Lactate induces osteoblast differentiation by stabilization of HIF1α

Lactate promotes bone healing by regulating the osteogenesis of bone marrow mesenchymal stem cells through activating Olfr1440

Bone malunion or nonunion leads to functional and esthetic problems and is a major healthcare burden. Activation of bone marrow mesenchymal stem cells (BMSCs) and subsequent induction of osteogenic differentiation by local metabolites are crucial steps for bone healing, which has not yet been completely investigated. Here, we found that lactate levels are rapidly increased at the local injury site during the early phase of bone defect healing, which facilitates the healing process by enhancing BMSCs regenerative capacity. Mechanistically, lactate serves as a ligand for the Olfr1440 olfactory receptor, to trigger an intracellular calcium influx that in turn activates osteogenic phenotype transition of BMSCs. Conversely, ablation of Olfr1440 delays skeletal repair and remodelling, as evidenced by thinner cortical bone and less woven bone formation in vivo. Administration of lactate in the defect area enhanced bone regeneration. These findings thus revealed the key roles of lactate in the osteogenic differentiation of BMSCs, which deepened our understanding of the bone healing process, as well as provided cues for a potential therapeutic option that might greatly improve bone defect treatment.

Metabolic pathways of glucose and fructose: II Spatiotemporal expression of genes involved in synthesis and transport of lactate in ovine conceptuses†

Lactate, an abundant molecule in fetal fluids and blood of mammalian species, is often overlooked as a metabolic waste product generated during pregnancy. Most of the glucose and fructose consumed by ovine conceptuses is converted to lactate, but proteins involved in lactate metabolism and transport have not been investigated. This study characterized total lactate produced by ovine conceptuses throughout gestation, as well as expression of mRNAs and proteins involved in lactate metabolism. Lactate increased in abundance in the uterine lumen during the preimplantation period and was more abundant than pyruvate. The abundance of lactate in allantoic and amniotic fluids increased with advancing days of gestation and most abundant on Day 125 of pregnancy (P < 0.05). Lactate dehydrogenase subunits A (converts pyruvate to lactate) and B (converts lactate to pyruvate) were expressed by conceptuses throughout gestation. Lactate is transported via monocarboxylic acid transporters SLC16A1 and SLC16A3, both of which were expressed by the conceptus throughout gestation. Additionally, the interplacentomal chorioallantois from Day 126 expressed SLC16A1 and SLC16A3 and transported lactate across the tissue. Hydrocarboxylic acid receptor 1 (HCAR1), a receptor for lactate, was localized to the uterine luminal and superficial glandular epithelia of pregnant ewes throughout gestation and conceptus trophectoderm during the peri-implantation period of gestation. These results provide novel insights into the spatiotemporal profiles of enzymes, transporters, and receptor for lactate by ovine conceptuses throughout pregnancy.

Fueling recovery: The importance of energy coupling between angiogenesis and osteogenesis during fracture healing

Approximately half of bone fractures that do not heal properly (non-union) can be accounted to insufficient angiogenesis. The processes of angiogenesis and osteogenesis are spatiotemporally regulated in the complex process of fracture healing that requires a substantial amount of energy. It is thought that a metabolic coupling between angiogenesis and osteogenesis is essential for successful healing. However, how this coupling is achieved remains to be largely elucidated. Here, we will discuss the most recent evidence from literature pointing towards a metabolic coupling between angiogenesis and osteogenesis. We will describe the metabolic profiles of the cell types involved during fracture healing as well as secreted products in the bone microenvironment (such as lactate and nitric oxide) as possible key players in this metabolic crosstalk.

The Bioactive Compounds of Epimedium and Their Potential Mechanism of Action in Treating Osteoporosis: A Network Pharmacology and Experimental Validation Study

Osteoporosis is a global health challenge characterized by bone loss and microstructure deterioration, which urgently requires the development of safer and more effective treatments due to the significant adverse effects and limitations of existing drugs for long-term treatment. Traditional Chinese medicine, like Epimedium, offers fewer side effects and has been used to treat osteoporosis, yet its active compounds and pharmacological mechanisms remain unclear. In this study, 65 potential active compounds, 258 potential target proteins, and 488 pathways of Epimedium were identified through network pharmacology analysis. Further network analysis and review of the literature identified six potential active compounds and HIF-1α for subsequent experimental validation. In vitro experiments confirmed that 2″-O-RhamnosylIcariside II is the most effective compound among the six potential active compounds. It can promote osteoblast differentiation, bind with HIF-1α, and inhibit both HIF-1α gene and protein expression, as well as enhance COL1A1 protein expression under hypoxic conditions. In vivo experiments demonstrated its ability to improve bone microstructures and reduce bone loss by decreasing bone marrow adipose tissue, enhancing bone formation, and suppressing HIF-1α protein expression. This study is the first to describe the therapeutic effects of 2-O-RhamnosylIcariside II on osteoporosis, which was done, specifically, through a mechanism that targets and inhibits HIF-1α. This study provides a scientific basis for the clinical application of Epimedium and offers a new candidate drug for the treatment of osteoporosis. Additionally, it provides new evidence supporting HIF-1α as a therapeutic target for osteoporosis.

Energy homeostasis in the bone

The bone serves as an energy reservoir and actively engages in whole-body energy metabolism. Numerous studies have determined fuel requirements and bioenergetic properties of bone under physiological conditions as well as the dysregulation of energy metabolism associated with bone metabolic diseases. Here, we review the main sources of energy in bone cells and their regulation, as well as the endocrine role of the bone in systemic energy homeostasis. Moreover, we discuss metabolic changes that occur as a result of osteoporosis. Exploration in this area will contribute to an enhanced comprehension of bone energy metabolism, presenting novel possibilities to address metabolic diseases.

Study on the effect of protein lysine lactylation modification in macrophages on inhibiting periodontitis in rats

BACKGROUND

Protein lysine lactylation (Kla) has been proved to be closely related to inflammatory diseases, but its role in periodontitis (PD) is unclear. Therefore, this study aimed to establish the global profiling of Kla in PD models in rats.

METHODS

Clinical periodontal samples were collected, the inflammatory state of tissues was verified by H&E staining, and lactate content was detected by a lactic acid kit. Kla levels were detected by immunohistochemistry (IHC) and Western blot. Subsequently, the rat model of PD was developed and its reliability verified by micro-CT and H&E staining. Mass spectrometry analysis was conducted to explore the expression profile of proteins and Kla in periodontal tissues. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were performed, and a protein-protein interaction (PPI) network was constructed. The lactylation in RAW264.7 cells was confirmed by IHC, immunofluorescence and Western blot. The relative expression levels of inflammatory factors IL-1β, IL-6, TNF-α, macrophage polarization-related factors CD86, iNOS, Arg1, and CD206 in RAW264.7 cells were detected by real time-quantitative polymerase chain reaction (RT-qPCR).

