ASIC1 and ASIC3 mediate cellular senescence of human nucleus pulposus mesenchymal stem cells during intervertebral disc degeneration

Biomolecular therapies for chronic discogenic low back pain: A narrative review

Chronic low back pain caused by intervertebral disc (IVD) degeneration, also termed chronic discogenic low back pain (CD-LBP), is one of the most prevalent musculoskeletal diseases. Degenerative processes in the IVD, such as inflammation and extra-cellular matrix breakdown, result in neurotrophin release. Local elevated neurotrophin levels will stimulate sprouting and innervation of sensory neurons. Furthermore, sprouted sensory nerves that are directly connected to adjacent dorsal root ganglia have shown to increase microglia activation, contributing to the maintenance and chronification of pain. Current pain treatments have shown to be insufficient or inadequate for long-term usage. Furthermore, most therapeutic approaches aimed to target the underlying pathogenesis of disc degeneration focus on repair and regeneration and neglect chronic pain. How biomolecular therapies influence the degenerative IVD environment, pain signaling cascades, and innervation and excitability of the sensory neurons often remains unclear. This review addresses the relatively underexplored area of chronic pain treatment for CD-LBP and summarizes effects of therapies aimed for CD-LBP with special emphasis on chronic pain. Approaches based on blocking pro-inflammatory mediators or neurotrophin activity have been shown to hamper neuronal ingrowth into the disc. Furthermore, the tissue regenerative and neuro inhibitory properties of extracellular matrix components or transplanted mesenchymal stem cells are potentially interesting biomolecular approaches to not only block IVD degeneration but also impede pain sensitization. At present, most biomolecular therapies are based on acute IVD degeneration models and thus do not reflect the real clinical chronic pain situation in CD-LBP patients. Future studies should aim at investigating the effects of therapeutic interventions applied in chronic degenerated discs containing established sensory nerve ingrowth. The in-depth understanding of the ramifications from biomolecular therapies on pain (chronification) pathways and pain relief in CD-LBP could help narrow the gap between the pre-clinical bench and clinical bedside for novel CD-LBP therapeutics and optimize pain treatment.

Puerarin modulates proliferation, inflammation and ECM metabolism in human nucleus pulposus mesenchymal stem cells via the lncRNA LINC01535

Background

Intervertebral disc degeneration (IVDD) is a highly prevalent musculoskeletal disorder characterized by progressive destruction of the intervertebral disc, leading to chronic low back pain and disability. Emerging evidence suggests that dysregulation of ferroptosis, a recently discovered form of regulated cell death, participates in IVDD pathogenesis. Puerarin, a natural flavonoid compound from Pueraria lobata, has shown promise in modulating ferroptosis in various diseases.

Methods

Human nucleus pulposus-derived mesenchymal stem cells (NPMSCs) were isolated and identified by flow cytometry. We investigated the effects of puerarin on human NPMSCs and examined the underlying molecular mechanisms.

Results

Puerarin significantly promoted human NPMSC proliferation, as evidenced by the increased cell viability and colony formation ability. Furthermore, puerarin suppressed the expression of cyclooxygenase-2 and the proinflammatory cytokine interleukin-6 in NPMSCs, demonstrating the anti-inflammatory properties of the compound. Notably, puerarin attenuated ECM breakdown by downregulating the ECM-degrading enzymes MMP3, MMP13 and ADAMTS5, and it increased ECM component synthesis, including collagen type II and aggrecan, by NPMSCs. Moreover, puerarin inhibited ferroptosis in NPMSCs by modulating the expression of key ferroptosis-related genes, including ACSL4, PTGS2 and GPX4. Depletion of LINC01535 abolished the effects of puerarin on proliferation, inflammation and ECM metabolism, suggesting a key role of this lncRNA in mediating the effects of puerarin.

Conclusion

Our findings show that puerarin promotes the proliferation of human NPMSCs and ECM synthesis by these cells. Furthermore, puerarin inhibits inflammation and ECM degradation by suppressing ferroptosis via LINC01535. These results provide insights into the molecular mechanisms underlying the therapeutic effects of puerarin in IVDD. Targeting ferroptosis and its regulatory factors, such as LINC01535, may have therapeutic potential for the treatment of IDD and other degenerative disorders of the intervertebral disc. Further studies are needed to uncover the translational potential of puerarin and its downstream targets in preclinical and clinical applications.

