Human mesenchymal stem cell differentiation to the osteogenic or adipogenic lineage is regulated by AMP-activated protein kinase

Geographical distribution, genetic diversity, and environmental adaptations of dromedary camel breeds in Saudi Arabia

The dromedary camel (Camelus dromedarius) in Saudi Arabia exhibits significant genetic diversity, driven by adaptation to diverse ecological niches such as deserts, mountains, and coastal areas. This study explores the genetic structure of these camel populations, correlating their genetic diversity with geographical regions rather than ecological classifications. Through whole-genome sequencing of 63 camel genomes, we identified substantial differences in heterozygosity and inbreeding across different ecotypes, particularly noting higher genetic diversity in mountainous populations and lower diversity in coastal populations. The study also revealed significant enrichment of specific gene sets associated with environmental adaptation, such as the HECT domain in desert populations, which is crucial for maintaining protein integrity under extreme conditions. Principal component and admixture analyses further highlighted the genetic distinctiveness of certain breeds, particularly the Awarik (beach ecotype), which showed signs of genetic isolation.

Effects of Nobiletin supplementation on the freezing diluent on porcine sperm cryo-survival and subsequent in vitro embryo development

Nobiletin (NOB) is a bioflavonoid compound isolated from citrus fruit peels. The present study aimed to elucidate whether NOB facilitates the porcine sperm cryosurvival and embryo development after in vitro fertilization (IVF). To this end, spermatozoa were diluted and cryopreserved in a freezing extender supplemented with 0 (control), 50, 100, 150, and 200 μM Nobiletin. The kinematic patterns of frozen-thawed (FT) sperm were assessed after 30 and 90 min incubation using a Sperm Class Analyzer (SCA). Viability, acrosome integrity, and mitochondrial membrane potential (MMP) were measured by fluorescence microscopy 30 min after thawing using SYBR-14/PI, PSA/FITC, and R123/PI, respectively. Lipid peroxidation was determined using MDA assay after incubation for 90 min. The addition of 100 μM and 150 μM NOB to the extender significantly improved sperm progressive motility, and acrosome integrity compared to the control group (P < 0.05). The proportion of viable spermatozoa was significantly higher in the 150 μM NOB group. MDA levels were less in 50 μM and 150 μM NOB treated groups compared to the control. In addition, IVF with FT sperm was used to assess the embryo developmental competence. Treatment with 150 μM NOB before cryopreservation increased the cleavage and blastocyst formation rates compared to the control group. Furthermore, the relative expression of POU5F1 and AMPK, genes related to pluripotency and cell differentiation were significantly upregulated in embryos resulting from NOB-treated sperm compared to the control group. These results suggest that Nobiletin is a functionally novel phytochemical to mitigate oxidative stress during the freezing-thawing of porcine spermatozoa as reflected by improved FT sperm quality and IVF outcome.

Alamandine attenuates ovariectomy-induced osteoporosis by promoting osteogenic differentiation via AMPK/eNOS axis

BACKGROUND

Alamandine is a newly characterized peptide of renin angiotensin system. Our study aims to investigate the osteo-preservative effects of alamandine, explore underlying mechanism and bring a potential preventive strategy for postmenopausal osteoporosis in the future.

METHODS

An ovariectomy (OVX)-induced rat osteoporosis model was established for in vivo experiments. Micro-computed tomography and three-point bending test were used to evaluate bone strength. Histological femur slices were processed for immunohistochemistry (IHC). Bone turnover markers and nitric oxide (NO) concentrations in serum were determined with enzyme-linked immunosorbent assay (ELISA). The mouse embryo osteoblast precursor (MC3T3-E1) cells were used for in vitro experiments. The cell viability was analysed with a Cell Counting Kit‑8. We performed Alizarin Red S staining and alkaline phosphatase (ALP) activity assay to observe the differentiation status of osteoblasts. Western blotting was adopted to detect the expression of osteogenesis related proteins and AMP-activated protein kinase/endothelial nitric oxide synthase (AMPK/eNOS) in osteoblasts. DAF-FM diacetate was used for semi-quantitation of intracellular NO.

RESULTS

In OVX rats, alamandine alleviated osteoporosis and maintained bone strength. The IHC showed alamandine increased osteocalcin and collagen type I α1 (COL1A1) expression. The ELISA revealed alamandine decreased bone turnover markers and restored NO level in serum. In MC3T3-E1 cells, alamandine promoted osteogenic differentiation. Western blotting demonstrated that alamandine upregulated the expression of osteopontin, Runt-related transcription factor 2 and COL1A1. The intracellular NO was also raised by alamandine. Additionally, the activation of AMPK/eNOS axis mediated the effects of alamandine on MC3T3-E1 cells and bone tissue. PD123319 and dorsomorphin could repress the regulating effect of alamandine on bone metabolism.

CONCLUSION

Alamandine attenuates ovariectomy-induced osteoporosis by promoting osteogenic differentiation via AMPK/eNOS axis.

Decreased CRISPLD2 expression impairs osteogenic differentiation of human mesenchymal stem cells during in vitro expansion

Human mesenchymal stem cells (hMSCs) are the cornerstone of regenerative medicine; large quantities of hMSCs are required via in vitro expansion to meet therapeutic purposes. However, hMSCs quickly lose their osteogenic differentiation potential during in vitro expansion, which is a major roadblock to their clinical applications. In this study, we found that the osteogenic differentiation potential of human bone marrow stem cells (hBMSCs), dental pulp stem cells (hDPSCs), and adipose stem cells (hASCs) was severely impaired after in vitro expansion. To clarify the molecular mechanism underlying this in vitro expansion-related loss of osteogenic capacity in hMSCs, the transcriptome changes following in vitro expansion of these hMSCs were compared. Cysteine-rich secretory protein LCCL domain-containing 2 (CRISPLD2) was identified as the most downregulated gene shared by late passage hBMSCs, hDPSCs, and hASCs. Both the secreted and non-secreted CRISPLD2 proteins progressively declined in hMSCs during in vitro expansion when the cells gradually lost their osteogenic potential. We thus hypothesized that the expression of CRISPLD2 is critical for hMSCs to maintain their osteogenic differentiation potential during in vitro expansion. Our studies showed that the knockdown of CRISPLD2 in early passage hBMSCs inhibited the cells' osteogenic differentiation in a siRNA dose-dependent manner. Transcriptome analysis and immunoblotting indicated that the CRISPLD2 knockdown-induced osteogenesis suppression might be attributed to the downregulation of matrix metallopeptidase 1 (MMP1) and forkhead box Q1 (FOXQ1). Furthermore, adeno-associated virus (AAV)-mediated CRISPLD2 overexpression could somewhat rescue the impaired osteogenic differentiation of hBMSCs during in vitro expansion. These results revealed that the downregulation of CRISPLD2 contributes to the impaired osteogenic differentiation of hMSCs during in vitro expansion. Our findings shed light on understanding the loss of osteogenic differentiation in hMSCs and provide a potential therapeutic target gene for bone-related diseases.

Spermidine Retarded the Senescence of Multipotent Mesenchymal Stromal Cells In Vitro and In Vivo through SIRT3-Mediated Antioxidation

Multipotent mesenchymal stromal cells (MSCs) expand in vitro and undergo replicative senescence, thereby restricting their clinical utilization. Thus, an effective strategy is required to impede MSC senescence. Since spermidine (SPD) supplementation can prolong the lifespan of yeast by inhibiting oxidative stress, spermidine is a potential option for delaying MSC senescence. In this study, to test our hypothesis, we first isolated primary human umbilical cord mesenchymal stem cells (hUCMSCs). Subsequently, the appropriate SPD dose was administered during continuous cell cultivation. Next, we evaluated the antisenescence effects by SA-β-gal staining, Ki67 expression, reactive oxygen species (ROS) levels, adipogenic or osteogenic ability, senescence-associated markers, and DNA damage markers. The results revealed that early SPD intervention significantly delays the replicative senescence of hUCMSCs and constrains premature H₂O₂-induced senescence. Additionally, by silencing SIRT3, the SPD-mediated antisenescence effects disappear, further demonstrating that SIRT3 is necessary for SPD to exert its antisenescence effects on hUCMSCs. Besides, the findings of this study also suggest that SPD in vivo protects MSCs against oxidative stress and delays cell senescence. Thus, MSCs maintain the ability to proliferate and differentiate efficiently in vitro and in vivo, which reflects the potential clinical utilization of MSCs in the future.

Inhibition of nucleotide biosynthesis disrupts lipid accumulation and adipogenesis

Energy balance and nutrient availability are key determinants of cellular decisions to remain quiescent, proliferate or differentiate into a mature cell. After assessing its environmental state, the cell must rewire its metabolism to support distinct cellular outcomes. Mechanistically, how metabolites regulate cell fate decisions is poorly understood. We used adipogenesis as our model system to ascertain the role of metabolism in differentiation. We isolated adipose tissue stromal vascular fraction (SVF) cells and profiled metabolites before and after adipogenic differentiation to identify metabolic signatures associated with these distinct cellular states. We found that differentiation alters nucleotide accumulation. Furthermore, inhibition of nucleotide biosynthesis prevented lipid storage within adipocytes and downregulated the expression of lipogenic factors. In contrast to proliferating cells, in which mTORC1 is activated by purine accumulation, mTORC1 signaling was unaffected by purine levels in differentiating adipocytes. Rather, our data indicated that purines regulate transcriptional activators of adipogenesis, PPARγ and C/EBPα to promote differentiation. Although de novo nucleotide biosynthesis has mainly been studied in proliferation, our study points to its requirement in adipocyte differentiation.

