A multi-hierarchical approach reveals d-serine as a hidden substrate of sodium-coupled monocarboxylate transporters.

Transporter research primarily relies on the canonical substrates of well-established transporters. This approach has limitations when studying transporters for the low-abundant micromolecules, such as micronutrients, and may not reveal physiological functions of the transporters. While d-serine, a trace enantiomer of serine in the circulation, was discovered as an emerging biomarker of kidney function, its transport mechanisms in the periphery remain unknown. Here, using a multi-hierarchical approach from body fluids to molecules, combining multi-omics, cell-free synthetic biochemistry, and ex vivo transport analyses, we have identified two types of renal d-serine transport systems. We revealed that the small amino acid transporter ASCT2 serves as a d-serine transporter previously uncharacterized in the kidney and discovered d-serine as a non-canonical substrate of the sodium-coupled monocarboxylate transporters (SMCTs). These two systems are physiologically complementary, but ASCT2 dominates the role in the pathological condition. Our findings not only shed light on renal d-serine transport, but also clarify the importance of non-canonical substrate transport. This study provides a framework for investigating multiple transport systems of various trace micromolecules under physiological conditions and in multifactorial diseases.

YY1 binds to α-synuclein 3'-flanking region SNP and stimulates antisense noncoding RNA expression.

α-synuclein (SNCA) is an established susceptibility gene for Parkinson's disease (PD), one of the most common human neurodegenerative disorders. Increased SNCA is considered to lead to PD and dementia with Lewy bodies. Four single-nucleotide polymorphisms (SNPs) in SNCA 3' region were prominently associated with PD among different ethnic groups. To examine how these SNPs influence disease susceptibility, we analyzed their potential effects on SNCA gene expression. We found that rs356219 showed allele-specific features. Gel shift assay using nuclear extracts from SH-SY5Y cells showed binding of one or more proteins to the protective allele, rs356219-A. We purified the rs356219-A-protein complex with DNA affinity beads and identified a bound protein using mass spectrometry. This protein, YY1 (Yin Yang 1), is an ubiquitous transcription factor with multiple functions. We next investigated SNCA expression change in SH-SY5Y cells by YY1 transfection. We also analyzed the expression of antisense noncoding RNA (ncRNA) RP11-115D19.1 in SNCA 3'-flanking region, because rs356219 is located in intron of RP11-115D19.1. Little change was observed in SNCA expression levels; however, RP11-115D19.1 expression was prominently stimulated by YY1. In autopsied cortices, positive correlation was observed among RP11-115D19.1, SNCA and YY1 expression levels, suggesting their functional interactions in vivo. Knockdown of RP11-115D19.1 increased SNCA expression significantly in SH-SY5Y cells, suggesting its repressive effect on SNCA expression. Our findings of the protective allele-specific YY1 and antisense ncRNA raised a novel possible mechanism to regulate SNCA expression.