Therapeutic Strategies Targeting Mitochondrial Calcium Signaling: A New Hope for Neurological Diseases?

Calcium (Ca2+) is a versatile secondary messenger involved in the regulation of a plethora of different signaling pathways for cell maintenance. Specifically, intracellular Ca2+ homeostasis is mainly regulated by the endoplasmic reticulum and the mitochondria, whose Ca2+ exchange is mediated by appositions, termed endoplasmic reticulum–mitochondria-associated membranes (MAMs), formed by proteins resident in both compartments. These tethers are essential to manage the mitochondrial Ca2+ influx that regulates the mitochondrial function of bioenergetics, mitochondrial dynamics, cell death, and oxidative stress. However, alterations of these pathways lead to the development of multiple human diseases, including neurological disorders, such as amyotrophic lateral sclerosis, Friedreich’s ataxia, and Charcot–Marie–Tooth. A common hallmark in these disorders is mitochondrial dysfunction, associated with abnormal mitochondrial Ca2+ handling that contributes to neurodegeneration. In this work, we highlight the importance of Ca2+ signaling in mitochondria and how the mechanism of communication in MAMs is pivotal for mitochondrial maintenance and cell homeostasis. Lately, we outstand potential targets located in MAMs by addressing different therapeutic strategies focused on restoring mitochondrial Ca2+ uptake as an emergent approach for neurological diseases.

Retrograde Analysis of Calcium Signaling by CaMPARI2 Shows Cytosolic Calcium in Chondrocytes Is Unaffected by Parabolic Flights

Calcium (Ca2+) elevation is an essential secondary messenger in many cellular processes, including disease progression and adaptation to external stimuli, e.g., gravitational load. Therefore, mapping and quantifying Ca2+ signaling with a high spatiotemporal resolution is a key challenge. However, particularly on microgravity platforms, experiment time is limited, allowing only a small number of replicates. Furthermore, experiment hardware is exposed to changes in gravity levels, causing experimental artifacts unless appropriately controlled. We introduce a new experimental setup based on the fluorescent Ca2+ reporter CaMPARI2, onboard LED arrays, and subsequent microscopic analysis on the ground. This setup allows for higher throughput and accuracy due to its retrograde nature. The excellent performance of CaMPARI2 was demonstrated with human chondrocytes during the 75th ESA parabolic flight campaign. CaMPARI2 revealed a strong Ca2+ response triggered by histamine but was not affected by the alternating gravitational load of a parabolic flight.

The Role of Neuropeptide-Stimulated cAMP-EPACs Signalling in Cancer Cells

Neuropeptides are autocrine and paracrine signalling factors and mainly bind to G protein-coupled receptors (GPCRs) to trigger intracellular secondary messenger release including adenosine 3′, 5′-cyclic monophosphate (cAMP), thus modulating cancer progress in different kind of tumours. As one of the downstream effectors of cAMP, exchange proteins directly activated by cAMP (EPACs) play dual roles in cancer proliferation and metastasis. More evidence about the relationship between neuropeptides and EPAC pathways have been proposed for their potential role in cancer development; hence, this review focuses on the role of neuropeptide/GPCR system modulation of cAMP/EPACs pathways in cancers. The correlated downstream pathways between neuropeptides and EPACs in cancer cell proliferation, migration, and metastasis is discussed to glimmer the direction of future research.

Melatonin Participates in Selenium-Enhanced Cold Tolerance of Cucumber Seedlings

Melatonin is an important and widespread plant hormone. However, the underlying physiological and molecular mechanisms of melatonin as a secondary messenger in improving cold tolerance by selenium are limited. This study investigated the effects of selenite on the cold stress of cucumber seedlings. The results showed that exogenous application of selenite improved the cold tolerance of cucumber seedlings, which was dependent on the concentration effect. In the present experiment, 1 μM of selenite showed the best effect on alleviating cold stress. Interestingly, we found that in the process of alleviating cold stress, selenite increased the content of endogenous melatonin by regulating the expression of melatonin biosynthesis genes (TDC, T5H, SNAT, and COMT). To determine the interrelation between selenite and melatonin in alleviating cold stress, melatonin synthesis inhibitor p-chlorophenylalanine and melatonin were used for in-depth study. This study provides a theoretical basis for cucumber cultivation and breeding.

