The intervertebral disc contains intrinsic circadian clocks that are regulated by age and cytokines and linked to degeneration

Exercise entrainment of musculoskeletal connective tissue clocks

The musculoskeletal system, crucial for movement and support, relies on the delicate balance of connective tissue homeostasis. Maintaining this equilibrium is essential for tissue health and function. There has been increasing evidence in the past decade that shows the circadian clock as a master regulator of extracellular matrix (ECM) homeostasis in several connective tissue clocks. Very recently, exercise has emerged as a significant entrainment factor for cartilage and intervertebral disk circadian rhythms. Understanding the implications of exercise on connective tissue peripheral clocks holds promise for enhancing tissue health and disease prevention. Exercise-induced factors such as heat, glucocorticoid release, mechanical loading, and inter-tissue cross talk may play pivotal roles in entraining the circadian rhythm of connective tissues. This mini review underscores the importance of elucidating the mechanisms through which exercise influences circadian rhythms in connective tissues to optimize ECM homeostasis. Leveraging exercise as a modulator of circadian rhythms in connective tissues may offer novel therapeutic approaches to physical training for preventing musculoskeletal disorders and enhancing recovery.

Nuclear receptor Rev-erbα alleviates intervertebral disc degeneration by recruiting NCoR-HDAC3 co-repressor and inhibiting NLRP3 inflammasome

Intervertebral discs (IVDs) are rhythmic tissues that experience daily low-load recovery. Notably, aging and abnormal mechanical stress predispose IVDs to degeneration due to dysrhythmia-induced disordered metabolism. Meanwhile, Rev-erbα acts as a transcriptional repressor in maintaining biorhythms and homeostasis; however, its function in IVD homeostasis and degeneration remains unclear. This study assessed the relationship between low Rev-erbα expression levels and IVD degeneration. Rev-erbα deficiency accelerated needle puncture or aging-induced IVD degeneration, characterized by increased extracellular matrix (ECM) catabolism and nucleus pulposus (NP) cell apoptosis. Mechanistically, Rev-erbα knockdown in NP cells aggravated rhIL1β-induced NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome activation, exacerbating the imbalanced ECM and NP cell apoptosis. Meanwhile, blocking NLRP3 inflammasome activation mitigated Rev-erbα deficiency and needle puncture-induced IVD degeneration. Particularly, Rev-erbα mediated the transcriptional repression of the NLRP3 inflammasome via the ligand heme-binding of nuclear receptor co-repressor (NCoR) and histone deacetylase 3 (HDAC3) complex. Thus, the increased expression of Rev-erbα in NP cells following short-term rhIL1β treatment failed to inhibit NLRP3 transcription in vitro owing to heme depletion. Pharmacological activation of Rev-erbα in vivo and in vitro alleviated IVD degeneration by altering the NLRP3 inflammasome. Taken together, targeting Rev-erbα may be a potential therapeutic strategy for alleviating IVD degeneration and its related diseases.

The specificities, influencing factors, and medical implications of bone circadian rhythms

Physiological processes within the human body are regulated in approximately 24-h cycles known as circadian rhythms, serving to adapt to environmental changes. Bone rhythms play pivotal roles in bone development, metabolism, mineralization, and remodeling processes. Bone rhythms exhibit cell specificity, and different cells in bone display various expressions of clock genes. Multiple environmental factors, including light, feeding, exercise, and temperature, affect bone diurnal rhythms through the sympathetic nervous system and various hormones. Disruptions in bone diurnal rhythms contribute to the onset of skeletal disorders such as osteoporosis, osteoarthritis and skeletal hypoplasia. Conversely, these bone diseases can be effectively treated when aimed at the circadian clock in bone cells, including the rhythmic expressions of clock genes and drug targets. In this review, we describe the unique circadian rhythms in physiological activities of various bone cells. Then we summarize the factors synchronizing the diurnal rhythms of bone with the underlying mechanisms. Based on the review, we aim to build an overall understanding of the diurnal rhythms in bone and summarize the new preventive and therapeutic strategies for bone disorders.

SR9009 attenuates inflammation-related NPMSC pyroptosis and IVDD through NR1D1/NLRP3/IL-1β pathway

Intervertebral disc is a highly rhythmical tissue. As a key factor linking biorhythm and inflammatory response, the shielding effect of NR1D1 in the process of intervertebral disc degeneration remains unclear. Here, we first confirmed that NR1D1 in the nucleus pulposus tissue presents periodic rhythmic changes and decreases in expression with intervertebral disc degeneration. Second, when NR1D1 was activated by SR9009 in vitro, NLRP3 inflammasome assembly and IL-1β production were inhibited, while ECM synthesis was increased. Finally, the vivo experiments further confirmed that the activation of NR1D1 can delay the process of disc degeneration to a certain extent. Mechanistically, we demonstrate that NR1D1 can bind to IL-1β and NLRP3 promoters, and that the NR1D1/NLRP3/IL-1β pathway is involved in this process. Our results demonstrate that the activation of NR1D1 can effectively reduce IL-1β secretion, alleviate LPS-induced NPMSC pyroptosis, and protect ECM degeneration.

The physiological role of TRP channels in sleep and circadian rhythm

TRP channels, are non-specific cationic channels that are involved in multiple physiological processes that include salivation, cellular secretions, memory extinction and consolidation, temperature, pain, store-operated calcium entry, thermosensation and functionality of the nervous system. Here we choose to look at the evidence that decisively shows how TRP channels modulate human neuron plasticity as it relates to the molecular neurobiology of sleep/circadian rhythm. There are numerous model organisms of sleep and circadian rhythm that are the results of the absence or genetic manipulation of the non-specific cationic TRP channels. Drosophila and mice that have had their TRP channels genetically ablated or manipulated show strong evidence of changes in sleep duration, sleep activity, circadian rhythm and response to temperature, noxious odours and pattern of activity during both sleep and wakefulness along with cardiovascular and respiratory function during sleep. Indeed the role of TRP channels in regulating sleep and circadian rhythm is very interesting considering the parallel roles of TRP channels in thermoregulation and thermal response with concomitant responses in growth and degradation of neurites, peripheral nerves and neuronal brain networks. TRP channels provide evidence of an ability to create, regulate and modify our sleep and circadian rhythm in a wide array of physiological and pathophysiological conditions. In the current review, we summarize previous results and novel recent advances in the understanding of calcium ion entry via TRP channels in different sleep and circadian rhythm conditions. We discuss the role of TRP channels in sleep and circadian disorders.

Increased HIF-2α activity in the nucleus pulposus causes intervertebral disc degeneration in the aging mouse spine

Hypoxia-inducible factors (HIFs) are essential to the homeostasis of hypoxic tissues. Although HIF-2α, is expressed in nucleus pulposus (NP) cells, consequences of elevated HIF-2 activity on disc health remains unknown. We expressed HIF-2α with proline to alanine substitutions (P405A; P531A) in the Oxygen-dependent degradation domain (HIF-2αdPA) in the NP tissue using an inducible, nucleus pulposus-specific K19CreERT allele to study HIF-2α function in the adult intervertebral disc. Expression of HIF-2α in NP impacted disc morphology, as evident from small but significantly higher scores of degeneration in NP of 24-month-old K19CreERT; HIF-2αdPA (K19-dPA) mice. Noteworthy, comparisons of grades within each genotype between 14 months and 24 months indicated that HIF-2α overexpression contributed to more pronounced changes than aging alone. The annulus fibrosus (AF) compartment in the 14-month-old K19-dPA mice exhibited lower collagen turnover and Fourier transform-infrared (FTIR) spectroscopic imaging analyses showed changes in the biochemical composition of the 14- and 24-month-old K19-dPA mice. Moreover, there were changes in aggrecan, chondroitin sulfate, and COMP abundance without alterations in NP phenotypic marker CA3, suggesting the overexpression of HIF-2α had some impact on matrix composition but not the cell phenotype. Mechanistically, the global transcriptomic analysis showed enrichment of differentially expressed genes in themes closely related to NP cell function such as cilia, SLIT/ROBO pathway, and HIF/Hypoxia signaling at both 14- and 24-month. Together, these findings underscore the role of HIF-2α in the pathogenesis of disc degeneration in the aged spine.

