Sirt6 overexpression suppresses senescence and apoptosis of nucleus pulposus cells by inducing autophagy in a model of intervertebral disc degeneration

Metformin prevents the onset and progression of intervertebral disc degeneration: New insights and potential mechanisms (Review)

Metformin has been the go‑to medical treatment for addressing type 2 diabetes mellitus (T2DM) as a frontline oral antidiabetic. Obesity, cancer and bone deterioration are linked to T2DM, which is considered a metabolic illness. Numerous diseases associated with T2DM, such as tumours, cardiovascular disease and bone deterioration, may be treated with metformin. Intervertebral disc degeneration (IVDD) is distinguished by degeneration of the spinal disc, accompanied by the gradual depletion of proteoglycans and water in the nucleus pulposus (NP) of the IVD, resulting in lower back pain. The therapeutic effect of metformin on IVDD has also attracted much attention. By stimulating AMP‑activated kinase, metformin could enhance autophagy and suppress cell senescence, apoptosis and inflammation, thus effectively delaying IVDD. The present review aimed to systematically explain the development of IVDD and mechanism of metformin in the treatment and prevention of IVDD to provide a reference for the clinical application of metformin as adjuvant therapy in the treatment of IVDD.

Expression analysis and biological regulation of silencing regulatory protein 6 (SIRT6) in cutaneous squamous cell carcinoma

BACKGROUND

Cutaneous squamous cell carcinoma (CSCC) is one of the most common types of skin cancer worldwide. Therefore, the identification of biomarkers associated with CSCC progression could aid in the early detection of high-risk squamous cell carcinoma and the development of novel therapeutic strategies.

OBJECTIVE

This study aimed to investigate the expression patterns of silent mating type Information Regulation 2 homolog 6 (SIRT6) in CSCC and its clinical significance.

METHODS

The protein expression level of SIRT6 in tissues was detected by immunohistochemistry, and the correlation between SIRT6 expression and clinicopathological parameters in CSCC patients was analyzed. The relative expression of SIRT6 in CSCC cell lineage and tissue specimens was determined by western blotting and PCR. The effect of SIRT6 silencing on cell proliferation was evaluated using cell counting kit 8. Wound healing, transwell method, and flow cytometry were used to investigate the migration, invasion, and cell cycle distribution/apoptosis of CSCC cells after SIRT6 silencing, respectively. Western blot was used to detect the expression of EMT (Epithelial-Mesenchymal Transition), cycle, apoptosis, and other related proteins.

RESULTS

The high expression of SIRT6 was correlated with the location of cancer tissue and Broder staging in CSCC patients. Knockdown of SIRT6 inhibited the proliferation, migration, invasion and EMT of CSCC cells, and promoted their apoptosis, with cells blocked in G1 phase.

STUDY LIMITATIONS

No animal experiments were conducted to further verify the results.

CONCLUSION

Decreased expression of SIRT6 can inhibit the occurrence and development of CSCC.

Nicotine induces senescence in spermatogonia stem cells by disrupting homeostasis between circadian oscillation and rhythmic mitochondrial dynamics via the SIRT6/Bmal1 pathway

Infertility is intricately linked with alterations in circadian rhythms along with physiological decline and stem cell senescence. Yet, the direct involvement of circadian mechanisms in nicotine-induced injury to the testes, especially the senescence of spermatogonia stem cells (SSCs), is not well comprehended. This study revealed that nicotine exposure induced testis injury by triggering SSCs senescence along with the upregulation of senescence marker genes and senescence-associated secretory phenotype components. Moreover, nicotine treatment caused mitochondrial hyper-fusion, increased oxidative stress, and DNA damage. Exposure to nicotine was found to suppress the expression of sirtuin 6 (SIRT6), which accelerated the senescence of spermatogonia stem cells (SSCs). This acceleration led to increased acetylation of brain and muscle ARNT-like protein (Bmal1), consequently reducing the expression of Bmal1 protein. Conversely, the overexpression of Bmal1 alleviated mitochondrial hyper-fusion and senescence phenotypes induced by nicotine. Overall, this study unveiled a novel molecular mechanism behind nicotine-induced disorders in spermatogenesis and highlighted the SIRT6/Bmal1 regulatory pathway as a potential therapeutic target for combating nicotine-associated infertility.

The role of sirtuins in intervertebral disc degeneration: Mechanisms and therapeutic potential

Intervertebral disc degeneration (IDD) is one of the main causes of low back pain, which affects the patients' quality of life and health and imposes a significant socioeconomic burden. Despite great efforts made by researchers to understand the pathogenesis of IDD, effective strategies for preventing and treating this disease remain very limited. Sirtuins are a highly conserved family of (NAD+)-dependent deacetylases in mammals that are involved in a variety of metabolic processes in vivo. In recent years, sirtuins have attracted much attention owing to their regulatory roles in IDD on physiological activities such as inflammation, apoptosis, autophagy, aging, oxidative stress, and mitochondrial function. At the same time, many studies have explored the therapeutic effects of sirtuins-targeting activators or micro-RNA in IDD. This review summarizes the molecular pathways of sirtuins involved in IDD, and summarizes the therapeutic role of activators or micro-RNA targeting Sirtuins in IDD, as well as the current limitations and challenges, with a view to provide possible solutions for the treatment of IDD.

S100A6 Regulates nucleus pulposus cell apoptosis via Wnt/β-catenin signaling pathway: an in vitro and in vivo study

BACKGROUND

Intervertebral disc degeneration (IDD) is a common musculoskeletal degenerative disease, which often leads to low back pain and even disability, resulting in loss of labor ability and decreased quality of life. Although many progresses have been made in the current research, the underlying mechanism of IDD remains unclear. The apoptosis of nucleus pulposus (NP) cells (NPCs) is an important pathological mechanism in intervertebral disc degeneration (IDD). This study evaluated the relationship between S100A6 and NPCs and its underlying mechanism.

METHODS

Mass spectrometry, bioinformatics, and quantitative real-time polymerase chain reaction (qRT-PCR) analyses were used to screen and verify hub genes for IDD in human IVD specimens with different degeneration degrees. Western blotting, immunohistochemistry (IHC), and/or immunofluorescence (IF) were used to detect the expression level of S100A6 in human NP tissues and NPCs. The apoptotic phenotype of NPCs and Wnt/β-catenin signaling pathway were evaluated using flow cytometry, western blotting, and IF. S100A6 was overexpressed or knocked down in NPCs to determine its impact on apoptosis and Wnt/β-catenin signaling pathway activity. Moreover, we used the XAV-939 to inhibit and SKL2001 to activate the Wnt/β-catenin signaling pathway. The therapeutic effect of S100A6 inhibition on IDD was also evaluated.

RESULTS

S100A6 expression increased in IDD. In vitro, increased S100A6 expression promoted apoptosis in interleukin (IL)-1β-induced NPCs. In contrast, the inhibition of S100A6 expression partially alleviated the progression of annulus fibrosus (AF) puncture-induced IDD in rats. Mechanistic studies revealed that S100A6 regulates NPC apoptosis via Wnt/β-catenin signaling pathway.

CONCLUSIONS

This study showed that S100A6 expression increased during IDD and promoted NPCs apoptosis by regulating the Wnt/β-catenin signaling pathway, suggesting that S100A6 is a promising new therapeutic target for IDD.

Sirtuins in intervertebral disc degeneration: current understanding

BACKGROUND

Intervertebral disc degeneration (IVDD) is one of the etiologic factors of degenerative spinal diseases, which can lead to a variety of pathological spinal conditions such as disc herniation, spinal stenosis, and scoliosis. IVDD is a leading cause of lower back pain, the prevalence of which increases with age. Recently, Sirtuins/SIRTs and their related activators have received attention for their activity in the treatment of IVDD. In this paper, a comprehensive systematic review of the literature on the role of SIRTs and their activators on IVDD in recent years is presented. The molecular pathways involved in the regulation of IVDD by SIRTs are summarized, and the effects of SIRTs on senescence, inflammatory responses, oxidative stress, and mitochondrial dysfunction in myeloid cells are discussed with a view to suggesting possible solutions for the current treatment of IVDD.

