Imaging and 3D Modeling a Key Focus at ACTRIMS 2024

Imaging and visualization techniques were a common topic at the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) Forum 2024. Among the presenters homing in on methodologies in this area, Niels Bergsland, PhD, University of Buffalo, gave an overview of imaging the choroid plexus (CP) and Krystyn Van Vliet, PhD, Cornell University, detailed the engineering of 3D models for drug discoveries in multiple sclerosis (MS).

Breaking Barriers in MS ACTRIMS Forum 2024 | image credit: forum.actrims.org

The Value of CP Imaging

Bergsland began by walking the audience through the anatomy and function of the CP. The CP is located in the brain within the lateral third and fourth ventricles. This is a highly vascularized tissue that makes up the blood–cerebrospinal fluid (CSF) barrier. Furthermore, the CP is involved in the production of CSF, maintaining ionic balance and chemical composition, delivery of nutrients, and removal of waste, and it plays a role in immunity as well.

The CP has been an area of interest in MS as prior research has continually demonstrated that the volume of CP is different in this patient population. Even in the early stages of their disease, this tissue volume is noticeably enlarged compared with in otherwise healthy patients, and this volume increase is believed to be reflective of inflammation in the CP.^1-3 In these previous studies, it was also observed that this change in CP volume is in fact an early feature of MS. Of the longitudinal studies that have tracked these changes over time, Bergsland pointed to 3 separate studies that all presented similar data on the annualized increase of CP volume, averaging at approximately 1.5% every year.^2,4,5

With these associations in mind, and amidst a plethora of conflicting information regarding the relationship between the CP and inflammation, neurodegeneration, gray matter atrophy, and chronic expanding lesions, Bergsland and colleagues saw a need to utilize additional imaging techniques to further characterize the functional and structural properties of the CP in patients with MS.

In their work, they took a look at differences in CP inflammation at baseline and after 5 years. In their cohort, they grouped patients whose Expanded Disability Status Scale scores improved or remained stable and split up patients who exhibited disease progression/worse scores. In their results, although the CP volume was greater in the disease progression group, this difference was not significant.

They did find a significant effect (P = .001) when they used a pseudo T2 (pT2) mapping technique, which is a validated approach where more intense imaging correlates with inflammation. This finding, derived from CP pT2 mapping, showcases the clinical relevance of CP volume to have a predictive power for disease progression.

“I think that it's still very early days in terms of using MRI in the face of patient data. I think the beautiful thing about this, though, is that just to measure volume doesn't require any specialized technique. This is something that people can go back and do with existing data,” Bergsland concluded.

Advantages of 3D Axonal Modeling

Van Vliet’s research is a product of collaborative efforts between clinicians, scientists, and engineers, she explained. The work of this team is primarily trying to understand the interactions in myelination, remyelination, and demyelination that occur between the oligodendrocytes and the neurons and axons they engage with. To explore these interactions fully, Van Vliet posited that “myelination is a 3D process. And if you really want to understand it, you need to be able to visualize it and measure it in a 3D context.” Furthermore, investigators need to recognize that oligodendrocytes are mechanosensitive. “So it's not just that it needs to be 3D. But the platform that you use to ask these questions, at least in the lab, needs to reflect the biophysical cues, including the stiffness of actual neuronal axons, in order to actually see and try to recapitulate the key aspects of myelination,” she said.

Considering these realities, Van Vliet described how her team has worked for years to create an artificial axon that can mimic the crucial features on neurons and the neuronal environment—the varying degrees of stiffness and squishiness—to adequately quantify myelination and cellular processes.

Why is this important? Van Vliet explained that neuronal and cellular environments, as well as drug delivery systems, impact cellular functioning. Engineering better approaches for therapeutic interventions, therefore, is a valuable venture.

To develop an artificial axon, they created a type of 3D printer that could mimic the necessary geometry (human neurons are 1 micrometer or less) and stiffness of axons. This project began with the invention of what was called the High-Resolution 3D Printer (HR-3DP).⁶ This device would generate 1 coverslip at a time, and eventually 1 well at a time, by shining light on a polymer that was UV-polymerized. Through this process, they were able to create fully customizable, completely synthetic fibers that resemble the size, density, stiffness, and architecture of axons to observe how oligodendrocytes would interact with them. As this invention advanced, what was deemed a High-Throughput 3D Printer (HT-3DP) was created that could rapidly produce scalable synthetic axons in seconds across multi-well plates.⁷ “But the advantage is that the registry allows optical microscopy and confocal microscopy, so that you can quantify that in terms of what we call the myelin wrapping index,” Van Vliet stated.

The ways oligodendrocytes were interacting with the artificial axons allowed them to ask further questions, including: Does axon stiffness matter for myelin potential? Does the diameter? Does the ligand presentation on the axon matter?

The success of this development allowed the team to start asking questions about how lesion environments or the delivery of different compounds would affect oligodendrocytes. This fabrication process enables the researchers to evaluate dosage curves and analyze differences in effects between compounds, which spotlights the benefits of referring to a 3D model.

“Thinking about these key cells as mechanosensitive and thinking about the myelination processes as 3D opens up new needs and more opportunities,” Van Vliet concluded.

References

1. Ricigliano VAG, Morena E, Colombi A, et al. Choroid plexus enlargement in inflammatory multiple sclerosis: 3.0-T MRI and translocator protein PET evaluation. Radiology. 2021;301(1):166-177. doi:10.1148/radiol.2021204426

2. Bergsland N, Dwyer MG, Jakimovski D, et al. Association of choroid plexus inflammation on MRI with clinical disability progression over 5 years in patients with multiple sclerosis. Neurology. 2023;100(9):e911-e920. doi:10.1212/WNL.0000000000201608

3. Klistorner S, Van der Walt A, Barnett MH, et al. Choroid plexus volume is enlarged in clinically isolated syndrome patients with optic neuritis. Mult Scler. 2023;29(4-5):540-548. doi:10.1177/13524585231157206

4. Jankowska A, Chwojnicki K, Grzywińska M, Trzonkowski P, Szurowska E. Choroid plexus volume change-A candidate for a new radiological marker of MS progression. Diagnostics. 2023;13(16):2668. doi:10.3390/diagnostics13162668

5. Klistorner S, Barnett MH, Wang C, Parratt J, Yiannikas C, Klistorner A. Longitudinal enlargement of choroid plexus is associated with chronic lesion expansion and neurodegeneration in RRMS patients. Mult Scler. Published online February 6, 2024. doi:10.1177/13524585241228423

6. Espinosa-Hoyos D, Du H, Fang NX, et al. Poly(HDDA)-based polymers for microfabrication and mechanobiology. MRS Advances. 2017;2:1315-1321. doi:10.1557/adv.2017.57

7. Yang M, Kowsari K, Van Vliet J, et al. Additive manufacturing of high aspect-ratio structures with self-focusing photopolymerization. Light: Adv Man. 2022;3(3):542-571. doi:10.37188/lam.2022.032