The role of selenium (Se) in metabolic disorders, particularly type 2 diabetes (T2D), is controversial, with epidemiological studies pointing towards either a protective or a deleterious role in disease incidence. Se is a micronutrient essential to life, and available as an over-the-counter dietary supplement in the USA. In our bodies, Se is processed into selenocysteine (Sec), an amino acid present at the core of selenoproteins. Selenoproteins mostly function in countering oxidative stress. In T2D, oxidative stress is elevated, which affects glucose utilization and homeostasis. Sec is decomposed into alanine and selenide by the enzyme Sec lyase (Scly), with selenide being the selenium form reutilized in selenoprotein translation, recycling Se. Characterization of a Scly KO mouse in our laboratory revealed this model to develop obesity, insulin resistance, and glucose intolerance, suggesting Scly participates in mechanisms regulating glucose homeostasis. Preliminary studies identified pyruvate carboxylase (Pcx) as an interactor of Scly. Following up on this surprising finding revealed increased amounts of pyruvate and two metabolites of glycine metabolism, glycine, and dimethylglycine, in livers of Scly KO mouse. Pcx catalyzes the conversion of pyruvate into oxaloacetate, the first committed step of gluconeogenesis, a mechanism by which glucose-starving hepatocytes can produce and utilize glucose. Our long-term objective is to understand the role of Se metabolism in disorders involving glucose metabolism, specifically T2D, a health disparity that is prevalent among Native Hawaiians and Pacific Islanders. The overall goal of this research proposal is thus to investigate the role of Scly in glucose homeostasis. Our central hypothesis is that Scly regulates glucose homeostasis through regulation of glycine metabolism and pyruvate levels via interaction with Pcx to fuel energy metabolism.
Aim 1 includes in vitro and in vivo confirmation of the interaction between Scly and Pcx, characterization of the subcellular location where interaction occurs, and whether Se levels regulate this interaction.
In Aim 2, we will investigate if the interaction of Scly and Pcx is dependent on glucose levels, if each binding partner is required for the effects on glucose utilization, and whether this regulatory mechanism is also physiologically relevant in an additional insulin target tissue, the adipocyte. Moreover, we will identify transcripts that are differentially expressed in liver and white adipose tissue in Scly KO and WT mice. These results will further our understanding of the crosstalk between the antioxidant micronutrient Se and energy metabolism, and incorporate a neglected micronutrient into hepatic and adipocyte physiology. Since Se is an over-the-counter dietary supplement that 19% of Americans consume, this innovative perspective of the research will provide a basis for improvements in Se nutritional guidelines and ultimately benefit mechanistic comprehension of T2D.
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