Imaging Promoter Assay of Adenylyl Cyclase A Gene in Dictyostelium discoideum during Fruiting Body Formation by Dual-Color Bioluminescence Microscopy

Cyclic adenosine monophosphate (cAMP), which is derived from adenosine triphosphate through adenylyl cyclase A (acaA), acts as an intracellular secondary messenger and an extracellular chemotactic substance in important biological processes. In the social amoebae Dictyostelium discoideum, cAMP mediates cell aggregation, development, and differentiation to spore and stalk cells during fruiting body formation. The acaA gene is transcribed under the control of three different alternative promoters. This study aimed to develop a promoter assay for acaA in D. discoideum using bioluminescence microscopy. Here, we inserted green- and red-emitting luciferase genes into downstream of promoter regions 1 and 3, respectively. Promoter activities were visualized by bioluminescence microscopy. We confirmed the differential expression of acaA under the control of promoters 1 and 3 at the different stages of D. discoideum development. We also demonstrated the application of dual-color bioluminescence imaging in the development of an imaging promoter assay.

Persister cells: formation, resuscitation and combative therapies

Persister cells, or superfits, have been strongly implicated in the recalcitrance and recurrence of chronic bacterial infection through the dormant (metabolically reduced) phenotype they display and the tolerance to antimicrobial agents this dormancy grants them. The complex biochemical events that lead to the formation of persister cells are not completely understood, though much research has linked the degradation of type II toxin/antitoxin systems and reduced cellular ATP levels to the rise in stress response molecules (where (p)ppGpp is of particular interest), which induce this dormant state. The equally complex mechanism of resuscitation is initiated by the cells’ ability to sense nutrient availability via chemotaxis systems. Levels of secondary messenger proteins (i.e., cAMP) within the cell are reduced to allow the resuscitation of ribosomes, by ribosomal resuscitation factor HflX, to reinstate protein synthesis and, therefore, growth to re-populate. Techniques of superfit eradication utilise one, or more, of three approaches (i) direct killing, (ii) re-sensitising persister cells to conventional antimicrobials, or (iii) prevention of persister formation though few laboratory findings have been translated to clinical practice. This work will outline current findings in the field with a critical approach, where possible.

Interplay between Mitochondrial Metabolism and Cellular Redox State Dictates Cancer Cell Survival

Mitochondria are the main powerhouse of the cell, generating ATP through the tricarboxylic acid cycle (TCA) and oxidative phosphorylation (OXPHOS), which drives myriad cellular processes. In addition to their role in maintaining bioenergetic homeostasis, changes in mitochondrial metabolism, permeability, and morphology are critical in cell fate decisions and determination. Notably, mitochondrial respiration coupled with the passage of electrons through the electron transport chain (ETC) set up a potential source of reactive oxygen species (ROS). While low to moderate increase in intracellular ROS serves as secondary messenger, an overwhelming increase as a result of either increased production and/or deficient antioxidant defenses is detrimental to biomolecules, cells, and tissues. Since ROS and mitochondria both regulate cell fate, attention has been drawn to their involvement in the various processes of carcinogenesis. To that end, the link between a prooxidant milieu and cell survival and proliferation as well as a switch to mitochondrial OXPHOS associated with recalcitrant cancers provide testimony for the remarkable metabolic plasticity as an important hallmark of cancers. In this review, the regulation of cell redox status by mitochondrial metabolism and its implications for cancer cell fate will be discussed followed by the significance of mitochondria-targeted therapies for cancer.

