Agonist versus antagonist muscle fatigue effects on thigh muscle activity and vertical ground reaction during drop landing

BackgroundAgonist and antagonist co-activation plays an important role for stabilizing the knee joint, especially after fatigue. However, whether selective fatigue of agonists or antagonist muscles would cause different changes in muscle activation patterns is unknown.HypothesisKnee extension fatigue would have a higher influence on landing biomechanics compared with a knee flexion protocol.Study designRepeated-measures design.MethodsTwenty healthy subjects (10 males and 10 females) performed two sets of repeated maximal isokinetic concentric efforts of the knee extensors (KE) at 120° s^?1 until they could no longer consistently produce 30% of maximum torque. On a separate day, a similar knee flexion (KF) fatigue protocol was also performed. Single leg landings from 30 cm drop height were performed before, in the middle and after the end of the fatigue test. The mean normalized electromyographic (EMG) signal of the vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF) and gastrocnemius (GAS) at selected landing phases were determined before, during and after fatigue. Quadriceps:hamstrings (Q:H) EMG ratio as well as sagittal hip and knee angles and vertical ground reaction force (GRF) were also recorded.ResultsTwo-way analysis of variance designs showed that KE fatigue resulted in significantly lower GRF and higher knee flexion angles at initial contact while maximum hip and knee flexion also increased (p < 0.05). This was accompanied by a significant decline of BF EMG, unaltered EMG of vastii and GAS muscles and increased Q:H ratio. In contrast, KF fatigue had no effects on vGRFs but it was accompanied by increased activation of VM, BF and GAS while the Q:H increased during before landing and decreased after impact.ConclusionFatigue responses during landing are highly dependent on the muscle which is fatigued.     

Candida albicans Hyphal Formation and Virulence Assessed Using a Caenorhabditis elegans Infection Model

Candida albicans colonizes the human gastrointestinal tract and can cause life-threatening systemic infection in susceptible hosts. We study here C. albicans virulence determinants using the nematode Caenorhabditis elegans in a pathogenesis system that models candidiasis. The yeast form of C. albicans is ingested into the C. elegans digestive tract. In liquid media, the yeast cells then undergo morphological change to form hyphae, which results in aggressive tissue destruction and death of the nematode. Several lines of evidence demonstrate that hyphal formation is critical for C. albicans pathogenesis in C. elegans. First, two yeast species unable to form hyphae (Debaryomyces hansenii and Candida lusitaniae) were less virulent than C. albicans in the C. elegans assay. Second, three C. albicans mutant strains compromised in their ability to form hyphae (efg1Δ/efg1Δ, flo8Δ/flo8Δ, and cph1Δ/cph1Δ efg1Δ/efg1Δ) were dramatically attenuated for virulence. Third, the conditional tet-NRG1 strain, which enables the external manipulation of morphogenesis in vivo, was more virulent toward C. elegans when the assay was conducted under conditions that permit hyphal growth. Finally, we demonstrate the utility of the C. elegans assay in a screen for C. albicans virulence determinants, which identified several genes important for both hyphal formation in vivo and the killing of C. elegans, including the recently described CAS5 and ADA2 genes. These studies in a C. elegans-C. albicans infection model provide insights into the virulence mechanisms of an important human pathogen.Candida albicans is the most common human fungal pathogen; however, our knowledge of its virulence mechanisms is incomplete, and our best antifungal agents are often ineffective in treating severe candidiasis (3). Infections with Candida species account for 70 to 90% of all invasive mycoses (32) and can be associated with devastating consequences, particularly in intensive care units where mortality rates reach 40% (24, 34). The drug resistance of pathogenic fungi exacerbates this problem and often limits therapeutic options (35). The identification of virulence pathways that can be targeted with novel antifungal therapies is urgently needed (31, 38, 46).One approach to understand the genetic mechanisms of virulence is to use invertebrates, such as the nematode Caenorhabditis elegans, as model hosts (43). Studies of C. elegans infection with Pseudomonas aeruginosa and Cryptococcus neoformans, for example, have led to the identification of evolutionarily conserved mechanisms of host immunity and microbial virulence (1, 21, 50). However, efforts to design an accurate nonmammalian model of C. albicans pathogenesis have been stymied, in part because it has been difficult to capture the role of Candida dimorphism in these systems.Morphogenesis in C. albicans is intricately related to pathogenesis and thus has been intensively studied. C. albicans hyphae are important for tissue destruction and host invasion (3). As such, C. albicans mutants and non-albicans Candida species that are unable to form true hyphae are attenuated for virulence (3, 37). However, C. albicans yeast cells also have virulence attributes (4, 33) that are likely involved in dissemination of the fungus through the bloodstream, and the establishment of infection at distant sites. To date, genetic screens to identify the determinants of Candida morphology have been conducted in vitro. Determining the role of these genes in virulence has traditionally involved separate and often laborious studies in mammals. Therefore, an expedient system to study morphogenesis of C. albicans in vivo and accurately model pathogenesis would offer many important advantages.Here, we study C. albicans pathogenesis using the invertebrate host C. elegans. C. albicans yeast cells are ingested into the gastrointestinal tract. In liquid media, the yeast cells form hyphae, which results in an aggressive infection that ultimately kills the nematode. Fungal hyphae destroy worm tissues and pierce the collagenous cuticle of the animal, a phenotype that is easily visible using a dissecting microscope. By studying mutants and genetically engineered C. albicans strains, we show that hyphal formation is required for full virulence in this system. Finally, we illustrate the utility of the C. elegans-C. albicans infection assay in a screen for genes involved in Candida morphogenesis and virulence.     

