# FKBP5 Regulates Osteogenesis of Human iPSC‐Derived Mesenchymal Stem Cells via FKBP5‐AKT‐FOXO1 Pathway

## TL;DR

This study shows that FKBP5 promotes bone formation in stem cells through a specific signaling pathway, offering a new approach for bone tissue regeneration.

## Contribution

The novel contribution is the identification of the FKBP5-AKT-FOXO1 pathway's role in promoting osteogenesis in iMSCs.

## Key findings

- FKBP5 overexpression enhances osteogenesis in human iPSC-derived mesenchymal stem cells.
- FKBP5 regulates osteogenesis via the AKT-FOXO1 signaling pathway.
- FKBP5-overexpressing iMSCs improved bone regeneration in a rat calvarial defect model.

## Abstract

The induced pluripotent stem cells derived mesenchymal stem cells (iMSCs) have shown great promise for bone tissue regeneration in critical‐sized calvarial defects. Still, the roles of FKBP5 in its osteogenesis are rarely known. It was observed that FKBP5 increased rapidly in iMSCs following osteogenic differentiation. To elucidate its role, FKBP5 was knocked down or overexpressed by lentivirus infection. Interestingly, the down‐regulation of FKBP5 impaired the osteogenesis of iMSCs, whereas the up‐regulation of FKBP5 promoted it. Proteomics analysis of iMSCs/oeFKBP5 and iMSCs/oeNC revealed that the protein variances are enriched in several signalling pathways associated with osteogenesis. Notably, the PI3K‐AKT signalling pathway was enriched highly at both D4 and D14. Co‐immunoprecipitation results demonstrated that the binding proteins of FKBP5 are AKT and pS473‐AKT, but not PI3K/p‐PI3K or FOXO1/pS256‐FOXO1; however, the ratios of pS473‐AKT/AKT and pS256‐FOXO1/FOXO1 were down‐regulated by FKBP5. FOXO1 inhibitor AS1842367 lessened the enhanced osteogenesis by FKBP5. Moreover, in a rat critical‐sized calvarial defect model, the iMSCs/oeFKBP5 delivery exhibited improved bone regeneration capability than iMSCs/oeNC in vivo. In conclusion, our findings first revealed that FKBP5 promotes the osteogenic differentiation of iMSCs partially through the FKBP5‐AKT‐FOXO1 pathway and presents a promising approach to iMSCs transplantation for clinical bone defects.