OTUB1 promotes osteoblastic bone formation through stabilizing FGFR2

AUTHORS

Qiong Zhu, Yesheng Fu, Chun-Ping Cui, Yi Ding, Zhikang Deng, Chao Ning, Fan Hu, Chen Qiu, Biyue Yu, Xuemei Zhou, Guan Yang, Jiang Peng, Weiguo Zou, Cui Hua Liu & Lingqiang Zhang

ABSTRACT

Bone homeostasis is maintained by the balance between osteoblastic bone formation and osteoclastic bone resorption. Dysregulation of this process leads to multiple diseases, including osteoporosis. However, the underlying molecular mechanisms are not fully understood. Here, we show that the global and conditional osteoblast knockout of a deubiquitinase Otub1 result in low bone mass and poor bone strength due to defects in osteogenic differentiation and mineralization. Mechanistically, the stability of FGFR2, a crucial regulator of osteogenesis, is maintained by OTUB1. OTUB1 attenuates the E3 ligase SMURF1-mediated FGFR2 ubiquitination by inhibiting SMURF1’s E2 binding. In the absence of OTUB1, FGFR2 is ubiquitinated excessively by SMURF1, followed by lysosomal degradation. Consistently, adeno-associated virus serotype 9 (AAV9)-delivered FGFR2 in knee joints rescued the bone mass loss in osteoblast-specific Otub1-deleted mice. Moreover, Otub1 mRNA level was significantly downregulated in bones from osteoporotic mice, and restoring OTUB1 levels through an AAV9-delivered system in ovariectomy-induced osteoporotic mice attenuated osteopenia. Taken together, our results suggest that OTUB1 positively regulates osteogenic differentiation and mineralization in bone homeostasis by controlling FGFR2 stability, which provides an optical therapeutic strategy to alleviate osteoporosis.

Peroxiredoxin 5 regulates osteogenic differentiation through interaction with hnRNPK during bone regeneration

AUTHORS

Eunjin Cho, Xiangguo Che, Mary Jasmin Ang, Seongmin Cheon, Jinkyung Lee, Kwang Soo Kim, Chang Hoon Lee, Sang-Yeop Lee, Hee-Young Yang, Changjong Moon, Chungoo Park, Je-Yong Choi, Tae-Hoon Lee

ABSTRACT

Peroxiredoxin 5 (Prdx5) is involved in pathophysiological regulation via the stress-induced cellular response. However, its function in the bone remains largely unknown. Here, we show that Prdx5 is involved in osteoclast and osteoblast differentiation, resulting in osteoporotic phenotypes in Prdx5 knockout (Prdx5Ko) male mice. To investigate the function of Prdx5 in the bone, osteoblasts were analyzed through immunoprecipitation (IP) and liquid chromatography combined with tandem mass spectrometry (LC–MS/MS) methods, while osteoclasts were analyzed through RNA-sequencing. Heterogeneous nuclear ribonucleoprotein K (hnRNPK) was identified as a potential binding partner of Prdx5 during osteoblast differentiation in vitro. Prdx5 acts as a negative regulator of hnRNPK-mediated osteocalcin (Bglap) expression. In addition, transcriptomic analysis revealed that in vitro differentiated osteoclasts from the bone marrow-derived macrophages of Prdx5Ko mice showed enhanced expression of several osteoclast-related genes. These findings indicate that Prdx5 might contribute to the maintenance of bone homeostasis by regulating osteoblast differentiation. This study proposes a new function of Prdx5 in bone remodeling that may be used in developing therapeutic strategies for bone diseases.

USP53 regulates bone homeostasis by controlling Rankl expression in osteoblasts and bone marrow adipocytes

AUTHORS

Hadla Hariri, Orhun Kose, Aren Bezdjian, Sam J Daniel, René St-Arnaud

ABSTRACT

In the skeleton, osteoblasts and osteoclasts synchronize their activities to maintain bone homeostasis and integrity. Investigating the molecular mechanisms governing bone remodeling is critical and helps understand the underlying biology of bone disorders. Initially, we have identified the ubiquitin-specific peptidase gene (Usp53) as a target of the parathyroid hormone in osteoblasts and a regulator of mesenchymal stem cell differentiation. Mutations in USP53 have been linked to a constellation of developmental pathologies. However, the role of Usp53 in bone has never been visited. Here we show that Usp53 null mice have a low bone mass phenotype in vivo. Usp53 null mice exhibit a pronounced decrease in trabecular bone indices including trabecular bone volume (36%) and trabecular number (26%) along with an increase in trabecular separation (13%). Cortical bone parameters are also impacted showing a reduction in cortical bone volume (12%) and cortical bone thickness (15%). As a result, the strength and mechanical bone properties of Usp53 null mice have been compromised. At the cellular level, the ablation of Usp53 perturbs bone remodeling, augments osteoblast-dependent osteoclastogenesis, and increases osteoclast numbers. Bone marrow adipose tissue volume increased significantly with age in Usp53-deficient mice. Usp53 null mice displayed increased serum RANKL levels and Usp53 deficient osteoblasts and bone marrow adipocytes have increased expression of Rankl. Mechanistically, USP53 regulates RANKL expression by enhancing the interaction between VDR and SMAD3. This is the first report describing the function of Usp53 during skeletal development. Our results put Usp53 in display as a novel regulator of osteoblast–osteoclast coupling and open the door for investigating the involvement of USP53 in pathologies.

