Pioglitazone Protects Compression-Mediated Apoptosis in Nucleus Pulposus Mesenchymal Stem Cells by Suppressing Oxidative Stress

Low-intensity pulsed ultrasound reduces alveolar bone resorption during orthodontic treatment via Lamin A/C-Yes-associated protein axis in stem cells

BACKGROUND

The bone remodeling during orthodontic treatment for malocclusion often requires a long duration of around two to three years, which also may lead to some complications such as alveolar bone resorption or tooth root resorption. Low-intensity pulsed ultrasound (LIPUS), a noninvasive physical therapy, has been shown to promote bone fracture healing. It is also reported that LIPUS could reduce the duration of orthodontic treatment; however, how LIPUS regulates the bone metabolism during the orthodontic treatment process is still unclear.

AIM

To investigate the effects of LIPUS on bone remodeling in an orthodontic tooth movement (OTM) model and explore the underlying mechanisms.

METHODS

A rat model of OTM was established, and alveolar bone remodeling and tooth movement rate were evaluated via micro-computed tomography and staining of tissue sections. In vitro, human bone marrow mesenchymal stem cells (hBMSCs) were isolated to detect their osteogenic differentiation potential under compression and LIPUS stimulation by quantitative reverse transcription-polymerase chain reaction, Western blot, alkaline phosphatase (ALP) staining, and Alizarin red staining. The expression of Yes-associated protein (YAP1), the actin cytoskeleton, and the Lamin A/C nucleoskeleton were detected with or without YAP1 small interfering RNA (siRNA) application via immunofluorescence.

RESULTS

The force treatment inhibited the osteogenic differentiation potential of hBMSCs; moreover, the expression of osteogenesis markers, such as type 1 collagen (COL1), runt-related transcription factor 2, ALP, and osteocalcin (OCN), decreased. LIPUS could rescue the osteogenic differentiation of hBMSCs with increased expression of osteogenic marker inhibited by force. Mechanically, the expression of LaminA/C, F-actin, and YAP1 was downregulated after force treatment, which could be rescued by LIPUS. Moreover, the osteogenic differentiation of hBMSCs increased by LIPUS could be attenuated by YAP siRNA treatment. Consistently, LIPUS increased alveolar bone density and decreased vertical bone absorption in vivo. The decreased expression of COL1, OCN, and YAP1 on the compression side of the alveolar bone was partially rescued by LIPUS.

CONCLUSION

LIPUS can accelerate tooth movement and reduce alveolar bone resorption by modulating the cytoskeleton-Lamin A/C-YAP axis, which may be a promising strategy to reduce the orthodontic treatment process.

Exploration of the role of oxidative stress-related genes in LPS-induced acute lung injury via bioinformatics and experimental studies

During the progression of acute lung injury (ALI), oxidative stress and inflammatory responses always promote each other. The datasets analyzed in this research were acquired from the Gene Expression Omnibus (GEO) database. The Weighted Gene Co-expression Network Analysis (WGCNA) and limma package were used to obtain the ALI-related genes (ALIRGs) and differentially expressed genes (DEGs), respectively. In total, two biological markers (Gch1 and Tnfaip3) related to oxidative stress were identified by machine learning algorithms, Receiver Operator Characteristic (ROC), and differential expression analyses. The area under the curve (AUC) value of biological markers was greater than 0.9, indicating an excellent power to distinguish between ALI and control groups. Moreover, 15 differential immune cells were selected between the ALI and control samples, and they were correlated to biological markers. The transcription factor (TF)-microRNA (miRNA)-Target network was constructed to explore the potential regulatory mechanisms. Finally, based on the quantitative reverse transcription polymerase chain reaction (qRT-PCR), the expression of Gch1 and Tnfaip3 was significantly higher in ALI lung tissue than in healthy controls. In conclusion, the differences in expression profiles between ALI and normal controls were found, and two biological markers were identified, providing a research basis for further understanding the pathogenesis of ALI.

Enhancing the therapeutic efficacy of mesenchymal stem cell transplantation in diabetes: Amelioration of mitochondrial dysfunction-induced senescence

Mesenchymal stem cell (MSC) transplantation offers significant potential for the treatment of diabetes mellitus (DM) and its complications. However, hyperglycemic conditions can induce senescence and dysfunction in both transplanted and resident MSCs, thereby limiting their therapeutic potential. Mitochondrial dysfunction and oxidative stress are key contributors to this process in MSCs exposed to hyperglycemia. As such, strategies aimed at mitigating mitochondrial dysfunction could enhance the therapeutic efficacy of MSC transplantation in DM. In this review, we provide an updated overview of how mitochondrial dysfunction mediates MSC senescence. We present experimental evidence for the molecular mechanisms behind high glucose-induced mitochondrial dysfunction in MSCs, which include impairment of mitochondrial biogenesis, mitochondrial calcium regulation, the mitochondrial antioxidant system, mitochondrial fusion-fission dynamics, mitophagy, and intercellular mitochondrial transfer. Furthermore, we propose potential pharmacological candidates that could improve the efficacy of MSC transplantation by enhancing mitochondrial function in patients with DM and related complications.

Strontium Ranelate Ameliorates Intervertebral Disc Degeneration via Regulating TGF-β1/NF-κB Axis

Intervertebral disc degeneration (IVDD) is a prevalent and debilitating condition characterized by chronic back pain and reduced quality of life. Strontium ranelate (SRR) is a compound traditionally used for treating osteoporosis via activating TGF-β1 signaling pathway. Recent studies have proved the anti-inflammatory effect of SRR on chondrocytes. Although the exact mechanism of IVDD remains unclear, accumulating evidences have emphasized the involvement of multifactorial pathogenesis including inflammation, oxidative stress damage, and etc. However, the biological effect of SRR on IVDD and its molecular mechanism has not been investigated. Firstly, this study proved the decreased expression of Transforming Growth Factor-beta 1(TGF-β1) in degenerated human intervertebral disc tissues. Subsequently, we confirmed for the first time that SRR could promote cell proliferation, mitigate inflammation and oxidative stress in human nucleus pulposus cells in vitro via increasing the expression of TGF-β1 and suppressing the Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells (NF-κB) pathway. The molecular docking result proved the interaction between SRR and TGF-β1 protein. To further verify this interaction, gain- and loss- of function experiments were conducted. We discovered that both TGF-β1 knockdown and overexpression influenced the activation of the NF-κB pathway. Taken together, SRR could mitigate IL-1β induced-cell dysfunction in human nucleus pulposus cells by regulating TGF-β1/NF-κB axis in vitro. Finally, the in vivo therapeutic effect of SRR on IVDD was confirmed. Our findings may contribute to the understanding of the complex interplay between inflammation and degenerative processes in the intervertebral disc and provide valuable insights into the development of targeted treatment-based therapeutics for IVDD.

