The standardized reporting of postoperative complications is essential for improving surgical quality and comparing outcomes. However, spinal surgery has historically lacked a universal system and has instead relied on ambiguous terms. This narrative review synthesizes the literature on the adaptation, validation, and application of the therapy-based Clavien-Dindo classification (CDC) and its modified versions in spinal surgery. It focuses on studies across various spinal procedures and patient populations. The evidence shows that adapted CDC systems demonstrate good to excellent inter- and intrarater reliability, particularly for severe complications. These systems also facilitate direct comparison of surgical techniques. Moreover, they reveal strong correlations between complication severity, prolonged hospital stay, and patient factors such as frailty. Nevertheless, key limitations include poor correlation with certain long-term patient-reported outcomes. The CDC cannot capture intraoperative events or the cumulative burden of multiple complications. Subjectivity also exists in grading milder events. Recent spine-specific modifications that improve neurologic deficit assessment have enhanced clinical relevance. Overall, the CDC provides a critical framework for standardizing complication reporting in spinal surgery. Optimal application requires awareness of its limitations. In complex scenarios, the CDC may be applied most effectively as a component within more comprehensive, spine-specific taxonomies that incorporate surgical complexity and structured neurological assessment. The CDC remains a vital tool for improving communication, benchmarking, and ultimately enhancing patient care.

Background:Magnesium-based implants facilitate bone regeneration via degradation. However, the epigenetic mechanisms, particularly N6-methyladenosine (m6A) modification regulated by Mg2+, remain incompletely understood. This study investigated the role of Mg2+ in osteogenic differentiation through the METTL3-RhoA axis and evaluated its potential in intervertebral fusion. Methods:The optimal Mg2+ concentration was identified using MC3T3-E1 cells. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) and MeRIP-PCR were employed to identify m6A target genes. Functional assays (knockdown, overexpression, and rescue) validated the METTL3-YTHDF1-RhoA pathway. A rat tail intervertebral fusion model with magnesium implants was used to assess in vivo effects. Results:Treatment with 4 mM Mg2+ significantly enhanced osteogenic activity and increased METTL3 levels. Mechanistically, METTL3 promoted m6A methylation of RhoA mRNA, which was subsequently bound by YTHDF1, enhancing translation and activating the RhoA/ROCK pathway. In vivo, magnesium implants accelerated fusion and improved trabecular bone quality; however, these effects were inhibited by METTL3 or RhoA inhibitors. Conclusion:Mg2+ enhances osteogenic differentiation through the METTL3-YTHDF1-RhoA/ROCK pathway. The translational potential of this article:This study provides an epigenetic framework for optimizing magnesium-based orthopedic implants and suggests that targeting the m6A-RhoA axis could improve spinal fusion outcomes.

The polarization state of microglia exerts an influence on neuroinflammation and neural tissue repair after injury. Modulating microglial polarization is emerging as a potential therapeutic strategy for various types of neural injuries and neurodegenerative diseases. However, the causal relationship between microglial polarization and mitochondrial dynamics, which include mitochondrial fusion and fission, remains to be fully clarified. Our study demonstrates that mitochondrial fusion promoter M1 promotes mitochondrial fusion in mouse microglial cells, leading to reduced glycolysis and increased fatty acid oxidation, and this metabolic reprogramming impacts microglial polarization. Additionally, in both cellular and animal experiments, it was observed that knocking down mitochondrial transcription factor A (TFAM) results in increased mitochondrial fission, decreased fatty acid β-oxidation, enhanced glycolysis, and promotes the polarization of microglia toward the pro-inflammatory M1 phenotype. In conclusion, our study has, for the first time, provided evidence that TFAM may play a role in the regulation of mitochondrial dynamics. Furthermore, we provide a detailed elucidation of the chronological sequence and underlying causal relationships among mitochondrial dynamics, mitochondrial metabolic reprogramming, and microglial polarization. These findings offer novel targets and strategies for the treatment of various neural injuries and neurodegenerative diseases.

