Integrated placental microarray and single-cell transcriptomic analysis prioritizes Trp–Kyn–NAD+ axis-related candidate markers in pre-eclampsia

CONTEXT: Pre-eclampsia (PE) involves placental dysfunction and immune dysregulation, but the cell-type localization of tryptophan-kynurenine-nicotinamide adenine dinucleotide (Trp-Kyn-NAD+) axis-related genes in PE placentas remains unclear. AIMS: This study aimed to localize Trp-Kyn-NAD+ axis-related expression across placental cell types and prioritize candidate axis-related markers using public transcriptomic datasets. METHODS: The placental microarray dataset GSE75010 was used for discovery, GSE24129 for supportive external evaluation, and the single-cell RNA sequencing dataset GSE173193 for descriptive cell-type localization. Single-cell annotation, combined axis-gene localization, differential-expression and co-expression analyses, fixed four-gene model evaluation, immune-signature analysis, exploratory ligand-receptor expression scoring and transcription factor-gene co-expression analysis were performed. KEY RESULTS: Combined single-cell analysis showed non-uniform localization of Trp-Kyn-NAD+ axis-related expression across placental cell types. Microarray-based screening prioritized AFMID, ENPP1, IDO1, and NT5E as candidate axis-related genes. The fixed four-gene model showed moderate internal discrimination, and results from the small external cohort were interpreted as supportive. Candidate genes were also associated with immune-signature variation, and ligand-receptor expression scoring identified exploratory communication-related transcriptional patterns. CONCLUSIONS: By prioritizing AFMID, ENPP1, IDO1, and NT5E and mapping their cell-type localization, this study placed established IDO1-related evidence within a broader Trp-Kyn-NAD+ axis-related transcriptomic context. AFMID, ENPP1, and NT5E represent additional candidates for evaluation in larger cohorts and experimental systems. IMPLICATIONS: These findings provide a cell-type-resolved transcriptomic context for prioritizing Trp-Kyn-NAD+ axis-related candidates for further validation in PE.