Gut dysbiosis-induced vitamin B6 metabolic disorder contributes to chronic stress-related abnormal behaviors in a cortisol-independent manner

Abstract

Chronic stress can result in various conditions, including psychological disorders, neurodegenerative diseases, and accelerated brain aging. Gut dysbiosis potentially contributes to stress-related brain disorders in individuals with chronic stress. However, the causal relationship and key factors between gut dysbiosis and brain disorders in chronic stress remain elusive, particularly under non-sterile conditions. Here, using a repeated restraint stress (RRS) rat model, we show that sequential transplantation of the cecal contents of different RRS stages to normal rats reproduced RRS-induced core phenotypes, including abnormal behaviors, increased peripheral blood corticosterone and inflammatory cytokines, and a unique gut microbial phenotype. This core phenotypic development was effectively inhibited with probiotic supplement. The RRS-induced unique gut microbial phenotypes at the genus level were positively or negatively associated with the levels of 20 plasma metabolites, including vitamin B6 metabolites 4-pyridoxic acid and 4-pyridoxate. Vitamin B6 supplement during RRS alleviated weight loss, abnormal behaviors, peripheral inflammation, and neuroinflammation, but did not affect the peripheral corticosterone levels in chronic stressed rats. Dampening inflammatory signaling via knocking out caspase 11 or caspase 1 inhibitor abolished RRS-induced abnormal behaviors and peripheral and neuroinflammation but did not decrease peripheral corticosterone in mice. These findings show that gut dysbiosis-induced vitamin B6 metabolism disorder is a new non-hypothalamic-pituitary-adrenal axis mechanism of chronic stress-related brain disorders. Both probiotics and vitamin B6 supplement have potential to be developed as therapeutic strategies for preventing and/or treating chronic stress-related illness.

Keywords: Chronic stress; gut microbial dysbiosis; restraint stress; vitamin B6.

Figure 1.

Sequential transplantation of rat cecal contents of different chronic stress stages to normal rats reproduced chronic stress-induced abnormal behaviors, increased blood corticosterone levels, and inflammatory cytokines.

Figure 2.

Sequential transplantation of rat cecal contents of different chronic stress stages to normal rats reproduced the chronic stress-induced gut microbiota phenotype.

Figure 3.

Probiotic supplementation during chronic stress partly prevented stress-induced gut dysbiosis.

Figure 4.

Nurturing a beneficial gut microbiota with probiotics prevented the development of abnormal behaviors, increased blood corticosterone, and inflammatory cytokines in chronically stressed rats.

Figure 5.

Chronic stress-induced gut dysbiosis altered plasma metabolites, including vitamin B6 metabolism.

Figure 6.

Intraperitoneal injection of vitamin B6 during stress alleviated weight loss, abnormal behaviors, peripheral inflammation and neuroinflammation, but did not affect peripheral corticosterone level in chronic stressed rats.

Figure 7.

Inflammation acting as a downstream effector of corticosterone plays a key role in the pathogenesis of chronic stress-induced abnormal behaviors in caspase 11 knockout mice.

Figure 8.

Inflammation acting as a downstream effector of corticosterone plays a key role in the pathogenesis of chronic stress-induced abnormal behaviors in mice pretreated with caspase 1 inhibitors.