The ATF3-OPG Axis Contributes to Bone Formation by Regulating the Differentiation of Osteoclasts, Osteoblasts, and Adipocytes

Serum asprosin and its association with bone mineral density, oxidative stress, and osteoprotegerin levels in Pakistani women with postmenopausal osteoporosis

OBJECTIVES

Raised asprosin may be related to the development of postmenopausal osteoporosis. This study aimed to determine the role of asprosin in oxidative stress in postmenopausal osteoporosis and its relation with estrogen, osteoprotegerin (OPG), and bone mineral density (BMD).

METHODS

A case-control study included 80 women, aged 42-65, presenting at Shalamar Hospital, Lahore, Pakistan. Informed consent was taken, and single blinding was done. Demographic details and a bone mineral density scan were done. Three ml of venous blood sample was taken to measure asprosin, glutathione (GSH), osteoprotegerin, and estrogen levels.

RESULTS

Women with osteoporosis had significantly higher levels of serum asprosin and lower levels of OPG than those without osteoporosis. (p < 0.05) Asprosin was negatively correlated with BMD, OPG, and GSH, and positively with body mass index (p < 0.05). The cutoff value of serum asprosin for screening postmenopausal osteoporosis by area under the curve was > 27.4 ng/ml with a sensitivity of 75% and a 1-specificity of 14%.

CONCLUSION

Higher serum asprosin and oxidative stress biomarkers are related to decreased bone mineral density in postmenopausal women. Asprosin may be used as a potential biomarker for early screening of postmenopausal osteoporosis. Small sample size and observational study design were the key limitations of this study.

TNFRSF11B-modified umbilical cord mesenchymal stem cells as a novel strategy for bone-related diseases by suppressing osteoclast activity

BACKGROUND AND OBJECTIVE

Mesenchymal stem cells (MSCs), possessing multilineage potential, are capable of differentiating into osteoblasts and thus serve as suitable seed cells for bone regeneration. Tumor necrosis factor receptor superfamily member 11B (TNFRSF11B) gene encodes osteoprotegerin (OPG), which has a critical role in repressing osteoclast differentiation and has been reported to influence the adipogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs). Nevertheless, the impact of TNFRSF11B on the osteogenic differentiation of umbilical cord mesenchymal stem cells (UCMSCs) remains unclear. This study aimed to investigate the role of TNFRSF11B in the osteogenesis of UCMSCs and bone remodeling.

METHODS

Differentially expressed genes (DEGs) were identified from the GEO database using R software. TNFRSF11B was transduced into UCMSCs by a lentiviral vector. Cell differentiation capacity was assessed by ALP staining, TRAP staining, and qRT-PCR assay. Proteomic analysis was performed to investigate the key proteins in TNFRSF11B-OE-UCMSCs that inhibit osteoclast differentiation.

RESULTS

We found that the TNFRSF11B gene was upregulated during osteogenic differentiation and downregulated during adipogenic differentiation of UCMSCs. UCMSCs overexpressing the TNFRSF11B gene were successfully generated via lentivirus transfection. However, neither the overexpression of TNFRSF11B nor treatment with exogenous OPG protein was sufficient to enhance the osteogenic potential of UCMSCs in vitro. Conditioned medium from TNFRSF11B-overexpressing UCMSCs significantly suppressed RANKL-induced osteoclast differentiation, while no significant effect was observed on osteoblast differentiation compared to the control group. Proteome analysis revealed that in the TNFRSF11B-OE-CM group, the expression of C1R, MDH1, and ACLY was significantly downregulated, while the expression of FETUB and METRNL was upregulated in the TNFRSF11B-OE-CM group, which was associated with the inhibition of osteoclast differentiation.

CONCLUSION

This study demonstrates that although TNFRSF11B overexpression does not promote osteogenesis in UCMSCs, it may participate in regulating bone remodeling by inhibiting osteoclast differentiation.