Alpha-SNAP (M105I) mutation promotes neuronal differentiation of neural stem/progenitor cells through overactivation of AMPK

Background: The M105I point mutation in α-SNAP (Soluble N-ethylmaleimide-sensitive factor attachment protein-alpha) leads in mice to a complex phenotype known as hyh (hydrocephalus with hop gait), characterized by cortical malformation and hydrocephalus, among other neuropathological features. Studies performed by our laboratory and others support that the hyh phenotype is triggered by a primary alteration in embryonic neural stem/progenitor cells (NSPCs) that leads to a disruption of the ventricular and subventricular zones (VZ/SVZ) during the neurogenic period. Besides the canonical role of α-SNAP in SNARE-mediated intracellular membrane fusion dynamics, it also negatively modulates AMP-activated protein kinase (AMPK) activity. AMPK is a conserved metabolic sensor associated with the proliferation/differentiation balance in NSPCs. Methods: Brain samples from hyh mutant mice (hydrocephalus with hop gait) (B6C3Fe-a/a-Napahyh/J) were analyzed by light microscopy, immunofluorescence, and Western blot at different developmental stages. In addition, NSPCs derived from WT and hyh mutant mice were cultured as neurospheres for in vitro characterization and pharmacological assays. BrdU labeling was used to assess proliferative activity in situ and in vitro. Pharmacological modulation of AMPK was performed using Compound C (AMPK inhibitor) and AICAR (AMPK activator). Results: α-SNAP was preferentially expressed in the brain, showing variations in the levels of α-SNAP protein in different brain regions and developmental stages. NSPCs from hyh mice (hyh-NSPCs) displayed reduced levels of α-SNAP and increased levels of phosphorylated AMPKα (pAMPKα^Thr172), which were associated with a reduction in their proliferative activity and a preferential commitment with the neuronal lineage. Interestingly, pharmacological inhibition of AMPK in hyh-NSPCs increased proliferative activity and completely abolished the increased generation of neurons. Conversely, AICAR-mediated activation of AMPK in WT-NSPCs reduced proliferation and boosted neuronal differentiation. Discussion: Our findings support that α-SNAP regulates AMPK signaling in NSPCs, further modulating their neurogenic capacity. The naturally occurring M105I mutation of α-SNAP provokes an AMPK overactivation in NSPCs, thus connecting the α-SNAP/AMPK axis with the etiopathogenesis and neuropathology of the hyh phenotype.

miR-4739/ITGA10/PI3K signaling regulates differentiation and apoptosis of osteoblast

Introduction

To probe the impacts and biological roles of miR-4739/ITGA10 on the proliferation, differentiation and apoptosis of osteoblasts.

Methods

Bioinformatics analysis was conducted to screen the key genes in osteoporosis. The upstream miRNAs of ITGA10 were predicted by TargetScan. KEGG pathway enrichment analysis was performed by DAVID database. The osteoblast proliferation and apoptosis were measured using CCK-8 and flow cytometry. The differentiation markers were measured by qRT-PCR and western blotting. The luciferase reporter assay was conducted to verify the binding of miR-4739 to ITGA10.

Results

ITGA10 was down-regulated in patients with osteoporosis and identified as the key gene in osteoporosis by the bioinformatics analysis. Then the prediction provided by TargetScan indicated that miR-4739 was the potential upstream miRNA for ITGA10. And the following luciferase reporter assay showed that miR-4739 could bind to ITGA10 3′UTR. Furthermore, the miR-4739 inhibitor promoted osteoblasts proliferation, differentiation, and inhibited cell apoptosis by increasing the expression of ITGA10 and subsequently activating the PI3K/AKT signaling pathway.

Conclusions

Overall, we proved that the higher expression of miR-4739 participated in the progression of osteoporosis by targeting ITGA10 and modulating PI3K/AKT signaling pathway, and perhaps miR-4739/ITGA10 axis could be potential diagnostic markers and therapeutic target for osteoporosis.

A-769662 stimulates the differentiation of bone marrow-derived mesenchymal stem cells into osteoblasts via AMP-activated protein kinase-dependent mechanism

AMP-activated protein kinase (AMPK) signaling shows an important role in energy metabolism and has recently been involved in osteogenic and adipogenic differentiation. In this study we aimed to investigate the role of AMPK activator, A-769662, in regulating the differentiation of mesenchymal stem cells derived from bone marrow (BMSCs) into osteoblastic and adipocytic cell lineage. The effect of A-769662 on osteogenesis was assessed by quantitative alkaline phosphatase (ALP) activity, matrix mineralization stained with Alizarin red, and gene expression analysis by quantitative polymerase chain reaction (qPCR). Adipogenesis was determined by Oil Red O staining for fat droplets and qPCR analysis of adipogenic markers. A-769662 activated the phosphorylation of AMPKα1 during the osteogenesis of mBMSCs as revealed by western blot analysis. A-769662 promoted the early stage of the commitment of mouse (m) BMSCs differentiation into osteoblasts, while inhibiting their differentiation into adipocytes in a dose-dependent manner. The effects of A-769662 on stimulating osteogenesis and inhibiting adipogenesis of mBMSCs were significantly eliminated in the presence of either AMPKα1 siRNA or Compound C, an inhibitor of AMPK pathway. In conclusion, we identified A-769662 as a new compound that promotes the commitment of BMSCs into osteoblasts versus adipocytes via AMPK-dependent mechanism. Thus our data show A-769662 as a potential osteo-anabolic drug for treatment of osteoporosis.

Pleiotropin enhances the osteo/dentinogenic differentiation potential of dental pulp stem cells

Purpose: Pleiotrophin (PTN) is a heparin-binding growth-associated molecule and expressed in ameloblasts and odontoblasts throughout tooth maturation. Our previous study has shown that PTN expressed more than 20-fold higher in dental tissue than dental stem cells. However, the role of PTN on proliferation and osteo/dentinogenesis of dental pulp stem cells (DPSCs) is unclear. The purpose of the present study was to investigate the role of PTN on the DPSCs' function.Methods: DPSCs were isolated from human third molars. Short hairpin RNAs (shRNAs) was used to knock down the PTN expression in DPSCs. Real-time RT-PCR, alizarin red staining, quantitative calcium analysis, in vivo transplantation and cell counting kit-8 (CCK8) assay were used to study the function of DPSCs. Possible mechanism was studied by RNA sequencing.Results: After PTN depletion, ALP activity and mineralization ability of DPSCs decreased. Expression of DMP-1 and BSP weakened. Proliferation of DPSCs at 48 h and 72 h was inhibited. Furthermore, 50 pg/mL PTN recombinant protein rescued the impaired osteo/dentinogenic differentiation potential and proliferation ability caused by PTN depletion. In addition, RNA sequencing showed 221 genes were downregulated and 233 genes upregulated in PTN depleted DPSCs. Several genes including BMP2 and IGFBP5 might be associated with PTN function on the DPSCs. P53 and the AMPK signaling pathways were involved. LncRNA analysis displayed 47 significantly upregulated lncRNA and 31 downregulated lncRNA comparing PTN depleted DPSCs with the control.Conclusion: Our research demonstrated that PTN has a positive role in maintaining DPSCs proliferation and osteo/dentinogenic differentiation potential.

Enhancement of osteoporotic bone regeneration by strontium-substituted 45S5 bioglass via time-dependent modulation of autophagy and the Akt/mTOR signaling pathway

Osteoporosis (OP) is a major systemic bone disease leading to an imbalance in bone homeostasis which remains a challenge in the current treatment of bone defects. Our previous studies on strontium (Sr) doping apparently stimulated osteogenesis of bioceramics, which suggested a promising strategy for the treatment of bone defects. However, the potential effects and the underlying mechanisms of Sr-doping on osteoporotic bone defects still remain unclear. Autophagy is a conventional self-degradation process of cells involved in bone homeostasis and regeneration under physiological and pathological conditions. Therefore, it is essential to design appropriate biomaterials and investigate the associated osteogenic mechanisms via autophagy. Based on this hypothesis, Sr-doped 45S5 bioglass (Sr/45S5) was fabricated, and ovariectomy bone marrow-derived mesenchymal stem cells (OVX-BMSCs) were applied as the in vitro cell culture model. First, the optimal Sr-doping concentration of 10 mol% was screened by cell proliferation, ALP staining, alizarin red S staining and the real-time PCR assay. Then, the results of western blot (WB) analysis showed that Sr-induced osteogenic differentiation of OVX-BMSCs was associated with time-dependent modulation of autophagy and related to the AKT/mTOR signaling pathway. Meanwhile, the autophagy in Sr-induced osteogenic differentiation of OVX-BMSCs was detected by WB, immunofluorescence staining and transmission electron microscopy. Furthermore, the effect of osteogenic differentiation of OVX-BMSCs has been significantly inhibited by the administration of autophagy inhibitors and the AKT/mTOR pathway inhibitors, respectively, in the early and late periods of osteogenic differentiation. Finally, the results of the model of femoral condyle defects in OVX-rats indicated that Sr10/45S5 granules remarkably enhanced bone regeneration which provided the evidences in vivo. Our research indicates that Sr-doping provides a promising strategy to promote osteogenic differentiation of OVX-BMSCs and bone regeneration in osteoporotic bone defects via early improvement of autophagy and late activation of the Akt/mTOR signaling pathway.

