SIRT1 expression is refractory to hypoxia and inflammatory cytokines in nucleus pulposus cells: Novel regulation by HIF-1α and NF-κB signaling

Integrating metabolomics and network pharmacology to study the mechanism of Er-Xian decoction in improving intervertebral disc degeneration

ETHNOPHARMACOLOGICAL RELEVANCE

Intervertebral disc degeneration (IDD) is the progressive deterioration of the structure and function of an intervertebral disc (IVD), which manifests as excessive catabolism of the IVD extracellular matrix, which may lead to the gradual loss of IVD proteoglycans and water, thus altering the IVD composition and eventually leading to degeneration. As a traditional Chinese medicine, Er-Xian decoction (EXD) can balance the body's yin and yang, tonify the liver and kidney, invigorate blood circulation, and prevent blood stasis. Pharmacological research has shown that EXD regulates antioxidant and endocrine metabolism, maintains immune balance, and improves microcirculation.

AIMS OF THE STUDY

To clarify the efficacy of EXD on treating IDD.

MATERIALS AND METHODS

Serum was collected from model IDD rabbits treated with EXD for metabolomics analysis, and its mechanism of action was predicted on the basis of the metabolomics and network pharmacology data. Nucleus pulposus cells (NPCs) were induced with IL-1β to build an in vitro IDD model, and EXD was administered along with an inhibitor. All groups of cells were subjected to CCK-8 assays, ELISA and flow cytometry, immunohistochemistry, Western blot, and immunofluorescence staining analyses to explore how EXD protects NPCs and the underlying mechanism.

RESULTS

EXD reduced inflammatory processes, restored IVD height, and alleviated IDD in rabbits. Integrated metabolomics and network pharmacology analyses revealed that EXD exerts its therapeutic effects on IDD primarily via the mTOR and HIF-1 signalling pathways, and the active components of EXD, including anhydroicaritin, β-sitosterol, kaempferol, quercetin, and stigmasterol, bound strongly to pivotal targets within these pathways. Moreover, EXD reduced the inflammatory factor levels, inhibited NPC apoptosis, and upregulated the key proteins p-mTOR, HIF-1α, and p-AKT. Conversely, the HIF-1 inhibitor BAY872243 increased the inflammatory factor levels and led to NPC deterioration.

CONCLUSION

EXD regulates disc cell metabolism and inflammatory responses by modulating the mTOR and HIF-1 signalling pathways, thereby slowing or reversing IDD.

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.

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.

Mitochondrial dysfunction: a new molecular mechanism of intervertebral disc degeneration

OBJECTIVE

Intervertebral disc degeneration (IVDD) is a chronic degenerative orthopedic illness that causes lower back pain as a typical clinical symptom, severely reducing patients' quality of life and work efficiency, and imposing a significant economic burden on society. IVDD is defined by rapid extracellular matrix breakdown, nucleus pulposus cell loss, and an inflammatory response. It is intimately related to the malfunction or loss of myeloid cells among them. Many mechanisms have been implicated in the development of IVDD, including inflammatory factors, oxidative stress, apoptosis, cellular autophagy, and mitochondrial dysfunction. In recent years, mitochondrial dysfunction has become a hot research topic in age-related diseases. As the main source of adenosine triphosphate (ATP) in myeloid cells, mitochondria are essential for maintaining myeloid cell survival and physiological functions.

METHODS

We searched the PUBMED database with the search term "intervertebral disc degeneration and mitochondrial dysfunction" and obtained 82 articles, and after reading the abstracts and eliminating 30 irrelevant articles, we finally obtained 52 usable articles.

RESULTS

Through a review of the literature, it was discovered that IVDD and cellular mitochondrial dysfunction are also linked. Mitochondrial dysfunction contributes to the advancement of IVDD by influencing a number of pathophysiologic processes such as mitochondrial fission/fusion, mitochondrial autophagy, cellular senescence, and cell death.

CONCLUSION

We examine the molecular mechanisms of IVDD-associated mitochondrial dysfunction and present novel directions for quality management of mitochondrial dysfunction as a treatment approach to IVDD.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Mitophagy-A New Target of Bone Disease

Bone diseases are usually caused by abnormal metabolism and death of cells in bones, including osteoblasts, osteoclasts, osteocytes, chondrocytes, and bone marrow mesenchymal stem cells. Mitochondrial dysfunction, as an important cause of abnormal cell metabolism, is widely involved in the occurrence and progression of multiple bone diseases, including osteoarthritis, intervertebral disc degeneration, osteoporosis, and osteosarcoma. As selective mitochondrial autophagy for damaged or dysfunctional mitochondria, mitophagy is closely related to mitochondrial quality control and homeostasis. Accumulating evidence suggests that mitophagy plays an important regulatory role in bone disease, indicating that regulating the level of mitophagy may be a new strategy for bone-related diseases. Therefore, by reviewing the relevant literature in recent years, this paper reviews the potential mechanism of mitophagy in bone-related diseases, including osteoarthritis, intervertebral disc degeneration, osteoporosis, and osteosarcoma, to provide a theoretical basis for the related research of mitophagy in bone diseases.

