Mechanisms of ischaemic neural progenitor proliferation: a regulatory role of the HIF‐1α‐CBX7 pathway

CBX7 promotes choroidal neovascularization by activating the HIF-1α/VEGF pathway in choroidal vascular endothelial cells

Vascular endothelial growth factor (VEGF) signaling is crucial for choroidal neovascularization (CNV), a major pathological feature of neovascular age-related macular degeneration (nAMD). Gene transcription of VEGF is mainly regulated by hypoxia-inducible factor 1-alpha (HIF-1α). The chromobox (CBX) family polycomb protein (Pc) subgroup includes CBX2, CBX4, CBX6, CBX7, and CBX8. CBX4 enhances hypoxia-induced VEGF expression and angiogenesis in hepatocellular carcinoma (HCC) cells by increasing HIF-1α's transcriptional activity. The objective of the study was to examine the functions of members of the CBX family Pc subgroup in choroidal vascular endothelial cells (CVECs) during CNV. CBX4 and CBX7 expression was up-regulated in hypoxic human choroidal vascular endothelial cells (HCVECs). In HCVECs, CBX7 facilitated HIF-1α transcription and expression, while CBX4 did not. In HCVECs, CBX7 stimulated HIF-1α's nuclear translocation and transcriptional activity, which in turn stimulated VEGF transcription and expression. The CBX7/HIF-1α/VEGF pathway promoted the migration, proliferation, and tube formation of HCVECs. The CBX7/HIF-1α/VEGF pathway was up-regulated in CVECs and in the mouse model with laser-induced CNV. Mouse CNV was lessened by the blockade of CBX7 through the down-regulation of HIF-1α/VEGF. In conclusion, CBX7 enhanced pro-angiogenic behaviors of hypoxic CVECs by up-regulating the HIF-1α/VEGF pathway, which contributing to the formation of mouse laser-induced CNV.

Hypoxia effects on glioblastoma progression through YAP/TAZ pathway regulation

The resistance of glioblastomas (GBM) to standard therapies poses a clinical challenge with limited survival despite interventions. The tumor microenvironment (TME) orchestrates GBM progression, comprising stromal and immune cells and is characterized by extensive hypoxic regions. Hypoxia activates the hypoxia-inducible factor 1 alpha (HIF-1α) pathway, interacting with the Hippo pathway (YAP/TAZ) in crucial cellular processes. We discuss here the related signaling crosstalk between YAP/TAZ and regions of hypoxia in the TME with particular attention on the MST1/2 and LATS1/2-regulated YAP/TAZ activation, impacting cell proliferation, invasion, and stemness. Moreover, the hypoxia-YAP/TAZ axis influence on angiogenesis, stem cells, and metabolic regulators is defined. By reviewing extracellular matrix alterations activation of YAP/TAZ, modulation of signaling pathways we also discuss the significance of spatial constraints and epigenetic modifications contribution to GBM progression, with potential therapeutic targets in YAP/TAZ-mediated gene regulation. Comprehensive understanding of the hypoxia-Hippo pathway-TME interplay offers insights for novel therapeutic strategies, aiming to provide new directions for treatment.

HIF-1α promotes astrocytic production of macrophage migration inhibitory factor following spinal cord injury

BACKGROUND

Macrophage migration inhibitory factor (MIF) is an important mediator of neuropathology in various central nervous system (CNS) diseases. However, little is known about its inducers for production from the nerve cells, as well as the underlying regulatory mechanism. Injury-induced HIF-1α has been shown to exacerbate neuroinflammation by activating multiple downstream target molecules. It is postulated that HIF-1α is involved in the regulation of MIF following spinal cord injury (SCI).

METHODS

SCI model of Sprague-Dawley rats was established by cord contusion at T8-T10. The dynamic changes of HIF-1α and MIF protein levels at lesion site of rat spinal cord were determined by Western blot. The specific cell types of HIF-1α and MIF expression were examined by immunostaining. Primary astrocytes were isolated from the spinal cord, cultured and stimulated with various agonist or inhibitor of HIF-1α for analysis of HIF-1α-mediated expression of MIF. Luciferase report assay was used to determine the relationship between HIF-1α and MIF. The Basso, Beattie, and Bresnahan (BBB) locomotor scale was used to assess the locomotor function following SCI.