AMPK: Potential Therapeutic Target for Vascular Calcification

Vascular calcification (VC) is an urgent worldwide health issue with no available medical treatment. It is an active cell-driven process by osteogenic differentiation of vascular cells with complex mechanisms. The AMP-activated protein kinase (AMPK) serves as the master sensor of cellular energy status. Accumulating evidence reveals the vital role of AMPK in VC progression. AMPK is involved in VC in various ways, including inhibiting runt-related transcription factor 2 signaling pathways, triggering autophagy, attenuating endoplasmic reticulum stress and dynamic-related protein 1-mediated mitochondrial fission, and activating endothelial nitric oxide synthase. AMPK activators, like metformin, are associated with reduced calcification deposits in certain groups of patients, indicating that AMPK is a potential therapeutic target for VC.

AMPKβ1 and AMPKβ2 define an isoform-specific gene signature in human pluripotent stem cells, differentially mediating cardiac lineage specification

AMP-activated protein kinase (AMPK) is a key regulator of energy metabolism that phosphorylates a wide range of proteins to maintain cellular homeostasis. AMPK consists of three subunits: α, β, and γ. AMPKα and β are encoded by two genes, the γ subunit by three genes, all of which are expressed in a tissue-specific manner. It is not fully understood, whether individual isoforms have different functions. Using RNA-Seq technology, we provide evidence that the loss of AMPKβ1 and AMPKβ2 lead to different gene expression profiles in human induced pluripotent stem cells (hiPSCs), indicating isoform-specific function. The knockout of AMPKβ2 was associated with a higher number of differentially regulated genes than the deletion of AMPKβ1, suggesting that AMPKβ2 has a more comprehensive impact on the transcriptome. Bioinformatics analysis identified cell differentiation as one biological function being specifically associated with AMPKβ2. Correspondingly, the two isoforms differentially affected lineage decision toward a cardiac cell fate. Although the lack of PRKAB1 impacted differentiation into cardiomyocytes only at late stages of cardiac maturation, the availability of PRKAB2 was indispensable for mesoderm specification as shown by gene expression analysis and histochemical staining for cardiac lineage markers such as cTnT, GATA4, and NKX2.5. Ultimately, the lack of AMPKβ1 impairs, whereas deficiency of AMPKβ2 abrogates differentiation into cardiomyocytes. Finally, we demonstrate that AMPK affects cellular physiology by engaging in the regulation of hiPSC transcription in an isoform-specific manner, providing the basis for further investigations elucidating the role of dedicated AMPK subunits in the modulation of gene expression.

Pathogenesis and Current Treatment of Osteosarcoma: Perspectives for Future Therapies

Osteosarcoma is the most common primary malignant bone tumor in children and young adults. The standard-of-care curative treatment for osteosarcoma utilizes doxorubicin, cisplatin, and high-dose methotrexate, a standard that has not changed in more than 40 years. The development of patient-specific therapies requires an in-depth understanding of the unique genetics and biology of the tumor. Here, we discuss the role of normal bone biology in osteosarcomagenesis, highlighting the factors that drive normal osteoblast production, as well as abnormal osteosarcoma development. We then describe the pathology and current standard of care of osteosarcoma. Given the complex heterogeneity of osteosarcoma tumors, we explore the development of novel therapeutics for osteosarcoma that encompass a series of molecular targets. This analysis of pathogenic mechanisms will shed light on promising avenues for future therapeutic research in osteosarcoma.

The role and mechanism of mitochondrial functions and energy metabolism in the function regulation of the mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that show self-renewal, multi-directional differentiation, and paracrine and immune regulation. As a result of these properties, the MSCs have great clinical application prospects, especially in the regeneration of injured tissues, functional reconstruction, and cell therapy. However, the transplanted MSCs are prone to ageing and apoptosis and have a difficult to control direction differentiation. Therefore, it is necessary to effectively regulate the functions of the MSCs to promote their desired effects. In recent years, it has been found that mitochondria, the main organelles responsible for energy metabolism and adenosine triphosphate production in cells, play a key role in regulating different functions of the MSCs through various mechanisms. Thus, mitochondria could act as effective targets for regulating and promoting the functions of the MSCs. In this review, we discuss the research status and current understanding of the role and mechanism of mitochondrial energy metabolism, morphology, transfer modes, and dynamics on MSC functions.

Mineral trioxide aggregate-induced AMPK activation stimulates odontoblastic differentiation of human dental pulp cells

AIM

To investigate the role of autophagy in MTA-induced odontoblastic differentiation of human dental pulp cells (HDPCs).

METHODOLOGY

In MTA-treated HDPCs, odontoblastic differentiation was assessed based on expression levels of dentine sialophosphoprotein (DSPP) and dentine matrix protein 1 (DMP1), alkaline phosphatase activity (ALP) activity by ALP staining and the formation of mineralized nodule by Alizarin red S staining. Expression of microtubule-associated protein 1A/1B-light chain3 (LC3), adenosine monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) signalling molecules and autophagy-related genes was analysed by Western blot analysis and Acridine orange staining was used to detect autophagic lysosome. For in vivo experiments, tooth cavity preparation models on rat molars were established and the expression of proteins-related odontogenesis and autophagy markers was observed by Immunohistochemistry and Western blot analysis. Kruskal-Wallis with Dunn's multiple comparison was used for statistical analysis.

RESULTS

Mineral trioxide aggregate (MTA) promoted odontoblastic differentiation of HDPCs, accompanied by autophagy induction, including formation of autophagic lysosome and cleavage of LC3 to LC3II (P < 0.05). Conversely, inhibition of autophagy through 3MA significantly attenuated the expression level of DSPP (P < 0.05) and DMP1 (P < 0.05) as well as formation of mineralized nodules (P < 0.05), indicating the functional significance of autophagy in MTA-induced odontoblastic differentiation. Also, MTA increased the activity of AMPK (P < 0.01), whereas inhibition of AMPK by compound C downregulated DSPP (P < 0.01) and DMP1 (P < 0.05), but increased the phosphorylation of mTOR (P < 0.05), p70S6 (P < 0.01) and Unc-51-like kinases 1 (ULK1) (ser757) (P < 0.01), explaining the involvement of AMPK pathway in MTA-induced odontoblast differentiation. In vivo study, MTA treatment after tooth cavity preparation on rat molars upregulated DMP-1 and DSPP as well as autophagy-related proteins LC3II and p62, and enhanced the phosphorylation of AMPK.

CONCLUSION

MTA induced odontoblastic differentiation and mineralization by modulating autophagy with AMPK activation in HDPCs. Autophagy regulation is a new insight on regenerative endodontic therapy using MTA treatment.

The Role of Autophagy in M2 Polarization of Macrophages Induced by Micro/Nano Topography

Background

The proper topography of implant surface can induce macrophages polarization, whereas the regulation mechanism has not been fully deciphered. The study aimed to examine the regulation mechanism of macrophages M2 polarization by titanium (Ti) implant surface micro/nano topography.

Results

Firstly, the titanium implant micropits-nanotubular surface with ~30 nm diameters (MNT) can induce the M2 polarization of RAW264.7 spontaneously, as indicated by the spindle-like cell morphological alteration and specific molecular marker arginase-1 (Arg1) expression. Next, the autophagic vacuoles (AVs) number is significantly increased on MNT surface, as confirmed by the monodansylcadaverine (MDC) and CYTO-ID staining as well as the transmission electron microscope (TEM) observation. In addition, increasing or decreasing the autophagosomes number by rapamycin or 3-methyladenine (3-MA) will result in augmentation or attenuation of Arg1. Furthermore, blocking the fusion between autophagosomes and lysosomes by bafilomycin also significantly reduces Arg1, even in the presence of rapamycin. Finally, the ERK phosphorylation is selectively upregulated on MNT surface and the AVs number and Arg1 expression are significantly suppressed by U0126 treatment.

Conclusion

Our findings suggest that the ERK-Beclin-1-autophagy axis may play a pivotal role in the regulation of M2 polarization induced by nanotopography.

β-mercaptoethanol promotes osteogenesis of human mesenchymal stem cells via sirt1-ERK pathway

Human umbilical cord-derived mesenchymal stem cells (hUMSCs) hold strong self-renewal capacity and low immunogenicity, which have attracted attention as potential candidates for bone repair and regeneration. However, insufficient osteogenic differentiation markedly hinders the clinical applications of hUMSCs. In the present study, the effect of β-mercaptoethanol (BME), a small molecule antioxidant which has been identified to regulate cell proliferation and differentiation, on osteogenic differentiation of hUMSCs and underlying signaling mechanism were investigated. The results indicated that under osteogenic induction conditions, BME treatment increased the alkaline phosphatase (ALP) activity and promoted calcium mineralization in hUMSCs. The gene and protein expression of osteogenesis-related markers such as ALP, osteopontin (OPN), osteocalcin (OCN) and collagen type I (COLI) were also significantly up-regulated. Besides, BME promoted the protein expression of silent information regulator type 1 (sirt1) and stimulated the activation of extracellular signal-related kinase (ERK), contributing to increased Runx2 expression. Furthermore, blocking the expression of sirt1 attenuated BME-enhanced ERK phosphorylation and osteogenic differentiation of hUMSCs. These results indicated that BME accelerated osteogenic differentiation of hUMSCs by activating the sirt1-ERK signaling pathway, thereby providing insights into the development of MSCs-based bone regeneration strategies.