Intervertebral disc-intrinsic Hedgehog signaling maintains disc cell phenotypes and prevents disc degeneration through both cell autonomous and non-autonomous mechanisms

Intervertebral disc degeneration is closely related to abnormal phenotypic changes in disc cells. However, the mechanism by which disc cell phenotypes are maintained remains poorly understood. Here, Hedgehog-responsive cells were found to be specifically localized in the inner annulus fibrosus and cartilaginous endplate of postnatal discs, likely activated by Indian Hedgehog. Global inhibition of Hedgehog signaling using a pharmacological inhibitor or Agc1-CreERT2-mediated deletion of Smo in disc cells of juvenile mice led to spontaneous degenerative changes in annulus fibrosus and cartilaginous endplate accompanied by aberrant disc cell differentiation in adult mice. In contrast, Krt19-CreER-mediated deletion of Smo specifically in nucleus pulposus cells led to healthy discs and normal disc cell phenotypes. Similarly, age-related degeneration of nucleus pulposus was accelerated by genetic inactivation of Hedgehog signaling in all disc cells, but not in nucleus pulposus cells. Furthermore, inactivation of Gli2 in disc cells resulted in partial loss of the vertebral growth plate but otherwise healthy discs, whereas deletion of Gli3 in disc cells largely corrected disc defects caused by Smo ablation in mice. Taken together, our findings not only revealed for the first time a direct role of Hedgehog-Gli3 signaling in maintaining homeostasis and cell phenotypes of annuls fibrosus and cartilaginous endplate, but also identified disc-intrinsic Hedgehog signaling as a novel non-cell-autonomous mechanism to regulate nucleus pulposus cell phenotype and protect mice from age-dependent nucleus pulposus degeneration. Thus, targeting Hedgehog signaling may represent a potential therapeutic strategy for the prevention and treatment of intervertebral disc degeneration.

The sonic hedgehog pathway suppresses oxidative stress and senescence in nucleus pulposus cells to alleviate intervertebral disc degeneration via GPX4

Disruption of intervertebral disc (IVD) homeostasis caused by oxidative stress and nucleus pulposus cell (NPC) senescence is a main cause of intervertebral disc degeneration (IDD). The sonic hedgehog (Shh) pathway plays an important role in IVD development, but its roles in IDD are unknown. This study aimed to investigate the effects of the Shh pathway on the alleviation of IDD and the related mechanisms. In vivo, the effect of the Shh pathway on IVD homeostasis was studied by intraperitoneal injection of recombinant Shh (rShh) and GANT61 based on puncture-induced IDD. GANT61, lentivirus-coated sh-Gli1 and rShh were used to investigate the role and mechanism of the Shh pathway in NPCs based on senescence induced by Braco19 and oxidative stress induced by TBHP. Shh pathway expression decreased, and senescence and oxidative stress increased with age. Intraperitoneal injection of rShh activated the Shh pathway to suppress oxidative stress and NPC senescence and consequently alleviated needle puncture-induced IDD. In vitro, the Shh pathway upregulated glutathione peroxidase 4 (GPX4) expression to suppress oxidative stress and senescence in NPCs. Moreover, GPX4 suppression in NPCs by si-GPX4 significantly reduced the protective effect of the Shh pathway on oxidative stress and senescence in NPCs. Our results demonstrate for the first time that the Shh pathway plays a key role in the alleviation of IDD by suppressing oxidative stress and cell senescence in NP tissues. This study provides a new potential target for the prevention and reversal of IDD.

A new perspective on intervertebral disc calcification-from bench to bedside

Disc degeneration primarily contributes to chronic low back and neck pain. Consequently, there is an urgent need to understand the spectrum of disc degeneration phenotypes such as fibrosis, ectopic calcification, herniation, or mixed phenotypes. Amongst these phenotypes, disc calcification is the least studied. Ectopic calcification, by definition, is the pathological mineralization of soft tissues, widely studied in the context of conditions that afflict vasculature, skin, and cartilage. Clinically, disc calcification is associated with poor surgical outcomes and back pain refractory to conservative treatment. It is frequently seen as a consequence of disc aging and progressive degeneration but exhibits unique molecular and morphological characteristics: hypertrophic chondrocyte-like cell differentiation; TNAP, ENPP1, and ANK upregulation; cell death; altered Pi and PPi homeostasis; and local inflammation. Recent studies in mouse models have provided a better understanding of the mechanisms underlying this phenotype. It is essential to recognize that the presentation and nature of mineralization differ between AF, NP, and EP compartments. Moreover, the combination of anatomic location, genetics, and environmental stressors, such as aging or trauma, govern the predisposition to calcification. Lastly, the systemic regulation of calcium and Pi metabolism is less important than the local activity of PPi modulated by the ANK-ENPP1 axis, along with disc cell death and differentiation status. While there is limited understanding of this phenotype, understanding the molecular pathways governing local intervertebral disc calcification may lead to developing disease-modifying drugs and better clinical management of degeneration-related pathologies.

Advanced glycation end products induce nucleus pulposus cell apoptosis by upregulating TXNIP via inhibiting glycolysis pathway in intervertebral disc degeneration

Accumulation of advanced glycation end products (AGEs) causes apoptosis in human nucleus pulposus cells (NPCs), contributing to intervertebral disc degeneration (IVDD). The purpose of this study was to determine the roles of thioredoxin-interacting protein (TXNIP) in the mechanisms underlying AGE-induced apoptosis of NPCs. TXNIP was silenced or overexpressed in HNPCs exposed to AGEs. Glycolysis was assessed using extracellular acidification rate (ECAR), ATP level, GLUT1, and GLUT4 measurements. AGEs, TXNIP, GLUT1, and GLUT4 levels in IVDD patients were measured as well. In NPCs, AGEs reduced cell viability, induced apoptosis, inhibited glycolysis, and increased TXNIP expression. Silencing TXNIP compromised the effects of AGEs on cell viability, apoptosis, and glycolysis in NPCs. Furthermore, TXNIP overexpression resulted in decreased cell viability, increased apoptotic cells, and glycolysis suppression. Furthermore, co-treatment with a glycolysis inhibitor improved TXNIP silencing's suppressive effects on AGE-induced cell injury in NPCs. In IVDD patients with Pfirrmann Grades II-V, increasing trends in AGEs and TXNIP were observed, while decreasing trends in GLUT1 and GLUT4. AGE levels had positive correlations with TXNIP levels. Both AGE and TXNIP levels correlated negatively with GLUT1 and GLUT4. Our study indicates that TXNIP plays a role in mediating AGE-induced cell injury through suppressing glycolysis. The accumulation of AGEs, the upregulation of TXNIP, and the downregulation of GLUT1 and GLUT4 are all linked to the progression of IVDD.

