Nucleus pulposus cellular longevity by telomerase gene therapy

Cellular Senescence in Intervertebral Disc Aging and Degeneration: Molecular Mechanisms and Potential Therapeutic Opportunities

Closely associated with aging and age-related disorders, cellular senescence (CS) is the inability of cells to proliferate due to accumulated unrepaired cellular damage and irreversible cell cycle arrest. Senescent cells are characterized by their senescence-associated secretory phenotype that overproduces inflammatory and catabolic factors that hamper normal tissue homeostasis. Chronic accumulation of senescent cells is thought to be associated with intervertebral disc degeneration (IDD) in an aging population. This IDD is one of the largest age-dependent chronic disorders, often associated with neurological dysfunctions such as, low back pain, radiculopathy, and myelopathy. Senescent cells (SnCs) increase in number in the aged, degenerated discs, and have a causative role in driving age-related IDD. This review summarizes current evidence supporting the role of CS on onset and progression of age-related IDD. The discussion includes molecular pathways involved in CS such as p53-p21CIP1, p16INK4a, NF-κB, and MAPK, and the potential therapeutic value of targeting these pathways. We propose several mechanisms of CS in IDD including mechanical stress, oxidative stress, genotoxic stress, nutritional deprivation, and inflammatory stress. There are still large knowledge gaps in disc CS research, an understanding of which will provide opportunities to develop therapeutic interventions to treat age-related IDD.

Cycloastragenol and Astragaloside IV activate telomerase and protect nucleus pulposus cells against high glucose-induced senescence and apoptosis

In diabetes-induced intervertebral disc degeneration (Db-IVDD), senescence and apoptosis of nucleus pulposus cells (NPCs) are major contributing factors. Telomere attrition and telomerase downregulation are some of the main reasons for senescence and eventual apoptosis. The derivatives of the Chinese herb Astragalus membranaceus, Cycloastragenol (CAG) and Astragaloside IV (AG-IV), are reportedly effective telomerase activators against telomere shortening; however, their effect in Db-IVDD have not been explored. The present study simultaneously investigated the regulation of these derivatives on senescence, apoptosis, telomeres and telomerase a model of high-glucose (HG)-induced stress using rat primary NPCs. The NPCs were stimulated with HG (50 mM) to evoke HG-induced stress, and the effects of CAG and AG-IV were observed on: i) The expression level of senescence marker p16; ii) β-Gal staining; iii) the expression levels of apoptosis markers cleaved-caspase 3 (c-C3), BAX and Bcl-2; iv) telomerase activation with telomerase reverse transcriptase (TERT) mRNA and protein expression, while telomere length was measured with reverse transcription-quantitative PCR. Cell proliferation was determined using the Cell Counting Kit-8 assay. Results demonstrated an upregulation in the expression levels of p16, c-C3 and BAX, and increased β-Gal staining; while the expression level of Bcl-2 was downregulated in a concentration-dependent manner. Pre-treatment of the NPCs with CAG and AG-IV downregulated the protein expression levels of p16, c-C3 and BAX, and decreased the percentage of β-Gal and FITC staining; while upregulating the Bcl-2 expression. These effects protected the cells from HG stress-induced senescence and apoptosis. HG also downregulated the expression profile of TERT and shortened the telomere length in a glucose concentration-dependent manner. While pretreatment with CAG and AG-IV upregulated TERT expression and ameliorated the telomere attrition. CAG and AG-IV also increased cell proliferation and improved cell morphology in HG conditions. Overall, these findings indicated that CAG and AG-IV suppressed HG stress-induced senescence and apoptosis, in addition to enhancing telomerase activation and lengthening of the Telomere. Therefore, CAG and AG-IV prolonged the replicative capability and longevity of the NPCs and they have the potential to be therapeutic agents in Db-IVDD.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

Drug delivery in intervertebral disc degeneration and osteoarthritis: Selecting the optimal platform for the delivery of disease-modifying agents

Osteoarthritis (OA) and intervertebral disc degeneration (IVDD) as major cause of chronic low back pain represent the most common degenerative joint pathologies and are leading causes of pain and disability in adults. Articular cartilage (AC) and intervertebral discs are cartilaginous tissues with a similar biochemical composition and pathophysiological aspects of degeneration. Although treatments directed at reversing these conditions are yet to be developed, many promising disease-modifying drug candidates are currently under investigation. Given the localized nature of these chronic diseases, drug delivery systems have the potential to enhance therapeutic outcomes by providing controlled and targeted release of bioactives, minimizing the number of injections needed and increasing drug concentration in the affected areas. This review provides a comprehensive overview of the currently most promising disease-modifying drugs as well as potential drug delivery systems for OA and IVDD therapy.

