Retinoid-X-Receptors (α/β) in Melanocytes Modulate Innate Immune Responses and Differentially Regulate Cell Survival following UV Irradiation

Understanding the molecular mechanisms of ultraviolet (UV) induced melanoma formation is becoming crucial with more reported cases each year. Expression of type II nuclear receptor Retinoid-X-Receptor α (RXRα) is lost during melanoma progression in humans. Here, we observed that in mice with melanocyte-specific ablation of RXRα and RXRβ, melanocytes attract fewer IFN-γ secreting immune cells than in wild-type mice following acute UVR exposure, via altered expression of several chemoattractive and chemorepulsive chemokines/cytokines. Reduced IFN-γ in the microenvironment alters UVR-induced apoptosis, and due to this, the survival of surrounding dermal fibroblasts is significantly decreased in mice lacking RXRα/β. Interestingly, post-UVR survival of the melanocytes themselves is enhanced in the absence of RXRα/β. Loss of RXRs α/β specifically in the melanocytes results in an endogenous shift in homeostasis of pro- and anti-apoptotic genes in these cells and enhances their survival compared to the wild type melanocytes. Therefore, RXRs modulate post-UVR survival of dermal fibroblasts in a “non-cell autonomous” manner, underscoring their role in immune surveillance, while independently mediating post-UVR melanocyte survival in a “cell autonomous” manner. Our results emphasize a novel immunomodulatory role of melanocytes in controlling survival of neighboring cell types besides controlling their own, and identifies RXRs as potential targets for therapy against UV induced melanoma.     

Relationship between Autophagy and Apoptotic Cell Death in Human Neuroblastoma Cells Treated with Paraquat: Could Autophagy be a “Brake” in Paraquat-Induced Apoptotic Death?

Paraquat (PQ) (1, 1’-dimethyl-4, 4’-bipyridinium dichloride), a widely used herbicide, has been suggested as a potential etiologic factor for the development of Parkinson’s disease (PD). In neurons from patients with PD display characteristics of autophagy, a degradative mechanism involved in the recycling and turnover of cytoplasmic constituents from eukaryotic cells. Low concentrations of paraquat have been recently found to induce autophagy in human neuroblastoma cells, and ultimately the neurons succumb to apoptotic death. Whereas caspase inhibition retarded cell death, autophagy inhibition accelerated the apoptotic cell death induced by paraquat. These findings suggest a relationship between autophagy and apoptotic cell death in human neuroblastoma cells treated with paraquat and open a new line of investigation to advance our knowledge regarding the origin of PD.

Addendum to

Inhibition of Paraquat-Induced Autophagy Accelerates the Apoptotic Cell Death in Neuroblastoma SH-SY5Y Cells

R.A. González-Polo, M. Niso-Santano, M.A. Ortíz-Ortíz, A. Gómez-Martín, J.M. Morán, L. García-Rubio, J. Francisco-Morcillo, C. Zaragoza , G. Soler and J.M. Fuentes

Toxicological Science 2007; In press     

Post-Tetanic and Depolarization-Induced Suppression of Inhibition in Hippocampal Cell Cultures: Are Similar Mechanisms Involved?

Several forms of short-term synaptic plasticity of GABA-ergic synaptic transmission selectively expressed only in a fraction of synaptic connections have been described earlier. In particular, this is the phenomenon termed “depolarization-induced suppression of inhibition” (DSI), a transient suppression of GABA-ergic synaptic transmission evoked by postsynaptic spike firing or brief depolarization of the membrane of postsynaptic neurons. On the other hand, the same tetanic stimulation (30 sec⁻¹, 4 sec) of the presynaptic neuron also revealed the heterogeneity of GABA-ergic synaptic connections: about 45% of the connections were facilitated, while 55% were depressed. In this work, we show that post-tetanic depression is predominantly expressed in neuronal pairs susceptible to DSI, and that both phenomena have a similar time course. Considering our own results and the retrograde involvement of endocannabinoids in DSI, we hypothesize that post-tetanic depression is also due to the release of endocannabinoids acting, in the latter case, on their autoreceptors.     

Is Hypothalamic GABA Involved in Immune Function in Relation to Dietary Protein During Aging?

