Raloxifene Stimulates Estrogen Signaling to Protect Against Age- and Sex-Related Intervertebral Disc Degeneration in Mice

The Role of Sex Hormones in Cartilaginous Tissues: A Scoping Review

Background

The use of sex hormones in the clinic for the management of musculoskeletal conditions is increasingly common. Despite this, the role of sex hormones in various joint tissues such as the intervertebral disc (IVD), temporomandibular joint (TMJ), and articular cartilage remains poorly understood. Here, we employ a database search strategy to critically examine the available literature in this field through a scoping review.

Methods

Using a 4-step protocol, primary research articles pertaining to sex hormones and the IVD, TMJ, or articular cartilage were identified and reviewed by two independent reviewers. ~3900 articles were identified in our initial search, and after review, ~140 were identified to be relevant to our tissues of interest and the effects of sex hormones.

Results

Within all joint tissues investigated here, there were limited investigations on the effects of testosterone. Studies reported here for these tissues indicate that sex hormones are likely beneficial in the context of age-associated joint diseases, but there are important limitations to how this translates to the clinic given that various animal models can display distinct responses to sex hormone exposure. Direct comparisons of sex hormone therapies are limited between biological sexes, but evidence indicates that the molecular responses are likely similar. Current evidence indicates that sex hormone exposure likely has anti-inflammatory effects within joint tissues at the level of gene and protein expression, but the mechanism is unknown.

Conclusion

Sex hormones such as testosterone and estrogen play an important role in inflammatory signaling within joint tissues, which could lead to novel interventions within the clinic for joint degeneration. However, understanding the biological mechanisms of hormones in these distinct tissues, between sexes, and with age is imperative for their proper implementation.

Myristic acid beneficially modulates intervertebral disc degeneration by preventing endplate osteochondral remodeling and vertebral osteoporosis in naturally aged mice

Background

The origin of intervertebral disc degeneration (IDD) is highly complex, where both cartilage endplate remodeling and vertebral osteoporosis are of utmost importance. Myristic acid (MA), a saturated fatty acid derived from nutmeg, a traditional Chinese herb, has been shown to boost memory. Additionally, its isomers have been verified to have anti-osteoporotic characteristics. However, the precise mechanism by which MA functions in relation to IDD remains unclear.

Methods

In vivo, a naturally aged animal model was used. The drug-administration method of MA was intraperitoneal injection to mice aged 22 months at a dose of 2 mg/kg·d for 2 months. Micro-CT observed vertebral bone mass and endplate changes, followed by Hematoxylin‒eosin (H&E), Masson, and Safranin-O staining of tissues. TRAP staining counted osteoclasts; immunohistochemistry detected the expressions of Aggrecan and Collagen II. Bioinformatics explored MA's anti-IDD mechanism. In vitro, MA-treated senescent endplate chondrocytes (induced by TBHP) were analyzed by RT-qPCR and immunofluorescence (IF) for senescence and matrix synthesis markers. TRAP and F-actin detected MA's effect on RAW264.7 osteoclast differentiation (induced by RANKL); qPCR examined the expressions of osteoclast genes.

Results

Using the naturally aged model, we found that MA tended to improve vertebral osteoporosis and endplate osteochondral remodeling, decreased the TRAP activity of the endplate, and alleviated IDD in naturally aged mice. Bioinformatics analysis suggested that the relationships among IDD, osteoporosis, and endplate degeneration were mainly linked to cellular senescence. In vitro, MA postponed the senescence of TBHP-induced endplate chondrocytes by increasing the expression of Aggrecan and decreasing the expressions of MMP-3, MMP-9, and the senescence markers p16 and p21. Additionally, MA notably inhibited osteoclast activity, as evidenced by a decrease in the number of osteoclasts and a significant suppression of F-actin formation. At the molecular level, MA efficiently reduced the expressions of osteoclast marker genes like ACP-5, CTSK, and DC-STAMP.

Conclusion

The findings of this research suggest that MA is capable of inhibiting endplate osteochondral remodeling and vertebral osteoporosis, diminishing osteoclastogenesis to preserve bone mass, and consequently delaying IDD in naturally aged mice. Hence, MA holds the potential to serve as an alternative therapeutic approach for IDD.

Engineered extracellular vesicle-based gene therapy for the treatment of discogenic back pain

Painful musculoskeletal disorders such as intervertebral disc (IVD) degeneration associated with chronic low back pain (termed "Discogenic back pain", DBP), are a significant socio-economic burden worldwide and contribute to the growing opioid crisis. Yet there are very few if any successful interventions that can restore the tissue's structure and function while also addressing the symptomatic pain. Here we have developed a novel non-viral gene therapy, using engineered extracellular vesicles (eEVs) to deliver the developmental transcription factor FOXF1 to the degenerated IVD in an in vivo model. Injured IVDs treated with eEVs loaded with FOXF1 demonstrated robust sex-specific reductions in pain behaviors compared to control groups. Furthermore, significant restoration of IVD structure and function in animals treated with FOXF1 eEVs were observed, with significant increases in disc height, tissue hydration, proteoglycan content, and mechanical properties. This is the first study to successfully restore tissue function while modulating pain behaviors in an animal model of DBP using eEV-based non-viral delivery of transcription factor genes. Such a strategy can be readily translated to other painful musculoskeletal disorders.

Low back pain and osteoarthritis pain: a perspective of estrogen

Low back pain (LBP) is the world's leading cause of disability and is increasing in prevalence more rapidly than any other pain condition. Intervertebral disc (IVD) degeneration and facet joint osteoarthritis (FJOA) are two common causes of LBP, and both occur more frequently in elderly women than in other populations. Moreover, osteoarthritis (OA) and OA pain, regardless of the joint, are experienced by up to twice as many women as men, and this difference is amplified during menopause. Changes in estrogen may be an important contributor to these pain states. Receptors for estrogen have been found within IVD tissue and nearby joints, highlighting the potential roles of estrogen within and surrounding the IVDs and joints. In addition, estrogen supplementation has been shown to be effective at ameliorating IVD degeneration and OA progression, indicating its potential use as a therapeutic agent for people with LBP and OA pain. This review comprehensively examines the relationship between estrogen and these pain conditions by summarizing recent preclinical and clinical findings. The potential molecular mechanisms by which estrogen may relieve LBP associated with IVD degeneration and FJOA and OA pain are discussed.