A Review of Gene Therapy Delivery Systems for Intervertebral Disc Degeneration

Background: :

Intervertebral Disc (IVD) degeneration is a major public health concern, and gene therapy seems a promising approach to delay or even reverse IVD degeneration. However, the delivery system used to transfer exogenous genes into intervertebral disc cells remains a challenge.

Methods::

The MEDLINE, Web of Science, and Scopus databases were searched for English-language articles related to gene therapy for IVD degeneration articles from 1999 to May 2019. The keywords included “gene therapy” AND “intervertebral disc”. The history of the development of different delivery systems was analysed, and the latest developments in viral and non-viral vectors for IVD degeneration treatment were reviewed.

Results: :

Gene therapy delivery systems for IVD degeneration are divided into two broad categories: viral and non-viral vectors. The most commonly used viral vectors are adenovirus, adeno-associated virus (AAV), and lentivirus. Enthusiasm for the use of adenovirus vectors has gradually declined and has been replaced by a preference for lentivirus and AAV vectors. New technologies, such as RNAi and CRISPR, have further enhanced the advantage of viral vectors. Liposomes are the classic non-viral vector, and their successors, polyplex micelles and exosomes, have more potential for use in gene therapy for IVD degeneration.

Conclusion::

Lentivirus and AAV are the conventional viral vectors used in gene therapy for IVD degeneration, and the new technologies RNAi and CRISPR have further enhanced their advantages. Nonviral vectors, such as polyplex micelles and exosomes, are promising gene therapy vectors for IVD degeneration.

A novel magnetic resonance imaging postprocessing technique for the assessment of intervertebral disc degeneration-Correlation with histological grading in a rabbit disc degeneration model

INTRODUCTION

Estimation of intervertebral disc degeneration on magnetic resonance imaging (MRI) is challenging. Qualitative schemes used in clinical practice correlate poorly with pain and quantitative techniques have not entered widespread clinical use.

METHODS

As part of a prior study, 25 New Zealand white rabbits underwent annular puncture to induce disc degeneration in 50 noncontiguous lumbar discs. At 16 weeks, the animals underwent multi-echo T2 MRI scanning and were euthanized. The discs were stained and examined histologically. Quantitative T2 relaxation maps were prepared using the nonlinear least squares method. Decay Variance maps were created using a novel technique of aggregating the deviation in the intensity of each echo signal from the expected intensity based on the previous rate of decay.

RESULTS

Decay Variance maps showed a clear and well demarcated nucleus pulposus with a consistent rate of decay (low Decay Variance) in healthy discs that showed progressively more variable decay (higher Decay Variance) with increasing degeneration. Decay Variance maps required significantly less time to generate (1.0 ± 0.0 second) compared with traditional T2 relaxometry maps (5 (±0.9) to 1788.9 (±116) seconds). Histology scores correlated strongly with Decay Variance scores (r = 0.82, P < .01) and weakly with T2 signal intensity (r = 0.32, P < .01) and quantitative T2 relaxometry (r = 0.39, P < .01). Decay Variance had superior sensitivity and specificity for the detection of degenerate discs when compared to T2 signal intensity or Quantitative T2 mapping.

CONCLUSION

Our results show that using a multi-echo T2 MRI sequence, Decay Variance can quantitatively assess disc degeneration more accurately and with less image-processing time than quantitative T2 relaxometry in a rabbit disc puncture model. The technique is a viable candidate for quantitative assessment of disc degeneration on MRI scans. Further validation on human subjects is needed.

Telomere Gene Therapy: Polarizing Therapeutic Goals for Treatment of Various Diseases

Modulation of telomerase maintenance by gene therapy must meet two polarizing requirements to achieve different therapeutic outcomes: Anti-aging/regenerative applications require upregulation, while anticancer applications necessitate suppression of various genes integral to telomere maintenance (e.g., telomerase, telomerase RNA components, and shelterin complex). Patients suffering from aging-associated illnesses often exhibit telomere attrition, which promotes chromosomal instability and cellular senescence, thus requiring the transfer of telomere maintenance-related genes to improve patient outcomes. However, reactivation and overexpression of telomerase are observed in 85% of cancer patients; this process is integral to cancer immortality. Thus, telomere-associated genes in the scope of cancer gene therapy must be inactivated or inhibited to induce anticancer effects. These contradicting requirements for achieving different therapeutic outcomes mean that any vector-mediated upregulation of telomere-associated genes must be accompanied by rigorous evaluation of potential oncogenesis. Thus, this review aims to discuss how telomere-associated genes are being targeted or utilized in various gene therapy applications and provides some insight into currently available safety hazard assessments.

