Background/Purpose: Juvenile Dermatomyositis (JDM) is a rare pediatric inflammatory myopathy with a complex pathophysiology. Previously our group showed a significant increase in Otoferlin mRNA expression in JDM patients’ PBMCs and muscle compared to healthy controls. Otoferlin is a member of the dysferlin family, which plays an essential role in regulating calcium-sensitive exocytosis in inner ears sensory hair cells. To understand the role of this novel aspect of JDM disease pathophysiology, we next identified the cell expressing of Otoferlin and its association with disease activity in untreated children with JDM.

Methods: This IRB approved study was conducted at the Ann & Robert H. Lurie Children’s Hospital of Chicago. Otoferlin expression was determined by qRT-PCR in peripheral blood mononuclear cells from untreated children with JDM and age, race, sex matched controls. The arm to freezer time was held at 2 hours or less. Clinical and laboratory variables, including age, gender, duration of untreated disease (DUD) and Disease Activity Scores (DAS skin, muscle, total), MSA, neopterin, and the status of the TNFα 308 allele were obtained from the Lurie Children’s Juvenile Myositis Registry REDCap database. To identify cells expressing otoferlin, the cells were first stained with live dead stain to exclude dead cell. The following surface markers were determined (CD45, CD3, CD19, CD16, CD56, CD14 and CD11b) to characterize the otoferlin positive cells. We fixed and permeabilized the cells and then stained for cytoplasmic otoferlin expression. The otoferlin positive cells were primarily B cells; more detailed flow cytometry was performed with the following markers (CD19, IgM, IgD, IgG, CD27, CD21, CD24 and CD38) to characterize these B cells further.

Results: 30 untreated JDM (87% female, 90 % white, 43% P155/140+ve, 13% MJ+ve. 13% Mi-2+ve ,7% MDA+ve) and 15 healthy controls were included in this study. With the live dead stain (trypan blue) the cells were >90% viable. There was a significant increase in otoferlin expression in JDM children compared to controls (Median 47.6 vs. 2.1; p=0.002). There was a positive correlation between mRNA otoferlin expression and disease activity markers: neopterin (R²=0.33, p=0.003), DAS-total (R²=0.23 p=0.008), DAS-Muscle (R²=0.18, p=0.024). Of note, otoferlin expression was not associated with DAS-Skin. Otoferlin expression was assessed by flowcytometry in 8 JDM patients and 3 controls which showed an increased percentage of otoferlin positive lymphocyte (Median 1.9% vs. 0.2% p= 0.03). The majority of the otoferlin positive cells were B cells (63% – 99.4%). Detailed B cell phenotyping in two samples showed that these B cells were IgD+, IgM+ CD27- naive B cell with 65-75% of them expressing plasmablast markers (CD19+, IgM+, CD38 hi, CD24-).

Conclusion: In this pilot study, we found that otoferlin expression by qRT-PCR was associated with muscle weakness, suggesting its possible utility as a biomarker of disease activity. Furthermore, we identified B cells and plasmablasts as the primary cells expressing otoferlin. Further investigation is required to identify the role of otoferlin in both B cell activation and its contribution to JDM pathophysiology.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/increased-otoferlin-expression-in-b-cells-is-associated-with-muscle-weakness-in-untreated-juvenile-dermatomyositis-a-pilot-study/