Activation of stress signaling molecules in bat brain during arousal from hibernation

Abstract

Induction of glucose-regulated proteins (GRPs) is a ubiquitous intracellular response to stresses such as hypoxia, glucose starvation and acidosis. The induction of GRPs offers some protection against these stresses in vitro, but the specific role of GRPs in vivo remains unclear. Hibernating bats present a good in vivo model to address this question. The bats must overcome local high oxygen demand in tissue by severe metabolic stress during arousal thermogenesis. We used brain tissue of a temperate bat Rhinolopus ferrumequinum to investigate GRP induction by high metabolic oxygen demand and to identify associated signaling molecules. We found that during 30 min of arousal, oxygen consumption increased from nearly zero to 11.9/kg/h, which was about 8.7-fold higher than its active resting metabolic rate. During this time, body temperature rose from 7°C to 35°C, and levels of TNF-a and lactate in brain tissue increased 2-2.5-fold, indicating a high risk of oxygen shortage. Concomitantly, levels of GRP75, GRP78 and GRP94 increased 1.5-1.7-fold. At the same time, c-Jun N-terminal protein kinase (JNK) activity increased 6.4-fold, and extracellular signal-regulated protein kinase (ERK) activity decreased to a similar degree (6.1-fold). p38 MAPK activity was very low and remained unchanged during arousal. In addition, survival signaling molecules protein kinase B (Akt) and protein kinase C (PKC) were activated 3-and 5-fold, respectively, during arousal. Taken together, our results showed that bat brain undergoes high oxygen demand during arousal from hibernation. Up-regulation of GRP proteins and activation of JNK, PKCc and Akt may be critical for neuroprotection and the survival of bats during the repeated process. Keywords: arousal from hibernation, metabolic oxygen demand, stress protein, survival signaling kinase.

Seasonal proteomic plasticity in the brain of a mammalian hibernator

“…3B and 4B). A comparable result was reported in our previous study, where Rhinolopus ferrumequinum showed a 2.5-fold increase in the neural lactate level during the same arousal period (Lee et al, 2002). The report also presented that the oxygen consumption rate was increased about 9-fold above the active resting metabolic rate during the arousal period.…”

“…In the case of bats, arousals repeat every 2 -8 days during dormancy, with each arousal lasting less than 9 hours (Park et al, 2000). Moreover, the initial phase of arousal (~30 min) is known to proceed with a remarkable increase in aerobic metabolism and shivering thermogenesis, which enable the bats to regain a normothermic physiological state (Lee et al, 2002). Because of the strenuous workload, however, the transition from pre-to post-arousal states may inevitably result in two serious problems in the brain: (1) oxygen and glucose deficiency, and (2) heat and mechanical stress.…”

“…Third, due to the potential stress of arousal (e.g., limited resources, rapid thermogenesis), stress-responsive proteins, such as heat shock proteins (HSPs), are likely to be upregulated in comparison to their levels in torpor. HSPs, including glucose regulated proteins (GRPs), play a neuroprotective role in adverse conditions such as heat stress, hypoxia, and glucose deprivation (Lee et al, 2002;Mamady et al, 2006).…”

Isoflavone-deprived soy peptide suppresses mammary tumorigenesis by inducing apoptosis

“…Normal rat mammary glands and mammary tumors (100 mg each) were homogenized in 800 μl of ice-cold homogenization buffer (20 mM HEPES [pH 7.4], 75 mM NaCl, 2.5 mM MgCl2, 0.2 mM EDTA, 0.05% Triton X-100, 20 mM β-glycerophosphate, 1 mM Na3VO4, 0.5 mM DTT, 10 mM NaF, and protease inhibitor cocktail (Roche, Mannheim, Germany) as described previously (Lee et al, 2002). Equal amounts of total tissue lysates (50 μg) were resolved by SDS-PAGE and subjected to immunoblotting with indicated primary antibodies against NF-κB (p65,1:500), HSP90 (1:1,000), p53 (1:1,000), p21 (1:500), and caspase-3 (1:1,000), followed by incubation with respective HRP-conjugated secondary antibodies for 1 h, and then detected by ECL reagent (Amersham Pharmacia Biotech, Arlington Heights, IL), as described previously (Park et al, 2005).…”

Brain ECF antioxidant interactions in hamsters during arousal from hibernation

“…In hamsters, shivering thermogenesis during arousal from hibernation to cenothermia is associated with peak metabolic rate and cortical blood flow in excess of 250% of basal resting values [30] and elevated brain lactate concentrations [14]. In other species of hibernators, the maximum metabolic rate during arousal from hibernation is recorded 22 during shivering thermogenesis and is associated with decreased hemoglobin O2 saturation [17] and increased brain tissue lactate [13]. Collectively this suggests that reduced oxygen tension and a period of mild ischemia are routinely tolerated during shivering thermogenesis at each arousal.…”