Monocarboxylate transporter-1 promotes osteoblast differentiation via suppression of p53, a negative regulator of osteoblast differentiation

Expression of Kielin/chordin-like protein is regulated by BMP-2 in osteoblasts

Bone morphogenetic protein (BMP), an osteoinductive factor, is a cytokine that induces osteoblast differentiation and mineralization, and expected to be applicable for hard tissue reconstruction. Kielin/chordin-like protein (Kcp), a member of the family of cysteine-rich proteins, enhances BMP signaling. The present study found that expression of Kcp in osteoblasts was induced by BMP-2 in a concentration- and time-dependent manner. Up-regulation of Kcp by BMP-2 was inhibited by Dorsomorphin, a SMAD signaling inhibitor. The involvement of up-regulation of Kcp by BMP-2 in induction of osteoblast differentiation by BMP-2 was also examined, which showed that suppression of Kcp expression by si Kcp partially inhibited induction of osteoblast differentiation and mineralization by BMP-2. Together, these results suggest that Kcp induced by BMP-2 functions to provide positive feedback for promotion of osteoblastic differentiation and mineralization by BMP-2 in osteoblasts.

It's a Trap! Aldolase-Prescribed C4 Deoxyradiofluorination Affords Intracellular Trapping and the Tracing of Fructose Metabolism by PET

Fructose metabolism has been implicated in various diseases, including metabolic disorders, neurodegenerative disorders, cardiac disorders, and cancer. However, the limited availability of a quantitative imaging radiotracer has hindered its exploration in pathology and diagnostic imaging. Methods: We adopted a molecular design strategy based on the catalytic mechanism of aldolase, a key enzyme in fructolysis. We successfully synthesized a radiodeoxyfluorinated fructose analog, [18F]4-fluoro-4-deoxyfructose ([18F]4-FDF), in high molar activity. Results: Through heavy isotope tracing by mass spectrometry, we demonstrated that C4-deoxyfluorination of fructose led to effective trapping as fluorodeoxysorbitol and fluorodeoxyfructose-1-phosphate in vitro, unlike C1- and C6-fluorinated analogs that resulted in fluorolactate accumulation. This observation was consistent in vivo, where [18F]6-fluoro-6-deoxyfructose displayed substantial bone uptake due to metabolic processing whereas [18F]4-FDF did not. Importantly, [18F]4-FDF exhibited low uptake in healthy brain and heart tissues, known for their high glycolytic activity and background levels of [18F]FDG uptake. [18F]4-FDF PET/CT allowed for sensitive mapping of neuro- and cardioinflammatory responses to systemic lipopolysaccharide administration. Conclusion: Our study highlights the significance of aldolase-guided C4 radiodeoxyfluorination of fructose in enabling effective radiotracer trapping, overcoming limitations of C1 and C6 radioanalogs toward a clinically viable tool for imaging fructolysis in highly glycolytic tissues.

Lactate-induced histone lactylation by p300 promotes osteoblast differentiation

Lactate, which is synthesized as an end product by lactate dehydrogenase A (LDHA) from pyruvate during anaerobic glycolysis, has attracted attention for its energy metabolism and oxidant effects. A novel histone modification-mediated gene regulation mechanism termed lactylation by lactate was recently discovered. The present study examined the involvement of histone lactylation in undifferentiated cells that underwent differentiation into osteoblasts. C2C12 cells cultured in medium with a high glucose content (4500 mg/L) showed increases in marker genes (Runx2, Sp7, Tnap) indicating BMP-2-induced osteoblast differentiation and ALP staining activity, as well as histone lactylation as compared to those cultured in medium with a low glucose content (900 mg/L). Furthermore, C2C12 cells stimulated with the LDH inhibitor oxamate had reduced levels of BMP-2-induced osteoblast differentiation and histone lactylation, while addition of lactate to C2C12 cells cultured in low glucose medium resulted in partial restoration of osteoblast differentiation and histone lactylation. These results indicate that lactate synthesized by LDHA during glucose metabolism is important for osteoblast differentiation of C2C12 cells induced by BMP-2. Additionally, silencing of p300, a possible modifier of histone lactylation, also inhibited osteoblast differentiation and reduced histone lactylation. Together, these findings suggest a role of histone lactylation in promotion of undifferentiated cells to undergo differentiation into osteoblasts.

