Angiogenic signaling in the lungs of a metabolically suppressed hibernating mammal (Ictidomys tridecemlineatus)

To conserve energy in times of limited resource availability, particularly during cold winters, hibernators suppress even the most basic of physiologic processes. Breathing rates decrease from 40 breaths/minute to less than 1 breath/min as they decrease body temperature from 37oC to ambient. Nevertheless, after months of hibernation, these incredible mammals emerge from torpor unscathed. This study was conducted to better understand the protective and possibly anti-inflammatory adaptations that hibernator lungs may use to prevent damage associated with entering and emerging from natural torpor. We postulated that the differential protein expression of soluble protein receptors (decoy receptors that sequester soluble ligands to inhibit signal transduction) would help identify inhibited inflammatory signaling pathways in metabolically suppressed lungs. Instead, the only two soluble receptors that responded to torpor were sVEGFR1 and sVEGFR2, two receptors whose full-length forms are bound by VEGF-A to regulate endothelial cell function and angiogenesis. Decreased sVEGFR1/2 correlated with increased total VEGFR2 protein levels. Maintained or increased levels of key ã-secretase subunits suggested that decreased sVEGFR1/2 protein levels were not due to decreased levels of intramembrane cleavage complex subunits. VEGF-A protein levels did not change, suggesting that hibernators may regulate VEGFR1/2 signaling at thes level of the receptor instead of increasing relative ligand

Inflammasome signaling could be used to sense and respond to endogenous damage in brown but not white adipose tissue of a hibernating ground squirrel

Small mammalian hibernators use metabolic suppression to enhance survival during the winter. Torpor is punctuated by periods of euthermia used to clear metabolic by-products and damaged cell components. The current study was performed to determine if the innate immune system, specifically NLRP and AIM2 inflammasome signaling, may detect and respond to cell stress during hibernation. Nlrp3, Casp1, and Il1b genes were significantly upregulated in brown adipose tissue (BAT) during arousal with respect to the euthermic control, suggesting increased NLRP3 inflammasome priming. NLRP3, IL-18, and gasdermin D protein levels increased during torpor, indicating a lag between inflammasome priming and formation. AIM2 and gasdermin D levels increased in BAT during arousal, as did caspase-1 activity. Thus, non-shivering thermogenesis may generate pro-inflammatory triggers of inflammasome signaling. This study is the first to support a role for inflammasome signaling in sensing cellular perturbations at various points of the torpor-arousal cycle, in metabolically-active BAT, but not white adipose tissue (WAT)

Turn down genes for WAT? Activation of anti-apoptosis pathways protects white adipose tissue in metabolically depressed thirteen-lined ground squirrels

During hibernation, the metabolic rate of thirteen-lined ground squirrels (Ictidomys tridecemlineatus) can drop to <5 % of normal resting rate at 37 °C, core body temperature can decrease to as low as 1–5 °C, and heart rate can fall from 350–400 to 5–10 bpm. Energy saved by hibernating allows squirrels to survive the winter when food is scarce, and living off lipid reserves in white adipose tissue (WAT) is crucial. While hibernating, some energy must be used to cope with conditions that would normally be damaging for mammals (e.g., low core body temperatures, ischemia) and could induce cell death via apoptosis. Cell survival is largely dependent on the relative amounts and activities of pro- and anti-apoptotic Bcl-2 family proteins. The present study analyzed how anti-apoptotic proteins respond to protect WAT cells during hibernation. Relative levels of several anti-apoptotic proteins were quantified in WAT via immunoblotting over six time points of the torpor-arousal cycle. These included anti-apoptotic Bcl-2 family members Bcl-2, Bcl-xL, and Mcl-l, as well as caspase inhibitors x-IAP and c-IAP. Changes in the relative protein levels and/or phosphorylation levels were also observed for various regulators of apoptosis (p-JAKs, p-STATs, SOCS, and PIAS). Mcl-1 and x-IAP protein levels increased whereas Bcl-xL, Bcl-2, and c-IAP protein/phosphorylation levels decreased signifying important roles for certain Bcl-2 family members in cell survival over the torpor-arousal cycl

Temperature and serine phosphorylation regulate glycerol-3-phosphate dehydrogenase in skeletal muscle of hibernating Richardson's ground squirrels

