Increased prevalence of the null allele of the p.Arg577Ter variant in the ACTN3 gene in Brazilian long-distance athletes: A retrospective study.

INTRODUCTION: The phenotypic consequences of the p.Arg577Ter variant in the α-actinin-3 (ACTN3) gene are suggestive of a trade-off between performance traits for speed and endurance sports. Although there is a consistent association of the c.1729C allele (aka R allele) with strength/power traits, there is still a debate on whether the null allele (c.1729T allele; aka X allele) influences endurance performance. The present study aimed to test the association of the ACTN3 p.Arg577Ter variant with long-distance endurance athlete status, using previously published data with the Brazilian population. METHODS: Genotypic data from 203 long-distance athletes and 1724 controls were analysed in a case-control approach. RESULTS: The frequency of the X allele was significantly higher in long-distance athletes than in the control group (51.5% vs. 41.4%; p = 0.000095). The R/X and X/X genotypes were overrepresented in the athlete group. Individuals with the R/X genotype instead of the R/R genotype had a 1.6 increase in the odds of being a long-distance athlete (p = 0.012), whereas individuals with the X/X genotype instead of the R/R genotype had a 2.2 increase in the odds of being a long-distance athlete (p = 0.00017). CONCLUSION: The X allele, mainly the X/X genotype, was associated with long-distance athlete status in Brazilians.

The Actin-Binding Protein Cortactin Promotes Sepsis Severity by Supporting Excessive Neutrophil Infiltration into the Lung.

Sepsis is a systemic infection that can lead to multi-organ failure. It is characterised by an uncontrolled immune response with massive neutrophil influx into peripheral organs. Neutrophil extravasation into tissues depends on actin remodeling and actin-binding proteins such as cortactin, which is expressed ubiquitously, except for neutrophils. Endothelial cortactin is necessary for proper regulation of neutrophil transendothelial migration and recruitment to sites of infection. We therefore hypothesised that cortactin plays a crucial role in sepsis development by regulating neutrophil trafficking. Using a murine model of sepsis induced by cecal ligation and puncture (CLP), we showed that cortactin-deficient (KO) mice survive better due to reduced lung injury. Histopathological analysis of lungs from septic KO mice revealed absence of oedema, reduced vascular congestion and mucus deposition, and better-preserved alveoli compared to septic wild-type (WT) mice. Additionally, sepsis-induced cytokine storm, excessive neutrophil infiltration into the lung and oxidative stress were significantly reduced in KO mice. Neutrophil depletion 12 h after sepsis improved survival in WT mice by averting lung injury, similar to both neutrophil-depleted and non-depleted KO mice. Our findings highlight a critical role of cortactin for lung neutrophil infiltration and sepsis severity.

Recombinant actin-depolymerizing factor of the apicomplexan Neospora caninum (NcADF) is susceptible to oxidation.

Neospora caninum is a member of Apicomplexa Phylum and the causative agent of neosporosis, a disease responsible for abortions in cattle. Apicomplexan parasites have a limited set of actin-binding proteins conducting the regulation of the dynamics of nonconventional actin. The parasite actin-based motility is implicated in the parasite invasion process in the host cell. Once no commercial strategy for the neosporosis control is available, the interference in the parasite actin function may result in novel drug targets. Actin-depolymerization factor (ADF) is a member of the ADF/cofilin family, primarily known for its function in actin severing and depolymerization. ADF/cofilins are versatile proteins modulated by different mechanisms, including reduction and oxidation. In apicomplexan parasites, the mechanisms involved in the modulation of ADF function are barely explored and the effects of oxidation in the protein are unknown so far. In this study, we used the oxidants N-chlorotaurine (NCT) and H2O2 to investigate the susceptibility of the recombinant N. caninum ADF (NcADF) to oxidation. After exposing the protein to either NCT or H2O2, the dimerization status and cysteine residue oxidation were determined. Also, the interference of NcADF oxidation in the interaction with actin was assessed. The treatment of the recombinant protein with oxidants reversibly induced the production of dimers, indicating that disulfide bonds between NcADF cysteine residues were formed. In addition, the exposure of NcADF to NCT resulted in more efficient oxidation of the cysteine residues compared to H2O2. Finally, the oxidation of NcADF by NCT reduced the ability of actin-binding and altered the function of NcADF in actin polymerization. Altogether, our results clearly show that recombinant NcADF is sensitive to redox conditions, indicating that the function of this protein in cellular processes involving actin dynamics may be modulated by oxidation.

