Tumor necrosis factor and nitric oxide production by resident retinal glial cells from rats presenting hereditary retinal degeneration

Abstract

The inherited retinal dystrophy observed in Royal College of Surgeons (RCS) rats is a widely used model for the study of the photoreceptor degeneration that occurs in retinitis pigmentosa and macular degeneration. The visual cell degeneration is accompanied by an abnormal accumulation of microglial cells in the retina of RCS rats presenting the dystrophy. In the present study, we show that combined stimulation of RCS dystrophic retinal Müller glial (RMG) cells with interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) induced the release in culture supernatants of significantly higher amounts of tumor necrosis factor (TNF) and nitric oxide (NO) compared to nondystrophic congenic controls. In contrast, the levels of TNF and NO found in the supernatants from microglial cells were not significantly different in both strains. Interestingly, as shown by thymidine incorporation, microglial cells from RCS dystrophic rats have a prominent capacity of proliferation in culture medium compared to microglia isolated from RCS non dystrophic controls. Incubation of RMG cells and microglia with the stereoselective inhibitor of NOS, NG-monomethyl-L-arginine (L-NMMA), inhibited nitrite release in LPS + IFN-gamma-stimulated RMG cells and microglia. The addition of TGF-beta with LPS + IFN-gamma clearly inhibited TNF release in supernatants from both dystrophic and control rat RMG cells and microglia. While TGF-beta significantly inhibited nitrite synthesis in RMG cells, the effect on nitrite synthesis by microglia was very low. The retinal dystrophy observed in RCS dystrophic rats could result from an abnormal reactivity of RMG and microglial cells to release TNF and NO in response to stimulants. The immunomodulatory cytokine TGF-beta and inhibitors of NOS could be negative regulators in the cytokine network and nitrite synthesis thus interfering with the development of photoreceptor cell death.

Proliferation of Microglia, but not Photoreceptors, in the Outer Nuclear Layer of therd-1Mouse

“…In addition, we demonstrate that proliferation of microglia occurs at all levels of the retina, including the outer nuclear layer. A similar finding has been noted in vitro by de Kozak et al,36 who demonstrated that microglial cells isolated from RCS rats have a higher capacity to proliferate in culture than those obtained from normal control animals. The distribution of proliferating microglial cells in our study coincides with the spatiotemporal pattern of photoreceptor death, implying that microglial cells are intimately engaged with the degenerative process.…”

“…On the one hand, they are a known source of neuronal cytotoxins such as tumor necrosis factor-␣, reactive oxygen intermediates, reactive nitrogen oxides, and excitatory amino acids. 36,37 Roque et al, 38 demonstrated that retina-derived microglial cells will kill photoreceptors by apoptosis in vitro, thus lending support to the hypothesis that microglia accelerate death of dystrophic photoreceptors. On the other hand, the protective effects of neurotrophic factors on photoreceptors may be mediated both directly (in the case of FGF2) or in the case of BDNF and CNTF (whose receptors are not present on photoreceptors), indirectly through activation of Müller cells and inner retinal neurons.…”

Cytokine Gene Polymorphism in Sympathetic Ophthalmia

“…TNF is a multifunctional cytokine secreted by monocytes (TNF␣), lymphocytes (TNF␤) and resident retinal cells. 32,33 It has potent proinflammatory effects since blocking its action in experimental models of uveitis reduces structural damage to the retina 34 whereas the administration of TNF leads to worsening of disease. 35 In contrast, chronic TNF exposure suppresses the cytokine and proliferative responses of T cells and drives Fas-dependent apoptosis.…”

Purinergic signaling in retinal degeneration and regeneration

“…Activated microglia contribute to neuronal and photoreceptor degeneration in the retina by the release of neurotoxic factors such as tumor necrosis factor-a (TNFa), IL-1b, oxygen and nitrogen free radicals, and Fas-ligand (De Kozak et al, 1997;Ju et al, 2006;Sivakumar et al, 2011;Roh et al, 2012;Zeng et al, 2014). Upregulation of TNFa, IL-1b, and IL-6 may be involved in the death of retinal ganglion cells that occurs with P2X 7 activation after elevation of the intraocular pressure .…”