Modest human immunodeficiency virus coreceptor function of CXCR3 is strongly enhanced by mimicking the CXCR4 ligand binding pocket in the CXCR3 receptor

CXCR3 participates in asymmetric division of mouse oocytes by modulating actin dynamics

Extensive research has been conducted on the role of CXCR3 in immune responses and inflammation. However, the role of CXCR3 in the reproductive system, particularly in oocyte development, remains unknown. In this study, we present findings on the involvement of CXCR3 in the meiotic division process of mouse oocytes. We found CXCR3 was expressed consistently throughout the entire maturation process of mouse oocyte. Inhibition of CXCR3 impaired the asymmetric division of oocyte, while the injection of Cxcr3 mRNA was capable of restoring these defects. Further study showed that inhibition of CXCR3 perturbed spindle migration by affecting LIMK/cofilin pathway-mediated actin remodeling. Knockout of CXCR3 led to an upregulation of actin-binding protein and an increased ATP level in GV-stage oocytes, while maintaining normal actin dynamics during the process of meiosis. Additionally, we noticed the expression level of DYNLT1 is markedly elevated in CXCR3-null oocytes. DYNLT1 bound with the Arp2/3 complex, and knockdown of DYNLT1 in CXCR3-null oocytes impaired the organization of cytoplasmic actin, suggesting the regulatory role of DYNLT1 in actin organization, and the compensatory expression of DYNLT1 may contribute to maintain normal actin dynamics in CXCR3-knockout oocytes. In summary, our findings provide insights into the intricate network of actin dynamics associated with CXCR3 during oocyte meiosis.

Female Sex Hormones Upregulate the Replication Activity of HIV-1 Sub-Subtype A6 and CRF02_AG but Not HIV-1 Subtype B

More than 50% of all people living with HIV worldwide are women. Globally, HIV/AIDS is the leading cause of death among women aged 15 to 44. The safe and effective methods of hormonal contraception are an essential component of preventive medical care in order to reduce maternal and infant mortality. However, there is limited knowledge regarding the effect of hormones on the rate of viral replication in HIV infection, especially non-B subtypes. The goal of the present work was to study in vitro how the female hormones β-estradiol and progesterone affect the replication of the HIV-1 subtypes A6, CRF02_AG, and B. The findings show that high doses of hormones enhanced the replication of HIV-1 sub-subtype A6 by an average of 1.75 times and the recombinant variant CRF02_AG by 1.4 times but did not affect the replication of HIV-1 subtype B. No difference was detected in the expression of CCR5 and CXCR4 co-receptors on the cell surface, either in the presence or absence of hormones. However, one of the reasons for the increased viral replication could be the modulated TLRs secretion, as it was found that high doses of estradiol and progesterone upregulated, to varying degrees, the expression of TLR2 and TLR9 genes in the PBMCs of female donors infected with HIV-1 sub-subtype A6.

CD8 lymphocytes mitigate HIV-1 persistence in lymph node follicular helper T cells during hyperacute-treated infection

HIV persistence in tissue sites despite ART is a major barrier to HIV cure. Detailed studies of HIV-infected cells and immune responses in native lymph node tissue environment is critical for gaining insight into immune mechanisms impacting HIV persistence and clearance in tissue sanctuary sites. We compared HIV persistence and HIV-specific T cell responses in lymph node biopsies obtained from 14 individuals who initiated therapy in Fiebig stages I/II, 5 persons treated in Fiebig stages III-V and 17 late treated individuals who initiated ART in Fiebig VI and beyond. Using multicolor immunofluorescence staining and in situ hybridization, we detect HIV RNA and/or protein in 12 of 14 Fiebig I/II treated persons on suppressive therapy for 1 to 55 months, and in late treated persons with persistent antigens. CXCR3+ T follicular helper cells harbor the greatest amounts of gag mRNA transcripts. Notably, HIV-specific CD8+ T cells responses are associated with lower HIV antigen burden, suggesting that these responses may contribute to HIV suppression in lymph nodes during therapy. These results reveal HIV persistence despite the initiation of ART in hyperacute infection and highlight the contribution of virus-specific responses to HIV suppression in tissue sanctuaries during suppressive ART.

