Programmed cell death in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is largely a process of destruction and failure of the extracellular matrix (ECM), and symptomatic IVD degeneration is thought to be one of the leading causes of morbidity or life quality deterioration in the elderly. To date, however, the mechanism of IVD degeneration is still not fully understood. Cellular loss from cell death in the process of IVD degeneration has long been confirmed and considered to contribute to ECM degradation, but the causes and the manners of IVD cell death remain unclear. Programmed cell death (PCD) is executed by an active cellular process and is extensively involved in many physiological and pathological processes, including embryonic development and human degenerative diseases. Thus, the relationship between PCD and IVD degeneration has become a new research focus of interest in recent years. By reviewing the available literature concentrated on PCD in IVD and discussing the methodology of detecting PCD in IVD cells, its inducing factors, the relationship of cell death to ECM degradation, and the potential therapy for IVD degeneration by modulation of PCD, we conclude that IVD cells undergo PCD via different signal transduction pathways in response to different stimuli, that PCD may play a role in the process of IVD degeneration, and that modulation of PCD might be a potential therapeutic strategy for IVD degeneration.     

Presynaptic terminals persist following degeneration of "flight" muscle during development of a flightless grasshopper

We have studied the development of a neuromuscular system for which mature function has been lost through evolution in the grasshopper, Barytettix psolus (Cohn and Cantrall, 1974). Barytettix is flightless throughout life and has only vestigial wings that are incapable of active movement. Adult Barytettix lack muscles homologous to the indirect flight muscles of locusts and grasshoppers that fly, while other thoracic muscles are similar. We have found, using light and electron microscopic examination of tissues from various developmental stages, that the metathoracic dorsal longitudinal muscle is present and is innervated during nymphal life but is absent in adults. Yet its nerve persists and, in the adult, contains axonal presynaptic specializations opposite inappropriate targets such as glial processes and basal lamina. Our findings indicate that selective muscle death during development is one mechanism underlying the reduction of the flight system of Barytettix through evolution. The finding that presynaptic terminals persist in the absence of the muscle indicates that the muscle and its innervation follow programs of development that are at least partially independent and reinforces the concept that in insects motorneurons, and perhaps neurons in general, are not dependent upon trophic influences from their targets for survival and maintenance of their differentiated phenotype.     

Death commitment in the anterior silk gland of the silkworm, Bombyx mori

The insect steroid hormone, 20-hydroxyecdysone (20E) triggers the programmed cell death (PCD) of the anterior silk glands (ASGs) of the silkworm, Bombyx mori. We tried to determine the time of commitment to die (death commitment) by examining ASG responses to 20E and juvenile hormone analogue (JHA) in vivo as well as in vitro. The ASGs obtained late on day 6 of the fifth instar completed PCD when cultured with 20E, while the ASGs obtained on day 4 and cultured with 20E did not undergo PCD. The ASGs became competent to respond to 20E at mid-day 5. The ASGs with responsiveness to 20E were not sensitive to JHA, indicating that the ASGs were committed to die before becoming capable of responding to 20E. Topical application of JHA on day 4 suppressed 20E-induced PCD, but that on day 5 failed to do so, indicating that the death commitment might occur between day 4 and 5. We also determined the time of death commitment after allatectomy of the fourth instar larvae, a procedure that induced the precocious PCD. Timed application of JHA and culture of ASGs with 20E in the presence of JHA showed that the ASGs had lost their sensitivity to JHA between 72 and 96 h after allatectomy, i.e. 24-48 h before precocious gut purge in the allatectomized larvae. This result is similar to that obtained in the fifth instar. We conclude that the cellular commitment to die takes place one day before the ASGs become competent to respond to 20E.     