Intracellular glucose starvation inhibits osteogenic differentiation in human periodontal ligament cells

BACKGROUND

Periodontal ligament cells (PDLCs), as mesenchymal cells in the oral cavity, are closely linked to periodontal tissue regeneration. However, the effect of local glucose deficiency on periodontal tissue regeneration, such as immediately post-surgery, remains unknown.

OBJECTIVE

In the present study, we investigated the effect of a low-glucose environment on the proliferation and osteogenic differentiation of PDLCs.

MATERIALS AND METHODS

We used media with five glucose concentrations (100, 75, 50, 25, and 0 mg/dL) and focused on the effects of a low-glucose environment on the proliferation, osteogenic differentiation, and autophagy of PDLCs. Additionally, we focused on changes in lactate production in a low-glucose environment and investigated the involvement of lactate with AZD3965, a monocarboxylate transporter-1 (MCT-1) inhibitor.

RESULTS

The low-glucose environment inhibited PDLCs proliferation, migration, and osteogenic differentiation, and induced the expression of the autophagy-related factors LC3 and p62. Lactate and ATP production were decreased under low-glucose conditions. The addition of AZD3965 (MCT-1 inhibitor) in normal glucose conditions caused a similar trend as in low-glucose conditions on PDLCs.

CONCLUSION

Our results suggest lactate production through glucose metabolism in the osteogenic differentiation of PDLCs. A low-glucose environment decreased lactate production, inhibiting cell proliferation, migration, and osteogenic differentiation and inducing autophagy in PDLCs.

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

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]/cm 3 [95% CI, 2.51 to 79.54 mg HA/cm 3 ]; p = 0.029) and the OVX + LAC group (mean difference, 40.40 mg HA/cm 3 [95% CI, 4.08 to 76.71 mg HA/cm 3 ]; 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.

Extracellular acidification augments sclerostin and osteoprotegerin production by Ocy454 mouse osteocytes

Osteocytes sense the microenvironmental stimuli, including mechanical stress, and regulate bone resorption by osteoclasts and bone formation by osteoblasts. Diabetes and cancer metastasis to bone raise l-lactic acid in the bone tissue, causing acidification. Here, we investigated the effects of l-lactic acid and extracellular acidification on the function of mouse Ocy454 osteocytes. L- and d-lactic acid with low chiral selectivity and acidification of the medium raised the production of sclerostin and osteoprotegerin by Ocy454 cells. The mRNA expression of their genes increased after either treatment of L- and d-lactic acid or acidification of the medium. Furthermore, the conditioned medium of Ocy454 cells cultured in an acidic environment suppressed the induction of alkaline phosphatase activity in MC3T3-E1 cells, which was recovered by the anti-sclerostin antibody. While it is reported that HDAC5 inhibits the transcription of the sclerostin gene, extracellular acidification reduced the nuclear localization of HDAC5 in Ocy454 cells. While calmodulin kinase II (CaMKII) is known to phosphorylate and induce extranuclear translocation of HDAC5, KN-62, an inhibitor of CaMKII lowered the expression of the sclerostin gene in Ocy454 cells. Collectively, extracellular acidification is a microenvironmental factor that modulates osteocyte functions.