CXCR7/ACKR3-targeting ligands interfere with X7 HIV-1 and HIV-2 entry and replication in human host cells

Chemokine receptors CCR5 and CXCR4 are considered the main coreceptors for initial HIV infection, replication and transmission, and subsequent AIDS progression. Over the years, other chemokine receptors, belonging to the family of G protein-coupled receptors, have also been identified as candidate coreceptors for HIV entry into human host cells. Amongst them, CXCR7, also known as atypical chemokine receptor 3 (ACKR3), was suggested as a coreceptor candidate capable of facilitating both HIV-1 and HIV-2 entry in vitro. In this study, a cellular infection model was established to further decipher the role of CXCR7 as an HIV coreceptor. Using this model, CXCR7-mediated viral entry was demonstrated for several clinical HIV isolates as well as laboratory strains. Of interest, the X4-tropic HIV-1 HE strain showed rapid adaptation towards CXCR7-mediated infection after continuous passaging on CD4- and CXCR7-expressing cells. Furthermore, we uncovered anti-CXCR7 monoclonal antibodies, small molecule CXCR7 inhibitors and the natural CXCR7 chemokine ligands as potent inhibitors of CXCR7 receptor-mediated HIV entry and replication. Even though the clinical relevance of CXCR7-mediated HIV infection remains poorly understood, our data suggest that divergent HIV-1 and HIV-2 strains can quickly adapt their coreceptor usage depending on the cellular environment, which warrants further investigation.

Probing Biased Signaling in Chemokine Receptors

The chemokine system mediates leukocyte migration during homeostatic and inflammatory processes. Traditionally, it is described as redundant and promiscuous, with a single chemokine ligand binding to different receptors and a single receptor having several ligands. Signaling of chemokine receptors occurs via two major routes, G protein- and β-arrestin-dependent, which can be preferentially modulated depending on the ligands or receptors involved, as well as the cell types or tissues in which the signaling event occurs. The preferential activation of a certain signaling pathway to the detriment of others has been termed signaling bias and can accordingly be grouped into ligand bias, receptor bias, and tissue bias. Bias has so far been broadly overlooked in the process of drug development. The low number of currently approved drugs targeting the chemokine system, as well as the broad range of failed clinical trials, reflects the need for a better understanding of the chemokine system. Thus, understanding the character, direction, and consequence of biased signaling in the chemokine system may aid the development of new therapeutics. This review describes experiments to assess G protein-dependent and -independent signaling in order to quantify chemokine system bias.

Pharmacological modulation of chemokine receptor function

G protein-coupled chemokine receptors and their peptidergic ligands are interesting therapeutic targets due to their involvement in various immune-related diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, HIV-1 infection and cancer. To tackle these diseases, a lot of effort has been focused on discovery and development of small-molecule chemokine receptor antagonists. This has been rewarded by the market approval of two novel chemokine receptor inhibitors, AMD3100 (CXCR4) and Maraviroc (CCR5) for stem cell mobilization and treatment of HIV-1 infection respectively. The recent GPCR crystal structures together with mutagenesis and pharmacological studies have aided in understanding how small-molecule ligands interact with chemokine receptors. Many of these ligands display behaviour deviating from simple competition and do not interact with the chemokine binding site, providing evidence for an allosteric mode of action. This review aims to give an overview of the evidence supporting modulation of this intriguing receptor family by a range of ligands, including small molecules, peptides and antibodies. Moreover, the computer-assisted modelling of chemokine receptor-ligand interactions is discussed in view of GPCR crystal structures. Finally, the implications of concepts such as functional selectivity and chemokine receptor dimerization are considered.

Synthesis and structure-activity relationships of azamacrocyclic C-X-C chemokine receptor 4 antagonists: analogues containing a single azamacrocyclic ring are potent inhibitors of T-cell tropic (X4) HIV-1 replication

Bis-tetraazamacrocycles such as the bicyclam AMD3100 (1) are a class of potent and selective anti-HIV-1 agents that inhibit virus replication by binding to the chemokine receptor CXCR4, the coreceptor for entry of X4 viruses. By sequential replacement and/or deletion of the amino groups within the azamacrocyclic ring systems, we have determined the minimum structural features required for potent antiviral activity in this class of compounds. All eight amino groups are not required for activity, the critical amino groups on a per ring basis are nonidentical, and the overall charge at physiological pH can be reduced without compromising potency. This approach led to the identification of several single ring azamacrocyclic analogues such as AMD3465 (3d), 36, and 40, which exhibit EC(50)'s against the cytopathic effects of HIV-1 of 9.0, 1.0, and 4.0 nM, respectively, antiviral potencies that are comparable to 1 (EC(50) against HIV-1 of 4.0 nM). More importantly, however, the key structural elements of 1 required for antiviral activity may facilitate the design of nonmacrocyclic CXCR4 antagonists suitable for HIV treatment via oral administration.