Increased HIF-2α Activity in the Nucleus Pulposus Causes Intervertebral Disc Degeneration in the Aging Mouse Spine

Hypoxia-inducible factors (HIFs) are essential to the homeostasis of hypoxic tissues. Although HIF-2α, is expressed in nucleus pulposus (NP) cells, consequences of elevated HIF-2 activity on disc health remains unknown. We expressed HIF-2α with proline to alanine substitutions (P405A;P531A) in the Oxygen-dependent degradation domain (HIF-2αdPA) in the NP tissue using an inducible, nucleus pulposus-specific K19 CreERT allele to study HIF-2α function in the adult intervertebral disc. Expression of HIF-2α in NP impacted disc morphology, as evident from small but significantly higher scores of degeneration in NP of 24-month-old K19 CreERT ; HIF-2α dPA (K19-dPA) mice. Noteworthy, comparisons of grades within each genotype between 14 months and 24 months indicated that HIF-2α overexpression contributed to more pronounced changes than aging alone. The annulus fibrosus (AF) compartment in the 14-month-old K19-dPA mice exhibited lower collagen turnover and Fourier transform-infrared (FTIR) spectroscopic imaging analyses showed changes in the biochemical composition of the 14-and 24-month-old K19-dPA mice. Moreover, there were changes in aggrecan, chondroitin sulfate, and COMP abundance without alterations in NP phenotypic marker CA3, suggesting the overexpression of HIF-2α had some impact on matrix composition but not the cell phenotype. Mechanistically, the global transcriptomic analysis showed enrichment of differentially expressed genes in themes closely related to NP cell function such as cilia, SLIT/ROBO pathway, and HIF/Hypoxia signaling at both 14- and 24-months. Together, these findings underscore the role of HIF-2α in the pathogenesis of disc degeneration in the aged spine.

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.

Tick tock, the cartilage clock

Osteoarthritis (OA) is the most common age-related joint disease, affecting articular cartilage and other joint structures, causing severe pain and disability. Due to a limited understanding of the underlying disease pathogenesis, there are currently no disease-modifying drugs for OA. Circadian rhythms are generated by cell-intrinsic timekeeping mechanisms which are known to dampen during ageing, increasing disease risks. In this review, we focus on one emerging area of chondrocyte biology, the circadian clocks. We first provide a historical perspective of circadian clock discoveries and the molecular underpinnings. We will then focus on the expression and functions of circadian clocks in articular cartilage, including their rhythmic target genes and pathways, links to ageing, tissue degeneration, and OA, as well as tissue niche-specific entrainment pathways. Further research into cartilage clocks and ageing may have broader implications in the understanding of OA pathogenesis, the standardization of biomarker detection, and the development of novel therapeutic routes for the prevention and management of OA and other musculoskeletal diseases.

Identification and experimental validation of key extracellular proteins as potential targets in intervertebral disc degeneration

Aims

This study aimed, through bioinformatics analysis and in vitro experiment validation, to identify the key extracellular proteins of intervertebral disc degeneration (IDD).

Methods

The gene expression profile of GSE23130 was downloaded from the Gene Expression Omnibus (GEO) database. Extracellular protein-differentially expressed genes (EP-DEGs) were screened by protein annotation databases, and we used Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) to analyze the functions and pathways of EP-DEGs. STRING and Cytoscape were used to construct protein-protein interaction (PPI) networks and identify hub EP-DEGs. NetworkAnalyst was used to analyze transcription factors (TFs) and microRNAs (miRNAs) that regulate hub EP-DEGs. A search of the Drug Signatures Database (DSigDB) for hub EP-DEGs revealed multiple drug molecules and drug-target interactions.

Results

A total of 56 EP-DEGs were identified in the differential expression analysis. EP-DEGs were enriched in the extracellular structure organization, ageing, collagen-activated signalling pathway, PI3K-Akt signalling pathway, and AGE-RAGE signalling pathway. PPI network analysis showed that the top ten hub EP-DEGs are closely related to IDD. Correlation analysis also demonstrated a significant correlation between the ten hub EP-DEGs (p＜0.05), which were selected to construct TF-gene interaction and TF-miRNA coregulatory networks. In addition, ten candidate drugs were screened for the treatment of IDD.

Conclusion

The findings clarify the roles of extracellular proteins in IDD and highlight their potential as promising novel therapeutic targets.

Patient-related risk factors and lifestyle factors for lumbar degenerative disc disease: a systematic review

OBJECTIVE

Back pain is a very widespread disease pattern and is one of the most frequent causes for consultation of a physician in general. In most cases, discogenic changes are the pathomorphological correlate of back pain. Numerous risk factors have been identified for these degenerative changes, but the influence and significance of the risk factors remain unclear, which was the aim of this systematic review.

METHODS

A systematic literature search of the commonly used Pubmed database was performed using specific MESH terms. Further selection of the included studies was performed according to the PRISMA scheme, taking into account scientific merit as well as the relation to the research question.

RESULTS

A total of 111 studies out of 1035 found were finally included in the literature search. 134 risk factors for disc degeneration and disc herniation were identified. These were divided into (1) patient-specific risk factors (n░=░34), (2) radiological risk factors (n░=░31), (3) lifestyle risk factors (n░=░6), (4) workplace-related risk factors (n░=░12), (5) genetic risk factors (n░=░50), and (6) other risk factors (n░=░1). Non-adjustable risk factors were age >50 years (OR 1.7/year), female gender (OR 1.41), family disposition (OR 4.0), comorbidities like atherosclerosis (OR 2.24), arthritic changes in other joints (OR 3.1) and history of injuries of the back (OR 3.1). Adjustable factors were elevated BMI (OR 2.77), comorbidities like hypertension (OR 1.25), dyslipidemia (OR 1.26) and diabetes mellitus (OR 6.8), as well as lifestyle habits like smoking (OR 3.8).

DISCUSSION

In summary, intervertebral disc degenerations and herniations represent multifactorial events whose risk factors can be partly influenced and partly not influenced. This systematic review highlights the current state of knowledge as a basis for creating patient-specific algorithms to calculate risk for the development or progression of degenerative disc changes and disc herniations.

The clock transcription factor BMAL1 is a key regulator of extracellular matrix homeostasis and cell fate in the intervertebral disc

The circadian clock in mammals temporally coordinates physiological and behavioural processes to anticipate daily rhythmic changes in their environment. Chronic disruption to circadian rhythms (e.g., through ageing or shift work) is thought to contribute to a multitude of diseases, including degeneration of the musculoskeletal system. The intervertebral disc (IVD) in the spine contains circadian clocks which control ∼6% of the transcriptome in a rhythmic manner, including key genes involved in extracellular matrix (ECM) homeostasis. However, it remains largely unknown to what extent the local IVD molecular clock is required to drive rhythmic gene transcription and IVD physiology. In this work, we identified profound age-related changes of ECM microarchitecture and an endochondral ossification-like phenotype in the annulus fibrosus (AF) region of the IVD in the Col2a1-Bmal1 knockout mice. Circadian time series RNA-Seq of the whole IVD in Bmal1 knockout revealed loss of circadian patterns in gene expression, with an unexpected emergence of 12 h ultradian rhythms, including FOXO transcription factors. Further RNA sequencing of the AF tissue identified region-specific changes in gene expression, evidencing a loss of AF phenotype markers and a dysregulation of ECM and FOXO pathways in Bmal1 knockout mice. Consistent with an up-regulation of FOXO1 mRNA and protein levels in Bmal1 knockout IVDs, inhibition of FOXO1 in AF cells suppressed their osteogenic differentiation. Collectively, these data highlight the importance of the local molecular clock mechanism in the maintenance of the cell fate and ECM homeostasis of the IVD. Further studies may identify potential new molecular targets for alleviating IVD degeneration.

