DNA Damage Does Not Cause BrdU Labeling of Mouse or Human ß-Cells.

ABSTRACT

Pancreatic ß-cell regeneration, the therapeutic expansion of ß-cell number to reverse diabetes, is an important goal. Replication of differentiated insulin-producing cells is the major source of new ß-cells in adult mice and juvenile humans. Nucleoside analogs such as BrdU, which are incorporated into DNA during S-phase, have been widely used to quantify ß-cell proliferation. However, reports of ß-cell nuclei labeling with both BrdU and γ-phosphorylated H2A histone family member X (γH2AX), a DNA damage marker, have raised questions about the fidelity of BrdU to label S-phase, especially during conditions when DNA damage is present. We performed experiments to clarify the causes of BrdU-γH2AX double labeling in mouse and human ß-cells. BrdU-γH2AX colabeling is neither an age-related phenomenon nor limited to human ß-cells. DNA damage suppressed BrdU labeling and BrdU-γH2AX colabeling. In dispersed islet cells, but not in intact islets or in vivo, pro-proliferative conditions promoted both BrdU and γH2AX labeling, which could indicate DNA damage, DNA replication stress, or cell cycle-related intrinsic H2AX phosphorylation. Strategies to increase ß-cell number must not only tackle the difficult challenge of enticing a quiescent cell to enter the cell cycle, but also achieve safe completion of the cell division process.