Methylation of Bone SOST, Its mRNA, and Serum Sclerostin Levels Correlate Strongly With Fracture Risk in Postmenopausal Women

Abstract

Inhibition of sclerostin, a glycoprotein secreted by osteocytes, offers a new therapeutic paradigm for treatment of osteoporosis (OP) through its critical role as Wnt/catenin signaling regulator. This study describes the epigenetic regulation of SOST expression in bone biopsies of postmenopausal women. We correlated serum sclerostin to bone mineral density (BMD), fractures, and bone remodeling parameters, and related these findings to epigenetic and genetic disease mechanisms. Serum sclerostin and bone remodeling biomarkers were measured in two postmenopausal groups: healthy (BMD T-score > -1) and established OP (BMD T-score < -2.5, with at least one low-energy fracture). Bone specimens were used to analyze SOST mRNAs, single nucleotide polymorphisms (SNPs), and DNA methylation changes. The SOST gene promoter region showed increased CpG methylation in OP patients (n ¼ 4) compared to age and body mass index (BMI) balanced controls (n ¼ 4) (80.5% versus 63.2%, p ¼ 0.0001) with replication in independent cohorts (n ¼ 27 and n ¼ 36, respectively). Serum sclerostin and bone SOST mRNA expression correlated positively with age-adjusted and BMIadjusted total hip BMD (r ¼ 0.47 and r ¼ 0.43, respectively; both p < 0.0005), and inversely to serum bone turnover markers. Five SNPs, one of which replicates in an independent population-based genomewide association study (GWAS), showed association with serum sclerostin or SOST mRNA levels under an additive model (p ¼ 0.0016 to 0.0079). Genetic and epigenetic changes in SOST influence its bone mRNA expression and serum sclerostin levels in postmenopausal women. The observations suggest that increased SOST promoter methylation seen in OP is a compensatory counteracting mechanism, which lowers serum sclerostin concentrations and reduces inhibition of Wnt signaling in an attempt to promote bone formation.

How to interpret epigenetic association studies: a guide for clinicians

“…For example, increased methylation of the SOST promoter has been reported in bone samples of patients with osteoporosis. 51 As sclerostin is an antianabolic factor, this finding may be counterintuitive; yet, it is in line with studies showing reduced SOST expression in osteoporosis. 51,71 Although the involved mechanisms are still unclear, it has been suggested that those changes are a compensatory response, rather than a driver of the bone loss.…”

“…These studies have small costs, but they miss information from the vast majority of the genome. More recently, Reppe 51 focused in the analysis of the methylation of the SOST promoter (the gene encoding sclerostin) and its association with BMD.…”

Sclerostin: Intracellular mechanisms of action and its role in the pathogenesis of skeletal and vascular disorders

“…It is considered as a compensatory, counteracting mechanism, which lowers sclerostin production and reduces inhibition of Wnt signaling in an attempt to promote bone formation. 38 However, serum sclerostin is unaffected by menopausal status or increase in age, perhaps due to kidney aging accompanied by deterioration of their excretory and biodegradation functions. It is generally accepted that sclerostin in postmenopausal women reflects bone mineral density.…”

“…Aside from the group of rare genetic diseases, the observable variability of serum sclerostin levels affects BMD of both cortical and cancellous bone in the general population. The molecular effect of sclerostin levels and BMD were studied by Reppe et al 30 They showed that the genetic and epigenetic changes in SOST influence its mRNA expression in bone and serum sclerostin levels in postmenopausal women. Serum sclerostin and bone SOST mRNA expression correlated positively with age-adjusted and BMI-adjusted total hip BMD (r = 0.47) and inversely to serum bone turnover markers.…”

“…The observations suggest that increased SOST promoter methylation, seen in osteoporosis, is a compensatory, counteracting, mechanism which lowers the production of sclerostin and reduces the inhibition of Wnt signaling in an attempt to promote bone formation. 30 Mödder et al measured serum sclerostin levels in a population-based sample of 362 women: 123 premenopausal, 152 postmenopausal not on estrogen treatment (ET), and 87 postmenopausal on ET; and 318 men, aged 21-97 years. Sclerostin levels were significantly higher in men than in women, and increased markedly with age.…”