RNA Methylation Enzyme METTL1 Drives Deadly Inflammation in Sepsis and Organ Injury
Scientists identify a key RNA-modifying enzyme that fuels runaway macrophage inflammation, offering a promising new drug target for sepsis and organ damage.
Summary
Researchers at Anhui Medical University discovered that METTL1, an enzyme that adds m7G chemical tags to RNA, drives harmful macrophage inflammation during acute kidney injury and sepsis. METTL1 stabilizes Sarm1 mRNA, which triggers a drop in NAD+ — a molecule critical for cellular energy and longevity. When METTL1 was genetically deleted in immune cells, mice were protected from multi-organ damage in sepsis models. A new pharmacological inhibitor, SA91-0178, replicated these protective effects. This research uncovers a previously unexplored RNA modification pathway in macrophages and positions METTL1 as a viable therapeutic target for systemic inflammatory conditions.
Detailed Summary
Uncontrolled macrophage inflammation is a central driver of sepsis, acute kidney injury, and multi-organ failure — conditions with high mortality and limited treatment options. Understanding the molecular switches that tip macrophages toward damaging inflammatory states is critical for developing effective therapies.
This study investigated the role of N7-methylguanosine (m7G) RNA modification — a chemical tag added by the enzyme METTL1 — in macrophage biology. The researchers observed elevated METTL1 and m7G levels in macrophages from both mouse and human tissues during acute kidney injury, suggesting a disease-relevant upregulation of this pathway.
Using genetic deletion of METTL1 specifically in myeloid cells, the team showed that loss of this enzyme significantly reduced inflammatory responses and protected mice from multi-organ damage in two clinically relevant models: cecal ligation and puncture (a sepsis model) and renal ischemia/reperfusion injury. Mechanistically, METTL1 was found to stabilize Sarm1 mRNA through m7G modification. SARM1 protein activity causes NAD+ depletion, disrupting macrophage metabolic reprogramming — a process known to fuel inflammatory activation. Restoring SARM1 expression reversed the protective effects of METTL1 deletion, confirming the pathway's centrality.
Critically, a small-molecule inhibitor of METTL1 called SA91-0178 recapitulated the genetic findings, reducing tissue injury in septic inflammation models and validating pharmacological tractability of this target.
These findings add m7G RNA modification to the growing list of epitranscriptomic mechanisms — alongside m6A — that regulate immune cell function. For the longevity field, the NAD+ connection is particularly significant, as NAD+ decline is a hallmark of aging and drives many age-related pathologies. Caveats include reliance on mouse models and limited human data.
Key Findings
- METTL1 and m7G RNA modifications are elevated in macrophages during acute kidney injury in mice and humans.
- Myeloid-specific METTL1 deletion protects mice from multi-organ damage in sepsis and ischemia-reperfusion models.
- METTL1 stabilizes Sarm1 mRNA via m7G methylation, leading to NAD+ depletion and metabolic reprogramming in macrophages.
- Pharmacological METTL1 inhibitor SA91-0178 reduces tissue injury in septic inflammation models.
- This identifies m7G modification as a previously unexplored epitranscriptomic regulator of macrophage inflammatory responses.
Methodology
The study used myeloid-specific genetic knockout mouse models alongside two in vivo inflammatory models: cecal ligation and puncture for sepsis and renal ischemia/reperfusion for acute kidney injury. Mechanistic findings were supported by SARM1 overexpression rescue experiments and validated pharmacologically with the METTL1 inhibitor SA91-0178. Human tissue macrophage data were also incorporated.
Study Limitations
The study relies primarily on mouse models, with human data limited to observational tissue analysis rather than functional studies. The pharmacological inhibitor SA91-0178 is not yet clinically tested, and long-term or systemic effects of METTL1 inhibition on immunity remain unknown.
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