The role of cyclophilin D in learning and memory

Pin1 and Alzheimer's disease

Alzheimer's disease (AD) is an immense and growing public health crisis. Despite over 100 years of investigation, the etiology remains elusive and therapy ineffective. Despite current gaps in knowledge, recent studies have identified dysfunction or loss-of-function of Pin1, a unique cis-trans peptidyl prolyl isomerase, as an important step in AD pathogenesis. Here I review the functionality of Pin1 and its role in neurodegeneration.

Cyclosporin A impairs neurogenesis and cognitive abilities in brain development via the IFN-γ-Shh-BDNF pathway

A wealth of evidence indicate that the peripheral immune activation alters brain development. However, it is still largely unclear whether and how peripheral immunosuppression affects neurodevelopment. Here, we found that the immunosuppressant cyclosporin A (CsA) decreased the number of BrdU+, BrdU+/DCX+, BrdU+/NeuN + cells in the hippocampus, impaired learning and memory and inhibited protein levels of the shh signaling pathway, including Shh, Smo and Gli1. However, the shh pathway receptor agonist SAG could block the impairment of cognitive ability and the decrease of hippocampal neurogenesis and brain-derived neurotrophic factor (BDNF) level induced by CsA. We also found that CsA decreased the level of interferon-gamma (IFN-γ), while up-regulation of IFN-γ altered the inhibitory effect of the shh signaling pathway and the decrease of BDNF induced by CsA. Collectively, these data indicate that peripheral CsA impairs neurogenesis and cognition in brain development through downregulating the IFN-γ-Shh-BDNF pathway. The present study guides us to correctly apply immunomodulatory drugs in early life and suggests that the IFN-γ-Shh-BDNF pathway may represent a novel protective target for neurodevelopment under the condition of immunosuppression.

Genetic Approach to Elucidate the Role of Cyclophilin D in Traumatic Brain Injury Pathology

Cyclophilin D (CypD) has been shown to play a critical role in mitochondrial permeability transition pore (mPTP) opening and the subsequent cell death cascade. Studies consistently demonstrate that mitochondrial dysfunction, including mitochondrial calcium overload and mPTP opening, is essential to the pathobiology of cell death after a traumatic brain injury (TBI). CypD inhibitors, such as cyclosporin A (CsA) or NIM811, administered following TBI, are neuroprotective and quell neurological deficits. However, some pharmacological inhibitors of CypD have multiple biological targets and, as such, do not directly implicate a role for CypD in arbitrating cell death after TBI. Here, we reviewed the current understanding of the role CypD plays in TBI pathobiology. Further, we directly assessed the role of CypD in mediating cell death following TBI by utilizing mice lacking the CypD encoding gene Ppif. Following controlled cortical impact (CCI), the genetic knockout of CypD protected acute mitochondrial bioenergetics at 6 h post-injury and reduced subacute cortical tissue and hippocampal cell loss at 18 d post-injury. The administration of CsA following experimental TBI in Ppif-/- mice improved cortical tissue sparing, highlighting the multiple cellular targets of CsA in the mitigation of TBI pathology. The loss of CypD appeared to desensitize the mitochondrial response to calcium burden induced by TBI; this maintenance of mitochondrial function underlies the observed neuroprotective effect of the CypD knockout. These studies highlight the importance of maintaining mitochondrial homeostasis after injury and validate CypD as a therapeutic target for TBI. Further, these results solidify the beneficial effects of CsA treatment following TBI.

Infantile Amnesia Is Related to Developmental Immaturity of the Maintenance Mechanisms for Long-Term Potentiation

