Identification and comparison of eleven rhesus macaque chemokine receptors

Derivation and Characterization of a CD4-Independent, Non-CD4-Tropic Simian Immunodeficiency Virus

CD4 tropism is conserved among all primate lentiviruses and likely contributes to viral pathogenesis by targeting cells that are critical for adaptive antiviral immune responses. Although CD4-independent variants of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) have been described that can utilize the coreceptor CCR5 or CXCR4 in the absence of CD4, these viruses typically retain their CD4 binding sites and still can interact with CD4. We describe the derivation of a novel CD4-independent variant of pathogenic SIVmac239, termed iMac239, that was used to derive an infectious R5-tropic SIV lacking a CD4 binding site. Of the seven mutations that differentiate iMac239 from wild-type SIVmac239, a single change (D178G) in the V1/V2 region was sufficient to confer CD4 independence in cell-cell fusion assays, although other mutations were required for replication competence. Like other CD4-independent viruses, iMac239 was highly neutralization sensitive, although mutations were identified that could confer CD4-independent infection without increasing its neutralization sensitivity. Strikingly, iMac239 retained the ability to replicate in cell lines and primary cells even when its CD4 binding site had been ablated by deletion of a highly conserved aspartic acid at position 385, which, for HIV-1, plays a critical role in CD4 binding. iMac239, with and without the D385 deletion, exhibited an expanded host range in primary rhesus peripheral blood mononuclear cells that included CCR5(+) CD8(+) T cells. As the first non-CD4-tropic SIV, iMac239-ΔD385 will afford the opportunity to directly assess the in vivo role of CD4 targeting on pathogenesis and host immune responses.

IMPORTANCE

CD4 tropism is an invariant feature of primate lentiviruses and likely plays a key role in pathogenesis by focusing viral infection onto cells that mediate adaptive immune responses and in protecting virions attached to cells from neutralizing antibodies. Although CD4-independent viruses are well described for HIV and SIV, these viruses characteristically retain their CD4 binding site and can engage CD4 if available. We derived a novel CD4-independent, CCR5-tropic variant of the pathogenic molecular clone SIVmac239, termed iMac239. The genetic determinants of iMac239's CD4 independence provide new insights into mechanisms that underlie this phenotype. This virus remained replication competent even after its CD4 binding site had been ablated by mutagenesis. As the first truly non-CD4-tropic SIV, lacking the capacity to interact with CD4, iMac239 will provide the unique opportunity to evaluate SIV pathogenesis and host immune responses in the absence of the immunomodulatory effects of CD4(+) T cell targeting and infection.

The apelin receptor APJ: journey from an orphan to a multifaceted regulator of homeostasis

The apelin receptor (APJ; gene symbol APLNR) is a member of the G protein-coupled receptor gene family. Neural gene expression patterns of APJ, and its cognate ligand apelin, in the brain implicate the apelinergic system in the regulation of a number of physiological processes. APJ and apelin are highly expressed in the hypothalamo-neurohypophysial system, which regulates fluid homeostasis, in the hypothalamic-pituitary-adrenal axis, which controls the neuroendocrine response to stress, and in the forebrain and lower brainstem regions, which are involved in cardiovascular function. Recently, apelin, synthesised and secreted by adipocytes, has been described as a beneficial adipokine related to obesity, and there is growing awareness of a potential role for apelin and APJ in glucose and energy metabolism. In this review we provide a comprehensive overview of the structure, expression pattern and regulation of apelin and its receptor, as well as the main second messengers and signalling proteins activated by apelin. We also highlight the physiological and pathological roles that support this system as a novel therapeutic target for pharmacological intervention in treating conditions related to altered water balance, stress-induced disorders such as anxiety and depression, and cardiovascular and metabolic disorders.

