Investigating the role of macrophages in newt lens regeneration

Abstract

Purpose : Previous studies have shown that macrophages are required for successful regeneration across a wide range of contexts. Newts are highly capable of regenerating many different tissues, including the lens. Our goal was to investigate the role of macrophages during lens regeneration in the newt Pleurodeles waltl.

Methods : To see how macrophage depletion affects lens regeneration, we depleted macrophages using clodronate liposomes, to induce apoptosis. Intraocular injections of control or clodronate were performed immediately after lentectomy, and at 2 and 4 days post-lentectomy (dpl). At 30 dpl, eyes were collected and processed for immunohistochemistry and histology. To examine if macrophage replenishment could restore regenerative competence, a secondary injury by iridectomy was performed in both control and clodronate injected eyes at 60 dpl, and collected at 100 dpl for histology. Exogenous FGF2 was supplemented to macrophage-depleted eyes by inserting heparin-coated polyacrylamide delivery beads after lentectomy into the vitreous chamber.

Results : Macrophage-depleted eyes failed to regenerate a lens. Early macrophage depletion resulted in a significant decrease in cell proliferation, prolonged inflammation, caused a fibrotic-like response, and induced abnormalities in extracellular matrix remodeling. Iridectomy, performed as a secondary injury after macrophage replenishment, was sufficient to re-start the lens regeneration process. Similarly, exogenous FGF2 was sufficient to induce lens regeneration in the absence of macrophages.

Conclusions : Macrophages are necessary for newt lens regeneration. Macrophage depletion elicits a fibrotic response reminiscent of mammalian fibrosis. Further investigation of the cellular and molecular mechanisms behind lens regeneration will contribute to efforts to modulate the immune environment to promote repair of the human visual system.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.