Transcription factor PpNAC1 and DNA demethylase PpDML1 synergistically regulate peach fruit ripening.

Fruit ripening is accompanied by dramatic changes in color, texture, and flavor and is regulated by transcription factors (TFs) and epigenetic factors. However, the detailed regulatory mechanism remains unclear. Gene expression patterns suggest that PpNAC1 (NAM/ATAF1/2/CUC) TF plays a major role in peach (Prunus persica) fruit ripening. DNA affinity purification (DAP)-seq combined with transactivation tests demonstrated that PpNAC1 can directly activate the expression of multiple ripening-related genes, including ACC synthase1 (PpACS1) and ACC oxidase1 (PpACO1) involved in ethylene biosynthesis, pectinesterase1 (PpPME1), pectate lyase1 (PpPL1), and polygalacturonase1 (PpPG1) related to cell wall modification, and lipase1 (PpLIP1), fatty acid desaturase (PpFAD3-1), and alcohol acyltransferase1 (PpAAT1) involved in volatiles synthesis. Overexpression of PpNAC1 in the tomato (Solanum lycopersicum) nor (nonripening) mutant restored fruit ripening, and its transient overexpression in peach fruit induced target gene expression, supporting a positive role of PpNAC1 in fruit ripening. The enhanced transcript levels of PpNAC1 and its target genes were associated with decreases in their promoter mCG methylation during ripening. Declining DNA methylation was negatively associated with increased transcripts of DNA demethylase1 (PpDML1), whose promoter is recognized and activated by PpNAC1. We propose that decreased methylation of the promoter region of PpNAC1 leads to a subsequent decrease in DNA methylation levels and enhanced transcription of ripening-related genes. These results indicate that positive feedback between PpNAC1 and PpDML1 plays an important role in directly regulating expression of multiple genes required for peach ripening and quality formation.

HIF-1α mediates osteoclast-induced disuse osteoporosis via cytoophidia in the femur of mice.

Osteoporosis induced by disuse because of bed rest or the aerospace industry has become one of the most common skeletal disorders. However, mechanisms underlying the disuse osteoporosis remain largely unknown. We validated the tail-suspended model in mice and demonstrated that there is bone loss in the trabecular and cortical bones of the femur. Importantly, we showed that genetical deletion of hypoxia-inducible factor-1α (HIF-1α) in osteoclasts ameliorated osteoclastic bone resorption in the trabecular bone whereas pharmacological treatment with HIF-1α inhibitor protected the hindlimb-unloaded mice from disuse-induced osteoporosis in the trabecular and cortical bones. The HIF-1α knockout RAW264.7 cells and RNA-sequencing proved that HIF-1α is vital for osteoclastogenesis and bone resorption because it regulated the level of inosine monophosphate dehydrogenase (IMPDH) and cytidine triphosphate synthetase (CTPS) via cellular myelocytomatosis (c-Myc) oncogene. The IMPDH and CTPS are vital nucleotide metabolic enzymes which have an important functional role in cell metabolism, and they can assemble into intracellular linear or ring-shaped structures to cope with cell stress. Interestingly, both in vitro and in vivo, the IMPDH and CTPS cytoophidia were found in osteoclasts, and the level of HIF-1α correlated with osteoclastogenesis and bone-resorbing activity. Our data revealed that HIF-1α/c-Myc/cytoophidia signalling might be required for osteoclasts to mediate cell metabolism in disuse-induced osteoporosis. Overall, our results revealed a new role of HIF-1α/c-Myc/cytoophidia in supporting osteoclastogenesis and bone resorption and exposed evidence for its role in the pathogenesis of disuse osteoporosis, which might provide promising therapeutic targets.

Hypoxia-induced factor 1α promotes osteotomy-induced regional acceleratory phenomenon via DC-STAMP mediated membrane fusion.

