2016-2017 KURE Cohort

Major: Biological Sciences Home City: Clovis, CA Contact: ebeltran6@ucmerced.edu Faculty Mentor: Dr. Edward Inscho

Activation of toll–like receptor 4 (TLR4) with lipopolysaccharide (LPS) increases reactive oxygen species (ROS) causing oxidative stress. Tempol, a superoxide dismutase mimetic, scavenges endogenous ROS, thereby reducing oxidative stress. Afferent arteriole autoregulatory behavior is impaired following 7 days of LPS treatment. Accordingly, we hypothesized that chronic co-treatment with LPS and Tempol preserves autoregulatory behavior. Three treatment groups were used (n=4/group): LPS (0.1mg/kg/day), LPS+Tempol (2mmol/L), and saline (0.9% NaCl)+Tempol. Rats received osmotic minipumps (day 0) for infusion of LPS or saline, placed inside metabolic cages, and Tempol was added to the drinking water on day 1. Systolic blood pressures (SBP, tail cuff) were measured (days 0, 3, and 7) and collected urine was analyzed for electrolytes, and protein. Kidneys were harvested on day 7 for juxtamedullary nephron experiments. SBPs were similar across all three groups, averaging 140±4, 124±9, 127±7 mmHg, respectively on day 7. Urine output averaged 8±0, 8±1, 6±1mL/24Hrs., respectively. Urinary protein excretion averaged 9.2±0.3, 9.2±0.2, and 9.3±0.6mg/24Hrs., respectively, consistent with normal glomerular function.  Autoregulatory behavior was assessed by increasing renal perfusion pressure from 65 to 170 mmHg (15 mmHg increments). Baseline diameters (100 mmHg) averaged 15.2±1.2, 14.0±1.0, and 15.0±1.5 microns, for saline (n=6), LPS (n=6) and LPS+Tempol (n=3), respectively. At 170 mmHg, arteriole diameter decreased by 25±1% (P<0.05) and 21±3% (P<0.05) in the saline and LPS + Tempol co-treated groups, respectively, signifying normal autoregulatory behavior whereas it did not change in the LPS group.  Therefore, chronic co-treatment with LPS+Tempol preserves renal autoregulatory behavior, by scavenging endogenous ROS.

 

Isaac Campos¹, Josh Speed, PhD², and David Pollock, PhD²; School of Natural Sciences, University of California, Merced¹; University of Alabama at Birmingham²

 

Circadian rhythms in physiologic function are mediated by a group of transcription factors that oscillate over a 24-hour period, termed the molecular clock. Disruption of clock mechanisms promotes cardiovascular disease (CVD). High salt (HS) intake promotes endothelin-1 (ET-1) production by the vasculature and is a risk factor for CVD; however, it is unknown if HS affects circadian clock components in the heart. Therefore, we hypothesized that HS intake disrupts components of the molecular clock in the heart, via activation of ET-1 receptors. Control and endothelin type B receptor (ETB) deficient (ETB def) rats were placed on either HS or normal salt (NS) for two weeks and euthanized every 4 hours over a 24-hour period. RNA expression was assessed for clock genes (Bmal1, Cry1, Per1, Per2, DBP, CLOCK) by RT-PCR. Cosinor analysis was performed to determine mesor (daily average), amplitude (trough-to-peak), and phase (timing of peak) of gene expression oscillations. Our results indicate that HS intake suppresses both the mesor and amplitude of Per1, Per2, CLOCK, Cry1, DBP, and Cry2 expression. These effects occurred similarly in control and ETB def rats. HS intake increased heart ventricle weight (HVW) to a similar level in both genotypes. Our data indicate that HS intake disrupts the molecular clock and promotes hypertrophy in the heart independent of ETB receptor activation. We speculate that alteration in circadian components may contribute to CVD risk associated with high dietary Na+.

 

Guillermo Najarro¹, Ijeoma Obi², Daian Chen, PhD²; School of Natural Sciences, University of California, Merced¹; Department of Medicine, University of Alabama at Birmingham²

 

Many forms of life have circadian rhythms to perform specific biological functions. Bmal1 is a transcription factor and central element of the molecular clock but its role in fluid and electrolyte regulation is unclear. We hypothesized that loss of Bmal1 would disrupt fluid and electrolyte balance in response to normal and high salt diets. To test this, we utilized Bmal1 knockout (Bmal1KO) and wildtype mice under both diets in metabolic cages and collected urine during active (lights-off) and inactive (lights-on) phases. Our results show that Bmal1KO have reduced water and food intakes on both diets compared to WT in the active-phase. Bmal1KO exhibit a loss of diurnal intake of water and food, which corresponds to a loss of diurnal blood pressure (BP) rhythm on both diets. On normal and high salt diet, WT had a diurnal pattern in sodium excretion that is higher in the active-phase and lower in the inactive-phase. Whereas, Bmal1KO had similar sodium excretion in the active and inactive-phases on both normal and high salt diets. BP followed a diurnal pattern in WT, but not Bmal1KO on both diets. We conclude that Bmal1 facilitates maintenance of a normal diurnal pattern in BP control, food and water intake and sodium excretion.