Understanding the Neuropsychiatric Symptoms of Systemic Lupus Erythematosus

Despite a prevalence of over 50% among patients with systemic lupus erythematosus (SLE), neuropsychiatric symptoms of SLE (NP-SLE), including anxiety and movement disorders, have not been well understood. The paucity of data examining underlying mechanisms is what spurred the work of Carla M. Cuda, PhD, pointing to microglia as a driver of disease.

Dr. Cuda, who is assistant professor of Rheumatology at Northwestern Medicine, and other Northwestern Medicine investigators were the first to show that microglial expression of disease-associated microglia (DAM)-associated genes correlates with the severity of hippocampal- and cerebellar-associated behavioral deficits in an NP-SLE model prior to overt systemic disease. While DAM have been extensively studied in Alzheimer's disease, no studies have specifically examined DAM in NP-SLE, until now.
Understanding the Neuropsychiatric Symptoms of Systemic Lupus Erythematosus
Featured Speaker:
Carla Cuda, PhD
Dr. Cuda is a Research Assistant Professor in the Division of Rheumatology, Feinberg School of Medicine, Northwestern University. Dr. Cuda obtained her PhD degree in Biomedical Sciences-Immunology from the University of Florida, and following her postdoctoral training in the Division of Rheumatology, Feinberg School of Medicine, Northwestern University, she remained with the division to pursue her independent academic research career. 

Learn more about Carla Cuda, PhD
Understanding the Neuropsychiatric Symptoms of Systemic Lupus Erythematosus

Melanie Cole (Host): Northwestern Medicine investigators were the first to show that microglial expression of a gene signature indicative of disease-associated microglia or DAM correlates with the severity of hippocampal and cerebellar-associated behavioral deficits in a neuropsychiatric symptoms of systemic lupus model prior to overt systemic disease. While DAM has been extensively studied in Alzheimer's disease, no studies have specifically examined DAM in NPSLE until now.

to Better Edge, a Northwestern Medicine Podcast for physicians. I'm Melanie Cole. Joining me is Dr. Carla Cuda. She's an Assistant Professor of Medicine in the Division of Rheumatology at Northwestern Medicine.

Dr. Cuda, thank you so much for joining us today. And before we get into your research, speak a little bit about the prevalence of neuropsychiatric symptoms in lupus patients, and what are some of the most neuropsychiatric symptoms that we're talking about here today.

Dr Carla Cuda: Hi. Thank you so much for having me. So to kind of go back, systemic lupus is a chronic autoimmune disease that can affect multiple organ systems, including the renal, cardiovascular, and nervous systems among others. And though the cause is unknown, genetic predisposition, epigenetics, environmental factors, viruses or infections have been shown to potentially play a role in disease.

And so, patients will experience variable manifestations of lupus, with differing organ systems affected. And any combination of criteria that will total 10 points in conjunction with a positive antinuclear antibody test will render a diagnosis of lupus according to a new classification system that just came out in 2019.

So, involvement of the nervous system is referred to as neuropsychiatric symptoms of lupus or NPSLE as mentioned before. And so similar to lupus in general, NPSLE is highly variable in patients and can involve both the peripheral and/or the central nervous systems. So, NPSLE can affect anywhere between 12% to 95% of SLE patients depending on the attribution model. And so, this wide range in prevalence in the literature is seemingly due to the highly subjective nature of the diagnostic criteria. So, these facts in combination with the list of somewhat non-specific symptoms makes NPSLE really difficult to diagnose.

And so in my lab, we're focusing on NPSLE of the central nervous system, which can then be subdivided into two syndromes, focal or diffuse. The focal syndrome includes symptoms like seizures, movement disorders, headaches. While the diffuse syndrome includes symptoms like anxiety disorder, mood disorder, psychosis, and cognitive impairment. So as you can see, these are really not specific to NPSLE, but the fact that these would be occurring in conjunction with systemic lupus is what really makes it an NPSLE diagnosis. So, the literature seems to suggest that damage associated with the central nervous system and the renal system accounts for the majority of lupus-attributed morbidity and mortality. Thus, we feel there's really a critically unmet need to interrogate NPSLE and its underlying mechanisms to improve patients' health-related quality of life.

Melanie Cole (Host): Wow, this is really interesting, Dr. Cuda. So, your research focuses on understanding the underlying immunologic mechanisms of lupus. Is this a relatively new area of research? I'd like you to please provide a brief overview of your research and why this is so important that we're doing this now.

Dr Carla Cuda: So, as I mentioned before, it's really hard to diagnose it. But even more challenging in the field is really understanding the underlying mechanisms of disease in some cases, especially for diffuse NPSLE, which is really what our lab focuses on. So, numerous mechanisms have been proposed, but my lab is focusing on immune cell-mediated inflammation as a causative factor of NPSLE. And we particularly emphasize our research on the role that microglia play in disease pathogenesis.

