Endothelin B Receptor and Venous Intimal Hyperplasia Development in Rat Arteriovenous Fistula
Molly Easter1,2, Maheshika S. Somarathna1, Tayana Isayeva-Waldrop1, Kelly Hyndman1, and Timmy C. Lee, PhD1; Department of Medicine, University of Alabama at Birmingham1; School of Natural Sciences, University of California, Merced2
The vascular access is the lifeline for hemodialysis patients. The preferred type of vascular access is an arteriovenous fistula, a direct connection between an artery and vein. However, 60% of AVFs fail due to poor vascular remodeling and venous intimal hyperplasia development. The role of Et-b receptor in the vascular homeostasis is complex. In some vascular beds Et-b receptors can stimulate vasoconstrictor signaling on vascular smooth muscle cells. On the contrary, stimulation of Et-b signaling on endothelium cells activates the vasodilator activities. The involvement of Et-b receptor signaling in venous intimal hyperplasia formation is unclear. In this study, we compared the formation of intimal hyperplasia in transgenic Et-b deficient rats to wild type rats. We hypothesize that the lack of Et-b receptors in the transgenic Et-b deficient rats will increase venous intimal hyperplasia in arteriovenous fistulas. Arteriovenous fistulas were created in the femoral artery and vein of ET-b-deficient transgenic and wild type rats. After 7 days, the fistulas were harvested for histological and morphometric analysis. Fistula veins were stained using the Verhoeff’s Van Gieson elastic tissue fiber stain. The Et-b deficient transgenic rats showed an increase in hyperplasia formation compared to the wild type transgenic rats. In conclusion, Et-b receptors play a role in decreasing the early development of venous intimal hyperplasia in arteriovenous fistulas. More research needs to be done to understand the interactions between Et-b receptors and venous intimal hyperplasia development in arteriovenous fistulas.
Increase in Alanine Availability Decrease Oxalate in Primary Hyperoxaluria Type 1
Brian Freeman, Sonia Fargue, MD, PhD, and John Knight, PhD; Department of Urology, University of Alabama at Birmingham; School of Natural Sciences, University of California, Merced
Primary Hyperoxaluria (PH) is a family of inborn disorders involving glyoxylate metabolism that causes excessive endogenous oxalate synthesis which can lead to kidney stone formation. There are limited therapeutic options to treat PH. PH type 1 is the most severe and common form. It is characterized by the enzymatic deficiency of alanine:glyoxylate amino transferase (AGT) in glyoxylate metabolism. In glyoxylate metabolism, glycolate oxidase converts nontoxic glycolate into glyoxylate, a toxic metabolite. AGT converts glyoxylate and alanine to glycine and pyruvate. When AGT is enzymatically deficient, glyoxylate can be converted to oxalate. We hypothesize that increasing availability of alanine will increase enzymatic efficiency of AGT normal and pathological variants, reducing oxalate synthesis. Four transfected Chinese hamster ovary (CHO) cell lines were used for experimentation: CHO.GO, CHO.AGT-MA, CHO.AGT-MI, and CHO.AGT170, a pathogenic variant. Untransfected cells were used as a control. Cells were treated with alanine (0-10 mM) and glycolate (0–0.75 mM) for 24 hours. Indirect toxicity from glyoxylate was measured using Cell Counting Kit 8 to determine the enzymatic efficiency of AGT. Extracellular oxalate levels were measured using ion chromatography/mass spectroscopy. Enzymatic efficiency of AGT in all variants was improved with increased availability of alanine. Extracellular oxalate levels were significantly lower in AGT variants with increased levels of alanine. Increasing alanine availability in AGT normal and pathogenic variants increases enzymatic efficiency and decreases oxalate synthesis. The increase in pathological AGT enzymatic efficiency warrants future investigation in PH mouse models to confirm the results of this study.
Cristhian Gutierrez Huerta
High Salt Intake Alters ETB Receptor Expression in Visceral Adipose
Cristhian Gutierrez Huerta1,2, Ana Sogorovic1, and Joshua S. Speed, PhD1; Department of Medicine, University of Alabama at Birmingham1; School of Natural Sciences, University of California, Merced2
A correlation between salt intake and obesity has been observed in numerous human populations; however mechanisms linking dietary salt and adiposity are lacking. High dietary salt is a stimulus for the production of Endothelin-1 (ET-1) in the vasculature and renal system. Previous in vitro studies indicate that ET-1 plays a key role in lipid metabolism by the adipocyte. Activation of the ETA receptor promotes lipolysis while the ETB receptor inhibits lipolysis. We hypothesized that an increase in ET-1 in response to high salt intake promotes adipose deposition and contributes to the development of obesity. The goal of the current study was to determine the relative distribution of ET-1 receptor subtypes in various sites of adipose deposition, and determine if high salt intake impacts relative distribution. Mice were fed normal (NS, 0.49% NaCl) or high (HS, 4% NaCl) salt diet and ETA and ETB receptor gene expression was measured in epididymal and subcutaneous. Our results indicate that ETB receptor expression is 17-fold higher than ETA expression in epidydimal fat of mice fed NS. Interestingly, HS fed mice had only a 6-fold difference (ETB/ETA) in ET-1 receptor expression. In contrast, subcutaneous adipose had 6.7 fold higher ETB to ETA expression, and HS had no effect on this ratio (6.7-fold ETB/ETA). These data indicate that ETB receptors are the dominant ET-1 receptor on adipose and ETB receptor expression on visceral fat is sensitive to changes in salt intake.
Major: Biological Sciences
Home City: Wilton
Faculty Mentor: Dr. David Pollock
Evidence for Reactive Oxygen Species Increasing Endothelin-1 and Renal Injury in Humanized Sickle Mouse
Eric Lee1,2, Malgorzata Kasztan, PhD1, and David M. Pollock, PhD1; Cardio-Renal Physiology & Medicine, Division of Nephrology, University of Alabama at Birmingham1; School of Natural Sciences, University of California, Merced2
Sickle cell disease (SCD) alters renal structure and function that often leads to morbidity and mortality. SCD creates a heightened state of hypoxia and increased oxidative stress, via increased reactive oxygen species (ROS). The effects are thought to contribute significantly to sickle cell nephropathy (SCN). Moreover, it has been shown that endothelin 1 (ET-1) is elevated in the plasma of SCD patients and contributes to the development and progression of SCN including glomerular ROS production. The aim of our study was to determine effects of the anti-oxidant drug, tempol, on ET-1 and glomerular injury in humanized sickle cell mice (HbSS). HbSS mice and genetic controls (HbAA) were treated with tempol (1mmol/L) or vehicle for two weeks and placed in metabolic cages for the last 2 days. Markers of kidney injury, urinary protein and albumin concentrations were measured using Bradford and immunoperoxidase assays, respectively. Urine osmolality was determined by vapor pressure osmometer. Glomeruli were isolated to determine ET-1 mRNA expression. Glomerular ET-1 mRNA expression in tempol-treated HbSS mice revealed significant decrease when compared to untreated HbSS group (1.03±0.22 vs. 2.57±0.17). Tempol also significantly reduced proteinuria and albuminuria in HbSS mice to levels similar to controls (3.9±0.3 vs. 5.9±0.8 and 45.3±10.6 vs. 94.1±24.9, respectively). Moreover, tempol-treated HbSS showed promising trend towards decrease in urine output and increase in urinary osmolality (n=4-7), but more experiments are needed. Tempol had no effect on control HbAA mice. These findings support the hypothesis that ROS contribute to elevated ET-1 and renal injury in HbSS mice.