Mesenchymal stromal cell response to intervertebral disc-like pH is tissue source dependent

Intervertebral disc (IVD) degeneration (IVDD) has become increasingly prevalent and is a common contributing factor to low back pain. Current treatment options are limited to either symptom management or surgery. A promising treatment option being explored is intradiscal administration of mesenchymal stromal cells (MSCs). However, there remains a gap in knowledge as to whether MSCs from different tissue sources have similar responses to the low pH microenvironment of the IVD and the possible mechanisms governing these responses. To study this, MSCs from three different tissue sources: adipose (adipose-derived mesenchymal stem cell), bone marrow (bone marrow mesenchymal stem cells), and amnion (amniotic membrane mesenchymal stem cell) were cultured at low pHs representative of IVDD. MSCs were assessed for survival, senescence, apoptosis, metabolic activity, and cytokine release profile. Additionally, western blot was utilized to assess acid sensing ion channel 1 and 3 expression. The results of this study indicated that MSC viability, cell proliferation, senescence, and metabolic activity is negatively affected by low pH and alters MSC cytokine production. This study also demonstrated that MSCs behavior is dependent on tissue source. Understanding how MSC behavior is altered by pH will allow further research aimed at increasing the efficacy of MSC therapy to promote in situ IVD tissue regeneration to combat IVDD.

Complex alterations in inflammatory pain and analgesic sensitivity in young and ageing female rats: involvement of ASIC3 and Nav1.8 in primary sensory neurons

OBJECTIVE AND DESIGN

Our aim was to determine an age-dependent role of Nav1.8 and ASIC3 in dorsal root ganglion (DRG) neurons in a rat pre-clinical model of long-term inflammatory pain.

METHODS

We compared 6 and 24 months-old female Wistar rats after cutaneous inflammation. We used behavioral pain assessments over time, qPCR, quantitative immunohistochemistry, selective pharmacological manipulation, ELISA and in vitro treatment with cytokines.

RESULTS

Older rats exhibited delayed recovery from mechanical allodynia and earlier onset of spontaneous pain than younger rats after inflammation. Moreover, the expression patterns of Nav1.8 and ASIC3 were time and age-dependent and ASIC3 levels remained elevated only in aged rats. In vivo, selective blockade of Nav1.8 with A803467 or of ASIC3 with APETx2 alleviated mechanical and cold allodynia and also spontaneous pain in both age groups with slightly different potency. Furthermore, in vitro IL-1β up-regulated Nav1.8 expression in DRG neurons cultured from young but not old rats. We also found that while TNF-α up-regulated ASIC3 expression in both age groups, IL-6 and IL-1β had this effect only on young and aged neurons, respectively.

CONCLUSION

Inflammation-associated mechanical allodynia and spontaneous pain in the elderly can be more effectively treated by inhibiting ASIC3 than Nav1.8.

Construction of a novel mRNA-miRNA-lncRNA/circRNA triple subnetwork associated with immunity and aging in intervertebral disc degeneration

OBJECTIVE

Intervertebral disk degeneration (IVDD) is one of the most common causes of low back pain. However, in the etiology of IVDD, the specific method by which nucleus pulposus (NP) cell senescence and the immune response induce disease is uncertain.

METHODS

Gene Expression Omnibus database was used to find differentially expressed genes (DEGs), differentially expressed miRNAs (DE miRNAs), differentially expressed lncRNAs (DE lncRNAs), and differentially expressed circRNAs (DE circRNAs). Functional enrichment analysis was performed through Enrichr database. Potential regulatory miRNAs, lncRNAs and circRNAs of mRNAs were predicted by ENCORI and circBank, respectively.

RESULTS

We identified 198 upregulated and 131 downregulated genes, 39 upregulated and 22 downregulated miRNAs, 2152 upregulated and 564 downregulated lncRNAs, and 352 upregulated and 279 downregulated circRNAs as DEGs, DE miRNAs, DE lncRNAs, DE circRNAs, respectively. Functional enrichment analysis revealed that they were significantly enriched in Toll-like receptor signaling route and the NF-kappa B signaling pathway. An mRNA-miRNA-lncRNA/circRNA network linked to the pathogenesis of NP cells in IVDD was constructed based on node degree and differential expression level. Eight immune-related DEGs (6 upregulated and 2 downregulated genes) and five aging-related DEGs (3 upregulated and 2 downregulated genes) were identified in the critical network.

CONCLUSION

We established a novel immune-related and aging-related triple regulatory network of mRNA-miRNA-lncRNA/circRNA ceRNA, among which all RNAs may be utilized as the pathogenesis biomarker of NP cells in IVDD.

Diagnostic value of serum COMP and ADAMTS7 for intervertebral disc degeneration

OBJECTIVE

Intervertebral disc degeneration (IVDD) is a major cause of morbidity and disability. Our study aimed to investigate the potential of cartilage oligomeric matrix protein (COMP) and ADAMTS7 (A disintegrin and metalloproteinases with thrombospondin motifs 7) as biomarkers for IVDD together with their functional relationship.

