Nucleus Pulposus Cells from Calcified Discs Promote the Degradation of the Extracellular Matrix through Upregulation of the GATA3 Expression

Objective Disc calcification is strongly associated with disc degeneration;however,the underlying mechanisms driving its pathogenesis are poorly understood.This study aimed to provide a gene expression profile of nucleus pulposus cells(NPCs)from calcified discs,and clarify the potential mechanism in disc degeneration.Methods Primary NPCs were isolated from calcified and control discs(CAL-NPC and CON-NPC),respectively.The proliferation and extracellular matrix(ECM)metabolism capacities of the cells were evaluated using MTT and Western blotting,respectively.RNA sequencing was used to identify differentially expressed genes(DEGs)in the CAL-NPCs.The biological functions of the DEGs were analyzed using the Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)databases.The transcription factor database and Cytoscape software were used to construct the transcription factor-DEGs regulatory network.The role of the verified transcription factor in NPC proliferation and ECM metabolism was also investigated.Results The CAL-NPCs exhibited a lower proliferation rate and higher ECM degradation capacity than the CON-NPCs.In total,375 DEGs were identified in the CAL-NPCs.The GO and KEGG analyses showed that the DEGs were primarily involved in the regulation of ribonuclease activity and NF-kappa B and p53 signaling pathways.GATA-binding protein 3(GATA3)with the highest verified levels was selected for further studies.Overexpression of GATA3 in the CON-NPCs significantly inhibited their proliferation and promoted their ECM degradation function,while the knockdown of GATA3 in the CAL-NPCs resulted in the opposite phenotypes.Conclusion This study provided a comprehensive gene expression profile of the NPCs from the calcified discs and supported that GATA3 could be a potential target for reversing calcification-associated disc degeneration.

Differentiation of Mesenchymal Stem Cells into Nucleus Pulposus Cells In Vitro

To find a new source of seed cells for constructing tissue-engineered intervertebral disc, nucleus pulposus （NP） cells and mesenchymal stem cells （MSCs） were isolated from New Zealand white rabbits. The nucleus pulposus cells population was fluorescence-ladled and co-cultured with MSCs with or without direct contact. Morphological changes were observed every 12 h. Semi-quantitaive reverse transcriptase-polymerase chain reaction was performed to assess the expression levels of Sox-9, aggreacan and type Ⅱ collagen every 24 h after the co-culture. MSCs treated with direct contact rounded up and presented a ring-like appearance. The expression of marker genes was significantly increased when cells were co-cultured with direct contact for 24 h. No significant change was found after coculture without direct contact. Co-culture of NP cells and MSCs with direct contact is a reliable method for generating large amount of NP cells used for cell-based tissue engineering therapy.

Normal and Degenerated Rabbit Nucleus Pulposus Cells in in vitro Cultures: A Biological Comparison

This study examined the biological characteristics of normal and degenerated rabbit nucleus pulposus （NP） cells in vitro in order to provide seed cells for intervertebral disc （IVD） tissue engineering. A total of 8 adult New Zealand white rabbits underwent annulus puncture to establish models ofintervertebral disc degeneration （IDD）. Four weeks later, normal and degenerated NP cells were obtained. Cell morphology was observed by light and electron microscopy. Cell viability was measured by MTT assay. Cell cycle and expression of extracellular matrix （ECM）-related genes （aggrecan and type II col- lagen） were determined by using flow cytometry and RT-PCR respectively. The growth curve of normal NP cells showed that the cells at passage 4 tended to slowly grow on the fifth day of culture. The density of normal NP cells at passages 5 to 7 was significantly less than that of the first-passage cells 2 or 3 days after seeding （P〈0.05）. The degenerated NP cells at passage 3 showed slow growth at 4th day. After 5 passages, the degenerated NP cells assumed stagnant growth and the growth seemed to stop at passage 7. The MTT assay revealed that for both normal and degenerated NP cells, the absorbance （.4） value at passages 4-7 was obviously decreased as compared with that at passage 1 （P〈0.05）. Cell cycle analysis showed that the proportion of normal NP cells at G1 phase was 65.4%-3.5%, significantly lower than that of degenerated NP cells at the same cell cycle phase With the value being 77.6%-4.8%. The degen- erated NP cells were predominantly arrested at Gt phase and failed to enter S phase. The expression of type II collagen and aggrecan was significantly decreased with passaging. It was concluded that normal NP cells possessed good viability and proliferative capacity by the third passage, and they could secrete large amounts of ECM within this period. The normal NP cells may serve as seed cells for IVD tissue engineering.

