Okubo Yumi, Masuyama Ritsuko, Iwanaga Akira, Koike Yuta, Kuwatsuka Yutaka, Ogi Tomoo, Yamamoto Yosuke, Endo Yuichiro, Tamura Hiroshi, Utani Atsushi
Department of Dermatology, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan.
Research and Clinical Center for Yusho and Dioxin (ReC2YD), Kyushu University Hospital, Fukuoka, Japan.
PLoS One. 2017 May 11;12(5):e0177375. doi: 10.1371/journal.pone.0177375. eCollection 2017.
Gamma-glutamyl carboxylase (GGCX) gene mutation causes GGCX syndrome (OMIM: 137167), which is characterized by pseudoxanthoma elasticum (PXE)-like symptoms and coagulation impairment. Here, we present a 55-year-old male with a novel homozygous deletion mutation, c.2,221delT, p.S741LfsX100, in the GGCX gene. Histopathological examination revealed calcium deposits in elastic fibers and vessel walls, and collagen accumulation in the mid-dermis. Studies of dermal fibroblasts from the patient (GGCX dermal fibroblasts) demonstrated that the mutated GGCX protein was larger, but its expression level and intracellular distribution were indistinguishable from those of the wild-type GGCX protein. Immunostaining and an enzyme-linked immunosorbent assay showed an increase in undercarboxylated matrix gamma-carboxyglutamic acid protein (ucMGP), a representative substrate of GGCX and a potent calcification inhibitor, indicating that mutated GGCX was enzymatically inactive. Under osteogenic conditions, calcium deposition was exclusively observed in GGCX dermal fibroblasts. Furthermore, GGCX dermal fibroblast cultures contained 23- and 7.7-fold more alkaline phosphatase (ALP)-positive cells than normal dermal fibroblast cultures (n = 3), without and with osteogenic induction, respectively. Expression and activity of ALP were higher in GGCX dermal fibroblasts than in normal dermal fibroblasts upon osteogenic induction. mRNA levels of other osteogenic markers were also higher in GGCX dermal fibroblasts than in normal dermal fibroblasts, which including bone morphogenetic protein 6, runt-related transcription factor 2, and periostin (POSTN) without osteogenic induction; and osterix, collagen type I alpha 2, and POSTN with osteogenic induction. Together, these data indicate that GGCX dermal fibroblasts trans-differentiate into the osteogenic lineage. This study proposes another mechanism underlying aberrant calcification in patients with GGCX syndrome.
γ-谷氨酰羧化酶（GGCX）基因突变导致GGCX综合征（OMIM：137167），其特征为弹性假黄瘤（PXE）样症状和凝血功能障碍。在此，我们报告一名55岁男性，其GGCX基因存在一种新的纯合缺失突变，即c.2221delT，p.S741LfsX100。组织病理学检查显示弹性纤维和血管壁中有钙沉积，真皮中层有胶原积累。对该患者的真皮成纤维细胞（GGCX真皮成纤维细胞）研究表明，突变的GGCX蛋白更大，但其表达水平和细胞内分布与野生型GGCX蛋白无异。免疫染色和酶联免疫吸附测定显示，GGCX的代表性底物且为强效钙化抑制剂的羧化不足基质γ-羧基谷氨酸蛋白（ucMGP）增加，表明突变的GGCX酶无活性。在成骨条件下，仅在GGCX真皮成纤维细胞中观察到钙沉积。此外，无论有无成骨诱导，GGCX真皮成纤维细胞培养物中碱性磷酸酶（ALP）阳性细胞分别比正常真皮成纤维细胞培养物（n = 3）多23倍和7.7倍。成骨诱导后，GGCX真皮成纤维细胞中ALP的表达和活性高于正常真皮成纤维细胞。在无成骨诱导时，GGCX真皮成纤维细胞中其他成骨标志物的mRNA水平也高于正常真皮成纤维细胞，这些标志物包括骨形态发生蛋白6、 runt相关转录因子2和骨膜蛋白（POSTN）；在有 成骨诱导时，这些标志物包括osterix、I型胶原α2和POSTN。总之，这些数据表明GGCX真皮成纤维细胞转分化为成骨谱系。本研究提出了GGCX综合征患者异常钙化的另一种潜在机制。
