Exendin-4 enhances proliferation of senescent osteoblasts through activation of the IGF-1/IGF-1R signaling pathway

Gut hormones and bone homeostasis: potential therapeutic implications

Bone resorption follows a circadian rhythm, with a marked reduction in circulating markers of resorption (such as carboxy-terminal telopeptide region of collagen type I in serum) in the postprandial period. Several gut hormones, including glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide 1 (GLP1) and GLP2, have been linked to this effect in humans and rodent models. These hormones are secreted from enteroendocrine cells in the gastrointestinal tract in response to a variety of stimuli and effect a wide range of physiological processes within and outside the gut. Single GLP1, dual GLP1-GIP or GLP1-glucagon and triple GLP1-GIP-glucagon receptor agonists have been developed for the treatment of type 2 diabetes mellitus and obesity. In addition, single GIP, GLP1 and GLP2 analogues have been investigated in preclinical studies as novel therapeutics to improve bone strength in bone fragility disorders. Dual GIP-GLP2 analogues have been developed that show therapeutic promise for bone fragility in preclinical studies and seem to exert considerable activity at the bone material level. This Review summarizes the evidence of the action of gut hormones on bone homeostasis and physiology.

Er-Xian decoction attenuates ovariectomy-induced osteoporosis by modulating fatty acid metabolism and IGF1/PI3K/AKT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Er-Xian decoction (EXD) is a traditional Chinese medicine (TCM) formula used to treat osteoporosis (OP). However, the anti-OP mechanism of EXD has not yet been fully elucidated.

AIM OF THE STUDY

The study aimed to verify the anti-OP effect of EXD and to explore its underlying mechanism.

METHODS

The anti-OP targets and mechanisms of EXD were predicted by network pharmacological analysis. Then, an ovariectomized (OVX) rat model was established to validate the key anti-OP mechanism of EXD. Firstly, the therapeutic effect of EXD on OP was confirmed using micro-CT bone analysis, pathological observation, and ELISA detection. Secondly, serum metabolites related to key biological processes were detected using an automatic biochemical analyzer and GC-MS. Finally, ELISA, qRT-PCR, and western blot were utilized to further explore the potential key anti-OP pathway of EXD.

RESULTS

A total of 159 anti-OP targets of EXD were identified. Functional annotation revealed that OP treatment using EXD was associated with lipid metabolism, fatty acid (FA) metabolism, and PI3K/AKT signaling pathway. Experimental studies confirmed that EXD ameliorated ovariectomy-induced bone loss and bone microstructure deterioration. EXD treatment also upregulated the level of serum estrogen and downregulated the level of OC, PⅠNP, CTX-1, TC, and LDL-C. Besides, principal component analysis (PCA) and heat map of serum FAs distinguished OVX rats from the SHAM and EXD groups. Serum concentrations of important n-3 FAs, including C20:3N3, C20:5N3, and C22:5N3, were significantly increased in the EXD group. The increased stearoyl-CoA desaturase 1 (SCD1) index 1 and index 2 in the OVX group were reversed by EXD administration. Additionally, EXD reversed the decreased serum IGF1 level and tibia IGF1R, PI3K, and AKT expression in OVX rats.

CONCLUSION

EXD ameliorated ovariectomy-induced bone loss by modulating lipid metabolism, FA metabolism, and IGF1/PI3K/AKT pathway.

Comprehensive ceRNA network for MACF1 regulates osteoblast proliferation

BACKGROUND

Previous studies have shown that microtubule actin crosslinking factor 1 (MACF1) can regulate osteoblast proliferation and differentiation through non-coding RNA (ncRNA) in bone-forming osteoblasts. However, the role of MACF1 in targeting the competing endogenous RNA (ceRNA) network to regulate osteoblast differentiation remains poorly understood. Here, we profiled messenger RNA (mRNA), microRNA (miRNA), and long ncRNA (lncRNA) expression in MACF1 knockdown MC3TC‑E1 pre‑osteoblast cells.

