Background Long-term exposure to ambient fine particulate matter (PM_2.5) is a significant risk factor for cardiometabolic disorders. However, the mechanisms of its interaction with the endogenous circadian system remain incompletely understood. Objective To investigate whether chronic PM_2.5 exposure interferes with the rhythmic expression of the cardiac circadian clock, thereby disrupting downstream antioxidant defenses and metabolic homeostasis, and ultimately driving cardiometabolic dysfunction. Methods Seventy-two male C57BL/6 mice were randomly divided into a PM_2.5 exposure group (PM group) and a filtered air control group (FA group). Whole-body exposure was conducted for 8 weeks in a meteorological environmental animal exposure system. Samples were collected at six distinct zeitgeber time (ZT) points post-exposure. The 24 h ambulatory blood pressure and serum lipid profiles were monitored. Rhythm parameters were derived via cosinor analysis to compare differences in Midline statistic of rhythm (Mesor), amplitude, and phase between the two groups. The rhythmic expression of core circadian clock genes and antioxidant genes in the myocardium was detected by quantitative polymerase chain reaction (qPCR). Myocardial reactive oxygen species (ROS) levels and downstream pathway protein expression were analyzed by immunofluorescence and Western blot (WB), respectively. The expression changes of the clock gene retinoic acid receptor-related orphan receptor α (RORα) were assessed at both the mRNA and protein levels. Finally, Spearman correlation analysis was used to explore the relationships among myocardial RORα expression, lipid profiles, and oxidative stress indicators. Results Compared to the FA group, mice in the PM group exhibited a blunted circadian rhythm in blood pressure, characterized by sustained elevation throughout the day. Chronic PM_2.5 exposure showed a significant interaction with ZT on systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) (F-interaction=9.11, 5.70, and 6.02, respectively; P<0.05), as well as on serum triglycerides (TG), total cholesterol (T-CHO), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) (F-interaction=16.32, 11.12, 15.39, and 28.09, respectively; P<0.05). Cosinor analysis further revealed that the Mesor values of T-CHO, TG, and LDL-C were significantly increased (P<0.05), while that of HDL-C was significantly decreased in the PM group (P<0.05). The oscillation amplitudes of SBP, DBP, and MAP showed a decreasing trend, whereas those of TG and LDL-C were significantly increased (P<0.05). Furthermore, SBP, T-CHO, and HDL-C all exhibited a significant phase delay (P<0.05). Mechanistically, PM_2.5 exposure significantly suppressed the expression of the positive circadian regulator RORα in the myocardium, leading to disordered rhythmic expression of core clock genes (Bmal1, Clock, Per1/2, and Cry1/2). This exposure also inhibited the rhythmic expression of antioxidant genes (GPX1, SOD2, and CAT), resulting in increased ROS generation and elevated expression of calcium/calmodulin-dependent protein kinase II (CaMKII) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) proteins. Correlation analysis further revealed that myocardial RORα expression level was negatively correlated with T-CHO, TG, and LDL-C (r=−0.55, −0.63, and −0.51, respectively; P<0.001), and positively correlated with HDL-C (r=0.37, P=0.010), and antioxidant genes GPX1, SOD2, and CAT expression (r=0.34, 0.35, and 0.56, respectively; P < 0.001). Conclusion Chronic PM_2.5 exposure induces cardiometabolic dysfunction by suppressing myocardial RORα expression. This suppression disrupts the cardiac circadian clock and the diurnal balance of oxidative stress, triggering oxidative damage and elevating expression of CaMKII/NADPH pathway proteins. Collectively, these alterations precipitate the loss of cardiac metabolic rhythms and subsequent functional impairment.

BACKGROUND:Bone tissue defects are one of the most common diseases in orthopedics,and the current treatments for this disease are inadequate.The development of tissue engineering brings new hope for bone defect repair:by regulating the release of bioactive substances and the process of vascularization and neurogenesis at the defect site,it can effectively improve the microenvironment of bone tissue and promote osseointegration,which is the most promising research idea for large-size bone defect repair. OBJECTIVE:To explore the research progress of regulating bone microenvironment changes in bone defect repair in recent years from the effects of bioactive substances,vascularization and neurotization on three aspects of bone microenvironment changes,and to provide new ideas and strategies for the treatment of large-size bone defects. METHODS:The search terms"bone tissue engineering,angiogenesis,neurotization,cytokines,bone morphogenetic protein,vascular endothelial growth factor,neuropeptides,bone microenvironment"in Chinese and English were used to search for articles on the influence of changes in the bone microenvironment and their application in bone tissue engineering published from January 1,2001 to December 31,2022 on CNKI,WanFang,Web of Science,Science Direct,and PubMed.Finally,109 articles were included for review. RESULTS AND CONCLUSION:(1)The bone microenvironment is essential for the induction of bone tissue stem cell growth and differentiation,and mainly consists of the extracellular matrix of the bone tissue seeds and the biochemical factors required for intercellular interactions,the local blood circulation network and the surrounding nerve tissue.(2)Bone defect repair is a continuous process divided into multiple phases that overlap and are mediated by multiple cytokines,and the same cytokine can have mutually synergistic or antagonistic effects in one or more healing phases.(3)Neovascular regeneration is key to initiating bone repair,as neovascularisation not only provides essential nutrients,osteoblasts and growth factors for bone repair,but is also a gateway for repair cells to enter the injury zone.(4)In addition to regulating the type,dose and timeliness of vascular-inducing factor release to achieve blood transport reconstruction.The study of differential release delivery systems of multiple factors and the application of gene transfer technology will be the future research direction to solve large bone defects.(5)Neuropeptides can bind to relevant receptors and act on specific signaling pathways to guide vascular growth and influence bone healing,bone regeneration and the balance between osteogenesis and osteolysis through a variety of pathways.(6)In the establishment of neuralized tissue-engineered bone,the role of changes in the bone tissue microenvironment and neuromodulation is bidirectional.Cytokines in the bone matrix can participate in neuronal signaling pathways through the blood-nerve barrier.Neuropeptides secreted by glial cells act on the bone microenvironment,affecting bone healing,bone regeneration and the balance between osteogenesis and osteolysis.(7)There are still many questions regarding the regulation of the bone microenvironment by bioactive substances and the processes of vascularization and neurogenesis,such as the rapid diffusion and degradation of cytokines in the body and their loss of activity,the temporal and spatial distribution of angiogenesis-related growth factors,and the establishment of neurogenesis through the body's feedback regulatory mechanism,which need to be improved by subsequent studies.