RESULTS

We observed substantial inflammatory cell infiltration in the PD tissues, and the lactate content and lactylation levels were significantly increased. The expression profiles of protein and Kla were obtained by mass spectrometry based on the established rat model of PD. Kla was confirmed in vitro and in vivo. After inhibiting the "writer" of lactylation P300 in RAW264.7 cells, the lactylation levels decreased, and the expression of inflammatory factors IL-1β, IL-6, and TNF-α increased. Meanwhile, the levels of CD86 and iNOS increased, and Arg1 and CD206 decreased.

CONCLUSIONS

Kla may play an important role in PD, regulating the release of inflammatory factors and polarization of macrophages.

2P-FLIM unveils time-dependent metabolic shifts during osteogenic differentiation with a key role of lactate to fuel osteogenesis via glutaminolysis identified

BACKGROUND

Human mesenchymal stem cells (hMSCs) utilize discrete biosynthetic pathways to self-renew and differentiate into specific cell lineages, with undifferentiated hMSCs harbouring reliance on glycolysis and hMSCs differentiating towards an osteogenic phenotype relying on oxidative phosphorylation as an energy source.

METHODS

In this study, the osteogenic differentiation of hMSCs was assessed and classified over 14 days using a non-invasive live-cell imaging modality-two-photon fluorescence lifetime imaging microscopy (2P-FLIM). This technique images and measures NADH fluorescence from which cellular metabolism is inferred.

RESULTS

During osteogenesis, we observe a higher dependence on oxidative phosphorylation (OxPhos) for cellular energy, concomitant with an increased reliance on anabolic pathways. Guided by these non-invasive observations, we validated this metabolic profile using qPCR and extracellular metabolite analysis and observed a higher reliance on glutaminolysis in the earlier time points of osteogenic differentiation. Based on the results obtained, we sought to promote glutaminolysis further by using lactate, to improve the osteogenic potential of hMSCs. Higher levels of mineral deposition and osteogenic gene expression were achieved when treating hMSCs with lactate, in addition to an upregulation of lactate metabolism and transmembrane cellular lactate transporters. To further clarify the interplay between glutaminolysis and lactate metabolism in osteogenic differentiation, we blocked these pathways using BPTES and α-CHC respectively. A reduction in mineralization was found after treatment with BPTES and α-CHC, demonstrating the reliance of hMSC osteogenesis on glutaminolysis and lactate metabolism.

CONCLUSION

In summary, we demonstrate that the osteogenic differentiation of hMSCs has a temporal metabolic profile and shift that is observed as early as day 3 of cell culture using 2P-FLIM. Furthermore, extracellular lactate is shown as an essential metabolite and metabolic fuel to ensure efficient osteogenic differentiation and as a signalling molecule to promote glutaminolysis. These findings have significant impact in the use of 2P-FLIM to discover potent approaches towards bone tissue engineering in vitro and in vivo by engaging directly with metabolite-driven osteogenesis.

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.

Progress of research into the pharmacological effect and clinical application of the traditional Chinese medicine Rehmanniae Radix

The traditional Chinese medicine (TCM) Rehmanniae Radix (RR) refers to the fresh or dried root tuber of the plant Rehmannia glutinosa Libosch of the family Scrophulariaceae. As a traditional Chinese herbal medicine (CHM), it possesses multiple effects, including analgesia, sedation, anti-inflammation, antioxidation, anti-tumor, immunomodulation, cardiovascular and cerebrovascular regulation, and nerve damage repair, and it has been widely used in clinical practice. In recent years, scientists have extensively studied the active components and pharmacological effects of RR. Active ingredients mainly include iridoid glycosides (such as catalpol and aucuboside), phenylpropanoid glycosides (such as acteoside), other saccharides, and unsaturated fatty acids. In addition, the Chinese patent medicine (CPM) and Chinese decoction related to RR have also become major research subjects for TCM practitioners; one example is the Bolus of Six Drugs, which includes Rehmannia, Lily Bulb and Rehmannia Decoction, and Siwu Decoction. This article reviews recent literature on RR; summarizes the studies on its chemical constituents, pharmacological effects, and clinical applications; and analyzes the progress and limitations of current investigations to provide reference for further exploration and development of RR.

Recent advances in the application and biological mechanism of silicon nitride osteogenic properties: a review

Silicon nitride, an emerging bioceramic material, is highly sought after in the biomedical industry due to its osteogenesis-promoting properties, which are a result of its unique surface chemistry and excellent mechanical properties. Currently, it is used in clinics as an orthopedic implant material. The osteogenesis-promoting properties of silicon nitride are manifested in its contribution to the formation of a local osteogenic microenvironment, wherein silicon nitride and its hydrolysis products influence osteogenesis by modulating the biological behaviors of the constituents of the osteogenic microenvironment. In particular, silicon nitride regulates redox signaling, cellular autophagy, glycolysis, and bone mineralization in cells involved in bone formation via several mechanisms. Moreover, it may also promote osteogenesis by influencing immune regulation and angiogenesis. In addition, the wettability, surface morphology, and charge of silicon nitride play crucial roles in regulating its osteogenesis-promoting properties. However, as a bioceramic material, the molding process of silicon nitride needs to be optimized, and its osteogenic mechanism must be further investigated. Herein, we summarize the impact of the molding process of silicon nitride on its osteogenic properties and clinical applications. In addition, the mechanisms of silicon nitride in promoting osteogenesis are discussed, followed by a summary of the current gaps in silicon nitride mechanism research. This review, therefore, aims to provide novel ideas for the future development and applications of silicon nitride.

