Limited Oxygen Builds Stronger Alligator Hearts, Study Finds

Alligators born from eggs exposed to low oxygen levels (hypoxia) have an important advantage compared to those that develop under normal oxygen levels:  they develop stronger, better functioning hearts.   

The discovery was made by a team of researchers led by Dr. Sarah Alderman, an adjunct professor in the Department of Integrative Biology.

According to Alderman, not all alligator eggs experience the same oxygen levels as they develop. Eggs located at the bottom of a buried clutch are oxygen limited compared to ones at the top.  This disparity led Alderman – a physiologist with a particular interest in how cardiac tissue responds to stress – to wonder how hypoxia might affect a developing alligator heart.

Working with collaborators in the United States, Alderman and her team obtained alligator eggs from a wildlife refuge in Louisiana and shipped them to the lab in the University of North Texas for the study. Half of the eggs were grown in low oxygen conditions, while the others were incubated at normal levels. As soon as the alligators hatched, the researchers analyzed the composition of proteins in hearts from both groups of hatchlings.  The alligators were allowed to grow under normal oxygen conditions for two years, at which time the researchers again examined their hearts. 

The team found important differences in the cardiac proteins between the two groups of alligators after hatching, differences that were still present two years later.

“I was surprised to see the persistence of changes in the protein expression induced by hypoxia to the juvenile stage,” says Alderman, noting that this meant the changes would likely last over the lifetime of the alligator.

One of the key differences discovered by the researchers was that hypoxia-exposed hearts had higher amounts of proteins involved in metabolizing fat for energy.  A healthy heart is one that preferentially burns fat over other forms of energy, preventing fat accumulation in cardiac tissue that would otherwise impair proper functioning. (In fact, in humans, cardiac tissue that switches from burning fat to burning carbohydrates is a sign of a diseased heart.)  That means that higher amounts of fat burning proteins indicates a better functioning alligator heart.   

Similarly, the team also found higher levels of “recycling proteins” in the low-oxygen alligator hearts.  These proteins play an important role in minimizing damage from oxidative stress, a common condition that occurs in cells when there is an imbalance between highly reactive molecules and the antioxidants that normally help neutralize them.  Recycling proteins will quickly breakdown any proteins damaged by the reactive molecules, before they can cause problems in the cell.

“Increasing the recycling machinery of the cell to reduce oxidative damage is an interesting strategy which I would like to follow up,” notes Alderman.

The study has received widespread interest because it isn’t just alligators that can be affected by hypoxia during early development. Humans can also experience low oxygen in the womb due to certain maternal medical conditions or if the mother smokes or lives at high altitudes, and chronic fetal hypoxia increases the risk of cardiovascular disease later in life.  By studying the effects of hypoxia in other species, researchers can gain valuable insights into the different ways that low oxygen can alter normal physiology, and even identify new treatment strategies in patients with weakened hearts. For example, the pathways that lead to increased fat utilisation in alligator hearts could also be targeted in humans with heart disease to reverse the high carbohydrate consumption in heart disease.

“There are many long-term potential benefits to this type of research,” says Alderman.  “Thanks to the life history of alligators and other reptiles that bury their eggs, we have a unique opportunity to study the different physiological strategies that have evolved to cope with hypoxic stress during early development.”

This study was funded by the Natural Sciences and Engineering Research Council and the National Science Foundation.

Read the full study in the journal Scientific Reports.

Read about other CBS Research Highlights.