Netrin-1 regulates ERK1/2 signaling pathway and autophagy activation in wear particle-induced osteoclastogenesis

Bafilomycin A1 mitigates subchondral bone degeneration and pain in TMJOA rats

BACKGROUND

Pain and disability are primary concerns for temporomandibular joint osteoarthritis (TMJOA) patients, and the efficacy of current treatments remains controversial. Overactive osteoclasts are associated with subchondral bone degeneration and pain in OA. The vacuolar H+-ATPase (V-ATPase) is crucial for differentiation and function in osteoclasts, but its role in TMJOA is not well defined. This study aims to evaluate the effects of the V-ATPase inhibitor, bafilomycin A1 (Baf A1) on the progression and pain of TMJOA.

MATERIALS AND METHODS

Pain behavior tests, histological staining, tartrate-resistant acid phosphatase (TRAP) staining, immunofluorescence staining, and micro-CT analysis were conducted to evaluate the therapeutic efficacy of Baf A1 in monosodium iodoacetate-induced TMJOA in rats. Additionally, TRAP staining, enzyme-linked immunosorbent assay and immunofluorescence staining were used to assess the inhibitory effects of Baf a1 on the osteoclastogenesis, secretion of netrin-1 and neurite growth of trigeminal ganglion (TG) neurons.

RESULTS

Baf A1 significantly mitigated subchondral bone degeneration by suppressing osteoclastogenesis and subsequently inhibited cartilage degradation in TMJOA rats. Baf A1 also effectively alleviated pain behavior by inhibiting expression of netrin-1 and innervation of sensory nerve in TMJOA rats. In vitro assays of osteoclast and TG further demonstrated the inhibitory effects of Baf A1 on osteoclastogenesis, secretion of netrin-1 and neurite outgrowth of TG.

CONCLUSIONS

This study demonstrates that Baf A1 inhibits V-ATPase to mitigate TMJOA degeneration and pain by suppressing osteoclastogenesis and secretion of netrin-1, thereby suggesting it as a potential clinical treatment option for degeneration and pain of TMJOA.

Regulation of bone homeostasis: signaling pathways and therapeutic targets

As a highly dynamic tissue, bone is continuously rebuilt throughout life. Both bone formation by osteoblasts and bone resorption by osteoclasts constitute bone reconstruction homeostasis. The equilibrium of bone homeostasis is governed by many complicated signaling pathways that weave together to form an intricate network. These pathways coordinate the meticulous processes of bone formation and resorption, ensuring the structural integrity and dynamic vitality of the skeletal system. Dysregulation of the bone homeostatic regulatory signaling network contributes to the development and progression of many skeletal diseases. Significantly, imbalanced bone homeostasis further disrupts the signaling network and triggers a cascade reaction that exacerbates disease progression and engenders a deleterious cycle. Here, we summarize the influence of signaling pathways on bone homeostasis, elucidating the interplay and crosstalk among them. Additionally, we review the mechanisms underpinning bone homeostatic imbalances across diverse disease landscapes, highlighting current and prospective therapeutic targets and clinical drugs. We hope that this review will contribute to a holistic understanding of the signaling pathways and molecular mechanisms sustaining bone homeostasis, which are promising to contribute to further research on bone homeostasis and shed light on the development of targeted drugs.

Arsenic aggravates the progression of diabetic nephropathy through miRNA-mRNA-autophagy axis

Environmental factors play an important role in the progression of diabetic nephropathy (DN), and previous study has shown that arsenic exposure can promote kidney damage in DN rats, however there is no relevant mechanism study so far. In this study, an arsenic-exposed (10 mg/L and 25 mg/L) DN mouse model was established through drinking water for 14 weeks. The results showed that 25 mg/L arsenic exposure increased the renal fibrosis in DN mice significantly, and urinary mAlb level increased with the increasing of arsenic exposure level. Transcriptome sequencing showed that autophagy-related pathways were significantly activated under the exposure dose of 25 mg/L, and levels of Beclin1 and p-ATG16L1/ATG16L1 were significantly higher in the 25 mg/L arsenic group compared to the control group. Silico analysis predicted the microRNAs those could regulate the hub genes of Mapk1, Rhoa and Cdc42, and dual-luciferase gene reporter assay was used to verify the targeted binding between these mRNAs and microRNAs. Our results suggested that high arsenic exposure could aggravate the progression of DN by altering autophagy, the miRNA-mRNA axles of let-7a-1-3p, let-7b-3p, let-7f-1-3p, miR-98-3p/Cdc42, Mapk1, Rhoa, could be considered promising targets to explore the mechanisms and therapeutic measures of DN after exposure to high levels of arsenic.

Regulatory mechanisms of autophagy-related ncRNAs in bone metabolic diseases

Bone metabolic diseases have been tormented and are plaguing people worldwide due to the lack of effective and thorough medical interventions and the poor understanding of their pathogenesis. Non-coding RNAs (ncRNAs) are heterogeneous transcripts that cannot encode the proteins but can affect the expressions of other genes. Autophagy is a fundamental mechanism for keeping cell viability, recycling cellular contents through the lysosomal pathway, and maintaining the homeostasis of the intracellular environment. There is growing evidence that ncRNAs, autophagy, and crosstalk between ncRNAs and autophagy play complex roles in progression of metabolic bone disease. This review investigated the complex mechanisms by which ncRNAs, mainly micro RNAs (miRNAs), long noncoding RNAs (lncRNAs), and circular RNAs (circRNAs), regulate autophagic pathway to assist in treating bone metabolism disorders. It aimed at identifying the autophagy role in bone metabolism disorders and understanding the role, potential, and challenges of crosstalk between ncRNAs and autophagy for bone metabolism disorders treatment.