Comprehensive analysis of mesenchymal cells reveals a dysregulated TGF-β/WNT/HOXB7 axis in patients with myelofibrosis

Despite the advances in the understanding and treatment of myeloproliferative neoplasm (MPN), the disease remains incurable with the risk of evolution to acute myeloid leukemia or myelofibrosis (MF). Unfortunately, the evolution of the disease to MF remains poorly understood, impeding preventive and therapeutic options. Recent studies in solid tumor microenvironment and organ fibrosis have shed instrumental insights on their respective pathogenesis and drug resistance, yet such precise data are lacking in MPN. In this study, through a patient sample-driven transcriptomic and epigenetic description of the MF microenvironment landscape and cell-based analyses, we identify homeobox B7 (HOXB7) overexpression and more precisely a potentially novel TGF-β/WNT/HOXB7 pathway as associated to a pro-fibrotic and pro-osteoblastic biased differentiation of mesenchymal stromal cells (MSCs). Using gene-based and chemical inhibition of this pathway, we reversed the abnormal phenotype of MSCs from patients with MF, providing the MPN field a potentially novel target to prevent and manage evolution to MF.

Single-cell RNA sequencing reveals the CRTAC1+ population actively contributes to the pathogenesis of spinal ligament degeneration by SPP1+ macrophage

Degenerative spinal stenosis is a chronic disease that affects the spinal ligaments and associated bones, resulting in back pain and disorders of the limbs among the elderly population. There are few preventive strategies for such ligament degeneration. We here aimed to establish a comprehensive transcriptomic atlas of ligament tissues to identify high-priority targets for pharmaceutical treatment of ligament degeneration. Here, single-cell RNA sequencing was performed on six degenerative ligaments and three traumatic ligaments to understand tissue heterogeneity. After stringent quality control, high-quality data were obtained from 32,014 cells. Distinct cell clusters comprising stromal and immune cells were identified in ligament tissues. Among them, we noted that collagen degradation associated with CTHRC1+ fibroblast-like cells and calcification linked to CRTAC1+ chondrocyte-like cells were key features of ligament degeneration. SCENIC analysis and further experiments identified ATF3 as a key transcription factor regulating the pathogenesis of CRTAC1+ chondrocyte-like cells. Typically, immune cells infiltrate localized organs, causing tissue damage. In our study, myeloid cells were found to be inflammatory-activated, and SPP1+ macrophages were notably enriched in degenerative ligaments. Further exploration via CellChat analysis demonstrated a robust interaction between SPP1+ macrophages and CRTAC1+ chondrocyte-like cells. Activated by SPP1, ATF3 propels the CRTAC1/MGP/CLU axis, fostering ligament calcification. Our unique resource provides novel insights into possible mechanisms underlying ligament degeneration, the target cell types, and molecules that are expected to mitigate degenerative spinal ligament. We also highlight the role of immune regulation in ligament degeneration and calcification, enhancing our understanding of this disease.

Protective effect of hydroxysafflor yellow a on thioacetamide-induced liver injury and osteopenia in zebrafish

Hydroxysafflor yellow A (HSYA) is the main water-soluble compound of safflower. It is commonly used in liver disease treatment and has anti-osteoporotic activity. However, the specific mechanism of HSYA is not yet fully understood. Thioacetamide (TAA) has toxic effects on the liver and is widely used in establishing animal models of cirrhosis and liver fibrosis. In research of liver-related diseases and bone deformation in vivo, the zebrafish has become a frequently utilized animal model. In establishing a TAA-induced zebrafish liver injury model, we found that TAA-induced zebrafish also developed osteopenia. The aim of our study is to investigate the protective effect of HSYA on TAA-induced liver injury and osteopenia in zebrafish. The findings demonstrated that HSYA alleviated hepatic oxidative stress, inhibited the release of inflammatory factors, and promoted in vivo skeletal mineralization in zebrafish larvae. Further Real-time Polymerase Chain Reaction and Western blotting analyses showed that HSYA altered the expression levels of SIRT1, HMGB1, TLR4, MYD88 and NF-ΚB, ameliorated TAA-induced liver injury, reduced the release of inflammation-related factors IL-6, IL-1β, TNF-α, regulated the ratio of RANKL/OPG, ameliorated TAA-induced osteopenia. In conclusion, our study demonstrated that HSYA exhibited a noteworthy beneficial influence on TAA-induced liver injury and osteopenia in zebrafish, this finding provide a foundation for the application of HSYA in clinical research.

