Expression and regulation of alarmin cytokine IL-1α in human retinal pigment epithelial cells. (July 2018)

• Record Type: Journal Article
• Authors: Bian, Zong-Mei; Field, Matthew G.; Elner, Susan G.; Elner, Victor M.
• Is Part Of: Experimental eye research. Volume 172(2018)
• Page Start: 10
• Page End: 20
• Publication Date: 2018-07
• Subjects: Retinal pigment epithelium -- RPE -- IL-1α -- Interleukin-1α -- Caspase-4 -- Non-canonical inflammasome -- TLR2 -- TLR4; Ophthalmology -- Periodicals; Eye -- Periodicals; Œil -- Périodiques; Ophthalmology; Periodicals; Electronic journals; 612.8405
• DOI: 10.1016/j.exer.2018.03.015
• Languages: English
• ISSNs: 0014-4835

Abstract

Abstract: Human retinal pigment epithelial (hRPE) cells play important immune-regulatory roles in a variety of retinal pathologic processes, including the production of inflammatory cytokines that are essential mediators of the innate immune response within the ocular microenvironment. The pro-inflammatory "alarmin" cytokine IL-1α has been implicated in both infectious and non-infectious retinal diseases, but its regulation in the retina is poorly understood. The purpose of this study was to elucidate the expression and regulation of IL-1α within hRPE cells. To do this, IL-1α mRNA and protein in hRPE cells was assessed by RT-PCR, qPCR, ELISA, Western blot, and immunofluorescence following treatment with a variety of stimuli and inhibitors. ER stress, LPS, IL-1β, and TLR2 activation all significantly increased intracellular IL-1α protein. Increasing intracellular calcium synergized both LPS- and Pam3CSK4-induced IL-1α protein production. Accordingly, blocking calcium signaling and calpain activity strongly suppressed IL-1α protein expression. Significant but more moderate inhibition occurred following blockage of TLR4, caspase-4, or caspase-1. Neutralizing antibodies to IL-1β and TLR2 partially eliminated LPS- and TLR2 ligand Pam3CSK4-stimulated IL-1α protein production. IFN-β induced caspase-4 expression and activation, and also potentiated LPS-induced IL-1α expression, but IFN-β alone had no effect on IL-1α protein production. Interestingly, all inhibitors targeting the PI3K/Akt pathway, with the exception of Ly294002, strongly increased IL-1α protein expression. This study improves understanding of the complex mechanisms regulating IL-1α protein expression in hRPE cells by demonstrating that TLR4 and TLR2 stimulation and exposure to IL-1β, ER stress and intracellular calcium all induce hRPE cells to produce intracellular IL-1α, which is negatively regulated by the PI3K/Akt pathway. Additionally, the non-canonical inflammasome pathway was shown to be involved in LPS-induced hRPE IL-1α expression through caspase-4 signaling. Highlights: hRPE cells upregulate IL-1α expression in response to pro-inflammatory signals. IL-1α production is negatively regulated by the PI3K/Akt pathway. LPS induces the non-canonical inflammasome in hRPE cells via caspase-4 signaling. Non-canonical inflammasome activation promotes IL-1α expression.