Abstract
Impacting a significant portion of the world's population with increasing incidence in minorities, the young, and the physically active, diabetes mellitus (DM) and its complications affect approximately 20 million individuals in the United States and over 100 million individuals worldwide. In particular, vascular disease from DM may lead to some of the most serious complications that can extend into both the cardiac and nervous systems. Unique strategies that can prevent endothelial cell (EC) demise and elucidate novel cellular mechanisms for vascular cytoprotection become vital for the prevention and treatment of vascular DM complications. Here, we demonstrate that erythropoietin (EPO), an agent that has recently been shown to extend cell viability in a number of systems extending beyond hematopoietic cells, prevents EC injury and apoptotic nuclear DNA degradation during elevated glucose exposure. More importantly, EPO employs Wnt1, a cysteine-rich glycosylated protein involved in gene expression, cell differentiation, and cell apoptosis, to confer EC cytoprotection and maintains the integrity of Wnt1 expression during elevated glucose exposure. In addition, application of anti-Wnt1 neutralizing antibody abrogates the protective capacity of both EPO and Wnt1, illustrating that Wnt1 is an important component in the cytoprotection of ECs during elevated glucose exposure. Intimately linked to this cytoprotection is the downstream Wnt1 pathway of glycogen synthase kinase (GSK-3beta) that requires phosphorylation of GSK-3beta and inhibition of its activity by EPO. Interestingly, inhibition of GSK-3beta activity during elevated glucose leads to enhanced EC survival, but does not synergistically improve protection by EPO or Wnt1, suggesting that EPO and Wnt1 are closely tied to the blockade of GSK-3beta activity. Our work exemplifies an exciting potential application for EPO in regards to the treatment of DM vascular disease complications and highlights a previously unrecognized role for Wnt1 and the modulation of the downstream pathway of GSK-3beta to promote vascular cell viability during DM.