Tissue physiology revolving around the clock: circadian rhythms as exemplified by the intervertebral disc

Stimuli-Responsive Delivery Systems for Intervertebral Disc Degeneration

As a major cause of low back pain, intervertebral disc degeneration is an increasingly prevalent chronic disease worldwide that leads to huge annual financial losses. The intervertebral disc consists of the inner nucleus pulposus, outer annulus fibrosus, and sandwiched cartilage endplates. All these factors collectively participate in maintaining the structure and physiological functions of the disc. During the unavoidable degeneration stage, the degenerated discs are surrounded by a harsh microenvironment characterized by acidic, oxidative, inflammatory, and chaotic cytokine expression. Loss of stem cell markers, imbalance of the extracellular matrix, increase in inflammation, sensory hyperinnervation, and vascularization have been considered as the reasons for the progression of intervertebral disc degeneration. The current treatment approaches include conservative therapy and surgery, both of which have drawbacks. Novel stimuli-responsive delivery systems are more promising future therapeutic options than traditional treatments. By combining bioactive agents with specially designed hydrogels, scaffolds, microspheres, and nanoparticles, novel stimuli-responsive delivery systems can realize the targeted and sustained release of drugs, which can both reduce systematic adverse effects and maximize therapeutic efficacy. Trigger factors are categorized into internal (pH, reactive oxygen species, enzymes, etc.) and external stimuli (photo, ultrasound, magnetic, etc.) based on their intrinsic properties. This review systematically summarizes novel stimuli-responsive delivery systems for intervertebral disc degeneration, shedding new light on intervertebral disc therapy.

Impact of physical therapy techniques and common interventions on sleep quality in patients with chronic pain: A systematic review

This systematic review aims to find effectful healthcare strategies, with special focus on drug-free interventions and physical therapy, as part of the treatment for sleep in patients with chronic musculoskeletal pain. Data search was conducted across seven scientific databases. This review is deposited in the Prospero International prospective register of systematic reviews (CRD42023452574). Seventeen RCTs from different healthcare fields complied with our inclusion criteria. Two RCTs investigated manual therapy, five RCTs therapeutic exercise, one RCT Fu's subcutaneous needling, two RCTs physical agents (one on balneotherapy and one on cryo-stimulation), two RCTs cognitive-behavioral therapy, and four RCTs pharmacological therapy and their effect on sleep quality and/or quantity in patients suffering from chronic pain. We included the four RCT's in this systematic review with the purpose to be able to compare natural interventions with allopathic ones. As allopathic interventions are more prone to have secondary negative effects than physical therapy, compare the two types of interventions could be in favor of choosing the most effective treatment with the least secondary negative effects. Additionally, two RCTs on neurofeedback and limbic neuromodulation were also included. The results of the included studies suggest that strategies such as manual therapy, therapeutic exercise, Fu's subcutaneous needling, balneotherapy, cryo-stimulation, neurofeedback, limbic neuromodulation, cognitive-behavioral therapy, and pharmacological therapies have positive effects on patients suffering from chronic pain and sleep disturbances, especially when they suffer musculoskeletal pain. Secondary negative effects were found for the possible overuse of certain medicines such as morphine, a huge problem in the United States. Sleep deficiency is an independent risk factor for many diseases, including chronic pain syndrome and therefore more studies are needed to find non-toxic interventions for people suffering sleep disorders associated with systemic diseases and pain.

A scenario of unhealthy life cycle: The role of circadian rhythms in health

Circadian rhythms are oscillations in physiology and behavior caused by the circadian regulator. Cryptochromes, Periods, and Bmal1 are circadian clock genes that have been linked to aging and cancer. Human pathologies alter circadian clock gene expression, and transgenic rats with clock gene defects progress to cancer and age prematurely. In the growth of age-linked pathologies and carcinogenesis, cell proliferation and genome integrity play critical roles. The relationship concerning the cell cycle regulation and circadian clock is discussed in this article. The circadian clock controls the behavior and countenance of many main cell cycle and cell cycle check-point proteins, and cell cycle-associated proteins, in turn, control the activity and expression of circadian clock proteins. The circadian clock can be reset by DNA disruption, providing a molecular mechanism for mutual control amid the cell cycle and the clock. This circadian clock-dependent regulation of cell proliferation, composed with other circadian clock-dependent physiological functions including metabolism control, genotoxic and oxidative stress response, and DNA repair, unlocks new avenues for studying the processes of aging and carcinogenesis.

