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Intestinal damage results from hidden cryptosporidium cell invasion, study shows

The intestinal parasite Cryptosporidium is a vicious trespasser, hiding within the cells that line the gut and causing intestinal damage.

"Cryptosporidium infections can be life-threatening, especially in children," explains Adam Sateriale, head of the Crick's Cryptosporidiosis Laboratory. "Even mild infections carry the risk of prolonged malnutrition, leading to growth stunting and other long-term consequences."

Cryptosporidium invades and reproduces inside epithelial cells in the gut, causing severe diarrhea. This is particularly dangerous for children in endemic regions and people with weakened immune systems. Despite its major impact on global public health, there are no fully effective treatments.

This parasitic invader has evolved to survive in the human gut by navigating the biological pathways and hijacking the metabolism of its host. But as part of a study published today in , Adam's team developed a way to map this labyrinth of survival routes and cut off Cryptosporidium's most important lifelines.

In a year-long scientific marathon, lead author Bishara Marzook teamed up with Ok-Ryul Song from the Crick's High Throughput Screening platform to design and build an experiment that could expose Cryptosporidium's survival network.

They conducted a genome-scale screening experiment using CRISPR genetic editing, which involved systematically disabling nearly 20,000 protein-coding genes in human intestinal cells one by one. They infected the cells with Cryptosporidium to see how each gene affected the survival of the parasite.

A metabolic tipping point

Bishara and Ok-Ryul saw that a group of genes involved in making cholesterol had a significant effect on parasite survival. But while some of these genes seemed to block Cryptosporidium, others boosted the parasite's ability to grow.

This balance hinged on a molecule midway through the cholesterol production line, called squalene. Removing genes before squalene production blocked infection, while removing genes after squalene production boosted infection.

Squalene is secreted from glands in our skin, where it is known to play a protective role, particularly against oxidative stress. The team discovered that squalene plays a similar role in the intestine: when squalene levels are high, reactive oxygen species (a hallmark of oxidative stress) are low and vice versa.

The primary way that humans control oxidative stress is through a molecule called glutathione. This antioxidant is vital to limiting oxidative damage and nearly all organisms have the capacity to make it. Surprisingly, the team discovered that, while the Cryptosporidium parasite uses glutathione, it cannot make its own. This leaves the parasite dependent on glutathione from the intestinal cell and particularly vulnerable to oxidative stress.

As Bishara explains, "At some point in its evolution, Cryptosporidium lost the ability to produce glutathione and instead hijacks the host's production of this essential molecule. This could be a clever way for Cryptosporidium to save its energy for other processes, but we've shown that it could also be its downfall."

Forgotten drug hits the right target

Having identified a key survival route, the team then looked at a way to cut off this lifeline. When the team searched through drugs that target cholesterol production, they found a previously abandoned drug that showed promise because it directly blocks squalene production. When mice infected with Cryptosporidium were given the drug, called lapaquistat, it reduced the infection and stopped further intestinal damage.

"There is already a huge amount of safety data for lapaquistat, making it easier to fast track clinical trials," adds Adam. He has now teamed up with researchers and clinicians in Zambia to put this forgotten drug to the test.

And for Bishara, there is much more of the genetic labyrinth to explore. "We now have a vast dataset of how almost every single gene in human gut cells affects Cryptosporidium infections. Beyond cholesterol production, we're now starting to look at other host properties that affect the parasite, opening new doors for research and shutting doors on parasite survival."