Hypothalamic GABAergic activity and immune response in spleen were not significantly changed with the increase of age from 3 to 6 months in adult male albino rats. Further increase of age from 6 to 9 months increased the GABAergic activity and decreased the cell viability in spleen without any change in its T-lymphocyte cytotoxicity. Consumption of low protein diet (LPD) for a short-term period (STP; 7 consecutive days) increased the hypothalamie GABAergic activity without changing the immune response in 3 months old rats. When supplemented for a long-term period (LTP; 30 consecutive days) to 3 months old rats, a reduction of hypothalamie GABAergic activity and the immune response was observed. Intake of high protein diet (HPD) for both STP and LTP increased the GABAergic activity and immune response, but the increase of GABAergic activity in hypothalamus under STP was greater than that observed under LTP. In 6 months old rats consumption of LPD for STP reduced the GABAergic activity without any alteration of its immune response. Long-term supplementation of this LPD to the same age group increased GABAergic activity and the mitotic activity of spleen cells without any alteration of the functional activity of the T-cells in spleen. Consumption of HPD for STP failed to produce any change in hypothalamic GABAergic activity and the immune response of 6 months old rats. Supplementation of HPD for LTP reduced the hypothalamic GABAergic activity and the immune response of the same age group. The reduction in hypothalamic GABAergic activity without any change in the immune response was observed following the supplementation of low protein diet to 9 months old rat for STP. Intake of the LPD for LTP also reduced the hypothalamie GABAergic activity and the mitotic activity of the spleen cells without any alteration of the functional activity of the T-cells in spleen of 9 months old rats. Supplementation of HPD for STP to this aged rat, on the other hand, failed to produced any change in hypothalamic GABAergic activity and the immune response. Intake of HPD for LTP by this aged rats increased the hypothalamie GABAergic activity along with the immune response. The results of this study, thus, suggest that hypothalamic GABAergic activity during aging is an index of immune response and it is modulated following the short- and long-term consumption of protein poor and protein rich diet.     

Are Global and Regional Improvements in Life Expectancy and in Child,Adult and Senior Survival Slowing?

Improvements in life expectancy have been considerable over the past hundred years. Forecasters have taken to applying historical trends under an assumption of continuing improvements in life expectancy in the future. A linear mixed effects model was used to estimate the trends in global and regional rates of improvements in life expectancy, child, adult, and senior survival, in 166 countries between 1950 and 2010. Global improvements in life expectancy, including both child and adult survival rates, decelerated significantly over the study period. Overall life expectancy gains were estimated to have declined from 5.9 to 4.0 months per year for a mean deceleration of -0.07 months/year²; annual child survival gains declined from 4.4 to 1.6 deaths averted per 1000 for a mean deceleration of -0.06 deaths/1000/year²; adult survival gains were estimated to decline from 4.8 to 3.7 deaths averted per 1000 per year for a mean deceleration of -0.08 deaths/1000/year². Senior survival gains however increased from 2.4 to 4.2 deaths averted per 1000 per year for an acceleration of 0.03 deaths/1000/year². Regional variation in the four measures was substantial. The rates of global improvements in life expectancy, child survival, and adult survival have declined since 1950 despite an increase in the rate of improvements among seniors. We postulate that low-cost innovation, related to the last half-century progress in health–primarily devoted to children and middle age, is reaping diminishing returns on its investments. Trends are uneven across regions and measures, which may be due in part to the state of epidemiological transition between countries and regions and disparities in the diffusion of innovation, accessible only in high-income countries where life expectancy is already highest.     

Plant Immune Responses Against Viruses: How Does a Virus Cause Disease?