Disassembly of the TRIM56-ATR complex promotes cytoDNA/cGAS/STING axis-dependent intervertebral disc inflammatory degeneration

As the leading cause of disability worldwide, low back pain (LBP) is recognized as a pivotal socioeconomic challenge to the aging population and is largely attributed to intervertebral disc degeneration (IVDD). Elastic nucleus pulposus (NP) tissue is essential for the maintenance of IVD structural and functional integrity. The accumulation of senescent NP cells with an inflammatory hypersecretory phenotype due to aging and other damaging factors is a distinctive hallmark of IVDD initiation and progression. In this study, we reveal a mechanism of IVDD progression in which aberrant genomic DNA damage promoted NP cell inflammatory senescence via activation of the cyclic GMP-AMP synthase/stimulator of IFN genes (cGAS/STING) axis but not of absent in melanoma 2 (AIM2) inflammasome assembly. Ataxia-telangiectasia-mutated and Rad3-related protein (ATR) deficiency destroyed genomic integrity and led to cytosolic mislocalization of genomic DNA, which acted as a powerful driver of cGAS/STING axis-dependent inflammatory phenotype acquisition during NP cell senescence. Mechanistically, disassembly of the ATR-tripartite motif-containing 56 (ATR-TRIM56) complex with the enzymatic liberation of ubiquitin-specific peptidase 5 (USP5) and TRIM25 drove changes in ATR ubiquitination, with ATR switching from K63- to K48-linked modification, c thereby promoting ubiquitin-proteasome-dependent dynamic instability of ATR protein during NP cell senescence progression. Importantly, an engineered extracellular vesicle-based strategy for delivering ATR-overexpressing plasmid cargo efficiently diminished DNA damage-associated NP cell senescence and substantially mitigated IVDD progression, indicating promising targets and effective approaches to ameliorate the chronic pain and disabling effects of IVDD.

Causal effects of body mass index, education, and lifestyle behaviors on intervertebral disc disorders: Mendelian randomization study

This study aimed to investigate the causal risk factors for intervertebral disc disorders (IVDD) to help establish prevention strategies for IVDD-related diseases. We performed two-sample Mendelian randomization analyses to investigate the causal effects of body mass index (BMI), education, and lifestyle behaviors (sedentary behavior, smoking, and sleeping) on thoracic/thoracolumbar/lumbosacral IVDD (TTL-IVDD) and cervical IVDD. The inverse-variance weighted (IVW) method was conducted as the primary model to pool effect sizes using odds ratio and 95% confidence interval. The strength of causal evidence was evaluated from the effect size and different Mendelian randomization methods (MR-Egger/weighted median/weighted mode method, Cochran's Q test, leave-one-out analysis, MR Steiger, MR-PRESSO and radial IVW analyses). We found strong evidence for the causal associations between IVDD and BMI (TTL-IVDD, 1.27 [1.18, 1.37], p = 2.40 × 10-10 ; cervical IVDD, 1.24 [1.12, 1.37, p = 6.58 × 10-5 ), educational attainment (TTL-IVDD, 0.57 [0.51, 0.64], p = 9.64 × 10-21 ; cervical IVDD, 0.58 [0.49, 0.68], p = 1.78 × 10-10 ), leisure television watching (TTL-IVDD, 1.54 [1.29, 1.84], p = 7.80 × 10-6 ; cervical IVDD, 1.65 [1.29, 2.11], p = 0.0001), smoking initiation (TTL-IVDD, 1.37 [1.25, 1.50], p = 1.78 × 10-10 ; cervical IVDD, 1.32 [1.16, 1.51], p = 6.49 × 10-5 ), short sleep (TTL-IVDD, 1.28 [1.09, 1.49], p = 0.0027; cervical IVDD, 1.53 [1.21, 1.94], p = 0.0008), or frequent insomnia (TTL-IVDD, 1.20 [1.11, 1.30], p = 1.54 × 10-5 ; cervical IVDD, 1.37 [1.20, 1.57], p = 7.80 × 10-6 ). This study provided genetic evidence that increased BMI, low educational attainment, sedentary behavior by leisure television watching, smoking initiation, short sleep, and frequent insomnia were causal risk factors for IVDD. More efforts should be directed toward increasing public awareness of these modifiable risk factors and mobilizing individuals to adopt healthy lifestyles.