Bone morphogenetic protein-7 retards cell subculture-induced senescence of human nucleus pulposus cells through activating the PI3K/Akt pathway

Background: Allogeneic disc cell is the main cellular resource in tissue engineering (TE)-based strategy to retard disc degeneration. However, the accessible disc cells often exhibit senescent phenotype when they are subcultured in vitro. Hence, alleviating senescence of human disc cells during cell subculture is important for TE-based strategy to regenerate degenerative disc tissue. Objective: The present study was aimed to investigate whether bone morphogenetic protein-7 (BMP-7) can alleviate subculture-induced senescence of human nucleus pulposus (NP) cells in vitro. Methods: NP cells from human disc tissue were subcultured in vitro for six passages. Exogenous BMP-7 was added along with the culture medium to investigate its effects on senescence of NP cells. The inhibitor LY294002 was used to investigate the role of the PI3K/Akt pathway. Results: Compared with the human disc NP cells cultured in the baseline culture medium, addition of BMP-7 increased cell proliferation potency and telomerase activity, decreased senescence-associated β-galactosidase (SA-β-Gal) activity and G₀/G₁ phase fraction, and down-regulated the expression of p16 and p53. Moreover, these positive effects of BMP-7 against senescence of human disc NP cells coincided with activation of the PI3K/Akt pathway. Further analysis showed that inhibitor LY294002 partly inhibited these protective effects of BMP-7 against senescence of human disc NP cells. Conclusion: BMP-7 alleviates subculture-induced senescence of human disc NP cells through activating the PI3K/Akt pathway. The present study provides new knowledge on allogeneic disc NP cell-based TE strategy to regenerate degenerative human disc tissue.

Effects of human parathyroid hormone 1-34 on bone loss and lumbar intervertebral disc degeneration in ovariectomized rats

PURPOSE

Lumbar intervertebral disc degeneration is a common cause of lower back pain that affects the physical and mental health of patients and increases social burden. Parathyroid hormone has been reported to be effective at inhibiting disc degeneration; however, these effects have not been fully established in vivo in ovariectomized (OVX) rats. Thus, in this study, we aimed to address this issue and examine the effects of parathyroid hormone treatment in OVX rats.

METHODS

Thirty female Sprague-Dawley rats, three months-old, were subjected to sham or ovariectomy surgery. Twelve weeks postsurgery, OVX rats were treated with either human parathyroid hormone [hPTH(1-34), 30 μg/kg/day] or vehicle (normal saline (NS)) treatment. The L3-6 spinal segments were harvested after 12 weeks treatment. Bone mineral density (BMD), micro-architectural parameters, and biomechanical assessment were measured at the lumbar vertebral bodies. Histology and immunohistochemistry were performed to analyze the characteristics of the lumbar intervertebral discs.

RESULTS

OVX + PTH rats had significantly higher BMD, percentage bone volume density, trabecular thickness, and biomechanical strength compared with those in Sham and OVX + NS rats. Histology and immunostaining revealed that disc degeneration was not significantly different between the OVX + NS rats and the OVX + PTH rats, compared with the Sham group; the structure of nucleus pulposus was disordered, the expression of collagen I was increased, and collagen II and aggrecan were decreased.

CONCLUSIONS

These findings confirmed that hPTH(1-34) treatment has substantial anabolic effects on bone mass and trabecular micro-architecture, while the excessively enhanced bone mass and strength were coupled with a non-significant effect on the disc degeneration in ovariectomized rats.

Sirt6 overexpression suppresses senescence and apoptosis of nucleus pulposus cells by inducing autophagy in a model of intervertebral disc degeneration

Treatment of intervertebral disc degeneration (IDD) seeks to prevent senescence and death of nucleus pulposus (NP) cells. Previous studies have shown that sirt6 exerts potent anti-senescent and anti-apoptotic effects in models of age-related degenerative disease. However, it is not known whether sirt6 protects against IDD. Here, we explored whether sirt6 influenced IDD. The sirt6 level was reduced in senescent human NP cells. Sirt6 overexpression protected against apoptosis and both replicative and stress-induced premature senescence. Sirt6 also activated NP cell autophagy both in vivo and in vitro. 3-methyladenine (3-MA) and chloroquine (CQ)-mediated inhibition of autophagy partially reversed the anti-senescent and anti-apoptotic effects of sirt6, which regulated the expression of degeneration-associated proteins. In vivo, sirt6 overexpression attenuated IDD. Together, the data showed that sirt6 attenuated cell senescence, and reduced apoptosis, by triggering autophagy that ultimately ameliorated IDD. Thus, sirt6 may be a novel therapeutic target for IDD treatment.

[Construction of human mucosa oral epithelial cell lines overexpressing telomerase reverse transcriptase gene mediated by lentivirus]

OBJECTIVE

To construct a cell line of oral mucosa epithelial cells that stably express human telomerase reverse transcriptase (hTERT) by lentiviral vectors, approaches for the establishment of stable and efficient immortalized oral mucosa epithelial cell lines were explored.