Endogenous Calcium Mediated The Seedling Growth And Fluoride Stress Tolerance In Four Bean Genotypes

Fluoride (F) pollution is a global environmental problem representing a severe risk for food and vegetables grown in contaminated soils. Phaseolus vulgaris L. is widely cultivated in arid and semi-arid regions and in F contaminated areas of the world. F tolerance during germination and seedling growth was evaluated for four bean ecotypes: Borlotto nano and three African genotypes (Lyamungu 85, Lyamungu 90 and Jesca).Seeds were grown in sand enriched with NaF or KF at three different levels (0, 80 and 200 mg kg-1). NaCl was used as a benchmark to determine a potential effect of different Na levels in plant. Total F content and minerals accumulation (Na, K and Ca) in roots and shoots were measured. The translocation factor, growth ratio, F tolerance index were evaluated to estimate plant-salt response. Germination rate decreased with increased F level. Borlotto was more F sensitive (0% germination with 200 mg kg-1of KF and NaF) than African genotypes. Under the highest F concentration (200 mg kg-1), F preferentially accumulated in shoots (Jesca 75.7 mg kg-1, Lyamungu 85 100.1 mg kg-1 and Lyamungu 90 115.4 mg kg-1). Ca content in roots was negatively correlated to F absorption, suggesting its antagonistic role to F mobility.Based on these parameters, Jesca and Lyamungu 85 were the most tolerant species recording a low F uptake and a high Ca content in the root. This study highlighted the central role of Ca, as a key secondary messenger in regulating the plant growth and development under F stress.

Functional metagenomic analysis of quorum sensing signaling in a nitrifying community

Quorum sensing (QS) can function to shape the microbial community interactions, composition, and function. In wastewater treatment systems, acylated homoserine lactone (AHL)-based QS has been correlated with the conversion of floccular biomass into microbial granules, as well as EPS production and the nitrogen removal process. However, the role of QS in such complex communities is still not fully understood, including the QS-proficient taxa and the functional QS genes involved. To address these questions, we performed a metagenomic screen for AHL genes in an activated sludge microbial community from the Ulu Pandan wastewater treatment plant (WWTP) in Singapore followed by functional validation of luxI activity using AHL biosensors and LC–MSMS profiling. We identified 13 luxI and 30 luxR homologs from the activated sludge metagenome. Of those genes, two represented a cognate pair of luxIR genes belonging to a Nitrospira spp. and those genes were demonstrated to be functionally active. The LuxI homolog synthesized AHLs that were consistent with the dominant AHLs in the activated sludge system. Furthermore, the LuxR homolog was shown to bind to and induce expression of the luxI promoter, suggesting this represents an autoinduction feedback system, characteristic of QS circuits. Additionally, a second, active promoter was upstream of a gene encoding a protein with a GGDEF/EAL domain, commonly associated with modulating the intracellular concentration of the secondary messenger, c-di-GMP. Thus, the metagenomic approach used here was demonstrated to effectively identify functional QS genes and suggests that Nitrospira spp. maybe QS is active in the activated sludge community.

The secondary messenger ppGpp interferes with cAMP-CRP regulon by promoting CRP acetylation in Escherichia coli

The cAMP-CRP regulon coordinates transcription regulation of several energy-related genes, the lac operon among them. Lactose, or IPTG, induces the lac operon expression by binding to the LacI repressor, and releasing it from the promoter sequence. At the same time, the expression of the lac operon requires the presence of the CRP-cAMP complex, which promotes the binding of the RNA polymerase to the promoter region. The modified nucleotide cAMP accumulates in the absence of glucose and binds to the CRP protein, but its ability to bind to DNA can be impaired by lysine-acetylation of CRP. Here we add another layer of control, as acetylation of CRP seems to be modified by ppGpp. In cells grown in glycerol minimal media, ppGpp seems to repress the expression of lacZ, where ΔrelA mutants show higher expression of lacZ than in WT. These differences between the WT and ΔrelA strains seem to depend on the levels of acetylated CRP. During the growth in minimal media supplemented with glycerol, ppGpp promotes the acetylation of CRP by the Nε-lysine acetyltransferases YfiQ. Moreover, the expression of the different genes involved in the production and degradation of Acetyl-phosphate (ackA-pta) and the enzymatic acetylation of proteins (yfiQ) are stimulated by the presence of ppGpp, depending on the growth conditions.