Synthesis of full-length viral DNA in CD4-positive membrane vesicles exposed to HIV-1. A model for studies of early stages of the hiv-1 life cycle

Dysfunctional stem and progenitor cells impair fracture healing with age

Successful fracture healing requires the simultaneous regeneration of both the bone and vasculature; mesenchymal stem cells (MSCs) are directed to replace the bone tissue, while endothelial progenitor cells (EPCs) form the new vasculature that supplies blood to the fracture site. In the elderly, the healing process is slowed, partly due to decreased regenerative function of these stem and progenitor cells. MSCs from older individuals are impaired with regard to cell number, proliferative capacity, ability to migrate, and osteochondrogenic differentiation potential. The proliferation, migration and function of EPCs are also compromised with advanced age. Although the reasons for cellular dysfunction with age are complex and multidimensional, reduced expression of growth factors, accumulation of oxidative damage from reactive oxygen species, and altered signaling of the Sirtuin-1 pathway are contributing factors to aging at the cellular level of both MSCs and EPCs. Because of these geriatric-specific issues, effective treatment for fracture repair may require new therapeutic techniques to restore cellular function. Some suggested directions for potential treatments include cellular therapies, pharmacological agents, treatments targeting age-related molecular mechanisms, and physical therapeutics. Advanced age is the primary risk factor for a fracture, due to the low bone mass and inferior bone quality associated with aging; a better understanding of the dysfunctional behavior of the aging cell will provide a foundation for new treatments to decrease healing time and reduce the development of complications during the extended recovery from fracture healing in the elderly.

Thermal stability of the human immunodeficiency virus type 1 (HIV-1) receptors, CD4 and CXCR4, reconstituted in proteoliposomes

BACKGROUND

The entry of human immunodeficiency virus (HIV-1) into host cells involves the interaction of the viral exterior envelope glycoprotein, gp120, and receptors on the target cell. The HIV-1 receptors are CD4 and one of two chemokine receptors, CCR5 or CXCR4.

METHODOLOGY/PRINCIPAL FINDINGS

We created proteoliposomes that contain CD4, the primary HIV-1 receptor, and one of the coreceptors, CXCR4. Antibodies against CD4 and CXCR4 specifically bound the proteoliposomes. CXCL12, the natural ligand for CXCR4, and the small-molecule CXCR4 antagonist, AMD3100, bound the proteoliposomes with affinities close to those associated with the binding of these molecules to cells expressing CXCR4 and CD4. The HIV-1 gp120 exterior envelope glycoprotein bound tightly to proteoliposomes expressing only CD4 and, in the presence of soluble CD4, bound weakly to proteoliposomes expressing only CXCR4. The thermal stability of CD4 and CXCR4 inserted into liposomes was examined. Thermal denaturation of CXCR4 followed second-order kinetics, with an activation energy (E(a)) of 269 kJ/mol (64.3 kcal/mol) and an inactivation temperature (T(i)) of 56°C. Thermal inactivation of CD4 exhibited a reaction order of 1.3, an E(a) of 278 kJ/mol (66.5 kcal/mol), and a T(i) of 52.2°C. The second-order denaturation kinetics of CXCR4 is unusual among G protein-coupled receptors, and may result from dimeric interactions between CXCR4 molecules.

CONCLUSIONS/SIGNIFICANCE

Our studies with proteoliposomes containing the native HIV-1 receptors allowed an examination of the binding of biologically important ligands and revealed the higher-order denaturation kinetics of these receptors. CD4/CXCR4-proteoliposomes may be useful for the study of virus-target cell interactions and for the identification of inhibitors.

Inhibition of HIV‐1 or bacterial activation of macrophages by products of HIV‐1‐resistant human cells

We have recently described the molecular basis of HIV-1 resistance factor (HRF)-mediated anti-viral activity in primary and transformed CD4 T cells. HRF+ cell culture supernatants or partially purified HRF were found to incapacitate the formation of the NF-kappaB/DNA complex, which is indispensable for long terminal promoter-driven transcription of virus genes. In this study, we tested whether HRF might have much broader activity against other organisms whose pathogenesis is linked to NF-kappaB activation. Specifically, we tested the effects of HRF on the NF-kappaB-mediated responses of primary macrophages to HIV-1 or several bacterial antigens. We found that exposure to HRF inhibited HIV-1 expression in macrophages and also induced the production of HRF-like activity by macrophages, which prevented replication of virus in HIV-1-infected peripheral blood lymphocytes cultured in the adjacent compartment. We investigated the mechanism of this inhibition and found that HRF impeded NF-kappaB/DNA binding in macrophages induced by either HIV-1 or lipopolysaccharide from several bacteria species, resulting in impaired tumor necrosis factor-alpha responses to these organisms.

