Upregulation of NLRP3 Inflammasome in the Tears and Ocular Surface of Dry Eye Patients.

Liangliang Niu,Ling Chen,Jihong Wu,Yan Wang,Shujie Zhang,Fulvio D'Acquisto

doi:10.1371/journal.pone.0126277

Liangliang Niu, Ling Chen + Show 4 more

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https://doi.org/10.1371/journal.pone.0126277

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Abstract

PurposeTo evaluate the mRNA and protein expressions of NLRP3 inflammasome and its downstream inflammatory factors in human dry eye.MethodsWe recruited 54 patients with Sjögren’s syndrome dry eye (SSDE), 50 patients with non-Sjögren’s syndrome dry eye (NSSDE), and 46 healthy controls. Tear film breakup time (TBUT), Schirmer I test, and fluorescein staining (FL) were performed on all subjects. Tear samples were obtained to analyze the inflammatory cytokine levels of IL-1β and IL-18 via enzyme-linked immunosorbent (ELISA). Conjunctival impression cytology (CIC) specimens were collected to detect the mRNA expression of NLRP3, caspase-1, IL-1β, and IL-18 using quantitative RT-PCR, and the protein expression of NLRP3 and caspase-1 by Western blotting.ResultsNLRP3 mRNA expression showed higher levels in both dry eye groups compared with controls, with a comparably significant elevation in the SSDE group (relative 2.47-fold upregulation, p<0.05). NLRP3 protein expression was also increased in SSDE group (relative1.94-fold upregulation) compared with the controls. mRNA expression of caspase-1 was significantly upregulated in both SSDE (relative 1.44-fold upregulation, p<0.05) and NSSDE (relative 1.32-fold upregulation, p<0.05). Procaspase-1 protein level was increased in SSDE (relative 1.84-fold upregulation) and NSSDE (relative 1.12-fold upregulation) versus controls; and caspase-1 protein expression was also increased in SSDE (relative 1.49-fold upregulation) and NSSDE (relative 1.17-fold upregulation) compared with the controls. The patients with SSDE and NSSDE had higher IL-1β and IL-18 mRNA values and protein expressions than the controls did. The relative mRNA expression of IL-1β upregulated 3.59-fold (p<0.001) in SSDE and 2.13-fold (p<0.01) in NSSDE compared with the controls. IL-1β protein level also showed significant upregulation in SSDE (p=0.01; vs. controls groups). IL-18 mRNA expression levels were significantly upregulated in the SSDE (relative 2.97-fold upregulation, p=0.001) and NSSDE (relative 2.05-fold upregulation, p=0.001) groups compared with the controls; tear IL-18 concentrations were also significantly increased in the SSDE (p<0.001) and NSSDE (p<0.05) groups.ConclusionsIn the current study, we found that mRNA and protein expressions of NLRP3 inflammasome were upregulated in human dry eyes, especially in SSDE; the downstream inflammatory factors caspase-1, IL-1β, and IL-18 were also elevated in dry eye patients. These observations suggest the involvement of NLRP3 inflammasome in the onset and development of the inflammation in dry eye.

Highlights

Dry eye is one of the most common ocular surface disorders that significantly affect the quality of human life
Nod-like receptor family pyrin domain containing 3 (NLRP3) protein expression was increased in s syndrome dry eye (SSDE) group compared with the controls. mRNA expression of caspase-1 was significantly upregulated in both SSDE and nonSjögren’s syndrome dry eye (NSSDE)
Procaspase-1 protein level was increased in SSDE and NSSDE versus controls; and caspase-1 protein expression was increased in SSDE and NSSDE compared with the controls

Summary

Introduction

Dry eye is one of the most common ocular surface disorders that significantly affect the quality of human life. The pathogenesis of dry eye has not been established clearly, there is increasing evidence that immune-based inflammation on the ocular surface might play a prominent role in the pathological damage of dry eye [1, 2]. The inflammasome is an intracellular protein complex that is stimulated by pathogen-associated molecular patterns (PAMPs) or danger-associated molecular patterns (DAMPs). It can activate procaspase, causing cleavage of pro-IL-1β and pro-IL-18. Previous studies have demonstrated critical roles for NLRP3 inflammasome activation in the immune responses of many diseases, such as asthma [14], T-cell-dependent immune complex glomerulonephritis[15], acute graft-versus-host disease (GvHD)[16], systemic lupus erythematosus (SLE)[17], metabolic disorders like type 2 diabetes[18], gout, and pseudogout [19]. Several reports found NLRP3 inflammasome involved the pathology of the age-related macular degeneration [20,21,22]

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