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

Abstract

Background 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. Methods 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). Results 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. Conclusions The AhR ligand I3C potently counter-acts microgliosis and light-induced retinal damage, highlighting a potential treatment concept for retinal degeneration.

Anti-inflammatory, antioxidant, antihypertensive, and antiarrhythmic effect of indole-3-carbinol, a phytochemical derived from cruciferous vegetables

“…To highlight, the anti-inflammatory and antioxidant effects of this phytochemical compound in cultured BV-2 cells exposed to LPS are consistent and reinforce a recent report ( Khan and Langmann, 2020 ). Moreover, these findings on LPS assure that Hsp70 overexpression mitigates oxidative stress and inflammatory status ( Mazzei et al., 2020 ).…”

Activating AhR alleviates cognitive deficits of Alzheimer's disease model mice by upregulating endogenous Aβ catabolic enzyme Neprilysin

“…Recent studies have shown that I3C has many biological effects on regulating autoimmunity and inflammation. I3C is considered to be a potential therapeutic agent for colitis 56 , systemic lupus erythematosus 57 , retinal degeneration 58 , cerebral ischemic stroke 59 , and Parkinson's disease 60 . Herein, both diosmin and I3C showed a significant therapeutic effect on cognitive deficits through AhR activation and NEP upregulated.…”

Macrophage Polarization and Plasticity in Systemic Lupus Erythematosus

“…AhR is a cytoplasmic receptor that exhibits numerous physiological functions in immune cells such as B cells, T cells, neutrophils, and macrophages (102). Emerging evidence suggests that I3C can be targeted to ameliorate diverse inflammatory and autoimmune conditions (103)(104)(105)(106). Furthermore, it is reported that I3C can immunoregulate macrophages by activating AhR (107).…”