Routing of Kv7.1 to endoplasmic reticulum plasma membrane junctions

AIM

The voltage-gated Kv7.1 channel, in association with the regulatory subunit KCNE1, contributes to the IKs current in the heart. However, both proteins travel to the plasma membrane using different routes. While KCNE1 follows a classical Golgi-mediated anterograde pathway, Kv7.1 is located in endoplasmic reticulum-plasma membrane junctions (ER-PMjs), where it associates with KCNE1 before being delivered to the plasma membrane.

METHODS

To characterize the channel routing to these spots we used a wide repertoire of methodologies, such as protein expression analysis (i.e. protein association and biotin labeling), confocal (i.e. immunocytochemistry, FRET, and FRAP), and dSTORM microscopy, transmission electron microscopy, proteomics, and electrophysiology.

RESULTS

We demonstrated that Kv7.1 targeted ER-PMjs regardless of the origin or architecture of these structures. Kv2.1, a neuronal channel that also contributes to a cardiac action potential, and JPHs, involved in cardiac dyads, increased the number of ER-PMjs in nonexcitable cells, driving and increasing the level of Kv7.1 at the cell surface. Both ER-PMj inducers influenced channel function and dynamics, suggesting that different protein structures are formed. Although exhibiting no physical interaction, Kv7.1 resided in more condensed clusters (ring-shaped) with Kv2.1 than with JPH4. Moreover, we found that VAMPs and AMIGO, which are Kv2.1 ancillary proteins also associated with Kv7.1. Specially, VAP B, showed higher interaction with the channel when ER-PMjs were stimulated by Kv2.1.

CONCLUSION

Our results indicated that Kv7.1 may bind to different structures of ER-PMjs that are induced by different mechanisms. This variable architecture can differentially affect the fate of cardiac Kv7.1 channels.

Hyperoxaluria Induces Endothelial Dysfunction in Preglomerular Arteries: Involvement of Oxidative Stress

Urolithiasis is a worldwide problem and a risk factor for kidney injury. Oxidative stress-associated renal endothelial dysfunction secondary to urolithiasis could be a key pathogenic factor, similar to obesity and diabetes-related nephropathy. The aim of the present study was to characterize urolithiasis-related endothelial dysfunction in a hyperoxaluria rat model of renal lithiasis. Experimental approach: Endothelial dysfunction was assessed in preglomerular arteries isolated from control rats and in which 0.75% ethylene glycol was administered in drinking water. Renal interlobar arteries were mounted in microvascular myographs for functional studies; superoxide generation was measured by chemiluminescence and mRNA and protein expression by RT-PCR and immunofluorescence, respectively. Selective inhibitors were used to study the influence of the different ROS sources, xanthine oxidase, COX-2, Nox1, Nox2 and Nox4. Inflammatory vascular response was also studied by measuring the RNAm expression of NF-κB, MCP-1 and TNFα by RT-PCR. Results: Endothelium-dependent vasodilator responses were impaired in the preglomerular arteries of the hyperoxaluric group along with higher superoxide generation in the renal cortex and vascular inflammation developed by MCP-1 and promoted by NF-κB. The xanthine oxidase inhibitor allopurinol restored the endothelial relaxations and returned superoxide generation to basal values. Nox1 and Nox2 mRNA were up-regulated in arteries from the hyperoxaluric group, and Nox1 and Nox2 selective inhibitors also restored the impaired vasodilator responses and normalized NADPH oxidase-dependent higher superoxide values of renal cortex from the hyperoxaluric group. Conclusions: The current data support that hyperoxaluria induces oxidative stress-mediated endothelial dysfunction and inflammatory response in renal preglomerular arteries which is promoted by the xanthine oxidase, Nox1 and Nox2 pathways.

Prognostic implications of Neutrophil Extracellular Traps in coronary thrombi of patients with ST-elevation myocardial infarction

AIMS

The mechanisms of coronary thrombosis can influence prognosis after STEMI and allow for different treatment groups to be identified; an association between neutrophil extracellular traps (NETs) and unfavorable clinical outcomes has been suggested. Our aim was to determine the role played by NETs in coronary thrombosis and their influence on prognosis. The role of other histological features in prognosis and the association between NETs and bacteria in the coronary thrombi were also explored.