Quercetin Suppresses Apoptosis and Attenuates Intervertebral Disc Degeneration via the SIRT1-Autophagy Pathway

Intervertebral disc degeneration (IDD) has been generally accepted as the major cause of low back pain (LBP), which causes an enormous socioeconomic burden. Previous studies demonstrated that the apoptosis of nucleus pulposus (NP) cells and the dyshomeostasis of extracellular matrix (ECM) contributed to the pathogenesis of IDD, and effective therapies were still lacking. Quercetin, a natural flavonoid possessing a specific effect of autophagy stimulation and SIRT1 activation, showed some protective effect on a series of degenerative diseases. Based on previous studies, we hypothesized that quercetin might have therapeutic effects on IDD by inhibiting the apoptosis of NP cells and dyshomeostasis of ECM via the SIRT1-autophagy pathway. In this study, we revealed that quercetin treatment inhibited the apoptosis of NP cells and ECM degeneration induced by oxidative stress. We also found that quercetin promoted the expression of SIRT1 and autophagy in NP cells in a dose-dependent manner. Autophagy inhibitor 3-methyladenine (3-MA) reversed the protective effect of quercetin on apoptosis and ECM degeneration. Moreover, SIRT1 enzymatic activity inhibitor EX-527, suppressed quercetin-induced autophagy and the protective effect on NP cells, indicating that quercetin protected NP cells against apoptosis and prevented ECM degeneration via SIRT1-autophagy pathway. In vivo, quercetin was also demonstrated to alleviate the progression of IDD in rats. Taken together, our results suggest that quercetin prevents IDD by promoting SIRT1-dependent autophagy, indicating one novel and effective therapeutic method for IDD.

PGC-1α acts as an mediator of Sirtuin2 to protect annulus fibrosus from apoptosis induced by oxidative stress through restraining mitophagy

Apoptosis of annulus fibrosus (AF) is observed widely in intervertebral disc degeneration (IVDD) which causes weaken of tension in the annulus of intervertebral disc. Previous studies reported that apoptosis of AF is induced mainly by oxidative stress. SIRT2 is a major regulator of mitochondria to mediate ROS production. However, the mechanism of SIRT2 in IVDD remains unclear. Here, the expression of SIRT2 was detected in AF cells exposed to tert-Butyl hydroperoxide (TBHP) by western blotting. Autophagic flux and apoptosis were assessed by western blotting, flow cytometry and immunofluorescence respectively. Safranin O staining, HE, and immunohistochemical were used to assess the IVDD after 3, 6 and 9 months of surgical procedure in vivo. The expression of SIRT2 was decreased in AF cells treated with TBHP. Repression of mitophagy alleviated the apoptosis of AF cells caused by TBHP. Overexpression of PGC-1α prevented AF cells from apoptosis and mitophagy after applying Lenti-PGC-1α to transfect AF cells. These protections of PGC-1α were reduced by FCCP. Furthermore, the expression of PGC-1α was reduced and the level of mitophagy was increased in IVDD models. In conclusion, this study indicates that the regulation of PGC-1α expression provide a new theoretical basis for the mechanism of IVDD.

TSG-6 secreted by bone marrow mesenchymal stem cells attenuates intervertebral disc degeneration by inhibiting the TLR2/NF-κB signaling pathway

Inflammation has been correlated with intervertebral disc degeneration (IDD). Recent evidence suggests that TNF-α-stimulated gene 6 protein (TSG-6) secreted by bone marrow mesenchymal stem cells (BMSCs) displays a remarkable ability to inhibit inflammatory processes in a variety of diseases. However, it is unknown whether BMSCs exert their therapeutic effect against IDD by secreting TSG-6. Here we investigated the effects of BMSCs and TSG-6 on IDD and explored the possible underlying mechanisms in vitro and in vivo. We found that BMSCs and TSG-6 reduced the expression of MMP-3 and MMP-13, and increased the expression of collagen II and aggrecan in the IL-1β-treated nucleus pulposus cells (NPCs), but the protective effects of BMSCs and TSG-6 were attenuated when TSG-6 expression was silenced. We also found that the activation of the TLR2/NF-κB pathway was inhibited by BMSCs and TSG-6. The levels of IL-6 and TNF-α in the degenerated NPCs were reduced and the proliferation of IL-1β-treated NPCs was increased in the presence of BMSCs and TSG-6. Furthermore, in vivo experiments showed that BMSCs and TSG-6 restored the MRI T2-weighted signal intensity and increased collagen II and aggrecan expression in the degenerated nucleus pulposus (NP) tissues. Finally, our results showed that BMSCs and TSG-6 downregulated the TLR2/NF-κB signaling and reduced the expression of MMPs and inflammatory cytokines in the degenerated NP tissues. The present study is the first to demonstrate the involvement of TLR2/NF-κB pathway in the potential anti-IDD therapeutic effect of TSG-6, and the results provide new insight into the beneficial effect of BMSCs in the treatment of IDD.