RESULTS

In total, 547 lncRNAs, 107 miRNAs, and 376 mRNAs were differentially expressed. Significantly altered lncRNAs, miRNAs, and mRNAs were primarily found on chromosome 2. A lncRNA-miRNA-mRNA network was constructed using a bioinformatics computational approach. The network indicated that mir-7063 and mir-7646 were the most potent ncRNA regulators and mef2c was the most potent target gene. Pathway enrichment analysis showed that the fluid shear stress and atherosclerosis, p53 signaling, and focal adhesion pathways were highly enriched and contributed to osteoblast proliferation. Importantly, the fluid shear stress and atherosclerosis pathway was co-regulated by lncRNAs and miRNAs. In this pathway, Dusp1 was regulated by AK079370, while Arhgef2 was regulated by mir-5101. Furthermore, Map3k5 was regulated by AK154638 and mir-466q simultaneously. AK003142 and mir-3082-5p as well as Ak141402 and mir-446 m-3p were identified as interacting pairs that regulate target genes.

CONCLUSION

This study revealed the global expression profile of ceRNAs involved in the differentiation of MC3TC‑E1 osteoblasts induced by MACF1 deletion. These results indicate that loss of MACF1 activates a comprehensive ceRNA network to regulate osteoblast proliferation.

Exendin-4 enhances osteogenic differentiation of adipose tissue mesenchymal stem cells through the receptor activator of nuclear factor-kappa B and osteoprotegerin signaling pathway

The capability of mesenchymal stem cells (MSCs) to repair bone damage and defects has long been investigated. The receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL) and the decoy receptor osteoprotegerin (OPG) axis is crucial to keep the equilibrium between osteoblastic and osteoclastic activity. Exendin-4 utilization increased bone formation and enhanced bone integrity. This study aimed to investigate the mentioned axis and determine the effect of exendin-4 upon adipose mesenchymal stem cells (Ad-MSCs) osteogenic differentiation. Ad-MSCs were isolated from rat epididymal fat, followed by characterization and then differentiation into osteocytes both in the presence or absence of exendin-4. Osteogenic differentiation was evaluated by alizarin red staining and the expression of osteogenic markers; using reverse transcriptase-quantitative polymerase chain reaction, western blotting and enzyme-linked immunoassay. MSCs derived from rat epididymal fat were isolated and characterized, along with their differentiation into osteocytes. The differentiated cells were alizarin red-stained, showing increased staining intensity upon addition of exendin-4. Moreover, the addition of exendin-4 elevated the messenger RNA expression levels of osteogenic markers; runt-related transcription factor-2 (RUNX-2), osteocalcin, and forkhead box protein O-1 while reducing the expression of the adipogenic marker peroxisome-proliferator-activated receptor-gamma. Exendin-4 addition elevated OPG levels in the supernatant of osteogenic differentiated cells. Moreover, exendin-4 elevated the protein levels of glucagon-like peptide-1 receptor and RUNX-2, while decreasing both RANK and RANKL. In conclusion, osteogenic differentiation of Ad-MSCs is associated with increased osteoblastic rather than osteoclastic activity. The findings of this study suggest that exendin-4 can enhance Ad-MSCs osteogenic differentiation partially through the RANK/RANKL/OPG axis.

Chronic Sleep Deprivation Impaired Bone Formation in Growing Rats and Down-Regulated PI3K/AKT Signaling in Bone Tissues

BACKGROUND

This study aimed to assess the effects of chronic sleep deprivation (CSD) on bone metabolism in growing rats and the likely underlying mechanism.

METHODS

Twenty 5-week-old male Wistar rats and randomly divided into the CSD and normal control (NC) groups after one-week acclimatization. After a 6-week intervention of sleep deprivation, the distal femurs of both groups were harvested for micro-computed tomography scans and histological analysis. Meanwhile, the femur tissues were measured the mRNA and protein expression via RNA sequencing and immunohistochemical analysis. Serum bone turnover markers were evaluated at 0, 2, 4, and 6 weeks.

RESULTS

CSD impaired the bone growth, showing an imbalance of bone turnover status, dysphasia in the metaphysis growth plate, and deterioration of bone microarchitecture. Further, CSD suppressed bone formation, showing that the expression of osteogenesis-related proteins (col1α1 and osteocalcin) and mRNA (igf1, bglap, runx2, col1α1, pth1r) are down-regulated. Differentially expressed genes were detected, and functional enrichment analyses revealed that the PI3K/AKT pathway was significantly down-regulated in the CSD group.