A Metformin-Responsive Metabolic Pathway Controls Distinct Steps in Gastric Progenitor Fate Decisions and Maturation

Cellular metabolism plays important functions in dictating stem cell behaviors, although its role in stomach epithelial homeostasis has not been evaluated in depth. Here, we show that the energy sensor AMP kinase (AMPK) governs gastric epithelial progenitor differentiation. Administering the AMPK activator metformin decreases epithelial progenitor proliferation and increases acid-secreting parietal cells (PCs) in mice and organoids. AMPK activation targets Krüppel-like factor 4 (KLF4), known to govern progenitor proliferation and PC fate choice, and PGC1α, which we show controls PC maturation after their specification. PC-specific deletion of AMPKα or PGC1α causes defective PC maturation, which could not be rescued by metformin. However, metformin treatment still increases KLF4 levels and suppresses progenitor proliferation. Thus, AMPK activates KLF4 in progenitors to reduce self-renewal and promote PC fate, whereas AMPK-PGC1α activation within the PC lineage promotes maturation, providing a potential suggestion for why metformin increases acid secretion and reduces gastric cancer risk in humans.

Porcine Circovirus Type 2 ORF5 Protein Induces Autophagy to Promote Viral Replication via the PERK-eIF2α-ATF4 and mTOR-ERK1/2-AMPK Signaling Pathways in PK-15 Cells

Porcine circovirus type 2 (PCV2) is the primary causative agent that causing porcine circovirus-associated disease (PCVAD). The open reading frame 5 (ORF5) protein is a newly discovered non-structural protein in PCV2, which the function in viral pathogenesis remains unknown. The aim of this study was to investigate the mechanism of PCV2 ORF5 protein on autophagy and viral replication. The pEGFP-tagged ORF5 gene was ectopic expressed in PK-15 cells and an ORF5-deficient PCV2 mutant strain (PCV2^ΔORF5) were used to infected PK-15 cells. This study demonstrated that the ORF5 is essential for the of PCV2-induced autophagy. The ORF5 protein triggers the phosphorylation of PERK, eIF2α and the expression of downstream transcription factor ATF4. In addition, ORF5 protein activated the AMPK-ERK1/2-mTOR signaling pathways. These findings suggest that ORF5 play essential roles in the induction of autophagy by PCV2. We further revealed that PCV2 ORF5 promotes viral replication through PERK-eIF2α-ATF4 and AMPK-ERK1/2-mTOR pathways. In conclusion, we showed that PCV2 ORF5 induces autophagy to promote virus replication in PK-15 cells.

Small molecules for mesenchymal stem cell fate determination

Mesenchymal stem cells (MSCs) are adult stem cells harboring self-renewal and multilineage differentiation potential that are capable of differentiating into osteoblasts, adipocytes, or chondrocytes in vitro, and regulating the bone marrow microenvironment and adipose tissue remodeling in vivo. The process of fate determination is initiated by signaling molecules that drive MSCs into a specific lineage. Impairment of MSC fate determination leads to different bone and adipose tissue-related diseases, including aging, osteoporosis, and insulin resistance. Much progress has been made in recent years in discovering small molecules and their underlying mechanisms control the cell fate of MSCs both in vitro and in vivo. In this review, we summarize recent findings in applying small molecules to the trilineage commitment of MSCs, for instance, genistein, medicarpin, and icariin for the osteogenic cell fate commitment; isorhamnetin, risedronate, and arctigenin for pro-adipogenesis; and atractylenolides and dihydroartemisinin for chondrogenic fate determination. We highlight the underlying mechanisms, including direct regulation, epigenetic modification, and post-translational modification of signaling molecules in the AMPK, MAPK, Notch, PI3K/AKT, Hedgehog signaling pathways etc. and discuss the small molecules that are currently being studied in clinical trials. The target-based manipulation of lineage-specific commitment by small molecules offers substantial insights into bone marrow microenvironment regulation, adipose tissue homeostasis, and therapeutic strategies for MSC-related diseases.

The Upstream Pathway of mTOR-Mediated Autophagy in Liver Diseases

Autophagy, originally found in liver experiments, is a cellular process that degrades damaged organelle or protein aggregation. This process frees cells from various stress states is a cell survival mechanism under stress stimulation. It is now known that dysregulation of autophagy can cause many liver diseases. Therefore, how to properly regulate autophagy is the key to the treatment of liver injury. mechanistic target of rapamycin (mTOR)is the core hub regulating autophagy, which is subject to different upstream signaling pathways to regulate autophagy. This review summarizes three upstream pathways of mTOR: the phosphoinositide 3-kinase (PI3K)/protein kinase (AKT) signaling pathway, the adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, and the rat sarcoma (Ras)/rapidly accelerated fibrosarcoma (Raf)/mitogen-extracellular activated protein kinase kinase (MEK)/ extracellular-signal-regulated kinase (ERK) signaling pathway, specifically explored their role in liver fibrosis, hepatitis B, non-alcoholic fatty liver, liver cancer, hepatic ischemia reperfusion and other liver diseases through the regulation of mTOR-mediated autophagy. Moreover, we also analyzed the crosstalk between these three pathways, aiming to find new targets for the treatment of human liver disease based on autophagy.

Resveratrol improves osteogenic differentiation of senescent bone mesenchymal stem cells through inhibiting endogenous reactive oxygen species production via AMPK activation

Objective: Resveratrol has been confirmed to improve bone quality and delay osteoporosis, but the mechanisms have not been thoroughly elucidated. In this report, we investigated the osteogenic differentiation effect of resveratrol on senescent bone mesenchymal stem cells (BMSCs) and the involvement of AMP-activated protein kinase (AMPK)/ reactive oxygen species (ROS) signaling pathway. Methods: Cell senescence, viability, and osteogenic differentiation of BMSCs influenced by resveratrol were investigated and ROS production and AMPK expression were detected. Results: Cell senescence, characterized by senescence β-galactosidase staining and senescence-related genes (p16, p21, and p53) expression, was attenuated by resveratrol. Cell viability, extracellular matrix calcification, and osteogenic-related genes expression were significantly enhanced after resveratrol treatment. ROS production in BMSCs was inhibited while AMPK expression was up-regulated by resveratrol. Inhibition of AMPK expression by compound C reduced resveratrol-prompted osteogenesis and ROS production down-regulation. Conclusion: These results provide a potential mechanism involving AMPK activation/ROS inhibition signaling pathway in osteogenic differentiation of BMSCs enhanced by resveratrol. It suggests that development of therapy towards ROS is an effective way for osteoporosis treatment.

Artemisinin Protects Human Retinal Pigmented Epithelial Cells Against Hydrogen Peroxide-induced Oxidative Damage by Enhancing the Activation of AMP-active Protein Kinase

Dry age-related macular degeneration (AMD), a leading cause of blindness in aged population, is directly associated with oxidative stress induced damage of the retinal pigmented epithelial (RPE) cells. In the current study, we investigated the role of AMPK in the protective effect of artemisinin, an FDA approved anti-malarial Chinese herbal drug, on RPE cell line D407, against H₂O₂ induced oxidative stress. Our results showed that artemisinin promoted the survival of D407 cells from H₂O₂. Artemisinin reduced intracellular ROS generation and oxidative stress, decreased LDH release and the loss of mitochondrial membrane potential in D407 cells treated with H₂O₂. Western blotting showed that artemisinin concentration- and time-dependently stimulated the phosphorylation of AMP-activated protein kinase (AMPK) in D407 cells while AMPK inhibitor Compound C or knock-down of AMPK by si-RNA, inhibited the survival protective effect of artemisinin. More importantly, artemisinin produced a similar protective effect in primary cultured retinal pigment cells which was also blocked by inhibitors of AMPK. Taken together, these results suggested that artemisinin promotes survival of human retinal pigment cells against H₂O₂-induced cell death at least in part through enhancing the activation of AMPK. Therefore, artemisinin may be a beneficial therapeutic candidate for the treatment of age-related diseases, including retinal disorders like AMD.

AMP-activated protein kinase complexes containing the β2 regulatory subunit are up-regulated during and contribute to adipogenesis

AMP-activated protein kinase (AMPK) is a heterotrimer of α-catalytic and β- and γ-regulatory subunits that acts to regulate cellular and whole-body nutrient metabolism. The key role of AMPK in sensing energy status has led to significant interest in AMPK as a therapeutic target for dysfunctional metabolism in type 2 diabetes, insulin resistance and obesity. Despite the actions of AMPK in the liver and skeletal muscle being extensively studied, the role of AMPK in adipose tissue and adipocytes remains less well characterised. Small molecules that selectively influence AMPK heterotrimers containing specific AMPKβ subunit isoforms have been developed, including MT47-100, which selectively inhibits complexes containing AMPKβ2. AMPKβ1 and AMPKβ2 are the principal AMPKβ subunit isoforms in rodent liver and skeletal muscle, respectively, yet the contribution of specific AMPKβ isoforms to adipose tissue function, however, remains largely unknown. This study therefore sought to determine the contribution of AMPKβ subunit isoforms to adipocyte biology, focussing on adipogenesis. AMPKβ2 was the principal AMPKβ isoform in 3T3-L1 adipocytes, isolated rodent adipocytes and human subcutaneous adipose tissue, as assessed by the contribution to total cellular AMPK activity. Down-regulation of AMPKβ2 with siRNA inhibited lipid accumulation, cellular adiponectin levels and adiponectin secretion during 3T3-L1 adipogenesis, whereas down-regulation of AMPKβ1 had no effect. Incubation of 3T3-L1 cells with MT47-100 selectively inhibited AMPK complexes containing AMPKβ2 whilst simultaneously inhibiting cellular lipid accumulation as well as cellular levels and secretion of adiponectin. Taken together, these data indicate that increased expression of AMPKβ2 is an important feature of efficient adipogenesis.

