Intradiscal treatment of the cartilage endplate for improving solute transport and disc nutrition

Region-specific mitophagy in nucleus pulposus, annulus fibrosus, and cartilage endplate of intervertebral disc degeneration: mechanisms and therapeutic strategies

Intervertebral disc degeneration (IVDD) is a prevalent condition contributing to various spinal disorders, posing a significant global health burden. Mitophagy plays a crucial role in maintaining mitochondrial quantity and quality and is closely associated with the onset and progression of IVDD. Well-documented region-specific mitophagy mechanisms in IVDD are guiding the development of therapeutic strategies. In the nucleus pulposus (NP), impaired mitochondria lead to apoptosis, oxidative stress, senescence, extracellular matrix degradation and synthesis, excessive autophagy, inflammation, mitochondrial instability, and pyroptosis, with key regulatory targets including AMPK, PGC-1α, SIRT1, SIRT3, Progerin, p65, Mfn2, FOXO3, NDUFA4L2, SLC39A7, ITGα5/β1, Nrf2, and NLRP3 inflammasome. In the annulus fibrosus (AF), mitochondrial damage induces apoptosis and oxidative stress mediated by PGC-1α, while in the cartilage endplate (CEP), mitochondrial dysfunction similarly triggers apoptosis and oxidative stress. These mechanistic insights highlight therapeutic strategies such as activating Parkin-dependent and Ub-independent mitophagy pathways for NP, enhancing Parkin-dependent mitophagy for AF, and targeting Parkin-mediated mitophagy for CEP. These strategies include the use of natural ingredients, hormonal modulation, gene editing technologies, targeted compounds, and manipulation of related proteins. This review summarizes the mechanisms of mitophagy in different regions of the intervertebral disc and highlights therapeutic approaches using mitophagy modulators to ameliorate IVDD. It discusses the complex mechanisms of mitophagy and underscores its potential as a therapeutic target. The objective is to provide valuable insights and a scientific basis for the development of mitochondrial-targeted drugs for anti-IVDD.

Lipid metabolic disorders and their impact on cartilage endplate and nucleus pulposus function in intervertebral disk degeneration

Lipid metabolism encompasses the processes of digestion, absorption, synthesis, and degradation of fats within biological systems, playing a crucial role in sustaining normal physiological functions. Disorders of lipid metabolism, characterized by abnormal blood lipid levels and dysregulated fatty acid metabolism, have emerged as significant contributors to intervertebral disk degeneration (IDD). The pathogenesis of IDD is multifaceted, encompassing genetic predispositions, nutritional and metabolic factors, mechanical stressors, trauma, and inflammatory responses, which collectively facilitate the progression of IDD. Although the precise mechanisms underlying IDD remain incompletely elucidated, there is substantial consensus regarding the close association between lipid metabolism disorders and its development. Intervertebral disks are essential for maintaining spinal alignment. Their primary functions encompass shock absorption, preservation of physiological curvature, facilitation of movement, and provision of stability. The elasticity and thickness of these disks effectively absorb daily impacts, safeguard the spine, uphold its natural curvature and flexibility, while also creating space for nerve roots to prevent compression and ensure normal transmission of nerve signals. Research indicates that such metabolic disturbances may compromise the functionality of cartilaginous endplates (CEP) and nucleus pulposus (NP), thereby facilitating IDD's onset and progression. The CEP is integral to internal material exchange and shock absorption while mitigating NP herniation under mechanical load conditions. As the central component of intervertebral disks, NP is essential for maintaining disk height and providing shock-absorbing capabilities; thus, damage to these critical structures accelerates IDD progression. Furthermore, lipid metabolism disorders contribute to IDD through mechanisms including activation of endoplasmic reticulum stress pathways, enhancement of oxidative stress levels, induction of cellular pyroptosis alongside inhibition of autophagy processes-coupled with the promotion of inflammation-induced fibrosis and fibroblast proliferation leading to calcification within intervertebral disks. This review delineates the intricate interplay between lipid metabolism disorders and IDD; it is anticipated that advancing our understanding of this pathogenesis will pave the way for more effective preventive measures and therapeutic strategies against IDD in future research.

The Different Influence of Cutibacterium acnes and Staphylococcus epidermidis in the Lumbar Disc : An in Vivo Study in Rabbits

STUDY DESIGN

Animal laboratory study.

OBJECTIVE

This study investigated the effects of Cutibacteriumacnes and Staphylococcusepidermidis on the lumbar discs of rabbits, as well as the outcomes of combined infection.

