Transcriptomic Profile of Pericontusional Tissue in Human Severe Traumatic Brain Injury

Abstract

Traumatic brain injury (TBI) is the leading cause of death and neurological disabilities in young adults, representing a significant psychological and economic burden for patients, families, and society. Morbidity and mortality in TBI involve pathophysiological events such as rupture of the blood–brain barrier, neuronal death, and neuroinflammation triggered by the initial trauma and subsequent secondary injuries. A proper understanding of these pathophysiological events involved in TBI is essential to find new targets for the treatment of this disease. The purpose of this study was to analyze the signaling pathways involved in pericontusional brain tissue in severe human TBI. Twenty-two frozen pericontusional brain tissue samples from patients with severe TBI indicated for surgery were analyzed and compared against autopsy brain tissue samples from neurologically healthy donors. The transcriptome analysis by large-scale RNA sequencing (RNA-Seq) was performed in TBI and controls in the exploratory phase. The QuantSeq 3′ mRNA-Seq RNASeq was performed to identify altered gene expression triggered by TBI. Signaling pathway enrichment analysis identified increased expression of gene sets involved in inflammation, angiogenesis, extracellular matrix remodeling, and wound healing pathways, while genes related to ion transport and synaptic transmission were downregulated in TBI relative to controls. Moreover, upregulation of signaling pathways involving TNFα, NFkB, IL6-JAK-STAT, cholesterol homeostasis, inflammatory response, TGFβ, epithelial–mesenchymal transition, coagulation, apoptosis, p53, and angiogenesis was detected with predominant downstream activation of six transcription factors: NFKB2, FOS, RELB, KLF4, ATF3, and EGR2. Specific brain cell compartment analysis based on gene expression profiles previously reported in single-cell transcriptomes confirmed the upregulation of genes related to microglia, immune cells, and endothelial cells, in contrast to the downregulation of genes related to neurons, astrocytes, and mature oligodendrocyte compartments. Notably, the expression of CCL2 was significant and uniquely correlated with SPHK1 expression, linking inflammatory response to angiogenesis. The transcriptome profile of TBI revealed several differentially expressed genes related to inflammatory response but also to concomitant activation of signaling pathways involved in tissue repair. More specifically, the CCL2-SPHK1 axis was validated at gene and protein expression levels in TBI. Further studies elucidating their role in angiogenesis and promotion of brain tissue repair, together with their potential applicability as therapeutic targets, are warranted.