Osteogenesis imperfecta (OI), a heritable disorder caused by abnormalities in synthesis or processing of type I collagen, is characterized by skeletal fragility. Type I collagen interacts with multiple components of the extracellular matrix (ECM) including other collagens types. Thus, alterations in structure or quantity may broadly affect ECM homeostasis. In fact, while OI is clinically categorized by severity of bone disease, patients can also present with extra-skeletal manifestations, including the pulmonary, muscle and cardiovascular systems. Parathyroid hormone (PTH) is a regulator of skeletal homeostasis but the receptor for PTH/PTH1R is expressed in a variety of other tissues. Given interactions between type I collagen with other collagens in the ECM and the potential for PTH action on tissues beyond the skeleton, we explored whether serum levels of non-type I collagens are altered in response to teriparatide (human parathyroid hormone 1-34). We measured biomarkers of collagens II, III, IV, V, and VI in serum from individuals with type I and types III/IV OI in response to an 18 month course of teriparatide or placebo. These results were compared to similar biomarker measures in postmenopausal (PM) women without OI treated with teriparatide. In type I OI, teriparatide therapy increased concentrations of biomarkers of collagens II, III, IV, V, and VI. In individuals with types III/IV OI these biomarker changes in response to teriparatide were blunted, as we previously reported with collagen I biomarkers during teriparatide therapy. In contrast to OI, in PM women there were no effects of teriparatide on the collagen biomarkers we assessed (II, V, and VI). These findings suggest that in OI teriparatide therapy has abnormal effects on the homeostasis of many ECM collagens likely derived from skeletal as well as extra-skeletal tissues.
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