# HBP21 Alleviates Sepsis-Induced Acute Kidney Injury by Targeting PI3K/AKT-Mediated M1 Macrophage Polarization

## TL;DR

HBP21 reduces kidney damage in sepsis by shifting macrophages to an anti-inflammatory state through the PI3K/AKT pathway.

## Contribution

HBP21's novel role in modulating macrophage polarization via PI3K/AKT signaling to treat sepsis-induced kidney injury is demonstrated.

## Key findings

- HBP21 overexpression promotes M2 macrophage polarization and activates PI3K/AKT signaling.
- HBP21 reduces tubular cell apoptosis and improves kidney function in a rat model of sepsis-induced AKI.
- Blocking PI3K/AKT reverses HBP21's protective effects, confirming pathway involvement.

## Abstract

Background: Sepsis-induced acute kidney injury (S-AKI), a life-threatening complication of systemic infection, is driven by macrophage-mediated inflammatory dysregulation. This study explores the role of heat shock binding protein 21 (HBP21) in attenuating renal injury through PI3K/AKT pathway modulation, employing cellular and animal models to dissect its therapeutic mechanisms and clinical relevance.

Methods: In vitro, RAW264.7 cells underwent LPS-induced M1 polarization, and HBP21 expression was manipulated to evaluate its role in macrophage phenotype and PI3K/AKT signaling activation. M1/M2 macrophage polarization was quantified by flow cytometry, while coculture with NRK-52E cells evaluated tubular epithelial cell viability (CCK-8) and apoptosis (flow cytometry). An S-AKI rat model was induced via cecal ligation and puncture (CLP). Renal function (serum creatinine [Scr]/blood urea nitrogen [BUN]), tissue damage (hematoxylin and eosin [H&E]/terminal dUTP nick-end labeling [TUNEL]), and inflammation (Western blot/IHC) were systematically analyzed.

Results: HBP21 overexpression promoted M2 macrophage polarization and activated PI3K/AKT signaling in LPS-stimulated macrophages. Knockdown of HBP21 obtained the opposite data. Inhibition with LY294002 or activation with 740 Y-P reversed these effects, confirming pathway involvement. Cocultured NRK-52E cells exposed to conditioned medium from HBP21-overexpressing macrophages showed a 62.32% increase in viability and a 56.11% reduction in apoptosis under LPS challenge. HBP21 overexpression in vivo lowered Scr (38.5%) and BUN (47.4%), alleviated tubular damage, and shifted renal macrophages toward an M2 anti-inflammatory phenotype with concurrent TNF-α/IL-6 downregulation.

Conclusion: These findings suggest that HBP21 mitigates S-AKI pathogenesis via PI3K/AKT-mediated M2 macrophage polarization, underscoring its translational potential in renal injury therapy.