Neuroinflamação, metabolismo energético e reprogramação epigenética na neurorregeneração hipocampal em modelo ex vivo de deficiência de tiamina

Abstract

Introduction: Thiamine (vitamin B1) is a cofactor for enzymes of central energy metabolism and its deficiency (TD) impairs oxidative phosphorylation, increases oxidative stress, and activates inflammatory processes that can lead to neurodegeneration. Wernicke-Korsakoff syndrome (SWK) is a consequence of chronic TD, which leads to extensive neuronal death, and is associated with neuropathological disorders, including cognitive deficits and amnesia. The hippocampus is one of the brain areas most affected by SWK. B1 replacement may not be enough to prevent the irreversible cognitive deficit associated with SWK. Materials and methods: An organotypic hippocampal slice culture (OHC) model was developed to investigate the molecular mechanisms underlying the imbalance between neuronal death and neurogenesis associated with TD. The main effects of B1 deprivation on OHCs were assessed by immunofluorescence and confocal microscopy and transcriptome analysis. Results: In OHCs cultured without B1, a significant reduction in neuronal density was observed after five days and, on the seventh day, the epigenetic marks H3K4me3 and H3K9me3, capable of modulating the chromatin state, were altered in mature neurons favoring gene transcription. Surprisingly, between the seventh and the fourteenth day of B1 deprivation, a pulse of neurogenesis was observed followed by a further massive neuron loss. The contrast between the transcriptomes of OHCs cultured with or without B1 for nine days revealed 89 differentially expressed genes. Functional enrichment analyzes showed increased expression of genes in the KEGG pathways of tryptophan metabolism and lysine degradation, and genes with Gene Ontology (GO) annotations related to the organization of the extracellular matrix, cell adhesion, and positive regulation of synaptic transmission. Several genes of the TNF and FoxO signaling pathways and genes with GO terms related to the inflammatory response were inhibited. The activation of Nsd1, whose product methylates histone H3 at lysine 36, was also observed in the TD group. Increased H3K36me3 in neurons was confirmed by immunofluorescence. Finally, the treatment of COHs in B1 deprivation with anti-inflammatory was effective in anticipating the pulse of neurogenesis, demonstrating the fundamental role of the immune response in the regulation of hippocampal neurogenesis during TD. Conclusion: The positive regulation of genes from pathways related to the synthesis of acetyl-CoA from amino acids suggests a metabolic adaptation capable of allowing neural progenitor cells to use oxidative phosphorylation as energy source for neurogenesis. The set of genes differentially expressed at the ninth day of B1 deprivation points to a genetic programming favorable to the maturation of neurons and the negative regulation of neurogenesis mediated by the H3K36me3 mark in already differentiated neurons. Above all, the reduction in the expression of inflammatory genes before repopulation of OHCs with new neurons suggests a causal relationship, which is supported by previous studies reporting neuroinflammation as a suppressive factor in neurogenesis. Therefore, neuroinflammation seems to be crucial in neurodegeneration associated with TD, and may also have a role in the pathophysiology of SWK.