METHODS

Whole RNA was extracted from 293T cells. The hTERT gene was amplified by polymerase chain reaction (PCR) and cloned into the lentiviral vector as pLVX-puro-hTERT. The lentivirus particles were successfully packaged and used to infect primary oral epithelial cells. The positive cell clones were selected by puromycin. Finally, the expression of hTERT was examined by real-time fluorescent quantitative PCR (qRT-PCR) and Western blot analysis.

RESULTS

The sequencing results confirmed the construction of the recombinant lentivirus pLVX-puro-hTERT. The morphology of infected cells was similar to that of normal oral mucosal epithelial cells, with a cobble stone-like appearance. The qRT-PCR and Western blot results showed that hTERT was overexpressed in infected cells compared with the normal group (P<0.05).

CONCLUSIONS

The oral epithelial cell line with stable expression of hTERT was successfully established by the lentivirus, which provides an experimental basis for the establishment of a highly efficient and stable oral epithelial immortalized cell line.

Disc cell senescence in intervertebral disc degeneration: Causes and molecular pathways

The accumulation of senescent disc cells in degenerative intervertebral disc (IVD) suggests the detrimental roles of cell senescence in the pathogenesis of intervertebral disc degeneration (IDD). Disc cell senescence decreased the number of functional cells in IVD. Moreover, the senescent disc cells were supposed to accelerate the process of IDD via their aberrant paracrine effects by which senescent cells cause the senescence of neighboring cells and enhance the matrix catabolism and inflammation in IVD. Thus, anti-senescence has been proposed as a novel therapeutic target for IDD. However, the development of anti-senescence therapy is based on our understanding of the molecular mechanism of disc cell senescence. In this review, we focused on the molecular mechanism of disc cell senescence, including the causes and various molecular pathways. We found that, during the process of IDD, age-related damages together with degenerative external stimuli activated both p53-p21-Rb and p16-Rb pathways to induce disc cell senescence. Meanwhile, disc cell senescence was regulated by multiple signaling pathways, suggesting the complex regulating network of disc cell senescence. To understand the mechanism of disc cell senescence better contributes to developing the anti-senescence-based therapies for IDD.

Effects of age, replicative lifespan and growth rate of human nucleus pulposus cells on selecting age range for cell-based biological therapies for degenerative disc diseases

Autologous disc cell implantation, growth factors and gene therapy appear to be promising therapies for disc regeneration. Unfortunately, the replicative lifespan and growth kinetics of human nucleus pulposus (NP) cells related to host age are unclear. We investigated the potential relations among age, replicative lifespan and growth rate of NP cells, and determined the age range that is suitable for cell-based biological therapies for degenerative disc diseases. We used NP tissues classified by decade into five age groups: 30s, 40s, 50s, 60s and 70s. The mean cumulative population doubling level (PDL) and population doubling rate (PDR) of NP cells were assessed by decade. We also investigated correlations between cumulative PDL and age, and between PDR and age. The mean cumulative PDL and PDR decreased significantly in patients in their 60s. The mean cumulative PDL and PDR in the younger groups (30s, 40s and 50s) were significantly higher than those in the older groups (60s and 70s). There also were significant negative correlations between cumulative PDL and age, and between PDR and age. We found that the replicative lifespan and growth rate of human NP cells decreased with age. The replicative potential of NP cells decreased significantly in patients 60 years old and older. Young individuals less than 60 years old may be suitable candidates for NP cell-based biological therapies for treating degenerative disc diseases.

Aging and age related stresses: a senescence mechanism of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a complicated process that involves both age-related change and tissue damage caused by multiple stresses. In a degenerative IVD, cellular senescence accumulates and is associated with reduced proliferation, compromised self-repair, increased inflammatory response, and enhanced catabolic metabolism. In this review, we decipher the senescence mechanism of IVD degeneration (IVDD) by interpreting how aging coordinates with age-related, microenvironment-derived stresses in promoting disc cell senescence and accelerating IVDD. After chronic and prolonged replication, cell senescence may occur as a natural part of the disc aging process, but can potentially be accelerated by growth factor deficiency, oxidative accumulation, and inflammatory irritation. While acute disc injury, excessive mechanical overloading, diabetes, and chronic tobacco smoking contribute to the amplification of senescence-inducing stresses, the avascular nature of IVD impairs the immune-clearance of the senescent disc cells, which accumulate in cell clusters, demonstrate inflammatory and catabolic phenotypes, deteriorate disc microenvironment, and accelerate IVDD. Anti-senescence strategies, including telomerase transduction, supply of growth factors, and blocking cell cycle inhibitors, have been shown to be feasible in rescuing disc cells from early senescence, but their efficiency for disc regeneration requires more in vivo validations. Guidelines dedicated to avoiding or alleviating senescence-inducing stresses might decelerate cellular senescence and benefit patients with IVD degenerative diseases.

