The immune response is a critical regulator of zebrafish retinal pigment epithelium regeneration

Abstract

Loss of the retinal pigment epithelium (RPE) because of dysfunction or disease can lead to blindness in humans. Harnessing the intrinsic ability of the RPE to self-repair is an attractive therapeutic strategy; however, mammalian RPE is limited in its regenerative capacity. Zebrafish possess tremendous intrinsic regenerative potential in ocular tissues, including the RPE, but little is known about the mechanisms driving RPE regeneration. Here, utilizing transgenic and mutant zebrafish lines, pharmacological manipulations, transcriptomics, and imaging analyses, we identified elements of the immune response as critical mediators of intrinsic RPE regeneration. After genetic ablation, the RPE express immune-related genes, including leukocyte recruitment factors such as interleukin 34. We demonstrate that macrophage/microglia cells are responsive to RPE damage and that their function is required for the timely progression of the regenerative response. These data identify the molecular and cellular underpinnings of RPE regeneration and hold significant potential for translational approaches aimed toward promoting a pro-regenerative environment in mammalian RPE.

mTOR activity is essential for retinal pigment epithelium regeneration in zebrafish

“…Interestingly, there were no significant differences in mTOR activity between MTZ + Dex-treated and DMSO-treated larvae (Fig 7L , 7N, and 7O). Dex-treatment does not affect macrophage/microglia recruitment post-RPE ablation [19], and therefore these data support a model in which it is an inflammation-independent function of macrophages/microglia that maintains mTOR activity in the RPE layer during regeneration.…”

“…p-values: � � 0.05, �� � 0.01, ���� � 0.0001. Statistical information can be found in S9 between macrophages/microglia and later mTOR activity in the RPE, we used the CSF1R inhibitor, pexidartinib (PLX3397), to deplete macrophages/microglia, an approach that has been shown to be effective in zebrafish [19,[65][66][67], and assessed the effects on mTOR activation. Importantly, the csf1ra and csf1rb genes were not significantly upregulated in the MTZ + RPE at 2dpi and therefore unlikely to be directly involved in the regenerative response of RPE cells at this time (S8 Table ).…”

“…In contrast to mammals, zebrafish possess remarkable regenerative capacity after injury in multiple tissues [ 13 , 17 ], including the RPE [ 18 , 19 ]. Previous work from our laboratory established a transgenic zebrafish RPE ablation model ( rpe65a :nfsB-eGFP) and demonstrated that RPE could intrinsically regenerate into a functional monolayer after widespread genetic ablation [ 18 ].…”

Ablation of mpeg+ Macrophages Exacerbates mfrp-Related Hyperopia

“…Recently, zebrafish RPE were shown to express leukocyte recruitment factors among other immune-related genes following genetic ablation. 37 Leach et al 37 went on to show that the macrophage and microglia cells that are recruited are also required for proper RPE regeneration, demonstrating that macrophages play a crucial role in the health of the RPE following injury. This raises the possibility that the RPE of mfrp –/– zebrafish exists in an injury-like state leading to recruitment of macrophages.…”

Comparative Study in Zebrafish and Medaka Unravels the Mechanisms of Tissue Regeneration

“…Sox2 is also one of the four Yamanaka factors that induced pluripotent stem cell status (Takahashi et al, 2007). In addition to retina, retinal pigment epithelium (RPE) regeneration was also recently described in zebrafish (Leach et al, 2021). Similar to heart regeneration, the immune response, particularly the macrophages and microglia cells, responds to injury and plays a critical role in retina and RPE regeneration, potentially associated with phagocytotic debris clearance and cytokine secretion (Mitchell et al, 2019;Leach et al, 2021).…”