Johns Hopkins University reveals details of brain's astrocyte cells

27 Nov 2025

Low-coherence holotomography and nanowire substrate allow study of cells in their natural state.

A project led by Johns Hopkins University has successfully imaged astrocytes, the brain's most abundant cells, in their natural state.

The star-shaped astrocytes are known to be responsible for regulating communication between neurons and helping to maintain the blood-brain barrier, with their behavior closely linked to their complex specialized 3D structures. But imaging them has proven challenging.

Attempts to visualize astrocytes in vitro have to date not fully replicated the natural morphology, with the shapes collapsing as soon as scientists attempt to study them on glass trays under microscopes. As a result researchers have been unable to reach a complete understanding of how the cells regulate the central nervous system.

"Frustratingly little is known about the stunning diversity of astrocyte morphology, and we also don't know much about the molecular machinery behind these shape shifts," said Ishan Barman from Johns Hopkins.

"They won't take on these shapes on glass, so the question for us was how do we replicate the in vivo shape but in vitro?"

The team's solution is an imaging platform combing glass nanowires as a substrate for the cells, and low-coherence holotomography (LC-HT) as the imaging technique. The findings were published in Advanced Science.

Nanowire glass mats can mimic the texture of brain tissue while remaining optically transparent, and astrocytes placed on this structure not only maintain their signature shape but grow and thrive.

"When grown on nanowire mats, astrocytes regain their star-like morphology, branching and maturing as they do in vivo in the brain," said Annalisa Convertino from project partner the National Research Council of Italy (CNR).

New ways to study neurological diseases

One method for imaging of normal cells is optical diffraction tomography (ODT), in which phase changes recorded from several angles of illumination contribute to a reconstructed tomographic image. But ODT struggles when the cells are mounted on nanowire substrates with inherently randomizing structures.

The project's LC-HT technique uses incoherent illumination sources like LEDs and "a self-interference-based phase retrieval scheme, eliminating the need for background calibration and dramatically reducing speckle noise," according to the project's paper. "This allows robust 3D reconstruction of cells even in the presence of complex, irregular substrates."

In trials comparing rat cortical astrocytes cultured on the disordered glass nanowire substrates with cells on conventional flat glass, LC-HT revealed differences in morphology between the two populations. Cells on the nanowires showed a characteristic stellate architecture much closer to their native presentation in vivo, the star-like forms thought to be markers of functional maturation.

LC-HT also let the project quantify the number of branch intersections per cell and the distance of each intersection from the nucleus, noted the team in its paper. More intersections and longer distances reflect higher capacity for the cells to regulate synaptic function and facilitate neurovascular coupling.

The project believes the new imaging platform could pave the way for a new generation of brain-on-a-chip models, as well as new ways to study neurological diseases, drug effects, and brain injuries.

"The ability to combine nanowire culture with high-resolution, label-free imaging was critical," said Anoushka Gupta from the Barman Lab. "It finally allows precise quantification of astrocyte morphology."