PURPOSE

This paper focuses on the molecular mechanisms by which SIRTs and their activators act on IVDD.

METHODS

A literature search was conducted in Pubmed and Web of Science databases over a 13-year period from 2011 to 2024 for the terms "SIRT", "Sirtuin", "IVDD", "IDD", "IVD", "NP", "Intervertebral disc degeneration", "Intervertebral disc" and "Nucleus pulposus".

RESULTS

According to the results, SIRTs and a large number of activators showed positive effects against IVDD.SIRTs modulate autophagy, myeloid apoptosis, oxidative stress and extracellular matrix degradation. In addition, they attenuate inflammatory factor-induced disc damage and maintain homeostasis during disc degeneration. Several clinical studies have reported the protective effects of some SIRTs activators (e.g., resveratrol, melatonin, honokiol, and 1,4-dihydropyridine) against IVDD.

CONCLUSION

The fact that SIRTs and their activators play a hundred different roles in IVDD helps to better understand their potential to develop further treatments for IVDD.

NOVELTY

This review summarizes current information on the mechanisms of action of SIRTs in IVDD and the challenges and limitations of translating their basic research into therapy.

Downregulation of VEGFA accelerates AGEs-mediated nucleus pulposus degeneration through inhibiting protective mitophagy in high glucose environments

Intervertebral disc degeneration (IVDD) contributes largely to low back pain. Recent studies have highlighted the exacerbating role of diabetes mellitus (DM) in IVDD, mainly due to the influence of hyperglycemia (HG) or the accumulation of advanced glycation end products (AGEs). Vascular endothelial growth factor A (VEGFA) newly assumed a distinct impact in nonvascular tissues through mitophagy regulation. However, the combined actions of HG and AGEs on IVDD and the involved role of VEGFA remain unclear. We confirmed the potential relation between VEGFA and DM through bioinformatics and biological specimen detection. Then we observed that AGEs induced nucleus pulposus (NP) cell degeneration by upregulating cellular reactive oxygen species (ROS), and HG further aggravated ROS level through breaking AGEs-induced protective mitophagy. Furthermore, this adverse effect could be strengthened by VEGFA knockdown. Importantly, we identified that the regulation of VEGFA and mitophagy were vital mechanisms in AGEs-HG-induced NP cell degeneration through Parkin/Akt/mTOR and AMPK/mTOR pathway. Additionally, VEGFA overexpression through local injection with lentivirus carrying VEGFA plasmids significantly alleviated NP degeneration and IVDD in STZ-induced diabetes and puncture rat models. In conclusion, the findings first confirmed that VEGFA protects against AGEs-HG-induced IVDD, which may represent a therapeutic strategy for DM-related IVDD.

From drugs to biomaterials: a review of emerging therapeutic strategies for intervertebral disc inflammation

Chronic low back pain (LBP) is an increasingly prevalent issue, especially among aging populations. A major underlying cause of LBP is intervertebral disc degeneration (IDD), often triggered by intervertebral disc (IVD) inflammation. Inflammation of the IVD is divided into Septic and Aseptic inflammation. Conservative therapy and surgical treatment often fail to address the root cause of IDD. Recent advances in the treatment of IVD infection and inflammation range from antibiotics and small-molecule drugs to cellular therapies, biological agents, and innovative biomaterials. This review sheds light on the complex mechanisms of IVD inflammation and physiological and biochemical processes of IDD. Furthermore, it provides an overview of recent research developments in this area, intending to identify novel therapeutic targets and guide future clinical strategies for effectively treating IVD-related conditions.

N-cadherin Alleviates Apoptosis and Senescence of Nucleus Pulposus Cells via Suppressing ROS-dependent ERS in the Hyper-osmolarity Microenvironment

The in-situ osmolarity is an important physicochemical factor that regulates cell fate of nucleus pulposus cells (NPCs). Our previous studies demonstrated that reduced N-cadherin (NCDH) expression in nucleus pulposus cells is associated with cellular damage under hyper-osmolarity microenvironment. This study was aimed at exploring the impacts of NCDH on senescence and apoptosis of NPCs, as well as the potential molecular mechanism. By comparing NPCs from patients with lumbar fractures and lumbar disc herniation, we identified a correlation between decreased NCDH expression and increased endoplasmic reticulum stress (ERS), resulting in undesirable cell fate (senescence and apoptosis). After blocking Reactive oxygen species (ROS) or ERS, it was indicated that hyper-osmolarity microenvironment induced ERS was ROS-dependent. Further results demonstrated the correlation in rat NPCs. Upregulation of NCDH expression reduced ROS-dependent ERS, thus limiting undesirable cell fates in vitro. This was further confirmed through the rat tail acupuncture injection model. NCDH overexpression successfully mitigated ERS, preserved extracellular matrix production and alleviating intervertebral disc degeneration in vivo. Together, NCDH can alleviate senescence and apoptosis of NPCs by suppressing ROS-dependent ERS via the ATF4-CHOP signaling axis in the hyper-osmolarity microenvironment, thus highlighting the therapeutic potential of NCDH in combating degenerative disc diseases.

Scientific Bibliometric and Visual Analysis of Studies on Autophagy in Intervertebral Disc Degeneration Based on Web of Science

OBJECTIVE

To analyze the current research trends and potential mechanisms related to the role of autophagy in intervertebral disc degeneration (IVDD) and to provide new ideas for future research in this field.

METHODS

All articles on IVDD and autophagy were retrieved and extracted from the Web of Science (WoS) core collection database. The results were evaluated and visualized using the bibliometric Web site, CiteSpace, and VOSviewer software, including annual articles published, countries, institutions, authors, journals, research areas, funding agencies, citations, and keywords.

RESULTS

From January 1, 2011, to December 31, 2022, 323 reviews and original articles were included, and the overall trend in the number of articles was increasing rapidly. China and the United States were the countries with the most scientific research achievements. The 323 articles received a total number of citations of 6949, with an H index of 43 and an average citation of 21.51. The top publication country, institution, author, journal, research area, and funding agency were China, Huazhong University of Science and Technology, Cao Yang of Tongji Medical College, Oxidative Medicine and Cellular Longevity, cell biology, and National Natural Science Foundation of China, respectively. Most of the keywords were associated with the mechanisms and regulatory networks of autophagy. In addition, with increasing evidence showing the key role of autophagy in IVDD, therapy, signaling pathway, and mitophagy are emerging as new research hot spots that should be paid more attention.

CONCLUSIONS

This study provided a scientific perspective on autophagy in IVDD and elucidated the current research status and hot spots in this field. The mechanism of autophagy and the application of regulating autophagy in the treatment of IVDD deserve further research.

Oxidative stress in intervertebral disc degeneration: Molecular mechanisms, pathogenesis and treatment

Low back pain (LBP) is a leading cause of labour loss and disability worldwide, and it also imposes a severe economic burden on patients and society. Among symptomatic LBP, approximately 40% is caused by intervertebral disc degeneration (IDD). IDD is the pathological basis of many spinal degenerative diseases such as disc herniation and spinal stenosis. Currently, the therapeutic approaches for IDD mainly include conservative treatment and surgical treatment, neither of which can solve the problem from the root by terminating the degenerative process of the intervertebral disc (IVD). Therefore, further exploring the pathogenic mechanisms of IDD and adopting targeted therapeutic strategies is one of the current research hotspots. Among the complex pathophysiological processes and pathogenic mechanisms of IDD, oxidative stress is considered as the main pathogenic factor. The delicate balance between reactive oxygen species (ROS) and antioxidants is essential for maintaining the normal function and survival of IVD cells. Excessive ROS levels can cause damage to macromolecules such as nucleic acids, lipids, and proteins of cells, affect normal cellular activities and functions, and ultimately lead to cell senescence or death. This review discusses the potential role of oxidative stress in IDD to further understand the pathophysiological processes and pathogenic mechanisms of IDD and provides potential therapeutic strategies for the treatment of IDD.