Melatonin Promotes BMSCs Osteoblastic Differentiation and Relieves Inflammation by Suppressing the NF-κB Pathways

Bone mesenchymal stem cells (BMSCs) play an important role in maintaining the dynamic balance of bone metabolism. Recent studies have reported that a decrease in the osteogenic function of MSCs is strongly associated with osteoporosis. Melatonin is a neuroendocrine hormone produced in the pineal gland and is essential in the physiological regulation. This study is aimed at exploring the effect of melatonin on MSCs osteoblastic differentiation and elucidate the underlying mechanisms. We isolated BMSCs from rat bone marrow and demonstrated that melatonin improved osteogenic differentiation of BMSCs by the alizarin red staining and ALP staining. We then showed that melatonin enhanced osteogenic gene expression in BMSCs, including ALP, Col 1, OCN, OPN, and RUNX2. We further revealed that melatonin inhibited the inflammatory response of BMSCs by suppressing the NF-κB signaling pathways. In light of this, we found that the NF-κB pathway-specific activator TNF-α activated the NF-κB pathway, inhibited osteogenic differentiation, and induced inflammatory response in BMSCs. Melatonin was found to reverse the inhibitory effect of TNF-α on osteogenic differentiation and inflammation in BMSCs. Taken together, these findings indicated that melatonin may have therapeutic potential to be used for the treatment of osteoporosis.

Hesperidin mitigates oxidative stress-induced ferroptosis in nucleus pulposus cells via Nrf2/NF-κB axis to protect intervertebral disc from degeneration

Intervertebral disc degeneration (IVDD), a widely known contributor to low back pain (LBP), has been proved to be a global health challenging conundrum. Hesperidin (hesperetin-7-O-rutinoside, HRD) is a flavanone glycoside that belongs to the subgroup of citrus flavonoids with therapeutic effect on various diseases due to its anti-inflammatory, antioxidant properties. However, the effect of HRD on IVDD remains elusive. The human nucleus pulposus tissues were harvested for isolating human nucleus pulposus (HNP) cells to verify the expression of Nrf2. The biological effect of HRD on HNP cells were assessed in vitro, and the in vivo therapeutic effects of HRD were assessed in mice. Firstly, we found that the expression of Nrf2 was decreased with the progression of degeneration in degenerated human nucleus pulposus tissue. Subsequently, we confirmed that HRD could mitigate oxidative stress-induced ferroptosis in nucleus pulposus cells via enhancing the expression of Nrf2 axis and suppressing the NF-κB pathway to protect intervertebral disc from degeneration in vitro. Finally, the therapeutic effects of HRD were confirmed in vivo. The current study proved for the first time that HRD may protect HNP cells from degeneration by suppressing ferroptosis in an oxidative stress-dependent via enhancing the expression of Nrf2 and suppressing the NF-κB pathway. The evidence will provide a possible basis for future targeted treatment for IVDD.

Acellular Biomaterials Associated with Autologous Bone Marrow-Derived Mononuclear Stem Cells Improve Wound Healing through Paracrine Effects

Wound healing is a complex process of repair that involves the interaction between different cell types and involves coordinated interactions between intracellular and extracellular signaling. Bone Marrow Mesenchymal Stem Cells (BMSCs) based and acellular amniotic membrane (AM) therapeutic strategies with the potential for treatment and regeneration of tissue. We aimed to evaluate the involvement of paracrine effects in tissue repair after the flap skin lesion rat model. In the full-thickness flap skin experiment of forty Wistar rats: A total of 40 male Wistar rats were randomized into four groups: group I: control (C; n = 10), with full-thickness lesions on the back, without (BMSCs) or AM (n = 10); group II: injected (BMSCs; n = 10); group III: covered by AM; group IV-injected (AM + BMSCs; n = 10). Cytokine levels, IL-1, and IL-10 assay kits, superoxide dismutase (SOD), glutathione reductase (GRs) and carbonyl activity levels were measured by ELISA 28th day, and TGF-β was evaluated by immunohistochemical, the expression collagen expression was evaluated by Picrosirius staining. Our results showed that the IL-1 interleukin was higher in the control group, and the IL-10 presented a higher mean when compared to the control group. The groups with BMSCs and AM showed the lowest expression levels of TGF-β. SOD, GRs, and carbonyl activity analysis showed a predominance in groups that received treatment from 80%. The collagen fiber type I was predominant in all groups; however, the AM + BMSCs group obtained a higher average when compared to the control group. Our findings suggest that the AM+ BMSCs promote skin wound healing, probably owing to their paracrine effect attributed to the promotion of new collagen for tissue repair.

Change in left ventricular diastolic function after pioglitazone treatment in patients with type 2 diabetes mellitus: A protocol for systematic review and meta-analysis

BACKGROUND

Pioglitazone is currently used as an anti-diabetic agent and can reduce cardiovascular events in in patients with type 2 diabetes mellitus (T2DM). Left ventricular diastolic dysfunction has been recognized as an early manifestation of myocardial dysfunction in T2DM patients. This systematic review and meta-analysis aimed to investigate changes in the left ventricular diastolic function after the treatment of pioglitazone.

METHODS

A systematic literature search of PubMed, Embase, and the Cochrane Library until May 2021 with keywords pioglitazone and left ventricular diastolic function was performed in accordance with the meta-analysis of observational studies in epidemiology guidelines and preferred reporting items for systematic reviews and meta-analyses statement. Three reviewers independently selected the studies and extracted data. Quality assessment of the included studies was undergone. A fixed effects model was used to calculate overall effect sizes. Subgroup analyses were subsequently performed. A fixed effects model was used to calculate the overall effect size. Subgroup analyses were then performed.

RESULTS

Seven studies with 233 patients were investigated. We found pioglitazone significantly improved hemoglobin A1c (%) in patients with T2DM and left ventricular diastolic function had an improvement tendency (weighted mean difference [WMD], 0.03; 95% confidence interval [CI], 0.01-0.05, P < .01) despite moderate heterogeneity (I2 = 66%). Subsequent subgroup analysis indicated that left ventricular diastolic function were significantly improved (WMD, 0.20; 95% CI, 0.12-0.29, P < .001) in T2DM patients whose average age < 55 after receiving pioglitazone treatment. However, in T2DM patients with mean age ≥ 55 years, there was no significant improvement of left ventricular diastolic function (WMD, 0.02; 95% CI, 0-0.04, P = .04).

