Inhibiting Heat Shock Protein 90 Protects Nucleus Pulposus-Derived Stem/Progenitor Cells From Compression-Induced Necroptosis and Apoptosis

Spotlight on necroptosis: Role in pathogenesis and therapeutic potential of intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is the leading cause of low back pain, which is one of the major factors leading to disability and severe economic burden. Necroptosis is an important form of programmed cell death (PCD), a highly regulated caspase-independent type of cell death that is regulated by receptor-interacting protein kinase 1 (RIPK1), RIPK3 and mixed lineage kinase domain-like protein (MLKL)-mediated, play a key role in the pathophysiology of various inflammatory, infectious and degenerative diseases. Recent studies have shown that necroptosis plays an important role in the occurrence and development of IDD. In this review, we provide an overview of the initiation and execution of necroptosis and explore in depth its potential mechanisms of action in IDD. The analysis focuses on the connection between NP cell necroptosis and mitochondrial dysfunction-oxidative stress pathway, inflammation, endoplasmic reticulum stress, apoptosis, and autophagy. Finally, we evaluated the possibility of treating IDD by inhibiting necroptosis, and believed that targeting necroptosis may be a new strategy to alleviate the symptoms of IDD.

Focused ultrasound-induced cell apoptosis for the treatment of tumours

Cancer is a serious public health problem worldwide. Traditional treatments, such as surgery, radiotherapy, chemotherapy, and immunotherapy, do not always yield satisfactory results; therefore, an efficient treatment for tumours is urgently needed. As a convenient and minimally invasive modality, focused ultrasound (FUS) has been used not only as a diagnostic tool but also as a therapeutic tool in an increasing number of studies. FUS can help treat malignant tumours by inducing apoptosis. This review describes the three apoptotic pathways, apoptotic cell clearance, and how FUS affects these three apoptotic pathways. This review also discusses the role of thermal and cavitation effects on apoptosis, including caspase activity, mitochondrial dysfunction, and Ca2+ elease. Finally, this article reviews various aspects of FUS combination therapy, including sensitization by radiotherapy and chemotherapy, gene expression upregulation, and the introduction of therapeutic gases, to provide new ideas for clinical tumour therapy.

Investigating the characteristics of mild intervertebral disc degeneration at various age stages using single-cell genomics

Introduction: Intervertebral disc degeneration often occurs in the elderly population, but in recent years, there has been an increasing incidence of disc degeneration in younger individuals, primarily with mild degeneration. Methods: In order to explore the underlying mechanisms of disc degeneration in both young and aging individuals, we collected four types of nucleus pulposus (NP) single-cell sequencing samples for analysis based on Pfirrmann grading: normal-young (NY) (Grade I), normal-old (NO) (Grade I), mild degenerative-young (MY) (Grade II-III), and mild degenerative-old (MO) (Grade II-III). Results: We found that most NP cells in NO and MY samples exhibited oxidative stress, which may be important pathogenic factors in NO and MY groups. On the other hand, NP cells in MO group exhibited endoplasmic reticulum stress. In terms of inflammation, myeloid cells were mainly present in the degenerative group, with the MY group showing a stronger immune response compared to the MO group. Interestingly, dendritic cells in the myeloid lineage played a critical role in the process of mild degeneration. Discussion: Our study investigated the molecular mechanisms of intervertebral disc degeneration from an age perspective, providing insights for improving treatment strategies for patients with disc degeneration at different age groups.

In vitro and in vivo inhibitory effects of the Sanghuang mushroom extracts against Candida albicans

Aim: To explore the antifungal potential of Sanghuang mushroom, a traditional Chinese medicine. Materials & methods: The antifungal properties and the potential mechanism of Sanghuang mushroom extracts against Candida albicans were studied in vitro and in vivo. Results: Sanghuang mushroom extracts inhibited the biofilm formation, increased the cell membrane permeability and promoted cell apoptosis of C. albicans in vitro. In a murine model of vulvovaginal candidiasis, Sanghuang mushroom extracts reduced the vaginal fungal load, improved inflammatory cell infiltration and downregulated the expression of TNF-α, IL-1β and IL-6. Untargeted metabolomic analysis suggested the presence of ten antifungal components in Sanghuang mushroom extracts. Conclusion: Sanghuang mushroom extracts showed promise as antifungal agent against candidiasis, with potential therapeutic implications.