Overexpression of SIRT6 alleviates apoptosis and enhances cell viability and monoclonal antibody expression in CHO-K1 cells

BACKGROUND

Chinese hamster ovary (CHO) cells are the most predominantly utilized host for the production of monoclonal antibodies (mAbs) and other complex glycoproteins. A major challenge in the process of CHO cell culture is the occurrence of cell death following different stressful conditions, which hinders the production yield. Engineering genes involved in pathways related to cell death is a remarkable strategy to delay apoptosis, improve cell viability and enhance productivity. SIRT6 is a stress-responsive protein that regulates DNA repair, maintains genome integrity, and is critical for longevity and cell survival in organisms.

METHODS AND RESULTS

In this study, SIRT6 was stably overexpressed in CHO-K1 cells and the impact of its expression on apoptosis related gene expression profile, viability, apoptosis, and mAb productivity was investigated. While a significant increase was observed in Bcl-2 mRNA level, caspase-3 and Bax mRNA levels were decreased in the SIRT6 engineered cells compared to the parental CHO-K1 cells. Moreover, improved cell viability and decreased rate of apoptotic progression was observed in a SIRT6-derived clone in comparision to the CHO-K1 cells during 5 days of batch culture. anti-CD52 IgG1 mAb titers were improved up to 1.7- and 2.8-fold in SIRT6-derived clone during transient and stable expression, respectively.

CONCLUSIONS

This study indicates the positive effects of SIRT6 overexpression on cell viability and anti-CD52 IgG1 mAb expression in CHO-K1 cells. Further studies are needed to examine the potential of SIRT6-engineered host cells for the production of recombinant biotherapeutics in industrial settings.

DNMT1 regulates polarization of macrophage-induced intervertebral disc degeneration by modulating SIRT6 expression and promoting pyroptosis in vivo

BACKGROUND

Intervertebral disc degeneration (IDD) is a complex phenomenon and a multifactorial degenerative disease that creates a heavy economic burden on health systems globally. Currently, there is no specific treatment proven to be effective in reversing and delaying the progression of IDD.

METHOD

This study consisted of animal and cell culture experiments. The role of DNA methyltransferase 1 (DNMT1) on regulating the M1/M2 macrophages polarization and pyroptosis, as well as its effect on Sirtuin 6 (SIRT6) expression in an IDD rat model and in tert-butyl hydroperoxide (TBHP)-treated nucleus pulposus cells (NPCs) were explored. Rat models were constructed, followed by transfection with lentiviral vector to inhibit DNMT1 or overexpress SIRT6. The NPCs were treated with THP-1-cells conditioned medium, and their pyroptosis, apoptosis, and viability were evaluated. Western blot, histological and immunohistochemistry staining, ELISA, PCR, and flow cytometry were all used to evaluate the role of DNMT1/ SIRT6 on macrophage polarization.

RESULTS

Silencing DNMT1 inhibited apoptosis, the expression of related inflammatory mediators (e.g., iNOS) and inflammatory cytokines (e.g., IL6 and TNF-α). Moreover, silencing DNMT1 significantly inhibited the expression of pyroptosis markers IL- 1β, IL-6, and IL-18 and decreased the NLRP3, ASC, and caspase-1 expression. On the other hand, M2 macrophage specific markers CD163, Arg-1, and MR were overexpressed upon silencing DNMT1 or SIRT6 overexpression. At the same time, silencing DNMT1 exerted a regulatory effect on increasing the SIRT6 expression.

CONCLUSIONS

DNMT1 may be a promising potential target for IDD treatment due to its ability to ameliorate the progression of the disease.

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.

The role of the miR-4306/PAK6 axis in degenerative nucleus pulposus cells in human intervertebral disc degeneration

Intervertebral disc degeneration (IDD), characterized by degenerative changes that occur in intervertebral discs due to aging or structural injury, is thought to be the most common cause of lower back pain. Recent studies have shown that microRNAs (miRNAs) have a critical role in the etiopathogenesis of IDD. In the current study, we aimed to determine the role of miRNAs in mediating the underlying mechanisms associated with IDD. First, differentially expressed miRNAs (DEmiRNAs) were identified using the GEO database, and subsequently confirmed by RT-qPCR and in situ hybridization. We found that miR-4306 expression was significantly decreased in human nucleus pulposus (NP) tissues compared with healthy controls, and was negatively correlated with the patients' Pfirrmann grade. To determine the mechanism by which miR-4306 was involved in IDD pathogenesis, we examined the effects of overexpressing or silencing miR-4306 on extracellular matrix (ECM) synthesis/degradation, proliferation, autophagy and apoptosis of human degenerated NP cells isolated from IDD patients. Next, we used dual-luciferase reporter assays to demonstrate that miR-4306 interacted with the 3'-untranslated regions of p21-activated kinase 6 (PAK6) mRNA, resulting in significant suppression of PAK6 expression. This effect was abolished by miR-4306 binding site mutations. Using miR-4306/PAK6 gain-of-function and loss-of-function studies in human degenerated NP cells, we demonstrated that miR-4306 promoted NP cell proliferation, ECM synthesis and autophagy, while inhibiting apoptosis and ECM degradation via PAK6. Thus, our findings indicate that miR-4306, acting via PAK6, has an important role in IDD and can be used as a promising therapeutic target for the treatment of patients with IDD.

Cocoa Polyphenol Extract Inhibits Cellular Senescence via Modulation of SIRT1 and SIRT3 in Auditory Cells

Cocoa, rich in polyphenols, has been reported to provide many health benefits due to its antioxidant properties. In this study, we investigated the effect of Cocoa polyphenols extract (CPE) against oxidative stress-induced cellular senescence using a hydrogen peroxide (H₂O₂)-induced cellular senescence model in three auditory cells lines derived from the auditory organ of a transgenic mouse: House Ear Institute-Organ of Corti 1 (HEI-OC1), Organ of Corti-3 (OC-k3), and Stria Vascularis (SV-k1) cells. Our results showed that CPE attenuated senescent phenotypes, including senescence-associated β-galactosidase expression, cell proliferation, alterations of morphology, oxidative DNA damage, mitochondrial dysfunction by inhibiting mitochondrial reactive oxygen species (mtROS) generation, and related molecules expressions such as forkhead box O3 (FOXO3) and p53. In addition, we determined that CPE induces expression of sirtuin 1 (SIRT1) and sirtuin 3 (SIRT3), and it has a protective role against cellular senescence by upregulation of SIRT1 and SIRT3. These data indicate that CPE protects against senescence through SIRT1, SIRT3, FOXO3, and p53 in auditory cells. In conclusion, these results suggest that Cocoa has therapeutic potential against age-related hearing loss (ARHL).

Serum SIRT6 Levels Are Associated with Frailty in Older Adults

OBJECTIVES

Frailty is one of the major health problems facing aging societies worldwide. We investigated the association between serum SIRT6 and frailty in older adults.

DESIGN

Cross-sectional analysis of associations of serum SIRT6 and frailty in older people.

SETTING

Enrolled community-dwelling and hospital outpatient clinic adults older than 65 years old in Wuhan City, Hubei Province, China.

PARTICIPANTS

A total of 540 community-dwelling older adults (age ≥ 65 years) in Wuhan were included in the study.

MEASURES

We used Frailty Phenotype criteria for classifying participants based on their frailty status. Serum SIRT6 was measured using an ELISA kit.

RESULTS

A total of 540 older adults were included in this cross-sectional study. Serum SIRT6 was lower in the slowness group (7.23±1.81 vs 5.89±1.74, p<0.001), weakness group (6.87±1.88 vs 5.68±1.64, p<0.001), and exhaustion group (6.73±1.90 vs 5.88±1.74, p<0.001) compare with the normal group. ROC curves were used to assess the efficiency of SIRT6 in predicting frailty in older adults. The AUC for SIRT6 was 0.792 (95% CI: 0.7514 to 0.8325), with the highest sensitivity of 68.0% and the specificity of 91.9%, and the optimal critical value of 4.65ng/ml according to Youden's index. Multivariate logistic regression analysis showed that serum SIRT6 level was independently associated with frailty in older people.

CONCLUSION

In conclusion, serum SIRT6 was decreased in frailty compared with robust older adults. A decreased serum SIRT6 was independently associated with an increased risk of frailty. SIRT6 may be a potential target for the treatment of patients with frailty.

