Jingjing Sun - Academia.edu (original) (raw)

Papers by Jingjing Sun

Melatonin Research

Melatonin has diverse effects, and has been reported to promote bone formation in addition to reg... more Melatonin has diverse effects, and has been reported to promote bone formation in addition to regulating the sleep–wake cycle. In the present study, we investigated the effects of melatonin on bone metabolism using ovariectomized (OVX) rats; a model of postmenopausal osteoporosis. Here, we focused on the differences in bone formation when melatonin was subcutaneous injected at day or early night. The OVX rats were injected with melatonin once daily (0.8 or 8 mg/head) between 11:00 to 14:00 or 18:00 to 19:30 for the day or early night, respectively, for six weeks. After completion of the injection, the femur and tibia in the OVX rats were dissected under general anesthesia and examined by quantitative computed tomography (pQCT) and histological analysis, respectively. Interestingly, the trabecular bone mineral density in the femur metaphysis of the OVX rats receiving 8 mg/head melatonin at early night was higher than those receiving melatonin during the day and they recovered to a si...

Journal of Molecular and Cellular Cardiology

Biological Sciences in Space

Exposure to microgravity during space flight has caused astronauts to experience decreased bone d... more Exposure to microgravity during space flight has caused astronauts to experience decreased bone density, resulting from bone resorption by osteoclastic activation. Activation of the nuclear factor-κB ligand (RANKL) of the RANKLproducing cells, a known osteoclastogenesispromoting factor, seems to be induced under microgravity. However, the role of the RANKLproducing cells under microgravity has not yet been demonstrated due to the lack of suitable in vitro organ culture of osteoblasts, osteoclasts, and osteocytes with the intact bone matrix under microgravity. Previous reports demonstrated that RANKL-producing cells were detected with a specific antiserum for goldfish RANKL in the regenerating goldfish scales. In this study, the response of RANKLproducing cells to simulated microgravity with a three-dimensional clinostat was examined using in vitro organ culture system with regenerating scales. In addition, mRNA expression analysis of osteoclastic and osteoblastic markers via quantitative real-time PCR was conducted together with histological analysis of RANKL-producing cells. After 4 days of exposure to simulated microgravity, the number of RANKL immune-positive cells increased compared with the RANKL immunepositive cells in control regenerating scales. The Rankl mRNA expression in the regenerating scales after simulated microgravity treatments was significantly higher than that in the control (1G) scales. The mRNA expression of osteoprotegerin (Opg), an osteoclastogenesis inhibitory factor, significantly decreased under simulated microgravity conditions. The ratio of Rankl/Opg in the simulated microgravity-treated scales was significantly higher than that in the scales of 1G control. The change in the ratio of Rankl/Opg implied that osteoclastic activation is promoted after simulated microgravity treatments. Actually, in the regenerating scales exposed to simulated microgravity, the mRNA expression of osteoclastic markers, such as receptor activator of NFκB, cathepsin K, integrin beta-3, and cellular-Src, significantly increased. On the other hand, the mRNA expression of the osteoblastic markers (collagen type I alpha 1 and osteocalcin) significantly decreased. The changes in the osteoclastic and osteoblastic markers were consistent with our previously reported experiment on the International Space Station. To the best of our knowledge, we are the first to demonstrate the activation of RANKL-producing cells under simulated microgravity conditions by in vitro organ culture using regenerating goldfish scales. We strongly emphasize that fish scales serve as an excellent bone model for the analysis of gravitational responses while maintaining conditions similar to in vivo.

Stem Cells

The maintenance and proliferation of hematopoietic stem cells (HSCs) are tightly regulated by the... more The maintenance and proliferation of hematopoietic stem cells (HSCs) are tightly regulated by their niches in the bone marrow. The analysis of niche cells or stromal cell lines that can support HSCs has facilitated the finding of novel supporting factors for HSCs. Despite large efforts in the murine bone marrow; however, HSC expansion is still difficult ex vivo, highlighting the need for new approaches to elucidate the molecular elements that regulate HSCs. The zebrafish provides a unique model to study hematopoietic niches as HSCs are maintained in the kidney, allowing for a parallel view of hematopoietic niches over evolution. Here, using a stromal cell line from the zebrafish kidney, zebrafish kidney stromal (ZKS), we uncover that an inhibitor of canonical Wnt signaling, IWR-1-endo, is a potent regulator of HSCs. Coculture assays revealed that ZKS cells were in part supportive of maintenance, but not expansion, of gata2a:GFP+runx1:mCherry+ (gata2a+runx1+) HSCs. Transcriptome anal...