CONCLUSION

These results suggest that CSD can significantly impaire bone health, and it may exert these effects in part by suppressing bone formation and osteoblast differentiation, and inactivating the PI3K/AKT signaling pathway.

Mini Review: Effect of GLP-1 Receptor Agonists and SGLT-2 Inhibitors on the Growth Hormone/IGF Axis

Accumulating evidence supports the early use of glucagon-like peptide-1 receptor agonists (GLP-1RAs) and sodium glucose transporter-2 inhibitors (SGLT-2is) for the treatment of type 2 diabetes. Indeed, these compounds exert numerous pleiotropic actions that favorably affect metabolism and diabetes comorbidities, showing an additional effect beyond glucose control. Although a substantial amount of knowledge has been generated regarding the mechanism of action of both drug classes, much remains to be understood. Growth hormone (GH) is an important driver for multiple endocrine responses involving changes in glucose and lipid metabolism, and affects several tissues and organs (e.g., bone, heart). It acts directly on several target tissues, including skeletal muscle and bone, but several effects are mediated indirectly by circulating (liver-derived) or locally produced IGF-1. In consideration of the multiple metabolic and cardiovascular effects seen in subjects treated with GLP-1RAs and SGLT-2is (e.g., reduction of hyperglycemia, weight loss, free/fat mass and bone remodeling, anti-atherosclerosis, natriuresis), it is reasonable to speculate that GH and IGF-1 may play a about a relevant role in this context. This narrative mini-review aims to describe the involvement of the GH/IGF-1/IGF-1R axis in either mediating or responding to the effects of each of the two drug classes.

Genes and Pathways Associated with Skeletal Sagittal Malocclusions: A Systematic Review

Skeletal class II and III malocclusions are craniofacial disorders that negatively impact people’s quality of life worldwide. Unfortunately, the growth patterns of skeletal malocclusions and their clinical correction prognoses are difficult to predict largely due to lack of knowledge of their precise etiology. Inspired by the strong inheritance pattern of a specific type of skeletal malocclusion, previous genome-wide association studies (GWAS) were reanalyzed, resulting in the identification of 19 skeletal class II malocclusion-associated and 53 skeletal class III malocclusion-associated genes. Functional enrichment of these genes created a signal pathway atlas in which most of the genes were associated with bone and cartilage growth and development, as expected, while some were characterized by functions related to skeletal muscle maturation and construction. Interestingly, several genes and enriched pathways are involved in both skeletal class II and III malocclusions, indicating the key regulatory effects of these genes and pathways in craniofacial development. There is no doubt that further investigation is necessary to validate these recognized genes’ and pathways’ specific function(s) related to maxillary and mandibular development. In summary, this systematic review provides initial insight on developing novel gene-based treatment strategies for skeletal malocclusions and paves the path for precision medicine where dental care providers can make an accurate prediction of the craniofacial growth of an individual patient based on his/her genetic profile.

GHRH expression plasmid improves osteoporosis and skin damage in aged mice

The hormone secretion of GHRH-GH-IGF-1 axis in animals was decreased as aging. These hormones play an important role in maintaining bone mass and bone structure, and also affect the normal structure and function of the skin. We used plasmid-based technology to deliver growth hormone releasing hormone (GHRH) to elderly mice. In the current study, 80 and 120 μg/kg pVAX-GHRH plasmid expression plasmid were injected into old mice, the serum GHRH and insulin-like growth factor-1(IGF-1) content were increased within three weeks (P < 0.05). In the groups of 80 and 120 μg/kg plasmid, the content of procollagen type I N-terminal pro-peptide (PINP) in the serum was increased(P < 0.05), and the content of C-terminal telopeptides of type I collagen (CTX-1) in the serum was reduced significantly (P < 0.05). Furthermore, the expression of osteoprotegerin (OPG) and osteocalcin (OCN) in the femur also was increased(P < 0.05). The bone mineral density(BMD)、trabecular bone volume (BV/TV) and trabecular number(Tb.N) of mouse femur were increased significantly (P < 0.05) and trabecular separation(Tb.Sp) was decreased(P < 0.05). There were more trabecular bones in the bone marrow cavity and the trabecular bones are thicker in the groups of 80 and 120 μg/kg plasmid relative to control. The superoxide dismutase (SOD) content in the skin was increased(P < 0.05), and the malondialdehyde (MDA) content was reduced significantly (P < 0.05). Meanwhile, the skin moisture content also increased significantly(P < 0.05). Moreover, the expression of matrix metalloproteinase 3(MMP3) and matrix metalloproteinase 9(MMP9) was decreased in the skin(P < 0.05). The thickness of the dermis and epidermis of the skin had increased significantly(P < 0.05). Skin structure is more dense and complete in the two groups. These results indicate that 80 and 120 μg/kg plasmid-mediated GHRH supplementation can improve osteoporosis and skin aging in aged mice.

