BHLHE40 promotes osteoclastogenesis and abnormal bone resorption via c-Fos/NFATc1

IGF-II regulates lysyl oxidase propeptide and mediates its effects in part via basic helix-loop-helix E40

Pulmonary fibrosis (PF) is a clinically severe and commonly fatal complication of Systemic Sclerosis (SSc). Our group has previously reported profibrotic roles for Insulin-like Growth Factor II (IGF-II) and Lysyl Oxidase (LOX) in SSc-PF. We sought to identify downstream regulatory mediators of IGF-II. In the present work, we show that SSc lung tissues have higher baseline levels of the total (N-glycosylated/unglycosylated) LOX-Propeptide (LOX-PP) than control lung tissues. LOX-PP-mediated changes were consistent with the extracellular matrix (ECM) deregulation implicated in SSc-PF progression. Furthermore, Tolloid-like 1 (TLL1) and Bone Morphogenetic Protein 1 (BMP1), enzymes that can cleave ProLOX to release LOX-PP, were increased in SSc lung fibrosis and the bleomycin (BLM)-induced murine lung fibrosis model, respectively. In addition, IGF-II regulated the levels of ProLOX, active LOX, LOX-PP, BMP1, and isoforms of TLL1. The Class E Basic Helix-Loop-Helix protein 40 (BHLHE40) transcription factor localized to the nucleus in response to IGF-II. BHLHE40 silencing downregulated TLL1 isoforms and LOX-PP, and restored features of ECM deregulation triggered by IGF-II. Our findings indicate that IGF-II, BHLHE40, and LOX-PP may serve as targets of therapeutic intervention to halt SSc-PF progression.

The bone nonunion microenvironment: A place where osteogenesis struggles with osteoclastic capacity

Bone nonunion is a common and serious orthopedic disorder, the occurrence of which is associated with a disruption of the dynamic balance between osteoblasts and osteoclasts during bone repair. However, the critical molecular mechanisms affecting this homeostasis are not well understood, and it is essential to investigate the specific components of this mechanism and to restore the balance between osteoblasts and osteoclasts to promote bone repair. First, we defined this complex local environmental factor as the "bone nonunion microenvironment" and identified the importance of the "struggle" between osteoblasts and osteoclasts, which is the most essential element in determining the process of repair. On this basis, we also explored the cellular factors that influence osteogenesis and the molecular signals that influence the balance between osteoclast and osteoblasts, which are important for restoring homeostasis. Further, we explored other factors involved in osteogenesis, such as the biomechanical environment, the nutritional environment, the acid-base environment, and the temperature environment, which are important players in osteogenesis. In conclusion, we found that the balance between osteoblasts and osteoclasts is the essence of bone healing, which is based on the "bone nonunion microenvironment". Therefore, investigating the role of the bone nonunion microenvironment in the system of osteoblast-osteoclast "struggle" provides an important basis for further understanding of the mechanism of nonunion and the development of new therapeutic approaches.

Myeloid zinc finger 1 knockdown promotes osteoclastogenesis and bone loss in part by regulating RANKL-induced ferroptosis of osteoclasts through Nrf2/GPX4 signaling pathway

