Morphological, cellular, and molecular basis of brain infection in COVID-19 patients.

Although increasing evidence confirms neuropsychiatric manifestations associated mainly with severe COVID-19 infection, long-term neuropsychiatric dysfunction (recently characterized as part of "long COVID-19" syndrome) has been frequently observed after mild infection. We show the spectrum of cerebral impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, ranging from long-term alterations in mildly infected individuals (orbitofrontal cortical atrophy, neurocognitive impairment, excessive fatigue and anxiety symptoms) to severe acute damage confirmed in brain tissue samples extracted from the orbitofrontal region (via endonasal transethmoidal access) from individuals who died of COVID-19. In an independent cohort of 26 individuals who died of COVID-19, we used histopathological signs of brain damage as a guide for possible SARS-CoV-2 brain infection and found that among the 5 individuals who exhibited those signs, all of them had genetic material of the virus in the brain. Brain tissue samples from these five patients also exhibited foci of SARS-CoV-2 infection and replication, particularly in astrocytes. Supporting the hypothesis of astrocyte infection, neural stem cell-derived human astrocytes in vitro are susceptible to SARS-CoV-2 infection through a noncanonical mechanism that involves spike-NRP1 interaction. SARS-CoV-2-infected astrocytes manifested changes in energy metabolism and in key proteins and metabolites used to fuel neurons, as well as in the biogenesis of neurotransmitters. Moreover, human astrocyte infection elicits a secretory phenotype that reduces neuronal viability. Our data support the model in which SARS-CoV-2 reaches the brain, infects astrocytes, and consequently, leads to neuronal death or dysfunction. These deregulated processes could contribute to the structural and functional alterations seen in the brains of COVID-19 patients.

Synapse preservation and decreased glial reactions following ventral root crush (VRC) and treatment with 4-hydroxy-tempo (TEMPOL).

Astrogliosis and microglial reactions are correlated with the formation of scar tissue and synapse loss. 4-hydroxy-tempo (TEMPOL) is a reactive oxygen species scavenger with proven neuroprotective efficacy in experimental models of traumatic injury and cerebral ischemia. TEMPOL has not, however, been applied following ventral root lesions, which are particularly correlated with the degeneration of spinal motoneurons following brachial plexus injuries. Thus, the present study investigated the effects of TEMPOL on motoneurons and adjacent glial reactions, with a particular focus on the preservation of excitatory and inhibitory spinal circuits. Adult female Sprague Dawley rats were subjected to ventral root crush (VRC) at the lumbar intumescence. Animals were divided into the following experimental groups: (a) VRC-saline treatment; (b) VRC-TEMPOL treatment (12 mg/kg, n = 5), and (c) VRC-TEMPOL treatment (250 mg/kg, n = 5). The spinal cord tissue located contralateral to the lesion was used as the control. Fourteen days after lesioning, the rats were euthanized and the spinal cords were removed for motoneuron counting and immunolabeling with glial (GFAP and Iba-1) and synapse markers (synaptophysin, VGLUT-1, and GAD65). Although TEMPOL did not exert neuroprotective effects at the studied concentrations, the modulation of glial reactions was significant at higher doses. Thus, synaptophysin staining was preserved and, in particular, VGLUT-1-positive inputs were maintained, thereby indicating that TEMPOL preserved proprioceptive glutamatergic inputs without exacerbating the rate of motoneuron degeneration. Consequently, its administration with other efficient neuroprotective substances may significantly improve the outcomes following spinal cord lesioning.