Biphasic regulation of osteoblast development via the ERK MAPK-mTOR pathway

Nonessential amino acid is not nonessential in geriatric patients: implications for maxillofacial wound healing and bone repair

BACKGROUND

Nonessential amino acids (NEAAs) are traditionally regarded as dispensable because they can be synthesized endogenously from glucose-derived intermediates. Emerging evidence, however, shows that the capacity for de novo NEAA biosynthesis declines in aged tissues, rendering several of these molecules conditionally essential during periods of stress such as surgery or fracture repair.

MAIN BODY

In the cranio-maxillofacial arena - where bone and soft-tissue regeneration must occur in an environment already compromised by osteoporosis, multimorbidity, and restricted oral intake - insufficient NEAA supply may translate into delayed union, wound dehiscence, and heightened infection risk. This narrative review integrates biochemical, preclinical, and clinical data to map age-dependent changes in the serine/glycine, glutamine/glutamate, arginine/citrulline, cysteine/trans-sulfuration, and alanine cycles, examines their impact on osteogenesis and mucosal healing, and evaluates nutritional or pharmacological strategies to restore NEAA sufficiency. Particular attention is paid to serine-one-carbon metabolism, the intestinal-renal arginine axis, and redox-sensitive cysteine pathways, all of which are intimately linked to collagen deposition, osteoblast differentiation, and immune modulation.

CONCLUSION

We conclude that proactive optimization of NEAA status - through targeted supplementation or metabolic activation - represents a low-risk, biologically rational adjunct to enhance postoperative outcomes in geriatric maxillofacial patients.

Molecular Evidence Supporting MEK Inhibitor Therapy in NF1 Pseudarthrosis

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic condition predisposing children to fracture pseudarthroses. MEK inhibitors are U.S. Food and Drug Administration-approved or are under study for the treatment of malignant pathologies associated with NF1. However, their potential to treat pseudarthrosis is largely unknown.

METHODS

Primary cells cultured from control bone or fracture pseudarthroses from children with NF1 were treated with vehicle or with the MEK inhibitors trametinib or selumetinib. Gene expression was evaluated with use of transcriptome sequencing (RNAseq), and the activation of the downstream signaling pathway was evaluated with use of western blotting. Results were replicated in an independent cohort of patient fracture pseudarthrosis-derived primary cells.

RESULTS

Pseudarthrosis samples were reproducibly associated with the reduced expression of gene signatures implicated in osteoblast differentiation, skeletal development, and the formation of the extracellular matrix. The expression of these gene signatures was significantly rescued following treatment with MEK inhibitors and concomitant reduced MEK/ERK (MAPK) pathway activation.

CONCLUSIONS

Our study identified molecular signatures associated with fracture pseudarthrosis that were rescued with MEK inhibitor treatment.

CLINICAL RELEVANCE

MEK inhibitors may promote the healing of fracture pseudarthroses in children with NF1.

Unraveling the Potential of SGK1 in Osteoporosis: From Molecular Mechanisms to Therapeutic Targets

Osteoporosis (OP) is a prevalent metabolic bone disease, with several million cases of fractures resulting from osteoporosis worldwide each year. This phenomenon contributes to a substantial increase in direct medical expenditures and poses a considerable socioeconomic burden. Despite its prevalence, our understanding of the underlying mechanisms remains limited. Recent studies have demonstrated the involvement of serum glucocorticoid-regulated protein kinase 1 (SGK1) in multiple signaling pathways that regulate bone metabolism and its significant role in the development of osteoporosis. Therefore, it is of great significance to deeply explore the mechanism of SGK1 in osteoporosis and its therapeutic potential. In this paper, we present a comprehensive review of the structure and activation mechanism of SGK1, its biological function, the role of SGK1 in different types of osteoporosis, and the inhibitors of SGK1. The aim is to comprehensively assess the latest research progress with regards to SGK1's role in osteoporosis, clarify its role in the regulation of bone metabolism and its potential as a therapeutic target, and lay the foundation for the development of novel therapeutic strategies and personalized treatment in the future. Furthermore, by thoroughly examining the interactions between SGK1 and other molecules or signaling pathways, potential biomarkers may be identified, thereby enhancing the efficacy of early screening and intervention for osteoporosis.

Effective mechanism of polysaccharides from Erxian herbal pair in promoting bone repair in traumatic osteomyelitis by activating osteoblast GPR41 and inhibiting the MEK/ERK/MAPK signalling axis

Polysaccharides are the key components of natural products; however, their effects on bone repair haven't been fully evaluated. This study aimed to assess the efficacy and mechanism of polysaccharides in promoting bone repair. The Erxian herb pair polysaccharide (EHP) was isolated and purified using water extraction (1:20 (w/v); 100 ± 2 °C; 5 h) and alcohol precipitation (80 ± 2 %). A traumatic osteomyelitis (TO) rat model was established using lipopolysaccharide (LPS). The gut microbiota was analysed through intestinal flora and metagenomic sequencing. The results revealed that the yields of crude polysaccharide and purified polysaccharide EHP were 3.73 ± 0.34 % and 0.48 ± 0.06 %, respectively. The total sugar content of EHP was 83.53 ± 0.16 %. The EHP, with a molecular weight of 31.964 kDa, was primarily composed of mannose, rhamnose, glucose, galactose, and arabinose. In vivo experiments demonstrated that EHP intervention (300 mg/kg/day) significantly augmented bone density and enhanced the activity of alkaline phosphatase (ALP) (P < 0.01). EHP upregulated the abundance of probiotics and increased the production of butyric acid (P < 0.05). In vitro experiments revealed that butyric acid (500-1000 μM) enhanced osteoblast activity and inhibited the expression of mitogen-activated protein kinase kinase (MEK) and extracellular signal-regulated kinase (ERK) (P < 0.01). These findings indicate that polysaccharides may represent a promising therapeutic agent for bone-healing.

