Browsing by Author "Fleet, James C."

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    Diet X Gene Interactions Control Femoral Bone Adaptation to Low Dietary Calcium
    (Wiley, 2022-08-19) Chanpaisaeng, Krittikan; Reyes-Fernandez, Perla C.; Dilkes, Brian; Fleet, James C.; Physical Therapy, School of Health and Human Sciences
    Genetics and dietary calcium (Ca) are each critical regulators of peak bone mass but it is unclear how genetics alters the physiologic response of bone to dietary Ca restriction (RCR). Here, we conducted genetic mapping in C57BL/6J × DBA/2J (BXD) recombinant inbred mouse lines to identify environmentally sensitive loci controlling whole-bone mass (bone mineral density [BMD], bone mineral content [BMC]), distal trabecular bone, and cortical bone midshaft of the femur. Mice were fed adequate (basal) or low Ca diets from 4-12 weeks of age. Femurs were then examined by dual-energy X-ray absorptiometry (DXA) and micro-computed tomography (μCT). Body size-corrected residuals were used for statistical analysis, genetic mapping, and to estimate narrow sense heritability (h2). Genetics had a strong impact on femoral traits (eg, bone volume fraction [BV/TV] basal Ca, h2 = 0.60) as well as their RCR (eg, BV/TV, h2 = 0.32). Quantitative trait locus (QTL) mapping identified up to six loci affecting each bone trait. A subset of loci was detected in both diet groups, providing replication of environmentally robust genetic effects. Several loci control multiple bone phenotypes suggesting the existence of genetic pleiotropy. QTL controlling the bone RCR did not overlap with basal diet QTL, demonstrating genetic independence of those traits. Candidate genes underlying select multi-trait loci were prioritized by protein coding effects or gene expression differences in bone cells. These include candidate alleles in Rictor (chromosome [chr] 15) and Egfl7 (chr 2) at loci affecting bone in the basal or low Ca groups and in Msr1 (chr 8), Apc, and Camk4 (chr 18) at loci affecting RCR. By carefully controlling dietary Ca and measuring traits in age-matched mice we identified novel genetic loci determining bone mass/microarchitecture of the distal femur as well as their physiologic adaptation to inadequate dietary Ca intake.
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    Gene-by-Diet Interactions Affect Serum 1,25-Dihydroxyvitamin D Levels in Male BXD Recombinant Inbred Mice
    (Oxford University Press, 2016-02) Fleet, James C.; Replogle, Rebecca A.; Reyes-Fernandez, Perla; Wang, Libo; Zhang, Min; Clinkenbeard, Erica L.; White, Kenneth E.; Department of Medical & Molecular Genetics, IU School of Medicine
    1,25-Dihydroxyvitamin D (1,25[OH]2D) regulates calcium (Ca), phosphate, and bone metabolism. Serum 1,25(OH)2D levels are reduced by low vitamin D status and high fibroblast growth factor 23 (FGF23) levels and increased by low Ca intake and high PTH levels. Natural genetic variation controls serum 25-hydroxyvitamin D (25[OH]D) levels, but it is unclear how it controls serum 1,25(OH)2D or the response of serum 1,25(OH)2D levels to dietary Ca restriction (RCR). Male mice from 11 inbred lines and from 51 BXD recombinant inbred lines were fed diets with either 0.5% (basal) or 0.25% Ca from 4 to 12 weeks of age (n = 8 per line per diet). Significant variation among the lines was found in basal serum 1,25(OH)2D and in the RCR as well as basal serum 25(OH)D and FGF23 levels. 1,25(OH)2D was not correlated to 25(OH)D but was negatively correlated to FGF23 (r = -0.5). Narrow sense heritability of 1,25(OH)2D was 0.67 on the 0.5% Ca diet, 0.66 on the 0.25% Ca diet, and 0.59 for the RCR, indicating a strong genetic control of serum 1,25(OH)2D. Genetic mapping revealed many loci controlling 1,25(OH)2D (seven loci) and the RCR (three loci) as well as 25(OH)D (four loci) and FGF23 (two loci); a locus on chromosome 18 controlled both 1,25(OH)2D and FGF23. Candidate genes underlying loci include the following: Ets1 (1,25[OH]2D), Elac1 (FGF23 and 1,25[OH]2D), Tbc1d15 (RCR), Plekha8 and Lyplal1 (25[OH]D), and Trim35 (FGF23). This report is the first to reveal that serum 1,25(OH)2D levels are controlled by multiple genetic factors and that some of these genetic loci interact with the dietary environment.
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    Iron deficiency drives an autosomal dominant hypophosphatemic rickets (ADHR) phenotype in fibroblast growth factor-23 (Fgf23) knock-in mice
    (2011-11-15) Farrow, Emily G.; Yu, Xijie; Summers, Leila J.; Davis, Siobhan I.; Fleet, James C.; Allen, Matthew R.; Robling, Alexander G.; Stayrook, Keith R.; Jideonwo, Victoria; Magers, Martin J.; Garringer, Holly J.; Vidal, Ruben; Chan, Rebecca J.; Goodwin, Charles B.; Hui, Siu L.; Peacock, Munro; White, Kenneth E.
    Autosomal dominant hypophosphatemic rickets (ADHR) is unique among the disorders involving Fibroblast growth factor 23 (FGF23) because individuals with R176Q/W and R179Q/W mutations in the FGF23 (176)RXXR(179)/S(180) proteolytic cleavage motif can cycle from unaffected status to delayed onset of disease. This onset may occur in physiological states associated with iron deficiency, including puberty and pregnancy. To test the role of iron status in development of the ADHR phenotype, WT and R176Q-Fgf23 knock-in (ADHR) mice were placed on control or low-iron diets. Both the WT and ADHR mice receiving low-iron diet had significantly elevated bone Fgf23 mRNA. WT mice on a low-iron diet maintained normal serum intact Fgf23 and phosphate metabolism, with elevated serum C-terminal Fgf23 fragments. In contrast, the ADHR mice on the low-iron diet had elevated intact and C-terminal Fgf23 with hypophosphatemic osteomalacia. We used in vitro iron chelation to isolate the effects of iron deficiency on Fgf23 expression. We found that iron chelation in vitro resulted in a significant increase in Fgf23 mRNA that was dependent upon Mapk. Thus, unlike other syndromes of elevated FGF23, our findings support the concept that late-onset ADHR is the product of gene-environment interactions whereby the combined presence of an Fgf23-stabilizing mutation and iron deficiency can lead to ADHR.