Zinc Signaling in Acute Kidney Injury

Acute kidney injury (AKI) is a life-threatening event prevalent in hospitalized patients but also not rare among endurance sports athletes. Hypoxia, oxidative stress, and sterile inflammation are the key pathophysiological factors driving kidney damage in AKI. Zinc is an essential trace element required for the intact function of approximately 3000 proteins (~10% of the human proteome), including over 300 enzymes for which zinc serves as a cofactor. Cell biological tasks of zinc signaling include adaptive responses to hypoxia and oxidative stress, as well as anti-inflammatory effects. The underlying molecular pathways involve modulation of hypoxia-inducible factor signaling, suppression of reactive oxygen species (ROS) generation, and inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), the latter being the major pro-inflammatory transcription factor. As a catalytic cofactor for the "classical" histone deacetylases, zinc is essential for epigenetic control of gene expression, thereby exerting further adaptive effects. Apart from the intracellular zinc signaling, extracellular zinc elicits cytoprotective and anti-inflammatory effects via the G Protein-Coupled Receptor 39 (GPR39). GPR39 activation by zinc binding may exert antioxidant and anti-inflammatory effects mediated by the zinc-finger protein A20 (TNFAIP3) and NF-κB suppression, followed by reduced production of pro-inflammatory cytokines such as tumor necrosis factor (TNF), interleukin-1β (IL-1β), and IL-6. At the same time, GPR39 signaling may stimulates the release of the anti-inflammatory cytokine IL-10, thus shifting the kidney tissue towards an anti-inflammatory milieu, promoting renal recovery. The present review focuses on the role of zinc in AKI to identify potential therapeutic strategies targeting zinc signaling for renoprotection and biomarker-based risk stratification.