Cleavage of the death domain kinase RIP by Caspase-8 prompts TNF-induced apoptosis

Although the molecular mechanisms of TNF signaling have been largely elucidated, the principle that regulates the balance of life and death is still unknown. We report here that the death domain kinase RIP, a key component of the TNF signaling complex, was cleaved by Caspase-8 in TNF-induced apoptosis. The cleavage site was mapped to the aspartic acid at position 324 of RIP. We demonstrated that the cleavage of RIP resulted in the blockage of TNF-induced NF-kappaB activation. RIPc, one of the cleavage products, enhanced interaction between TRADD and FADD/MORT1 and increased cells' sensitivity to TNF. Most importantly, the Caspase-8 resistant RIP mutants protected cells against TNF-induced apopotosis. These results suggest that cleavage of RIP is an important process in TNF-induced apoptosis. Further more, RIP cleavage was also detected in other death receptor-mediated apoptosis. Therefore, our study provides a potential mechanism to convert cells from life to death in death receptor-mediated apoptosis.     

Antigen-induced and zymosan-induced arthritis in mice: studies on in vivo cartilage proteoglycan synthesis and chondrocyte death.

The influence of joint inflammation on patellar hyaline articular cartilage was studied in mice. Antigen-induced and zymosan-induced arthritis were used as models for immunologically and non-immunologically induced joint inflammation. The contribution of newly formed proteoglycan to the cartilage proteoglycan content, as measured by labelling of the cartilage after i.v. administration of 35S-sulphate, was decreased in parallel with the severity of inflammation during both zymosan-induced and antigen-induced arthritis. The decreased 35S content of the cartilage was due to inhibition of synthesis rather than breakdown of newly synthesized proteoglycan, since no accelerated release of 35S from arthritic cartilage could be demonstrated in vitro. Antigen-induced arthritis was associated with progressive chondrocyte damage. Loss of chondrocytes was consistently found in the central part of the patella, without nearby presence of pannus. It would appear that, in addition to enzymatic breakdown of cartilage, other phenomena are important in cartilage destruction: inhibition of proteoglycan synthesis and chondrocyte death, apparently unrelated to pannus formation.     

Apoptotic chondrocyte death in cell-matrix biocomposites used in autologous chondrocyte transplantation.

Tissue engineering may be a promising approach for the treatment of focal articular cartilage defects. Programmed cell death (apoptosis) plays an important role in multiple degenerative processes of cartilage (e.g. osteoarthritis). It is known that matrix provides a trophic signal for the cells and an altered matrix may influence the availability of factors that regulate apoptosis. In this study we investigate the viability of chondrocytes seeded on a Chondrogide scaffold (Geistlich Biomaterials, CH), which we use in matrix-induced autologous chondrocyte transplantation (MACT). By now, we have studied material from 29 patients treated for localized articular cartilage defects in the knee. Our results indicate that light microscopy (Mayer's hematoxylin-eosin, Masson-Goldner, Trypan-blue and TUNEL method) and electron microscopy can be used to investigate for apoptotic cells grown on a Chondrogide resorbable scaffold. Neither the handling of the cell-matrix biocomposite nor the procedures for fixation could destroy the scaffold or the cell sheet adhering firmly to the matrix. Apoptotic cells were revealed in all samples and with all techniques used. Mayer's hematoxylin-eosin and Masson-Goldner staining show cells with a condensed, pycnotic nucleus and shrunken cytoplasm. In electron microscopy we observed cells with chromatin condensation and volume shrinkage consistent with apoptosis. The results of the Trypan-blue staining show a mean viability of 92.1 +/- 9.8% (range 57-100%). The TUNEL method revealed 44.6 +/- 20.4% positive cells. Our results indicate that apoptosis plays an important role in chondrocytes grown on a scaffold. An optimal scaffold will determine the growth, morphology and phenotype of the chondrocytes by its physical and chemical characteristics.     

