Screening of pro-apoptotic genes upregulated in an experimental street rabies virus-infected neonatal mouse brain

Autophagy and Apoptosis in Rabies Virus Replication

Rabies virus (RABV) is a single-stranded negative-sense RNA virus belonging to the Rhabdoviridae family and Lyssavirus genus, which is highly neurotropic and can infect almost all warm-blooded animals, including humans. Autophagy and apoptosis are two evolutionarily conserved and genetically regulated processes that maintain cellular and organismal homeostasis, respectively. Autophagy recycles unnecessary or dysfunctional intracellular organelles and molecules in a cell, whereas apoptosis eliminates damaged or unwanted cells in an organism. Studies have shown that RABV can induce both autophagy and apoptosis in target cells. To advance our understanding of pathogenesis of rabies, this paper reviews the molecular mechanisms of autophagy and apoptosis induced by RABV and the effects of the two cellular events on RABV replication.

Exogenous Players in Mitochondria-Related CNS Disorders: Viral Pathogens and Unbalanced Microbiota in the Gut-Brain Axis

Billions of years of co-evolution has made mitochondria central to the eukaryotic cell and organism life playing the role of cellular power plants, as indeed they are involved in most, if not all, important regulatory pathways. Neurological disorders depending on impaired mitochondrial function or homeostasis can be caused by the misregulation of "endogenous players", such as nuclear or cytoplasmic regulators, which have been treated elsewhere. In this review, we focus on how exogenous agents, i.e., viral pathogens, or unbalanced microbiota in the gut-brain axis can also endanger mitochondrial dynamics in the central nervous system (CNS). Neurotropic viruses such as Herpes, Rabies, West-Nile, and Polioviruses seem to hijack neuronal transport networks, commandeering the proteins that mitochondria typically use to move along neurites. However, several neurological complications are also associated to infections by pandemic viruses, such as Influenza A virus and SARS-CoV-2 coronavirus, representing a relevant risk associated to seasonal flu, coronavirus disease-19 (COVID-19) and "Long-COVID". Emerging evidence is depicting the gut microbiota as a source of signals, transmitted via sensory neurons innervating the gut, able to influence brain structure and function, including cognitive functions. Therefore, the direct connection between intestinal microbiota and mitochondrial functions might concur with the onset, progression, and severity of CNS diseases.

Mitochondrial calcium signaling in the brain and its modulation by neurotropic viruses

Calcium (Ca²⁺) plays fundamental and diverse roles in brain cells as a second messenger of many signaling pathways. Given the high energy demand in the brain and the generally non-regenerative state of neurons, the role of brain mitochondrial calcium [Ca²⁺]_m in particular, in regulating ATP generation and determination of cell fate by initiation or inhibition of programmed cell death (PCD) becomes critical. Since [Ca²⁺]_m signaling has a central role in brain physiology, it represents an ideal target for viruses to hijack the Ca²⁺ machinery to favor their own persistence, replication and/or dissemination by modulating cell death. This review discusses the ways by which neurotropic viruses are known to exploit the [Ca²⁺]_m signaling of their host cells to regulate cell death in the brain, particularly in neurons. We hope our review will highlight the importance of [Ca²⁺]_m handling in the virus-infected brain and stimulate further studies towards exploring novel [Ca²⁺]_m related therapeutic strategies for viral effects on the brain.

Endoplasmic reticulum & mitochondrial calcium homeostasis: The interplay with viruses

Calcium ions (Ca²⁺) act as secondary messengers in a plethora of cellular processes and play crucial role in cellular organelle function and homeostasis. The average resting concentration of Ca²⁺ is nearly 100 nM and in certain cells it can reach up to 1 µM. The high range of Ca²⁺ concentration across the plasma membrane and intracellular Ca²⁺ stores demands a well-coordinated maintenance of free Ca²⁺ via influx, efflux, buffering and storage. Endoplasmic Reticulum (ER) and Mitochondria depend on Ca²⁺ for their function and also serve as major players in intracellular Ca²⁺ homeostasis. The ER-mitochondria interplay helps in orchestrating cellular calcium homeostasis to avoid any detrimental effect resulting from Ca²⁺ overload or depletion. Since Ca²⁺ plays a central role in many biological processes it is an essential component of the virus-host interactions. The large gradient across membranes enable the viruses to easily modulate this buffered environment to meet their needs. Viruses exploit Ca²⁺ signaling to establish productive infection and evade the host immune defense. In this review we will detail the interplay between the viruses and cellular & ER-mitochondrial calcium signaling and the significance of these events on viral life cycle and disease pathogenesis.

