Melatonin Suppresses Estrogen Deficiency-Induced Osteoporosis and Promotes Osteoblastogenesis by Inactivating the NLRP3 Inflammasome

Abstract

Postmenopausal osteoporosis induced by estrogen deficiency causes inadequate new bone formation and affects millions of women worldwide. Melatonin can improve bone mineral density at the femoral neck in postmenopausal women with osteopenia. This study aimed to investigate the mechanism of melatonin in estrogen deficiency-induced osteoporosis by focusing on osteoblast differentiation. 12-week-old female C57BL/6J mice were ovariectomized (OVX) and intraperitoneally injected with 10 or 50 mg/kg of melatonin for 8 weeks. Micro-computerized tomography scanning demonstrated that melatonin alleviated OVX-induced bone loss in a dose-dependent manner. Serum levels of ALP and osteocalcin (OCN) were further increased, whereas tartrate-resistant acid phosphatase level was decreased by melatonin in OVX-treated mice. Melatonin promoted osteoblast differentiation in primary bone marrow mesenchymal stem cells from OVX mice. It also inhibited activation of NLRP3 inflammasome in femoral bone protein and in induced osteoblasts stimulated by OVX. Knockdown of NLRP3 attenuated OVX-induced repression of osteogenic differentiation. The NLRP3 inflammasome activator monosodium urate partly abrogated the effect of melatonin on the expression of osteoblastogenic markers, including Runx2 and OCN. Additionally, the results showed that melatonin suppressed NLRP3 inflammasome activation by regulating Wnt/β-catenin signaling, which was confirmed by the Wnt/β-catenin inhibitor recombinant DKK1. These results indicated that melatonin ameliorates estrogen deficiency-induced osteoporosis and impaired osteogenic differentiation potential by suppressing activation of the NLRP3 inflammasome via mediating the Wnt/β-catenin pathway.

Melatonin up‐regulates bone marrow mesenchymal stem cells osteogenic action but suppresses their mediated osteoclastogenesis via MT2‐inactivated NF‐κB pathway

“…Both 10 nM and 100 nM were close to the physiological concentration of melatonin, so this study is more likely to reflect the real in vivo micro‐environment than other studies (Han, Kim, Kim, Bae, & Kim, ; Maria et al, ; Nakade, Koyama, Ariji, Yajima, & Kaku, ; Xu et al, ), in which much higher doses were used to demonstrate the functions of melatonin on bone. Our data indicated that melatonin at its physiological concentration was sufficient to promote the osteogenic differentiation of bone marrow mesenchymal stem cells and affect bone marrow mesenchymal stem cell‐mediated osteoclastogenesis, especially at 10 nM, which was used the concentration used in these experiments.…”

“…In line with these findings, light/dark cycle‐mediated melatonin secretion is tensely associated with human bone physiology and melatonin supplementation could profoundly improve bone mass in perimenopause period (Witt‐Enderby et al, ). Accumulating evidence has also confirmed that melatonin (1–50 μM) could successfully promote anabolic effects on skeleton (Han, Kim, Kim, & Lee, ; Xu et al, ) and that much higher concentration (100 μM) of melatonin can reduce the negative effects of pro‐inflammatory cytokines on bone (Lian et al, ). However, the concentrations that are used are much higher than physiological levels and do not represent physiological situation, which limits the exploration of real phenomenon and its clinical use.…”

Melatonin and inflammation—Story of a double‐edged blade

“…In cultured keratinocytes, exposure to elevated glucose concentrations caused NLRP3 activation, which was inhibited by melatonin, findings that were interpreted as a means for promoting wound healing in diabetics . In mice, osteoporosis induced by ovariectomy was shown to involve NLRP3 activation . This inflammatory facet of osteoporosis might not appear that much surprising with regard to the development of osteoclasts from monocytes, but instead effects mainly concerned osteogenesis.…”

“…NLRP3 knockdown was reported to attenuate the inhibition of osteogenesis and similar results were obtained with melatonin, findings that were interpreted in terms of Wnt/β‐catenin signaling. A further argument for the involvement of NLRP3 inhibition in the osteogenic action of melatonin was deduced from the counteraction by the NLRP3 activator, monosodium urate . As the role of melatonin in the balance of osteogenic differentiation and osteoclastic activity seems to be much more complex and may also require the consideration of SIRT1, further studies may be necessary to clarify the relative contributions of the melatonin effects.…”

Melatonin: Another avenue for treating osteoporosis?

“…In vivo, 1‐year nightly oral melatonin (15 mg/L) given to Her2/neu female mice increased pErk1/2, pErk5, Runx2, osteoprotegerin, and receptor activator of NF‐kB (RANK) ligand (RANKL) levels in bone . Recent work by Xu et al indicated that melatonin suppresses estrogen deficiency‐induced osteoporosis and promotes osteoblastogenesis by inactivating the NLRP3 inflammasome. Melatonin inhibits fatty acid‐induced triglyceride accumulation in ROS17/2.8 cells, which may promote osteoblast differentiation and inhibit bone loss .…”