FcgammaRI up-regulation induced by local adenoviral-mediated interferon-gamma production aggravates chondrocyte death during immune complex-mediated arthritis

Using various FcgammaR-deficient mice, we have obtained suggestive evidence that FcgammaRI on macrophages is responsible for severe cartilage destruction during arthritis mediated by immune complexes (ICs). This role of FcgammaRI is pronounced in the presence of activated Th1 cells and a likely Th1 cell-derived cytokine mediating up-regulation of FcgammaRI expression is interferon (IFN)-gamma. We now investigated whether local overexpression of IFN-gamma using an adenoviral vector is able to elevate cartilage destruction during experimental immune complex-mediated arthritis (ICA) and to what extent this process is FcgammaRI-mediated. IFN-gamma overexpression during ICA had no significant effect on the total cell mass infiltrating the knee joint. However, a higher percentage of macrophages expressing markers for a proinflammatory phenotype was found and these macrophages were situated in close proximity of the cartilage surface. Interestingly, cartilage destruction as studied by matrix metalloproteinase (MMP)-mediated proteoglycan damage (VDIPEN expression), chondrocyte death, and erosion was significantly increased. This effect of IFN-gamma was only found in the presence of ICs, as IFN-gamma overexpression during zymosan-induced arthritis, which is not IC-dependent, did not lead to severe cartilage destruction. These results imply a crucial role for ICs and the IgG-binding receptors in the aggravation of cartilage damage by IFN-gamma. Local overexpression of IFN-gamma induced increased FcgammaRI mRNA levels in synovium. To study whether this up-regulation of FcgammaRI mediates aggravation of cartilage destruction, ICA was raised in FcgammaRI(-/-) and their wild-type controls. IFN-gamma resulted in elevated VDIPEN expression, which was still present in FcgammaRI(-/-). Of great interest, chondrocyte death remained low in FcgammaRI(-/-). These results indicate that IFN-gamma overexpression deteriorates cartilage destruction in the presence of ICs and that FcgammaRI is crucial in the development of chondrocyte death.     

Role of apoptosis inhibition in various chondrocyte culture systems

Apoptosis may limit the utility of cell-based therapies for articular cartilage disorders. We tested the hypothesis that chondrocyte apoptosis can be reduced by optimizing the conditions employed to expand chondrocyte numbers in culture. Chondrocyte apoptosis was examined in monolayer and suspension culture, in the presence of fetal bovine serum (FBS) or autologous serum, and for culture periods of 2 or 4 days. The effect of these variables was assessed by measuring cell viability, Annexin V labeling and mitochondrial membrane potential. After 2 days of culture, the greatest increase in viable cell number (3.7-fold) occurred in monolayer cultures with autologous serum. After 4 days of culture, the greatest increase in cell number (9.0-fold) occurred in monolayer cultures supplemented with FBS. By Annexin V staining, the proportion of cells undergoing apoptosis after 2 days was not affected by the type of serum used or by culture in monolayer versus suspension. After 4 days of culture, the proportion of apoptotic cells was significantly reduced (35% to 13%, p<0.02) in suspension cultures with autologous serum. Apoptosis assessed by loss of mitochondrial membrane potential was decreased in the presence of autologous serum. These data suggest that suspension culture with autologous serum is useful in simultaneously maintaining cell proliferation and minimizing apoptosis in cultured human articular chondrocytes.     

