Effect and Mechanism of CircPTPN4 Expression in Carboxylated Single-Walled Carbon Nanotubes on Renal Fibrosis

Abstract

This research was aimed to investigate the effect of circPTPN4 overexpression in carboxylated single-walled carbon nanotubes (SWCNT-COOH) on renal fibrosis (RF) in mice. SWCNT was oxidized to SWCNT-COOH by concentrated sulfuric acid and nitric acid (3:1, v/v). After characterization and analysis, the effect of SWCNT-COOH on erythrocyte status was detected. The RF mice (RFM) model was induced by SWCNT-COOH, normal mice as normal control (NC), and 1×108 TU/mL lenti-NC was injected into the tail vein as negative control, and 1×108 TU/mL lenti-circPTPN4 was injected for circPTPN4 overexpression. The expression of circPTPN4 was tested by qRT-PCR. Serum creatinine (Cr), blood urea nitrogen (BUN), interleukin 1β (IL-1β), IL-6, transforming growth factor β1 (TGF-β1), kidney injury molecule 1 (KIM-1), and neutrophil gelatinase-associated lipocalin (NGAL) were tested by ELISA. HE, Masson, and immunohistochemistry were used to detect the pathological changes of kidney tissue. The protein expressions of collagen I (COL1), fibronectin (Fn), α-SMA, TGF-β1, Smad3, p-Smad3, and Smad7 were tested by Western blot (WB). It presented SWCNT-COOH was successfully prepared by chemical oxidation method, with an average particle size of 98.1 nm and an average Zeta potential of −38.91 mV. SWCNT-COOH had good hydrophilicity, and did not cause aggregation and morphology changes of red blood cells. As against NC, the expression of circPTPN4 in RFM and lenti-NC groups was decreased; the kidney coefficient was increased, and the normal structure of the kidney was abnormal, accompanied by inflammatory cell infiltration and collagen microformation; serum Cr, BUN, IL-1β, IL-6, and TGF-β1 were increased, and KIM-1 and NGAL in renal cortex were decreased; the protein expressions of COL1, Fn, α-SMA, TGF-β1, and p-Smad3 in the kidney were increased, and the protein expression of Smad7 was decreased (P <0.05). As against RFM, the expression of circPTPN4 in lenti-circPTPN4 group was increased; the kidney coefficient decreased and the kidney structure returned to normal; COL1, Fn, α-SMA, TGF-β1, and p-Smad3 in the kidney were decreased, and that of Smad7 was increased (P <0.05). SWCNT-COOH has good blood compatibility characteristics and can induce RF in mice. The expression of circPTPN4 was down-regulated in the RFM. Overexpression of circPTPN4 can restore the normal renal function of RFM, inhibiting the inflammatory response and RF process.