Viable RNaseH1 knockout mice show RNaseH1 is essential for R loop processing, mitochondrial and liver function

Area of Science:

• Molecular Biology
• Hepatology
• Mitochondrial Biology

Background:

• Ribonucleic acid-hybrid (RNA-DNA) hybrids, or R-loops, are nucleic acid structures implicated in various cellular processes.
• RNase H1 is an enzyme that degrades RNA in RNA-DNA hybrids, playing a role in maintaining genome stability and regulating gene expression.

Purpose of the Study:

• To investigate the function of RNase H1 in hepatocytes and its role in mitochondrial homeostasis and liver function.
• To determine the necessity of RNase H1 for the efficacy of antisense oligonucleotides (ASOs).

Main Methods:

• Generation of liver-specific RNase H1 knockout mice (constitutive and tamoxifen-inducible models).
• Analysis of R-loop levels, mitochondrial DNA and mRNA, mitochondrial morphology, and liver integrity.
• Assessment of RNase H1 activity in vitro and in vivo using antisense oligonucleotides.

Main Results:

• RNase H1 knockout hepatocytes exhibited elevated R-loop levels and reduced mitochondrial DNA/mRNA, indicating impaired mitochondrial transcription and replication.
• Mitochondrial dysfunction, characterized by altered fusion/fission dynamics and morphology, was observed.
• Liver degeneration, including apoptosis and fibrosis, occurred, alongside elevated transaminase levels.
• RNase H1 was demonstrated to be essential for the activity of DNA-like ASOs.

Conclusions:

• RNase H1 is critical for processing R-loops in mitochondria, maintaining mitochondrial DNA and mRNA levels, and supporting overall liver function.
• RNase H1 is indispensable for the therapeutic activity of DNA-like ASOs.
• Partial restoration of mitochondrial and liver function was observed during liver regeneration in RNase H1-expressing hepatocytes.