Role of Fgl2 in macrophage polarization during acute kidney injury in mice

To investigate the role of fibrinogen-like protein 2 (Fgl2) in macrophage polarization during cisplatin (Cis)-induced acute kidney injury (Cis-AKI).

Twelve male wild-type (Fgl2^+/+) mice and 12 Fgl2 gene knockout (Fgl2^-/-) mice, aged 8~10 weeks and weighing 20~25 g, were selected, and then after being administered with a single intraperitoneal injection of either saline or Cis for 3 d, they were randomly divided into 4 groups (n=6): Fgl2^+/+ Saline group, Fgl2^+/+ Cis group, Fgl2^-/- Saline group and Fgl2^-/- Cis group. Kidney function indicators such as serum creatinine (Scr) and blood urea nitrogen (BUN) levels were measured 3 d later, and kidney injury was assessed by HE staining. Western blot analysis was performed to evaluate the expression of Fgl2 and kidney injury molecule 1 (Kim-1) in the renal tissues. RT-qPCR was conducted to assess the expression levels of Fgl2, Kim-1, neutrophil gelatinase-associated lipocalin (NGAL), IL-6, IL-12p40, IL-1β, inducible nitric oxide synthase (iNOS) and TNF-α in the renal tissues. Immunohistochemical assay was employed to detect the expression of Fgl2 and macrophages (F4/80⁺) in the kidneys. Immunofluorescence staining was utilized to examine the expression of macrophages (F4/80⁺) and M1-type macrophages (F4/80⁺CD86⁺) in the renal tissues. Flow cytometry was employed to analyze the expression of macrophages (F4/80⁺) as well as M1-type macrophages (F4/80⁺MHC Ⅱ⁺) and M2-type macrophages (F4/80⁺CD206⁺) in the renal tissues.

Compared with the Fgl2^+/+ Saline group, the Fgl2^+/+ Cis group exhibited a significant decline in renal function (P<0.05), a notable increase in pathological score of renal tubular injury (P<0.05), and an obvious upregulation of renal tissue Fgl2 expression (P<0.05). Compared with the Fgl2^+/+ Cis group, the Fgl2^-/- Cis group demonstrated a significant decline in renal function (P<0.05), an elevation in the expression of renal injury-associated molecules Kim-1 and NGAL (P<0.05), an increase in pathological score of renal tubular injury (P<0.05), increase in macrophage infiltration (P<0.05), and an upregulation in the expression of M1-type macrophage-related molecules IL-6, IL-1β, TNF-α and iNOS (P<0.05), as well as obviously increase in the percentage of M1-type macrophages as indicated by flow cytometry (P<0.05), while there was no significant change in the percentage of M2-type macrophages, and the proportion of M1-type macrophages was significantly higher than that of M2-type macrophages (P<0.05).

Fgl2 gene knockout exacerbates Cis-AKI by promoting macrophage polarization towards the M1 phenotype.