Protein enters mouse brain, flips switch, and vanishes

Researchers report a way to deliver a protein to the brain quickly, effectively, and briefly. The protein degrades naturally after performing its task.

Many diseases have at their origin a protein that does not function properly. The new work has both therapeutic and scientific implications, including repairing spinal cord injuries and a range of other localized injection applications.

“We found that we could successfully deliver a protein into mouse brains,” says Jean-Philippe Pellois, professor and associate head for graduate program in the biochemistry and biophysics department at Texas A&M College of Agriculture and Life Sciences. “Proteins are large molecules that don’t easily enter cells or cross cell membranes, but we’ve created a trick to achieve this.

“We wanted to make sure we had reagents that are very gentle on the cell, that can enter cells without disrupting them and then leave without a trace,” says Pellois, who is also a researcher with Texas A&M AgriLife Research.

Because proteins can have powerful effects, cells are picky about which proteins they let in. The method the team used to counteract this is a little like mixing vegetables into macaroni and cheese to tempt a picky kid.

“Cells have the equivalent of the digestive tract, called the endocytic pathway,” Pellois says. “We are managing to cause a cell to ingest proteins and our delivery tool. The delivery tool, once internalized in the endocytic pathway, then allows the proteins to enter the rest of the cell, particularly the nucleus, where we can trigger a response.”

Other labs have discovered that the human immunodeficiency virus contains a small sequence of amino acids—a peptide—that cells prefer to ingest. The team further improved that peptide’s knack for entering cells. Once inside the cell, the peptide escapes the cell’s “digestive tract,” and the target protein comes too.

“People have used a part of this peptide with a protein of interest,” says Cédric Geoffroy, assistant professor in the neuroscience and experimental therapeutics department in the School of Medicine. “Our system goes one step further. You don’t have to modify the protein—most will be delivered.”

Mixing the target protein and the peptide in solution, then injecting the mixture into mouse brains, the team found that their protein readily enters brain cells. The mice were specially bred so that the protein created a visual signal, fluorescence, if it arrived as intended.

Indeed, brain cells near the injection site began to fluoresce only after the protein and its delivery tool were injected together.

“If the protein enters cells, these cells become red fluorescent,” Pellois says. “So by simply looking at whether the cells have become fluorescent, we can tell whether the protein has managed to enter.”

Geoffroy, who specializes in neurotrauma and spinal cord injuries, says the study provides needed evidence that the method works in a living brain.

Further work will focus on improving the method to target just one cell type, he says. Another limitation is that the method currently only works with local injections. Traveling, the study opens a path to many potential applications.

“One key application would be to use this approach for localized injections, such as at the site of a spinal cord injury,” Pellois says. “We are also looking at the possibility of doing this in knee joints for cartilage repair or to fight off the inflammation that diseases like arthritis can cause.”

The method might help deliver therapies other than proteins, Geoffroy says. “This could also enhance the delivery of drugs. If you have an anti-cancer drug, which is very toxic, this method could reduce the amount of drug we deliver.”

The study appears in Science Advances.

The National Institute of General Medical Sciences; the Cancer Prevention and Research Institute of Texas; the Craig H. Neilsen Foundation; and the Institute for Rehabilitation and Research Foundation funded the work.

Geoffroy and Pellois have filed a patent on the method’s components. They have also founded a company to take the research closer toward applications.

Source: Texas A&M University

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