CERVICAL STABILITY AFTER CUTTING-ASPIRATION OF NUCLEUS PULPOSUS

The effects of cutting-aspiration of nucleus pulposus on the momements of the cervical spine in flexion,extension and lateral bending with fresh cervical spine specimens were tested by means of contacting measement with the dial indicators when loaded with the electronic universal testing machine.The results showed:(1) Cutting-aspiration of nucleus pulposus only removed part of the nucleus pulposus,which was consistent with the clinical observation;(2)The ranges or motion(ROMs) of the operative segment had not increased in direction of flexion,extension and lateral bending after cutting-aspiration of nucleus pulposus:(3)After nucleotomy,the ROMs corresponding upon the operative segment apparently increased in flexion and extension,but had no change in lateral bending;(4)Hemilaminectomy of cervical spine which was an operation or partial removal of the ligamentum flavum and the lamina only had little afrection on the cervical stability. The biomechanical data can not only demonstrate the reliability of percutaneous dlscectomy,but also present a new enlightement for the clinical therapy of cervical disc herniation with spinal canal stenosis.

The role of transcriptional factor brachyury in the development and repair of nucleus pulposus

Transcription factor Brachyury,a protein containing 435 amino acids,has been widely investigated and reported in notochord differentiation and nucleus pulposus development.The crucial functions and underlying mechanisms by Brachyury are discussed in this paper,which suggests Brachyury can be developed into a potential novel target for the therapy of intervertebral disc degeneration.

An esterase-responsive ibuprofen nano-micelle pre-modified embryo derived nucleus pulposus progenitor cells promote the regeneration of intervertebral disc degeneration

Stem cell-based transplantation is a promising therapeutic approach for intervertebral disc degeneration(IDD).Current limitations of stem cells include with their insufficient cell source,poor proliferation capacity,low nucleus pulposus(NP)-specific differentiation potential,and inability to avoid pyroptosis caused by the acidic IDD microenvironment after transplantation.To address these challenges,embryo-derived long-term expandable nucleus pulposus progenitor cells(NPPCs)and esterase-responsive ibuprofen nano-micelles(PEG-PIB)were prepared for synergistic transplantation.In this study,we propose a biomaterial pre-modification cell strategy;the PEG-PIB were endocytosed to pre-modify the NPPCs with adaptability in harsh IDD microenvironment through inhibiting pyroptosis.The results indicated that the PEG-PIB pre-modified NPPCs exhibited inhibition of pyroptosis in vitro;their further synergistic transplantation yielded effective functional recovery,histological regeneration,and inhibition of pyroptosis during IDD regeneration.Herein,we offer a novel biomaterial pre-modification cell strategy for synergistic transplantation with promising therapeutic effects in IDD regeneration.

Transplantation of gene-modified nucleus pulposus cells reverses rabbit intervertebral disc degeneration

Background Intervertebral disc degeneration is the main cause of low back pain. The purpose of this study was to explore potential methods for reversing the degeneration of lumbar intervertebral discs by transplantation of gene-modified nucleus pulposus cells into rabbit degenerative lumbar intervertebral discs after transfecting rabbit nucleus pulposus cells with adeno-associated virus 2 （AAV2）-mediated connective tissue growth factor （CTGF） and tissue inhibitor of metalloproteinases 1 （TIMP1） genes in vitro. Methods Computer tomography （CT）-guided percutaneous annulus fibrosus injury was performed to build degenerative lumbar intervertebral disc models in 60 New Zealand white rabbits, rAAV2-CTGF-IRES-TIMPI-transfected rabbit nucleus pulposus cells were transplanted into degenerative lumbar intervertebral discs （transplantation group）, phosphate-buffered saline （PBS） was injected into degenerative lumbar intervertebral discs （degeneration control group） and normal lumbar intervertebral discs served as a blank control group. After 6, 10 and 14 weeks, the disc height index （DHI） and signal intensity in intervertebral discs were observed by X-ray and magnetic resonance imaging （MRI） analysis The expression of CTGF and TIMP1 in nucleus pulposus tissue was determined by Western blotting analysis, the synthesis efficiency of proteoglycan was determined by a 35S-sulfate incorporation assay, and the mRNA expression of type II collagen and proteoglycan was detected by RT-PCR. Results MRI confirmed that degenerative intervertebral discs appeared two weeks after percutaneous puncture. Transgenic nucleus pulposus cell transplantation could retard the rapid deterioration of the DHI. MRI indicated that degenerative intervertebral discs were relieved in the transplantation group compared with the degeneration control group. The expression of collagen II mRNA and proteoglycan mRNA was significantly higher in the transplantation group and the blank control group compared with the degeneration control group （P 〈0.05）. Conclusions CT-guided percutaneous puncture can successfully build rabbit degenerative intervertebral disc models. Both CTGF and TIMPl-transfected cell transplantation helps to maintain disc height, and promotes the biosynthesis of tvDe II collaQen and proteoalvcan in intervertebral discs, reversinq the de（：ieneration of intervertebral discs.