Lactate Mediates the Bone Anabolic Effect of High-Intensity Interval Training by Inducing Osteoblast Differentiation

AUTHORS

Zhu, Zhenglin; Chen, Yi; Zou, Jing; Gao, Shengqiang; Wu, Dandong; Li, Xuelun; Hu, Ning; Zhao, Jinzhong; Huang, Wei; Chen, Hong

ABSTRACT

Background:

High-intensity interval training (HIIT) reportedly improves bone metabolism and increases bone mineral density (BMD). The purpose of the present study was to investigate whether lactate mediates the beneficial effects of exercise on BMD, bone microarchitecture, and biomechanical properties in an established osteoporotic animal model. In addition, we hypothesized that lactate-induced bone augmentation is achieved through enhanced osteoblast differentiation and mineralization.

Methods:

A total of 50 female C57BL/6 mice were randomly allocated into 5 groups: the nonovariectomized group, the ovariectomized group (OVX), the HIIT group (OVX + HIIT), the HIIT with lactate transporter inhibition group (OVX + HIIT + INH), and the lactate subcutaneous injection group (OVX + LAC). After 7 weeks of intervention, bone mass, bone strength, and bone formation/resorption processes were evaluated via microcomputed tomography (micro-CT), biomechanical testing, histological analysis, and serum biochemical assays; in vitro studies were performed to explore the bone anabolic effect of lactate at the cellular level.

Results:

Micro-CT revealed significantly increased BMD in both the OVX + HIIT group (mean difference, 41.03 mg hydroxyapatite [HA]/cm3 [95% CI, 2.51 to 79.54 mg HA/cm3]; p = 0.029) and the OVX + LAC group (mean difference, 40.40 mg HA/cm3 [95% CI, 4.08 to 76.71 mg HA/cm3]; p = 0.031) compared with the OVX group. Biomechanical testing demonstrated significantly improved mechanical properties in those 2 groups. However, the beneficial effects of exercise on bone microstructure and biomechanics were largely abolished by blocking the lactate transporter. Notably, histological and biochemical results indicated that increased bone formation was responsible for the bone augmentation effects of HIIT and lactate. Cell culture studies showed a marked increase in the expression of osteoblastic markers with lactate treatment, which could be eliminated by blocking the lactate transporter.

Conclusions:

Lactate may have mediated the bone anabolic effect of HIIT in osteoporotic mice, which may have resulted from enhanced osteoblast differentiation and mineralization.

Clinical Relevance:

Lactate may mediate the bone anabolic effect of HIIT and serve as a potential inexpensive therapeutic strategy for bone augmentation.

Blocking FGF23 signaling improves the growth plate of mice with X-linked hypophosphatemia

AUTHORS

Rocío Fuente, Eva-Maria Pastor-Arroyo, Nicole Gehring, Patricia Oro Carbajosa, Laura Alonso-Durán, Ivan Zderic, James Tapia-Dean, Ahmad Kamal Hamid, Carla Bettoni, Fernando Santos, Carsten A. Wagner, and Isabel Rubio-Aliaga

ABTRACT

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone. X-linked hypophosphatemia (XLH) is the most prevalent inherited phosphate wasting disorder due to mutations in the PHEX gene, which cause elevated circulating FGF23 levels. Clinically, it is characterized by growth impairment and defective mineralization of bones and teeth. Treatment of XLH is challenging. Since 2018 neutralizing antibodies against FGF23 have dramatically improved therapy of XLH patients, although not all patients fully respond to the treatment, and it is very costly. C-terminal fragments of FGF23 have recently emerged as blockers of intact FGF23 signaling. Here, we analyzed the effect on growth and bone of a short 26 residues long C-terminal FGF23 (cFGF23) fragment and two N-acetylated and C-amidated cFGF23 peptides using young XLH mice (PhexC733RMhda mice). Although no major changes in blood parameters were observed after 7 days treatment with these peptides, bone length and growth plate structure improved. The modified peptides accelerated growth rate probably by improving growth plate structure and dynamics. The processes of chondrocyte proliferation, death, hypertrophy, and the cartilaginous composition in the growth plate were partially improved in young treated XLH mice. In conclusion, these findings contribute to understand the role of FGF23 signaling in growth plate metabolism and show that this may occur despite continuous hypophosphatemia.

Effect of vitamin D metabolites on bone histomorphometry in healthy black and white women: An attempt to unravel the so-called vitamin D paradox in blacks

AUTHORS

Shijing Qiu, George Divine, Sudhaker D.Rao

ABSTRACT

An apparent vitamin D paradox, characterized by lower serum 25-hydroxyvitamin D (25(OH)D) levels and higher bone mineral density, is present in black population. In contrast, blacks have higher serum 1,25-dihydroxyvitamin D (1,25(OH)2D) levels. The effect of 1,25(OH)2D on the skeleton is not fully understood. We examined serum 25(OH)D, 1,25(OH)2D and bone histomorphometry in 50 black and white women (25 each) matched for age, menstrual status, and BMI. Histomorphometric indices related to bone structure, remodeling and mineralization were measured in cancellous bone in iliac bone biopsies. Data analyses led to the following results: 1) serum 25(OH)D was significantly lower and 1,25(OH)2D was significantly higher in black than in white women, but neither blacks nor whites revealed significant correlation between these two vitamin D metabolites. 2) there was no significant difference in PTH levels between blacks and whites. 3) except for greater trabecular thickness (Tb.Th) in blacks, there were no significant differences in other histomorphometric variables between the two ethnic groups. 4) osteoid surface (OS/BS), unlabeled osteoid surface (ulOS/BS), and osteoblast surface (ObS/BS) significantly correlated with serum 1,25(OH)2D levels. We conclude that lower serum 25(OH)D levels in blacks do not impair bone structure and remodeling, nor decrease bone mineralization. Higher serum 1,25(OH)2D levels in blacks may help preserve bone mass by stimulating bone formation via increasing osteoblast number and function, but moderately inhibit terminal bone mineralization as shown by higher ulOS/BS.