There are currently no approved therapies to slow down the accumulation of neurological disability that occurs independently of relapses in multiple sclerosis. International agencies are working to expedite the development of novel strategies capable of modifying disease progression, reducing persistent central nervous system inflammation, and preventing the degeneration of axons in people with progressive multiple sclerosis. Therefore, a key priority of the lab is to identify the fuels and drivers of disease progression to design new approaches for the development of next generation therapies that will benefit patients.
Smouldering disease and neurodegeneration
Multiple sclerosis is a lifelong chronic inflammatory condition of the central nervous system that is characterised by demyelination, axonal/neuronal degeneration, and persistent activation of microglia and astrocytes. Nearly 85% of multiple sclerosis patients present with a relapsing-remitting disease course, while the remaining ~15% present with a primary progressive disease course that is characterised by a continuous neurological deterioration in the absence of clinically defined relapses. Despite great successes in the development of disease-modifying therapies, as the disease evolves, most patients with relapsing-remitting multiple sclerosis will advance to a secondary progressive disease course 15–20 years from disease onset. This has created a gap in available treatment options that benefit patients with progressive multiple sclerosis, which is due to an incomplete understanding of the specific mechanisms that characterise progression. These degenerative mechanisms are distinct from those present in relapsing-remitting multiple sclerosis and are insufficiently targeted by the currently approved immunomodulatory compounds.
In relapsing remitting multiple sclerosis, active lesions predominate and present with a diffuse perivascular and parenchymal T cell infiltration that is the substrate of clinical attacks. As the disease evolves, and patients advance to the progressive phase of the disease, there is a shift from a T cell mediated adaptive immune response towards innate immune activation. This is characterised by a persistent state of central nervous system inflammation that is driven by cells of the myeloid lineage, such as microglia. In progressive multiple sclerosis, myeloid cells are found in the normal appearing white matter, in subpial cortical lesions and, most importantly, in smouldering lesions. These are slowly expanding lesions that are characterised by a rim of activated myeloid cells and astrocytes. Here, the activation of myeloid cells and astrocytes correlates with increasing demyelination and axonal loss, which leads to worsening symptoms. These observations point to slowly expanding, myeloid and astrocyte-mediated smouldering neuroinflammation as the core feature from which progression starts and evolves in multiple sclerosis. Importantly, smouldering or low-grade inflammation is also a main feature of a variety of metabolic diseases, including obesity, diabetes, and cardiovascular diseases. It also participates to the initiation and progression of several disorders of the immune system, including rheumatoid arthritis, psoriatic arthritis, and allergic diseases and chronic diseases of the nervous system.
Therefore, understanding fuels and drivers that contribute to the destructive myeloid cell and astrocyte activation in the central nervous system holds great promise in identifying new targets to treat and/or delay disease progressions.
The fuel hypothesis | Group leader Luca Peruzzotti-Jametti, MD, PhD
Compelling evidence exists that patients with progressive multiple sclerosis display pathological changes in neural metabolism and mitochondrial function. However, it is unknown if a similar degree of metabolic dysfunction occurs also in non-neural cells in the central nervous system. Specifically, it remains to be clarified (i) the full extent of metabolic changes in tissue-resident microglia and infiltrating macrophages after prolonged neuroinflammation (e.g., at the level of chronic active lesions), and (ii) whether these alterations underlie a unique pathogenic phenotype that is amenable for therapeutic targeting.
Metabolites are molecules deriving from chemical reactions that regulate how energy is produced and consumed in cells. Our lab has shown that modifying the ways in which mitochondria produce energy can reduce inflammation in the brain. We have also shown that certain mitochondrial metabolites can act as signalling molecules that disrupt the brain's normal response to inflammation.
Currently, we are focusing on metabolites and mitochondria to find novel ways to block persistent inflammation and favour the regeneration of the damaged brain. To do so, we use cutting edge techniques to detect metabolic changes in cells, animal models of disease, and human tissues and correlate them with changes in gene and protein expression.