CONCLUSION

Pioglitazone treatment significantly improved left ventricular diastolic function in type 2 diabetic patients with a mean age of < 55 years, but did not improve left ventricular diastolic function in patients with a mean age of ≥ 55 years.

Cystathionine γ-lyase mediates cell proliferation, migration, and invasion of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an epithelia-derived malignancy with a distinctive geographic distribution. Cystathionine γ-lyase (CSE) is involved in cancer development and progression. Nevertheless, the role of CSE in the growth of NPC is unknown. In this study, we found that CSE levels in human NPC cells were higher than those in normal nasopharyngeal cells. CSE overexpression enhanced the proliferative, migrative, and invasive abilities of NPC cells and CSE downregulation exerted reverse effects. Overexpression of CSE decreased the expressions of cytochrome C, cleaved caspase (cas)-3, cleaved cas-9, and cleaved poly-ADP-ribose polymerase, whereas CSE knockdown exhibited reverse effects. CSE overexpression decreased reactive oxygen species (ROS) levels and the expressions of phospho (p)-extracellular signal-regulated protein kinase 1/2, p-c-Jun N-terminal kinase, and p-p38, but promoted the expressions of p-phosphatidylinositol 3-kinase (PI3K), p-AKT, and p-mammalian target of rapamycin (mTOR), whereas CSE knockdown showed oppose effects. In addition, CSE overexpression promoted NPC xenograft tumor growth and CSE knockdown decreased tumor growth by modulating proliferation, angiogenesis, cell cycle, and apoptosis. Furthermore, DL-propargylglycine (an inhibitor of CSE) dose-dependently inhibited NPC cell growth via ROS-mediated mitogen-activated protein kinase (MAPK) and PI3K/AKT/mTOR pathways without significant toxicity. In conclusion, CSE could regulate the growth of NPC cells through ROS-mediated MAPK and PI3K/AKT/mTOR cascades. CSE might be a novel tumor marker for the diagnosis and prognosis of NPC. Novel donors/drugs that inhibit the expression/activity of CSE can be developed in the treatment of NPC.

Correlations between circulating methylmalonic acid levels and all-cause and cause-specific mortality among patients with diabetes

Aims

Evidence regarding serum methylmalonic acid (MMA) levels and mortality in individuals with diabetes is limited. This study aimed to evaluate the correlation between MMA and all-cause and cause-specific deaths in patients with diabetes.

Materials and methods

This is a population-based cohort study based on data from both the National Health and Nutrition Examination Survey (NHANES) and National Death Index from 1999 to 2014. We assessed the association of serum MMA concentrations with mortality using Cox proportional hazard models after adjusting for lifestyle, demographic factors, and comorbidities.

Results

Among the 3,097 participants, 843 mortalities occurred during a median follow-up of 4.42 years. There were 242 deaths due to cardiovascular disease (CVD) and 131 cancer-associated deaths. After multivariate adjustment, elevated serum MMA levels were markedly correlated with a high risk of all-cause, CVD-, and cancer-related deaths. Each one-unit increase in the natural log-transformed MMA level correlated with increased risk of all-cause mortality (2.652 times), CVD mortality risk (3.153 times), and cancer-related mortality risk (4.514). Hazard ratios (95% confidence intervals [CIs]) after comparing participants with MMA &lt; 120 and ≥250 nmol/L were 2.177 (1.421–3.336) for all-cause mortality, 3.560 (1.809–7.004) for CVD mortality, and 4.244 (1.537–11.721) for cancer mortality.

Conclusion

Higher serum MMA levels were significantly associated with higher all-cause, CVD, and cancer mortality. These findings suggest that maintaining lower MMA status may lower mortality risk in individuals with diabetes.

Matrix from urine stem cells boosts tissue-specific stem cell mediated functional cartilage reconstruction

Articular cartilage has a limited capacity to self-heal once damaged. Tissue-specific stem cells are a solution for cartilage regeneration; however, ex vivo expansion resulting in cell senescence remains a challenge as a large quantity of high-quality tissue-specific stem cells are needed for cartilage regeneration. Our previous report demonstrated that decellularized extracellular matrix (dECM) deposited by human synovium-derived stem cells (SDSCs), adipose-derived stem cells (ADSCs), urine-derived stem cells (UDSCs), or dermal fibroblasts (DFs) provided an ex vivo solution to rejuvenate human SDSCs in proliferation and chondrogenic potential, particularly for dECM deposited by UDSCs. To make the cell-derived dECM (C-dECM) approach applicable clinically, in this study, we evaluated ex vivo rejuvenation of rabbit infrapatellar fat pad-derived stem cells (IPFSCs), an easily accessible alternative for SDSCs, by the abovementioned C-dECMs, in vivo application for functional cartilage repair in a rabbit osteochondral defect model, and potential cellular and molecular mechanisms underlying this rejuvenation. We found that C-dECM rejuvenation promoted rabbit IPFSCs' cartilage engineering and functional regeneration in both ex vivo and in vivo models, particularly for the dECM deposited by UDSCs, which was further confirmed by proteomics data. RNA-Seq analysis indicated that both mesenchymal-epithelial transition (MET) and inflammation-mediated macrophage activation and polarization are potentially involved in the C-dECM-mediated promotion of IPFSCs' chondrogenic capacity, which needs further investigation.

Oxidative Stress and Intervertebral Disc Degeneration: Pathophysiology, Signaling Pathway, and Therapy

Intervertebral disc degeneration (IDD), characterized as decreased proteoglycan content, ossification of endplate, and decreased intervertebral height, is one of the major reasons of low back pain, which seriously affects the quality of life and also brings heavy economic burden. However, the mechanisms leading to IDD and its therapeutic targets have not been fully elucidated. Oxidative stress refers to the imbalance between oxidation and antioxidant systems, between too many products of reactive oxygen species (ROS) and the insufficient scavenging function. Excessive ROS can damage cell lipids, nucleic acids and proteins, which has been proved to be related to the development of a variety of diseases. In recent years, an increasing number of studies have reported that oxidative stress is involved in the pathological process of IDD. Excessive ROS can accelerate the IDD process via inducing the pathological activities, such as inflammation, apoptosis, and senescence. In this review, we focused on pathophysiology and molecular mechanisms of oxidative stress-induced IDD. Moreover, the present review also summarized the possible ideas for the future therapy strategies of oxidative stress-related IDD.