Achilles' Heel-The Significance of Maintaining Microenvironmental Homeostasis in the Nucleus Pulposus for Intervertebral Discs

The dysregulation of intracellular and extracellular environments as well as the aberrant expression of ion channels on the cell membrane are intricately linked to a diverse array of degenerative disorders, including intervertebral disc degeneration. This condition is a significant contributor to low back pain, which poses a substantial burden on both personal quality of life and societal economics. Changes in the number and function of ion channels can disrupt the water and ion balance both inside and outside cells, thereby impacting the physiological functions of tissues and organs. Therefore, maintaining ion homeostasis and stable expression of ion channels within the cellular microenvironment may prove beneficial in the treatment of disc degeneration. Aquaporin (AQP), calcium ion channels, and acid-sensitive ion channels (ASIC) play crucial roles in regulating water, calcium ions, and hydrogen ions levels. These channels have significant effects on physiological and pathological processes such as cellular aging, inflammatory response, stromal decomposition, endoplasmic reticulum stress, and accumulation of cell metabolites. Additionally, Piezo 1, transient receptor potential vanilloid type 4 (TRPV4), tension response enhancer binding protein (TonEBP), potassium ions, zinc ions, and tungsten all play a role in the process of intervertebral disc degeneration. This review endeavors to elucidate alterations in the microenvironment of the nucleus pulposus during intervertebral disc degeneration (IVDD), with a view to offer novel insights and approaches for exploring therapeutic interventions against disc degeneration.

Mechanical loading and hyperosmolarity as a daily resetting cue for skeletal circadian clocks

Daily rhythms in mammalian behaviour and physiology are generated by a multi-oscillator circadian system entrained through environmental cues (e.g. light and feeding). The presence of tissue niche-dependent physiological time cues has been proposed, allowing tissues the ability of circadian phase adjustment based on local signals. However, to date, such stimuli have remained elusive. Here we show that daily patterns of mechanical loading and associated osmotic challenge within physiological ranges reset circadian clock phase and amplitude in cartilage and intervertebral disc tissues in vivo and in tissue explant cultures. Hyperosmolarity (but not hypo-osmolarity) resets clocks in young and ageing skeletal tissues and induce genome-wide expression of rhythmic genes in cells. Mechanistically, RNAseq and biochemical analysis revealed the PLD2-mTORC2-AKT-GSK3β axis as a convergent pathway for both in vivo loading and hyperosmolarity-induced clock changes. These results reveal diurnal patterns of mechanical loading and consequent daily oscillations in osmolarity as a bona fide tissue niche-specific time cue to maintain skeletal circadian rhythms in sync.

Integrated analysis of single-cell transcriptome and structural biology approach reveals the dynamics changes of NP subtypes and roles of Menaquinone in attenuating intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a progressive and chronic disease, the mechanisms have been studied extensively as a whole, while the cellular heterogeneity of cells in nucleus pulposus (NP) tissues remained controversial for a long time. This study conducted integrated analysis through single-cell sequencing analysis, weighted gene co-expression network analysis (WGCNA), and differential expression analysis, to systematically decipher the longitudinal alterations of distinct NP subtypes, and also analyzed the most essential genes in the development of IDD. Then, this study further conducted structural biology method to discover the potential lead compounds through a suite of advanced approaches like high-throughput screening (HTVS), pharmaceutical characteristics assessment, CDOCKER module as well as molecular dynamics simulation, etc., aiming to ameliorate the progression of IDD. Totally 5 NP subpopulations were identified with distinct biological functions based on their unique gene expression patterns. The predominant dynamics changes mainly involved RegNPs and EffNPs, the RegNPs were mainly aggregated in normal NP tissues and drastically decreased in degenerative NP, while EffNPs, as pathogenic subtype, exhibited opposite phenomenon. Importantly, this study further reported the essential roles of Menaquinone in alleviating degenerative NP cells for the first time, which could provide solid evidence for the application of nutritional therapy in the treatment of IDD. This study combined scRNA-seq, bulk-RNA seq and HTVS techniques to systematically decipher the longitudinal changes of NP subtypes during IDD. EffNPs were considered to be 'chief culprit' in IDD progression, while the novel natural drug Menaquinone could reverse this phenomenon.Communicated by Ramaswamy H. Sarma.