Desorption electrospray ionization - Imaging Mass Spectrometry ( DESI-IMS) ion image of the distribution of myelin-derived lipid species (as denoted by SHexCer 42:1; O2 intensities, visualised according to heatmap with intensities ranging 0-429617) in the white matter of a healthy, aged posterior brain case. (photo credits: Vincent Wu and Monica Emili Garcia-Segura).
Cory Willis, PhD Research Associate (2021 National MS Society Postdoctoral fellow) is a Project leader that aims to understand how a Kreb’s cycle metabolite, succinate, hijacks the signalling axis between microglia and astrocytes to perpetuate the persistent inflammation observed in smouldering lesions in progressive multiple sclerosis patients. Using human stem-cell derived microglia and astrocytes, he aims to model this interaction in dish using CRISPR gene editing techniques that are complemented by in vivo animal disease models of chronic inflammation and focal demyelination. This will be paired with transcriptomic and metabolomic analyses coupled to metabolic flux analysis that will uncover the role of succinate in perpetuating maladaptive, pathogenic responses in microglia and astrocytes.
A Representative light microscopy sagittal section of a mouse brain showing SUCNR1 expression (arrowhead) detected by immunohistochemistry. B subventricular zone with choroid plexus (empty arrowhead). C cortical lesion. D hippocampal formation, and Emeninges and cerebellum. Tissue was collected from a C57Bl6 mouse with MOG35-55-induced experimental autoimmune encephalomyelitis (EAE) at 15 days post-immunization and was co-stained with haematoxylin (purple) (photo credits; Greg Krzak).
The diver hypothesis | Group leader Stefano Pluchino, MD, PhD
Advances in healthcare have significantly increased the life expectancy of populations across the globe. As a result, the total number of people over the age of 65 is expected to double by 2050. This will lead to an increase in the number of people living with age-related neurodegenerative disorders, which will result in an enormous financial burden on health facilities to manage and care for these patients. Currently no treatments exist that can reverse or slow the progression of these diseases. One feature found across ageing and in neurodegenerative disease is smouldering neuroinflammation.
New research in the lab is focused on how intrinsic and extrinsic factors in cell types can drive and maintain smouldering inflammation. Here, we use advanced techniques, such as conditional gene editing in human cells, human stem cell-based disease modelling, mini-brain technology, and computer-aided analytical processing to further uncover the main fuels and drivers of smouldering inflammation.
Alexandra Nicaise, PhD Research Associate (2020 ECTRIMS Postdoctoral Research fellow and 2023 UK MS Society Cambridge Centre for Myelin Research Fellow) is a project leader that is using patient-based model systems to interrogate new mechanisms of disease in progressive multiple sclerosis. Using induced neural stem cells (iNSCs) she found that those from progressive MS patients display an accelerated ageing phenotype, called senescence. She is now leading projects to interrogate how these cells may intrinsically and extrinsically contribute to smouldering neuroinflammation. This includes analyses on their metabolic functionality, their maintenance of genome integrity, as well as work examining their unique epigenetic profiles and how this may influence their behaviour. Here they take advantage of patient-based human models, including 2D and 3D systems, proteomics, metabolic flux analyses, sequencing technologies, CRISPR knockouts, and post-mortem human tissue analyses to address our questions. Using these novel models she anticipates disentangling new pathways and regulatory interactions that form the causal background of the disease.
Mitochondrial network (Tom20, white) in human iNSCs. Nuclei are counterstained with DAPI (blue) (photo credits; Bristena Ionescu).
Tools and Objectives
We have developed a robust toolbox of next generation techniques, such as CRISPR gene editing, mini brains-in-a-dish, human cell modelling, and transcriptomic and metabolomic analyses to uncover the mechanisms of neuro-immune signalling in diseases of the brain and spinal cord. These findings will aid in the development of more effective therapies that provide significant neuroprotection in the disease brain.
Our goal is to discover new biological pathways towards the development of targeted precision medicines to stop the irreversible accumulation of brain damage in neurodegenerative diseases in an effort that shall help preserving the neurological reserve of the brain.