Pathological and immunological characterization of bluetongue virus serotype 1 infection in type I interferons blocked immunocompetent adult mice

Introduction

Wild-type adult mice with intact interferon (IFN) system were neither susceptible to bluetongue virus (BTV) infection nor showed signs of morbidity/mortality. Establishment of immunologically competent wild-type adult mouse model with type I IFNs blockade is necessary to assess the pathogenesis, immune responses and testing of BTV vaccines.

Objectives

Present study aimed to establish and characterize BTV serotype 1 infection in immunocompetent adult mice with type I IFNs blockade at the time of infection by studying immune responses and sequential pathology.

Methods

Adult mice were administered with anti-mouse IFN-α/β receptor subunit-1 (IFNAR1) blocking antibody (Clone: MAR1-5A3) 24 h before and after BTV serotype 1 infection, and sacrificed at various time points. Sequential pathology, BTV localization by immunohistochemistry and quantification by qRT-PCR, immune cell kinetics and apoptosis by flow cytometry, and cytokines estimation by c-ELISA and qRT-PCR were studied.

Results

IFNAR blocked-infected mice developed clinical signs and typical lesions of BT; whereas, isotype-infected control mice did not develop any disease. The IFNAR blocked-infected mice showed enlarged, edematous, and congested lymph nodes (LNs) and spleen, and vascular (congestion and hemorrhage) and pneumonic lesions in lungs. Histopathologically, marked lymphoid depletion with “starry-sky pattern” due to lymphocytes apoptosis was noticed in the LNs and spleen. BTV antigen was detected and quantified in lymphoid organs, lungs, and other organs at various time points. Initial leukopenia (increased CD4⁺/CD8⁺ T cells ratio) followed by leukocytosis (decreased CD4⁺/CD8⁺ T cells ratio) and significantly increased biochemical values were noticed in IFNAR blocked-infected mice. Increased apoptotic cells in PBMCs and tissues coincided with viral load and levels of different cytokines in blood, spleen and draining LNs and notably varied between time points in IFNAR blocked-infected mice.

Conclusion

Present study is first to characterize BTV serotype 1 infection in immunocompetent adult mouse with type I IFNs blockade. The findings will be useful for studying pathogenesis and testing the efficacy of BTV vaccines.

Phosphoprotein Gene Contributes to the Enhanced Apoptosis Induced by Wild-Type Rabies Virus GD-SH-01 In Vitro

Previous research demonstrated that the matrix protein (M) and glycoprotein (G) of attenuated rabies virus (RABV) strains are involved in the induction of host cell apoptosis. In this work, we show that wild-type (wt) RABV GD-SH-01 induces significantly greater apoptosis than the attenuated strain HEP-Flury. In order to identify the gene(s) accounting for this phenotype, five recombinant RABVs (rRABVs) were constructed by replacing each single gene of HEP-Flury with the corresponding gene of GD-SH-01. By using these rRABVs, we found that not only M and G, but also the phosphoprotein (P) plays an important role in inducing apoptosis. In order to figure out the different role of P gene in inducing apoptosis from the highly divergent background, another rRABV rGDSH-P, which carries the P gene of HEP-Flury in the background of the GD-SH-01 was generated. It was found that infection of NA cells with GD-SH-01 or the recombinant strain rHEP-shP, which carries P gene of GD-SH-01, induced significantly greater apoptosis than HEP-Flury or rGDSH-P in a caspase-dependent pathway that ultimately leads to the activation of the intrinsic apoptotic pathway, which is well characterized with the downregulation of bcl-2, the decrease of mitochondrial membrane potential, the release of mitochondrial cytochrome c, the activation of caspase-9 and caspase-3, and finally the cleavage of poly (ADP-ribose) polymerase. Our results imply that wt P from GD-SH-01 mediates this effect may partly by facilitating viral RNA synthesis but not by viral replication. In sum, we demonstrate a wt RABV strain GD-SH-01 to induce stronger apoptosis than an attenuated RABV HEP-Flury and propose that wt P from GD-SH-01 is involved in this process.