The overactivation of the osteoclasts is a crucial pathological factor in the development of osteoporosis. MZF1, belonging to the scan-zinc finger family, plays a significant role in various processes associated with tumor malignant progression and acts as an essential transcription factor regulating osteoblast expression. However, the exact role of MZF1 in osteoclasts has not been determined. In this study, the purpose of our study was to elucidate the role of MZF1 in osteoclastogenesis. First, we established MZF1-deficient female mice and evaluated the femur bone phenotype by micro-computed tomography and histological staining. Our findings indicate that MZF1-/- mice exhibited a low bone mass osteoporosis phenotype. RANKL could independently induce the differentiation of RAW264.7 cells into osteoclasts, and we found that the expression level of MZF1 protein decreased gradually. Then, the CRISPR/Cas 9 gene-editing technique was used to build a RAW264.7 cell model with MZF1 knockout, and RANKL was used to independently induce MZF1-/- and wild-type cells to differentiate into mature osteoclasts. Tartrate-resistant acid phosphatase staining and F-actin fluorescence results showed that the MZF1-/- group produced more tartrate-resistant acid phosphatase-positive mature osteoclasts and larger actin rings. The expression of osteoclast-associated genes (including tartrate-resistant acid phosphatase, CTSK, c-Fos, and NFATc1) was evaluated by reverse transcription quantitative polymerase chain reaction and Western blot. The expression of key genes of osteoclast differentiation in the MZF1-/- group was significantly increased. Furthermore, we found that cell viability was increased in the early stages of RANKL-induced cell differentiation in the MZF1-/- group cells. We examined some prevalent ferroptosis markers, including malondialdehyde, glutathione, and intracellular Fe, the active form of iron in the cytoplasm during the early stages of osteoclastogenesis. The results suggest that MZF1 may be involved in osteoclast differentiation by regulating RANKL-induced ferroptosis of osteoclasts. Collectively, our findings shed light on the essential involvement of MZF1 in the regulation of osteoclastogenesis in osteoporosis and provide insights into its potential underlying mechanism.

Basic-helix-loop-helix family member e41 suppresses osteoclastogenesis and abnormal bone resorption disease via NFATc1

Overactivation of osteoclasts due to altered osteoclastogenesis causes multiple bone metabolic diseases. However, how osteoclast differentiation is tightly regulated and involved in multiple pathophysiological states remains mystery. In this study, we noticed that the downregulation of BHLHE41 (basic-helix-loop-helix family member e41) was tightly associated with osteoclast differentiation and osteoporosis. Functionally, the upregulation or downregulation of BHLHE41 suppressed or promoted osteoclast differentiation, respectively, in vitro. A mechanism study indicated that the direct binding of BHLHE41 to the promoter region of NFATc1 that led to its downregulation. Notably, the inhibition of NFATc1 abrogated the enhanced osteoclast differentiation in BHLHE41-knockdown bone marrow macrophages (BMMs). Additionally, upregulation of BHLHE41 impeded bone destruction in OVX mice with osteoporosis. Therefore, our research reveals the mechanism by which BHLHE41 regulates osteoclast differentiation and bone resorption via NFATc1, and targeting BHLHE41 is a potential strategy for the treatment of osteoporosis.

Unveiling the Mechanisms of Bone Marrow Toxicity Induced by Lead Acetate Exposure

Lead (Pb), a widespread heavy metal, causes severe toxicity in human and animal organs (e.g., bone marrow), whereas the mechanisms of the bone marrow toxicity induced by Pb exposure are unclear. Hence, this study was designed to reveal the hub genes involved in Pb-induced bone marrow toxicity. GSE59894 dataset obtained from Gene Expression Omnibus (GEO) was composed of lead acetate (PbAc2)-treated and control bone marrow samples. Totally 120 and 85 differentially expressed genes (DEGs) were identified on the 1st day, while 153 and 157 DEGs on the 3rd day in the bone marrow treated with 200 and 600 mg/kg of PbAc2, respectively. Notably, a total of 28 and 32 overlapping DEGs were identified in the bone marrow on the 1st and 3rd day treated with PbAc2, respectively. Biological process analysis suggested that the common DEGs were primarily participated in cell differentiation, the response to drug, xenobiotic stimulus, and organic cyclic compound. Pathway analysis demonstrated that the overlapping DEGs were primarily linked to PI3K-Akt, TGF-β, MAPK, and osteoclast differentiation signaling pathways. Moreover, the hub genes, including PLD2, DAPK1, ALB, TNF, FOS, CDKN1A, and TGFB3, might contribute to PbAc2-induced bone marrow toxicity. Overall, our study offers an important insight into the molecular mechanisms of Pb-induced bone marrow toxicity.