Plants respond to pathogens using elaborate networks of genetic interactions. Recently, significant progress has been made in understanding RNA silencing and how viruses counter this apparently ubiquitous antiviral defense. In addition, plants also induce hypersensitive and systemic acquired resistance responses, which together limit the virus to infected cells and impart resistance to the noninfected tissues. Molecular processes such as the ubiquitin proteasome system and DNA methylation are also critical to antiviral defenses. Here, we provide a summary and update of advances in plant antiviral immune responses, beyond RNA silencing mechanisms—advances that went relatively unnoticed in the realm of RNA silencing and nonviral immune responses. We also document the rise of Brachypodium and Setaria species as model grasses to study antiviral responses in Poaceae, aspects that have been relatively understudied, despite grasses being the primary source of our calories, as well as animal feed, forage, recreation, and biofuel needs in the 21st century. Finally, we outline critical gaps, future prospects, and considerations central to studying plant antiviral immunity. To promote an integrated model of plant immunity, we discuss analogous viral and nonviral immune concepts and propose working definitions of viral effectors, effector-triggered immunity, and viral pathogen-triggered immunity.     

Autophagy,Bafilomycin and Cell Death: The “A-B-Cs” of Plecomacrolide-Induced Neuroprotection

Bafilomycin A1 (BafA1), which is a member of the plecomacrolide sub-class of macrolide antibiotics, has differential, concentration-dependent effects on neuronal cell viability. When used at high concentrations, BafA1 inhibits vacuolar ATPase (V-ATPase), promotes the accumulation of autophagic vacuoles and triggers Bax-dependent apoptosis. These effects are similar to those induced by the lysosomotropic agent chloroquine. Conversely, at concentrations below its reported ability to completely inhibit V-ATPase, BafA1 dramatically attenuates chloroquine-induced apoptosis. The protective effects of BafA1 appear to be independent of the chloroquine-induced accumulation of autophagosomes. Rather, BafA1 appears to inhibit events downstream of chloroquine-induced autophagosome accumulation, such as the loss mitochondrial or lysosomal integrity. Our finding that BafA1 inhibits the death of neurons induced by autophagic stress suggests a potentially novel mechanism of action apart from its ability to inhibit V-ATPase. Here we provide further evidence of neuroprotection against chloroquine-induced death by plecomacrolide antibiotics that are structurally similar to BafA1, including bafilomycin B1 and concanamycin A, and discuss potential mechanism(s) of neuroprotection against autophagic stress.

Addendum to:

Bafilomycin A1 Inhibits Chloroquine-Induced Death of Cerebellar Granule Neurons

John J. Shacka, Barbara J. Klocke, Masahiro Shibata, Yasuo Uchiyama, Geeta Datta, Robert E. Schmidt and Kevin A. Roth

Mol Pharmacol 2006; 69:1125-36     

Autophagy and Self-Preservation: A Step Ahead from Cell Plasticity?

Silencing the SPINK-related gene Kazal1 in hydra gland cells induces an excessive autophagy of both gland and digestive cells, leading to animal death. Moreover, during regeneration, autophagosomes are immediately detected in regenerating tips, where Kazal1 expression is lowered. When Kazal1 is completely silenced, hydra no longer survive the amputation stress (Chera S, de Rosa R, Miljkovic-Licina M, Dobretz K, Ghila L, Kaloulis K, and Galliot B. Silencing of the hydra serine protease inhibitor Kazal1 gene mimics the human Spink1 pancreatic phenotype. J Cell Sci 2006; 119:846-57). These results highlight the essential digestive and cytoprotective functions played by Kazal1 in hydra. In mammals, autophagy of exocrine pancreatic cells is also induced upon SPINK1/Spink3 inactivation, whereas SPINK3 is activated in injured pancreatic cells. Hence SPINKs, by preventing an excessive autophagy, appear to act as key players of the stress-induced self-preservation program. In hydra, this program is a prerequisite to the early cellular transition, whereby digestive cells of the regenerating tips transform into a head-organizer center. Enhancing the self-preservation program in injured tissues might therefore be the condition for unmasking their potential cell and/or developmental plasticity.

Addendum to:

Silencing of the Hydra Serine Protease Inhibitor Kazal1 Gene Mimics the HumanSpink1 Pancreatic Phenotype

S. Chera, R. de Rosa, M. Miljkovic-Licina, K. Dobretz, L. Ghila, K. Kaloulis and B. Galliot

J Cell Sci 2006; 119:846-57     

Molecular Mechanism of 5-Fluoro-2′-deoxyuridine-induced dNTP Imbalance Cell Death: Purification of an Endonuclease Involved in DNA Double Strand Breaks During dNTP Imbalance Death

Abstract

We have detected, isolated and purified an endonuclease from 5-fluoro-2′-deoxyuridine-treated FM3A cells. The molecular mass of the endonuclease was approximately 40 kDa as judged by sodium dodecyl sulfate-polyacrylamide DNA-containing gel electrophoresis. The endonuclease causes double strand breaks in DNA, with an optimum pH at 6.     

