HHV-6B reduces autophagy and induces ER stress in primary monocytes impairing their survival and differentiation into dendritic cells

Neurotropic virus infection and neurodegenerative diseases: Potential roles of autophagy pathway

Neurodegenerative diseases (NDs) constitute a group of disorders characterized by the progressive deterioration of nervous system functionality. Currently, the precise etiological factors responsible for NDs remain incompletely elucidated, although it is probable that a combination of aging, genetic predisposition, and environmental stressors participate in this process. Accumulating evidence indicates that viral infections, especially neurotropic viruses, can contribute to the onset and progression of NDs. In this review, emerging evidence supporting the association between viral infection and NDs is summarized, and how the autophagy pathway mediated by viral infection can cause pathological aggregation of cellular proteins associated with various NDs is discussed. Furthermore, autophagy-related genes (ARGs) involved in Herpes simplex virus (HSV-1) infection and NDs are analyzed, and whether these genes could link HSV-1 infection to NDs is discussed. Elucidating the mechanisms underlying NDs is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of NDs.

Herpesviridae, Neurodegenerative Disorders and Autoimmune Diseases: What Is the Relationship between Them?

Alzheimer's disease and Parkinson's disease represent the most common forms of cognitive impairment. Multiple sclerosis is a chronic inflammatory disease of the central nervous system responsible for severe disability. An aberrant immune response is the cause of myelin destruction that covers axons in the brain, spinal cord, and optic nerves. Systemic lupus erythematosus is an autoimmune disease characterized by alteration of B cell activation, while Sjögren's syndrome is a heterogeneous autoimmune disease characterized by altered immune responses. The etiology of all these diseases is very complex, including an interrelationship between genetic factors, principally immune associated genes, and environmental factors such as infectious agents. However, neurodegenerative and autoimmune diseases share proinflammatory signatures and a perturbation of adaptive immunity that might be influenced by herpesviruses. Therefore, they might play a critical role in the disease pathogenesis. The aim of this review was to summarize the principal findings that link herpesviruses to both neurodegenerative and autoimmune diseases; moreover, briefly underlining the potential therapeutic approach of virus vaccination and antivirals.

Roseola Infantum: An Updated Review

BACKGROUND

Roseola infantum is a common viral disease that occurs during childhood worldwide.

OBJECTIVE

The purpose of this article is to familiarize pediatricians with the clinical manifestations, evaluation, diagnosis, and management of roseola infantum.

METHODS

A search was conducted in April, 2022, in PubMed Clinical Queries using the key terms "roseola infantum" OR "exanthem subitum" OR "sixth disease". The search strategy included all clinical trials, observational studies, and reviews published within the past 10 years. Only papers published in the English literature were included in this review. The information retrieved from the above search was used in the compilation of the present article.

RESULTS

Roseola infantum is a viral illness characterized by high fever that lasts 3 to 4 days, followed by the sudden appearance of rash at defervescence. The disease occurs most frequently in children between 6 months and 2 years of age. Human herpesvirus-6 (HHV-6) is the major cause of roseola infantum, followed by HHV-7. Transmission of the infection most likely results from the asymptomatic shedding of the virus in the saliva of the caregivers or other close contacts. Characteristically, the rash is discrete, rose-pink in color, circular or elliptical, macular or maculopapular, measuring 2 to 3 mm in diameter. The eruption is first seen on the trunk. It then spreads to the neck and proximal extremities. Typically, the rash blanches on pressure and subsides in 2 to 4 days without sequelae. Most children look well otherwise and appear to be happy, active, alert, and playful. The diagnosis is mainly clinical. Febrile seizures occur in 10 to 15 % of children with roseola infantum during the febrile period. In general, serious complications are rare and occur more often in individuals who are immunocompromised. There is no specific treatment. An antipyretic may be used to reduce fever and discomfort.

CONCLUSION

Roseola infantum is generally a benign and self-limited disease. Failure to recognize this condition may result in undue parental fear, unnecessary investigations, delay in treatment for conditions that mimic roseola infantum and complications from roseola infantum, unnecessary treatment of roseola infantum per se, and misuse of healthcare expenditure.