SP1/CTR1-mediated oxidative stress-induced cuproptosis in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is an age-related disease and is responsible for low back pain. Oxidative stress-induced cell death plays a fundamental role in IDD pathogenesis. Cuproptosis is a recently discovered form of programmed cell death dependent on copper availability. Whether cuproptosis is involved in IDD progression remains unknown. Herein, we established in vitro and in vivo models to investigate cuproptosis in IDD and the mechanisms by which oxidative stress interacts with copper sensitivity in nucleus pulposus cells (NPCs). We found that ferredoxin-1 (FDX1) content increased in both rat and human degenerated discs. Sublethal oxidative stress on NPCs led to increased FDX1 expression, tricarboxylic acid (TCA) cycle-related proteins lipoylation and aggregation, and cell death in the presence of Cu2+ at physiological concentrations, while FDX1 knockdown inhibited cell death. Since copper homeostasis is involved in copper-induced cytotoxicity, we investigated the role of copper transport-related proteins, including importer (CTR1) and efflux pumps (ATPase transporter, ATP7A, and ATP7B). CTR1 and ATP7A content increased under oxidative stress, and blocking CTR1 reduced oxidative stress/copper-induced TCA-related protein aggregation and cell death. Moreover, oxidative stress promoted the expression of specific protein 1 (SP1) and SP1-mediated CTR1 transcription. SP1 inhibition decreased cell death rates, preserved disc hydration, and alleviated tissue degeneration. This suggests that oxidative stress upregulates FDX1 expression and copper flux through promoting SP1-mediated CTR1 transcription, leading to increased TCA cycle-related protein aggregation and cuproptosis. This study highlights the importance of cuproptosis in IDD progression and provides a promising therapeutic target for IDD treatment.

HSP90B1 regulates autophagy via PI3K/AKT/mTOR signaling, mediating HNSC biological behaviors

Background

Autophagy, a crucial cellular mechanism, facilitates the degradation and removal of misfolded proteins and impaired organelles. Recent research has increasingly highlighted the intimate connection between autophagy and heat shock proteins (HSPs) in the context of tumor development. However, the specific role and underlying mechanisms of heat shock protein 90 beta family member 1 (HSP90B1) in modulating autophagy within head and neck squamous cell carcinoma (HNSCC) remain elusive.

Methods

Quantitative real-time PCR (qRT-PCR), Western blot (WB), immunohistochemistry (IHC) were used to detect the expression in HNSC cell lines and tissues. The relationship between HSP90B1 and clinicopathologic features was explored based on TCGA (The Cancer Genome Atlas) data and IHC results. The biological functions of HSP90B1 were analyzed through in vitro and in vivo models to evaluate proliferation, migration, invasion, and autophagy. The mechanisms of HSP90B1 were studied using bioinformatics and WB.

Results

HSP90B1 was upregulated in HNSC cells and tissues. High HSP90B1 levels were associated with T-stage, M-stage, clinical stage, and poor prognosis in HNSC patients. Functionally, HSP90B1 promotes HNSC cell proliferation, migration, invasion and inhibits apoptosis. We discovered that HSP90B1 obstructs autophagy and advances HNSC progression through the PI3K/Akt/mTOR pathway.

Conclusion

Our study demonstrates that HSP90B1 is highly expressed in HNSC. Furthermore, HSP90B1 may regulate autophagy through the PI3K/Akt/mTOR pathway, mediating HNSC cell biological behaviors. These provide new insights into potential biomarkers and targets for HNSC therapy.

