Multiple sclerosis (MS) is an inflammatory demyelinating disease of the CNS and is the most common cause of neurological disability in young adults after trauma. In MS, infiltrating immune cells from the periphery attack oligodendroglial cells and mediate demyelination and secondary neurodegeneration. Despite decades of study, the molecular mechanisms of injury remain poorly understood. While there are several effective therapies for MS are available today, many patient’s disease gradually gets worse over time causing them to accumulate a high level of permanent disability. We believe that with further study, the mechanisms of inflammatory myelin damage can be better understood and targeted for intervention. The Calabresi laboratory is committed to elucidating the details of these pathways in hopes of identifying improved therapies for multiple sclerosis.
Oligodendrocyte Precursor Cells (OPCs) in Inflammation:
An area of special interest is the observation that endogenous remyelination can occur as a result of mobilization and differentiation of OPCs. Despite extensive indirect or observational evidence that immune cells may suppress remyelination, there is remarkably little known regarding the cellular signaling pathways by which immune cells affect OPCs.
Studying OPCs in vivo
Our lab uses the animal models experimental autoimmune encephalomyelitis (EAE) and cuprizone to model the inflammatory and demyelinating aspects of the disease. While both models have been instrumental in better characterizing CNS inflammation and myelination, they both have significant limitations. Cuprizone lacks a prominent lymphocyte component and there is very little remyelination present in EAE. To address these issues we recently developed a novel model capitalizing on aspects of both EAE and cuprizone which we refer to as adoptive transfer cuprizone (ATCup). In ATCup, myelin specific TEffector cells are injected into mice after 4 weeks of cuprizone feeding and the mice are sacrificed 2 weeks later (Baxi et al J Neurosci 2015). We have shown that myelin reactive T cells secreting both IFNγ and IL-17 inhibit the endogenous remyelination that normally occurs in the cuprizone model. In order to examine the molecular mechanisms underlying the effects of inflammatory T cells on OPCs we have developed in vivo (lineage fate mapping in PDGFαR_CreER; Rosa26_YFP mice) systems to map the fate of and transcriptionally profile OPCs under the influence of an inflammatory milieu.
Effects of interferon-gamma on OPCs
Interferon-gamma (IFNγ) is one of the primary proinflammatory cytokines secreted by activated T cells in multiple sclerosis. While it is known that IFNγ can generally inhibit differentiation and induce death in OPCs, it's exact effects on OPC biology are still unclear. To determine why OPCs respond to IFNγ in this manner, we conducted a microarray analysis of OPCs and oligodendrocytes in response to pro and anti-inflammatory cytokines including IFNγ. To corroborate and expand upon the results of these investigations we are using a transgenic mouse model originating from Brian Popko in which astrocytes express IFNγ in an inducible fashion. Using this model in combination with our in vitro studies we hope to gain insight into the downstream consequences of IFNγ in the central nervous system.
Complement in CNS inflammation:
Recent studies have revealed that the complement system, a set of blood soluble proteins primarily thought to participate in the body’s immune response to pathogens, plays a key role in a variety of CNS disorders such as schizophrenia and Alzheimer’s disease. Our preliminary genetic studies in patients with multiple sclerosis have shown that gene variants in the classical complement pathway may be associated with more rapid degeneration. To clarify this association we have initiated in vitro and in vivo investigations using transgenic mouse models and pharmaceutical agents to better understand the role of complement in central nervous system autoimmunity.
Animal Models of Meningeal Inflammation:
Leptomeningeal inflammation has been noted in relapsing remitting MS as well as progressive MS and has been associated with a more severe disease course and increased cortical demyelination. B cells are an important component of these meningeal infiltrates and in a subset of MS patients, ectopic lymphoid follicle like structures can be identified in the meninges. Meningeal inflammatory infiltrates in MS patients can now be detected on MRI imaging providing a possible marker of therapeutic response for trials targeting this process. However, the testing of potential therapeutic agents is hampered by the lack of a suitable animal model.
We performed ultra-high field MRI (11.7 T) in mice with relapsing-remitting EAE late in their disease course and identified meningeal contrast enhancement that pathologically corresponds to meningeal inflammation. These meningeal infiltrates are composed primarily of B and T cells and are associated with demyelination and axonal damage in the adjacent cortex. These lesions also persist and accumulate over time providing a potential marker to test the efficacy of therapies targeting meningeal inflammation. We are currently in the process of further defining the effects of meningeal inflammation on the adjacent cortex and testing new therapeutic agents that could impact the various components of the meningeal infiltrates.
Multiple Sclerosis Biomarkers:
There is a major unmet need for biomarkers of MS disease progression. Our lab is currently focusing on the utility of new “omics” technologies such as metabolomics and lipidomics in identifying both prognostic and diagnostic biomarkers for MS. Metabolomics and lipidomics refer to the use of mass spectrometry coupled with liquid or gas chromatography to identify levels of multiple metabolites / lipid species in biological matrices such as plasma and CSF. Current projects involve utilizing metabolomics to identify a metabolic signature of MS, identifying metabolic pathways that are related to progression in MS and utilizing metabolomics to understand the mechanism of action of the disease modifying agent dimethyl fumarate. We are also tracking a large cohort of patients longitudinally to determine whether serum lipidomic profiles predict progression of disease over time. These studies could help better understand the pathophysiology of the disease and provide markers for use in the testing of new therapies for progressive MS.