巩膜MMP-2通过促进MMP-13和MMP-14的表达参与巩膜胶原降解及近视形成

Myopia is the most prevalent refractive error worldwide, but its pathogenesis is poorly understood. Even though increased collagen degradation is a key event during myopia development, the mechanism involved in this process remains to be studied in depth. As previously reported, scleral matrix metalloproteinase-2 (MMP-2) expression was significantly increased during the progression of myopia; however, the cause-effect relationship between MMP-2 and myopia development still needs further investigation. Another uncertainty pertains to the regulatory mechanism of MMP-2 underlying scleral collagen degradation. In our previous study, we demonstrated in the mice model that: i) the scleral MMP-2 expression was up-regulated during myopia development; ii) elevating the level of scleral MMP-2 could induce myopia that was accompanied by enhanced MMP-13 and MMP-14 expression; iii) reducing the level of scleral MMP-2 could inhibit the progression of form deprivation myopia. These findings prompt our hypothesis than an increase in scleral MMP-2 expression contributes to enhancing collagen degradation and myopia development by promoting the expression of other collagen-degrading-matrix metalloproteinases. To study test this hypothesis, we will first determine if scleral fibroblast specific knockout of MMP-2 inhibits form deprivation myopia in mice. Such an approach determines if scleral MMP-2 upregulation contributes to myopia development. Subsequently, we will determine if MMP-2 induces expression of MMP-13 and MMP-14 during the scleral extracellular matrix remodeling process both in vivo and in vitro. By characterizing the role of MMP-2, needed insight will be gained into identifying novel drug targets whose modulation provide improved management of myopia.

近视是全球发病率最高的屈光不正，但发病机制未明，巩膜胶原降解增多是近视发生时的关键改变，但其调控机制未明。既往研究发现近视发生时巩膜MMP-2表达升高，但MMP-2增多与近视的因果关系及MMP-2调控胶原降解的机制未明。我们前期研究表明：形觉剥夺性近视小鼠巩膜MMP-2表达升高；增加巩膜MMP-2可促进巩膜MMP-13和MMP-14的表达，并可诱导近视形成；而抑制巩膜MMP-2可抑制小鼠近视的形成。因此基于以上研究结果，提出本项目的科学假设“巩膜MMP-2增多通过促进MMP-13和MMP-14的表达参与胶原降解，导致巩膜胶原减少及近视形成”。本项目将首先研究敲除巩膜成纤维细胞MMP-2对近视的影响，进一步明确巩膜MMP-2增多是近视形成的原因，然后再结合体内和体外实验阐述MMP-2参与胶原降解的机制。通过本研究，不仅进一步阐述巩膜胶原降解及近视的发病机制，也为近视的药物干预提供理论基础。

巩膜胶原降解增多是近视形成的关键诱因之一，然而其调控机制尚不明确。本研究发现：①巩膜MMP-2增多是巩膜胶原降解增加、近视形成的原因：近视形成时巩膜MMP-2的mRNA及蛋白水平均上调、活性形式MMP-2增多，增加巩膜MMP-2表达可通过增加MMP-13和MMP-14表达促进胶原降解诱导近视形成，抑制巩膜MMP-2表达可抑制胶原降解抑制近视形成，此外，敲除成纤维细胞MMP-2可抑制27%的近视形成（研究结果发表于：Am J Pathol. 2018 Aug;188(8):1754-176；排名第一作者，受本项目资助）；②近视发生时巩膜巨噬细胞数量增多，并通过分泌MMP-2参与近视形成，敲除巨噬细胞MMP-2可抑制59%的近视形成（研究结果发表于：Am J Pathol. 2020 Sep;190(9):1888-1908；排名第一作者，受本项目资助）。上述研究成果表明巩膜MMP-2增多是巩膜胶原降解增多导致近视形成的原因，也表明了巩膜成纤维细胞和巨噬细胞均为MMP-2的来源。然而诱导两类细胞表达MMP-2增多的因素尚不明确。本课题组前期突破性研究成果表明：巩膜缺氧通过抑制胶原合成、促进成纤维细胞转分化诱导小鼠和豚鼠的近视形成（相关研究结果发表于：Proc Natl Acad Sci U S A. 2018 Jul 24;115(30):E7091-E7100；共同第一作者）。进一步研究发现：巩膜缺氧也是人类近视的形成的关键诱因（研究结果发表于：EBioMedicine. 2020 Jul;57:102878；排名第一作者，受本项目资助）。体外实验表明，缺氧可以促进人巩膜成纤维细胞和巨噬细胞MMP-2的表达上调。综上所述，巩膜成纤维细胞和巨噬细胞均通过分泌MMP-2促进胶原降解，进而导致近视形成；而巩膜缺氧可能是巩膜MMP-2增多的触发因素。这不仅完善了巩膜胶原降解机制，也为近视的药物干预提供了新的靶点。