Two distinct CCR5 domains can mediate coreceptor usage by human immunodeficiency virus type 1.

The chemokine receptor CCR5 is the major fusion coreceptor for macrophage-tropic strains of human immunodeficiency virus type 1 (HIV-1). To define the structures of CCR5 that can support envelope (Env)-mediated membrane fusion, we analyzed the activity of homologs, chimeras, and mutants of human CCR5 in a sensitive gene reporter cell-cell fusion assay. Simian, but not murine, homologs of CCR5 were fully active as HIV-1 fusion coreceptors. Chimeras between CCR5 and divergent chemokine receptors demonstrated the existence of two distinct regions of CCR5 that could be utilized for Env-mediated fusion, the amino-terminal domain and the extracellular loops. Dual-tropic Env proteins were particularly sensitive to alterations in the CCR5 amino-terminal domain, suggesting that this domain may play a pivotal role in the evolution of coreceptor usage in vivo. We identified individual residues in both functional regions, Asp-11, Lys-197, and Asp-276, that contribute to coreceptor function. Deletion of a highly conserved cytoplasmic motif rendered CCR5 incapable of signaling but did not abrogate its ability to function as a coreceptor, implying the independence of fusion and G-protein-mediated chemokine receptor signaling. Finally, we developed a novel monoclonal antibody to CCR5 to assist in future studies of CCR5 expression.     

Characterization of the receptor binding residues of kisspeptins by positional scanning using peptide photoaffinity probes

Kisspeptins, endogenous peptide ligands for GPR54, play an important role in GnRH secretion. Since in vivo administration of kisspeptins induces increased plasma LH levels, GPR54 agonists hold promise as therapeutic agents for the treatment of hormonal secretion diseases. To facilitate the design of novel potent GPR54 ligands, residues in kisspeptins that involve in the interaction with GPR54 were investigated by kisspeptin-based photoaffinity probes. Herein, we report the design and synthesis of novel kisspeptin-based photoaffinity probes, and the application to crosslinking experiments for GPR54-expressing cells.     

CCR5 interactions with the variable 3 loop of gp120

The G-protein coupled receptor CCR5 functions pathologically as the primary co-receptor for macrophage tropic (R5) strains of HIV-1. The interactions responsible for co-receptor activity are unknown. Molecular-dynamics simulations of the extracellular and adjacent transmembrane domains of CCR5 were performed with explicit solvation utilizing a rhodopsin-based homology model. The functional unit of co-receptor binding was constructed via docking and molecular-dynamics simulation of CCR5 and the variable 3 loop of gp120, which is a dominant determinant of co-receptor utilization. The variable 3 loop was demonstrated to interact primarily with the amino terminus and the second extracellular loop of CCR5, providing novel structural information regarding the co-receptor-binding site. Alanine mutants that alter chemokine binding and co-receptor activity were examined. Molecular-dynamics simulations with and without the variable 3 loop of gp120 were able to rationalize the activities of these mutants successfully, providing support for the proposed model. Based on these results, the global complex of CCR5, gp120 including the V3 loop and CD4, was investigated. The utilization of computational analysis, in combination with molecular biological data, provides a powerful approach for understanding the use of CCR5 as a co-receptor by HIV-1.     

Identification of ENV determinants in V3 that influence the molecular anatomy of CCR5 utilization

The V3 loop of the ENV glycoprotein exerts a dominant influence on the interaction of gp120 with coreceptors. Primary env genes cloned from sequential isolates from two seroconverters revealed Pro-->Ala conversion in the conserved GPG motif of the V3 crown in seven of 17 R5 ENV. ENV containing the GPG motif in the V3 crown had fusogenic activity with chimeric receptors containing either the N terminus or loops of CCR5, whereas those with the GAG variant utilized only the former. Site-directed mutagenesis of multiple primary and prototypic R5 env genes demonstrated that the GPG motif was necessary for dual utilization of the N terminus and body of CCR5 in both gain and loss-of-function experiments. All ENV containing the GPG V3 crown showed CCR5 binding in the presence of soluble CD4, whereas it was not detected with the GAG variants. Molecular dynamic simulations of a V3 peptide predicts that the Pro-->Ala substitution results in a conformational change with loss of the crown structure. These studies demonstrate that sequences in the third hypervariable region determine the specificity of coreceptor utilization for fusion, and that a conserved motif in the crown directly influences the molecular anatomy of the interaction between gp120 and CCR5.     

