SPI1 exacerbates iron accumulation and promotes osteoclast formation through inhibiting the expression of Hepcidin.

BACKGROUND: Osteoporosis (OP) can be caused by an overactive osteoclastic function. Anti-osteoporosis considerable therapeutic effects in tissue repair and regeneration because bone resorption is a unique osteoclast function. In this study, we mainly explored the underlying mechanisms of osteoclasts' effects on osteoporosis. METHODS: RAW264.7 cells were used and induced toward osteoclast and iron accumulation by M-CSF and RANKL administration. We investigated Hepcidin and divalent metal transporter 1 (DMT1) on iron accumulation and osteoclast formation in an ovariectomy (OVX)-induced osteoporosis. Osteoporosis was induced in mice by OVX, and treated with Hepcidin (10, 20, 40, 80 mg/kg, respectively) and overexpression of DMT1 by tail vein injection. Hepcidin, SPI1, and DMT1 were detected by immunohistochemical staining, western blot and RT-PCR. The bioinformatics assays, luciferase assays, and Chromatin Immunoprecipitation (ChIP) verified that Hepcidin was a direct SPI1 transcriptional target. Iron accumulation was detected by laser scanning confocal microscopy, Perl's iron staining and iron content assay. The formation of osteoclasts was assessed using tartrate-resistant acid phosphatase (TRAP) staining. RESULTS: We found that RAW264.7 cells differentiated into osteoclasts when exposed to M-CSF and RANKL, which increased the protein levels of osteoclastogenesis-related genes, including c-Fos, MMP9, and Acp5. We also observed higher concentration of iron accumulation when M-CSF and RANKL were administered. However, Hepcidin inhibited the osteoclast differentiation cells and decreased intracellular iron concentration primary osteoclasts derived from RAW264.7. Spi-1 proto-oncogene (SPI1) transcriptionally repressed the expression of Hepcidin, increased DMT1, facilitated the differentiation and iron accumulation of mouse osteoclasts. Overexpression of SPI1 significantly declined luciferase activity of HAMP promoter and increased the enrichment of HAMP promoter. Furthermore, our results showed that Hepcidin inhibited osteoclast differentiation and iron accumulation in mouse osteoclasts and OVX mice. CONCLUSION: Therefore, the study revealed that SPI1 could inhibit Hepcidin expression contribute to iron accumulation and osteoclast formation via DMT1 signaling activation in mouse with OVX.

Iron accumulation induced by hepcidin1 knockout accelerates the progression of aging osteoporosis.

OBJECTIVE: Iron accumulation is associated with osteoporosis. This study aims to explore the effect of chronic iron accumulation induced by hepcidin1 deficiency on aging osteoporosis. METHODS: Iron accumulation in hepcidin1 knockout aging mice was assessed by atomic absorption spectroscopy and Perl's staining. Bone microarchitecture was observed using Micro-CT. Hepcidin, ferritin, oxidative stress, and markers of bone turnover in serum were detected by enzyme-linked immunosorbent assay. Bone formation and resorption markers were measured by real-time quantitative PCR. Cell aging was induced by D-galactose treatment. CCK-8, flow cytometry, EdU assays, and Alizarin red staining were performed to reveal the role of hepcidin1 knockout in cell model. Iron Colorimetric Assay Kit and western blot were applied to detect iron and ferritin levels in cells, respectively. RESULTS: In hepcidin1-knockout mice, the ferritin and iron contents in liver and tibia were significantly increased. Iron accumulation induced by hepcidin1 knockout caused a phenotype of low bone mass and deteriorated bone microarchitecture. Osteogenic marker was decreased and osteoclast marker was increased in mice, accompanied by increased oxidative stress level. The mRNA expression levels of osteoclast differentiation markers (RANKL, Mmp9, OPG, Trap, and CTSK) were up-regulated, while bone formation markers (OCN, ALP, Runx2, SP7, and Col-1) were down-regulated in model group, compared to wild type mice. In vitro, hepcidin1 knockdown inhibited proliferation and osteogenic differentiation, while promoted apoptosis, with increased levels of iron and ferritin. CONCLUSION: Iron accumulation induced by hepcidin1 deficiency aggravates the progression of aging osteoporosis via inhibiting osteogenesis and promoting osteoclast genesis.

ATF1/miR-214-5p/ITGA7 axis promotes osteoclastogenesis to alter OVX-induced bone absorption.