Relationship between Initial Telomere Length, Initial Telomerase Activity, Age, and Replicative Capacity of Nucleus Pulposus Chondrocytes in Human Intervertebral Discs: What Is a Predictor of Replicative Potential?

There is evidence that telomere length (TL), telomerase activity (TA), and age are related to the replicative potential of human nucleus pulposus chondrocytes (NPCs). However, it has not yet been established if any of these factors can serve as predictors of the replicative potential of NPCs. To establish predictors of the replicative potential of NPCs, we evaluated potential relationships between replicative capacity of NPCs, initial TL (telomere length at the first passage), initial TA (telomerase activity at the first passage), and age. Nucleus pulposus specimens were obtained from 14 patients of various ages undergoing discectomy. NPCs were serially cultivated until the end of their replicative lifespans. Relationships among cumulative population doubling level (PDL), initial TL, initial TA, and age were analyzed. Initial TA was negatively correlated with age (r = -0.674, P = 0.008). However, no correlation between initial TL and age was observed. Cumulative PDL was also negatively correlated with age (r = -0.585, P = 0.028). Although the cumulative PDL appeared to increase with initial TL or initial TA, this trend was not statistically significant. In conclusion, age is the sole predictor of the replicative potential of human NPCs, and replicative potential decreases with age. Initial TL and initial TA are not predictors of replicative potential, and can serve only as reference values.

Expression and significance of telomerase in the nucleus pulposus tissues of degenerative lumbar discs

The pathogenesis of lumbar disc degeneration is extremely complex, and the expression and role of telomerase in degenerative lumbar disc tissues remains unclear. The aim of the present study was to detect telomerase expression in nucleus pulposus tissues of degenerative lumbar discs and to explore the correlation between telomerase expression and other factors typical of disc degeneration. A total of 8 patients with degenerative nucleus pulposus were included as the experimental group and compared with 8 control patients without evident lumbar disc degeneration. The expression of telomerase in nucleus pulposus tissues was detected by immunohistochemical staining. ELISA was performed to determine the differential expression of telomerase, type II collagen and chondroitin sulfate between the two groups. In addition, a correlation analysis was performed to form associations between these factors. Finally, 5 cases in the experimental group and 5 in the control group were involved in the analysis. Immunohistochemistry results showed that telomerase expression in the experimental group was significantly lower compared to the control group and the percentage in the unit field of view showed significant differences between the two groups (P<0.05). Similarly, the ELISA test results showed lower expression levels of telomerase, type II collagen and chondroitin sulfate in the experimental group when compared with the control group (P<0.05). The correlation analysis revealed that telomerase was positively correlated with type II collagen and chondroitin sulfate (correlation coefficients, 0.673 and 0.528, respectively; P<0.01). In conclusion, telomerase is involved in the degeneration process of nucleus pulposus tissue in lumbar discs and has a positive correlation with other factors typically associated with degeneration.

Delivery systems for the treatment of degenerated intervertebral discs

The intervertebral disc (IVD) is the most avascular and acellular tissue in the body and therefore prone to degeneration. During IVD degeneration, the balance between anabolic and catabolic processes in the disc is deregulated, amongst others leading to alteration of extracellular matrix production, abnormal enzyme activities and production of pro-inflammatory substances like cytokines. The established treatment strategy for IVD degeneration consists of physiotherapy, pain medication by drug therapy and if necessary surgery. This approach, however, has shown limited success. Alternative strategies to increase and prolong the effects of bioactive agents and to reverse the process of IVD degeneration include the use of delivery systems for drugs, proteins, cells and genes. In view of the specific anatomy and physiology of the IVD and depending on the strategy of the therapy, different delivery systems have been developed which are reviewed in this article.

The inhibitory effect of salmon calcitonin on intervertebral disc degeneration in an ovariectomized rat model

PURPOSE

Intervertebral disc degeneration related to postmenopausal osteoporosis is an important issue in spinal disorder research. This study aimed to investigate the effects of salmon calcitonin (sCT), as an antiresorptive medication, on lumbar intervertebral disc degeneration using a rat ovariectomy (OVX) model.

METHODS

Thirty 3-month-old female Sprague-Dawley rats were randomly divided into three groups: the sham-operated (Sham) group and two ovariectomized groups treated with vehicle (OVX+V) or sCT (OVX+CT; 16 IU/kg, sc) on alternate days for 6 months. Treatment began after OVX and continued for 6 months. At the end of the experiment, bone mineral density (BMD), micro-CT analysis, biomechanical testing, histology, and immunohistochemistry were performed for all groups.