Osteoporosis a is a metabolic bone disease caused by an imbalance in bone homeostasis, which is regulated by osteoblasts and osteoclasts. Protein palmitoylation modification is a post-translational modification that affects protein function, localization, and targeting by attaching palmitoyl groups to specific amino acid residues of proteins. Recent studies have shown that protein palmitoylation is involved in the regulation of osteoclast overproduction, osteoblast migration, osteogenic differentiation, dysfunctional autophagy, and endocrine hormone membrane receptors in osteoporosis. Exactly to what extent palmitoylation modifications can regulate osteoporosis, and whether palmitoylation inhibition can delay osteoporosis, is a key question that needs to be investigated urgently. In this review, we observed that palmitoylation modifications act mainly through two target cells - osteoblasts and osteoclasts - and that the targets of palmitoylation modifications are focused on plasma membrane proteins or cytosolic proteins of the target cells, which tend to assume the role of receiving extracellular signals. We also noted that different palmitoyl transferases acting on different substrate proteins exert conflicting regulation of osteoblast function. We concluded that the regulation of osteocyte function, bone homeostasis, and osteoporosis by palmitoylation modifications is multidimensional, diverse, and interconnected. Perfecting the palmitoylation modification network can enhance our ability to utilize post-translational modifications to resist osteoporosis and lay the foundation for targeting palmitoyl transferases to treat osteoporosis in the future.

Intervertebral disc degeneration (IVDD) is a leading cause of low back pain, but existing therapies fail to halt its progression. Here, we develop an exosome-loaded methacrylated silk fibroin hydrogel (SM@ME) that synergistically activates the mitochondrial unfolded protein response (UPRmt) to combat IVDD. SilkMA hydrogel, optimized for mechanical compatibility with nucleus pulposus (NP) tissue, enables sustained release of Cavin-2engineered exosomes (M-EXO). RNA sequencing revealed that SM@ME upregulates DKK2, which suppresses the Wnt/beta-catenin pathway while activating UPRmt, thereby reducing apoptosis, and senescence in rat and human NP cells. In vivo, SM@ME injection into puncture-induced IVDD rats attenuated histological degeneration. Notably, lentiviral-mediated overexpression of DKK2 in NP tissues resulted in therapeutic effects similar to those of SM@ME treatment. This work suggests that hydrogel-delivered exosomes can modulate UPRmt for IVDD therapy, offering a novel biomaterial strategy for disc regeneration.

With the aging of the global population, the prevalence of intervertebral disc degeneration (IVDD) disease is gradually increasing. This disease not only leads to a substantial reduction in the quality of life of patients but also imposes a considerable burden on the health care system. At present, the understanding of its pathogenesis is relatively limited, and in-depth research is urgently needed to identify effective treatment methods. One of the main causes of IVDD is the compression of the spine caused by body weight. The objective of this study was to investigate the potential regulatory mechanism underlying IVDD induced by excessive compression. Moreover, to investigate whether FBXW7 is involved in the regulation of mitophagy and ferroptosis, we used 1 MPa pressure to induce nucleus pulposus cell (NPC) degeneration and then constructed plasmids or small interfering RNAs to overexpress or knock down FBXW7. In addition, in vivo animal experiments were performed to verify the function of FBXW7. We found that FBXW7 expression was decreased in degenerative NP tissues. Compression promoted the initiation of mitophagy, but blocked autophagic flux and ultimately caused ferroptosis in NPCs. However, overexpression of FBXW7 can activate mitophagy, improve autophagic flux, and alleviate ferroptosis. Moreover, FBXW7 can bind to mTOR and promote its ubiquitination and degradation, thus increasing the expression of PINK1 and Parkin. Taken together, the results of both in vitro and in vivo experiments suggested that FBXW7 induced mitophagy, alleviated ferroptosis, and delayed IVDD via the mTOR signaling pathway.

Intervertebral disc degeneration (IVDD) is the primary contributor to a range of spinal diseases. Dynamin-related protein 1 (Drp1)-mediated mitochondrial fission has recently been identified as a new cause of nucleus pulposus cell (NPC) death and IVDD, but the underlying mechanisms remain unclear. Although the effects of Drp1 phosphorylation in IVDD have been studied, it is currently unknown if small ubiquitin-like modifications (SUMOylation) of Drp1 regulate IVDD. This study aimed to investigate the functions and mechanisms of mitochondria-anchored protein ligase (MAPL), a mitochondrial SUMO E3 ligase, during IVDD progression. The expression of genes related to SUMOylation and mitochondrial dynamics in TNF-α-stimulated NPCs was analysed via RNA sequencing. The levels of total and mitochondrial SUMO1 conjugates were elevated with MAPL upregulation in TNF-α-treated NPCs. Additionally, mitochondrial fragmentation and dysfunction were induced by TNF-α stimulation. MAPL overexpression promoted mitochondrial SUMOylation and SUMO1 modification of Drp1, thereby facilitating the mitochondrial translocation of Drp1 and mitochondrial fission. MAPL-induced ROS accumulation and ΔΨm loss led to increased NPC apoptosis. Mutation of the SUMO-acceptor lysine residues of Drp1 hindered its SUMOylation and rescued the mitochondrial phenotypes caused by MAPL. SENP5 overexpression phenocopied MAPL silencing, negatively modulating the SUMO1 modification of Drp1 and mitochondrial fission in NPCs. In a rat IVDD model, forced expression of MAPL by using an adeno-associated virus (AAV) vector aggravated IVD tissue damage, whereas the knockdown of MAPL delayed IVDD progression. Our findings highlight the importance of SUMOylation in IVDD. The inhibition of MAPL-mediated Drp1 SUMOylation alleviates mitochondrial fission and limits IVDD development, providing a potential strategy for IVDD treatment.

