Uterine Dysfunction in Biglycan and Decorin Deficient Mice Leads to Dystocia during Parturition

Cesarean birth rates are rising. Uterine dysfunction, the exact mechanism of which is unknown, is a common indication for Cesarean delivery. Biglycan and decorin are two small leucine-rich proteoglycans expressed in the extracellular matrix of reproductive tissues and muscle. Mice deficient in biglycan display a mild muscular dystrophy, and, along with mice deficient in decorin, are models of Ehlers-Danlos Syndrome, a connective tissue anomaly associated with uterine rupture. As a variant of Ehlers-Danlos Syndrome is caused by a genetic mutation resulting in abnormal biglycan and decorin secretion, we hypothesized that biglycan and decorin play a role in uterine function. Thus, we assessed wild-type, biglycan, decorin and double knockout pregnancies for timing of birth and uterine function. Uteri were harvested at embryonic days 12, 15 and 18. Nonpregnant uterine samples of the same genotypes were assessed for tissue failure rate and spontaneous and oxytocin-induced contractility. We discovered that biglycan/decorin mixed double-knockout dams displayed dystocia, were at increased risk of delayed labor onset, and showed increased tissue failure in a predominantly decorin-dependent manner. In vitro spontaneous uterine contractile amplitude and oxytocin-induced contractile force were decreased in all biglycan and decorin knockout genotypes compared to wild-type. Notably, we found no significant compensation between biglycan and decorin using quantitative real time PCR or immunohistochemistry. We conclude that the biglycan/decorin mixed double knockout mouse is a model of dystocia and delayed labor onset. Moreover, decorin is necessary for uterine function in a dose-dependent manner, while biglycan exhibits partial compensatory mechanisms in vivo. Thus, this model is poised for use as a model for testing novel targets for preventive or therapeutic manipulation of uterine dysfunction.

剖宫产率呈逐年上升趋势。子宫功能障碍（uterine dysfunction）是剖宫产分娩的常见指征，但其确切发病机制尚未阐明。双糖链蛋白聚糖（biglycan）与核心蛋白聚糖（decorin）是两类在生殖组织与肌肉细胞外基质（extracellular matrix）中表达的富含亮氨酸小分子蛋白聚糖（small leucine-rich proteoglycans）。双糖链蛋白聚糖敲除小鼠可表现出轻度肌营养不良症，而双糖链蛋白聚糖与核心蛋白聚糖双敲除小鼠则可作为埃勒斯-当洛综合征（Ehlers-Danlos Syndrome, EDS）的模型——该综合征是一类与子宫破裂相关的结缔组织异常疾病。由于埃勒斯-当洛综合征的一种变异亚型由可导致双糖链蛋白聚糖与核心蛋白聚糖分泌异常的基因突变引发，我们提出假说：双糖链蛋白聚糖与核心蛋白聚糖在子宫功能中发挥调控作用。为此，我们对野生型（wild-type, WT）、单基因敲除（biglycan敲除、decorin敲除）及双基因敲除孕鼠的分娩时间与子宫功能进行了评估。分别在胚胎发育第12、15、18天收取子宫组织；同时对相同基因型的未妊娠子宫样本，检测其组织破裂率、自发性收缩活性与催产素诱导的收缩活性。研究发现，双糖链蛋白聚糖/核心蛋白聚糖混合双敲除孕鼠可出现难产，分娩启动延迟风险升高，且组织破裂率显著升高，该效应主要以核心蛋白聚糖依赖性方式介导。体外实验显示，与野生型小鼠相比，所有双糖链蛋白聚糖与核心蛋白聚糖单敲除基因型小鼠的子宫自发收缩幅度及催产素诱导的收缩力均有所降低。值得注意的是，通过实时定量聚合酶链式反应（quantitative real-time PCR, qRT-PCR）与免疫组织化学法（immunohistochemistry, IHC）检测，我们未发现双糖链蛋白聚糖与核心蛋白聚糖之间存在显著的代偿交互作用。综上，双糖链蛋白聚糖/核心蛋白聚糖混合双敲除小鼠可作为难产与分娩启动延迟的动物模型。此外，核心蛋白聚糖以剂量依赖性方式对子宫功能至关重要，而双糖链蛋白聚糖在体内仅发挥部分代偿作用。因此，该模型可用于靶向测试子宫功能障碍的新型预防性或治疗性干预靶点。