Impact of caspase-1/11, -3, -7, or IL-1β/IL-18 deficiency on rabies virus-induced macrophage cell death and onset of disease

Rabies virus is a highly neurovirulent RNA virus, which causes about 59000 deaths in humans each year. Previously, we described macrophage cytotoxicity upon infection with rabies virus. Here we examined the type of cell death and the role of specific caspases in cell death and disease development upon infection with two laboratory strains of rabies virus: Challenge Virus Standard strain-11 (CVS-11) is highly neurotropic and lethal for mice, while the attenuated Evelyn–Rotnycki–Abelseth (ERA) strain has a broader cell tropism, is non-lethal and has been used as an oral vaccine for animals. Infection of Mf4/4 macrophages with both strains led to caspase-1 activation and IL-1β and IL-18 production, as well as activation of caspases-3, -7, -8, and -9. Moreover, absence of caspase-3, but not of caspase-1 and -11 or -7, partially inhibited virus-induced cell death of bone marrow-derived macrophages. Intranasal inoculation with CVS-11 of mice deficient for either caspase-1 and -11 or -7 or both IL-1β and IL-18 led to general brain infection and lethal disease similar to wild-type mice. Deficiency of caspase-3, on the other hand, significantly delayed the onset of disease, but did not prevent final lethal outcome. Interestingly, deficiency of caspase-1/11, the key executioner of pyroptosis, aggravated disease severity caused by ERA virus, whereas wild-type mice or mice deficient for either caspase-3, -7, or both IL-1β and IL-18 presented the typical mild symptoms associated with ERA virus. In conclusion, rabies virus infection of macrophages induces caspase-1- and caspase-3-dependent cell death. In vivo caspase-1/11 and caspase-3 differently affect disease development in response to infection with the attenuated ERA strain or the virulent CVS-11 strain, respectively. Inflammatory caspases seem to control attenuated rabies virus infection, while caspase-3 aggravates virulent rabies virus infection.

Mitochondrial p53 Contributes to Reovirus-Induced Neuronal Apoptosis and Central Nervous System Injury in a Mouse Model of Viral Encephalitis

The tumor suppressor p53 plays a critical part in determining cell fate both as a regulator of the transcription of several proapoptotic genes and through its binding interactions with Bcl-2 family proteins at mitochondria. We now demonstrate that p53 protein levels are increased in infected brains during reovirus encephalitis. This increase occurs in the cytoplasm of reovirus-infected neurons and is associated with the activation of caspase 3. Increased levels of p53 in reovirus-infected brains are not associated with increased expression levels of p53 mRNA, suggesting that p53 regulation occurs at the protein level. Increased levels of p53 are also not associated with the increased expression levels of p53-regulated, proapoptotic genes. In contrast, upregulated p53 accumulates in mitochondria. Previous reports demonstrated that the binding of p53 to Bak at mitochondria causes Bak activation and results in apoptosis. We now show that Bak is activated and that activated Bak is bound to p53 during reovirus encephalitis. In addition, survival is enhanced in reovirus-infected Bak(-/-) mice compared to controls, demonstrating a role for Bak in reovirus pathogenesis. Inhibition of the mitochondrial translocation of p53 with pifithrin μ prevents the formation of p53/Bak complexes following reovirus infection of ex vivo brain slice cultures and results in decreased apoptosis and tissue injury. These results suggest that the mitochondrial localization of p53 regulates reovirus-induced pathogenesis in the central nervous system (CNS) through its interactions with Bak.

IMPORTANCE

There are virtually no specific treatments of proven efficacy for virus-induced neuroinvasive diseases. A better understanding of the pathogenesis of virus-induced CNS injury is crucial for the rational development of novel therapies. Our studies demonstrate that p53 is activated in the brain following reovirus infection and may provide a therapeutic target for virus-induced CNS disease.

Wild-type rabies virus induces autophagy in human and mouse neuroblastoma cell lines

Different rabies virus (RABV) strains have their own biological characteristics, but little is known about their respective impact on autophagy. Therefore, we evaluated whether attenuated RABV HEP-Flury and wild-type RABV GD-SH-01 strains triggered autophagy. We found that GD-SH-01 infection significantly increased the number of autophagy-like vesicles, the accumulation of enhanced green fluorescent protein (EGFP)-LC3 fluorescence puncta and the conversion of LC3-I to LC3-II, while HEP-Flury was not able to induce this phenomenon. When evaluating autophagic flux, we found that GD-SH-01 infection triggers a complete autophagic response in the human neuroblastoma cell line (SK), while autophagosome fusion with lysosomes was inhibited in a mouse neuroblastoma cell line (NA). In these cells, GD-SH-01 led to apoptosis and mitochondrial dysfunction while triggering autophagy, and apoptosis could be decreased by enhancing autophagy. To further identify the virus constituent causing autophagy, 5 chimeric recombinant viruses carrying single genes of HEP-Flury instead of those of GD-SH-01 were rescued. While the HEP-Flury virus carrying the wild-type matrix protein (M) gene of RABV triggered LC3-I to LC3-II conversion in SK and NA cells, replacement of genes of nucleoprotein (N), phosphoprotein (P) and glycoprotein (G) produced only minor autophagy. But no one single structural protein of GD-SH-01 induced autophagy. Moreover, the AMPK signaling pathway was activated by GD-SH-01 in SK. Therefore, our data provide strong evidence that autophagy is induced by GD-SH-01 and can decrease apoptosis in vitro. Furthermore, the M gene of GD-SH-01 may cooperatively induce autophagy.

