Nanotube Bridges Reveal New Connections Between Neurons

Super-resolution microscopes have uncovered an entirely new form of connection linking neurons in mouse and human brains.

Nanotube bridges between neurons

In laboratory experiments, Johns Hopkins University neuroscientist Minhyeok Chang and colleagues found minute tubular bridges at the branching ends of cultured neurons. Subsequent tests in mouse models of Alzheimer's disease suggested that these bridges directly transfer calcium and molecules linked to the disease from one cell to another.

"[Similar] structures can transport a vast range of materials, from small ions (10⁻¹⁰m) to large mitochondria (10⁻⁶ m)," the team writes in their paper.

"In cultured neurons, we observed these nanotubes forming dynamically and confirmed that they possessed a distinct internal structure, setting them apart from other neuronal extensions."

Neurons are already known to send swift signals through synapses, conveying both electrical and chemical information. However, other cell types can exchange molecules through physically connected bridging tubes. By combining advanced imaging with machine learning, Chang's team has now confirmed that neurons also form a comparable kind of tubular bridge.

Amyloid-beta transport in Alzheimer's disease

The team saw the nanotubes carrying amyloid-beta molecules after injecting them into mouse brain cells. Amyloid-beta has been associated with neurodegenerative conditions such as Alzheimer's disease, in which the molecules can accumulate in abnormal clumps.

Preventing the bridges from developing also stopped amyloid-beta from moving between cells, confirming that the nanotubes functioned as direct passageways.

"Our computational model supported these findings, predicting that overactivation in the nanotube network could accelerate the toxic accumulation of amyloid in specific neurons, thereby providing a mechanistic link between nanotube alterations and the progression of Alzheimer's pathology," the researchers explain.

What remains unknown about neuronal nanotubes

The investigation is still at a very early stage. Because these tubes have only recently been discovered, scientists do not yet know what they naturally carry, how frequently they form, or how they operate across the human brain as a whole.

Malfunctions in these tubes could potentially play a part in other diseases as well, making researchers eager to understand more about these tiny bridges.

This research was published in Science.