Infantile amnesia (IA) refers to the inability of adults to recall episodic memories from infancy or early childhood. While several hypotheses have been proposed to explain the occurrence of IA, the neurobiological and molecular bases for this accelerated forgetting phenomenon remain elusive. Using hippocampus-dependent object-location memory and contextual fear conditioning tasks, we confirmed that infant mice trained at postnatal day 20 (P20) displayed deficits in long-term memory retention compared to adult (P60) mice. The percentage of CA1 pyramidal neurons expressing phosphorylated cAMP-responsive element-binding protein after fear conditioning was significantly lower in P20 than P60 mice. P20 mice exhibited attenuated basal excitatory synaptic transmission and early-phase long-term potentiation (E-LTP) at Schaffer collateral-CA1 synapses compared to P60 mice, but conversely, P20 mice have a greater susceptibility to induce time-dependent reversal of LTP by low-frequency afferent stimulation than P60 mice. The protein levels of GluN2B subunit of N-methyl-D-aspartate receptors (NMDARs), protein kinase Mζ (PKMζ), and protein phosphatase 2B (PP2B) in hippocampal CA1 region were significantly higher in P20 than P60 mice. We also found that the levels of calcium/calmodulin-dependent protein kinase II α autophosphorylation at Thr286, GluA1 phosphorylation at Ser831, and PKMζ protein biosynthesis occurred during the ensuing maintenance of E-LTP were significantly lower in P20 than P60 mice. Pharmacological blockade of GluN2B-containing NMDARs or PP2B effectively restored deficits of E-LTP and long-term memory retention observed in P20 mice. Altogether, these findings suggest that developmental immaturity of the maintenance mechanisms for E-LTP is linked to the occurrence of IA.

The involvement of brain-derived neurotrophic factor in 3,4-methylenedioxymethamphetamine-induced place preference and behavioral sensitization

3,4-Methylenedioxymethamphetamine (MDMA) is known to induce dependence and psychosis in humans. Brain-derived neurotrophic factor (BDNF) is involved in the synaptic plasticity and neurotrophy in midbrain dopaminergic neurons. This study aimed to investigate the role of BDNF in MDMA-induced dependence and psychosis. A single dose of MDMA (10mg/kg) induced BDNF mRNA expression in the prefrontal cortex, nucleus accumbens, and amygdala, but not in the striatum or the hippocampus. However, repeated MDMA administration for 7 days induced BDNF mRNA expression in the striatum and hippocampus. Both precursor and mature BDNF protein expression increased in the nucleus accumbens, mainly in the neurons. Additionally, rapidly increased extracellular serotonin levels and gradually and modestly increased extracellular dopamine levels were noted within the nucleus accumbens of mice after repeated MDMA administration. Dopamine receptor antagonists attenuated the effect of repeated MDMA administration on BDNF mRNA expression in the nucleus accumbens. To examine the role of endogenous BDNF in the behavioral and neurochemical effects of MDMA, we used mice with heterozygous deletions of the BDNF gene. MDMA-induced place preference, behavioral sensitization, and an increase in the levels of extracellular serotonin and dopamine within the nucleus accumbens, were attenuated in BDNF heterozygous knockout mice. These results suggest that BDNF is implicated in MDMA-induced dependence and psychosis by activating the midbrain serotonergic and dopaminergic neurons.

Knockout of Cyclophilin-D Provides Partial Amelioration of Intrinsic and Synaptic Properties Altered by Mild Traumatic Brain Injury

Mitochondria are central to cell survival and Ca²⁺ homeostasis due to their intracellular buffering capabilities. Mitochondrial dysfunction resulting in mitochondrial permeability transition pore (mPTP) opening has been reported after mild traumatic brain injury (mTBI). Cyclosporine A provides protection against the mPTP opening through its interaction with cyclophilin-D (CypD). A recent study has found that the extent of axonal injury after mTBI was diminished in neocortex in cyclophilin-D knockout (CypDKO) mice. Here we tested whether this CypDKO could also provide protection from the increased intrinsic and synaptic neuronal excitability previously described after mTBI in a mild central fluid percussion injury mice model. CypDKO mice were crossed with mice expressing yellow fluorescent protein (YFP) in layer V pyramidal neurons in neocortex to create CypDKO/YFP-H mice. Whole cell patch clamp recordings from axotomized (AX) and intact (IN) YFP+ layer V pyramidal neurons were made 1 and 2 days after sham or mTBI in slices from CypDKO/YFP-H mice. Both excitatory post synaptic currents (EPSCs) recorded in voltage clamp and intrinsic cellular properties, including action potential (AP), afterhyperpolarization (AHP), and depolarizing after potential (DAP) characteristics recorded in current clamp were evaluated. There was no significant difference between sham and mTBI for either spontaneous or miniature EPSC frequency, suggesting that CypDKO ameliorates excitatory synaptic abnormalities. There was a partial amelioration of intrinsic properties altered by mTBI. Alleviated were the increased slope of the AP frequency vs. injected current plot, the increased AP, AHP and DAP amplitudes. Other properties that saw a reversal that became significant in the opposite direction include the current rheobase and AP overshoot. The AP threshold remained depolarized and the input resistance remained increased in mTBI compared to sham. Additional altered properties suggest that the CypDKO likely has a direct effect on membrane properties, rather than producing a selective reduction of the effects of mTBI. These results suggest that inhibiting CypD after TBI is an effective strategy to reduce synaptic hyperexcitation, making it a continued target for potential treatment of network abnormalities.

