Department of Regenerative Medicine and Cell Biology, Medical University of South Carolina, Charleston, 29425, USA.
Dev Biol. 2011 Sep 1;357(1):152-64. doi: 10.1016/j.ydbio.2011.06.041. Epub 2011 Jul 1.
In fetal valve maturation the mechanisms by which the relatively homogeneous proteoglycan-rich extracellular matrix (ECM) of endocardial cushions is replaced by a specialized and stratified ECM found in mature valves are not understood. Therefore, we reasoned that uncovering proteases critical for 'remodeling' the proteoglycan rich (extracellular matrix) ECM may elucidate novel mechanisms of valve development. We have determined that mice deficient in ADAMTS5, (A Disintegrin-like And Metalloprotease domain with ThromboSpondin-type 1 motifs) which we demonstrated is expressed predominantly by valvular endocardium during cardiac valve maturation, exhibited enlarged valves. ADAMTS5 deficient valves displayed a reduction in cleavage of its substrate versican, a critical cardiac proteoglycan. In vivo reduction of versican, in Adamts5(-/-) mice, achieved through Vcan heterozygosity, substantially rescued the valve anomalies. An increase in BMP2 immunolocalization, Sox9 expression and mesenchymal cell proliferation were observed in Adamts5(-/-) valve mesenchyme and correlated with expansion of the spongiosa (proteoglycan-rich) region in Adamts5(-/-) valve cusps. Furthermore, these data suggest that ECM remodeling via ADAMTS5 is required for endocardial to mesenchymal signaling in late fetal valve development. Although adult Adamts5(-/-) mice are viable they do not recover from developmental valve anomalies and have myxomatous cardiac valves with 100% penetrance. Since the accumulation of proteoglycans is a hallmark of myxomatous valve disease, based on these data we hypothesize that a lack of versican cleavage during fetal valve development may be a potential etiology of adult myxomatous valve disease.
在胎儿瓣膜成熟过程中，尚不清楚心内膜垫中相对均质的富含蛋白聚糖的细胞外基质（ECM）被成熟瓣膜中特化和分层的 ECM 取代的机制。因此，我们推测，揭示对于“重塑”富含蛋白聚糖（细胞外基质） ECM 的关键蛋白酶可能阐明瓣膜发育的新机制。我们已经确定，ADAMTS5 缺乏的小鼠（一种具有血栓素样 1 基序的解整合素样金属蛋白酶域），我们证明其在心脏瓣膜成熟过程中主要由瓣膜心内膜表达，表现出瓣膜增大。ADAMTS5 缺乏的瓣膜显示其底物 versican 的裂解减少，versican 是一种关键的心脏蛋白聚糖。通过 Vcan 杂合性，在 Adamts5(-/-) 小鼠中体内降低 versican 水平，可显著挽救瓣膜异常。在 Adamts5(-/-)瓣膜间质中观察到 BMP2 免疫定位、Sox9 表达和间充质细胞增殖增加，并且与 Adamts5(-/-)瓣膜瓣叶海绵状区（富含蛋白聚糖）的扩张相关。此外，这些数据表明，通过 ADAMTS5 的 ECM 重塑对于胎儿晚期瓣膜发育中心内膜向间质的信号转导是必需的。尽管成年 Adamts5(-/-) 小鼠存活，但它们不能从发育性瓣膜异常中恢复，并且具有 100%外显率的黏液瘤性心脏瓣膜。由于蛋白聚糖的积累是黏液瘤性瓣膜病的标志，基于这些数据，我们假设在胎儿瓣膜发育过程中 versican 裂解的缺乏可能是成年黏液瘤性瓣膜病的潜在病因。