Autologous nucleus pulposus transplantation to lumbar 5 dorsal root ganglion after epineurium discission in rats： a modified model of non-compressive lumbar herniated intervertebral disc

Background Nucleus pulposus of intervertebral discs has proinflammatory characteristics that play a key role in neuropathic pain in lumbar herniated intervertebral disc. One of the most commonly used animal models （the traditional model） of non-compressive lumbar herniated intervertebral disc is created by L4-L5 hemilaminectomy and the application of autologous nucleus pulposus to cover the left L4 and L5 nerve roots in rats. However, such procedures have the disadvantages of excessive trauma and low success rate. We proposed a modified model of non-compressive lumbar herniated intervertebral disc in which only the left L5 dorsal root ganglion is exposed and transplanted with autologous nucleus pulposus following incision of epineurium. We aimed to compare the modified model with the traditional one with regard to trauma and success rate. Methods Thirty Sprague-Dawley male rats were randomized into three groups： sham operation group （n=6）, traditional group （n=12）, and modified group （n=12）. The amount of blood loss and operative time for each group were analyzed. The paw withdrawal threshold of the left hind limb to mechanical stimuli and paw withdrawal latency to heat stimuli were examined from the day before surgery to day 35 after surgery. Results Compared with the traditional group, the modified group had shorter operative time, smaller amount of blood loss, and higher success rate （91.7% versus 58.3%, P 〈0.05）. There was no decrease in paw withdrawal latency in any group. The sham operation group had no decrease in postoperative paw withdrawal threshold, whereas the modified and traditional groups had significant reduction in paw withdrawal threshold after surgery （mechanical hyperalgesia）. Conclusions Transplantation of nucleus pulposus onto the L5 dorsal root ganglion following incision of epineurium in rats established an improved animal model of non-compressive lumbar herniated intervertebral disc with less trauma and more stable pain ethology.

Evaluation of CD24 as a marker to rapidly define the mesenchymal stem cell phenotype and its differentiation in human nucleus pulposus

Background Recent studies have indicated that human nucleus pulposus contain mesenchymal stem cells （NP-MSCs）. However, the immunophenotypic variation of NP-MSCs in vitro was unclear. The present study was conducted to address the immunophenotypic variation of mesenchymal stem cells in nucleus pulposus under continuous proliferation in vitro and show the difference between mesenchymal stem cells and nucleus pulposus cell. Methods Tissue samples were obtained from thoracolumbar burst fracture patients and degenerative disc disease patients who underwent discectomy and fusion procedures. Flow cytometric and laser scanning confocal microscope （LSCM） were used to detect the variation of mesenchymal stem cells in nucleus pulposus which were expressing CD105 and CD24 in condition with or without transforming growth factor [31 （TGF-131）. Results More than 90% of the analyzed primary cells of mesenchymal stem cells in nucleus pulposus fulfilled the general immunophenotyping criteria for MSCs, such as CD44, CD105 and CD29, but the marker of mature NP cells characterized as CD24 was negative. In continuous cultures, the proportion of mesenchymal stem cells which were expressing CD44, CD105 and CD29 in nucleus pulposus gradually decreased. The mesenchymal stem cells in nucleus pulposus cells were positive for CD105 and CD29, with slight positivity for CD44. The CD24 expression gradually increased in proliferation. Bi- parametric flow cytometry and laser scanning confocal microscopy confirmed the presence of cells which were expressing CD105 and CD24 independently, and only a small part of cells expressed both CD105 and CD24 simultaneously. TGF-{31 could stimulate mesenchymal stem cells in nucleus pulposus to express CD24. Conclusions Non-degenerative and degenerative NP contains mesechymal stem cells. The variation of CD24 can be used as a marker to identify the NP-MSCs differentiation into NP-like cells.

