It has been a longstanding mystery why CNS neurons die after axotomy. One idea has been that axotomy interrupts a retrograde neurotrophic signal. Because injured spinal cords contain neuroinflammatory microglia and/or macrophages24, we hypothesized axotomy could also induce formation of A1s which in turn kill axotomized neurons. We used optic nerve crush (ONC) in postnatal rats and mice as a model system. ONC rapidly induced robust A1 generation that was temporally paired with death of RGCs (Fig. 4i–o). Weekly injection of neutralizing antibodies to Il-1α, TNFα, and C1q together into the vitreous of the eye from the time of injury inhibited A1 formation and prevented death of RGCs at least as long as 14 days post-ONC (Fig. 4g–j). Finally, we performed optic nerve crushes in double (Il-1α−/−TNFα−/−) and triple (Il-1α−/−TNFα−/−C1q−/−) knock-out mice that fail to generate A1s, and found that 7 days following optic nerve crush RGCs remained viable unlike their wild-type control counterparts (Fig. 4k). These data provide strong evidence that death of RGCs after axotomy is not due to trophic deprivation but is instead due to release of a toxic signal from nearby neurotoxic A1 reactive astrocytes.