Correlation of inducible nitric oxide synthase (iNOS) inhibition with TNF-α, caspase-1, FasL and TLR-3 in pathogenesis of rabies in mouse model

The role of inflammatory cytokines such as interleukin-1α/β (IL-1α/β), IL-6, IL-10, tumour necrosis factor-alpha (TNF-α), interferons, nitric oxide (NO) and inducible nitric oxide synthase (iNOS) in pathogenesis of rabies is being actively pursued. Presently, levels of certain immune molecules in pathogenesis of rabies in mice have been investigated. CVS strain of rabies infection resulted in early increase in iNOS, TNF-α, caspase-1, Fas ligand (FasL) and toll-like receptor-3 (TLR-3) mRNA levels in brain, and nitric oxide levels in serum. The severity of clinical signs and microscopic lesions largely correlated with NO levels. Aminoguanidine (AG; iNOS inhibitor) decreased NO production with delay in development of clinical signs and increase in survival time. Prolonged survival time correlated with reduced viral load evident by real-time PCR, reduced fluorescent signals of rabies antigen in brain and reduced immunohistochemistry signals in neuronal cytoplasm. These parameters suggested that nitric oxide did influence the rabies virus replication. Inhibition of iNOS by AG administration led to decreased expression of TNF-α, caspase-1, FasL and TLR-3 mRNA levels suggesting that increase in NO levels in rabies virus infection possibly contributed to development of disease through inflammation, apoptosis and immune-evasive mechanisms.

Screening of Upregulated Genes in Suckling Mouse Central Nervous System during the Disease Stage of Rabies Virus Infection

The pathogenesis of hydrophobia remains unclear. The aim of this study was to identify the differentially upregulated genes that correlated with disease development in an experimental mouse model to provide better understanding of pathological mechanisms in rabies. The present work employed Clontech mouse array 1.2 II containing 1,176 gene transcripts. Suckling mice were intracerebrally infected with canine rabies virus. The gene expression profiles on day 2, 4 and 6 post inoculation were followed. The results show genes whose expression increased at least twofold above the control, mock-infected brain. The numbers of genes showing altered expression level were 29, 109 and 98 genes on day 2, 4 and 6, respectively. The genes with altered expression were classified into eight major groups, namely immune response, metabolism, receptor and transporter, growth factors, death mediated factors, transcription and translation factors, proteases, and kinases. The numbers of upregulated genes during the disease stage was much higher than during the asymptomatic stage. This suggested that direct interaction between RABV and target cells induced massive destruction of a cellular homeostasis which may lead to functional termination of the CNS.

Role of apoptosis in rabies viral encephalitis: a comparative study in mice, canine, and human brain with a review of literature

To evaluate the role of apoptosis in rabies encephalitis in humans and canines infected with wild-type street virus, in comparison with rodent model infected with street and laboratory passaged CVS strain, we studied postmortem brain tissue from nine humans, six canines infected with street rabies virus, and Swiss albino mice inoculated intramuscularly (IM) and intracerebrally (IC) with street and CVS strains. Encephalitis and high rabies antigen load were prominent in canine and human brains compared to rodents inoculated with street virus. Neuronal apoptosis was detectable only in sucking mice inoculated with CVS strain and minimal in street virus inoculated mice. In a time point study in suckling mice, DNA laddering was noted only terminally (7 days p.i.) following IC inoculation with CVS strain but not with street virus. In weanling and adult mice, apoptosis was restricted to inflammatory cells and absent in neurons similar to human and canine rabies-infected brains. Absence of neuronal apoptosis in wild-type rabies may facilitate intraneuronal survival and replication while apoptosis in inflammatory cells prevents elimination of the virus by abrogation of host inflammatory response.