The complexity and diversity of the actin cytoskeleton of trypanosomatids.

Trypanosomatids are a monophyletic group of parasitic flagellated protists belonging to the order Kinetoplastida. Their cytoskeleton is primarily made up of microtubules in which no actin microfilaments have been detected. Although all these parasites contain actin, it is widely thought that their actin cytoskeleton is reduced when compared to most eukaryotic organisms. However, there is increasing evidence that it is more complex than previously thought. As in other eukaryotic organisms, trypanosomatids encode for a conventional actin that is expected to form microfilament-like structures, and for members of three conserved actin-related proteins probably involved in microfilament nucleation (ARP2, ARP3) and in gene expression regulation (ARP6). In addition to these canonical proteins, also encode for an expanded set of actins and actin-like proteins that seem to be restricted to kinetoplastids. Analysis of their amino acid sequences demonstrated that, although very diverse in primary sequence when compared to actins of model organisms, modelling of their tertiary structure predicted the presence of the actin fold in all of them. Experimental characterization has been done for only a few of the trypanosomatid actins and actin-binding proteins. The most studied is the conventional actin of Leishmania donovani (LdAct), which unusually requires both ATP and Mg2+ for polymerization, unlike other conventional actins that do not require ATP. Additionally, polymerized LdAct tends to assemble in bundles rather than in single filaments. Regulation of actin polymerization depends on their interaction with actin-binding proteins. In trypanosomatids, there is a reduced but sufficient core of actin-binding proteins to promote microfilament nucleation, turnover and stabilization. There are also genes encoding for members of two families of myosin motor proteins, including one lineage-specific. Homologues to all identified actin-family proteins and actin-binding proteins of trypanosomatids are also present in Paratrypanosoma confusum (an early branching trypanosomatid) and in Bodo saltans (a closely related free-living organism belonging to the trypanosomatid sister order of Bodonida) suggesting they were all present in their common ancestor. Secondary losses of these genes may have occurred during speciation within the trypanosomatids, with salivarian trypanosomes having lost many of them and stercorarian trypanosomes retaining most.

Functional characterisation of the actin-depolymerising factor from the apicomplexan Neospora caninum (NcADF).

Neospora caninum is an apicomplexan parasite that causes infectious abortion in cows. As an obligate intracellular parasite, N. caninum requires a host cell environment to survive and replicate. The locomotion and invasion mechanisms of apicomplexan parasites are centred on the actin-myosin system to propel the parasite forwards and into the host cell. The functions of actin, an intrinsically dynamic protein, are modulated by actin-binding proteins (ABPs). Actin-depolymerising factor (ADF) is a ubiquitous ABP responsible for accelerating actin turnover in eukaryotic cells and is one of the few known conserved ABPs from apicomplexan parasites. Apicomplexan ADFs have nonconventional properties compared with ADF/cofilins from higher eukaryotes. In the present paper, we characterised the ADF from N. caninum (NcADF) using computational and in vitro biochemical approaches to investigate its function in rabbit muscle actin dynamics. Our predicted computational tertiary structure of NcADF demonstrated a conserved structure and phylogeny with respect to other ADF/cofilins, although certain differences in filamentous actin (F-actin) binding sites were present. The activity of recombinant NcADF on heterologous actin was regulated in part by pH and the presence of inorganic phosphate. In addition, our data suggest a comparatively weak disassembly of F-actin by NcADF. Taken together, the data presented herein represent a contribution to the field towards the understanding of the role of ADF in N. caninum and a comparative analysis of ABPs in the phylum Apicomplexa.