Heat Shock Protein 90 in Parkinson's Disease: Profile of a Serial Killer

Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by abnormal α-synuclein misfolding and aggregation, mitochondrial dysfunction, oxidative stress, as well as progressive death of dopaminergic neurons in the substantia nigra. Molecular chaperones play a role in stabilizing proteins and helping them achieve their proper structure. Previous studies have shown that overexpression of heat shock protein 90 (HSP90) can lead to the death of dopaminergic neurons associated with PD. Inhibiting HSP90 is considered a potential treatment approach for neurodegenerative disorders, as it may reduce protein aggregation and related toxicity, as well as suppress various forms of regulated cell death (RCD). This review provides an overview of HSP90 and its role in PD, focusing on its modulation of proteostasis and quality control of LRRK2. The review also explores the effects of HSP90 on different types of RCD, such as apoptosis, chaperone-mediated autophagy (CMA), necroptosis, and ferroptosis. Additionally, it discusses HSP90 inhibitors that have been tested in PD models. We will highlight the under-investigated neuroprotective effects of HSP90 inhibition, including modulation of oxidative stress, mitochondrial dysfunction, PINK/PARKIN, heat shock factor 1 (HSF1), histone deacetylase 6 (HDAC6), and the PHD2-HSP90 complex-mediated mitochondrial stress pathway. By examining previous literature, this review uncovers overlooked neuroprotective mechanisms and emphasizes the need for further research on HSP90 inhibitors as potential therapeutic strategies for PD. Finally, the review discusses the potential limitations and possibilities of using HSP90 inhibitors in PD therapy.

HSPA8 acts as an amyloidase to suppress necroptosis by inhibiting and reversing functional amyloid formation

Ultra-stable fibrous structure is a hallmark of amyloids. In contrast to canonical disease-related amyloids, emerging research indicates that a significant number of cellular amyloids, termed 'functional amyloids', contribute to signal transduction as temporal signaling hubs in humans. However, it is unclear how these functional amyloids are effectively disassembled to terminate signal transduction. RHIM motif-containing amyloids, the largest functional amyloid family discovered thus far, play an important role in mediating necroptosis signal transduction in mammalian cells. Here, we identify heat shock protein family A member 8 (HSPA8) as a new type of enzyme - which we name as 'amyloidase' - that directly disassembles RHIM-amyloids to inhibit necroptosis signaling in cells and mice. Different from its role in chaperone-mediated autophagy where it selects substrates containing a KFERQ-like motif, HSPA8 specifically recognizes RHIM-containing proteins through a hydrophobic hexapeptide motif N(X1)φ(X3). The SBD domain of HSPA8 interacts with RHIM-containing proteins, preventing proximate RHIM monomers from stacking into functional fibrils; furthermore, with the NBD domain supplying energy via ATP hydrolysis, HSPA8 breaks down pre-formed RHIM-amyloids into non-functional monomers. Notably, HSPA8's amyloidase activity in disassembling functional RHIM-amyloids does not require its co-chaperone system. Using this amyloidase activity, HSPA8 reverses the initiator RHIM-amyloids (formed by RIP1, ZBP1, and TRIF) to prevent necroptosis initiation, and reverses RIP3-amyloid to prevent necroptosis execution, thus eliminating multi-level RHIM-amyloids to effectively prevent spontaneous necroptosis activation. The discovery that HSPA8 acts as an amyloidase dismantling functional amyloids provides a fundamental understanding of the reversibility nature of functional amyloids, a property distinguishing them from disease-related amyloids that are unbreakable in vivo.

