Mouse study finds capillaries build natural coronary bypasses

A blocked coronary artery leaves heart muscle short of blood and oxygen. In mouse hearts recovering from an induced heart attack, researchers led by Mingjun Zhang found that the tiny vessels called capillaries did most of the work of building new coronary collateral arteries—natural bypasses around the blockage. 85.7% of the cells in those new vessels came from capillaries, not mature arteries.

The finding challenged a long-standing view that existing arteries were the main source of these backup channels. Using color-coded genetic switches and three-dimensional fluorescence microscopy, the team followed vessel cells as they changed identity. Capillaries became larger, mature arteries through a process called capillary arterialization.

When the researchers used a genetic kill switch to remove them selectively, the injured mice developed massive heart scarring and severely weakened heart function. The team traced the transformation to a chain in which VEGF-A activates YY1, which recruits SETD1A to alter DNA packaging and activate HES1, a gene that helps instruct capillary cells to become robust arteries.

The practical implication is a possible treatment strategy that would encourage the heart to build its own alternate blood supply after injury. In adult mice, a brief burst of VEGF-A delivered through modified messenger RNA increased functional collateral vessels.

The distance to a clinical therapy is still substantial. The evidence comes from engineered mouse models and adult-mouse experiments; no human treatment or clinical result is reported. For now, the advance is a clearer map of the heart’s repair system—and a molecular handle for testing whether that system can be strengthened safely.