Calcium signaling as a mediator of cell energy demand and a trigger to cell death

Calcium signaling is pivotal to a host of physiological pathways. A rise in calcium concentration almost invariably signals an increased cellular energy demand. Consistent with this, calcium signals mediate a number of pathways that together serve to balance energy supply and demand. In pathological states, calcium signals can precipitate mitochondrial injury and cell death, especially when coupled to energy depletion and oxidative or nitrosative stress. This review explores the mechanisms that couple cell signaling pathways to metabolic regulation or to cell death. The significance of these pathways is exemplified by pathological case studies, such as those showing loss of mitochondrial calcium uptake 1 in patients and ischemia/reperfusion injury.

SPG7 Is an Essential and Conserved Component of the Mitochondrial Permeability Transition Pore

Mitochondrial permeability transition is a phenomenon in which the mitochondrial permeability transition pore (PTP) abruptly opens, resulting in mitochondrial membrane potential (ΔΨm) dissipation, loss of ATP production, and cell death. Several genetic candidates have been proposed to form the PTP complex, however, the core component is unknown. We identified a necessary and conserved role for spastic paraplegia 7 (SPG7) in Ca(2+)- and ROS-induced PTP opening using RNAi-based screening. Loss of SPG7 resulted in higher mitochondrial Ca(2+) retention, similar to cyclophilin D (CypD, PPIF) knockdown with sustained ΔΨm during both Ca(2+) and ROS stress. Biochemical analyses revealed that the PTP is a heterooligomeric complex composed of VDAC, SPG7, and CypD. Silencing or disruption of SPG7-CypD binding prevented Ca(2+)- and ROS-induced ΔΨm depolarization and cell death. This study identifies an ubiquitously expressed IMM integral protein, SPG7, as a core component of the PTP at the OMM and IMM contact site.

Calcineurin inhibition blocks within-, but not between-session fear extinction in mice

Memory extinction involves the formation of a new associative memory that inhibits a previously conditioned association. Nonetheless, it could also depend on weakening of the original memory trace if extinction is assumed to have multiple components. The phosphatase calcineurin (CaN) has been described as being involved in extinction but not in the initial consolidation of fear learning. With this in mind, we set to study whether CaN could have different roles in distinct components of extinction. Systemic treatment with the CaN inhibitors cyclosporin A (CsA) or FK-506, as well as i.c.v. administration of CsA, blocked within-session, but not between-session extinction or initial learning of contextual fear conditioning. Similar effects were found in multiple-session extinction of contextual fear conditioning and in auditory fear conditioning, indicating that CaN is involved in different types of short-term extinction. Meanwhile, inhibition of protein synthesis by cycloheximide (CHX) treatment did not affect within-session extinction, but disrupted fear acquisition and slightly impaired between-session extinction. Our results point to a dissociation of within- and between-session extinction of fear conditioning, with the former being more dependent on CaN activity and the latter on protein synthesis. Moreover, the modulation of within-session extinction did not affect between-session extinction, suggesting that these components are at least partially independent.

Pterostilbene attenuates lipopolysaccharide-induced learning and memory impairment possibly via inhibiting microglia activation and protecting neuronal injury in mice

The present study aims to evaluate the effects of pterostilbene on lipopolysaccharide (LPS)-induced learning and memory impairment as well as the possible changes of microglia and neurons. Firstly, learning and memory function was investigated by behavioral tests. Pterostilbene attenuated LPS-induced learning and memory impairment tested by Y-maze and Morris water maze. Secondly, immunohistochemical method was used to study the changes of microglia and neurons. The results showed that pterostilbene produced a significant decrease in the number of Iba-1 and Doublecortin (DCX) positive cells and a significant increase in neuronal nuclear antigen (NeuN)-stained area of neurons in mouse hippocampal compared to the LPS group. Finally, an in vitro study was performed to further confirm the inhibitory effect on microglia activation and protective effect on neurons exerted by pterostilbene. The results demonstrated that pterostilbene significantly inhibited microglia activation, showing the obvious decrease of LPS-induced production of NO, TNF-α and IL-6 in N9 microglial cells. In addition, the viability of SH-SY5Y cells decreased by conditioned media of LPS-activated N9 microglial cells was remarkably recovered by pterostilbene. In summary, the present study demonstrated for the first time that pterostilbene attenuated LPS-induced learning and memory impairment, which may be associated with its inhibitory effect on microglia activation and protective effect on neuronal injury.