METHODS

IVD tissues and peripheral blood samples were collected from IVDD rabbit models over 1-4 weeks. Tissues and blood samples were also collected from clinical patients those were stratified into four equal groups according to Pfirrmann IVDD grading (I-V) with baseline data collected for each participant. COMP and ADAMTS7 expression were analyzed and biomarker characteristics were assessed using linear regression and receiver operating curve (ROC) analyses.

RESULTS

COMP and ADAMTS7 expression increased in tissues and serum during IVDD progression. Serum COMP (sCOMP) and serum ADAMTS7 (sADAMTS7) levels increased in a time-dependent manner following IVD damage in the rabbit model while significant positive correlations were detected between sCOMP and sADAMTS7 and Pfirrmann grade in human subjects. ROC analysis showed that combining sCOMP and sADAMTS7 assay results produced an improved diagnostic measure for IVDD compared to individual sCOMP or sADAMTS7 tests. In vitro assays conducted on human cell isolates revealed that COMP prevented extracellular matrix degradation and antagonized ADAMTS7 expression although this protective role was uncoupled under microenvironmental conditions mimicking IVDD.

CONCLUSIONS

Increases in circulating COMP and ADAMTS7 correlate with IVDD progression and may play regulatory roles. Assays for sCOMP and/or sADAMTS7 levels can discriminate between healthy subjects and IVDD patients, warranting further clinical assessment.

Mechanisms and therapeutic strategies for senescence-associated secretory phenotype in the intervertebral disc degeneration microenvironment

As a permanent state of cell cycle arrest, cellular senescence has become an important factor in aging and age-related diseases. As a central regulator of physiology and pathology associated with cellular senescence, the senescence associated secretory phenotype can create an inflammatory and catabolic environment through autocrine and paracrine ways, ultimately affecting tissue microstructure. As an age-related disease, the correlation between intervertebral disc degeneration and cellular senescence has been confirmed by many studies. Various pathological factors in the microenvironment of intervertebral disc degeneration promote senescent cells to produce and accumulate and express excessive senescence associated secretory phenotype. In this case, senescence associated secretory phenotype has received considerable attention as a potential target for delaying or treating disc degeneration. Therefore, we reviewed the latest research progress of senescence associated secretory phenotype, related regulatory mechanisms and intervertebral disc cell senescence treatment strategies. It is expected that further understanding of the underlying mechanism between cellular senescence pathology and intervertebral disc degeneration will help to formulate reasonable senescence regulation strategies, so as to achieve ideal therapeutic effects.

The translational potential of this article

Existing treatment strategies often fall short in addressing the challenge of repairing intervertebral disc Intervertebral disc degeneration（IVD） degeneration. The accumulation of senescent cells and the continuous release of senescence-associated secretory phenotype (SASP) perpetually impede disc homeostasis and hinder tissue regeneration. This impairment in repair capability presents a significant obstacle to the practical clinical implementation of strategies for intervertebral disc degeneration. As a result, we present a comprehensive overview of the latest advancements in research, the associated regulatory mechanisms, and strategies for treating SASP in IVD cells. This article aims to investigate effective interventions for delaying the onset and progression of age-related intervertebral disc degeneration. In an era where the aging population is becoming increasingly prominent, this endeavor holds paramount practical and translational significance.

FSTL1 Accelerates Nucleus Pulposus Cell Senescence and Intervertebral Disc Degeneration Through TLR4/NF-κB Pathway

Intervertebral disc degeneration (IVDD) is a major contributor to low back pain (LBP), and inflammatory factors play crucial roles in its pathogenesis. Follistatin-like 1 (FSTL1) has been reported to induce an inflammatory response in chondrocytes, microglia and preadipocytes, but its role in the pathogenesis of nucleus pulposus cell (NPC) degeneration remains unclear. In this study, we mainly utilized an acidosis-induced NPC degeneration model and a rabbit puncture IVDD model to investigate the role of FSTL1 in IVDD both in vitro and in vivo. We confirmed that FSTL1 expression significantly increased in nucleus pulposus (NP) tissues from IVDD patients and rabbit puncture IVDD models. The expression levels of FSTL1 were significantly increased in all three models of NPC degeneration under harsh microenvironments. In addition, recombinant human FSTL1 (rh-FSTL1) was found to upregulate the expression of p16 and p21, increase the number of senescence-associated β-galactosidase (SA-β-gal)-positive cells, induce senescence-related secretory phenotypes (SASP), and downregulate extracellular matrix (ECM) protein expressions, leading to an imbalance in ECM metabolism destructions. Conversely, silencing of FSTL1 by small interfering RNA (siRNA) ameliorated senescence of NPCs associated with inflammation in IVDD. Furthermore, Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) pathway plays a crucial role in regulating NPC senescence through FSTL1 regulation. Inhibition of TLR4 expression partly reversed the effects of rh-FSTL1 on NPC senescence-associated inflammation. Finally, rabbit IVDD model experiments demonstrated that the specific FSTL1 siRNA markedly repressed the development of IVDD. These findings may offer a therapeutic approach for mitigating inflammation-induced senescence associated with IVDD.

