Attenuated Mycobacterium tuberculosis SO2 Vaccine Candidate Is Unable to Induce Cell Death

It has been proposed that Mycobacterium tuberculosis virulent strains inhibit apoptosis and trigger cell death by necrosis of host macrophages to evade innate immunity, while non-virulent strains induce typical apoptosis activating a protective host response. As part of the characterization of a novel tuberculosis vaccine candidate, the M. tuberculosis phoP mutant SO2, we sought to evaluate its potential to induce host cell death. The parental M. tuberculosis MT103 strain and the current vaccine against tuberculosis Bacillus Calmette-Guérin (BCG) were used as comparators in mouse models in vitro and in vivo. Our data reveal that attenuated SO2 was unable to induce apoptotic events neither in mouse macrophages in vitro nor during lung infection in vivo. In contrast, virulent MT103 triggers typical apoptotic events with phosphatidylserine exposure, caspase-3 activation and nuclear condensation and fragmentation. BCG strain behaved like SO2 and did not induce apoptosis. A clonogenic survival assay confirmed that viability of BCG- or SO2-infected macrophages was unaffected. Our results discard apoptosis as the protective mechanism induced by SO2 vaccine and provide evidence for positive correlation between classical apoptosis induction and virulent strains, suggesting apoptosis as a possible virulence determinant during M. tuberculosis infection.     

Plant–pollinator networks in semi‐natural grasslands are resistant to the loss of pollinators during blooming of mass‐flowering crops

Mass‐flowering crops lead to spatial redistributions of pollinators and to transient shortages within nearby semi‐natural grasslands, but the impacts on plant–pollinator interactions remain largely unexplored. Here, we characterised which pollinator species are attracted by oilseed rape and how this affected the structure of plant–pollinator networks in nearby grasslands. We surveyed 177 networks from three countries (Germany, Sweden and United Kingdom) in 24 landscapes with high crop cover, and compared them to 24 landscapes with low or no oilseed rape during and after crop blooming. On average 55% of grassland pollinator species were found on the crop, which attracted 8–35% of individuals away from grasslands. However, networks in the grasslands were resistant to these reductions, since mainly abundant and highly mobile species were attracted. Nonetheless, simulations indicated that network structural changes could be triggered if > 50% of individuals were attracted to the crop (a value well‐above that found in our study system), which could affect community stability and resilience to further disturbance.     

Natamycin blocks fungal growth by binding specifically to ergosterol without permeabilizing the membrane

Natamycin is a polyene antibiotic that is commonly used as an antifungal agent because of its broad spectrum of activity and the lack of development of resistance. Other polyene antibiotics, like nystatin and filipin are known to interact with sterols, with some specificity for ergosterol thereby causing leakage of essential components and cell death. The mode of action of natamycin is unknown and is investigated in this study using different in vitro and in vivo approaches. Isothermal titration calorimetry and direct binding studies revealed that natamycin binds specifically to ergosterol present in model membranes. Yeast sterol biosynthetic mutants revealed the importance of the double bonds in the B-ring of ergosterol for the natamycin-ergosterol interaction and the consecutive block of fungal growth. Surprisingly, in strong contrast to nystatin and filipin, natamycin did not change the permeability of the yeast plasma membrane under conditions that growth was blocked. Also, in ergosterol containing model membranes, natamycin did not cause a change in bilayer permeability. This demonstrates that natamycin acts via a novel mode of action and blocks fungal growth by binding specifically to ergosterol.     

Recurrent seasonal changes in bacterial growth efficiency,metabolism and community composition in coastal waters

The microbial response to environmental changes in coastal waters of the eastern Cantabrian Sea was explored for four years by analysing a broad set of environmental variables along with bacterial community metabolism and composition. A recurrent seasonal cycle emerged, consisting of two stable periods, characterized by low bacterial metabolic activity (winter) from October to March, and high bacterial metabolic activity (summer) from May to August. These two contrasting periods were linked by short transition periods in April (T_A) and September (T_S). The phylogenetic groups Alphaproteobacteria and Bacteroidetes were dominant during winter and summer respectively, and their recurrent alternation was mainly driven by the bloom of eukaryotic phytoplankton before T_A and the bloom of prokaryotic phytoplankton before T_S. Bacterial growth efficiency remained high and stable during the winter and summer periods but dropped during the two short transition periods. Our results suggest that bacterial growth efficiency should be considered a very resilient property that reflects different stages in the adaptation of the bacterial community composition to the environmental changes occurring throughout the seasonal cycle in this coastal ecosystem.     

The benefits of aging: cellular senescence in normal development

Senescence is a form of cellular aging that limits the proliferative capacity of cells. Senescence can be triggered by different stress stimuli, such as DNA damage or oncogene activation. Two recent articles published in Cell have uncovered an unexpected role for cellular senescence during development, as a process that contributes to remodeling and patterning of the embryo. These findings are exciting and have important implications for the understanding of normal developmental and the evolutionary origin of senescence.     

