On day 5 after hatching, a fly with an overactive ERO1L gene in its neurons behaves as usual: it crawls along the wall, it does not suffocate from an excess of reactive oxygen species. But inside its nerve cells, a hidden restructuring is already underway. A neuron is like a city that has learned of a long siege: first it reinforces the walls and fills the warehouses, but meanwhile order begins to slip in the archives.
ERO1L is an enzyme that helps proteins fold into the right shape, and along the way it produces hydrogen peroxide. When there is too much of it, the cell takes a double hit: both a load on the protein factory and extra oxidants. To survive, the neuron launches protective programs. In a proteomic analysis on day 5, the scientists saw a rise in proteins that quench oxidative stress and supply energy, along with a decline in proteins responsible for DNA packaging and nuclear structure. The city reinforces its walls and lights the furnaces, but the librarians leave their posts.
Chromatin is how DNA is packed inside the nucleus: the thread wraps around proteins, like wire around spools. How tightly the regions are wound determines which genes are available to be read. In flies with elevated ERO1L, already on day 5 the amount of the protein HP1 and of the H3K9me2 mark, which keep part of the chromatin in a dense, silent state, had decreased. At the same time, mobile genetic elements became active: DNA fragments capable of moving around the genome. The archive was not just left unattended; random hands began rearranging it.
By day 10, the city no longer hides its fatigue: oxidative stress appears, and the fly climbs the wall less well. But the key discovery is that vulnerability arose earlier than the symptoms. Previously, scientists saw only the finale: damaged neurons and impaired movement. Now they have managed to catch the moment when the cell is still compensating for the load but has already lost chromatin stability. It is like noticing a crack in the foundation while the walls still stand straight.
For now this is pure knowledge, with no applications in sight. But if we can figure out exactly what links the metabolic restructuring to the weakening of chromatin, it may become possible to look for ways to slow brain aging at the earliest stage, before the city starts to crumble.
In flies with elevated ERO1L only in their neurons, lifespan was cut in half: from 49.5 to 24 days. Yet the same enzyme in muscles or fat body had no effect on survival, and in glia the effect was weak.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.