CCR2 Antagonists for the Treatment of Diseases Associated with Inflammation

The CCR2 and MCP-1 pathway has become one of the most-studied chemokine systems for therapeutic use in inflammatory diseases and conditions. It plays a pivotal role in inflammatory diseases, especially those that are characterized by monocyte-rich infiltration. This chapter reviews the biology of CCR2 and MCP-1, and their roles in diseases and conditions related to inflammation such as rheumatoid arthritis, multiple sclerosis, asthma, obesity, type 2 diabetes, atherosclerosis, nephropathy, cancer, pulmonary fibrosis and pain. Intense drug-discovery efforts over the past 15 years have generated a large number of CCR2 antagonists in diverse structural classes. Mutagenesis studies have elucidated important residues on CCR2 that interact with many classes of these CCR2 antagonists. To facilitate understanding of CCR2 antagonist SAR, a simple pharmacophore model is used to summarize the large number of diverse chemical structures. The majority of published compounds are classified based on their central core structures using this model. Key SAR points in the published literature are briefly discussed for most of the series. Lead compounds in each chemical series are highlighted where information is available. The challenges in drug discovery and development of CCR2 antagonists are briefly discussed. Clinical candidates in various diseases in the public domain are summarized with a brief discussion about the clinical challenges.

Expansion of a subset of CD14highCD16negCCR2low/neg monocytes functionally similar to myeloid-derived suppressor cells during SIV and HIV infection

Monocytes have been categorized in three main subpopulations based on CD14 and CD16 surface expression. Classical monocytes express the CD14(++)CD16(-)CCR2(+) phenotype and migrate to inflammatory sites by quickly responding to CCL2 signaling. Here, we identified and characterized the expansion of a novel monocyte subset during HIV and SIV infection, which were undistinguishable from classical monocytes, based on CD14 and CD16 expression, but expressed significantly lower surface CCR2. Transcriptome analysis of sorted cells demonstrated that the CCR2(low/neg) cells are a distinct subpopulation and express lower levels of inflammatory cytokines and activation markers than their CCR2(high) counterparts. They exhibited impaired phagocytosis and greatly diminished chemotaxis in response to CCL2 and CCL7. In addition, these monocytes are refractory to SIV infection and suppress CD8(+) T cell proliferation in vitro. These cells express higher levels of STAT3 and NOS2, suggesting a phenotype similar to monocytic myeloid-derived cells, which suppress expansion of CD8(+) T cells in vivo. They may reflect an antiproliferative response against the extreme immune activation observed during HIV and SIV infections. In addition, they may suppress antiviral responses and thus, have a role in AIDS pathogenesis. Antiretroviral therapy in infected macaque and human subjects caused this population to decline, suggesting that this atypical phenotype is linked to viral replication.

Cloning and analysis of sooty mangabey alternative coreceptors that support simian immunodeficiency virus SIVsmm entry independently of CCR5

Natural host sooty mangabeys (SM) infected with simian immunodeficiency virus SIVsmm do not develop AIDS despite high viremia. SM and other natural hosts express very low levels of CCR5 on CD4(+) T cells, and we recently showed that SIVsmm infection and robust replication occur in vivo in SM genetically lacking CCR5, indicating the use of additional entry pathways. SIVsmm uses several alternative coreceptors of human origin in vitro, but which molecules of SM origin support entry is unknown. We cloned a panel of putative coreceptors from SM and tested their ability to mediate infection, in conjunction with smCD4, by pseudotypes carrying Envs from multiple SIVsmm subtypes. smCXCR6 supported efficient infection by all SIVsmm isolates with entry levels comparable to those for smCCR5, and smGPR15 enabled entry by all isolates at modest levels. smGPR1 and smAPJ supported low and variable entry, whereas smCCR2b, smCCR3, smCCR4, smCCR8, and smCXCR4 were not used by most isolates. In contrast, SIVsmm from rare infected SM with profound CD4(+) T cell loss, previously reported to have expanded use of human coreceptors, including CXCR4, used smCXCR4, smCXCR6, and smCCR5 efficiently and also exhibited robust entry through smCCR3, smCCR8, smGPR1, smGPR15, and smAPJ. Entry was similar with both known alleles of smCD4. These alternative coreceptors, particularly smCXCR6 and smGPR15, may support virus replication in SM that have restricted CCR5 expression as well as SM genetically lacking CCR5. Defining expression of these molecules on SM CD4(+) subsets may delineate distinct natural host target cell populations capable of supporting SIVsmm replication without CD4(+) T cell loss.