Methods in Molecular Biology

Biochemical and Biophysical Research Communications, 2020

Melatonin has been implicated in the regulation of bone metabolism; however, the molecular mechan... more Melatonin has been implicated in the regulation of bone metabolism; however, the molecular mechanisms underlying its involvement in fracture healing are still obscure. We previously developed an in vivo fracture healing model using the scale of a double-transgenic zebrafish, trap:GFP; osterix:mCherry, which labels osteoclasts and osteoblasts with GFP and mCherry, respectively. Here we show using this model that melatonin inhibits both osteoblast and osteoclast differentiation under fracture stress through the repression of Erk signaling in epidermal cells of the scale. Melatonin treatment resulted in reduced numbers of both osteoblasts and osteoclasts in the fractured scale. Immunochemistry analysis revealed that Erk signals in epidermal cells, which express melatonin receptors, were greatly enhanced in response to fracture stress, but this enhancement was blocked by melatonin treatment. Moreover, inhibition of Erk signaling phenocopied the effects of melatonin treatment in the fractured scale. Collectively, these data suggest that the activation of epidermal Erk signaling is required for both osteoblast and osteoclast differentiation in the early stage of fracture healing, and melatonin suppresses epidermal Erk signaling, leading to impaired fracture healing.

Communications Biology, 2020

Differentiation of osteoclasts (OCs) from hematopoietic cells requires cellular interaction with ... more Differentiation of osteoclasts (OCs) from hematopoietic cells requires cellular interaction with osteoblasts (OBs). Due to the difficulty of live-imaging in the bone, however, the cellular and molecular mechanisms underlying intercellular communication involved in OC differentiation are still elusive. Here, we develop a fracture healing model using the scale of trap:GFP; osterix:mCherry transgenic zebrafish to visualize the interaction between OCs and OBs. Transplantation assays followed by flow cytometric analysis reveal that most trap:GFPhigh OCs in the fractured scale are detected in the osterix:mCherry+ fraction because of uptake of OB-derived extracellular vesicles (EVs). In vivo live-imaging shows that immature OCs actively interact with osterix:mCherry+ OBs and engulf EVs prior to convergence at the fracture site. In vitro cell culture assays show that OB-derived EVs promote OC differentiation via Rankl signaling. Collectively, these data suggest that EV-mediated intercellula...

Scientific Reports, 2019

Hematopoietic stem cells (HSCs) maintain the entire blood system throughout life and are utilized... more Hematopoietic stem cells (HSCs) maintain the entire blood system throughout life and are utilized in therapeutic approaches for blood diseases. Prospective isolation of highly purified HSCs is crucial to understand the molecular mechanisms underlying regulation of HSCs. The zebrafish is an elegant genetic model for the study of hematopoiesis due to its many unique advantages. It has not yet been possible, however, to purify HSCs in adult zebrafish due to a lack of specific HSC markers. Here we show the enrichment of zebrafish HSCs by a combination of two HSC-related transgenes, gata2a:GFP and runx1:mCherry. The double-positive fraction of gata2a:GFP and runx1:mCherry (gata2a+runx1+) was detected at approximately 0.16% in the kidney, the main hematopoietic organ in teleosts. Transcriptome analysis revealed that gata2a+runx1+ cells showed typical molecular signatures of HSCs, including upregulation of gata2b, gfi1aa, runx1t1, pbx1b, and meis1b. Transplantation assays demonstrated that...

Experimental Hematology, 2019

Development, 2019

In order to efficiently derive hematopoietic stem cells (HSCs) from pluripotent precursors, it is... more In order to efficiently derive hematopoietic stem cells (HSCs) from pluripotent precursors, it is crucial to understand how mesodermal cells acquire hematopoietic and endothelial identities, two divergent, but closely related cell fates. Although Npas4 has been recently identified as a conserved master regulator of hemato-vascular development, the molecular mechanisms underlying cell fate divergence between hematopoietic and vascular endothelial cells are still unclear. Here, we show in zebrafish that mesodermal cell differentiation into hematopoietic and vascular endothelial cells is regulated by Junctional adhesion molecule 3b (Jam3b) via two independent signaling pathways. Mutation of jam3b led to a reduction in npas4l expression in the posterior lateral plate mesoderm and defects in both hematopoietic and vascular development. Mechanistically, we uncover that Jam3b promotes endothelial specification by regulating npas4l expression through repression of the Rap1a-Erk signaling ca...