The impact of liver transplantation on the phenotype of primary biliary cirrhosis patients in the UK-PBC cohort

BACKGROUND & AIMS

Liver transplantation improves survival in end-stage primary biliary cirrhosis (PBC), but the benefit for systemic symptoms including fatigue is less clear. The aim of this study was to utilise the comprehensive UK-PBC Research Cohort, including 380 post-transplant patients and 2300 non-transplanted patients, to answer key questions regarding transplantation for PBC.

METHODS

Cross-sectional study of post-transplant PBC patients and case-matched non-transplanted patients. Detailed clinical information was collected, together with patient systemic symptom impact data using validated assessment tools.

RESULTS

Over 25% of patients in the transplant cohort were grafted within 2 years of PBC diagnosis suggesting advanced disease at presentation. Transplanted patients were significantly younger at presentation than non-transplanted (mean 7 years) and >35% of all patients in the UK-PBC cohort who presented under 50 years had already undergone liver transplantation at the study censor point (>50% were treatment failures (post-transplant or unresponsive to UDCA)). Systemic symptom severity (fatigue and cognitive symptoms) was identical in female post-transplant patients and matched non-transplanted controls and unrelated to disease recurrence or immunosuppression type. In males, symptoms were worse in transplanted than in non-transplanted patients.

CONCLUSIONS

Age at presentation is a major risk factor for progression to transplant (as well as UDCA non-response) in PBC. Although both confirmatory longitudinal studies, and studies utilising objective as well as subjective measures of function, are needed if we are to address the question definitively, we found no evidence of improved systemic symptoms after liver transplantation in PBC and patients should be advised accordingly. Consideration needs to be given to enhancing rehabilitation approaches to improve function and life quality after liver transplant for PBC.

Xanthoceraside attenuates learning and memory deficits via improving insulin signaling in STZ-induced AD rats

Xanthoceraside, a triterpenoid saponin extracted from the fruit husks of Xanthoceras sorbifolia Bunge, has been shown to reverse the cognitive deficits observed in several Alzheimer's disease (AD) animal models. Increasing evidence suggests the involvement of the insulin signaling pathway in neurodegenerative disorders such as AD. Thus, we used an AD animal model of cognitive impairment induced by the intracerebroventricular (ICV) injection of streptozotocin (STZ) to test the effects of xanthoceraside on behavioral impairments and insulin signaling mechanisms. In our present study, memory impairment was assessed using the Morris water maze test. The expression of IR, IGF-1R and Raf-1/ERK/CREB was tested by western blotting. The STZ group showed memory deficits in the Morris water maze test and significant decreases in IR and IGF-1R protein levels in the hippocampus. Xanthoceraside treatment significantly rescued memory deficits, as well as IR and IGF-1R protein expression levels. STZ inhibited the Ras/ERK signaling cascade and decreased the phosphorylation of CREB; these effects were also attenuated by xanthoceraside treatment. These results suggest the potential use of xanthoceraside for the treatment of neurodegenerative disorders in which brain insulin signaling may be involved.

Physiologic functions of cyclophilin D and the mitochondrial permeability transition pore

This review focuses on the role of cyclophilin D (CypD) as a prominent mediator of the mitochondrial permeability transition pore (MPTP) and subsequent effects on cardiovascular physiology and pathology. Although a great number of reviews have been written on the MPTP and its effects on cell death, we focus on the biology surrounding CypD itself and the non-cell death physiologic functions of the MPTP. A greater understanding of the physiologic functions of the MPTP and its regulation by CypD will likely suggest novel therapeutic approaches for cardiovascular disease, both dependent and independent of programmed necrotic cell death mechanisms.  