Recombination-mediated changes in coreceptor usage confer an augmented pathogenic phenotype in a nonhuman primate model of HIV-1-induced AIDS

Evolution of the env gene in transmitted R5-tropic human immunodeficiency virus type 1 (HIV-1) strains is the most widely accepted mechanism driving coreceptor switching. In some infected individuals, however, a shift in coreceptor utilization can occur as a result of the reemergence of a cotransmitted, but rapidly controlled, X4 virus. The latter possibility was studied by dually infecting rhesus macaques with X4 and R5 chimeric simian simian/human immunodeficiency viruses (SHIVs) and monitoring the replication status of each virus using specific primer pairs. In one of the infected monkeys, both SHIVs were potently suppressed by week 12 postinoculation, but a burst of viremia at week 51 was accompanied by an unrelenting loss of total CD4+ T cells and the development of clinical disease. PCR analyses of plasma viral RNA indicated an env gene segment containing the V3 region from the inoculated X4 SHIV had been transferred into the genetic background of the input R5 SHIV by intergenomic recombination, creating an X4 virus with novel replicative, serological, and pathogenic properties. These results indicate that the effects of retrovirus recombination in vivo can be functionally profound and may even occur when one of the recombination participants is undetectable in the circulation as cell-free virus.

The chemokine receptor CCR5 in the central nervous system

The expression and the role of the chemokine receptor CCR5 have been mainly studied in the context of HIV infection. However, this protein is also expressed in the brain, where it can be crucial in determining the outcome in response to different insults. CCR5 expression can be deleterious or protective in controlling the progression of certain infections in the CNS, but it is also emerging that it could play a role in non-infectious diseases. In particular, it appears that, in addition to modulating immune responses, CCR5 can influence neuronal survival. Here, we summarize the present knowledge about the expression of CCR5 in the brain and highlight recent findings suggesting its possible involvement in neuroprotective mechanisms.

Species selectivity of small-molecular antagonists for the CCR5 chemokine receptor

The species selectivity of four structurally different compounds, SCH-351125, E-913, TAK-779 and UK-427857 has been examined using cloned human, rhesus, and mouse CCR5 receptors. SCH-351125 and E-913 potently inhibited the binding of [125I]-CCL3 to human CCR5, but their inhibitory activities against rhesus CCR5 were more than 10-fold weaker. In contrast, TAK-779 and UK-427857 inhibited binding to human and rhesus CCR5 with similar potency. The inhibitory activities of all four compounds against mice CCR5 receptors were weak. The inhibitory activities of the CCR5 antagonists in the [125I]-CCL3 binding assay agreed well with those induced by CCL3 in the intracellular calcium ([Ca(2+)]i) elevation assay. Mutational analysis of the human CCR5 receptor showed that its Ile198 component plays a critical role in the inhibitory activities of both SCH-351125 and E-913, but not that of TAK-779 or UK-427857. These results provide a structural basis for understanding how specific antagonists interact with CCR5, and will aid the process of creating new, improved CCR5 antagonists.

