Apoptotic Vesicles Regulate Bone Metabolism via the miR1324/SNX14/SMAD1/5 Signaling Axis

AUTHORS

Yuan Zhu, Kunkun Yang, Yawen Cheng, Yaoshan Liu, Ranli Gu, Xuenan Liu, Hao Liu, Xiao Zhang, Yunsong Liu

ABSTRACT

Mesenchymal stem cells (MSCs) are widely used in the treatment of diseases. After their in vivo application, MSCs undergo apoptosis and release apoptotic vesicles (apoVs). This study investigates the role of apoVs derived from human bone marrow mesenchymal stem cells (hBMMSCs) in bone metabolism and the molecular mechanism of the observed effects. The results show that apoVs can promote osteogenesis and inhibit osteoclast formation in vitro and in vivo. ApoVs may therefore attenuate the bone loss caused by primary and secondary osteoporosis and stimulate bone regeneration in areas of bone defect. The mechanisms responsible for apoV-induced bone regeneration include the release of miR1324, which inhibit expression of the target gene Sorting Nexin 14 (SNX14) and thus activate the SMAD1/5 pathway in target cells. Given that MSC-derived apoVs are easily obtained and stored, with low risks of immunological rejection and neoplastic transformation, The findings suggest a novel therapeutic strategy to treat bone loss, including via cell-free approaches to bone tissue engineering.

Inhibiting Wnt Secretion Reduces High Bone Mass Caused by Sost Deficiency or Point Mutations in Lrp5

AUTHORS

Bart Williams, Cassandra Diegel, Gabrielle Foxa, Mitchell McDonald, Zachary Madaj, Ina Kramer, Charles Moes, Sabine Guth, Jun Liu, Jennifer Harris, Michaela Kneissel

ABSTRACT

Proper regulation of Wnt signaling is critical for normal bone development and homeostasis. Mutations in several Wnt signaling components, which increase the pathway's activity in the skeleton, cause high bone mass in human patients and mouse models. Increased bone mass is often accompanied by severe headaches from increased intracranial pressure, which can lead to fatality and loss of vision or hearing due to the entrapment of cranial nerves. In addition, progressive bossing of the forehead and mandibular overgrowth occur in almost all patients. Treatments that would provide symptomatic relief in these patients are limited. Porcupine-mediated palmitoylation is necessary for Wnt secretion and binding to the Frizzled receptor. Chemical inhibition of porcupine is a highly selective inhibitor of all Wnt signaling. We treated three different mouse models of high bone mass caused by aberrant Wnt signaling: homozygosity for loss-of-function in SOST, which models Sclerosteosis, and two strains of mice carrying different point mutations in LRP5 (equivalent to human G171V and A214V) with porcupine inhibitors for 5–6 weeks. Treatment significantly reduced both trabecular and cortical bone mass in all three models. This demonstrates that porcupine inhibition is potentially therapeutic for symptomatic relief in patients who suffer from these disorders and further establishes that the continued production of Wnts is necessary for sustaining high bone mass in these models.

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.

NADPH oxidase and endoplasmic reticulum stress is associated with neuronal degeneration in orbitofrontal cortex of individuals with alcohol use disorder

AUTHORS

Liya Qin, Ryan P. Vetreno, Fulton T. Crews

ABSTRACT

Many disorders of the central nervous system (CNS), including alcohol use disorder (AUD), are associated with induction of proinflammatory neuroimmune signalling and neurodegeneration. In previous studies, we found increased expression of Toll-like receptors (TLRs), activated NF-κB p65 (RELA), and other proinflammatory signalling molecules. Proinflammatory NADPH oxidases generate reactive oxygen species, which are linked to neurodegeneration. We tested the hypothesis that AUD increased RELA activation increases NADPH oxidase-oxidative stress and endoplasmic reticulum (ER) stress cell death cascades in association with neuronal cell death in the human orbitofrontal cortex (OFC). In the AUD OFC, we report mRNA induction of several NADPH oxidases, the dual oxidase DUOX2, and the oxidative stress lipid peroxidation marker 4-HNE and the DNA oxidation marker 8-OHdG that correlate with RELA, a marker of proinflammatory NF-κB activation. This was accompanied by increased expression of the ER stress-associated regulator protein glucose-regulated protein 78 (GRP78), transmembrane sensors activating transcription factor 6 (ATF6), protein kinase RNA-like endoplasmic reticulum kinase (PERK), and inositol-requiring kinase/endonuclease 1 (pIRE1), and the pro-apoptotic transcription factor C/EBP homologous protein (CHOP). Expression of NADPH oxidase-oxidative stress markers correlate with ER stress-associated molecules. Induction of oxidative stress and ER stress signalling pathways correlate with expression of cell death-associated caspases and neuronal cell loss. These data support the hypothesis that proinflammatory RELA-mediated induction of NADPH oxidase-oxidative stress and ER stress-associated signalling cascades is associated with neuronal cell death in the post-mortem human OFC of individuals with AUD.