Geranylgeranylacetone-Induced HSP70 Modulates AQP4 Trafficking via SNX27-Retromer to Alleviate Retinal Ischemia/Reperfusion Injury.

Retinal ischemia/reperfusion (I/R) injury is a major cause of vision loss, characterized by retinal edema and progressive retinal ganglion cell (RGC) death. Aquaporin-4 (AQP4), a water channel abundantly expressed in glial cells, plays a pivotal role in edema formation by regulating water homeostasis. Geranylgeranylacetone (GGA), a clinically approved anti-ulcer drug, functions as a potent and non-toxic inducer of heat shock protein 70 (HSP70) and has recently been implicated in the regulation of aquaporin trafficking. In parallel, the sorting nexin 27 (SNX27)-retromer complex is a key mediator of endosomal sorting and recycling of membrane proteins back to the plasma membrane, thereby maintaining their functional activity. In this study, we demonstrate that retinal I/R injury triggers altered subcellular localization of AQP4, with enhanced internalization compared with sham retinas. Concomitantly, SNX27-retromer expression was significantly upregulated at both mRNA and protein levels, and biochemical as well as imaging assays confirmed its interaction with AQP4. In a pre-ischemia dosing paradigm (prophylactic), GGA markedly attenuated retinal edema and RGC loss, and promoted the interaction between HSP70 and the SNX27-retromer complex. Importantly, GGA treatment reduced SNX27-retromer expression, thereby limiting AQP4 recycling to the plasma membrane and favoring its lysosome-associated trafficking. These effects were largely reversed by quercetin, a pharmacological inhibitor of HSP70, highlighting an HSP70-dependent mechanism. Together, our findings identify a previously unrecognized role of HSP70 in regulating SNX27-retromer-mediated AQP4 trafficking. By disrupting AQP4 recycling, GGA alleviates early retinal edema following I/R injury, providing mechanistic rationale for future therapeutic development.