College of Graduate Studies News

The Grad Post Program Spotlight For Fall 201

Faster femoral artery blood velocity kinetics at the onset of exercise following short-term training.

OBJECTIVE: The hypothesis that the adaptation to endurance exercise training included a faster increase in blood flow at the onset of exercise was tested in 12 healthy young men who endurance-trained (ET) 2 h/day, for 10 days at 65% VO2 peak on a cycle ergometer, and in 11 non-training control (C) subjects. METHODS: Blood flow was estimated from changes in femoral artery mean blood velocity (MBV) by pulsed Doppler. Beat-by-beat changes in cardiac output (CO) and mean arterial pressure (MAP) were obtained by impedance cardiography and a Finapres finger cuff, respectively. MBV, MAP and CO were measured at rest and during 5 min of dynamic knee extension exercise. Both legs worked alternately with 2 s raising and lowering a weight (15% maximal voluntary contraction) followed by 2 s rest while the other leg raised and lowered the weight. RESULTS: In the ET group the time to 63% (T63%) of the approximately exponential increase in MBV following 10 days of training (8.6 +/- 1.2 s, mean +/- s.e.) was significantly faster than the Day 0 response (14.2 +/- 2.1 s, P \u3c 0.05). The T63% of femoral artery vascular conductance (VCfa) was also faster following 10 days of ET (9.4 +/- 0.9 s) versus Day 0 (16.0 +/- 2.5 s) (0.05). There was no change in the T63% of both MBV and VCfa for the C group. The kinetics of CO were not significantly affected by ET, but the amplitude of CO in the adaptive phase, and at steady state, were significantly greater (P \u3c 0.05) at Day 10 compared to Day 0 for the ET group with no change in the C group. CONCLUSIONS: These data supported the hypothesis that endurance training resulted in faster adaptation of blood flow to exercising muscle, and further showed that this response occurred early in the training program

Modelflow estimates of cardiac output compared with Doppler ultrasound during acute changes in vascular resistance in women

We compared Modelflow (MF) estimates of cardiac stroke volume (SV) from the finger pressure-pulse waveform (Finometer®) with pulsed Doppler ultrasound (DU) of the ascending aorta during acute changes in total peripheral resistance (TPR) in the supine and head-up-tilt (HUT) postures. Twenty-four women were tested during intravenous infusion of 0.005 or 0.01 μg kg -1 min-1 isoprenaline, 10 or 50 ng kg-1 min-1 noradrenaline and 0.3 mg sublingual nitroglycerine. Responses to static hand-grip exercise (SHG), graded lower body negative pressure (LBNP, from -20 to -45 mmHg) and 45 deg HUT were evaluated on separate days. Bland-Altman analysis indicated that SVMF yielded lower estimates than SVDU during infusion of 0.01 μg kg-1 min -1 isoprenaline (SVMF 92.7 ± 15.5 versus SV DU 104.3 ± 22.9 ml, P = 0.03) and SHG (SVMF 78.8 ± 12.0 versus SVDU 106.1 ± 28.5 ml, P \u3c 0.01), while larger estimates were recorded with SVMF during -45 mmHg LBNP (SVMF 52.6 ± 10.7 versus SVDU 46.2 ± 14.5 ml, P = 0.04) and HUT (SVMF 59.3 ± 13.6 versus SVDU 45.2 ± 11.3 ml, P \u3c 0.01). Linear regression analysis revealed a relationship (r2 = 0.41, P \u3c 0.01) between the change in TPR from baseline and the between-methods discrepancy in SV measurements. This relationship held up under all of the experimental protocols (regression for fixed effects, P = 0.46). These results revealed a discrepancy in MF estimates of SV, in comparison with those measured by DU, during acute changes in TPR. © 2010 The Physiological Society

Implications of Therapy-Induced Selective Autophagy on Tumor Metabolism and Survival

Accumulating evidence indicates that therapies designed to trigger apoptosis in tumor cells cause mitochondrial depolarization, nuclear damage, and the accumulation of misfolded protein aggregates, resulting in the activation of selective forms of autophagy. These selective forms of autophagy, including mitophagy, nucleophagy, and ubiquitin-mediated autophagy, counteract apoptotic signals by removing damaged cellular structures and by reprogramming cellular energy metabolism to cope with therapeutic stress. As a result, the efficacies of numerous current cancer therapies may be improved by combining them with adjuvant treatments that exploit or disrupt key metabolic processes induced by selective forms of autophagy. Targeting these metabolic irregularities represents a promising approach to improve clinical responsiveness to cancer treatments given the inherently elevated metabolic demands of many tumor types. To what extent anticancer treatments promote selective forms of autophagy and the degree to which they influence metabolism are currently under intense scrutiny. Understanding how the activation of selective forms of autophagy influences cellular metabolism and survival provides an opportunity to target metabolic irregularities induced by these pathways as a means of augmenting current approaches for treating cancer

Critical analysis of cerebrovascular autoregulation during repeated head-up tilt.