Sirtuins and chemokines as markers of replicative and induced senescence of human endotheliocytes

Background. One of the factors of the pathogenesis of atherosclerosis and other cardiovascular diseases is induced endothelial senescence. In this regard, the urgent task of molecular biology and medicine is the search for molecules that affect the process of vascular endotheliocytes senescence.The aim. To assess the expression of Sirt-1,3,6 and chemokines IL-4, CXCL11 in the replicative and induced senescence of human endotheliocytes.Materials and methods. The study was conducted on the primary culture of isolated human umbilical vein endothelial cells (HUVECs). HUVECs were cultured under conditions of replicative (natural) and lipopolysaccharide induced senescence.Results. The synthesis of Sirt-1,3,6, IL-4 and CXCL11 was evaluated using western blot analysis. We revealed a decrease in Sirt-1,3,6 synthesis by 1.6–1.8 times (р < 0.05) in the conditions of HUVEC replicative senescence. Induced senescence of endotheliocytes is characterized by a more pronounced decrease (1.7–3.4 times; р < 0.05) in the Sirt-1,3,6 synthesis. CXCL11 synthesis increases by 1.4 times (р < 0.05) in replicative and by 3.4 times (р < 0.05) in induced HUVEC senescence. IL-4 synthesis increases by 4.7 times in conditions of induced HUVEC senescence and doesn’t have changes in replicative senescence of endotheliocytes.Conclusion. These data obtained indicate that sirtuins and chemokines play an important role in the development of endothelial dysfunction observed in natural and induced senescence.

Cyanidin attenuates the apoptosis of rat nucleus pulposus cells and the degeneration of intervertebral disc via the JAK2/STAT3 signal pathway in vitro and in vivo

CONTEXT

Cyanidin has been shown to have therapeutic potential in osteoarthritis. However, it is unclear whether cyanidin prevents the progression of intervertebral disc degeneration (IVDD).

OBJECTIVE

This study evaluates the effects of cyanidin on IVDD in vitro and in vivo.

MATERIALS AND METHODS

Nucleus pulposus cells (NPCs) isolated from lumbar IVD of 4-week-old male Sprague-Dawley (SD) rats were exposed to 20 ng/mL IL-1β, and then treated with different doses (0-120 µM) of cyanidin for 24 h. SD rats were classified into three groups (n = 8) and treated as follows: control (normal saline), IVDD (vehicle), IVDD + cyanidin (50 mg/kg). Cyanidin was administered intraperitoneally for 8 weeks.

RESULTS

The IC₅₀ of cyanidin for NPCs was 94.78 µM, and cyanidin had no toxicity at concentrations up to 500 mg/kg in SD rats. Cyanidin inhibited the apoptosis of NPCs induced by IL-1β (12.73 ± 0.61% vs. 18.54 ± 0.60%), promoted collagen II (0.82-fold) and aggrecan (0.81-fold) expression, while reducing MMP-13 (1.02-fold) and ADAMTS-5 (1.40-fold) expression. Cyanidin increased the formation of autophagosomes in IL-1β-induced NPCs, and promoted LC3II/LC3I (0.83-fold) and beclin-1 (0.85-fold) expression, which could be reversed by chloroquine. Cyanidin inhibited the phosphorylation of JAK2 (0.47-fold) and STAT3 (0.53-fold) in IL-1β-induced NPCs. The effects of cyanidin could be enhanced by AG490. Furthermore, cyanidin mitigated disc degeneration in IVDD rats in vivo.

DISCUSSION AND CONCLUSIONS

Cyanidin improved the function of NPCs in IVDD by regulating the JAK2/STAT3 pathway, which may provide a novel alternative strategy for IVDD. The mechanism of cyanidin improving IVDD still needs further work for in-depth investigation.

Long non-coding RNAs LINC00689 inhibits the apoptosis of human nucleus pulposus cells via miR-3127-5p/ATG7 axis-mediated autophagy

This study aimed to explore the effects of long non-coding RNAs LINC00689 (LINC00689) in human nucleus pulposus cells (NPCs). NPCs were isolated and their morphology was observed. The proliferation and apoptosis of NPCs, and the levels of LINC00689, miR-3127-5p, Bax, Bcl-2, Cleaved caspase-3, ATG5, ATG7, p62, and LC3Ⅱ/LC3I were detected. Interrelations of LINC00689, miR-3127-5p, and ATG7 were analyzed. LINC00689 was down-regulated yet miR-3127-5p was up-regulated in NPCs. LINC00689 could competitively bind with miR-3127-5p, and ATG7 was targeted by miR-3127-5p in NPCs. Overexpressed LINC00689 promoted proliferation yet inhibited apoptosis of NPCs, whereas LINC00689 silencing did the opposite. Overexpressed LINC00689 raised ATG7 level and LC3Ⅱ/LC3I value yet reduced that of p62 level, but the depletion of LINC00689 did the contrary. ATG7 silencing abolished the effects of overexpressed LINC00689 in NPCs, and likewise, up-regulation of miR-3127-5p overturned the effects of overexpressed LINC00689 in NPCs. Collectively, the up-regulation of LINC00689 inhibits the apoptosis of NPCs via miR-3127-5p/ATG7 axis-mediated autophagy.

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.

Role of Nrf2 and HO-1 in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common age-related disease with clinical manifestations of lumbar and leg pain and limited mobility. The pathogenesis of IDD is mainly mediated by the death of intervertebral disc (IVD) cells and the imbalance of extracellular matrix (ECM) synthesis and degradation. Oxidative stress and inflammatory reactions are the important factors causing this pathological change. Therefore, the regulation of reactive oxygen species and production of inflammatory factors may be an effective strategy to delay the progression of IDD. In recent years, nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream regulated protein heme oxygenase-1 (HO-1) have received special attention due to their antioxidant, anti-inflammatory and anti-apoptotic protective effects. Recent studies have elucidated the important role of these two proteins in the treatment of IDD disease. However, Nrf2 and HO-1 have not been systematically reported in IDD-related diseases. Therefore, this review describes the biological characteristics of Nrf2 and HO-1, the relationship between Nrf2- and HO-1-regulated oxidative stress and the inflammatory response and IDD, and the progress in research on some extracts targeting Nrf2 and HO-1 to improve IDD. Understanding the role and mechanism of Nrf2 and HO-1 in IDD may provide novel ideas for the clinical treatment and development of Nrf2- and HO-1-targeted drugs.

Injectable cartilage matrix hydrogel loaded with cartilage endplate stem cells engineered to release exosomes for non-invasive treatment of intervertebral disc degeneration

Low back pain, mainly caused by intervertebral disc degeneration (IVDD), is a common health problem; however, current surgical treatments are less than satisfactory. Thus, it is essential to develop novel non-invasive surgical methods for IVDD treatment. Here, we describe a therapeutic strategy to inhibit IVDD by injecting hydrogels modified with the extracellular matrix of costal cartilage (ECM-Gels) that are loaded with cartilage endplate stem cells (CESCs). After loaded with CESCs overexpressing Sphk2 (Lenti-Sphk2-CESCs) and injected near the cartilage endplate (CEP) of rats in vivo, ECM-Gels produced Sphk2-engineered exosomes (Lenti-Sphk2-Exos). These exosomes penetrated the annulus fibrosus (AF) and transported Sphk2 into the nucleus pulposus cells (NPCs). Sphk2 activated the phosphatidylinositol 3-kinase (PI3K)/p-AKT pathway as well as the intracellular autophagy of NPCs, ultimately ameliorating IVDD. This study provides a novel and efficient non-invasive combinational strategy for IVDD treatment using injectable ECM-Gels loaded with CESCs that express Sphk2 with sustained release of functional exosomes.

Targeting Autophagy for Developing New Therapeutic Strategy in Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is a prevalent cause of low back pain. IVDD is characterized by abnormal expression of extracellular matrix components such as collagen and aggrecan. In addition, it results in dysfunctional growth, senescence, and death of intervertebral cells. The biological pathways involved in the development and progression of IVDD are not fully understood. Therefore, a better understanding of the molecular mechanisms underlying IVDD could aid in the development of strategies for prevention and treatment. Autophagy is a cellular process that removes damaged proteins and dysfunctional organelles, and its dysfunction is linked to a variety of diseases, including IVDD and osteoarthritis. In this review, we describe recent research findings on the role of autophagy in IVDD pathogenesis and highlight autophagy-targeting molecules which can be exploited to treat IVDD. Many studies exhibit that autophagy protects against and postpones disc degeneration. Further research is needed to determine whether autophagy is required for cell integrity in intervertebral discs and to establish autophagy as a viable therapeutic target for IVDD.

