Scientists have discovered a fungus that can change shape to fit your brain.
Cryptococcus neoformans (C. neoformans), a pathogenic fungus, can change shape on its own to pass through the blood-brain barrier, a protective layer used to keep pathogens out of the brain, according to an article published in the journal Cell host and microbe.
“The changes it goes through when it first enters the body is pretty incredible, and we’re still trying to understand it,” said Jessica Brown, a University of Utah pathologist and co-author of the paper. News week.
C. neoformans occurs naturally on rotting wood or in bird droppings. According to the CDC, when inhaled, the fungus can infect the lungs and other organs, including the brain, leading to cryptococcal meningitis.
The researchers found that the smallest cells of C. neoformans made their way into the brains of mice they studied, and that the surfaces of these small cells changed when they entered the brain.
“Cryptococcus cells in the lungs are very diverse with different sizes and different appearances. So when my graduate student showed me pictures of the uniformity of cells from the brain, I was shocked,” Brown said in a statement.
“We show that the formation of a small C. neoformans morphotype — termed ‘sperm cells’ for their colonizing ability — is critical for extrapulmonary organ entry,” the authors wrote in the paper. “Sperm cells show changes in fungal cell size and surface expression that result in enhanced macrophage update.”
These sperm cells have an altered cell surface that allows them to be taken up by macrophages (immune cells), Brown said.
“In a number of tissues, macrophages are responsible for containing invaders, so they will take them in and try to sequester and destroy the invader,” she said.
“We think that sperm cells take advantage of this tendency, are more easily carried into the organ by the macrophage, and then escape and grow into their new organ environment when conditions are right, such as in the brain.”
According to Brown, after a sperm cell enters the brain, the first type of cells to form are called titanium cells because they are gigantic and contain at least four times as many copies of TNZT as a “normal” C. neoformans cell.
“These titanium cells form directly from the infecting” [seed] cells,” Brown told News week. “The sperm cells we study, the small ones that enter the brain, probably don’t form when another cell shrinks.
“Instead, we think that sperm cells form over generations: a normal or titanium cell receives a signal, and when it then divides to form a new cell, it makes a sperm cell as its progeny rather than a cell like itself. cells are then likely to produce more sperm when they divide.”
The fungus has previously been found to increase its cell mass by up to 10 times in the human lung, so the fact that it can enter the brain is worrisome.
“The scary thing about this fungus is that we don’t think it wants to get into the brain per se,” Brown said. “It’s not passed from person to person, so there’s not really an evolutionary selection to grow in a person, like with respiratory viruses, for example.
“Instead, we think this is an evolutionary accident. C. neoformans grows extremely well on inositol, which is found in large amounts in the spinal fluid, spinal cord and brain tissue. This may be a result of its natural environment, which consists of soil, trees and bird droppings, because plant material contains a lot of inositol.”
“We therefore think that C. neoformans has been given the ability to grow on inositol in its environmental niche and that ability becomes problematic when humans are infected because when C. neoformans reaches the inositol rich central nervous system it grows well and there is not much to it to stop doing that.”
The researchers fear that the effects of climate change could make C. neoformans more adept at infecting humans.
“One concern in the future is that as the climate changes, microbes such as fungi will become more adapted to stressful conditions (extreme temperatures, drought, etc.) which will increase their ability to survive the stressful conditions in the human body,” Brown said.
However, the researchers also hope that their discovery could lead to new strategies for blocking C. neoformans infection.