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Declining kidney function is associated with sequential systemic changes in mineral homeostasis leading to pathologic alterations in the cardiovascular system and the skeleton. One of the earliest changes in response to renal injury is the increased osteocyte production of secreted factors including the anti-anabolic protein, sclerostin. Elevated sclerostin is associated with reduced Wnt/β-catenin signaling in bone and decreased osteoblast differentiation/activity. Agents that directly or indirectly inhibit β-catenin signaling have differential skeletal effects suggesting additional mechanisms contribute to the diversity of renal osteodystrophies. Similarly, Wnt/β-catenin activation in smooth muscle cells contributes to cardiovascular calcification yet emerging data suggests that this pathway may also be protective when elevated in neighboring tissues. The ongoing epidemiology studies examining the relationship between circulating sclerostin and cardiovascular disease, particularly those that investigate stage specific and/or patient sub-populations, will be useful in understanding the overall contributions of this pathway, its antagonist sclerostin, and the progression of CKD-MBD.

The SOST gene, which encodes the protein sclerostin, was identified through genetic linkage analysis of sclerosteosis and van Buchem's disease patients. Sclerostin is a secreted glycoprotein that binds to the low-density lipoprotein receptor-related proteins 4, 5, and 6 to inhibit Wnt signaling. Since the initial discovery of sclerostin, much understanding has been gained into the role of this protein in the regulation of skeletal biology. In this article, we discuss the latest findings in the regulation of SOST expression, sclerostin mechanisms of action, and the potential utility of targeting sclerostin in conditions of low bone mass.

Bone formation is suppressed in glucocorticoid-induced osteoporosis. One of the mechanisms by which glucocorticoids depress bone formation is through their effects on the Wnt/β-catenin signaling pathway, a critical regulator of osteoblastogenesis. Thus, Wnt signaling induces the differentiation of osteoblast precursors toward mature osteoblasts and prevents osteoblast and osteocyte apoptosis. Glucocorticoids increase the expression of Wnt signaling antagonists (sclerostin and Dkk-1) in experimental studies in rodents and cell cultures. However, the scarce data of their effects in humans are somewhat contradictory, probably due to the dose and duration of treatment as well as the characteristics of the patients. A progressive decrease in Dkk-1 serum levels and an increase in circulating sclerostin levels at long-term follow-up have recently been reported in patients treated with high doses of glucocorticoids. This review describes the most recent data on the effects of glucocorticoids on the Wnt signaling pathway, especially on their antagonists, sclerostin and Dkk-1.

The striking clinical benefits of intermittent parathyroid hormone in osteoporosis have begun a new era of skeletal anabolic agents. Recombinant human parathyroid hormone (rhPTH) (1-34) is the first US Food and Drug Administration-approved anabolic therapy. Its use has been limited by the need for subcutaneous injection. Newer delivery systems include transdermal and oral preparations. Newer anabolic therapies include monoclonal antibody to sclerostin, a potent inhibitor of osteoblastogenesis; and use of bone morphogenetic proteins and parathyroid hormone-related protein PTHrP, a calcium-regulating hormone similar to PTH.