OBJECTIVES: The mechanisms of regional acceleratory phenomenon (RAP) induced by orthognathic osteotomy are unclear. It was not known if locally hypoxic microenvironment changes were involved in this phenomenon. METHODS: Hypoxia-induced factor-1α knockout mice harboring Cathepsin K (CTSK) Cre were used to investigate the effect of hypoxia-driven osteoclasts on alveolar bone remodeling. RAW264.7 cells were induced by CoCl2 to observe the effects of dendritic cell-specific transmembrane protein (DC-STAMP) on the fusion and differentiation of osteoclasts. RESULTS: We found mandibular osteotomy of C57 mice induced active alveolar osteoclasts and increased hypoxia-induced factor-1α (HIF-1α) positive staining areas. Alveolar bone density of the 10-week-old HIF-1α conditional knockout (CKO) mouse was increased at 10 and 14 days after bilateral mandibular osteotomy. Moreover, decreased numbers of osteoclasts and matrix metalloproteinase 9 (MMP-9)-positive cells were observed on the surface of bone resorption lacunae in the CKO group. HIF-1α could increase the expression level of DC-STAMP to enhance osteoclastogenesis and cell fusion in active RAW264.7 cells. CONCLUSION: Our data considered hypoxia-driven osteoclasts resorption to be an adaptive mechanism to permit alveolar bone loss after bilateral mandibular osteotomy of mice.

HIF-1α regulates osteoclast activation and mediates osteogenesis during mandibular bone repair via CT-1.

OBJECTIVES: Hypoxia is one of the characteristics of microenvironmental changes after orthognathic surgery for fractures. HIF-1α is a main regulator of the hypoxic response and plays a crucial role in bone formation, remodelling, and homeostasis. Osteoclasts participate in bone absorption and affect osteogenesis, and osteoclasts differentiate in a path from the oxygen-rich bone marrow to oxygen-deficient bone lesions. Thus, we aimed to study the key functions of HIF-1α in osteoclasts during mandibular healing after osteotomy. MATERIALS AND METHODS: The function of HIF-1α in osteoclasts during fracture healing in osteoclast-specific HIF-1α-conditional-knockout mice was investigated in mandibular osteotomy. Primary osteoclasts were used to explore the expression of HIF-1α and cardiotrophin-1 (CT-1) at both the mRNA and protein levels. The ability of BMSCs co-cultured with conditioned media from osteoclast-specific HIF-1α-knockout primary osteoclasts was detected using osteoclast-mediated osteogenesis experiments. RESULTS: Hypoxia-inducible factor-1α increased osteoclastogenesis and bone resorption, and a delay in bone healing was found in osteoclast-specific HIF-1α-conditional-knockout mice compared with normal mice. HIF-1α-knockout primary osteoclasts inhibited bone resorption and CT-1 expression, and HIF-1α enhanced the osteoclast-mediated stimulation of BMSC differentiation by secreting CT-1. CONCLUSIONS: Hypoxia-inducible factor-1α can play a key role in the physiology and pathogenesis of bone resorption by promoting osteoclastogenesis during fracture and influencing osteogenesis through CT-1 during bone healing.

[Study of digital visual mandible].

OBJECTIVE: To build a digital visible model of the mandible in order to provide morphological data for image diagnosis and operation of mandible diseases. METHODS: A male adult cadaver specimen was taken for the purpose of study. A digital human databank was got after fixation, perfusion, refrigeration, embedding, section and photograph of the specimen. The thickness of each layer was 0.1 mm. To select mandible image data from chin to condyle and to draw an outline of mandible and teeth image of each layer in 2D Adobe photoshop 8.0. Finally, reconstruct 3D model of mandible was set up in Amira reconstruction software. RESULTS: A 3D model of mandible was formed accurately using of digital human data. The model was fine, visible and displayed cross-section image of mandible. The anatomical shape of nmandible and mandibular teeth were vividly reappeared in three-dimension. The location and trend of mandibular nerve canal were clearly appeared in the transparent model of mandible. The model could be revolved in 3D. CONCLUSION: The study got a complete and exact cross-section data. The visualization of mandible can be realized in Amira reconstruction software. The reconstituted organs can be recovered to the natural state.

[Study of three dimensional reconstruction and visualization of human mandible].

PURPOSE: This study is designed to reconstruct 3-D digital visible mandibular model using digital human database. METHODS: An appropriate cadaver was fixed, and fused through arterial infusion, then embedded and sliced. The 2-D imaging data of mandible were obtained from this virtual human, and the virtual mandible was reconstructed using Amira software. RESULTS: Complete and accurate data of the mandible sections were collected, with which the virtual mandible was reconstructed three dimensionally. This virtual mandible displayed accurately the anatomical structure of the actual mandible, including the location and direction of the mandibular teeth and the mandibular canal. CONCLUSION: The 3-D mandible was constructed through the database of the digital human. The visible mandibular model will be an important learning tool in oral and maxillofacial anatomy and surgery, diagnosis and operation of mandibular diseases, and mandibular dental implantation.