Glycerol-3-phosphate dehydrogenase (G3PDH) bridges carbohydrate and lipid metabolism by interconverting glycerol-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). This reversible reaction converts G3P derived from triglyceride hydrolysis to DHAP that can then enter glycolysis or gluconeogenesis and, in the reverse reaction, makes G3P for use in triglyceride biosynthesis. Small hibernating mammals rely almost exclusively on triglyceride reserves as their fuel for energy production during torpor and the recovery of glycerol after lipolysis is an important source of carbohydrate over the nonfeeding winter months. G3PDH (∼37 kDa) was purified from skeletal muscle of euthermic and hibernating Richardson's ground squirrels (Urocitellus richardsonii) using three column chromatography steps. Analysis of enzyme kinetic properties revealed that G3PDH from hibernator muscle had higher affinities for G3P and NAD at low (5 °C) assay temperature compared with high (21 or 37 °C) and a greater stability in the presence of den

The squirrel with the lagging eIF2: Global suppression of protein synthesis during torpor

Hibernating mammals use strong metabolic rate depression and a reduction in body temperature to near-ambient to survive the cold winter months. During torpor, protein synthesis is suppressed but can resume during interbout arousals. The current study aimed to identify molecular targets responsible for the global suppression of protein synthesis during torpor as well as possible mechanisms that could allow for selective protein translation to continue over this time. Relative changes in protein expression and/or phosphorylation levels of key translation factors (ribosomal protein S6, eIF4E, eIF2α eEF2) and their upstream regulators (mTOR, TSC2, p70 S6K, 4EBP) were analyzed in liver and kidney of 13-lined ground squirrels (Ictidomys tridecemlineatus) sampled from six points over the torpor-arousal cycle. The results indicate that both organs reduce protein synthesis during torpor by decreasing mTOR and TSC2 phosphorylation between 30 and 70% of control levels. Translation resumes during interbout arousal when p-p70 S6K, p-rpS6, and p-4EBP levels returned to control values or above. Only liver translation factors were activated or disinhibited during periods of torpor itself, with >3-fold increases in total eIF2α and eEF2 protein levels, and a decrease in p-eEF2 (T56) to as low as 16% of the euthermic control value. These data shed light on a possible molecular mechanism involving eIF2α that could enable the translation of key transcripts during times of cell stress

Response of the JAK-STAT pathway to mammalian hibernation in 13-lined ground squirrel striated muscle

Over the course of the torpor-arousal cycle, hibernators must make behavioral, physiological, and molecular rearrangements in order to keep a very low metabolic rate and retain organ viability. 13-lined ground squirrels (Ictidomys tridecemlineatus) remain immobile during hibernation, and although the mechanisms of skeletal muscle survival are largely unknown, studies have shown minimal muscle loss in hibernating organisms. Additionally,

Influence of hook type and live bait on the hooking performance of inline spinners in the context of catch-and-release brook trout Salvelinus fontinalis fishing in lakes

The objective of catch-and-release angling is for the fish to survive with minimal fitness consequences. However, fish survival can be compromised by a number of factors, especially anatomical hooking location. To evaluate whether hook type or bait influence hooking outcomes, we tested different combinations of hook (treble or single siwash hooks) and bait (hook tipped with worm or no worm) while angling for brook trout (Salvelinus fontinalis) with inline spinner-style fishing lures. The study was conducted at spring water temperatures (∼20 °C) in small lakes stocked with trout in southwestern Quebec, Canada. Incidences of hooking in the interior of the mouth (i.e. internal hooking) were uncommon (19%), did not differ significantly between hook types or bait treatments, and occurred independently of fish size. Reflex impairments after hook removal were not related to hook or bait treatment. Short-term mortality was quantified with 24 h holding in net pens and was determined to be infrequent for all treatment groups (treble/worm: 6%; treble/no worm: 5%; single/worm: 2%; single/no worm: 0%). Although no fish were hooked in the gills, esophagus, stomach, odds of mortality increased by 14.21 when fish were hooked internally, which is consistent with the position that hook placement is an important predictor of the fate of fish released by anglers. However, our finding that neither hook nor bait type significantly increased the odds of internal hooking, bleeding, reflex impairment, or mortality in this study suggests that restrictions imposed on the use of baited lures or certain hook types attached to lures when fishing may have little influence on short-term catch-and-release mortality of brook trout at these temperatures