The nucleus pulposus is in a hypoxic environment in the human body, and when intervertebral disc degeneration (IVDD) occurs, the hypoxic environment is disrupted. Nucleus pulposus cell (NPC) ferroptosis is one of the causes of IVDD. N6-methyladenosine (m6A) and its reader protein YTHDF1 regulate cellular activities by affecting RNA metabolism. However, the regulation of ferroptosis in NPCs by m6A-modified RNAs under hypoxic conditions has not been as well studied. In this study, through in vitro and in vivo experiments, we explored the underlying mechanism of HIF-1α and YTHDF1 in regulating ferroptosis in NPCs. The results indicated that the overexpression of HIF-1α or YTHDF1 suppressed NPC ferroptosis; conversely, the knockdown of HIF-1α or YTHDF1 increased ferroptosis levels in NPCs. Luciferase reporter assays and chromatin immunoprecipitation demonstrated that HIF-1α regulated YTHDF1 transcription by directly binding to its promoter region. Polysome profiling results showed that YTHDF1 promoted the translation of SLC7A11 and consequently the expression of the anti-ferroptosis protein GPX4 by binding to m6A-modified SLC7A11 mRNA. In conclusion, HIF-1α-induced YTHDF1 expression reduces NPC ferroptosis and delays IVDD by promoting SLC7A11 translation in a m6A-dependent manner.

Abstract Background Cartilaginous endplate (CEP) degeneration, which is an important contributor to intervertebral disc degeneration (IVDD), is characterized by chondrocyte death. Accumulating evidence has revealed that dynamin-related protein 1 (Drp1)-mediated mitochondrial fission and dysfunction lead to apoptosis during CEP degeneration and IVDD. Exosomes are promising agents for the treatment of many diseases, including osteoporosis, osteosarcoma, osteoarthritis and IVDD. Despite their major success in drug delivery, the full potential of exosomes remains untapped. Materials and methods In vitro and in vivo models of CEP degeneration were established by using lipopolysaccharide (LPS). We designed genetically engineered exosomes (CAP-Nrf2-Exos) expressing chondrocyte-affinity peptide (CAP) on the surface and carrying the antioxidant transcription factor nuclear factor E2-related factor 2 (Nrf2). The affinity between CAP-Nrf2-Exos and CEP was evaluated by in vitro internalization assays and in vivo imaging assays. qRT‒PCR, Western blotting and immunofluorescence assays were performed to examine the expression level of Nrf2 and the subcellular localization of Nrf2 and Drp1. Mitochondrial function was measured by the JC-1 probe and MitoSOX Red. Mitochondrial morphology was visualized by MitoTracker staining and transmission electron microscopy (TEM). After subendplate injection of the engineered exosomes, the degree of CEP degeneration and IVDD was validated radiologically and histologically. Results We found that the cargo delivery efficiency of exosomes after cargo packaging was increased by surface modification. CAP-Nrf2-Exos facilitated chondrocyte-targeted delivery of Nrf2 and activated the endogenous antioxidant defence system in CEP cells. The engineered exosomes inhibited Drp1 S616 phosphorylation and mitochondrial translocation, thereby preventing mitochondrial fragmentation and dysfunction. LPS-induced CEP cell apoptosis was alleviated by CAP-Nrf2-Exo treatment. In a rat model of CEP degeneration, the engineered exosomes successfully attenuated CEP degeneration and IVDD and exhibited better repair capacity than natural exosomes. Conclusion Collectively, our findings showed that exosome-mediated chondrocyte-targeted delivery of Nrf2 was an effective strategy for treating CEP degeneration. Graphic abstract CAP-Nrf2-Exos delivered Nrf2 into CEP cells and alleviated LPS-induced apoptosis by inhibiting Drp1-mediated mitochondrial fission

