Biomechanical Effects of Mechanical Stress on Cells Involved in Fracture Healing.

Fracture healing is a complex staged repair process in which the mechanical environment plays a key role. Bone tissue is very sensitive to mechanical stress stimuli, and the literature suggests that appropriate stress can promote fracture healing by altering cellular function. However, fracture healing is a coupled process involving multiple cell types that balance and limit each other to ensure proper fracture healing. The main cells that function during different stages of fracture healing are different, and the types and molecular mechanisms of stress required are also different. Most previous studies have used a single mechanical stimulus on individual mechanosensitive cells, and there is no relatively uniform standard for the size and frequency of the mechanical stress. Analyzing the mechanisms underlying the effects of mechanical stimulation on the metabolic regulation of signaling pathways in cells such as in bone marrow mesenchymal stem cells (BMSCs), osteoblasts, chondrocytes, and osteoclasts is currently a challenging research hotspot. Grasping how stress affects the function of different cells at the molecular biology level can contribute to the refined management of fracture healing. Therefore, in this review, we summarize the relevant literature and describe the effects of mechanical stress on cells associated with fracture healing, and their possible signaling pathways, for the treatment of fractures and the further development of regenerative medicine.

MSCs-derived exosomes containing miR-486-5p attenuate cerebral ischemia and reperfusion (I/R) injury.

OBJECTIVES: This study aims to investigate the impact of mesenchymal stem cell (MSC)-derived exosomes (Exo) on cerebral ischemia and reperfusion (I/R) injury, along with the underlying mechanism. METHODS: An animal model of cerebral ischemia was induced using middle cerebral artery occlusion (MCAO), and a cell model utilizing Neuro-2a cells was established through oxygen-glucose deprivation/reoxygenation (OGD/R). Exosomes isolated from mouse MSCs were administered to mice or used to stimulate Neuro-2a cells. Exosomes from MSCs transfected with miR-NC, miR-486-5p mimics, miR-486-5p inhibitor, or phosphatase and tensin homolog (PTEN) short hairpin RNAs (sh-PTEN) were employed to stimulate Neuro-2a cells. The regulatory axis of miR-486-5p and PTEN was confirmed through rescue experiments. RESULTS: Exo-miR-486-5p mimics alleviated cerebral I/R injury, improving neurological deficits and reducing the infarct ratio. Furthermore, Exo-miR-486-5p mimics attenuated OGD/R-induced defects in cell viability and inhibited apoptosis in Neuro-2a cells. These mimics also reduced levels of lactate dehydrogenase (LDH) and malondialdehyde (MDA) while enhancing superoxide dismutase (SOD) activity, both in brain tissue homogenates of mice and cell supernatants. Mechanistically, PTEN was identified as a target of miR-486-5p, and the downregulation of PTEN notably elevated Exo-miR-486-inhibitor-induced reductions in cell viability while mitigating cell apoptosis. CONCLUSION: The results of this study demonstrate the potential of exosomes derived from MSCs to protect against cerebral I/R injury via the miR-486-5p and PTEN axis.

Histone demethylase KDM5D represses the proliferation, migration and invasion of hepatocellular carcinoma through the E2F1/TNNC1 axis.

OBJECTIVE: This study focused on investigating the mechanism in which the KDM5D/E2F1/TNNC1 axis affected hepatocellular carcinoma (HCC) development. METHODS: At first, we determined HCC cell proliferation, migration, invasion, and apoptosis, as well as SOD activity, MDA content, and ROS level. ChIP assay was subsequently conducted to examine H3K4me3 modification in the E2F1 promoter region and the binding of E2F1 to the TNNC1 promoter region after KDM5D overexpression. Meanwhile, we performed western blot for testing KDM5D, H3K4me3, and E2F1 expression after KDM5D overexpression in Huh-7 cells. The binding of transcription factor E2F1 to the TNNC1 promoter region was assessed by dual luciferase reporter gene assay. We further observed the tumor growth ability in nude mice transplanted tumor models. RESULTS: Overexpressed KDM5D suppressed HCC proliferation, migration, and invasion, promoted the apoptosis, suppressed SOD activity, elevated MDA content and ROS level, and promoted ferroptosis. KDM5D suppressed H3K4me3 modification in the E2F1 promoter region and suppressed E2F1 expression in HCC cells. Reduced KDM5D, H3K4me3, and E2F1 expression was found after KDM5D overexpression in Huh-7 cells. Overexpressing E2F1 reversed the inhibitory effects of KDM5D on HCC cell proliferative, migratory, and invasive behaviors. KDM5D repressed TNNC1 transcription by inhibiting E2F1 binding to the TNNC1 promoter. In vivo KDM5D overexpression inhibited HCC development via the E2F1/TNNC1 axis. CONCLUSION: KDM5D inhibits E2F1 expression by suppressing H3K4me3 modification in the E2F1 promoter region, which in turn suppresses the binding of E2F1 to the TNNC1 promoter region, thus leading to the inhibition of HCC development.

Activation of Hypoxia Inducible Factor-1 Alpha-Mediated DNA Methylation Enzymes (DNMT3a and TET2) Under Hypoxic Conditions Regulates S100A6 Transcription to Promote Lung Cancer Cell Growth and Metastasis.

Aims: This research was aimed at investigating the effects of hypoxia inducible factor-1 alpha (HIF-1α)-mediated DNA methylation enzymes (ten-eleven translocase-2 [TET2] and DNA methyltransferase-3a [DNMT3a]) under hypoxic conditions on S100A6 transcription, thereby promoting the growth and metastasis of lung cancer cells. Methods: The expression of HIF-1α or S100A6 in lung cancer cells was interfered with under normoxic and hypoxic conditions, and the cell proliferative, migratory, and invasive properties were assessed. The mechanism of HIF-1α-regulated TET2 and DNMT3 effects on S100A6 transcription under hypoxic conditions was further investigated. Results: Functionally, S100A6 over-expression promoted lung cancer cell proliferation and metastasis. S100A6 over-expression reversed the inhibitory effects of HIF-1α interference on the proliferation and metastasis of lung cancer cells. S100A6 was induced to express in an HIF-1α-dependent manner under hypoxic conditions, and silencing S100A6 or HIF-1α suppressed lung cancer cell proliferation and metastasis under hypoxic conditions. Further, The Cancer Genome Atlas-lung adenocarcinoma database analysis revealed that S100A6 mRNA levels had a negative correlation with methylation levels. Mechanistically, CpG hypomethylation status in the S100A6 promoter hypoxia response element had an association with HIF-1α induction. TET2 was enriched in S100A6 promoter region of lung cancer cells under hypoxic conditions, whereas DNMT3a enrichment was reduced in S100A6 promoter region. HIF-1α-mediated S100A6 activation was linked to DNMT3a-associated epigenetic inactivation and TET2 activation. Innovation: The activation of HIF-1α-mediated DNA methylation enzymes under hypoxic conditions regulated S100A6 transcription, thereby promoting lung cancer cell growth and metastasis. Conclusion: In lung cancer progression, hypoxia-induced factor HIF-1α combined with DNA methylation modifications co-regulates S100A6 transcriptional activation and promotes lung cancer cell growth and metastasis.