TMT-Based Proteomics Analysis of Senescent Nucleus Pulposus from Patients with Intervertebral Disc Degeneration

Lower back pain, a leading cause of disability worldwide, is associated with intervertebral disc degeneration (IDD) in approximately 40% of cases. Although nucleus pulposus (NP) cell senescence is a major contributor to IDD, the underlying mechanisms remain unclear. We collected NP samples from IDD patients who had undergone spinal surgery. Healthy and senescent NP tissues (n = 3) were screened using the Pfirrmann grading system combined with immunohistochemistry, as well as hematoxylin and eosin, Safranin O, Alcian blue, and Masson staining. Differentially expressed proteins (DEPs) were identified using quantitative TMT-based proteomics technology. Bioinformatics analyses included gene ontology (GO) annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and protein-protein interaction (PPI) analyses. In addition, immunofluorescence was used to verify protein expression. In total, 301 DEPs were identified in senescent NP tissues, including 92 upregulated and 209 downregulated proteins. In GO, DEPs were primarily associated with NF-kappaB transcription factor, extracellular regions, cellular protein metabolic processes, and post-translational protein modification. The enriched KEGG pathways included TGF-β, Wnt, RAP1, interleukin-17, extracellular matrix-receptor adhesion, and PI3K/Akt signaling pathways. PPI analysis demonstrated interactions between multiple proteins. Finally, immunofluorescence verified the expressions of MMP3, LUM, TIMP1, and CDC42 in senescent NP cells. Our study provides valuable insights into the mechanisms underlying senescent NP tissues in IDD patients. DEPs provide a basis for further investigation of the effects of senescent factors on IDD.

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.

Circ-STC2 promotes the ferroptosis of nucleus pulposus cells via targeting miR-486-3p/TFR2 axis

BACKGROUND

Low back pain (LBP) has become the second leading cause of disability worldwide, which has brought great economic burden to people. It is generally believed that intervertebral disc degeneration (IDD) is the main cause of LBP. This study aimed to explore the role of circ-STC2 in the pathogenesis of IDD.

METHODS

Nucleus pulposus cells (NPCs) were treated with T-Butyl Hydrogen Peroxide (TBHP) to establish IDD model in vitro. RT-qPCR was performed to detect mRNA expressions. The cell viability was detected with CCK-8 assay. The levels of lactate dehydrogenase (LDH), malondialdehyde (MDA), Fe2+ and glutathione (GSH) of NPCs were measured by corresponding kits. The protein expressions were determined by western blot. Dual-luciferase reporter and RNA pull-down assays were conducted to verify the relationship between circ-STC2 or transferrin recepto 2 (TFR2) and miR-486-3p.

RESULTS

Circ-STC2 and TFR2 expressions were up-regulated in IDD tissues, and miR-486-3p expression was down-regulated. Knockdown of circ-STC2 promoted the cell viability and inhibited the ferroptosis of the NPCs. The GSH levels, and glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) protein expressions were increased, the LDH, MDA and Fe2+ levels and achaete-scute complexlike 4 (ASCL4) protein expressions were decreased after circ-STC2 knockdown. Knockdown of miR-486-3p abrogated the si-circ-STC2 effects and overexpression of TFR2 reversed the miR-486-3p mimic effects.

CONCLUSIONS

Circ-STC2 inhibits the cell viability, induced the ferroptosis of the TBHP treated NPCs via targeting miR-486-3p/TFR2 axis.

Loss of function mutation in Ank causes aberrant mineralization and acquisition of osteoblast-like-phenotype by the cells of the intervertebral disc

Pathological mineralization of intervertebral disc is debilitating and painful and linked to disc degeneration in a subset of human patients. An adenosine triphosphate efflux transporter, progressive ankylosis (ANK) is a regulator of extracellular inorganic pyrophosphate levels and plays an important role in tissue mineralization. However, the function of ANK in intervertebral disc has not been fully explored. Herein we analyzed the spinal phenotype of Ank mutant mice (ank/ank) with attenuated ANK function. Micro-computed tomography and histological analysis showed that loss of ANK function results in the aberrant annulus fibrosus mineralization and peripheral disc fusions with cranial to caudal progression in the spine. Vertebrae in ank mice exhibit elevated cortical bone mass and increased tissue non-specific alkaline phosphatase-positive endplate chondrocytes with decreased subchondral endplate porosity. The acellular dystrophic mineral inclusions in the annulus fibrosus were localized adjacent to apoptotic cells and cells that acquired osteoblast-like phenotype. Fourier transform infrared spectral imaging showed that the apatite mineral in the outer annulus fibrosus had similar chemical composition to that of vertebral bone. Transcriptomic analysis of annulus fibrosus and nucleus pulposus tissues showed changes in several biological themes with a prominent dysregulation of BMAL1/CLOCK circadian regulation. The present study provides new insights into the role of ANK in the disc tissue compartments and highlights the importance of local inorganic pyrophosphate metabolism in inhibiting the mineralization of this important connective tissue.

The circadian clock and extracellular matrix homeostasis in aging and age-related diseases

The extracellular matrix (ECM) is the noncellular scaffolding component present within all tissues and organs. It provides crucial biochemical and biomechanical cues to instruct cellular behavior and has been shown to be under circadian clock regulation, a highly conserved cell-intrinsic timekeeping mechanism that has evolved with the 24-hour rhythmic environment. Aging is a major risk factor for many diseases, including cancer, fibrosis, and neurodegenerative disorders. Both aging and our modern 24/7 society disrupt circadian rhythms, which could contribute to altered ECM homeostasis. Understanding the daily dynamics of ECM and how this mechanism changes with age will have a profound impact on tissue health, disease prevention, and improving treatments. Maintaining rhythmic oscillations has been proposed as a hallmark of health. On the other hand, many hallmarks of aging turn out to be key regulators of circadian timekeeping mechanisms. In this review, we summarize new work linking the ECM with circadian clocks and tissue aging. We discuss how the changes in the biomechanical and biochemical properties of ECM during aging may contribute to circadian clock dysregulation. We also consider how the dampening of clocks with age could compromise the daily dynamic regulation of ECM homeostasis in matrix-rich tissues. This review aims to encourage new concepts and testable hypotheses about the two-way interactions between circadian clocks and ECM in the context of aging.

ERBB2-PTGS2 axis promotes intervertebral disc degeneration by regulating senescence of nucleus pulposus cells

Intervertebral disc degeneration (IDD) is considered one of the main causes of low back pain and lumbar disc herniation. Various studies have shown that disc cell senescence plays a critical role in this process. however, its role in IDD is yet unclear. In this study, we explored the role of senescence-related genes (SR-DEGs) and its underlying mechanism in IDD. A total of 1325 differentially expressed genes (DEGs) were identified using Gene Expression Omnibus (GEO) database GSE41883. 30 SR-DEGs were identified for further functional enrichment and pathway analysis, and two hub SR-DEGs (ERBB2 and PTGS2) were selected to construct transcription factor (TF)-gene interaction and TF-miRNA coregulatory networks, and 10 candidate drugs were screened for the treatment of IDD. Last but not least, in vitro experiments show that ERBB2 expression decreased and PTGS2 expression increased in human nucleus pulposus (NP) cell senescence model treated with TNF-α. After lentivirus-mediated overexpression of ERBB2, the expression of PTGS2 decreased and the senescence level of NP cells decreased. Overexpression of PTGS2 reversed the anti-senescence effects of ERBB2. The findings in this study suggested that ERBB2 overexpression further reduced NP cell senescence by inhibiting PTGS2 levels, which ultimately alleviated IDD. Taken together, our findings provide new insights into the roles of senescence-related genes in IDD and highlight a novel target of ERBB2-PTGS2 axis for therapeutic strategies.