Strontium promotes osteogenic differentiation by activating autophagy via the the AMPK/mTOR signaling pathway in MC3T3‑E1 cells

Strontium (Sr) is an alkaline earth metal that exerts the dual effect of improving bone formation and suppressing bone resorption, resulting in increased bone apposition rates and bone mineral density. However, the mechanisms through which Sr exerts these beneficial effects on bone have yet to be fully elucidated. The present study aimed to reveal the underlying molecular mechanisms associated with Sr‑induced osteogenic differentiation. The effects of Sr on cell proliferation and osteogenic differentiation were analyzed by MTT assay, RT‑qPCR, western blot analysis, alkaline phosphatase (ALP) and Alizarin red staining assays. The extent of autophagy was determined by monodansylcadaverine (MDC) staining and western blot analysis of two markers of cellular autophagic activity, the steatosis‑associated protein, sequestosome‑1 (SQSTM1/p62), and the two isoforms of microtubule‑associated protein 1 light chain 3 (LC3), LC‑3‑I/II. The expression levels of AMP‑activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) were also detected by western blot analysis. Sr at a concentration of 3 mM exerted the most pronounced effect on osteogenic differentiation, without any apparent cell toxicity. At the same time, cellular autophagy was active during this process. Subsequently, autophagy was blocked by 3‑methyladenine, and the enhancement of osteogenic differentiation in response to Sr was abrogated. Additionally, the phosphorylation level of AMPK was significantly increased, whereas that of mTOR was significantly decreased, in the Sr‑treated group. Taken together, the findings of the present study demonstrate that Sr stimulates AMPK‑activated autophagy to induce the osteogenic differentiation of MC3T3‑E1 cells.

Secretome of Mesenchymal Stem Cells and Its Potential Protective Effects on Brain Pathologies

Previous studies have indicated that mesenchymal stem cells (MSCs) have a fundamental role in the repair and regeneration of damaged tissues. There is strong evidence showing that much of the beneficial effects of these cells are due to the secretion of bioactive molecules-besides microRNAs, hormones, and neurotrophins-with anti-inflammatory, immunoregulatory, angiogenic, and trophic effects. These factors have been reported by many studies to possess protective effects on the nervous tissue. Although the beneficial effects of the secretory factors of MSCs have been suggested for various neurological diseases, their actions on astrocytic cells are not well understood. Hence, it is important to recognize the specific effects of MSCs derived from adipose tissue, in addition to the differences presented by the secretome, depending on the source and methods of analysis. In this paper, the different sources of MSCs and their main characteristics are described, as well as the most significant advances in regeneration and protection provided by the secretome of MSCs. Also, we discuss the possible neuroprotective mechanisms of action of the MSC-derived biomolecules, with special emphasis on the effect of MSCs derived from adipose tissue and their impact on glial cells and brain pathologies.

SIRT6 overexpression inhibits cementogenesis by suppressing glucose transporter 1

Cementum, which shares common features with bone in terms of biochemical composition, is important for the homeostasis of periodontium during periodontitis and orthodontic treatment. Sirtuin 6 (SIRT6), as a member of the sirtuin family, plays key roles in the osteogenic differentiation of bone marrow mesenchymal stem cells. However, the involvement of SIRT6 in cementoblast differentiation and mineralization and the underlying mechanisms remain unknown. In this study, we observed that the expression of SIRT6 increased during cementoblast differentiation initially. Analysis of the gain- and loss-of-function indicated that overexpressing SIRT6 in OCCM-30 cells suppresses cementoblast differentiation and mineralization and downregulating SIRT6 promotes cementogenesis. GLUT1, a glucose transporter necessary in cementogenesis, was inhibited by SIRT6. Overexpressing GLUT1 in SIRT6-overexpressed OCCM-30 cells rescued the inhibitory effect of SIRT6 on cementoblast differentiation and mineralization. Moreover, AMPK was activated after overexpressing SIRT6 and inhibited cementoblast differentiation and mineralization. Downregulating the expression of SIRT6 inhibited AMPK activity. Meanwhile, GLUT1 overexpression significantly decreased AMPK activity. Overall, on one hand, SIRT6 inhibited cementoblast differentiation and mineralization by suppressing GLUT1. On the other hand, SIRT6 inhibited cementoblast differentiation and mineralization by activating the AMPK pathway. GLUT1 overexpression also rescued the increased AMPK pathway activated by SIRT6.

Phloretin Promotes Adipogenesis via Mitogen-Activated Protein Kinase Pathways in Mouse Marrow Stromal ST2 Cells

Phloretin, a glucose transporter (GLUT) inhibitor, has pleiotropic effects. The present study examined the effects of phloretin on the commitment of marrow stromal cells to adipocytes, using the mouse marrow stromal cell line ST2. Oil red O staining showed that treatment with phloretin 10–100 µM promoted lipid accumulation. Real-time PCR showed that phloretin significantly increased the expression of adipogenic markers, including PPARγ, C/EBPα, fatty acid synthase, fatty acid-binding protein 4, and adiponectin. Western blotting showed that phloretin inhibited ERK1/2 and JNK but activated p38 MAPK. Treatment with a MAPK/ERK kinase inhibitor and a JNK inhibitor enhanced adipogenesis, similar to phloretin. In contrast, a p38 MAPK inhibitor suppressed phloretin-induced adipogenesis. Although phloretin phosphorylated AMP-activated protein kinase (AMPK), co-incubation with an AMPK inhibitor did not block phloretin-induced adipogenesis. The 2-deoxyglucose colorimetric assay showed that phloretin and siRNA silencing of GLUT1 decreased glucose uptake. However, unlike phloretin treatment, GLUT1 silencing inhibited adipogenesis. In addition, phloretin enhanced adipogenesis in GLUT1 knocked-down cells. Taken together, phloretin induced adipogenesis of marrow stromal cells by inhibiting ERK1/2 and JNK and by activating p38 MAPK. The adipogenic effects of phloretin were independent of glucose uptake inhibition. Phloretin may affect energy metabolism by influencing adipogenesis and adiponectin expression.

Ex vivo gut culture for studying differentiation and migration of small intestinal epithelial cells

Epithelial cultures are commonly used for studying gut health. However, due to the absence of mesenchymal cells and gut structure, epithelial culture systems including recently developed three-dimensional organoid culture cannot accurately represent in vivo gut development, which requires intense cross-regulation of the epithelial layer with the underlying mesenchymal tissue. In addition, organoid culture is costly. To overcome this, a new culture system was developed using mouse embryonic small intestine. Cultured intestine showed spontaneous peristalsis, indicating the maintenance of the normal gut physiological structure. During 10 days of ex vivo culture, epithelial cells moved along the gut surface and differentiated into different epithelial cell types, including enterocytes, Paneth cells, goblet cells and enteroendocrine cells. We further used the established ex vivo system to examine the role of AMP-activated protein kinase (AMPK) on gut epithelial health. Tamoxifen-induced AMPKα1 knockout vastly impaired epithelial migration and differentiation of the developing ex vivo gut, showing the crucial regulatory function of AMPK α1 in intestinal health.

Inhibition of adenosine monophosphate-activated protein kinase suppresses bone morphogenetic protein-2-induced mineralization of osteoblasts via Smad-independent mechanisms

Previous studies showed that adenosine monophosphate-activated protein kinase (AMPK), which plays as an intracellular energy sensor, promotes the differentiation and mineralization of osteoblasts via enhancing expression of bone morphogenetic protein (BMP)-2, which is a potent inducer of osteoblastogenesis. Thus, the aim of this study was to examine the roles of AMPK in BMP-2-induced osteoblastogenesis. We used a murine osteoblastic cell line MC3T3-E1 and a murine marrow stromal cell line ST2. BMP-2 (50 and 100 ng/mL) stimulated alkaline phosphatase (ALP) activity and enhanced mineralization of MC3T3-E1 cells, while the effects of BMP-2 were partly abolished by an inhibitor of AMPK, ara-A (0.1 mM). Real-time PCR showed that BMP-2 significantly increased the mRNA expressions of Alp, osteocalcin (Ocn), Runx2, Osterix and Dlx-5 in MC3T3-E1 cells, while co-incubation of ara-A significantly decreased the BMP-2-stimulated expression of Alp, Ocn, and Runx2. Moreover, co-incubation of ara-A suppressed the BMP-2-induced upregulation of Alp and Ocn in ST2 cells. Western blot analysis showed that BMP-2 phosphorylated Smad1/5 although it did not affect AMPK phosphorylation in MC3T3-E1 cells. Furthermore, a BMP receptor inhibitor LDN-193189 inhibited the phosphorylation of Smad1/5, but did not affect AMPK. In addition, co-incubation of ara-A did not affect BMP-2-induced phosphorylation of Smad1/5. These findings suggest that the inhibition of AMPK activation reduces the osteo-inductive effects of BMP-2 by decreasing the expression of Alp, Ocn, and Runx2 through Smad-independent mechanisms in osteoblastic cells.