Microporous Polylactic Acid Scaffolds Enable Fluorescence-Based Perfusion Imaging of Intrinsic In Vivo Vascularization

In vivo tissue engineering (TE) techniques like the AV loop model provide an isolated and well-defined microenvironment to study angiogenesis-related cell interactions. Functional visualization of the microvascular network within these artificial tissue constructs is crucial for the fundamental understanding of vessel network formation and to identify the underlying key regulatory mechanisms. To facilitate microvascular tracking advanced fluorescence imaging techniques are required. We studied the suitability of microporous polylactic acid (PLA) scaffolds with known low autofluorescence to form axial vascularized tissue constructs in the AV loop model and to validate these scaffolds for fluorescence-based perfusion imaging. Compared to commonly used collagen elastin (CE) scaffolds, the total number of vessels and cells in PLA scaffolds was lower. In detail, CE-based constructs exhibited significantly higher vessel numbers on day 14 and 28 (d14: 316 ± 53; d28: 610 ± 74) compared to the respective time points in PLA-based constructs (d14: 144 ± 18; d28: 327 ± 34; each p < 0.05). Analogously, cell counts in CE scaffolds were higher compared to corresponding PLA constructs (d14: 7661.25 ± 505.93 and 5804.04 ± 716.59; d28: 11211.75 + 1278.97 and 6045.71 ± 572.72, p < 0.05). CE scaffolds showed significantly higher vessel densities in proximity to the main vessel axis compared to PLA scaffolds (200-400 µm and 600-800 µm on day 14; 400-1000 µm and 1400-1600 µm on day 28). CE scaffolds had significantly higher cell counts on day 14 at distances from 800 to 2000 µm and at distances from 400 to 1600 µm on day 28. While the total number of vessels and cells in PLA scaffolds were lower, both scaffold types were ideally suited for axial vascularization techniques. The intravascular perfusion of PLA-based constructs with fluorescence dye MHI148-PEI demonstrated dye specificity against vascular walls of low- and high-order branches as well as capillaries and facilitated the fluorescence-based visualization of microcirculatory networks. Fluorophore tracking may contribute to the development of automated quantification methods after 3D reconstruction and image segmentation. These technologies may facilitate the characterization of key regulators within specific subdomains and add to the current understanding of vessel formation in axially vascularized tissue constructs.

The Role of HIF-1α in Bone Regeneration: A New Direction and Challenge in Bone Tissue Engineering

The process of repairing significant bone defects requires the recruitment of a considerable number of cells for osteogenesis-related activities, which implies the consumption of a substantial amount of oxygen and nutrients. Therefore, the limited supply of nutrients and oxygen at the defect site is a vital constraint that affects the regenerative effect, which is closely related to the degree of a well-established vascular network. Hypoxia-inducible factor (HIF-1α), which is an essential transcription factor activated in hypoxic environments, plays a vital role in vascular network construction. HIF-1α, which plays a central role in regulating cartilage and bone formation, induces vascular invasion and differentiation of osteoprogenitor cells to promote and maintain extracellular matrix production by mediating the adaptive response of cells to changes in oxygen levels. However, the application of HIF-1α in bone tissue engineering is still controversial. As such, clarifying the function of HIF-1α in regulating the bone regeneration process is one of the urgent issues that need to be addressed. This review provides insight into the mechanisms of HIF-1α action in bone regeneration and related recent advances. It also describes current strategies for applying hypoxia induction and hypoxia mimicry in bone tissue engineering, providing theoretical support for the use of HIF-1α in establishing a novel and feasible bone repair strategy in clinical settings.

Lysosomal acid lipase regulates bioenergetic process during the cytodifferentiation of human periodontal ligament cells

Lipid metabolism is one of energy metabolic pathways that produce adenosine triphosphate (ATP). In this pathway, lysosomal acid lipase (LAL) encoded by Lipase A (LIPA), plays an important role in catalyzing lipids to fatty acids (FAs), which drive oxidative phosphorylation (OXPHOS) and generate ATP. Previously, we found that a LIPA single nucleotide polymorphism rs143793106, which decreases the LAL activity, suppressed the cytodifferentiation of human periodontal ligament (HPDL) cells. However, the mechanisms underlying that suppression are still not fully clarified. Thus, we aimed to investigate the mechanisms regulating the cytodifferentiation of HPDL cells by LAL in terms of energy metabolism. We performed the osteogenic induction of HPDL cells with or without Lalistat-2, a LAL inhibitor. To visualize lipid droplet (LD) utilization, we performed confocal microscopy on HPDL cells. We also performed real-time PCR to analyze the gene expression of calcification-related and metabolism-related genes. Furthermore, we measured the ATP production rate from two major energy production pathways, OXPHOS and glycolysis, and OXPHOS-related parameters of HPDL cells during their cytodifferentiation. We found that LDs were utilized during the cytodifferentiation of HPDL cells. Alkaline phosphatase (ALPL), collagen type 1 alpha 1 chain (COL1A1), ATP synthase F1 subunit alpha (ATP5F1A), and carnitine palmitoyltransferase 1A (CPT1A) mRNA expressions were upregulated, whereas lactate dehydrogenase A (LDHA) mRNA expression was downregulated. Additionally, total ATP production rate was significantly increased. In contrast, in the presence of Lalistat-2, LD utilization was inhibited and ALPL, COL1A1, and ATP5F1A mRNA expression was downregulated. Additionally, ATP production rate and spare respiratory capacity of the OXPHOS pathway were decreased in HPDL cells during their cytodifferentiation. Collectively, the defect of LAL in HPDL cells decreased LD utilization and OXPHOS capacity, resulting in reduced energy to sustain the adequate ATP production required for the cytodifferentiation of HPDL cells. Thus, LAL is important for periodontal tissue homeostasis as a regulator of bioenergetic process of HPDL cells.

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.

Hypoxia Pathway in Osteoporosis: Laboratory Data for Clinical Prospects

The hypoxia pathway not only regulates the organism to adapt to the special environment, such as short-term hypoxia in the plateau under normal physiological conditions, but also plays an important role in the occurrence and development of various diseases such as cancer, cardiovascular diseases, osteoporosis. Bone, as a special organ of the body, is in a relatively low oxygen environment, in which the expression of hypoxia-inducible factor (HIF)-related molecules maintains the necessary conditions for bone development. Osteoporosis disease with iron overload endangers individuals, families and society, and bone homeostasis disorder is linked to some extent with hypoxia pathway abnormality, so it is urgent to clarify the hypoxia pathway in osteoporosis to guide clinical medication efficiently. Based on this background, using the keywords "hypoxia/HIF, osteoporosis, osteoblasts, osteoclasts, osteocytes, iron/iron metabolism", a matching search was carried out through the Pubmed and Web Of Science databases, then the papers related to this review were screened, summarized and sorted. This review summarizes the relationship and regulation between the hypoxia pathway and osteoporosis (also including osteoblasts, osteoclasts, osteocytes) by arranging the references on the latest research progress, introduces briefly the application of hyperbaric oxygen therapy in osteoporosis symptoms (mechanical stimulation induces skeletal response to hypoxic signal activation), hypoxic-related drugs used in iron accumulation/osteoporosis model study, and also puts forward the prospects of future research.