1-Oleoyl Lysophosphatidic Acid: A New Mediator of Emotional Behavior in Rats

The role of lysophosphatidic acid (LPA) in the control of emotional behavior remains to be determined. We analyzed the effects of the central administration of 1-oleoyl-LPA (LPA 18∶1) in rats tested for food consumption and anxiety-like and depression-like behaviors. For this purpose, the elevated plus-maze, open field, Y maze, forced swimming and food intake tests were performed. In addition, c-Fos expression in the dorsal periaqueductal gray matter (DPAG) was also determined. The results revealed that the administration of LPA 18∶1 reduced the time in the open arms of the elevated plus-maze and induced hypolocomotion in the open field, suggesting an anxiogenic-like phenotype. Interestingly, these effects were present following LPA 18∶1 infusion under conditions of novelty but not under habituation conditions. In the forced swimming test, the administration of LPA 18∶1 dose-dependently increased depression-like behavior, as evaluated according to immobility time. LPA treatment induced no effects on feeding. However, the immunohistochemical analysis revealed that LPA 18∶1 increased c-Fos expression in the DPAG. The abundant expression of the LPA₁ receptor, one of the main targets for LPA 18∶1, was detected in this brain area, which participates in the control of emotional behavior, using immunocytochemistry. These findings indicate that LPA is a relevant transmitter potentially involved in normal and pathological emotional responses, including anxiety and depression.     

hxc2, an Arabidopsis mutant with an altered hypersensitive response to Xanthomonas campestris pv. campestris

A chemical mutagenized population of Arabidopsis Col-0-gl plants was screened for an altered hypersensitive response (HR) after spray inoculation with an HR-inducing isolate of Xanthomonas campestris pv. campestris (strain 147). Three classes of mutant were identified: those exhibiting an HR- phenotype or partial loss of HR; hyper-responsive mutants showing necrotic lesions rapidly leading to the collapse of leaves; and susceptible mutants. One mutant belonging to the susceptible class, hxc-2, was extensively characterized. The compatible phenotype observed several days after initiation of the interaction was confirmed by measurement of in planta bacterial growth and use of bacterial strains constitutively expressing the GUS reporter gene. In the same way, accumulation of autofluorescent compounds, salicylic acid production and defence gene expression in the mutant were found to be similar to that displayed by the susceptible ecotype. Inoculation of hxc-2 with different avirulent bacteria suggests that the mutation is specific for the interaction with the Xcc 147 strain, although the mutation has been shown to affect a single dominant locus, different from the resistance locus defined by genetic analysis of resistance to Xcc 147. Genetic mapping of the mutation indicated that it is located on chromosome III, defining a previously unknown resistance function in response to X. c. campestris.     

BH3-Mimetics- and Cisplatin-Induced Cell Death Proceeds through Different Pathways Depending on the Availability of Death-Related Cellular Components

Background

Owing to their important function in regulating cell death, pharmacological inhibition of Bcl-2 proteins by dubbed BH3-mimetics is a promising strategy for apoptosis induction or sensitization to chemotherapy. However, the role of Apaf-1, the main protein constituent of the apoptosome, in the process has yet not been analyzed. Furthermore as new chemotherapeutics develop, the possible chemotherapy-induced toxicity to rapidly dividing normal cells, especially sensitive differentiated cells, has to be considered. Such undesirable effects would probably be ameliorated by selectively and locally inhibiting apoptosis in defined sensitive cells.

Methodology and Principal Findings

Mouse embryonic fibroblasts (MEFS) from Apaf-1 knock out mouse (MEFS KO Apaf-1) and Bax/Bak double KO (MEFS KO Bax/Bak), MEFS from wild-type mouse (MEFS wt) and human cervix adenocarcinoma (HeLa) cells were used to comparatively investigate the signaling cell death-induced pathways of BH3-mimetics, like ABT737 and GX15-070, with DNA damage-inducing agent cisplatin (cis-diammineplatinum(II) dichloride, CDDP). The study was performed in the absence or presence of apoptosis inhibitors namely, caspase inhibitors or apoptosome inhibitors. BH3-mimetic ABT737 required of Apaf-1 to exert its apoptosis-inducing effect. In contrast, BH3-mimetic GX15-070 and DNA damage-inducing CDDP induced cell death in the absence of both Bax/Bak and Apaf-1. GX15-070 induced autophagy-based cell death in all the cell lines analyzed. MEFS wt cells were protected from the cytotoxic effects of ABT737 and CDDP by chemical inhibition of the apoptosome through QM31, but not by using general caspase inhibitors.

Conclusions

BH3-mimetic ABT737 not only requires Bax/Bak to exert its apoptosis-inducing effect, but also Apaf-1, while GX15-070 and CDDP induce different modalities of cell death in the absence of Bax/Bak or Apaf-1. Inclusion of specific Apaf-1 inhibitors in topical and well-localized administrations, but not in systemic ones, to avoid interferences with chemotherapeutics would be of interest to prevent chemotherapeutic-induced unwanted cell death which could improve cancer patient care.     

Overlapping expression of microRNAs in human embryonic colon and colorectal cancer

MicroRNAs (miRNAs) are essential for regulating cell differentiation and maintaining the pluripotent state of stem cells. Although dysregulation of specific miRNAs has been associated with certain types of cancer, to date no evidence has linked miRNA expression in embryonic and tumor tissues. We assessed the expression of mature miRNAs in human embryonic colon tissue, and in colorectal cancer and paired normal colon tissue. Overlapping miRNA expression was detected between embryonic colonic mucosa and colorectal cancer. We have found that the miR-17-92 cluster and its target, E2F1, exhibit a similar pattern of expression in human colon development and colonic carcinogenesis, regulating cell proliferation in both cases. In situ hybridization confirmed the high level of expression of miR-17-5p in the crypt progenitor compartment. We conclude that miRNA pathways play a major role in both embryonic development and neoplastic transformation of the colonic epithelium.