title: Krox20/EGR2 deficiency accelerates cell growth and differentiation in the monocytic lineage and decreases bone mass.
abstract: Krox20/EGR2, one of the 4 early growth response genes, is a highly conserved transcription factor implicated in hindbrain development, peripheral nerve myelination, tumor suppression, and monocyte/macrophage cell fate determination. Here, we established a novel role for Krox20 in postnatal skeletal metabolism. Microcomputed tomographic analysis of 4- and 8-week-old mice revealed a low bone mass phenotype (LBM) in both the distal femur and the vertebra of Krox20(+/-) mice. This was attributable to accelerated bone resorption as demonstrated in vivo by increased osteoclast number and serum C-terminal telopeptides, a marker for collagen degradation. Krox20 haploinsufficiency did not reduce bone formation in vivo, nor did it compromise osteoblast differentiation in vitro. In contrast, growth and differentiation were significantly stimulated in preosteoclast cultures derived from Krox20(+/-) splenocytes, suggesting that the LBM is attributable to Krox20 haploinsufficiency in the monocytic lineage. Furthermore, Krox20 silencing in preosteoclasts increased cFms expression and response to macrophage colony-stimulating factor, leading to a cell-autonomous stimulation of cell-cycle progression. Our data indicate that the antimitogenic role of Krox20 in preosteoclasts is the predominant mechanism underlying the LBM phenotype of Krox20-deficient mice. Stimulation of Krox20 expression in preosteoclasts may present a viable therapeutic strategy for high-turnover osteoporosis.
authors: Department of Biochemistry and Molecular Biology, Keck School of Medicine at University of Southern California, Los Angeles, CA 90033, USA.
authors: Yankel
authors: Y
authors: Gabet
authors: Sanjeev K
authors: SK
authors: Baniwal
authors: Nathalie
authors: N
authors: Leclerc
authors: Yunfan
authors: Y
authors: Shi
authors: Alice E
authors: AE
authors: Kohn-Gabet
authors: Jon
authors: J
authors: Cogan
authors: Alexis
authors: A
authors: Dixon
authors: Marilyn
authors: M
authors: Bachar
authors: Lixin
authors: L
authors: Guo
authors: Jack E
authors: JE
authors: Turman
authors: Baruch
authors: B
authors: Frenkel
mesh_terms: D000818:Animals; D001483:Base Sequence; D001862:Bone Resorption / Q000209:etiology / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D001842:Bone and Bones / Q000378:metabolism*; D002453:Cell Cycle; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D049109:Cell Proliferation; D017931:DNA Primers / Q000235:genetics; D004195:Disease Models, Animal; D051767:Early Growth Response Protein 2 / Q000172:deficiency* / Q000235:genetics; D005260:Female; D057895:Haploinsufficiency; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology; D010010:Osteoclasts / Q000378:metabolism / Q000473:pathology; D010012:Osteogenesis; D010024:Osteoporosis / Q000209:etiology* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D034741:RNA, Small Interfering / Q000235:genetics; D015398:Signal Transduction
chemical_list: D017931:DNA Primers; D051767:Early Growth Response Protein 2; C497327:Egr2 protein, mouse; D034741:RNA, Small Interfering