WNT16 Influences Bone Mineral Density, Cortical Bone Thickness, Bone Strength, and Osteoporotic Fracture Risk

Abstract

We aimed to identify genetic variants associated with cortical bone thickness (CBT) and bone mineral density (BMD) by performing two separate genome-wide association study (GWAS) meta-analyses for CBT in 3 cohorts comprising 5,878 European subjects and for BMD in 5 cohorts comprising 5,672 individuals. We then assessed selected single-nucleotide polymorphisms (SNPs) for osteoporotic fracture in 2,023 cases and 3,740 controls. Association with CBT and forearm BMD was tested for ∼2.5 million SNPs in each cohort separately, and results were meta-analyzed using fixed effect meta-analysis. We identified a missense SNP (Thr>Ile; rs2707466) located in the WNT16 gene (7q31), associated with CBT (effect size of −0.11 standard deviations [SD] per C allele, P = 6.2×10−9). This SNP, as well as another nonsynonymous SNP rs2908004 (Gly>Arg), also had genome-wide significant association with forearm BMD (−0.14 SD per C allele, P = 2.3×10−12, and −0.16 SD per G allele, P = 1.2×10−15, respectively). Four genome-wide significant SNPs arising from BMD meta-analysis were tested for association with forearm fracture. SNP rs7776725 in FAM3C, a gene adjacent to WNT16, was associated with a genome-wide significant increased risk of forearm fracture (OR = 1.33, P = 7.3×10−9), with genome-wide suggestive signals from the two missense variants in WNT16 (rs2908004: OR = 1.22, P = 4.9×10−6 and rs2707466: OR = 1.22, P = 7.2×10−6). We next generated a homozygous mouse with targeted disruption of Wnt16. Female Wnt16−/− mice had 27% (P<0.001) thinner cortical bones at the femur midshaft, and bone strength measures were reduced between 43%–61% (6.5×10−13<P<5.9×10−4) at both femur and tibia, compared with their wild-type littermates. Natural variation in humans and targeted disruption in mice demonstrate that WNT16 is an important determinant of CBT, BMD, bone strength, and risk of fracture.

Disruption of Lrp4 function by genetic deletion or pharmacological blockade increases bone mass and serum sclerostin levels

“…Importantly, the increased bone mass phenotype was observed in both cancellous and cortical bone compartments of either sex, which is in line with the impact of Sost/sclerostin deficiency and its pharmacologic blockade on the skeleton (37)(38)(39)(40)(41)(42). This finding differs from the selective impact that individual WNTs can have on either bone compartment (43)(44)(45). In addition, we found increased osteoblast function coupled with a nonsignificant decrease in osteoclast activity as a result of Lrp4 osteoblast/osteocyte deficiency in line with the phenotype of Sost knockout mice (37,38).…”

The bone-sparing effects of estrogen and WNT16 are independent of each other

“…In the brain, estrogen signaling activates WNT by down-regulating dickkopf-1 (Dkk1), a WNT antagonist, to prevent neurodegeneration (27). In the uterus, estrogen prompts the canonical WNT signaling pathway in the uterine epithelium to induce uterine epithelial cell growth (28), and in breast cancer, ERα activation enhances cell growth via WNT signaling (29).Human genetic studies followed by subsequent mechanistic studies have recently revealed that WNT16 is a key physiological regulator of cortical bone mass and nonvertebral fracture risk (4,5,(30)(31)(32)(33). We recently demonstrated that WNT16 is osteoblast-derived and inhibits osteoclastogenesis both directly by acting on osteoclast progenitors and indirectly by increasing expression of osteoprotegerin (Opg) in osteoblasts (3).…”

Genetic Studies of Endophenotypes From Spine CT Scans Provide Novel Insights Into the Contribution of Mechanosensory Pathways to Vertebral Fractures and Spinal Curvature

“…Alternatively, specific characteristics (endophenotypes) can be measured directly using higher resolution methods such as computer tomography (CT) which, when underpinning genetic studies has, has led to important new insights compared with those obtained from DXA alone, despite the smaller size of data collections. For example, GWAS based on tibial peripheral quantitative CT (pQCT) led to the identification of the wnt 16 locus as an important determinant of cortical thickness (2) , as well as several new loci for trabecular vBMD (3) .…”