Tuesday, August 4, 2015
Genetic adaptation keeps Ethiopians heart-healthy despite high altitudes
Ethiopians have lived at high altitudes for thousands of years, providing a natural experiment for studying human adaptations to low oxygen, a condition known as hypoxia. One factor that may enable Ethiopians to tolerate high altitudes and hypoxia is the endothelin receptor type B (EDNRB) gene. Researchers at University of California, San Diego School of Medicine now find that mice with lower-than-normal levels of EDNRB protein are remarkably tolerant to hypoxia. The study provides a mechanism for the gene's role in adaptation to life at high altitudes and suggests that EDNRB could be targeted to treat sea level diseases that stem from lack of oxygen. "This is the first demonstration that a gene involved in high altitude adaptation is critical in protecting cardiac function in moderate to severe hypoxia at sea level," said senior author Gabriel Haddad, MD, Distinguished Professor and chair of the Department of Pediatrics at UC San Diego School of Medicine and physician-in-chief and chief scientific officer at Rady Children's Hospital-San Diego. "In addition to improving the health of the more than 140 million people living above 8,000 feet, information on how Ethiopians have adapted to high altitude life might help us develop new and better therapies for low oxygen-related diseases at sea level - heart attack and stroke, for example." Whole-genome sequencing previously identified EDNRB as a candidate gene for high altitude tolerance in Ethiopians. To investigate further, Haddad and his team turned to a mouse model that produces low levels of the protein. The researchers found that even under extremely hypoxic conditions - 5% oxygen, even lower than you'd find atop Mount Everest - low-EDNRB mice performed much better than normal mice. Under these conditions, normal mice experienced a 40%-50% drop in cardiac output, which meant they were unable to maintain their blood pressure and none of them survived to finish the minimum exposure time. In contrast, mice with low EDNRB maintained normal heart rhythm and blood pressure in severe hypoxia. Low-EDNRB mice in hypoxia were also better able to maintain oxygen delivery to vital organs and keep blood lactate levels low. "Lowering EDNRB does wonders for mice when environmental oxygen levels are low, leading us to conclude that the EDNRB gene plays a key role in human adaptation to low oxygen and high altitude," said Haddad, who is also a pediatric pulmonologist at Rady Children's Hospital-San Diego.