Single-cell sequencing: New insights for intervertebral disc degeneration

Over the past decade, single-cell RNA sequencing (scRNA-seq) has revolutionized research on biological mechanisms of diseases. Moreover, this technique has been utilized to identify and characterize unique cell types and subpopulations, thereby illuminating cellular heterogeneity. The true value of scRNA-seq lies in its ability to detect transcriptional alterations or perturbed pathways within specific cell types under pathological conditions. In the context of intervertebral disc degeneration (IVDD), the pathophysiological foundation is largely rooted in inflammation. The primary target cells of IVDD are nucleus pulposus cells, annulus fibrosus cells, cartilage endplate cells, and macrophages. The advancements in scRNA-seq technology have triggered remarkable progress in IVDD treatment, leading to breakthroughs in the identification of cell subsets, functional analysis, novel therapeutic targets, and the differentiation and development of various cell types. This review is the first of its kind to introduce the application of scRNA-seq techniques in IVDD, with a focus on the most recent scRNA-seq studies that have defined the populations of various cell types and specific cell-cell interactions in IVDD. Furthermore, we highlight several promising future research directions for scRNA-seq in IVDD.

Umbilical cord mesenchymal stem cells for regenerative treatment of intervertebral disc degeneration

Intervertebral disc degeneration is thought to be a major contributor to low back pain, the etiology of which is complex and not yet fully understood. To compensate for the lack of drug and surgical treatment, mesenchymal stem cells have been proposed for regenerative treatment of intervertebral discs in recent years, and encouraging results have been achieved in related trials. Mesenchymal stem cells can be derived from different parts of the body, among which mesenchymal stem cells isolated from the fetal umbilical cord have excellent performance in terms of difficulty of acquisition, differentiation potential, immunogenicity and ethical risk. This makes it possible for umbilical cord derived mesenchymal stem cells to replace the most widely used bone marrow-derived and adipose tissue derived mesenchymal stem cells as the first choice for regenerating intervertebral discs. However, the survival of umbilical cord mesenchymal stem cells within the intervertebral disc is a major factor affecting their regenerative capacity. In recent years biomaterial scaffolds in tissue engineering have aided the survival of umbilical cord mesenchymal stem cells by mimicking the natural extracellular matrix. This seems to provide a new idea for the application of umbilical cord mesenchymal stem cells. This article reviews the structure of the intervertebral disc, disc degeneration, and the strengths and weaknesses of common treatment methods. We focus on the cell source, cell characteristics, mechanism of action and related experiments to summarize the umbilical cord mesenchymal stem cells and explore the feasibility of tissue engineering technology of umbilical cord mesenchymal stem cells. Hoping to provide new ideas for the treatment of disc degeneration.

Circadian Clock Regulation via Biomaterials for Nucleus Pulposus

Circadian clock disorder during tissue degeneration has been considered the potential pathogenesis for various chronic diseases, such as intervertebral disc degeneration (IVDD). In this study, circadian clock-regulating biomaterials (ClockMPs) that can effectively activate the intrinsic circadian clock of nucleus pulposus cells (NPCs) in IVDD and improve the physiological function of NPCs for disc regeneration are fabricated via air-microfluidic technique and the chemical cross-linking between polyvinyl alcohol and modified-phenylboronic acid. In vitro experiments verified that ClockMPs can scavenge reactive oxygen species to maintain a stable microenvironment for the circadian clock by promoting the binding of BMAL1 and CLOCK proteins. ClockMPs can regulate the expression of core circadian clock genes by activating the PI3K-AKT pathway in NPCs to remodel the intrinsic circadian clock and promote extracellular matrix synthesis. Furthermore, in vivo experiments of IVDD treated with ClockMPs proved that ClockMPs can promote disc regeneration by regulating the circadian clock of NPCs. In conclusion, ClockMPs provided a novel and promising strategy for circadian clock regulation during tissue regeneration.

