Age-related decline in melatonin contributes to enhanced osteoclastogenesis via disruption of redox homeostasis.

BACKGROUND: Increased oxidative stress contributes to enhanced osteoclastogenesis and age-related bone loss. Melatonin (MT) is an endogenous antioxidant and declines with aging. However, it was unclear whether the decline of MT was involved in the enhanced osteoclastogenesis during the aging process. METHODS: The plasma level of MT, oxidative stress status, bone mass, the number of bone marrow-derived monocytes (BMMs) and its osteoclastogenesis were analyzed in young (3-month old) and old (18-month old) mice (n = 6 per group). In vitro, BMMs isolated from aged mice were treated with or without MT, followed by detecting the change of osteoclastogenesis and intracellular reactive oxygen species (ROS) level. Furthermore, old mice were treated with MT for 2 months to investigate the therapeutic effect. RESULTS: The plasma level of MT was markedly lower in aged mice compared with young mice. Age-related decline in MT was accompanied by enhanced oxidative stress, osteoclastogenic potential and bone loss. MT intervention significantly suppressed the receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis, decreased intracellular ROS and enhanced antioxidant capacity of BMMs from aged mice. MT supplementation significantly attenuated oxidative stress, osteoclastogenesis, bone loss and deterioration of bone microstructure in aged mice. CONCLUSIONS: These results suggest that age-related decline of MT enhanced osteoclastogenesis via disruption of redox homeostasis. MT may serve as a key regulator in osteoclastogenesis and bone homeostasis, thereby highlighting its potential as a preventive agent for age-related bone loss.

Tanshinone IIA attenuates osteoarthritis via inhibiting aberrant angiogenesis in subchondral bone.

Excessive angiogenesis in subchondral bone is a pathological feature of osteoarthritis (OA). Tanshinone IIA (TIIA), an active compound found in Salvia miltiorrhiza, demonstrates significant anti-angiogenic properties. However, the effect of TIIA on abnormal subchondral angiogenesis in OA is still unclear. This study aims to investigate the mechanism of TIIA in modulating subchondral bone angiogenesis during OA and assess its therapeutic potential in OA. Our findings demonstrate that TIIA attenuated articular cartilage degeneration, normalized subchondral bone remodeling, and effectively suppressed aberrant angiogenesis within subchondral bone in monosodium iodoacetate (MIA)-induced OA mice. Additionally, the angiogenesis capacity of primary CD31hiEmcnhi endothelial cells was observed to be significantly reduced after treatment with TIIA in vitro. Mechanically, TIIA diminished the proportion of hypertrophic chondrocytes, ultimately leading to a substantial reduction in the secretion of vascular endothelial growth factor A (VEGFA). The supernatant of hypertrophic chondrocytes promoted the tube formation of CD31hiEMCNhi endothelial cells, whereas TIIA inhibited this process. Furthermore, TIIA effectively suppressed the expression of vascular endothelial growth factor receptor 2 (VEGFR2) along with its downstream MAPK pathway in CD31hiEmcnhi endothelial cells. In conclusion, our data indicated that TIIA could effectively inhibit the abnormal angiogenesis in subchondral bone during the progression of OA by suppressing the VEGFA/VEFGR2/MAPK pathway. These findings significantly contribute to our understanding of the abnormal angiogenesis in OA and offer a promising therapeutic target for OA treatment.

CircRBM23 regulates the switch between osteogenesis and adipogenesis of mesenchymal stem cells via sponging miR-338-3p.

BACKGROUND: The disruption of the balance between osteogenic and adipogenic differentiation of mesenchymal stem cells (MSCs) in bone marrow contributes to the adipocytes accumulation and bone loss, which leads to the development of osteoporosis (OP). The circular RNA (circRNA), circRBM23, was generated from the RNA binding motif protein 23 (RBM23) gene. It was reported that circRBM23 was down-regulated in OP patients, but it remains unknown whether its down-regulation is involved in the lineage switch of MSCs. OBJECTIVE: We aimed to explore the role and mechanism of circRBM23 in regulating the switch between osteogenic and adipogenic differentiation of MSCs. METHODS: The expression and function of circRBM23 in vitro were detected by qRT-PCR, alizarin red staining, and oil Red O staining. The interactions between circRBM23 and microRNA-338-3p (miR-338-3p) were analyzed by RNA pull-down assay, FISH, and dual-luciferase reporter assay. MSCs treated with lentivirus overexpression of circRBM23 was applied for both in vitro and in vivo experiments. RESULTS: CircRBM23 was expressed at lower levels in OP patients. Besides, circRBM23 was up-regulated during osteogenesis and down-regulated during adipogenesis of MSCs. CircRBM23 could promote the osteogenic differentiation but inhibit the adipogenic differentiation of MSCs. Mechanistically, circRBM23 acted as a sponge for microRNA-338-3p (miR-338-3p) to enhance the expression of RUNX family transcription factor 2 (RUNX2). CONCLUSIONS: Our research indicates that circRBM23 could promote the switch from adipogenic to osteogenic differentiation of MSCs via sponging miR-338-3p. It might improve the understanding of the lineage switch of MSCs and provide a potential target for diagnosing and treating OP.

