HHV-6, like some other herpesviruses, dysregulates autophagy in multiple cell types, with important biological consequences.
Three top experts on HHV-6A/B teamed up to write a comprehensive review and propose criteria for establishing HHV-6A/B to MS, epilepsy and Alzheimer’s disease.
Dysregulation of the microRNA miR155 is associated with pathophysiological progression of Alzheimer’s disease. HHV-6A has been shown to suppress miR155.
Researchers at the NIH used RNA-Seq cells from skin and blood to study the underlying mechanisms in DIHS/DRESS and identified both HHV-6 and JAK-STAT pathways as potential targets. Central memory CD4+T cells were enriched with HHV-6B.
A team led by Steven Jacobson, PhD at NINDS analyzed RNA-seq datasets from 901 brains, and found only 1.2% of Alzheimer’s patients and 0.4% of controls positive for HHV-6 RNA. They also found HHV-6 DNA in less than 4% of samples tested by ddPCR.
Two groups have challenged the widely-publicized 2018 study in 2018, that found increased HHV-6A & 7 abundance and an association with clinical and pathology scores in Alzheimer’s. The topic has become the focus vigorous debate.
Building on their prior work, an Italian team has shown that HHV-6A is able to induce dysregulation of autophagy in neurons and astrocytoma cells, increasing amyloid beta and tau production.
HHV-6A infection of microglia cells increases inflammatory markers and Aβ and tau expression dramatically, supporting the hypothesis that plaque development in Alzheimer’s disease may be an innate immune response to pathogens
Investigators propose that the induction of endoplasmic reticulum stress, likely exacerbated by autophagy inhibition, could contribute to the immune suppression induced by HHV-6B in exanthem subitem patients.
Researchers from GlaxoSmithKline found a significant overlap in differentially expressed genes shared by those with herpesvirus infections, Alzheimer’s and Parkinson’s. On the other hand, there was no significant overlap between herpesviruses and Type 2 diabetes or Huntington’s disease.
Swedish researchers report that viruses interact with proteins to form a coating or protein corona that facilitates the formation of amyloid plaque, supporting previous findings by Harvard’s Rudy Tanzi and Robert Moir.
MIT examined transcription across tens of thousands of individual cells in both Alzheimer’s and healthy brains and found APOE strongly upregulated in the microglia and perturbation in myelination-related processes in multiple cell types including oligodendrocytes.
The cellular housekeeping function of autophagy may play a role in Alzheimer’s as dysfunction could result in the accumulation of amyloid. HHV-6A, HHV-6B and HSV1 can infect central nervous system cells and dysregulate autophagy.
MS patients with a particular haplotype on natural killer cells are more susceptible to HHV-6A infection. Similarly, HHV-6A/B may contribute to Alzheimer’s by utilizing a specific NK cell inhibitory receptor to disrupt the ability of NK cells to clear infected cells.
German investigators have identified a marker for what they believe is the earliest stage of viral reactivation, or “transactivation” marked by transcription of several viral small non-coding RNAs in the absence of detectable viral replication. The group believes that these viral small RNAs could be developed as biomarkers.
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