Isolation of two highly potent and non-toxic inhibitors of human immunodeficiency virus type 1 (HIV-1) integrase from Salvia miltiorrhiza

Water soluble extracts of the herbal plant, Salvia miltiorrhiza (Danshen) exhibited potent effect against HIV-1 integrase activity in vitro and viral replication in vivo. We have developed an extensive purification scheme to isolate effective, non-toxic inhibitors against human immunodeficiency virus type 1 (HIV-1) using the 3'-processing activity of integrase as a purification guide and assay. Two water soluble compounds, M(5)22 and M(5)32, have been discovered by isolating them from S. miltiorrhiza roots in purities of >99.5% as shown by NMR spectral analysis with yields of 0.018 and 0.038%, respectively. Structural determination revealed that M(5)22 is lithospermic acid and M(5)32 is lithospermic acid B. These two structurally related compounds are potent anti-HIV inhibitors and showed no cytotoxicity to H9 cells at high concentrations (CC(100)>297 microM for M(5)22 and >223 microM for M(5)32). The IC50 for inhibition of 3'-processing by HIV-1 integrase was found to be 0.83 microM for M(5)22 and 0.48 microM for M(5)32. In addition, M(5)22 and M(5)32 inhibited HIV-1 integrase catalytic activities of 3'-joining to the target DNA with IC50 of 0.48 microM for M(5)22 and 0.37 microM for M(5)32. Furthermore, kinetic and mechanistic studies suggested that drug binding to HIV-1 integrase and inhibition of enzymatic activity occur at a fast rate. Both M(5)22 and M(5)32 do not prevent HIV entry in H9 cells. They also show no inhibition of reverse transcriptase activity in infected cells. The levels of intracellular strong stop and full-length viral DNA remained unchanged following drug treatment. However, both inhibitors strongly suppressed the acute HIV-1 infection of H9 cells with IC50 values of 2 and 6.9 microM for M(5)22 and M(5)32, respectively. Thus these two selective integrase inhibitors hold promise as a novel class of therapeutic drugs for AIDS based on their high potencies and absence of cytotoxicity.

Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry

Baicalin (BA) is a flavonoid compound purified from medicinal plant Scutellaria baicalensis Georgi and has been shown to possess anti-inflammatory and anti-HIV-1 activities. In an effort to elucidate the mechanism of the anti-inflammatory effect of BA, we recently found that this flavonoid compound was able to form complexes with selected chemokines and attenuated their capacity to bind and activate receptors on the cell surface. These observations prompted us to investigate whether BA could inhibit HIV-1 infection by interfering with viral entry, a process known to involve interaction between HIV-1 envelope proteins and the cellular CD4 and chemokine receptors. We found that BA at the noncytotoxic concentrations, inhibited both T cell tropic (X4) and monocyte tropic (R5) HIV-1 Env protein mediated fusion with cells expressing CD4/CXCR4 or CD4/CCR5. Furthermore, presence of BA at the initial stage of HIV-1 viral adsorption blocked the replication of HIV-1 early strong stop DNA in cells. Since BA did not inhibit binding of HIV-1 gp120 to CD4, we propose that BA may interfere with the interaction of HIV-1 Env with chemokine coreceptors and block HIV-1 entry of target cells. Therefore, BA can be used as a basis for developing novel anti-HIV-1 agents.

Synthesis of virus-specific high-mobility DNA after temperature upshift of SC-1 cells chronically infected with moloney murine leukemia virus mutant ts1

Premature termination products of reverse transcription that consist physically of viral minus-sense single-stranded DNA that is shorter than one long terminal repeat and partial DNA duplexes are dramatically increased in the central nervous system (CNS) of FVB/N mice that are infected by ts1, a temperature-sensitive mutant of Moloney murine leukemia virus. Due to their migration in agarose gels, these incomplete physical forms of DNA have been designated high-mobility (HM) DNA. In non-CNS tissues, the level of HM DNA is either low or not detectable. In order to determine the conditions that are necessary for the synthesis of HM DNA in vivo, we have characterized the physical forms of HM DNA that were synthesized in vitro in chronically infected SC-1 cells after temperature upshift. At the permissive temperature of 34 degrees C, the chronically infected SC-1 cells did not synthesize HM DNA. After temperature upshift of the cultured cells from 34 to 37 degrees C, the chronically infected SC-1 cells developed extremely high levels of HM DNA. Following temperature downshift of the cultured cells from 37 to 34 degrees C, a decrease in the level of HM DNA and an increase in the level of unintegrated linear proviral DNA occurred simultaneously. These results suggested that the accumulation of HM DNA both in vitro and in vivo may be the result of superinfection.