LL-37 Suppresses Alpha-synuclein Clumping in Parkinson’s

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by Marta Figueiredo PhD |

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LL-37, a natural antimicrobial molecule present in the brain and gut, selectively binds to harmful clumps of the alpha-synuclein protein — a hallmark of Parkinson’s disease — and prevents their further aggregation and toxic effects in lab-grown nerve cells, a study shows.

The discovery of such a strong suppressor of alpha-synuclein clumping in the same tissues where this harmful process takes place in Parkinson’s suggests that “LL-37’s activity might respond to a mechanism developed by the body itself as a means to naturally fight this disease,” the study’s authors said in a press release.

“There is a possibility that a therapy for Parkinson’s disease already lies in our interior and that it only needs to be activated correctly,” said Salvador Ventura, PhD, the study’s senior author of the Institute for Biotechnology and Biomedicine (IBB) at the Universitat Autònoma de Barcelona, in Spain.

The study’s findings, which included the determination of the optimal structural and physicochemical traits of a strong and selective suppressor of toxic alpha-synuclein aggregation, may help to develop new effective treatment approaches for Parkinson’s, the researchers noted.

The study, “α-Helical peptidic scaffolds to target α-synuclein toxic species with nanomolar affinity,” was published in the journal Nature Communications.

Nerve cell loss in Parkinson’s disease is triggered mainly by the toxic buildup of clumps of alpha-synuclein, a protein abundant in the brain and thought to help regulate nerve cell function and communication.

Previous studies have identified two types of small aggregates of alpha-synuclein, or oligomers, with non-toxic type A oligomers undergoing structural reorganization to form the intrinsically toxic type B.

Notably, type B oligomers are considered the most harmful forms of alpha-synuclein to nerve cells and they, along with even larger clumps called fibrils, are responsible for spreading the disease in the brain.

As such, scientists have focused on finding ways to neutralize these toxic forms and prevent further aggregation and resulting toxicity, as they are considered one of the most promising therapeutic approaches for Parkinson’s.

However, the identification and design of molecules that target specific forms of alpha-synuclein toxic clumps “is challenging because of the [diverse], dynamic, and transient nature of these species,” the researchers wrote.

Now, Ventura and his team at the IBB, along with colleagues at the University of Zaragoza’s Institute for Biocomputation and Physics of Complex Systems (BIFI), in Spain, explored the biophysical properties of toxic alpha-synuclein clumps to identify molecules that could specifically bind to these forms, without affecting the function of free alpha-synuclein.

After determining the optimal structural and biophysical properties of a molecule with the ability to potently and selectively bind to toxic alpha-synuclein aggregates, the researchers were able to identify a small molecule produced by bacteria that fulfilled all the requirements.

Several analyses, using a number of techniques and also lab-grown nerve cells, showed this molecule, called PSM-alpha-3, selectively bound to toxic forms of alpha-synuclein, preventing the conversion of type B oligomers into fibrils.

It also protected cells from oligomers-induced damage, namely the known increase in reactive oxygen species (ROS), the chemically reactive forms of oxygen that, when unbalanced, create damaging cellular environments broadly known as oxidative stress.

Based on these findings, the researchers designed Scaffold_19, a molecule structurally similar to PSM-alpha-3, but with lower DNA sequence complexity, which was found to have an anti-aggregation activity comparable to PSM-alpha-3.

This further confirmed the structural and biophysical traits need for a molecule to suppress alpha-synuclein clumping.

The team then wondered if there was a molecule with these optimal properties naturally present in the human body.

They conducted a structure-guided search over 25,000 human molecules from several databases that resulted in the identification of LL-37, a molecule present mainly in the brain and gastrointestinal tract — two sites of alpha-synuclein aggregation in Parkinson’s.

Notably, alpha-synuclein clumps have been shown to spread from the gut to the brain in mice.

LL-37’s presence “in both tissues is engaging, as the brain-gut axis connection is gaining momentum in [Parkinson’s disease],” the researchers wrote.

LL-37, originally discovered for its antimicrobial properties, was found to bind to type B oligomers and fibrils in a stronger way than PSM-alpha-3, while showing a weak interaction with type A oligomers and no binding with free alpha-synuclein.

The human molecule also completely abolished the production of ROS in lab-grown nerve cells. These results highlight LL-37 as a potential therapeutic, natural molecule for treating Parkinson’s.

Notably, LL-37’s DNA sequence is not related to PSM-alpha-3 or Scaffold_19, but the three “share the same structural and physicochemical traits,” the researchers wrote, adding “this confirms that a linear combination of these properties suffices to identify, and potentially design, potent inhibitors of [alpha-synuclein] aggregation.”

In addition to representing a potential therapeutic approach for Parkinson’s and other conditions associated with alpha-synuclein clumps, also known as synucleinopathies, these molecules may help in the diagnosis and monitoring of the disease, given that they discriminate between non-toxic and toxic alpha-synuclein forms.

Nunilo Cremades, one of the study’s co-coordinators at the BIFI, said that “until now there were no molecules capable of selectively and efficiently identifying toxic [alpha-synuclein] aggregates,” and the identified molecules “are unique and, therefore, have great potential as diagnostic and prognostic tools.”

“Overall, the molecular entities we describe in this work may help to develop therapeutic and diagnostic strategies for synucleinopathies,” the researchers concluded.

The team plans to study how LL-37 levels can be regulated and if this strategy can become a safe and effective therapy to slow Parkinson’s progression.

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