Sympathetic β₁-adrenergic signaling contributes to regulation of human bone metabolism

BACKGROUND. Evidence from rodent studies indicates that the sympathetic nervous system (SNS) regulates bone metabolism, principally via β₂-adrenergic receptors (β₂-ARs). Given the conflicting human data, we used multiple approaches to evaluate the role of the SNS in regulating human bone metabolism. METHODS. Bone biopsies were obtained from 19 young and 19 elderly women for assessment of ADRB1, ADRB2, and ADRB3 mRNA expression. We examined the relationship of β-blocker use to bone microarchitecture by high-resolution peripheral quantitative CT in a population sample of 248 subjects. A total of 155 postmenopausal women were randomized to 1 of 5 treatment groups for 20 weeks: placebo; propranolol, 20 mg b.i.d.; propranolol, 40 mg b.i.d.; atenolol, 50 mg/day; or nebivolol, 5 mg/day. We took advantage of the β₁-AR selectivity gradient of these drugs (propranolol [nonselective] atenolol [relatively β₁-AR selective] < nebivolol [highly β₁-AR selective]) to define the β-AR selectivity for SNS effects on bone. RESULTS. ADRB1 and ADRB2, but not ADRB3, were expressed in human bone; patients treated clinically with β₁-AR-selective blockers had better bone microarchitecture than did nonusers, and relative to placebo, atenolol and nebivolol, but not propranolol, reduced the bone resorption marker serum C-telopeptide of type I collagen (by 19.5% and 20.6%, respectively; P < 0.01) and increased bone mineral density of the ultradistal radius (by 3.6% and 2.9%; P < 0.01 and P < 0.05, respectively). CONCLUSIONS. These 3 independent lines of evidence strongly support a role for adrenergic signaling in the regulation of bone metabolism in humans, principally via β₁-ARs. TRIAL REGISTRATION. ClinicalTrials.gov NCT02467400.