Effects of degenerative autologous nucleus pulposus on the lumbar sympathetic trunk: Sympathetic inflammation in rats

Objective: We have reported the presence of discogenic visceral pain secondary to anterior herniation of the lumbar disc. The aim of this study was to observe the inflammatory response of the sympathetic trunk to an autologous degenerative nucleus pulposus(NP) injection under fluoroscopy. Methods: A total of 72 rats were used. In 24 rats,the autologous NP suspension was injected into the right sympathetic trunk. Next,food intake and body weight of each rat were monitored for 14 days. Fourteen days after the injection,the right lumbar sympathetic trunk was harvested for histological assessment,and protein levels of IL-1 β,IL-6,and TNF-α were quantified via ELISA. Results: In the NP-treated group,endoneural hyperemia and intensive infiltration of inflammatory cells could be identified in sections of the sympathetic trunk by the hematoxylin and eosin(H&E) stain. Meanwhile,elevated concentrations of IL-1 β,IL-6,and TNF-α were determined in the sympathetic trunk of the NP group as compared to that of the na?ve and control groups,which indicated the development of an inflammatory response. Furthermore,food intake and body weight of rats in the NP group decreased significantly. Conclusions: The results indicated that an inflammatory response in the sympathetic trunk can be caused by anterior herniation of the lumbar disc,which can generate a sympathetic inflammatory pain response.

How to enhance the ability of mesenchymal stem cells to alleviate intervertebral disc degeneration

Intervertebral disc(ID)degeneration(IDD)is one of the main causes of chronic low back pain,and degenerative lesions are usually caused by an imbalance between catabolic and anabolic processes in the ID.The environment in which the ID is located is harsh,with almost no vascular distribution within the disc,and the nutrient supply relies mainly on the diffusion of oxygen and nutrients from the blood vessels located under the endplate.The stability of its internal environment also plays an important role in preventing IDD.The main feature of disc degeneration is a decrease in the number of cells.Mesenchymal stem cells have been used in the treatment of disc lesions due to their ability to differentiate into nucleus pulposus cells in a nonspecific anti-inflammatory manner.The main purpose is to promote their regeneration.The current aim of stem cell therapy is to replace the aged and metamorphosed cells in the ID and to increase the content of the extracellular matrix.The treatment of disc degeneration with stem cells has achieved good efficacy,and the current challenge is how to improve this efficacy.Here,we reviewed current treatments for disc degeneration and summarize studies on stem cell vesicles,enhancement of therapeutic effects when stem cells are mixed with related substances,and improvements in the efficacy of stem cell therapy by adjuvants under adverse conditions.We reviewed the new approaches and ideas for stem cell treatment of disc degeneration in order to contribute to the development of new therapeutic approaches to meet current challenges.

Comparison of microendoscopic discectomy and open discectomy for single-segment lumbar disc herniation

BACKGROUND Lumbar disc herniation is a common disease.Endoscopic treatment may have more advantages than traditional surgery.AIM To compare the clinical efficacy and safety of microendoscopic discectomy(MED)and open discectomy with lamina nucleus enucleation in the treatment of singlesegment lumbar intervertebral disc herniation.METHODS Ninety-six patients who were operated at our hospital were selected for this study.Patients with single-segment lumbar disc herniation were admitted to the hospital from March 2018 to March 2019 and were randomly divided into the observation group and the control group with 48 cases in each group.The former group underwent lumbar discectomy and the latter underwent laparotomy and nucleus pulpectomy.Surgical effects were compared between the two groups.RESULTS In terms of surgical indicators,the observation group had a longer operation time,shorter postoperative bedtime and hospital stay,less intraoperative blood loss,and smaller incision length than the control group(P<0.05).The excellent recovery rate did not differ significantly between the observation group(93.75%)and the control group(91.67%).Visual analogue scale pain scores were significantly lower in the observation group than in the control group at 1 d,3 d,1 mo,and 6 mo after surgery(P<0.05).The incidence of complications was significantly lower in the observation group than in the control group(6.25%vs 22.92%,P<0.05).CONCLUSION Both MED and open discectomy can effectively improve single-segment lumbar disc herniation,but MED is associated with less trauma,less bleeding,and a lower incidence of complications.