BACKGROUND: The dynamic balance of osteoblast and osteoclast is critical for bone homeostasis and overactive osteoclastic function may lead to osteoporosis. Activating transcription factor 1 (ATF1) is involved in osteoclastogenesis. However, the detailed mechanisms remain to be explored. METHODS: RAW264.7 cells were used and induced toward osteoclast by RANKL administration. We performed flow cytometry, CCK-8 assay and tartrate-resistant acid phosphatase (TRAP) staining to examine cell apoptosis, proliferation and differentiation of RAW264.7 cells, respectively. Mice were subjected to ovariectomy to induce osteoporosis. Micro CT, HE staining and TRAP staining were performed to evaluate bone loss in the OVX mouse model. Bioinformatics methods, luciferase assays and Chromatin Immunoprecipitation (ChIP) were used to predict and validate the interaction among ATF1, miR-214-5p, and ITGA7. RESULTS: ATF1 and miR-214-5p were up-regulated while ITGA7 was inhibited in RANKL-induced osteoclasts. MiR-214-5p was transcriptionally activated by ATF1. ATF1 knockdown suppressed osteoclast formation by miR-214-5p inhibition. ITGA7 was the direct target of miR-214-5p. Knockdown of miR-214-5p abolished osteoclastogenesis, which was reversed by ITGA7 knockdown. In OVX model, miR-214-5p knockdown suppressed osteoclast differentiation and prevented bone loss. CONCLUSION: ATF1/miR-214-5p/ITGA7 axis regulated osteoclast formation both in vivo and in vitro, thereby affecting OVX-induced bone resorption in mice. Knockdown of ATF1 might be a promising strategy to manage osteoporosis.

Influence of vertebral column distraction on spinal cord volume: an experimental study in a goat model.

INTRODUCTION: Spinal cord injury may be related to excessive distraction of the spinal cord during surgical correction of spinal deformities by vertebral column resection. This study aimed to investigate how vertebral column distraction influences spinal cord volume to establish the safe range in a goat model. MATERIALS AND METHODS: A vertebral column resection was performed on the tenth thoracic vertebra of 11 goats. The spinal cord was distracted until the somatosensory evoked potential signals were decreased to 50 % from baseline amplitude or were delayed by 10 % of the baseline peak latency. The osteotomy segment was stabilized with a PEEK mesh cage filled with bone graft, and the pedicle screws on the rods were then tightened in this position. Spinal cord volume was calculated using Mimics software, and T10 height, disk height, osteotomy segment height, and spinal segment height were measured using the MRI image workstation. RESULTS: Three goats were excluded, and data obtained from the eight remaining goats were analyzed. The safe limit of distraction distance was 11.8 ± 3.65 mm, and the distraction distance was strongly correlated with the difference between the pre- and postoperative measurements (d value) of spinal cord volume per 1 mm of osteotomy segment height (r = -0.952, p < 0.001), but was not correlated with T10 body height (r = 0.16, p = 0.71), spinal segment height (r = 0.29, p = 0.49), disk height (r = -0.12, p = 0.98), or the d value (pre-post) of spinal cord volume per 1 mm of spinal segment height (r = 0.45, p = 0.26). The mean d value (pre-post) of spinal cord volume per 1 mm of osteotomy segment height was 10.05 ± 0.02 mm(3) (range 10.02-10.08 mm(3)). CONCLUSION: The maximum change in spinal cord volume per 1-mm change in height was in the osteotomy segment, and its safe limit was 10.05 ± 0.02 mm(3). The safe limit of spinal cord distraction can be calculated using the spinal cord volume per unit 1-mm change in height.

Relationship between Spinal Cord Volume and Spinal Cord Injury due to Spinal Shortening.

Vertebral column resection is associated with a risk of spinal cord injury. In the present study, using a goat model, we aimed to investigate the relationship between changes in spinal cord volume and spinal cord injury due to spinal shortening, and to quantify the spinal cord volume per 1-mm height in order to clarify a safe limit for shortening. Vertebral column resection was performed at T10 in 10 goats. The spinal cord was shortened until the somatosensory-evoked potential was decreased by 50% from the baseline amplitude or delayed by 10% relative to the baseline peak latency. A wake-up test was performed, and the goats were observed for two days postoperatively. Magnetic resonance imaging was used to measure the spinal cord volume, T10 height, disc height, osteotomy segment height, and spinal segment height pre- and postoperatively. Two of the 10 goats were excluded, and hence, only data from eight goats were analyzed. The somatosensory-evoked potential of these eight goats demonstrated meaningful changes. With regard to neurologic function, five and three goats were classified as Tarlov grades 5 and 4 at two days postoperatively. The mean shortening distance was 23.6 ± 1.51 mm, which correlated with the d-value (post-pre) of the spinal cord volume per 1-mm height of the osteotomy segment (r = 0.95, p < 0.001) and with the height of the T10 body (r = 0.79, p = 0.02). The mean d-value (post-pre) of the spinal cord volume per 1-mm height of the osteotomy segment was 142.87 ± 0.59 mm3 (range, 142.19-143.67 mm3). The limit for shortening was approximately 106% of the vertebral height. The mean volumes of the osteotomy and spinal segments did not significantly change after surgery (t = 0.310, p = 0.765 and t = 1.241, p = 0.255, respectively). Thus, our results indicate that the safe limit for shortening can be calculated using the change in spinal cord volume per 1-mm height.