Why lone kidney grows large when other is lost

Scientists have given an explanation to why in case you end up with just one kidney, the lone organ gets bigger.

When a kidney is removed due to injury or for transplantation, the other kidney can rapidly get 50 to 60 percent bigger, an apparent physiological attempt to expand its capacity.

The increased blood flow to the kidney that results from going from two to one also delivers more protein-building amino acids, which trigger the growth.

"Everybody thinks it makes sense that the kidney gets bigger, but how does the remaining kidney even know that the other kidney is gone?" said Jian-Kang Chen, a pathologist and kidney researcher at the Medical College of Georgia at the Georgia Regents University.

A decade ago, Chen showed that activation of a protein called mTOR plays a major role in the hypertrophy of the lone kidney.

Now, the research team found that in mice the increased availability of amino acids prompts increased activation of a compound called mTORC1.

In the kidneys, mTORC1 functions at a level that maintains the healthy status quo and regulates protein synthesis, cell growth and a nutrient sensor.

When one kidney is lost, mTORC1 senses more amino acids coming to the remaining kidney.

"For a cell to grow bigger, it has to have increased protein synthesis, which is regulated by mTORC1," Chen noted.

Amino acids come from the proteins we consume, enabling us to make proteins so that we can build muscles, bones, and other key tissues.

The study was published in the journal of Clinical Investigation.