[4‑(Arylethyl)‑pyrrolo[2,3-d] pyrimidine improves post-traumatic stress disorder in mice by inhibiting mGluR5-regulated ERK1/2-SGK1 signaling pathway]

OBJECTIVES

To observe the effect of 4-(arylethynyl)-pyrrolo[2,3-d] pyrimidine (10b) on post-traumatic stress disorder (PTSD)-like behaviors and ERK1/2-SGK1 signaling pathway in mice.

METHODS

C57BL/6 mouse models exposed to single prolonged stress (SPS) were treated with daily gavage of saline, 10b at low, moderate and high doses, or paroxetine for 14 days. The changes in PTSD-like behaviors of SPS mice with different treatments were observed using behavioral tests. Western blotting and immunofluorescence assay were used to detect the protein expression levels of mGluR5, p-ERK, and SGK1 in the hippocampus of the mice. Pathological changes in the liver and kidney tissues of the mice were examined using HE staining. Molecular docking and molecular dynamics analyses were employed to evaluate the binding stability between the compound 10b and mGluR5.

RESULTS

Compared to the normal control mice, the SPS mice exhibited obvious PTSD-like behaviors with increased hippocampal expressions of mGluR5 and p-ERK proteins and decreased SGK1 protein expression. Compound 10b significantly ameliorated behavioral abnormalities in SPS mice, inhibited mGluR5 expression, and reversed the dysregulation of p-ERK and SGK1. No obvious liver or kidney toxicity was observed after 10b treatment. Molecular docking and dynamics studies demonstrated a stable interaction between 10b and mGluR5.

CONCLUSIONS

The compound 10b ameliorates PTSD-like behaviors induced by SPS in mice possibly by inhibiting mGluR5 expression to modulate the ERK1/2-SGK1 signaling pathway.

Knockdown of IER3 Promotes Osteogenic Differentiation of Human Mesenchymal Stem Cells

Background: The differentiation process of human mesenchymal stem cells (hMSCs) is regulated by a variety of chemical, physical, and biological factors. These factors activate distinct signaling pathways and transcriptional networks, thereby regulating the lineage-specific differentiation of hMSCs. Objective: This study aims to investigate the role of Immediate Early Response 3 (IER3) in the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and explore the underlying regulatory mechanisms by which IER3 influences osteogenesis. Methods: The expression levels of IER3 and osteogenesis-related genes were quantified when hMSCs were subjected to in vitro osteogenic induction. Then, stable IER3-knockdown hMSCs were generated using IER3-targeted shRNA lentiviral vectors, and the impact of IER3 on osteogenic differentiation was evaluated through both in vitro cell induction and hMSCs subcutaneous implantation model of nude mice. Moreover, RNA-seq and functional inhibition assays were performed to elucidate the signaling pathway through which IER3 regulates the osteogenic differentiation of hMSCs. Results: IER3 expression was significantly downregulated during osteogenic differentiation. Knockdown of IER3 markedly upregulated the expression of ALP and RUNX2, enhancing the osteogenic differentiation capacity of hMSCs, both in vitro and in vivo. Mechanistic studies revealed that IER3 knockdown significantly increased phosphorylated ERK1/2 levels, activating the MAPK/ERK signaling pathway. Furthermore, inhibition of the MAPK/ERK signaling pathway reversed the enhanced osteogenic differentiation observed following IER3 knockdown. Conclusions: Knockdown of IER3 promotes osteogenic differentiation of hMSCs through regulation of the MAPK/ERK signaling pathway, indicating IER3 represents a potential therapeutic target for the treatment of osteoporosis and bone defect-related diseases.

MK-4 Ameliorates Diabetic Osteoporosis in Angiogenesis-Dependent Bone Formation by Promoting Mitophagy in Endothelial Cells

Purpose

Diabetic osteoporosis (DOP), one of the usual complications in diabetic patients, poses a significant threat to bone health. Type H vessels in metaphysis and medial cortical bone are associated with osteogenesis. As a form of Vitamin K2, menaquinone-4 (MK-4) is a potential treatment for osteoporosis. We aimed to investigate whether MK-4 ameliorates DOP by promoting bone formation through protecting type H vessels and its associated mechanisms.

Methods

High fat diet (HDF) feeding and streptozotocin (STZ) injection were applied to establish a mouse model of type 2 diabetic osteoporosis (T2DOP). Micro-CT, Masson staining, HE staining and IHC staining were applied to observe bone mass and the osteoblastic ability of osteoblasts. Tissue immunofluorescence (IF) staining and flow cytometry were employed to assess alteration of type H blood vessels. In vitro, to evaluate the functional level and mitophagy of ECs under high glucose conditions, wound healing assay, tube formation assay, EdU assay and IF were employed. Osteogenic differentiation ability in vitro was evaluated by ALP staining, AR staining, Western blot and RT-qPCR.

Results

MK-4 alleviated type H vessel injury and angiogenesis-dependent osteogenesis in DOP mice, thereby maintaining the bone mass. The vitro results showed that MK-4 could mitigate the dysfunction of ECs subjected to HG treatment, and further facilitate the osteogenic differentiation of MC3T3-E1 cells. Moreover, mechanism exploration found that PINK1/Parkin-mediated mitophagy was required for the impact of MK-4 on ECs. Meanwhile, ERK signal pathway is necessary for the improvement of MK-4 in PINK1/Parkin-mediated mitophagy.