YAP1 activation by human papillomavirus E7 promotes basal cell identity in squamous epithelia

Persistent human papillomavirus (HPV) infection of stratified squamous epithelial cells causes nearly 5% of cancer cases worldwide. HPV-positive oropharyngeal cancers harbor few mutations in the Hippo signaling pathway compared to HPV-negative cancers at the same anatomical site, prompting the hypothesis that an HPV-encoded protein inactivates the Hippo pathway and activates the Hippo effector yes-associated protein (YAP1). The HPV E7 oncoprotein is required for HPV infection and for HPV-mediated oncogenic transformation. We investigated the effects of HPV oncoproteins on YAP1 and found that E7 activates YAP1, promoting YAP1 nuclear localization in basal epithelial cells. YAP1 activation by HPV E7 required that E7 binds and degrades the tumor suppressor protein tyrosine phosphatase non-receptor type 14 (PTPN14). E7 required YAP1 transcriptional activity to extend the lifespan of primary keratinocytes, indicating that YAP1 activation contributes to E7 carcinogenic activity. Maintaining infection in basal cells is critical for HPV persistence, and here we demonstrate that YAP1 activation causes HPV E7 expressing cells to be retained in the basal compartment of stratified epithelia. We propose that YAP1 activation resulting from PTPN14 inactivation is an essential, targetable activity of the HPV E7 oncoprotein relevant to HPV infection and carcinogenesis.

The ‘epithelial’ cells that cover our bodies are in a constant state of turnover. Every few weeks, the outermost layers die and are replaced by new cells from the layers below. For scientists, this raises a difficult question. Cells infected by human papillomaviruses, often known as HPV, can become cancerous over years or even decades. How do infected cells survive while the healthy cells around them mature and get replaced?

One clue could lie in PTPN14, a human protein which many papillomaviruses eliminate using their viral E7 protein; this mechanism could be essential for the virus to replicate and cause cancer. To find out the impact of losing PTPN14, Hatterschide et al. used human epithelial cells to make three-dimensional models of infected tissues. These experiments showed that, when papillomaviruses destroy PTPN14, a human protein called YAP1 turns on in the lowest, most long-lived layer of the tissue. Cells in which YAP1 is activated survive while those that carry the inactive version mature and die. This suggests that papillomaviruses turn on YAP1 to remain in tissues for long periods.

Papillomaviruses cause about five percent of all human cancers. Finding ways to stop them from activating YAP1 has the potential to prevent disease. Overall, the research by Hatterschide et al. also sheds light on other epithelial cancers which are not caused by viruses.

Evasion of the Host Immune Response by Betaherpesviruses

The human immune system boasts a diverse array of strategies for recognizing and eradicating invading pathogens. Human betaherpesviruses, a highly prevalent subfamily of viruses, include human cytomegalovirus (HCMV), human herpesvirus (HHV) 6A, HHV-6B, and HHV-7. These viruses have evolved numerous mechanisms for evading the host response. In this review, we will highlight the complex interplay between betaherpesviruses and the human immune response, focusing on protein function. We will explore methods by which the immune system first responds to betaherpesvirus infection as well as mechanisms by which viruses subvert normal cellular functions to evade the immune system and facilitate viral latency, persistence, and reactivation. Lastly, we will briefly discuss recent advances in vaccine technology targeting betaherpesviruses. This review aims to further elucidate the dynamic interactions between betaherpesviruses and the human immune system.

ER Stress, UPR Activation and the Inflammatory Response to Viral Infection

The response to invading pathogens such as viruses is orchestrated by pattern recognition receptor (PRR) and unfolded protein response (UPR) signaling, which intersects and converges in the activation of proinflammatory pathways and the release of cytokines and chemokines that harness the immune system in the attempt to clear microbial infection. Despite this protective intent, the inflammatory response, particularly during viral infection, may be too intense or last for too long, whereby it becomes the cause of organ or systemic diseases itself. This suggests that a better understanding of the mechanisms that regulate this complex process is needed in order to achieve better control of the side effects that inflammation may cause while potentiating its protective role. The use of specific inhibitors of the UPR sensors or PRRs or the downstream pathways activated by their signaling could offer the opportunity to reach this goal and improve the outcome of inflammation-based diseases associated with viral infections.

PGE2 Released by Pancreatic Cancer Cells Undergoing ER Stress Transfers the Stress to DCs Impairing Their Immune Function