Programmed Cell Death in Floral Organs: How and Why do Flowers Die?

BACKGROUND: Flowers have a species-specific, limited life span with an irreversible programme of senescence, which is largely independent of environmental factors, unlike leaf senescence, which is much more closely linked with external stimuli. TIMING: Life span of the whole flower is regulated for ecological and energetic reasons, but the death of individual tissues and cells within the flower is co-ordinated at many levels to ensure correct timing. Some floral cells die selectively during organ development, whereas others are retained until the whole organ dies. TRIGGERS: Pollination is an important floral cell death trigger in many species, and its effects are mediated by the plant growth regulator (PGR) ethylene. In some species ethylene is a major regulator of floral senescence, but in others it plays a very minor role and the co-ordinating signals involved remain elusive. Other PGRs such as cytokinin and brassinosteroids are also important but their role is understood only in some specific systems. MECHANISMS: In two floral cell types (the tapetum and the pollen-tube) there is strong evidence for apoptotic-type cell death, similar to that in animal cells. However, in petals there is stronger evidence for an autophagous type of cell death involving endoplasmic reticulum-derived vesicles and the vacuole. Proteases are important, and homologues to animal caspases, key regulators of animal cell death, exist in plants. However, their role is not yet clear. COMPARISON WITH OTHER ORGANS: There are similarities to cell death in other plant organs, and many of the same genes are up-regulated in both leaf and petal senescence; however, there are also important differences for example in the role of PGRs. CONCLUSIONS: Understanding gene regulation may help to understand cell death in floral organs better, but alone it cannot provide all the answers.     

Life or Death? A Physiogenomic Approach to Understand Individual Variation in Responses to Hemorrhagic Shock

Severe hemorrhage due to trauma is a major cause of death throughout the world. It has often been observed that some victims are able to withstand hemorrhage better than others. For decades investigators have attempted to identify physiological mechanisms that distinguish survivors from nonsurvivors for the purpose of providing more informed therapies. As an alternative approach to address this issue, we have initiated a research program to identify genes and genetic mechanisms that contribute to this phenotype of survival time after controlled hemorrhage. From physiogenomic studies using inbred rat strains, we have demonstrated that this phenotype is a heritable quantitative trait, and is therefore a complex trait regulated by multiple genes. Our work continues to identify quantitative trait loci as well as potential epigenetic mechanisms that might influence survival time after severe hemorrhage. Our ultimate goal is to improve survival to traumatic hemorrhage and attendant shock via regulation of genetic mechanisms and to provide knowledge that will lead to genetically-informed personalized treatments.     

Statins, Bcl-2, and Apoptosis: Cell Death or Cell Protection?

Statins have proven their effectiveness in the treatment of cardiovascular disease. This class of drugs has also attracted attention as a potential treatment for dissimilar diseases such as certain types of cancers and neurodegenerative diseases. What appears to be a contradiction is that, in the case of cancer, it has been suggested that statins increase apoptosis and alter levels of Bcl-2 family members (e.g., reduce Bcl-2 and increase Bax), whereas studies mainly using noncancerous cells report opposite effects. This review examined studies reporting on the effects of statins on Bcl-2 family members, apoptosis, cell death, and cell protection. Much, but not all, of the evidence supporting the pro-apoptotic effects of statins is based on data in cancer cell lines and the use of relatively high drug concentrations. Studies indicating an anti-apoptotic effect of statins are fewer in number and generally used much lower drug concentrations and normal cells. Those conclusions are not definitive, and certainly, there is a need for additional research to determine if statin repositioning is justified for noncardiovascular diseases.     