So, microglia are a brain-resident macrophage-like cell that help to maintain homeostasis in the brain through various functions, including surveillance, phagocytosis, which means chopping up cells, and then synapse pruning, which will keep things clean in the brain. However, when you have aberrant microglial functions, if any of these processes go awry, this can lead to dyshomeostasis. So for example, the inflammatory response that's mediated by activated microglia plays a major role in neuronal cell death in neurodegenerative diseases like Alzheimer's disease. So, we are focusing our efforts on studying this heterogeneous population of cells in the context of NPSLE.

Melanie Cole (Host): So, you recently published findings in Frontiers In Immunology that you presented at the ACR annual meeting last November regarding that role of microglia in NPSLE. Can you tell us specifically about that work and the methods that you used?

Dr Carla Cuda: Yes, of course. So, the investigation into microglia is relatively new. I would say maybe within the past five years, there was previous literature which seemed to suggest that there was, based on postmortem brain biopsies, that there was activation of microglia. But this is all really difficult to grasp, because you're looking at sections of tissue and really no functional data.

So in our lab, we utilize multiple mouse models of lupus that will also display NPSLE-like disease, and that they will show deficits when put through behavioral tasks for things like anxiety, memory, motor coordination or fear response. And what's interesting is that these behavioral tasks are also designed to implicate affected brain regions, which is even more cool because then you can hone in on looking at particular populations of the cells within that region that's affected. So, we can then isolate microglia from brains of these mice and obtain gene expression signatures using either bulk or single cell RNA sequencing technology to evaluate potential functional changes that occur with disease.

So, one of our recent and impactful findings that we just published in Frontiers a few years ago is that microglia from multiple models of NPSLE express a common signature that we call an NPSLE signature. And in addition to that, they also express genes associated with this recently discovered DAM population thought to be critical in Alzheimer's disease. And so, this particular microglia subset has been shown to localize around amyloid beta plaques to aid in plaque clearance through phagocytic functions. And further, so when we looked at how these signatures are expressed in the microglia, the extent of expression actually correlates with the severity of behavioral deficits in young lupus-prone mice. So, it really makes us believe that this population and potentially the DAM subset are really critical for either tracking disease or possibly contributing to disease pathogenesis.

Melanie Cole (Host): This is so interesting. So, what are your more recent findings? Are your new findings any different from what's currently available? Tell us a little bit about some of the meaningful endpoints of your study.

Dr Carla Cuda: Yeah. So our new findings, so we're the first really to look at DAM in the context of lupus. There's maybe one or two other articles that even sort of mentioned what's happening here. And so, we really go in depth into looking at this population in our new dataset. So first of all, we're the first to show that an established model of lupus previously unexplored for NPSLE-like disease actually exhibits heightened anxiety and defects in motor coordination early in life.

And what's really great about this is that the more models that we have that mimic certain aspects of human disease, the better that we can then try to pinpoint the underlying mechanisms of each of these symptoms because one can assume that what causes anxiety may not cause psychosis. So, the fact that we have models now, which display certain aspects of human diseases, is really great. And some of this anxiety and motor coordination defects, and impairments and these issues will actually implicate the amygdala and the cerebellum, and mirror defects that are observed in lupus patients exhibiting NPSLE.

So using single-cell RNA sequencing technology, we profiled the heterogeneity of microglia early and late in life, and were able to identify the DAM population at both early and late time points in NPSLE as well as control strains in mice. And so, looking specifically at the DAM, we've seen an expansion of this population in aged NPSLE-prone mice. When we look at what genes changed in the NPSLE DAM compared to control DAM, we find that genes involved in antigen processing and presentation in the context of MHC I, as well as the response to type I and type II interferon, are upregulated in NPSLE DAM.

And so, similar to our data mentioned before, we also find that phagocytic functions may be depleted in DAM of our NPSLE-prone mice, which is in contrast to DAM in neurodegenerative disease. So in DAM in Alzheimer's disease, phagocytic functions are actually upregulated, but we're finding this is dampened in our NPSLE DAM.

And so, interestingly though, even at a young age, the E genes involved in the antigen processing and presentation in the context of MHC I and the response to type II interferon are already upregulated in NPSLE DAM. So already at a very early time point, prior to this mouse experiencing systemic lupus at really any great degree, there's already something happening in the microglia in the brain, which is also corresponding to behavioral deficits, particularly anxiety.

So when we compared time points within each strain, we also find that the DAM are more enriched for the DAM signature with age than control DAM. So, these data and other data not mentioned here suggests that DAM not only are elevated in numbers, they actually fully differentiate into more of a DAM-like cell, and that maybe this is a pathogenic population in NPSLE. And so again, this is also in contrast to their proposed protective role in early development of Alzheimer's disease.

