From The New York Times:
When ticking off the benefits of physical activity, few of us would include intracellular housecleaning. But a new study suggests that the ability of exercise to speed the removal of garbage from inside our body’s cells may be one of its most valuable, if least visible, effects. In the new research, which was published last month in Nature, scientists at the University of Texas Southwestern Medical Center in Dallas gathered two groups of mice. One set was normal, with a finely tuned cellular scrubbing system. The other had been bred to have a blunted cleaning system. It’s long been known that cells accumulate flotsam from the wear and tear of everyday living. Broken or misshapen proteins, shreds of cellular membranes, invasive viruses or bacteria, and worn-out, broken-down cellular components, like aged mitochondria, the tiny organelles within cells that produce energy, form a kind of trash heap inside the cell.
In most instances, cells diligently sweep away this debris. They even recycle it for fuel. Through a process with the expressive name of autophagy, or “self-eating,” cells create specialized membranes that engulf junk in the cell’s cytoplasm and carry it to a part of the cell known as the lysosome, where the trash is broken apart and then burned by the cell for energy. Without this efficient system, cells could become choked with trash and malfunction or die. In recent years, some scientists have begun to suspect that faulty autophagy mechanisms contribute to the development of a range of diseases, including diabetes, muscular dystrophy, Alzheimer’s and cancer. The slowing of autophagy as we reach middle age is also believed to play a role in aging. Most metabolism researchers think that the process evolved in response to the stress of starvation; cells would round up and consume superfluous bits of themselves to keep the rest of the cell alive. In petri dishes, the rate of autophagy increases when cells are starved or otherwise placed under physiological stress. Exercise, of course, is physiological stress. But until recently, few researchers had thought to ask whether exercise might somehow affect the amount of autophagy within cells and, if so, whether that mattered to the body as a whole.