Mechanism of liponecrosis,a distinct mode of programmed cell death

An exposure of the yeast Saccharomyces cerevisiae to exogenous palmitoleic acid (POA) elicits “liponecrosis," a mode of programmed cell death (PCD) which differs from the currently known PCD subroutines. Here, we report the following mechanism for liponecrotic PCD. Exogenously added POA is incorporated into POA-containing phospholipids that then amass in the endoplasmic reticulum membrane, mitochondrial membranes and the plasma membrane. The buildup of the POA-containing phospholipids in the plasma membrane reduces the level of phosphatidylethanolamine in its extracellular leaflet, thereby increasing plasma membrane permeability for small molecules and committing yeast to liponecrotic PCD. The excessive accumulation of POA-containing phospholipids in mitochondrial membranes impairs mitochondrial functionality and causes the excessive production of reactive oxygen species in mitochondria. The resulting rise in cellular reactive oxygen species above a critical level contributes to the commitment of yeast to liponecrotic PCD by: (1) oxidatively damaging numerous cellular organelles, thereby triggering their massive macroautophagic degradation; and (2) oxidatively damaging various cellular proteins, thus impairing cellular proteostasis. Several cellular processes in yeast exposed to POA can protect cells from liponecrosis. They include: (1) POA oxidation in peroxisomes, which reduces the flow of POA into phospholipid synthesis pathways; (2) POA incorporation into neutral lipids, which prevents the excessive accumulation of POA-containing phospholipids in cellular membranes; (3) mitophagy, a selective macroautophagic degradation of dysfunctional mitochondria, which sustains a population of functional mitochondria needed for POA incorporation into neutral lipids; and (4) a degradation of damaged, dysfunctional and aggregated cytosolic proteins, which enables the maintenance of cellular proteostasis.     

Tissue inhibitors of metalloproteinases and programmed cell death: conundrums, controversies and potential implications

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases, which can synergistically degrade the major components of extracellular matrix (ECM). A key role in maintaining the balance between ECM deposition and degradation in several physio-pathological processes is carried out, through multiple biological functions, by four members of the tissue inhibitors of metalloproteinases (TIMPs) family. TIMP-1 and TIMP-2 are capable of inhibiting the activities of MMPs, can inhibit tumour growth, invasion and metastasis, exhibit growth factor-like activity, can inhibit angiogenesis and suppress programmed cell death (PCD) independently of the MMP-inhibitory activity. TIMP-3 is the only member which is tightly bound to ECM, inhibits TNF- converting enzyme and induces PCD through the stabilization of TNF- receptors on the cell surface. TIMP-4 plays a role in ECM homeostasis in a tissue-specific fashion and its overexpression induces PCD. The aim of this article is to review the exciting and intriguing literature on TIMPs, with special emphasis on their conflicting-paradoxical roles in PCD and their potential clinical usefulness.     

Larval-to-adult conversion of a myogenic system in the frog, Xenopus laevis, by larval-type myoblast-specific control of cell division, cell differentiation, and programmed cell death by triiodo-L-thyronine

For the clarification of larval-to-adult muscle conversion, the authors established primary culture methods for adult- and larval-type myoblasts in the frog, Xenopus laevis, and examined the hormonal response in each case. The cell types were enzymatically dissociated from adult frog leg and tadpole tail muscles, respectively. The cells became attached to culture plates, proliferated, and fused with each other to form multinucleated myotubes within one week. Five significant differences between the two cell types were noted. (1) Adult cells showed greater proliferation activity than larval cells, the former increasing 5.5-fold over 6 days while the latter increase only 2.5-fold. (2) Differentiation (fusion) of larval type myoblasts started earlier. Cell fusion began on day 2 or 3 in larval cells and on day 4 in adult cells. (3) The metamorphic hormone, triiodo-L-thyronine (T3) decreased larval cell numbers to 56% of that of control-cultures on day 7 but had no effect on adult cell number. DNA synthetic activity (3H-thymidine incorporation) in larval cells decreased under T3 (10(-8) M) to 45% of the control level on day 7. (4) Differentiation of adult myoblasts into myotubes was promoted by T3, whereas that of larval cells diminished by half. (5) Myotube death was induced by T3 specifically in larval but not in adult cultures. In addition to the myotube death, double staining with TUNEL (in situ DNA nick end labeling) and anti-desmin antibody indicated that T3 induces myoblast (desmin+ cell) death specifically in larval but not in adult cells. It is thus evident that the conversion of a larval-type myogenic system during metamorphosis becomes possible through nearly totally specific control of cell division, cell differentiation, and programmed cell death at a precursor cell level by T3.     

