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Navigating through crowded, dynamically changing environments requires the ability to keep track of other individuals. Grid cells in the entorhinal cortex are a central component of self-related navigation but whether they also track others’ movement is unclear. Here, we propose that entorhinal grid-like codes make an essential contribution to socio-spatial navigation. Sixty human participants underwent functional magnetic resonance imaging (fMRI) while observing and re-tracing different paths of a demonstrator that navigated a virtual reality environment. Results revealed that grid-like codes in the entorhinal cortex tracked the other individual navigating through space. The activity of grid-like codes was time-locked to increases in co-activation and entorhinal-cortical connectivity that included the striatum, the hippocampus, parahippocampal and right posterior parietal cortices. Surprisingly, the grid-related effects during observation were stronger the worse participants performed when subsequently re-tracing the demonstrator’s paths. Our findings suggests that network dynamics time-locked to entorhinal grid-cell-related activity might serve to distribute information about the location of others throughout the brain. Navigating through everyday environments requires the ability to keep track of others. Here, the authors show this ability is linked to grid-like codes in the human entorhinal cortex that signal the spatial paths other individuals take.

Eye movements, such as saccades, allow us to gather information about the environment and, in this way, can shape memory. In non-human primates, saccades are associated with the activity of grid cells in the entorhinal cortex. Grid cells are essential for spatial navigation, but whether saccade-based grid-like signals play a role in human memory formation is currently unclear. Here, human participants undergo functional magnetic resonance imaging and continuous eye gaze monitoring while studying scene images. Recognition memory is probed immediately thereafter. Results reveal saccade-based grid-like codes in the left entorhinal cortex that are specific to later remembered trials during study, a finding that we replicate with an independent data set. The grid-related effects are time-locked to activation increases in the frontal eye fields. Unexpectedly, lower saccade-based grid-like codes are associated with better subsequent recognition memory performance. Our findings suggest an entorhinal map of visual space that is timed with neural activity in oculomotor regions, and negatively associated with subsequent memory. Grid-like codes, entorhinal cortex, saccades, frontal eye fields (FEF), memory, functional magnetic resonance imaging (fMRI) Eye movements during scene viewing are tied to grid-like codes in the entorhinal cortex. Grid signals are specific to later remembered scenes, covary with activity in visuo-oculomotor regions, and are linked to weaker memory.

The spike (S) protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is activated by the host cell proteases cathepsin L or TMPRSS2. The ancestral virus circulating in Wuhan in 2020 and early variants mainly use TMPRSS2 for entry into Calu-3 lung cells while the Omicron subvariant BA.1 and most subsequently circulating Omicron subvariants employ both cathepsin L and TMPRSS2 for Calu-3 cell entry. Here, we investigated which amino acid residues in the S protein of the Omicron subvariant BA.1 control protease choice. We show that Y655 promotes S protein cleavage and cathepsin L-dependent entry while H655 jointly with N969 promotes TMPRSS2-dependent entry. These results define molecular signatures of SARS-CoV-2 protease choice and lung cell infection.

Several SARS-CoV-2 variants emerged that harbor mutations in the surface unit of the viral spike (S) protein that enhance infectivity and transmissibility. Here, we analyzed whether ten naturally-occurring mutations found within the extended loop harboring the S1/S2 cleavage site of the S protein, a determinant of SARS-CoV-2 cell tropism and pathogenicity, impact S protein processing and function. None of the mutations increased but several decreased S protein cleavage at the S1/S2 site, including S686G and P681H, the latter of which is found in variants of concern B.1.1.7 (Alpha variant) and B.1.1.529 (Omicron variant). None of the mutations reduced ACE2 binding and cell-cell fusion although several modulated the efficiency of host cell entry. The effects of mutation S686G on viral entry were cell-type dependent and could be linked to the availability of cathepsin L for S protein activation. These results show that polymorphisms at the S1/S2 site can modulate S protein processing and host cell entry.

