During Infection, Theiler's Virions Are Cleaved by Caspases and Disassembled into Pentamers.

UNLABELLED: Infected macrophages in spinal cords of mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV) undergo apoptosis, resulting in restricted virus yields, as do infected macrophages in culture. Apoptosis of murine macrophages in culture occurs via the intrinsic pathway later in infection (>10 h postinfection [p.i.]) after maximal virus titers (150 to 200 PFU/cell) have been reached, with loss of most infectious virus (<5 PFU/cell) by 20 to 24 h p.i. Here, we show that BeAn virus RNA replication, translation, polyprotein processing into final protein products, and assembly of protomers and pentamers in infected M1-D macrophages did not differ from those processes in TMEV-infected BHK-21 cells, which undergo necroptosis. However, the initial difference from BHK-21 cell infection was seen at 10 to 12 h p.i., where virions from the 160S peak in sucrose gradients had incompletely processed VP0 (compared to that in infected BHK-21 cells). Thereafter, there was a gradual loss of the 160S virion peak in sucrose gradients, with replacement by a 216S peak that was observed to contain pentamers among lipid debris in negatively stained grids by electron microscopy. After infection or incubation of purified virions with activated caspase-3 in vitro, 13- and 17-kDa capsid peptide fragments were observed and were predicted by algorithms to contain cleavage sites within proteins by cysteine-dependent aspartate-directed proteases. These findings suggest that caspase cleavage of sites in exposed capsid loops of assembled virions occurs contemporaneously with the onset and progression of apoptosis later in the infection. IMPORTANCE: Theiler's murine encephalomyelitis virus (TMEV) infection in mice results in establishment of virus persistence in the central nervous system and chronic inflammatory demyelinating disease, providing an experimental animal model for multiple sclerosis. Virus persistence takes place primarily in macrophages recruited into the spinal cord that undergo apoptosis and in turn may facilitate viral spread via infected apoptotic blebs. Infection of murine macrophages in culture results in restricted virus yields late in infection. Here it is shown that the early steps of the virus life cycle in infected macrophages in vitro do not differ from these processes in TMEV-infected BHK-21 cells, which undergo necroptosis. However, the findings late in infection suggest that caspases cleave sites in exposed capsid loops and possibly internal sites of assembled virions occurring contemporaneously with onset and progression of apoptosis. Mechanistically, this would explain the dramatic loss in virus yields during TMEV-induced apoptosis and attenuate the virus, enabling persistence.

The antiapoptotic protein Mcl-1 controls the type of cell death in Theiler's virus-infected BHK-21 cells.

Theiler's murine encephalomyelitis virus (TMEV) results in a persistent central nervous system infection (CNS) and immune-mediated demyelination in mice. TMEV largely persists in macrophages (Ms) in the CNS, and infected Ms in vitro undergo apoptosis, whereas the infection of other rodent cells produces necrosis. We have found that necrosis is the dominant form of cell death in BeAn virus-infected BHK-21 cells but that ~20% of cells undergo apoptosis. Mcl-1 was highly expressed in BHK-21 cells, and protein levels decreased upon infection, consistent with onset of apoptosis. In infected BHK-21 cells in which Mcl-1 expression was knocked down using silencing RNAs there was a 3-fold increase in apoptotic cell death compared to parental cells. The apoptotic program switched on by BeAn virus is similar to that in mouse Ms, with hallmarks of activation of the intrinsic apoptotic pathway in a tumor suppressor protein p53-dependent manner. Infection of stable Mcl-1-knockdown cells led to restricted virus titers and increased physical to infectious particle (PFU) ratios, with additional data suggesting that a late step in the viral life cycle after viral RNA replication, protein synthesis, and polyprotein processing is affected by apoptosis. Together, these results indicate that Mcl-1 acts as a critical prosurvival factor that protects against apoptosis and allows high yields of infectious virus in BHK-21 cells.

Perspectives on the evaluation and adoption of complex in vitro models in drug development: Workshop with the FDA and the pharmaceutical industry (IQ MPS Affiliate).