SUMMARY OF BACKGROUND DATA

Many studies have indicated that bacterial infections are associated with lumbar disc degeneration (LDD). The most commonly cultured bacteria from disc tissues are C. acnes and S. epidermidis .

METHODS

New Zealand white rabbits (n=40) were randomly divided into control, C. acnes , S. epidermidis , and C. acnes plus S. epidermidis ( i.e. , combined) groups. All groups except the control were injected with 25 μL of saline at L4-L5 and 25 μL of bacteria (1×10 7 CFU/mL) at L5-L6. All injections were performed under x-ray guidance. Weight measurements, haematological evaluations, and magnetic resonance imaging were performed after 4, 8, and 12 weeks. Histological examination and gene expression detection were performed 12 weeks after surgery.

RESULTS

Inflammatory factors in the blood and weight did not differ among the groups after 4, 8, and 12 weeks ( P >0.05). However, after 4 weeks, LDD occurred in the C. acnes group, and discitis occurred in the S. epidermidis and combined groups, all of which worsened after 8 weeks. After 12 weeks, the nucleus pulposus (NP) protruded and compressed the spinal cord in the C. acnes group, and tissue staining showed decreased NP tissue and cartilaginous endplate fracture. In the S. epidermidis and combined groups, the discitis was more confined, but tissue staining revealed a significant decrease in NP tissue, and loss of the normal disc structure.

CONCLUSIONS

In the early stage of infection in rabbits, C. acnes caused LDD, and S. epidermidis caused discitis. Coinfection with C. acnes and S. epidermidis caused discitis but was more limited in scope than infection with S. epidermidis alone.

The Role of Microvascular Variations in the Process of Intervertebral Disk Degeneration and Its Regulatory Mechanisms: A Literature Review

Microvascular changes are considered key factors in the process of intervertebral disk degeneration (IDD). Microvascular invasion and growth into the nucleus pulposus (NP) and cartilaginous endplates are unfavorable factors that trigger IDD. In contrast, the rich distribution of microvessels in the bony endplates and outer layers of the annulus fibrosus is an important safeguard for the nutrient supply and metabolism of the intervertebral disk (IVD). In particular, the adequate supply of microvessels in the bony endplates is the main source of the nutritional supply for the entire IVD. Microvessels can affect the progression of IDD through a variety of pathways. Many studies have explored the effects of microvessel alterations in the NP, annulus fibrosus, cartilaginous endplates, and bony endplates on the local microenvironment through inflammation, apoptosis, and senescence. Studies also elucidated the important roles of microvessel alterations in the process of IDD, as well as conducted in-depth explorations of cytokines and biologics that can inhibit or promote the ingrowth of microvessels. Therefore, the present manuscript reviews the published literature on the effects of microvascular changes on IVD to summarize the roles of microvessels in IVD and elaborate on the mechanisms of action that promote or inhibit de novo microvessel formation in IVD.

From structure to therapy: the critical influence of cartilaginous endplates and microvascular network on intervertebral disc degeneration

The intervertebral disc (IVD) is the largest avascular structure in the human body. The cartilaginous endplate (CEP) is a layer of translucent cartilage located at the upper and lower edges of the vertebral bodies. On one hand, CEPs endure pressure from within the IVD and the tensile and shear forces of the annulus fibrosus, promoting uniform distribution of compressive loads on the vertebral bodies. On the other hand, microvascular diffusion channels within the CEP serve as the primary routes for nutrient supply to the IVD and the transport of metabolic waste. Degenerated CEP, characterized by increased stiffness, decreased permeability, and reduced water content, impairs substance transport and mechanical response within the IVD, ultimately leading to intervertebral disc degeneration (IDD). Insufficient nutrition of the IVD has long been considered the initiating factor of IDD, with CEP degeneration regarded as an early contributing factor. Additionally, CEP degeneration is frequently accompanied by Modic changes, which are common manifestations in the progression of IDD. Therefore, this paper comprehensively reviews the structure and physiological functions of CEP and its role in the cascade of IDD, exploring the intrinsic relationship between CEP degeneration and Modic changes from various perspectives. Furthermore, we summarize recent potential therapeutic approaches targeting CEP to delay IDD, offering new insights into the pathological mechanisms and regenerative repair strategies for IDD.

