Electric foot shock stress-induced exacerbation of α-galactosylceramide-triggered apoptosis in mouse liver

Abstract

Recently, liver natural killer T (NKT) cells, which are specifically stimulated by ␣-galactosylceramide (␣-GalCer), were found to play a critical role in intrahepatic immunity to several infections and certain hepatic disorders. However, the role of psychophysical stress on NKT cell-dependent liver injury induced by ␣-GalCer still remains to be elucidated. In this study, we employed inescapable electric foot shock as the mode of psychophysical stress and evaluated its effect on ␣-GalCer-induced hepatitis. Pre-exposure of 12 hours of foot shock stress before ␣-GalCer administration significantly enhanced ␣-GalCer-triggered increase in serum alanine aminotransferase levels, followed by increases in both liver caspase-3 activity and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive hepatocytes, thus indicating that the liver NKT cell-dependent apoptotic response was exacerbated by stress. Foot shock stress also significantly increased both the number of liver NKT cells and Fas expression levels on hepatocytes. Pretreatment with RU-486, a glucocorticoid (GC) receptor antagonist, completely reversed such stress-induced enhancement of the ␣-GalCer-triggered serum alanine aminotransferase and hepatocyte Fas antigen responses. In contrast, such a reversal effect was not found in the mice pretreated with naloxone, a -opioid receptor antagonist, which thus suggests that an elevation of endogenous GCs, but not ␤-endorphin, as responsible for such stress-induced aggravation in mouse hepatitis models. A ccumulating evidence shows that gut function bidirectionally interacts with brain function by way of a mechanism that is regulated by the complex networks of the endocrine and autonomic nerve systems. [1][2][3] Researchers have preferentially called this interaction the brain-gut axis. Interestingly, some recent works on the brain-gut axis have further expanded this notion into the novel view that such a bidirectional interaction also exists between the brain and liver. It has been reported that intracisternal injection of thyrotropin-releasing hormone in the medulla, in particular in the left dorsal vagal complex, induces stimulation of hepatic blood flow 4,5 and hepatic proliferation, 6 and consequently protects against experimental liver injury 7 through vagal and cholinergic nerve pathways. Furthermore, corticotropin-releasing factor injected intracisternally has been also shown to elicit an inhibition of hepatic blood flow 8 and exacerbate experimental liver injury 9 through sympathetic and noraderenergic nerve pathways. In addition to these animal studies, some early clinical studies also revealed that emotional stress such as that induced by hypnotic suggestion of "fear" and "anxiety" decreases hepatic blood flow 10 and that the severity of psychosocial stress was significantly correlated with the exaggeration of inflammatory and fibrosing changes in alcoholic liver injury. 11 Taken together, these findings suggest the presence of the close communication between the liver and the br...

Apolipoprotein E-Mediated Immune Regulation in Sepsis

“…As CD8 ϩ T cells are known to be influenced by NKT cell activation (32,33), this trend could be attributed to the downstream effects of NKT cells. NKT cell activation reportedly plays a critical role in the intrahepatic immunity to several infections and liver injury (9,34). We found ALT levels to be significantly increased after apoE treatment, which suggests that NKT cell activation contributes to sepsis-induced mortality.…”

“…Studies have also shown that apoE can bind LPS, attenuate the host inflammatory response, and, thus, protect against LPS-induced mortality (8). Distinctively, apoE has also recently been implicated in the activation of NKT cells by acting as a molecular chaperone for bacterial Ags, delivering them to APCs via LDLR to activate NKT cells by CD1d, a nonclassical class-I-like Ag-presenting molecule (9). NKT cells are characterized by the NK marker (NK1.1) and a semi-invariant TCR expressing the V␣14/J␣281 gene segments.…”

Social Disruption Stress Exacerbates α-Galactosylceramide-Induced Hepatitis in Mice

“…In brief, the liver was collected immediately after the fi nal SDR and was passed through a stainless-steel mesh, and the resulting dissociated cells were suspended in PBS, washed, resuspended in an isotonic 30% Percoll solution (Amersham, Wikströms, Sweden) containing heparin (100 U/ml, Shimizu Pharmaceutical, Shizuoka, Japan), and then centrifuged at 500 g for 15 min at room temperature. The cell pellet was resuspended in 0.83% NH 4 Cl solution for 10 min and then washed once in PBS supplemented with 2% FCS and 0.1% sodium azide (staining buffer). The number of MNCs was counted in a Bürker hemocytometer.…”

“…Hepatic mononuclear cells (MNCs) were prepared as previously described [4] . In brief, the liver was collected immediately after the fi nal SDR and was passed through a stainless-steel mesh, and the resulting dissociated cells were suspended in PBS, washed, resuspended in an isotonic 30% Percoll solution (Amersham, Wikströms, Sweden) containing heparin (100 U/ml, Shimizu Pharmaceutical, Shizuoka, Japan), and then centrifuged at 500 g for 15 min at room temperature.…”

“…Results: The stressexposed wild-type mice exhibited signifi cantly reduced thymus weight loss compared with the control animals. Moreover, this stress regimen led to a signifi cant increase in serum alanine aminotransferase levels in both the wild-type and the HBs-tg mice, although the increase evated endogenous glucocorticoids, and consequently exacerbated ␣ -GalCer-induced liver injury via both the expansion of liver NKT cells and the upregulation of hepatocyte Fas antigen [4] . However, the application of these results to psychosocial stress in humans is limited because electric foot-shock stress is generally considered to include many physical factors.…”