The role of cellular senescence induced by radiation in bone loss has attracted much attention. As one of the common complications of anticancer radiotherapy, irradiation-induced bone deterioration is common and clinically significant, but the pathological mechanism has not been elucidated. This study was performed to explore the cellular senescence and senescence-associated secretory phenotype (SASP) induction of bone marrow-derived mesenchymal stem cells (BMSCs) by irradiation and its role in osteogenic differentiation dysfunction. It was observed that irradiated BMSCs lost typical fibroblast-like morphology, exhibited suppressed viability and differentiation potential accompanied with senescence phenotypes, including an increase in senescence-associated β-galactosidase (SA-β-gal) staining-positive cells, and upregulated senescence-related genes p53/p21, whereas no changes happened to p16. Additionally, DNA damage γ-H2AX foci, G0/G1 phase of cell cycle arrest, and cellular and mitochondrial reactive oxygen species (ROS) increased in an irradiation dose-dependent manner. Meanwhile, the JAK1/STAT3 pathway was activated and accompanied by an increase in SASP secretion, such as IL-6, IL-8, and matrix metalloproteinase-9 (MMP9), whereas 0.8 μM JAK1 inhibitor (JAKi) treatment effectively inhibited the JAK pathway and SASP production. Furthermore, conditioned medium (CM) from irradiation-induced senescent (IRIS) BMSCs exhibited a markedly reduced ability in osteogenic differentiation and marker gene expression of osteoblasts, whereas CM with JAKi intervention may effectively improve these deterioration effects. In conclusion, irradiation could provoke BMSC senescence and SASP secretion and further aggravate osteogenic differentiation dysfunction via paracrine signaling, whereas SASP targeting may be a possible intervention strategy for alleviating irradiation-induced bone loss.

Irradiation‐induced bone loss is widely reported, especially in radiotherapy‐induced osteoporosis. In addition to the mechanism of osteogenesis inhibition and osteoclastogenesis promotion, the regulation effect of osteocytes, which also send signals to modulate osteoclastogenesis, should be elucidated. In this study, the effect of irradiation on osteocyte and its accommodation to osteoclastogenesis via the release of high mobility group box 1 (HMGB1) was explored. Furthermore, the control response of HMGB1 inhibitor on receptor activator of nuclear factor‐κB ligand (RANKL) and osteoprotegerin (OPG) expression in osteocyte and osteocyte‐induced osteoclastogenesis was assessed. It was observed that irradiated osteocyte‐like MLO‐Y4 cells exhibited polygonal‐shaped morphological changes and shortened dendrites, inhibited cell viability and induced cellular apoptosis, along with the reduction in dendritic E11 protein/messenger RNA expression at a doses of 4 Gy. Additionally, the secretion of HMGB1 in supernatants was promoted, accompanied by the decreased OPG and elevated RANKL expression. When the RAW264.7 cells were cocultured with irradiated MLO‐Y4 cells or its conditioned medium, enhanced migration and differentiation of osteoclast precursor was observed, and this difference was alleviated with anti‐HMGB1 neutralizing antibody. In conclusion, this study demonstrated that irradiation deteriorated osteocytes’ potential to promote recruitment and differentiation of osteoclast precursor via stimulating HMGB1 release and subsequent elevation of RANKL/OPG level. This study will assist in designing the intervention programs for irradiation‐induced bone loss.

