Circulating sclerostin associated with vertebral bone marrow fat in older men but not women.

Abstract

Osteocyte activity is crucial to the maintenance of bone quality. Sclerostin, an osteocyte product, inhibits bone formation, yet higher circulating sclerostin is associated with higher bone density. Bone marrow fat (MF) is associated with osteoporosis, but little is known about the relationship between osteocyte activity and MF. Our objective was to assess the relationships between circulating sclerostin, vertebral MF, volumetric bone mineral density (vBMD), and other fat depots in older adults. We conducted a cross-sectional study in the Age Gene/Environment Susceptibility-Reykjavik cohort. Outcome measures included vertebral MF (L1-L4) measured with magnetic resonance spectroscopy and vBMD (spine and hip) and abdominal fat measured with quantitative computed tomography. After excluding subjects with bone-active medication use (n = 50), inadequate serum (n = 2), or inadequate magnetic resonance spectroscopy (n = 1), analyses included 115 men and 134 women (mean age 79 y, mean body mass index 27.7 kg/m(2)). In men, but not women, vertebral MF was greater in those with higher serum sclerostin levels. MF was 52.2 % in the lowest tertile of serum sclerostin and 56.3% in the highest tertile in men (P for trend <.01) in models adjusted for age, body mass index, and diabetes. Sclerostin was positively associated with cortical and trabecular total hip vBMD, weight in men and women, and total fat mass in men but was not associated with total lean mass or abdominal fat depots. Circulating sclerostin levels are associated with higher vertebral marrow fat in men, suggesting a relationship between osteocyte function and marrow adipogenesis.