Irisin enhances osteogenic differentiation of mouse MC3T3-E1 cells via upregulating osteogenic genes

Osteoporosis affects millions of individuals and remains a clinical challenge in terms of prevention and treatment. The present study aimed to investigate the effect of irisin on osteogenic differentiation by exposing MC3T3-E1 cells to different concentrations of irisin. Treated cells were assayed for osteoblast proliferation and osteogenic differentiation by measuring alkaline phosphatase (ALP) activity, calcium deposition, formation of mineralized nodules and the expression of osteogenic genes using reverse transcription-quantitative PCR. The proliferation of MC3T3-E1 cells was unaffected by irisin at the concentrations tested of up to 100 ng/ml (P>0.05). ALP activity and mineralized nodule formation were significantly enhanced by irisin in a dose- and time-dependent manner, indicating that irisin promotes osteoblast differentiation of MC3T3-E1 cells. The expression of osteogenic genes, including ALP, collagen I, runt-related transcription factor 2, osterix, osteopontin, osteocalcin, osteoprotegerin and estrogen receptor α, increased significantly after irisin treatment. The present study demonstrated that irisin promoted the osteogenic differentiation of MC3T3-E1 cells, possibly by upregulating the expression of osteogenic genes and markers. Therefore, irisin may be worthy of further investigation as a potential therapeutic agent for osteoporosis.

Compromised Lactate Efflux Renders Vulnerability of Oligodendrocyte Precursor Cells to Metabolic Stresses

Among the brain cells, oligodendrocyte progenitor cells (OPCs) are the most vulnerable in response to hypoxic and ischemic insults, of which the mechanism remains unknown. Brain cells are known to import or export lactate via differentially expressed monocarboxylate transporters (MCTs) to maintain energy metabolism and pH homeostasis. The present study aims to determine the role of MCT1 in the high vulnerability of OPCs. Here we show that a mild ischemic condition equivalent to ischemic preconditioning caused detectable loss of OPCs. MCT1, which is primarily expressed in oligodendrocyte lineage cells including OPCs, was up-regulated immediately under oxygen-glucose deprivation (OGD) conditions. However, persistent hypoxia, but not hypoglycemia, inhibited the function of MCT1, leading to an intracellular lactate accumulation and acidosis in OPCs. Neurons, which express primarily MCT2, were able to export lactate and maintain an intracellular pH homeostasis under similar conditions. The results support that compromised lactate efflux resulting from hypoxia-induced dysfunction of MCT1 contributes to the high vulnerability of OPCs.

Deciphering the potential pharmaceutical mechanism of Guzhi Zengsheng Zhitongwan on rat bone and kidney based on the "kidney governing bone" theory

BACKGROUND

Guzhi Zengsheng Zhitongwan (GZZSZTW) is an effective Chinese medicinal formulation for the treatment of osteoarthritis (OA) designed according to the "kidney governing bone" theory, which has been widely used as a golden guide for treating bone and cartilage diseases in traditional Chinese medicine. The aim of this study was to explore the molecular mechanism underlying its effects on the bone and kidney.

METHODS

Preparation and quality control were performed as previously described. Since GZZSZTW is orally administered in the form of pills prepared in boiled water, the Chinese materia medica (CMM) mixture of this formula was extracted with distilled water by a reflux method and was then filtered through a 0.45-μm Hollow Fiber Cartridge (GE Healthcare, USA). The filtrate was freeze-dried by a Heto PowerDry LL3000 Freeze Dryer (Thermo, USA) and stored at - 80 °C. The effects of GZZSZTW on gene expression and regulation of both kidney and bone tissues were investigated using a state-of-the-art RNA-seq technology.

RESULTS

We demonstrated that GZZSZTW could enhance kidney function and suppress bone formation and resorption by modulating the activities of osteoblast and osteoclast, and might subsequently contribute to the inhibition of osteophyte formation during the process of OA. These effects might be achieved by the synergistic interactions of various herbs and their active components in GZZSZTW, which increased the expression levels of functional genes participating in kidney function, regulation, and repair, and then decreased the expression levels of genes involved in bone formation and resorption. Thus, our findings were consistent with the "kidney governing bone" theory, which has been widely used as a guide in clinical practice for thousands of years.

CONCLUSIONS

This study has deepened the current knowledge about the molecular effects of GZZSZTW on bone and kidney regulation. Furthermore, this study might be able to provide possible strategies to further prevent and treat joint diseases by using traditional Chinese medicinal formulations following the "kidney governing bone" theory.

