Autophagy in stem cells

Autophagy is a highly conserved cellular process by which cytoplasmic components are sequestered in autophagosomes and delivered to lysosomes for degradation. As a major intracellular degradation and recycling pathway, autophagy is crucial for maintaining cellular homeostasis as well as remodeling during normal development, and dysfunctions in autophagy have been associated with a variety of pathologies including cancer, inflammatory bowel disease and neurodegenerative disease. Stem cells are unique in their ability to self-renew and differentiate into various cells in the body, which are important in development, tissue renewal and a range of disease processes. Therefore, it is predicted that autophagy would be crucial for the quality control mechanisms and maintenance of cellular homeostasis in various stem cells given their relatively long life in the organisms. In contrast to the extensive body of knowledge available for somatic cells, the role of autophagy in the maintenance and function of stem cells is only beginning to be revealed as a result of recent studies. Here we provide a comprehensive review of the current understanding of the mechanisms and regulation of autophagy in embryonic stem cells, several tissue stem cells (particularly hematopoietic stem cells), as well as a number of cancer stem cells. We discuss how recent studies of different knockout mice models have defined the roles of various autophagy genes and related pathways in the regulation of the maintenance, expansion and differentiation of various stem cells. We also highlight the many unanswered questions that will help to drive further research at the intersection of autophagy and stem cell biology in the near future.     

VMP1 is a new player in the regulation of the autophagy-specific phosphatidylinositol 3-kinase complex activation

We have elucidated a novel mechanism through which the autophagy-specific class III phosphatidylinositol 3-kinase (PtdIns3K) complex can be recruited to the PAS in mammalian cells, through the interaction between BECN1 and the vacuole membrane protein 1 (VMP1), an integral autophagosomal membrane protein. This interaction involves the binding between the C-terminal 20 amino acids of the VMP1 hydrophilic domain, which we have named the VMP1 autophagy-related domain (VMP1-AtgD), and the BH3 domain of BECN1. The association between these two proteins allows the formation of the autophagy-specific PtdIns3K complex, which activity favors the generation of phosphatidylinositol-3-phosphate (PtdIns3P) and the subsequent association of the autophagy-related (ATG) proteins, including ATG16L1, with the phagophore membranes. Therefore, VMP1 regulates the PtdIns3K activity on the phagophore membrane through its interaction with BECN1. Our data provide a novel model describing one of the key steps in phagophore assembly site (PAS) formation and autophagy regulation, and positions VMP1 as a new interactor of the autophagy-specific PtdIns3K complex in mammalian cells.     

Coal Fly Ash Impairs Airway Antimicrobial Peptides and Increases Bacterial Growth

Air pollution is a risk factor for respiratory infections, and one of its main components is particulate matter (PM), which is comprised of a number of particles that contain iron, such as coal fly ash (CFA). Since free iron concentrations are extremely low in airway surface liquid (ASL), we hypothesize that CFA impairs antimicrobial peptides (AMP) function and can be a source of iron to bacteria. We tested this hypothesis in vivo by instilling mice with Pseudomonas aeruginosa (PA01) and CFA and determine the percentage of bacterial clearance. In addition, we tested bacterial clearance in cell culture by exposing primary human airway epithelial cells to PA01 and CFA and determining the AMP activity and bacterial growth in vitro. We report that CFA is a bioavailable source of iron for bacteria. We show that CFA interferes with bacterial clearance in vivo and in primary human airway epithelial cultures. Also, we demonstrate that CFA inhibits AMP activity in vitro, which we propose as a mechanism of our cell culture and in vivo results. Furthermore, PA01 uses CFA as an iron source with a direct correlation between CFA iron dissolution and bacterial growth. CFA concentrations used are very relevant to human daily exposures, thus posing a potential public health risk for susceptible subjects. Although CFA provides a source of bioavailable iron for bacteria, not all CFA particles have the same biological effects, and their propensity for iron dissolution is an important factor. CFA impairs lung innate immune mechanisms of bacterial clearance, specifically AMP activity. We expect that identifying the PM mechanisms of respiratory infections will translate into public health policies aimed at controlling, not only concentration of PM exposure, but physicochemical characteristics that will potentially cause respiratory infections in susceptible individuals and populations.     

Adenosine-Mediated Enteric Neuromuscular Function Is Affected during Herpes Simplex Virus Type 1 Infection of Rat Enteric Nervous System

Adenosine plays an important role in regulating intestinal motility and inflammatory processes. Previous studies in rodent models have demonstrated that adenosine metabolism and signalling are altered during chronic intestinal inflammatory diseases. However, the involvement of the adenosinergic system in the pathophysiology of gut dysmotility associated to a primary neurodysfunction is still unclear. Recently, we showed that the neurotropic Herpes simplex virus type-1 (HSV-1), orally inoculated to rodents, infects the rat enteric nervous system (ENS) and affects gut motor function without signs of systemic infection. In this study we examined whether changes in purinergic metabolism and signaling occur during permanent HSV-1 infection of rat ENS. Using isolated organ bath assays, we found that contraction mediated by adenosine engagement of A₁ or A_2A receptors was impaired at 1 and 6 weeks post-viral administration. Immunofluorescence studies revealed that viral infection of ENS led to a marked redistribution of adenosine receptors: A₁ and A_2B receptors were confined to the muscle layers whereas A_2A and A₃ receptors were expressed mainly in the myenteric plexus. Viral-induced ENS neurodysfunction influenced adenosine metabolism by increasing adenosine deaminase and CD73 levels in longitudinal muscle-myenteric plexus with no sign of frank inflammation. This study provides the first evidence for involvement of the adenosinergic system during HSV-1 infection of the ENS. As such, this may represent a valid therapeutic target for modulating gut contractility associated to a primary neurodysfunction.     