VDR promotes nucleus pulposus cell mitophagy as a protective mechanism against oxidative stress injury

Intervertebral disk degeneration (IDD) is a common aging disease. Excessive apoptosis of nucleus pulposus (NP) cells has been widely considered a main contributor to IDD. Emerging science has shown that autophagy plays a protective role against apoptosis under oxidative stress. Vitamin D receptor (VDR) is a steroid hormone receptor that can regulate autophagy. The purpose of this study was to clarify whether VDR alleviates IDD by promoting autophagy. H₂O₂ stimulation was used to establish oxidative stress conditions. Initially, the expression level of VDR in human degenerative NP tissues was measured by immunohistochemistry. In addition, the CRISPR-dCas9-VPR system and siRNA were utilized to upregulate or downregulate VDR and Parkin expression, respectively. Autophagic and apoptotic markers were determined by Western blotting and RT-qPCR. Transmission electron microscopy was used to monitor the occurrence of autophagy in rat NP cells. VDR expression was downregulated in human degenerative NP tissues and H₂O₂-stimulated rat NP cells, indicating a negative correlation between VDR expression and IDD. VDR overexpression promoted mitophagy and prevented apoptosis and mitochondrial injury under oxidative stress. Additionally, mitophagy inhibition by 3-MA abolished the protective effect of VDR activation in vitro. Furthermore, VDR activation promoted mitophagy via the PINK1/Parkin pathway in H₂O₂-treated NP cells. This study demonstrates that VDR activation ameliorates oxidative damage and decreases NP cell apoptosis by promoting PINK1/Parkin-dependent mitophagy, indicating that VDR may serve as a promising therapeutic target in the management of IDD.

Periostin promotes nucleus pulposus cells apoptosis by activating the Wnt/β-catenin signaling pathway

Intervertebral disc (IVD) degeneration (IVDD) is closely linked to degenerative spinal disease, resulting in disability, poor quality of life, and financial burden. Apoptosis of nucleus pulposus (NP) cells (NPCs) is a key pathological basis of IVDD. Periostin (POSTN), an extracellular matrix protein, is expressed in many tissues, whereas its abnormal expression is associated with IVDD. The conventional Wnt/β-catenin pathway is also involved in IVDD and contributes to NPCs apoptosis. However, research on the mechanisms of POSTN in IVDD is lacking. This study investigated the relationship between POSTN and β-catenin expression in degenerated IVDs. We detected the expression of POSTN, β-catenin, and cleaved-caspase-3 (C-caspase3) in degenerated and non-degenerated IVD tissues of different grades (n = 8) using RT-qPCR, immunohistochemical staining, and western blotting analysis. Next, we explored the effects of recombinant periostin (rPOSTN) and isoquercitrin (Iso), an inhibitor of the Wnt/β-catenin pathway, on NPCs apoptosis. Finally, we inhibited the expression of POSTN in degenerated NPCs in vivo and investigated the anti-apoptotic effect. The expression of β-catenin, POSTN, and C-caspase3 in severe degenerative IVDs was significantly higher than that in mild degenerative IVDs. These findings were confirmed in rat and cell-based degenerative models. When treated with rPOSTN, the Wnt/β-catenin pathway activity and cell apoptosis were time- and dose-dependent. However, rPOSTN-induced NPCs apoptosis decreased after iso-induced inhibition of the Wnt/β-catenin pathway. POSTN inhibition reduced apoptosis but was restored by rPOSTN re-addition. Lastly, POSTN inhibition ameliorated puncture-induced IVDD in vivo. Overall, our study demonstrated that POSTN promotes NPCs apoptosis and aggravates degeneration by activating the Wnt/β-catenin pathway.

Regulation of Gene Expression through Food—Curcumin as a Sirtuin Activity Modulator

The sirtuin family comprises NAD⁺-dependent protein lysine deacylases, mammalian sirtuins being either nuclear (SIRT1, SIRT2, SIRT6, and SIRT7), mitochondrial (SIRT3, SIRT4, and SIRT5) or cytosolic enzymes (SIRT2 and SIRT5). They are able to catalyze direct metabolic reactions, thus regulating several physiological functions, such as energy metabolism, stress response, inflammation, cell survival, DNA repair, tissue regeneration, neuronal signaling, and even circadian rhythms. Based on these data, recent research was focused on finding molecules that could regulate sirtuins’ expression and/or activity, natural compounds being among the most promising in the field. Curcumin (1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) can induce, through SIRT, modulation of cancer cell senescence, improve endothelial cells protection against atherosclerotic factors, enhance muscle regeneration in atrophy models, and act as a pro-longevity factor counteracting the neurotoxicity of amyloid-beta. Although a plethora of protective effects was reported (antioxidant, anti-inflammatory, anticancer, etc.), its therapeutical use is limited due to its bioavailability issues. However, all the reported effects may be explained via the bioactivation theory, which postulates that curcumin’s observed actions are modulated via its metabolites and/or degradation products. The present article is focused on bringing together the literature data correlating the ability of curcumin and its metabolites to modulate SIRT activity and its consequent beneficial effects.

Mitochondrial Dysfunction in Oxidative Stress-Mediated Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is the most common contributor to low back pain (LBP). Recent studies have found that oxidative stress and reactive oxygen species (ROS) play an important role in IVDD. As a by‐product of aerobic respiration, ROS is mainly produced in the mitochondria by the electron transport chain and other mitochondrial located proteins. With the excessive accumulation of ROS, mitochondria are also the primary target of ROS attack in disc cells. A disrupted balance between intracellular ROS production and antioxidant capacity will lead to oxidative stress, which is the key contributor to cell apoptosis, cell senescence, excessive autophagy, and mitochondrial dysfunction. As the pivotal ingredient of oxidative stress, mitochondrial dysfunction manifests as imbalanced mitochondrial dynamics and dysregulated mitophagy. Mitochondria can alter their own dynamics through the process of fusion and fission, so that disabled mitochondria can be separated from the mitochondrial pool. Moreover, mitophagy participates by clearing these dysfunctional mitochondria. Abnormality in any of these processes either increases the production or decreases the clearance of ROS, leading to a vicious cycle that results in the death of intervertebral disc cells in large quantities, combined with degradation of the extracellular matrix and overproduction of matrix metalloproteinase. In this review, we explain the changes in mitochondrial morphology and function during oxidative stress‐mediated IVDD and highlight the important role of mitochondria in this process. Eventually, we summarize the IVDD therapeutic strategies targeting mitochondrial dysfunction based on current understanding of the role of oxidative stress in IVDD.

Luteolin suppresses TNF‑α‑induced inflammatory injury and senescence of nucleus pulposus cells via the Sirt6/NF‑κB pathway

Luteolin (3',4',5,7-tetrahydroxy flavone) is a flavonoid, which is widely distributed in various plants including flowers, vegetables, and medicinal herbs and spices. Luteolin can be applied in the treatment of various diseases due to its multiple biological activities, such as anti-inflammatory, anticancer, and antioxidative activity. However, its role in intervertebral disc degeneration has not been previously reported. Therefore, the purpose of the present study was to explore the effects of luteolin on Tumor necrosis factor (TNF)-α-induced inflammatory injury and senescence of human nucleus pulposus cells (HNPCs), as well as the underlying mechanisms of action of this compound. Cell viability and apoptosis were assessed by MTT assay and TUNEL staining, respectively. ELISA kits were applied to detect the levels of inflammatory cytokines and the activity of telomerase. Senescence β-galactosidase staining was used to detect the activity levels of β-galactosidase in the cells. Cell transfection was performed to achieve interference of sirtuin 6 (Sirt6). The protein expression levels were detected by western blot analysis. TUNEL staining and western blot analysis were performed to assess the expression levels of apoptosis-related proteins. The results indicated that TNF-α induced a significant decrease in HNPC viability and an increase in inflammatory factor levels, while the application of luteolin effectively increased cell viability and decreased intracellular interleukin (IL)-1β and IL-6 expression levels. Furthermore, luteolin decreased apoptosis compared with the TNF-α groups in a dose-dependent manner. In addition, the results of the detection kits suggested that luteolin reversed TNF-α-induced senescence. Notably, interference with Sirt6 partially reduced the protective effect of luteolin on TNF-α-induced HNPC senescence via the Sirt6/NF-κB pathway. In summary, the data indicated that luteolin suppresses TNF-α-induced inflammatory injury and senescence of HNPCs via the Sirt6/NF-κB pathway.

