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Obesity and its underlying insulin resistance are caused by environmental and genetic factors. DNA methylation provides a mechanism by which environmental factors can regulate transcriptional activity. The overall goal of the work herein was to (1) identify alterations in DNA methylation in human skeletal muscle with obesity and its underlying

Obesity and its underlying insulin resistance are caused by environmental and genetic factors. DNA methylation provides a mechanism by which environmental factors can regulate transcriptional activity. The overall goal of the work herein was to (1) identify alterations in DNA methylation in human skeletal muscle with obesity and its underlying insulin resistance, (2) to determine if these changes in methylation can be altered through weight-loss induced by bariatric surgery, and (3) to identify DNA methylation biomarkers in whole blood that can be used as a surrogate for skeletal muscle.

Assessment of DNA methylation was performed on human skeletal muscle and blood using reduced representation bisulfite sequencing (RRBS) for high-throughput identification and pyrosequencing for site-specific confirmation. Sorbin and SH3 homology domain 3 (SORBS3) was identified in skeletal muscle to be increased in methylation (+5.0 to +24.4 %) in the promoter and 5’untranslated region (UTR) in the obese participants (n= 10) compared to lean (n=12), and this finding corresponded with a decrease in gene expression (fold change: -1.9, P=0.0001). Furthermore, SORBS3 was demonstrated in a separate cohort of morbidly obese participants (n=7) undergoing weight-loss induced by surgery, to decrease in methylation (-5.6 to -24.2%) and increase in gene expression (fold change: +1.7; P=0.05) post-surgery. Moreover, SORBS3 promoter methylation was demonstrated in vitro to inhibit transcriptional activity (P=0.000003). The methylation and transcriptional changes for SORBS3 were significantly (P≤0.05) correlated with obesity measures and fasting insulin levels. SORBS3 was not identified in the blood methylation analysis of lean (n=10) and obese (n=10) participants suggesting that it is a muscle specific marker. However, solute carrier family 19 member 1 (SLC19A1) was identified in blood and skeletal muscle to have decreased 5’UTR methylation in obese participants, and this was significantly (P≤0.05) predicted by insulin sensitivity.

These findings suggest SLC19A1 as a potential blood-based biomarker for obese, insulin resistant states. The collective findings of SORBS3 DNA methylation and gene expression present an exciting novel target in skeletal muscle for further understanding obesity and its underlying insulin resistance. Moreover, the dynamic changes to SORBS3 in response to metabolic improvements and weight-loss induced by surgery.
ContributorsDay, Samantha Elaine (Author) / Coletta, Dawn K. (Thesis advisor) / Katsanos, Christos (Committee member) / Mandarino, Lawrence J. (Committee member) / Shaibi, Gabriel Q. (Committee member) / Dinu, Valentin (Committee member) / Arizona State University (Publisher)
Created2017
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Description
Elevated triglycerides (TG) are a hallmark of insulin resistance, which is generally caused by lower lipoprotein lipase (LPL) activity in the vasculature. LPL hydrolyzes TGs into free fatty acids in plasma for use and/or storage in tissues (i.e., adipose tissue, skeletal muscle). Plasma apolipoproteins (Apos) C3 and C2 interact with

