Full title: High glucose protects mesenchymal stem cells from metformin-induced apoptosis through the AMPK-mediated mTOR pathway

Micro- and macro-vascular events are directly associated with hyperglycemia in patients with type 2 diabetes mellitus (T(2)DM), but whether intensive glucose control decreases the risk of diabetic cardiovascular complications remains uncertain. Many studies have confirmed that impaired quality and quantity of mesenchymal stem cells (MSCs) plays a pathogenic role in diabetes. Our previous study found that the abundance of circulating MSCs was significantly decreased in patients with T(2)DM, which was correlated with the progression of diabetic complications. In addition, metformin-induced MSC apoptosis is one of the reasons for the decreased quantity of endogenous or exogenous MSCs during intensive glucose control. However, the role of glucose in metformin-induced MSC apoptosis during intensive glucose control in T(2)DM remains unknown. In this study, we found that metformin induces MSC apoptosis during intensive glucose control, while high glucose (standard glucose control) could significantly reverse its adverse effect in an AMPK-mTOR pathway dependent manner. Thus, our results indicate that the poorer clinical benefit of the intensive glucose control strategy may be related to an adverse effect due to metformin-induced MSC apoptosis during intensive glucose control therapy in patients with T(2)DM.