The effect of short-chain fatty acids on the susceptibility of human umbilical vein endothelial cells to human cytomegalovirus infection

Cytomegalovirus infection disrupts the influence of short-chain fatty acid producers on Treg/Th17 balance

BACKGROUND

Both the gut microbiota and chronic viral infections have profound effects on host immunity, but interactions between these influences have been only superficially explored. Cytomegalovirus (CMV), for example, infects approximately 80% of people globally and drives significant changes in immune cells. Similarly, certain gut-resident bacteria affect T-cell development in mice and nonhuman primates. It is unknown if changes imposed by CMV on the intestinal microbiome contribute to immunologic effects of the infection.

RESULTS

We show that rhesus cytomegalovirus (RhCMV) infection is associated with specific differences in gut microbiota composition, including decreased abundance of Firmicutes, and that the extent of microbial change was associated with immunologic changes including the proliferation, differentiation, and cytokine production of CD8+ T cells. Furthermore, RhCMV infection disrupted the relationship between short-chain fatty acid producers and Treg/Th17 balance observed in seronegative animals, showing that some immunologic effects of CMV are due to disruption of previously existing host-microbe relationships.

CONCLUSIONS

Gut microbes have an important influence on health and disease. Diet is known to shape the microbiota, but the influence of concomitant chronic viral infections is unclear. We found that CMV influences gut microbiota composition to an extent that is correlated with immunologic changes in the host. Additionally, pre-existing correlations between immunophenotypes and gut microbes can be subverted by CMV infection. Immunologic effects of CMV infection on the host may therefore be mediated by two different mechanisms involving gut microbiota. Video Abstract.

A circadian model for viral persistence

Persistently infecting DNA viruses depend heavily on host cell DNA synthesis machinery. Replication of cellular and viral DNA is inhibited by mutagenic stress. It is hypothesized that diurnal regulation of viral DNA replication may occur at the level of cell cycle checkpoints and DNA repair, to protect DNA from exposure to UV light or other mutagens. This highly conserved mechanism is traced back to viruses that persist in prokaryotes and eukaryotes. Inhibition of viral DNA replication and the cell cycle in response to UV light may represent a functional building block in the evolution of circadian-gated DNA replication. Viral DNA replication appears to be closely linked to the circadian clock by interaction of viral promoters, early viral proteins and transcription factors. It is proposed here that under certain conditions viral oncogene expression is phase-shifted relative to that of tumor suppressor and DNA repair genes. The resulting desynchrony of checkpoint controls and DNA repair from diurnal genotoxic exposure produces cyclic periods of suboptimal response to DNA damage. This temporal vulnerability to genotoxic stress produces a "mutator phenotype" with inherent genome instability. The proposed model delineates areas of research with implications for viral pathogenesis and therapeutics.

Two clinical isolates and the Toledo strain of cytomegalovirus contain endothelial cell tropic variants that are not present in the AD169, Towne, or Davis strains

The highly fibroblast-passaged AD169, Towne, and Davis strains of cytomegalovirus (CMV) were found to have a restricted capacity to infect endothelial cells in vitro. Although such replication could be increased by a combination of low speed centrifugation and sodium butyrate treatment, the extracellular virus produced was infectious for fibroblasts but not for endothelial cells. In contrast, the low passage Toledo strain, and a low passage fibroblast-grown clinical isolate of CMV, C1F, could be continually passaged in endothelial cells, giving the strains C1FE and Toledo.E. Whilst, using the conditions described above, initial infection of endothelial cells with AD169 or C1F resulted in similar titres of extracellular virus as assayed on fibroblasts, only the virus from the C1F strain was infectious for endothelial cells. Passage of C1F in fibroblasts decreased its ability to infect endothelial cells, whilst retaining equal ability to infect fibroblasts. Although endothelial-cell-passaged cell-free C1FE virus was endothelial cell-tropic, it was still much more infectious for fibroblasts than for endothelial cells. It is concluded that the C1F and Toledo strains, but not the AD169, Towne, or Davis strains, contained endothelial cell tropic variants, which could be lost on passage through fibroblasts, but retained on passage through endothelial cells. Furthermore, virus in an ex vivo source of CMV, a blood specimen, was found to be more tropic for fibroblasts than for endothelial cells, suggesting that in vivo CMV exists as quasi strains with different cell tropism, some of which might be lost in vitro by passage in an inappropriate cell type.

Isolation, characterization, and biologic features of bone marrow endothelial cells

Bone marrow endothelial cells (BMECs) are an integral part of the bone marrow microenvironment and are likely to play an important role in the regulation of hematopoiesis, either by producing growth factors or inhibitory cytokines or by displaying adhesion molecules that can interact with hematopoietic progenitors. In the present study we demonstrate the isolation, propagation, and characterization of BMECs with regard to morphology, growth characteristics, phenotype, and production of cytokines. Furthermore, we report the creation of a cell line with "BMEC-like" characteristics and compare the characteristics of primary BMEC cultures to those of the immortalized cell line. In addition, we demonstrate that BMECs are susceptible to infection by a laboratory strain of human cytomegalovirus (CMV), suggesting that CMV infection of endothelial cells in vivo could potentially play a role in the hematologic abnormalities observed during CMV infection.