What we really care about…
Proteasomes
Protein homeostasis is essential for cellular survival. The main non-lysosomal protein degradation machinery in eukaryotic cells is the proteasome, a large macromolecule equipped with proteases. The core proteasome particle has been widely accepted to function intracellularly (cytosol and nucleus) and produce 3-30 amino acid-long peptide molecules as a result of protein breakdown. Beyond its conventional role in preserving protein homeostasis, the proteasome has been shown to be integral to neuronal functions such as synaptic transmission and plasticity.
Neuronal membrane proteasomes (NMPs)
The proteasome complex has recently been found to localize to the plasma membrane specifically in neurons. These neuronal membrane proteasomes (NMPs) modulate neuronal signaling by degrading intracellular proteins and releasing bioactive peptide fragments into the extracellular space, representing a novel form of neuronal communication. The NMP complex is exposed to the extracellular space, catalytically active upon neuronal stimulation, and tightly associated with the plasma membrane. The localization of the proteasome to the plasma membrane has been recently shown to be drastically reduced in an AD model, which suggests a potential role for the NMP in initiation and progression of neurodegenerative diseases. Furthermore, upon neuronal stimulation, the NMP degrades newly synthesized intracellular proteins into extracellular peptides, pointing to a novel co-translational degradation mechanism. Most importantly, NMP-derived peptides, once purified and added onto naïve neurons, modulate neuronal signaling. Thus, we hypothesize that NMP and its peptide products modulate neuronal signaling in health and disease.
Huntington’s disease (HD)
Neurodegenerative disorders are characterized by damage and eventual death of neurons. Huntington’s disease (HD) is one of the rare but still fatal forms of neurodegeneration and is caused by a CAG trinucleotide repeat expansion in the huntingtin (HTT) gene, resulting in the production of mutant huntingtin protein (mHtt) with an extended polyglutamine (polyQ) tract. When the number of CAG repeats exceeds 40, mHtt becomes prone to aggregation, forming intracellular inclusion bodies over time. These aggregates contribute to widespread brain atrophy, particularly in the striatum and cerebral cortex. HD affects 5-10 people per 100.000 in the Western country populations. Despite the known genetic cause of HD, the molecular mechanisms underlying its progression remain poorly understood. Like Alzheimer’s and Parkinson’s, HD also presents itself with impaired protein balance in neurons, contributing to rapid decline in neuronal health. Our major objective is to investigate a neuron-specific mechanism of protein degradation known as the neuronal membrane proteasome (NMP) and its role in the initiation and progression of Huntington’s disease.
Neuronal membrane proteasomes (NMPs)
The proteasome complex has recently been found to localize to the plasma membrane specifically in neurons. These neuronal membrane proteasomes (NMPs) modulate neuronal signaling by degrading intracellular proteins and releasing bioactive peptide fragments into the extracellular space, representing a novel form of neuronal communication. The NMP complex is exposed to the extracellular space, catalytically active upon neuronal stimulation, and tightly associated with the plasma membrane. The localization of the proteasome to the plasma membrane has been recently shown to be drastically reduced in an AD model, which suggests a potential role for the NMP in initiation and progression of neurodegenerative diseases. Furthermore, upon neuronal stimulation, the NMP degrades newly synthesized intracellular proteins into extracellular peptides, pointing to a novel co-translational degradation mechanism. Most importantly, NMP-derived peptides, once purified and added onto naïve neurons, modulate neuronal signaling. Thus, we hypothesize that NMP and its peptide products modulate neuronal signaling in health and disease.
Adapted from Ramachandran et al., 2017 and Türker et al., 2024
Huntington’s disease
Neurodegenerative disorders are characterized by damage and eventual death of neurons. Huntington’s disease (HD) is one of the rare but still fatal forms of neurodegeneration and is caused by a CAG trinucleotide repeat expansion in the huntingtin (HTT) gene, resulting in the production of mutant huntingtin protein (mHtt) with an extended polyglutamine (polyQ) tract. When the number of CAG repeats exceeds 40, mHtt becomes prone to aggregation, forming intracellular inclusion bodies over time. These aggregates contribute to widespread brain atrophy, particularly in the striatum and cerebral cortex. HD affects 5-10 people per 100.000 in the Western country populations. Despite the known genetic cause of HD, the molecular mechanisms underlying its progression remain poorly understood. Like Alzheimer’s and Parkinson’s, HD also presents itself with impaired protein balance in neurons, contributing to rapid decline in neuronal health. Our major objective is to investigate a neuron-specific mechanism of protein degradation known as the neuronal membrane proteasome (NMP) and its role in the initiation and progression of Huntington’s disease.
Project 1. Changes in cell surface proteome in Huntington’s disease
To date, no study has comprehensively investigated global membrane protein dynamics in HD models, even though significant alterations in specific membrane proteins, such as major modulators of neurotransmission (AMPA and NMDA receptors), have been linked to HD pathology. We aim to compile the first large dataset of global membrane proteome changes in the striatum of a transgenic HD mouse model (R6/2 mice), providing a valuable resource for future research and other research groups.
Project 2. Regulation of NMP in R6/2 Huntington’s disease mouse model
Our primary aim is to rigorously investigate NMP biology across distinct brain regions in HD mice of varying ages, each exhibiting distinct molecular pathology and HD phenotypes. The use of different brain regions will enable us to learn and correlate the link between aggregate formation and NMP dynamics since aggregation will not be evenly distributed across all brain regions. Also, we aim to analyze the NMP-dependent changes in brain pathology by tracking the behavioral and molecular disease markers. We investigate changes in behavioral phenotypes of disease, such as clasping, weight loss, anxiety-like behavior as well as molecular and structural markers following NMP inhibition.
Project 3. NMP dynamics in Huntington’s disease in vitro models
We use the HD cell culture model (STHdhQ111/Q111) to compare the NMP dynamics at the cellular level to healthy neurons and investigate the role of neuronal membrane proteasome (NMP) inhibition in HD phenotypes.
The STHdhQ111/Q111 cell line is derived from striatal neurons of knock-in mice homozygous for 111 CAG repeats in the huntingtin (HTT) gene, similar to the genetic mutation seen in HD patients and R6/2 mice. These cells exhibit critical HD phenotypes, including impaired intracellular trafficking, mitochondrial dysfunction, and altered neuronal viability, and mutant huntingtin protein (mHtt) aggregation under proteotoxic stress.
Project 4. Investigation of proteasome and NMP biology using microfluidics platforms, with a focus on HD models
This proeject aims to investigate the role of NMPs in specific neuronal compartments using advanced microfluidic technology. The key objectives are to (i) evaluate how NMP inhibition impacts neural transmission by reconstructing a cortico-hippocampal network on a microfluidic platform, (ii) develop an Huntington’s disease model-on-a-chip to study the role of NMP in disease progression, and (iii) explore the therapeutic potential of NMP-derived bioactive peptides. This research has the potential to provide insights into NMP-dependent signaling pathways in neurons and open new avenues for therapeutic strategies in neurodegenerative diseases, including HD.
