# Inosine promotes erythrocyte metabolic reprogramming and restores oxygen release for rejuvenation via 2,3-BPG-PNP axis

## TL;DR

This study shows that inosine helps aging red blood cells release more oxygen by compensating for metabolic changes, offering a potential therapy for age-related tissue dysfunction.

## Contribution

The study identifies inosine as a rejuvenating therapy for aging by linking 2,3-BPG-PNP axis to RBC metabolic reprogramming.

## Key findings

- Aging reduces RBC oxygen release due to decreased 2,3-BPG levels and BPGM activity.
- Inosine compensates for impaired glucose metabolism in aging RBCs by being converted to ribose 1-phosphate.
- 2,3-BPG inhibits PNP activity, and its decline during aging increases inosine catabolism as an alternative fuel.

## Abstract

Aging-related diseases are aggravated by tissue hypoxia; however, the underlying mechanism remains unknown. Here, we report that the oxygen (O2) release capacity of red blood cells (RBCs) gradually decreases with age and is closely associated with aging-related tissue dysfunction. Metabolomic profiling of human and mouse RBCs and genetic studies in mice revealed that the reduction in 2,3-bisphosphoglyceric acid (2,3-BPG) content mediated by a decrease in bisphosphoglycerate mutase (BPGM) activity is a metabolic checkpoint underlying decreased RBC O2 release capability and dysfunction with advancing age. When glucose metabolism is impaired, erythroid inosine, transported by equilibrative nucleoside transporter 1 and converted to ribose 1-phosphate by increased purine nucleoside phosphorylase (PNP) activity, is an important compensatory fuel for RBCs during aging. In a preclinical study, inosine supplementation successfully alleviated the age-dependent reduction in BPGM activity that mediates glucose metabolic impairment, decreased O2 delivery, and tissue dysfunction. Finally, we unexpectedly discovered that 2,3-BPG acts as an inhibitor of PNP in RBCs by competing with the phosphate (Pi)-binding domain and interacting with residues serine 33 and alanine 116. Our studies revealed that impaired glucose metabolic reprogramming resulting from decreased BPGM activity underlies RBC bioenergetic decline and is a novel hallmark of aging. As 2,3-BPG levels decrease during aging, its inhibitory effect on PNP is reduced, resulting in increased PNP activity and inosine catabolism as an alternative fuel, suggesting that inosine is a potential rejuvenating therapy.