Conclusion

MK-4 is capable of alleviating the PINK1/Parkin-mediated mitophagy of ECs via the ERK pathway, thereby facilitating angiogenesis-dependent bone formation and further ameliorating DOP.

Investigating the Role of Shikonin in Enhancing Osteogenesis and Angiogenesis for the Treatment of Osteoporosis

Osteoporosis, characterized by an increased risk of fractures, represents a significant global public health issue. Natural compounds have emerged as promising candidates for addressing this condition. Shikonin, derived from Lithospermum erythrorhizon as a purple-red naphthoquinone pigment, exhibits a diverse array of biological activities, including antibacterial, anti-inflammatory, and anticancer properties. Despite the well-documented bone-protective properties of shikonin, the precise molecular mechanisms underlying its role in the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) into osteoblasts, along with its implications on angiogenesis, are not fully elucidated. Our study showcases shikonin's ability to stimulate the differentiation of BMSCs into osteoblasts, leading to an upregulation of osteoblast-specific marker genes such as OC, Runx2, BMP2, and ALP. Furthermore, shikonin intervention triggers the upregulation of phosphorylation of p38, ERK, and JNK in the MAPK signaling pathway. Furthermore, shikonin has been shown to enhance the migration and angiogenic capabilities of human umbilical vein endothelial cells (HUVECs). Notably, the augmentation of HUVEC migration by shikonin can be counteracted by the addition of a JNK inhibitor. Furthermore, our findings indicate that shikonin effectively improves osteoporosis in aged mice by promoting osteoblast differentiation. In summary, our study elucidates the molecular mechanisms through which shikonin exerts its beneficial effects in the treatment of osteoporosis, highlighting its potential as a novel therapeutic option for both the prevention and management of this condition.

Valorization of fishery byproducts: Large-scale production of olive flounder functional protein ingredients and their effects on muscle regeneration

Use of olive flounder byproducts, which constitute nearly 50 % of the total fish mass, offers a promising strategy for maximizing protein-rich resources.In this study, we optimized a Prozyme 2000P® enzyme-assisted olive flounder byproduct hydrolysate (OFBP) for large-scale production using response surface methodology and evaluated its efficacy in muscle-atrophy models. The final OFBP exhibited 87.5 % protein content, with over 60 % of peptides under 700 Da, promoting high bioavailability and absorption. In vitro, OFBP (300 µg/mL) enhanced de novo protein synthesis in murine C2C12 myotubes by more than two-fold compared with the untreated control (p < 0.05). In a zebrafish model of dexamethasone-induced muscle atrophy, 1 % OFBP supplementation restored up to 80 % of normal activity levels and significantly increased muscle cross-sectional area relative to atrophic controls (p < 0.05). Lipidomic analysis further revealed that dexamethasone-associated elevations in ceramide and sphingomyelin were downregulated by OFBP, indicating a protective effect on sphingolipid metabolism. Taken together, these findings demonstrate that enzymatic hydrolysis of fish byproducts can yield a nutritionally rich ingredient that not only mitigates muscle atrophy through enhanced protein synthesis but also modulates lipid homeostasis. This work highlights OFBP as a sustainable, functional food candidate for supporting muscle health and addressing waste-utilization needs.

Impaired MC3T3-E1 osteoblast differentiation triggered by oncogenic HRAS is rescued by the farnesyltransferase inhibitor Tipifarnib

HRAS is a ubiquitously expressed protein and functions as a central regulator of cellular homeostasis. In somatic cells, mutations in this gene cause cancer, while germline mutations trigger a developmental disorder known as Costello syndrome (CS). Among numerous pathologies, adult CS patients develop osteoporosis. Previous studies revealed that HRAS is implicated in bone homeostasis by controlling osteoblast differentiation, adaptation to mechanical strain and repression of RANKL expression in mature osteoblasts, and by regulating osteoclast differentiation. However, the impact of HRAS on osteoblast differentiation is still debatable. In this study, we created stable doxycycline inducible cell lines overexpressing HRAS G12 mutants in MC3T3-E1 preosteoblast cell line and analyzed their impact on osteoblast differentiation. We demonstrated an inhibitory role of HRAS G12S and HRAS G12V mutants on osteogenic differentiation and identified an increased expression of Opn in an HRAS-dependent manner, which directly correlated with impaired osteogenesis, and was rescued by the farnesyl transferase inhibitor Tipifarnib. At the molecular level, Tipifarnib was not able to block HRAS activation, but impaired HRAS localization to the plasma membrane, and inhibited MAPK activation and Opn expression. Thus, HRAS abundance/activation and its potential crosstalk with OPN may be more critical for osteogenic differentiation than previously assumed.

Unraveling the Mechanism of Impaired Osteogenic Differentiation in Osteoporosis: Insights from ADRB2 Gene Polymorphism

Osteoporosis is characterized by increased resorption and decreased bone formation; it is predominantly influenced by genetic factors. G-protein coupled receptors (GPCRs) play a vital role in bone homeostasis, and mutations in these genes are associated with osteoporosis. This study aimed to investigate the impact of single nucleotide polymorphism (SNP) rs1042713 in the ADRB2 gene, encoding the beta-2-adrenergic receptor, on osteoblastogenesis. Herein, using quantitative polymerase chain reaction, western immunoblotting, immunofluorescence assays, and flow cytometry, we examined the expression of ADRB2 and markers of bone matrix synthesis in mesenchymal stem cells (MSCs) derived from osteoporosis patient (OP-MSCs) carrying ADRB2 SNP in comparison with MSCs from healthy donor (HD-MSCs). The results showed significantly reduced ADRB2 expression in OP-MSCs at both the mRNA and protein levels, alongside decreased type 1 collagen expression, a key bone matrix component. Notably, OP-MSCs exhibited increased ERK kinase expression during differentiation, indicating sustained cell cycle progression, unlike that going to HD-MSC. These results provide novel insights into the association of ADRB2 gene polymorphisms with osteogenic differentiation. The preserved proliferative activity of OP-MSCs with rs1042713 in ADRB2 contributes to their inability to undergo effective osteogenic differentiation. This research suggests that targeting genetic factors may offer new therapeutic strategies to mitigate osteoporosis progression.