Endocytic mechanisms and osteoinductive profile of hydroxyapatite nanoparticles in human umbilical cord Wharton's jelly-derived mesenchymal stem cells

Background

As a potentially bioactive material, the widespread application of nanosized hydroxyapatite (nano-HAP) in the field of bone regeneration has increased the risk of human exposure. However, our understanding of the interaction between nano-HAP and stem cells implicated in bone repair remains incomplete.

Methods

Here, we characterized the adhesion and cellular internalization of HAP nanoparticles (HANPs) with different sizes (20 nm np20 and 80 nm np80) and highlighted the involved pathway in their uptake using human umbilical cord Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs). In addition, the effects of HANPs on cell viability, apoptosis response, osteogenic differentiation, and underlying related mechanisms were explored.

Results

It was shown that both types of HANPs readily adhered to the cellular membrane and were transported into the cells compared to micro-sized HAP particles (m-HAP; 12 μm). Interestingly, the endocytic routes of np20 and np80 differed, although they exhibited similar kinetics of adhesion and uptake. Our study revealed involvement of clathrin- and caveolin-mediated endocytosis as well as macropinocytosis in the np20 uptake. However, for np80, clathrin-mediated endocytosis and some as-yet-unidentified important uptake routes play central roles in their internalization. HANPs displayed a higher preference to accumulate in the cytoplasm compared to m-HAP, and HANPs were not detected in the nucleolus. Exposure to np20 for 24 h caused a decrease in cell viability, while cells completely recovered with an exposure time of 72 h. Furthermore, HANPs did not influence apoptosis and necrosis of hWJ-MSCs. Strikingly, HANPs enhanced mRNA levels of osteoblast-related genes and stimulated calcium mineral deposition, and this directly correlated with the activation in c-Jun N-terminal kinases and p38 pathways.

Conclusion

Our data provide additional insight about the interactions of HANPs with MSCs and suggest their application potential in hard tissue regeneration.

Effects of Hexachlorophene, a Chemical Accumulating in Adipose Tissue, on Mouse and Human Mesenchymal Stem Cells

The hexachlorophene (HCP) is a highly lipophilic chlorinated bisphenol present in hygienic and dermatological products. The HCP accumulates preferentially in adipose tissue that is a privileged source of mesenchymal stem cells (MSCs). The evaluation of the potential effects of HCP on MSCs is important for their medical application. Here we examined the effects of HCP on murine adipose tissue-derived stem cells (ADSCs) and human umbilical cord-derived stem cells (UCSCs) in cell culture. We found that 10⁻⁴ and 10⁻⁵ M HCP inhibits proliferation, osteogenesis and increases apoptosis of ADSCs and UCSCs. While the effect of HCP on proliferation and differentiation potential of these two cell lines was similar, the UCSCs appeared much more resistant to HCP-induced apoptosis than ADSCs. These results suggest that the adipose tissue-derived ADSCs have higher sensitive for HCP than umbilical cord-derived UCSCs and indicate that the umbilical cord can be a preferable source of MSCs for prospective medical applications in the future.

Melatonin alleviates oxidative stress-inhibited osteogenesis of human bone marrow-derived mesenchymal stem cells through AMPK activation

Oxidative stress plays an important role in the pathogenesis of aging-related osteoporosis through the increased bone resorption or reduced bone formation. Melatonin, which can exert beneficial actions through antioxidant, anti-inflammatory, and bone-preserving effects, shows promise in preventing oxidative stress-inhibited osteogenesis. However, specific mechanisms by which melatonin rescues oxidative stress-inhibited osteogenesis of human mesenchymal stem cells (MSCs) have not been fully elucidated yet. We therefore investigated whether activation of AMPK by melatonin regulates the antagonistic crosstalk between oxidative stress and osteogenic differentiation in human MSCs. Melatonin treatment significantly enhanced osteogenic differentiation of human MSCs through activation of AMPK and upregulation of FOXO3a and RUNX2 which were known as master transcription factors responsible for the mechanistic link between oxidative stress and osteogenic phenotype. Osteogenic differentiation determined by calcium deposition was significantly increased by melatonin treatment against oxidative stress. In addition, melatonin treatment reconstituted activation of AMPK and expression of FOXO3a and RUNX2 inhibited by oxidative stress. Overall, these results demonstrate that melatonin enhances osteogenic differentiation of human MSCs and restores oxidative stress-inhibited osteogenesis through AMPK activation in human MSCs, suggesting that activation of AMPK by melatonin may represent a promising new therapeutic strategy for treating metabolic bone diseases such as osteoporosis.

Bifunctional enzyme ATIC promotes propagation of hepatocellular carcinoma by regulating AMPK-mTOR-S6 K1 signaling

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the cancer types with poor prognosis. To effectively treat HCC, new molecular targets and therapeutic approaches must be identified. 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/inosine monophosphate (IMP) cyclohydrolase (ATIC), a bifunctional protein enzyme, catalyzes the last two steps of the de novo purine biosynthetic pathway. Whether ATIC contributes to cancer development remains unclear.

METHODS

ATIC mRNA levels in different types of human HCC samples or normal tissues were determined from Gene Expression across Normal and Tumor tissue (GENT) database. The expression level of ATIC in human HCC samples or cell lines were examined by RT-PCR and western blot. Overall survival and disease-free survival of HCC patients in the ATIC low and ATIC high groups were determined by Kaplan-Meier analysis. Effects of ATIC knockdown by lentivirus infection were evaluated on cell-proliferation, cell-apoptosis, colony formation and migration. The mechanisms involved in HCC cells growth, apoptosis and migration were analyzed by western blot and Compound C (C-C) rescue assays.

RESULTS

Here, we first demonstrated that expression of ATIC is aberrantly up-regulated in HCC tissues and high level of ATIC is correlated with poor survival in HCC patients. Knockdown of ATIC expression resulted in a dramatic decrease in proliferation, colony formation and migration of HCC cells. We also identified ATIC as a novel regulator of adenosine monophosphate-activated protein kinase (AMPK) and its downstream signaling mammalian target of rapamycin (mTOR). ATIC suppresses AMPK activation, thus activates mTOR-S6 K1-S6 signaling and supports growth and motility activity of HCC cells.

CONCLUSION

Taken together, our results indicate that ATIC acts as an oncogenic gene that promotes survival, proliferation and migration by targeting AMPK-mTOR-S6 K1 signaling.

AMPK downregulates ALK2 via increasing the interaction between Smurf1 and Smad6, leading to inhibition of osteogenic differentiation

Activin A receptor type I or activin receptor-like kinase 2 (ACVRI/ALK2) belongs to type I TGF-β family and plays an important role in bone development. Activating mutations of ALK2 containing the R206 to H mutation, are present in 95% in the rare autosomal genetic disease fibrodysplasia ossificans progressiva (FOP), which leads to the development of ectopic bone formation in muscle. The effect of AMP-activated protein kinase (AMPK) activation on ALK2R206H-mediated signaling in fibroblasts obtained from a FOP patient was assessed in the present study. The activity of the mutated ALK2 was suppressed by pharmacological AMPK activators such as metformin and aspirin, while their actions were blocked by the dominant negative mutant of AMPK and mimicked by the constitutively active mutant of AMPK. Furthermore, activation of AMPK upregulated Smad6 and Smurf1 and thereby enhanced their interactions, resulting in its proteosome-dependent degradation of ALK2. In contrast, knockdown of Smad6 or Smurf1 prevented metformin-induced reduction of ALK2. To evaluate the biological relevance of AMPK action on ALK2 activity, we induced FOP fibroblasts into iPS cells and found that their osteogenic differentiation in vitro was inhibited by metformin. Our studies provide novel insight into potential approaches to treatment of FOP, since several AMPK activators (e.g. metformin, berberine, and aspirin) are already in clinical use for the treatment of diabetes and metabolic syndromes.

AMP-activated protein kinase: a therapeutic target in intestinal diseases

Adenosine monophosphate (AMP)-activated protein kinase (AMPK), a highly conserved energy sensor, has a crucial role in cardiovascular, neurodegenerative and inflammatory diseases, as well as in cancer and metabolic disorders. Accumulating studies have demonstrated that AMPK activation enhances paracellular junctions, nutrient transporters, autophagy and apoptosis, and suppresses inflammation and carcinogenesis in the intestine, indicating an essential role of AMPK in intestinal health. AMPK inactivation is an aetiological factor in intestinal dysfunctions. This review summarizes the favourable outcomes of AMPK activation on intestinal health, and discusses AMPK as a potential therapeutic target for intestinal diseases.