Role of Necroptosis in Intervertebral Disc Degeneration

Apoptosis has historically been considered the primary form of programmed cell death (PCD) and is responsible for regulating cellular processes during development, homeostasis, and disease. Conversely, necrosis was considered uncontrolled and unregulated. However, recent evidence has unveiled the significance of necroptosis, a regulated form of necrosis, as an important mechanism of PCD alongside apoptosis. The activation of necroptosis leads to cellular membrane disruption, inflammation, and vascularization. This process is crucial in various pathological conditions, including intervertebral disc degeneration (IVDD), neurodegeneration, inflammatory diseases, multiple cancers, and kidney injury. In recent years, extensive research efforts have shed light on the molecular regulation of the necroptotic pathway. Various stimuli trigger necroptosis, and its regulation involves the activation of specific proteins such as receptor-interacting protein kinase 1 (RIPK1), RIPK3, and the mixed lineage kinase domain-like (MLKL) pseudokinase. Understanding the intricate mechanisms governing necroptosis holds great promise for developing novel therapeutic interventions targeting necroptosis-associated IVDD. The objective of this review is to contribute to the growing body of scientific knowledge in this area by providing a comprehensive overview of necroptosis and its association with IVDD. Ultimately, these understandings will allow the development of innovative drugs that can modulate the necroptotic pathway, offering new therapeutic avenues for individuals suffering from necroptosis.

Extracellular Vesicle-Conjugated Functional Matrix Hydrogels Prevent Senescence by Exosomal miR-3594-5p-Targeted HIPK2/p53 Pathway for Disc Regeneration

Nucleus pulposus stem cells (NPSCs) senescence plays a critical role in the progression of intervertebral disc degeneration (IDD). Stem cell-derived extracellular vesicles (EV) alleviate cellular senescence. Whereas, the underlying mechanism remains unclear. Low stability largely limited the administration of EV in vivo. RGD, an arginine-glycine-aspartic acid tripeptide, strongly binds integrins expressed on the EV membranes, allowing RGD to anchor EV and prolong their bioavailability. An RGD-complexed nucleus pulposus matrix hydrogel (RGD-DNP) is developed to enhance the therapeutic effects of small EV (sEV). RGD-DNP prolonged sEV retention in vitro and ex vivo. sEV-RGD-DNP promoted NPSCs migration, decreased the number of SA-β-gal-positive cells, alleviated cell cycle arrest, and reduced p16, p21, and p53 activation. Small RNA-seq showed that miR-3594-5p is enriched in sEV, and targets the homeodomain-interacting protein kinase 2 (HIPK2)/p53 pathway. The HIPK2 knockdown rescues the impaired therapeutic effects of sEV with downregulated miR-3594-5p. RGD-DNP conjugate with lower amounts of sEV achieved similar disc regeneration with free sEV of higher concentrations in DNP. In conclusion, sEV-RGD-DNP increases sEV bioavailability and relieves NPSCs senescence by targeting the HIPK2/p53 pathway, thereby alleviating IDD. This work achieves better regenerative effects with fewer sEV and consolidates the theoretical basis for sEV application for IDD treatment.

Inhibiting Heat Shock Protein 90 Attenuates Nucleus Pulposus Fibrosis and Pathologic Angiogenesis Induced by Macrophages via Down-Regulating Cell Migration-Inducing Protein

Intervertebral disc (IVD) degeneration (IVDD) is usually accompanied by nucleus pulposus (NP) fibrosis and pathologic angiogenesis, which are possibly associated with macrophage infiltration. Previous research indicates a destructive role of macrophages and the protective effect of inhibiting heat shock protein 90 (HSP90) in IVDD. Herein, the effects of inhibiting HSP90 on NP fibrosis and pathologic angiogenesis induced by macrophages were investigated further. Single-cell RNA-sequencing analysis was used to classify fibrotic NP cell (NPC) clusters and healthy NPC clusters in human NP tissues. The fibrotic NPC clusters were possibly associated with angiogenesis-related biological processes. Immunostaining showed the spatial association between blood vessel ingrowth and macrophage infiltration, as well as elevated levels of cell migration-inducing protein (CEMIP) and vascular endothelial growth factor A in severely degenerated human IVD tissues. Particularly, HSP90 inhibitor tanespimycin (17-AAG) ameliorated macrophage-induced fibrotic phenotype of NPCs via inhibiting CEMIP. M2, but not M1, macrophages promoted the pro-angiogenic ability of endothelial cells, which was attenuated by 17-AAG or HSP90 siRNA. Reversing the fibrotic phenotype of NPCs by Cemip siRNA also mitigated the pro-angiogenic effects of M2-conditioned medium-treated NPCs. Moreover, the murine IVDD model supported the 17-AAG-induced amelioration of NP fibrosis and endothelial cell invasion in IVD tissues. In conclusion, inhibiting HSP90 attenuated two interrelated pathologic processes, NP fibrosis and pathologic angiogenesis, induced by macrophages via down-regulating CEMIP.

