The Immunomodulatory Role of Math-Only Proteins (MOPs) in Macrophages and Ankylosing Spondylitis

Objectives Inflammation is a fundamental immune defense that protects the body from infection, injury, and tissue damage. However, exacerbated or unresolved inflammation contributes to chronic autoimmune disorders such as spondyloarthritis and rheumatoid arthritis.[1] Meprin and TRAF-C Homology (MATH) domain-containing proteins, including TRAF1-6 and Speckle-type POZ protein (SPOP), regulate immune signaling through Toll-like receptor (TLR)-NF-κB pathways (Figure 1).[1-3] Recent evidence demonstrates that SPOP suppresses inflammation by promoting MyD88 degradation, underscoring the anti-inflammatory potential of MATH-containing proteins.[2,3] Both TRAF and SPOP contain additional catalytic or adaptor domains, leaving the function of proteins composed exclusively of the MATH domain unexplored. In both human and mouse genomes, genes encoding only the MATH domain have been identified; we designate these as MATH-only proteins (MOPs). This study aims to characterize MOPs and investigate whether their overexpression mitigates inflammatory responses in macrophages. Methods A mixed-methods design integrating in vitro and in vivo approaches was employed. Bone-marrow-derived macrophages (BMDMs) from C57BL/6 and SKG mice, and human THP-1 macrophages, were stimulated with LPS (100 ng/mL). MOP isoforms (murine: 37, 11, 246; human: 212, 217, 220) and cytokines (IL-1β, IL-10) were quantified by RT-qPCR. Lentiviral constructs (pLenti-MOP 212, 220) were packaged in HEK293T cells (psPAX2 + pMD2.G) and used to transduce THP-1 cells. Phospho-flow cytometry assessed NF-κB (p65) and MAPK (ERK1/2) activation, while curdlan-treated SKG mice served as an in vivo model of autoimmune inflammation (Figure 1.2). Results Our results demonstrate that MOPs expression were significantly induced upon LPS stimulation in both murine and human macrophages (Figure 1.3-4). In BMDMs, MOP 37, 11, and 246 peaked at 6 h post-LPS, paralleling IL-10 expression. In THP-1 cells, MOP 212 and 217 were progressively upregulated to 48 h. In the SKG in-vivo model, MOPs were elevated, validating the relevance of these pathways (Figure 1.5). MOP-220 overexpression in THP-1 cells selectively enhanced NF-κB and reduced ERK signaling (Figure 1.6), leading to upregulation of inflammatory cytokines (IL-1β, TNF-α) at the mRNA level. Together, findings highlight MOPs as potential modulators of inflammatory signaling (Figure 1.7). Conclusion This study identifies and characterizes MATH-only proteins (MOPs) as novel regulators of inflammation. MOPs expression is dynamically induced by TLR activation in murine and human systems and correlates with cytokine responses in vivo. These findings suggest that MOPs may modulate NF-κB and MAPK-driven cytokine signaling, providing a new molecular framework for immunoregulation. Ongoing MOPs overexpression and knockout studies aim to delineate their mechanisms in chronic inflammation and autoimmune disease. References [1.] Abdul-Sater AA. Nat Immunol 2017;18:26-35. [2.] Nakamura A. Sci Transl Med 2021;13:eabg1210. [3.] Hu YH. Cell Mol Immunol 2021;18:1708-17.