Hypoxia within solid tumors is a major determinant of outcome after anticancer therapy. Analysis of gene expression changes during hypoxia indicated that unfolded protein response genes were one of the most robustly induced groups of genes. In this study, we investigated the hypoxic regulation of X-box binding protein (XBP1), a major transcriptional regulator of the unfolded protein response. Hypoxia induced XBP1 at the transcriptional level and activated splicing of its mRNA, resulting in increased levels of activated XBP1 protein. After exposure to hypoxia, apoptosis increased and clonogenic survival decreased in XBP1-deficient cells. Loss of XBP1 severely inhibited tumor growth due to a reduced capacity for these transplanted tumor cells to survive in a hypoxic microenvironment. Taken together, these studies directly implicate XBP1 as an essential survival factor for hypoxic stress and tumor growth.

Bile acids are steroid acids found predominantly in the bile of mammals. The bile acid conjugate tauroursodeoxycholic acid (TUDCA) is a neuroprotective agent in different animal models of stroke and neurological diseases. However, the anti-inflammatory properties of TUDCA in the central nervous system (CNS) remain unknown.

Tumors encounter endoplasmic reticulum stress during tumor growth and activate an adaptive pathway known as the unfolded protein response (UPR). Because this pathway is induced by the tumor microenvironment, it is a promising target for cancer therapy. We have previously demonstrated that X-box binding protein 1 (XBP-1), a key regulator of the UPR, was required for survival under hypoxia and critical for tumor growth in tumor xenografts. In this study, we investigated the role of XBP-1 in regulating tumor angiogenesis. We used an intradermal angiogenesis model to quantify the effect of XBP-1 on angiogenesis. We also used a human tumor xenograft model to assay for tumor growth delay. We determined vascular endothelial growth factor (VEGF) expression by quantitative polymerase chain reaction and ELISA. Finally, we stained human pancreatic adenocarcinoma specimens for XBP-1 expression and correlated the expression pattern of XBP-1 with CD31 (endothelial cell marker) expression. We demonstrated that XBP-1 is essential for angiogenesis during early tumor growth. Inhibiting XBP-1 expression by short-hairpin RNA sequence specific for XBP-1 reduced blood vessel formation in tumors from mouse embryonic fibroblast cells and human fibrosarcoma tumor cells (HT1080). Expressing a dominant-negative form of IRE1alpha also reduced blood vessel formation in tumors. Moreover, expression of spliced XBP-1 (XBP-1s) restored angiogenesis in IRE1alpha dominant-negative expressing cells. We further demonstrated that XBP-1-mediated angiogenesis does not depend on VEGF. We propose that the IRE1alpha-XBP-1 branch of the UPR modulates a complex proangiogenic, VEGF-independent response that depends on signals received from the tumor microenvironment.

Bile acids (BAs) are cholesterol derivatives synthesized in the liver and released into the digestive tract to facilitate lipid uptake during the digestion process. Most of these BAs are reabsorbed and recycled back to the liver. Some of these BAs progress to other tissues through the bloodstream. The presence of BAs in the central nervous system (CNS) has been related to their capacity to cross the blood–brain barrier (BBB) from the systemic circulation. However, the expression of enzymes and receptors involved in their synthesis and signaling, respectively, support the hypothesis that there is an endogenous source of BAs with a specific function in the CNS. Over the last decades, BAs have been tested as treatments for many CNS pathologies, with beneficial effects. Although they were initially reported as neuroprotective substances, they are also known to reduce inflammatory processes. Most of these effects have been related to the activation of the Takeda G protein-coupled receptor 5 (TGR5). This review addresses the new challenges that face BA research for neuroscience, focusing on their molecular functions. We discuss their endogenous and exogenous sources in the CNS, their signaling through the TGR5 receptor, and their mechanisms of action as potential therapeutics for neuropathologies.

Glycolysis is the metabolic pathway that converts glucose into pyruvate. Central nervous system (CNS) pathologies, such as spinal cord injury (SCI) and ischemia, are accompanied by an increase of the glycolytic pathway in the damaged areas as part of the inflammatory response. Pyruvate kinase is a key glycolytic enzyme that converts phosphoenolpyruvate and ADP to pyruvate and ATP. The protein has two isoforms, PKM1 and PKM2, originated from the same gene. As a homodimer, PKM2 loses the pyruvate kinase activity and acts as a transcription factor that regulates the expression of target genes involved in glycolysis and inflammation. After SCI, resident microglia and hematogenous macrophages are key inducers of the inflammatory response with deleterious effects. Activation of the bile acid receptor TGR5 inhibits the pro-inflammatory NFκB pathway in microglia and macrophages. In the present study we have investigated whether bile acids affect the expression of glycolytic enzymes and their regulation by PKM2. Bacterial lipopolysaccharide (LPS) induced the expression of PKM1, PKM2 and its target genes in primary cultures of microglial and Raw264.7 macrophage cells. SCI caused an increase of PKM2 immunoreactivity in macrophages after SCI. Pretreatment with tauroursodeoxycholic acid (TUDCA) or taurolithocholic acid (TLCA) reduced the expression of PKM2 and its target genes in cell cultures. Similarly, after SCI, TUDCA treatment reduced the expression of PKM2 in the lesion center. These results confirm the importance of PKM2 in the inflammatory response in CNS pathologies and indicate a new mechanism of bile acids as regulators of PKM2 pathway.