Noncanonical functions of BCL-2 proteins in the nervous system

Contribution of apoptosis-associated signaling pathways to epileptogenesis: lessons from Bcl-2 family knockouts

Neuronal cell death is a pathophysiological consequence of many brain insults that trigger epilepsy and has been implicated as a causal factor in epileptogenesis. Seizure-induced neuronal death features excitotoxic necrosis and apoptosis-associated signaling pathways, including activation of multiple members of the Bcl-2 gene family. The availability of mice in which individual Bcl-2 family members have been deleted has provided the means to determine whether they have causal roles in neuronal death and epileptogenesis in vivo. Studies show that multiple members of the Bcl-2 family are activated following status epilepticus and the seizure and damage phenotypes of eight different knockouts of the Bcl-2 family have now been characterized. Loss of certain pro-apoptotic members, including Puma, protected against seizure-induced neuronal death whereas loss of anti-apoptotic Mcl-1 and Bcl-w enhanced hippocampal damage. Notably, loss of two putatively pro-apoptotic members, Bak and Bmf, resulted in more seizure-damage while deletion of Bid had no effect, indicating the role of certain Bcl-2 family proteins in epileptic brain injury is distinct from their contributions following other stressors or in non-CNS tissue. Notably, Puma-deficient mice develop fewer spontaneous seizures after status epilepticus suggesting neuroprotection may preserve functional inhibition, either directly by preserving neuronal networks or indirectly, for example by limiting reactive gliosis and pro-inflammatory responses to neuronal death. Together, these studies support apoptosis-associated molecular mechanisms controlling neuronal death as a component of epileptogenesis which might be targetable to protect against seizure-damage, cognitive deficits and mitigate the severity of syndrome following epilepsy-precipitating injuries to the brain.

Multipolar functions of BCL-2 proteins link energetics to apoptosis

Classical apoptotic cell death is now sufficiently well understood to be interrogated with mathematical modeling and manipulated with targeted drugs for clinical benefit. However, a biological black hole has emerged with the realization that apoptosis regulators are functionally multipolar. BCL-2 family proteins appear to have much greater effects on cells than can be explained by their known roles in apoptosis. Although these effects may be observable simply because the cell is not dead, the general assumption is that BCL-2 proteins have undiscovered biochemical activities. Conversely, these as yet uncharacterized day-jobs also may underlie their profound effects on cell survival, challenging current assumptions about classical apoptosis. Even their sub-mitochondrial localizations remain controversial. Here we attempt to integrate seemingly conflicting information with the prospect that BCL-2 proteins themselves may be the critical crosstalk between life and death.

Intermediate progenitors are increased by lengthening of the cell cycle through calcium signaling and p53 expression in human neural progenitors

During development, neurons can be generated directly from a multipotent progenitor or indirectly through an intermediate progenitor (IP). This last mode of division amplifies the progeny of neurons. The mechanisms governing the generation and behavior of IPs are not well understood. In this work, we demonstrate that the lengthening of the cell cycle enhances the generation of neurons in a human neural progenitor cell system in vitro and also the generation and expansion of IPs. These IPs are insulinoma-associated 1 (Insm1)(+)/BTG family member 2 (Btg2)(-), which suggests an increase in a self-amplifying IP population. Later the cultures express neurogenin 2 (Ngn2) and become neurogenic. The signaling responsible for this cell cycle modulation is investigated. It is found that the release of calcium from the endoplasmic reticulum to the cytosol in response to B cell lymphoma-extra large overexpression or ATP addition lengths the cell cycle and increases the number of IPs and, in turn, the final neuron outcome. Moreover, data suggest that the p53-p21 pathway is responsible for the changes in cell cycle. In agreement with this, increased p53 levels are necessary for a calcium-induced increase in neurons. Our findings contribute to understand how calcium signaling can modulate cell cycle length during neurogenesis.

Cell signaling underlying epileptic behavior

Epilepsy is a complex disease, characterized by the repeated occurrence of bursts of electrical activity (seizures) in specific brain areas. The behavioral outcome of seizure events strongly depends on the brain regions that are affected by overactivity. Here we review the intracellular signaling pathways involved in the generation of seizures in epileptogenic areas. Pathways activated by modulatory neurotransmitters (dopamine, norepinephrine, and serotonin), involving the activation of extracellular-regulated kinases and the induction of immediate early genes (IEGs) will be first discussed in relation to the occurrence of acute seizure events. Activation of IEGs has been proposed to lead to long-term molecular and behavioral responses induced by acute seizures. We also review deleterious consequences of seizure activity, focusing on the contribution of apoptosis-associated signaling pathways to the progression of the disease. A deep understanding of signaling pathways involved in both acute- and long-term responses to seizures continues to be crucial to unravel the origins of epileptic behaviors and ultimately identify novel therapeutic targets for the cure of epilepsy.

Antitumor activity of total paeony glycoside against human chronic myelocytic leukemia K562 cell lines in vitro and in vivo

To explore the molecular mechanisms of human leukemia cells by total paeony glycoside (TPG), which is extracted from the root of Radix Paeoniae Rubra. The viability of K562 cells was assessed by MTT assay. Flow cytometry was used to detect apoptosis and cell cycle analysis. The changes in intracellular Ca(2+) concentration were determined by fluorescent dye Fluo-3, and mitochondrial membrane potential was determined by the retention of the dye Rh123. The cytoplasmic Bax, Bcl-xL, and Bcl-2 protein expressions were determined by western blot. The mRNA expression of caspase-3, caspase-8, and caspase-9 was detected by RT-PCR. K562 cells were subcutaneously inoculated into nude mice to study the in vivo antitumor effects of TPG. The growth of K562 cells was inhibited and arrested in G0/G1 phase by TPG. TPG also caused apoptosis in K562 cells evidenced by cytosolic accumulation of cytochrome c, caspase-9, and caspase-3. TPG could down-regulate Bcl-2 and Bcl-xL and up-regulate Bax in K562 cells. TPG showed a significant decreased tumor volume and tumor weight in nude mice inoculated with K562 cells. TPG can be developed as a promising anti-chronic myeloid leukemia drug.

Role and treatment of mitochondrial DNA-related mitochondrial dysfunction in sporadic neurodegenerative diseases

Several sporadic neurodegenerative diseases display phenomena that directly or indirectly relate to mitochondrial function. Data suggesting altered mitochondrial function in these diseases could arise from mitochondrial DNA (mtDNA) are reviewed. Approaches for manipulating mitochondrial function and minimizing the downstream consequences of mitochondrial dysfunction are discussed.