Elimination of cancer stem cells and reactivation of latent HIV-1 via AMPK activation: Common mechanism of action linking inhibition of tumorigenesis and the potential eradication of HIV-1

Although promising treatments are currently in development to slow disease progression and increase patient survival, cancer remains the second leading cause of death in the United States. Cancer treatment modalities commonly include chemoradiation and therapies that target components of aberrantly activated signaling pathways. However, treatment resistance is a common occurrence and recent evidence indicates that the existence of cancer stem cells (CSCs) may underlie the limited efficacy and inability of current treatments to effectuate a cure. CSCs, which are largely resistant to chemoradiation therapy, are a subpopulation of cancer cells that exhibit characteristics similar to embryonic stem cells (ESCs), including self-renewal, multi-lineage differentiation, and the ability to initiate tumorigenesis. Interestingly, intracellular mechanisms that sustain quiescence and promote self-renewal in adult stem cells (ASCs) and CSCs likely also function to maintain latency of HIV-1 in CD4⁺ memory T cells. Although antiretroviral therapy is highly effective in controlling HIV-1 replication, the persistence of latent but replication-competent proviruses necessitates the development of compounds that are capable of selectively reactivating the latent virus, a method known as the "shock and kill" approach. Homeostatic proliferation in central CD4⁺ memory T (T_CM) cells, a memory T cell subset that exhibits limited self-renewal and differentiation and is a primary reservoir for latent HIV-1, has been shown to reinforce and stabilize the latent reservoir in the absence of T cell activation and differentiation. HIV-1 has also been found to establish durable and long-lasting latency in a recently discovered subset of CD4⁺ T cells known as T memory stem (T_SCM) cells. T_SCM cells, compared to T_CM cells, exhibit stem cell properties that more closely match those of ESCs and ASCs, including self-renewal and differentiation into all memory T cell subsets. It is our hypothesis that activation of AMPK, a master regulator of cellular metabolism that plays a critical role in T cell activation and differentiation of ESCs and ASCs, will lead to both T cell activation-induced latent HIV-1 reactivation, facilitating virus destruction, as well as "activation", differentiation, and/or apoptosis of CSCs, thus inhibiting tumorigenesis. We also propose the novel observation that compounds that have been shown to both facilitate latent HIV-1 reactivation and promote CSC differentiation/apoptosis (e.g. bryostatin-1, JQ1, metformin, butyrate, etc.) likely do so through a common mechanism of AMPK activation.

Functional restoration of replicative senescent mesenchymal stem cells by the brown alga Undaria pinnatifida

The brown alga Undaria pinnatifida, which is called Mi-Yoek in Korea, has been traditionally consumed as a health food in East Asian countries. Recent studies have reported that U. pinnatifida has beneficial effects on arteriosclerosis, inflammation, fat metabolism, and tumors. In this study, we examined the anti-senescence effects of ethanol extracts of U. pinnatifida (UP-Ex) in human bone marrow mesenchymal stem cells (hBM-MSCs). UP-Ex protected hBM-MSCs against oxidative injury, as determined by MTT assays. This effect was confirmed by immunoblot analysis of the oxidation-sensitive protein p53 and the apoptotic protein cleaved caspase-3. Excessive intracellular reactive oxygen species (ROS) accumulation induced by oxidative stress was moderated in UP-Ex-treated hBM-MSCs (UP-Ex-MSCs). Similarly, expression of the ROS-scavenging enzymes superoxide dismutase 1 (SOD1), SOD2, and catalase was recovered in UP-Ex-MSCs. Excessive ROS induced by long-term cell expansion (passage 17) was significantly decreased along with restoration of the senescence proteins p53, p21, and p16 in UP-Ex-MSCs. UP-Ex treatment also improved the ability of these replicative, senescent hBM-MSCs (passage 17) to differentiate into osteocytes or adipocytes, suggesting that UP-Ex ameliorates the functional decline of senescent stem cells and may provide better therapeutic efficacy in stem cell therapy.

Abbreviations: hBM-MSCs: human bone marrow mesenchymal stem cells; DCF: 2′,7′-dichlorodihydrofluorescein; DCFH-DA: 2′,7′-dichlorofluorescein diacetate; MTT: 3-(4,5-dimethylthiazol-2-yl-)2,5-diphenyltetrazolium bromide; PBS: phosphate-buffered saline; PFA: paraformaldehyde; RIPA: radioimmunoprecipitation assay; ROS: reactive oxygen species; SOD1: superoxide dismutase 1; SOD2: superoxide dismutase 2.

Role of PIN1 on in vivo periodontal tissue and in vitro cells

BACKGROUND

Although expression of peptidyl-prolyl cis/trans isomerase NIMA-interacting 1 (PIN1) was reported in bone tissue, the precise role of PIN1 in periodontal tissue and cells remain unclear.

MATERIAL & METHODS

To elucidate the roles of PIN1 in periodontal tissue, its expression in periodontal tissue and cells, and effects on in vitro 4 osteoblast differentiation and the underlying signaling mechanisms were evaluated.

RESULTS

PIN1 was expressed in mouse periodontal tissues including periodontal ligament cells (PDLCs), cementoblasts and osteoblasts at the developing root formation stage (postnatal, PN14) and functional stage of tooth (PN28). Treatment of PIN1 inhibitor juglone, and gene silencing by RNA interference promoted osteoblast differentiation in PDLCs and cementoblasts, whereas the overexpression of PIN1 inhibited. Moreover, osteogenic medium-induced activation of AMPK, mTOR, Akt, ERK, p38 and NF-jB pathways were enhanced by PIN1 siRNA, but attenuated by PIN1 overexpression. Runx2 expressions were induced by PIN1 siRNA, but downregulated by PIN1 overexpression.

CONCLUSION

In summary, this study is the first to demonstrate that PIN1 is expressed in developing periodontal tissue, and in vitro PDLCs and cementoblasts. PIN1 inhibition stimulates osteoblast differentiation, and thus may play an important role in periodontal regeneration.

AMPK promotes mitochondrial biogenesis and function by phosphorylating the epigenetic factors DNMT1, RBBP7, and HAT1

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) acts as a master regulator of cellular energy homeostasis by directly phosphorylating metabolic enzymes and nutrient transporters and by indirectly promoting the transactivation of nuclear genes involved in mitochondrial biogenesis and function. We explored the mechanism of AMPK-mediated induction of gene expression. We identified AMPK consensus phosphorylation sequences in three proteins involved in nucleosome remodeling: DNA methyltransferase 1 (DNMT1), retinoblastoma binding protein 7 (RBBP7), and histone acetyltransferase 1 (HAT1). DNMT1 mediates DNA methylation that limits transcription factor access to promoters and is inhibited by RBBP7. Acetylation of histones by HAT1 creates a more relaxed chromatin-DNA structure that favors transcription. AMPK-mediated phosphorylation resulted in the activation of HAT1 and inhibition of DNMT1. For DNMT1, this inhibition was both a direct effect of phosphorylation and the result of increased interaction with RBBP7. In human umbilical vein cells, pharmacological AMPK activation or pulsatile shear stress triggered nucleosome remodeling and decreased cytosine methylation, leading to increased expression of nuclear genes encoding factors involved in mitochondrial biogenesis and function, such as peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), transcription factor A (Tfam), and uncoupling proteins 2 and 3 (UCP2 and UCP3). Similar effects were seen in the aortas of mice given pharmacological AMPK activators, and these effects required AMPK2α. These results enhance our understanding of AMPK-mediated mitochondrial gene expression through nucleosome remodeling.

Metformin suppresses adipogenesis through both AMP-activated protein kinase (AMPK)-dependent and AMPK-independent mechanisms

People with Type 2 diabetes mellitus (T2DM) have reduced bone mineral density and an increased risk of fractures due to altered mesenchymal stem cell (MSC) differentiation in the bone marrow. This leads to a shift in the balance of differentiation away from bone formation (osteogenesis) in favour of fat cell development (adipogenesis). The commonly used anti-diabetic drug, metformin, activates the osteogenic transcription factor Runt-related transcription factor 2 (Runx2), which may suppress adipogenesis, leading to improved bone health. Here we investigate the involvement of the metabolic enzyme, AMP-activated protein kinase (AMPK), in these protective actions of metformin. The anti-adipogenic actions of metformin were observed in multipotent C3H10T1/2 MSCs, in which metformin exerted reciprocal control over the activities of Runx2 and the adipogenic transcription factor, PPARγ, leading to suppression of adipogenesis. These effects appeared to be independent of AMPK activation but rather through the suppression of the mTOR/p70^S6K signalling pathway. Basal AMPK and mTOR/p70^S6K activity did appear to be required for adipogenesis, as demonstrated by the use of the AMPK inhibitor, compound C. This observation was further supported by using AMPK knockout mouse embryo fibroblasts (MEFs) where adipogenesis, as assessed by reduced lipid accumulation and expression of the adipogeneic transcription factor, C/EBPβ, was found to display an absolute requirement for AMPK. Further activation of AMPK in wild type MEFS, with either metformin or the AMPK-specific activator, A769662, was also associated with suppression of adipogenesis. It appears, therefore, that basal AMPK activity is required for adipogenesis and that metformin can inhibit adipogenesis through AMPK-dependent or -independent mechanisms, depending on the cellular context.

Calcium phosphate-phosphorylated adenosine hybrid microspheres for anti-osteosarcoma drug delivery and osteogenic differentiation

Biocompatibility, biodegradability and bioactivity are significantly important in practical applications of various biomaterials for bone tissue engineering. Herein, we develop a functional inorganic-organic hybrid system of calcium phosphate-phosphorylated adenosine (CPPA). Both calcium phosphate and phosphorylated adenosine molecules in CPPA are fundamental components in mammalians and play important roles in biological metabolism. In this work, we report our three leading research qualities: (1) CPPA hybrid microspheres with hollow and porous structure are synthesized by a facile one-step microwave-assisted solvothermal method; (2) CPPA hybrid microspheres show high doxorubicin loading capacity and pH-responsive drug release properties, and demonstrate positive therapeutic effects on six osteosarcoma cell lines in vitro and a mouse model of 143B osteosarcoma subcutaneous tumor in vivo; (3) CPPA hybrid microspheres are favorable to promote osteogenic differentiation of human bone mesenchymal stem cells (hBMSCs) by activating the AMPK pathway, with satisfactory evidences from cellular alkaline phosphatase staining, alizarin red staining, real time PCR and western analysis. The as-prepared CPPA hybrid microspheres are promising in anti-osteosarcoma and bone regeneration, which simultaneously display excellent properties on drug delivery and osteogenic differentiation of hBMSCs.