Long Term Effects of Aversive Reinforcement on Colour Discrimination Learning in Free-Flying Bumblebees

The results of behavioural experiments provide important information about the structure and information-processing abilities of the visual system. Nevertheless, if we want to infer from behavioural data how the visual system operates, it is important to know how different learning protocols affect performance and to devise protocols that minimise noise in the response of experimental subjects. The purpose of this work was to investigate how reinforcement schedule and individual variability affect the learning process in a colour discrimination task. Free-flying bumblebees were trained to discriminate between two perceptually similar colours. The target colour was associated with sucrose solution, and the distractor could be associated with water or quinine solution throughout the experiment, or with one substance during the first half of the experiment and the other during the second half. Both acquisition and final performance of the discrimination task (measured as proportion of correct choices) were determined by the choice of reinforcer during the first half of the experiment: regardless of whether bees were trained with water or quinine during the second half of the experiment, bees trained with quinine during the first half learned the task faster and performed better during the whole experiment. Our results confirm that the choice of stimuli used during training affects the rate at which colour discrimination tasks are acquired and show that early contact with a strongly aversive stimulus can be sufficient to maintain high levels of attention during several hours. On the other hand, bees which took more time to decide on which flower to alight were more likely to make correct choices than bees which made fast decisions. This result supports the existence of a trade-off between foraging speed and accuracy, and highlights the importance of measuring choice latencies during behavioural experiments focusing on cognitive abilities.     

Two new endemic species of Ophiorrhiza L. (Rubiaceae: Ophiorrhizeae) from Davao Oriental,Philippines

Two new species of Ophiorrhiza collected from Mt Hamiguitan Range Wildlife Sanctuary in Davao Oriental, Philippines, are herein described and illustrated. Ophiorrhiza erythropilosa is the third Philippine species possessing involucral bracts and is further characterized by its predominantly villose stems that appear red due to strikingly red-violet trichomes, subpersistent bifid stipules, linear involucral bracts without prominent midrib, and 4 mm long urceolate corolla that is villose outside and lightly puberulous inside. Ophiorrhiza hamiguitanensis is characterized by its coriaceous, lanceolate leaves with attenuate apex and base, brochidodromous venation, subpersistent bilobed stipules with slightly recurved acute tips, presence of 1.5–2.5 mm long linear ensiform bracts, heterostylous flowers, clavate calyces and broadly obcordate capsules.     

A retrospective study of DNA prevalence of porcine parvoviruses in Mexico and its relationship with porcine circovirus associated disease

Worldwide, many emerging porcine parvoviruses (PPVs) have been linked to porcine circovirus-2 (PCV2) associated disease (PCVAD), which includes post-weaning multi-systemic wasting syndrome (PMWS), PCV2-related reproductive failure (PCV2-RF), as well as other syndromes. To determine the DNA prevalence of PPVs and their relationship with PMWS and PCV2-RF in Mexico, 170 formalin-fixed paraffin-embedded tissues were selected from archival collections to detect PPVs using a nested polymerase chain reaction. The tissues were composed of 50 PMWS cases, 20 age-matched tissues from healthy pigs, 56 PCV2-related reproductive failure (PCV2⁺-RF) cases, and 44 PCV2^--RF cases. Overall, PPV2 and PPV6 were the most prevalent species (90.0% and 74.7%, respectively). In 8–11 week old pigs, the highest prevalence was for PPV6 and PPV3. Concerning reproductive failure, the PCV2-affected farms had a significantly higher prevalence for PPV6 (61.6%) and PPV5 (36.4%) than the PCV2-unaffected farms (35.0% and 5.0%, respectively). The concurrent infection rate was high, being significant for PPV2/PPV4 and PPV1/PPV5 within the PMWS cases and for PPV6/PPV5 among the PCV2⁺-RF tissues. PPV5 showed a significant relationship with PMWS, whereas PPV5 and PPV6 were significant for PCVAD. The prevalence and coinfection rate of PPVs in Mexico were markedly higher than that described in other countries, denoting that PPV5 and PPV6 might have a potential role in PCVAD in Mexico. It is concluded that it is likely that the density population of pigs in Mexico is contributing to high PPV inter-species and PCV2 coinfections which might lead to a different pathogenic outcome.     

When size does matter: organelle size influences the properties of transport mediated by molecular motors

Background

Organelle transport is driven by the action of molecular motors. In this work, we studied the dynamics of organelles of different sizes with the aim of understanding the complex relation between organelle motion and microenvironment.

Methods

We used single particle tracking to obtain trajectories of melanosomes (pigmented organelles in Xenopus laevis melanophores). In response to certain hormones, melanosomes disperse in the cytoplasm or aggregate in the perinuclear region by the combined action of microtubule and actin motors.

Results and conclusions

Melanosome trajectories followed an anomalous diffusion model in which the anomalous diffusion exponent (α) provided information regarding the trajectories' topography and thus of the processes causing it. During aggregation, the directionality of big organelles was higher than that of small organelles and did not depend on the presence of either actin or intermediate filaments (IF). Depolymerization of IF significantly reduced α values of small organelles during aggregation but slightly affect their directionality during dispersion.

General significance

Our results could be interpreted considering that the number of copies of active motors increases with organelle size. Transport of big organelles was not influenced by actin or IF during aggregation showing that these organelles are moved processively by the collective action of dynein motors. Also, we found that intermediate filaments enhance the directionality of small organelles suggesting that this network keeps organelles close to the tracks allowing their efficient reattachment. The higher directionality of small organelles during dispersion could be explained considering the better performance of kinesin-2 vs. dynein at the single molecule level.