The p15gag and p12gag regions are both necessary for the pathogenicity of the murine AIDS virus

Neuropathophysiology of coronavirus disease 2019: neuroinflammation and blood brain barrier disruption are critical pathophysiological processes that contribute to the clinical symptoms of SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) is caused by the novel SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) first discovered in Wuhan, Hubei province, China in December 2019. SARS-CoV-2 has infected several millions of people, resulting in a huge socioeconomic cost and over 2.5 million deaths worldwide. Though the pathogenesis of COVID-19 is not fully understood, data have consistently shown that SARS-CoV-2 mainly affects the respiratory and gastrointestinal tracts. Nevertheless, accumulating evidence has implicated the central nervous system in the pathogenesis of SARS-CoV-2 infection. Unfortunately, however, the mechanisms of SARS-CoV-2 induced impairment of the central nervous system are not completely known. Here, we review the literature on possible neuropathogenic mechanisms of SARS-CoV-2 induced cerebral damage. The results suggest that downregulation of angiotensin converting enzyme 2 (ACE2) with increased activity of the transmembrane protease serine 2 (TMPRSS2) and cathepsin L in SARS-CoV-2 neuroinvasion may result in upregulation of proinflammatory mediators and reactive species that trigger neuroinflammatory response and blood brain barrier disruption. Furthermore, dysregulation of hormone and neurotransmitter signalling may constitute a fundamental mechanism involved in the neuropathogenic sequelae of SARS-CoV-2 infection. The viral RNA or antigenic peptides also activate or interact with molecular signalling pathways mediated by pattern recognition receptors (e.g., toll-like receptors), nuclear factor kappa B, Janus kinase/signal transducer and activator of transcription, complement cascades, and cell suicide molecules. Potential molecular targets and therapeutics of SARS-CoV-2 induced neurologic damage are also discussed.

Bacterial lipopolysaccharide enhances cardiac dysfunction but not retroviral replication in murine AIDS: roles of macrophage infiltration and toll-like receptor 4 expression

Cardiovascular disease is an important complication of human immunodeficiency virus/acquired immune deficiency syndrome (AIDS), but the mechanism(s) involved are poorly understood. Although co-infecting pathogens have been implicated as an important factor in AIDS progression, no studies have investigated these interactions in cardiac tissue. We recently demonstrated that the murine AIDS model (LPBM5 retroviral infection) mimics human immunodeficiency virus-related cardiac dysfunction and pathology. We tested the hypothesis that subseptic lipopolysaccharide exposure (LPS) would enhance LPBM5 progression and exacerbate cardiovascular dysfunction during murine AIDS development. LPS (5 mg/kg, Escherichia coli 0111:B4) was administered at 1, 6, and 8 weeks during LPBM5 infection, and cardiac performance was evaluated at 10 weeks using noninvasive echocardiography. LPS alone had no significant effects, whereas it amplified abnormalities in cardiac structure and function observed in murine AIDS. Cardiac dysfunction was associated with selective increases in nonfocal infiltration of CD68(+) cells and correlated with the extent of cardiac dysfunction. Retroviral progression and cardiac retroviral content remained unaltered, but cardiac toll-like receptor 4 was increased in retrovirus + LPS. We provide first-time evidence of multipathogen enhancements to retrovirus-related cardiac complications and implicate innate immune responses, not co-pathogen-induced retroviral replication, as the primary mechanism in this setting.

Role of a cytotoxic-T-lymphocyte epitope-defined, alternative gag open reading frame in the pathogenesis of a murine retrovirus-induced immunodeficiency syndrome

LP-BM5 murine leukemia virus-infected C57BL/6 mice develop profound immunodeficiency and B-cell lymphomas. The LP-BM5 complex contains a mixture of defective (BM5def) and replication-competent helper viruses among which BM5def is the primary causative agent of disease. The BM5def primary open reading frame (ORF1) encodes the single gag precursor protein (Pr60gag). Our lab has recently demonstrated that a novel immunodominant cytotoxic-T-lymphocyte (CTL) epitope (SYNTGRFPPL) is expressed from a +1-nucleotide translational open reading frame of BM5def during the course of normal retrovirus expression. The SYNTGRFPPL CTL epitope may be generated from either of two initiation methionines present, ORF2a or ORF2b, located downstream of the ORF1 initiation site. This study investigates the role(s) of the alternative ORF2-derived gag protein(s) of BM5def in viral pathogenesis. We have examined the disease-inducing capabilities of mutant viruses in which the translational potential of either the initiating ORF2a or ORF2b AUG has been disrupted. Although these mutated viruses are capable of wild-type ORF1 expression, they are unable to induce disease. Our data strongly suggest the existence of a novel ORF2 product(s) that is required for LP-BM5-induced pathogenesis and have potentially broad implications for other retroviral diseases.

