Abstract
Purpose :
Mutations in the ubiquitous, nuclear NAD-synthesizing enzyme nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1) often result in severe visual defects in patients; however, the specific functions of NMNAT1 in the retina are not well understood. We sought to investigate the role of NMNAT1 in retinal development and maintenance through generation and characterization of a retina-specific NMNAT1 knockout mouse model.
Methods :
An NMNAT1 conditional knockout mouse model was generated by crossing a "floxed” NMNAT1 mouse line (generous gift from Dr. Laura Conforti) with a mouse line expressing Cre recombinase under a retina-specific promoter (‘Six3-Cre’). Retinal morphology was assessed using hematoxylin and eosin staining of retinal sections. Levels of retinal metabolites were quantified at postnatal day 4 (P4) using liquid-chromatography-tandem mass spectrometry (LC-MS/MS), and retinal transcriptomes were analyzed at P4 using RNA-seq. Metabolomic data was analyzed using Metaboanalyst, and RNA-seq data was analyzed using a HISAT2-StringTie-DeSeq2 pipeline. Gene ontology and functional enrichment analysis was performed with DAVID.
Results :
Retinal deletion of NMNAT1 leads to severe degeneration which begins between birth and P4 and is largely complete by P60. Metabolomic analysis at P4 indicates accumulation of metabolites including several glycolytic intermediates, aspartic acid, and nicotinamide mononucleotide (NMN). As expected, significant decreases in levels of NAD and nicotinamide were observed. Significant accumulation of thiamine was also observed in knockout retina, despite unchanged expression of thiamine pathway enzymes. Gene ontology analysis and functional annotation clustering reveal broad deregulation of pathways including cilium morphogenesis and transcriptional regulation.
Conclusions :
Our results support a crucial function for NMNAT1 in retinal development. Loss of retinal NMNAT1 causes specific metabolic changes which in some cases may be a result of altered transcriptional regulation. Our combination of metabolomic and transcriptomic analyses allows for a more thorough characterization of metabolic disruption upon loss of NMNAT1. Overall, this study provides a solid foundation for ongoing work clarifying the specific roles of NMNAT1 and nuclear NAD synthesis in the developing mammalian retina.
This is a 2020 ARVO Annual Meeting abstract.