So, what we find too is that these patterns hold true in another model of NPSLE that we study in the lab, suggesting that these are truly penetrant defects in multiple models of NPSLE-like disease. So, this is really cool to us because always, when you can validate with another model, it really only concretely provides a mechanism that you can hold onto.

So switching gears, positron emission tomography or PET analysis has been widely used to assess brain function and metabolism through the use of a glucose analog radiotracer. So, this is what's commonly referred to as FDG PET. So however, this is relatively non-specific in terms of understanding the cells that are involved. So in recent years, numerous tracers have been developed to target other biologically relevant pathways. In particular, there's been tracers that have been developed that target mitochondrial translocator protein or TSPO, and so I'll use that going forward.

And so, these radiotracers have been used to detect activated microglia in both patients and animal models of other diseases as levels of TSPO will increase with activation, and so then you can expect increased radiotracer uptake in areas where you have microglial activation. So, we utilized a novel tracer targeting TSPO, developed in the Center for Translational Imaging in conjunction with, I believe, the University of Chicago and saw an increased tracer uptake in our NPSLE microglia in our models indicating increased microglial activation. And what was really cool was that this was really in the cerebellum and potentially the amygdala, and this coincides then nicely with our behavioral testing implicating defects in these particular regions in this mouse.

So when we look within each microglial subset, again going back to our single-cell data, we find that the DAM cluster of cells is the only population of microglia in the NPLE-prone strain with a significant increase in the expression of TSPO. So, these data suggests that DAM might be the source of the elevated TSPO detected by PET analysis in the brain regions impacted by disease, which is really cool for us.

Melanie Cole (Host): It is really cool, and this is such important work you're doing with far-reaching implications. So as we're talking about the neuropsychiatric symptoms of lupus, how do you feel your research impacts patient care? How do you feel it might impact physicians' treatment of lupus patients further down the line? Take us from bench to bedside.

Dr Carla Cuda: So, in the field, and especially within the clinic, there are very few diagnostic criteria or targetable mechanisms, whether it be pathogenic cell populations or proteins. Generally, diagnosis is occurring through eliminating everything else, and then you end up with a diagnosis of NPSLE. So, what we're hoping is that our research will expand our knowledge base to potentially provide information to be able to develop improved diagnostics and treatment strategies. And again, whether we can find a population of cells that's pathogenic, that we can detect potentially maybe in the cerebral spinal fluid of patients or protein in the same area, or maybe this is even something we can translate into the serum of patients so that we don't have to get CSF from these people, that we can find either an improved diagnostic measure or potentially a targetable mechanism that can be then used for enhanced treatment strategies.

So, specifically when we're thinking about imaging, so imaging for diagnostics, so the PET imaging for TSPO levels and microglial activation has only recently been piloted in cognitively impaired lupus patients. I believe there's maybe only one or two studies out there. So though this is a promising tool potentially to interrogate microglial activation in NPSLE patients, more work will still need to be done to verify its utility as a diagnostic tool. But I think we're on the way.

Melanie Cole (Host): What a great interview. And as we wrap up, do you have anything you'd like to tell other providers? What's next for you when it comes to this area of study or what you would like them to know are the key takeaways from this podcast?

Dr Carla Cuda: So, yeah, I think, at the bench side, we're trying to figure out what is an underlying cause and I think it's really difficult to dissect. But I'm hoping, from this podcast, that it will be taken away, that potentially microglia are a root cause, something happening early in disease prior to any contributions of systemic involvement. This has always been the Issue with lupus, is that what comes first? Does a systemic disease cause potentially a breakdown in the blood-brain barrier, which then leads to infiltration of either a cell type or a circulating meteor that affects the brain? Or is the brain itself already having changes early on which then contribute to having these manifestations occur?

And what's interesting too is that sometimes the neuropsychiatric manifestations predate actual lupus diagnosis. So, you know, they'll give a patient diagnosis of lupus and find out that, years earlier, there was some event, which potentially was the first start of their lupus. So, I think these pieces of information that are in the literature and scattered throughout lead us to believe that there's probably something happening within the brain, potentially within microglial populations. And because we're never going to get brain biopsies from patients and we understand that, we have to utilize these mouse models in as many ways as possible to dissect out disease pathogenesis.

And so, we hope to get buy-in from providers to see if we can collect samples from patients if possible, to really try to move what we find in the mouse models to patients, and that's what we hope the gold standard.

Melanie Cole (Host): Thank you so much, Dr. Cuda, for joining us. And I hope you'll come on again and update us as things progress in your research. Thank you again. And to refer your patient or for more information, please visit our website at breakthroughsforphysicians.nm.org/rheum, that's R-H-E-U-M, to get connected with one of our providers. And that concludes this episode of Better Edge, a Northwestern Medicine Podcast for physicians. I'm Melanie Cole.