Suppression of programmed cell death regulates the cyclical degeneration of organs in a colonial urochordate

The survival of animal tissues and organs is controlled through both activation and suppression of programmed cell death. In the colonial urochordate Botryllus schlosseri, the entire parental generation of zooids in a colony synchronously dies every week as the asexually derived generation of buds reaches functional maturity. This process, called takeover, involves massive programmed cell death (PCD) of zooid organs via apoptosis followed by programmed removal of cell corpses by blood phagocytes within approximately 1 day. We have previously reported that developing buds in conjunction with circulating phagocytes are key effectors of zooid resorption and macromolecular recycling during takeover, and as such engineer the reconstitution of a functional asexual generation every week [Lauzon, R.J., Ishizuka, K.J., Weissman, I.L., 2002. Cyclical generation and degeneration of organs in a colonial urochordate involves crosstalk between old and new: a model for development and regeneration. Dev. Biol. 249, 333-348]. Here, we demonstrate that zooid lifespan during cyclic blastogenesis is regulated by two independent signals: a bud-independent signal that activates zooid PCD and a bud-dependent, survival signal that acts in short-range fashion via the colonial vasculature. As zooids represent a transient, mass-produced commodity during Botryllus asexual development, PCD regulation in this animal via both activation and suppression enables it to remove and recycle its constituent zooids earlier when intra-colony resources are low, while maintaining the functional filter-feeding state when resources are adequate. We propose that this crosstalk mechanism between bud and parent optimizes survival of a B. schlosseri colony with each round of cyclic blastogenesis.     

Programmed cell death in flight muscle histolysis of the house cricket

We have characterized the process of flight muscle histolysis in the female house cricket, Acheta domesticus, through analysis of alterations of tissue wet weight, total protein content, and percent shortening of the dorsal longitudinal flight muscles (DLMs). Our objectives were to (1) define the normal course of histolysis in the cricket, (2) analyze the effects of juvenile hormone (JH) removal and replacement, (3) determine the effects of cycloheximide treatment, and (4) examine patterns of protein expression during histolysis. Our results suggest that flight muscle histolysis in the house cricket is an example of an active, developmentally regulated cell death program induced by an endocrine signal. Initial declines of total protein in DLMs indicated the JH signal that induced histolysis occurred by Day 2 and that histolysis was essentially complete by Day 3. Significant reductions in tissue weight and percent muscle shortening were observed in DLMs from Day 3 crickets. Cervical ligation of Day 1 crickets prevented histolysis but this inhibition could be reversed by continual topical treatments with methoprene (an active JH analog) although ligation of Day 2 crickets did not prevent histolysis. A requirement for active protein expression was demonstrated by analysis of synthesis block by cycloheximide and short-term incorporation of (35)S-methionine. Treatment with cycloheximide prevented histolysis. Autofluorographic imaging of DLM proteins separated by electrophoresis revealed apparent coordinated regulation of protein expression.     

Thoracic morphology of a flightless mexican grasshopper,Barytettix psolus: Comparison with the locust,Schistocerca gregaria

The thoracic morphology of a flightless grasshopper, Barytettix psolus, is described and compared to that of locusts, Schistocerca gregaria, to evaluate modifications to skeleton, muscles, and the nervous system which have accompanied secondary loss of flight. Barytettix lacks hindwings, has immobile vestiges of forewings and is devoid of skeletal specializations for wing movement and flight. Its pterothoracic musculature resembles that of Schistocerca except for the absence of those muscles which, in locusts, have the primary function of moving the wings, the dorsal longitudinal, tergosternal, first basalar, pleuroalar, and dorsal accessory muscles. Pterothoracic ganglia of Barytettix resemble those of Schistocerca in their gross features, number, and primary branching pattern of nerves, with differences in detail relating to reduction of the flight muscles. The combination of features exhibited in Barytettix represents an extreme reduction in the specialization for wing movements and flight displayed by most acridids, at a level which exceeds that of many brachypterous and some apterous species. While skeletal fusion and loss of muscles indicate loss of flight, the accompanying thoracic stiffening and increase in overall body density may promote more efficient jumping as a means of locomotion.     

Apoptotic activity of a nuclear form of mitogaligin, a cell death protein

Galig, an internal gene to the galectin-3 gene, encodes two proteins and induces cell death in human cells. Mitogaligin, one of these proteins, contains a mitochondrial targeting sequence and promotes the release of cytochrome c into the cytosol. Here, we show that mitogaligin can also localize to nucleus. The nuclear form of mitogaligin induced cell death through a pathway exhibiting typical properties of apoptosis. These observations indicate for the first time that mitogaligin expresses cytotoxic properties not only when addressed to mitochondria but also when targeted to the nucleus.     

