Early Passage Mesenchymal Stem Cells Display Decreased Radiosensitivity and Increased DNA Repair Activity.

Po-Kuei Wu,Shih-Chieh Hung,Jir-You Wang,Ming-Chau Chang,Kuang-Yu Chao,Cheng-Fong Chen,Wei-Ming Chen

doi:10.1002/sctm.15-0394

Abstract

Cell therapies using human mesenchymal stem cells (MSCs) have received much attention in the past decade. In pursuit of the therapeutic potential of MSCs, cell expansion is required to generate a great number of cells with desired phenotype and functionality. Long‐term expansion in vitro, however, can lead to altered functions. To explore the changes in DNA damage responses (DDR) in MSCs expanded, DDR pathways following irradiation were characterized in early‐ and late‐passage bone marrow MSCs. Seventy‐two hours after irradiation, the percentage of sub‐G1 cells in early‐passage MSCs did not change significantly. Reduced TUNEL staining was observed in early‐passage MSCs compared to late‐passage MSCs 4 h after irradiation. Comet assay also revealed that early‐passage MSCs were more resistant to irradiation or DNA damages induced by genotoxic agents than late‐passage MSCs. ATM phosphorylation and γ‐H2AX and phospho‐p53 increased in early‐passage MSCs while decreased in late‐passage MSCs. Through inhibition by KU55933, DDR pathway in early‐passage MSCs was shown to be ATM‐dependent. Higher levels of poly (ADP‐ribose) polymerase‐1 (PARP‐1) and PAR synthesis were observed in early‐passage MSCs than in late‐passage MSCs. Knockdown of PARP‐1 in early‐passage MSCs resulted in sensitization to irradiation‐induced apoptosis. Overexpression of PARP‐1 in late passage MSCs could render irradiation resistance. Lower activity of DDR in late‐passage MSCs was associated with rapid proteasomal degradation of PARP‐1. In conclusion, early‐passage MSCs are more irradiation‐resistant and have increased DDR activity involving PARP‐1, ATM and their downstream signals. Stem Cells Translational Medicine 2017;6:1504–1514

Highlights

Mesenchymal stem cells (MSCs), the nonhematopoietic stromal cells residing in human bone marrow and most of connective tissues, are able to self-renew and differentiate into mesenchymal cells and nonmesenchymal cells [1]
The results indicated that underlying mechanisms associated with increased DNA damage responses in early-passage mesenchymal stem cells (MSCs) are linked to poly (ADP-ribose) polymerase-1 (PARP-1), ATM and their downstream signals
In late-passage MSCs, poly (ADPRibose) Polymerase-1 (PARP)-1 rapidly degraded in the absence of MG132 and maintained the same in the presence of MG132 (Supporting Information Fig. 3B). These results indicate that PARP-1 protein rapidly degraded through the participation of proteasomal pathway in late-passage MSCs

Summary

Introduction

Mesenchymal stem cells (MSCs), the nonhematopoietic stromal cells residing in human bone marrow and most of connective tissues, are able to self-renew and differentiate into mesenchymal cells and nonmesenchymal cells [1]. MSCs are known to be genetically stable through culture expansion, and no tumor is induced after transplantation for a long-term in vivo [2,3,4]. Cellbased therapies using MSCs have received increasing attention in recent years. Cell expansion of MSCs is required to generate a great number of cells with desired phenotype and functionality to drive the potential therapeutic uses. The therapeutic application of MSCs largely relies on culture expansion. There is a lack of data demonstrating the similarities of expanded MSCs to the native MSCs within their niches [5]

Objectives

Methods

Results

Conclusion