Posted December 8, 2023

Betsy Barnes, Ph.D., Feinstein Institute for Medical Research

Betsy Barnes, Ph.D., Feinstein Institute for Medical Research
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Systemic lupus erythematosus (SLE) is a form of lupus associated with severe clinical manifestations and significant organ damage. Innate immunity factors are part of the body’s defense system. Proteins such as interferons (IFNs), absent in melanoma 2 (Aim2), ubiquitin-conjugating enzyme E2I (Ube2i), and apoptosis-associated speck-like protein containing a caspase recruitment domain (Asc) are key components to immune responses. These factors may contribute to the development and severity of SLE. Aim2 is a DNA sensor that recognizes pathogens and regulates inflammation responses. Aim2 recruits Asc to help perform inflammasome functions. Previous research has suggested that Aim2 deficiency contributes to SLE severity.1 In vivo research (within a living organism) is more representative of human conditions as compared to in vitro research (in a petri dish). In vivo evidence of Aim2 activity has been lacking, and Dr. Barnes’ research sought to fill this gap.

With a Fiscal Year 2017 Impact Award, Dr. Barnes was funded to investigate the function of such innate immune regulators in SLE. This study compared strains of mice deficient in Aim2 and Asc to healthy mice. Researchers injected mice with either pristane, a lupus-inducing agent, or saline, and monitored the various strains for survival. Researchers extracted blood from the mice and evaluated antibody levels using an enzyme-linked immunoassay (ELISA). They also extracted kidney sections and stained kidney cells to determine antibody levels. After pristane injection, Aim2-deficient mice developed severe SLE while none of the ASC-deficient mice developed SLE and all survived healthily. This indicates that Aim2 functions to protect mice from pristane-induced lupus, while Asc-deficient mice were protected from disease development. Aim2-deficient mice produced increased amounts of antibodies and IFN-stimulated genes even after saline injection. Independent of the injection, mice with lower levels of Aim2 were more likely to develop SLE.

Furthermore, plasmacytoid dendritic cells (pDCs), cells that secrete IFNs, were present in significantly higher numbers in the kidneys of Aim2-deficient mice than in healthy mice, even in the absence of pristane. Researchers assumed the IFN signature would also be high; however, interferon-alpha (IFNα) and interferon-beta (IFNβ) mRNA were only slightly elevated in the kidneys of Aim2-deficient mice. This implies there may be a different expression of inflammatory factors between cells in vivo and cells in vitro. Researchers determined that not all aspects of adaptive immunity contribute to SLE development in Aim2-deficient mice.

For further analysis, researchers utilized a yeast two-hybrid screen, a common technique for the examination of protein-protein interactions, to figure out what molecules interact with Aim2. The Mouse Kidney Matchmaker cDNA Library indicated the most frequent binding partner to Aim2 was Ube2i. The research team confirmed the interaction between Aim2 and Ube2i in yeast cells. Aim2 acts like a chaperone for Ube2i, making sure it functions properly. Ube2i is necessary for sumoylation, which is a process that regulates protein interactions and immune responses. Without sumoylation signals, IFN responses are overpowering. The excessive production of IFNs can lead to unnecessary inflammation. Researchers determined that when Aim2 is absent, the altered Ube2i activity led to excessive production of IFNs and development of severe SLE.

Understanding the mechanisms by which SLE develops provides an opportunity to target aspects of the pathways to hinder pathogenesis. Because SLE can cause severe symptoms and organ damage, the discovery and development of effective treatments is vital. The study team discovered that SLE severity is more likely due to increased IFN signals than inflammasome functions. Providing in vivo evidence, this research revealed the Aim2-Ube2i complex is a prime target for intervention. Dr. Barnes and her team hope further research can use the discovery of this immune complex to implement targeted therapies for the treatment of SLE to improve quality of life.

Publications:
Lu A, Wu S, Niu J, et al. 2021. Aim2 couples with Ube2i for sumoylation‐mediated repression of interferon signatures in systemic lupus erythematosus. Arthritis & Rheumatology 73(8):1467-1477.

References:
¹ Choubey D, and Panchanathan R. 2017. Absent in melanoma 2 proteins in SLE. Clinical Immunology 176:42-48.

Link:
Public and Technical Abstracts: Targeting IRF5 Hyperactivation in SLE as a Driver of Disease Risk and Pathogenesis

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Last updated Friday, December 8, 2023