Identification of a special cell type as a determinant of the kidney tropism of SARS-CoV-2

Kidney organoids reveal redundancy in viral entry pathways during ACE2-dependent SARS-CoV-2 infection

With a high incidence of acute kidney injury among hospitalized COVID-19 patients, considerable attention has been focussed on whether SARS-CoV-2 specifically targets kidney cells to directly impact renal function, or whether renal damage is primarily an indirect outcome. To date, several studies have utilized kidney organoids to understand the pathogenesis of COVID-19, revealing the ability for SARS-CoV-2 to predominantly infect cells of the proximal tubule (PT), with reduced infectivity following administration of soluble ACE2. However, the immaturity of standard human kidney organoids represents a significant hurdle, leaving the preferred SARS-CoV-2 processing pathway, existence of alternate viral receptors, and the effect of common hypertensive medications on the expression of ACE2 in the context of SARS-CoV-2 exposure incompletely understood. Utilizing a novel kidney organoid model with enhanced PT maturity, genetic- and drug-mediated inhibition of viral entry and processing factors confirmed the requirement for ACE2 for SARS-CoV-2 entry but showed that the virus can utilize dual viral spike protein processing pathways downstream of ACE2 receptor binding. These include TMPRSS- and CTSL/CTSB-mediated non-endosomal and endocytic pathways, with TMPRSS10 likely playing a more significant role in the non-endosomal pathway in renal cells than TMPRSS2. Finally, treatment with the antihypertensive ACE inhibitor, lisinopril, showed negligible impact on receptor expression or susceptibility of renal cells to infection. This study represents the first in-depth characterization of viral entry in stem cell-derived human kidney organoids with enhanced PTs, providing deeper insight into the renal implications of the ongoing COVID-19 pandemic.

IMPORTANCE

Utilizing a human iPSC-derived kidney organoid model with improved proximal tubule (PT) maturity, we identified the mechanism of SARS-CoV-2 entry in renal cells, confirming ACE2 as the sole receptor and revealing redundancy in downstream cell surface TMPRSS- and endocytic Cathepsin-mediated pathways. In addition, these data address the implications of SARS-CoV-2 exposure in the setting of the commonly prescribed ACE-inhibitor, lisinopril, confirming its negligible impact on infection of kidney cells. Taken together, these results provide valuable insight into the mechanism of viral infection in the human kidney.

SARS-CoV-2 nucleocapsid urine antigen in hospitalized patients with Covid-19

Background

SARS-CoV-2 nucleocapsid antigen (N-Ag) can be detected in the blood of patients with Covid-19. We used a highly sensitive and specific assay to explore the presence of N-Ag in urine during the course of Covid-19, and explore its relationship with the severity of the disease.

Methods

We studied urine and blood N-Ag using highly sensitive immunoassay in 82 patients with a SARS-CoV-2 infection proven by PCR.

Results

In the first and second weeks of Covid-19, hospitalized patients tested positive for urinary N-Ag (81.25% and 71.79%, respectively), and blood N-Ag (93.75% and 94.87%, respectively). High urinary N-Ag levels were associated with the absence of SARS-CoV-2 nucleocapsid antibodies, admission in intensive care units, high C-reactive protein levels, lymphopenia, eosinopenia, and high lactate dehydrogenase. A higher accuracy was observed for urine N-Ag as a predictor of severe Covid-19 compared to blood N-Ag.

Conclusions

Our study demonstrate that N-Ag is present in the urine of patients hospitalized in the early phase of Covid-19. As a direct marker of SARS-CoV-2, urinary N-Ag reflects the dissemination of viral compounds in the body. Urine N-Ag may be a useful marker for disease severity of SARS-CoV-2 infections.

Spotlight on COVID-19: eighteen months on

In this Editorial, we highlight the contents of The FEBS Journal’s second Special Issue focussed on COVID‐19. The issue covers a variety of aspects related to COVID‐19, ranging from the most recent improvements in therapies and the significant impact of rapidly developed COVID‐19 vaccines to the emergence of variants of SARS‐CoV‐2, the role of the immune system in the various stages of the disease and the impact of the disease in different organs. We hope that this collection of articles will give readers an informative and critical perspective on recent advances in understanding and treating COVID‐19.