Influence of proinflammatory cytokines and chemokines on the neuropathogenesis of oncornavirus and immunosuppressive lentivirus infections

Retroviral infection of the CNS can lead to severe debilitating neurological diseases in humans and other animals. Four general types of pathogenic effects with various retroviruses have been observed including: hemorrhage (TR1.3), spongiform encephalopathy (CasBrE, FrCasE, PVC211, NT40, Mol-ts1), demyelination with inflammatory lesions (HTLV-1, visna, CAEV), and encephalopathy with gliosis and proinflammatory chemokines and cytokines, usually with microglial giant cells and nodules [human immunodeficiencyvirus (HIV), feline immunodeficiencyvirus (FIV), simian immunodeficiency virus (SIV), Fr98]. This review focuses on this fourth group of retroviruses. In this latter group, proinflammatory cytokine and chemokine upregulation accompanies the disease process, and may influence pathogenesis by direct effects on resident CNS cells. The review first discusses the Fr98 murine polytropic virus system with particular reference to the roles of cytokines and chemokines in the pathogenic process. The Fr98 data are then compared and contrasted to the cytokine and chemokine data in the lentivirus systems, HIV, SIV, and FIV. Finally, various mechanisms are presented by which tumor necrosis factor (TNF) and several chemokines may alter the pathogenesis of retrovirus infection of the CNS.

Comparative studies on mucosal and intravenous transmission of simian immunodeficiency virus (SIVsm): evolution of coreceptor use varies with pathogenic outcome

Coreceptor usage of isolates from 30 cynomolgus macaques infected intrarectally (n=22) or intravenously (n=8) with simian immunodeficiency virus of sooty mangabey origin (SIVsm) was evaluated in U87.CD4 and GHOST(3) cell lines. Based on progression rate, the animals were divided into progressors (18 animals), slow progressors (five animals) and long-term non-progressors (seven animals). There was no difference in how many or which coreceptors were used according to route of infection. All isolates but one used CCR5 for cell entry, and CCR5 was also the major coreceptor in 70 out of 105 isolates tested. In general, early isolates were multitropic, using CCR5, CXCR6 and/or gpr15. Interestingly, CXCR4-using viruses could be isolated on human peripheral blood mononuclear cells (PBMCs), but not on cynomolgus macaque PBMCs, suggesting that human PBMCs select for variants with CXCR4 use. Even though CXCR4-using SIV isolates have been reported rarely, we could recover CXCR4-using viruses from 13 monkeys. CXCR4 use either appeared early during the acute phase of infection and disappeared later or only appeared late in infection during immunodeficiency. Surprisingly, one late isolate from a progressor monkey did not use CCR5 at all and used the CXCR4 receptor with high efficiency. The ability to use many different receptors decreased over time in long-term non-progressor monkeys, whilst the majority of progressor monkeys showed broadening of coreceptor use, stable coreceptor use or fluctuation between the different coreceptor-usage patterns. The results indicate that, in the infected host, evolution of SIV coreceptor usage occurs, involving changes in the mode of coreceptor use.

Molecular cloning and radioligand binding characterization of the chemokine receptor CCR5 from rhesus macaque and human

The aim of this study was to determine if macaque represents a suitable species for the pre-clinical evaluation of novel CCR5 antagonists, such as maraviroc (UK-427,857). To do this we cloned and expressed CCR5 from rhesus macaque and compared the binding properties of [125I]-MIP-1beta and [3H]-maraviroc with human recombinant CCR5. [125I]-MIP-1beta bound with similar high affinity to CCR5 from macaque (K(d) = 0.24 +/- 0.05 nM) and human (K(d) = 0.23 +/- 0.05 nM) and with similar kinetic properties. In competition binding studies the affinity of a range of human chemokines for macaque CCR5 was also similar to human CCR5. Maraviroc inhibited binding of [125I]-MIP-1beta to CCR5 from macaque and human with similar potency (IC50 = 17.50 +/- 1.24 nM and 7.18 +/- 0.93 nM, respectively) and antagonised MIP-1beta induced intracellular calcium release mediated through CCR5 from macaque and human with similar potency (IC50 = 17.50 +/- 3.30 nM and 12.07 +/- 1.89, respectively). [3H]-maraviroc bound with high affinity to CCR5 from macaque (K(d) = 1.36+/-0.07 nM) and human (K(d) = 0.86 +/- 0.08 nM), but was found to dissociate approximately 10-fold more quickly from macaque CCR5. However, as with the human receptor, maraviroc was shown to be a high affinity, potent functional antagonist of macaque CCR5 thereby indicating that the macaque should be a suitable species in which to evaluate the pharmacology, safety and potential mechanism-related toxicology of novel CCR5 antagonists.

