By Lila Rouland | Published September 16, 2025 | 3 min read
#ModifiedRNA
#ADK #ADAL #CellularToxicity #Metabolism #Purines #AMPK #MetabolicDiseases
#Lysosomes #Pharmacology
RNAs
undergo more than 170 post-transcriptional modifications. Their degradation
generates modified nucleosides, some of which are toxic. This study identifies
N6-methyladenosine (m⁶A), N6,N6-dimethyladenosine (m⁶,⁶A), and
isopentenyladenosine (i⁶A) as particularly cytotoxic. A conserved metabolic
mechanism involving adenosine kinase (ADK) and adenosine deaminase-like (ADAL)
transforms these nucleosides into inosine monophosphate (IMP). Inactivation of
this pathway leads to severe cellular toxicity, glucose intolerance, and
lysosomal dysfunction.
Fast
detox: how cells clear threatening adenosines
Tests in 14 human cell lines showed that m⁶A, m⁶,⁶A, and i⁶A significantly
reduce cell viability in a dose-dependent manner. Injected into mice, these
nucleosides are rapidly metabolized, without plasma or urinary accumulation,
pointing to enzymatic detoxification rather than excretion.
When RNA
turns toxic, ADK steps in
High-throughput screening identified ADK as the key enzyme phosphorylating m⁶A,
m⁶,⁶A, and i⁶A. Deletion of ADK caused toxic accumulation of these nucleosides
and postnatal lethality in mice. In vitro, ADK efficiently phosphorylated these
substrates into m⁶AMP, m⁶,⁶AMP, and i⁶AMP, with catalytic activity comparable
to unmodified adenosine.
RNA
detox: ADAL turns danger into useful metabolites
ADAL then deaminates these modified nucleotides into IMP, a harmless metabolite
reintegrated into purine biosynthesis. In ADAL-KO cells and mice, modified AMP
species accumulate, though levels of native IMP and AMP remain stable,
suggesting compensatory mechanisms. Molecular modeling shows ADAL’s strict
specificity for modified substrates through its catalytic DD motif and
conserved hydrophobic fold.
When
modified RNAs disrupt blood sugar
Modified AMPs allosterically inhibit AMPK, a master regulator of glucose
metabolism. Adal-KO mice showed glucose intolerance, reduced fasting AMPK
activation, and downregulation of carbohydrate metabolism genes. Docking
simulations confirmed that these nucleotides bind at AMPK’s CBS3 site, blocking
native AMP activation.
When ADK
falters, lipid metabolism collapses
Human ADK mutations (e.g., G13E, D218A), associated with hepatic and
neurological disorders, abolish enzymatic activity for modified substrates.
ADK-deficient mice display reduced lipogenic enzymes (FASN, SCD1), induction of
autophagy, and decreased fatty acid uptake. Contrary to earlier hypotheses,
these effects do not depend on methionine metabolism.
Lysosomes:
first victims of toxic RNAs
Biotinylated adenosine interactome analysis revealed binding to lysosomal
proteins, particularly ATP6V1A, a subunit essential for lysosomal
acidification. Accumulation of modified nucleosides disrupts this localization,
reduces ATPase activity, raises lysosomal pH, and triggers lysosomal cell death
(LCD). The lysosomal membrane stabilizer quinacrine restored lysosomal and
lipid functions, confirming this mechanism of toxicity.
An
ancestral metabolic pathway with major clinical implications
This work uncovers a new biosynthetic pathway for IMP from modified RNAs,
linking epitranscriptome biology to energy metabolism. The ADK–ADAL axis acts
as an essential detoxification system. Its dysfunction is implicated in
diabetes, lipid disorders, and hepatic and neurological diseases. These
findings open therapeutic avenues targeting purine metabolism imbalances.
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About the author – Lila Rouland
Doctor of Oncology, specialized in Biotechnology and Management
