Radiation-Induced Osteocyte Senescence Alters Bone Marrow Mesenchymal Stem Cell Differentiation Potential via Paracrine Signaling.

Linshan Xu,Li Ren,Guoying Zhu,Yuyang Wang,Jianglong Zhai,Jianping Wang

doi:10.3390/ijms22179323

Abstract

Cellular senescence and its senescence-associated secretory phenotype (SASP) are widely regarded as promising therapeutic targets for aging-related diseases, such as osteoporosis. However, the expression pattern of cellular senescence and multiple SASP secretion remains unclear, thus leaving a large gap in the knowledge for a desirable intervention targeting cellular senescence. Therefore, there is a critical need to understand the molecular mechanism of SASP secretion in the bone microenvironment that can ameliorate aging-related degenerative pathologies including osteoporosis. In this study, osteocyte-like cells (MLO-Y4) were induced to cellular senescence by 2 Gy γ-rays; then, senescence phenotype changes and adverse effects of SASP on bone marrow mesenchymal stem cell (BMSC) differentiation potential were investigated. The results revealed that 2 Gy irradiation could hinder cell viability, shorten cell dendrites, and induce cellular senescence, as evidenced by the higher expression of senescence markers p16 and p21 and the elevated formation of senescence-associated heterochromatin foci (SAHF), which was accompanied by the enhanced secretion of SASP markers such as IL-1α, IL-6, MMP-3, IGFBP-6, resistin, and adiponectin. When 0.8 μM JAK1 inhibitors were added to block SASP secretion, the higher expression of SASP was blunted, but the inhibition in osteogenic and adipogenic differentiation potential of BMSCs co-cultured with irradiated MLO-Y4 cell conditioned medium (CM- 2 Gy) was alleviated. These results suggest that senescent osteocytes can perturb BMSCs’ differential potential via the paracrine signaling of SASP, which was also demonstrated by in vivo experiments. In conclusion, we identified the SASP factor partially responsible for the degenerative differentiation of BMSCs, which allowed us to hypothesize that senescent osteocytes and their SASPs may contribute to radiation-induced bone loss.

Highlights

With the rapid aging of the global population, research on effective treatment for aging-related diseases has been widely concerned with extending both life and health spans [1]
We focus on the radiation-induced senescence phenotype changes in osteocytes and their regulatory influence on the differentiation potential of bone marrow mesenchymal stem cell (BMSC) toward osteogenesis and adipogenesis, and we sought to identify the hallmarks and functions of the osteocyte senescence-associated secretory phenotype (SASP) of cellular senescence within the bone microenvironment
Osteocyte-like MLO-Y4 cells were identified by F-actin fluorescence staining, and they were found to exhibit typical dendritic structures and E11 expression that represented early osteocytes (Figure 1A,D)

Summary

Introduction

With the rapid aging of the global population, research on effective treatment for aging-related diseases has been widely concerned with extending both life and health spans [1]. One of the main causes of age-related bone loss is an increase in senescent cells and their proinflammatory factors in the bone microenvironment, which may cause substantial pathogenic effects and ageing phenotypes [4,5]. In vivo studies have revealed that the accumulation of senescent cells in tissue can damage the self-repair of tissues, establish a senescent microenvironment, affect the physiological functions of surrounding normal cells, and lead to tissue dysfunction and diseases [6,7]. Ionizing radiation induces DNA damage, chromosomal aberrations, increased amounts of reactive oxygen species, and cellular senescence in cells within the bone microenvironment, which leads to senescence-like conditions [13]. During the period of cancer treatment, with the occurrence of bone aging and tissue dysfunction, the adverse effects of senescence that cause dysfunction in other tissues appear to occur in bone tissue; these include impaired osteoblast progenitor cell function, defective bone formation, and enhanced osteoclastogenesis [14]

Methods

Results

Conclusion