Mitochondrial homeostasis plays a crucial role in degenerative joint diseases, including cartilaginous endplate (CEP) degeneration. To date, research into mitochondrial dynamics in IVDD is at an early stage. Since Piezo1 is a novel Ca 2+ -permeable channel, we asked whether Piezo1 could modulate mitochondrial fission through Ca 2+ signalling during CEP degeneration. In vitro and in vivo models of inflammation-induced CEP degeneration were established with lipopolysaccharide (LPS). We found increased expression of Piezo1 in degenerated CEP tissues and LPS-treated CEP cells. The Piezo1 activator Yoda1 exacerbated CEP cell senescence and apoptosis by triggering Ca 2+ influx. Yoda1 also induced mitochondrial fragmentation and dysfunction. In contrast, the Piezo1 inhibitor GsMTx4 exerted cytoprotective effects in LPS-treated CEP cells. Additionally, the CaMKII inhibitor KN-93 reversed Yoda1-induced mitochondrial fission and restored mitochondrial function. Mechanistically, the phosphorylation and mitochondrial translocation of Drp1 were regulated by the Ca 2+ /CaMKII signalling. The Drp1 inhibitor Mdivi-1 suppressed mitochondrial fission, then reduced mitochondrial dysfunction and CEP cell death. Moreover, knockdown of Piezo1 by siRNA hindered CaMKII and Drp1 activation, facilitating the redistribution of mitochondrial Drp1 to the cytosol in LPS-treated CEP cells. Piezo1 silencing improved mitochondrial morphology and function, thereby rescuing CEP cell senescence and apoptosis under inflammatory conditions. Finally, subendplate injection of GsMTx4 or AAV-shPiezo1 alleviated CEP degeneration in a rat model. Thus, Piezo1 may exacerbate inflammation-induced CEP degeneration by triggering mitochondrial fission and dysfunction via the Ca 2+ /CaMKII/Drp1 axis.

Intervertebral disc degeneration (IVDD) is one of the main causes of low back pain, which brings heavy burdens to individuals and society. The mechanism of IVDD is complex and diverse. One of the important reasons is that the abnormal accumulation of reactive oxygen species (ROS) in nucleus pulposus cells (NPCs) leads to endoplasmic reticulum stress (ERS), which causes increased apoptosis of NPCs. Nuclear factor E2-related factor 2 (Nrf-2) and its downstream antioxidant proteins are key molecular switches for sensing oxidative stress and regulating antioxidant responses in cells. Sulforaphane (SFN), a natural compound derived from Brassicaceae plants, is a Nrf-2 agonist that displays potent antioxidant potential in vitro and in vivo. Here, we used advanced glycation end products (AGEs) to construct an in vitro degeneration model of NPCs, and we found that AGEs elevated ROS level in NPCs and caused severe ERS and apoptosis. While SFN can promote the entry of Nrf-2 into the nucleus and increase the expression level of heme oxygenase 1 (HO-1) in vitro, thus clearing the accumulated ROS in cells and alleviating ERS and cell apoptosis. Moreover, the protection of SFN on NPCs was greatly attenuated after HO-1 was inhibited. We also used AGEs to construct a rat IVDD model. Consistent with the in vitro experiments, SFN could attenuate ERS in NPCs in vivo and delay disc degeneration in rats. This study found that SFN can be used as a new and promising agent for the treatment of IVDD.