Bitter acids from Humulus lupulus L. alleviate D-galactose induced osteoblastic senescence and bone loss via regulating AKT/mTOR-mediated autophagy

Bitter acids (BA) are main component of Humulus lupulus L. (hops). They are known for beer brewing and have various biological and pharmacological properties, especially the bone-protective effect confirmed by our previous in vivo study. Here we aimed to elucidate the anti-senior osteoporosis (SOP) effect of BA on osteoblasts and explore its underlying mechanism. In vitro SOP model was established by D-galactose (D-gal) injured osteoblasts, and the bone formation markers and apoptosis level were measured. mCherry-EGFP-LC3 adenovirus infection and autophagic markers including beclin1 and LC3 proteins were detected to investigate the autophagy level in osteoblasts. To further verify whether BA play the bone-protective role through regulating autophagy, the autophagy inhibitor 3-MA was used, and the cell proliferation, ALP activity, bone mineralization, apoptosis rate and SA-β-gal staining areas were measured. Finally, the protein expressions of AKT/mTOR signaling pathway were detected by Western blotting, and AKT agonist SC79 and mTOR agonist MHY1485 were used to further study the mechanism of BA on AKT/mTOR-mediated autophagy. The results showed that BA stimulated osteoblastic differentiation and inhibited apoptosis proteins Bcl-2/Bax in D-gal-treated osteoblasts. BA also increased the expression of autophagic markers beclin1 and LC3-II/LC3-I in D-gal-treated osteoblasts. mCherry-EGFP-LC3 autophagic double fluorescent adenovirus showed BA promoted the generation of autolysosomes and autophagosomes in D-gal-injured osteoblasts, indicating that BA might prevent osteoblastic bone loss through activating autophagy. Autophagy inhibitor 3-MA was used to further verify whether BA played the bone-protective role via regulating autophagy. The results revealed the promotion effects of BA on proliferation, ALP activity, and mineralized nodule formation in D-gal-injured osteoblasts were eliminated after autophagy blocking with 3-MA, and the inhibitory effects of BA on apoptosis rate and SA-β-gal staining areas were also eliminated. Moreover, BA reduced the phosphorylation levels of AKT, mTOR, p70S6K, and 4EBP in AKT/mTOR pathway, and the promotion of BA on the autophagic markers was blocked after the activation of AKT and mTOR by SC79 and MHY1485. In conclusion, it was the first time to demonstrate that BA improved cell activities and bone formation in aging osteoblasts, and revealed the mechanism of BA against SOP in osteoblasts was activating AKT/mTOR-mediated autophagy.

Sex hormone-binding globulin promotes the osteogenic differentiation potential of equine adipose-derived stromal cells by activating the BMP signaling pathway

Background

Musculoskeletal injuries and chronic degenerative diseases pose significant challenges in equine health, impacting performance and overall well-being. Sex Hormone-Binding Globulin (SHBG) is a glycoprotein determining the bioavailability of sex hormones in the bloodstream, and exerting critical metabolic functions, thus impacting the homeostasis of many tissues including the bone.

Methods

In this study, we investigated the potential role of SHBG in promoting osteogenesis and its underlying mechanisms in a model of equine adipose-derived stromal cells (ASCs). An SHBG-knocked down model has been established using predesigned siRNA, and cells subjected to osteogenic induction medium in the presence of exogenous SHBG protein. Changes in differentiation events where then screened using various analytical methods.

Results

We demonstrated that SHBG treatment enhances the expression of key osteoconductive regulators in equine ASCs CD34+ cells, suggesting its therapeutic potential for bone regeneration. Specifically, SHBG increased the cellular expression of BMP2/4, osteocalcin (OCL), alkaline phosphatase (ALP), and osteopontin (OPN), crucial factors in early osteogenesis. Furthermore, SHBG treatment maintained adequate apoptosis and enhanced autophagy during osteogenic differentiation, contributing to bone formation and remodeling. SHBG further targeted mitochondrial dynamics, and promoted the reorganization of the mitochondrial network, as well as the expression of dynamics mediators including PINK, PARKIN and MFN1, suggesting its role in adapting cells to the osteogenic milieu, with implications for osteoblast maturation and differentiation.

Conclusion

Overall, our findings provide novel insights into SHBG's role in bone formation and suggest its potential therapeutic utility for bone regeneration in equine medicine.

Paeoniflorin protects hepatocytes from APAP-induced damage through launching autophagy via the MAPK/mTOR signaling pathway

BACKGROUND

Drug-induced liver injury (DILI) is gradually becoming a common global problem that causes acute liver failure, especially in acute hepatic damage caused by acetaminophen (APAP). Paeoniflorin (PF) has a wide range of therapeutic effects to alleviate a variety of hepatic diseases. However, the relationship between them is still poorly investigated in current studies.

PURPOSE

This work aimed to explore the protective effects of PF on APAP-induced hepatic damage and researched the potential molecular mechanisms.