A novel rat tail disc degeneration model induced by static bending and compression

Background:A new rat tail intervertebral disc degeneration model was established to observe the morphologic and biologic changes of static bending and compression applied to the discs.Methods:In total,20 Sprague-Dawley rats with similar weight were randomly di-vided into 4 groups.Group 1 served as a control group for a baseline assessment of normal discs.Group 2 underwent a sham surgery,using an external device to bend the vertebrae of coccygeal 8-10.Groups 3 and 4 were the loaded groups,and exter-nal devices were instrumented to bend the spine with a compression level of 1.8 N and 4.5 N,respectively.Magnetic resonance imaging(MRI),histological,and quanti-tative real-time PCR(qRT-PCR)analysis were performed on all animals on day 14 of the experiment.Results:Magnetic resonance imaging and histological results showed that the changes of intervertebral disc degeneration increased with the size of compression load.Some architecture disorganizations in nucleus pulposus and annulus fibro-sus were found on both of the convex and concave side in the groups of 1.8 N and 4.5 N.An upregulation of MM-3,MM-13,and collagen 1-α1 mRNA expression and a downregulation of collagen 2-α1 and aggrecan mRNA expression were observed in the sham and loading groups.Significant changes were found between the loading groups,whereas the sham group showed similar results to the control group.Conclusions:Static bending and compression could induce progressive disc degen-eration,which could be used for biologic study on disc degeneration promoted by static complex loading.

Specific Inhibitory Protein Dkk-1 Blocking Wnt/β-catenin Signaling Pathway Improve Protectives Effect on the Extracellular Matrix

The present study examined the role of Wnt/β-catenin signaling pathway in the degeneration of nucleus pulposus cells and the protective effect of DKK1 on nucleus pulposus cells. The model of nucleus pulposus cell degeneration was induced by intra-disc injection of TNF-α, and the expression of β-catenin protein was detected by Western blotting. The cultured rabbit nucleus pulposus cells were divided into 4 groups. In group A, the cells were cultured with normal medium and served as control group. In group B, the cells were cultured with TNF-α and acted as degeneration group. In group C, the cells were cultured with TNF-α and transfected with Adv-eGFP and was used as fluorescence control group. In group D, the cells were cultured with TNF-α and transfected with Adv-hDKK1-eGFP, serving as intervention group. The expression of typeⅡcollagen, proteoglycan, β-catenin, and MMP-13 in each group was detected by immunocytochemistry and RT-PCR. The result showed that TNF-α increased the expression of β-catenin and MMP-13, and significantly inhibited the synthesis of type Ⅱ collagen and proteoglycan, which resulted in the degeneration of nucleus pulposus cells. This effect could be obviously reversed by DKK1. We are led to concluded that TNF-α could activate the Wnt/β-catenin signaling pathway, and increase the expression of MMP-13, thereby resulting in disc degeneration. Specifically blocking Wnt/β-catenin signaling pathway by DKK-1 could protect the normal metabolism of intervertebral disc tissue. The Wnt pathway plays an important role in the progression of the intervertebral disc degeneration.

Barriers to mesenchymal stromal cells for low back pain

Intervertebral disc degeneration is the main cause of low back pain.In the past 20 years,the injection of mesenchymal stromal cells(MSCs)into the nucleus pulposus of the degenerative disc has become the main approach for the treatment of low back pain.Despite the progress made in this field,there are still many barriers to overcome.First,intervertebral disc is a highly complex loadbearing composite tissue composed of annulus fibrosus,nucleus pulposus and cartilaginous endplates.Any structural damage will change its overall biomechanical function,thereby causing progressive degeneration of the entire intervertebral disc.Therefore,MSC-based treatment strategies should not only target the degenerated nucleus pulposus but also include degenerated annulus fibrosus or cartilaginous endplates.Second,to date,there has been relatively little research on the basic biology of annulus fibrosus and cartilaginous endplates,although their pathological changes such as annular tears or fissures,Modic changes,or Schmorl's nodes are more commonly associated with low back pain.Given the high complexity of the structure and composition of the annulus fibrosus and cartilaginous endplates,it remains an open question whether any regeneration techniques are available to achieve their restorative regeneration.Finally,due to the harsh microenvironment of the degenerated intervertebral disc,the delivered MSCs die quickly.Taken together,current MSC-based regenerative medicine therapies to regenerate the entire disc complex by targeting the degenerated nucleus pulposus alone are unlikely to be successful.

The utilization of interventional therapy in recovery of cervical spondylopathy

Objective To assess the efficacy of percutaneous diskectomy (PCD) in recovery of cervical spondylopathy. Methods Review analysis 26 patients receiving PCD treatment,observing the improvement of cervical spondylopathy patients’ clinical symptoms.Results Success ratio of PCD is 100%,14 patients’ symptom disappear,10 patients’ symptom apparent alleviate and 2 patients’ symptom mild alleviate. Conclusion PCD is a kind of easy, safe and efficient method to treat cervical spondylopathy,it is very important to the recovery of cervical spondylopathy.