Accumulation of ß-aminoisobutyric acid mediates hyperalgesia in ovariectomized mice through Mas-related G protein-coupled receptor D signaling.

Hyperalgesia is typified by reduced pain thresholds and heightened responses to painful stimuli, with a notable prevalence in menopausal women, but the underlying mechanisms are far from understood. ß-Aminoisobutyric acid (BAIBA), a product of valine and thymine catabolism, has been reported to be a novel ligand of the Mas-related G protein coupled receptor D (MrgprD), which mediates pain and hyperalgesia. Here, we established a hyperalgesia model in 8-week-old female mice through ovariectomy (OVX). A significant increase in BAIBA plasma level was observed and was associated with decline of mechanical withdrawal threshold, thermal and cold withdrawal latency in mice after 6 weeks of OVX surgery. Increased expression of MrgprD in dorsal root ganglion (DRG) was shown in OVX mice compared to Sham mice. Interestingly, chronic loading with BAIBA not only exacerbated hyperalgesia in OVX mice, but also induced hyperalgesia in gonadally intact female mice. BAIBA supplementation also upregulated the MrgprD expression in DRG of both OVX and intact female mice, and enhanced the excitability of DRG neurons in vitro. Knockout of MrgprD markedly suppressed the effects of BAIBA on hyperalgesia and excitability of DRG neurons. Collectively, our data suggest the involvement of BAIBA in the development of hyperalgesia via MrgprD-dependent pathway, and illuminate the mechanisms underlying hyperalgesia in menopausal women.

Age-related accumulation of advanced oxidation protein products promotes osteoclastogenesis through disruption of redox homeostasis.

Enhanced osteoclastogenesis is one of the major causes of age-related bone loss. Aging is accompanied by accumulation of advanced oxidation protein products (AOPPs). However, whether AOPPs accumulation contributing to the osteoclastogenesis with aging remains unclear. Here, we showed that AOPPs accumulation was associated with the enhanced osteoclastogenesis and deterioration of bone microstructure in aged mice. In vitro, AOPPs directly induced osteoclastogenesis by interaction with receptor activator of nuclear factor κ B (RANK) and the receptor for advanced glycation end products (RAGE) in the primary bone marrow monocytes. Bindings of AOPPs to RANK and RAGE were able to activate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, trigger generation of reactive oxygen species, then induce phosphorylation of mitogen-activated protein kinases and c-fos, upregulation of the nuclear factor of activated T cell c1, eventually induce bone marrow monocytes to differentiate into mature osteoclasts. Chronic exposure to AOPPs enhanced osteoclastogenesis and bone loss in mice, which could be alleviated by NADPH oxidase inhibitor apocynin. Local injection of AOPPs into subperiosteal area induced bone resorption at the site of administration, which was similar to the effect of RANK ligand. Together, these results suggested that AOPPs could serve as a novel regulator of osteoclastogenesis and AOPPs accumulation might play an important role in the development of age-related bone loss.

Oxidative Stress Contributes to Hyperalgesia in Osteoporotic Mice.

PURPOSE: Chronic pain is one of the most common complications of postmenopausal osteoporosis. Since oxidative stress is involved in the pathogenesis of postmenopausal osteoporosis, we explored whether oxidative stress contributes to postmenopausal osteoporotic pain. METHODS: Osteoporosis was induced in mice by ovariectomy (OVX). Pain-related behaviours were assessed by measuring sensitivity to mechanical, thermal and cold stimulation. The expression of pain-related transcripts, such acid-sensing ion channel 3 (ASIC3), transient receptor potential vanilloid 1 (TRPV1) and calcitonin gene-related peptide (CGRP), was evaluated. Plasma markers of oxidative stress were also measured. In addition, the effects of the reactive oxygen species scavenger phenyl N-tert-butylnitrone (PBN) on these parameters were assessed. RESULTS: The OVX mice presented hyperalgesia, as demonstrated by decreased paw withdrawal thresholds to mechanical stimulation and withdrawal latencies to thermal and cold stimulation, along with upregulated expression of ASIC3, TRPV1 and CGRP in the dorsal root ganglia, spinal cord and thalamus tissue. OVX elevated the plasma levels of malondialdehyde (MDA) and advanced oxidation protein products (AOPPs). However, the administration of PBN alleviated these effects. CONCLUSION: Our results indicated that oxidative stress contributes to hyperalgesia in OVX mice. Enhanced oxidative stress may be associated with osteoporotic pain. Antioxidant treatment could help alleviate chronic pain in postmenopausal osteoporotic patients.