Omarigliptin Prevents TNF-α-Induced Cellular Senescence in Rat Aorta Vascular Smooth Muscle Cells

Cellular senescence is one of the most significant factors involved in aging and age-related diseases. Senescence of vascular smooth muscle cells (VSMCs) adversely affects the function of the cardiovascular system and contributes to the development of atherosclerosis, hypertension, and other cardiovascular diseases. Glucagon-like peptide-1 (GLP-1) is an important incretin hormone involved in insulin release and vascular tone. GLP-1 is quickly degraded by the enzyme dipeptidyl peptidase-4 (DPP-4). Omarigliptin is a new DPP-4 inhibitor that has demonstrated anti-inflammatory and antioxidative stress properties. In the present study, we investigated the effects of the selective DPP-4 inhibitor omarigliptin (OMG) on VSMCs exposed to insult from tumor necrosis factor-α (TNF-α), one of the main inflammatory signaling molecules involved in cellular senescence. We found that OMG could suppress TNF-α-induced expression of pro-inflammatory cytokines (interleukin-1β (IL-1β), IL-6, and IL-8) and inhibit oxidative stress by reducing the production of H2O2 and protein carbonyl. OMG ameliorated the increase in senescence-associated β-galactosidase (SA-β-gal) and telomerase activity induced by TNF-α. The plasminogen activator inhibitor-1 (PAI-1)/p53/p21 pathway is a key inducer of cellular senescence. OMG ameliorated the acetylation of p53 at lysine 382 (K382) and subsequent activation of p21 via inhibition of PAI-1. Importantly, our experiments revealed that blockage of silent information-regulator 1 (SIRT1) abolished the inhibitory effects of OMG on p53 acetylation, SA-β-gal activity, and telomerase activity in VSMCs. These results suggest that OMG may have the potential to delay or prevent the progression of age-related cardiovascular diseases by modulating the activity of SIRT1.

Regulation of the IGF1 signaling pathway is involved in idiopathic pulmonary fibrosis induced by alveolar epithelial cell senescence and core fucosylation

Idiopathic pulmonary fibrosis (IPF) mainly occurs in elderly people over the age of sixty. IPF pathogenesis is associated with alveolar epithelial cells (AECs) senescence. Activation of PI3K/AKT signaling induced by insulin-like growth factor 1 (IGF1) participates in AEC senescence and IPF by releasing CTGF, TGF-β1, and MMP9. Our previous study demonstrated that core fucosylation (CF) modification, catalyzed by a specific core fucosyltransferase (FUT8) can regulate the activation of multiple signaling pathways, and inhibiting CF can alleviate pulmonary fibrosis in mice induced by bleomycin. However, whether CF is involved in IGF1-mediated AEC senescence in IPF remains unclear. In this study, we found that the IGF1/PI3K/AKT signaling pathway was activated in IPF lung tissue. Meanwhile, CF was present in senescent AECs. We also showed that IGF1 could induce AECs senescence with enhanced CF in vivo and in vitro. Inhibiting CF alleviated AECs senescence and pulmonary fibrosis induced by IGF1. In addition, activation of IGF1/PI3K/AKT signaling depends on CF. In conclusion, this study confirmed that CF is an important target regulating the IGF1 signaling pathway in AEC senescence and IPF, which might be a candidate target to treat IPF in the future.