The ubiquitin-proteasome pathway is important for dengue virus infection in primary human endothelial cells

Dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) are the most severe forms of dengue virus infection with hemorrhage and plasma leakage. However, pathogenic mechanisms of DHF and DSS remain poorly understood. We therefore investigated host responses as determined by changes in the cellular proteome of primary human endothelial cells upon infection with dengue virus serotype 2 (DEN-2) at a multiplicity of infection (MOI) of 10 for 24 h. Two-dimensional PAGE and quantitative intensity analysis revealed 38 significantly altered protein spots (16 upregulated and 22 downregulated) in DEN-2-infected cells compared to mock controls. These altered proteins were successfully identified by mass spectrometry, including those involved in oxidative stress response, transcription and translation, cytoskeleton assembly, protein degradation, cell growth regulation, apoptosis, cellular metabolism, and antiviral response. The proteomic data were validated by Western blot analyses [upregulated ubiquitin-activating enzyme E1 (UBE1) and downregulated annexin A2] and an immunofluorescence study (upregulated MxA). Interestingly, we found that MxA was colocalized with DEN-2 viral capsid protein, strengthening its role as an antiviral protein. Moreover, we also identified upregulation of a proteasome subunit. Our functional study revealed the significant role of ubiquitination in dengue infection and UBE1 inhibition by its specific inhibitor (UBEI-41) caused a significant reduction in the level of viral protein synthesis and its infectivity. Our findings suggest that various biological processes were triggered in response to dengue infection, particularly antiviral IFN and ubiquitin-proteasome pathways.

Bid regulates the pathogenesis of neurotropic reovirus

Reovirus infection leads to apoptosis in both cultured cells and the murine central nervous system (CNS). NF-kappaB-driven transcription of proapoptotic cellular genes is required for the effector phase of the apoptotic response. Although both extrinsic death-receptor signaling pathways and intrinsic pathways involving mitochondrial injury are implicated in reovirus-induced apoptosis, mechanisms by which either of these pathways are activated and their relationship to NF-kappaB signaling following reovirus infection are unknown. The proapoptotic Bcl-2 family member, Bid, is activated by proteolytic cleavage following reovirus infection. To understand how reovirus integrates host signaling circuits to induce apoptosis, we examined proapoptotic signaling following infection of Bid-deficient cells. Although reovirus growth was not affected by the absence of Bid, cells lacking Bid failed to undergo apoptosis. Furthermore, we found that NF-kappaB activation is required for Bid cleavage and subsequent proapoptotic signaling. To examine the functional significance of Bid-dependent apoptosis in reovirus disease, we monitored fatal encephalitis caused by reovirus in the presence and absence of Bid. Survival of Bid-deficient mice was significantly enhanced in comparison to wild-type mice following either peroral or intracranial inoculation of reovirus. Decreased reovirus virulence in Bid-null mice was accompanied by a reduction in viral yield. These findings define a role for NF-kappaB-dependent cleavage of Bid in the cell death program initiated by viral infection and link Bid to viral virulence.

The cell biology of rabies virus: using stealth to reach the brain

Rabies virus, the prototypical neurotropic virus, causes one of the most lethal zoonotic diseases. According to official estimates, over 55,000 people die of the disease annually, but this is probably a severe underestimation. A combination of virulence factors enables the virus to enter neurons at peripheral sites and travel through the spinal cord to the brain of the infected host, where it often induces aggression that facilitates the transfer of the virus to a new host. This Review summarizes the current knowledge of the replication cycle of rabies virus and virus- host cell interactions, both of which are fundamental elements in our quest to understand the life cycle of rabies virus and the pathogenesis of rabies.

Genomic expression profiling of peripheral blood leukocytes of pigs infected with highly virulent classical swine fever virus strain Shimen

Classical swine fever (CSF), caused by a virus of the same name (CSFV), is a highly contagious swine pyrexic disease featuring extensive haemorrhagic lesions and leukopenia, but little is known about the molecular mechanisms of its pathogenesis. To gain insight into the interaction between the virus and host cells, microarray analyses were performed to detect alterations in genomic expression of pig peripheral blood leukocytes (PBLs) following CSFV infection. Three healthy pigs were inoculated with a lethal dose of highly virulent CSFV strain Shimen. PBLs were isolated at the onset of typical clinical signs and total RNA was subjected to microarray analyses with Affymetrix Porcine Genome Array GeneChips. Of all 20 201 pig genes arrayed in the chip, 1745 showed altered expression (up- or downregulation) after infection. These were classified into eight functional groups, relating to cell proliferation (3.6 %), immune response (2.1 %), apoptosis (1.4 %), kinase activity (1.4 %), signal transduction (1.4 %), transcription (0.7 %), receptor activity (0.7 %) and cytokines/chemokines (0.4 %). The remaining 88.3 % of genes had unknown functions. Alterations in genomic expression were confirmed by real-time RT-PCR of selected cellular genes and Western blotting of annexin 2, a cellular protein relating to virus infection. The observed expression changes of numerous genes involved in immune and inflammatory responses and in the apoptosis process indicate that CSFV has developed sophisticated mechanisms to cause leukopenia in infected pigs. These data provide a basis for exploring the molecular pathogenesis of CSFV infection through an understanding of the interaction between viral and cellular components.

