Data from: Vitamin D receptor gene expression and function in a South African population: ethnicity, vitamin D and FokI

Polymorphisms of the vitamin D receptor gene (VDR) have been associated inconsistently with various diseases, across populations of diverse origin. The T(f) allele of the functional SNP FokI, in exon 2 of VDR, results in a longer vitamin D receptor protein (VDR) isoform, proposed to be less active. Genetic association of VDR with disease is likely confounded by ethnicity and environmental factors such as plasma 25(OH)D3 status. We hypothesized that VDR expression, VDR level and transactivation of target genes, CAMP and CYP24A1, depend on vitamin D, ethnicity and FokI genotype. Healthy volunteers participated in the study (African, n = 40 and White, n = 20). Plasma 25(OH)D3 levels were quantified by LC-MS and monocytes cultured, with or without 1,25(OH)2D3. Gene expression and protein level was quantified using qRT-PCR and flow cytometry, respectively. Mean plasma 25(OH)D3 status was normal and not significantly different between ethnicities. Neither 25(OH)D3 status nor 1,25(OH)2D3 supplementation significantly influenced expression or level of VDR. Africans had significantly higher mean VDR protein levels (P<0.050), nonetheless transactivated less CAMP expression than Whites. Genotyping the FokI polymorphism by pyrosequencing together with HapMap data, showed a significantly higher (P<0.050) frequency of the CC genotype in Africans than in Whites. FokI genotype, however, did not influence VDR expression or VDR level, but influenced overall transactivation of CAMP and 1,25(OH)2D3-elicited CYP24A1 induction; the latter, interacting with ethnicity. In conclusion, differential VDR expression relates to ethnicity, rather than 25(OH)D3 status and FokI genotype. Instead, VDR transactivation of CAMP is influenced by FokI genotype and, together with ethnicity, influence 1,25(OH)2D3-elicited CYP24A1 expression. Thus, the expression and role of VDR to transactivate target genes is determined not only by genetics, but also by ethnicity and environment involving complex interactions which may confound disease association.

在不同血统的人群中，维生素D受体基因（vitamin D receptor gene, VDR）的多态性与多种疾病的关联始终缺乏一致性。位于VDR第2外显子的功能性单核苷酸多态性（single nucleotide polymorphism, SNP）FokI的T(f)等位基因，可编码产生更长的维生素D受体蛋白（VDR）亚型，该亚型被认为活性较弱。VDR与疾病的遗传关联很可能受到种族及血浆25(OH)D3水平等环境因素的混杂影响。本研究提出假说：VDR的表达水平、蛋白含量以及靶基因CAMP与CYP24A1的反式激活能力，均受维生素D水平、种族及FokI基因型的调控。本研究共招募健康志愿者参与，其中非洲裔人群40例，白人20例。采用液相色谱-质谱联用法（liquid chromatography-mass spectrometry, LC-MS）定量检测受试者血浆25(OH)D3水平，并对分离得到的单核细胞进行体外培养，分别添加或不添加1,25(OH)2D3。分别通过实时荧光定量聚合酶链反应（quantitative real-time polymerase chain reaction, qRT-PCR）与流式细胞术，定量检测细胞的基因表达水平与蛋白表达水平。所有受试者的平均血浆25(OH)D3水平处于正常参考范围内，且不同种族间的该指标无显著差异。无论是血浆25(OH)D3基础水平，还是1,25(OH)2D3补充处理，均未对VDR的基因表达或蛋白水平产生显著影响。非洲裔人群的平均VDR蛋白水平显著高于白人（P<0.050），但其对CAMP基因的反式激活水平却显著低于白人。通过焦磷酸测序对FokI多态性进行基因分型，并结合国际人类基因组单体型图计划（HapMap）数据，结果显示非洲裔人群的CC基因型频率显著高于白人（P<0.050）。然而，FokI基因型并未对VDR的基因表达或蛋白水平产生影响，但可显著影响CAMP的整体反式激活水平，以及1,25(OH)2D3诱导的CYP24A1表达，且后者与种族存在交互作用。综上，VDR的表达差异与种族相关，而非血浆25(OH)D3水平或FokI基因型。与之相反，VDR对CAMP的反式激活作用受FokI基因型调控，且该作用与种族共同影响1,25(OH)2D3诱导的CYP24A1表达。由此可见，VDR的表达及其对靶基因的反式激活作用，不仅由遗传因素决定，还受到种族与环境的复杂交互作用影响，这类交互作用可能会混淆VDR多态性与疾病的关联分析结果。