Single-granule profiling reveals that RNP granule pH marks cellular translation

Ribonucleoprotein (RNP) granules reshape RNA metabolism in eukaryotic cells, yet their biophysical properties remain poorly understood due to the lack of probes targeting these small, dynamic condensates. Herein, we developed RNP granule-pH (RNPg-pH), a ratiometric and targetable probe, to map the pH of processing bodies (P-bodies) and stress granules (SGs) at the single-granule level. This approach revealed a spatial pH heterogeneity within RNP granules, with a more alkaline periphery and a more acidic region near the nucleus. Stresses including oxidative stress, hyperosmotic stress, and translational inhibition induced granule acidification and reduced translation level, suggesting that RNPg-pH served as a sensitive marker of translation activity. Notably, compounds like myrtenol and oridonin reversed hydrogen peroxide (H₂O₂)-induced acidification, restored translation activity, and delayed cellular senescence, implying that RNPg-pH has the potential for screening anti-aging reagents. Our work provides an approach for monitoring RNP granules, shedding light on their roles in RNA metabolism and cell functions.