Understanding necroptosis and its therapeutic target for intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a complex pathological condition associated with the development of low back pain. Despite numerous studies, the specific molecular mechanisms underlying IVDD remain unclear. At the cellular level, IVDD involves a series of changes, including cell proliferation, cell death, and inflammation. Of these, cell death plays a critical role in the progression of the condition. In recent years, necroptosis has been identified as a new form of programmed cell death (PCD). Necroptosis can be activated by ligands of death receptors, which then interact with RIPK1, RIPK3 and MLKL and lead to necrosome formation.. According to various previous studies, the necroptosis related pathway is activated in IVDD, and plays a significant role in the pathogenesis of IVDD. Furthermore, necroptosis may serve as a target for the IVDD treatment. Recently, several studies have reported the role of necroptosis in IVDD, but few studies have summarized the association between IVDD and necroptosis. The review gives a brief summary of the research progress of necroptosis, and discusses strategies and mechanisms that target necroptosis in IVDD. Lastly, matters needing attention in the necroptosis targeted therapy of IVDD are put forward at last. To the best of our knowledge, the review paper is the first one that integrates current research about the impact of necroptosis on IVDD, and contributes to the future therapy of IVDD from new perspectives.

HSP90 mediates the connection of multiple programmed cell death in diseases

Heat shock protein (HSP) 90, an important component of the molecular chaperone network, is closely concerned with cellular signaling pathways and stress response by participating in the process of maturation and activation of client proteins, playing a crucial role both in the normal and abnormal operation of the organism. In functionally defective tissues, programmed cell death (PCD) is one of the regulable fundamental mechanisms mediated by HSP90, including apoptosis, autophagy, necroptosis, ferroptosis, and others. Here, we show the complex relationship between HSP90 and different types of PCD in various diseases, and discuss the possibility of HSP90 as the common regulatory nodal in multiple PCD, which would provide a new perspective for the therapeutic approaches in disease.

Role of Caspase Family in Intervertebral Disc Degeneration and Its Therapeutic Prospects

Intervertebral disc degeneration (IVDD) is a common musculoskeletal degenerative disease worldwide, of which the main clinical manifestation is low back pain (LBP); approximately, 80% of people suffer from it in their lifetime. Currently, the pathogenesis of IVDD is unclear, and modern treatments can only alleviate its symptoms but cannot inhibit or reverse its progression. However, in recent years, targeted therapy has led to new therapeutic strategies. Cysteine-containing aspartate proteolytic enzymes (caspases) are a family of proteases present in the cytoplasm. They are evolutionarily conserved and are involved in cell growth, differentiation, and apoptotic death of eukaryotic cells. In recent years, it has been confirmed to be involved in the pathogenesis of various diseases, mainly by regulating cell apoptosis and inflammatory response. With continuous research on the pathogenesis and pathological process of IVDD, an increasing number of studies have shown that caspases are closely related to the IVDD process, especially in the intervertebral disc (IVD) cell apoptosis and inflammatory response. Therefore, herein we study the role of caspases in IVDD with respect to the structure of caspases and the related signaling pathways involved. This would help explore the strategy of regulating the activity of the caspases involved and develop caspase inhibitors to prevent and treat IVDD. The aim of this review was to identify the caspases involved in IVDD which could be potential targets for the treatment of IVDD.