RESULTS

Salmon calcitonin significantly maintained vertebrae BMD, percent bone volume, and biomechanical strength, when compared with the OVX+V group. The changes of mucoid degeneration in the nucleus pulposus and calcification in the middle cartilage endplate were more moderate in the OVX+CT group compared with the OVX+V group, and immunohistochemistry revealed a significant increase in aggrecan and type II collagen expressions, but marked reductions in matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13 expressions in the OVX+CT group.

CONCLUSIONS

Salmon calcitonin treatment was effective in delaying the process of the disc degeneration in OVX rats. The underlying mechanisms may be related to preservation of structural integrity and function of vertebrae, and affecting extracellular matrix metabolism by modulating the expressions of MMPs, aggrecan and type II collagen to protect the disc from degeneration.

Quantitative T2 magnetic resonance imaging compared to morphological grading of the early cervical intervertebral disc degeneration: an evaluation approach in asymptomatic young adults

Objective

The objective of this study was to evaluate the efficacy of quantitative T2 magnetic resonance imaging (MRI) for quantifying early cervical intervertebral disc (IVD) degeneration in asymptomatic young adults by correlating the T2 value with Pfirrmann grade, sex, and anatomic level.

Methods

Seventy asymptomatic young subjects (34 men and 36 women; mean age, 22.80±2.11 yr; range, 18–25 years) underwent 3.0-T MRI to obtain morphological data (one T1-fast spin echo (FSE) and three-plane T2-FSE, used to assign a Pfirrmann grade (I–V)) and for T2 mapping (multi-echo spin echo). T2 values in the nucleus pulposus (NP, n = 350) and anulus fibrosus (AF, n = 700) were obtained. Differences in T2 values between sexes and anatomic level were evaluated, and linear correlation analysis of T2 values versus degenerative grade was conducted.

Findings

Cervical IVDs of healthy young adults were commonly determined to be at Pfirrmann grades I and II. T2 values of NPs were significantly higher than those of AF at all anatomic levels (P<0.000). The NP, anterior AF and posterior AF values did not differ significantly between genders at the same anatomic level (P>0.05). T2 values decreased linearly with degenerative grade. Linear correlation analysis revealed a strong negative association between the Pfirrmann grade and the T2 values of the NP (P = 0.000) but not the T2 values of the AF (P = 0.854). However, non-degenerated discs (Pfirrmann grades I and II) showed a wide range of T2 relaxation time. T2 values according to disc degeneration level classification were as follows: grade I (>62.03 ms), grade II (54.60–62.03 ms), grade III (<54.60 ms).

Conclusions

T2 quantitation provides a more sensitive and robust approach for detecting and characterizing the early stage of cervical IVD degeneration and to create a reliable quantitative in healthy young adults.

Prolonged expansion of human nucleus pulposus cells expressing human telomerase reverse transcriptase mediated by lentiviral vector

Human degenerative disc disease (DDD) is characterized by progressive loss of human nucleus pulposus (HNP) cells and extracellular matrix, in which the massive deposition are secreted by HNP cells. Cell therapy to supplement HNP cells to degenerated discs has been thought to be a promising strategy to treat DDD. However, obtaining a large quality of fully functional HNP cells has been severely hampered by limited proliferation capacity of HNP cells in vitro. Previous studies have used lipofectamine or recombinant adeno-associated viral (rAAV) vectors to deliver human telomerase reverse transcriptase (hTERT) into ovine or HNP cells to prolong the activity of nucleus pulposus cells with limited success. Here we developed a lentiviral vector bearing both hTERT and a gene encoding green fluorescence protein (L-hTERT/EGFP). This vector efficiently mediated both hTERT and EGFP into freshly isolated HNP cells. The expressions of both transgenes in L-hTERT/EGFP transduced HNP cells were detected up to day 210 post viral infection, which was twice as long as rAAV vector did. Furthermore, we observed restored telomerase activity, maintained telomere length, delayed cell senescence, and increased cell proliferation rate in those L-hTERT/EGFP transduced HNP cells. Our study suggests that lentiviral vector might be a useful gene delivery vehicle for HNP cell therapy to treat DDD.

Biocompatibility, biodegradability, and drug carrier ability of hybrid collagen-based hydrogel nanocomposites

The biocompatibility, biodegradability, and drug carrier capacity of new types of hybrid hydrogels were evaluated for potential medical applications. The effects of swelling and deswelling of the hybrid hydrogels on drug loading and release capacity were evaluated. The hybrid hydrogels with Dellite® 67G and Cloisite® 93A had superior collagenase resistance compared to hydrogels without the inorganic nanoparticles. The effect of the hybrid hydrogels on the immune response parameters was followed by evaluating the chronic inflammation in rats. These hybrid hydrogels have the potential for medical and pharmaceutical applications as well as for scaffolds production in the reconstruction and regeneration of burned tissues with control of inflammatory processes.

