Spatial transcriptomics uncovers progressive osteopontin expression, mitochondrial dysfunction, and IL-6 inflammatory signature in dermatomyositis-associated calcinosis cutis

Summary: Abstract Body: To understand the pathophysiology of calcinosis cutis in dermatomyositis, we conducted spatial transcriptomics on 4 active calcinosis samples from adult DM patients meeting 2017 ACR/EULAR criteria and 3 control samples from healthy adults. Analysis revealed a distinct inflammatory signature characterized by elevated IL-6 expression, upregulation of macrophage markers CD68 and MSR1, and increased expression of IgG/A heavy, light, and J chains (p<0.01). ECM composition showed global dysregulation, with elevated MMPs 1/9/13, cartilage-specific collagens X and XI, and markedly increased osteopontin, a glycoprotein implicated in pathological calcification (p<0.01). UMAP analysis identified distinct clusters of spatial transcriptomic spots arranged such that linear movement through UMAP space traversing these clusters corresponded to increasing calcification burden. Differential expression analysis along this trajectory revealed three distinct phases. The early, pre-calcific phase showed barrier dysfunction, immunoglobulin transcription, elevated IL-6 target gene FOS expression, and loss of stemness maintenance genes (p<0.01). The middle, propagative remodeling phase was characterized by enhanced MMP9 expression, increased transcription of lysosomal enzymes, and distinctly dysregulated extracellular matrix deposition (p<0.01). The late-stage calcification phase exhibited increased expression of 11 mitochondrial genes, and ferritin heavy and light chains (p<0.01), suggesting an oxidative stress response. Osteopontin expression increased consistently until final transition to acellular calcification (p<0.01). These findings reveal a complex pathogenic cascade involving early antibody synthesis and macrophage recruitment, IL-6/FOS signaling, extracellular matrix dysregulation, and mitochondrial dysfunction leading to eventual tissue replacement with calcinosis. This spatial analysis provides the first detailed molecular map of calcinosis progression in dermatomyositis. Cassie Parks¹, York Wang¹, Lisa Christopher-Stine¹, Shira Ziegler¹, Joel Sunshine¹, Chistopher Mecoli¹ 1. Johns Hopkins University, Baltimore, MD, United States. Adaptive and Auto-Immunity