Breast cancer brain metastasis commonly occurs in one-fourth of breast cancer patients and is associated with poor prognosis. Abnormal glucose metabolism is found to promote cancer metastasis. Moreover, the tumor microenvironment is crucial and plays an active role in the metabolic adaptations and survival of cancer cells. Glucose transporters are overexpressed in cancer cells to increase glucose uptake. The glucose transporter 3 (GLUT3) is a high-affinity glucose transporter that is highly expressed in mammalian neurons. GLUT3 is also overexpressed in several malignant brain tumors. However, the role of GLUT3 in breast cancer brain metastasis remains unknown. The results of the present study demonstrated that GLUT3 is highly overexpressed in brain metastatic breast cancers and mediates glucose metabolic reprogramming. Furthermore, knockdown of cAMP-response element binding protein (CREB) could directly regulate GLUT3 expression in brain metastatic breast cancer cells. Notably, we verified and provided a novel role of GLUT3 in mediating glucose metabolism and assisting breast cancer cells to survive in the brain to promote brain metastasis.

Ischemic stroke is a leading cause of human death in present times. Two phases of pathological impact occur during an ischemic stroke, namely, ischemia and reperfusion. Both periods include individual characteristic effects on cell injury and apoptosis. Moreover, these conditions can cause severe cell defects and harm the blood-brain barrier (BBB). Also, the BBB components are the major targets in ischemia-reperfusion injury. The BBB owes its enhanced protective roles to capillary endothelial cells, which maintain BBB permeability. One of the nerve growth factor (NGF) receptors initiating cell signaling, once activated, is the p75 neurotrophin receptor (p75NTR). This receptor is involved in both the survival and apoptosis of neurons. Although many studies have attempted to explain the role of p75NTR in neurons, the mechanisms in endothelial cells remain unclear. Endothelial cells are the first cells to encounter p75NTR stimuli. In this study, we found the upregulated p75NTR expression and reductive expression of tight junction proteins after in vivo and in vitro ischemia-reperfusion injury. Moreover, astaxanthin (AXT), an antioxidant drug, was utilized and was found to reduce p75NTR expression and the number of apoptotic cells. This study verified that p75NTR plays a prominent role in endothelial cell death and provides a novel downstream target for AXT.

Breast cancer brain metastases (BBMs) are found in 15–20 % of breast cancer patients. And it results in a high mortality once the brain metastases are diagnosed. Therefore, making it more comprehensive about the mechanisms of BBMs is emergently necessary. Several studies have demonstrated that tumor microenvironment has potent roles in the tumor progression and metastasis. Besides, according to the former studies, cells in different organs using glucose might be various; as well as the dominant glucose transporters used are distinct. Here, we analyzed the brain metastatic breast cancer (BR) cells collected from intracardiac injection of nude mice and found the utilization of glucose transporters in the BR cells were different from the parental breast cancer cells; the elevated expressions of glucose transporter 3 were observed. In addition, the higher anaerobic glycolysis ability was found in BR cells. And after GLUT3 knockdown, the glucose reprogramming in BR cells was significantly decreased as well as the cancer malignant behaviors both in vitro and in vivo. Besides manipulating GLUT3 expressions, we also provide a potential mechanism that CREB could be a potent regulator of GLUT3 in BR cells by chromatin immunoprecipitation (ChIP) and knockdown assay. After decreasing the expressions of CREB in BR cells, the expressions of GLUT3 were also significantly reduced. In sum, our results reveal that GLUT3 plays an important role in provoking breast cancer cells surviving in brain by mediating glucose utilizations. And these results could provide a potential therapeutic way to target BBMs. Support or Funding Information 1. Ministry of Science and Technology, R.O.C 2. Molecular Medicine Taiwan International Graduate Program, Academia Sinica