BACKGROUND AND PURPOSE: Cerebrovascular autoregulation has been described with a phase lead of cerebral blood flow preceding changes in cerebral perfusion pressure (CPP), but there has been less focus on the effect of CPP on cerebral vascular resistance. We investigated these relations during spontaneous fluctuations (control) and repeated head-up tilt. METHODS: Eight healthy adults were studied in supine rest and repeated tilt with 10-second supine, 10 seconds at 45 degrees head-up tilt for a total of 12 cycles. Cerebral blood flow was estimated from mean flow velocity (MFV) by transcranial Doppler ultrasound, CPP was estimated from corrected finger pressure (CPP(F)), and cerebrovascular resistance index (CVRi) was calculated in the supine position from CPP(F)/MFV. Gain and phase relations were assessed by cross-spectral analysis. RESULTS: In the supine position, MFV preceded CPP(F), but changes in CVRi followed CPP(F). Gain and phase relations for CPP(F) as input and MFV as output were similar in supine and repeated tilt experiments. Thus, changes in cerebrovascular resistance must have had a similar pattern in the supine and tilt experiments. CONCLUSIONS: Cerebrovascular autoregulation is achieved by changes in resistance in response to modulations in perfusion pressure whether spontaneous or induced by repeated tilt. The phase lead of MFV before CPP(F) is a mathematical and physiological consequence of the relation the input variable (CPP(F)) and the manipulated variable (cerebrovascular resistance) that should not be taken as an indication of independent control of cerebral blood flow

When Cells Suffocate: Autophagy in Cancer and Immune Cells under Low Oxygen

Hypoxia is a signature feature of growing tumors. This cellular state creates an inhospitable condition that impedes the growth and function of all cells within the immediate and surrounding tumor microenvironment. To adapt to hypoxia, cells activate autophagy and undergo a metabolic shift increasing the cellular dependency on anaerobic metabolism. Autophagy upregulation in cancer cells liberates nutrients, decreases the buildup of reactive oxygen species, and aids in the clearance of misfolded proteins. Together, these features impart a survival advantage for cancer cells in the tumor microenvironment. This observation has led to intense research efforts focused on developing autophagy-modulating drugs for cancer patient treatment. However, other cells that infiltrate the tumor environment such as immune cells also encounter hypoxia likely resulting in hypoxia-induced autophagy. In light of the fact that autophagy is crucial for immune cell proliferation as well as their effector functions such as antigen presentation and T cell-mediated killing of tumor cells, anticancer treatment strategies based on autophagy modulation will need to consider the impact of autophagy on the immune system

WISE-2005: prolongation of left ventricular pre-ejection period with 56 days head-down bed rest in women

This study tested the hypothesis that prolonged physical deconditioning affects the coupling of left ventricular depolarization to its ejection (the pre-ejection period, PEPi) and that this effect is minimized by exercise countermeasures. Following assignment to non-exercise (Control) and exercise groups (Exercise), 14 females performed 56 days of continuous head-down tilt bed rest. Measurements of the electrocardiogram (ECG) and stroke volume (Doppler ultrasound) during supine rest were obtained at baseline prior to (Pre) and after (Post) the head-down tilt bed rest (HDBR) period. Compared with Pre, the PEPi was increased following head-down tilt bed rest (main effect, P \u3c 0.005). This effect was most dominant in the Control group [Pre = 0.038 ± 0.06 s (s.d.) versus Post = 0.054 ± 0.011 s; P \u3c 0.001]. In the Exercise group, PEPi was 0.032 ± 0.005 s Pre and 0.038 ± 0.018 s Post; P= 0.08. Neither the QRS interval nor cardiac afterload was modified by head-down tilt bed rest in Control or Exercise groups. Low-dose isoprenaline infusion reversed the head-down tilt bed rest-induced delay in the PEPi. These results suggest that head-down tilt bed rest leads to a delayed onset of systolic ejection following left ventricular depolarization in a manner that is affected little by the exercise countermeasure but is related to Β-adrenergic pathways. The delayed onset of systole following head-down tilt bed rest appears to be related to mechanism(s) affecting contraction of the left ventricle rather than its depolarization. © 2010 The Authors. Journal compilation © 2010 The Physiological Society

Structural basis for the binding of tryptophan-based motifs by δ-COP.

Coatomer consists of two subcomplexes: the membrane-targeting, ADP ribosylation factor 1 (Arf1):GTP-binding βγδζ-COP F-subcomplex, which is related to the adaptor protein (AP) clathrin adaptors, and the cargo-binding αβ'ε-COP B-subcomplex. We present the structure of the C-terminal μ-homology domain of the yeast δ-COP subunit in complex with the WxW motif from its binding partner, the endoplasmic reticulum-localized Dsl1 tether. The motif binds at a site distinct from that used by the homologous AP μ subunits to bind YxxΦ cargo motifs with its two tryptophan residues sitting in compatible pockets. We also show that the Saccharomyces cerevisiae Arf GTPase-activating protein (GAP) homolog Gcs1p uses a related WxxF motif at its extreme C terminus to bind to δ-COP at the same site in the same way. Mutations designed on the basis of the structure in conjunction with isothermal titration calorimetry confirm the mode of binding and show that mammalian δ-COP binds related tryptophan-based motifs such as that from ArfGAP1 in a similar manner. We conclude that δ-COP subunits bind Wxn(1-6)[WF] motifs within unstructured regions of proteins that influence the lifecycle of COPI-coated vesicles; this conclusion is supported by the observation that, in the context of a sensitizing domain deletion in Dsl1p, mutating the tryptophan-based motif-binding site in yeast causes defects in both growth and carboxypeptidase Y trafficking/processing.We should like to thank the beamline scientists at the Diamond Light Source and Mike Lewis (MRC LMB), Gerry Johnston (Dalhousie University), and Mark Rose (Princeton University) for helpful discussions and technical advice. RJS and DJO are funded by a Wellcome Trust fellowship to DJO (090909). PPP was funded by Canadian Institute of Health Research. RD acknowledges support from the DFG Excellence Cluster “Inflammation and Interfaces” (ECX306) and the University of Lübeck. SMT and FMH acknowledge support from NIH (GM071574). PRE is funded by MRC grant U105178845This is the author accepted manuscript. The final version is available from PNAS via http://dx.doi.org/10.1073/pnas.150618611