The interaction of the SARS-CoV-2 spike protein (S) with the cellular receptor ACE2 is considered essential for infection and constitutes the key target for antibodies induced upon infection and vaccination. Here, using a surrogate system for viral entry, we provide evidence that a naturally occurring mutation can liberate SARS-CoV-2 from ACE2-dependence and that ACE2-independent entry may protect the virus from neutralization by an antibody used for COVID-19 therapy. SARS-CoV-2 variants of concern (VOC) acquired mutations in the spike (S) protein, including E484K, that confer resistance to neutralizing antibodies. However, it is incompletely understood how these mutations impact viral entry into host cells. Here, we analyzed how mutations at position 484 that have been detected in COVID-19 patients impact cell entry and antibody-mediated neutralization. We report that mutation E484D markedly increased SARS-CoV-2 S-driven entry into the hepatoma cell line Huh-7 and the lung cell NCI-H1299 without augmenting ACE2 binding. Notably, mutation E484D largely rescued Huh-7 but not Vero cell entry from blockade by the neutralizing antibody Imdevimab and rendered Huh-7 cell entry ACE2-independent. These results suggest that the naturally occurring mutation E484D allows SARS-CoV-2 to employ an ACE2-independent mechanism for entry that is largely insensitive against Imdevimab, an antibody employed for COVID-19 therapy. IMPORTANCE The interaction of the SARS-CoV-2 spike protein (S) with the cellular receptor ACE2 is considered essential for infection and constitutes the key target for antibodies induced upon infection and vaccination. Here, using a surrogate system for viral entry, we provide evidence that a naturally occurring mutation can liberate SARS-CoV-2 from ACE2-dependence and that ACE2-independent entry may protect the virus from neutralization by an antibody used for COVID-19 therapy.

The COVID-19 pandemic, caused by SARS-CoV-2, demonstrated that zoonotic transmission of animal sarbecoviruses threatens human health but the determinants of transmission are incompletely understood. Here, we show that most spike (S) proteins of horseshoe bat and Malayan pangolin sarbecoviruses employ ACE2 for entry, with human and raccoon dog ACE2 exhibiting broad receptor activity. The insertion of a multibasic cleavage site into the S proteins increased entry into human lung cells driven by most S proteins tested, suggesting that acquisition of a multibasic cleavage site might increase infectivity of diverse animal sarbecoviruses for the human respiratory tract. In contrast, two bat sarbecovirus S proteins drove cell entry in an ACE2-independent, trypsin-dependent fashion and several ACE2-dependent S proteins could switch to the ACE2-independent entry pathway when exposed to trypsin. Several TMPRSS2-related cellular proteases but not the insertion of a multibasic cleavage site into the S protein allowed for ACE2-independent entry in the absence of trypsin and may support viral spread in the respiratory tract. Finally, the pan-sarbecovirus antibody S2H97 enhanced cell entry driven by two S proteins and this effect was reversed by trypsin while trypsin protected entry driven by a third S protein from neutralization by S2H97. Similarly, plasma from quadruple vaccinated individuals neutralized entry driven by all S proteins studied, and availability of the ACE2-independent, trypsin-dependent pathway reduced neutralization sensitivity. In sum, our study reports a pathway for entry into human cells that is ACE2-independent, can be supported by TMPRSS2-related proteases and may be associated with antibody evasion.

In 2024, a clade 2.3.4.4b H5N1 highly pathogenic avian influenza virus (HPAIV) emerged in dairy cattle in the United States and spread rapidly to over 1,000 herds across multiple states. At least 41 human infections have occurred through contact with infected cattle, though no fatalities have been reported so far. This raises questions about whether the human innate immune system provides a barrier to bovine H5N1 HPAIV and whether seasonal influenza vaccines offer cross-protection. To address these questions, we used pseudoviruses bearing hemagglutinin (HA) and neuraminidase (NA) from seasonal influenza A or various H5Ny HPAIV strains (from cattle, duck, and seal). Pseudoviruses bearing H5N1 HPAIV HA and NA entered a wide range of mammalian and avian cell lines, including multiple cell lines from the human respiratory tract, while entry into A549 human lung cells was reduced when IFITM proteins were expressed. Additionally, preincubation of pseudovirus particles bearing H5N1 HPAIV HA and NA with plasma from individuals vaccinated with seasonal influenza vaccines inhibited viral entry. Collectively, these results suggest that the human innate immune system imposes a barrier against bovine H5N1 HPAIV infection and that seasonal influenza vaccines can induce cross-neutralizing activity against bovine H5N1 HPAIV.

Since the beginning of the COVID-19 pandemic, multiple SARS-CoV-2 variants have emerged. While some variants spread only locally, others, referred to as variants of concern, disseminated globally and became drivers of the pandemic. All SARS-CoV-2 variants harbor mutations relative to the virus circulating early in the pandemic, and mutations in the viral spike (S) protein are considered of particular relevance since the S protein mediates host cell entry and constitutes the key target of the neutralizing antibody response. As a consequence, mutations in the S protein may increase SARS-CoV-2 infectivity and enable its evasion of neutralizing antibodies. Furthermore, mutations in the S protein can modulate viral transmissibility and pathogenicity.