Analysis of the helper virus in murine retrovirus-induced immunodeficiency syndrome: evidence for immunoselection of the dominant and subdominant CTL epitopes of the BM5 ecotropic virus

In genetically susceptible strains, such as C57BL/6 (B6) mice, LP-BM5 causes murine AIDS (MAIDS). LP-BM5 is a complex mixture of murine leukemia viruses (MuLV) that includes replication competent ecotropic (BM5eco) and mink cell focus inducing (MCF), and replication defective (BM5d) MuLV. At present, for the BM5eco virus, sequence information on only the gag region is available. In this paper, we describe for the first time the sequencing of the entire BM5eco viral genome as well as analysis of homology with two other previously sequenced and well-characterized MuLVs, Emv-11 and Emv-2, the latter constituting the parental virus for BM5eco. We propose that the detailed sequence comparisons herein provide cogent evidence that BM5eco utilizes variations in cytotoxic T lymphocytes (CTL) epitopes as an immune escape mechanism. This CTL evasion mechanism may contribute substantially to the underlying prototypic susceptibility of B6 mice to LP-BM5-induced MAIDS.

Mutational analysis of the R peptide cleavage site of Moloney murine leukaemia virus envelope protein

Moloney murine leukaemia virus (MoMLV) enters host cells by membrane fusion between the viral envelope and the host cell membrane. The cytoplasmic tail (R peptide) of the MoMLV envelope protein (Env) is cleaved by the viral protease during virion maturation. R peptide-truncated Env induces syncytia in susceptible cells but R peptide-containing Env does not, indicating that the R peptide inhibits membrane fusion. To examine the function of amino acid residues at the R peptide cleavage site in virus entry, mutant Env expression plasmids containing amino acid substitutions at these cleavage site residues were constructed. Some of these mutants induced syncytia in NIH 3T3 cells, even though they expressed the R peptide, indicating the importance of these residues for membrane fusion inhibition by the R peptide. Some mutants in which R peptide cleavage was detected had comparable transduction efficiency to wild-type Env, but mutants in which R peptide cleavage was not detected had lower transduction efficiency than wild-type Env. This result strongly supports that R peptide cleavage is required for virus entry.

Relationship of cytokines and cytokine signaling to immunodeficiency disorders in the mouse

The contributions of cytokines to the development and progression of disease in a mouse model of retrovirus-induced immunodeficiency (MAIDS) are controversial. Some studies have indicated at etiologic role for type 2 cytokines, while others have emphasized the importance of type 1 cytokines. We have used mice deficient in expression of IL-4, IL-10, IL-4 and IL-10, IFN-gamma, or ICSBP-a transcriptional protein involved in IFN signaling-to examine their contributions to this disorder. Our results demonstrate that expression of type 2 cytokines is an epiphenomenon of infection and that IFN-gamma is a driving force in disease progression. In addition, exogenously administered IL-12 prevents many manifestations of disease while blocking retrovirus expression. Interruption of the IFN signaling pathways in ICSBP-/- mice blocks induction of MAIDS. Predictably, ICSBP-deficient mice exhibit impaired responses to challenge with several other viruses. This immunodeficiency is associated with impaired production of IFN-gamma and IL-12. Unexpectedly, however, the ICSBP-/- mice also develop a syndrome with many similarities to chronic myelogenous leukemia in humans. The chronic phase of this disease is followed by a fatal blast crisis characterized by clonal expansions of undifferentiated cells. ICSBP is thus an important determinant of hematopoietic growth and differentiation as well as a prominent signaling molecule for IFNs.

The murine AIDS virus Gag precursor protein binds to the SH3 domain of c-Abl

The Pr60gag protein of the murine AIDS (MAIDS) defective virus promotes the proliferation of the infected target B cells and is responsible for inducing a severe immunodeficiency disease. Using the yeast two-hybrid system, we identified the SH3 domain of c-Abl as interacting with the proline-rich p12 domain of Pr60gag. The two proteins were shown to associate in vitro and in vivo in MAIDS virus-infected B cells. Overexpression of Pr60(gag) in these cells led to a detectable increase of the levels of c-Abl protein and to its translocation at the membrane. These results suggest that this viral protein serves as a docking site for signaling molecules and that c-Abl may be involved in the proliferation of infected B cells.

