2017-2018 KURE Cohort

Major: Biological Sciences Home City: Contact: measter@ucmerced.edus Faculty Mentor: Dr. Timmy Lee

 

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^1,2, 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.

 

Eric Lee^1,2, 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.