Gli1 depletion induces oxidative stress and apoptosis of nucleus pulposus cells via Fos in intervertebral disc degeneration

Background

Intervertebral disc degeneration (IDD) is the most common chronic disease. Oxidative stress and apoptosis of nucleus pulposus (NP) cells disrupt intervertebral disc (IVD) homeostasis, which is the main cause of IDD. Glioma-associated oncogene 1 (Gli1) is an important transcription factor in the Hedgehog (Hh) pathway. Depletion of Gli1 accelerates the occurrence and development of degenerative diseases. This study aimed to explore the role of aging related Gli1 depletion in the progression of IDD.

Methods

The relationship between aging related Gli1 depletion and IDD was studied in the NP tissues of human and rats of different ages, and the levels of oxidative stress and NP cell apoptosis during IDD were explored. Gli1 depletion of NP cells were established by targeting inhibitor GANT61 or lentivirus-coated Gli1 sh-RNA (sh-Gli1) to explore the role of Gli1 in NP cells and underlying mechanism. Exogenous Gli1 depletion induced IDD of rats was established by intraperitoneal injection of GANT61. Also, the roles of Fos in the Gli1 depletion induced NP cell oxidative stress, apoptosis and IDD were investigated.

Results

Gli1 was down-regulated in the tissues of degenerative NP, and the level of Gli1 was negatively correlated with the severity of aging related IDD in human and rats. Furthermore, we found enhanced oxidative stress and apoptosis in degenerative NP tissues. Gli1 depletion promoted oxidative stress and apoptosis of NP cells and resulted in the degradation of extracellular matrix (ECM) and decreased ECM synthesis. Transcriptome sequencing showed that Gli1 depletion caused Fos activation in NP cells. the effect of Gli1 depletion on the oxidative stress and apoptosis of NP cells were retarded by Fos inhibitor. In vivo, Fos inhibition alleviated the IDD induced by exogenous Gli1 depletion.

Conclusions

This study revealed for the first time that Gli1 is gradually depleted in NP with IDD progression. Exogenous Gli1 depletion causes oxidative stress and apoptosis of NP cells both in vivo and in vitro. Fos suppression effectively retards the destructive effects of Gli1 depletion on IVD homoeostasis.The translational potential of this article: This study may provide new potential targets for preventing and reversing IDD. Maintaining Gli1 expression in NP and suppressing Fos activation may be an effective treatment strategy for IDD.

Tissue-Engineered Injectable Gelatin-Methacryloyl Hydrogel-Based Adjunctive Therapy for Intervertebral Disc Degeneration

Gelatin-methacryloyl (GelMA) hydrogels are photosensitive with good biocompatibility and adjustable mechanical properties. The GelMA hydrogel composite system is a prospective therapeutic material based on a tissue engineering platform for treating intervertebral disc (IVD) degeneration (IVDD). The potential application value of the GelMA hydrogel composite system in the treatment of IVDD mainly includes three aspects: first, optimization of the current clinical treatment methods, including conservative treatment and surgical treatment; second, regeneration of IVD cells to reverse or repair IVDD; and finally, IVDD instead of injury plays a biomechanical role. In this paper, we summarized and analyzed the preparation of GelMA hydrogels and their excellent biological characteristics as carriers and comprehensively demonstrated the research status and prospects of GelMA hydrogel composite systems in IVDD treatment. In addition, the challenges facing the application of GelMA hydrogel composite systems and the progress of research on new hydrogels modified by GelMA hydrogels are presented. Hopefully, this study will provide theoretical guidance for the future application of GelMA hydrogel composite systems in IVDD.

Cellular rejuvenation: molecular mechanisms and potential therapeutic interventions for diseases

The ageing process is a systemic decline from cellular dysfunction to organ degeneration, with more predisposition to deteriorated disorders. Rejuvenation refers to giving aged cells or organisms more youthful characteristics through various techniques, such as cellular reprogramming and epigenetic regulation. The great leaps in cellular rejuvenation prove that ageing is not a one-way street, and many rejuvenative interventions have emerged to delay and even reverse the ageing process. Defining the mechanism by which roadblocks and signaling inputs influence complex ageing programs is essential for understanding and developing rejuvenative strategies. Here, we discuss the intrinsic and extrinsic factors that counteract cell rejuvenation, and the targeted cells and core mechanisms involved in this process. Then, we critically summarize the latest advances in state-of-art strategies of cellular rejuvenation. Various rejuvenation methods also provide insights for treating specific ageing-related diseases, including cellular reprogramming, the removal of senescence cells (SCs) and suppression of senescence-associated secretory phenotype (SASP), metabolic manipulation, stem cells-associated therapy, dietary restriction, immune rejuvenation and heterochronic transplantation, etc. The potential applications of rejuvenation therapy also extend to cancer treatment. Finally, we analyze in detail the therapeutic opportunities and challenges of rejuvenation technology. Deciphering rejuvenation interventions will provide further insights into anti-ageing and ageing-related disease treatment in clinical settings.

Constructing intervertebral disc degeneration animal model: A review of current models

Low back pain is one of the top disorders that leads to disability and affects disability-adjusted life years (DALY) globally. Intervertebral disc degeneration (IDD) and subsequent discogenic pain composed major causes of low back pain. Recent studies have identified several important risk factors contributing to IDD's development, such as inflammation, mechanical imbalance, and aging. Based on these etiology findings, three categories of animal models for inducing IDD are developed: the damage-induced model, the mechanical model, and the spontaneous model. These models are essential measures in studying the natural history of IDD and finding the possible therapeutic target against IDD. In this review, we will discuss the technical details of these models, the duration between model establishment, the occurrence of observable degeneration, and the potential in different study ranges. In promoting future research for IDD, each animal model should examine its concordance with natural IDD pathogenesis in humans. We hope this review can enhance the understanding and proper use of multiple animal models, which may attract more attention to this disease and contribute to translation research.

Effect of Circadian Rhythm Disturbance on the Human Musculoskeletal System and the Importance of Nutritional Strategies

The circadian system in the human body responds to daily environmental changes to optimise behaviour according to the biological clock and also influences various physiological processes. The suprachiasmatic nuclei are located in the anterior hypothalamus of the brain, and they synchronise to the 24 h light/dark cycle. Human physiological functions are highly dependent on the regulation of the internal circadian clock. Skeletal muscles comprise the largest collection of peripheral clocks in the human body. Both central and peripheral clocks regulate the interaction between the musculoskeletal system and energy metabolism. The skeletal muscle circadian clock plays a vital role in lipid and glucose metabolism. The pathogenesis of osteoporosis is related to an alteration in the circadian rhythm. In the present review, we discuss the disturbance of the circadian rhythm and its resultant effect on the musculoskeletal system. We also discuss the nutritional strategies that are potentially effective in maintaining the system's homeostasis. Active collaborations between nutritionists and physiologists in the field of chronobiological and chrononutrition will further clarify these interactions. This review may be necessary for successful interventions in reducing morbidity and mortality resulting from musculoskeletal disturbances.