Widespread Shortening of 3’ Untranslated Regions and Increased Exon Inclusion Are Evolutionarily Conserved Features of Innate Immune Responses to Infection

The contribution of pre-mRNA processing mechanisms to the regulation of immune responses remains poorly studied despite emerging examples of their role as regulators of immune defenses. We sought to investigate the role of mRNA processing in the cellular responses of human macrophages to live bacterial infections. Here, we used mRNA sequencing to quantify gene expression and isoform abundances in primary macrophages from 60 individuals, before and after infection with Listeria monocytogenes and Salmonella typhimurium. In response to both bacteria we identified thousands of genes that significantly change isoform usage in response to infection, characterized by an overall increase in isoform diversity after infection. In response to both bacteria, we found global shifts towards (i) the inclusion of cassette exons and (ii) shorter 3’ UTRs, with near-universal shifts towards usage of more upstream polyadenylation sites. Using complementary data collected in non-human primates, we show that these features are evolutionarily conserved among primates. Following infection, we identify candidate RNA processing factors whose expression is associated with individual-specific variation in isoform abundance. Finally, by profiling microRNA levels, we show that 3’ UTRs with reduced abundance after infection are significantly enriched for target sites for particular miRNAs. These results suggest that the pervasive usage of shorter 3’ UTRs is a mechanism for particular genes to evade repression by immune-activated miRNAs. Collectively, our results suggest that dynamic changes in RNA processing may play key roles in the regulation of innate immune responses.     

Expression of Cell Cycle-Related Genes During Neuronal Apoptosis: Is there a Distinct Pattern?

An emerging hypothesis considers the process of neuronal apoptosis as a consequence of unscheduled and unsynchronized induction of cell cycle mediators. Induction of several cell cycle genes precedes neuronal apoptosis and may be involved in determination of cell fate. We have now characterized changes in expression of cell cycle genes during apoptosis induced by oxidative stress in chick post-mitotic sympathetic neurons. Induction of cyclin B occurred prior to the commitment of neurons to both dopamine- and peroxide-triggered apoptosis. Both the neuronal death and the rise in cyclin B were inhibited by antioxidant treatment, suggesting a functional role for cyclin B induction during neuronal apoptosis. Induction of the cyclin dependent kinase CDK5 protein coincided with the time point when neurons were irreversibly committed to die. Expression of other cell cycle mediators such as cyclin D1 and the cyclin dependent kinases CDC2 and CDK2 was undetected and not induced by exposure to oxidative stress. Comparative analysis of the profile of cell cycle mediators induced during neuronal apoptosis of different neuronal cell populations revealed no distinct pattern of events. There are no cell cycle stage-specific mediators that are ultimately stimulated during neuronal apoptosis, suggesting that multiple pathways of re-activating the dormant cell-cycle, converge to determine entry into apoptosis. Nevertheless, the existence of some cell cycle mediators, that were not reported so far to be induced in post mitotic neurons during oxidative stress, substantiate them as part of the strong differentiating forces.     

Autophagy: dual roles in life and death?

Autophagy is an evolutionarily conserved mechanism for the degradation of cellular components in the cytoplasm, and serves as a cell survival mechanism in starving cells. Recent studies indicate that autophagy also functions in cell death, but the precise role of this catabolic process in dying cells is not clear. Here I discuss the possible roles for autophagy in dying cells and how understanding the relationship between autophagy, cell survival and cell death is important for health and development.     

Plasmodesmata the Nano Bridges in Plant Cell: Are the Answer for All the Developmental Processes?

Russian Journal of Plant Physiology - Plants establish tiny, cellular signaling pathways playing a unique coordination role in growth and development. Plasmodesmata are playing a central role in...     

Life or death? Autophagy in anticancer therapies with statins and histone deacetylase inhibitors

Autophagy, which could be either cytoprotective or cytotoxic, is often observed in tumor cells in response to chemotherapy. Understanding the signaling pathways involved in the regulation of autophagy represents a new direction in the development of anticancer therapies. Our recent studies investigate the role of autophagy in the anticancer effects of statins and histone deacetylase: inhibitors (HDACi). Inhibition of autophagy enhances the efficacy of statins, whereas autophagic cell death in cancer cells is induced by HDACi. Here, we will discuss the differential signaling pathways elicited by statins and HDACi. We find that AMPK, cytoplasmic p21 and Akt signaling are crucial determinants of cell fates (i.e., life or death) while autophagy is induced.