RESULTS

The protein levels of HIF-1α and MIF at lesion site were significantly elevated by SCI. Immunofluorescence demonstrated that both HIF-1α and MIF were abundantly expressed in the astrocytes of the spinal cord. By using various agonists or inhibitors of HIF-1α, it was shown that HIF-1α sufficiently induced astrocytic production of MIF. Mechanistically, HIF-1α promoted MIF expression through interaction with MIF promoter. Inhibition of HIF-1α activity using specific inhibitor markedly reduced the protein levels of MIF at lesion site following SCI, which in turn favored for the functional recovery.

CONCLUSION

SCI-induced activation of HIF-1α is able to promote MIF production from astrocytes. Our results have provided new clues for SCI-induced production of DAMPs, which may be helpful for clinical treatment of neuroinflammation.

CBX7 Rejuvenates Late Passage Dental Pulp Stem Cells by Maintaining Stemness and Pro-angiogenic Ability

BACKGROUND

Ever-growing tissue regeneration causes pressing need for large population of stem cells. However, extensive cell expansion eventually leads to impaired regenerative potentials. In this study, chromobox protein homolog 7 (CBX7) was overexpressed to rejuvenate late passage dental pulp stem cells (DPSCs-P9).

METHODS

The recruitment of copper ions (Cu2+)-activated hypoxia-inducible factor-1α (HIF-1α) to the CBX7 gene promoter was confirmed by chromatin immunoprecipitation assay. Functions subsequent to Cu2+-induced or recombinant overexpression of CBX7 on proliferation, multipotency, odontoblastic differentiation and angiogenesis were investigated in vitro, while murine subcutaneous transplantation model was used to further detect the effects of Cu2+-induced CBX7 overexpression in vivo.

RESULTS

Our data displayed that CBX7 overexpression maintain proliferation and multipotency of DPSCs-P9 almost as strong as those of DPSCs-P3. Both gene level of odontoblast-lineage markers and calcium precipitation were nearly the same between CBX7 overexpressed DPSCs-P9 and normal DPSCs-P3. Moreover, we also found upregulated expression of vascular endothelial growth factor in DPSCs-P9 with CBX7 overexpression, which increased the number of capillary-like structures and migrating co-cultured human umbilical vein endothelial cells as well. These findings indicate CBX7 as an effective factor to rejuvenate late passage stem cells insusceptible to cell expansion. Cu2+ has been proved to achieve CBX7 overexpression in DPSCs through the initiation of HIF-1α-CBX7 cascade. Under Cu2+ stimulation since P3, DPSCs-P9 exhibited ameliorated regenerative potential both in vitro and in vivo.

CONCLUSION

Long-term stimulation of Cu2+ to overexpress CBX7 could be a new strategy to manufacture large population of self-renewing stem cells.

Neuroprotection of chromobox 7 knockout in the mouse after cerebral ischemia-reperfusion injury via nuclear factor E2-related factor 2/hemeoxygenase-1 signaling pathway

OBJECTIVE

To explore the mechanism of chromobox 7 (CBX7)-mediated nuclear factor E2-related factor 2 (Nrf2)/hemeoxygenase-1 (HO-1) signaling pathway in the cerebral ischemia/reperfusion (I/R) injury.

METHODS

The experimental wild-type (WT) and CBX7^-/- mice were used to establish cerebral I/R models using the middle cerebral artery occlusion (MCAO) surgery to determine CBX7 levels at different time points after MCAO injury. For all mice, neurological behavior, infarct size, water content, and oxidative stress-related indicators were determined, and transferase (TdT)-mediated dUTP-biotin nick-end labeling (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL)) staining method was employed to observe cell apoptosis, while Western blot to measure the expression of CBX7 and Nrf/HO-1 pathway-related proteins.

RESULTS

At 6 h, 12 h, 24 h, 3 days, and 7 days after mice with MCAO, CBX7 expression was gradually up-regulated and the peak level was reached at 24 h. Mice in the WT + MCAO group had increased infarct size, with significant increases in the modified neurological severity scores and water content in the brain, as well as the quantity of TUNEL-positive cells. For the oxidative stress-indicators, an increase was seen in the content of MDA (malondial dehyde), but the activity of SOD (superoxide dismutase) and content of GSH-PX (glutathione peroxidase) and CAT (catalase) were decreased; meanwhile, the protein expression of CBX7, HO-1, and nuclear Nrf2 was up-regulated, while the cytoplasmic Nrf2 was down-regulated. Moreover, CBX7 knockout attenuated I/R injury in mice.

