RESUMO
COVID-19 is a disease caused by coronavirus SARS-CoV-2. In addition to respiratory illness, COVID-19 patients exhibit neurological symptoms that can last from weeks to months (long COVID). It is unclear whether these neurological manifestations are due to infection of brain cells. We found that a small fraction of cortical neurons, but not astrocytes, were naturally susceptible to SARS-CoV-2. Based on the inhibitory effect of blocking antibodies, the infection seemed to depend on the receptor angiotensin-converting enzyme 2 (ACE2), which was expressed at very low levels. Although only a limited number of neurons was infectable, the infection was productive, as demonstrated by the presence of double-stranded RNA in the cytoplasm (the hallmark of viral replication), abundant synthesis of viral late genes localized throughout the neuronal cell, and an increase in viral RNA in the culture medium within the first 48 h of infection (viral release). The productive entry of SARS-CoV-2 requires the fusion of the viral and cellular membranes, which results in the delivery of viral genome into the cytoplasm of the target cell. The fusion is triggered by proteolytic cleavage of the viral surface protein spike, which can occur at the plasma membrane or from endo/lysosomes. Using specific combinations of small-molecule inhibitors, we found that SARS-CoV-2 infection of human neurons was insensitive to nafamostat and camostat, which inhibit cellular serine proteases found on the cell surface, including TMPRSS2. In contrast, the infection was blocked by apilimod, an inhibitor of phosphatidyl-inositol 5 kinase (PIK5K) that regulates endosomal maturation. ImportanceCOVID-19 is a disease caused by coronavirus SARS-CoV-2. Millions of patients display neurological symptoms, including headache, impairment of memory, seizures and encephalopathy, as well as anatomical abnormalities such as changes in brain morphology. Whether these symptoms are linked to brain infection is not clear. The mechanism of the virus entry into neurons has also not been characterized. Here we investigated SARS-CoV-2 infection using a human iPSC-derived neural cell model and found that a small fraction of cortical neurons was naturally susceptible to infection. The infection depended on the ACE2 receptor and was productive. We also found that the virus used the late endosomal/lysosomal pathway for cell entry and that the infection could be blocked by apilimod, an inhibitor of the cellular phosphatidyl-inositol 5 kinase.
RESUMO
COVID-19 severity has varied widely, with demographic and cardio-metabolic factors increasing risk of severe reactions to SARS-CoV-2 infection, but the underlying mechanisms for this remain uncertain. We investigated phenotypic and genetic factors associated with subcutaneous adipose tissue expression of Angiotensin I Converting Enzyme 2 (ACE2), which has been shown to act as a receptor for SARS-CoV-2 cellular entry. In a meta-analysis of three independent studies including up to 1,471 participants, lower adipose tissue ACE2 expression was associated with adverse cardio-metabolic health indices including type 2 diabetes (T2D) and obesity status, higher serum fasting insulin and BMI, and lower serum HDL levels (P<5.32x10-4). ACE2 expression levels were also associated with estimated proportions of cell types in adipose tissue; lower ACE2 expression was associated with a lower proportion of microvascular endothelial cells (P=4.25x10-4) and higher macrophage proportion (P=2.74x10-5), suggesting a link to inflammation. Despite an estimated heritability of 32%, we did not identify any proximal or distal genetic variants (eQTLs) associated with adipose tissue ACE2 expression. Our results demonstrate that at-risk individuals have lower background ACE2 levels in this highly relevant tissue. Further studies will be required to establish how this may contribute to increased COVID-19 severity.