Global identification of genes related to nutrient deficiency in intervertebral disc cells in an experimental nutrient deprivation model

Background

Intervertebral disc degeneration is a significant cause of degenerative spinal diseases. Nucleus pulposus (NP) cells reportedly fail to survive in large degenerated discs with limited nutrient availability. Therefore, understanding the regulatory mechanism of the molecular response of NP cells to nutrient deprivation may reveal a new strategy to treat disc degeneration. This study aimed to identify genes related to nutrient deprivation in NP cells on a global scale in an experimental nutrient deprivation model.

Methodology/Principal Findings

Rat NP cells were subjected to serum starvation. Global gene expression was profiled by microarray analysis. Confirmation of the selected genes was obtained by real-time polymerase chain reaction array analysis. Western blotting was used to confirm the expression of selected genes. Functional interactions between p21^Cip1 and caspase 3 were examined. Finally, flow cytometric analyses of NP cells were performed. Microarray analysis revealed 2922 differentially expressed probe sets with ≥1.5-fold changes in expression. Serum starvation of NP cells significantly affected the expression of several genes involved in DNA damage checkpoints of the cell cycle, including Atm, Brca1, Cdc25, Gadd45, Hus1, Ppm1D, Rad 9, Tp53, and Cyclin D1. Both p27^Kip1 and p53 protein expression was upregulated in serum-starved cells. p21^Cip1 expression remained in NP cells transfected with short interfering RNA targeting caspase 3 (caspase 3 siRNA). Both G1 arrest and apoptosis induced by serum starvation were inhibited in cells transfected with caspase 3 siRNA.

Conclusions/Significance

Nutrient deprivation in NP cells results in the activation of a signaling response including DNA damage checkpoint genes regulating the cell cycle. These results provide novel possibilities to improve the success of intervertebral disc regenerative techniques.

Nucleic acid therapy for lifespan prolongation: present and future

Lifespan prolongation is a common desire of the human race. With advances in biotechnology, the mechanism of aging has been gradually unraveled, laying the theoretical basis of nucleic acid therapy for lifespan prolongation. Regretfully, clinically applicable interventions do not exist without the efforts of converting theory into action, and it is the latter that has been far from adequately addressed at the moment. This was demonstrated by a database search on PubMed and Web of Science, from which only seven studies published between 2000 and 2010 were found to directly touch on the development of nucleic acid therapy for anti-aging and/or longevity enhancing purposes. In light of this, the objective of this article is to overview the current understanding of the intimate association between genes and longevity, and to bring the prospect of nucleic acid therapy for lifespan prolongation to light.

Caspase 3 as a therapeutic target for regulation of intervertebral disc degeneration in rabbits

OBJECTIVE

Although the etiology of intervertebral disc degeneration is poorly understood, one possible approach for its regulation is apoptosis inhibition. This study was undertaken to investigate the antiapoptotic effects of caspase 3 in intervertebral disc degeneration in rabbits.

METHODS

We investigated the effects of caspase 3 small interfering RNA (siRNA) on rabbit nucleus pulposus cells in a serum-starved medium. The effects of direct injection of Alexa Fluor 555-labeled caspase 3 siRNA into the intervertebral disc were also determined in vivo using the rabbit anular needle puncture model.

RESULTS

Rabbit nucleus pulposus cells transfected with caspase 3 siRNA showed a significant decrease in serum-starved apoptotic cells. After local injection of caspase 3 siRNA into intervertebral discs, red fluorescence was observed in the nucleus pulposus upon treatment with Alexa Fluor 555-labeled caspase 3 siRNA. Caspase 3 messenger RNA and protein were down-regulated in the caspase 3 siRNA group. Magnetic resonance imaging and histologic evaluation showed that degenerative changes were significantly suppressed in the caspase 3 siRNA group 4 and 8 weeks after injection. Quantification of TUNEL staining showed that the caspase 3 siRNA group had significantly fewer apoptotic nucleus pulposus cells than the control siRNA group.

CONCLUSION

Our findings indicate that caspase 3 knockdown in rabbit intervertebral disc cells is effective in preventing apoptotic cell death, thus regulating intervertebral disc degeneration.