CONCLUSION

Knockout of CBX7 may protect mice from cerebral I/R injury by reducing cell apoptosis and oxidative stress, possibly via activating the Nrf2/HO-1 pathway.

The role of hypoxia in stem cell regulation of the central nervous system: From embryonic development to adult proliferation

Hypoxia is involved in the regulation of various cell functions in the body, including the regulation of stem cells. The hypoxic microenvironment is indispensable from embryonic development to the regeneration and repair of adult cells. In addition to embryonic stem cells, which need to maintain their self-renewal properties and pluripotency in a hypoxic environment, adult stem cells, including neural stem cells (NSCs), also exist in a hypoxic microenvironment. The subventricular zone (SVZ) and hippocampal dentate gyrus (DG) are the main sites of adult neurogenesis in the brain. Hypoxia can promote the proliferation, migration, and maturation of NSCs in these regions. Also, because most neurons in the brain are non-regenerative, stem cell transplantation is considered as a promising strategy for treating central nervous system (CNS) diseases. Hypoxic treatment also increases the effectiveness of stem cell therapy. In this review, we firstly describe the role of hypoxia in different stem cells, such as embryonic stem cells, NSCs, and induced pluripotent stem cells, and discuss the role of hypoxia-treated stem cells in CNS diseases treatment. Furthermore, we highlight the role and mechanisms of hypoxia in regulating adult neurogenesis in the SVZ and DG and adult proliferation of other cells in the CNS.

CBX7 is Dualistic in Cancer Progression Based on its Function and Molecular Interactions

Chromobox protein homolog 7 (CBX7) is a member of the Chromobox protein family and participates in the formation of the polycomb repressive complex 1(PRC1). In cells, CBX7 often acts as an epigenetic regulator to regulate gene expression. However, pathologically, abnormal expression of CBX7 can lead to an imbalance of gene expression, which is closely related to the occurrence and progression of cancers. In cancers, CBX7 plays a dual role; On the one hand, it contributes to cancer progression in some cancers by inhibiting oncosuppressor genes. On the other hand, it suppresses cancer progression by interacting with different molecules to regulate the synthesis of cell cycle-related proteins. In addition, CBX7 protein may interact with different RNAs (microRNAs, long noncoding RNAs, circular RNAs) in different cancer environments to participate in a variety of pathways, affecting the development of cancers. Furthermore, CBX7 is involved in cancer-related immune response and DNA repair. In conclusion, CBX7 expression is a key factor in the occurrence and progression of cancers.

Neuroprotection of chromobox 7 knockout in the mouse after cerebral ischemia-reperfusion injury via nuclear factor E2-related factor 2/hemeoxygenase-1 signaling pathway

OBJECTIVE

To explore the mechanism of chromobox 7 (CBX7)-mediated nuclear factor E2-related factor 2 (Nrf2)/hemeoxygenase-1 (HO-1) signaling pathway in the cerebral ischemia/reperfusion (I/R) injury.

METHODS

The experimental wild-type (WT) and CBX7^-/- mice were used to establish cerebral I/R models using the middle cerebral artery occlusion (MCAO) surgery to determine CBX7 levels at different time points after MCAO injury. For all mice, neurological behavior, infarct size, water content, and oxidative stress-related indicators were determined, and transferase (TdT)-mediated dUTP-biotin nick-end labeling (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL)) staining method was employed to observe cell apoptosis, while Western blot to measure the expression of CBX7 and Nrf/HO-1 pathway-related proteins.

RESULTS

At 6 h, 12 h, 24 h, 3 days, and 7 days after mice with MCAO, CBX7 expression was gradually up-regulated and the peak level was reached at 24 h. Mice in the WT + MCAO group had increased infarct size, with significant increases in the modified neurological severity scores and water content in the brain, as well as the quantity of TUNEL-positive cells. For the oxidative stress-indicators, an increase was seen in the content of MDA (malondial dehyde), but the activity of SOD (superoxide dismutase) and content of GSH-PX (glutathione peroxidase) and CAT (catalase) were decreased; meanwhile, the protein expression of CBX7, HO-1, and nuclear Nrf2 was up-regulated, while the cytoplasmic Nrf2 was down-regulated. Moreover, CBX7 knockout attenuated I/R injury in mice.

CONCLUSION

Knockout of CBX7 may protect mice from cerebral I/R injury by reducing cell apoptosis and oxidative stress, possibly via activating the Nrf2/HO-1 pathway.