Cell Senescence and Central Regulators of Immune Response

Pathways regulating cell senescence and cell cycle underlie many processes associated with ageing and age-related pathologies, and they also mediate cellular responses to exposure to stressors. Meanwhile, there are central mechanisms of the regulation of stress responses that induce/enhance or weaken the response of the whole organism, such as hormones of the hypothalamic-pituitary-adrenal (HPA) axis, sympathetic and parasympathetic systems, thymic hormones, and the pineal hormone melatonin. Although there are many analyses considering relationships between the HPA axis and organism ageing, we found no systematic analyses of relationships between the neuroendocrine regulators of stress and inflammation and intracellular mechanisms controlling cell cycle, senescence, and apoptosis. Here, we provide a review of the effects of neuroendocrine regulators on these mechanisms. Our analysis allowed us to postulate a multilevel system of central regulators involving neurotransmitters, glucocorticoids, melatonin, and the thymic hormones. This system finely regulates the cell cycle and metabolic/catabolic processes depending on the level of systemic stress, stage of stress response, and energy capabilities of the body, shifting the balance between cell cycle progression, cell cycle stopping, senescence, and apoptosis. These processes and levels of regulation should be considered when studying the mechanisms of ageing and the proliferation on the level of the whole organism.

BRD4 Inhibition Suppresses Senescence and Apoptosis of Nucleus Pulposus Cells by Inducing Autophagy during Intervertebral Disc Degeneration: An In Vitro and In Vivo Study

Intervertebral disc degeneration (IDD) is the most common chronic skeletal muscle degeneration disease. Although the underlying mechanisms remain unclear, nucleus pulposus (NP) autophagy, senescence, and apoptosis are known to play a critical role in this process. Previous studies suggest that bromodomain-containing protein 4 (BRD4) promotes senescent and apoptotic effects in several age-related degenerative diseases. It is not known, however, if BRD4 inhibition is protective in IDD. In this study, we explored whether BRD4 influenced IDD. In human clinical specimens, the BRD4 level was markedly increased with the increasing Pfirrmann grade. At the cellular level, BRD4 inhibition prevented IL-1β-induced senescence and apoptosis of NP cells and activated autophagy via the AMPK/mTOR/ULK1 signaling pathway. Inhibition of autophagy by 3-methyladenine (3-MA) partially reversed the antisenescence and antiapoptotic effects of BRD4. In vivo, BRD4 inhibition attenuated IDD. Taken together, the results of this study showed that BRD4 inhibition reduced NP cell senescence and apoptosis by induced autophagy, which ultimately alleviated IDD. Therefore, BRD4 may serve as a novel potential therapeutic target for the treatment of IDD.

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.

Sirt6 regulates autophagy in AGE-treated endothelial cells via KLF4

BACKGROUND AND AIMS

High glucose and its byproducts are important factors causing dysfunction of endothelial cells. Autophagy is critical for endothelial cellular homeostasis. However, the specific molecular mechanism of how autophagy is regulated in endothelial cells under high-glucose condition remains unknown. We aim to explore the role Sirt6 plays in regulating autophagy in AGE-treated endothelial cells and how this function is exerted via KLF4.

METHODS AND RESULTS

Our results indicate that autophagy level increased in AGE-treated endothelial cells alongside with higher Sirt6 and KLF4 expression level. What's more, knock-in of Sirt6 by adenovirus led to augmented autophagy level while knockdown of Sirt6 led to the opposite. We also verified that Sirt6 affected KLF4 expression positively but KLF4 didn't influence Sirt6 expression level while knocking out of KLF4 impaired Sirt6-enhanced autophagy. Finally we found that STZ-induced diabetic mice showed more autophagosomes in endothelium and Sirt6 knockdown by adeno-associated virus reduced the number of autophagosomes. Knockdown of Sirt6 also caused impaired endothelium integrity but echocardiography indicated there were no significant functional differences.

CONCLUSION

Our research reveals more about how Sirt6 regulates autophagy in endothelial cells under high-glucose simulated condition and provides further insight into the relationships between Sirt6 and KLF4.

SKI knockdown suppresses apoptosis and extracellular matrix degradation of nucleus pulposus cells via inhibition of the Wnt/β-catenin pathway and ameliorates disc degeneration

This study aimed to determine the effects of SKI on interleukin (IL)-1β-induced apoptosis of nucleus pulposus (NP) cells, intervertebral disc degeneration (IDD), and the Wnt signaling pathway. NP tissue specimens of different Pfirrmann grades (II-V) were collected from patients with different grades of IDD. Real-time polymerase chain reaction and western blotting were used to compare SKI mRNA and protein expression in NP tissues from patients. Using the IL-1β-induced IDD model, NP cells were infected with lentivirus-coated si-SKI to downregulate the expression of SKI and treated with LiCl to evaluate the involvement of the Wnt/β-catenin signaling pathway. Western blotting, immunofluorescence, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to detect NP cell apoptosis, extracellular matrix (ECM) metabolism, and related protein expression changes in the Wnt/β-catenin signaling pathway. To investigate the role of SKI in vivo, a rat IDD model was established by needle puncture of the intervertebral disc. Rats were injected with lentivirus-coated si-SKI and evaluated by magnetic resonance imaging (MRI), and hematoxylin and eosin (HE) and safranin O staining. SKI expression positively correlated with the severity of human IDD. In the IL-1β-induced NP cell degeneration model, SKI expression increased significantly and reached a peak at 24 h. SKI knockdown protected against IL-1β-induced NP cell apoptosis and ECM degradation. LiCl treatment reversed the protective effects of si-SKI on NP cells. Furthermore, lentivirus-coated si-SKI injection partially reversed the NP tissue damage in the IDD model in vivo. SKI knockdown reduced NP cell apoptosis and ECM degradation by inhibiting the Wnt/β-catenin signaling pathway, ultimately protecting against IDD. Therefore, SKI may be an effective target for IDD treatment.

Apigenin Alleviates Intervertebral Disc Degeneration via Restoring Autophagy Flux in Nucleus Pulposus Cells

Oxidative stress–induced apoptosis and senescence of nucleus pulposus (NP) cells play a crucial role in the progression of intervertebral disc degeneration (IVDD). Accumulation of studies has shown that activated autophagy and enhanced autophagic flux can alleviate IVDD. In this study, we explored the effects of apigenin on IVDD in vitro and in vivo. Apigenin was found to inhibit tert-butyl hydroperoxide (TBHP)–induced apoptosis, senescence, and ECM degradation in NP cells. In addition, apigenin treatment can restore the autophagic flux blockage caused by TBHP. Mechanistically, we found that TBHP may induce autophagosome and lysosome fusion interruption and lysosomal dysfunction, while apigenin alleviates these phenomena by promoting the nuclear translocation of TFEB via the AMPK/mTOR signaling pathway. Furthermore, apigenin also exerts a protective effect against the progression of IVDD in the puncture-induced rat model. Taken together, these findings indicate that apigenin protects NP cells against TBHP-induced apoptosis, senescence, and ECM degradation via restoration of autophagic flux in vitro, and it also ameliorates IVDD progression in rats in vivo, demonstrating its potential for serving as an effective therapeutic agent for IVDD.

