Browsing by Subject "Hibernation"

Now showing 1 - 4 of 4
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    Molecular dissection of compensatory pathways in models of severe heart failure
    (2015-01) Heinis, Frazer
    Cardiovascular diseases are the leading cause of death in America, and heart failure (HF) is an important and increasingly difficult to manage disease. HF, a clinical syndrome of impaired heart pump function, has poor prognosis, increasing incidence, and no cure. Clinical treatment guidelines focus on the treatment of symptoms rather than acting to directly restore heart pump function, and better therapeutics are necessary to reverse the course of HF pathology. Normal heart pump function is driven by the release and reuptake of Ca2+ ions from the cytoplasm of cardiac myocytes. In healthy cardiac tissue, transient release of Ca2+ occurs rapidly to trigger contraction, and removal is likewise swift in order to allow the heart to relax and refill with blood for the next beat. In failing myocardium, Ca2+ release is weak and reuptake is slow, which leads to inadequate ejection of blood to the body and poor refilling for the next beat. Over time, this results in the progressive loss of cardiac pump function and, subsequently, worsening quality of life. The protein responsible for most diastolic Ca2+ reuptake to the cardiac sarcoplasmic reticulum (SR) compartment is the SR Ca2+ ATPase, SERCA2a. SERCA2a expression and activity are decreased in failing hearts, and experimental therapeutics are currently under development to restore its activity in humans. We have utilized a mouse model of inducible Serca2 deletion, the Serca2fl/fl mouse, to study the progression of cardiac dysfunction as this key enzyme is lost. Surprisingly, Serca2KO mice survive 7-10 weeks following inducible Serca2 deletion and loss of most SERCA2a protein. The mechanisms by which Serca2KO mice maintain survival for so long with minimal apparent in vivo pathology are not well defined, so we investigated cardiac performance in Serca2KO hearts and mice by several methods. We determined the function of KO hearts outside the body, in the absence of systemic signaling that may be supporting function in vivo, and found that isolated KO hearts had severely impaired function even at short times following gene deletion; we studied adaptive changes in cardiac Ca2+ handling proteins, including SERCA2a, that occur in hibernating mammals between the summer and winter seasons; and we enacted a thorough mechanistic dissection of ß-adrenergic signaling pathways in SERCA2a-depleted hearts. We found that Serca2KO hearts deficient in normal Ca2+ handling remained able to support a significant functional response to adrenergic stimulation, despite the near complete absence of SERCA2a, which is normally a key functional substrate for the adrenergic response. This finding indicated that other targets of adrenergic signaling in SERCA-deficient heart were surprisingly capable of supporting significant pump function despite poor cardiac Ca2+ transport capabilities, and we have identified the myofilament protein, cardiac troponin I (cTnI), as a key component of an intact adrenergic response under pathological Ca2+ handling conditions.
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    Multi-omic analysis of hibernator skeletal muscle and calcium handling regulation
    (2016-05) Anderson, Kyle
    Mammalian hibernation is a strategy employed by many species to survive fluctuations in resource availability and environmental conditions. Hibernating mammals endure conditions of dramatically depressed heart rate, body temperature, and oxygen consumption; yet do not show the typical pathological responses. Because of the high abundance and metabolic cost of skeletal muscle, not only must it adjust to the constraints of hibernation, but it is also positioned to play a more active role in the initiation and maintenance of the hibernation phenotype. My M.S. thesis research has primarily focused on the generation and analysis of two high-throughput ‘omics screens in thirteen-lined ground squirrel skeletal muscle. A transcriptomic analysis using Illumina HiSeq2000 technology identified 1,466 differentially expressed genes throughout their circannual cycle. This RNAseq data allowed for greater protein identifications in an iTRAQ based proteogeomic analysis of the same animals. Of the 1,563 proteins identified by this proteogenomic approach, 232 were differentially expressed. These data support previously reported physiological transitions, while also offering new insight into specific mechanisms of how hibernator muscles might be reducing nitrogenous waste, preserving mass and function, and signaling to other tissues. Sarcolipin is a specific gene of interest that shows a 10-fold difference in expression between hibernation and spring collection points. Because of sarcolipin’s interaction with the SERCA pump and their role in muscle-based thermogenesis and calcium homeostasis bioenergetics, I have developed methods to measure the consequences of this differential expression.