Nimbolide targeting SIRT1 mitigates intervertebral disc degeneration by reprogramming cholesterol metabolism and inhibiting inflammatory signaling

Inflammation,abnormal cholesterol metabolism,and macrophage infiltration are involved in the destruction of the extracellular matrix of the nucleus pulposus(NP),culminating in intervertebral disc degeneration(IDD).Whether nimbolide(Nim),a natural extract,can alleviate IDD is unclear.In this study,we demonstrated that Nim promotes cholesterol efflux and inhibits the activation of the nuclear factor kappa B(NF-κB)and mitogen-activated protein kinase(MAPK)signaling pathways by activating sirtuin 1(SIRT1)in nucleus pulposus cells(NPCs)during inflammation.Thus,Nim balanced matrix anabolism and catabolism of NPCs.However,the inhibition of SIRT1 significantly attenuated the effects of Nim.We also found that Nim promoted the expression of SIRT1 in RAW 264.7,which enhanced the proportion of M2 macrophages by facilitating cholesterol homeostasis reprogramming and impeded M1-like macrophages polarization by blocking the activation of inflammatory signaling.Based on these results,Nim can improve the microenvironment and facilitate matrix metabolism equilibrium in NPCs.Furthermore,in vivo treatment with Nim delayed IDD progression by boosting SIRT1 expression,modulating macrophage polarization and preserving the extracellular matrix.In conclusion,Nim may represent a novel therapeutic strategy for treating IDD.

腰椎间盘髓核退变的MRI研究(英文)

Objective The purpose of this study was to correlate T2 signal intensity values in nucleus pulposus of lumbar discs with patient age,gender and stage of nucleus pulposus degeneration.Methods Lumbar imaging findings of 422 cases subjects were retrospectively reviewed through T2 signal intensity values of nucleus pulposus evaluated based on the signal intensity values of MR T2-weighted mid-sagittal images of the lumbar spine,the t2 signal intensity values at all five lumbar levels (from L5-S1 to L1-L2) between male and female were used independent sample t-test and the Spearman correlation analysis.The age and grade of nucleus pulposus of disc degeneration and T2 signal intensity values were estimated by calculating and Chi-square test and the Spearman correlation analysis.The t-test was used to correlate the different anatomic levels of disc degeneration;T2 signal intensity values among the five different anatomic levels using non-parametric correlation analysis.Results There were significantly differences in T2 signal intensity values of nucleus pulposus at the same grade and anatomic level between male and female.Advanced with age,T2 signal intensity values of nucleus pulposus decreased and stage of disc degeneration increased accordingly.T2 signal intensity values may represent the nucleus pulposus degeneration of interverterbral disc.L4-L5 was the highest incidence among the nucleus pulposus degeneration of intervertebral disc.Conclusions The T2 signal intensity values based approach may be a feasible and practical tool to determine nucleus pulposus degeneration.T2 signal intensity values of nucleus pulposus of lumbar intervertebral disc are correlated with grade of degeneration and patient age.

AAV6 as an effective gene delivery vector for prolonged transgene expression in intervertebral disc cells in vivo

Intervertebral disc degeneration is the main contributor to low back pain,now the leading cause of disability worldwide.Gene transfer,either in a therapeutic attempt or in basic research to understand the mechanisms of disc degeneration,is a fascinating and promising tool to manipulate the complex physiology of the disc.Viral vectors based on the adeno-associated virus(AAV)have emerged as powerful transgene delivery vehicles yet a systematic investigation into their respective tropism,transduction efficiency,and relative toxicity have not yet been performed in the disc in vivo.Herein,we used in vivo bioluminescence imaging to systematically compare multiple AAV serotypes,injection volumes,titers,promoters,and luciferase reporters to determine which result in high transduction efficiency of murine nucleus pulposus(NP)cells in vivo.We find that AAV6 using a CAG promoter to drive transgene expression,delivered into the NP of murine caudal discs at a titer of 1011 GC/mL,provides excellent transduction efficiency/kinetics and low toxicity in vivo.We also show,for the first time,that the transduction of NP cells can be significantly boosted in vivo by the use of small cell permeabilization peptides.Finally,to our knowledge,we are the first to demonstrate the use of optical tissue clearing and three-dimensional lightsheet microscopy in the disc,which was used to visualize fine details of tissue and cell architecture in whole intact discs following AAV6 delivery.Taken together,these data will contribute to the success of using AAV-mediated gene delivery for basic and translational studies of the IVD.