Advances in the therapeutic application and pharmacological properties of kinsenoside against inflammation and oxidative stress-induced disorders

Extensive research has implicated inflammation and oxidative stress in the development of multiple diseases, such as diabetes, hepatitis, and arthritis. Kinsenoside (KD), a bioactive glycoside component extracted from the medicinal plant Anoectochilus roxburghii, has been shown to exhibit potent anti-inflammatory and anti-oxidative abilities. In this review, we summarize multiple effects of KD, including hepatoprotection, pro-osteogenesis, anti-hyperglycemia, vascular protection, immune regulation, vision protection, and infection inhibition, which are partly responsible for suppressing inflammation signaling and oxidative stress. The protective action of KD against dysfunctional lipid metabolism is also associated with limiting inflammatory signals, due to the crosstalk between inflammation and lipid metabolism. Ferroptosis, a process involved in both inflammation and oxidative damage, is potentially regulated by KD. In addition, we discuss the physicochemical properties and pharmacokinetic profiles of KD. Advances in cultivation and artificial synthesis techniques are promising evidence that the shortage in raw materials required for KD production can be overcome. In addition, novel drug delivery systems can improve the in vivo rapid clearance and poor bioavailability of KD. In this integrated review, we aim to offer novel insights into the molecular mechanisms underlying the therapeutic role of KD and lay solid foundations for the utilization of KD in clinical practice.

Mesenchymal Stromal Cells Overexpressing Farnesoid X Receptor Exert Cardioprotective Effects Against Acute Ischemic Heart Injury by Binding Endogenous Bile Acids

Bile acid metabolites have been increasingly recognized as pleiotropic signaling molecules that regulate cardiovascular functions, but their role in mesenchymal stromal cells (MSC)-based therapy has never been investigated. It is found that overexpression of farnesoid X receptor (FXR), a main receptor for bile acids, improves the retention and cardioprotection of adipose tissue-derived MSC (ADSC) administered by intramyocardial injection in mice with myocardial infarction (MI), which shows enhanced antiapoptotic, proangiogenic, and antifibrotic effects. RNA sequencing, LC-MS/MS, and loss-of-function studies reveal that FXR overexpression promotes ADSC paracrine angiogenesis via Angptl4. FXR overexpression improves ADSC survival in vivo but fails in vitro. By performing bile acid-targeted metabolomics using ischemic heart tissue, 19 bile acids are identified. Among them, cholic acid and deoxycholic acid significantly increase Angptl4 secretion from ADSC overexpressing FXR and further improve their proangiogenic capability. Moreover, ADSC overexpressing FXR shows significantly lower apoptosis by upregulating Nqo-1 expression only in the presence of FXR ligands. Retinoid X receptor α is identified as a coactivator of FXR. It is first demonstrated that there is a bile acid pool in the myocardial microenvironment. Targeting the bile acid-FXR axis may be a novel strategy for improving the curative effect of MSC-based therapy for MI.

Andrographolide protects bone marrow mesenchymal stem cells against glucose and serum deprivation under hypoxia via the NRF2 signaling pathway

Background

Bone marrow mesenchymal stem cell (BMSCs) therapy is an important cell transplantation strategy in the regenerative medicine field. However, a severely ischemic microenvironment, such as nutrient depletion and hypoxia, causes a lower survival rate of transplanted BMSCs, limiting the application of BMSCs. Therefore, improving BMSCs viability in adverse microenvironments is an important means to improve the effectiveness of BMSCs therapy.

Objective

To illustrate the protective effect of andrographolide (AG) against glucose and serum deprivation under hypoxia (1% O₂) (GSDH)-induced cell injury in BMSCs and investigate the possible underlying mechanisms.

Methods

An in vitro primary rat BMSCs cell injury model was established by GSDH, and cellular viability, proliferation and apoptosis were observed after AG treatment under GSDH. Reactive oxygen species levels and oxidative stress-related genes and proteins were measured by flow cytometry, RT-qPCR and Western blotting. Mitochondrial morphology, function and number were further assessed by laser confocal microscopy and flow cytometry.

Results

AG protected BMSCs against GSDH-induced cell injury, as indicated by increases in cell viability and proliferation and mitochondrial number and decreases in apoptosis and oxidative stress. The metabolic status of BMSCs was changed from glycolysis to oxidative phosphorylation to increase the ATP supply. We further observed that the NRF2 pathway was activated by AG, and treatment of BMSCs with a specific NRF2 inhibitor (ML385) blocked the protective effect of AG.

Conclusion

Our results suggest that AG is a promising agent to improve the therapeutic effect of BMSCs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-03016-6.

Causes of and Molecular Targets for the Treatment of Intervertebral Disc Degeneration: A Review

Intervertebral disc degeneration (IVDD) is a pathological condition that can lead to intractable back pain or secondary neurological deficits. There is no fundamental cure for this condition, and current treatments focus on alleviating symptoms indirectly. Numerous studies have been performed to date, and the major strategy for all treatments of IVDD is to prevent cell loss due to programmed or regulated cell death. Accumulating evidence suggests that several types of cell death other than apoptosis, including necroptosis, pyroptosis, and ferroptosis, are also involved in IVDD. In this study, we discuss the molecular pathway of each type of cell death and review the literature that has identified their role in IVDD. We also summarize the recent advances in targeted therapy at the RNA level, including RNA modulations through RNA interference and regulation of non-coding RNAs, for preventing cell death and subsequent IVDD. Therefore, we review the causes and possible therapeutic targets for RNA intervention and discuss the future direction of this research field.

Effect of lentivirus-mediated growth and differentiation factor-5 transfection on differentiation of rabbit nucleus pulposus mesenchymal stem cells

Background

Intervertebral disc degeneration (IDD) is a natural progression of age-related processes. Associated with IDD, degenerative disc disease (DDD) is a pathologic condition implicated as a major cause of chronic lower back pain, which can have a severe impact on the quality of life of patients. As degeneration progression is associated with elevated levels of inflammatory cytokines, enhanced aggrecan and collagen degradation, and changes in the disc cell phenotype. The purpose of this study was to investigate the biological and cytological characteristics of rabbit nucleus pulposus mesenchymal stem cells (NPMSCs)—a key factor in IDD—and to determine the effect of the growth and differentiation factor-5 (GDF5) on the differentiation of rabbit NPMSCs transduced with a lentivirus vector.

Methods

An in vitro culture model of rabbit NPMSCs was established and NPMSCs were identified by flow cytometry (FCM) and quantitative real-time PCR (qRT-PCR). Subsequently, NPMSCs were randomly divided into three groups: a transfection group (the lentiviral vector carrying GDF5 gene used to transfect NPMSCs); a control virus group (the NPMSCs transfected with an ordinary lentiviral vector); and a normal group (the NPMSCs alone). FCM, qRT-PCR, and western blot (WB) were used to detect the changes in NPMSCs.

