The role of nicotinamide N-methyltransferase in choroidal endothelial cells: possible role in macular neovascularization

Navratil, Emma Mae, Flamme-Wiese, Miles J., Khan, Adnan, Liu, Xiuying, Wiley, Luke A., Stone, Edwin M., Tucker, Budd A. and Mullins, Robert F. (2024) The role of nicotinamide N-methyltransferase in choroidal endothelial cells: possible role in macular neovascularization. Investigative Ophthalmology & Visual Science, 65 (7), [4969].

Abstract

Purpose: macular neovascularization (MNV) is one of two advanced forms of age-related macular degeneration. Though anti-VEGF drugs have provided an effective treatment for this condition, much remains to be learned about the mechanisms by which MNVs form in the eye. Recent work published by our lab has shown that nicotinamide N-methyltransferase is upregulated in endothelial cells in human eyes with MNV according to spatial transcriptomics and single cell RNA-sequencing, as well as in a mouse model with laser induced CNV. Current work is aimed at investigating the function of NNMT in choroidal endothelial cells (CECs) of the eye during MNV pathogenesis.

Methods: we conducted immunohistochemical colocalization studies to investigate NNMT localization in 3 human eyes with MNV. Immortalized human CECs were incubated with a small molecule inhibitor of NNMT followed by scratch assays to determine the effect of NNMT inhibition on cell proliferation and movement.

Results: initial IHC studies suggest that NNMT colocalizes with smooth muscle actin (SMA), traditionally a marker of smooth muscle cells and myofibroblasts. NNMT did not colocalize with UEA-1 (endothelial cells), GFAP (astroglia), or IBA-1 (microglia). Preliminary wound healing assays using immortalized CECs suggest a trend toward slightly faster wound closing with application of NNMT inhibitor. In contrast, application of AREDS2 vitamins appears to slow wound healing.

Conclusions: the upregulation of NNMT in MNV endothelial cells, combined with colocalization of NNMT with SMA but not UEA-1, suggests that NNMT expression may be related to endothelial to mesenchymal transition in MNV pathogenesis. Further work will be aimed at validating these results in other model systems (iPSC CECs and human organ culture), as well as determining the molecular changes that occur in endothelial cells when NNMT is overexpressed.

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Contributors

Author: Adnan Khan

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