Roles of monocarboxylate transporter subtypes in promotion and suppression of osteoclast differentiation and survival on bone

Monocarboxylate transporters (MCTs) provide transmembrane transport of monocarboxylates such as lactate and pyruvate. The present results showed that α-cyano-4-hydroxycinnamic acid (CHC), an inhibitor of MCTs, promoted osteoclast differentiation from macrophages at lower concentrations (0.1–0.3 mM) and suppressed that at a higher concentration (1.0 mM). On the other hand, CHC reduced the number of mature osteoclasts on the surface of dentin in a concentration-dependent manner. Additionally, macrophages and osteoclasts were found to express the Mct1, Mct2, and Mct4 genes, with Mct1 and Mct4 expression higher in macrophages, and that of Mct2 higher in osteoclasts. Although Mct1 gene knockdown in macrophages enhanced osteoclast formation induced by RANKL, Mct2 gene knockdown suppressed that. Finally, Mct2 gene silencing in mature osteoclasts decreased their number and, thereby, bone resorption. These results suggest that MCT1 is a negative regulator and MCT2 a positive regulator of osteoclast differentiation, while MCT2 is required for bone resorption by osteoclasts.

Herbacetin treatment remitted LPS induced inhibition of osteoblast differentiation through blocking AKT/NF-κB signaling pathway

Inflammation, a common situation during the process of bone healing, is reported to play a negative role in bone regeneration. Up to date, therapeutic strategies for inflammation triggered inhibition of osteoblast differentiation are still limited. The aim of this study was to explore the potential roles and molecular mechanisms of Herbacetin in the process of osteoblast differentiation under LPS-mediated inflammatory environment. By using MC3T3-E1, C2C12 and primary mouse calvarial osteoblast (PMCO) cells as experimental models, we observed that LPS stimulation suppressed osteoblast differentiation via inhibiting alkaline phosphatase (ALP) activity and the expression of several osteoblastic genes (osterix, runx2 and osteocalcin). However, the negative role of LPS during osteoblast differentiation could be restored by Herbacetin treatment. Mechanistical studies revealed that Herbacetin treatment suppressed AKT activation and in turn blocked NF-κB signaling pathway. Furthermore, reactivating AKT by a selective PTEN inhibitor SF1670 suppressed the effect of Herbacetin. These data suggested that Herbacetin might play a protective role in osteoblast differentiation in MC3T3-E1/C2C12/PMCO cells under LPS stimulation.

Astragalin Promotes Osteoblastic Differentiation in MC3T3-E1 Cells and Bone Formation in vivo

Astragalin (AG) is a biologically active flavonoid compound that can be extracted from a number of medicinal plants. However, the effects of AG on osteoblastic differentiation in mouse MC3T3-E1 cells and on bone formation in vivo have not been studied fully. In this study, we found that the activities of alkaline phosphatase (ALP) and mineralized nodules in MC3T3-E1 cells were both significantly increased after treatment with AG (5, 10, and 20 μM). Meanwhile, the mRNA and protein levels of osteoblastic marker genes in MC3T3-E1 cells after AG treatment were markedly increased compared with a control group. In addition, the levels of BMP-2, p-Smad1/5/9, and Runx2 were significantly elevated in AG-treated MC3T3-E1 cells. Moreover, we found that the protein levels of Erk1/2, p-Erk1/2, p38, p-p38, and p-JNK were also significantly increased in AG-treated MC3T3-E1 cells compared to those in the control group. Finally, in vivo experiments demonstrated that AG significantly promoted bone formation in an ovariectomized (OVX)-induced osteoporotic mouse model. This was evidenced by significant increases in the values of osteoblast-related parameters (BFR/BS, MAR, Ob.S/BS, and Ob.N/B.Pm) and bone histomorphometric parameters (BMD, BV/TV, Tb.Th, and Tb.N.) in OVX mice after AG treatment (5, 10, and 20 mg/kg). Collectively, these results demonstrated that AG may promote osteoblastic differentiation in MC3T3-E1 cells via the activation of the BMP and MAPK pathways and promote bone formation in vivo. These novel findings indicated that AG may be a useful bone anabolic agent for the prevention and treatment of osteoporosis.