A novel small molecule Hsp90 inhibitor, C-316-1, attenuates acute kidney injury by suppressing RIPK1-mediated inflammation and necroptosis

Acute kidney injury (AKI) is marked by a fast deterioration of the kidney function that may be caused by a variety of factors. Recently, although our group found that PPBICA alleviated programmed cell death in AKI, poor water solubility limited its bioavailability. In this research, we screened a series of derivatives and found that C-316-1 had the best suppressive effect on preventing necroptosis and inflammation in cisplatin- and ischemia/reperfusion-induced AKI in vitro and in vivo with lower toxicity and better water solubility. Mass spectrometry results showed that C-316-1 bound to heat shock protein 90 (Hsp90), which was further confirmed by molecular docking and surface plasmon resonance. Additionally, the Hsp90 expression was upregulated in the blood and tissues of AKI patients. We discovered that C-316-1 decreased the RIPK1 protein level without affecting its mRNA expression. The proteasome inhibitor, MG132 restored the level of RIPK1 reduced by C-316-1, suggesting that C-316-1 limits necroptosis by promoting the degradation of RIPK1 rather than by reducing its production. Immunoprecipitation further showed that pretreatment with C-316-1 disrupted the Hsp90-Cdc37 protein-protein Interactions (PPIs). Thereby, C-316-1 inhibited the Hsp90-Cdc37 complex formation and led to a significant decrease in RIPK1, which in turn reduced necroptosis. Moreover, C-316-1 treatment did not protect against kidney injury in vivo and in vitro when Hsp90 was knocked down and R46, E47, and S50 in Cdc37 binding site of Hsp90 might form an important active pocket with C-316-1. These findings suggest that C-316-1 is a potential therapeutic agent against RIPK1-Mediated Necroptosis in AKI.

Maslinic Acid Inhibits Myocardial Ischemia-Reperfusion Injury-Induced Apoptosis and Necroptosis via Promoting Autophagic Flux

Apoptosis, necroptosis, and autophagy are the major programmed cell death in myocardial ischemia-reperfusion injury (MIRI). Maslinic acid (MA) has been found to regulate pathophysiological processes that mediate programmed cell death in MIRI, such as inflammation and oxidative stress. However, its effects on MIRI remain unclear. This study intends to explore the role of MA in MIRI. In vitro, MA had no obvious cytotoxic effects on H9C2 cells, and significantly improved the impaired cell viability caused by hypoxia reoxygenation (HR). In vivo, MA significantly alleviated ischemia reperfusion (IR)-induced left ventricular myocardial tissue injury, downregulated creatine kinase-myocardial band (CK-MB), and lactate dehydrogenase (LDH) levels in serum as well as reducing infarct size. Moreover, MA inhibited HR-induced mitochondrial apoptosis and necroptosis in vitro and in vivo. Of interest, MA interacts with lysosome-associated membrane protein 2 (LAMP2). MA protected LAMP2 from IR and promoting autophagic flux to inhibit apoptosis and necroptosis, whereas these effects were reversed by co-treatment with lysosomal inhibitor BarfA1. In conclusion, MA can inhibit MIRI-induced apoptosis and necroptosis by promoting autophagic flux. These results support that MA is a potential agent to ameliorate MIRI.

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.

HSP70 attenuates compression-induced apoptosis of nucleus pulposus cells by suppressing mitochondrial fission via upregulating the expression of SIRT3

Compression-induced apoptosis of nucleus pulposus (NP) cells plays a pivotal role in the pathogenesis of intervertebral disc degeneration (IVDD). Recent studies have shown that the dysregulation of mitochondrial fission and fusion is implicated in the pathogenesis of a variety of diseases. However, its role in and regulatory effects on compression-induced apoptosis of NP cells have not yet been fully elucidated. Heat shock protein 70 (HSP70) is a major cytoprotective heat shock protein, but its physiological role in IVDD, especially its effect on mitochondrial fission and fusion, is still unknown. Herein, we found that compression could induce mitochondrial fission, which ultimately trigger apoptosis of NP cells via the mitochondrial apoptotic pathway. In addition, we identified the cytoprotective effects of HSP70 on NP cells, and we found that promoting the expression of HSP70 could protect NP cells from abnormal mechanical loading in vitro and in vivo. Finally, we showed that HSP70 inhibited compression-induced mitochondrial fission by promoting SIRT3 expression, thereby attenuating mitochondrial dysfunction and the production of reactive oxygen species and ultimately inhibiting the mitochondrial apoptotic pathway in NP cells. In conclusion, our results demonstrated that HSP70 could attenuate compression-induced apoptosis of NP cells by suppressing mitochondrial fission via upregulating SIRT3 expression. Promoting the expression of HSP70 might be a novel strategy for the treatment of IVDD.