METHODS

C57BL/6J male mice were injected with APAP to establish DILI model and were given PF for five consecutive days for treatment. Aiming to clarify the pharmacological effects, the molecular mechanisms of PF in APAP-induced DILI was elucidated by high-throughput and other techniques.

RESULTS

The results demonstrated that serum levels of ALP, γ-GT, AST, TBIL, and ALT were decreased in APAP mice by the preventive effects of PF. Moreover, PF notably alleviated hepatic tissue inflammation and edema. Meanwhile, the results of TUNEL staining and related apoptotic factors coincided with the results of transcriptomics, suggesting that PF inhibited hepatocyte apoptosis by regulated MAPK signaling. Besides, PF also acted on reactive oxygen species (ROS) to regulate the oxidative stress for recovery the damaged mitochondria. More importantly, transmission electron microscopy showed the generation of autophagosomes after PF treatment, and PF was also downregulated mTOR and upregulated the expression of autophagy markers such as ATG5, ATG7, and BECN1 at the mRNA level and LC3, p62, ATG5, and ATG7 at the protein level, implying that the process by which PF exerted its effects was accompanied by the occurrence of autophagy. In addition, combinined with molecular dynamics simulations and western blotting of MAPK, the results suggested p38 as a direct target for PF on APAP. Specifically, PF-activated autophagy through the downregulation of MAPK/mTOR signaling, which in turn reduced APAP injury.

CONCLUSIONS

Paeoniflorin mitigated liver injury by activating autophagy to suppress oxidative stress and apoptosis via the MAPK/mTOR signaling pathway. Taken together, our findings elucidate the role and mechanism of paeoniflorin in DILI, which is expected to provide a new therapeutic strategy for the development of paeoniflorin.

Skeletal health in DYRK1A syndrome

DYRK1A syndrome results from a reduction in copy number of the DYRK1A gene, which resides on human chromosome 21 (Hsa21). DYRK1A has been implicated in the development of cognitive phenotypes associated with many genetic disorders, including Down syndrome (DS) and Alzheimer's disease (AD). Additionally, overexpression of DYRK1A in DS has been implicated in the development of abnormal skeletal phenotypes in these individuals. Analyses of mouse models with Dyrk1a dosage imbalance (overexpression and underexpression) show skeletal deficits and abnormalities. Normalization of Dyrk1a copy number in an otherwise trisomic animal rescues some skeletal health parameters, and reduction of Dyrk1a copy number in an otherwise euploid (control) animal results in altered skeletal health measurements, including reduced bone mineral density (BMD) in the femur, mandible, and skull. However, little research has been conducted thus far on the implications of DYRK1A reduction on human skeletal health, specifically in individuals with DYRK1A syndrome. This review highlights the skeletal phenotypes of individuals with DYRK1A syndrome, as well as in murine models with reduced Dyrk1a copy number, and provides potential pathways altered by a reduction of DYRK1A copy number, which may impact skeletal health and phenotypes in these individuals. Understanding how decreased expression of DYRK1A in individuals with DYRK1A syndrome impacts bone health may increase awareness of skeletal traits and assist in the development of therapies to improve quality of life for these individuals.

The absence of the ribosomal protein Rpl2702 elicits the MAPK-mTOR signaling to modulate mitochondrial morphology and functions

Ribosomes mediate protein synthesis, which is one of the most energy-demanding activities within the cell, and mitochondria are one of the main sources generating energy. How mitochondrial morphology and functions are adjusted to cope with ribosomal defects, which can impair protein synthesis and affect cell viability, is poorly understood. Here, we used the fission yeast Schizosaccharomyces Pombe as a model organism to investigate the interplay between ribosome and mitochondria. We found that a ribosomal insult, caused by the absence of Rpl2702, activates a signaling pathway involving Sty1/MAPK and mTOR to modulate mitochondrial morphology and functions. Specifically, we demonstrated that Sty1/MAPK induces mitochondrial fragmentation in a mTOR-independent manner while both Sty1/MAPK and mTOR increases the levels of mitochondrial membrane potential and mitochondrial reactive oxygen species (mROS). Moreover, we demonstrated that Sty1/MAPK acts upstream of Tor1/TORC2 and Tor1/TORC2 and is required to activate Tor2/TORC1. The enhancements of mitochondrial membrane potential and mROS function to promote proliferation of cells bearing ribosomal defects. Hence, our study reveals a previously uncharacterized Sty1/MAPK-mTOR signaling axis that regulates mitochondrial morphology and functions in response to ribosomal insults and provides new insights into the molecular and physiological adaptations of cells to impaired protein synthesis.

The IFITM5 mutation in osteogenesis imperfecta type V is associated with an ERK/SOX9-dependent osteoprogenitor differentiation defect

Osteogenesis imperfecta (OI) type V is the second most common form of OI, distinguished by hyperplastic callus formation and calcification of the interosseous membranes, in addition to the bone fragility. It is caused by a recurrent, dominant pathogenic variant (c.-14C>T) in interferon-induced transmembrane protein 5 (IFITM5). Here, we generated a conditional Rosa26-knockin mouse model to study the mechanistic consequences of the recurrent mutation. Expression of the mutant Ifitm5 in osteo-chondroprogenitor or chondrogenic cells resulted in low bone mass and growth retardation. Mutant limbs showed impaired endochondral ossification, cartilage overgrowth, and abnormal growth plate architecture. The cartilage phenotype correlates with the pathology reported in patients with OI type V. Surprisingly, expression of mutant Ifitm5 in mature osteoblasts caused no obvious skeletal abnormalities. In contrast, earlier expression in osteo-chondroprogenitors was associated with an increase in the skeletal progenitor cell population within the periosteum. Lineage tracing showed that chondrogenic cells expressing the mutant Ifitm5 had decreased differentiation into osteoblastic cells in diaphyseal bone. Moreover, mutant IFITM5 disrupted early skeletal homeostasis in part by activating ERK signaling and downstream SOX9 protein, and inhibition of these pathways partially rescued the phenotype in mutant animals. These data identify the contribution of a signaling defect altering osteo-chondroprogenitor differentiation as a driver in the pathogenesis of OI type V.