SIRT1 Attenuates Apoptosis of Nucleus Pulposus Cells by Targeting Interactions between LC3B and Fas under High-Magnitude Compression

Mechanical overloading-induced nucleus pulposus cell (NPC) apoptosis plays a core role in the pathogenesis of intervertebral disc degeneration. In this study, we investigated the involvement of mammalian silent information regulator 2 homolog (SIRT1) in NPC apoptosis under high-magnitude compression. Our results showed that high-magnitude compression aggravated cellular apoptosis and attenuated the expression levels of SIRT1 and microtubule-associated protein-1 light chain-3B (LC3B) in rat NPCs in a three-dimensional (3D) cell culture model and an in vivo rat tail compression model, whereas SIRT1 overexpression in NPCs partially reversed these indicators. Moreover, SIRT1 overexpression increased the formation of the LC3B/Fas complex, alleviated activation of the NF-κB pathway, and reduced NPC apoptosis. Finally, downregulation of LC3B partially activated the NF-κB pathway and aggravated NPC apoptosis. Overall, upregulation of SIRT1 increases formation of the LC3B/Fas complex, which contributes to suppression of NPC apoptosis by inhibiting the NF-κB pathway under high compressive stress.

Molecular mechanisms of dietary restriction promoting health and longevity

Dietary restriction with adequate nutrition is the gold standard for delaying ageing and extending healthspan and lifespan in diverse species, including rodents and non-human primates. In this Review, we discuss the effects of dietary restriction in these mammalian model organisms and discuss accumulating data that suggest that dietary restriction results in many of the same physiological, metabolic and molecular changes responsible for the prevention of multiple ageing-associated diseases in humans. We further discuss how different forms of fasting, protein restriction and specific reductions in the levels of essential amino acids such as methionine and the branched-chain amino acids selectively impact the activity of AKT, FOXO, mTOR, nicotinamide adenine dinucleotide (NAD⁺), AMP-activated protein kinase (AMPK) and fibroblast growth factor 21 (FGF21), which are key components of some of the most important nutrient-sensing geroprotective signalling pathways that promote healthy longevity.

The Potential Role of Cytokines in Diabetic Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) is a major cause of low back pain. Diabetes mellitus is a chronic inflammatory disease that may cause or aggravate IVDD; however, the mechanism by which diabetes induce IVDD is currently unclear. Compared to non-diabetic individuals, diabetic patients have higher levels of plasma cytokines, especially TNF-α, IL-1β, IL-5, IL-6, IL-7, IL-10, and IL-18. Due to the crucial role of cytokines in the process of intervertebral disc degeneration, we hypothesized that elevation of these cytokines in plasma of diabetic patients may be involved in the process of diabetes-induced IVDD. In this review, changes in plasma cytokine levels in diabetic patients were summarized and the potential role of elevated cytokines in diabetes-induced IVDD was discussed. Results showed that some cytokines such as TNF-α and IL-1β may accelerate the development of IVDD, while others such as IL-10 is supposed to prevent its development. Apoptosis, senescence, and extracellular matrix metabolism were found to be regulated by these cytokines in IVDD. Further studies are required to validate the cytokines targeted strategy for diabetic IVDD therapy.

Advances and Prospects in Biomaterials for Intervertebral Disk Regeneration

Low-back and neck-shoulder pains caused by intervertebral disk degeneration are highly prevalent among middle-aged and elderly people globally. The main therapy method for intervertebral disk degeneration is surgical intervention, including interbody fusion, disk replacement, and diskectomy. However, the stress changes caused by traditional fusion surgery are prone to degeneration of adjacent segments, while non-fusion surgery has problems, such as ossification of artificial intervertebral disks. To overcome these drawbacks, biomaterials that could endogenously regenerate the intervertebral disk and restore the biomechanical function of the intervertebral disk is imperative. Intervertebral disk is a fibrocartilaginous tissue, primarily comprising nucleus pulposus and annulus fibrosus. Nucleus pulposus (NP) contains high water and proteoglycan, and its main function is absorbing compressive forces and dispersing loads from physical activities to other body parts. Annulus fibrosus (AF) is a multilamellar structure that encloses the NP, comprises water and collagen, and supports compressive and shear stress during complex motion. Therefore, different biomaterials and tissue engineering strategies are required for the functional recovery of NP and AF based on their structures and function. Recently, great progress has been achieved on biomaterials for NP and AF made of functional polymers, such as chitosan, collagen, polylactic acid, and polycaprolactone. However, scaffolds regenerating intervertebral disk remain unexplored. Hence, several tissue engineering strategies based on cell transplantation and growth factors have been extensively researched. In this review, we summarized the functional polymers and tissue engineering strategies of NP and AF to endogenously regenerate degenerative intervertebral disk. The perspective and challenges of tissue engineering strategies using functional polymers, cell transplantation, and growth factor for generating degenerative intervertebral disks were also discussed.

The Effects of SRT1720 Treatment on Endothelial Cells Derived from the Lung and Bone Marrow of Young and Aged, Male and Female Mice

Angiogenesis is critical for successful fracture healing. Age-related alterations in endothelial cells (ECs) may cause impaired bone healing. Therefore, examining therapeutic treatments to improve angiogenesis in aging may enhance bone healing. Sirtuin 1 (SIRT1) is highly expressed in ECs and its activation is known to counteract aging. Here, we examined the effects of SRT1720 treatment (SIRT1 activator) on the growth and function of bone marrow and lung ECs (BMECs and LECs, respectively), derived from young (3-4 month) and old (20-24 month) mice. While aging did not alter EC proliferation, treatment with SRT1720 significantly increased proliferation of all LECs. However, SRT1720 only increased proliferation of old female BMECs. Vessel-like tube assays showed similar vessel-like structures between young and old LECs and BMECs from both male and female mice. SRT1720 significantly improved vessel-like structures in all LECs. No age, sex, or treatment differences were found in migration related parameters of LECs. In males, old BMECs had greater migration rates than young BMECs, whereas in females, old BMECs had lower migration rates than young BMECs. Collectively, our data suggest that treatment with SRT1720 appears to enhance the angiogenic potential of LECs irrespective of age or sex. However, its role in BMECs is sex- and age-dependent.

Cycloastragenol and Astragaloside IV activate telomerase and protect nucleus pulposus cells against high glucose-induced senescence and apoptosis

In diabetes-induced intervertebral disc degeneration (Db-IVDD), senescence and apoptosis of nucleus pulposus cells (NPCs) are major contributing factors. Telomere attrition and telomerase downregulation are some of the main reasons for senescence and eventual apoptosis. The derivatives of the Chinese herb Astragalus membranaceus, Cycloastragenol (CAG) and Astragaloside IV (AG-IV), are reportedly effective telomerase activators against telomere shortening; however, their effect in Db-IVDD have not been explored. The present study simultaneously investigated the regulation of these derivatives on senescence, apoptosis, telomeres and telomerase a model of high-glucose (HG)-induced stress using rat primary NPCs. The NPCs were stimulated with HG (50 mM) to evoke HG-induced stress, and the effects of CAG and AG-IV were observed on: i) The expression level of senescence marker p16; ii) β-Gal staining; iii) the expression levels of apoptosis markers cleaved-caspase 3 (c-C3), BAX and Bcl-2; iv) telomerase activation with telomerase reverse transcriptase (TERT) mRNA and protein expression, while telomere length was measured with reverse transcription-quantitative PCR. Cell proliferation was determined using the Cell Counting Kit-8 assay. Results demonstrated an upregulation in the expression levels of p16, c-C3 and BAX, and increased β-Gal staining; while the expression level of Bcl-2 was downregulated in a concentration-dependent manner. Pre-treatment of the NPCs with CAG and AG-IV downregulated the protein expression levels of p16, c-C3 and BAX, and decreased the percentage of β-Gal and FITC staining; while upregulating the Bcl-2 expression. These effects protected the cells from HG stress-induced senescence and apoptosis. HG also downregulated the expression profile of TERT and shortened the telomere length in a glucose concentration-dependent manner. While pretreatment with CAG and AG-IV upregulated TERT expression and ameliorated the telomere attrition. CAG and AG-IV also increased cell proliferation and improved cell morphology in HG conditions. Overall, these findings indicated that CAG and AG-IV suppressed HG stress-induced senescence and apoptosis, in addition to enhancing telomerase activation and lengthening of the Telomere. Therefore, CAG and AG-IV prolonged the replicative capability and longevity of the NPCs and they have the potential to be therapeutic agents in Db-IVDD.