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.

Disrupted diurnal oscillations of the gut microbiota in patients with alcohol dependence

Background

Patients with alcohol dependence (AD) can exhibit gut dysbacteria. Dysbacteria may co-occur with disruptions of circadian rhythmicity of the gut flora, which can aggravate AD. Herein, this study aimed to investigate diurnal oscillations of the gut microbiota in AD patients.

Methods

Thirty-two patients with AD, based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, and 20 healthy subjects were enrolled in this study. Demographic and clinical data were collected by self-report questionnaires. Fecal samples at 7:00 AM, 11:00 AM, 3:00 PM, and 7:00 PM were collected from each subject. 16S rDNA sequencing was conducted. Wilcoxon and Kruskal-Wallis tests were performed to characterize alterations and oscillations of the gut microbiota.

Results

We found that β-diversity of the gut microbiota in AD patients oscillated diurnally compared with healthy subjects (p = 0.01). Additionally, 0.66% of operational taxonomic units oscillated diurnally in AD patients versus 1.68% in healthy subjects. At different taxonomic levels, bacterial abundance oscillated diurnally in both groups, such as Pseudomonas and Prevotella pallens (all p < 0.05). β-diversity of the gut microbiota in AD patients with high daily alcohol consumption, high-level cravings, short AD durations, and mild withdrawal symptoms oscillated diurnally compared with other AD patients (all p < 0.05).

Conclusion

The gut microbiota in AD patients exhibits disruptions of diurnal oscillation, which may provide novel insights into mechanisms of AD and the development of therapeutic strategies.

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 dynamic kidney matrisome - is the circadian clock in control?

The circadian clock network in mammals is responsible for the temporal coordination of numerous physiological processes that are necessary for homeostasis. Peripheral tissues demonstrate circadian rhythmicity and dysfunction of core clock components has been implicated in the pathogenesis of diseases that are characterized by abnormal extracellular matrix, such as fibrosis (too much disorganized matrix) and tissue breakdown (too little matrix). Kidney disease is characterized by proteinuria, which along with the rate of filtration, displays robust circadian oscillation. Clinical observation and mouse studies suggest the presence of 24 h kidney clocks responsible for circadian oscillation in kidney function. Recent experimental evidence has also revealed that cell-matrix interactions and the biomechanical properties of extracellular matrix have key roles in regulating peripheral circadian clocks and this mechanism appears to be cell- and tissue-type specific. Thus, establishing a temporally resolved kidney matrisome may provide a useful tool for studying the two-way interactions between the extracellular matrix and the intracellular time-keeping mechanisms in this critical niche tissue. This review summarizes the latest genetic and biochemical evidence linking kidney physiology and disease to the circadian system with a particular focus on the extracellular matrix. We also review the experimental approaches and methodologies required to dissect the roles of circadian pathways in specific tissues and outline the translational aspects of circadian biology, including how circadian medicine could be used for the treatment of kidney disease.

Oscillations of the circadian clock protein, BMAL-1, align to daily cycles of mechanical stimuli: a novel means to integrate biological time within predictive in vitro model systems

PURPOSE

In vivo, the circadian clock drives 24-h rhythms in human physiology. Isolated cells in vitro retain a functional clockwork but lack necessary timing cues resulting in the rapid loss of tissue-level circadian rhythms. This study tests the hypothesis that repeated daily mechanical stimulation acts as a timing cue for the circadian clockwork. The delineation and integration of circadian timing cues into predictive in vitro model systems, including organ-on-a-chip (OOAC) devices, represent a novel concept that introduces a key component of in vivo physiology into predictive in vitro model systems.

METHODS

Quiescent bovine chondrocytes were entrained for 3 days by daily 12-h bouts of cyclic biaxial tensile strain (10%, 0.33 Hz, Flexcell) before sampling during free-running conditions. The core clock protein, BMAL-1, was quantified from normalised Western Blot signal intensity and the temporal oscillations characterised by Cosinor linear fit with 24-h period.

RESULTS

Following entrainment, the cell-autonomous oscillations of the molecular clock protein, BMAL-1, exhibited circadian (24 h) periodicity (p < 0.001) which aligned to the diurnal mechanical stimuli. A 6-h phase shift in the mechanical entrainment protocol resulted in an equivalent shift of the circadian clockwork. Thus, repeated daily mechanical stimuli synchronised circadian rhythmicity of chondrocytes in vitro.

CONCLUSION

This work demonstrates that daily mechanical stimulation can act as a timing cue that is sufficient to entrain the peripheral circadian clock in vitro. This discovery may be exploited to induce and sustain circadian physiology within into predictive in vitro model systems, including OOAC systems. Integration of the circadian clock within these systems will enhance their potential to accurately recapitulate human diurnal physiology and hence augment their predictive value as drug testing platforms and as realistic models of human (patho)physiology.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s44164-022-00032-x.

The Japan Frailty Scale is a promising screening test for frailty and pre-frailty in Japanese elderly people

Frailty is one of the most important problems in a super-aged society. It is necessary to identify frailty quickly and easily at the bedside. We developed a simple patient-reported frailty screening scale, the Japan Frailty Scale (JFS), based on the aging concept of Kampo medicine. Eight candidate questions were prepared by Kampo medicine experts, and a simple prediction model was created in the development cohort (n=434) and externally validated in an independent validation cohort (n=276). The physical indicators and questionnaires associated with frailty were also comprehensively evaluated. The reference standard for frailty or pre-frailty was determined based on the Kihon checklist. In the development cohort, four questions, nocturia (0-2), lumbago (0-2), cold sensitivity (0-2), exhaustion (0-4), and age (0-1) were selected by multivariable logistic regression analysis. The total JFS score is 0-11. Receiver-operating characteristic curve analysis of the JFS for identifying frailty status showed moderately good discrimination (area under the curve (AUC) =0.78, 95% confidence interval (CI): 0.73-0.82). At the JFS cutoff value of 3/4 for frailty or pre-frailty, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were 86.9%, 53.3%, 62.8%, and 81.7%, respectively. External validation of the JFS showed moderately good discrimination (AUC=0.76, 95% CI: 0.70-0.81). The sensitivity, specificity, PPV, and NPV were 79.9%, 61.4%, 69.3%, and 73.7%, respectively. These results indicate that the JFS is a promising patient-reported clinical scale for early identification of pre-frail/frail patients at the bedside in primary care.

Interleukin-18 Inhibition Protects Against Intervertebral Disc Degeneration via the Inactivation of Caspase-3/9 Dependent Apoptotic Pathways

BACKGROUND

The present study was designed to identify and understand the potential effectiveness of therapeutic target in intervertebral disc degeneration (IVDD) and its regulation mechanism.

METHODS

The role and mechanism of interleukin-18 (IL-18) in the disease were investigated. The IVDD degenerative nucleus pulposus (NP) tissues from the human and mouse models were used.A total of three groups of Male BALB/c mice were randomly made i.e control, IVDD, and IVDD+Ad-shIL-18 groups. After Ad-shIL-18 transfection, the expression of ECM synthesis related protein Aggrecan (ACAN) and Collagen II, apoptotic effector Caspases (Caspase-3, 8, 9, 12 and Cleaved-Caspase 3, 8, 9, 12), pro-apoptotic gene Bax and anti-apoptotic factors Bcl-2 in NP cells of the human were evaluated.

