Injury-Induced Epithelial Spp1 Engages Cd44 to Promote Neutrophil Recruitment and Exacerbate Acute Kidney Injury

Acute kidney injury (AKI) severely impairs renal function. In early AKI, tubular cells release damage-associated molecular patterns (DAMPs) that induce neutrophil recruitment. Infiltrating neutrophils can exacerbate kidney injury through degranulation or formation of neutrophil extracellular traps (NETs), but the specific DAMPs mediating early neutrophil chemotaxis remain unclear.

We integrated single-cell and spatial transcriptomic data from early AKI kidneys to identify signaling pathways underlying crosstalk between injured tubular cells and neutrophils. A murine unilateral ischemia-reperfusion injury (uIRI) model was then established, with intraperitoneal administration of the anti-inflammatory drug mesalazine (5-aminosalicylic acid, 5-ASA) during the perioperative period, followed by assessment of renal histopathology and function. In vitro, polymorphonuclear neutrophils (PMNs) were isolated from mouse peripheral blood and co-cultured with renal tubular cells in a Transwell migration system under hypoxia/reoxygenation (H/R), with 5-ASA treatment or Spp1 knockdown to evaluate effects on PMN migration.

Integrated single-cell and spatial transcriptomic analyses revealed that injured tubular cells upregulate Spp1, which interacts with Cd44 on neutrophils. In vivo and in vitro, injured tubular cells released Spp1 in a paracrine manner, enhancing Cd44⁺ neutrophil migration, impairing tubular regeneration, and aggravating AKI progression. 5-ASA attenuated this process by suppressing Spp1 expression and paracrine signaling, thereby reducing early Cd44⁺ neutrophil infiltration, promoting tubular cell proliferation, and improving renal function.

This study provides the first evidence that tubular cell-derived Spp1 functions as a key DAMP mediating the early recruitment of Cd44⁺ neutrophils in AKI. By inhibiting paracrine Spp1, 5-ASA limits neutrophil migration and ameliorates renal injury, supporting its therapeutic potential in AKI. Targeting Spp1 may represent a promising new strategy for AKI treatment.