A single amino acid change and truncated TM are sufficient for simian immunodeficiency virus to enter cells using CCR5 in a CD4-independent pathway

Entry of HIV and SIV into susceptible cells is mediated by CD4 and chemokine receptors, which act as coreceptors. To study cell entry of SIV, we constructed a cell line, xKLuSIV, derived from non-susceptible human K562 cells, that express the firefly luciferase reporter gene under control of a minimal SIV long terminal repeat (LTR). Using these susceptible cells, we studied the entry of a well-characterized molecularly cloned macrophage-tropic SIV. xKLuSIV cells that express rhesus macaque CD4 and/or the rhesus chemokine receptor CCR5 are susceptible to infection with the macrophage-tropic, neurovirulent strain SIV/17E-Fr, but only xKLuSIV cells expressing both CCR5 and CD4 were susceptible to infection by the macrophage-tropic, non-neurovirulent strain SIV/17E-Cl. CCR5-dependent, CD4-independent infection by SIV/17E-Fr was abrogated by pre-incubation of the cells with AOP-RANTES, a ligand for CCR5. In addition to viral entry occurring by a CD4-independent mechanism, neutralization of SIV/17E-Fr with rhesus mAbs from 3 different neutralization groups blocked entry into x KLuSIV cells by both CD4-dependent and -independent mechanisms. Triggering the env glycoprotein of SIV-17 EFr with soluble CD4 had no significant effect in infectivity, but triggering of the same glycoprotein of SIV/17E-Cl allowed it to enter cells in a CD4-independent fashion. Using mutant molecular clones, we studied the determinants for CD4 independence, all of which are confined to the env gene. We report here that truncation of the TM at amino acid 764 and changing a single amino acid (R751G) in the SIV envelope transmembrane protein (TM) conferred the observed CD4-independent phenotype. Our data suggest that the envelope from the neurovirulent SIV/17E-Fr interacts with CCR5 in a CD4-independent manner, and changes in the TM protein of this virus are important components that contribute to neurovirulence in SIV.

Evolution of coreceptor use and CD4-independence in envelope clones derived from SIVsm-infected macaques

Coreceptor use of HIV can evolve during infection. We previously examined coreceptor use of related SIVsm inoculum viruses and sequential reisolates from cynomolgus macaques. These viruses exhibited broad coreceptor specificities and, generally, CCR5 use remained efficient and stable, while alternative coreceptor use decreased longitudinally. Here we demonstrate that individual envelopes (Envs) from inoculum and reisolate viruses fuse via a range of coreceptors, including CCR5, CCR8, CXCR6, GPR15, GPR1, and APJ. On the whole, coreceptor use of Envs from sequential reisolates recapitulated that of reisolate viruses, thus CCR5 use remained stable while alternative coreceptor use tended to decrease over time. Rhesus CCR5, GPR15, and CXCR6 supported fusion to a similar extent as their human counterparts. Additionally, a number of Envs mediated CD4-independent fusion via CCR5 and GPR15. Envs from different inoculum viruses exhibited distinct dependencies on CD4 for fusion via CCR5, ranging from strictly CD4-dependent to efficiently CD4-independent. Early reisolates from macaques infected with CD4-independent inoculums maintained or evolved Envs with a broad range of CD4-independence. CD4-independence became less variable/efficient in late reisolates from macaques that developed neutralizing antibodies. Infection with a CD4-dependent virus resulted in evolution of CD4-independent Envs in late reisolates. While CD4 independence can potentially broaden tropism in vivo, CD4-independent viruses are particularly sensitive to neutralizing antibodies. Therefore, interplay between receptor tropism and neutralization may shape viral evolution and SIV pathogenesis.