Metabolomic analysis to elucidate the change of the n-3 polyunsaturated fatty acids in senescent osteoblasts

Senile osteoporosis is a major public health concern, and yet, effective treatment methods do not exist. Herein, we used metabolomics to analyze the change of n-3 polyunsaturated fatty acids (PUFA) in senescent osteoblasts. We found that with an increase in the number of passages, the osteoblasts proliferative ability, alkaline phosphatase activity, and expression levels of bone metabolism genes decreased, the expression levels of aging-related genes increased, the damage caused by oxidative stress became more severe. Furthermore, levels of n-3 PUFA family members were downregulated in passage 10 than in passage 3 osteoblasts. These findings indicated that multiple passages led to more severe oxidative stress damage in senescent osteoblasts, which could be related to a decrease in n-3 PUFA levels. We believe that unsaturated fatty acid metabolism is a key factor involved in osteoblast senescence and that a proper dietary intake of n-3 PUFA may delay the occurrence senile osteoporosis.

A quinoxaline-based compound ameliorates bone loss in ovariectomized mice

DMB (6,7-dichloro-2-methylsulfonyl-3-Ntert-butylaminoquinoxaline) is a quinoxaline-based compound that has been investigated as a glucagon-like peptide-1 receptor (GLP-1R) agonist. To clarify anti-osteoporosis effect of DMB, an osteoporotic mice model was established by ovariectomy (OVX) operation. The OVX mice were given intraperitoneally DMB, exendin-4 (EX-4), or 17β-estradiol (E₂) for two months. Then bone mass and structure, and bone morphometric parameters were examined by micro-CT. Weight gain and food consumption, bone turnover markers, and biomechanical strength of the femur were tested, and bone histomorphometry was analyzed. The food intake and weight gain was obviously reduced by E₂ or EX-4, but not DMB. However, DMB or EX-4 treatment obviously inhibited skeletal deterioration and enhanced bone strength. The improvement involved in the increased osteoblast number and level of bone formation markers, and reduced osteoclasts number and level of bone resorption markers. In addition, DMB was found to stimulate osteoblastogenesis-related marker gene expression. These results demonstrated that DMB ameliorated bone loss mainly via induction of bone formation, which suggests that the small molecule compound might be applied to the management of postmenopausal osteoporosis.

The Impact of Glucagon-Like Peptide 1 Receptor Agonists on Bone Metabolism and Its Possible Mechanisms in Osteoporosis Treatment

Diabetes mellitus and osteoporosis are closely related and have complex influencing factors. The impact of anti-diabetic drugs on bone metabolism has received more and more attention. Type 2 diabetes mellitus (T2DM) would lead to bone fragility, high risk of fracture, poor bone repair and other bone-related diseases. Furthermore, hypoglycemic drugs used to treat T2DM may have notable detrimental effects on bones. Thus, the clinically therapeutic strategy for T2DM should not only effectively control the patient's glucose levels, but also minimize the complications of bone metabolism diseases. Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are novel and promising drug for the treatment of T2DM. Some studies have found that GLP-1RAs may play an anti-osteoporotic effect by controlling blood sugar levels, promoting bone formation and inhibiting bone resorption. However, in clinical practice, the specific effects of GLP-1RA on fracture risk and osteoporosis have not been clearly defined and evidenced. This review summarizes the current research findings by which GLP-1RAs treatment of diabetic osteoporosis, postmenopausal osteoporosis and glucocorticoid-induced osteoporosis and describes possible mechanisms, such as GLP-1R/MAPK signaling pathway, GLP-1R/PI3K/AKT signaling pathway and Wnt/β-catenin pathway, that are associated with GLP-1RAs and osteoporosis. The specific role and related mechanisms of GLP-1RAs in the bone metabolism of patients with different types of osteoporosis need to be further explored and clarified.

Loureirin B activates GLP-1R and promotes insulin secretion in Ins-1 cells

Loureirin B (LB) is a natural product derived from Sanguis draconis, which has hypoglycaemic effects. In order to research the possible target of LB in the treatment of diabetes, molecular docking was used to simulate the interaction between LB and potential targets, and among them, glucagon‐like peptide‐1 receptor (GLP‐1R) had the optimal results. Further, spectroscopy and surface plasmon resonance (SPR) experiments were applied to detect the interaction between LB and GLP‐1R. Ultimately, after GLP‐1R siRNA interfering the expression of GLP‐1R in Ins‐1 cell, the promoting insulin secretion of LB was weaken, which directly proved that GLP‐1R plays an important role. These results show that LB promotes insulin secretion of Ins‐1 cells through GLP‐1R. Hence, the strategy of LB as a prodrug will provide a potential approach for non‐peptide GLP‐1R agonist.