Schwann cells are normally quiescent, myelinating glia cells of the peripheral nervous system. Their aberrant proliferation and transformation underlie the development of benign tumors (neurofibromas) as well as deadly malignant peripheral nerve sheath tumors (MPNSTs). We discovered a new driver of MPNSTs, an oncogenic GTPase named RABL6A, that functions in part by inhibiting the RB1 tumor suppressor. RB1 is a key mediator of cellular senescence, a permanent withdrawal from the cell cycle that protects against cell immortalization and transformation. Based on the RABL6A-RB1 link in MPNSTs, we explored the hypothesis that RABL6A promotes Schwann cell proliferation and abrogates their senescence by inhibiting RB1. Using sequentially passaged normal human Schwann cells (NHSCs), we found that the induction of replicative senescence was associated with reduced expression of endogenous RABL6A. Silencing RABL6A in low passage NHSCs caused premature stress-induced senescence, which was largely rescued by co-depletion of RB1. Consistent with those findings, Rabl6-deficient MEFs displayed impaired proliferation and accelerated senescence compared to wildtype MEFs. These results demonstrate that RABL6A is required for maintenance of proper Schwann cell proliferation and imply that aberrantly high RABL6A expression may facilitate malignant transformation.

Ebola virus (EBOV) causes severe human disease. During late infection, EBOV virions are on the skin’s surface; however, the permissive skin cell types and the route of virus translocation to the epidermal surface are unknown. We describe a human skin explant model and demonstrate that EBOV infection of human skin via basal media increases in a time-dependent and dose-dependent manner. In the dermis, cells of myeloid, endothelial, and fibroblast origin were EBOV antigen–positive whereas keratinocytes harbored virus in the epidermis. Infectious virus was detected on the apical epidermal surface within 3 days, indicating that virus propagates and traffics through the explants. Purified human fibroblasts and keratinocytes supported EBOV infection ex vivo and both cell types required the phosphatidylserine receptor, AXL, and the endosomal protein, NPC1, for virus entry. This platform identified susceptible cell types and demonstrated dynamic trafficking of EBOV virions. These findings may explain person-to-person transmission via skin contact.

Orthoebolavirus zairense is the species name for Zaire Ebola virus (EBOV) within Filoviridae. This group of viruses can cause severe disease in humans, characterized by hemorrhagic shock, coagulation abnormalities, and severe inflammation. While tissue macrophages are critical targets early during EBOV infection, other cell types support viral replication as disease progresses. At late stages of infection, infectious EBOV is found on the surface of the skin, which may be a critical source of infectious virus transmitted between individuals during outbreaks. Human skin contains a number of cellular targets of EBOV, including keratinocytes. Here, we demonstrate EBOV infection of telomerase-immortalized normal human skin keratinocytes (NHSK-1), as well as EBOVΔVP30 infection of NHSK-1 cells that were stably complemented with EBOV transcription factor VP30. Infection with EBOVΔVP30 did not elicit detectable endogenous interferon responses; however, exogenous pre-treatment of NHSK-1 cells with type I, II, and III interferon (IFN) inhibited EBOVΔVP30 infection and infection of an additional low-containment model of EBOV, rVSV/EBOV GP, in a dose-dependent manner. Analysis of the transcriptome of IFN-treated keratinocytes identified multiple genes unique to each IFN and a subset of ISGs upregulated by all three IFNs. Our results indicate that ISGs induced by IFN pre-treatment of keratinocytes can reduce infection, underlining that ISGs may serve as EBOV-targeting therapeutics.

Orthoebolavirus zairense, or Zaire Ebola virus (EBOV) is a species within the virus family Filoviridae, a group of viruses that can cause severe disease in humans characterized by hemorrhagic shock, coagulation abnormalities, and severe inflammation. While tissue macrophages are critical targets early during EBOV infection, other cell types support viral replication as disease progresses. At late stages of infection, infectious EBOV is found on the surface of the skin, which may be a critical source of infectious virus transmitted be-tween individuals during outbreaks. Human skin contains a number of cellular targets of EBOV, including keratinocytes. Here, we demonstrate EBOV infection of telomerase-immortalized normal human skin keratinocytes (NHSK-1) as well as EBOVΔVP30 infection of NHSK-1 cells that were stably complemented with the EBOV transcription factor VP30. Infection with EBOVΔVP30 did not elicit detectable endogenous interferon responses, however, exogenous pre-treatment of NHSK-1 cells with type I, II, and III interferon (IFN) inhibited EBOVΔVP30 infection and infection of an additional low containment model of EBOV, rVSV/EBOV GP, in a dose-dependent manner. Analysis of the transcriptome of IFN-treated keratinocytes identified multiple genes unique to each IFN and a subset of ISGs upregulated by each IFN. Our results indicate that ISGs induced by IFN pre-treatment of keratinocytes can reduce infection, underlining possible anti-EBOV ISGs for development of EBOV-targeting therapeutics.

Adipocytes can be infected by SARS-CoV-2, potentially contributing to the obesity-associated severity of COVID-19. Circumstantial evidence points to angiotensin-converting enzyme 2 (ACE2) as the necessary receptor for adipocyte infection, but this has not been demonstrated experimentally. Using differentiated immortalized human preadipocyte lines that we developed, we found that visceral adipocytes express higher levels of ACE2 and are more susceptible to SARS-CoV-2 spike (S)-mediated luciferase-VSV infection than subcutaneous adipocytes. Overexpression of ACE2 significantly increased infection, whereas knockout of ACE2 significantly decreased S-mediated infection. Visceral adipocytes at baseline were susceptible to infection by SARS-CoV-2 (Delta variant); however, increased levels of viral transcript with time were not apparent. ACE2 knockout significantly decreased the susceptibility of visceral adipocytes to SARS-CoV-2, whereas overexpression of ACE2 resulted in increased SARS-CoV-2 infection and was associated with increased viral transcript levels with time, as well as induction of IL6, a marker of the proinflammatory response. Our results demonstrate that ACE2 confers susceptibility to SARS-CoV-2 infection of visceral adipocytes. Higher levels of ACE2 in these cells may play a role in establishment of infection and a proinflammatory response, potentially leading to pathogenesis.