Endothelin promotes neurite elongation by a mechanism dependent on c-Jun N-terminal kinase

Prolyl hydroxylase regulates axonal rewiring and motor recovery after traumatic brain injury

Prolyl 4-hydroxylases (PHDs; PHD1, PHD2, and PHD3) are a component of cellular oxygen sensors that regulate the adaptive response depending on the oxygen concentration stabilized by hypoxia/stress-regulated genes transcription. In normoxic condition, PHD2 is required to stabilize hypoxia inducible factors. Silencing of PHD2 leads to the activation of intracellular signaling including RhoA and Rho-associated protein kinase (ROCK), which are key regulators of neurite growth. In this study, we determined that genetic or pharmacological inhibition of PHD2 in cultured cortical neurons prevents neurite elongation through a ROCK-dependent mechanism. We then explored the role of PHDs in axonal reorganization following a traumatic brain injury in adult mice. Unilateral destruction of motor cortex resulted in behavioral deficits due to disruption of the corticospinal tract (CST), a part of the descending motor pathway. In the spinal cord, sprouting of fibers from the intact side of the CST into the denervated side is thought to contribute to the recovery process following an injury. Intracortical infusion of PHD inhibitors into the intact side of the motor cortex abrogated spontaneous formation of CST collaterals and functional recovery after damage to the sensorimotor cortex. These findings suggest PHDs have an important role in the formation of compensatory axonal networks following an injury and may represent a new molecular target for the central nervous system disorders.

Thromboxane A2 stimulates neurite outgrowth in cerebral cortical neurons via mitogen activated protein kinase signaling

Thromboxane A2 (TXA2) is a central prostanoid in the cardiovascular system and is a crucial mediator of vascular homeostasis and platelet aggregation. In this study, we report a novel role for TXA2 in neurite outgrowth. TXA2 receptor is expressed in rat cortical neurons, and treatment with the TXA2 agonist U-46619 promotes neurite outgrowth in a concentration-dependent manner. We investigated the molecular mechanism underlying U-46619-induced neurite outgrowth in cortical neurons. Blockade of the phosphorylation of mitogen activated protein kinase (MAPK) prevents U-46619-mediated neurite outgrowth. These data indicates that TXA2 functions as a positive regulator of neurite outgrowth via a mechanism dependent on MAPKs in cortical neurons.

Exogenous endothelin-1 induces cell migration and matrix metalloproteinase expression in U251 human glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and lethal type of primary brain tumor characterized by its rapid infiltration to surrounding tissues during the early stages. The fast spreading of GBM obscures the initiation of the tumor mass making the treatment outcome undesirable. Endothelin-1 is known as a secretory protein presented in various types of brain cells, which has been indicated as a factor for cancer pathology. The aim of the present study was to investigate the molecular mechanism of cell migration in GBM. We found that various malignant glioma cells expressed higher amounts of endothelin-1, ETA, and ETB receptors than nonmalignant human astrocytes. The application of endothelin-1 enhanced the migratory activity in human U251 glioma cells corresponding to increased expression of matrix metalloproteinase (MMP)-9 and MMP-13. The endothelin-1-induced cell migration was attenuated by MMP-9 and MMP-13 inhibitors and inhibitors of mitogen-activated protein (MAP) kinase and PI3 kinase/Akt. Furthermore, the elevated levels of phosphate c-Jun accumulation in the nucleus and activator protein-1 (AP-1)-DNA binding activity were also found in endothelin-1 treated glioma cells. In migration-prone sublines, cells with greater migration ability showed higher endothelin-1, ETB receptor, and MMP expressions. These results indicate that endothelin-1 activates MAP kinase and AP-1 signaling, resulting in enhanced MMP-9 and MMP-13 expressions and cell migration in GBM.

Endothelin-1-induced down-regulation of NaV1.7 expression in adrenal chromaffin cells: attenuation of catecholamine secretion and tau dephosphorylation

Endothelin-1 and voltage-dependent sodium channels are involved in control and suppression of neuropathological factors, which contribute to sculpting the neuronal network. We previously demonstrated that veratridine-induced NaV1.7 sodium channel activation caused intracellular calcium elevation, catecholamine secretion and tau dephosphorylation in adrenal chromaffin cells. The aim of this study was to examine whether endothelin-1 could modulate NaV1.7. Our results indicated that endothelin-1 decreased the protein level of NaV1.7 and the veratridine-induced increase in intracellular calcium. In addition, it also abolished the veratridine-induced dephosphorylation of tau and the phosphorylation of glycogen synthase kinase-3β and extracellular signal-regulated kinase. These findings suggest that the endothelin-1-induced down-regulation of NaV1.7 diminishes NaV1.7-related catecholamine secretion and dephosphorylation of tau.

Angiogenesis induced by CNS inflammation promotes neuronal remodeling through vessel-derived prostacyclin

Angiogenesis is a prominent feature of central nervous system (CNS) disease and has roles in both the continued promotion of inflammation and the subsequent repair processes. Here we report that prostacyclin (or prostaglandin I(2) (PGI(2))) derived from new vessels promotes axonal remodeling of injured neuronal networks after CNS inflammation. In a localized model of experimental autoimmune encephalomyelitis (EAE), new vessels formed around the inflammatory lesion, followed by sprouting of adjacent corticospinal tract (CST) fibers. These sprouting fibers formed a compensatory motor circuit, leading to recovery of motor function. Capillary endothelial cell-derived prostacyclin bound to its receptor, the type I prostaglandin receptor (IP receptor), on CST neurons, promoting sprouting of CST fibers and contributing to the repair process. Inhibition of prostacyclin receptor signaling impaired motor recovery, whereas the IP receptor agonist iloprost promoted axonal remodeling and motor recovery after the induction of EAE. These findings reveal an important function of angiogenesis in neuronal rewiring and suggest that prostacyclin is a promising molecule for enhancing functional recovery from CNS disease.