Formal reasoning on qualitative models of coinfection of HIV and Tuberculosis and HAART therapy

BACKGROUND

Several diseases, many of which nowadays pandemic, consist of multifactorial pathologies. Paradigmatic examples come from the immune response to pathogens, in which cases the effects of different infections combine together, yielding complex mutual feedback, often a positive one that boosts infection progression in a scenario that can easily become lethal. HIV is one such infection, which weakens the immune system favouring the insurgence of opportunistic infections, amongst which Tuberculosis (TB). The treatment with antiretroviral therapies has shown effective in reducing mortality. An in-depth understanding of complex systems, like the one consisting of HIV, TB and related therapies, is an open great challenge, on the boundaries of bioinformatics, computational and systems biology.

RESULTS

We present a simplified formalisation of the highly dynamic system consisting of HIV, TB and related therapies, at the cellular level. The progression of the disease (AIDS) depends hence on interactions between viruses, cells, chemokines, the high mutation rate of viruses, the immune response of individuals and the interaction between drugs and infection dynamics. We first discuss a deterministic model of dual infection (HIV and TB) which is able to capture the long-term dynamics of CD4 T cells, viruses and Tumour Necrosis Factor (TNF). We contrast this model with a stochastic approach which captures intrinsic fluctuations of the biological processes. Furthermore, we also integrate automated reasoning techniques, i.e. probabilistic model checking, in our formal analysis. Beyond numerical simulations, model checking allows general properties (effectiveness of anti-HIV therapies) to be verified against the models by means of an automated procedure. Our work stresses the growing importance and flexibility of model checking techniques in bioinformatics. In this paper we i) describe HIV as a complex case of infectious diseases; ii) provide a number of different formal descriptions that suitably account for aspects of interests; iii) suggest that the integration of different models together with automated reasoning techniques can improve the understanding of infections and therapies through formal analysis methodologies.

CONCLUSION

We argue that the described methodology suitably supports the study of viral infections in a formal, automated and expressive manner. We envisage a long-term contribution of this kind of approaches to clinical Bioinformatics and Translational Medicine.

Molecular characterization of the env gene of two CCR5/CXCR4-independent human immunodeficiency 2 primary isolates

Human immunodeficiency virus 2 (HIV-2) infection is characterized by a slower disease progression and lower transmission rates. The molecular features that could be assigned as directly involved in this in vivo phenotype remain essentially unknown, and the importance of HIV-2 as a model to understand pathogenicity of HIV infection has been frequently underestimated. The early events of the HIV replication cycle involve the interaction between viral envelope glycoproteins and cellular receptors: the CD4 molecule and a chemokine receptor, usually CCR5 or CXCR4. Despite the importance of these two chemokine receptors in human immunodeficiency virus 1 (HIV-1) entry into cells, we have previously shown that in some HIV-2 asymptomatic individuals, a viral population exists that is unable to use both CCR5 and CXCR4. The goal of the present study was to investigate whether possible regions in the env gene of these viruses might account for this phenotype. From the molecular characterization of these env genes we could not detect any correlation between V3 loop sequence and viral phenotype. In contrast, it reveals the existence of remarkable differences in the V1/V2 and C5 regions of the surface glycoprotein, including the loss of a putative glycosilation site. Moreover, in the transmembrane glycoprotein some unique sequence signatures could be detected in the central ectodomain and second heptad repeat (HR2). Some of the mutations affect well-conserved residues, and may affect the conformation and/or the dynamics of envelope glycoproteins complex, including the SU-TM association and the modulation of viral entry function.

Citrullination of CXCL10 and CXCL11 by peptidylarginine deiminase: a naturally occurring posttranslational modification of chemokines and new dimension of immunoregulation

Interactions between chemokines and enzymes are vital in immunoregulation. Structural protein citrullination by peptidylarginine deiminase (PAD) has been associated with autoimmunity. In this report, we identified a novel naturally occurring posttranslational modification of chemokines, that is, the deimination of arginine at position 5 into citrulline of CXC chemokine ligand 10 (CXCL10) by rabbit PAD and human PAD2. Citrullination reduced (≥ 10-fold) the chemoattracting and signaling capacity of CXCL10 for CXC chemokine receptor 3 (CXCR3) transfectants; however, it did not affect CXCR3 binding. On T lymphocytes, though, citrullinated CXCL10 remained active but was again weaker than authentic CXCL10. PAD was also able to convert CXCL11, causing an impairment of CXCR3 signaling and T-cell activation, though less pronounced than for CXCL10. Similarly, receptor binding properties of CXCL11 were not altered by citrullination. However, deimination decreased heparin binding properties of both CXCL10 and CXCL11. Overall, chemokines are the first immune modulators reported of being functionally modified by citrullination. These data provide new structure-function dimensions for chemokines in leukocyte mobilization, disclosing an anti-inflammatory role for PAD. Additionally because citrullination has severe consequences for chemokine biology, this invites to reassess the involvement and impact of PAD and citrullinated peptides in inflammation, autoimmunity, and hematologic disorders.