Results

The GDF5-transfected NPMSCs displayed an elongated shape, with decreased cell density, and significantly increased GDF5 positivity rate in the transfected group compared to the other two groups (P < 0.01). The mRNA levels of Krt8, Krt18, and Krt19 in the transfected group were significantly higher in comparison with the other two groups (P < 0.01), and the WB results were consistent with that of qRT-PCR.

Conclusions

GDF5 could induce the differentiation of NPMSCs. The lentiviral vector carrying the GDF5 gene could be integrated into the chromosome genome of NPMSCs and promoted differentiation of NPMSCs into nucleus pulposus cells. Our findings advance the development of feasible and effective therapies for IDD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40001-021-00624-5.

Arginase II Promotes Intervertebral Disc Degeneration Through Exacerbating Senescence and Apoptosis Caused by Oxidative Stress and Inflammation via the NF-κB Pathway

Intervertebral disc degeneration (IDD) has been generally accepted as the major cause of low back pain (LBP), which imposes massive clinical and socioeconomic burdens. Previous studies have demonstrated that oxidative stress and inflammation-induced senescence and apoptosis of nucleus pulposus cells (NPCs) are the main cellular processes that cause IDD. Arginase II (ARG2), an enzyme involved in a variety of pathological processes, including cellular senescence, apoptosis, oxidative stress, and inflammation, has been shown to promote degeneration in several degenerative diseases, including osteoarticular diseases. Based on previous studies, we hypothesized that ARG2 deficiency might be conducive to the treatment of IDD by inhibiting the dyshomeostasis of the extracellular matrix (ECM), and the oxidative stress and inflammatory response-induced senescence and apoptosis via NF-κB. In this study, we found that ARG2 deficiency inhibited senescence and apoptosis of NPCs, and degeneration of the ECM induced by oxidative stress and the inflammatory response. Similar results were found with the selective NF-κB pathway inhibitor JSH-23. In contrast, overexpression of ARG2 had the opposite effect. Taken together, our results suggest that ARG2 deficiency prevents IDD via NF-κB, and may therefore, be a potential therapeutic strategy for IDD.

Targeting Programmed Cell Death to Improve Stem Cell Therapy: Implications for Treating Diabetes and Diabetes-Related Diseases

Stem cell therapies have shown promising therapeutic effects in restoring damaged tissue and promoting functional repair in a wide range of human diseases. Generations of insulin-producing cells and pancreatic progenitors from stem cells are potential therapeutic methods for treating diabetes and diabetes-related diseases. However, accumulated evidence has demonstrated that multiple types of programmed cell death (PCD) existed in stem cells post-transplantation and compromise their therapeutic efficiency, including apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis. Understanding the molecular mechanisms in PCD during stem cell transplantation and targeting cell death signaling pathways are vital to successful stem cell therapies. In this review, we highlight the research advances in PCD mechanisms that guide the development of multiple strategies to prevent the loss of stem cells and discuss promising implications for improving stem cell therapy in diabetes and diabetes-related diseases.

Bergenin alleviates H2 O2 -induced oxidative stress and apoptosis in nucleus pulposus cells: Involvement of the PPAR-γ/NF-κB pathway

Bergenin is a C-glucoside of 4-O-methyl gallic acid with a variety of biological activities, such as antioxidant and anti-inflammatory. Herein, we investigated the involvement of bergenin in the protective effect against H₂ O₂ -induced oxidative stress and apoptosis in human nucleus pulposus cells (HNPCs) and the underlying mechanisms. HNPCs were cotreated with various concentrations of bergenin and 200 μM H₂ O₂ for 24 h. Cell viability was detected by Cell Counting Kit-8 and lactate dehydrogenase release assays. Reactive oxygen species (ROS) was evaluated utilizing 2',7'-dichlorofluorescein-diacetate. Superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) levels were measured to assess oxidative stress. Apoptosis was evaluated using terminal deoxynucleotidyl transferase dUTP nick end labeling and caspase-3/7 activity assays. Expression of protein was determined by western blotting. Results indicated that treatment with bergenin significantly alleviated H₂ O₂ -induced viability reduction and ROS overproduction in HNPCs in a dose-dependent manner. Bergenin alleviated H₂ O₂ -induced oxidative stress in HNPCs by increased activity of superoxide dismutase and level of glutathione peroxidase. H₂ O₂ -induced apoptosis and activity of caspase-3/7 were also suppressed by bergenin treatment in HNPCs. Western blotting showed that H₂ O₂ -induced decrease in expression of peroxisome proliferator-activated receptor γ (PPAR-γ) and increase in nuclear factor κB (NF-κB) were inhibited by bergenin. However, the inhibitory effect of bergenin on H₂ O₂ -induced viability reduction, oxidative stress and apoptosis were noticeably abrogated in PPAR-γ knockdown HNPCs. In conclusion, our results indicated that bergenin alleviates H₂ O₂ -induced oxidative stress and apoptosis in HNPCs by activating PPAR-γ and suppressing NF-κB pathway.

Exosomes Derived from Bone Mesenchymal Stem Cells Alleviate Compression-Induced Nucleus Pulposus Cell Apoptosis by Inhibiting Oxidative Stress

Oxidative stress is relevant in compression-induced nucleus pulposus (NP) cell apoptosis and intervertebral disc (IVD) degeneration. Exosomes derived from bone mesenchymal stem cells (BMSCs-Exos) are key secretory products of MSCs, with important roles in tissue regeneration. This research is aimed at studying the protective impact of BMSCs-Exos on NP cell apoptosis caused by compression and investigating the underlying mechanisms. Our results indicated that we isolated BMSCs successfully. Exosomes were isolated from the BMSCs and found to alleviate the inhibitory effect that compression has on proliferation and viability in NP cells, decreasing the toxic effects of compression-induced NP cells. AnnexinV/PI double staining and TUNEL assays indicated that the BMSCs-Exos reduced compression-induced apoptosis. In addition, our research found that BMSCs-Exos suppressed compression-mediated NP oxidative stress by detecting the ROS and malondialdehyde level. Furthermore, BMSCs-Exos increased the mitochondrial membrane potential and alleviated compression-induced mitochondrial damage. These results indicate that BMSCs-Exos alleviate compression-mediated NP apoptosis by suppressing oxidative stress, which may provide a promising cell-free therapy for treating IVD degeneration.

