Coordination between metabolic transitions and gene expression by NAD+ availability during adipogenic differentiation in human cells.

Adipocytes are the main cell type in adipose tissue, a critical regulator of metabolism, highly specialized in storing energy as fat. Adipocytes differentiate from multipotent mesenchymal stromal cells through adipogenesis, a tightly controlled differentiation process involving closely interplay between metabolic transitions and sequential programs of gene expression. However, the specific gears driving this interplay remain largely obscure. Additionally, the metabolite nicotinamide adenine dinucleotide (NAD+) is becoming increasingly recognized as a regulator of lipid metabolism, being postulated as promising therapeutic target for dyslipidemia and obesity. Here, we explored the effect of manipulating NAD+ bioavailability during adipogenic differentiation from human mesenchymal stem cells. We found a previously unappreciated strong repressive role for NAD+ on adipocyte commitment, while a functional NAD+-dependent deacetylase SIRT1 appeared crucial for terminal differentiation of pre-adipocytes. Remarkably, repressing the NAD+ biosynthetic salvage pathway during adipogenesis promoted the adipogenic transcriptional program, suggesting that SIRT1 activity during adipogenesis is independent from the NAD+ salvage pathway, while two photon microscopy and extracellular flux analyses suggest that its activation relies on the metabolic switch. Interestingly, SIRT1-directed control of subcellular compartmentalization of redox metabolism during adipogenesis was evidenced by two-photon fluorescence lifetime microscopy. Significance StatementAdipocyte differentiation occurs from mesenchymal stem cells through the adipogenic process, involving sequential activation of both transcriptional and metabolic programs in a tightly coordinated manner. However, how transcriptional and metabolic transitions reciprocally interact during adipogenic differentiation remains largely obscure. Here we describe that the metabolite NAD+ is suppresses adipogenesis trough rewiring transcription, while a functional NAD+-dependent deacetylase SIRT1 is essential for terminal differentiation of pre-adipocytes. Using two-photon fluorescence lifetime microscopy, we created a metabolic map of NADH and lipid content simultaneously in live cells and described a new role for SIRT1 in the control of compartmentalization of redox metabolism during adipogenesis. These findings advance our understanding to improve therapeutical approaches targeting the NAD+-SIRT1 axis as treatment for obesity and dyslipemia.