No abstract

Post-traumatic stress disorder (PTSD) is a mental health disorder that arises after experiencing or witnessing a traumatic event. Despite affecting around 7% of the population, there are currently no definitive biological signatures or biomarkers used in the diagnosis of PTSD. Thus, the search for clinically relevant and reproducible biomarkers has been a major focus of the field. With significant advances of large-scale multi-omic studies that include genomic, proteomic, and metabolomic data, promising findings have been made, but the field still has fallen short. Amongst the possible biomarkers examined, one area is often overlooked, understudied, or inappropriately investigated: the field of redox biology. Redox molecules are free radical and/or reactive species that are generated as a consequence of the necessity of electron movement for life. These reactive molecules, too, are essential for life, but in excess are denoted as “oxidative stress” and often associated with many diseases. The few studies that have examined redox biology parameters have often utilized outdated and nonspecific methods, as well as have reported confounding results, which has made it difficult to conclude the role for redox in PTSD. Herein, we provide a foundation of how redox biology may underlie diseases like PTSD, critically examine redox studies of PTSD, and provide future directions the field can implement to enhance standardization, reproducibility, and accuracy of redox assessments for the use of diagnosis, prognosis, and therapy of this debilitating mental health disorder.

Post-traumatic stress disorder (PTSD), a consequence of psychological trauma, is associated with increased inflammation and an elevated risk of developing comorbid inflammatory diseases. However, the mechanistic link between this mental health disorder and inflammation remains elusive. Using a pre-clinical model of PTSD known as repeated social defeat stress (RSDS), we previously identified that S100a8 and S100a9 mRNA, genes that encode the protein calprotectin, were significantly upregulated in T-lymphocytes after psychological trauma. Calprotectin expression positively correlated with inflammatory gene expression and the mitochondrial redox environment in T-lymphocytes, therefore, we hypothesized that genetic deletion of calprotectin would attenuate the inflammatory and redox phenotype displayed after RSDS. Using pharmacological and genetic manipulation of S100a9 (which functionally eliminates calprotectin) in mice, we unexpectedly observed worsening of behavioral pathology, inflammation, and the mitochondrial redox environment in mice after RSDS compared to wild-type (WT) animals. Furthermore, loss of calprotectin significantly enhanced the metabolic demand on T-lymphocytes suggesting this protein may play an undescribed role in mitochondrial regulation. This was further supported by single-cell RNA sequencing analysis demonstrating that RSDS and loss of S100a9 primarily altered genes associated with mitochondrial function and oxidative phosphorylation. Taken together, these data demonstrate the loss of calprotectin potentiates the RSDS-induced phenotype, which suggests its observed upregulation after psychological trauma may provide previously unexplored protective functions.