Antioxidant Effects of Resveratrol in Intervertebral Disk

Intervertebral disk (IVD) degeneration (IVDD) can cause various spinal degenerative diseases. Cumulative evidence has indicated that IVDD can result from inflammation, apoptosis, autophagy, biomechanical changes and other factors. Currently, lack of conservative treatment for degenerative spinal diseases leads to an urgent demand for clinically applicable medication to ameliorate the progression of IVDD. Resveratrol (3,5,4'-trihydroxy-trans-stilbene), a polyphenol compound extracted from red wine or grapes, has shown protective effects on IVD, alleviating the progression of IVDD. Resveratrol has been demonstrated as a scavenger of free radicals both in vivo and in vitro. The antioxidant effects of resveratrol are likely attributed to its regulation on mitochondrial dysfunction or the elimination of reactive oxygen species. This review will summarize the mechanisms of the reactive oxygen species production and elaborate the mechanisms of resveratrol in retarding IVDD progression, providing a comprehensive understanding of the antioxidant effects of resveratrol in IVD.

HIF-1α-Mediated miR-623 Regulates Apoptosis and Inflammatory Responses of Nucleus Pulposus Induced by Oxidative Stress via Targeting TXNIP

Excessive apoptosis and inflammatory responses of nucleus pulposus (NP) cells induced by oxidative stress contribute to intervertebral disc degeneration (IVDD). Though some microRNAs are associated with IVDD, the specific microRNA that can mediate apoptotic and inflammatory responses of NP cells induced by oxidative stress synchronously still needs further identification. Here, we find that microRNA-623 (miR-623) is downregulated in IVDD and its expression is regulated by hypoxia-inducible factor-1α (HIF-1α) under oxidative stress conditions. Mechanistically, HIF-1α is observed to promote miR-623 expression by directly binding to its promoter region (-1,994/-1,987 bp). Functionally, miR-623 is found to work as an intermediator in alleviating apoptosis and inflammatory responses of NP cells induced by oxidative stress via regulating thioredoxin-interacting protein (TXNIP) expression by directly targeting its 3'-untranslated region (3'-UTR). Thus, on elucidating the expression and functional mechanisms of miR-623, our study suggests that miR-623 can be a valuable therapeutic target for treating oxidative stress-induced IVDD.

Intervertebral Disc Stem/Progenitor Cells: A Promising "Seed" for Intervertebral Disc Regeneration

Intervertebral disc (IVD) degeneration is considered to be the primary reason for low back pain (LBP), which has become more prevalent from 21 century, causing an enormous economic burden for society. However, in spite of remarkable improvements in the basic research of IVD degeneration (IVDD), the effects of clinical treatments of IVDD are still leaving much to be desired. Accumulating evidence has proposed the existence of endogenous stem/progenitor cells in the IVD that possess the ability of proliferation and differentiation. However, few studies have reported the biological properties and potential application of IVD progenitor cells in detail. Even so, these stem/progenitor cells have been consumed as a promising cell source for the regeneration of damaged IVD. In this review, we will first introduce IVD, describe its physiology and stem/progenitor cell niche, and characterize IVDSPCs between homeostasis and IVD degeneration. We will then summarize recent studies on endogenous IVDSPC-based IVD regeneration and exogenous cell-based therapy for IVDD. Finally, we will discuss the potential applications and future developments of IVDSPC-based repair of IVD degeneration.

Drp1-mediated mitochondrial fission is involved in oxidized low-density lipoprotein-induced AF cella poptosis

This study aimed to assess the negative effect of oxidized low-density lipoprotein (oxLDL) on annulus fibrosus (AF) cells and decipher the mechanism of action of the process. After treating AF cells with various concentrations (0, 25, 50, 100, and 200 μg/mL) of oxLDL for 24 and 48 hours, their viability was evaluated using cell counting kit-8 and live/dead staining. The percentage of AF cell death was determined with Annexin V/propidium iodide apoptosis staining. The expression of proteins related to the mitochondrial apoptosis pathway was determined using Western blot. Additionally, mitochondrial membrane potential (MMP) and intracellular reactive oxygen species (ROS) were assessed with JC-1 staining and dichlorodihydrofluorescein diacetate ormitoSOX probes, respectively. Mitochondrial morphology was observed with a transmission electron microscope. After treatment with oxLDL, AF cell viability decreased, pro-apoptosis proteins (such as Bax, cleaved caspase-9, and cleaved caspase-3) increased, and anti-apoptosis proteins (Bcl-2) declined. Excessive ROS and diminished MMP were also detected during this process, as were enhanced mitochondrial fission and augmented Drp1 expression. Furthermore, knocking down the expression of Drp1 rescued oxLDL-induced AF cell death. Collectively, these results suggest that oxLDL induces AF cell death through a mitochondria-related pathway. Enhanced mitochondrial fission was involved in oxLDL-induced AF cell death. Targeting Drp1, a target for regulating the process of mitochondrial fission, may be a feasible strategy for preventing intervertebral disc degeneration in hyperlipidemia.

Proper animal experimental designs for preclinical research of biomaterials for intervertebral disc regeneration

Low back pain is a vital musculoskeletal disease that impairs life quality, leads to disability and imposes heavy economic burden on the society, while it is greatly attributed to intervertebral disc degeneration (IDD). However, the existing treatments, such as medicines, chiropractic adjustments and surgery, cannot achieve ideal disc regeneration. Therefore, advanced bioactive therapies are implemented, including stem cells delivery, bioreagents administration, and implantation of biomaterials etc. Among these researches, few reported unsatisfying regenerative outcomes. However, these advanced therapies have barely achieved successful clinical translation. The main reason for the inconsistency between satisfying preclinical results and poor clinical translation may largely rely on the animal models that cannot actually simulate the human disc degeneration. The inappropriate animal model also leads to difficulties in comparing the efficacies among biomaterials in different reaches. Therefore, animal models that better simulate the clinical charateristics of human IDD should be acknowledged. In addition, in vivo regenerative outcomes should be carefully evaluated to obtain robust results. Nevertheless, many researches neglect certain critical characteristics, such as adhesive properties for biomaterials blocking annulus fibrosus defects and hyperalgesia that is closely related to the clinical manifestations, e.g., low back pain. Herein, in this review, we summarized the animal models established for IDD, and highlighted the proper models and parameters that may result in acknowledged IDD models. Then, we discussed the existing biomaterials for disc regeneration and the characteristics that should be considered for regenerating different parts of discs. Finally, well-established assays and parameters for in vivo disc regeneration are explored.

Exosomes derived from pioglitazone-pretreated MSCs accelerate diabetic wound healing through enhancing angiogenesis

BACKGROUND

Enhanced angiogenesis can promote diabetic wound healing. Mesenchymal stem cells (MSCs)-derived exosomes, which are cell-free therapeutics, are promising candidates for the treatment of diabetic wound healing. The present study aimed to investigate the effect of exosomes derived from MSCs pretreated with pioglitazone (PGZ-Exos) on diabetic wound healing.

