Caffeine: cardiorespiratory effects and tissue protection in animal models

The aim of this review is to analyze the cardiorespiratory and tissue-protective effects of caffeine in animal models. Peer-reviewed literature published between 1975 and 2021 was retrieved from CAB Abstracts, PubMed, ISI Web of Knowledge, and Scopus. Extracted data were analyzed to address the mechanism of action of caffeine on cardiorespiratory parameters (heart rate and rhythm), vasopressor effects, and some indices of respiratory function; we close this review by discussing the current debate on the research carried out on the effects of caffeine on tissue protection. Adenosine acts through specific receptors and is a negative inotropic and chronotropic agent. Blockage of its cardiac receptors can cause tachycardia (with arrhythmogenic potential) due to the intense activity of β1 receptors. In terms of tissue protection, caffeine inhibits hyperoxia-induced pulmonary inflammation by decreasing proinflammatory cytokine expression in animal models. The protection that caffeine provides to tissues is not limited to the CNS, as studies have demonstrated that it generates attenuation of inflammatory effects in pulmonary tissue. It inhibits the effects of some pro-inflammatory cytokines and prevents functional and structural changes.     

Adaptive downregulation of pheomelanin‐related Slc7a11 gene expression by environmentally induced oxidative stress

Pheomelanin is a sulphur‐containing yellow‐to‐reddish pigment whose synthesis consumes the main intracellular antioxidant (glutathione; GSH) and its precursor cysteine. Cysteine used for pheomelanogenesis cannot be used for antioxidant protection. We tested whether the expression of Slc7a11, the gene regulating the transport of cysteine to melanocytes for pheomelanogenesis, is environmentally influenced when cysteine/GSH are most required for antioxidant protection. We found that zebra finches Taeniopygia guttata developing pheomelanin‐pigmented feathers during a 12‐day exposure to the pro‐oxidant diquat dibromide downregulated the expression of Slc7a11 in feather melanocytes, but not the expression of other genes that affect pheomelanogenesis by mechanisms different from cysteine transport such as MC1R and Slc45a2. Accordingly, diquat‐treated birds did not suffer increased oxidative stress. This indicates that some animals have evolved an adaptive epigenetic lability that avoids damage derived from pheomelanogenesis. This mechanism should be explored in human Slc7a11 to help combat some cancer types related to cysteine consumption.     

NMR structural biology of sulfated glycans

Sulfated fucans, sulfated galactans, and glycosaminoglycans are extensively studied worldwide in terms of both structure and biomedical functions. Liquid-state nuclear magnetic resonance (NMR) spectroscopy is the most employed analytical technique in structural analysis of these sulfated glycans. This is due to the fact that NMR-based analyses enable a series of achievements such as (i) accurate structure characterization/determination; (ii) measurements of parameters regarding molecular motion (dynamics); (iii) assessment of the 3D structures (usually assisted by computational techniques of Molecular Modeling and/or Molecular Dynamics) of the composing monosaccharides (ring conformers) and the overall conformational states of the glycan chains either free in solution or bound to proteins; and (iv) analysis of the resultant intermolecular complexes with functional proteins through either the protein or the carbohydrate perspective. In this review, after a general introduction about the principal NMR parameters utilized for achieving this set of structural information, discussion is given on NMR-based studies of some representative sulfated fucans, sulfated galactans, and glycosaminoglycans. Due to the growing number of studies concerning both structure and function of sulfated glycans and the widely use of NMR spectroscopy in such studies, a review paper discussing (i) the most experiments employed for analysis, (ii) procedures used in data interpretation, and (iii) the general aspects of the sulfated glycans, is timely in the literature.     

