CRISPR/Cas9 knockout of MTA1 enhanced RANKL-induced osteoclastogenesis in RAW264.7 cells partly via increasing ROS activities

Redox signaling and antioxidant defense in osteoclasts

Bone remodeling is essential for the repair and replacement of damaged or aging bones. Continuous remodeling is necessary to prevent the accumulation of bone damage and to maintain bone strength and calcium balance. As bones age, the coupling mechanism between bone formation and absorption becomes dysregulated, and bone loss becomes dominant. Bone development and repair rely on interaction and communication between osteoclasts and surrounding cells. Osteoclasts are specialized cells that are accountable for bone resorption and degradation, and any abnormalities in their activity can result in notable alterations in bone structure and worsen disease symptoms. Recent findings from transgenic mouse models and bone analysis have greatly enhanced our understanding of the origin, differentiation pathway, and activation stages of osteoclasts. In this review, we explore osteoclasts and discuss the cellular and molecular events that drive their generation, focusing on intracellular oxidative and antioxidant signaling. This knowledge can help develop targeted therapies for diseases associated with osteoclast activation.

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.

Anemoside B4 attenuates RANKL-induced osteoclastogenesis by upregulating Nrf2 and dampens ovariectomy-induced bone loss

Increased numbers and functional overactivity of osteoclasts are the pathological basis for bone loss diseases such as osteoporosis, which are characterized by cortical bone thinning, decreased trabecular bone quantity, and reduced bone mineral density. Effective inhibition of osteoclast formation and bone resorption are important means of treating such skeletal diseases. Anemoside B4 (AB4), the main active component of Pulsatilla chinensis, possesses a wide range of anti-inflammatory and immunoregulatory effects. However, its effect and mechanism in osteoclast differentiation remain unclear. In this study, we found through tartrate-resistant acidic phosphatase (TRAcP) staining and immunofluorescence staining that AB4 inhibited the differentiation, fusion, and bone-resorption functions of osteoclasts induced by receptor activator of nuclear factor κB ligand (RANKL) in vitro. Additionally, real time PCR (RT-qPCR) and western blot analysis showed AB4 downregulated the expression of osteoclast marker genes, including Nfatc1, Fos, and Ctsk, while upregulating Nrf2 expression. AB4 (5 mg/kg) alleviated bone loss in ovariectomized mice by inhibiting osteoclast formation. Furthermore, the knockout of Nrf2 weakened the inhibitory effects of AB4 on osteoclast formation and related gene expression. In summary, the results suggest AB4 can inhibit osteoclast differentiation and function by activating Nrf2 and indicate AB4 may be a candidate drug for osteoporosis.