Complex in vitro models (CIVM) offer the potential to improve pharmaceutical clinical drug attrition due to safety and/ or efficacy concerns. For this technology to have an impact, the establishment of robust characterization and qualifi­cation plans constructed around specific contexts of use (COU) is required. This article covers the output from a workshop between the Food and Drug Administration (FDA) and Innovation and Quality Microphysiological Systems (IQ MPS) Affiliate. The intent of the workshop was to understand how CIVM technologies are currently being applied by pharma­ceutical companies during drug development and are being tested at the FDA through various case studies in order to identify hurdles (real or perceived) to the adoption of microphysiological systems (MPS) technologies, and to address evaluation/qualification pathways for these technologies. Output from the workshop includes the alignment on a working definition of MPS, a detailed description of the eleven CIVM case studies presented at the workshop, in-depth analysis, and key take aways from breakout sessions on ADME (absorption, distribution, metabolism, and excretion), pharmacology, and safety that covered topics such as qualification and performance criteria, species differences and concordance, and how industry can overcome barriers to regulatory submission of CIVM data. In conclusion, IQ MPS Affiliate and FDA scientists were able to build a general consensus on the need for animal CIVMs for preclinical species to better determine species concordance. Furthermore, there was acceptance that CIVM technologies for use in ADME, pharmacology and safety assessment will require qualification, which will vary depending on the specific COU.

Theiler's murine encephalomyelitis virus leader protein is the only nonstructural protein tested that induces apoptosis when transfected into mammalian cells.

Theiler's murine encephalomyelitis virus (TMEV) induces two distinct cell death programs, necrosis and apoptosis. The apoptotic pathway is of particular interest because TMEV persists in the central nervous system of mice, largely in infiltrating macrophages, which undergo apoptosis. Infection of murine macrophages in culture induces apoptosis that is Bax dependent through the intrinsic or mitochondrial pathway, restricting infectious-virus yields and raising the possibility that apoptosis represents a mechanism to attenuate TMEV yet promote macrophage-to-macrophage spread during persistent infection. To help define the cellular stressors and upstream signaling events leading to apoptosis during TMEV infection, we screened baby hamster kidney (BHK-21) cells transfected to express individual nonstructural genes (except 3B) of the low-neurovirulence BeAn virus strain for cell death. Only expression of the leader protein led to apoptosis, as assessed by fluorescence-activated cell sorting analysis of propidium iodide- and annexin V-stained transfected cells, immunoblot analysis of poly(ADP-ribose) polymerase and caspase cleavages, electron microscopy, and inhibition of apoptosis by the pancaspase inhibitor qVD-OPh. After transfection, Bak and not Bax expression increased, suggesting that the apical pathway leading to activation of these Bcl-2 multi-BH-domain proapoptotic proteins differs in BeAn virus infection versus L transfection. Mutation to remove the CHCC Zn finger motif from L, a motif required by L to mediate inhibition of nucleocytoplasmic trafficking, significantly reduced L-protein-induced apoptosis in both BHK-21 and M1-D macrophages.

Novel three dimensional human endocervix cultures respond to 28-day hormone treatment.

The endocervix has both anatomical and biological functions that participate in the delicate balance between tolerance necessary for conception and protection from pathogens. Our goal was to develop a robust 3-dimensional (3D) endocervix model that was a reliable representation of the in vivo tissues and to identify the physiological responses to changing levels of steroid hormones during a 28-day time period. Human endocervical cells were grown on polystyrene scaffolds, and the morphologic and hormonal responses of cultured cells were assessed in response to fluctuating levels of estradiol (E2) or progesterone (P4). Morphologically, the 3D cultures were composed of a mixed population of cells, including epithelial and stromal cells. Treatment with E2 and P4 (d 28) increased cell growth and proliferation as compared with no treatment control. Cells expressed estrogen receptor and P4 receptor and produced both neutral and acidic mucins, including Mucin 16. In addition, a 45-plex Luminex assay identified numerous factors secreted and regulated by hormones. Specifically, IL-1ß and leukemia inhibitory factor significantly decreased in the presence of E2 and P4 as compared with the no hormone control at day 26. Cotreatment with RU486 (mifepristone) attenuated the inhibition of IL-1ß and leukemia inhibitory factor secretion. In summary, a robust, novel 3D endocervical culture was developed, and physiologic responses to the menstrual cycle mimic of E2 and P4 levels for a period of 28 days were identified.