# Proteome-wide analysis by liquid chromatography tandem mass spectrometry reveals the role of retinoic acid during adipogenesis in human bone mesenchymal stem cells

## TL;DR

This study uses mass spectrometry to show how retinoic acid affects protein expression during fat cell development in human bone stem cells, potentially linking it to osteoporosis.

## Contribution

The study provides a proteome-wide analysis of retinoic acid's role in adipogenesis using LC-MS/MS in human bone mesenchymal stem cells.

## Key findings

- ATRA upregulated Wnt, Hippo, and MAPK signaling pathways and cytoskeleton-related processes.
- ATRA downregulated AMPK and PPAR pathways, inhibiting fat cell differentiation and lipid accumulation.
- Blocking actin cytoskeleton pathways reduced ATRA's inhibition of adipogenesis.

## Abstract

Retinoic acid (RA), an active metabolite of vitamin A, may regulate adipogenesis and is associated with osteoporosis. To clarify the regulatory mechanism of RA in adipogenesis and its relationship with the occurrence and development of osteoporosis, we investigated the role of all-trans retinoic acid (ATRA) in protein expression profiling during human bone mesenchymal stem cells (hBMSCs) adipogenesis.

Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to determine the protein profile, and raw data were analyzed against the UniProt database using MaxQuant with the Andromeda search engine. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases were used for functional annotation of differentially expressed proteins (DEPs). The interaction relationships of DEPs were assessed using the STRING database, and Cytoscape was used to visualize the protein interaction network.

A total of 5,611 proteins were identified by LC-MS/MS in 15 samples, of which 5,470 proteins showed quantifiable data. When treated with ATRA for seven and 14 days after adipogenic induction, 470 and 1,408 DEPs were upregulated and 508 and 1,345 DEPs were downregulated. Gene functional annotation of DEPs showed that ATRA upregulated classic signaling pathways, such as Wnt, Hippo, and MAPK, as well as cytoskeleton related pathways, including focal adhesion, extracellular matrix (ECM)-receptor interaction, and the regulation of actin cytoskeleton. ATRA downregulated many pathways related to metabolism, including the AMP-activated protein kinase (AMPK) and peroxisome proliferator activated receptor (PPAR) pathways, to repress adipocyte differentiation and lipid accumulation. Specifically, the inhibition of adipogenesis by ATRA was significantly attenuated when the Rho-associated protein kinase (ROCK) inhibitor Y27632 was used to block the regulation of actin cytoskeleton pathways.

Our study suggests that ATRA downregulates metabolism-related pathways to inhibit the adipogenesis of hBMSCs by upregulating some classic signaling pathways and cytoskeleton-related pathways, indicating that ATRA may be a broad-spectrum metabolic inhibitor.