Hypoxia-Inducible Factor (HIF) in Ischemic Stroke and Neurodegenerative Disease

Hypoxia is one of the most common pathological conditions, which can be induced by multiple events, including ischemic injury, trauma, inflammation, tumors, etc. The body's adaptation to hypoxia is a highly important phenomenon in both health and disease. Most cellular responses to hypoxia are associated with a family of transcription factors called hypoxia-inducible factors (HIFs), which induce the expression of a wide range of genes that help cells adapt to a hypoxic environment. Basic mechanisms of adaptation to hypoxia, and particularly HIF functions, have being extensively studied over recent decades, leading to the 2019 Nobel Prize in Physiology or Medicine. Based on their pivotal physiological importance, HIFs are attracting increasing attention as a new potential target for treating a large number of hypoxia-associated diseases. Most of the experimental work related to HIFs has focused on roles in the liver and kidney. However, increasing evidence clearly demonstrates that HIF-based responses represent an universal adaptation mechanism in all tissue types, including the central nervous system (CNS). In the CNS, HIFs are critically involved in the regulation of neurogenesis, nerve cell differentiation, and neuronal apoptosis. In this mini-review, we provide an overview of the complex role of HIF-1 in the adaptation of neurons and glia cells to hypoxia, with a focus on its potential involvement into various neuronal pathologies and on its possible role as a novel therapeutic target.

Hypoxia-inducible factor (HIF) inhibitors: a patent survey (2016-2020)

Introduction: Hypoxia-inducible factor (HIF) is a master regulator of oxygen homeostasis. The increased expression of genes targeted by HIF is associated with many human diseases, including ischemic cardiovascular disease, stroke, chronic lung disease, and cancer.Areas covered: This patent survey summarizes the information about patented HIF inhibitors over the last 5 years.Expert opinion: HIF inhibitors have shown promise for the treatment of hypoxic pulmonary hypertension, a circadian rhythm disorder, calcific aortic valve disease, cerebrovascular accident, and heterotopic ossification. In addition, HIF-2α inhibitors can be used for the treatment or prevention of iron overload disorders, Crohn's disease, ulcerative colitis, and thyroid eye disease, or to improve muscle generation and repair. PT2385 completed phase I clinical trials for the treatment of clear cell renal cell carcinoma. It exerted a higher synergistic inhibitory effect on tumor growth in combination with anti-PD-1 antibody, in comparison with each treatment alone, indicating that effective immunotherapy for solid tumors counteracts of the immunosuppression induced by hypoxia. Therefore, considering the effects of hypoxia on cancer cells, stromal cells, and effector immune cells, it is important to develop inhibitors of molecular pathways activated by hypoxia for successful treatments.

CBX7 suppression prevents ischemia-reperfusion injury-induced endoplasmic reticulum stress through the Nrf-2/HO-1 pathway

Renal ischemia-reperfusion injury (I/R) usually occurs in renal transplantation and partial nephrectomy, which could lead to acute kidney injury. However, the effective treatment for renal I/R still remains limited. In the present study, we investigated whether inhibition of chromobox 7 (CBX7) could attenuate renal I/R injury in vivo and in vitro as well as the potential mechanisms. Adult male mice were subjected to right renal ischemia and reperfusion for different periods, both with and without the CBX7 inhibitor UNC3866. In addition, human kidney cells (HK-2) were subjected to a hypoxia/reoxygenation (H/R) process for different periods, both with or without the CBX7 inhibitor or siRNA for CBX7. The results showed that expression of CBX7, glucose regulator protein-78 (GRP78), phosphorylated eukaryotic translation initiation factor-2α (p-eIF2α), and C/EBP homologous protein (CHOP) were increased after extension of I/R and H/R periods. Moreover, overexpression of CBX7 could elevate the expression of CBX7, GRP78, p-eIF2α, and CHOP. However, CBX7 inhibition with either UNC3866 or genetic knockdown led to reduced expression of GRP78, p-eIF2α, and CHOP through nuclear factor-erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 activation in I/R and H/R injury. Furthermore, ML385, the Nrf2 inhibitor, could elevate endoplasmic reticulum stress levels, abrogating the protective effects of UNC3866 against renal I/R injury. In conclusion, our results demonstrated that CBX7 inhibition alleviated acute kidney injury by preventing endoplasmic reticulum stress via the Nrf2/HO-1 pathway, indicating that CBX7 inhibitor could be a potential therapeutic target for renal I/R injury.