The mitochondrial benzodiazepine receptor and avoidance learning in the day-old chick

FGIN-1-27 Inhibits Melanogenesis by Regulating Protein Kinase A/cAMP-Responsive Element-Binding, Protein Kinase C-β, and Mitogen-Activated Protein Kinase Pathways

FGIN-1-27 is a synthetic mitochondrial diazepam binding inhibitor receptor (MDR) agonist that has demonstrated pro-apoptotic, anti-anxiety, and steroidogenic activity in various studies. Here we report, for the first time, the anti-melanogenic efficacy of FGIN-1-27 in vitro and in vivo. FGIN-1-27 significantly inhibited basal and α-melanocyte-stimulating hormone (α-MSH)-, 1-Oleoyl-2-acetyl-sn-glycerol (OAG)- and Endothelin-1 (ET-1)-induced melanogenesis without cellular toxicity. Mushroom tyrosinase activity assay showed that FGIN-1-27 did not directly inhibit tyrosinase activity, which suggested that FGIN-1-27 was not a direct inhibitor of tyrosinase. Although it was not capable of modulating the catalytic activity of mushroom tyrosinase in vitro, FGIN-1-27 downregulated the expression levels of key proteins that function in melanogenesis. FGIN-1-27 played these functions mainly by suppressing the PKA/CREB, PKC-β, and MAPK pathways. Once inactivated, it decreased the expression of MITF, tyrosinase, TRP-1, TRP-2, and inhibited the tyrosinase activity, finally inhibiting melanogenesis. During in vivo experiments, FGIN-1-27 inhibited the body pigmentation of zebrafish and reduced UVB-induced hyperpigmentation in guinea pig skin, but not a reduction of numbers of melanocytes. Our findings indicated that FGIN-1-27 exhibited no cytotoxicity and inhibited melanogenesis in both in vitro and in vivo models. It may prove quite useful as a safer skin-whitening agent.

Characterization of the Metabolic, Clinical and Neuropsychological Phenotype of Female Carriers of the Premutation in the X-Linked FMR1 Gene

The X-linked FMR1 premutation (PM) is characterized by a 55-200 CGG triplet expansion in the 5'-untranslated region (UTR). Carriers of the PM were originally thought to be asymptomatic; however, they may present general neuropsychiatric manifestations including learning disabilities, depression and anxiety, among others. With age, both sexes may also develop the neurodegenerative disease fragile X-associated tremor/ataxia syndrome (FXTAS). Among carriers, females are at higher risk for developing immune disorders, hypertension, seizures, endocrine disorders and chronic pain, among others. Some female carriers younger than 40 years old may develop fragile X-associated primary ovarian insufficiency (FXPOI). To date, no studies have addressed the metabolic footprint - that includes mitochondrial metabolism - of female carriers and its link to clinical/cognitive manifestations. To this end, we performed a comprehensive biochemical assessment of 42 female carriers (24-70 years old) compared to sex-matched non-carriers. By applying a multivariable correlation matrix, a generalized bioenergetics impairment was correlated with diagnoses of the PM, FXTAS and its severity, FXPOI and anxiety. Intellectual deficits were strongly correlated with both mitochondrial dysfunction and with CGG repeat length. A combined multi-omics approach identified a down-regulation of RNA and mRNA metabolism, translation, carbon and protein metabolism, unfolded protein response, and up-regulation of glycolysis and antioxidant response. The suboptimal activation of the unfolded protein response (UPR) and endoplasmic-reticulum-associated protein degradation (ERAD) response challenges and further compromises the PM genetic background to withstand other, more severe forms of stress. Mechanistically, some of the deficits were linked to an altered protein expression due to decreased protein translation, but others seemed secondary to oxidative stress originated from the accumulation of either toxic mRNA or RAN-derived protein products or as a result of a direct toxicity of accumulated metabolites from deficiencies in critical enzymes.