自噬基因在骨关节炎软骨细胞凋亡过程中的保护和平衡效应

背景：软骨细胞在低营养供给下可发生细胞自噬,细胞自噬和细胞坏死、凋亡不同,可以使软骨细胞在营养供给不足时,能够存活下来,可能是软骨细胞自身的重要保护机制之一。 目的：综合阐述自噬基因保护关节软骨及抑制骨关节炎等方面的机制和作用。 方法：应用计算机检索中国知网、万方数据库及PubMed数据库2000年1月至2015年1月关于自噬基因与骨关节炎的相关研究的文章,中文检索词为“自噬基因、骨关节炎、关节软骨、软骨细胞”,英文检索词为“autophagy、osteoarthritis、beclin1、LC3”。选择自噬基因与骨关节炎的相关文章,初检得到269余篇文献,根据纳入标准选择其中的38篇进行综述。  结果与结论：软骨细胞的损伤凋亡是软骨退变的主要机制,不予控制,就可能会进一步发展为骨性关节炎。细胞的损伤凋亡是软骨退变的重要机制之一,因此防止软骨细胞的损伤凋亡,可能有利于损伤软骨的修复,以此来缓解骨关节炎的病情发展。自噬现象能够抑制受损软骨细胞凋亡,发现其可将改变传统治疗骨关节炎的局限,但目前自噬基因与骨关节炎相关的研究还处于初级阶段,特别是对自噬途径在软骨中如何被诱导,如何进行信号转导,如何对软骨细胞生存产生影响等方面的认识还不够全面,有待进一步的研究。     

Short-term exposure of cartilage to blood results in chondrocyte apoptosis

Studies have shown that joint bleeding leads to cartilage degradation independent of concurrent synovitis. We hypothesized that the blood-induced cartilage damage is because of increased chondrocyte apoptosis after short-term exposure of whole blood or isolated mononuclear cells plus red blood cells to cartilage. Human cartilage tissue samples were co-cultured for 4 days with whole blood (50% v/v) or with mononuclear cells plus red blood cells (50% v/v equivalents). Cartilage matrix proteoglycan synthesis ((35)SO(4)(2-) incorporation) was determined after 4 days as well as at day 16 (after a 12-day recovery period in the absence of any additions). To test the involvement of apoptosis a specific caspase-3 inhibitor (acDEVDcho, 0 to 500 micro mol/L) as well as a pan-caspase inhibitor (zVADfmk, 0 to 500 micro mol/L) were added. Chondrocyte apoptosis was evaluated by immunohistochemical staining of single-strand DNA and by terminal dUTP nick-end labeling. Cartilage co-cultured with whole blood as well as mononuclear cells plus red blood cells induced a long-term inhibition of proteoglycan synthesis (74% and 78% inhibition on day 16, respectively). Immunohistochemistry showed a threefold increase in apoptotic chondrocytes in cultures with 50% whole blood as well as with mononuclear cells plus red blood cells. Both the specific caspase-3 inhibitor and the pan-caspase inhibitor partially restored proteoglycan synthesis in the cartilage after blood exposure. This effect was accompanied by a decrease in the number of apoptotic chondrocytes. These data suggest that a single joint hemorrhage (a 4-day exposure of cartilage to 50% v/v blood) results in induction of chondrocyte apoptosis, responsible for the observed inability of the chondrocytes to restore the proteoglycan synthesis during recovery from a short-term exposure to blood. This reduced restoration could eventually lead to cartilage degeneration and ultimately joint destruction.     

Preventing chondrocyte programmed cell death caused by iatrogenic injury

Cartilage repair technology is advancing at a rapid pace. However, all techniques share a common weakness-unintentional chondrocyte cell death resulting from cartilage injury that occurs during preparation of the defect site. The loss of chondrocytes at the edge of host cartilage is likely to contribute to failed integration of regenerated tissue or grafts to the surrounding cartilage. Recent studies have demonstrated that "apoptosis", or programmed cell death (PCD), may be responsible for much of the cell death caused by cartilage injury. Theoretically, inhibitors of key pathways responsible for PCD could rescue chondrocytes and improve the results of cartilage repair surgery. The purpose of this study was to test the hypothesis that short-term, intra-articular PCD inhibitor treatment can limit chondrocyte death in vivo following simulated preparation of host cartilage for a repair procedure. A microcurette was used to create full-thickness articular cartilage injuries to the femoral condyles of adult New Zealand White rabbits. Animals received daily intra-articular injections either with a potent PCD inhibitor or with vehicle alone. Treatment with the inhibitor resulted in a significant reduction in the percentage of chondrocytes undergoing PCD compared to controls [treated=10.1+/-2.4%; controls=26.5+/-3.6%; (p=0.0013)]. These results provide proof of concept for the use of PCD inhibitors to enhance the results of cartilage repair surgeries.     

