The effect of oxidative stress and hypoxic conditioning on mesenchymal stem cell differentiation

Abstract

Introduction South Africa is ranked the third most obese country after the United States of America and Great Britain. According to a study conducted by the South African Medical Research Council, 61% of the South African population is overweight, obese, or severely obese. Research into obesity and its contributing factors has increased as the problem continues to increase on a global scale. Adipose-derived stromal/stem cells (ASCs), formerly known as mesenchymal stem cells (MSCs), are obtained from adipose tissue and have self-renewal properties and multipotential capabilities. A subpopulation of these cells with stem cell characteristics has the potential to differentiate down the adipogenic lineage. This provides a human primary cell model to study the mechanisms of adipogenesis including hyperplasia (cell number proliferation and/or differentiation) and hypertrophy (cell size increase due to lipid droplet accumulation). The stromal/stem cells are said to reside in hypoxic niches where the physiological O2 tension is lower than ambient O2 tension (21% O2) and thus oxidative stress may be reduced. Obesity is correlated with increased oxidative stress and chronic inflammation. Inflammation is associated with the generation of ROS and the accumulation of ROS leads to oxidative stress. ROS is also important in signal transduction pathways. Adipogenesis is triggered by signaling molecules leading to the conversion of a subpopulation of ASCs to preadipocytes, which further differentiate into mature adipocytes. Differentiation down specific lineages coincides with the migration of these stromal/stem cells out of the hypoxic niche. This motivated the assessment of the effect of oxidative stress and a hypoxic mimetic, Dimethyloxalylglycine (DMOG) on adipogenesis in vitro. Methods ASCs were induced to differentiate into adipocytes using adipogenic-inducing medium. The use of the pro-oxidant, H2O2, and the antioxidants, Trolox and CoQ10 allowed for the modulation of ROS in the ASC cultures. Hypoxia was mimicked by the addition of DMOG to ASCs that were induced to differentiate into adipocytes. The adipogenic differentiation was quantitatively detected using flow cytometry and the emission profiles of Nile Red. Results It was demonstrated that ROS added exogenously to adipogenic-induced ASCs enhanced adipogenesis. It was also observed that H2O2 added to non-induced ASCs caused lipid accumulation. Trolox and CoQ10 attenuated the increase in ROS and thus a decrease in adipogenesis was seen. Removal of pyruvate, a ROS scavenger, was necessary to see these effects. The addition of DMOG resulted in a trend towards the reduction in adipogenesis over the 14 and 21-day induction periods. Conclusion ASCs provide a primary cell model for investigating adipogenesis and the effects of oxidative stress and hypoxia on this process. This is relevant for many diseases and therapeutic options. The study also showed that flow cytometry is a powerful technique that can aid in the quantitative detection of adipogenesis and the cell sub-populations that make up this process. This research underscores the importance of assessing the effects of both oxidative stress and hypoxia on adipogenesis at a gene and protein level in the future.