Environmental polycyclic aromatic hydrocarbon exposure is associated with low back pain

Several studies have assessed the influence of several often-ignored environmental factors on low back pain (LBP), but the effects of environmental polycyclic aromatic hydrocarbon (PAH) exposure on LBP are unclear. During the 2001-2004 cycle of the National Health and Nutrition Examination Survey (NHANES), our study was given to a representative sample of US participants older than 20 (N = 2743). Environmental PAH exposure was calculated using urinary PAH metabolite concentrations. Weighted logistic regression was performed to assess the connection between PAH levels and LBP, with mediation analysis utilised to explore the underlying mechanism. Levels of 1-hydroxynaphthalene (1-OHNa), 2-hydroxynaphthalene (2-OHNa) and total PAHs had a statistically significant positive association with LBP. The odds ratios per 1-unit increase for log-transformed levels of urinary 1-OHNa, 2-OHNa, and total PAHs with LBP were 1.01 (95% CI 1.02-1.19), 1.19 (95% CI 1.04-1.36) and 1.16 (95% CI 1.03-1.32), respectively. The results revealed a strong dose-response association between 1-OHNa, 2-OHNa, total PAHs, and LBP risk. Subgroup analysis indicated that 2&3-OHPh may increase the risk of LBP in the lower family income subgroup. Gamma-glutamyl transaminase (GGT), known as a biomarker of oxidative stress, was strongly related to PAHs. The relationship between total PAHs and LBP was mediated in part by GGT. Our study demonstrates associations between environmental PAH exposure and LBP that need more research to determine the precise effects of various PAH compounds on LBP.

Determinants of diurnal variation in lumbar intervertebral discs and paraspinal muscles: A prospective quantitative magnetic resonance imaging study

PURPOSE

To prospectively investigate the determinants of diurnal variations in lumbar intervertebral discs and paraspinal muscles.

METHOD

71 females aged 19 ∼ 31 years were examined by morning-evening T2 mapping/diffusion kurtosis imaging (DKI), with weight and lifestyle information (time in night bed-rest [TIB], bed-napping, activity time, and sitting time) assessed by standardized questionnaires. Diurnal shifts in T2, mean diffusivity and mean kurtosis (T2-DS, MD-DS and MK-DS; morning-value minus evening-value) were evaluated for L4-S1 discs (normal, Pfirrmann grade Ⅰ/Ⅱ; degenerative, III/IV). T2 and T2-DS were assessed for L4/5 multifidus and erector spinalis.

RESULTS

For normal discs, bed-napping correlated with MD-DS and MK-DS in disc entirety (p = 0.001 and 0.004); increased activity time suggested higher T2-DS in nucleus pulposus (p = 0.004); prolonged sitting time predicted greater T2-DS in disc entirety and posterior inner annulus fibrosus (PI-AF, p ≤ 0.011); decreased TIB and weight suggested lower T2-DS and higher MK-DS in PI-AF (p = 0.001 ∼ 0.035). For degenerative discs, bed-napping predicted lower T2-DS in nucleus pulposus and PI-AF (p = 0.019); increased TIBsuggested higher T2-DS and lower MK-DS in PI-AF (p = 0.006 and 0.034); longer sitting time predicted higher MK-DS in PI-AF (p = 0.020). Paraspinal muscles exhibited diurnal T2 variation (p < 0.001) which did not correlate with lifestyle factors (p > 0.050).

CONCLUSIONS

Lifestyle and weight have causal effects on the diurnal variation of lumbar discs. Bed-rest may correlate with disc hydration and microstructural stability reserves for subsequent daytime activities. Sitting behavior could induce greater dehydration in normal discs and may alleviate diurnal microstructural rearrangement in degenerative discs. T2 mapping and DKI are promising tools to evaluate disc biomechanics in clinics.

Association of Low Back Pain with Shift Work: A Meta-Analysis

Shift work (SW) is the main working schedule worldwide, and it may cause sleep disorders, breast cancer, and cardiovascular disease. Low back pain (LBP) is a common problem in the workplace; however, the association between LBP and SW remains unclear. Therefore, we conducted a meta-analysis to determine the association between SW and LBP. This study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The PubMed, Embase, and Web of Science databases using a set of associated keywords were queried. The inclusion criteria were as follows: (1) adult employees hired by a company or organization; (2) SW exposure; and (3) the outcome of LBP according to examination or assessment. A total of 40 studies were included that met the inclusion criteria for the meta-analysis. SW was significantly associated with LBP (odds ratio [OR]: 1.31, 95% confidence interval [CI]: 1.18−1.47, p < 0.00001). Furthermore, it was observed that LBP was significantly associated with night shift (NS) (OR: 1.49, 95% CI: 1.24−1.82, p < 0.0001) but not with rotating shift (RS) (OR: 0.96, 95% CI: 0.76−1.22, p = 0.49). Moreover, LBP was significantly associated with SW in health care workers (HCWs) (OR: 1.40, 95% CI: 1.20−1.63, p < 0.0001) but not in non-HCWs (OR: 1.19, 95% CI: 0.94−1.50, p = 0.14). SW was significantly associated with LBP. Furthermore, the subgroup analysis showed that NS, but not RS, was associated with LBP. Compared with SW in non-HCWs, SW in HCWs was significantly associated with LBP.

