No abstract

HSV-1 can induce damage in brain regions that include the hippocampus and associated limbic structures. These neurogenic niches are important because they are associated with memory formation and are highly enriched with neural progenitor cells (NPCs). The susceptibility and fate of HSV-1 infected NPCs is largely unexplored. We differentiated human induced pluripotent stem cells (iPSCs) into NPCs to generate two-dimensional (2D) and three-dimensional (3D) culture models to examine the interaction of HSV-1 with NPCs. Here, we show that: i) NPCs can be efficiently infected by HSV-1, but infection does not result in cell death of most NPCs, even at high multiplicity of infections (MOIs); ii) limited HSV-1 replication and gene expression can be detected in the infected NPCs; iii) a viral silencing mechanism is established in NPCs exposed to antivirals (E)-5-(2-bromovinyl)-2′-deoxyuridine (5BVdU) and interferon-α (IFN-α). When the antivirals are removed, spontaneous reactivation can occur at low frequency; iv) HSV-1 impairs the ability of NPCs to migrate in a dose-dependent fashion in the presence of 5BVdU + IFN-α; and v) 3D cultures of NPCs are less susceptible to HSV-1 infection than 2D cultures, yet still retain latent genomes. These results suggest that NPC pools could be sites of HSV-1 reactivation in the CNS. Finally, our results highlight the potential value of iPSC 3D cultures to model HSV-1-NPCs interaction. IMPORTANCE This study employed human induced pluripotent stem cells (hiPSCs) to model the interaction of HSV-1 with NPCs, which reside in the neurogenic niches of the CNS and play a fundamental role in adult neurogenesis. Herein, we provide evidence that in NPCs infected at an MOI as low as 0.001 HSV-1 can establish a latent state, suggesting that i) HSV-1 latency is not only restricted to mature neurons, but it can be established during earlier stages of neuronal differentiation; ii) neurogenic niches in the brain may constitute additional HSV-1 latent reservoirs. Lytic HSV-1 infections impaired NPCs migration, which represents a critical step in neurogenesis. Difference in susceptibility to HSV-1 infection between two-dimensional (2D) and three-dimensional (3D) NPC cultures was observed, highlighting the potential value of 3D cultures for modeling host-pathogen interactions. Together, our results are relevant in light of observations relating HSV-1 infection to post-encephalitic cognitive dysfunction.

Alzheimer's disease is a progressive neurodegenerative disease characterized neuropathologically by presence of extracellular amyloid plaques composed of fibrillar amyloid beta (Aβ) peptides and intracellular neurofibrillary tangles. Post-mortem and in vivo studies implicate HSV-1 infection in the brain as a precipitating factor in disease/pathology initiation. HSV-1 infection of two-dimensional (2D) neuronal cultures causes intracellular accumulation of Aβ42 peptide, but these 2D models do not recapitulate the three-dimensional (3D) architecture of brain tissue. We employed human induced pluripotent stem cells (hiPSCs) to compare patterns of Aβ42 accumulation in HSV-1 infected 2D (neuronal monolayers) and 3D neuronal cultures (brain organoids). Akin to prior studies, HSV-1-infected 2D cultures showed Aβ42 immunoreactivity in cells expressing the HSV-1 antigen ICP4 (ICP4+). Conversely, accumulation of Aβ42 in ICP4+ cells in infected organoids was rarely observed. These results highlight the importance of considering 3D cultures to model host-pathogen interaction. IMPORTANCE The “pathogen” hypothesis of Alzheimer’s disease (AD) proposes that brain HSV-1 infection could be an initial source of amyloid beta (Aβ) peptide-containing amyloid plaque development. Aβ accumulation was reported in HSV-1-infected 2D neuronal cultures and neural stem cell cultures, as well as in HSV-1-infected 3D neuronal culture models. The current study extends these findings by showing different patterns of Aβ42 accumulation following HSV-1 infection of 2D compared to 3D neuronal cultures (brain organoids). Specifically, 2D neuronal cultures showed Aβ42-immunoreactivity mainly in HSV-1-infected cells and only rarely in uninfected cells or infected cells exposed to antivirals. Conversely, 3D brain organoids showed accumulation of Aβ42 mainly in non-infected cells surrounding HSV-1-infected cells. We suggest that because brain organoids better recapitulate architectural features of a developing brain than 2D cultures, they may be a more suitable model to investigate the involvement of HSV-1 in the onset of AD pathology.