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J Clin Invest. 2019 May 21;129:3058-3071. doi: 10.1172/JCI122936.

Cathepsin K-deficient osteocytes prevent lactation-induced bone loss and parathyroid hormone suppression.

Author information

1
Division of Bone and Mineral Research, Department of Oral Medicine, Infection and Immunity, Harvard School of Dental Medicine, Boston, Massachusetts, USA.
2
Department of Physiology and Skeletal Disorders Research Unit, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand.
3
Departments of Medical Biochemistry and Genetics and Medicine, University of Turku, Turku, Finland.
4
Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
5
Center for Advanced Orthopedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
6
Harvard Medical School, Department of Medicine, Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts, USA.

Abstract

Lactation induces bone loss to provide sufficient calcium in the milk, a process that involves osteoclastic bone resorption but also osteocytes and perilacunar resorption. The exact mechanisms by which osteocytes contribute to bone loss remain elusive. Osteocytes express genes required in osteoclasts for bone resorption, including cathepsin K (Ctsk), and lactation elevates their expression. We show that Ctsk deletion in osteocytes prevented the increase in osteocyte lacunar area seen during lactation, as well as the effects of lactation to increase osteoclast numbers and decrease trabecular bone volume, cortical thickness and mechanical properties. In addition, Ctsk deletion in osteocytes increased bone Parathyroid Hormone related Peptide (PTHrP), prevented the decrease in serum Parathyroid Hormone (PTH) induced by lactation, but amplified the increase in serum 1,25(OH)2D. The net result of these changes is to maintain serum and milk calcium levels in the normal range, ensuring normal offspring skeletal development. Our studies confirm the fundamental role of osteocytic perilacunar remodeling in physiological states of lactation and provides genetic evidence that osteocyte-derived Ctsk contributes not only to osteocyte perilacunar remodeling, but also to the regulation of PTH, PTHrP, 1,25-Dyhydroxyvitamin D (1,25(OH)2D), osteoclastogenesis and bone loss in response to the high calcium demand associated with lactation.

KEYWORDS:

Bone Biology; Bone disease; Calcium; Endocrinology; Osteoporosis

PMID:
31112135
PMCID:
PMC6668688
[Available on 2019-11-01]
DOI:
10.1172/JCI122936
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