Tumor Necrosis Factor-Alpha Is Produced by Dying Retinal Neurons and Is Required for Müller Glia Proliferation during Zebrafish Retinal Regeneration

Abstract

Intense light exposure causes photoreceptor apoptosis in dark-adapted adult albino zebrafish (Danio rerio). Subsequently, Müller glia increase expression of the Achaete-scute complex-like 1a (Ascl1a) and Signal transducer and activator of transcription 3(Stat3) transcription factors and reenter the cell cycle to yield undifferentiated neuronal progenitors that continue to proliferate, migrate to the outer nuclear layer, and differentiate into photoreceptors. A proteomic analysis of light-damaged retinal homogenates, which induced Müller glia proliferation when injected into an undamaged eye, revealed increased expression of Tumor necrosis factor α (TNFα) signaling proteins relative to undamaged retinal homogenates. TNFα expression initially increased in apoptotic photoreceptors and later in Müller glia. Morpholino-mediated knockdown of TNFα expression prior to light damage diminished the expression of both Ascl1a and Stat3 in Müller glia and significantly reduced the number of proliferating Müller glia without affecting photoreceptor cell death. Knockdown of TNFα expression in the Müller glia resulted in fewer proliferating Müller glia, suggesting that Müller glial-derived TNFα recruited additional Müller glia to reenter the cell cycle. While TNFα is required for increased Ascl1a and Stat3 expression, Ascl1a and Stat3 are both necessary for TNFα expression in Müller glia. Apoptotic inner retinal neurons, resulting from intravitreal injection of ouabain, also exhibited increased TNFα expression that was required for Müller glia proliferation. Thus, TNFα is the first molecule identified that is produced by dying retinal neurons and is necessary to induce Müller glia to proliferate in the zebrafish retinal regeneration response.

Glucocorticoid receptors in the retina, Müller glia and the formation of Müller glia-derived progenitors

“…Activation of GCR appears to directly inhibit FGF2/MAPK signaling and the initiation of Müller glial de-differentiation in undamaged retinas, whereas Müller glia in NMDA-damaged retinas appear to be influenced by many signaling pathways in addition to GCR and MAPK. These pathways probably include Wnt/β-catenin (Osakada et al, 2007;Ramachandran et al, 2011), Jak/Stat3 (Nelson et al, 2012), TGFβ/Smad (Close et al, 2005;Lenkowski et al, 2013) and TNFα (Nelson et al, 2013). Any one of these pathways in the damaged retina could influence Notch signaling independently of MAPK and GCR signaling.…”

mTor-signaling is required for the formation of proliferating Müller glia-derived progenitor cells in the chick retina

“…The Müller glia are common to the eyes of all vertebrate classes and are the only type of retinal glia that is derived from embryonic neuroepithelial stem cells. In several vertebrate classes the Müller glia are capable of de-differentiating, proliferating and acquiring a progenitor-like state in response to acute retinal injury (Bernardos et al, 2007;Fausett and Goldman, 2006;Fischer and Reh, 2001;Karl et al, 2008;Ooto et al, 2004) or in response to exogenous growth factors (Fischer et al, 2002;Kassen et al, 2009;Nelson et al, 2013;Wan et al, 2012). Müller glia have been identified as the cellular source of retinal regeneration in zebrafish (Bernardos et al, 2007;Fausett and Goldman, 2006), birds (Fischer and Reh, 2001) and rodent models (Karl et al, 2008;Ooto et al, 2004).…”

Leptin and IL-6 Family Cytokines Synergize to Stimulate Müller Glia Reprogramming and Retina Regeneration

“…Following retinal injury, MG reprogram so they acquire progenitor characteristics that allow them to regenerate all major retinal cell types (Bernardos et al, 2007; Fausett and Goldman, 2006; Fimbel et al, 2007; Ramachandran et al, 2010a; Ramachandran, 2010). A key event in MG reprogramming is the activation of ascl1a gene expression (Fausett et al, 2008), which encodes a nodal transcription factor impacting reprogramming genes and signaling cascades that affect almost all aspects of retina regeneration (Lenkowski et al, 2013; Nelson et al, 2013; Nelson et al, 2012; Powell et al, 2012; Ramachandran et al, 2010a; Ramachandran et al, 2011, 2012; Wan, 2012). Importantly, ASCL1 also controls MG reprogramming in the postnatal mouse retina (Pollak et al, 2013).…”

“…However, this expression is detected in all retinal layers and in the inner nuclear layer (INL), quiescent MG as well as proliferating MG express Stat3 (Kassen et al, 2007; Nelson et al, 2012). This expression pattern, along with the assumption that injury-induced Stat3 expression reflects that of activated p-Stat3 (Kassen et al, 2007), has led to models assigning different roles for injury-induced Stat3 in quiescent MG, MG stem cells and MG-derived progenitors (Gorsuch and Hyde, 2013; Nelson et al, 2013; Nelson et al, 2012). However, it remains unknown whether total Stat3 is a true indicator of p-Stat3 in the injured retina, nor is it known if endogenous cytokines acting via Jak/Stat signaling stimulate MG reprogramming and retina regeneration following retinal injury.…”