Dynamic movement and turnover of extracellular matrices during tissue development and maintenance

Extracellular matrices (ECMs) are essential for the architecture and function of animal tissues. ECMs have been thought to be highly stable structures; however, too much stability of ECMs would hamper tissue remodelling required for organ development and maintenance. Regarding this conundrum, this article reviews multiple lines of evidence that ECMs are in fact rapidly moving and replacing components in diverse organisms including hydra, worms, flies, and vertebrates. Also discussed are how cells behave on/in such dynamic ECMs, how ECM dynamics contributes to embryogenesis and adult tissue homoeostasis, and what molecular mechanisms exist behind the dynamics. In addition, it is highlighted how cutting-edge technologies such as genome engineering, live imaging, and mathematical modelling have contributed to reveal the previously invisible dynamics of ECMs. The idea that ECMs are unchanging is to be changed, and ECM dynamics is emerging as a hitherto unrecognized critical factor for tissue development and maintenance.

The Nrf2 antioxidant defense system in intervertebral disc degeneration: Molecular insights

Intervertebral disc degeneration (IDD) is a common degenerative musculoskeletal disorder and is recognized as a major contributor to discogenic lower back pain. However, the molecular mechanisms underlying IDD remain unclear, and therapeutic strategies for IDD are currently limited. Oxidative stress plays pivotal roles in the pathogenesis and progression of many age-related diseases in humans, including IDD. Nuclear factor E2-related factor 2 (Nrf2) is a master antioxidant transcription factor that protects cells against oxidative stress damage. Nrf2 is negatively modulated by Kelch-like ECH-associated protein 1 (Keap1) and exerts important effects on IDD progression. Accumulating evidence has revealed that Nrf2 can facilitate the transcription of downstream antioxidant genes in disc cells by binding to antioxidant response elements (AREs) in promoter regions, including heme oxygenase-1 (HO-1), glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and NADPH quinone dehydrogenase 1 (NQO1). The Nrf2 antioxidant defense system regulates cell apoptosis, senescence, extracellular matrix (ECM) metabolism, the inflammatory response of the nucleus pulposus (NP), and calcification of the cartilaginous endplates (EP) in IDD. In this review, we aim to discuss the current knowledge on the roles of Nrf2 in IDD systematically.

Insights into the activity of a protein that regulates gene expression and protects cells against oxidative stress could yield novel treatments for lower back pain. Intervertebral disc degeneration (IDD) is a common cause of lower back pain, but the molecular mechanisms underlying IDD are unclear, meaning treatment options are limited. Oxidative stress is implicated in IDD, and scientists have begun exploring the role of nuclear factor E2-related factor 2 (Nrf2), a master regulator of the body’s antioxidant responses, in regulating IDD progression. In a review of recent research, Weishi Li at Peking University Third Hospital, Beijing, China, and co-workers point out that boosting the activity of Nrf2-related signaling pathways alleviates oxidative stress in intervertebral disc cells. The researchers suggest that therapies based on non-coding RNAs may prove valuable in activating Nrf2 in IDD patients.

New Hope for Treating Intervertebral Disc Degeneration: Microsphere-Based Delivery System

Intervertebral disc (IVD) degeneration (IVDD) has been considered the dominant factor in low back pain (LBP), and its etiological mechanisms are complex and not yet fully elucidated. To date, the treatment of IVDD has mainly focused on relieving clinical symptoms and cannot fundamentally solve the problem. Recently, a novel microsphere-based therapeutic strategy has held promise for IVD regeneration and has yielded encouraging results with in vitro experiments and animal models. With excellent injectability, biocompatibility, and biodegradability, this microsphere carrier allows for targeted delivery and controlled release of drugs, gene regulatory sequences, and other bioactive substances and supports cell implantation and directed differentiation, aiming to improve the disease state of IVD at the source. This review discusses the possible mechanisms of IVDD and the limitations of current therapies, focusing on the application of microsphere delivery systems in IVDD, including targeted delivery of active substances and drugs, cellular therapy, and gene therapy, and attempts to provide a new understanding for the treatment of IVDD.