A so-called chaperone protein that assists other proteins in correctly folding helps to prevent compression-induced cell death in the intervertebral discs responsible for cushioning the spine. Binwu Hu from Huazhong University of Science and Technology, Wuhan, China, and coworkers showed that mitochondria in the cells from the jelly-like substance found in vertebral discs in the spine tended to divide when exposed to abnormal mechanical loading. This fission resulted in cell death. In cell culture experiments and in mice, the researchers found that boosting levels of the molecular chaperone HSP70 (heat shock protein 70) prevented this mitochondrial dysfunction, in part by activating another stress-response protein called SIRT3. The findings point to HSP70 as a promising drug target for addressing intervertebral disc degeneration, a common cause of chronic back pain.

Update on the Correlation Between Mitochondrial Dysfunction and Intervertebral Disk Degeneration

Low back pain (LBP) is a common disorder in orthopedic outpatients, affecting people of all ages, and some patients may develop chronic LBP. As a complex organelle, mitochondria are not only energy workstations but also regulate cell senescence, apoptosis, and homeostasis. Mitochondrial dysfunction promotes disk degeneration by affecting a variety of pathophysiological processes, including oxidative stress, mitophagy, mitochondrial homeostasis, cellular senescence, and cell death. We review the molecular mechanisms underlying the relationship between mitochondrial dysfunction and intervertebral disk degeneration (IDD) to provide a theoretical basis for IDD treatment using pharmacological or tissue-engineering approaches.

HSP90 Inhibitor 17-AAG Attenuates Nucleus Pulposus Inflammation and Catabolism Induced by M1-Polarized Macrophages

Overactivated inflammation and catabolism induced by proinflammatory macrophages are involved in the pathological processes of intervertebral disc (IVD) degeneration (IVDD). Our previous study suggested the protective role of inhibiting heat shock protein 90 (HSP90) in IVDD, while the underlying mechanisms need advanced research. The current study investigated the effects of HSP90 inhibitor 17-AAG on nucleus pulposus (NP) inflammation and catabolism induced by M1-polarized macrophages. Immunohistochemical staining of degenerated human IVD samples showed massive infiltration of macrophages, especially M1 phenotype, as well as elevated levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α and matrix metalloproteinase (MMP)13. The conditioned medium (CM) of inflamed NP cells (NPCs) enhanced M1 polarization of macrophages, while the CM of M1 macrophages but not M2 macrophages promoted the expression of inflammatory factors and matrix proteases in NPCs. Additionally, we found that 17-AAG could represent anti-inflammatory and anti-catabolic effects by modulating both macrophages and NPCs. On the one hand, 17-AAG attenuated the pro-inflammatory activity of M1 macrophages via inhibiting nuclear factor-κB (NF-κB) pathway and mitogen-activated protein kinase (MAPK) pathways. On the other hand, 17-AAG dampened M1-CM-induced inflammation and catabolism in NPCs by upregulating HSP70 and suppressing the Janus kinase 2 (JAK2)-signal transducer and activator of transcription 3 (STAT3) pathway. Moreover, both in vitro IVD culture models and murine disc puncture models supported that 17-AAG treatment decreased the levels of inflammatory factors and matrix proteases in IVD tissues. In conclusion, HSP90 inhibitor 17-AAG attenuates NP inflammation and catabolism induced by M1 macrophages, suggesting 17-AAG as a promising candidate for IVDD treatment.

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.

Network Pharmacology and Experimental Validation to Reveal the Pharmacological Mechanisms of Liuwei Dihuang Decoction Against Intervertebral Disc Degeneration

Purpose

To explore the pharmacological mechanisms of Liuwei Dihuang Decoction (LWDHD) against intervertebral disc (IVD) degeneration (IVDD) via network pharmacology analysis combined with experimental validation.