[Zinc finger protein-36 deficiency inhibits osteogenic differentiation of mouse bone marrow-derived mesenchymal stem cells and preosteoblasts by activating the ERK/MAPK pathway]

OBJECTIVE

To explore the role of zinc finger protein 36(ZFP36) in regulating osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and preosteoblasts.

METHODS

ZFP36 expression was observed in primary mouse BMSCs and mouse preosteoblasts (MC3T3-E1 cells) during induced osteogenic differentiation. Zfp36-deficient cell models were constructed in the two cells using RNA interference technique and the changes in differentiation capacities of the transfected cells into osteoblasts were observed. Transcriptome sequencing was used to investigate the potential mechanisms of ZFP36 for regulating osteoblast differentiation of the two cells. U0126, a ERK/MAPK signal suppressor, was used to verify the regulatory mechanism of Zfp36 in osteogenic differentiation of Zfp36-deficient cells.

RESULTS

During the 14-day induction of osteogenic differentiation, both mouse BMSCs and MC3T3-E1 cells exhibited increased expression of ZFP36, and its mRNA expression reached the peak level on Day 7(P < 0.0001). The Zfp36-deficient cell models showed reduced intensity of alkaline phosphatase (ALP) staining and alizarin red staining with significantly lowered expressions of the osteogenic marker genes including Alpl, Sp7, Bglap and Ibsp (P < 0.01). Transcriptome sequencing verified the reduction of bone mineralization-related gene expressions in Zfp36-deficient cells and indicated the involvement of ERK signaling in the potential regulatory mechanism of Zfp36. Immunoblotting showed that pERK protein expression increased significantly in Zfp36-deficient cells compared with the control cells. In Zfp36-deficient MC3T3-E1 cells, inhibition of activated ERK/MAPK signaling with U0126 resulted in obviously enhanced ALP staining and significantly increased expressions of osteoblast differentiation markers Runx2 and Bglap (P < 0.05).

CONCLUSIONS

ZFP36 is involved in the regulation of osteoblast differentiation of mouse BMSCs and preosteoblasts, and ZFP36 deficiency causes inhibition of osteoblast differentiation of the cells by activating the ERK/MAPK signaling pathway.

Apoptotic Vesicles Derived from Dental Pulp Stem Cells Promote Bone Formation through the ERK1/2 Signaling Pathway

Osteoporosis is a common degenerative bone disease. The treatment of osteoporosis remains a clinical challenge in light of the increasing aging population. Human dental pulp stem cells (DPSCs), a type of mesenchymal stem cells (MSCs), are easy to obtain and have a high proliferation ability, playing an important role in the treatment of osteoporosis. However, MSCs undergo apoptosis within a short time when used in vivo; therefore, apoptotic vesicles (apoVs) have attracted increasing attention. Currently, the osteogenic effect of DPSC-derived apoVs is unknown; therefore, this study aimed to determine the role of DPSC-derived apoVs and their potential mechanisms in bone regeneration. We found that MSCs could take up DPSC-derived apoVs, which then promoted MSC osteogenesis in vitro. Moreover, apoVs could increase the trabecular bone count and bone mineral density in the mouse osteoporosis model and could promote bone formation in rat cranial defects in vivo. Mechanistically, apoVs promoted MSC osteogenesis by activating the extracellular regulated kinase (ERK)1/2 signaling pathway. Consequently, we propose a novel therapy comprising DPSC-derived apoVs, representing a promising approach to treat bone loss and bone defects.

PTH 1-34 reduced apoptosis of MLO-Y4 osteocyte-like cells by activating autophagy and inhibiting ER stress under RPM conditions

Osteocytes, as mechanosensitive cells residing within bone tissue, hold a pivotal role in averting the occurrence and progression of osteoporosis. The apoptosis of osteocytes induced by unloading is one of the contributing factors to osteoporosis, although the underlying molecular mechanisms have not been fully elucidated. PTH 1-34 is known to promote bone formation and inhibit bone loss by targeting osteoblasts and osteocytes. However, it is not known whether PTH 1-34 can inhibit osteocyte apoptosis under unloading conditions and the molecular mechanisms involved. In this study, we employed a Random Positioning Machine (RPM) to emulate unloading conditions and cultured MLO-Y4 osteocyte-like cells, in order to unravel the mechanisms through which PTH 1-34 constrains osteocyte apoptosis amidst unloading circumstances. Our findings revealed that PTH 1-34 activated autophagy while suppressing endoplasmic reticulum stress by curtailing the generation of reactive oxygen species (ROS) in MLO-Y4 osteocyte-like cells during unloading conditions. By shedding light on the osteoporosis triggered by skeletal unloading, this study contributes vital insights that may pave the way for the development of pharmacological interventions.