Cognitive impairment and increased brain neurosteroids in adult rats perinatally exposed to low millimolar blood alcohol concentrations

Epidemiological evidence suggests that adolescents and adults perinatally exposed to alcohol, even at low doses, show high prevalence of cognitive impairment and social behavior deficits, which may be in part related to alcohol-induced changes of the gamma-aminobutyric acid (GABA)ergic neurotransmission. The endogenous neurosteroid 3alpha-hydroxy,5alpha-pregnan-20-one (3alpha,5alpha-tetrahydroprogesterone/3alpha,5alpha-THP), a potent positive allosteric modulator of GABA(A) receptor function, is implicated in the physiological tuning of GABA-mediated fast inhibition and in various alcohol's actions in the brain. This study was undertaken to determine whether perinatal exposure to low millimolar blood alcohol concentrations alters cognitive skills (social discrimination and inhibitory avoidance tests), emotional reactivity (elevated plus maze test), and neurosteroid content in brain cortex and hippocampus of adult male offspring. Dams had access to a 3% alcohol solution or to an equicaloric sucrose solution from gestational day 15 to postnatal day 9. Eighty-day old alcohol-exposed male offspring exhibited impaired social recognition memory, but unchanged inhibitory avoidance performance and normal behavior on the elevated-plus maze. The concentrations of 3alpha,5alpha-THP and its precursor progesterone were more than doubled in brain cortex and hippocampus of alcohol-exposed rats, whereas in plasma only progesterone was increased. Thus, exposure to low millimolar blood alcohol concentrations has a long-lasting impact on the developing brain as it causes an impairment of social recognition as well as an increase of brain neurosteroid content in mature animals. The latter may be consequent to altered expression/activity of brain steroidogenic enzymes, as reflected by the enduring increase of the GABA(A) receptor-active neurosteroid 3alpha,5alpha-THP in brain cortex and hippocampus, but not in plasma. It is speculated that, by inducing a greater amplification of GABA(A) receptor function, the elevation of 3alpha,5alpha-THP brain content contributes to the cognitive impairment exhibited by adult alcohol-exposed offspring.

Mitochondrial criticality: a new concept at the turning point of life or death

A variety of stressors can cause the collapse of mitochondrial membrane potential (DeltaPsi(m)), but the events leading up to this catastrophic cellular event are not well understood at the mechanistic level. Based on our recent studies of oscillations in mitochondrial energetics, we have coined the term "mitochondrial criticality" to describe the state in which the mitochondrial network of cardiomyocytes becomes very sensitive to small perturbations in reactive oxygen species (ROS), resulting in the scaling of local mitochondrial uncoupling and DeltaPsi(m) loss to the whole cell, and the myocardial syncytium. At the point of criticality, the dynamics of the mitochondrial network bifurcate to oscillatory behavior. These energetic changes are translated into effects on the electrical excitability of the cell, inducing dramatic changes in the morphology and the threshold for activating an action potential. Emerging evidence suggests that this mechanism, by creating spatial and temporal heterogeneity of excitability in the heart during ischemia and reperfusion, underlies the genesis of potentially lethal cardiac arrhythmias.

Characterization of the GABA(A) receptor in the brain of the adult male bullfrog, Rana catesbeiana

Little is known about the properties of GABA receptors in the amphibian brain. The GABA(A) receptor is widespread in the mammalian brain, and can be specifically labeled with the receptor agonist [3H]muscimol. The binding of [3H]muscimol to membrane preparations from the brain of the bullfrog, Rana catesbeiana, was investigated in kinetic, saturation, and inhibition experiments to determine whether this species possessed a GABA(A)-like receptor. Binding of 20 nM [3H]muscimol to membranes was specific and could be displaced by 1 mM GABA. Association binding curves showed that steady state occurred rapidly, within 2 min, and dissociation occurred within 5 min. The receptor was saturable with a single, high-affinity binding site (K(D)=19.2 nM; B(max)=1.8 pmol/mg protein). Binding of [3H]muscimol was inhibited in a dose-dependent fashion by muscimol, GABA, bicuculline methiodide, and bicuculline (in order of potency). Baclofen (at doses from 10(-9) to 10(-3) M) failed to displace [3H]muscimol. The binding characteristics and ligand specificity of [3H]muscimol binding sites in the bullfrog brain support the hypothesis that this amphibian possesses a GABA(A)-like receptor protein similar to the GABA(A) receptor characterized in mammals.

