The brain's sweet spot: why microglia can run on fructose metabolism

Microglia are the resident myeloid cells of the central nervous system (CNS), and their identity and function are shaped by developmental origin, local signaling, and metabolic specialization. The fructose transporter GLUT5 (SLC2A5) stands out as a selective and conserved microglial marker that remains strongly associated with resident microglia across homeostatic and disrupted CNS states. In the CNS, fructose appears to be regulated locally rather than reflecting circulating levels, raising the possibility that fructose metabolism serves a unique functional role in microglia. Recent studies suggest that this pathway has a meaningful functional role. Fructose availability in the CNS can directly reshape microglial behavior by altering phagocytosis, redox balance, metabolic state, and downstream immune signaling in contexts ranging from neurodevelopment to glioblastoma. Our recent study showed that microglia fructose metabolism in glioblastoma drives an immunosuppressive state, limiting antigen presentation and downstream anti-tumor immunity. In this review, we examine microglial identity and metabolism in the context of GLUT5 and fructose uptake, summarize evidence that fructose acts as a context-dependent regulator of microglial function, and discuss how this may reflect broader metabolic strategies used by resident cells in distinct fluid and tissue barriers. We propose that microglial fructose metabolism is not simply an incidental feature of these cells, but a biologically meaningful feature of CNS physiology with important implications for development, injury, and disease, though the mechanistic basis of this relationship remains an active area of investigation.