AMPK promotes osteogenesis and inhibits adipogenesis through AMPK-Gfi1-OPN axis

Several metabolic, genetic and oncogenic bone diseases share the common pathological phenotype of defective bone marrow stromal cell (BMSC) differentiation. Many reports in bone science in the past several years have suggested that the skeleton also has an endocrine role. The role of AMP-activated protein kinase (AMPK) as an energy metabolism sensor and how it regulates BMSC differentiation is largely unknown. In the current study, we used AMPK agonists to activate AMPK in MC3T3-E1 cells to investigate the functional roles of AMPK in osteogenesis. However, metformin and AICAR failed to activate AMPK consistently. Therefore, we established MC3T3-E1 and 3T3-L1 cell models of AMPK α subunit overexpression through lentivirus vector, in which AMPK was overactivated. AMPK hyperactivation stimulated MC3T3-E1 cell osteogenesis and inhibited 3T3-L1 cell adipogenesis. Osteopontin (OPN) mediated AMPK regulation of osteogenesis and adipogenesis. Furthermore, we provided evidence that the transcriptional repressor growth factor independence-1 (Gfi1) was downregulated and disassociated from the OPN promoter in response to AMPK activation, resulting in the upregulation of OPN. Overexpression of wild-type and dominant-negative Gfi1 modulated MC3T3-E1 osteogenesis and 3T3-L1 adipogenesis. Further evidence suggested that AMPK enhanced ectopic bone formation of MC3T3-E1 cells through the AMPK-Gfi1-OPN axis. In conclusion, AMPK was sufficient to stimulate osteogenesis of MC3T3-E1 cells and inhibit adipogenesis of 3T3-L1 cells through the AMPK-Gfi1-OPN axis. These findings helped elucidate the molecular mechanisms underlying AMPK regulation of osteogenesis and adipogenesis.

TGFβ-induced switch from adipogenic to osteogenic differentiation of human mesenchymal stem cells: identification of drug targets for prevention of fat cell differentiation

BACKGROUND

Patients suffering from osteoporosis show an increased number of adipocytes in their bone marrow, concomitant with a reduction in the pool of human mesenchymal stem cells (hMSCs) that are able to differentiate into osteoblasts, thus leading to suppressed osteogenesis.

METHODS

In order to be able to interfere with this process, we have investigated in-vitro culture conditions whereby adipogenic differentiation of hMSCs is impaired and osteogenic differentiation is promoted. By means of gene expression microarray analysis, we have investigated genes which are potential targets for prevention of fat cell differentiation.

RESULTS

Our data show that BMP2 promotes both adipogenic and osteogenic differentiation of hMSCs, while transforming growth factor beta (TGFβ) inhibits differentiation into both lineages. However, when cells are cultured under adipogenic differentiation conditions, which contain cAMP-enhancing agents such as IBMX of PGE2, TGFβ promotes osteogenic differentiation, while at the same time inhibiting adipogenic differentiation. Gene expression and immunoblot analysis indicated that IBMX-induced suppression of HDAC5 levels plays an important role in the inhibitory effect of TGFβ on osteogenic differentiation. By means of gene expression microarray analysis, we have investigated genes which are downregulated by TGFβ under adipogenic differentiation conditions and may therefore be potential targets for prevention of fat cell differentiation. We thus identified nine genes for which FDA-approved drugs are available. Our results show that drugs directed against the nuclear hormone receptor PPARG, the metalloproteinase ADAMTS5, and the aldo-keto reductase AKR1B10 inhibit adipogenic differentiation in a dose-dependent manner, although in contrast to TGFβ they do not appear to promote osteogenic differentiation.

CONCLUSIONS

The approach chosen in this study has resulted in the identification of new targets for inhibition of fat cell differentiation, which may not only be relevant for prevention of osteoporosis, but also of obesity.

Rat Osteosarcoma Cells as a Therapeutic Target Model for Osteoregeneration via Sclerostin Knockdown

There are various conceptually different strategies to improve bone regeneration and to treat osteoporosis, each with distinct inherent advantages and disadvantages. The use of RNA interference strategies to suppress the biological action of catabolic factors or antagonists of osteogenic proteins is promising, and such strategies can be applied locally. They are comparably inexpensive and do not suffer from stability problems as protein-based approaches. In this study, we focus on sclerostin, encoded by the SOST gene, a key regulator of bone formation and remodeling. Sclerostin is expressed by mature osteocytes but also by late osteogenically differentiated cells. Thus, it is difficult and requires long-term cultures to investigate the effects of SOST silencing on the expression of osteogenic markers using primary cells. We, therefore, selected a rat osteosarcoma cell line, UMR-106, that has been shown to express SOST and secrete sclerostin in a comparable fashion as late osteoblasts and osteocytes. We investigated the effects of differentiating supplements on SOST expression and sclerostin secretion in UMR-106 cells and found that addition of 100 ng/ml of bone morphogenetic protein (BMP)-2 strongly induced sclerostin secretion, whereas dexamethasone inhibited secretion. Effects of silencing SOST in UMR-106 cells cultured in various differentiation media including BMP-2 and/or dexamethasone were determined next with the aim to find promising test conditions for a readout system for the evaluation of future small interfering RNA release formulations for local induction of bone formation. We found a direct correlation between attenuated SOST expression and an increase in the osteogenic potential of UMR-106 cells. The combination of SOST silencing and BMP-2 could synergistically improve osteogenic factors. A lowered proliferation rate in silenced groups may indicate a faster switch to differentiation.

Synergistic effect of bioactive lipid and condition medium on cardiac differentiation of human mesenchymal stem cells from different tissues

Human umbilical cord mesenchymal stem cells (hUCMSCs) and human adipose tissue mesenchymal stem cells (hATMSCs) have the potential to differentiate into cardiomyocytes, making them promising therapeutic candidates for treating damaged cardiac tissues. Currently, however, the differentiated cells induced from hUCMSCs or hATMSCs can hardly display functional characteristics similar to cardiomyocytes. In this study, we have investigated the effects of bioactive lipid sphingosine-1-phosphate (S1P) on cardiac differentiations of hUCMSCs and hATMSCs in condition medium composed of cardiac myocytes culture medium or 5-azacytidine. Cardiac differentiations were identified through immunofluorescence staining, and the results were observed with fluorescence microscopy and confocal microscopy. Synergistic effects of S1P and condition medium on cell viability were evaluated by MTT assays. Functional characteristics similar to cardiomyocytes were evaluated through detecting calcium transient. The differentiated hUCMSCs or hATMSCs in each group into cardiomyocytes showed positive expressions of cardiac specific proteins, including α-actin, connexin-43 and myosin heavy chain-6 (MYH-6). MTT assays showed that suitable differentiation time was 14 days and that the optimal concentration of S1P was 0.5 μM. Moreover, incorporation of S1P and cardiac myocytes culture medium gave rise to calcium transients, an important marker for displaying in vivo electrophysiological properties. This feature was not observed in the S1P-5-azacytidine group, indicating the possible lack of cellular stimuli such as transforming growth factor-beta, TGF-β.

AMPK/Snf1 signaling regulates histone acetylation: Impact on gene expression and epigenetic functions

AMP-activated protein kinase (AMPK) and its yeast homolog, Snf1, are critical regulators in the maintenance of energy metabolic balance not only stimulating energy production but also inhibiting energy-consuming processes. The AMPK/Snf1 signaling controls energy metabolism by specific phosphorylation of many metabolic enzymes and transcription factors, enhancing or suppressing their functions. The AMPK/Snf1 complexes can be translocated from cytoplasm into nuclei where they are involved in the regulation of transcription. Recent studies have indicated that AMPK/Snf1 activation can control histone acetylation through different mechanisms affecting not only gene transcription but also many other epigenetic functions. For instance, AMPK/Snf1 enzymes can phosphorylate the histone H3S10 (yeast) and H2BS36 (mammalian) sites which activate specific histone acetyltransferases (HAT), consequently enhancing histone acetylation. Moreover, nuclear AMPK can phosphorylate type 2A histone deacetylases (HDAC), e.g. HDAC4 and HDAC5, triggering their export from nuclei thus promoting histone acetylation reactions. AMPK activation can also increase the level of acetyl CoA, e.g. by inhibiting fatty acid and cholesterol syntheses. Acetyl CoA is a substrate for HATs, thus increasing their capacity for histone acetylation. On the other hand, AMPK can stimulate the activity of nicotinamide phosphoribosyltransferase (NAMPT) which increases the level of NAD(+). NAD(+) is a substrate for nuclear sirtuins, especially for SIRT1 and SIRT6, which deacetylate histones and transcription factors, e.g. those regulating ribosome synthesis and circadian clocks. Histone acetylation is an important epigenetic modification which subsequently can affect chromatin remodeling, e.g. via bromodomain proteins. We will review the signaling mechanisms of AMPK/Snf1 in the control of histone acetylation and subsequently clarify their role in the epigenetic regulation of ribosome synthesis and circadian clocks.