High dickkopf-1 levels in sera and leukocytes from children with 21-hydroxylase deficiency on chronic glucocorticoid treatment

Abstract

Children with 21-hydroxylase deficiency (21-OHD) need chronic glucocorticoid (cGC) therapy to replace congenital deficit of cortisol synthesis, and this therapy is the most frequent and severe form of drug-induced osteoporosis. In this study, we enrolled 18 patients (9 females) and 18 sex-and agematched controls. We found in 21-OHD patients high serum and leukocyte levels of dickkopf-1 (DKK1), a secreted antagonist of the Wnt/␤-catenin signaling pathway known to be a key regulator of bone mass. In particular, we demonstrated by flow cytometry, confocal microscopy, and real-time PCR that monocytes, T lymphocytes, and neutrophils from patients expressed high levels of DKK1, which may be related to the cGC therapy. In fact, we showed that dexamethasone treatment markedly induced the expression of DKK1 in a dose-and time-dependent manner in leukocytes. The serum from patients containing elevated levels of DKK1 can directly inhibit in vitro osteoblast differentiation and receptor activator of NF-B ligand (RANKL) expression. We also found a correlation between both DKK1 and RANKL or COOH-terminal telopeptides of type I collagen (CTX) serum levels in 21-OHD patients on cGC treatment. Our data indicated that DKK1, produced by leukocytes, may contribute to the alteration of bone remodeling in 21-OHD patients on cGC treatment.dickkopf-1; 21-hydroxylase deficiency patients; glucocorticoid-induced osteoporosis; leukocytes; glucocorticoids CHILDREN WITH 21-HYDROXYLASE DEFICIENCY (21-OHD), the most common cause of congenital adrenal hyperplasia (CAH) due to deletions or mutations of the P450 21-hydroxylase gene (CYP21), need chronic glucocorticoid (cGC) therapy as soon as the diagnosis has been made to replace congenital deficit in cortisol synthesis and to reduce androgen secretion by adrenal cortex (18). One of the most serious problems of cGC therapy is glucocorticoid-induced osteoporosis (GIO), although the patients are treated with glucocorticoids (GCs) at replacement doses. However, the risk of GC overreplacement or neuroendocrine modifications during treatment (i.e., abnormal growth hormone secretion and pulsatility) should be taken in consideration as potential factors determining bone loss even in subjects treated with apparent "physiological doses" of GCs (29, 54). GIO results in an early, transient increase in bone resorption accompanied by a decrease in bone formation, which is maintained for the duration of GC therapy (3). Therefore, 21-OHD patients are at risk of a great incidence of low bone mass, although studies on bone mineral density (BMD) have reported discordant results. In fact, an increased (46), decreased (2,8,12,15,16,20,36,44), or normal BMD (5, 13, 14, 30, 47), as well as contrasting results about the evaluation of serum biochemical markers of bone turnover, has been reported in these patients (12,13,36,44). In our previous work (10), we demonstrated a high osteoclastogenic potential of peripheral blood mononuclear cells in children with 21-OHD on cGC treatment, which seems to be supported by the pr...

Glucocorticoid-Induced Osteoporosis

“…The patients’ sera inhibited osteoblast differentiation in vitro (although the inhibition—of ALP activity—was small), and the effect was ameliorated after administration of anti-DKK1 antibodies [99]. Additional data obtained from these patients suggested that the excess DKK1 could be partly biosynthesized by leukocytes, and that it played a role in regulating RANKL levels in these patients [99].…”

“…The patients’ sera inhibited osteoblast differentiation in vitro (although the inhibition—of ALP activity—was small), and the effect was ameliorated after administration of anti-DKK1 antibodies [99]. Additional data obtained from these patients suggested that the excess DKK1 could be partly biosynthesized by leukocytes, and that it played a role in regulating RANKL levels in these patients [99]. Dkk1 mRNA was also elevated in mouse bones in vivo after 56 days of prednisolone treatment [20]; this study, however, raises the question of whether GC-mediated stimulation of Dkk1 is a primary event in the mouse because the early time point in vivo (7-days) indicated decreased, not increased DKK1 mRNA levels [20].…”

The Interplay between the Bone and the Immune System

“…Thus, RANKL expression in neutrophils differed from that in activated CD3 + lymphocytes, which express both cell surface and soluble RANKL [207, 208]. Moreover, neutrophils can affect OB functions in children on chronic glucocorticoid therapy as well as in tophaceous gout leading to decreased bone formation and increased bone resorption [209, 210]. …”

Cytokine-Mediated Bone Destruction in Rheumatoid Arthritis

“…Thus, the effect of RANKL in activated neutrophils is predominantly mediated by the membrane-bound form, in contrast to activated T cells, where RANKL signaling is mediated by both cell surface and soluble RANKL [106, 107]. In addition, neutrophils affect the function of osteoblasts in children on chronic glucocorticoid therapy and in patients with tophaceous gout, resulting in altered bone remodeling [108, 109]. …”