Evaluation of the Impact of SARS-CoV-2 Spike protein on the developing brain

Exposure to viruses can be detrimental to the developing brain, yet the impact of SARS-CoV-2 exposure during development is unclear. Although the ability of SARS-CoV-2 to cross the placental barrier is still debated, the viral Spike (S) protein has been detected at the maternal–fetal interface and can potentially generate neurotoxic effects. This suggests that viral components, independent of active infection, may interfere with gliogenesis, synapse formation, and brain connectivity.

This study investigated how developmental exposure to the S protein affects neural excitability, glial reactivity, and synaptic organization. To model this, 10 μL (1 μg/μL) of S protein was subcutaneously injected into postnatal day 1 Swiss mice, while controls (Veh) received 10 μL saline. At P10, neural excitability was assessed using Heat-Induced Seizure (HIS) and Heat- and Sound-Induced Seizure (HSIS) tests at 48 °C. Brains were then collected for qPCR analysis of inflammatory markers and immunofluorescence (IF) to examine astrocytes (GFAP), microglia (Iba1), and excitatory synapses (SYN+HOMER1) in the hippocampus. Group differences were analyzed using unpaired Student’s t-tests.

Behaviourally, Spike-exposed mice exhibited a shorter latency to seizure onset compared to Veh (HIS n=14 Veh, 10 Spike; p=0.01; HSIS n=16 Veh, 14 Spike; p=0.01), indicating increased early-life hyperexcitability. IF analyses showed increased GFAP intensity in CA1 (n=5/group; p=0.01). Although Iba1 intensity did not differ significantly (n=5/group; p=0.07), microglia displayed a more activated morphology. A reduction in excitatory puncta was observed (n=5 Veh, 6 Spike; p=0.01), with similar patterns in CA3 and DG. qPCR revealed elevated iNOS, TNF-α, IL-1β, and COX-2 (n=12 Veh, 8 Spike; p<0.0001, p=0.03, p=0.03, p<0.0001).

These findings indicate that developmental exposure to the S protein promotes early-life hyperexcitability, accompanied by astrocytic activation, neuroinflammation, and synaptic loss.