Myo/Nog Cells in the lens are nonprofessional phagocytes

Abstract

Purpose : : Myo/Nog cells, named for their expression of the skeletal muscle specific transcription factor MyoD and bone morphogenetic protein noggin, are present in the eyes of multiple species. Targeted depletion of Myo/Nog cells during cataract surgery in rabbits prevents the accumulation of myofibroblasts and capsular wrinkles, and reduces posterior capsule opacification to clinically insignificant levels. Myo/Nog cells are the progenitors of myofibroblasts in human lens tissue. In this study we examined the capacity for Myo/Nog cells to phagocytose dead cells in the lens and their relationship to macrophages and granulocytes in the anterior segment.

Methods : : Anterior human lens tissue was removed by capsulorhexis during cataract surgery. Procurement of tissue was carried out in accordance with the Declaration of Helsinki and approved by the Philadelphia College of Osteopathic Medicine’s Institutional Review Board. Dying cells were incubated with IncuCyte pHrodo red^TM that fluoresces following phagocytosis and internalization into acidic compartments of the cell. Myo/Nog cells were identified with the G8 monoclonal antibody (mAb). Cataract surgery was performed on New Zealand white rabbits in compliance with the Statement for the Use of Animals in Ophthalmic and Vision Research. Anterior segments were embedded in paraffin, sectioned and double labeled with G8 and the Iba1 mAb, a marker for macrophages. Nuclei were stained with Hoechst dye.

Results : A subpopulation of G8-positive (+) cells in human lens tissue contained pHrodo red dye. Two nuclei were present within the cytoplasm of dye laden cells. Myo/Nog cell mediated phagocytosis also was observed outside of the lens. No Iba1-positive (+) cells were present in this tissue or the rabbit lens following cataract surgery. Separate populations of G8+ and Iba1+ cells were observed in the ciliary body and cornea. Myo/Nog cell nuclei were not segmented.

Conclusions : Myo/Nog cells phagocytosed cell corpses in explants of human lens tissue. Macrophages were not observed in the lens. The absence of overlap of G8 and Iba1 in the anterior segment and other tissues indicates that Myo/Nog cells are distinct from macrophages. The lack of segmented nuclei in Myo/Nog cells distinguishes them from granulocytes, including neutrophils. These results indicate that Myo/Nog cells are non-professional phagocytes, defined as cells whose primary functions are unrelated to clearance but are capable of engulfment.

This is a 2020 ARVO Annual Meeting abstract.