Suppression of PTPN6 exacerbates aluminum oxide nanoparticle-induced COPD-like lesions in mice through activation of STAT pathway

Abstract

Background: Inhaled nanoparticles can deposit in the deep lung where they interact with pulmonary cells. Despite numerous studies on pulmonary nanotoxicity, detailed molecular mechanisms of specific nanomaterial-induced lung injury have yet to be identified.

Results: Using whole-body dynamic inhalation model, we studied the interactions between aluminum oxide nanoparticles (Al₂O₃ NPs) and the pulmonary system in vivo. We found that seven-day-exposure to Al₂O₃ NPs resulted in emphysema and small airway remodeling in murine lungs, accompanied by enhanced inflammation and apoptosis. Al₂O₃ NPs exposure led to suppression of PTPN6 and phosphorylation of STAT3, culminating in increased expression of the apoptotic marker PDCD4. Rescue of PTPN6 expression or application of a STAT3 inhibitor, effectively protected murine lungs from inflammation and apoptosis, as well as, in part, from the induction of chronic obstructive pulmonary disease (COPD)-like effects.

Conclusion: In summary, our studies show that inhibition of PTPN6 plays a critical role in Al₂O₃ NPs-induced COPD-like lesions.

Keywords: Aluminum oxide nanoparticles; PTPN6; Experimental COPD; Inflammation.

Fig. 1

Pulmonary inflammation induced by Al₂O₃ NPs exposure. a sRAW was significantly increased in Al₂O₃ NPs-exposed mice (n = 10, ^* P < 0.05, compared with controls; ^*** P < 0.001, compared with control on the same day). b Inflammatory mediators were significantly increased in Al₂O₃ NPs-exposed BALF of mice (n = 4, ^* P < 0.05, ^** P < 0.01). c The total cell number, monocytic cells number and neutrophils number in BALF of Al₂O₃ NPs-exposed mice were significantly increased compared with FRA control (n = 4, ^* P < 0.05, ^*** P < 0.001). d Representative images of normal airway and airway surrounded by inflammatory cells (showed by arrow). e Representative images of distant alveoli (FRA control) f Representative images of macrophages, lymphocytes and neutrophil infiltration in alveolar area (Al₂O₃ NPs exposure) (shown by arrow). The images in the right bottom of each panel are magnified of the cell in original images highlighted with black arrows

Fig. 2

Exposure to Al₂O₃ NPs led to experimental COPD in a murine model. a Representative images of normal alveolar area and emphysema. The images on the right bottom of each panel are magnified (400) of area from the original one. b Lm was significantly increased in Al₂O₃ NPs-exposed mouse lungs (n = 36, ^*** P < 0.001). c Representative images of PAS staining, the PAS⁺ cells suggested hypersecretion of airway epithelial cells (shown by arrows). d Representative images of Masson’s Trichorome staining. Deposit of collagen around airway was stained purple. e Representative images of TUNEL staining and percentage of TUNEL⁺ cells. The TUNEL⁺ cells were shown by arrows. (n = 30, ^*** P < 0.001, compared with control group)

Fig. 3

Overexpression of PTPN6 inhibited PDCD4 expression levels both in vitro and in vivo. a expression of PTPN6, PDCD4, BAX and APP in mouse lungs exposed to Al₂O₃ NPs (n = 10, ^* P < 0.05, ^** P < 0.01, ^*** P < 0.001). b mRNA and protein expression levels of PTPN6, PDCD4, BAX and APP in A549 and HBE cells (n = 6, ^* P < 0.05, compared with vehicle-treated control, ^** P < 0.01, compared with vehicle-treated control, ^*** P < 0.001, compared with vehicle-treated control, ^## P < 0.01, compared with vehicle/Al₂O₃ NPs-exposed group, ^### P < 0.001, compared with vehicle/Al₂O₃ NPs-exposed group). c Representative images of PDCD4 expression in mouse lung tissues. LTV: lentivirus; OEX: overexpression

Fig. 4

PTPN6 inhibited PDCD4 expression in a STAT3-dependent manner. a Representative images of p-STAT3 in mouse lung tissues. b The STAT3 inhibitor (S3I-201) inhibited activation of STAT3 and expression of PDCD4 in A549 and HBE cells. c The STAT3 inhibitor (S3I-201) did not inhibit expression of PTPN6 in mouse lung tissues (n = 6, ^*** P < 0.001, compared with vehicle control). d The STAT3 inhibitor (S3I-201) inhibited expression of PDCD4 in mouse lung tissues (n = 6, ^*** P < 0.001, compared with vehicle control, ^### P < 0.001, compared with Al₂O₃ NPs-treated vehicle mice). e Representative images of PDCD4 expression in mouse lung tissues f Representative images of emphysema and Lm in mouse lungs (n = 36, ^** P < 0.01, compared with vehicle control, ^*** P < 0.001, compared with vehicle control, ^### P < 0.001, compared with Al₂O₃ NPs-exposed vehicle mice). g Representative images of airway remodeling and thickness of fibrosis layer around airway in mouse lungs (n = 36, ^*** P < 0.001, compared with vehicle control, ^### P < 0.001, compared with Al₂O₃ NPs-exposed vehicle mice)

Fig. 5

Overexpression of PTPN6 rescued experimental COPD in mouse model. a sRAW of conscious mice (n = 10, ^* P < 0.05, compared with WT control, ^*** P < 0.001, compared with WT control, ^### P < 0.001, compared with Al₂O₃ NPs-exposed WT mice). b Levels of inflammatory mediators in BALF (n = 4, ^*** P < 0.001, compared with WT control, ^### P < 0.001, compared with Al₂O₃ NPs-exposed WT mice). c Expression levels of MMP-9 in mouse lungs (n = 6, ^** P < 0.01, compared with WT control, ^# P < 0.05, compared with Al₂O₃ NPs-exposed WT mice). d Representative images of emphysema and Lm in mouse lungs (n = 36, ^* P < 0.05, compared with WT control, ^*** P < 0.001, compared with WT control, ^## P < 0.01, compared with Al₂O₃ NPs-exposed WT mice). e Representative images of airway remodeling and thickness of fibrosis layer around airway in mouse lungs (n = 36, ^* P < 0.05, compared with WT control, ^*** P < 0.001, compared with WT control, ^### P < 0.001, compared with Al₂O₃ NPs-exposed WT mice). f Representative images of TUNEL staining and percentage of TUNEL⁺ cells in airway epithelia and alveolar epithelia (n = 30, ^*** P < 0.001, compared with WT control, ^## P < 0.01, ^### P < 0.001, compared with Al₂O₃ NPs-exposed WT mice)

Fig. 6

Key molecular pathway involved in Al₂O₃ NPs-induced COPD-like lesions