Decorin inhibits nucleus pulposus apoptosis by matrix-induced autophagy via the mTOR pathway

Decorin (Dcn) is a member of the class I small leucine-rich proteoglycans, whose expression in the nucleus pulposus (NP) of intervertebral discs (IVDs) has been shown to increase with aging in humans and sheep. Dcn induces autophagy in endothelial cells; however, its precise role in NP and IVD degeneration during aging is not well understood. We addressed this question in the present study by treating rat nucleus pulposus cells (NPCs) with different concentrations of Dcn. The Western blot analysis and terminal deoxynucleotidyl transferase dUTP nick end labeling assay results showed that Dcn treatment induced autophagy and decreased apoptosis caused by interleukin (IL)-1β application. This effect was dependent on the protein kinase B/mechanistic target of rapamycin (mTOR)/p70 S6 kinase signaling. Dcn treatment also decreased the expression of matrix metalloproteinase-3 and -13 and decreased the IL-1β-induced attenuation of collagen type II and aggrecan levels. The role of Dcn in stimulating autophagy was further supported by the fact that the observed effects were abrogated by knocking down autophagy-related protein 7 with Atg7 small interfering RNA. Thus, Dcn protects NPCs in IVDs from IL-1β-induced apoptosis and degeneration by promoting autophagy through mTOR signaling.

Current insights into the implications of m6A RNA methylation and autophagy interaction in human diseases

Autophagy is a conserved degradation process crucial to maintaining the primary function of cellular and organismal metabolism. Impaired autophagy could develop numerous diseases, including cancer, cardiomyopathy, neurodegenerative disorders, and aging. N6-methyladenosine (m6A) is the most common RNA modification in eukaryotic cells, and the fate of m6A modified transcripts is controlled by m6A RNA binding proteins. m6A modification influences mRNA alternative splicing, stability, translation, and subcellular localization. Intriguingly, recent studies show that m6A RNA methylation could alter the expression of essential autophagy-related (ATG) genes and influence the autophagy function. Thus, both m6A modification and autophagy could play a crucial role in the onset and progression of various human diseases. In this review, we summarize the latest studies describing the impact of m6A modification in autophagy regulation and discuss the role of m6A modification-autophagy axis in different human diseases, including obesity, heart disease, azoospermatism or oligospermatism, intervertebral disc degeneration, and cancer. The comprehensive understanding of the m6A modification and autophagy interplay may help in interpreting their impact on human diseases and may aid in devising future therapeutic strategies.

Autophagic Degradation of Gasdermin D Protects against Nucleus Pulposus Cell Pyroptosis and Retards Intervertebral Disc Degeneration In Vivo

Intervertebral disc degeneration (IDD) is the primary culprit of low back pain and renders heavy social burden worldwide. Pyroptosis is a newly discovered form of programmed cell death, which is also involved in nucleus pulposus (NP) cells during IDD progression. Moderate autophagy activity is critical for NP cell survival, but its relationship with pyroptosis remains unknown. This study is aimed at investigating the relationship between autophagy and pyroptotic cell death. The pyroptosis executor N-terminal domain of gasdermin D (GSDMD-N) and inflammation-related proteins were measured in lipopolysaccharide- (LPS-) treated human NP cells. Inhibition of autophagy by siRNA transfection and chemical drugs aggravated human NP cell pyroptosis. Importantly, we found that the autophagy-lysosome pathway and not the proteasome pathway mediated the degradation of GSDMD-N as lysosome dysfunction promoted the accumulation of cytoplasmic GSDMD-N. Besides, P62/SQSTM1 colocalized with GSDMD-N and mediated its degradation. The administration of the caspase-1 inhibitor VX-765 could reduce cell pyroptosis as confirmed in a rat disc IDD model in vivo, whereas ATG5 knockdown significantly accelerated the progression of IDD. In conclusion, our study indicated that autophagy protects against LPS-induced human NP cell pyroptosis via a P62/SQSTM1-mediated degradation mechanism and the inhibition of pyroptosis retards IDD progression in vivo. These findings deepen the understanding of IDD pathogenesis and hold implications in unraveling therapeutic targets for IDD treatment.

Long non-coding RNA RP11-81H3.2 suppresses apoptosis by targeting microRNA-1539/COL2A1 in human nucleus pulposus cells

Intervertebral disk degeneration (IDD) is a severe health problem that results in lower back pain and disability. Previous evidence has indicated that excessive apoptosis of nucleus pulposus (NP) cell is involved in the occurrence and development of IDD. However, the underlying mechanisms regulating NP cell apoptosis are unclear. The present study aimed to investigate the function of a novel long non-coding RNA RP11-81H3.2 in modulating NP cell apoptosis and the potential underlying mechanisms. The results demonstrated that the RP11-81H3.2 expression levels were significantly decreased in NP tissues from patients with IDD compared with those from healthy controls, and that lower expression levels were associated with higher-grade disk degeneration. Functionally, RP11-81H3.2 silencing promoted apoptosis and decreased the viability of NP cells derived from tissue samples of patients with IDD, whereas RP11-81H3.2 overexpression induced opposite effects. Bioinformatics analysis, luciferase assays and reverse transcription-quantitative PCR revealed that microRNA (miR)-1539 was a direct target of RP11-81H3.2. A mechanistic analysis demonstrated that RP11-81H3.2 functioned as an RNA sink to downregulate miR-1539, which led to the upregulation of collagen type 2 α 1 chain (COL2A1), a target of miR-1539. Collectively, the present results suggested that lower RP11-81H3.2 expression levels were associated with higher-grade IDD, and that RP11-81H3.2 inhibited NP cell apoptosis by decreasing the levels of miR-1539 to increase COL2A1 expression levels. The present study identified a beneficial role of RP11-81H3.2 against NP cell apoptosis.

Autophagy as a potential therapeutic target in intervertebral disc degeneration

Autophagy is an evolutionarily conserved intracellular recirculation system that delivers cytoplasmic content to lysosomes for degradation, thereby maintaining metabolism and homeostasis. Recent studies have found that autophagy plays a dual role in intervertebral disc degeneration (IDD). Most studies have shown that inducing autophagy can slow down the process of IDD. A few studies have shown that extensive autophagy activation-mediated apoptosis accelerates IDD. In this review, we describe the pathophysiological characteristics of intervertebral disc (IVD), the mechanism of autophagy and the application of regulating autophagy in the treatment of IDD, hoping to provide a certain theoretical basis for the biotherapy of IDD.

Krüppel like factor 10 prevents intervertebral disc degeneration via TGF-β signaling pathway both in vitro and in vivo

Background

Krüppel like factor 10 (KLF10), which is also known as TGF-β Inducible Early Gene-1 (TIEG1), plays a crucial role in regulating cell proliferation, cell apoptosis and inflammatory reaction in human carcinoma cells. Moreover, KLF10 knockout in mice leads to severe defects associated with muscle, skeleton and heart etc. However, the function of KLF10 in intervertebral disc degeneration (IVDD) has not been reported yet.

Methods

The relationship between KLF10 and IVDD were investigated in nucleus pulposus (NP) tissues from human and rats. The role of KLF10 in NP cells was explored via loss or gain of function experiments. IVDD rat models were constructed through needle puncture and the effects of KLF10 in IVDD model of rats were investigated via intradiscal injection of KLF10.

Results

We first found that KLF10 was lowly expressed in degenerative NP tissues and the level of KLF10 showed negative correlation with the disc grades of IVDD patients. Loss or gain of function experiments demonstrated that KLF10 could inhibit apoptosis and enhance migration and proliferation of IL-1β induced NP cells. And KLF10 overexpression reduced extracellular matrix (ECM) degeneration and enhanced ECM synthesis, whereas knockdown of KLF10 resulted in adverse effects. These positive effects of KLF10 could be reversed by the inhibition of TGF-β signaling pathway. In vivo, KLF10 overexpression alleviated IVDD.

Conclusions

This is the first study to reveal that KLF10 was dysregulated in IVDD and overexpressed KLF10 could alleviate IVDD by regulating TGF-β signaling pathway both in vitro and in vivo, which were involved in prohibiting apoptosis, promoting proliferation and migration of NP cells.The translational potential of this article: Overexpression of KLF10 might be an effective therapeutic strategy in the treatment of IVDD.