Research Progress on the Role of Cartilage Endplate in Intervertebral Disc Degeneration

Low back pain significantly impacts individuals' quality of life, with intervertebral disc degeneration (IDD) being a primary contributor to this condition. Currently, IDD treatment primarily focuses on symptom management and does not achieve a definitive cure. The cartilage endplate (CEP), a crucial nutrient-supplying tissue of the intervertebral disc, plays a pivotal role in disc degeneration. This review examines the mechanisms underlying CEP degeneration, summarizing recent advancements in understanding the structure and function of CEP, the involvement of various signaling pathways, and the roles of cartilage endplate stem cells (CESCs) and exosomes (Exos) in this process. The aim of this review is to provide a comprehensive reference for future research on CEP. Despite progress in understanding the role of CEP in IDD, the mechanisms underlying CEP degeneration remain incompletely elucidated. Future research poses significant challenges, necessitating further investigations to elucidate the complexities of CEP.

A comparative analysis of TonEBP conditional knockout mouse models reveals inter-dependency between compartments of the intervertebral disc

Interactions between notochord and sclerotome are required for normal embryonic spine patterning, but whether the postnatal derivatives of these tissues also require interactions for postnatal intervertebral disc (IVD) growth and maintenance is less established. We report here the comparative analysis of four conditional knockout mice deficient for TonEBP, a transcription factor known to allow cells to adapt to changes in extracellular osmotic pressure, in specific compartments of the IVD. We show that TonEBP deletion in nucleus pulposus (NP) cells does not affect their survival or aggrecan expression, but promoted cell proliferation in the NP and in adjacent vertebral growth plates (GPs). In cartilage end plates/GPs, TonEBP deletion induced cell death, but also structural alterations in the adjacent NP cells and vertebral bodies. Embryonic or postnatal TonEBP loss generated similar IVD changes. In addition to demonstrating the requirement of TonEBP in the different compartments of the IVD, this comparative analysis uncovers the in vivo interdependency of the different IVD compartments during the growth of the postnatal IVD-vertebral units.

Non-enzymatic glycation reduces glucose transport in the human cartilage endplate independently of matrix porosity or proteoglycan content

Background

Intervertebral disc degeneration is associated with low back pain, which is a leading cause of disability. While the precise causes of disc degeneration are unknown, inadequate nutrient and metabolite transport through the cartilage endplate (CEP) may be one important factor. Prior work shows that CEP transport properties depend on the porosity of the CEP matrix, but little is known about the role of CEP characteristics that could influence transport properties independently from porosity. Here, we show that CEP transport properties depend on the extent of non-enzymatic glycation of the CEP matrix.

Methods and Results

Using in vitro ribosylation to induce non-enzymatic glycation and promote the formation of advanced glycation end products, we found that ribosylation reduced glucose partition coefficients in human cadaveric lumbar CEP tissues by 10.7%, on average, compared with donor- and site-matched CEP tissues that did not undergo ribosylation (p = 0.04). These reductions in glucose uptake were observed in the absence of differences in CEP porosity (p = 0.89) or in the amounts of sulfated glycosaminoglycans (sGAGs, p = 0.47) or collagen (p = 0.61). To investigate whether ribosylation altered electrostatic interactions between fixed charges on the sGAG molecules and the mobile free ions, we measured the charge density in the CEP matrix using equilibrium partitioning of a cationic contrast agent using micro-computed tomography. After contrast enhancement, mean X-ray attenuation was 11.9% lower in the CEP tissues that had undergone ribosylation (p = 0.02), implying the CEP matrix was less negatively charged.

Conclusions

Taken together, these findings indicate that non-enzymatic glycation negatively impacts glucose transport in the CEP independent of matrix porosity or sGAG content and that the effects may be mediated by alterations to matrix charge density.

Emerging role and therapeutic implications of p53 in intervertebral disc degeneration

Lower back pain (LBP) is a common degenerative musculoskeletal disease that imposes a huge economic burden on both individuals and society. With the aggravation of social aging, the incidence of LBP has increased globally. Intervertebral disc degeneration (IDD) is the primary cause of LBP. Currently, IDD treatment strategies include physiotherapy, medication, and surgery; however, none can address the root cause by ending the degeneration of intervertebral discs (IVDs). However, in recent years, targeted therapy based on specific molecules has brought hope for treating IDD. The tumor suppressor gene p53 produces a transcription factor that regulates cell metabolism and survival. Recently, p53 was shown to play an important role in maintaining IVD microenvironment homeostasis by regulating IVD cell senescence, apoptosis, and metabolism by activating downstream target genes. This study reviews research progress regarding the potential role of p53 in IDD and discusses the challenges of targeting p53 in the treatment of IDD. This review will help to elucidate the pathogenesis of IDD and provide insights for the future development of precision treatments.

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.