Molecular Therapy

Doubling Down on Mitochondrial dsRNAs in Sjӧgren’s Syndrome

Courtney Bricker-Anthony, PhD - January 06, 2023

From the Molecular Therapy family: Read a summary on mitochondrial double-stranded RNAs and watch our first-ever video abstract.

Led by researchers at the Korea Advanced Institute of Science and Technology (KAIST), an international team discovered a new role for mitochondrial double-stranded RNA (dsRNA) in the pathogenesis of Sjögren’s syndrome, as reported in their recent article in Molecular Therapy – Nucleic Acids.

In Sjögren’s syndrome, a chronic autoimmune disease broadly characterized by dry eye and mouth, cytotoxic T cells attack tear and salivary glands. These immune cells drive inflammation and tissue damage that impair tear and saliva production, causing significant pain and discomfort. Although the exact cause of Sjögren’s syndrome is unclear, some researchers have hypothesized that viral infection triggers the initial immune response.

In support of this hypothesis, a type I interferon (I-IFN) signature has been detected in patient biopsies and blood samples, suggesting an immune response raised against viral dsRNAs. However, Joon and colleagues noted that both viral dsRNAs and endogenous mitochondrial dsRNAs can activate the pattern recognition receptors that produce the I-IFN signature. Moreover, the high levels of oxidative stress and mitochondrial dysfunction in Sjögren’s salivary gland tissue could drive increased generation of mitochondrial dsRNAs, amplifying the I-IFN signaling initially triggered by viral dsRNAs. To test the hypothesis that mitochondrial dsRNAs contribute to aberrant I-IFN signaling and glandular dysfunction in Sjögren’s, Joon and colleagues analyzed tear and saliva samples from patients, salivary glands from Sjögren’s model mice, and 2D and 3D human salivary gland acinar cell cultures.

Strand-specific reverse transcription revealed elevated expression of mitochondrial dsRNAs in tear and saliva samples from patients with Sjögren’s, and strand-specific RT-qPCR showed similar results in salivary gland tissue from aged NOD mice, a commonly used Sjögren’s animal model. Poly(I:C) stimulation, used to mimic viral dsRNA exposure, upregulated cytosolic release of mitochondrial dsRNAs in both 2D and 3D acinar cell cultures. This resulted in increased interaction between mitochondrial dsRNAs and the pattern recognition receptor protein kinase R (PKR), which could drive further I-IFN signaling. Poly(I:C) treatment also downregulated water channel aquaporin 5 (AQP5) and tight junction proteins zonula occludens-1 (ZO-1) and occludin, indicating compromised secretory function.

Since acetylcholine-mediated secretory function is impaired in Sjögren’s, the authors applied acetylcholine to acinar cell cultures to examine its effect. The application of acetylcholine attenuated both I-IFN signaling and the induction of mitochondrial dsRNAs, but the depletion of mitochondrial dsRNAs diminished the effect of acetylcholine on I-IFN signaling, indicating that mitochondrial dsRNAs mediate acetylcholine’s protective effect. The authors also co-applied patient-derived IgGs and acetylcholine to salivary gland cells stimulated with poly(I:C) and confirmed that IgGs upregulate I-IFN signaling and mitochondrial RNA expression, effectively interfering with acetylcholine’s protective effects.

Further experiments revealed the induction of mitochondrial dsRNAs and I-IFN signaling is dependent upon the JAK/STAT pathway. In acinar cell cultures pre-treated with a JAK1 inhibitor (upadacitinib), the authors found a significant reduction in mitochondrial dsRNAs and IFN signaling following poly(I:C) application. Decreased phosphorylation of PKR and increased cell viability were also observed.

In a final series of experiments, the authors demonstrated that mitochondrial dsRNAs exacerbate the immune response triggered by poly(I:C). DEG analysis and RT-qPCR revealed that depletion of mitochondrial dsRNAs in acinar cell cultures prior to poly(I:C) application decreased the expression of genes linked to I-IFN signaling. Mitochondrial dsRNA depletion also decreased PKR phosphorylation and I-IFN signaling, in addition to partially rescuing cell viability and preserving the expression of AQP5, ZO-1, and occludin.

Overall, these experiments provide evidence of a mechanistic role for mitochondrial dsRNAs in the pathogenesis of exocrine dysfunction in Sjögren’s syndrome. Yoon and colleagues speculate that mitochondrial dsRNAs detected in tear/saliva samples could serve as a biomarker to aid diagnosis. Furthermore, therapeutics targeting mitochondrial dsRNA synthesis or decay could help break the cycle of PKR stimulation, I-IFN signaling, and glandular dysfunction.

Video Abstract: Ectopic clotting factor VIII expression and misfolding in hepatocytes as a cause for hepatocellular carcinoma

Watch our first video abstract on Molecular Therapy's website and YouTube. U.S. and Canadian researchers studied how FVIII misfolding impacts hepatocellular carcinoma development using hepatocyte DNA delivery to express three proteins from the same parental vector: (1) well-folded cytosolic dihydrofolate reductase (DHFR); (2) BDD-FVIII, which is prone to misfolding in the ER; and (3) N6-FVIII, which folds more efficiently than BDD-FVIII.

Learn more about what the researchers found below.

ASGCT members can publish research in the journals for a discount! Learn more and share your research with us.

Courtney Bricker-Anthony, PhD, is ASGCT's scientific editor.

 

Related Articles

Molecular Therapy

Hear Dr. Maxim Berezovski on the Molecular Therapy Podcast

Listen now! - February 13, 2024
Molecular Therapy

Hear Dr. Richard Vile on the Molecular Therapy Podcast

Listen now! - January 09, 2024
ASGCT News

Mohamed Abou-el-Enein Appointed Editor of Molecular Therapy Methods and Clinical Development

Dr. Abou-el-Enein began five-year term Jan. 1. - January 04, 2024
Molecular Therapy

First Episode of Molecular Therapy Podcast Features Dr. Norbert Pardi

Listen now! - December 12, 2023