Expression and characterization of the chemokine receptor CCR2B from rhesus monkey

Species selectivity of chemokine receptor antagonists is a potential deterrent to making preclinical assessments in vivo. To determine if rhesus monkey disease models could support these assessments, we pharmacologically and functionally characterized recombinant rhesus CCR2B receptor. For these studies we obtained the CCR2B coding region by PCR from genomic rhesus DNA and expressed the receptor as stable transfectants in Chinese Hamster Ovary cells. The surface expression of recombinant rhesus CCR2B was detected by flow cytometry using a commercially available monoclonal anti-hCCR2B antibody. This antibody was used to detect rhCCR2B on monocytes in peripheral blood mononuclear cell preparations from rhesus whole blood. The recombinantly expressed CCR2B exhibited similar high affinity binding to the CCR2 chemokine ligands from rhesus and human 125I-rhMCP-1 (K(d)=433+/-14 pM) and 125I-hMCP-1 (K(d)=550+/-256 pM). In competition binding, the receptor exhibited selective high affinity binding to the monocyte chemoattractant protein (MCP) family chemokines with little affinity for most other members of the CC family of chemokines. One exception was eotaxin, a high affinity ligand for CCR3, which bound to rhesus CCR2B receptor (K(i)=1467+/-205 pM). Chemokines which exhibited binding affinity for the receptor were tested for their ability to induce intracellular calcium release. In these experiments the relative potencies of the MCP family of chemokines for rhCCR2B were similar to the observed binding affinities. In contrast, eotaxin was functionally inactive as an antagonist or agonist to this receptor. TAK-799 (N,N-dimethyl-N-[4-[[[2-(4-methylphenyl)-6,7-dihydro-5H-benzocyclohepten-8-yl]carbonyl]amino]benzyl]tetrahydro-2H-pyran-4-aminium chloride), a dual CCR2/CCR5 antagonist, demonstrated high affinity for the rhesus CCR2B in competition with 125I-hMCP-1 binding to the receptor (K(i)=0.5 nM) and also potently blocked the MCP-1 induced calcium mobilization mediated through the receptor.

Functional expression and characterization of macaque C-C chemokine receptor 3 (CCR3) and generation of potent antagonistic anti-macaque CCR3 monoclonal antibodies

Eosinophils are major effector cells implicated in a number of chronic inflammatory diseases in humans, particularly bronchial asthma and allergic rhinitis. The beta-chemokine receptor C-C chemokine receptor 3 (CCR3) provides a mechanism for the selective recruitment of eosinophils into tissue and thus has recently become an attractive biological target for therapeutic intervention. In order to develop in vivo models of inflammatory diseases, it is essential to identify and characterize the homologues of human eotaxin (C-C chemokine ligand 11) and CCR3 from other species, such as non-human primates. Accordingly, we cloned the macaque eotaxin and CCR3 genes and revealed that they were 91 and 92% identical at the amino acid level to their human homologues, respectively. Macaque CCR3 expressed in the murine pre-B L1-2 cell line bound macaque eotaxin with high affinity (K(d) = 0.1 nm) and exhibited a robust eotaxin-induced Ca(2+) flux and chemotaxis. Characterization of beta-chemokines on native macaque CCR3 on eosinophils was performed by means of eotaxin-induced shape change in whole blood using a novel signaling assay known as gated autofluorescence forward scatter. Additionally, mAbs were raised against macaque CCR3 using two different immunogens: a 30-amino acid synthetic peptide derived from the predicted NH(2) terminus of macaque CCR3 and intact macaque CCR3-transfected cells. These anti-macaque CCR3 monoclonal antibodies exhibited potent antagonist activity in receptor binding and functional assays. The characterization of the macaque eotaxin/CCR3 axis and development of antagonistic anti-macaque CCR3 monoclonal antibodies will facilitate the development of CCR3 small molecule antagonists with the hope of ameliorating chronic inflammatory diseases in humans.