BACKGROUND:Spinal cord injury (SCI) brings a heavy burden to individuals and society, and there is no effective treatment at present. Exosomes (EX) are cell secreted vesicles containing molecules such as nucleic acids and proteins, which hold promise for the treatment of SCI. Netrin-1 is an axon guidance factor that regulates neuronal growth. We investigated the effects of engineered EX enriched in netrin-1 chemically synthetic modified message RNA (modRNA) in treating SCI in an attempt to find a novel therapeutic approach for SCI.METHODS:Netrin-1 modRNA was transfected into bone marrow mesenchymal stem cells to obtain EX enriched with netrin-1 (EX-netrin1). We built an inflammatory model in vitro with lipopolysaccharide (LPS) in vitro to study the therapeutic effect of EX-netrin1 on SCI. For experiments in vitro, ELISA, CCK-8 assay, immunofluorescence staining, lactate dehydrogenase release experiments test, real-time quantitative polymerase chain reaction, and western blot were conducted. At the same time, we constructed a rat model of SCI. MRI, hematoxylin-eosin and Nissl staining were used to assess the extent of SCI in rats.RESULTS:In vitro experiments showed that EX had no effect on the viability of oligodendrocytes and PC12 cells. EX-netrin1 could attenuate LPS-induced inflammation and pyroptosis and accelerate axonal/dentritic growth in PC12 cells/oligodendrocytes. In addition, netrin-1 could activate the PI3K/AKT/mTOR signalling pathway upon binding to its receptor unc5b. When Unc5b and PI3K were inhibited, the effect of EX-netrin1 was weakened, which could be reversed by PI3K or mTOR activator. Our in vivo experiments indicated that EX-netrin1 could promote recovery in rats with SCI.CONCLUSION:We found that EX-netrin1 regulated inflammation, pyroptosis and axon growth in SCI via the Unc5b/PI3K/AKT/mTOR pathway, which provides a new strategy for the treatment of SCI.

Low back pain (LBP) is an extremely common disorder and is a major cause of disability globally. Intervertebral disc degeneration (IVDD) is the main contributor to LBP. Nevertheless, the specific mechanisms underlying the pathogenesis of IVDD remain unclear. Mitochondria are highly dynamic organelles that continuously undergo fusion and fission, known as mitochondrial dynamics. Accumulating evidence has revealed that aberrantly activated mitochondrial fission leads to mitochondrial fragmentation and dysfunction, which are involved in the development and progression of IVDD. To date, research into mitochondrial dynamics in IVDD is at an early stage. The present narrative review aims to summarize the most recent findings about the role of mitochondrial fission in the pathogenesis of IVDD.

Lower back pain (LBP) is an extremely common symptom and is recognized as a leading contributor to disability and disease burden globally. Intervertebral disc degeneration (IDD) represents a major cause of LBP. However, the molecular mechanisms involved in the pathogenesis of IDD remain unclear, and currently available treatments, including conservative and surgical options, fail to effectively delay, stop or reverse the progression of IDD. Circular RNAs (circRNAs) are a newly discovered group of covalently closed, single-stranded and endogenous non-coding RNAs. A growing body of research has revealed that a number of circRNAs are widely and aberrantly expressed in IDD tissues. Furthermore, they play important roles in the pathogenesis of IDD, including proliferation, apoptosis, senescence, mitophagy, inflammation and extracellular matrix metabolism, mainly by acting as sponges for microRNAs. The present review aims to summarize the current understanding on the mechanisms of circRNA-mediated regulation in IDD.

Eosinophilic pleural effusion (EPE) is defined as a pleural fluid with an eosinophilic count exceeding 10% and currently considered to be mainly caused by malignancy. However, the incidence, etiology and prognostic significance of malignant eosinophilic pleural effusion ( MEPE) have not been studied extensively yet. Thus, the objective of this review was to summarize medical studies regarding MEPE to 2020 throughout an extensive search of PubMed. Overall, MEPE was a disease associated with multiple-cytokines-mediated immunity and varied from 4% to 92% of patients who had EPE. The discrepancy of the MEPE prevalence among studies could be explained by the development of diagnostic technology, disparity of study population, or various disease spectrum over time. Data summarized in this review demonstrated that the incidence of malignancy was lower in EPEs than in non-EPEs (29.7% vs. 32.9%). Additionally, MEPE could be a manifestation of a great variety of tumor subtypes, among which lung cancer was the most common cause and accounted for more than 34% of cases. The second common causes were non-Hodgkin lymphoma and metastatic cancers with unknown primary site which were observed in around 5% of cases, respectively. The presence of eosinophils in the pleural effusion may be associated with a positive prognosis of MEPE. Besides, the prognosis of MEPE may be related to the percentage of eosinophils in the pleural fluid. More extensive studies, however, are warranted to validate these findings.

Racial minority patients were more likely to be diagnosed an advanced-stage disease at presentation, and received less cancer-directed surgery and other standard care. We hypothesized that access to adequate health insurance coverage among patients with lung cancer play an important role in these racial disparities, because many previous studies have shown a significant association between lack of insurance status and poor cancer outcomes.