Temporal metabolic profiling of bone healing in a caprine tibia segmental defect model

Bone tissue engineering is an emerging field of regenerative medicine, with a wide array of biomaterial technologies and therapeutics employed. However, it is difficult to objectively compare these various treatments during various stages of tissue response. Metabolomics is rapidly emerging as a powerful analytical tool to establish broad-spectrum metabolic signatures for a target biological system. Developing an effective biomarker panel for bone repair from small molecule data would provide an objective metric to readily assess the efficacy of novel therapeutics in relation to natural healing mechanisms. In this study we utilized a large segmental bone defect in goats to reflect trauma resulting in substantial volumetric bone loss. Characterization of the native repair capacity was then conducted over a period of 12 months through the combination of standard (radiography, computed tomography, histology, biomechanics) data and ultra-high-performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) metabolic profiling. Standard metrics demonstrated that samples formed soft callus structures that later mineralized. Small molecule profiles showed distinct temporal patterns associated with the bone tissue repair process. Specifically, increased lactate and amino acid levels at early time points indicated an environment conducive to osteoblast differentiation and extracellular matrix formation. Citrate and pyruvate abundances increased at later time points indicating increasing mineral content within the defect region. Taurine, shikimate, and pantothenate distribution profiles appeared to represent a shift toward a more homeostatic remodeling environment with the differentiation and activity of osteoclasts offsetting the earlier deposition phases of bone repair. The generation of a comprehensive metabolic reference portfolio offers a potent mechanism for examining novel biomaterials and can serve as guide for the development of new targeted therapeutics to improve the rate, magnitude, and quality of bone regeneration.

Mechanical Force Modulates Alveolar Bone Marrow Mesenchymal Cells Characteristics for Bone Remodeling during Orthodontic Tooth Movement through Lactate Production

Orthodontic tooth movement (OTM) relies on mechanical force-induced bone remodeling. As a metabolic intermediate of glycolysis, lactate has recently been discovered to participate in bone remodeling by serving as a signaling molecule. However, whether lactate could respond to mechanical stimulus during OTM, as well as whether lactate has an impact on the alveolar bone remodeling during orthodontics, remain to be further elucidated. In the current study, we observed physiologically elevated production of lactate along with increased osteogenic differentiation, proliferation, and migration of alveolar bone marrow mesenchymal cells (ABMMCs) under mechanical force. Inhibition of lactate, induced by cyclic mechanical stretch by GNE-140, remarkably suppressed the osteogenic differentiation, proliferation, and migration, yet enhanced apoptosis of ABMMCs. Mechanistically, these regulatory effects of lactate were mediated by histone lactylation. Taken together, our results suggest that force-induced lactate is involved in controlling bone remodeling-related cellular activities in ABMMCs and plays a vital role in the alveolar bone remodeling during OTM. Our findings indicate that lactate might be a critical modulator for alveolar bone remodeling during OTM, providing a novel therapeutic target for the purpose of more effectively controlling tooth movement and improving the stability of orthodontic results.

4D label-free quantitative proteomics analysis to screen potential drug targets of Jiangu Granules treatment for postmenopausal osteoporotic rats

Background: Postmenopausal osteoporosis (PMOP) is a disease with a high prevalence in postmenopausal women and is characterized by an imbalance in bone metabolism, reduced bone mass, and increased risk of fracture due to estrogen deficiency. Jiangu granules (JG) is a compound prescription used in traditional Chinese medicine to treat PMOP. However, its definitive mechanism in PMOP is unclear. This study used a 4D label-free quantitative proteomics method to explore the potential therapeutic mechanism of JG in an ovariectomy (OVX) rats' model. Materials and methods: A rat model of PMOP was established by removing the ovaries bilaterally. Nine 3-month-old specific-pathogen-free female SD rats. The nine rats were randomly divided into 3 groups (n = 3 in each group): the sham-operated group (J), the ovariectomy group (NC), and the JG treatment (ZY) group. Proteins extracted from the bone tissue of the lumbar spine (L3, L4) of three groups of rats were analyzed by 4D label-free quantitative proteomics, and proteins differentially expressed after JG treatment and proteins differentially expressed after de-ovulation were intersected to identify proteins associated with the mechanism of PMOP by JG treatment. Result: There were 104 up-regulated and 153 down-regulated differentially expressed proteins (DEPs) in the J group vs. NC group, 107 up-regulated and 113 down-regulated DEPs in the J group vs. ZY group, and 15 up-regulated and 32 down-regulated DEPs in the NC group vs. ZY group. Six potential target proteins for JG regulation of osteoblast differentiation in OVX rats were identified by taking intersections of differential proteins in the J group vs. NC group and NC group vs. ZY group. Conclusion: JG may exert therapeutic effects by modulating the expression levels of target proteins associated with osteoblast differentiation to enhance osteoblast differentiation in OVX rats. These results further uncovered the target proteins and specific mechanisms of JG in treating PMOP, providing an experimental basis for the clinical application of JG in treating PMOP.

Advances in Glycolysis Metabolism of Atherosclerosis

Glycolysis is an important way for various cells such as vascular wall endothelial cells, smooth muscle cells, macrophages, and other cells to obtain energy. In pathological conditions, it can participate in the process of AS by regulating lipid deposition, calcification, angiogenesis in plaques, etc., together with its metabolite lactic acid. Recent studies have shown that lactate-related lactylation modifications are ubiquitous in the human proteome and are involved in the regulation of various inflammatory diseases. Combined with the distribution and metabolic characteristics of cells in the plaque in the process of AS, glycolysis-lactate-lactylation modification may be a new entry point for targeted intervention in atherosclerosis in the future. Therefore, this article intends to elaborate on the role and mechanism of glycolysis-lactate-lactylation modification in AS, as well as the opportunities and challenges in targeted therapy, hoping to bring some help to relevant scholars in this field. In atherosclerosis, glycolysis, lactate, and lactylation modification as a metabolic sequence affect the functions of macrophages, smooth muscle cells, endothelial cells, lymphocytes, and other cells and interfere with processes such as vascular calcification and intraplaque neovascularization to influence the progression of atherosclerosis.

