ABSTRACT Through our multidisciplinary clinical and research collaboration, we have established a rare cohort of children and adolescents who fulfilled the 2016 adult Sjögren’s disease (SjD) criteria (namely, cSjD for childhood Sjögren’s disease). Since autoimmune SjD typically affects elderly females, whether cSjD is a unique disease entity or an early manifestation of SjD is completely unknown. The overall goal is to characterize mechanisms by which mitochondrial dsRNAs (mtdsRNA) are released into the cytoplasm and activate the cytosolic dsRNA sensor, protein kinase R (PKR), for the proinflammatory signature found in cSjD CD14+ monocytes. Our preliminary data from scRNA-seq of cSjD monocytes revealed the aberrant expression of mtdsRNA processors, such as SUV3 (ATP-dependent RNA helicase, suppressor of variegation 3, SUPV3L1 gene) and PNPase (polyribonucleotide nucleotidyltransferase, PNPT1 gene), PKR, type I IFN signature (I-IFN), STAT1, and CD52. A higher percentage of cSjD monocytes were positive for particulate cytoplasmic dsRNA with downregulated SUV3 and upregulated PNPase when compared to healthy control monocytes. SUV3-deficient cell lines concurred consistently with cytoplasmic mtdsRNA accumulation, PKR activation, and ISG induction. In addition, we found mitochondrial RNA binding proteins (mtRBPs) crucial in maintaining mtdsRNA stability within the matrix and novel endogenous short duplex RNAs (e-sdRNA) bound to PKR, which may sequester PKR as a monomer to prevent its activation. Furthermore, our scRNA-seq data of PBMC clearly pinpoint CD52 downregulation detected only in cSjD monocytes compared to monocytes from other pediatric groups or adult SjD. Therefore, we propose our novel central hypothesis that defective mtdsRNA degradation by the aberrant SUV3 and PNPase expression in the mitochondria leads to cytoplasmic mtdsRNA accumulation, which activates the cytosolic dsRNA sensor, PKR, in cSjD monocytes. The three proposed aims included: Aim 1. Characterize PKR sensing of mtdsRNA in cSjD monocytes. We will determine if PKR is the key cytosolic sensor for autologous mtdsRNAs in I-IFN+CD14+cSjD Mo and if novel e-sdRNAs bound to PKR regulate its activation. Aim 2. Identify molecules involved in impaired mtdsRNA degradation and release into the cytoplasm. We will identify the impact of upregulated PNPase in cSjD Mo by hypothesizing that PNPase overexpression amplifies PKR activation through the degradation of e-sdRNAs bound to PKR. Additionally, novel mtRBPs will be tested to determine if they permit mtdsRNA to escape into the cytoplasm by altering the methylation status of mitochondrial transcripts. Aim 3. Stratify biological and clinical features of cSjD for precision medicine. We will test if the downregulation of anti- inflammatory, anti-adhesion CD52 in cSjD Mo is mediated by the mtdsRNA-PKR-STAT1 pathway to enhance extravasation through endothelial cells for tissue homing. We will also stratify transcriptomic, immunological, genetic,...