Maria Cecilia Barone

Mitochondria, nitric oxide, and cardiovascular dysfunction ☆

Cardiovascular diseases encompass a wide spectrum of abnormalities with diverse etiologies. The molecular mechanisms underlying these disorders include a variety of responses such as changes in nitric oxide- (NO) dependent cell signaling and increased apoptosis. An interesting aspect that has received little or no attention is the role mitochondria may play in the vascular changes that occur in both atherosclerosis and hypertension. With the changing perspective of the organelle from simply a role in metabolism to a contributor to signal transduction pathways, the role of mitochondria in cells with relatively low energy demands such as the endothelium has become important to understand. In this context, the definition of the NO-cytochrome c oxidase signaling pathway and the influence this has on cytochrome c release is particularly important in understanding apoptotic mechanisms involving the mitochondrion. This review examines the role of compromised mitochondrial function in a variety of vascular pathologies and the modulation of these effects by NO. The interaction of NO with the various mitochondrial respiratory complexes and the role NO plays in modulating mitochondrial-mediated apoptosis in these systems will be discussed.

Targeting Hypoxia-Inducible Factor (HIF) as a Therapeutic Strategy for CNS Disorders

Hypoxia occurs when oxygen availability drops below the levels necessary to maintain normal rates of metabolism. Because of its high metabolic activity, the brain is highly sensitive to hypoxia. Severe or prolonged oxygen deprivation in the brain contributes to the damage associated with stroke and a variety of other neuronal disorders. Conversely, the extreme hypoxic environment found in the core of many brain tumors supports the growth of the tumor and the survival of tumor cells. Normal cells exposed to transient or moderate hypoxia are generally able to adapt to the hypoxic conditions largely through activation of the hypoxia-inducible transcription factor HIF. HIF-regulated genes encode proteins involved in energy metabolism, cell survival, erythropoiesis, angiogenesis, and vasomotor regulation. In many instances of hypoxia or hypoxia and ischemia, the induction of HIF target genes may be beneficial. When these same insults occur in tissues that are normally poorly vascularized, such as the retina and the core of solid tumors, induction of the same HIF target genes can promote disease. Major new insights into the molecular mechanisms that regulate the oxygen-sensitivity of HIF, and in the development of compounds with which to manipulate HIF activity, are forcing serious consideration of HIF as a therapeutic target for diverse CNS disorders associated with hypoxia.

Control of respiration by nitric oxide in Keilin-Hartree particles, mitochondria and SH-SY5Y neuroblastoma cells

The pattern of cytochrome c oxidase inhibition by nitric oxide (NO) was investigated polarographically using Keilin-Hartree particles, mitochondria and human neuroblastoma cells. NO reacts with purified cytochrome c oxidase forming either a nitrosyl- or a nitrite-inhibited derivative, displaying distinct kinetics and light sensitivity of respiration recovery in the absence of free NO. Keilin-Hartree particles or cells, respiring either on endogenous substrates alone or in the presence of ascorbate, as well as state 3and state 4mitochondria respiring on glutamate and malate, displayed the rapid recovery characteristic of the nitrite derivative. All systems, when respiring in the presence of tetramethyl-p-phenylenediamine, were characterised by the slower, light-sensitive recovery typical of the nitrosyl derivative. Together the results suggest that the reaction of NO with cytochrome c oxidase in situ follows two alternative inhibition pathways, depending on the electron flux through the respiratory chain.

Pin1 promotes cell death in NGF-dependent neurons through a mechanism requiring c-Jun activity.

Developing neurons deprived of trophic support undergo apoptosis mediated by activation of c‐Jun N‐terminal kinases (JNK) and c‐Jun, induction of the Bcl‐2 homology 3‐only protein BimEL, Bax‐dependent loss of mitochondrial cytochrome c, and caspase activation. However, the mechanisms that regulate each of these events are only partially understood. Here we show that the prolyl isomerase Pin1 functions as a positive regulator of neuronal death through a c‐Jun‐dependent mechanism. Ectopic Pin1 promoted caspase‐dependent death of NGF‐maintained neurons that was associated with an accumulation of Ser63‐phosphorylated c‐Jun in neuronal nuclei and was partially dependent on Bax. Downregulating Pin1 prior to NGF withdrawal suppressed the accumulation of phosphorylated c‐Jun, inhibited the release of cytochrome c, and significantly delayed cell death. Pin1 knockdown inhibited NGF deprivation‐induced death to a similar extent in Bim (+/+) and Bim (−/−) neurons. The protective effect of Pin1 knockdown was significantly greater than that caused by loss of Bim and nearly identical to that caused by a dominant negative form of c‐Jun. Finally, cell death induced by ectopic Pin1 was largely blocked by expression of dominant negative c‐Jun. These results suggest a novel mechanism by which Pin1 promotes cell death involving activation of c‐Jun.