Fructotoxity and mitochondrial dysfunction in 3T3L1 cells

Obesity is an energy balance disorder and a worldwide growing epidemic problem. It has been proposed that increased obesity rates may be due to increased consumption of fructose derived from dietary high-fructose corn syrup. As mitochondria are the primary organelles regulating metabolic and energy homeostasis, mitochondrial dysfunction is thought to play a key role in the pathogenesis of metabolic disorders in obesity. In obesity, nutrient overloading may lead to the accumulation of misfolded proteins in mitochondria. The mitochondrial quality control machinery is mainly composed of chaperones and proteases, which are up-regulated through a retrograde signaling pathway to the nucleus to degrade and remove damaged mitochondrial proteins maintaining mitochondrial homeostasis. Differentiation of preadipocytes into adipocytes is a highly regulated process whereby a series of transcription factors. During adipogenesis, adipocyte differentiation program requires large amount of energy and biogenesis of mitochondria is stimulated. Nutritional, pharmacological, and genetic impairments of adipose mitochondrial function lead to the dysregulation of homeostasis. Highly refined fructose intake increases visceral adiposity and mitochondrial dysfunction although the mechanism(s) remain unclear Given the potential connections between fructose intake and obesity, we examined the effects of fructose on adipocyte differentiation. Also we want to show the detrimental impacts of fructose on the mitochondrial dysfuction during adipogenesis in 3T3-L1 preadipocyte cells. Adipocyte differentiation was shown with oil red-O staining. In all experimental conditions with and without fructose, expression rates of mitochondrial and adipocyte biogenesis genes (peroxisome proliferator-activated receptor gamma (PPARγ), PPARγ coactivator-1 alpha (PGC-1α), CCAAT-enhancer binding protein alpha (CEBPα), CCAAT-enhancer binding protein beta (CEBPβ) and also stress genes related to mitochondrial unfolded protein response (mitochondrial heat shock protein 60 (mtHsp60), mitochondrial heat shock protein 70 (mtHsp70), mitochondrial-processing peptidase subunit beta (Pmpcb), Clp like protease (ClpP), endonuclease G (Endog), ubiquinol-cytochrome c reductase complex assembly factor 1(Uqcc) were measured on the second, fourth, sixth and eighth days of the experiment. We demonstrated that, fructose treatment of 3T3-L1cells incubated in standard differentiation medium increases adipogenesis. Expression of CEBPα, CEBPβ, Pmpcb, Clpp, Endog, Uqcc genes were significantly higher in fructose applied cells. Our study showed the deleterious effects of fructose on mitochondrial functions in adipocytes.