Lactate inhibits osteogenic differentiation of human periodontal ligament stem cells via autophagy through the MCT1-mTOR signaling pathway

BACKGROUND

Periodontal ligament stem cells (PDLSCs) play a crucial role in periodontal bone regeneration. Lactate used to be considered a waste product of glucose metabolism. In recent years, a few pieces of evidence revealed its roles in regulating the osteogenic differentiation of stem cells, but the standpoints were controversial. This study aims to investigate the effects and the mechanisms of lactate on the osteogenic differentiation of human periodontal ligament stem cells (hPDLSCs).

METHODS

The hPDLSCs were treated with different concentrations of lactic acid and lactate to differentiate the effects of the acidic PH and ion lactate. Proliferation and cytotoxicity were measured by Cell Counting Kit-8 (CCK8) assay and Live/Dead assay. The osteogenic differentiation of hPDLSCs was analyzed by alizarin red staining, alkaline phosphatase (ALP) staining, and then osteogenic proteins and genes were measured by western blot and reverse transcription-quantitative PCR (qRT-PCR). To investigate the potential signaling pathways, MCT1 inhibitor, G-protein inhibitors, and rapamycin were used, and then autophagy-related proteins and osteogenic proteins were measured by western blot.

RESULTS

The inhibition of lactic acid on the osteogenic differentiation of hPDLSCs was more significant than lactate at the same concentration. Lactate inhibited the expression of ALP which can be rescued by Gα inhibitor. Alizarin red staining, the protein expression levels of osteocalcin (OCN), osteoprotegerin (OPN), osterix (OSX), and beclin1, LC3-II/LC3-I were decreased by lactate and partly rescued by MCT1 inhibitor. Rapamycin restored the protein expression levels of beclin1, LC3-II/LC3-I and OCN, OPN, OSX under the high lactate conditions.

CONCLUSIONS

Lactate inhibits the expression of ALP via Gα subunit signaling, and inhibits mineralized nodules formation and the expression of osteogenic-related proteins via reducing autophagy through the MCT1-mTOR signaling pathway.

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.

Bioenergetic Metabolism In Osteoblast Differentiation

PURPOSE OF REVIEW

Osteoblasts are responsible for bone matrix production during bone development and homeostasis. Much is known about the transcriptional regulation and signaling pathways governing osteoblast differentiation. However, less is known about how osteoblasts obtain or utilize nutrients to fulfill the energetic demands associated with osteoblast differentiation and bone matrix synthesis. The goal of this review is to highlight and discuss what is known about the role and regulation of bioenergetic metabolism in osteoblasts with a focus on more recent studies.

RECENT FINDINGS

Bioenergetic metabolism has emerged as an important regulatory node in osteoblasts. Recent studies have begun to identify the major nutrients and bioenergetic pathways favored by osteoblasts as well as their regulation during differentiation. Here, we highlight how osteoblasts obtain and metabolize glucose, amino acids, and fatty acids to provide energy and other metabolic intermediates. In addition, we highlight the signals that regulate nutrient uptake and metabolism and focus on how energetic metabolism promotes osteoblast differentiation. Bioenergetic metabolism provides energy and other metabolites that are critical for osteoblast differentiation and activity. This knowledge contributes to a more comprehensive understanding of osteoblast biology and may inform novel strategies to modulate osteoblast differentiation and bone anabolism in patients with bone disorders.

Energy Metabolism in Osteogenic Differentiation and Reprogramming: A Possible Future Strategy for Periodontal Regeneration

Energy metabolism is crucial in stem cells as they harbor various metabolic pathways depending on their developmental stages. Moreover, understanding the control of their self-renewal or differentiation via manipulation of their metabolic state may yield novel regenerative therapies. Periodontal ligament (PDL) cells existing between the tooth and alveolar bone are crucial for maintaining homeostasis in the periodontal tissue. In addition, they play a pivotal role in periodontal regeneration, as they possess the properties of mesenchymal stem cells and are capable of differentiating into osteogenic cells. Despite these abilities, the treatment outcome of periodontal regenerative therapy remains unpredictable because the biological aspects of PDL cells and the mechanisms of their differentiation remain unclear. Recent studies have revealed that metabolism and factors affecting metabolic pathways are involved in the differentiation of PDL cells. Furthermore, understanding the metabolic profile of PDL cells could be crucial in manipulating the differentiation of PDL cells. In this review, first, we discuss the energy metabolism in osteoblasts and stem cells to understand the metabolism of PDL cells. Next, we summarize the metabolic preferences of PDL cells during their maintenance and cytodifferentiation. The perspectives discussed have potential applicability for creating a platform for reliable regenerative therapies for periodontal tissue.

Self-Organization Provides Cell Fate Commitment in MSC Sheet Condensed Areas via ROCK-Dependent Mechanism

Multipotent mesenchymal stem/stromal cells (MSC) are one of the crucial regulators of regeneration and tissue repair and possess an intrinsic program from self-organization mediated by condensation, migration and self-patterning. The ability to self-organize has been successfully exploited in tissue engineering approaches using cell sheets (CS) and their modifications. In this study, we used CS as a model of human MSC spontaneous self-organization to demonstrate its structural, transcriptomic impact and multipotent stromal cell commitment. We used CS formation to visualize MSC self-organization and evaluated the role of the Rho-GTPase pathway in spontaneous condensation, resulting in a significant anisotropy of the cell density within the construct. Differentiation assays were carried out using conventional protocols, and microdissection and RNA-sequencing were applied to establish putative targets behind the observed phenomena. The differentiation of MSC to bone and cartilage, but not to adipocytes in CS, occurred more effectively than in the monolayer. RNA-sequencing indicated transcriptional shifts involving the activation of the Rho-GTPase pathway and repression of SREBP, which was concordant with the lack of adipogenesis in CS. Eventually, we used an inhibitory analysis to validate our findings and suggested a model where the self-organization of MSC defined their commitment and cell fate via ROCK1/2 and SREBP as major effectors under the putative switching control of AMP kinase.

Glucose Metabolism in Osteoblasts in Healthy and Pathophysiological Conditions

Bone tissue in vertebrates is essential to performing movements, to protecting internal organs and to regulating calcium homeostasis. Moreover, bone has also been suggested to contribute to whole-body physiology as an endocrine organ, affecting male fertility; brain development and cognition; and glucose metabolism. A main determinant of bone quality is the constant remodeling carried out by osteoblasts and osteoclasts, a process consuming vast amounts of energy. In turn, clinical conditions associated with impaired glucose metabolism, including type I and type II diabetes and anorexia nervosa, are associated with impaired bone turnover. As osteoblasts are required for collagen synthesis and matrix mineralization, they represent one of the most important targets for pharmacological augmentation of bone mass. To fulfill their function, osteoblasts primarily utilize glucose through aerobic glycolysis, a process which is regulated by various molecular switches and generates adenosine triphosphate rapidly. In this regard, researchers have been investigating the complex processes of energy utilization in osteoblasts in recent years, not only to improve bone turnover in metabolic disease, but also to identify novel treatment options for primary bone diseases. This review focuses on the metabolism of glucose in osteoblasts in physiological and pathophysiological conditions.