Adipokinetic response of a flightless grasshopper (Barytettix psolus): Functional components,defective response

The mature flightless grasshopper Barytettix psolus shows a very small adipokinetic response when injected with extracts of its own corpora cardiaca, although the fat body contains enough lipid for a strong response. When these extracts were injected into Melanoplus differentialis, a grasshopper capable of flight, or the moth Manduca sexta, much stronger adipokinetic responses were observed. Upon analysis of B. psolus extracts by HPLC, two components with adipokinetic activity were obtained. The major component appears to be identical to locust adipokinetic hormone (AKH) I. Extracts of B. psolus corpora cardiaca also activated fat body glycogen phosphorylase in B. psolus. This activation, however, did not result in an increase in hemolymph sugar, probably because of low levels of glycogen in the fat body. B. psolus hemolymph contains a high-density lipophorin (HDLp) consisting of the apolipophorins (apoLp) I and II and lipid. Both apoproteins are glycosylated. The hemolymph also contains apoLp-III, although this apoprotein apparently does not associate with HDLp to form a low-density lipophorin (LDLp) following AKH or corpora cardiaca extract injections. When B. psolus lipophorin and AKH were injected into Schistocerca americana, lipophorin took up lipids and combined with apoLp-III, forming LDLp. ApoLp-III from B. psolus injected into S. americana can also form LDLp, demonstrating that the components are functional. A lipid transfer particle isolated from M. sexta and injected into B. psolus does not improve the adipokinetic response. Thus, it appears that the adipokinetic response of B. psolus is not deficient because of the lack of AKH or functional lipophorins, but may be caused by the lack of a full response to AKH by fat body or the deficiency in hemolymph of some as yet unknown factor.     

Natural cyclic degeneration by a sequence of programmed cell death modes in <Emphasis Type="Italic">Semibalanus balanoides</Emphasis> (Linnaeus, 1767) (Crustacea,Cirripedia Thoracica)

The male reproductive system of the barnacle Semibalanus balanoides (Linnaeus, 1767) is a perfect model system for investigating naturally occurring cyclic nonpathological degeneration and programmed cell death (PCD). Every year after copulation, the barnacle degenerates its gonads, eggs, spermatids and penis initiated by severe environmental constraints. This is apparently a useful strategy for saving energy. By careful ultrastructural and immunohistochemical analysis of the male reproductive organs, we identified autophagic cell death in the penis and spermatids, both morphologically on ultrathin sections as well as histochemically for the first time on semithin tissue sections with the new antibody against microtubule-associated protein 1 light chain 3 (LC3). Apoptosis in the testis and vesicula seminalis was determined based on the morphological characters on the apoptosis-specific antibody against the apoptosis inducing factor (AIF), and on positive TUNEL (terminal in situ nick end labeling) nuclei. Secondary necrosis in late degrading stages occurred in all tissues investigated, based on morphological characters and weak TUNEL staining. Moreover, the ultrastructural screening showed transient forms of cell death in the ductus ejaculatorius epithelium, the epidermis, and the longitudinal muscles of the penis. According to the immunohistochemical tests, the cyclic degeneration of the male reproductive system follows a sequence of programmed cell death modes from autophagic cell death via apoptosis to secondary necrosis.     