Light response in seedlings of a temperate (<Emphasis Type="Italic">Quercus petraea</Emphasis>) and a sub-Mediterranean species (<Emphasis Type="Italic">Quercus pyrenaica</Emphasis>): contrasting ecological strategies as potential keys to regeneration performance in mixed marginal populations

In order to understand better the ecology of the temperate species Quercus petraea and the sub-Mediterranean species Quercus pyrenaica, two deciduous oaks, seedlings were raised in two contrasting light environments (SH, 5.3% full sunlight vs. HL, 70% full sunlight) for 2 years, and a subset of the SH seedlings were transferred to HL (SH–HL) in the summer of the second year. We predicted that Q. pyrenaica would behave more as a stress-tolerant species, with lower specific leaf area (SLA), allocation to leaf mass, and growth rate and less responsiveness to light in these metrics, than Q. petraea, presumed to be more competitive when resources, especially light and water, are abundant. Seedlings of Q. petraea had larger leaves with higher SLA, and exhibited a greater relative growth rate (RGR) in both SH and HL. They also displayed a higher proportion of biomass in stems (SMF), and a lower root to shoot ratio (R/S) in HL than those of Q. pyrenaica, which sprouted profusely, and had higher rates of photosynthesis (A_n) and stomatal conductance (g_wv), but lower whole-plant net assimilation rate (NAR). On exposure to a sudden increase in light, SH–HL seedlings of both species showed a short period of photoinhibition, but fully acclimated photosynthetic features within 46 days after transference; height, main stem diameter, RGR and NAR all increased at the end of the experiment compared to SH seedlings, with these increases more pronounced in Q. petraea. Observed differences in traits and responses to light confirmed a contrasting ecology at the seedling stage in Q. petraea and Q. pyrenaica in consonance with differences in their overall distribution. We discuss how the characteristics of Q. petraea may limit the availability of suitable regeneration niches to microsites of high-resource availability in marginal populations of Mediterranean climate, with potential negative consequences for its recruitment under predicted climatic changes.     

Tau – an inhibitor of deacetylase HDAC6 function

Analysis of brain microtubule protein from patients with Alzheimer's disease showed decreased alpha tubulin levels along with increased acetylation of the alpha tubulin subunit, mainly in those microtubules from neurons containing neurofibrillary tau pathology. To determine the relationship of tau protein and increased tubulin acetylation, we studied the effect of tau on the acetylation-deacetylation of tubulin. Our results indicate that tau binds to the tubulin-deacetylase, histone deacetylase 6 (HDAC6), decreasing its activity with a consequent increase in tubulin acetylation. As expected, increased acetylation was also found in tubulin from wild-type mice compared with tubulin from mice lacking tau because of the tau-mediated inhibition of the deacetylase. In addition, we found that an excess of tau protein, as a HDAC6 inhibitor, prevents induction of autophagy by inhibiting proteasome function.     

Plant Virus Cell-to-Cell Movement Is Not Dependent on the Transmembrane Disposition of Its Movement Protein

The cell-to-cell transport of plant viruses depends on one or more virus-encoded movement proteins (MPs). Some MPs are integral membrane proteins that interact with the membrane of the endoplasmic reticulum, but a detailed understanding of the interaction between MPs and biological membranes has been lacking. The cell-to-cell movement of the Prunus necrotic ringspot virus (PNRSV) is facilitated by a single MP of the 30K superfamily. Here, using a myriad of biochemical and biophysical approaches, we show that the PNRSV MP contains only one hydrophobic region (HR) that interacts with the membrane interface, as opposed to being a transmembrane protein. We also show that a proline residue located in the middle of the HR constrains the structural conformation of this region at the membrane interface, and its replacement precludes virus movement.Plant viruses encode movement proteins (MPs) that mediate the intra- and intercellular spread of the viral genome via plasmodesmata, membranous channels that traverse the walls of plant cells and enable intercellular transport and communication. There is a range of diversity in the number and type of viral proteins required for viral movement (21). Research on tobacco mosaic virus (TMV) has played a leading role in understanding MP activity (2). The genome of TMV encodes a single 30-kDa multidomain protein, the namesake of the 30K superfamily (7). Viral RNA is associated with the membrane of the endoplasmic reticulum (ER) and microtubules in the presence of this MP (23, 30).A large number of plant viruses have 30K MPs, which share common abilities, including binding nucleic acids, localizing and increasing the size exclusion limit of plasmodesmata, and interacting with the ER membrane. A topological model has been proposed in which the TMV MP has two putative transmembrane (TM) helices, both the N and C termini oriented toward the cytoplasm, and a short loop exposed in the ER lumen (4). There is less experimental information for other 30K MPs, but they are likely to have some membrane interaction.Direct experimental evidence of the integration of MPs into the membrane has been obtained only for small hydrophobic MPs that do not belong to the 30K superfamily. There are two TM segments in the p9 protein of carnation mottle virus (41), whereas the p6 protein of beet yellow virus (29) and the p7B protein of melon necrotic spot virus (22) have a single TM segment. In viruses with genomes that include three partially overlapping open reading frames, termed the triple-gene block (TGB), all three TGB proteins are required for movement where the two smaller proteins, TGBp2 and TGBp3, are also TM proteins (24). Furthermore, cross-linking experiments with carnation mottle virus p9 protein demonstrated that its membrane insertion occurs cotranslationally in a signal recognition particle-dependent manner and throughout the cellular membrane integration components, the translocon (33, 34).Prunus necrotic ringspot virus (PNRSV) is a tripartite, positive-strand RNA virus in the genus Ilarvirus of the family Bromoviridae. RNAs 1 and 2 encode the polymerase proteins P1 and P2, respectively. RNA 3 is translated into a single 30K-type MP. The coat protein is translated from a subgenomic RNA 4 produced during virus replication.The present study tackled the association of the PNRSV MP with biological membranes. The in vitro translation of model integral membrane protein constructs in the presence of microsomal membranes demonstrated that the hydrophobic region (HR) of the PNRSV MP did not span the membranes. Different biochemical and biophysical experiments suggested that the protein is tightly associated with, but does not traverse, the membrane, leaving both its N- and C-terminal hydrophilic regions facing the cytosol. Finally, a mutational analysis of the HR revealed that both the helicity and hydrophobicity of the region are essential for viral cell-to-cell movement.     

