Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Yan Huang

Committee Member

Wayne Kuenzel

Second Committee Member

Jiangchao Zhao

Third Committee Member

Young Min Kwon

Keywords

Adipogenesis, Brown adipogenesis, Energy regulation, EPA and DHA, Myogenesis, Trans-differentiaion

Abstract

Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) supplementation commonly suggested during pregnancy confers many health benefits on offspring and more recently improves fetal BAT development and induces myoblast trans-differentiation into adiopocytes through activating PPARs expression. Embryonic myoblast is a highly flexible cell showing great capacity to change its phenotype into adipocyte in response to EPA and DHA supplementation in many in vitro models. However, a little is known about the identity of derived adipocytes, whether, they change into brown or white adipocyte, and in vivo evidence is still missing. Given that the myogeneis process is initiated at the mid of gestation and fetal BAT development is formed at the late stage of pregnancy, we sought to investigate the effect of EPA and DHA supplementation on fetal muscle growth and energy regulation. To achieve our goal, the study was mapped in two patterns: three in vitro experiments, devoted to test the effect of combined and isolated EPA and DHA on C2C12 undergoing differentiation into white and brown adipocytes, and in vivo experiment devoted to investigate the effect of maternal ingestion of EPA and DHA enriched diet on muscle growth, BAT activity, lipid metabolism regulation in liver, and browning of sWAT. C2C12 cell have frequently been used as a representative model of myoblasts in preclinical trials. In vitro, Cells were induced to differentiate into white or brown adipocytes using hormonal cocktail in the absence (CON) or presence of (50 µm) EPA and (50 µm) DHA in combination or separately. The results suggested that EPA and DHA treatments potentiate the route of C2C12 trans-differentiation into white- like adipocytes with a greater potency of DHA in compared to EPA. The effect was mediated via inhibiting myogenesis and mitochondrial biogenesis processes and up-regulating the expression of WAT signature genes and impairing the aquistion of brown adipocyte phenotype. Changing genes profile was concurrent with increasing lipid droplets formation and impairing mitochondrial function. In vivo, mice were fed a diet containing (3.05%) fish oil (FA) enriched with EPA and DHA or diet devoid of fish oil (CON) throughout the entire period of gestation and lactation. The results showed partial inconsistency with in vitro trials where transient increase in myogenesis regulating genes and MHC4 without increasing muscle mass were observed in FA treated group. An increasing intramuscular fat infiltration as a result of stimulating the expression of adipogenesis regulating genes was predominant in FA treated group at day 1 and 21 post-parturition. Also, maternal EPA/ DHA intake induced up-regulation the expression of fatty acids catabolism regulating genes in liver. Stimulating BAT development and activity and browning of subcutaneous white adipose tissue were demonstrated in FA treated group in weaned mice. Taken together, EPA and DHA supplementation is associated with ectopic lipid accumulation in skeletal muscle but not on the expense of myoblasts, and it can be suggested as an excellent therapeutic option to combat childhood obesity as a result of their potential role in stimulating energy expenditure transcriptional program.

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