Fas-mediated apoptotic signaling in the mouse brain following reovirus infection

Type 3 (T3) reovirus strains induce apoptotic neuronal cell death and lethal encephalitis in infected mice. T3 strain Dearing (T3D)-induced apoptosis in primary neuronal cultures occurs by a Fas-mediated mechanism and requires the activation of caspase 8. We now show that Fas mRNA is upregulated in the brains of mice infected with encephalitic reovirus T3D and T3 strain Abney (T3A) but not following infection with nonencephalitic reovirus type 1 strain Lang. Fas is upregulated in regions of the brain that are injured during infection with T3 reovirus strains and colocalizes with virus antigen in individual neurons. In contrast, levels of FasL mRNA induced by encephalitic and nonencephalitic reovirus strains do not differ significantly. Caspase 8, the initiator caspase associated with Fas-mediated apoptosis, is activated in the cortex and hippocampal regions of both T3D- and T3A-infected mice. Furthermore, Bid cleavage and the activation of caspase 9 in the brains of T3D-infected mice suggest that the caspase 8-dependent activation of mitochondrial apoptotic signaling contributes to virus-induced apoptosis. We have previously shown that the inhibition of c-Jun N-terminal kinase (JNK) signaling blocks T3D-induced apoptosis and improves the outcome of virus-induced encephalitis. We now show that the reovirus-induced upregulation of Fas requires JNK signaling, thereby providing a link between reovirus-induced death receptor signaling and mitogen-activated protein kinase pathways and a potential mechanism for the therapeutic action of JNK inhibition.

Cytobiological consequences of calcium-signaling alterations induced by human viral proteins

Since calcium-signaling regulates specific and fundamental cellular processes, it represents the ideal target of viral proteins, in order for the virus to control cellular functions and favour its persistence, multiplication and spread. A detailed analysis of reports focused on the impact of viral proteins on calcium-signaling has shown that virus-related elevations of cytosolic calcium levels allow increased viral protein expression (HIV-1, HSV-1/2), viral replication (HBx, enterovirus 2B, HTLV-1 p12(I), HHV-8, EBV), viral maturation (rotavirus), viral release (enterovirus 2B) and cell immortalization (EBV). Interestingly, virus-induced decreased cytosolic calcium levels have been found to be associated with inhibition of immune cells functions (HIV-1 Tat, HHV-8 K15, EBV LMP2A). Finally, several viral proteins are able to modulate intracellular calcium-signaling to control cell viability (HIV-1 Tat, HTLV-1 p13(II), HCV core, HBx, enterovirus 2B, HHV-8 K7). These data point out calcium-signaling as a key cellular target for viral infection and should stimulate further studies exploring new calcium-related therapeutic strategies.

Mechanisms of escape phenomenon of spinal cord and brainstem in human rabies

Background

Rabies virus preferentially involves brainstem, thalamus and spinal cord in human furious and paralytic rabies beginning in the early stage of illness. Nevertheless, rabies patient remains alert until the pre-terminal phase. Weakness of extremities develops only when furious rabies patient becomes comatose; whereas peripheral nerve dysfunction is responsible for weakness in paralytic rabies.

Methods

Evidence of apoptosis and mitochondrial outer membrane permeabilization in brain and spinal cord of 10 rabies patients was examined and these findings were correlated with the presence of rabies virus antigen.

Results

Although apoptosis was evident in most of the regions, cytochrome c leakage was relatively absent in spinal cord of nearly all patients despite the abundant presence of rabies virus antigen. Such finding was also noted in brainstem of 5 patients.

Conclusion

Cell death in human rabies may be delayed in spinal cord and the reticular activating system, such as brainstem, thus explaining absence of weakness due to spinal cord dysfunction and preservation of consciousness.