Synchronized whole cell oscillations in mitochondrial metabolism triggered by a local release of reactive oxygen species in cardiac myocytes

Reactive oxygen species (ROS) and/or Ca2+ overload can trigger depolarization of mitochondrial inner membrane potential (DeltaPsim) and cell injury. Little is known about how loss of DeltaPsim in a small number of mitochondria might influence the overall function of the cell. Here we employ the narrow focal excitation volume of the two-photon microscope to examine the effect of local mitochondrial depolarization in guinea pig ventricular myocytes. Remarkably, a single local laser flash triggered synchronized and self-sustained oscillations in DeltaPsim, NADH, and ROS after a delay of approximately 40s, in more than 70% of the mitochondrial population. Oscillations were initiated only after a specific threshold level of mitochondrially produced ROS was exceeded, and did not involve the classical permeability transition pore or intracellular Ca2+ overload. The synchronized transitions were abolished by several respiratory inhibitors or a superoxide dismutase mimetic. Anion channel inhibitors potentiated matrix ROS accumulation in the flashed region, but blocked propagation to the rest of the myocyte, suggesting that an inner membrane, superoxide-permeable, anion channel opens in response to free radicals. The transitions in mitochondrial energetics were tightly coupled to activation of sarcolemmal KATP currents, causing oscillations in action potential duration, and thus might contribute to catastrophic arrhythmias during ischemia-reperfusion injury.

Mitochondrial DNA modifies cognition in interaction with the nuclear genome and age in mice

Several lines of evidence indicate an association between mitochondrial DNA (mtDNA) and the functioning of the nervous system. As neuronal development and structure as well as axonal and synaptic activity involve mitochondrial genes, it is not surprising that most mtDNA diseases are associated with brain disorders. Only one study has suggested an association between mtDNA and cognition, however. Here we provide direct evidence of mtDNA involvement in cognitive functioning. Total substitution of mtDNA was achieved by 20 repeated backcrosses in NZB/BlNJ (N) and CBA/H (H) mice with different mtDNA origins. All 13 mitochondrial genes were expressed in the brains of the congenic quartet. In interaction with nuclear DNA (nDNA), mtDNA modified learning, exploration, sensory development and the anatomy of the brain. The effects of mtDNA substitution persisted with age, increasing in magnitude as the mice got older. We observed different effects with input of mtDNA from N versus H mice, varying according to the phenotypes. Exchanges of mtDNA may produce phenotypes outside the range of scores observed in the original mitochondrial and nuclear combinations. These findings show that mitochondrial polymorphisms are not as neutral as was previously believed.

Involvement of the sigma receptor in passive-avoidance learning in the day-old chick during the second wave of neuronal activity

The specific sigma-receptor agonist (+)-SKF 10047 and antagonist BD 1047 were used to investigate whether this receptor was involved in passive-avoidance training in the day-old chick. We found 300 microM (+)-SKF 10047 to be amnesic when injected into the lobus parolfactorius 5 h after training (p < .01). Higher or lower concentrations of (+)-SKF 10047 did not disrupt memory formation. The amnesia produced by the efficacious dose of (+)-SKF 10047 was reversed by the specific antagonist, BD 1047. It is suggested that the sigma-receptor may exert its effect on passive-avoidance memory consolidation during the later stages of long-term memory formation by modulation of memory-related neurotransmission.