Similar hypotensive responses to resistance exercise with and without blood flow restriction

Low intensity resistance exercise (RE) with blood flow restriction (BFR) has gained attention in the literature due to the beneficial effects on functional and morphological variables, similar to those observed during traditional RE without BFR, while the effects of BFR on post-exercise hypotension remain unclear. The aim of the present study was to compare the blood pressure (BP) response of trained normotensive individuals to RE with and without BFR. In this cross-over randomized trial, eight male subjects (23.8 ± 4 years, 74 ± 3 kg, 174 ± 4 cm) completed two exercise protocols: traditional RE (3 x 10 repetitions at 70% one-repetition maximum [1-RM]) and low intensity RE (3 x 15 repetitions at 20% 1-RM) with BFR. Blood pressure measurements were performed after 15 min of seated rest (0), immediately after and 10 min, 20 min, 30 min, 40 min, 50 min and 60 min after the experimental sessions. Similar hypotensive effects for systolic BP (SBP) were observed for both protocols (P < 0.05) after exercise, with no differences between groups (P > 0.05) and no statistically significant difference for diastolic BP (P > 0.05). These results suggest that in normotensive trained individuals, both traditional RE and RE with BFR induce hypotension for SBP, which is important to prevent cardiovascular disturbances.     

Long-term treadmill exercise improves spatial memory of male APPswe/PS1dE9 mice by regulation of BDNF expression and microglia activation

Increasing evidence suggests that physical activity could delay or attenuate the symptoms of Alzheimer''s disease (AD). But the underlying mechanisms are still not fully understood. To investigate the effect of long-term treadmill exercise on the spatial memory of AD mice and the possible role of β-amyloid, brain-derived neurotrophic factor (BDNF) and microglia in the effect, male APPswe/PS1dE9 AD mice aged 4 months were subjected to treadmill exercise for 5 months with 6 sessions per week and gradually increased load. A Morris water maze was used to evaluate the spatial memory. Expression levels of β-amyloid, BDNF and Iba-1 (a microglia marker) in brain tissue were detected by immunohistochemistry. Sedentary AD mice and wildtype C57BL/6J mice served as controls. The results showed that 5-month treadmill exercise significantly decreased the escape latencies (P < 0.01 on the 4th day) and improved the spatial memory of the AD mice in the water maze test. Meanwhile, treadmill exercise significantly increased the number of BDNF-positive cells and decreased the ratios of activated microglia in both the cerebral cortex and the hippocampus. However, treadmill exercise did not significantly alleviate the accumulation of β-amyloid in either the cerebral cortex or the hippocampus of the AD mice (P > 0.05). The study suggested that long-term treadmill exercise could improve the spatial memory of the male APPswe/PS1dE9 AD mice. The increase in BDNF-positive cells and decrease in activated microglia might underpin the beneficial effect.     

Identification of novel non-peptide CXCR4 antagonists by ligand-based design approach

The design and synthesis of novel non-peptide CXCR4 antagonists is described. The peptide backbone of highly potent cyclic peptide-based CXCR4 antagonists was entirely replaced by an indole framework, which was expected to reproduce the disposition of the key pharmacophores consistent with those of potential bioactive conformations of the original peptides. A structure–activity relationship study on a series of modified indoles identified novel small-molecule antagonists having three pharmacophore functional groups through the appropriate linkers.