The transcription factor FBI‐1/OCZF/LRF is expressed in osteoclasts and regulates RANKL‐induced osteoclast formation in vitro and in vivo

Abstract

Objective. Since transcription factors expressed in osteoclasts are possible targets for regulation of bone destruction in bone disorders, we investigated the expression of the transcription factor FBI-1/OCZF/LRF (in humans, factor that binds to inducer of short transcripts of human immunodeficiency virus type 1; in rats, osteoclast-derived zinc finger; in mice, leukemia/ lymphoma-related factor) in patients with rheumatoid arthritis (RA), and assessed its role in osteoclastogenesis in vivo.Methods. Expression of FBI-1/OCZF was investigated in subchondral osteoclasts in human RA and in rat adjuvant-induced arthritis (AIA) using immunostaining and in situ hybridization, respectively. Transgenic mice overexpressing OCZF (OCZF-Tg) under the control of the cathepsin K promoter were generated, and bone mineral density and bone histomorphometric features were determined by peripheral quantitative computed tomography, calcein double-labeling, and specific staining for osteoclasts and osteoblasts. LRF/OCZF expression and the consequence of LRF inhibition were assessed in vitro with RANKL-induced osteoclast differentiation.Results. FBI-1/OCZF was detected in the nuclei of osteoclasts in rat AIA and human RA. RANKL increased the levels of LRF messenger RNA and nuclearlocalized LRF protein in primary macrophages. In OCZF-Tg mice, bone volume was significantly decreased, the number of osteoclasts, but not osteoblasts, was increased in long bones, and osteoclast survival was promoted. Conversely, inhibition of LRF expression suppressed the formation of osteoclasts from macrophages in vitro.Conclusion. FBI-1/OCZF/LRF regulates osteoclast formation and apoptosis in vivo, and may become a useful marker and target in treating disorders leading to reduced bone density, including chronic arthritis.

Regulation of osteoclastogenesis through Tim-3: possible involvement of the Tim-3/galectin-9 system in the modulation of inflammatory bone destruction

“…[17][18][19] Bone marrow cells were obtained from the tibia and femur of 4-6-week-old male SD rats or 5-week-old female C57BL/6 mouse. Rat bone marrow cells were cultured in 24-well plates (1 Â 10 6 cells per well) in a-MEM (Gibco, Grand Island, NY, USA) containing 15% FBS (Biosource, Rockville, MD, USA) in the presence of 10 À 8 M 1a,25(OH) 2 D 3 , 20 ng/ml of RANKL, and 10% heat-treated ROS17/2.8 cell-conditioned medium (htROSCM).…”

Role of LRF/Pokemon in lineage fate decisions

“…55 In a follow-up publication, Kukita and colleagues finely described the function of LRF in osteoclastogenesis. 63 Taking advantage of a previous analysis of a transgenic mouse model overexpressing LRF in osteoclast progenitors under the Ctsk gene promoter, these authors linked the high levels of LRF to fragile bones and significantly lower bone mineral content and bone mineral density, as well as to a marked increase in the number of osteoclasts, but not osteoblasts. 63 Mechanistically, Kukita and colleagues defined LRF as a positively regulated downstream target gene of RANKL signaling that is essential to the elevation of levels of NFATc1.…”

“…63 Taking advantage of a previous analysis of a transgenic mouse model overexpressing LRF in osteoclast progenitors under the Ctsk gene promoter, these authors linked the high levels of LRF to fragile bones and significantly lower bone mineral content and bone mineral density, as well as to a marked increase in the number of osteoclasts, but not osteoblasts. 63 Mechanistically, Kukita and colleagues defined LRF as a positively regulated downstream target gene of RANKL signaling that is essential to the elevation of levels of NFATc1. Interestingly, they also showed that LRF decreases p21 expression in precursor cells but increases expression of p21 and p27 in osteoclasts, suggesting different roles for LRF in proliferating osteoclast precursors and mature osteoclasts.…”

“…Interestingly, they also showed that LRF decreases p21 expression in precursor cells but increases expression of p21 and p27 in osteoclasts, suggesting different roles for LRF in proliferating osteoclast precursors and mature osteoclasts. 63 In a recent publication, however, Takayanagi's group has unveiled new and important insights into the function of LRF in osteoclastogenesis. 64 Conditional Lrf gene deletion during the early or late stage of osteoclast development in 2 different engineered mouse models (Lrf Flox/Flox ;Mx1-Cre and Lrf Flox/Flox ; Ctsk-Cre) has revealed a biphasic role for LRF during osteoclastogenesis.…”

Stage-specific functions of leukemia/lymphoma-related factor (LRF) in the transcriptional control of osteoclast development

“…Recently, mice overexpressing LRF in osteoclasts were shown to exhibit an osteoporotic phenotype due to the increased number of osteoclasts (24). However, the physiological function of LRF in bone remodeling has not been demonstrated, because global deletion of LRF results in embryonic lethality (14).…”