Intervertebral Disc Degeneration: Biomaterials and Tissue Engineering Strategies toward Precision Medicine

Intervertebral disc degeneration is a common cause of discogenic low back pain resulting in significant disability. Current conservative or surgical intervention treatments do not reverse the underlying disc degeneration or regenerate the disc. Biomaterial-based tissue engineering strategies exhibit the potential to regenerate the disc due to their capacity to modulate local tissue responses, maintain the disc phenotype, attain biochemical homeostasis, promote anatomical tissue repair, and provide functional mechanical support. Despite preliminary positive results in preclinical models, these approaches have limited success in clinical trials as they fail to address discogenic pain. This review gives insights into the understanding of intervertebral disc pathology, the emerging concept of precision medicine, and the rationale of personalized biomaterial-based tissue engineering tailored to the severity of the disease targeting early, mild, or severe degeneration, thereby enhancing the efficacy of the treatment for disc regeneration and ultimately to alleviate discogenic pain. Further research is required to assess the relationship between disc degeneration and lower back pain for developing future clinically relevant therapeutic interventions targeted towards the subgroup of degenerative disc disease patients.

Circadian Rhythm Modulates the Therapeutic Activity of Pulsed Electromagnetic Fields on Intervertebral Disc Degeneration in Rats

Circadian rhythm (CR) imparts significant benefits in treating multiple diseases, such as heart diseases and arthritis. But the CR effect on intervertebral disc degeneration (IVDD) therapy remains unclear. Recent studies revealed that pulsed electromagnetic fields (PEMF) are capable of alleviating IVDD. In this study, we evaluated the CR-mediated regulation of PEMF therapeutic effect on IVDD induced by rat tail disc needle puncture. Our results demonstrated that the daytime PEMF stimulation (DPEMF) is more effective than the nighttime PEMF (NPEMF) in delaying IVDD. Moreover, the rats treated with DPEMF maintained better disc stability and histology after 8 weeks, relative to NPEMF. CR and PEMF cotherapies were also examined in cellular models, whereby serum shock was used to induce different levels of clock gene expression in the nucleus pulposus (NP), thus imitating CR in vitro. PEMF at ZT8 (higher level of clock gene expression) correlated with a higher extracellular matrix (ECM) component expression, compared to ZT20 (lower level of clock gene expression). Taken together, these data suggest a strong role of CR in regulating the beneficial effect of PEMF on IVDD. Our findings provide a potential clinical significance of CR in optimizing PEMF positive effects on IVDD.

Chronotypes and disabling musculoskeletal pain: A Finnish birth cohort study

BACKGROUND

It has been suggested that chronotype, the individual preference for 24-hour circadian rhythms, influences health. Sleep problems and mental distress are among the greatest risk factors for musculoskeletal (MS) pain. The aims of this study were first, to explore the associations between chronotypes and MS pain, with special reference to disabling MS pain, and second, to test whether mental distress and insomnia have a modifying role in the associations between chronotypes and MS pain.

METHODS

The dataset of 4,961 individuals was composed of Northern Finns surveyed on MS pain, chronotypes, and confounding factors (sex, insomnia, sleep duration, smoking, mental distress, occupational status, education level, and number of co-existing diseases) at 46 years. The relationships between chronotypes (evening [E], intermediate [I], and morning [M]) and MS pain were evaluated using multinomial logistic regression. To address the second aim, we included an interaction term (chronotype*mental distress, chronotype*insomnia) in the logistic model.

RESULTS

Compared to the M-types, both the E- and I-types had increased odds of suffering 'disabling pain' in the unadjusted model (odds ratio [OR] 1.79, 95% confidence interval [CI] 1.37-2.33; OR 1.54, 95% CI 1.29-1.84, respectively). However, the association remained statistically significant only after adjusting for all covariates among the I-types (OR 1.39, 95% CI 1.15-1.67). Neither mental distress nor insomnia was found to modify the chronotype-MS pain association.

CONCLUSIONS

The results highlight the importance of chronotypes for individuals' MS health but suggest the presence of confounding factors in the interplay between these factors.

