Centromere Instability Drives Chromosome Damage and Autoantigen Exposure in Systemic Sclerosis

Systemic sclerosis (SSc) is a fibrotic autoimmune disease in which genomic sources of instability and their immunological consequences remain poorly defined. We show that bleomycin, a widely used SSc fibrosis model, induces DNA double-strand breaks (DSBs) at active centromeres. Similar centromeric damage signatures were observed in fibroblasts from patients with limited cutaneous SSc, consistent with prior observations. Quantification of α-satellite repeat content revealed dynamic changes in repeat abundance, consistent with deletions and insertions and incomplete restoration following damage. These breaks are repaired primarily ATM-dependent, RAD51-associated homologous recombination, but repair remains incomplete. Incomplete repair is associated with altered kinetochore assembly, chromosome missegregation, and increased formation of micronuclei and cytoplasmic chromatin enriched in centromere proteins. These fragments escape via nuclear envelope rupture and show spatial colocalization with MHC class II molecules. Together, these findings establish bleomycin-induced centromere damage as a tractable model to study active-centromere instability, its incomplete repair, and the resulting chromatin mislocalization in fibroblasts, with features relevant to systemic sclerosis.