Building arks for tRNA: Structure and function of the Arc1p family of non-catalytic tRNA-binding proteins

Following the intricate architecture of the eukaryotic cell, protein synthesis involves formation of many macromolecular assemblies, some of which are composed by tRNA-aminoacylation enzymes. Protein-protein and protein-tRNA interactions in these complexes can be facilitated by non-catalytic tRNA-binding proteins. This review focuses on the dissection of the molecular, structural and functional properties of a particular family of such proteins: yeast Arc1p and its homologues in prokaryotes and higher eukaryotes. They represent paradigms of the strategies employed for the organization of sophisticated and dynamic nanostructures supporting spatio-temporal cellular organization.     

The Quest for Renal Disease Proteomic Signatures: Where Should We Look?

Renal diseases are prevalent and important. However, despite significant strides in medicine, clinical nephrology still relies on nonspecific and inadequate markers such as serum creatinine and total urine protein for monitoring and diagnosis of renal disease. In case of glomerular renal diseases, biopsy is often necessary to establish the diagnosis. With new developments in proteomics technology, numerous studies have emerged, searching for better markers of kidney disease diagnosis and/or prognosis. Blood, urine, and renal biopsy tissue have been explored as potential sources of biomarkers. Some interesting individual or multiparametric biomarkers have been found; however, none have yet been validated or entered clinical practice. This review focuses on some studies of biomarkers of glomerular renal diseases, as well as addresses the question of which sample type(s) might be most promising in preliminary discovery phases of candidate proteins.     

Inhibitors of foot and mouth disease virus targeting a novel pocket of the RNA-dependent RNA polymerase

Background

Foot-and-Mouth Disease Virus (FMDV) is a picornavirus that infects cloven-hoofed animals and leads to severe losses in livestock production. In the case of an FMD outbreak, emergency vaccination requires at least 7 days to trigger an effective immune response. There are currently no approved inhibitors for the treatment or prevention of FMDV infections.

Methodology/Principal Findings

Using a luciferase-based assay we screened a library of compounds and identified seven novel inhibitors of 3Dpol, the RNA-dependent RNA polymerase of FMDV. The compounds inhibited specifically 3Dpol (IC₅₀s from 2-17 µM) and not other viral or bacterial polymerases. Enzyme kinetic studies on the inhibition mechanism by compounds 5D9 and 7F8 showed that they are non-competitive inhibitors with respect to NTP and nucleic acid substrates. Molecular modeling and docking studies into the 3Dpol structure revealed an inhibitor binding pocket proximal to, but distinct from the 3Dpol catalytic site. Residues surrounding this pocket are conserved among all 60 FMDV subtypes. Site directed mutagenesis of two residues located at either side of the pocket caused distinct resistance to the compounds, demonstrating that they indeed bind at this site. Several compounds inhibited viral replication with 5D9 suppressing virus production in FMDV-infected cells with EC₅₀ = 12 µM and EC₉₀ = 20 µM).