ASIC3 roles in mechanosensitive elongation of nucleus pulposus cells

Morphological changes of the nucleus pulposus (NP) cells occur concomitantly as part of the intervertebral disc (IVD) degeneration and excessive mechanical loading has been speculated as a significant key factor for contributing to such morphological changes. Therefore, we hypothesize that stress exerted on NP cells can cause a deformity of nucleus in response. The changes of cell morphology is observed in degenerative nucleus pulposus. One of the reasons for degeneration of NP is due to overloading of NP especially in the obese population. So the nucleus deformity caused by stress/force is of our study interest. To delineate the effects and role of mechanical stress, we developed a 3D assay using hydrogel cultures with a circular hole generated with needle indentation to simulate a local stress concentration along the edge of the hole. A stressed zone, encompassing 100 μm of range from the circular edge, is defined based on stress concentration calculation to enable quantitative analysis against the control zone. Our results demonstrated that the circular hole produces stress-induced morphological changes in NP cells. The tangential elongation of NP cells and their nucleus shape changes in the stressed zone are significantly increased compared to the non-stressed control zone. It is proposed that the cell elongation is a direct response to elevated stress within the stressed zone. Subsequently we found the stress induced morphological changes of the NP cells can be significantly reduced by inhibiting ASIC3. This suggests ASIC3 plays an important role of play in mechano-signaling of NP cells.

How to enhance the ability of mesenchymal stem cells to alleviate intervertebral disc degeneration

Intervertebral disc (ID) degeneration (IDD) is one of the main causes of chronic low back pain, and degenerative lesions are usually caused by an imbalance between catabolic and anabolic processes in the ID. The environment in which the ID is located is harsh, with almost no vascular distribution within the disc, and the nutrient supply relies mainly on the diffusion of oxygen and nutrients from the blood vessels located under the endplate. The stability of its internal environment also plays an important role in preventing IDD. The main feature of disc degeneration is a decrease in the number of cells. Mesenchymal stem cells have been used in the treatment of disc lesions due to their ability to differentiate into nucleus pulposus cells in a nonspecific anti-inflammatory manner. The main purpose is to promote their regeneration. The current aim of stem cell therapy is to replace the aged and metamorphosed cells in the ID and to increase the content of the extracellular matrix. The treatment of disc degeneration with stem cells has achieved good efficacy, and the current challenge is how to improve this efficacy. Here, we reviewed current treatments for disc degeneration and summarize studies on stem cell vesicles, enhancement of therapeutic effects when stem cells are mixed with related substances, and improvements in the efficacy of stem cell therapy by adjuvants under adverse conditions. We reviewed the new approaches and ideas for stem cell treatment of disc degeneration in order to contribute to the development of new therapeutic approaches to meet current challenges.

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.

Senescence-associated alterations in the extracellular matrix: deciphering their role in the regulation of cellular function

The extracellular matrix (ECM) is a dynamic structural network that provides a physical scaffolding, as well as biochemical factors that maintain normal tissue homeostasis and thus its disruption is implicated in many pathological conditions. On the other hand, senescent cells express a particular secretory phenotype, affecting the composition and organization of the surrounding ECM and modulating their microenvironment. As accumulation of senescent cells may be linked to the manifestation of several age-related conditions, senescence-associated ECM alterations may serve as targets for novel anti-aging treatment modalities. Here, we will review characteristic changes in the ECM elicited by cellular senescence and we will discuss the complex interplay between ECM and senescent cells, in relation to normal aging and selected age-associated pathologies.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Cellular Senescence in Intervertebral Disc Aging and Degeneration: Molecular Mechanisms and Potential Therapeutic Opportunities

Closely associated with aging and age-related disorders, cellular senescence (CS) is the inability of cells to proliferate due to accumulated unrepaired cellular damage and irreversible cell cycle arrest. Senescent cells are characterized by their senescence-associated secretory phenotype that overproduces inflammatory and catabolic factors that hamper normal tissue homeostasis. Chronic accumulation of senescent cells is thought to be associated with intervertebral disc degeneration (IDD) in an aging population. This IDD is one of the largest age-dependent chronic disorders, often associated with neurological dysfunctions such as, low back pain, radiculopathy, and myelopathy. Senescent cells (SnCs) increase in number in the aged, degenerated discs, and have a causative role in driving age-related IDD. This review summarizes current evidence supporting the role of CS on onset and progression of age-related IDD. The discussion includes molecular pathways involved in CS such as p53-p21CIP1, p16INK4a, NF-κB, and MAPK, and the potential therapeutic value of targeting these pathways. We propose several mechanisms of CS in IDD including mechanical stress, oxidative stress, genotoxic stress, nutritional deprivation, and inflammatory stress. There are still large knowledge gaps in disc CS research, an understanding of which will provide opportunities to develop therapeutic interventions to treat age-related IDD.