中华蜜蜂工蜂咽下腺胚后发育过程中细胞的增殖和凋亡

【目的】咽下腺(hypopharyngeal gland)是蜜蜂重要的外分泌腺,是工蜂合成和分泌蜂王浆的主要腺体。本研究的目的在于了解中华蜜蜂Apis cerana cerana工蜂咽下腺的胚后发育特点。【方法】通过组织形态学、Brd U免疫组织化学和TUNEL细胞凋亡检测等技术,对中华蜜蜂工蜂咽下腺的胚后发育过程及组织结构特点进行了比较研究。【结果】中华蜜蜂工蜂的咽下腺起源自预蛹阶段口器内壁的陷入,细胞分裂活动的高峰期集中在蛹发育的前3 d,随后分裂细胞数减少,并一直持续到蛹发育的第7天左右结束;分泌腺泡的出现大约在蛹发育的第5天。到蛹发育的末期,咽下腺已基本形成,但是没有发育完全;哺育蜂的咽下腺高度发育,分泌活动旺盛;采集蜂的咽下腺中有许多分泌细胞凋亡。【结论】本研究揭示了中蜂工蜂咽下腺胚后发育过程中细胞增殖和凋亡的模式,为昆虫咽下腺的发育和功能研究提供了一定的理论依据。     

Cockroach midgut peptides that regulate cell proliferation, differentiation, and death in vitro

Summary The number of insect midgut cells is maintained homeostatically in vivo and in vitro. However, during starvation, the midgut shrinks and the rate of cell replacement appears to be suppressed. When they undergo metamorphosis, the internal organs of insects are drastically remodeled by cell proliferation, differentiation, and apoptotic processes, and the net number of cells usually increases. An extract of 1650 midguts ofPeriplaneta americana was fractionated by highperformance liquid chromatography (HPLC) to obtain the peptides that regulate these processes. The HPLC fractions were tested for myotropic activity in the foregut and for effects on cell proliferation or loss in primary cultures of larvalHeliothis virescens midgut cells and in a cell line derived from the last-instar larval fat body ofMamestra brassicae. Some fractions stimulated midgut stem cell proliferation and differentiation, while others caused loss of differentiated columnar and goblet cells. Other fractions stimulated cell proliferation in the larval fat body cells. Mention of products in this article does not imply endorsement by the U.S. Department of Agriculture.     

Uth1p: a yeast mitochondrial protein at the crossroads of stress, degradation and cell death

UTH1 is a yeast aging gene that has been identified on the basis of stress resistance and longer life span of mutants. It was also shown to participate in mitochondrial biogenesis. The absence of Uth1p was found to trigger resistance to autophagy induced by rapamycin. Uth1p is therefore the first mitochondrial protein proven to be required for the autophagic degradation of mitochondria. Since this protein is also involved in yeast cell death induced by heterologous expression of the pro-apoptotic protein Bax, the results are discussed in the light of evidence suggesting a co-regulation of apoptosis and autophagy in mammalian cells.     

Apoptosis in a unicellular eukaryote (Trypanosoma cruzi): implications for the evolutionary origin and role of programmed cell death in the control of cell proliferation, differentiation and survival

The origin of programmed cell death (PCD) has been linked to the emergence of multicellular organisms. Trypanosoma cruzi, a member of one of the earliest diverging eukaryotes, is a protozoan unicellular parasite that undergoes three major differentiation changes and requires two different hosts. We report that the in vitro differentiation of the proliferating epimastigote stage into the G0/G1 arrested trypomastigote stage is associated with massive epimastigote death that shows the cytoplasmic and nuclear morphological features and DNA fragmentation pattern of apoptosis, the most frequent phenotype of PCD in multicellular organisms. Apoptosis could be accelerated or prevented by modifying culture conditions or cell density, indicating that extracellular signals influenced the epimastigote decision between life and death. Epimastigotes responded to complement-mediated immunological agression by undergoing apoptosis, while undergoing necrosis in response to nonphysiological saponin-mediated damage. PCD may participate into the optimal adaptation of T. cruzi to its different hosts, and the avoidance of a local competition between a G0/G1 arrested stage and its proliferating progenitor. The existence of a regulated cell death programme inducing an apoptotic phenotype in a unicellular eukaryote provides a paradigm for a widespread role for PCD in the control of cell survival, which extends beyond the evolutionary constraints that may be specific to multicellular organisms and raises the question of the origin and nature of the genes involved. Another implication is that PCD induction could represent a target for therapeutic strategies against unicellular pathogens.     