Possible origin of murine AIDS (MAIDS) virus: conversion of an endogenous retroviral p12gag sequence to a MAIDS-inducing sequence by frameshift mutations

The murine AIDS (MAIDS) virus has a unique sequence in its p12gag region, which is responsible for MAIDS development. A transcript hybridizing with this sequence is expressed in normal C57BL/6 mice. The transcript, designated Edv, has been previously cloned and sequenced (Y. Kubo, Y. Nakagawa, K. Kakimi, H. Matsui, K. Higo, L. Wang, H. Kobayashi, T. Hirama, and A. Ishimoto, J. Gen. Virol. 75:881-888, 1994). Compared with the nucleotide sequence of the helper LP-BM5 ecotropic virus, the pathogenic replication-defective MAIDS virus has a 16-bp deletion and a 1-bp insertion in the 5' and 3' regions of the p12gag sequence, respectively, and the Edv transcript contains only a 3-bp deletion. Therefore, the amino acid sequence of the defective MAIDS virus p12gag region is not homologous to that of the helper virus and the Edv transcript because of the frameshift. To determine whether the amino acid sequence resulting from the frameshift is critical for MAIDS development, we constructed chimeric viruses that contained the p12gag regions of the helper virus and the Edv transcript, respectively, with and without the same frame as the defective MAIDS virus by the artificial frameshift mutations. The mutant viruses with the frameshift mutations induced MAIDS in inoculated mice, but the viruses without the mutations did not. These results suggested that the MAIDS virus was generated by frameshift mutations in the p12gag region of Edv or a related sequence.

Quantitative assessment of murine retrovirus LP-BM5 infection in MAIDS by PCR and anion exchange HPLC

In vitro amplification of DNA by PCR is a powerful tool to detect small amounts of DNA. It is now widely used for detection of pathogenic agents from extracellular fluids and organs. The use of anion exchange HPLC to quantify the PCR product resulting from the specific amplification of the DNA from the replicative-defective viral DNA responsible for MAIDS is described. This technique allows precise quantification of MAIDS virus DNA in different organs and circumvents the use of radioactivity and gel electrophoresis.

Alpha/beta interferons increase host resistance to murine AIDS

Murine AIDS (MAIDS) is caused by a defective retrovirus present in the LP-BM5 murine leukemia virus mixture. Strains of inbred mice differ in resistance to MAIDS development; some are susceptible (e.g., C57BL/6), while others are resistant (e.g., CBA and B10.BR). As an early block to viral replication in resistant mice has been demonstrated previously by PCR studies, we postulated that alpha/beta interferons (IFN-alpha/beta) may be involved in resistance to MAIDS. Susceptible C57BL/6 mice infected with LP-BM5 were treated with IFN-alpha/beta or Newcastle disease virus. Newcastle disease virus induces high endogenous IFN-alpha/beta production in mice. Both treatments delayed the development of MAIDS, as assessed by splenomegaly and T- and B-cell proliferation. In addition, an IFN-alpha/beta response was detected by reverse transcription-PCR and dot blotting 3, 6, and 9 h after LP-BM5 infection in resistant mice but not in susceptible mice. These results suggest that the ability to produce IFN-alpha/beta in response to LP-BM5 infection may contribute to host resistance to MAIDS.

Evidence that the murine AIDS defective virus does not encode a superantigen

The T-cell receptor repertoire was analyzed in C57BL/6 mice upon infection with helper-free stocks of the pathogenic murine AIDS (MAIDS) defective virus in order to demonstrate if, as previously reported, this virus encodes a superantigen. A polyclonal T-cell stimulation involving T cells expressing multiple V beta subsets occurred within the first week of infection, while late in the disease we could note only a 50% deletion of V beta 5 CD8+ cells. Transfection of the MAIDS virus genomic DNA into fibroblasts and B cells expressing major histocompatibility complex class II molecules failed to show any stimulation of cells expressing the specific V beta (V beta 5) previously reported to respond to MAIDS virus-infected cells. In addition, mice lacking V beta 5 cells did not show any significant decrease in susceptibility to the disease compared with mice expressing V beta 5 and bred on the same genetic background. Our in vivo and in vitro results fail to demonstrate a role for a superantigen encoded by the MAIDS defective viral genome in the pathogenesis of MAIDS.

Frequent disruption of the Nf1 gene by a novel murine AIDS virus-related provirus in BXH-2 murine myeloid lymphomas

Evi-2, a common site of viral integration in BXH-2 myeloid lymphomas, is located within a large intron of the Nf1 tumor suppressor gene. Viral integration at Evi-2 appears to induce disease by disrupting normal Nf1 expression. During our attempts to characterize the nature of the proviruses located at Evi-2, we found that approximately half of the proviruses were defective nonecotropic proviruses (A. M. Buchberg, H. G. Bedigian, N. A. Jenkins, and N. G. Copeland, Mol. Cell. Biol. 10:4658-4666, 1990). This was surprising, since most proviruses characterized at other BXH-2 common integration sites are full-length ecotropic viruses. In the studies described here, we found that this defective provirus carries two large deletions, one in pol and one in env, and is structurally related to another murine retrovirus, the murine AIDS retrovirus. By using oligonucleotide probes specific for this defective provirus, designated MRV, we showed that MRV-related proviruses are carried as endogenous germ line proviruses in most inbred strains. In addition, we identified the endogenous MRV provirus that gives rise to the defective proviruses identified at Evi-2. We present a model that accounts for the positive selection of MRV proviruses at Evi-2, which may allow selective identification of common viral integration sites harboring tumor suppressor genes.