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Context: Vitamin D deficiency is associated with many adverse health outcomes, yet little is known about the genetic epidemiology of vitamin D or its metabolites., Objective: Our objective was to examine the relationship among three vitamin D-related genes and levels of 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] in Hispanics (HAs) and African Americans (AAs)., Design and Setting: The cross-sectional Insulin Resistance Atherosclerosis Family Study recruited and examined subjects in: Los Angeles, California (AAs; 513 individuals from 42 families); San Luis Valley (SLV), Colorado (HAs; 513 individuals from 30 families); and San Antonio (SA), Texas (HAs; 504 individuals from 58 families)., Main Outcome Measures: Plasma levels of 25(OH)D and 1,25(OH)2D were measured., Results: Levels of 25(OH)D were highest in SLV-HAs [18.3 +/- 7.7 ng/ml (45.7 +/- 19.2 nmol/liter)], lower in SA-HAs [14.6 +/- 6.4 ng/ml (36.4 +/- 16.0 nmol/liter)], and lowest in AAs [11.0 +/- 5.4 ng/ml (27.5 +/- 13.5 nmol/liter)]. Levels of 1,25(OH)2D were similar in AAs [43.5 +/- 13.9 pg/ml (113.1 +/- 36.1 pmol/liter)] and SLV-HAs [43.2 +/- 13.3 pg/ml (112.3 +/- 34.6 pmol/liter)], but higher in SA-HAs [48.6 +/- 17.0 pg/ml (126.4 +/- 44.2 pmol/liter)]. After adjusting for gender and age within the site, two single nucleotide polymorphisms (SNPs) in the vitamin D binding protein gene (DBP), rs4588 and rs7041, were associated with 25(OH)D, and one SNP in the DBP, rs4588, was associated with 1,25(OH)2D at all three study centers., Conclusions: SNPs in the DBP are associated with levels of 25(OH)D and 1,25(OH)2D in HA and AA participants in the Insulin Resistance Atherosclerosis Family Study.

Isolation of distinct subpopulations of density-fractionated normal human B lymphocytes reveals that the requirements for up-regulation of the vitamin D receptor (VDR) and initiation of 1alpha,25-dihydroxyvitamin D3 [1alpha,25-(OH)2D3]-mediated genomic trans-activation are dependent upon the state of cellular activation. The kinetics of the response differ widely among these B cell subpopulations. However, these density-fractionated B cell subpopulations are phenotypically diverse and therefore are not representative of distinct stages of B cell maturation and differentiation. To examine the role of B cell differentiation on the induction and maintenance of biological receptivity to 1,25-(OH)2D3, we purified naive, germinal center, and memory B cells based on their expression of CD38 and CD44 surface antigens and surface Ig isotype. These phenotypically defined B cell subpopulations were all found to constitutively express VDR, and all exhibited similar activation requirements and kinetics for initiation of 1,25(OH)2D3-mediated genomic trans-activation. Taken together, these results suggest that defined stages of differentiation in normal B cells are not significant predicators of VDR expression or receptivity to 1,25-(OH)2D3. Rather, the degree of cellular activation, regardless of maturation stage, determines whether the effects of this immunoregulatory hormone will influence a mature B lymphocyte.

1 alpha,25(OH)2vitamin-D3, [1 alpha,25(OH)2D3] is a potent steroid hormone that produces a wide array of biologic effects in a variety of target tissues within the body through its ability to modulate gene transcription of specific target genes. Evidence for transcription regulation of a specific gene typically includes 1 alpha,25(OH)2D3-induced modulation in mRNA levels. Additionally, evidence may include measurements of transcription and/or the presence of a vitamin D response element within the promoter region of the gene. To date, over 50 genes have been reported to be transcriptionally regulated by 1 alpha,25(OH)2D3. We present a current list of these genes and the evidence supporting their inclusion on the list.

We previously reported that 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25-(OH)2D3] specifically stimulates production of the third component of complement (C3) by murine osteoblastic cells and marrow-derived stromal cells (ST2) in vitro. In the present study we examined tissue-specific production of C3 in vivo in vitamin D-deficient mice, some of which received supplemental 1 alpha,25-(OH)2D3. Western blot analysis indicated that the C3 protein band in bone was undetectable in vitamin D-deficient mice, but became distinct 48 h after 1 alpha,25-(OH)2D3 administration. The mRNA expression of C3 in bone was also undetectable in vitamin D-deficient mice and appeared as early as 24 h after 1 alpha,25-(OH)2D3 administration. mRNA expression apparently preceded the appearance of C3 protein. In contrast, there was no significant difference in the expression of hepatic C3 mRNA among normal mice fed laboratory chow and vitamin D-deficient mice with and without 1 alpha,25-(OH)2D3 administration. The serum concentration of C3 in vitamin D-deficient mice was almost identical to that in normal mice and was unchanged after 1 alpha,25-(OH)2D3 administration. 1 alpha,25-(OH)2D3 receptor (VDR) mRNAs were detected in the kidney and intestine, whereas no appreciable mRNA expression of VDR occurred in the liver. Osteopontin mRNA was expressed in response to 1 alpha,25-(OH)2D3 in the kidney, but not in the intestine. Immunohistochemical studies showed that in normal mice, the C3 protein was located mainly in the periosteal regions of calvaria and on the surfaces of bone trabeculae in the tibial metaphyses. These results demonstrate that 1 alpha,25-(OH)2D3 tissue-specifically regulates in vivo production of C3 in bone. The production of bone C3 cannot be attributed to the presence of VDR alone, and we speculate that other tissue-specific factors are required.