NLRX1 increases human retinal pigment epithelial autophagy and reduces H2O2-induced oxidative stress and inflammation by suppressing FUNDC1 phosphorylation and NLRP3 activation

Abstract

Background: Age-related macular degeneration (AMD) is a leading cause of impaired vision as well as some earlier effects, such as reading and face recognition. Oxidative damage and inflammation of retinal pigment epithelial (RPE) cells are major causes of AMD. Additionally, autophagy in RPE cells can lead to cellular homeostasis under oxidative stress. Nucleotide-binding oligomerization domain (NOD)-like receptor X1 (NLRX1) is a mysterious modulator of the immune system function which inhibits inflammatory response, attenuates reactive oxygen species (ROS) production, and regulates autophagy. This study attempted to explore the role of NLRX1 in oxidative stress, inflammation, and autophagy in AMD. Methods: An in vitro model of AMD was built in human retinal pigment epithelial cell line 19 (ARPE-19) treated with H2O2. The cell viability, NLRX1 expressions, levels of superoxide dismutase (SOD), glutathione (GHS), and ROS, concentrations of interleukin (IL)-1β, tumor necrosis factor-α (TNF-α), IL-6, and monocyte chemoattractant protein-1 (MCP-1), expressions of NLRX1, p62, LC3-II/LC3-I, FUNDC1, and NOD-like receptor protein 3 (NLRP3) inflammasome were expounded by cell counting kit-8, colorimetric, enzyme-linked immunosorbent serologic assay (ELISA), and Western blot assay. Results: H2O2 treatment notably reduced the relative protein expression of NLRX1. Meanwhile, H2O2 incubation decreased cell viability, diminished SOD and GSH concentrations, accompanied with the increased level of ROS, enhanced IL-1β, TNF-α, IL-6, and MCP-1 concentrations, and aggrandized the relative protein expression of p62 with reduced LC3-II/LC3-I ratio. Moreover, these results were further promoted with knockdown of NLRX1 and reversed with overexpression. Mechanically, silencing of NLRX1 further observably enhanced the relative levels of phosphorylated FUNDC1/FUNDC1, and NLRP3 inflammasome-related proteins, while overex-pression of NLRX1 exhibited inverse results in the H2O2-induced ARPE-19 cells. Conclusion: NLRX1 suppressed H2O2-induced oxidative stress and inflammation, and facilitated autophagy by suppressing FUNDC1 phosphorylation and NLRP3 activation in ARPE-19 cells.

Potential application of traditional Chinese medicine in age-related macular degeneration—focusing on mitophagy

“…Frontiers in Pharmacology frontiersin.org protein, nucleotide-binding oligomerization domain (NOD)-like receptor X1 (NLRX1), an immune system regulator, is known to diminish inflammatory responses, reduce ROS generation, and regulate autophagy. Increased NLRX1 expression reduces the relative levels of FUNDC1 phosphorylation and NLRP3 inflammasome-associated proteins in ARPE-19 cells, thereby preventing the development of AMD (Wang et al, 2023a). The exact mechanism of FUNDC1 action in mitophagy in AMD is not well characterized; however, studies suggest that the FUNDC1 pathway plays an integral role in obesity and metabolic disorders (Tan et al, 2018;Ren et al, 2020), as the excessive intake of saturated fatty acids affects the stability of mitophagy receptor FUNDC1 and mitochondrial mass, leading to mitochondrial dysfunction, obesity, and metabolic disorders (Chen et al, 2023).…”

Autophagy Activation Promoted by Pulses of Light and Phytochemicals Counteracting Oxidative Stress during Age-Related Macular Degeneration

“…The disorder is clinically evident as a loss of visual acuity [ 1 ] and the presence of visual distortion (metamorphopsia) [ 1 , 2 , 3 ]. At early stages, visual impairment is restricted to specific skills such as reading text and facial recognition [ 4 ]. In fact, the disease mostly impairs those photoreceptors placed in the macula, which provide the highest visual discrimination and feed the highest cortical integration [ 2 , 4 ].…”

“…At early stages, visual impairment is restricted to specific skills such as reading text and facial recognition [ 4 ]. In fact, the disease mostly impairs those photoreceptors placed in the macula, which provide the highest visual discrimination and feed the highest cortical integration [ 2 , 4 ]. This is why, at early stages, AMD involves those photoreceptors projecting to the primary visual cortex that carry information to be delivered within the cortical ventral stream [ 5 ], thus providing the inputs which allow facial recognition.…”

“…This mostly occurs in the RPE as well as within outer segment of cones placed in the external retina, which are included between the cell processes of the RPE. In fact, outer retina and mostly RPE are primarily affected in the course of AMD [ 3 , 4 , 11 , 12 ]. This is mainly due to the physiological role of RPE, which is constantly engaged by a large number of reactive oxygen species (ROS) produced during direct exposure to natural light in the macula.…”

“…A number of mechanisms and stimuli are powerful autophagy inducers; the intense research in the field of retinal metabolism provides increasing evidence of multiple facets of retinal autophagy beyond counteracting retinal oxidation. For instance, in a recent study, Wang et al [ 4 ] demonstrated that RPE cells produce nucleotide-binding oligomerization domain (NOD)-like receptor X1 (NLRX1), an autophagy inducer, which counteracts retinal oxidative damage and inflammation. In fact, ROS trigger the formation of pro-inflammatory compounds in the retina such as interleukin 1beta (IL-1β), tumor necrosis factor alfa (TNF-α), IL-6 and macrophage proteine-1 (MCP-1) [ 4 ] ( Figure 2 ).…”