The discovery of the Glymphatic System a few years ago was met with significant fanfare, and rightly so – the story is one of clever researchers asking good questions, doing intricate science and reporting findings that had important clinical implications.
In this nicely titled (and open access) feature for Scientific American, two of the key researchers provide a very accessible summary of the discovery process, mechanics of the glymphatic system, clinical considerations and future research directions.
The human brain weighs only about three pounds, or roughly 2 percent of the average adult body mass. Yet its cells consume 20 to 25 percent of the body’s total energy. In the process, inordinate amounts of potentially toxic protein wastes and biological debris are generated. Each day, the adult brain eliminates a quarter of an ounce of worn-out proteins that must be replaced with newly made ones, a figure that translates into the replacement of half a pound of detritus a month and three pounds, the brain’s own weight, over the course of a year.
In our research, we found an undiscovered system for clearing proteins and other wastes from the brain—and learned that this system is most active during sleep. The need to remove potentially toxic wastes from the brain may, in fact, help explain the mystery of why we sleep and hence retreat from wakefulness for a third of our lives. We fully expect that an understanding of what happens when this system malfunctions will lead us to both new diagnostic techniques and treatments for a host of neurological illnesses.
“Sleep, those little slices of death — how I loathe them”
– Edgar Allan Poe
Fellow night owls will understand Poe’s words – so much to do, so much to read, and so little time – but the relationship between efficient glymphatic drainage and sleep is sobering reading:
The power of sleep
Having demonstrated that the expansion and contraction of the interstitial space during sleep were important to both brain function and protein-waste clearance, we then wanted to test a corollary to this observation: Could sleep deprivation precipitate neurodegenerative disease? Experiments that we conducted in mice showed that during sleep, the glymphatic system did indeed remove beta-amyloid from the brain with remarkable efficiency: its clearance rate more than doubled with sleep. On the other hand, mice genetically engineered so that they lacked aquaporin-4 water channels in astrocytes demonstrated markedly impaired glymphatic function, clearing 40 percent less beta-amyloid than control animals.
So have a read of the article and get a bit more up to date on the brain, but don’t lose any sleep over it.