Genetics association study and functional analysis on osteoporosis susceptibility gene BDNF.

To explore the relationship between brain-derived neurotrophic factor (BDNF) gene and bone mineral density (BMD) in Chinese Han population, we performed association analysis of 14 tag SNPs on BDNF gene with hip/spine BMD in 1300 Han Chinese samples from Shaanxi Province. We found that 8 of the 14 SNPs were significantly associated with hip or spine BMD (P < 0.05). Moreover, the SNP rs16917237 was significantly associated with both hip and spine BMD, with significant Bonferroni correlation (P value 0.05/14 = 0.0036) in hip BMD. To further explore the regulatory mechanism of BDNF gene in osteoporosis, we further performed a set of data analyses, including linkage disequilibrium and haplotype analysis, epigenetic annotation, expression quantitative trait locus (eQTL) analysis and metabolic pathway analysis. Further, we have established a mouse pre-osteoblasts differentiation cell model (MC3T3-E1) by recombination human bone morphogenetic protein (rh-BMP2) induction. siRNA- mediated knock down of BDNF in this cell model showed that all 14 SNPs are in the same haplotype block. Strong signals of active histone H3K4me1, H3K4me3, H3K27ac modifications and P300 binding were observed in osteoblasts, in the region surrounding the most significant SNP rs16917237, suggesting that this SNP might have a regulatory function in osteoblasts. Furthermore, analysis of genotype data of rs16917237 and BDNF expression in multiple tissues from GTEx showed that rs16917237 SNP could significantly affect the expression of BDNF in 11 tissues. Through analysis of the various BDNF pathways, we showed that BDNF participates in the MAPK pathway, which is a vital and well-established pathway affecting osteoblasts proliferation and differentiation. siRNA knock down of BDNF significantly decreased the mRNA and protein levels of CREB, which is important in the MAPK pathway in osteoblast differentiation. These findings suggest that BDNF might affect osteoblast differentiation via regulation of CREB expression. In conclusion, our results from combined genetic association and functional analyses show that BDNF is a vital osteoporosis susceptibility gene, which can affect BMD not only in Chinese Han but also likely in other populations.