Department of Biomedical Sciences, Texas A&M University College of Dentistry, Dallas, Texas, USA,
Department of Biomedical Sciences, Texas A&M University College of Dentistry, Dallas, Texas, USA.
Cells Tissues Organs. 2019;208(1-2):25-36. doi: 10.1159/000506005. Epub 2020 Feb 26.
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.
家族成员 20 相似性蛋白 C（FAM20C）是一种蛋白激酶，可使分泌蛋白磷酸化，包括对钙化组织形成和矿化至关重要的蛋白质。以前，我们报道了 Fam20c 在小鼠中的失活导致低磷性佝偻病/骨软化症，同时伴有循环成纤维细胞生长因子 23（FGF23）水平升高和牙齿缺陷。在这项研究中，我们研究了高磷（hPi）饮食是否可以挽救 Fam20c 缺陷小鼠的骨骼缺陷。通过将 Fam20c 条件敲除（cKO）小鼠（Fam20cfl/fl）与 Sox2-Cre；Fam20cfl/+ 雄性小鼠交配，生成 Fam20c 条件敲除小鼠。在怀孕的 Fam20cfi/fl 母鼠中，直到幼崽断奶，给予正常或 hPi 饮食。cKO 和对照后代在断奶后连续给予正常或 hPi 饮食 4 周。进行普通 X 射线放射摄影、微计算机断层扫描、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）分析，以评估 hPi 饮食对小鼠骨骼的影响。普通 X 射线放射摄影和微计算机断层扫描分析表明，hPi 饮食改善了 Fam20c 缺陷小鼠股骨/胫骨的形状和矿化密度，并挽救了长骨生长板缺陷。组织学分析进一步表明，hPi 饮食几乎完全挽救了长骨生长板增宽缺陷，并将扩大的肥大区恢复到几乎正常宽度。这些结果表明，hPi 饮食显著改善了 Fam20c 缺陷小鼠的骨骼发育，表明低磷血症部分导致 Fam20c 缺陷患者的骨骼缺陷。
