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2021 OMIG Abstract

Muramyl Dipeptide Cleaved by Human Corneal Epithelial Cell
N-Acetylmuramoyl-L-Alanine Amidase (NAMAA) Retain Cytopathic Activity


Marlyn P. Langford, Laura Perilloux-Lyons and Thomas B. Redens
Department of Ophthalmology, Louisiana State University Health Sciences Center, Shreveport, Louisiana

Purpose: The inhibitory action of corneal epithelial cell N-acetylmuramyl-L-alanine amidase (NAMAA); AKA peptidoglycan (PGN) recognition protein 2 (PGRP2), against the cytopathic effects of muramyl dipeptide (MDP) was investigated.

Methods: PGRP2 expression by HCEC was detected by immunofluorescent antibody. Fluorochrome-tagged MDP cleavage by HCEC conditioned media and lysate, serum, tear, and recombinant human PGRP2 was determined by analysis of signal shifts following agarose gel electrophoresis. Inhibition of MDP cytopathy was assessed in rabbit kidney (RK13) cells by quantification of caspase-3 activation and polymeric DNA fragments.

Results: HCEC conditioned media and lysate cleaved MDP in a concentration and time-dependent manner. Serum and tear, but not recombinant PGRP2 or lysozyme cleaved fluorochrome-tagged MDP. HCEC lysate cleaved MDP induced caspase-mediated cell death in RK13 cells characterized by caspase-3 activation and DNA fragmentation. Nucleotide-binding and oligomerization domain-(NOD) inhibition prevented cleaved MDP cytopathy.

Conclusions: PGRP2 expression and MDP cleavage are consistent with HCEC NAMAA activity. Cytopathic activity of cleaved MDP is NOD-dependent. The results suggest MDP and likely other muropeptide containing PGNs are cleaved by NAMAA but retain biological activity consistent with recent reports that the pro-inflammatory response to bacterial PGN required PGRP2.

Disclosure: N

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