Increase of aerobic glycolysis mediated by activated T helper cells drives synovial fibroblasts towards an inflammatory phenotype: new targets for therapy?

BACKGROUND

A dysregulated glucose metabolism in synovial fibroblasts (SF) has been associated with their aggressive phenotype in rheumatoid arthritis (RA). Even though T helper (Th) cells are key effector cells in the propagation and exacerbation of synovitis in RA, little is known about their influence on the metabolism of SF. Thus, this study investigates the effect of Th cells on the glucose metabolism and phenotype of SF and how this is influenced by the blockade of cytokines, janus kinases (JAKs) and glycolysis.

METHODS

SF from patients with RA or osteoarthritis (OA) were cultured in the presence of a stable glucose isotopomer ([U-13C]-glucose) and stimulated with the conditioned media of activated Th cells (ThCM). Glucose consumption and lactate production were measured by proton nuclear magnetic resonance (1H NMR) spectroscopy. Cytokine secretion was quantified by ELISA. The expression of glycolytic enzymes was analysed by PCR, western blot and immunofluorescence. JAKs were blocked using either baricitinib or tofacitinib and glycolysis by using either 3-bromopyruvate or FX11.

RESULTS

Quiescent RASF produced significantly higher levels of lactate, interleukin (IL)-6 and matrix metalloproteinase (MMP) 3 than OASF. Stimulation by ThCM clearly changed the metabolic profile of both RASF and OASF by inducing a shift towards aerobic glycolysis with strongly increased lactate production together with a rise in IL-6 and MMP3 secretion. Interestingly, chronic stimulation of OASF by ThCM triggered an inflammatory phenotype with significantly increased glycolytic activity compared to unstimulated, singly stimulated or re-stimulated OASF. Finally, in contrast to cytokine-neutralizing biologics, inhibition of JAKs or glycolytic enzymes both significantly reduced lactate production and cytokine secretion by Th cell-stimulated SF.

CONCLUSIONS

Soluble mediators released by Th cells drive SF towards a glycolytic and pro-inflammatory phenotype. Targeting of JAKs or glycolytic enzymes both potently modulate SF's glucose metabolism and decrease the release of IL-6 and MMP3. Thus, manipulation of glycolytic pathways could represent a new therapeutic strategy to decrease the pro-inflammatory phenotype of SF.

MiR-34a suppresses osteoblast differentiation through glycolysis inhibition by targeting lactate dehydrogenase-A (LDHA)

Bone formation (osteogenesis) is mediated through recruitment of bone marrow mesenchymal stem cells (MSCs) with capacity to differentiate into osteoblasts, a process which is regulated by transcriptional and post-transcriptional mechanisms. Multiple studies have suggested that miRNAs might have important roles in osteoblast differentiation. Expressions of miR-34a were detected by qRT-PCR. Cellular glucose metabolism was assessed by measurements of glucose uptake and lactate production. mRNA expressions of glycolysis enzymes were detected by qRT-PCR. Osteogenic differentiation of human MSCs (hMSCs) was analyzed by alkaline phosphatase (ALP) activity and Alizarin red staining. Here, we report that microRNA-34a is upregulated during the osteoblast differentiation from hMSCs. miR-34a overexpressing inhibited late osteoblast differentiation of hMSCs in vitro. The ALP activity and Alizarin red staining were significantly decreased by miR-34a in hMSCs. Target prediction analysis reveals that the lactate dehydrogenase-A (LDHA) is a potential target of miR-34a. We hypothesized that miR-34a inhibits osteoblast differentiation through targeting the LDHA-mediated cellular glycolysis. Results from Western blotting and luciferase assay validated that miR-34a could directly target 3'UTR of LDHA mRNA. In addition, we demonstrated that overexpression of miR-34a inhibits cellular anaerobic glycolysis through targeting LHDA. The protein and mRNA expressions of glycolysis enzymes, Hexokinase 2 (HK2), glucose transporter 1 (GLUT1), and LDHA were significantly downregulated by miR-34a overexpression in hMSCs. Furthermore, we showed that LDHA restoration in miR-34a overexpressing hMSCs successfully rescued the osteoblast differentiation of hMSCs. This study demonstrated the roles of miR-34a in regulating osteoblast differentiation, suggesting that miR-34a inhibition could be a new therapeutic strategy for improving bone formation.

Effects of Dietary Supplementation with Combination of Tributyrin and Essential Oil on Gut Health and Microbiota of Weaned Piglets

Simple Summary

The dietary inclusion of the combination of tributyrin with either oregano or methyl salicylate as a substitution to antibiotics improved intestinal morphological structure of weaned piglets and resulted in major changes in the profiles of intestine microbiota and metabolites, which exerted beneficial effects on intestinal health of piglets. Our study indicated that the combination of tributyrate with oregano or methyl salicylate could be used as an alternative feed additive to the antibiotics.

Abstract

The aim of this study was to determine the effects of dietary inclusion of the combination of tributyrin with oregano or methyl salicylate as a substitute to antibiotics on gut health and microbiota of piglets. A total of 48 weaned crossbred piglets (Duroc × Large White × Landrace, 8.79 ± 0.97 kg, 21 ± 1 d) were randomly allocated to four experimental groups and fed for 4 weeks: the basal diet (Con); the control plus antibiotics (AB); the control plus oregano and tributyrin (OT); and the control plus methyl salicylate and tributyrin (MT). Although a numerical improvement on feed intake, weight gain and feed conversion ratio was observed in the OT and MT as well as the AB group, the difference was not significant (p > 0.05). The OT and MT groups were larger in villus height in the duodenum compared to the Con (p < 0.05), and were larger in relative abundance of Firmicutes/Bacaeroides in the intestine compared to Con and AB groups (p < 0.01). The amount of major different metabolites was 6, 8 and 8 for the AB, OT and MT groups when compared to the Con, respectively. In conclusion, as a substitute for antibiotics the inclusion of the combination of tributyrin with either oregano or methyl salicylate to the diet of weaned piglets improved the intestinal morphological structure and altered intestinal microbiota and metabolites, which were beneficial to the animal health.

