Human promoter analysis of the Programmed Axon Death genes NMNAT2 and SARM1

Abstract

SARM1 and NMNAT2 are two well described players in the Programmed Axon Death (PAxD) pathway. However, less is known about their transcriptional regulation, especially in humans, despite evidence that their expression levels influence axon vulnerability and thus modulation of expression presents a potential therapeutic target. Here, we used in-cell luciferase assays to functionally study the promoter regions of the human NMNAT2 and SARM1 genes. We find that human NMNAT2 expression can be driven by cAMP, acting through one cAMP response element (CRE), compared to two in mice. Naturally occurring single-nucleotide variants exist within the CRE, some of which lower NMNAT2 promoter activity by more than 50%. We also report an ultra-rare single nucleotide variant in the NMNAT2 promoter in an ALS patient in Project MinE. This variant demonstrates pathogenic potential by lowering NMNAT2 promoter activity in our assay. Project MinE also reveals a common SARM1 promoter variant that significantly increases SARM1 promoter activity in our assay. Thus, several single nucleotide changes in the NMNAT2 and SARM1 promoters modify transcription levels in the direction that would predict an increase in susceptibility to PAxD. These promoter variants refine our understanding of regulatory mechanisms affecting NMNAT2 and SARM1 expression and, together with previously reported coding variants for these genes, expand the catalogue of functionally relevant variants for future association studies in neurodegenerative diseases, including peripheral neuropathies and motor nerve disorders.