H3K18 lactylation-mediated SPHK1-SIRT1 feedback loop accelerates pyroptosis of tubular epithelial cells in sepsis-associated acute kidney injury

BACKGROUND: Lactate accumulation exacerbates the severity of sepsis-associated acute kidney injury (SA-AKI), although the mechanism remains unclear. Since pyroptosis contributes to renal tubular epithelial cell (RTEC) death during SA-AKI, this study explores whether lactate exacerbates pathogenesis by promoting RTEC pyroptosis. METHODS: The clinical correlation between lactate and SA-AKI was examined using the Medical Information Mart for Intensive Care IV (MIMIC-IV) database and patient samples. Lactate's role in RTEC pyroptosis was evaluated in lipopolysaccharide (LPS)-exposed HK-2 cells and in cecal ligation and puncture (CLP)-induced mice. Cross-analyzing bioinformatics and RNA-seq data from LPS/lactate-exposed HK-2 cells revealed pyroptosis genes associated with SA-AKI. Molecular mechanisms were explored via Western blot, ELISA, mitochondrial function assays, chromatin immunoprecipitation (ChIP), and co-immunoprecipitation (co-IP). High-throughput drugs screening was conducted to identify candidates acting on the Sphingosine kinase 1(SPHK1)/Sirtuin 1(SIRT1) axis, which were validated in vitro and in vivo. RESULTS: Lactate aggravated SA-AKI by promoting RTEC pyroptosis. Bioinformatic and functional studies identified SPHK1 as the key mediator. Both SPHK1 knockdown and its inhibitor PF-543 alleviated lactate-augmented pyroptosis. Drug screening identified nicotinamide adenine dinucleotide (NAD⁺), which simultaneously suppressed SPHK1 expression and the RTEC injury marker kidney injury molecule-1 (KIM-1). Combining NAD⁺ and PF-543 synergistically attenuated SA-AKI. Sepsis-induced lactate accumulation promoted P300-mediated histone H3 lysine 18 lactylation (H3K18la) at the SPHK1 promoter, epigenetically enhancing its transcription. SPHK1 then phosphorylated and degraded SIRT1, inducing peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α) hyperacetylation, thereby impairing SIRT1/PGC-1α signaling and triggering NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-driven pyroptosis. Reciprocally, SIRT1 acted as a delactylase delactylase to reduce H3K18la and inhibit SPHK1 transcription, forming a SPHK1-SIRT1 negative feedback loop. CONCLUSIONS: The study identifies an H3K18la-mediated SPHK1-SIRT1 axis as a key factor of RTEC pyroptosis in SA-AKI. The combined pharmacological strategy of NAD⁺ supplementation and SPHK1 inhibition represents a promising therapeutic strategy for SA-AKI.