What is intracellular junk?

Our cells are constantly breaking down parts of themselves that have been damaged or that have served their purpose and are no longer needed. This is extremely critical to the effective functioning of our system. However, the processes of degradation are not perfect — occasionally, molecules are targeted for degradation but don't go quietly, because the cell lacks the machinery to break down the particular type of damage they've suffered. These stubborn wastes (or “intracellular aggregates” as they are technically known) accumulate in the cell and eventually take up so much room that cell function is compromised.

How does the damage set in?

Cells have a lot of reasons to break down big molecules and structures into their component parts, and a lot of ways to do so. Unfortunately, one of the main reasons to break things down is because they have been damaged so that they no longer work, and sometimes these chemical modifications create structures that are so weird that none of the cell's degradation machinery works on them. This is very rare, but in the long run enough of these undegraded wastes build up that it starts to be a problem. The place where they accumulate is called the lysosome, a special vessel that contains the most powerful degradation machinery in the cell; if something can't even be broken down there, it just stays there forever. This doesn't matter in cells that divide regularly, because division dilutes the junk away, but some of the most important cells of the body – cells in the heart, the back of the eye, some nerve cells (especially motor neurons) and, most of all, white blood cells trapped within the artery wall – don’t normally divide, and instead their lysosomes gradually get clogged with junk, impairing cell function.

Resultant Diseases

Atherosclerosis, macular degeneration, and neurodegenerative diseases such as Alzheimer's disease, are all caused in part by the intracellular accumulation of substances that impair cellular function and viability.

Solution

While scientists have tried using drugs to dissolve these aggregates, this has not proved to be very effective, as they are very hard to break down. On the other hand, these substances are naturally degraded in the soil and water by microorganisms after we die. Research is going on to find the enzymes that these microorganisms use to degrade these harmful aggregates, and tweak them in ways that could let us deliver them directly to our cells, clearing out the lysosomes and restoring normal cell function.