PAPPA2基因在发育性髋关节发育不良发病机制中的作用研究

Developmental dysplasia of the hip (DDH) is a severe birth defect threatening the population health in China, and determined by genetic and environmental factors. The predisposing genes of DDH still remain unknown. In our previous study, A SNP of rs726252 within pregnancy-associated plasma protein A2 (PAPPA2) gene was confirmed associated with DDH by genome-wide scan and case-control analysis. The PAPPA2 gene was therefore a probable susceptibility gene of DDH. PAPPA2, a proteinase of insulin-like growth factor binding protein 5 (IGFBP-5), can regulate the bioavailability and activity of IGF by proteolyzing IGFBP-5. Meanwhile, the IGF signaling can modulate the synthesis of collagen in fibroblasts and the development of growth plate by interacting with the PTHrP and Ihh pathway in chondrocytes. However, the abnormal development in chondrocytes and fibroblasts are the main pathological features of DDH. Thus, we presumed that the PAPPA2 gene could play an important role in the development of DDH by IGF signaling pathway. Based on the previous study, we will sequentially endeavor to find the susceptive SNP genotype to DDH in the coded region of PAPPA2 gene by genotyping strategy, and investigate the expression of PAPPA2 in DDH at the level of RNA and protein. In vitro, we will further observe the effect of PAPPA2 to the development of cultured chondrocytes and fibroblasts. In addition, in vivo study, we will investigate the fetal development of the hip in mouse with the PAPPA2 gene silenced by RNAi technique. By this study, we expect to elucidate the effects of PAPPA2 gene in the pathogenesis of developmental dysplasia of the hip.

发育性髋关节发育不良(Developmental dysplasia of the hip, DDH)是严重威胁我国出生人口素质的重大出生缺陷，其病因不清。前期，我们通过全基因组扫描，发现rs726252与DDH相关联。该位点位于PAPPA2基因内，提示PAPPA2基因可能是DDH的易感基因，推测PAPPA2基因可能是间接通过IGF途径导致DDH的。我们将在前期基础上，进一步对该基因的编码区及调控区进行突变筛查，并在RNA及蛋白水平证实PAPPA2基因与DDH的相关性及其表达调控机制；通过体外实验，明确PAPPA2在软骨细胞及成纤维细胞IGF信号通路中的作用；通过动物体内实验，采用跨胎盘RNA干扰，结合胎仔外科及激光捕获显微切割技术，观察PAPPA2基因沉默后对IGF信号通路的影响及胚胎髋臼软骨、髋周软组织发育与正常的差异，从而阐明PAPPA2基因导致DDH发生的分子生物学机制。

发育性髋关节发育不良（Developmental dysplasia of the hip, DDH）是遗传因素与环境因素共同作用的结果，但遗传因素的作用机制现仍不清楚。前期我们通过DDH家系的全基因组扫描发现PAPPA2基因与DDH相连锁，并进一步验证PAPPA2基因与散发的DDH也相关联。PAPPA2是IGFBP5的特异性水解蛋白酶，我们推测它可能是通过IGF信号通路发挥作用的，并进一步从体外、体内实验等两方面进行了功能验证。首先，从细胞水平研究发现，高水平PAPPA2可以上调成纤维细胞和软骨细胞IGF信号通路相关蛋白的表达，如IGF, COL1A1, COL1A2, ACAN, COL2等；相反，PAPPA2的RNA干扰实验及高水平的IGFBP5均可下调上述蛋白的表达，从而抑制成纤维细胞及软骨细胞的增殖表达。另外，我们通过胎鼠羊膜腔注射及新生鼠髋关节周围注射进行动物体内PAPPA2的沉默实验，对髋关节软骨IGF信号通路相关蛋白检测，其表达趋势与体外实验相同，同时观察髋臼骺板增殖细胞柱变矮，软骨细胞排列紊乱。本研究从体内实验及体外实验均证实PAPPA2可以影响髋关节成纤维细胞及软骨细胞的功能表达，与髋关节的发育相关。进一步研究应通过基因敲除动物模型来观察髋关节的形态学发育。

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