RESULTS

We isolated PGZ-Exos from the supernatants of pioglitazone-treated BMSCs and found that PGZ-Exos significantly promote the cell viability and proliferation of Human Umbilical Vein Vascular Endothelial Cells (HUVECs) injured by high glucose (HG). PGZ-Exos enhanced the biological functions of HUVECs, including migration, tube formation, wound repair and VEGF expression in vitro. In addition, PGZ-Exos promoted the protein expression of p-AKT, p-PI3K and p-eNOS and suppressed that of PTEN. LY294002 inhibited the biological function of HUVECs through inhibition of the PI3K/AKT/eNOS pathway. In vivo modeling in diabetic rat wounds showed that pioglitazone pretreatment enhanced the therapeutic efficacy of MSCs-derived exosomes and accelerated diabetic wound healing via enhanced angiogenesis. In addition, PGZ-Exos promoted collagen deposition, ECM remodeling and VEGF and CD31 expression, indicating adequate angiogenesis in diabetic wound healing.

CONCLUSIONS

PGZ-Exos accelerated diabetic wound healing by promoting the angiogenic function of HUVECs through activation of the PI3K/AKT/eNOS pathway. This offers a promising novel cell-free therapy for treating diabetic wound healing.

Mesenchymal Stem Cells Transplantation in Intracerebral Hemorrhage: Application and Challenges

Intracerebral hemorrhage (ICH) is one of the leading causes of death and long-term disability worldwide. Mesenchymal stem cell (MSC) therapies have demonstrated improved outcomes for treating ICH-induced neuronal defects, and the neural network reconstruction and neurological function recovery were enhanced in rodent ICH models through the mechanisms of neurogenesis, angiogenesis, anti-inflammation, and anti-apoptosis. However, many key issues associated with the survival, differentiation, and safety of grafted MSCs after ICH remain to be resolved, which hinder the clinical translation of MSC therapy. Herein, we reviewed an overview of the research status of MSC transplantation after ICH in different species including rodents, swine, monkey, and human, and the challenges for MSC-mediated ICH recovery from pathological microenvironment have been summarized. Furthermore, some efficient strategies for the outcome improvement of MSC transplantation were proposed.

Decellularized Disc Hydrogels for hBMSCs tissue-specific differentiation and tissue regeneration

Tissue specificity, a key factor in the decellularized tissue matrix (DTM), has shown bioactive functionalities in tuning cell fate-e.g., the differentiation of mesenchymal stem cells. Notably, cell fate is also determined by the living microenvironment, including material composition and spatial characteristics. Herein, two neighboring tissues within intervertebral discs, the nucleus pulposus (NP) and annulus fibrosus (AF), were carefully processed into DTM hydrogels (abbreviated DNP-G and DAF-G, respectively) to determine the tissue-specific effects on stem cell fate, such as specific components and different culturing methods, as well as in vivo regeneration. Distinct differences in their protein compositions were identified by proteomic analysis. Interestingly, the fate of human bone marrow mesenchymal stem cells (hBMSCs) also responds to both culturing methods and composition. Generally, hBMSCs cultured with DNP-G (3D) differentiated into NP-like cells, while hBMSCs cultured with DAF-G (2D) underwent AF-like differentiation, indicating a close correlation with the native microenvironments of NP and AF cells, respectively. Furthermore, we found that the integrin-mediated RhoA/LATS/YAP1 signaling pathway was activated in DAF-G (2D)-induced AF-specific differentiation. Additionally, the activation of YAP1 determined the tendency of NP- or AF-specific differentiation and played opposite regulatory effects. Finally, DNP-G and DAF-G specifically promoted tissue regeneration in NP degeneration and AF defect rat models, respectively. In conclusion, DNP-G and DAF-G can specifically determine the fate of stem cells through the integrin-mediated RhoA/LATS/YAP1 signaling pathway, and this tissue specificity is both compositional and spatial, supporting the utilization of tissue-specific DTM in advanced treatments of intervertebral disc degeneration.

The role and mechanism of mitochondrial functions and energy metabolism in the function regulation of the mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that show self-renewal, multi-directional differentiation, and paracrine and immune regulation. As a result of these properties, the MSCs have great clinical application prospects, especially in the regeneration of injured tissues, functional reconstruction, and cell therapy. However, the transplanted MSCs are prone to ageing and apoptosis and have a difficult to control direction differentiation. Therefore, it is necessary to effectively regulate the functions of the MSCs to promote their desired effects. In recent years, it has been found that mitochondria, the main organelles responsible for energy metabolism and adenosine triphosphate production in cells, play a key role in regulating different functions of the MSCs through various mechanisms. Thus, mitochondria could act as effective targets for regulating and promoting the functions of the MSCs. In this review, we discuss the research status and current understanding of the role and mechanism of mitochondrial energy metabolism, morphology, transfer modes, and dynamics on MSC functions.

Activation of HSP70 impedes tert-butyl hydroperoxide (t-BHP)-induced apoptosis and senescence of human nucleus pulposus stem cells via inhibiting the JNK/c-Jun pathway

The endogenous repair failure of degenerated intervertebral disk (IVD) is highly related to the exhaustion of nucleus pulposus stem cells (NPSCs). Excessive oxidative stress could induce apoptosis and senescence of NPSCs, thus, declining the quantity and quality of NPSCs. Heat shock protein 70 (HSP70) is a family of cytoprotective and antioxidative proteins. However, there is no report on the protective effects of HSP70 on oxidative stress-induced NPSC impairments and underlying mechanisms. In the present study, we treated NPSCs with tert-butyl hydroperoxide (t-BHP) in vitro to simulate an oxidative stress condition. HSP70 inducer TRC051384 was used to evaluate the cytoprotective effects of HSP70. The results suggested that HSP70 impeded t-BHP-mediated cell viability loss and protected the ultrastructure of NPSCs. Moreover, t-BHP could induce mitochondrial apoptosis and p53/p21-mediated senescence of NPSCs, both of which were significantly inhibited in HSP70 activation groups. Excessive oxidative stress and mitochondrial dysfunction reinforced each other and contributed to the cellular damage processes. HSP70 decreased reactive oxygen species (ROS) production, rescued mitochondrial membrane potential (MMP) collapse, and blocked ATP depletion. Finally, our data showed that HSP70 downregulated the JNK/c-Jun pathway. Taken together, activation of HSP70 could protect against t-BHP-induced NPSC apoptosis and senescence, thus, improving the quantity and quality of NPSCs. Therefore, HSP70 may be a promising therapeutic target for IVD degeneration.