HIF-1α/PDK4/autophagy pathway protects against advanced glycation end-products induced vascular smooth muscle cell calcification

Osteogenic differentiation of VSMC is one of the main causes of diabetic vascular calcification, and AGEs accumulation accelerates the calcification of VSMCs in diabetic patients. Autophagy has also been found to play an important role in the process of vascular calcification. However, the potential link between AGEs, autophagy and vascular calcification is still unclear and was investigated in this study. Primary VSMCs were isolated from the thoracic aorta of Sprague Dawley rats and cultured with AGEs-BSA to induce osteogenic differentiation. VSMCs calcification was evaluated by measuring the calcium content, RUNX2 protein levels, and by Alizarin red S staining. We demonstrated that treatment of VSMCs with AGE-BSA increased the expression of HIF-1α and PDK4. AGE-BSA treatment increased LC3-II and decreased p62 protein levels. AGE-BSA exposure enhanced autophagic flux determined by mRFP-GFP-LC3 adenovirus, induced co-localization of LC3-II and LAMP-1, and increased the number of autophagasome under TEM. HIF-1α/PDK4 pathway was activated during AGEs-induced autophagy of VSMCs. In addition, autophagy played a protective role during AGE-induced calcification of VSMCs. In conclusion, AGEs enhance autophagy via the HIF-1α/PDK4 signaling pathway, and autophagy helps attenuate AGE-induced calcification of VSMCs.

Identification of functional lncRNAs based on competing endogenous RNA network in osteoblast differentiation

Adult human mesenchymal stem cells have the potential to differentiate into osteoblast, which plays crucial roles in bone regeneration and repair. Some transcriptional factors (TFs), such as BMP-2 and RUNX2, have been demonstrated to control the differentiation processes. It is important to discover more key regulators in osteoblast differentiation. Recently, some studies found long noncoding RNAs (lncRNAs) participating in osteoblast differentiation, such as MALAT1, DANCR, and ANCR. In this study, we performed a network-based computational analysis to investigate the lncRNA-messenger RNA (mRNA) crosstalks via integrating microRNA (miRNA)-RNA interactions, gene coexpression, and protein-protein interactions. First, multiple topology analyses were performed to osteoblast-differentiation-related lncRNA-mRNA network (ODLMN). Several lncRNAs with central topology structures were identified as key regulators. Results showed that these lncRNAs participated in osteoblast differentiation via phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinase, and Ras signals. Previous studies have demonstrated that lncRNAs exert functions by involving in close modules. Second, after performing module searching in ODLMN, two functional modules were identified, which played crucial roles through involving in PI3K/protein kinase B, cyclic adenosine 3',5'-monophosphate, and hypoxia-inducible factor 1 pathways. Third, a subset of core lncRNA-TF crosstalks that might form feedback loops to control the biological processes in osteoblast differentiation was identified. These core lncRNA-TF feedback loops showed more TF binding affinity than other lncRNAs. All these results can help us to uncover the molecular mechanism and provide new targets for bone regeneration and repair.

Lactate accelerates calcification in VSMCs through suppression of BNIP3-mediated mitophagy

Arterial media calcification is one of the major complications of diabetes mellitus, which is related to oxidative stress and apoptosis. Mitophagy is a special regulation of mitochondrial homeostasis and takes control of intracellular ROS generation and apoptotic pathways. High circulating levels of lactate usually accompanies diabetes. The potential link between lactate, mitophagy and vascular calcification is investigated in this study. Lactate treatment accelerated VSMC calcification, evaluated by measuring the calcium content, ALP activity, RUNX2, BMP-2 protein levels, and Alizarin red S staining. Lactate exposure caused excessive intracellular ROS generation and VSMC apoptosis. Lactate also impaired mitochondrial function, determined by mPTP opening rate, mitochondrial membrane potential and mitochondrial biogenesis markers. Western blot analysis of LC3-II and p62 and mRFP-GFP-LC3 adenovirus detection for autophagy flux revealed that lactate blocked autophagy flux. LC3-II co-staining with LAMP-1 and autophagosome quantification revealed lactate inhibited autophagy. Furthermore, lactate inhibited mitophagy, which was confirmed by TOMM20 and BNIP3 protein levels, LC3-II colocalization with BNIP3 and TEM assays. In addition, BNIP3-mediated mitophagy played a protective role against VSMC calcification in the presence of lactate. This study suggests that lactate accelerates osteoblastic phenotype transition of VSMC and calcium deposition partly through the BNIP3-mediated mitophagy deficiency induced oxidative stress and apoptosis.

Advanced glycation end products accelerate calcification in VSMCs through HIF-1α/PDK4 activation and suppress glucose metabolism

Arterial media calcification is associated with diabetes mellitus. Previous studies have shown that advanced glycation end products (AGEs) are responsible for vascular smooth muscle cell (VSMC) calcification, but the underlying mechanisms remain unclear. Hypoxia-inducible factor-1α (HIF-1α), one of the major factors during hypoxia, and pyruvate dehydrogenase kinase 4 (PDK4), an important mitochondrial matrix enzyme in cellular metabolism shift, have been reported in VSMC calcification. The potential link among HIF-1α, PDK4, and AGEs-induced vascular calcification was investigated in this study. We observed that AGEs elevated HIF-1α and PDK4 expression levels in a dose-dependent manner and that maximal stimulation was attained at 24 h. Two important HIF-1α-regulated genes, vascular endothelial growth factor A (VEGFA) and glucose transporter 1 (GLUT-1), were significantly increased after AGEs exposure. Stabilization or nuclear translocation of HIF-1α increased PDK4 expression. PDK4 inhibition attenuated AGEs-induced VSMC calcification, which was evaluated by measuring the calcium content, alkaline phosphatase (ALP) activity and runt-related transcription factor 2 (RUNX2) expression levels and by Alizarin red S staining. In addition, the glucose consumption, lactate production, key enzymes of glucose metabolism and oxygen consumption rate (OCR) were decreased during AGEs-induced VSMC calcification. In conclusion, this study suggests that AGEs accelerate vascular calcification partly through the HIF-1α/PDK4 pathway and suppress glucose metabolism.