Radiotherapy, one of the clinical treatments of cancer, is accompanied by a high risk of damage to healthy tissues, such as bone loss and increased risk of fractures. The aim of the present study was to establish a rat model of local and systemic bone injury by focal irradiation, in order to study the etiological mechanism and intervention. The proximal metaphyseal region of the left hindlimb of male Sprague-Dawley rats were exposed to a single 2 Gy or three 8 Gy doses delivered on days 1, 3 and 5 using a small animal irradiator, the changes in bone volume and microarchitecture were evaluated, and the mineral apposition rate (MAR) was assessed. Furthermore, bone marrow-derived macrophages (BMMs) were isolated and induced to osteoclasts. It has been demonstrated that a single dose of 2 Gy may result in a significant loss of lumbar bone density at 3 days post-irradiation, however this is restored at 30 days post-irradiation. In the 3x8 Gy irradiation rat model, there was a rapid decrease in the aBMD of lumbar spine at 3 days and at 7 days post-irradiation, and the aBMD decline persisted even at 60 days post-irradiation. In addition, microCT analysis revealed a persistent decline in bone volume and damage in microarchitecture in the 3x8 Gy irradiation model, accompanied by a decrease in MAR, index of the decline in bone-forming ability. In the cellular mechanism, a single 2 Gy local irradiation mainly manifested as an enhancement of the BMMs osteoclastogenesis potential, which was different from the osteoclastogenesis inhibition after high-dose focal irradiation (3x8 Gy). In summary, the irradiation with simulated clinical focal fractionated radiotherapy exerts short- and long-term systemic injury on bone tissue, characterized by different osteoclastogenesis potential between the high dose mode and a single 2 Gy focal irradiation. Physicians must consider the irreversibility of bone damage in clinical radiotherapy.

Rabies remains a major public health concern in many developing countries. The precise neuropathogenesis of rabies is unknown, though it is hypothesized to be due to neuronal death or dysfunction. Mice that received intranasal inoculation of an attenuated rabies virus (RABV) strain HEP-Flury exhibited subtle clinical signs, and eventually recovered, which is different from the fatal encephalitis caused by the virulent RABV strain CVS-11. To understand the neuropathogenesis of rabies and the mechanisms of viral clearance, we applied RNA sequencing (RNA-Seq) to compare the brain transcriptomes of normal mice vs. HEP-Flury or CVS-11 intranasally inoculated mice. Our results revealed that both RABV strains altered positively and negatively the expression levels of many host genes, including genes associated with innate and adaptive immunity, inflammation and cell death. It is found that HEP-Flury infection can activate the innate immunity earlier through the RIG-I/MDA-5 signaling, and the innate immunity pre-activated by HEP-Flury or Newcastle disease virus (NDV) infection can effectively prevent the CVS-11 to invade central nervous system (CNS), but fails to clear the CVS-11 after its entry into the CNS. In addition, following CVS-11 infection, genes implicated in cell adhesion, blood vessel morphogenesis and coagulation were mainly up-regulated, while the genes involved in synaptic transmission and ion transport were significantly down-regulated. On the other hand, several genes involved in the MHC class II-mediated antigen presentation pathway were activated to a greater extent after the HEP-Flury infection as compared with the CVS-11 infection suggesting that the collaboration of CD4+ T cells and MHC class II-mediated antigen presentation is critical for the clearance of attenuated RABV from the CNS. The differentially regulated genes reported here are likely to include potential therapeutic targets for expanding the post-exposure treatment window for RABV infection.

Ionizing radiation-induced bone loss is a potential health concern in radiotherapy, occupational exposure, and astronauts. Although impaired bone vasculature and reduced proliferation of bone-forming osteoblasts has been implicated in this process, it has not been clearly characterized that whether radiation affects the growth of bone-resorbing osteoclasts. The molecular crosstalk between different cell populations in the skeletal system has not yet been elucidated in detail, especially between the increased bone resorption at early stage of post-irradiation and bone marrow-derived endothelial progenitor cells (BM-EPCs). In order to further understand the mechanisms involved in radiation-induced bone loss at the cellular level, we assessed the effects of irradiation on angiogenesis of BM-EPCs and osteoclastogenesis of receptor activator for nuclear factor-κB ligand (RANKL)-stimulated RAW 264.7 cells and crosstalk between these cell populations. We herein found significantly dysfunction of BM-EPCs in response to irradiation at a dose of 2 Gy, including inhibited proliferation, migration, tube-forming abilities, and downregulated expression of pro-angiogenesis vascular endothelial growth factors A (VEGF A). Meanwhile, we observed that irradiation promoted osteoclastogenesis of RANKL-stimulated RAW 264.7 cells directly or indirectly. These results provide quantitative evidences of irradiation induced osteoclastogenesis at a cellular level, and strongly suggest the involvement of osteoclastogenesis, angiogenesis and crosstalk between bone marrow cells in the radiation-induced bone loss. This study may provide new insights for the early diagnosis and intervention of bone loss post-irradiation.