Lactate: a pearl dropped in the ocean-an overlooked signal molecule in physiology and pathology

Lactate, once recognized as a wasty product from anaerobic glycolysis, is proved to be a pivotal signal molecule. Lactate accumulation occurs in diverse physiological and pathological settings due to the imbalance between lactate production and clearance. Under the condition with drastic changes in local microenvironment, such as tumorigenesis, inflammation, and microbial infection, the glycolysis turns to be active in surrounding cells leading to increased lactate release. Meanwhile, lactate can be utilized by these cells as an energy substrate and acts as a signal molecule to regulate cell functions through receptor-dependent or independent pathways. In this review, we tended to tease out the contribution of lactate in tumor progression and immunomodulation. And we also discussed the accessory role of lactate, beyond as the energy source only, in the growth of invading pathogens.

Modulators of ASIC1a and its potential as a therapeutic target for age-related diseases

Age-related diseases have become more common with the advancing age of the worldwide population. Such diseases involve multiple organs, with tissue degeneration and cellular apoptosis. To date, there is a general lack of effective drugs for treatment of most age-related diseases and there is therefore an urgent need to identify novel drug targets for improved treatment. Acid-sensing ion channel 1a (ASIC1a) is a degenerin/epithelial sodium channel family member, which is activated in an acidic environment to regulate pathophysiological processes such as acidosis, inflammation, hypoxia, and ischemia. A large body of evidence suggests that ASIC1a plays an important role in the development of age-related diseases (e.g., stroke, rheumatoid arthritis, Huntington's disease, and Parkinson's disease.). Herein we present: 1) a review of ASIC1a channel properties, distribution, and physiological function; 2) a summary of the pharmacological properties of ASIC1a; 3) and a consideration of ASIC1a as a potential therapeutic target for treatment of age-related disease.

The Influence of Intervertebral Disc Microenvironment on the Biological Behavior of Engrafted Mesenchymal Stem Cells

Intervertebral disc degeneration is the main cause of low back pain. Traditional treatment methods cannot repair degenerated intervertebral disc tissue. The emergence of stem cell therapy makes it possible to regenerate and repair degenerated intervertebral disc tissue. At present, mesenchymal stem cells are the most studied, and different types of mesenchymal stem cells have their own characteristics. However, due to the harsh and complex internal microenvironment of the intervertebral disc, it will affect the biological behaviors of the implanted mesenchymal stem cells, such as viability, proliferation, migration, and chondrogenic differentiation, thereby affecting the therapeutic effect. This review is aimed at summarizing the influence of each intervertebral disc microenvironmental factor on the biological behavior of mesenchymal stem cells, so as to provide new ideas for using tissue engineering technology to assist stem cells to overcome the influence of the microenvironment in the future.

Proanthocyanidins inhibit the apoptosis and aging of nucleus pulposus cells through the PI3K/Akt pathway delaying intervertebral disc degeneration

BACKGROUND

Low back pain is a common symptom of intervertebral disc degeneration (IDD), which seriously affects the quality of life of patients. The abnormal apoptosis and senescence of nucleus pulposus (NP) cells play important roles in the pathogenesis of IDD. Proanthocyanidins (PACs) are polyphenolic compounds with anti-apoptosis and anti-aging effects. However, their functions in NP cells are not yet clear. Therefore, this study was performed to explore the effects of PACs on NP cell apoptosis and aging and the underlying mechanisms of action.

METHODS

Cell viability was evaluated by cell counting kit-8 (CCK-8) assay. The apoptosis rate was determined TUNEL assays. Levels of apoptosis-associated molecules (Bcl-2, Bax, C-caspase-3 and Caspase-9) were evaluated via western blot. The senescence was observed through SA-β-gal staining and western blotting analysis was performed to observe the expression of senescence-related molecules (p-P53, P53, P21 and P16).

RESULTS

Pretreatment with PACs exhibited protective effects against IL-1β-induced NP cell apoptosis including apoptosis rate, expressions of proapoptosis and antiapoptosis related genes and protein. PACs could also alleviate the increase of p-p53, P21, and P16 in IL-1β-treated NP cells. SA-β-gal staining showed that IL-1β-induced senescence of NP cells was prevented by PACs pertreatment. In addition, PACs activated PI3K/Akt pathway in IL-1β-stimulated NP cells. However, these protected effects were inhibited after LY294002 treatment.

