Indole-3-carbinol regulates microglia homeostasis and protects the retina from degeneration

• Published in: Journal of neuroinflammation Vol. 17; no. 1; p. 327
• Main Authors: Khan, Amir Saeed, Langmann, Thomas
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 03-11-2020; BioMed Central; BMC
• Subjects: Animals; Apoptosis - drug effects; Aryl hydrocarbon receptor; Biological products; Biotechnology; Blindness; Care and treatment; Caspase-3; Cell culture; Cell death; Cell Line; Cytology; Enzyme-linked immunosorbent assay; Female; Gene expression; Health aspects; Homeostasis; Homeostasis - drug effects; Immunoglobulins; Immunomodulation; Indole-3-carbinol; Indoles; Indoles - pharmacology; Indoles - therapeutic use; Inflammation; Inflammation - chemically induced; Inflammation - drug therapy; Inflammation - pathology; Interleukin 6; Ligands; Light damage; Lipopolysaccharides; Male; Mice; Microglia; Microglia - drug effects; Microglia - pathology; Mimicry; Monocyte chemoattractant protein 1; Neurodegeneration; Neurodegenerative diseases; Neuroprotection; Neuroprotective Agents - pharmacology; Neuroprotective Agents - therapeutic use; Phagocytosis; Phagocytosis - drug effects; Photoreceptors; Proteins; Retina; Retina - drug effects; Retina - pathology; Retinal degeneration; Retinal Degeneration - prevention & control; Western blotting; Germany; St Louis Missouri; United States > US; Indole-3-carbinol; Retinal degeneration; Aryl hydrocarbon receptor; Light damage; Microglia
• ISSN: 1742-2094; 1742-2094
• DOI: 10.1186/s12974-020-01999-8

Retinal degenerative diseases significantly contribute to visual impairment and blindness. Microglia reactivity is a hallmark of neurodegenerative diseases including retinal cell death and immunomodulation emerges as a therapeutic option. Indole-3-carbinol (I3C) is a natural ligand of aryl hydrocarbon receptor (AhR), with potent immunomodulatory properties. Here, we hypothesized that I3C may inhibit microglia reactivity and exert neuroprotective effects in the light-damaged murine retina mimicking important immunological aspects of retinal degeneration.
BV-2 microglia were treated in vitro with I3C followed by lipopolysaccharide (LPS) stimulation to analyze pro-inflammatory and anti-oxidant responses by quantitative real-time PCR (qRT-PCR) and Western blots. Nitric oxide (NO) secretion, caspase 3/7 levels, phagocytosis rates, migration, and morphology were analyzed in control and AhR knockdown cells. I3C or vehicle was systemically applied to light-treated BALB/cJ mice as an experimental model of retinal degeneration. Pro-inflammatory and anti-oxidant responses in the retina were examined by qRT-PCR, ELISA, and Western blots. Immunohistochemical staining of retinal flat mounts and cryosections were performed. The retinal thickness and structure were evaluated by in vivo imaging using spectral domain-optical coherence tomography (SD-OCT).
The in vitro data showed that I3C potently diminished LPS-induced pro-inflammatory gene expression of I-NOS, IL-1ß, NLRP3, IL-6, and CCL2 and induced anti-oxidants gene levels of NQO1, HMOX1, and CAT1 in BV-2 cells. I3C also reduced LPS-induced NO secretion, phagocytosis, and migration as important functional microglia parameters. siRNA-mediated knockdown of AhR partially prevented the previously observed gene regulatory events. The in vivo experiments revealed that I3C treatment diminished light-damage induced I-NOS, IL-1ß, NLRP3, IL-6, and CCL2 transcripts and also reduced CCL2, I-NOS, IL-1ß, p-NFkBp65 protein levels in mice. Moreover, I3C increased anti-oxidant NQO1 and HMOX1 protein levels in light-exposed retinas. Finally, I3C therapy prevented the accumulation of amoeboid microglia in the subretinal space and protected from retinal degeneration.
The AhR ligand I3C potently counter-acts microgliosis and light-induced retinal damage, highlighting a potential treatment concept for retinal degeneration.