Adenosine Kinase and ADAL Coordinate Detoxification of Modified Adenosines to Safeguard Metabolism

RNA contains diverse post-transcriptional modifications, and its catabolic breakdown yields numerous modified nucleosides requiring correct processing, but the mechanisms remain unknown. Here, we demonstrate that three RNA-derived modified adenosines, N6-methyladenosine (m6A), N6,N6-dimethyladenosine (m6,6A), and N6-isopentenyladenosine (i6A), are sequentially metabolized into inosine monophosphate (IMP) to mitigate their intrinsic cytotoxicity. After phosphorylation by adenosine kinase (ADK) they undergo deamination by adenosine deaminase-like (ADAL). In Adal knockout mice, N6-modified adenosine monophosphates (AMPs) accumulate and allosterically inhibit AMP-activated protein kinase (AMPK), dysregulating glucose metabolism. Furthermore, ADK deficiency, linked to human inherited disorders of purine metabolism, elevates levels of the three modified adenosines, resulting in early lethality in mice. Mechanistically, excessive m6A, m6,6A, and i6A impairs lysosomal function by interfering with lysosomal membrane proteins, thereby disrupting lipid metabolism and causing cellular toxicity. Through this nucleotide metabolism pathway and mechanism, cells detoxify modified adenosines, linking modified RNA metabolism to human disease. Overall design: To investigate the impact of ADK and ADAL-mediated metabolism of m6A, m6,6A, i6A, we generated constitutive ADK knockout mice and ADAL knockout mice. We performed RNA-seq using liver and brain from age-matched postnatal ADK KO mice and WT mice (P4), and liver, soleus, and gastrocnemius (GC) muscle of adult ADAL KO mice and WT mice at age of 10-weeks-old.