Elevated triglycerides (TG) are a hallmark of insulin resistance, which is generally caused by lower lipoprotein lipase (LPL) activity in the vasculature. LPL hydrolyzes TGs into free fatty acids in plasma for use and/or storage in tissues (i.e., adipose tissue, skeletal muscle). Plasma apolipoproteins (Apos) C3 and C2 interact with LPL to modulate its function, and by inhibiting or activating LPL, respectively. Therefore, these proteins play key role in plasma lipid metabolism, but their role in regulating LPL activity in human insulin resistant (IR) (i.e., pre-diabetic) state is not known. Thus, the purpose of this research was to evaluate the concentrations of ApoC3 and ApoC2 in plasma along with the endothelial-bound LPL availability and activity in IR humans and in healthy, insulin sensitive (IS)/control humans. Insulin resistance was evaluated from plasma insulin and glucose responses to an oral glucose tolerance test, and by calculating the Matsuda index. Subjects were placed in the following groups: IR subjects, Matsuda index <4.0 (N=7; 4 males, 3 females); IS, Matsuda index >7.0 (N=11, 9 males, 2 females). IR and IS subjects received an intravenous infusion of insulin (1 mU/kg/min and 0.5 mU/kg/min, respectively) for 30 minutes to stimulate LPL activity. Whole-body endothelial-bound LPL was released from the vasculature by intravenous infusion of heparin. Plasma samples were collected 10 minutes after heparin infusion and analyzed for LPL concentration and activity, and ApoC3 and ApoC2 concentrations. Although plasma LPL concentrations were not different between groups (IR = 457 ± 17 ng/ml, IS = 453 ± 27 ng/ml, P = 0.02), plasma LPL activity was higher in the IR subjects (IR = 665 ± 113 nmol/min/ml, IS = 365 ± 59 nmol/min/ml, P = 0.02). IR subjects had higher concentrations of plasma ApoC3 (IR = 3.6 ± 0.5 mg/dl, IS = 2.7 ± 0.2 mg/dl, P=0.03). However, ApoC2 concentration was not different between groups (IR = 0.15 ± 0.03 mg/dl, IS = 0.11 ± 0.01 mg/dl, P = 0.11). These findings suggest that circulating APOC3 and ApoC2 are not key determinants regulating LPL activity during hyperinsulinemia in the vasculature of insulin resistant humans.
ContributorsJohnsson, Kailin Alexis (Author) / Katsanos, Christos (Thesis advisor) / Herman, Richard (Committee member) / De Filippis, Elena (Eleanna) (Committee member) / Arizona State University (Publisher)
Created2023
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Description
Type 2 diabetes mellitus (T2DM) is a life-long disease that affects over 27 million individuals in the United States alone. There are many different risk factors and pre-indicators of T2DM. One of them is insulin resistance. Insulin resistance occurs when the body is unable to appropriately respond to insulin. This

Type 2 diabetes mellitus (T2DM) is a life-long disease that affects over 27 million individuals in the United States alone. There are many different risk factors and pre-indicators of T2DM. One of them is insulin resistance. Insulin resistance occurs when the body is unable to appropriately respond to insulin. This in turn leads to increased levels of glucose and insulin in the bloodstream. Unlike T2DM, insulin resistance is a reversible diagnosis. The purpose of this project was to identify the most influential genetic and dietary factors of insulin resistance and to see if individuals have some extent of control to possibly avoid the diagnosis of insulin resistance and possibly T2DM entirely.
A total of 26 human subjects were used in this study. Each subject was classified as either lean or obese, according to their BMI measurement. First, the subjects underwent an oral glucose tolerance test. Blood samples were taken to measure glucose levels in the blood. After the test subject characteristics for each subject was obtained. These included age, BMI, body fat percentage, fat free mass (FFM), height, total mass, waist circumference, hip circumference, and waist to hip ratio. After the subject characteristics and blood glucose were measured the blood samples taken previously were then centrifuged, and the blood plasma was extracted. The blood plasma was then used to undergo an Insulin ELISA test. After extensive analysis, the Matsuda Index of each subject was obtained. Subjects with a Matsuda value of 6.0 or under were considered insulin resistant while subjects with a Matsuda value higher than 6.0 were considered insulin sensitive. Subjects were also required to submit a dietary record over the course of three days. The food intake was then put into a food processing software which gave a daily average of the macro and micro nutrients for each subject. Both the subject and dietary values were put into a multiple regression with a significance factor of p < 0.5 to see which factors contributed most to the Matsuda value.
It was found that BMI, height, total mass, insulin and fat free mass, all of which were subject characteristics, were considered to be significant. Some of these factors an individual has no control over, such as height and insulin. However other factors such as BMI, total mass and fat free mass can be affected by both a healthy diet and frequent exercise. This study validated that diet and physical activity can greatly influence an individual’s susceptibility to insulin resistance and ultimately T2DM.
ContributorsBrinkerhoff, Catalina Marie (Author) / Katsanos, Christos (Thesis director) / Shaffer, Zachary (Committee member) / College of Health Solutions (Contributor) / School of Life Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05