RESULTS

The results of our study revealed that the mRNA and protein expression levels of IL-18 were notably increased in the NP tissues of IVDD patients and mice models. In the IVDD mice model, Ad-sh-IL-18 treatment reversed the IVDD progression. The levels of Aggrecan and Collagen II, contributing to ECM degradation in NP cells, were also significantly increased. Additionally, Ad-sh-IL-18 could inhibit the NP cell's apoptosis via regulating the caspase-3/9 pathway.

CONCLUSION

The IL-18 knockdown via the caspase-3/9 pathway, might reduce the NP cell's death as well as the imbalance between catabolism and anabolism of ECM in IVDD.

Targeting clock-controlled gene Nrf2 ameliorates inflammation-induced intervertebral disc degeneration

BACKGROUND

Intervertebral disc (IVD) is a highly rhythmic tissue, which experiences a diurnal cycle of high/low mechanical loading via the changes of activity/rest phase. There are signs that disruption of the peripheral IVD clock is related to the process of intervertebral disc degeneration (IDD). However, it is still unclear whether inflammation could disturb the IVD clock and thus induce the process of IDD.

METHODS AND RESULTS

In this study, we used IL-1β, a commonly used inflammatory factor, to induce IDD and found that the IVD clock was dampened in degenerated human nucleus pulposus specimens, rat nucleus pulposus (NP) tissues, and cells. In this study, we found that the circadian clock of NP cells was totally disrupted by knockdown of the core clock gene brain and muscle arnt-like protein-1 (Bmal1), which thus induced the dysfunction of NP cells. Next, we explored the mechanism of dampened clock-induced IDD and found that knockdown of Bmal1 decreased the expression of nuclear factor erythroid2-related factor 2 (NRF2), a downstream target gene of Bmal1, and increased inflammatory response, oxidative stress reaction, and apoptosis of NP cells. In addition, NRF2 activation attenuated the dysfunction of NP cells induced by the dampened IVD clock and the degenerative process of NP tissues in an organotypic tissue-explant model.

CONCLUSIONS

Taken together, our study extends the relationship between peripheral clock and IVD homeostasis and provides a potential therapeutic method for the prevention and recovery of IDD by targeting the clock-controlled gene Nrf2.

Monoterpenes as Sirtuin-1 Activators: Therapeutic Potential in Aging and Related Diseases

Sirtuin 1 (SIRT) is a class III, NAD⁺-dependent histone deacetylase that also modulates the activity of numerous non-histone proteins through deacylation. SIRT1 plays critical roles in regulating and integrating cellular energy metabolism, response to stress, and circadian rhythm by modulating epigenetic and transcriptional regulation, mitochondrial homeostasis, proteostasis, telomere maintenance, inflammation, and the response to hypoxia. SIRT1 expression and activity decrease with aging, and enhancing its activity extends life span in various organisms, including mammals, and improves many age-related diseases, including cancer, metabolic, cardiovascular, neurodegenerative, respiratory, musculoskeletal, and renal diseases, but the opposite, that is, aggravation of various diseases, such as some cancers and neurodegenerative diseases, has also been reported. Accordingly, many natural and synthetic SIRT1 activators and inhibitors have been developed. Known SIRT1 activators of natural origin are mainly polyphenols. Nonetheless, various classes of non-polyphenolic monoterpenoids have been identified as inducers of SIRT1 expression and/or activity. This narrative review discusses current information on the evidence that supports the role of those compounds as SIRT1 activators and their potential both as tools for research and as pharmaceuticals for therapeutic application in age-related diseases.

In vivo fluid transport in human intervertebral discs varies by spinal level and disc region

Background

The lumbar discs are large, dense tissues that are primarily avascular, and cells residing in the central region of the disc are up to 6-8 mm from the nearest blood vessel in adults. To maintain homeostasis, disc cells rely on nutrient transport between the discs and adjacent vertebrae. Thus, diminished transport has been proposed as a factor in age-related disc degeneration.

Methods

In this study, we used magnetic resonance imaging (MRI) to quantify diurnal changes in T2 relaxation time, an MRI biomarker related to disc hydration, to generate 3D models of disc fluid distribution and determine how diurnal changes in fluid varied by spinal level. We recruited 10 participants (five males/five females; age: 21-30 years; BMI: 19.1-29.0 kg/m2) and evaluated the T2 relaxation time of each disc at 8:00 AM and 7:00 PM, as well as degeneration grade (Pfirrmann). We also measured disc height, volume, and perimeter in a subset of individuals as a preliminary comparison of geometry and transport properties.

Results

We found that the baseline (AM) T2 relaxation time and the diurnal change in T2 relaxation time were greatest in the cranial lumbar discs, decreasing along the lumbar spine from cranial to caudal. In cranial discs, T2 relaxation times decreased in each disc region (nucleus pulposus [NP], inner annulus fibrosus [IAF], and outer annulus fibrosus [OAF]), whereas in caudal discs, T2 relaxation times decreased in the NP but increased in the AF.

Conclusions

Fluid transport varied by spinal level, where transport was greatest in the most cranial lumbar discs and decreased from cranial to caudal along the lumbar spine. Future work should evaluate what level-dependent factors affect transport.

Gut Microbiota Dysbiosis Induced by Decreasing Endogenous Melatonin Mediates the Pathogenesis of Alzheimer's Disease and Obesity

Lifestyle choices, external environment, aging, and other factors influence the synthesis of melatonin. Although the physiological functions of melatonin have been widely studied in relation to specific organs, the systemic effects of endogenous melatonin reduction has not been reported. This study evaluates the systemic changes and possible pathogenic risks in an endogenous melatonin reduction (EMR) mouse model deficient in the rate limiting enzyme in melatonin production, arylalkylamine N-acetyltransferase (Aanat) gene. Using this model, we identified a new relationship between melatonin, Alzheimer’s disease (AD), and gut microbiota. Systematic changes were evaluated using multi-omics analysis. Fecal microbiota transplantation (FMT) was performed to examine the role of gut microbiota in the pathogenic risks of EMR. EMR mice exhibited a pan-metabolic disorder, with significant transcriptome changes in 11 organs, serum metabolome alterations as well as microbiota dysbiosis. Microbiota dysbiosis was accompanied by increased gut permeability along with gut and systemic inflammation. Correlation analysis revealed that systemic inflammation may be related to the increase of Ruminiclostridium_5 relative abundance. 8-month-old EMR mice had AD-like phenotypes, including Iba-1 activation, A β protein deposition and decreased spatial memory ability. Moreover, EMR mice showed decreased anti stress ability, under high-fat diet, EMR mice had greater body weight and more obvious hepatic steatosis compared with WT group. FMT improved gut permeability, systemic inflammation, and AD-related phenotypes, while reducing obesity in EMR mice. Our findings suggest EMR causes systemic changes mediated by gut microbiota dysbiosis, which may be a pathogenic factor for AD and obesity, we further proved the gut microbiota is a potential target for the prevention and treatment of AD and obesity.

Synthetic gene circuits for preventing disruption of the circadian clock due to interleukin-1-induced inflammation

The circadian clock regulates tissue homeostasis through temporal control of tissue-specific clock-controlled genes. In articular cartilage, disruptions in the circadian clock are linked to a procatabolic state. In the presence of inflammation, the cartilage circadian clock is disrupted, which further contributes to the pathogenesis of diseases such as osteoarthritis. Using synthetic biology and tissue engineering, we developed and tested genetically engineered cartilage from murine induced pluripotent stem cells (miPSCs) capable of preserving the circadian clock in the presence of inflammation. We found that circadian rhythms arise following chondrogenic differentiation of miPSCs. Exposure of tissue-engineered cartilage to the inflammatory cytokine interleukin-1 (IL-1) disrupted circadian rhythms and degraded the cartilage matrix. All three inflammation-resistant approaches showed protection against IL-1-induced degradation and loss of circadian rhythms. These synthetic gene circuits reveal a unique approach to support daily rhythms in cartilage and provide a strategy for creating cell-based therapies to preserve the circadian clock.