The dual role of autophagy in periprosthetic osteolysis

Periprosthetic osteolysis (PPO) induced by wear particles is an important cause of aseptic loosening after artificial joint replacement, among which the imbalance of osteogenesis and osteoclastic processes occupies a central position. The cells involved in PPO mainly include osteoclasts (macrophages), osteoblasts, osteocytes, and fibroblasts. RANKL/RANK/OGP axis is a typical way for osteolysis. Autophagy, a mode of regulatory cell death and maintenance of cellular homeostasis, has a dual role in PPO. Although autophagy is activated in various periprosthetic cells and regulates the release of inflammatory cytokines, osteoclast activation, and osteoblast differentiation, its beneficial or detrimental role remains controversy. In particular, differences in the temporal control and intensity of autophagy may have different effects. This article focuses on the role of autophagy in PPO, and expects the regulation of autophagy to become a powerful target for clinical treatment of PPO.

Netrin-1: A Modulator of Macrophage Driven Acute and Chronic Inflammation

Netrins belong to the family of laminin-like secreted proteins, which guide axonal migration and neuronal growth in the developing central nervous system. Over the last 20 years, it has been established that netrin-1 acts as a chemoattractive or chemorepulsive cue in diverse biological processes far beyond neuronal development. Netrin-1 has been shown to play a central role in cell adhesion, cell migration, proliferation, and cell survival in neuronal and non-neuronal tissue. In this context, netrin-1 was found to orchestrate organogenesis, angiogenesis, tumorigenesis, and inflammation. In inflammation, as in neuronal development, netrin-1 plays a dichotomous role directing the migration of leukocytes, especially monocytes in the inflamed tissue. Monocyte-derived macrophages have long been known for a similar dual role in inflammation. In response to pathogen-induced acute injury, monocytes are rapidly recruited to damaged tissue as the first line of immune defense to phagocyte pathogens, present antigens to initiate the adaptive immune response, and promote wound healing in the resolution phase. On the other hand, dysregulated macrophages with impaired phagocytosis and egress capacity accumulate in chronic inflammation sites and foster the maintenance-and even the progression-of chronic inflammation. In this review article, we will highlight the dichotomous roles of netrin-1 and its impact on acute and chronic inflammation.

miR-21-5p targets SKP2 to reduce osteoclastogenesis in a mouse model of osteoporosis

Osteoporosis results from an imbalance between bone formation and bone resorption. Traditional drugs for treating osteoporosis are associated with serious side effects, and thus, new treatment methods are required. This study investigated the role of differentially expressed microRNAs during osteoclast differentiation and osteoclast activity during osteoarthritis as well as the associated underlying mechanisms. We used a microarray to screen microRNAs that decreased in the process of osteoclast differentiation and verified miR-21-5p to decrease significantly using RT-qPCR. In follow-up experiments, we found that miR-21-5p targets SKP2 to regulate osteoclast differentiation. In vivo, ovariectomized mice were used to simulate perimenopausal osteoporosis induced by estrogen deficiency, and miR-21-5p treatment inhibited bone resorption and maintained bone cortex and trabecular structure. These results suggest that miR-21-5p is a new therapeutic target for osteoporosis.

Netrin-1 regulates ERK1/2 signaling pathway and autophagy activation in wear particle-induced osteoclastogenesis

Background

Artificial joint replacement surgery is often accompanied by osteolysis induced aseptic loosening around the prosthesis. Wear particles from joint replacement are thought to be one of the main factors leading to local inflammation and osteolysis at the prosthesis site. The aim of this study was to investigate the molecular mechanism of osteoclast formation and dissolution induced by wear particles and the potential roles of Netrin‐1, the ERK1/2 pathway and autophagy activation in this process.

Methods

The messenger RNA levels in cells and tissues were detected with real‐time quantitative PCR. The western blotting was used to detect the expression of proteins. A CCK‐8 kit was used to detect the viability of RAW 264.7 cells. Moreover, an air pouch model of bone resorption was established. Immunohistochemistry was used to detect the expression of TRAP and Netrin‐1 in rat bone tissue. Cell culture supernatants were collected in the rat air pouch model of bone resorption, and the levels of RANKL and OPG were detected with enzyme‐linked immunosorbent assay. The protein levels of TRAP and Netrin‐1 in bone tissue were examined by immunohistochemistry.

Results

Titanium wear particles induced osteoclast formation and autophagy activation. Moreover, blocking autophagy suppressed the osteoclastogenesis after exposure to wear particles in vitro. The activation of the ERK1/2 pathway and the overexpression of Netrin‐1 were both found to play important roles in osteoclastogenesis mediated by autophagy. Moreover, 3‐MA effectively decreased the secretion of proinflammatory cytokines mediated by wear particles.

Conclusion

Blockade of autophagy inhibits the osteoclastogenesis and inflammation induced by wear particles, thus potentially providing novel treatment strategies for abnormal osteoclastogenesis and aseptic prosthesis loosening induced by wear particles.