METHODS AND RESULTS

We studied 406 patients with STEMI in which coronary thrombi were consecutively obtained by aspiration during angioplasty between 2012 and 2018. Analysis of NETs in paraffin-embedded thrombi was based on the colocalization of specific NET components by means of confocal microscopy. Immunohistochemistry stains were used to identify plaque fragments. Fluorescence in situ hybridization was used to detect bacteria. NETs were detected in 51% of the thrombi [NET density, median (IQR): 25% (17-38%)]. The median follow-up was 47 months (95% CI 43-51); 105 (26%) patients experienced major adverse cardiac events (MACE). A significant association was found between the presence of NETs in coronary aspirates and the occurrence of MACE in the first 30 days after infarction (HR 2.82; 95% CI 1.26-6.35, p=.012), mainly due to cardiac deaths and stent thrombosis.

CONCLUSIONS

The presence of NETs in coronary thrombi was associated with a worse prognosis soon after STEMI. In some patients, NETs could be a treatment target and a feasible way to prevent reinfarction.

Metabolic syndrome contributes to renal injury mediated by hyperoxaluria in a murine model of nephrolithiasis

Metabolic syndrome (MS) individuals have a higher risk of developing chronic kidney disease through unclear pathogenic mechanisms. MS has been also related with higher nephrolithiasis prevalence. To establish the influence of MS on renal function, we designed a murine model of combined metabolic syndrome and hyperoxaluria. Four groups of male Sprague-Dawley rats were established: (1) control group (n = 10) fed with standard chow; (2) stone former group (SF) (n = 10) fed with standard chow plus 0.75% ethylene glycol administered in the drinking water; (3) metabolic syndrome group (MS) (n = 10), fed with 60% fructose diet; (4) metabolic syndrome + stone former group (MS + SF) (n = 10), 60% fructose diet and 0.75% EG in the drinking water. MS group showed a significant injury to renal function when hyperoxaluria was induced. It was demonstrated by a significant decrease of creatinine clearance (p < 0.001), with higher tubular damage (34.3%, CI 95% 23.9-44.7, p < 0.001), produced by deposition of crystals, and increased tubular synthesis of osteopontin as a response to tubular damage. Induction of hyperoxaluria in rats with MS causes severe morphological alterations with a significant impairment of renal function. This impairment is not produced in rats without MS. Therefore, this model can be useful for the study of the influence of MS in stone formation.

An adult myometrial pluripotential precursor that promotes healing of damaged muscular tissues

The use of adult stem cells for tissue and organ regeneration constitutes a promising alternative therapy in many human diseases that are currently not treatable. We have isolated a new cell type from mouse adult uterine biopsies (murine adult myometrial precursors or mAMPs) by means of using a simple and non-invasive approach. These cells have been characterized by surface markers, being positive for CD31, CD34, CD44, CD117, Stro-1 and Sca-1. A similar cell population (hAMPs) was isolated from human biopsies. AMPs can differentiate in vitro into a number of mesodermal (smooth and skeletal muscle, osteoblasts and adipocytes) as well as epidermal lineages (all neural lineages). AMPs are unusual adult stem cells as they still express some embryonic antigens and remain undifferentiated through a high number of passages before entering senescence. Importantly, when injected into animal models of muscular disease, AMPs can regenerate new muscle fibers, and promote functional muscular recovery. Moreover, these cells can regenerate the uterine lining after wound healing, reconstructing the uterine muscular architecture. In addition, these cells can form new vessels both in vitro and in vivo. We believe that these cells have superior features to other known adult stem cells and, consequently, their use holds great promise for regenerative medicine, drug development and basic research.

The mitochondrial cycle of Arabidopsis shoot apical meristem and leaf primordium meristematic cells is defined by a perinuclear tentaculate/cage-like mitochondrion

Plant cells exhibit a high rate of mitochondrial DNA (mtDNA) recombination. This implies that before cytokinesis, the different mitochondrial compartments must fuse to allow for mtDNA intermixing. When and how the conditions for mtDNA intermixing are established are largely unknown. We have investigated the cell cycle-dependent changes in mitochondrial architecture in different Arabidopsis (Arabidopsis thaliana) cell types using confocal microscopy, conventional, and three-dimensional electron microscopy techniques. Whereas mitochondria of cells from most plant organs are always small and dispersed, shoot apical and leaf primordial meristematic cells contain small, discrete mitochondria in the cell periphery and one large, mitochondrial mass in the perinuclear region. Serial thin-section reconstructions of high-pressure-frozen shoot apical meristem cells demonstrate that during G1 through S phase, the large, central mitochondrion has a tentaculate morphology and wraps around one nuclear pole. In G2, both types of mitochondria double their volume, and the large mitochondrion extends around the nucleus to establish a second sheet-like domain at the opposite nuclear pole. During mitosis, approximately 60% of the smaller mitochondria fuse with the large mitochondrion, whose volume increases to 80% of the total mitochondrial volume, and reorganizes into a cage-like structure encompassing first the mitotic spindle and then the entire cytokinetic apparatus. During cytokinesis, the cage-like mitochondrion divides into two independent tentacular mitochondria from which new, small mitochondria arise by fission. These cell cycle-dependent changes in mitochondrial architecture explain how these meristematic cells can achieve a high rate of mtDNA recombination and ensure the even partitioning of mitochondria between daughter cells.