Discovery and Application of Postnatal Nucleus Pulposus Progenitors Essential for Intervertebral Disc Homeostasis and Degeneration

Intervertebral disc degeneration (IDD) results from the dysfunction of nucleus pulposus (NP) cells and the exhaustion of NP progenitors (ProNPs). The cellular applications of NP cells during IDD are currently limited due to the lack of in vivo studies showing whether NP cells are heterogeneous and contain ProNPs throughout postnatal stages. In this study, single-cell RNA sequencing of purified NP cells is used to map four molecularly defined populations and urotensin II receptor (UTS2R)-expressing postnatal ProNPs is identified, which are markedly exhausted during IDD, in mouse and human specimens. The lineage tracing shows that UTS2R⁺ ProNPs preferentially resides in the NP periphery with its niche factor tenascin-C and give rise to functional NP cells. It is also demonstrated that transplanting UTS2R⁺ ProNPs with tenascin-C into injured intervertebral discs attenuate the progression of IDD. The study provides a novel NP cell atlas, identified resident ProNPs with regenerative potential, and revealed promising diagnostic and therapeutic targets for IDD.

Treatment of Intervertebral Disc Degeneration

Intervertebral disc degeneration (IDD) causes a variety of signs and symptoms, such as low back pain (LBP), intervertebral disc herniation, and spinal stenosis, which contribute to high social and economic costs. IDD results from many factors, including genetic factors, aging, mechanical injury, malnutrition, and so on. The pathological changes of IDD are mainly composed of the senescence and apoptosis of nucleus pulposus cells (NPCs), the progressive degeneration of extracellular matrix (ECM), the fibrosis of annulus fibrosus (AF), and the inflammatory response. At present, IDD can be treated by conservative treatment and surgical treatment based on patients' symptoms. However, all of these can only release the pain but cannot reverse IDD and reconstruct the mechanical function of the spine. The latest research is moving towards the field of biotherapy. Mesenchymal stem cells (MSCs) are regard as the potential therapy of IDD because of their ability to self-renew and differentiate into a variety of tissues. Moreover, the non-coding RNAs (ncRNAs) are found to regulate many vital processes in IDD. There have been many successes in the in vitro and animal studies of using biotherapy to treat IDD, but how to transform the experimental data to real therapy which can apply to humans is still a challenge. This article mainly reviews the treatment strategies and research progress of IDD and indicates that there are many problems that need to be solved if the new biotherapy is to be applied to clinical treatment of IDD. This will provide reference and guidance for clinical treatment and research direction of IDD.

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.

Effects of Human RelA Transgene on Murine Macrophage Inflammatory Responses

The NFκB transcription factors are major regulators of innate immune responses, and NFκB signal pathway dysregulation is linked to inflammatory disease. Here, we utilised bone marrow-derived macrophages from the p65-DsRedxp/IκBα-eGFP transgenic strain to study the functional implication of xenogeneic (human) RelA(p65) protein introduced into the mouse genome. Confocal imaging showed that human RelA is expressed in the cells and can translocate to the nucleus following activation of Toll-like receptor 4. RNA sequencing of lipid A-stimulated macrophages, revealed that human RelA impacts on murine gene transcription, affecting both non-NFκB and NFκB target genes, including immediate-early and late response genes, e.g., Fos and Cxcl10. Validation experiments on NFκB targets revealed markedly reduced mRNA levels, but similar kinetic profiles in transgenic cells compared to wild-type. Enrichment pathway analysis of differentially expressed genes revealed interferon and cytokine signaling were affected. These immune response pathways were also affected in macrophages treated with tumor necrosis factor. Data suggests that the presence of xenogeneic RelA protein likely has inhibitory activity, altering specific transcriptional profiles of key molecules involved in immune responses. It is therefore essential that this information be taken into consideration when designing and interpreting future experiments using this transgenic strain.

Senolytics: Eliminating Senescent Cells and Alleviating Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the main cause of cervical and lumbar spondylosis. Over the past few years, the relevance between cellular senescence and IVDD has been widely studied, and the senescence-associated secretory phenotype (SASP) produced by senescent cells is found to remodel extracellular matrix (ECM) metabolism and destruct homeostasis. Elimination of senescent cells by senolytics and suppression of SASP production by senomorphics/senostatics are effective strategies to alleviate degenerative diseases including IVDD. Here, we review the involvement of senescence in the process of IVDD; we also discuss the potential of senolytics on eliminating senescent disc cells and alleviating IVDD; finally, we provide a table listing senolytic drugs and small molecules, aiming to propose potential drugs for IVDD therapy in the future.

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.

Endoplasmic Reticulum Stress: An Emerging Therapeutic Target for Intervertebral Disc Degeneration

Low back pain (LBP) is a global health issue. Intervertebral disc degeneration (IDD) is a major cause of LBP. Although the explicit mechanisms underpinning IDD are unclear, endoplasmic reticulum (ER) stress caused by aberrant unfolded or misfolded proteins may be involved. The accumulation of unfolded/misfolded proteins may result in reduced protein synthesis and promote aberrant protein degradation to recover ER function, a response termed the unfolded protein response. A growing body of literature has demonstrated the potential relationships between ER stress and the pathogenesis of IDD, indicating some promising therapeutic targets. In this review, we summarize the current knowledge regarding the impact of ER stress on the process of IDD, as well as some potential therapeutic strategies for alleviating disc degeneration by targeting different pathways to inhibit ER stress. This review will facilitate understanding the pathogenesis and progress of IDD and highlights potential therapeutic targets for treating this condition.

Catching the circadian rhythm of intervertebral disc and association with clinical outcomes by twice-a-day magnetic resonance imaging

OBJECTIVES

We conducted a prospective magnetic resonance imaging(MRI) surveillance program of the whole spine twice a day to aim at investigating the diurnal prevalence of MRI parameters of intervertebral discs and their associations with relevant symptoms.

METHODS

Sixty-four young volunteers underwent MRI of the whole spine twice on the same day (in the morning and evening). Sagittal T2-weighted MRIs of the whole spine were compared and analyzed. Two independent observers assessed the images for the disc height, anterior-posterior distance, and T2 values. Subject demographics and clinical findings were assessed by standardized questionnaires.

RESULTS

There was a statistically significant diurnal disc height change in all the disc level groups. Except four lumbar levels, there was no statistically significant diurnal disc AP distance change seen in other levels. There were statistically significant diurnal T2 value changes in all intervertebral discs except T3/4 levels. The multivariate linear regression analysis showed a positive linear trend association between BMI and the diurnal variations of T1/2 T2 value, T12/L1, L1/2, L2/3, L3/4,L4/5 and L5/S1 disc heights (p < 0.05) . Smoking and passive smoking affected cervical levels of T2 value changes. Interestingly, a reverse trend was observed in all disc changes in the case of more than ten years shift work history.

CONCLUSION

Smoking and passive smoking are associated with cervical disc T2 value diurnal changes and BMI is associated with lumbar disc height changes. Long time disruption of circadian clock may cause reverse changes of discs, however not in short or medium-time shift workers.