Restoring the dampened expression of the core clock molecule BMAL1 protects against compression-induced intervertebral disc degeneration

The circadian clock participates in maintaining homeostasis in peripheral tissues, including intervertebral discs (IVDs). Abnormal mechanical loading is a known risk factor for intervertebral disc degeneration (IDD). Based on the rhythmic daily loading pattern of rest and activity, we hypothesized that abnormal mechanical loading could dampen the IVD clock, contributing to IDD. Here, we investigated the effects of abnormal loading on the IVD clock and aimed to inhibit compression-induced IDD by targeting the core clock molecule brain and muscle Arnt-like protein-1 (BMAL1). In this study, we showed that BMAL1 KO mice exhibit radiographic features similar to those of human IDD and that BMAL1 expression was negatively correlated with IDD severity by systematic analysis based on 149 human IVD samples. The intrinsic circadian clock in the IVD was dampened by excessive loading, and BMAL1 overexpression by lentivirus attenuated compression-induced IDD. Inhibition of the RhoA/ROCK pathway by Y-27632 or melatonin attenuated the compression-induced decrease in BMAL1 expression. Finally, the two drugs partially restored BMAL1 expression and alleviated IDD in a diurnal compression model. Our results first show that excessive loading dampens the circadian clock of nucleus pulposus tissues via the RhoA/ROCK pathway, the inhibition of which potentially protects against compression-induced IDD by preserving BMAL1 expression. These findings underline the importance of the circadian clock for IVD homeostasis and provide a potentially effective therapeutic strategy for IDD.

Single-Cell Transcriptome Profiling Reveals Multicellular Ecosystem of Nucleus Pulposus during Degeneration Progression

Although degeneration of the nucleus pulposus (NP) is a major contributor to intervertebral disc degeneration (IVDD) and low back pain, the underlying molecular complexity and cellular heterogeneity remain poorly understood. Here, a comprehensive single-cell resolution transcript landscape of human NP is reported. Six novel human NP cells (NPCs) populations are identified by their distinct molecular signatures. The potential functional differences among NPC subpopulations are analyzed. Predictive transcripts, transcriptional factors, and signal pathways with respect to degeneration grades are explored. It is reported that fibroNPCs is the subpopulation for end-stage degeneration. CD90+NPCs are observed to be progenitor cells in degenerative NP tissues. NP-infiltrating immune cells comprise a previously unrecognized diversity of cell types, including granulocytic myeloid-derived suppressor cells (G-MDSCs). Integrin αM (CD11b) and oxidized low density lipoprotein receptor 1 (OLR1) as surface markers of NP-derived G-MDSCs are uncovered. The G-MDSCs are found to be enriched in mildly degenerated (grade II and III) NP tissues compared to severely degenerated (grade IV and V) NP tissues. Their immunosuppressive function and alleviation effects on NPCs' matrix degradation are revealed in vitro. Collectively, this study reveals the NPC-type complexity and phenotypic characteristics in NP, thereby providing new insights and clues for IVDD treatment.

(-)-Epigallocatechin-3-gallate Ameliorates Intervertebral Disc Degeneration Through Reprogramming of the Circadian Clock

The circadian clock is vital in the management of our daily physiological as well as metabolic processes. Disturbances of the clock can cause degenerative and age-related diseases. Increasing evidence has indicated that the intervertebral discs contain an internal biological clock related to degeneration. However, to date, no bioactive compounds have been found that can ameliorate intervertebral disc degeneration (IDD) by restoring the circadian clock. (-)-Epigallocatechin-3-gallate (EGCG) is a nutritious food with powerful antioxidant properties, as well as entraining biological clock to improve health. The purpose of this study was to determine whether the protective effects of EGCG on nucleus pulposus (NPCs) under oxidative stress is related to the circadian clock. First, we found that EGCG attenuated H₂O₂-induced extracellular matrix degradation in NPCs and inhibited H₂O₂-induced NPC apoptosis. Our in vivo experiments also confirmed this finding. Furthermore, EGCG attenuated H₂O₂-triggered dampening of phase shifts and daily oscillations in circadian clock gene transcription as well as protein expression levels. Intriguingly, core clock gene (Bmal1) knockdown notably blocked the protective effects of EGCG. To our knowledge, this study provides the first convincing evidence that EGCG prevents IDD in a Bmal1-dependent manner. In general, EGCG supplementation can be used as a nutritional prevention strategy for the rehabilitation of degenerative diseases related to the circadian clock.