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

Monocarboxylate transporter-1 (MCT-1) is a transmembrane transporter for monocarboxylates including lactate and pyruvate. Silencing Mct1 by its small interfering RNA (siRNA) suppressed the expression of marker genes for osteoblast differentiation, namely, Tnap, Runx2, and Sp7, induced by BMP-2 in mouse myoblastic C2C12 cells. Mct1 siRNA also suppressed alkaline phosphatase activity, as well as expressions of Tnap and Bglap mRNAs in mouse primary osteoblasts. On the other hand, Mct1 siRNA did not have effects on the Smad1/5 or ERK/JNK pathways in BMP-2-stimulated C2C12 cells, while it up-regulated the mRNA expression of p53 (Trp53) as well as nuclear accumulation of p53 in C2C12 cells in a BMP-2-independent manner. Suppression of osteoblastic differentiation by Mct1 siRNA in C2C12 cells was abolished by co-transfection of Trp53 siRNA. Together, these results suggest that MCT-1 functions as a positive regulator of osteoblast differentiation via suppression of p53.

Lactate enhanced the effect of parathyroid hormone on osteoblast differentiation via GPR81-PKC-Akt signaling

Osteoblast uses aerobic glycolysis to meet the metabolic needs in differentiation process. Lactate, the end product of glycolysis, presents in the environment with elevated PTH and osteoblast differentiation. Although previous findings showed that lactate promoted osteoblast differentiation, whether lactate affects PTH-mediated osteoblast differentiation is unclear. To investigate this, pre-osteoblast cell line MC3T3-E1 was treated PTH with or without physiological dose of lactate. Lactate increases ALP positive cell formation, increases ALP activity and expression of differentiation related markers, enriches the CREB transcriptional factor target genes in PTH treated cells. Using inhibitors for MCT-1 reveales that lactate effects are MCT-1 independent. Lactate selectively increases Akt and p38 activation but not Erk1/2 and β-Catenin activation. The inhibitors for Akt and p38 inhibit lactate effects on PTH mediated osteoblast differentiation. Using inhibitors for Gαi signaling of GPR81 further increases Alp mRNA levels in lactate and PTH co-treatment cells. However, with the inhibitors for Gβγ-PLC-PKC signaling, the effect of lactate on PTH mediated osteoblast differentiation is inhibited. Our data demonstrate that lactate activates GPR81-Gβγ-PLC-PKC-Akt signaling to regulate osteoblast differentiation that mediated by PTH treatment.

Derivatization method for the quantification of lactic acid in cell culture media via gas chromatography and applications in the study of cell glycometabolism

Lactic acid represents an important metabolite that reflects mitochondria function and may further serve as energy source for cancer cells. In light of this physiological and pathological significance, we developed a novel and sensitive gas chromatography method to detect lactic acid in cell culture media. Here, ethyl chloroformate was selected as derivative reagent and the derivatization process was further optimized in terms of number of reagents and reaction time as well as extraction reagents. Under optimal conditions, good linearity was achieved in the tested calibration range. The limit of detection (LOD) was determined to be 0.67 μmol/L, the recovery rates were 99.6%-106% and the precision rate RSD was <5.49%. Furthermore, this method has been applied to quantify the secretion of lactic acid in cells exposed to mono‑2‑ethylhexyl phthalate at different doses and in cancer cells over time. Taken in concert, our method proved to be both sensitive and reliable and may be applied for studies on mitochondrial function and cell glycolysis conditions.

Involvement of bone morphogenetic protein-related pathways in the effect of aucubin on the promotion of osteoblast differentiation in MG63 cells

Aucubin, an iridoid glycoside found in several plants, such as Eucommia ulmoide and Rehmannia, has various pharmacological effects. Bone formation is a complex process in which osteoblast differentiation plays an important role. This study aimed to investigate the promotion effects of aucubin on osteoblast differentiation in MG63 cells, a human osteoblast-like cell line. Aucubin not only improved osteoblast differentiation, as shown by enhanced ALP (alkaline phosphatase) concentration and mineralization in cells, but increased the expression of various cytokines, including collagen I, osteocalcin, osteopontin, integrin β1, and Osterix. Aucubin strongly enhanced the levels of BMP2 (bone morphogenetic proteins-2) in MG63 cells, which play a central role during osteoblast differentiation. Further data show that aucubin exposure after 1 day, 7 days, and 14 days enhanced the expression of Smad1, 5, and 8, and the phosphoresced levels of MAPKs (mitogen-activated protein kinases) family Erk (extracellular signal-regulated kinases), JNK (c-Jun-NH2-terminal kinases), P38, and Akt (serine/threonine protein kinase)/mTOR (mammalian target of rapamycin)/p70s6k in MG63 cells. This study shows the improved effects of aucubin on osteoblast differentiation in MG63 cells, related to the signaling of BMP2-mediated Smads (drosophila mothers against decapentaplegic proteins), MAPKs, and Akt/mTOR/p70S6K. This study indicates the potential of aucubin for osteoporosis treatment.

Nε-carboxymethyl-lysine promotes calcium deposition in VSMCs via intracellular oxidative stress-induced PDK4 activation and alters glucose metabolism

Diabetes and vascular calcification are intrinsically linked. We previously reported that advanced glycation end products (AGEs) accelerate calcium deposition in vascular smooth muscle cells (VSMCs) via excessive oxidative stress. However, the underlying mechanism remains poorly understood. Pyruvate dehydrogenase kinase 4 (PDK4) is an important mitochondrial matrix enzyme in cellular energy metabolism. Since hyperactivation of PDK4 has been reported in calcified vessels and in patients with diabetes mellitus, inhibition of PDK4 expression may be a strategy for the prevention of diabetic vascular calcification. In this study, we used a rat VSMC model to investigate the role of PDK4 in diabetic vascular calcification and further explore the underlying mechanisms. We observed that Nε-carboxymethyl-lysine (CML), which is a major immunogen of AGEs, accelerated calcium deposition in VSMCs through PDK4 activation. An elevated level of reactive oxygen species (ROS) acted as a signal transduction intermediate to increase PDK4 expression. Either inhibition of PDK4 expression or RAGE (receptor for AGEs) blockade attenuated CML-induced VSMC calcification, as shown by decreased alkaline phosphatase (ALP) activity and runt-related transcription factor 2 (RUNX2) expression. Glucose consumption and lactate production were increased during CML-induced VSMC calcification. Importantly, CML accelerates glycolysis in VSMCs via a PDK4-dependent pathway. In conclusion, this study demonstrates a novel mechanism by which CML promotes VSMC calcification via PDK4 activation and alters glucose metabolism in VSMCs.