| Osteoporosis is a public health problem in the elderly, especially in the females. Osteoporosis is a systemic skeletal disorder characterized by low bone mass and micro-architectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. Low bone mineral density (BMD) is one of the strongest risk factors for osteoporosis and fracture with high heritability. Compared with other types of fracture, hip fracture is the most closely linked with BMD and associated with significant morbidity and mortality. In the field of genetics for osteoporosis, previous studies for influences of genes to osteoporosis mainly focus on RNA and DNA levels. As the direct executors of gene functions in biological organisms, protein diversity cannot be fully characterized by gene expression analysis alone, making proteomics. an emerging tool for characterizing cells and tissues of interest and analyzing protein expression at the post-translational level. As progenitors of bone-resorbing osteoclasts, human peripheral blood monocytes (PBMs) are also a source of cytokines and chemokines affecting bone metabolism. Human PBMs may help to maintaining bone homeostasis by regulating osteoclastic differentiation, and used for an important target for revealing the effect of osteoclasts in osteoporosis. So far, genes influencing BMD and specific functional mechanism of PBMs in the pathogenesis of osteoporosis are far from clear.We performed a proteome-wide protein expression study of PBM in a discovery sample of34Caucasian premenopausal women with extremely discordant BMD. Proteins differentially expressed between low vs. high BMD subjects were identified and subject to validation by western blotting. For genes differentially expressed, we further studied mRNA expression in PBM in two independent Caucasian premenopausal women samples with extremely discordant BMD (N=29and40, respectively). Moreover, we performed SNPs association analyses in Caucasian and Chinese samples (N=2,280and1,621) respectively to explore significance of gene(s) of interest to hip BMD in large human populations.In the discovery sample, GSN protein expression in PBM was down-regulated3.0-fold in subjects with low BMD (P<0.05). The Western blotting results confirmed the significant expression difference of GSN between low and high BMD subjects (P<0.05).In the two independent replication samples, GSN mRNA expression in PBM was also significantly down-regulated in subjects with low BMD (P<0.05). Furthermore, seven SNPs (rs10739594, rs4837827, rs7857673, rs4837832, rs4837835, rs306761, and rs306772) at GSN locus were significant associated with hip BMD (P<0.05), and the strongest association signals detected at SNP rs306761(p=0.006) in sample4. In Sample5, eleven SNPs (rs4837817, rs10985190, rs12349092, rs4837827, rs4837832, rs4837835, rs306761, rs2900193, rs16910520, rs2289069and rs2164298) within GSN locus were associated with hip BMD (P<0.05). The strongest association signals was observed at SNP rs2164298(P0.0004). Four SNPs (rs306761, rs4837827, rs4837832and rs4837835) were also associated with hip BMD in Sample5(P<0.05), suggesting ethnic-general effect of the three SNPs on hip BMD.Based on the above integrative evidence at protein, mRNA, and DNA levels, we conclude that GSN is an important susceptibility gene involved in the pathogenesis of osteoporosis in human. Further functional studies of GSN gene will provide new insight in the vital physiological functions in bone biology and etiology of osteoporosis. |