CONCLUSION

The results of the present study showed that PACs inhibit IL-1β-induced apoptosis and aging of NP cells by activating the PI3K/Akt pathway, and suggested that PACs have therapeutic potential for IDD.

Mechanisms of Action of the Peptide Toxins Targeting Human and Rodent Acid-Sensing Ion Channels and Relevance to Their In Vivo Analgesic Effects

Acid-sensing ion channels (ASICs) are voltage-independent H⁺-gated cation channels largely expressed in the nervous system of rodents and humans. At least six isoforms (ASIC1a, 1b, 2a, 2b, 3 and 4) associate into homotrimers or heterotrimers to form functional channels with highly pH-dependent gating properties. This review provides an update on the pharmacological profiles of animal peptide toxins targeting ASICs, including PcTx1 from tarantula and related spider toxins, APETx2 and APETx-like peptides from sea anemone, and mambalgin from snake, as well as the dimeric protein snake toxin MitTx that have all been instrumental to understanding the structure and the pH-dependent gating of rodent and human cloned ASICs and to study the physiological and pathological roles of native ASICs in vitro and in vivo. ASICs are expressed all along the pain pathways and the pharmacological data clearly support a role for these channels in pain. ASIC-targeting peptide toxins interfere with ASIC gating by complex and pH-dependent mechanisms sometimes leading to opposite effects. However, these dual pH-dependent effects of ASIC-inhibiting toxins (PcTx1, mambalgin and APETx2) are fully compatible with, and even support, their analgesic effects in vivo, both in the central and the peripheral nervous system, as well as potential effects in humans.

Smooth muscle Acid-sensing ion channel 1a as a therapeutic target to reverse hypoxic pulmonary hypertension

Acid-sensing ion channel 1a (ASIC1a) is a voltage-independent, non-selective cation channel that conducts both Na⁺ and Ca²⁺. Activation of ASIC1a elicits plasma membrane depolarization and stimulates intracellular Ca²⁺-dependent signaling pathways in multiple cell types, including vascular smooth muscle (SM) and endothelial cells (ECs). Previous studies have shown that increases in pulmonary vascular resistance accompanying chronic hypoxia (CH)-induced pulmonary hypertension requires ASIC1a to elicit enhanced pulmonary vasoconstriction and vascular remodeling. Both SM and EC dysfunction drive these processes; however, the involvement of ASIC1a within these different cell types is unknown. Using the Cre-LoxP system to generate cell-type-specific Asic1a knockout mice, we tested the hypothesis that SM-Asic1a contributes to CH-induced pulmonary hypertension and vascular remodeling, whereas EC-Asic1a opposes the development of CH-induced pulmonary hypertension. The severity of pulmonary hypertension was not altered in mice with specific deletion of EC-Asic1a (Tek^Cre-Asic1a^fl/fl). However, similar to global Asic1a knockout (Asic1a^−/-) mice, mice with specific deletion of SM-Asic1a (MHC^CreER-Asic1a^fl/fl) were protected from the development of CH-induced pulmonary hypertension and right heart hypertrophy. Furthermore, pulmonary hypertension was reversed when deletion of SM-Asic1a was initiated in conditional MHC^CreER-Asic1a^fl/fl mice with established pulmonary hypertension. CH-induced vascular remodeling was also significantly attenuated in pulmonary arteries from MHC^CreER-Asic1a^fl/fl mice. These findings were additionally supported by decreased CH-induced proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) from Asic1a^−/- mice. Together these data demonstrate that SM-, but not EC-Asic1a contributes to CH-induced pulmonary hypertension and vascular remodeling. Furthermore, these studies provide evidence for the therapeutic potential of ASIC1a inhibition to reverse pulmonary hypertension.

Specific PFKFB3 Inhibitor Memorably Ameliorates Intervertebral Disc Degeneration via Inhibiting NF-κB and MAPK Signaling Pathway and Reprogramming of Energy Metabolism of Nucleus Pulposus Cells

