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. 2015 Jul 2;7(9):1179–1197. doi: 10.15252/emmm.201505298

Figure 8. Upregulation of IL-1β expression in infiltrating microglia potentiates photoreceptor apoptosis.

Figure 8

  1. Microglia infiltrating the rd10 retina upregulate IL-1β expression during degeneration. Iba1+ microglia (green) were immunonegative for IL-1β (red) at P18 but become prominently IL-1β immunopositive at P22 (arrows). Scale bars, 25 μm.
  2. Depletion of infiltrating microglia in the rd10 retina decreases IL-1β levels. Cytokine levels in rd10/CreDTA mouse retinas were assayed following tamoxifen-induced microglial depletion (from P21 to P37–50, green bars; n = 9 animals) and compared with their untreated littermate controls (white bars, n = 8 animals; values normalized to control animals in the same litter). IL-1β protein levels were significantly lowered following microglial depletion, but IL-6, CCL2, or TNFα were not significantly changed.
  3. Inhibition of microglial phagocytosis results in decreased microglial IL-1β expression. Eyes of rd10 animals were treated with intravitreal injections of cRGD at P20, and analyzed at P23 by immunohistochemistry for Iba1 (green) and IL-1β (red), and compared to uninjected eyes and with eyes injected with inactive analog, cRAD (n = 3 eyes in each category). Immunopositivity was high in infiltrating microglia (indicated by arrows) for untreated and cRAD-injected control eyes and significantly reduced in microglia in cRGD-injected eyes (upper panel), as demonstrated by the quantification of IL-1β expression (area of immunopositivity as a fraction of the ONL) (lower left panel). ONL thickness correlated negatively with the extent of IL-1β immunopositivity (lower right panel). Scale bar, 25 μm.
  4. IL-1R signaling during rod degeneration was inhibited by intravitreal injections of recombinant IL-1 receptor antagonist, anakinra (from P20–22 to P26–27) in one eye of each rd10 animal, while the contralateral eye was injected with PBS as a control. Upper panels show representative retinal sections from control PBS-injected and IL-1RA-injected eyes from the same animal. ONL atrophy in control eyes was more advanced compared to IL-1RA-injected eyes, with greater mean ONL thickness and lower mean density of TUNEL+ ONL nuclei in IL-1RA-injected eyes (lower panels) (n = 15 animals; measurements in IL-1RA-injected eyes normalized to contralateral control eyes, paired t-test). Scale bar, 25 μm.

Data information: Column heights (in B, C, D) indicate mean, error bars indicate ± SEM.