Resveratrol controlled the fate of porcine pancreatic stem cells through the Wnt/β-catenin signaling pathway mediated by Sirt1

Porcine pancreatic stem cells (PSCs) are considered promising transplant materials that may be used to treat diabetes, but some problems, such as insufficient cell number and low differentiation efficiency, should be solved before its clinical application. Resveratrol is a natural polyphenolic compound that can alleviate the complications of diabetes. In this study, we aimed to explore the specific effect of resveratrol on porcine PSCs. We treated porcine PSCs with 10 μM, 25 μM resveratrol to explore the effect of resveratrol on porcine PSCs. We found that 10 μM resveratrol improved the proliferation of porcine PSCs, increased the expression of A-β-catenin (active β-catenin), Pcna, C-Myc, Bcl-2 and sirtuin-1 (Sirt1), and decreased the expression of P53, Caspase3. While 25 μM resveratrol had almost opposite effect compared with 10 μM resveratrol group. The utilization of Dickkopf-related protein 1 (DKK1, Wnt signaling pathway inhibitor) and nicotinamide (Sirt1 inhibitor) suggested that resveratrol regulated cell proliferation by controlling Wnt signaling pathway and this effect was mediated by Sirt1. Our results further revealed that 10 μM resveratrol promoted the formation of β-like cells regulated by Wnt/β-catenin signal pathway. Relatively low-dose resveratrol could improve porcine PSCs fate. It lays theoretical foundation for diabetes treatment with cell transplantation in future.

Metformin preconditioning provide neuroprotection through enhancement of autophagy and suppression of inflammation and apoptosis after spinal cord injury

Spinal cord injury (SCI) is one of the most serious nervous system disorders characterised by high morbidity and disability. Inflammatory and autophagy responses play an important role in the development of SCI. Metformin, a first-line drug for type-2 diabetes, features autophagy promotion as well as anti-inflammatory and anti-apoptotic properties in the nervous system. In this study, we investigated the neuroprotection effects of metformin preconditioning on rats after SCI. Results of Basso, Beattie and Bresnahan scores, HE staining and Nissl staining showed that the function and quantity of motor neurons were protected by metformin after SCI. Western blot revealed that the expression of Beclin-1 and LC3B-II was enhanced, and the phosphorylation levels of the mammalian target of rapamycin (mTOR) protein and p70S6K were reduced by metformin after SCI. Metformin significantly reduced the expression of NF-κB. Moreover, Western blot and immunofluorescence results indicated that caspase 3 activation was reduced, whereas bcl-2 level was significantly increased by metformin. Hence, metformin attenuated SCI by inhibiting apoptosis and inflammation and enhancing the autophagy via the mTOR/p70S6K signalling pathway.

Regulation of a disintegrins and metalloproteinase with thrombospondin motifs 7 during inflammation in nucleus pulposus (NP) cells: role of AP-1, Sp1 and NF-κB signaling

AIM

The objective of this study is to explore the effect of inflammatory cytokines on a disintegrins and metalloproteinase with thrombospondin motifs 7 (ADAMTS7) and to demonstrate the role of Sp1, AP-1 and NF-κB signaling on the ADAMTS7 regulation during inflammation in NP cells.

METHODS

Real-time PCR was to detect the effect of ADAMTS7 knockdown on the expression of catabolic enzymes during inflammatory condition in NP cells. Real-time PCR, western blot, immunofluorescence and transfection experiments were used to observe the effect of tumor necrosis factor-α (TNF-α) or interleukin-1β on the expression and the activity of ADAMTS7, and demonstrated the role to Sp1, AP-1 and NF-κB in the regulation of ADAMTS7 during inflammation.

RESULTS

As other cells, ADAMTS7 knockdown suppressed the mRNA expression of catabolic factors during inflammation in human NP cells. However, the expression of ADAMTS7 mRNA and protein and the activity of ADAMTS7 promoter were refractory to inflammatory cytokines. In addition, Sp1, AP-1, not NF-κB signaling sustained the expression of ADAMTS7 mRNA, protein, as well as promoter activity during inflammation in NP cells.

CONCLUSION

ADAMTS7 played a crucial role in the expression of catabolic genes in the presence of TNF-α and AP-1, Sp1, not NF-κB signaling were critical for the maintenance of ADAMTS7 expression during inflammation in NP cells.