Intervertebral disc (IVD) degeneration (IVDD) is a characteristic of the dominating pathological processes of nucleus pulposus (NP) cell senescence, abnormal synthesis and irregular distribution of extracellular matrix (ECM), and tumor necrosis factor-α (TNF-α) induced inflammation. Nowadays, IVD acid environment variation which accelerates the pathological processes mentioned above arouses researchers' attention. KAN0438757 (KAN) is an effective inhibitor of selective metabolic kinase phosphofructokinase-2/fructose-2,6-bisphosphatase 3 (PFKFB3) that has both energy metabolism reprogramming and anti-inflammatory effects. Therefore, a potential therapeutic benefit of KAN lies in its ability to inhibit the development of IVDD. This study examined in vitro KAN toxicity in NP primary cells (NPPs). Moreover, KAN influenced tumor necrosis factor-α (TNF-α) induced ECM anabolism and catabolism; the inflammatory signaling pathway activation and the energy metabolism phenotype were also examined in NPPs. Furthermore, KAN's therapeutic effect was investigated in vivo using the rat tail disc puncture model. Phenotypically speaking, the KAN treatment partially rescued the ECM degradation and glycolysis energy metabolism phenotypes of NPPs induced by TNF-α. In terms of mechanism, KAN inhibited the activation of MAPK and NF-κB inflammatory signaling pathways induced by TNF-α and reprogramed the energy metabolism. For the therapeutic aspect, the rat tail disc puncture model demonstrated that KAN has a significant ameliorated effect on the progression of IVDD. To sum up, our research successfully authenticated the potential therapeutic effect of KAN on IVDD and declaimed its mechanisms of both novel energy metabolism reprogramming and conventional anti-inflammation effect.

Acid-sensitive ion channel 1a mediates osteoarthritis chondrocyte senescence by promoting Lamin B1 degradation

Osteoarthritis (OA) is a common and debilitating chronic joint disease, which is characterized by degeneration of articular cartilage and the aging of chondrocytes. Acid-sensitive ion channel 1a (ASIC1a) is a proton-activated cationic channel abundant in chondrocytes, which senses and regulates joint cavity pH. Our previous study demonstrated that ASIC1a was involved in acid-induced rat articular chondrocyte senescence, but the mechanistic basis remained unclear. In this study, we explored the mechanism of ASIC1a in chondrocyte senescence and OA. The results showed that senescence-related-β-galactosidase, senescence-related markers (p53 and p21) and the autophagy-related protein Beclin-1 were found to be increased, but Lamin B1 was found to be reduced with acid (pH 6.0) treatment. These effects were inhibited by ASIC1a-specific blocker psalmotoxin-1 or ASIC1a-short hairpin RNA respectively in chondrocytes. Moreover, Silencing of Lamin B1 enhanced ASIC1a-mediated chondrocyte senescence, this effect was reversed by overexpression of Lamin B1, indicating that Lamin B1 was involved in ASIC1a-mediated chondrocyte senescence. Further, blockade of ASIC1a inhibits acid-induced autophagosomes and Beclin-1 protein expression, suggesting that ASIC1a is involved in acid-induced chondrocyte autophagy. Blocking autophagy with chloroquine inhibited Beclin-1 and increased Lamin B1 in acid-induced chondrocyte senescence. We further demonstrated that ASIC1a-mediated reduction of Lamin B1 expression was caused by autophagy pathway-dependent protein degradation. Finally, blocking ASIC1a protected cartilage tissue, restored Lamin B1 levels and inhibited chondrocyte senescence in a rat OA model. In summary, these findings suggest that ASIC1a may promote Lamin B1 degradation to mediate osteoarthritis chondrocyte senescence through the autophagy pathway.

[Effect of resveratrol on high mobility group box-1 protein signaling pathway in cartilage endplate degeneration caused by inflammation]

Objective

To investigate the effect of resveratrol (RES) on inflammation-induced cartilage endplate (CEP) degeneration, and its regulatory mechanism on high mobility group box-1 protein (HMGB1) signaling pathway.

Methods

The intervertebral CEP cells of Sprague Dawley (SD) rats aged 3 weeks were extracted and identified by toluidine blue staining and immunofluorescence staining of rabbit anti-rat collagen type Ⅱ. The cell counting kit 8 (CCK-8) method was used to screen the optimal concentration of RES on intervertebral CEP cells. Gene chip analysis was used to determine the target of RES on intervertebral CEP cells. Interleukin 1β (IL-1β) was used to construct the intervertebral CEP cell degeneration model caused by inflammation and the 7-8-week-old SD rat intervertebral disc degeneration model, and pcDNA3.1-HMGB1 (pcDNA3.1) was used as the control of RES effect. Flow cytometry and TUNEL staining were used to detect the apoptotic rate of intervertebral CEP cells and rat intervertebral disc tissue cells, respectively. ELISA kit was used to detect the content of interleukin 10 (IL-10) and tumor necrosis factor α (TNF-α) in the cell supernatant and rat serum. Western blot was used to detect the expressions of HMGB1, extracellular signal-regulated protein kinase (ERK), phosphorylated ERK (p-ERK), B cell lymphoma/leukemia 2 gene (Bcl-2), and Bcl-2-associated X protein (Bax).

