FAM20C (family with sequence similarity 20 – member C) is a protein kinase that phosphorylates secretory proteins, including the proteins that are essential to the formation and mineralization of calcified tissues. Previously, we reported that inactivation of Fam20c in mice led to hypophosphatemic rickets/osteomalacia along with increased circulating fibroblast growth factor 23 (FGF23) levels and dental defects. In this study, we examined whether a high-phosphate (hPi) diet could rescue the skeletal defects in Fam20c-deficient mice. Fam20c conditional knockout (cKO) mice were generated by crossing female Fam20c-floxed mice (Fam20cfl/fl) with male Sox2-Cre;Fam20cfl/+ mice. The pregnant female Fam20cfi/fl mice were fed either a normal or hPi diet until the litters were weaned. The cKO and control offspring were continuously given a normal or hPi diet for 4 weeks after weaning. Plain X-ray radiography, micro-CT, histology, immunohistochemistry (FGF23, DMP1, OPN, and SOX9), and in situ hybridization (type II and type X collagen) analyses were performed to evaluate the effects of an hPi diet on the mouse skeleton. Plain X-ray radiography and micro-CT radiography analyses showed that the hPi diet improved the shape and mineral density of the Fam20c-deficient femurs/tibiae, and rescued the growth plate defects in the long bone. Histology analyses further demonstrated that an hPi diet nearly completely rescued the growth plate-widening defects in the long bone and restored the expanded hypertrophic zone to nearly normal width. These results suggested that the hPi diet significantly improved the skeletal development of the Fam20c-deficient mice, implying that hypophosphatemia partially contributed to the skeletal defects in Fam20c-deficient subjects.

中文翻译：

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高磷酸盐饮食改善Fam20c缺陷小鼠的骨骼发育

FAM20C（序列相似性为 20 的家族 - 成员 C）是一种蛋白激酶，可磷酸化分泌蛋白，包括对钙化组织的形成和矿化至关重要的蛋白质。以前，我们报道了小鼠 Fam20c 的失活导致低磷佝偻病/骨软化症以及循环成纤维细胞生长因子 23 (FGF23) 水平增加和牙齿缺陷。在这项研究中，我们检查了高磷酸盐 (hPi) 饮食是否可以挽救 Fam20c 缺陷小鼠的骨骼缺陷。Fam20c 条件性敲除 (cKO) 小鼠是通过将雌性 Fam20c-floxed 小鼠 (Fam20cfl/fl) 与雄性 Sox2-Cre;Fam20cfl/+ 小鼠杂交产生的。怀孕的雌性 Fam20cfi/fl 小鼠被喂食正常或 hPi 饮食，直到断奶。cKO 和对照后代在断奶后连续 4 周接受正常或 hPi 饮食。进行 X 射线平片、显微 CT、组织学、免疫组织化学（FGF23、DMP1、OPN 和 SOX9）和原位杂交（II 型和 X 型胶原蛋白）分析以评估 hPi 饮食对小鼠的影响骨骼。X 射线平片和显微 CT 影像分析表明，hPi 饮食改善了 Fam20c 缺陷股骨/胫骨的形状和矿物质密度，并挽救了长骨中的生长板缺陷。组织学分析进一步表明，hPi 饮食几乎完全挽救了长骨中生长板加宽的缺陷，并将扩大的肥大区恢复到接近正常的宽度。