DURING starvation a person is able to survive for a considerable stretch of time. Despite the obvious stress, the body is able to cope because of an internal physiological process of “self-cannibalisation” through which the body makes use of its inessential and damaged cellular components by breaking them down and reassembling them into useful proteins and the nutrients needed to sustain its essential functions. This is called autophagy, which literally means “self-devouring” in ancient Greek (auto meaning self, and phagein meaning to eat). It is a process that has been evolutionarily conserved and is intrinsic to all organisms, from unicellular yeast to multicellular mammalian systems like humans.
In fact, without autophagy our cells could not survive. It is an essential part of the body’s self-renewal process. As the scientist Juleen Zierath, a member of the Nobel Committee for Physiology or Medicine, pointed out in a post-announcement interview, every day 200-300 grams of proteins need to be replaced in the human body, but, on average, the intake is only about 70 g of proteins, which is insufficient to take care of the requirement to make new proteins. “Because of this machinery, we are able to rely on some of our own proteins so that we can sustain and we survive,” she said.
Thus, autophagy maintains normal functioning “homeostasis” (the tendency of a biological system to actively maintain the fairly stable internal equilibrium conditions necessary for survival despite changing external conditions) by protein degradation and the recycling of destroyed components from the cytoplasm of cells (the part exterior to the cell nucleus) for new cell formation. This year’s Nobel Prize in Physiology or Medicine has been awarded to the 71-year-old Japanese biologist Yoshinori Ohsumi of the Tokyo Institute of Technology for unravelling in the 1990s the underlying molecular mechanism of autophagy. He was the first to visually observe the process.
The concept of autophagy was known in the 1960s itself. In fact, the phrase was coined in 1963 by the Belgian scientist Christian de Duve, who was awarded the 1974 Nobel Prize in Medicine for his discovery in the 1950s of what is called lysosome. However, the mechanism and physiological relevance remained poorly understood until Ohsumi appeared on the scene. His work dramatically transformed the understanding of this important physiological process.