TMEM166, a novel transmembrane protein,regulates cell autophagy and apoptosis

Programmed cell death can be divided into apoptosis and autophagic cell death. We describe the biological activities of TMEM166 (transmembrane protein 166, also known as FLJ13391), which is a novel lysosome and endoplasmic reticulum-associated membrane protein containing a putative TM domain. Overexpression of TMEM166 markedly inhibited colony formation in HeLa cells. Simultaneously, typical morphological characteristics consistent with autophagy were observed by transmission electron microscopy, including extensive autophagic vacuolization and enclosure of cell organelles by double-membrane structures. Further experiments confirmed that the overexpression of TMEM166 increased the punctate distribution of MDC staining and GFP-LC3 in HeLa cells, as well as the LC3-II/LC3-I proportion. On the other hand, TMEM166-transfected HeLa and 293T cells succumbed to cell death with hallmarks of apoptosis including phosphatidylserine externalization, loss of mitochondrial transmembrane potential, caspase activation and chromatin condensation. Kinetic analysis revealed that the appearance of autophagy-related biochemical parameters preceded the nuclear changes typical of apoptosis in TMEM166-transfected HeLa cells. Suppression of TMEM166 expression by small interference RNA inhibited starvation-induced autophagy in HeLa cells. These findings show for the first time that TMEM166 is a novel regulator involved in both autophagy and apoptosis.     

Autophagy in plants and phytopathogens

Plants and plant-associated microorganisms including phytopathogens have to adapt to drastic changes in environmental conditions. Because of their immobility, plants must cope with various types of environmental stresses such as starvation, oxidative stress, drought stress, and invasion by phytopathogens during their differentiation, development, and aging processes. Here we briefly describe the early studies of plant autophagy, summarize recent studies on the molecular functions of ATG genes, and speculate on the role of autophagy in plants and phytopathogens. Autophagy regulates senescence and pathogen-induced cell death in plants, and autophagy and pexophagy play critical roles in differentiation and the invasion of host cells by phytopathogenic fungi.     

Ceramide Induces Apoptosis to Immature Cerebellar Granule Cells in Culture

A recent study revealed that ceramide acts as a second messenger in the sphingomyelin pathway and thus plays an important regulatory role in programmed cell death (apoptosis) to cell the lines induced by tumor-necrosis factor (TNF)- and interleukin (IL)-1, although its effect remains controversial regarding primary neuronal culture. We investigated the effect of a cell-permeable ceramide analog (C₂-ceramide) on cultures of cerebellar granule cells, which is thought to have active sphingomyelin pathway during development. The presence of C₂-ceramide decreased the number of cerebellar granule cells (CGCs) in a concentration-dependent manner when added at DIV 1 (1 day in vitro). The ED₅₀ was 60 M. After DIV2, CGCs became less sensitive to C₂-ceramide and the ED₅₀ was 200 M at DIV 7. DNA staining with Hoechst 33258 showed the morphology of apoptotic nuclei in the degenerating neurons. Internucleosomal DNA degradation could also be observed by gel electrophoresis. Protein and RNA synthesis inhibitors prevented the death of neurons. C₂-dihydroceramide, which lacks the 4–5 trans double bond and failed to induce neuronal death. These results thus demonstrated that C₂-ceramide induces apoptosis to the CGCs at the early stage in vitro, however the CGCs were found to be less sensitive to C₂-ceramide at the later stage in vitro.     

环境因子诱导的植物细胞程序性死亡

细胞发生程序性死亡（Programmed cell death,PCD）是多细胞生物用以消除多余的或有害的细胞的一种重要方式。对于植物个体来说,细胞发生程序性死亡（PCD）是抵抗逆境的一种十分有效的途径。因此,揭示环境因子诱导的植物PCD现象的分子本质就具有十分重要的现实意义。近十年来,有关环境因子诱导的植物PCD研究报道逐年增加。本文重点综述了环境因子与植物PCD相关的研究进展,并对植物PCD的主要生物学意义和研究展望进行了讨论。     

植物细胞程序化死亡研究进展

细胞程序化死亡 (PCD)是一种由基因控制的、主动的细胞死亡过程 ,它在植物正常生长发育过程中起着重要作用。本文就植物PCD的近期研究进展和其分子信号调控机制作一综合阐述     

植物细胞程序性死亡研究进展

植物细胞死亡分为坏死和程序性死亡。细胞程序性死亡是具有信号或一系列分子参与,并且由细胞内在的死亡程序介导的有序过程。它在植物生长发育和抵御外界胁迫中具有重要作用。简要介绍了植物PCD的特征,对植物PCD中的信号分子和类caspase的作用等进行了综述,并对植物PCD存在的问题进行分析和展望,为深入研究植物PCD提供参考。