This study shows that pancreatic cancer cells undergoing cell death by valproic acid (VPA) treatment activated dendritic cells (DCs) more efficiently than those treated with trichostatin A (TSA), as demonstrated by CD86 and CD80 surface expression. Surprisingly though, DCs cultured in the presence of supernatant derived from VPA-treated cancer cells showed a reduced allostimulatory capacity and an increased release of IL10 and IL8 cytokines in comparison with those exposed to TSA-treated cell culture supernatant. Searching for molecular mechanisms leading to such differences, we found that VPA treatment dysregulated choline metabolism and triggered a stronger endoplasmic reticulum (ER) stress in pancreatic cancer cells than TSA, upregulating CCAAT/enhancer-binding protein homologous protein, and activated cyclooxygenase-2, thus promoting the release of prostaglandin (PG) E2. Interestingly, dysfunctional DCs cultured in the presence of VPA-treated cells culture supernatant showed a higher level of intracellular reactive oxygen species, 4-hydroxy-trans-2-nonenal protein adducts, and ER stress, as evidenced by the upregulation of spliced X-box binding protein 1 (XBP1s), effects that were reduced when DCs were exposed to supernatant of cancer cells treated with Celecoxib before VPA. Celecoxib prevented PGE2 release, restoring the function of DCs exposed to VPA-treated cells culture supernatant, and a similar effect was obtained by silencing XBP1s in DCs treated with VPA-treated cells culture supernatant. These results suggest that PGE2 could be one of the yet unidentified factors able to transfer the stress from cancer cells to DCs, resulting in an impairment of their function.

Human Herpesviruses 6A and 6B in Brain Diseases: Association versus Causation

Human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B), collectively termed HHV-6A/B, are neurotropic viruses that permanently infect most humans from an early age. Although most people infected with these viruses appear to suffer no ill effects, the viruses are a well-established cause of encephalitis in immunocompromised patients. In this review, we summarize the evidence that the viruses may also be one trigger for febrile seizures (including febrile status epilepticus) in immunocompetent infants and children, mesial temporal lobe epilepsy, multiple sclerosis (MS), and, possibly, Alzheimer's disease. We propose criteria for linking ubiquitous infectious agents capable of producing lifelong infection to any neurologic disease, and then we examine to what extent these criteria have been met for these viruses and these diseases.

The cross-talk between STAT1/STAT3 and ROS up-regulates PD-L1 and promotes the release of pro-inflammatory/immune suppressive cytokines in primary monocytes infected by HHV-6B

Programmed death ligand 1 (PD-L1) up-regulation on antigen presenting cells induces T cell dysfunction, strongly impairing immune response. Human Herpesviruses (HHV) 6B is a β-herpesvirus that, although displays a higher tropism for T cells, can infect other immune cells including monocytes and dendritic cells (DCs) and neuronal cells. We have previously shown that HHV-6B infection of primary monocytes reduced autophagy and induced Endoplasmic Reticulum (ER) stress/ Unfolded Protein Response (UPR), impairing their survival and differentiation into DCs. In this study, we found that PD-L1 expression was up-regulated by HHV-6B on the surface of infected monocytes and that its extracellular release also increased, effects known to lead to an impairment of anti-viral immune response. At molecular level, PD-L1 up-regulation correlated with the activation of a positive regulatory circuit between the increase of intracellular ROS and the activation of STAT1 and STAT3 induced by HHV-6B, accompanied by a high release of pro-inflammatory/immune suppressive cytokines. In conclusion, this study unveils new strategies put in place by HHV-6B to induce immune dysfunction and the underlying molecular pathways that could be targeted to counteract such immune suppressive effects.

Perturbation of bulk and selective macroautophagy, abnormal UPR activation and their interplay pave the way to immune dysfunction, cancerogenesis and neurodegeneration in ageing

A plethora of studies has indicated that ageing is characterized by an altered proteostasis, ROS accumulation and a status of mild/chronic inflammation, in which macroautophagy reduction and abnormal UPR activation play a pivotal role. The dysregulation of these inter-connected processes favors immune dysfunction and predisposes to a variety of several apparently unrelated pathological conditions including cancer and neurodegeneration. Given the progressive ageing of the population, a better understanding of the mechanisms regulating autophagy, UPR and their interplay is needed in order to design new therapeutic strategies able to counteract the effects of ageing and concomitantly restrain the onset/progression of age-related diseases that represent a private and public health problem.

HHV-6A infection dysregulates autophagy/UPR interplay increasing beta amyloid production and tau phosphorylation in astrocytoma cells as well as in primary neurons, possible molecular mechanisms linking viral infection to Alzheimer's disease

HHV-6A and HHV-6B are neurotropic viruses able to dysregulate autophagy and activate ER stress/UPR in several cell types. The appropriate functioning of these processes is required for cell homeostasis, particularly in post-mitotic cells such as neuronal cells. Interestingly, neurodegenerative diseases such as Alzheimer's disease (AD) are often accompanied by autophagy dysregulation and abnormal UPR activation. This study demonstrated for the first time that HHV-6A infection of astrocytoma cells and primary neurons reduces autophagy, increases Aβ production and activates ER stress/UPR promoting tau protein hyper-phosphorylation. Our results support previous studies suggesting that HHV-6A infection may play a role in AD and unveil the possible underlying molecular mechanisms involved.