Diminished SUV3 expression and its functional implications in the IFN-enriched monocyte subset of childhood Sjögren's...

This study investigates the molecular and functional implications of reduced Suv3-like RNA helicase (SUV3) expression in the interferon (IFN)-enriched subset of monocytes from childhood Sjögren's disease (cSjD). SUV3 is known to unwind double-stranded RNAs (dsRNAs) for homeostatic RNA decay within mitochondria.

Using single-cell RNA sequencing, we analysed highly inflammatory IFN-enriched CD14+ monocytes from cSjD patients. To model SUV3 deficiency, we performed SUV3 knockdown in monocytic cells and studied the origin, localization and accumulation of dsRNAs in the cytosol. Formaldehyde crosslinking immunoprecipitation (fCLIP)-qPCR identified an intracellular sensor of dsRNAs. We further examined patient monocytes using J2 anti-dsRNA antibodies and transmission electron microscopy (TEM) for subcellular localization. In vitro assays assessed the impact of SUV3 knockdown on oxidative stress, ATP production, migration and phagocytosis.

SUV3 knockdown led to the accumulation of mitochondrial-dsRNAs (mt-dsRNAs) outside of the mitochondria, where they interacted with protein kinase R (PKR). This activated PKR, triggering a type I IFN signature and upregulating proinflammatory cytokines linked to fatigue. TEM revealed mt-dsRNAs in mitochondrial-derived vesicles and multi-vesicular bodies. Notably, cSjD monocytes had a significantly higher frequency of dsRNA-positive cells compared with controls (39% vs 0.08%, P < 0.002). SUV3 depletion also increased superoxide and ROS production, while impairing ATP synthesis, migration and phagocytosis, which are key innate immune functions. These defects were partially or fully reversed by co-knockdown of PKR.

SUV3 is the key driver for defective innate immune functions through mt-dsRNA-mediated PKR activation, which enhances cellular stress, mitochondrial dysfunction and inflammatory signatures, uncovering a novel mechanism in cSjD pathogenesis.