Differentiating plant cells switched to proliferation remodel the functional organization of nuclear domains

The immature pollen grain, the microspore, under stress conditions can switch its developmental program towards proliferation and embryogenesis. The comparison between the gametophytic and sporophytic pathways followed by the microspore permitted us to analyse the nuclear changes in plant differentiating cells when switched to proliferation. The nucleus is highly dynamic, the architecture of its well organised functional domains--condensed chromatin, interchromatin region, nuclear bodies and nucleolus--changing in response to DNA replication, RNA transcription, processing and transport. In the present work, the rearrangements of the nuclear domains during the switch to proliferation have been determined by in situ molecular identification methods for the subcellular localization of chromatin at different functional states, rDNA, elements of the nuclear machinery (PCNA, splicing factors), signalling and stress proteins. The study of the changes in the nuclear domains was determined by a correlative approach at confocal and electron microscopy levels. The results showed that the switch of the developmental program and the activation of the proliferative activity affected the functional organization of the nuclear domains, which accordingly changed their architecture and functional state. A redistribution of components, among them various signalling molecules which targeted structures within the interchromatin region upon translocation from the cytoplasm, was also observed.

Spontaneous chromosome doubling results from nuclear fusion during in vitro maize induced microspore embryogenesis

A multidisciplinary study was carried out to analyse the chromosome doubling process during the early stages of in vitro maize microspore embryogenesis. The main stages (microspore derivatives) that were formed in the course of the culture were analysed. Chromosome number was determined from squashed cells, and DNA content was measured by cytometry. In parallel, an ultrastructural analysis of the microspore derivatives demonstrated the occurrence of a nuclear fusion process. It seems likely that nuclear fusion ensures chromosome doubling at early stages of induced microspore embryogenesis. It occurs precisely at the 5/7 day stage in the embryonic domain and probably leads to polyploidy in the endosperm domain of the microspore derivatives. As a conclusion a scheme summarises the results and proposes an interpretation of the sequence of chromosome doubling events during early maize microspore embryogenesis. Understanding of this process will be important for future efforts to increase the percentage of homozygous plants for crop improvement.

MAPKs entry into the nucleus at specific interchromatin domains in plant differentiation and proliferation processes

Mitogen-activated protein kinases (MAPKs) are involved in the signaling of extracellular stimuli in eukaryotes, including plants. Different MAPKs have recently been shown to be expressed during plant cell proliferation and developmental processes such as pollen development and embryogenesis, but the structural subdomain where these MAPKs are targeted in the nucleus has not yet been characterized. We have determined the changes in the expression and subcellular localization of ERK homologues, proteins belonging to the MAPK family, and MAPK-active forms in two plant developmental processes which involved differentiation (pollen maturation) and proliferation (the initials of pollen embryogenesis). Immunofluorescence and immunogold labeling in the species studied showed that the progression of differentiation and proliferation was accompanied by an increase in the expression of ERKs and MAPK activation together with a translocation to the nucleus. Combining ultrastructural cytochemistry and immunogold for RNA and phosphorylated proteins we have identified the nuclear sites housing these MAPKs in areas of the interchromatin region enriched in RNA and phosphoproteins that include clusters of interchromatin granules. This could suggest a role of these MAPKs in the early events of activation of the transcription and processing machinery, via phosphorylation, which subsequently would be recruited to the transcription sites. The association of the nuclear localization of MAPKs with the progression through the cell cycle and the commitment toward differentiation in the two plant developmental processes can be correlated.

