Using Polymer-Lipid Nanodiscs to Better Understand Alzhemier's Disease

Posted on April 18, 2022

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If you read the most recent Lipid Leader Interview featuring Dr. Ayyalusamy Ramamoorthy, you know that his group develops synthetic polymers that can be used to form lipid-nanodiscs. The full utility of these polymer-based lipid nanodiscs has yet to be fully realized. They are a versatile tool for biophysical and biochemical research offering a detergent-free solubilization method for studying membrane proteins in their native lipid environments. So, even if that was all that his group was interested in, they would be doing exciting research.

But not only do they work towards making new polymers for these nanodiscs, but they also use them to study amyloids, antimicrobial peptides, membrane proteins, and in NMR spectroscopy studies. So, let’s first look at their development of one of Avanti’s polymers, polymethacrylate co-polymer (PMA), and then see how they used PMA to study β-amyloid and islet amyloid polypeptide aggregation.

The Making of PMA

As previously stated, Avanti’s PMA polymer product was initially developed by Dr. Ramamoorthy at the University of Michigan. The idea behind its development was to offer an alternative to the commonly used styrene-maleic acid (SMA) copolymer which has also been shown to spontaneously form lipid nanodiscs. SMA has application limits due to the strong absorption of the styrene moieties’ aromatic rings in experimental measurements. The styrene group interferes with some of the most commonly used techniques in biophysical studies such as circular dichroism, UV/vis, and fluorescence spectroscopy. In addition to interference in these techniques, there are undesirable π-interactions of the styrene group with embedded proteins and the lipid bilayer.

To address these problems, they investigated a library of styrene-free nanodisc-forming polymers designed around a polymethacrylate framework. The library of polymethacrylate polymers has several advantages to the commonly used styrene containing polymers:

  • Synthesis via radical polymerization allows for easier control
  • A variety of monomers with side chain variations can be employed
  • Low-cost, large-scale production capabaility

To determine how well each polymethacrylate polymer solubilized lipids, each one was used to carry out a turbidity study. Large unilamellar vesicles (LUVs) composed of DMPC were used in the study and in most cases a decrease in solution turbidity was seen. This is evidence of lipid nanodisc formation. Their experiments led to the determination that an optimization of amphiphilic balance was important, as well as the molecular weight of the polymer. Low molecular weight polymers were ineffective at solubilizing LUVs compared to polymers of higher molecular weight. Finally, they used electron microscopy and NMR experiments to determine that the polymers were able to produce monodispersed homogenous polymer lipid nanodiscs. With this information they concluded that these polymers could be used for structural and functional studies on a variety of membrane proteins, including amyloids.

Using a Cationic Polymethacrylate Copolymer to Study Amylin Fibrillation

Aggregation of amyloidogenic proteins is involved in several neurodegenerative diseases including Alzheimer’s Disease (AD) and type-2 diabetes (T2D). However, our understanding of the role that these aggregations play in AD and T2D is lacking. And there is still no treatment for the aggregation of these proteins. Small molecules have so far failed to offer any kind of therapy for these conditions, and with the significant clinical trial challenges that they face, research has been aimed at finding an alternative. In this particular study, they demonstrate the modulation of amyloid aggregation using a polymethacrylate derived copolymer (PMAQA). PMAQA has already been implicated in several biological studies for the enhancement of drug delivery and modulation of bioavailability.

They were able to demonstrate that PMAQA has different effects on different amyloidogenic proteins. In the case of amylin, PMAQA inhibited aggregation at substoichiometric concentrations. But in the case of β-amyolid-1-40, PMAQA increased its aggregation significantly which altered its equilibrium state turning it from an unfolded structure to a β-sheet structure. These findings give us a better understanding of peptide self-assembly and might one day aid in the development of a successful therapeutic inhibitor. This also shows the utility of polymethacrylate-derived polymers in modulating other amyloid proteins involved in diseases.

Thank you, Dr. Ramamoorthy for trusting Avanti with all your lipid needs, but also for working with us to get your polymethacrylate-derived copolymer (PMA N-C4-52-6.9) on the market! We are excited to see the work being done by your group and can’t wait to see what you uncover in the future.

If you are interested in using a polymethacrylate-derived copolymer in your own studies, take a look at Avanti’s PMA product. And please read the full research articles published by Dr. Ramamoorthy and his group at the University of Michigan.

Preparation and Study of Polymethacrylate-derived Coploymers

A cationic polymethacrylate-copolymer acts as an agonist for β-amyloid and an antagonist for amylin fibrillation