，但目标2研究了 结果过量的Vcan对心肌细胞谱系的贡献，发展主动脉瓣， Adamts 5-/-; Smad 2 +/-小鼠和其他BAV鼠模型。我们的初步数据显示心肌谱系 需要Adamts 5的表达来清除富含Vcan的ECM并形成主动脉瓣的非冠状尖。 由于BAV中Vcan过量的流行，对ECM周转的研究将使我们了解 主动脉瓣疾病的分子和细胞起源，这可能导致治疗进展。

Summary: Approximately 1.5% of individuals have a Bicuspid Aortic Valve (BAV) that can result in insufficient blood flow and organ damage (1, 2). A BAV is also an independent risk factor for ascending aortic wall complications that can lead to rupture and sudden death. However, the cell and molecular basis for the BAV is unknown. Even basic aspects of BAV formation are undefined due to contributions from multiple cell lineages and a lack of highly penetrant viable BAV mouse models. Dysfunctional aortic valves exhibit massive accumulation of the extracellular matrix (ECM) proteoglycans versican (Vcan) and aggrecan (Acan) (3-7) but the origin and consequence of excess proteoglycans is largely unknown. Since proteoglycans are highly stable, abundance is regulated primarily by proteolytic degradation which led us to investigate a role for proteoglycan cleavage. We discovered that loss of a single ECM proteoglycanase, Adamts5, results in enlarged aortic valves with ascending aortopathies (100%). These defects co-localize with substantial increases in Vcan and Acan in the affected tissues (8-10) that mirror the human condition. Mechanistically, in Adamts5-/- aortic valve primordia with excess Vcan there is a reduction of pSmad2, and when Smad2 is reduced further by generating Adamts5-/- ;Smad2+/- mice, there is a high penetrance of BAV (75%), much higher than seen in other mouse BAV models. The objective of this proposal is to utilize the viable Adamts5-/-;Smad2+/- mice that exhibit a high percentage of BAV, to define morphological events, cell behaviors and factors that when disrupted contribute to BAV formation. Since excess Vcan is a hallmark of dysfunctional and diseased valves, use of a model with mutations that impact the control of Vcan content, may shed light on how proteoglycan metabolism is regulated in development and may also give insight into disease. Experiments test the hypothesis that ECM Vcan cleavage coordinates mesenchymal cell behaviors and myocardial cell contributions that are required for the tricuspid morphology of aortic valves. The hypothesis is tested in two aims: Aim 1 tests the impact of altered Vcan cleavage on mesenchymal cell lineage behaviors that are required for aortic valve formation. Our preliminary data show that loss of Vcan cleaved fragments and excess intact Vcan, disrupted lineage-specific patterning in the developing aortic valves of the BAV Adamts5-/-;Smad2+/-mice. A combination of ex vivo, and in vivo approaches will decipher the lineage-specific cell behaviors, and guidance factors that are dependent on Vcan cleavage and to prevent BAV. Although dogma states that valve cusps arise from mesenchymal cells, Aim 2 investigates the consequence of excess Vcan on the myocardial cell lineage contributions to the developing aortic valve in Adamts5-/-;Smad2+/- mice and other murine models of BAV. Our preliminary data show myocardial lineage expression of Adamts5 is required to clear Vcan-rich ECM and to form the non-coronary cusp of the aortic valve. Due to the emerging prevalence of excess Vcan in BAV, the investigation into ECM turnover will allow insight into the molecular and cellular origins of aortic valve diseases, which may lead to therapeutic advances.