Modulation of the pre-metastatic bone niche: molecular changes mediated by bone-homing prostate cancer extracellular vesicles

Prostate cancer (PCa) is a leading male malignancy worldwide, often progressing to bone metastasis, with limited curative options. Extracellular vesicles (EVs) have emerged as key players in cancer communication and metastasis, promoting the formation of supportive microenvironments in distant sites. Our previous studies have highlighted the role of PCa EVs in modulating osteoblasts and facilitating tumor progression. However, the early pre-metastatic changes induced by PCa EVs within the bone microenvironment remain poorly understood. To investigate the early effects of repeated exposure to PCa EVs in vivo, mimicking EVs being shed from the primary tumor, PCa EVs isolated from cell line PC3MLuc2a were fluorescently labelled and repeatedly administered via tail vein injection to adult CD1 NuNu male mice for a period of 4 weeks. In vivo imagining, histological analysis and gene expression profiling were performed to assess the impact of PCa EVs on the bone microenvironment. We demonstrate for the first time that PCa EVs home to both bone and lymph nodes following repeated exposures. Furthermore, the accumulation of EVs within the bone leads to distinct molecular changes indicative of disrupted bone homeostasis (e.g., changes to signaling pathways such as Paxillin p = 0.0163, Estrogen Receptor p = 0.0271, RHOA p = 0.0287, Ribonucleotide reductase p = 0.0307 and ERK/MAPK p = 0.0299). Changes in key regulators of these pathways were confirmed in vitro on human osteoblasts. In addition, our data compares the known gene signature of osteocytes and demonstrates a high proportion of overlap (52.2%), suggesting a potential role for this cell type in response to PCa EV exposure. No changes in bone histology or immunohistochemistry were detected, indicating that PCa EV mediated changes were induced at the molecular level. This study provides novel insights into the alterations induced by PCa EVs on the bone microenvironment. The observed molecular changes indicate changes in key pathways and suggest a role for osteocytes in these EV mediated early changes to bone. Further research to understand these early events may aid in the development of targeted interventions to disrupt the metastatic cascade in PCa.

Bone health in children undergoing solid organ transplantation

PURPOSE OF REVIEW

Pediatric solid organ transplant recipients are a unique and growing patient population who are at risk for metabolic bone disease both before and after transplantation.

RECENT FINDINGS

The odds of sustaining a fracture in adulthood are significantly higher if an individual has sustained at least one childhood fracture, therefore, close monitoring before and after transplant is essential. Emerging data in patients with chronic kidney disease mineral and bone disorder (CKD-MBD) and hepatic osteodystrophy highlights the role of fibroblast growth factor 23 in the pathogenesis of metabolic bone disease in these conditions. While dual X-ray absorptiometry (DXA) is the most widely used imaging modality for assessment of bone mass in children, quantitative computer tomography (QCT) is an emerging modality, especially for patients with glucocorticoid-induced osteoporosis.

SUMMARY

Solid organ transplantation improves organ function and quality of life; however, bone mineral density can decline following transplantation, particularly during the first three to six months. Immunosuppressive medications, including glucocorticoids, are a major contributing factor. Following transplant, treatment should be tailored to achieve mineral homeostasis, correct nutritional deficiencies, and improve physical conditioning. In summary, early identification and treatment of metabolic bone disease can improve the bone health status of pediatric transplant recipients as they enter adulthood.

VIDEO ABSTRACT

http://links.lww.com/MOP/A71.

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

Fluconazole-Induced Protein Changes in Osteogenic and Immune Metabolic Pathways of Dental Pulp Mesenchymal Stem Cells of Osteopetrosis Patients

Osteopetrosis is a rare inherited disease caused by osteoclast failure, resulting in increasing bone density in humans. Patients with osteopetrosis possess several dental and cranial complications. Since carbonic anhydrase II (CA-II) deficiency is a major cause of osteopetrosis, CA-II activators might be an attractive potential treatment option for osteopetrosis patients. We conducted comprehensive label-free quantitative proteomics analysis on Fluconazole-treated Dental Pulp Mesenchymal Stem/Stromal Cells from CA-II-Deficient Osteopetrosis Patients. We identified 251 distinct differentially expressed proteins between healthy subjects, as well as untreated and azole-treated derived cells from osteopetrosis patients. Twenty-six (26) of these proteins were closely associated with osteogenesis and osteopetrosis disease. Among them are ATP1A2, CPOX, Ap2 alpha, RAP1B and some members of the RAB protein family. Others include AnnexinA1, 5, PYGL, OSTF1 and PGAM4, all interacting with OSTM1 in the catalytic reactions of HCO3 and the Cl- channel via CAII regulation. In addition, the pro-inflammatory/osteoclast regulatory proteins RACK1, MTSE, STING1, S100A13, ECE1 and TRIM10 are involved. We have identified proteins involved in osteogenic and immune metabolic pathways, including ERK 1/2, phosphatase and ATPase, which opens the door for some CA activators to be used as an alternative drug therapy for osteopetrosis patients. These findings propose that fluconazole might be a potential treatment agent for CAII- deficient OP patients. Altogether, our findings provide a basis for further work to elucidate the clinical utility of azole, a CA activator, as a therapeutic for OP.

An angiogenic approach to osteoanabolic therapy targeting the SHN3-SLIT3 pathway

Often, disorders of impaired bone formation involve not only a cell intrinsic defect in the ability of osteoblasts to form bone, but moreover a broader dysfunction of the skeletal microenvironment that limits osteoblast activity. Developing approaches to osteoanabolic therapy that not only augment osteoblast activity but moreover correct this microenvironmental dysfunction may enable both more effective osteoanabolic therapies and also addressing a broader set of indications where vasculopathy or other forms microenvironment dysfunction feature prominently. We here review evidence that SHN3 acts as a suppressor of not only the cell intrinsic bone formation activity of osteoblasts, but moreover of the creation of a local osteoanabolic microenvironment. Mice lacking Schnurri3 (SHN3, HIVEP3) display a very robust increase in bone formation, that is due to de-repression of ERK pathway signaling in osteoblasts. In addition to loss of SHN3 augmenting the differentiation and bone formation activity of osteoblasts, loss of SHN3 increases secretion of SLIT3 by osteoblasts, which in a skeletal context acts as an angiogenic factor. Through this angiogenic activity, SLIT3 creates an osteoanabolic microenvironment, and accordingly treatment with SLIT3 can increase bone formation and enhance fracture healing. These features both validate vascular endothelial cells as a therapeutic target for disorders of low bone mass alongside the traditionally targeted osteoblasts and osteoclasts and indicate that targeting the SHN3/SLIT3 pathway provides a new mechanism to induce therapeutic osteoanabolic responses.

