# Suppression of ATP-dependent (S)-NAD(P)H-hydrate dehydratase expression inhibits adipocyte differentiation of 3T3-L1 preadipocytes by increasing excessive accumulation of NADHX

## TL;DR

This study shows that a specific enzyme, NAXD, is important for fat cell development by preventing the buildup of a modified form of NADH.

## Contribution

The study reveals a novel role of NAXD in adipocyte differentiation by linking it to NADHX accumulation.

## Key findings

- NAXD is essential for normal adipocyte differentiation in 3T3-L1 preadipocytes.
- Excess NADHX accumulation inhibits adipocyte differentiation and reduces key transcription factors.
- NAD+ supplementation does not restore differentiation in NAXD-deficient cells.

## Abstract

ATP-dependent (S)-NAD(P)H-hydrate dehydratase (NAXD) is a crucial enzyme in the nicotinamide adenine dinucleotide repair system that regenerates NAD(P)H, an essential electron donor in metabolic redox reactions. NAD+-related metabolic pathways connect cellular metabolism and the expression of genes responsible for adipogenesis; however, the biological significance of the NAXD-mediated repair pathway remains unclear. Herein, we showed that NAXD is essential for normal adipocyte differentiation of 3T3-L1 murine preadipocytes. Silencing of the Naxd gene attenuated differentiation-induced lipid accumulation with excessive accumulation of hydrated NADH (NADHX) without altering NAD+ levels. FK866, a specific inhibitor of NAMPT, further reduced lipid accumulation even in Naxd-silenced cells with substantial decrease in NAD+. Supplementation with nicotinamide mononucleotide, a precursor of NAD+, restored NAD+ levels comparably in Naxd- and LacZ-silenced cells treated with FK866, but failed to recover adipocyte differentiation of Naxd-silenced cells to the level of LacZ-silenced cells. In contrast, exposure of wild-type 3T3-L1 cells to NADHX recapitulated the Naxd deficiency-elicited inhibitory effects on adipocyte differentiation with reduced expression of master transcriptional regulators of adipogenesis, peroxisome proliferator-activated receptor γ and CCAAT/enhancer binding protein α. These results suggest that NAXD supports normal adipogenesis, in part, by inhibiting excessive accumulation of NADHX.

Graphical Abstract