The mouse pubic symphysis as a remodeling system: morphometrical analysis of proliferation and cell death during pregnancy, partus and postpartum

Marked changes in mice pubic symphysis occur by the end of pregnancy. Tissue remodeling involves a dynamic balance between cell proliferation and programmed cell death as well as changes in the extracellular matrix components. Therefore, it is important to consider both of these cellular behaviors when investigating the mechanism that regulates interpubic tissue remodeling, growth during late pregnancy and partus ensuring involution during the postpartum period. Proliferating and programmed death cells were identified by immunohistochemistry (proliferating cell nuclear antigen and TUNEL detection, respectively) and the rates at which these processes occurred were determined by morphometric analysis. The results demonstrated that cellular proliferation was intense during the period of ligament formation, from D15 to D18, thereafter abruptly declining on D19. From parturition (D19) onwards, an ever-increasing decline in the cellular proliferation levels could be observed. The quantitative analyses of cellular death showed opposite results when compared to cellular proliferation. During early pregnancy the cycle of cellular renovation was clearly proliferative and during late mouse pregnancy the cycle was directed by programmed cellular death. Although the high levels of cellular death during postpartum involution could be shown by the TUNEL-positive cells, we were unable to observed picnotic nucleus at the light microscopy.     

Cytochrome c is released from coupled mitochondria of yeast en route to acetic acid-induced programmed cell death and can work as an electron donor and a ROS scavenger

To gain insight into the processes by which acetic acid-induced programmed cell death (AA-PCD) takes place in yeast, we investigated both cytochrome c release from yeast mitochondria and mitochondrial coupling over the time course of AA-PCD. We show that the majority of cytochrome c release occurs early in AA-PCD from intact coupled mitochondria which undergo only gradual impairment. The released cytochrome c can be reduced both by ascorbate and by superoxide anion and in turn be oxidized via cytochrome c oxidase, thus working both as a ROS scavenger and a respiratory substrate. Late in AA-PCD, the released cytochrome c is degraded.     

The peptidases of Trypanosoma cruzi: Digestive enzymes, virulence factors, and mediators of autophagy and programmed cell death

Trypanosoma cruzi, the agent of the American Trypanosomiasis, Chagas disease, contains cysteine, serine, threonine, aspartyl and metallo peptidases. The most abundant among these enzymes is cruzipain, a cysteine proteinase expressed as a mixture of isoforms, some of them membrane-bound. The enzyme is an immunodominant antigen in human chronic Chagas disease and seems to be important in the host/parasite relationship. Inhibitors of cruzipain kill the parasite and cure infected mice, thus validating the enzyme as a very promising target for the development of new drugs against the disease. In addition, a 30 kDa cathepsin B-like enzyme, two metacaspases and two autophagins have been described. Serine peptidases described in the parasite include oligopeptidase B, a member of the prolyl oligopeptidase family involved in Ca²⁺-signaling during mammalian cell invasion; a prolyl endopeptidase (Tc80), against which inhibitors are being developed, and a lysosomal serine carboxypeptidase. Metallopeptidases homologous to the gp63 of Leishmania spp. are present, as well as two metallocarboxypeptidases belonging to the M32 family, previously found only in prokaryotes. The proteasome has properties similar to those of other eukaryotes, and its inhibition by lactacystin blocks some differentiation steps in the life cycle of the parasite. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.     

In the early phase of programmed cell death in Tobacco Bright Yellow 2 cells the mitochondrial adenine nucleotide translocator, adenylate kinase and nucleoside diphosphate kinase are impaired in a reactive oxygen species-dependent manner

To investigate whether and how mitochondria can change in plant programmed cell death (PCD), we used the non-photosynthetic Tobacco Bright Yellow 2 (TBY-2) cells. These can be synchronized to high levels, stand out in terms of growth rate and homogeneity and undergo PCD as a result of heat shock. Using these cells we investigated the activity of certain mitochondrial proteins that have a role in providing ATP and/or other nucleoside triphosphates (NTPs). We show that, already after 2 h from the heat shock, when cell viability remains unaffected, the rate of ADP/ATP exchange due to adenine nucleotide translocator (ANT) activity, and the rate of the reactions catalysed by adenylate kinase (ADK; EC 2.7.4.3) and nucleoside diphosphate kinase (NDPK; EC 2.7.4.6) are inhibited in a non-competitive-like manner. In all cases, externally added ascorbate partially prevented the inhibition. These effects occurred in spite of minor (for ANT) or no changes in the mitochondrial protein levels as immunologically investigated. Interestingly, a decrease of both the steady state level of the ascorbate pool and of the activity of l-galactono-γ-lactone dehydrogenase (GLDH) (EC 1.3.2.3), the mitochondrial enzyme catalysing the last step of ascorbate biosynthesis, were also found.