Regulation of apoptosis in nucleus pulposus cells by optimized exogenous Bcl-2 overexpression

Although the etiology of intervertebral disc degeneration is poorly understood, one possible approach to regulate the process of intervertebral disc degeneration may include the inhibition of apoptosis. We investigated the anti-apoptotic effects of bcl-2 in nucleus pulposus cells to enhance disc cell survival. Rat nucleus pulposus cells were transfected in vitro with a codon optimized rat bcl-2 gene. Forty-eight hours after transfection, cells were cultured in serum-deprived medium. After serum withdrawal, the cells were evaluated for bcl-2 protein levels and cell apoptosis. To investigate the effects of bcl-2 overexpression on the final apoptotic pathways and on basic genes important for nucleus pulposus homeostasis, mRNA levels of caspase-3, type II collagen, and aggrecan were also quantified. Nucleus pulposus cells were successfully transfected with codon optimized bcl-2 gene, which effectively reduced serum starvation-induced cell apoptosis. Overexpression of bcl-2 also reduced the mRNA expression level of caspase-3. mRNA levels of type II collagen and aggrecan were significantly higher in bcl-2 transfected groups compared to control plasmid vector groups after serum withdrawal. We firstly showed that bcl-2 overexpression in intervertebral disc cells was effective in preventing in vitro apoptotic cell death, indicating the potential advantages of this therapeutic approach in regulating disc degeneration.

Nucleus pulposus explant culture model

Many of the therapeutic interventions for intervertebral disc degeneration attempt to repopulate the nucleus pulposus (NP) tissue; however, NP cells are heterogeneous and not well characterized. To address this, we have investigated the morphology, extracellular gene and protein expression, and apoptosis changes in NP explants cultured in vitro with or without chondrogenic reagents for different periods. We also compared the susceptibility of the explants to different treatments by comparing: treatment of NP explants with GDF5 protein, transfection of NP explants with GDF5 plasmid, and infection of NP explants with GDF5 adenovirus vector. We found that expression levels of two of the major extracellular proteins found in NP tissue, that is, collagen II and aggrecan, could be maintained in an NP explant culture model with a chondrogenic medium up to 7 days, and were significantly higher than that of fresh NP tissue after 14 days of culture in vitro, whether or not chondrogenic medium was used. In addition, the NP explant responded to treatment with growth factor, and could be infected by virus and transfected by plasmid for further evaluation of growth factor gene therapy. NP explant culture could therefore provide an easy in vitro culture model to characterize NP cells and evaluate potential therapeutic reagents.

Gene therapy approach for disc degeneration and associated spinal disorders

Disc degeneration is deeply associated with many spinal disorders and thus has a significant clinical impact on society. The currently available surgical treatment often necessitates removing a pathological disc and spinal fusion. However, it is also well known that these surgical treatments have many potential problems including invasion and cost. Therefore, biological approaches for regenerating these pathological discs have received much attention. Gene therapy is one of these biological approaches. Gene therapy involves the transfer of genes to cells so the recipient cells express these genes and thereby synthesize the RNA and protein they encode in a continuous fashion. One of the significant advantages of gene therapy is that we can expect a lasting duration of biological effect which is potentially beneficial for most disc degeneration associated disorders, as they are, by nature, chronic conditions. Originally, gene therapy was mediated by viral vectors, but recent technological progress has enabled us to opt for non-virus-mediated gene therapy for the disc. Furthermore, the development of the RNA interference technique has enabled us to down-regulate a specific gene expression in the disc opening the door for a new generation of intradiscal gene therapy.

The cell biology of intervertebral disc aging and degeneration

Intervertebral disc degeneration, which mimics disc aging but occurs at an accelerated rate, is considered to be related to neck or low back pain and disc herniation. Degenerated discs show breakdown of the extracellular matrix and thus fail to bear the daily loadings exerted on the spine. Rather than a passive process of wear and tear, disc degeneration is an aberrant, cell-mediated response to progressive structural failure due to aging and other environmental factors such as abnormal mechanical stress. With aging and degeneration, disc cells undergo substantially biologic changes, including alternation of cell type in the nucleus pulposus, increased cell density but decreased number of viable cells as a result of increased cell death and increased cell proliferation, increased cell senescence, and altered cell phenotype which is characterized by compromised capability of synthesizing correct matrix components and by enhanced catabolic metabolism. These changes are involved in the process of disc degeneration through the complicated interactions among them. To retard or reverse disc degeneration, the abnormal conditions of the decreased viable cell population and the altered cell phenotype should be corrected. As potential therapies for disc degeneration, intradiscal protein injection, gene transfer and cell implantation are being understudied in vivo. Suppression of excessive apoptosis and accelerated senescence of disc cells may be other choices for treating disc degeneration. When performing a biologic therapy in order to repair or regenerate the degenerated disc, nutrient and biomechanical factors should also be incorporated, because they are the major causes of the biologic changes experienced by disc cells. Moreover, a very early intervention is indicated by the finding that the onset of human disc degeneration occurs as early as by adolescence.