Osteocytic Sclerostin Expression as an Indicator of Altered Bone Turnover

Abstract

Renal osteodystrophy (ROD) is a complex and serious complication of chronic kidney disease (CKD), a major global health problem caused by loss of renal function. Currently, the gold standard to accurately diagnose ROD is based on quantitative histomorphometric analysis of trabecular bone. Although this analysis encompasses the evaluation of osteoblast and osteoclast number/activity, tfigurehe interest in osteocytes remains almost nihil. Nevertheless, this cell type is evidenced to perform a key role in bone turnover, particularly through its production of various bone proteins, such as sclerostin. In this study, we aim to investigate, in the context of ROD, to which extent an association exists between bone turnover and the abundance of osteocytes and osteocytic sclerostin expression in both the trabecular and cortical bone compartments. Additionally, the effect of parathyroid hormone (PTH) on bone sclerostin expression was examined in parathyroidectomized rats. Our results indicate that PTH exerts a direct inhibitory function on sclerostin, which in turn negatively affects bone turnover and mineralization. Moreover, this study emphasizes the functional differences between cortical and trabecular bone, as the number of (sclerostin-positive) osteocytes is dependent on the respective bone compartment. Finally, we evaluated the potential of sclerostin as a marker for CKD and found that the diagnostic performance of circulating sclerostin is limited and that changes in skeletal sclerostin expression occur more rapidly and more pronounced. The inclusion of osteocytic sclerostin expression and cortical bone analysis could be relevant when performing bone histomorphometric analysis for diagnostic purposes and to unravel pathological mechanisms of bone disease.

Sclerostin, Osteocytes, and Wnt Signaling in Pediatric Renal Osteodystrophy

“…In adult CKD, sclerostin was a good predictor of low bone turnover and bone volume, while PTH and FGF-23 predicted high bone turnover [25,58]. Recent work highlights that a progressive increase in FGF-23 and sclerostin in blood and bone is associated with a decrease in kidney function, which suggests using the correlations of bone turnover and sclerostin or FGF-23 could improve patient management in CKD patients with turnover abnormalities [59][60][61][62][63]. In our pediatric population, adynamic bone was associated with elevated serum sclerostin compared with normal or high bone turnover.…”