Results

The extracted cells were identified as rat intervertebral CEP cells. CCK-8 method screened out the highest activity of intervertebral CEP cells treated with 30 μmol/L RES. The gene chip analysis confirmed that the HMGB1-ERK signal was the target of RES. Both cell experiments and animal experiments showed that RES treatment can significantly down-regulate the apoptosis rate of intervertebral CEP cells, inhibit the release of TNF-α, and increase the content of IL-10; and down-regulate the expressions of HMGB1, p-ERK, and Bax, and increase Bcl-2; and pcDNA3.1 could partially reverse these effects of RES, and the differences were all significant (P<0.05).

Conclusion

RES can significantly inhibit the apoptosis of intervertebral CEP cells induced by inflammation, which is related to inhibiting the expression of HMGB1.

Sa12b Improves Biological Activity of Human Degenerative Nucleus Pulposus Mesenchymal Stem Cells in a Severe Acid Environment by Inhibiting Acid-Sensitive Ion Channels

Sa12b is a wasp peptide that can inhibit acid-sensitive ion channels (ASICs). The biological effects of nucleus pulposus mesenchymal stem cells (NP-MSCs) have not been investigated. Therefore, this study investigated the effect of Sa12b on the biological activity of NP-MSCs through ASICs in the acidic environment of intervertebral disc degeneration (IVDD). In this study, NP-MSCs were isolated from the nucleus pulposus (NP) in patients who underwent lumbar disc herniation surgery, identified by flow cytometry and tertiary differentiation, and cultured in vitro in an acidic environment model of IVDD with a pH of 6.2. Proliferation, and apoptosis were observed after different Sa12b concentrations were added to P2 generation NP-MSCs. The Ca²⁺ influx was detected using flow cytometry and laser confocal scanning microscopy, and qPCR was used to detect the relative expression of stem cell–associated genes (Oct4, Nanog, Jag1, and Notch1), the relative expression of extracellular matrix (ECM)–associated genes (collagen II, aggrecan, and SOX-9), and the relative expression of genes encoding ASICs (ASIC1, ASIC2, ASIC3, and ASIC4). Western blotting was used to detect the protein expression of collagen II and aggrecan in different treatment groups. Cells isolated and cultured from normal NP were spindle-shaped and adherent, and they exhibited expansion in vitro. Flow cytometry results showed that the cells exhibited high expression of CD73 (98.1%), CD90 (97.5%), and CD105 (98.3%) and low expression of HLA-DR (0.93%), CD34 (2.63%), and CD45 (0.33%). The cells differentiated into osteoblasts, adipocytes, and chondrocytes. According to the International Society for Cellular Therapy criteria, the isolated and cultured cells were NP-MSCs. With an increase in Sa12b concentration, the cell proliferation rate of NP-MSCs increased, and the apoptosis rate decreased significantly, reaching the optimal level when the concentration of Sa12b was 8 μg/μl. When the Sa12b concentration was 8 μg/μl and contained the ASIC non-specific inhibitor amiloride, the Ca²⁺ influx was the lowest, followed by that when the Sa12b concentration was 8 μg/μl. The Ca²⁺ influx was the highest in the untreated control group. qPCR results showed that as the concentration of Sa12b increased, the relative expression of Oct4, Nanog, Jag1, Notch1, collagen II, aggrecan, and SOX-9 increased, while that of ASIC1, ASIC2, ASIC3, and ASIC4 decreased. The difference was statistically significant (p < 0.05). In conclusion, Sa12b can improve the biological activity of NP-MSCs in severely acidic environments of the intervertebral disc by reducing Ca²⁺ influx via AISC inhibition and, probably, the Notch signaling pathway. This study provides a new approach for the biological treatment of IVDD. Inhibition of AISCs by Sa12b may delay IVDD and improve low back pain.

Lactic acid in tumor invasion

Invasion involves tumor cells altering their cell-matrix interactions and acquiring motility for metastatic spread. Invasive tumor cells exhibit dysregulated metabolism and enhanced aerobic glycolysis, leading to nutrient depletion, hypoxia, and lactic acid production. Lactic acid is a byproduct of glycolysis capable of promoting oncogenic progression, but its role in tumor invasion is unclear. A growing number of studies have demonstrated that lactic acid regulates the degradation of collagen Ⅳ, collagen Ⅶ, and glycoprotein; the synthesis of collagen Ⅰ; and multiple signaling pathways, including TGF-β/Smad, Wnt/β-catenin, IL-6/STAT3, and HGF/MET, which are associated with basement membrane (BM) remodeling and epithelial-mesenchymal transition (EMT), two hallmarks of the tumor invasive process. In the present review, we summarize BM remodeling and EMT in tumor invasion, discuss the emerging roles and molecular mechanisms of lactic acid in these processes, and provide insights for further research.