Lipolysis products from triglyceride-rich lipoproteins induce stress protein ATF3 in osteoblasts

High fat diets overwhelm the physiological mechanisms for absorption, storage, and utilization of triglycerides (TG); consequently TG, TG-rich lipoproteins (TGRL), and TGRL remnants accumulate, circulate systemically, producing dyslipidemia. This associates with, or is causative for increased atherosclerotic cardiovascular risk, ischemic stroke, fatty liver disease, and pancreatitis. TGRL hydrolysis by endothelial surface-bound lipoprotein lipase (LPL) generates metabolites like free fatty acids which have proinflammatory properties. While osteoblasts utilize fatty acids as an energy source, dyslipidemia is associated with negative effects on the skeleton. In this study we investigated the effects of TGRL lipolysis products (TGRL-LP) on expression of a stress responsive transcription factor, termed activating transcription factor 3 (ATF3), reactive oxygen species (ROS), ATF3 target genes, and angiopoietin-like 4 (Angptl4) in osteoblasts. As ATF3 negatively associates with osteoblast differentiation, we also investigated the skeletal effects of global ATF3 deletion in mice. TGRL-LP increased expression of Atf3, proinflammatory proteins Ptgs2 and IL-6, and induced ROS in MC3T3-E1 osteoblastic cells. Angptl4 is an endogenous inhibitor of LPL which was transcriptionally induced by TGRL-LP, while recombinant Angptl4 prevented TG-driven Atf3 induction. Atf3 global knockout male mice demonstrated increased trabecular and cortical microarchitectural parameters. In summary, we find that TGRL-LP induce osteoblastic cell stress as evidenced by expression of ATF3, which may contribute to the negative impact of dyslipidemia in the skeleton. Further, concomitant induction of Angptl4 in osteoblasts might play a protective role by reducing local lipolysis.

Exercise and osteoimmunology in bone remodeling

Bones can form the scaffolding of the body, support the organism, coordinate somatic movements, and control mineral homeostasis and hematopoiesis. The immune system plays immune supervisory, defensive, and regulatory roles in the organism, which mainly consists of immune organs (spleen, bone marrow, tonsils, lymph nodes, etc.), immune cells (granulocytes, platelets, lymphocytes, etc.), and immune molecules (immune factors, interferons, interleukins, tumor necrosis factors, etc.). Bone and the immune system have long been considered two distinct fields of study, and the bone marrow, as a shared microenvironment between the bone and the immune system, closely links the two. Osteoimmunology organically combines bone and the immune system, elucidates the role of the immune system in bone, and creatively emphasizes its interdisciplinary characteristics and the function of immune cells and factors in maintaining bone homeostasis, providing new perspectives for skeletal-related field research. In recent years, bone immunology has gradually become a hot spot in the study of bone-related diseases. As a new branch of immunology, bone immunology emphasizes that the immune system can directly or indirectly affect bones through the RANKL/RANK/OPG signaling pathway, IL family, TNF-α, TGF-β, and IFN-γ. These effects are of great significance for understanding inflammatory bone loss caused by various autoimmune or infectious diseases. In addition, as an external environment that plays an important role in immunity and bone, this study pays attention to the role of exercise-mediated bone immunity in bone reconstruction.

The Relationship between Renin-Angiotensin-Aldosterone System (RAAS) Activity, Osteoporosis and Estrogen Deficiency in Type 2 Diabetes

Type 2 diabetes (T2D) is associated with a plethora of comorbidities, including osteoporosis, which occurs due to an imbalance between bone resorption and formation. Numerous mechanisms have been explored to understand this association, including the renin-angiotensin-aldosterone system (RAAS). An upregulated RAAS has been positively correlated with T2D and estrogen deficiency in comorbidities such as osteoporosis in humans and experimental studies. Therefore, research has focused on these associations in order to find ways to improve glucose handling, osteoporosis and the downstream effects of estrogen deficiency. Upregulation of RAAS may alter the bone microenvironment by altering the bone marrow inflammatory status by shifting the osteoprotegerin (OPG)/nuclear factor kappa-Β ligand (RANKL) ratio. The angiotensin-converting-enzyme/angiotensin II/Angiotensin II type 1 receptor (ACE/Ang II/AT1R) has been evidenced to promote osteoclastogenesis and decrease osteoblast formation and differentiation. ACE/Ang II/AT1R inhibits the wingless-related integration site (Wnt)/β-catenin pathway, which is integral in bone formation. While a lot of literature exists on the effects of RAAS and osteoporosis on T2D, the work is yet to be consolidated. Therefore, this review looks at RAAS activity in relation to osteoporosis and T2D. This review also highlights the relationship between RAAS activity, osteoporosis and estrogen deficiency in T2D.