Identification of Novel Diagnostic Biomarkers and Classification Patterns for Osteoarthritis by Analyzing a Specific Set of Genes Related to Inflammation

Osteoarthritis (OA) is a prevalent joint disease globally. TNFA is recognized as a crucial inflammatory cytokine that plays a significant role in the pathophysiological mechanisms that occur during the progression of OA. However, the TNFA_SIGNALING_VIA_NFKB (TSVN)-related genes (TRGs) during the progression of OA remain unclear. By conducting a combinatory analysis of OA transcriptome data from three datasets, various differentially expressed TRGs were identified. The logistic regression model was used to mine hub TRGs for OA, and a nomogram prediction model was subsequently constructed using these TRGs. To identify new molecular subgroups, we performed consensus clustering. We then conducted functional analyses, including GO, KEGG, GSVA, and GSEA, to elucidate the underlying mechanisms. To determine the immune microenvironment, we applied xCell. The logistic regression analysis identified three hub TRGs (BHLHE40, BTG2, and CCNL1) as potential biomarkers for OA. Based on these TRGs, we constructed an OA predictive model. This model has demonstrated promising results in enhancing the accuracy of OA diagnosis, as evident from the ROC analysis (AUC merged dataset = 0.937, AUC validating dataset = 0.924). We identified two molecular subtypes, C1 and C2, and found that the C1 subtype showed activation of immune- and inflammation-related pathways. The involvement of TSVN in the development and progression of OA has been established. We identified several hub genes, such as BHLHE40, BTG2, and CCNL1, that may have a significant association with the progression of OA. Furthermore, our logistic regression model based on these genes has shown promising results in accurately diagnosing OA patients.

A Recombinant Parathyroid Hormone-Related Peptide Locally Applied in Osteoporotic Bone Defect

The local application of drug-loaded bioactive scaffold materials is one of the important directions to solve the clinical problem of osteoporotic (OP) bone defects. This study retains the advantages of drug loading and mechanical properties of natural 3D bioactive scaffolds. The scaffolds are functionally modified through chemical and self-assembly approaches with application of polydopamine (PDA) nanoparticles and parathyroid hormone-related peptide-1 (PTHrP-1) for efficient local drug loading. This study investigates the effects of the novel bioactive scaffolds on ossification, osteoclastogenesis, and macrophage polarization. This work elucidates the effects of the scaffolds in regulating osteoclastic activity and new bone formation in vitro. Further studies on the establishment and repair of OP bone defects in small animals are conducted, and the potential of natural bioactive porous scaffold materials to promote the repair of OP bone defects is initially verified. The preparation of safe and economical anti-OP bone repair material provides a theoretical basis for clinical translational applications.

Strontium Ranelate Inhibits Osteoclastogenesis through NF-κB-Pathway-Dependent Autophagy

Strontium ranelate (SR) is a pharmaceutical agent used for the prevention and treatment of osteoporosis and fragility fracture. However, little attention has been paid to the effect of SR on alveolar bone remodeling during orthodontic tooth movement and its underlying mechanism. Here, we investigated the influence of SR on orthodontic tooth movement and tooth resorption in Sprague–Dawley rats and the relationship between the nuclear factor–kappa B (NF-κB) pathway, autophagy, and osteoclastogenesis after the administration of SR in vitro and in vivo. In this study, it was found that SR reduced the expression of autophagy-related proteins at the pressure side of the first molars during orthodontic tooth movement. Similarly, the expression of these autophagy-related proteins and the size and number of autophagosomes were downregulated by SR in vitro. The results also showed that SR reduced the number of osteoclasts and suppressed orthodontic tooth movement and root resorption in rats, which could be partially restored using rapamycin, an autophagy inducer. Autophagy was attenuated after pre-osteoclasts were treated with Bay 11-7082, an NF-κB pathway inhibitor, while SR reduced the expression of the proteins central to the NF-κB pathway. Collectively, this study revealed that SR might suppress osteoclastogenesis through NF-κB-pathway-dependent autophagy, resulting in the inhibition of orthodontic tooth movement and root resorption in rats, which might offer a new insight into the treatment of malocclusion and bone metabolic diseases.