Post-genome wide association studies and functional analyses identify association of MPP7 gene variants with site-specific bone mineral density

Abstract

Our previous genome-wide association study (GWAS) in a Hong Kong Southern Chinese population with extreme bone mineral density (BMD) scores revealed suggestive association with MPP7, which ranked second after JAG1 as a candidate gene for BMD. To follow-up this suggestive signal, we replicated the top single-nucleotide polymorphism rs4317882 of MPP7 in three additional independent Asian-descent samples (n= 2684). The association of rs4317882 reached the genome-wide significance in the meta-analysis of all available subjects (P(meta)= 4.58 × 10(-8), n= 4204). Site heterogeneity was observed, with a larger effect on spine than hip BMD. Further functional studies in a zebrafish model revealed that vertebral bone mass was lower in an mpp7 knock-down model compared with the wide-type (P= 9.64 × 10(-4), n= 21). In addition, MPP7 was found to have constitutive expression in human bone-derived cells during osteogenesis. Immunostaining of murine MC3T3-E1 cells revealed that the Mpp7 protein is localized in the plasma membrane and intracytoplasmic compartment of osteoblasts. In an assessment of the function of identified variants, an electrophoretic mobility shift assay demonstrated the binding of transcriptional factor GATA2 to the risk allele 'A' but not the 'G' allele of rs4317882. An mRNA expression study in human peripheral blood mononuclear cells confirmed that the low BMD-related allele 'A' of rs4317882 was associated with lower MPP7 expression (P= 9.07 × 10(-3), n= 135). Our data suggest a genetic and functional association of MPP7 with BMD variation.

Quantitative assessment of the regenerative and mineralogenic performances of the zebrafish caudal fin

“…Thus, we tested a new approach to evaluate mineralogenic effects within the transverse plane, using the longitudinal plane images collected for the area-based analysis. As it also happens with other fluorescent dyes, like calcein13, this approach assumes that AR-S staining (within the longitudinal plane) will be enhanced in high density or thicker-ray areas, thus displaying a stronger fluorescence signal48. In this regard, in longitudinal plane images, regions of higher density/thickness would be translated into brighter pixels (i.e.…”

Notch Signaling in Skeletal Stem Cells

“…This leads to sustained NOTCH2 activation [20, 21]. Also, supporting Notch’s role in bone homeostasis is a genome wide association study demonstrating an association between bone mineral density and JAG1 polymorphisms in a Chinese population and in a population of mixed European and Chinese ancestry [22–24]. Hence, Notch signaling is essential for proper skeletal patterning during development and also for postnatal skeleton homeostasis.…”

Functional validation of GWAS gene candidates for abnormal liver function during zebrafish liver development

“…Zebrafish embryos have previously been used as a tool for rapidly confirming and examining GWAS results in multiple organ systems, such as the kidney, bone and the hematopoietic system (Gieger et al, 2011; Liu et al, 2011; Pattaro et al, 2012; Xiao et al, 2012). Here, we show that GWAS results that provide a long list of gene candidates can be prioritized to characterize a feasible number of candidates for biological validation in zebrafish.…”