Methods

First, active ingredients and related targets of LWDHD, as well as related genes of IVDD, were collected from public databases. The protein–protein interaction (PPI) network, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analyses were performed to predict the core targets and pathways of LWDHD against IVDD. Secondly, the IVDD model of mice treated with LWDHD was selected to validate the major targets predicted by network pharmacology.

Results

By searching the intersection of the active ingredient targets and IVDD targets, a total of 110 targets matched the related targets of 30 active ingredients in LWDHD and IVDD were retrieved. PPI network analysis indicated that 17 targets, including Caspase-3, IL-1β, P53, etc., were hub targets. GO and KEGG enrichment analyses showed that the apoptosis pathway was enriched by multiple targets and served as the target for in vivo experimental study validation. The results of animal experiments revealed that LWDHD administration not only restored the decrease in disc height and abnormal degradation of matrix metabolism in IVDD mice but also reversed the high expression of Bax, Caspase-3, IL-1β, P53, and low expression of Bcl-2, thereby inhibiting the apoptosis of IVD tissue and ameliorating the progression of IVDD.

Conclusion

Using a comprehensive network pharmacology approach, our findings predicted the active ingredients and potential targets of LWDHD intervention for IVDD, and some major target proteins involved in the predictive signaling pathway were validated experimentally, which gave us a new understanding of the pharmacological mechanism of LWDHD in treating IVDD at the comprehensive level.

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.

Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Stem cell-based therapy raises hopes for a better approach to promoting tissue repair and functional recovery. However, transplanted stem cells show a high death percentage, creating challenges to successful transplantation and prognosis. Thus, it is necessary to investigate the mechanisms underlying stem cell death, such as apoptotic cascade activation, excessive autophagy, inflammatory response, reactive oxygen species, excitotoxicity, and ischemia/hypoxia. Targeting the molecular pathways involved may be an efficient strategy to enhance stem cell viability and maximize transplantation success. Notably, a more complex network of cell death receives more attention than one crucial pathway in determining stem cell fate, highlighting the challenges in exploring mechanisms and therapeutic targets. In this review, we focus on programmed cell death in transplanted stem cells. We also discuss some promising strategies and challenges in promoting survival for further study.

Curcumin Modulates the Crosstalk Between Macrophages and Bone Mesenchymal Stem Cells to Ameliorate Osteogenesis

Bone healing is thought to be influenced by the cross-talk between bone forming and immune cells. In particular, macrophages play a crucial role in the regulation of osteogenesis. Curcumin, the major bioactive polyphenolic ingredient of turmeric, has been shown to regulate inflammatory response and osteogenic activities. However, whether curcumin could regulate macrophage polarization and subsequently influence osteogenesis remain to be elucidated. In this study, the potential immunomodulatory capability of curcumin on inflammatory response and phenotype switch of macrophages and the subsequent impact on osteogenic differentiation of MSCs are investigated. We demonstrated that curcumin exhibited significant anti-inflammatory effect by polarizing the macrophages toward anti-inflammatory phenotype, with increased expression of IL-4, IL-10, and CD206, and decreased expression of IL-1β, TNF-α, CCR7, and iNOS. In addition, curcumin could improve the osteo-immune microenvironment via promoting osteogenesis-related regenerative cytokine BMP-2 and TGF-β production. Moreover, the co-cultured test of macrophages and BMSCs showed that curcumin-modulated macrophages conditioned medium could promote osteogenic differentiation of BMSCs with increased gene (ALP, Runx-2, OCN, and OPN) and protein (Runx-2 and OCN) expression levels, enhanced ALP activity, and obvious formation of mineralized nodules. Taken together, with the interaction between curcumin-conditioned macrophage and curcumin-stimulated BMSCs, curcumin could remarkably enhance the osteogenic differentiation of BMSCs in LPS-activated inflammatory macrophage-BMSCs coculture system.

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.