TNF-induced enterocyte apoptosis and detachment in mice: induction of caspases and prevention by a caspase inhibitor, ZVAD-fmk

Injection of mouse recombinant TNF to mice induced apoptosis and detachment of the enterocytes of the tip of the villi, evident after 30 to 90 minutes, which resulted in a shrinkage of the villi. Injection of TNF increased the expression of caspase 1, 2, 3, and 6 as well as of cathepsin D in the mucosal wall, which was maximal 30 minutes after TNF injection. Caspase 1 and 3 were not induced in TNFR1-deficient mice in which TNF does not induce apoptosis and detachment. The administration of a caspase inhibitor (ZVAD-fmk, 300 microg) decreased enterocyte detachment and apoptosis, as well as villus atrophy, whereas a caspase 3 inhibitor (Z-DEVD-cmk) had no effect. The results indicate that the induction of caspases by TNF is the cause of their detachment in the lumen and of the resulting villus atrophy.     

沉默Smo基因对大鼠原代软骨细胞增殖与凋亡的影响

目的观察沉默Smo基因后对大鼠原代软骨细胞增殖与凋亡的影响。方法用机械-酶消化法获取原代大鼠软骨细胞,经免疫细胞化学Ⅱ型胶原(ColⅡ)鉴定后,将实验分为对照组、control siRNA组和Smo siRNA 1~3组,以慢病毒为载体将siRNA转入软骨细胞,72 h后,MTT法检测细胞活力;反转录PCR(RT-PCR)及蛋白印迹(Western blot)检测Smo的表达量;流式细胞术检测细胞凋亡率。结果各组序列经慢病毒载体成功转染到原代软骨细胞中,Smo siRNA1~3均不同程度的抑制Smo的表达,以Smo siRNA2组最为明显,其mRNA及蛋白的表达分别为0.19±0.03和0.39±0.07;同时,Smo siRNA2组细胞活力最低(77.38%±7.19%)而凋亡率最高(21.43%±2.97%)。结论沉默Smo可抑制原代软骨细胞增殖,并诱导软骨细胞凋亡,Smo具有保护软骨细胞免遭凋亡的作用。     

血管内皮生长因子和缺氧诱导因子对软骨细胞凋亡的作用

背景：骨关节炎是一种关节疾病,主要影响软骨,随着软骨细胞胞外基质的变化,软骨细胞发生凋亡,血管内皮生长因子在促进血管内皮细胞分裂与增殖、诱导血管生成中起重要作用。缺氧诱导因子是一种在细胞环境中的转录因子,因氧含量而产生不同反应,血管内皮生长因子和缺氧诱导因子在抑制软骨细胞凋亡中的作用受到研究者的重视。 目的：阐述血管内皮生长因子和缺氧诱导因子及其他可能因素对软骨细胞凋亡的影响。 方法：分析、总结近年来软骨细胞凋亡的影响因素的相关文献,从骨关节炎进程中软骨细胞血管内皮生长因子表达变化,血管内皮生长因子和缺氧诱导因子对软骨细胞凋亡的调控等方面进行阐述。 结果与结论：血管内皮生长因子通过上调抑制细胞凋亡因子的表达促进软骨细胞存活,缺氧诱导因子能增加软骨细胞活性和细胞外基质合成,成为抑制骨细胞凋亡的重要靶点,血管内皮生长因子与缺氧诱导因子的相关性还有待进一步研究。 中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Saving death: apoptosis for intervention in transplantation and autoimmunity