Significance

We identified several non-competitive inhibitors of FMDV 3Dpol that target a novel binding pocket, which can be used for future structure-based drug design studies. Such studies can lead to the discovery of even more potent antivirals that could provide alternative or supplementary options to contain future outbreaks of FMD.     

The cancer cell secretome: A good source for discovering biomarkers?

Cancer is a leading cause of death. Early detection is usually associated with better clinical outcomes. Recent advances in genomics and proteomics raised hopes that new biomarkers for diagnosis, prognosis or monitoring therapeutic response will soon be discovered. Proteins secreted by cancer cells, referred also as “the cancer cell secretome”, is a promising source for biomarker discovery. In this review we will summarize recent advances in cancer cell secretome analysis, focusing on the five most fatal cancers (lung, breast, prostate, colorectal, and pancreatic). For each cancer type we will describe the proteomic approaches utilized for the identification of novel biomarkers. Despite progress, identification of markers that are superior to those currently used has proven to be a difficult task and very few, if any, newly discovered biomarker has entered the clinic the last 10 years.     

The destruction and conservation of the Egyptian Fruit bat Rousettus aegyptiacus in Cyprus: a historic review

In Cyprus, there are 16 species of bats most of which are threatened with extinction. With the exception of the megachiropteran Egyptian Fruit bat Rousettus aegyptiacus that feeds on fruit, the rest of them are insectivorous microchiropterans. The Fruit bat was declared as a pest by the Department of Agriculture of the Ministry of Agriculture, Natural Resources and Environment of Cyprus since the early 1900s. To reduce the number of this “pest”, the above-mentioned Department, since 1927, used fumigation, shooting, and the purchase of dead bats. Fumigating and closing caves not only destroyed Fruit bats by direct poisoning, but the entire cave ecosystems, including highly beneficial and protected insectivorous species. The first attempt to protect bats on the island was in 1988 with law No. 24 of 1988, ratifying the Convention on the Conservation of European Wildlife and Natural Habitats, 82/72/EEC. This convention protects all microchiroptera species except Pipistrellus pipistrellus that is strictly protected. R. aegyptiacus is rare, with small populations that are not at present endangered or vulnerable but at risk. Cyprus recently became a member state of the European Union. This provided the opportunity to include R. aegyptiacus in the Annexes II and IV of the council directive 92/42/EEC of May 21, 1993 on the conservation of natural habitats and of wild fauna and flora, which will guarantee the long-range protection and survival of this species.     

Kallikrein-mediated cell signalling: targeting proteinase-activated receptors (PARs)

We tested the hypothesis that human tissue kallikreins (hKs) may regulate signal transduction by cleaving and activating proteinase-activated receptors (PARs). We found that hK5, 6 and 14 cleaved PAR N-terminal peptide sequences representing the cleavage/activation motifs of human PAR1 and PAR2 to yield receptor-activating peptides. hK5, 6 and 14 activated calcium signalling in rat PAR2-expressing (but not background) KNRK cells. Calcium signalling in HEK cells co-expressing human PAR1 and PAR2 was also triggered by hK14 (via PAR1 and PAR2) and hK6 (via PAR2). In isolated rat platelets that do not express PAR1, but signal via PAR4, hK14 also activated PAR-dependent calcium signalling responses and triggered aggregation. The aggregation response elicited by hK14 was in contrast to the lack of aggregation triggered by hK5 and 6. hK14 also caused vasorelaxation in a phenylephrine-preconstricted rat aorta ring assay and triggered oedema in an in vivo model of murine paw inflammation. We propose that, like thrombin and trypsin, the kallikreins must now be considered as important 'hormonal' regulators of tissue function, very likely acting in part via PARs.     

The epigenetic basis for the aberrant expression of kallikreins in human cancers

The tissue kallikrein gene family consists of 15 genes tandemly arranged on human chromosome 19q13.4. Most kallikrein genes are characterized by aberrant expression patterns in various human cancers, a feature that makes them ideal cancer biomarkers. In the present study, we investigated the effect of the epigenetic drug compound 5-aza-2'-deoxycytidine on the expression of downregulated kallikrein genes in prostate, breast, and ovarian cancer cell lines. Reactivation of multiple kallikrein genes was observed, although some of these genes do not contain CpG islands in their genomic sequence. Epigenetic regulation provides a new mechanism for the pharmacological modulation of kallikreins in human cancers with putative therapeutic implications.