Establishment of a BRAF V595E-mutant canine prostate cancer cell line and the antitumor effects of MEK inhibitors against canine prostate cancer

Canine prostate cancer (cPCa) is a malignant neoplasm with no effective therapy. The BRAF V595E mutation, corresponding to the human BRAF V600E mutation, is found frequently in cPCa. Activating BRAF mutations are recognized as oncogenic drivers, and blockade of MAPK/ERK phosphorylation may be an effective therapeutic target against BRAF-mutated tumours. The aim of this study was to establish a novel cPCa cell line and to clarify the antitumor effects of MEK inhibitors on cPCa in vitro and in vivo. We established the novel CHP-2 cPCa cell line that was derived from the prostatic tissue of a cPCa patient. Sequencing of the canine BRAF gene in two cPCa cell lines revealed the presence of the BRAF V595E mutation. MEK inhibitors (trametinib, cobimetinib and mirdametinib) strongly suppressed cell proliferation in vitro, and trametinib showed the highest efficacy against cPCa cells with minimal cytotoxicity to non-cancer COPK cells. Furthermore, we orally administered 0.3 or 1.0 mg/kg trametinib to CHP-2 xenografted mice and examined its antitumor effects in vivo. Trametinib reduced tumour volume, decreased phosphorylated ERK levels, and lowered Ki-67 expression in xenografts in a dose-dependent manner. Although no clear adverse events were observed with administration, trametinib-treated xenografts showed osteogenesis that was independent of dosage. Our results indicate that trametinib induces cell cycle arrest by inhibiting ERK activation, resulting in cPCa tumour regression in a dose-dependent manner. MEK inhibitors, in addition to BRAF inhibitors, may be a targeted agent option for cPCa with the BRAF V595E mutation.

microRNA-142-3p regulates osteogenic differentiation of human periodontal ligament stem cells via mediating SGK1

OBJECTIVE

Human periodontal ligament stem cells (hPDLSCs) refer to one kind of somatic stem cells that are capable of differentiating into multiple cell kinds and undergoing robust clonal self-renewal. This work was unearthed to elucidate the possible molecular mechanism of miR-142-3p in mediating osteogenic differentiation of hPDLSCs by targeting SGK1.

METHODS

The hPDLSCs were isolated, cultured, and identified. hPDLSCs were identified by immunofluorescence staining and multiple differentiation ability detection. Cell proliferation ability was assessed by CCK-8 assay. hPDLSCs were induced using osteogenic differentiation medium. ALP activity was detected by alkaline phosphatase (ALP) staining  and ALP activity assay, and mineralized nodule formation was determined by alizarin red staining. The expression levels of osteogenic differentiation marker proteins ALP, RUNX2, and OCN were measured by RT-qPCR. miR-142-3p candidate targets were obtained through bioinformatics analysis. The relationship between miR-142-3p and SKG1 was verified.

RESULTS

miR-142-3p in hPDLSCs after osteogenic induction was down-regulated. Elevated miR-142-3p restricted hPDLSCs proliferation, and diminished ALP activity and mineralized nodule formation, as well as the expression of ALP, RUNX2, and OCN, while miR-142-3p inhibition led to inverse results. miR-142-3p inhibited SKG1 expression. SKG1 overexpression promoted hPDLSC proliferation and osteogenic differentiation, and reversed the inhibitory function of miR-142-3p on hPDLSCs.

CONCLUSION

This study highlights that miR-142-3p represses osteogenic differentiation of hPDLSCs by reducing SGK1 expression.

Contrasting effects of <i>Ksr2</i>, an obesity gene, on trabecular bone volume and bone marrow adiposity

Pathological obesity and its complications are associated with an increased propensity for bone fractures. Humans with certain genetic polymorphisms at the kinase suppressor of ras2 (KSR2) locus develop severe early-onset obesity and type 2 diabetes. Both conditions are phenocopied in mice with <i>Ksr2</i> deleted, but whether this affects bone health remains unknown. Here we studied the bones of global <i>Ksr2</i> null mice and found that <i>Ksr2</i> negatively regulates femoral, but not vertebral, bone mass in two genetic backgrounds, while the paralogous gene, <i>Ksr1</i>, was dispensable for bone homeostasis. Mechanistically, KSR2 regulates bone formation by influencing adipocyte differentiation at the expense of osteoblasts in the bone marrow. Compared with <i>Ksr2</i>'s known role as a regulator of feeding by its function in the hypothalamus, pair-feeding and osteoblast-specific conditional deletion of <i>Ksr2</i> reveals that <i>Ksr2</i> can regulate bone formation autonomously. Despite the gains in appendicular bone mass observed in the absence of <i>Ksr2</i>, bone strength, as well as fracture healing response, remains compromised in these mice. This study highlights the interrelationship between adiposity and bone health and provides mechanistic insights into how <i>Ksr2</i>, an adiposity and diabetic gene, regulates bone metabolism.