Long considered immunologically "bland," apoptotic cells are now recognized as important modulators of immune responses. The role of apoptosis in immunological homeostasis has been inferred from several findings, for example, induction of tolerance after injection of apoptotic cells and the capacity of APCs like macrophages and DCs to induce and maintain tolerance after phagocytosis of dead cells. Processing of apoptotic cells by DCs is of particular interest, because DCs are the only known APCs capable of activating na?ve T lymphocytes to become effector or regulatory cells. In that regard, recent evidence suggests that phagocytosis of apoptotic cells by DCs can induce Tregs, a finding that has significant implications for the treatment of a variety of immune-mediated inflammatory disorders. Here, we review the relationship between apoptotic cells, DCs, and Tregs, and its impact on prevention of transplant rejection and treatment of autoimmune diseases.     

Cell death in granulomata: the role of apoptosis.

Unequivocal apoptosis were seen by light microscopy in examples of leprosy, sarcoidosis, tuberculosis, Crohn's disease and foreign body granulomata. A limited electron microscopic investigation showed typical apoptotic bodies in both sarcoid and leprosy granulomata. The number of apoptosis and mitoses in granulomata were counted and their densities calculated. The wide variation in the results between individual lesions may reflect differences in disease activity.     

Cell death by apoptosis in acute leukaemia

We have previously demonstrated that when freshly isolated childhood T-cell acute lymphoblastic leukaemia cells are incubated in growth medium after isolation from blood, chromatin is rapidly cleaved into nucleosomal sized fragments that are multiples of 200 bp. The fragmentation is similar to that observed in other types of cells undergoing apoptosis or programmed cell death. In this study we describe a more comprehensive approach to the study of DNA fragmentation in leukaemia. Fragmentation was observed in freshly isolated cells from patients with T-cell acute lymphoblastic leukaemia and in one with common acute lymphoblastic leukaemia. Frozen samples of T-cell acute lymphoblastic leukaemia, common acute lymphoblastic leukaemia, and acute myeloid leukaemia cells also showed fragmentation of DNA. However, no fragmentation was evident in normal leukocytes treated under the same conditions. Ultrastructural studies on the isolated leukaemia cells demonstrate that the chromatin cleavage observed biochemically is associated with morphological changes characteristic of apoptosis.     

12/15-脂氧合酶抑制剂黄芩素对软骨细胞凋亡的抑制作用研究

目的探讨12/15-脂氧合酶抑制剂黄芩素(Baicalein)对硝普钠(SNP)诱导的软骨细胞凋亡的抑制作用及可能机制。方法取8周雄性SD大鼠膝关节软骨,采用Ⅱ型胶原酶消化法提取软骨细胞并体外培养。设置对照组、SNP凋亡组和Baicalein给药组,以0.5 m M SNP作用24小时诱导软骨细胞凋亡,以5 M,25 M,50 M,100 M不同浓度的Baicalein作用细胞,确定最适浓度,对照组仅加入同体积溶剂(蒸馏水)。CCK8法检测药物对细胞毒性;Annexin V/PI双染法检测细胞凋亡;免疫荧光观测凋亡诱导因子(AIF)在软骨细胞中的定位。结果 Baicalein在各浓度下对软骨细胞无明显毒性,与对照组相比,凋亡组软骨细胞活性明显下降(0.01),与凋亡组相比,给药组细胞活性浓度依赖性地升高(0.01);流式检测显示对照组软骨细胞早期凋亡率3.16%,凋亡组27.8%,100 M Baicalein给药组14.1%;免疫荧光检测显示,凋亡组AIF出现核内移位,100 M Baicalein给药组AIF核移位受到抑制。结论 Baicalein通过抑制12/15-脂氧合酶活性,进而抑制AIF从线粒体中的释放及核转位,发挥抗软骨细胞凋亡作用。