Viral Membrane Protein Topology Is Dictated by Multiple Determinants in Its Sequence

The targeting, insertion, and topology of membrane proteins have been extensively studied in both prokaryotes and eukaryotes. However, the mechanisms used by viral membrane proteins to generate the correct topology within cellular membranes are less well understood. Here, the effect of flanking charges and the hydrophobicity of the N-terminal hydrophobic segment on viral membrane protein topogenesis are examined systematically. Experimental data reveal that the classical topological determinants have only a minor effect on the overall topology of p9, a plant viral movement protein. Since only a few individual sequence alterations cause an inversion of p9 topology, its topological stability is robust. This result further indicates that the protein has multiple, and perhaps redundant, structural features that ensure that it always adopts the same topology. These critical topogenic sequences appear to be recognized and acted upon from the initial stages of protein biosynthesis, even before the ribosome ends protein translation.     

Antioxidant machinery differs between melanic and light nestlings of two polymorphic raptors

Colour polymorphism results from the expression of multiallelic genes generating phenotypes with very distinctive colourations. Most colour polymorphisms are due to differences in the type or amount of melanins present in each morph, which also differ in several behavioural, morphometric and physiological attributes. Melanin-based colour morphs could also differ in the levels of glutathione (GSH), a key intracellular antioxidant, because of the role of this molecule in melanogenesis. As GSH inhibits the synthesis of eumelanin (i.e. the darkest melanin form), individuals of darker morphs are expected to have lower GSH levels than those of lighter morphs. We tested this prediction in nestlings of two polymorphic raptors, the booted eagle Hieraaetus pennatus and the Eleonora's falcon Falco eleonorae, both of which occur in two morphs differing in the extent of eumelanic plumage. As expected, melanic booted eagle nestlings had lower blood GSH levels than light morph eagle nestlings. In the Eleonora's falcon, however, melanic nestlings only had lower GSH levels after controlling for the levels of other antioxidants. We also found that melanic female eagle nestlings had higher levels of antioxidants other than GSH and were in better body condition than light female eagle nestlings. These findings suggest an adaptive response of melanic nestlings to compensate for reduced GSH levels. Nevertheless, these associations were not found in falcons, indicating species-specific particularities in antioxidant machinery. Our results are consistent with previous work revealing the importance of GSH on the expression of melanic characters that show continuous variation, and suggest that this pathway also applies to discrete colour morphs. We suggest that the need to maintain low GSH levels for eumelanogenesis in dark morph individuals may represent a physiological constraint that helps regulate the evolution and maintenance of polymorphisms.