Diabetes Mellitus, Mitochondrial Dysfunction and Ca2+-Dependent Permeability Transition Pore

Diabetes mellitus is one of the most common metabolic diseases in the developed world, and is associated either with the impaired secretion of insulin or with the resistance of cells to the actions of this hormone (type I and type II diabetes, respectively). In both cases, a common pathological change is an increase in blood glucose—hyperglycemia, which eventually can lead to serious damage to the organs and tissues of the organism. Mitochondria are one of the main targets of diabetes at the intracellular level. This review is dedicated to the analysis of recent data regarding the role of mitochondrial dysfunction in the development of diabetes mellitus. Specific areas of focus include the involvement of mitochondrial calcium transport systems and a pathophysiological phenomenon called the permeability transition pore in the pathogenesis of diabetes mellitus. The important contribution of these systems and their potential relevance as therapeutic targets in the pathology are discussed.

Biodegradable hollow mesoporous organosilica nanotheranostics (HMON) for multi-mode imaging and mild photo-therapeutic-induced mitochondrial damage on gastric cancer

Background

CuS-modified hollow mesoporous organosilica nanoparticles (HMON@CuS) have been preferred as non-invasive treatment for cancer, as near infrared (NIR)-induced photo-thermal effect (PTT) and/or photo-dynamic effect (PDT) could increase cancer cells’ apoptosis. However, the certain role of HMON@CuS-produced-PTT&PDT inducing gastric cancer (GC) cells’ mitochondrial damage, remained unclear. Moreover, theranostic efficiency of HMON@CuS might be well improved by applying multi-modal imaging, which could offer an optimal therapeutic region and time window. Herein, new nanotheranostics agents were reported by Gd doped HMON decorated by CuS nanocrystals (called HMON@CuS/Gd).

Results

HMON@CuS/Gd exhibited appropriate size distribution, good biocompatibility, l-Glutathione (GSH) responsive degradable properties, high photo-thermal conversion efficiency (82.4%) and a simultaneous reactive oxygen species (ROS) generation effect. Meanwhile, HMON@CuS/Gd could efficiently enter GC cells, induce combined mild PTT (43–45 °C) and PDT under mild NIR power density (0.8 W/cm²). Surprisingly, it was found that PTT might not be the only factor of cell apoptosis, as ROS induced by PDT also seemed playing an essential role. The NIR-induced ROS could attack mitochondrial transmembrane potentials (MTPs), then promote mitochondrial reactive oxygen species (mitoROS) production. Meanwhile, mitochondrial damage dramatically changed the expression of anti-apoptotic protein (Bcl-2) and pro-apoptotic protein (Bax). Since that, mitochondrial permeability transition pore (mPTP) was opened, followed by inducing more cytochrome c (Cyto C) releasing from mitochondria into cytosol, and finally activated caspase-9/caspase-3-depended cell apoptosis pathway. Our in vivo data also showed that HMON@CuS/Gd exhibited good fluorescence (FL) imaging (wrapping fluorescent agent), enhanced T1 imaging under magnetic resonance imaging (MRI) and infrared thermal (IRT) imaging capacities. Guided by FL/MRI/IRT trimodal imaging, HMON@CuS/Gd could selectively cause mild photo-therapy at cancer region, efficiently inhibit the growth of GC cells without evident systemic toxicity in vivo.

Conclusion

HMON@CuS/Gd could serve as a promising multifunctional nanotheranostic platform and as a cancer photo-therapy agent through inducing mitochondrial dysfunction on GC.

SIRT1 alleviates high-magnitude compression-induced senescence in nucleus pulposus cells via PINK1-dependent mitophagy

Mechanical overloading-induced nucleus pulposus (NP) cells senescence plays an important role in the pathogenesis of intervertebral disc degeneration (IVDD). The silent mating type information regulator 2 homolog-1 (SIRT1)-mediated pathway preserves the normal NP cell phenotype and mitochondrial homeostasis under multiple stresses. We aimed to investigate the role of SIRT1 in IVDD by assessing the effects of SIRT1 overexpression on high-magnitude compression-induced senescence in NP cells. High-magnitude compression induced cellular senescence and mitochondrial dysfunction in human NP cells. Moreover, SIRT1 overexpression tended to alleviate NP cell senescence and mitochondrial dysfunction under compressive stress. Given the mitophagy-inducing property of SIRT1, activity of mitophagy was evaluated in NP cells to further demonstrate the underlying mechanism. The results showed that SIRT1-overexpression attenuated senescence and mitochondrial injury in NP cells subjected to high-magnitude compression. However, depletion of PINK1, a key mitophagic regulator, impaired mitophagy and blocked the protective role of SIRT1 against compression induced senescence in NP cells. In summary, these results suggest that SIRT1 plays a protective role in alleviating NP cell senescence and mitochondrial dysfunction under high-magnitude compression, the mechanism of which is associated with the regulation of PINK1-dependent mitophagy. Our findings may provide a potential therapeutic approach for IVDD treatment.

Compression-induced senescence of nucleus pulposus cells by promoting mitophagy activation via the PINK1/PARKIN pathway

The current research aimed to explore the possible relationship between PINK1/PARKIN-mediated mitophagy and the compression-induced senescence of nucleus pulposus cells (NPCs). Therefore, the stages of senescence in NPCs were measured under compression lasting 0, 24 and 48 hours. The mitophagy-related markers, autophagosomes and mitochondrial membrane potential were tested to determine the levels of PINK1/PARKIN-mediated mitophagy under compression. The PINK1 and PARKIN levels were also measured by immunohistochemistry of human and rat intervertebral disc (IVD) tissues taken at different degenerative stages. A specific mitophagy inhibitor, cyclosporine A (CSA) and a constructed PINK1-shRNA were used to explore the relationship between mitophagy and senescence by down-regulating the PINK1/PARKIN-mediated mitophagy levels. Our results indicated that compression significantly enhanced the senescence of NPCs in a time-dependent manner. Also, PINK1/PARKIN-mediated mitophagy was found to be activated by the extended duration of compression on NPCs as well as the increased degenerative stages of IVD tissues. After inhibition of PINK1/PARKIN-mediated mitophagy by CSA and PINK1-shRNA, the senescence of NPCs induced by compression was strongly rescued. Hence, the excessive degradation of mitochondria in NPCs by mitophagy under continuous compression may accelerate the senescence of NPCs. Regulating PINK1/PARKIN-mediated mitophagy might be a potential therapeutic treatment for IVD degeneration.