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    Optimization of a hibernation-based small-volume resuscitation fluid
    (2014-09) Pérez de Lara Rodríguez, Cecilia Edna
    Background: Hemorrhagic shock is the number one cause of preventable deaths after trauma. Hibernation exemplifies a physiological state in which blood flow is reduced to a magnitude comparable to that of hemorrhagic shock. However, hibernators are naturally shielded from the insults that a similar reduction in blood flow would cause in a non-hibernating mammal. Our laboratory previously published a small volume resuscitation fluid based on hibernation physiology:BHB/M. It has three main components: 1) 4 M BHB, 2) 43 mM melatonin, and 3) 20% DMSO. Only the indicated concentration of each component of BHB/M has been previously tested. For that reason, worked towards the optimization of the composition and delivery of BHB/M in order to enhance survival in a rat model of hemorrhagic shock.Methods and Results: Previously, BHB/M was given as a 1 ml/kg bolus followed by a 100 µl/hr slow infusion. BHB/M was administered as either a single bolus or a bolus plus slow infusion in acutely operated rats. There were no statistical differences (p>0.05) in mean survival times when comparing the bolus only (mean survival 496.67 ± 314.59 min. n=6) to the bolus plus slow infusion (mean survival 149.20 ±142.71 min. n=5) protocol.Two separate dose-ranging studies were conducted for both BHB and Melatonin. In the BHB dose-ranging study, BHB was administered at either a 4 M,2 M, or 0.4 M concentration in conjunction with 4.3 mM melatonin and 10% DMSO. 10-day mean survival showed a dose-dependent trend where the higher the concentration of BHB infused the longer the rats survived (4 M BHB, 7.38 ± 1.75 days; 2 M BHB, 5.25 ± 2.22 days; 0.4 M BHB, 2.07 ± 2.05 days). In the melatonin dose-ranging study, melatonin was administered at either a 4.3 mM, 0.43 mM 0.0043 mM, 0.000043 mM, or 0 mM concentration in conjunction with 4 M BHB and 2% DMSO. An osmolarity control composed of 4 M NaCl and 0.000043 mM melatonin in 2 % DMSO was also included. Administering 4 M BHB without melatonin resulted in very low mean survival times (4.38 ± 1.42 days); the same was true when infusing 0.000043 mM melatonin with 4 M NaCl (4.58 ± 1.42). All treatments containing both 4 M BHB and melatonin, regardless of concentration, resulted in mean survival times of ~7.5 days.A large-volume experiment was conducted in order to compare isotonic BHB/M to the standard of care (LR). Rats subjected to 60% blood loss were infused with either LR, LR plus 4.3 mM melatonin, 140 mM BHB with 1.5x10-6 mM Mel, or 140 mM BHB with 4.3 mM Mel. LR and LR plus 4.3 mM melatonin had statistically higher (p<0.05) mean survival times (7.35 ± 1.59 days and 6.73 ± 1.57 days, respectively) than 140 mM BHB with 1.5x10-6 mM Mel (2.08 ± 1.18 days).Conclusions: BHB/M can be administered as a single 1 ml/kg bolus; following the bolus with a 100 µl/hr slow infusion is not necessary to obtain a maximum survival benefit. BHB must be administered at a 4 M concentration as there is a dose-dependent trend in which the lower the concentration of BHB administered the lower the percent survival to 10 days. Melatonin provides therapeutic effects at very low concentrations evident by the survival observed when administering a solution containing melatonin at a concentration a million-fold lower than previously published. Furthermore, melatonin is essential for survival since 4 M BHB without melatonin had a considerably reduced survival rate. A large volume dilute BHB/M is not a viable alternative to the standard of care.
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    The role of metabolic hormone Fibroblast Growth Factor 21 (FGF21) in mammalian hibernation using transgenic ground squirrels
    (2012-10) Nelson, Bethany Theresa
    Hibernation is a natural adaptation that allows certain mammals to survive physiological extremes that are lethal to humans. Near freezing body temperatures, heart rates of 4 to 6 beats per minute and depressed metabolism are characteristic of hibernation torpor bouts that are periodically interrupted by brief interbout arousals (IBAs). The molecular basis of torpor induction is unknown, however studies of fibroblast growth factor 21 (FGF21) in starved mice have shown the involvement of this hormone in promoting fat utilization and reducing body temperature and physical activity--all hallmarks of mammalian hibernation. We hypothesized that increased FGF21 sensitizes the natural hibernating thirteen-lined ground squirrel (Ictidomys tridecemlineatus) to enter torpor and changes the metabolic profile to indicate increased lipolysis. In this study we isolated the FGF21 cDNA from the ground squirrel and found that levels of FGF21 mRNA in liver and FGF21 protein in serum are elevated during IBAs compared to summer active animals. The effects of elevating circulating FGF21 concentrations 50 to 100-fold via adenoviral-mediated overexpression were examined at key times in the annual hibernation cycle. FGF21 overexpression decreased blood insulin and free fatty acid concentrations sampled 7 days after injection in fed squirrels kept at 23 °C with a 12:12 l:d cycle in April, effects similar to those observed in obese mice. However, elevated FGF21 concentrations did not cause torpor in thirteen-lined ground squirrels. We conclude that FGF21 is strongly regulated during torpor and IBA in hibernating thirteen-lined ground squirrels but that its overexpression is not sufficient to cause torpor.