Objective:To explore the effect of flipped classroom combined with scenario simulation in the teaching reform on four basic medical puncture techniques of clinical skills training.Methods:A total of 1 275 students majoring in five-year clinical medicine in Guangzhou Medical University were enrolled in the study. The control group (647 cases from Batch 2015) were given the traditional teaching pattern and the experimental group (628 cases from Batch 2016) adopted flipped classroom combined with scenario simulation. At the end of the course, the performance in the tests of four basic medical puncture techniques in the objective structured clinical examination (OSCE) of the two groups were compared. The feedback and evaluation of this teaching mode in the experimental group were investigated by questionnaires. SPSS 19.0 was used for independent samples t test. Results:All the scores of the tests of four basic medical puncture techniques in the experimental group were significantly higher than those in the control group: abdominocentesis [(87.89±7.13) vs. (82.60±10.74) points], thoracocentesis [(85.20±7.39) vs. (81.96±7.76) points], bone marrow aspiration [(88.13±6.00) vs. (83.50±9.63) points], and lumbar puncture [(91.91±7.19) vs. (80.74±12.20) points], with significant differences ( P<0.001). The results about the feedback and evaluation in the experimental group showed that the students gave an average score of 8.4 points to their satisfaction with the new teaching mode. The approval rates of the teaching effect evaluation items such as teaching arrangement, improving learning ability, improving clinical practice ability and school promotion were higher than 90.0%. Conclusion:Flipped classroom combined with scenario simulation, which is worthy to be popularized, can not only improve the students' performance in the tests of four basic medical puncture techniques in the OCSE, but also improve teaching satisfaction and teaching effect.

BACKGROUND AND OBJECTIVE: Undiagnosed pleural effusions (UPEs) are a common problem of respiratory medicine, leading to an increased diagnostic burden globally. However, the most efficient and cost-effective approaches to UPEs remain controversial. This study aimed to assess the diagnostic value of ultrasound-guided needle biopsy (UGNB) in UPEs. METHODS: We conducted a search of PubMed, Embase, the Cochrane Library and reference lists of retrieved studies with no publication data limitation. Articles that investigated the diagnostic accuracy of UGNB in UPEs were included. The quality of eligible studies was assessed using Quality Assessment of Diagnostic Accuracy Studies-2. The diagnostic value of UGNB was evaluated by calculating the pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds rate, and the area under the curve for the summary receiver operating characteristic curve using a random effects model. RESULTS: Seven studies comprising 165 patients with UPEs met the inclusion criteria. UGNB had a pooled sensitivity of 83% (95% confidence intervals [CI], 75% - 89%), a specificity of 100% (95% CI, 90% - 100%), a positive likelihood ratio of 8.89 (95% CI, 3.29 - 24.02), a negative likelihood ratio of 0.23 (95% CI, 0.16 - 0.33), a diagnostic odds rate of 51.47 (95% CI, 14.70 - 180.16), and an area under the curve of 0.94. Six pneumothorax cases (3.6%), 5 local wound infections (3.0%), and 1 empyema case (less than 1%) were observed. There was no significant heterogeneity or publication bias in this study. CONCLUSIONS: Based on current evidence, UGNB is a safe and convenient procedure with a high accuracy for diagnosing UPEs. However, physicians should still be cautious in interpreting negative UGNB results.

There is growing evidence demonstrating the relationship between herpes simplex virus type 1 (HSV-1) infection and Alzheimer's disease (AD). We searched PubMed, Embase, and Cochrane databases for relevant articles. The Newcastle-Ottawa Scale (NOS) was used to evaluate the qualities of these studies. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using random-effects mod els. We also performed subgroup analyses stratified by apolipoprotein 64 (APOE 64), NOS score, and the method of confirming AD. A total of 21 studies between 1990 and 2020 were identified. The pooled OR suggested that HSV-1 infection is a risk factor of AD: pooled OR 1.40 (95% CI: 1.13-1.75; I-2 = 3%, P = 0.42). In the subgroup analyses, the pooled ORs of HSV-1 infection associated with AD were 0.75 (95% CI: 0.24-2.37) among the APOE 64-positive individuals; 0.85 (95% CI: 0.61-1.17) among the APOE 64-negative individuals; 1.51 (95% CI: 1.10-2.06) in the high NOS score studies; 1.23 (95% CI: 0.85-1.76) in the moderate NOS score studies; 1.47 (95% CI: 1.16-1.87) in the clinical diagnosis group, and 1.20 (95% CI: 0.77-1.87) in the autopsy group. Our up-to-date systematic review and meta-analysis suggest that HSV-1 infection is a risk factor of AD. (C) 2020 Elsevier Ltd. All rights reserved.