Defined nuclear changes accompany the reprogramming of the microspore to embryogenesis

The switch of the gametophytic developmental program toward pollen embryogenesis to form a haploid plant represents an important alternative for plant breeding. In the present study, the switch of the gametophytic developmental program toward a sporophytic pathway, "embryogenesis," has been studied in three different plant species, Brassica, tobacco, and pepper. The switch has been induced by stress (heat shock) at the very responsive stage of the microspore, which is the vacuolate period. As a result, the cell nucleus undergoes striking structural changes with regard to late gametophytic development, including alterations of biosynthetic activities and proliferative activity. An enrichment in HSP70 heat-shock protein and in the presence of Ntf6-MAP kinase was observed after inductive treatment in the nuclei during early embryogenesis. This apparently reflected the possible roles of these proteins, specifically the protective role of HSP70 for the nuclear machinery, and signal transduction of Ntf6-MAPK for the entry of cells into proliferation. Importantly, the observed nuclear changes were similar in the three species investigated and represented convenient markers for early monitoring of embryogenesis and selection purposes for obtaining double-haploid plants in plant breeding.

Ultrastructural distribution of a MAP kinase and transcripts in quiescent and cycling plant cells and pollen grains

Mitogen-activated protein kinases (MAPKs) are components of a kinase module that plays a central role in the transduction of diverse extracellular stimuli, including mitogens, specific differentiation and developmental signals and stress treatments. This shows that reversible protein phosphorylation cascades play a pivotal role in signal transduction in animal cells and yeast, particularly the entry into mitosis of arrested cells. Homologues of MAPKs have been found and cloned in various plant species, but there have been no data about their in situ localization at the subcellular level and their expression in plant cells so far. In the present paper we report the first data on the ultrastructural in situ localization of MAPK and their mRNAs in various plant cells. Proliferating and quiescent meristematic plant cells were studied to evaluate whether changes in MAPK presence, distribution and expression accompany the entry into proliferation of dormant cells. Moreover, MAPK localization was analyzed in vacuolate microspores. Polyclonal antibodies against the deduced MAPK from the tobacco Ntf6 clone were able to recognize homologue epitopes by immunocytochemical techniques in the cell types studied. The pattern of protein distribution is similar in all the cases studied: it is localized in the cytoplasm and in the nucleus, mainly in the interchromatin region. The quantitative study of the density showed that MAPK labelling is more abundant in cycling than in quiescent cells, also suggesting that, in plants, MAPK pathways might play a role in cell proliferation. RNA probes for conserved regions of the catalytic domain of plant MAPK homologue genes were used to study MAPK expression in those plant cells. In situ hybridization (ISH) showed the presence of MAPK transcripts in the three plant cell types studied, but levels were very low in quiescent cells compared to those in cycling cells. The quantification of labelling density of ISH signals strongly suggests a higher level of MAPK expression in proliferating cells, but also some basal messenger presence and/or expression in the quiescent ones. Immunogold and ISH results show the presence and distribution of MAPK proteins and mRNAs in vacuolate microspores. This represents a very dynamic stage during pollen development in which the cell nucleus is being prepared for an asymmetrical mitotic division, giving rise to both the generative and the vegetative nuclei of the bicellular pollen grain. Taken together, the data indicate a role played by MAPK in the re-entry into proliferation in plant cells.

Influence of salt concentration on the susceptibility of moderately halophilic bacteria to antimicrobials and its potential use for genetic transfer studies

The influence of salinity on the susceptibility of 13 moderately halophilic collection strains belonging to the genera Chromohalobacter, Deleya, Halomonas, Vibrio, and Volcaniella to 10 common antimicrobials has been studied. Three different patterns of tolerance were found when salinity was varied from 10 to 1% (wt/vol) total salts in the testing media. The first one included the responses to ampicillin and rifampicin, where only minimal effects on the susceptibility were found. All moderate halophiles showed a high sensitivity to rifampicin regardless of the salt concentration. In the second group, including the responses to the aminoglycosides gentamycin, kanamycin, neomycin, and streptomycin, a remarkable and gradual increase of the toxicity was detected at lower salinities. Thirdly, the highest heterogeneity was found for the rest of antimicrobials assayed (trimethoprim, nalidixic acid, spectinomycin, and tetracycline), where the effect of salinity was moderate and dependent on both the individual strain and the antimicrobial tested. The data presented here should facilitate genetic studies on moderate halophiles. Thus, they simplify the design of selection media for genetic exchange experiments. Besides, by using low-salinity media, genes encoding resistance to a number of antimicrobials, especially to aminoglycosides, can be used as genetic markers for plasmids or transposons to be transferred to these extremophiles.