MAGE-D1 regulates expression of depression-like behavior through serotonin transporter ubiquitylation

The ubiquitin-proteasome system (UPS) controls the stability of most cellular proteins. The polymorphism of UPS-related genes is associated with major depression disorder, but less is known about the molecule that plays a role in depression by modulating the UPS. Melanoma antigen gene-D1 (MAGE-D1) interacts with RING E3 ubiquitin ligase and is implicated in protein degradation. MAGE-D1 may thus play an important role in the CNS via ubiquitylation. Here, we clarified a novel role of MAGE-D1 in emotional functions, namely its modulation of ubiquitylation to the serotonin transporter (SERT). The MAGE-D1 knock-out and knockdown by small interfering RNA (siRNA) in the prefrontal cortex showed depression-like behavior, such as a decrease in exploratory behavior in both the home cage and novel apparatus, a decrease in social interaction, increased immobility time during forced swimming and tail suspension, and a decrease in sucrose preference without any anxiety, or cognitive or motor dysfunction. Acute and chronic (28 d) administration of sertraline (10 mg/kg) and imipramine (20 mg/kg) reversed all or part of depression-like behavior in knock-out mice. In these mice, the serotonergic function in the prefrontal cortex and hippocampus was hypoactive, accompanied by hyperexpression of SERT attributable to a decrease in ubiquitylation. Furthermore, MAGE-D1 binds to SERT via the necdin homology domain. MAGE-D1 overexpression in cells resulted in a decrease in serotonin uptake activity and the protein level of SERT but an increase in ubiquitylated SERT. Together, the present findings suggest a novel role for MAGE-D1 in depressive behaviors: modulating SERT ubiquitylation.

Therapeutic implications of down-regulation of cyclophilin D in bipolar disorder

We previously reported that neuron-specific mutant Polg1 (mitochondrial DNA polymerase) transgenic (Tg) mice exhibited bipolar disorder (BD)-like phenotypes such as periodic activity change and altered circadian rhythm. In this study, we re-evaluated two datasets resulting from DNA microarray analysis to estimate a biological pathway associated with the disorder. The gene lists were derived from the comparison between post-mortem brains of BD patients and control subjects, and from the comparison between the brains of Tg and wild-type mice. Gene ontology analysis showed that 16 categories overlapped in the altered gene expression profiles of BD patients and the mouse model. In the brains of Tg mice, 33 genes showed similar changes in the frontal cortex and hippocampus compared to wild-type mice. Among the 33 genes, SFPQ and PPIF were differentially expressed in post-mortem brains of BD patients compared to control subjects. The only gene consistently down-regulated in both patients and the mouse model was PPIF, which encodes cyclophilin D (CypD), a component of the mitochondrial permeability transition pore. A blood-brain barrier-permeable CypD inhibitor significantly improved the abnormal behaviour of Tg mice at 40 mg/kg.d. These findings collectively suggest that CypD is a promising target for a new drug for BD.

Pin1 and PKMzeta sequentially control dendritic protein synthesis

Some forms of learning and memory and their electrophysiologic correlate, long-term potentiation (LTP), require dendritic translation. We demonstrate that Pin1 (protein interacting with NIMA 1), a peptidyl-prolyl isomerase, is present in dendritic spines and shafts and inhibits protein synthesis induced by glutamatergic signaling. Pin1 suppression increased dendritic translation, possibly through eukaryotic translation initiation factor 4E (eIF4E) and eIF4E binding proteins 1 and 2 (4E-BP1/2). Consistent with increased protein synthesis, hippocampal slices from Pin(-/-) mice had normal early LTP (E-LTP) but significantly enhanced late LTP (L-LTP) compared to wild-type controls. Protein kinase C zeta (PKCzeta) and protein kinase M zeta (PKMzeta) were increased in Pin1(-/-) mouse brain, and their activity was required to maintain dendritic translation. PKMzeta interacted with and inhibited Pin1 by phosphorylating serine 16. Therefore, glutamate-induced, dendritic protein synthesis is sequentially regulated by Pin1 and PKMzeta signaling.

Cyclosporine A reduces dendritic outgrowth of neuroblasts in the subgranular zone of the dentate gyrus in C57BL/6 mice

In the present study, we observed the effects of cyclosporine A (CsA), an efficient immunosuppressant, on cell proliferation and neuroblast differentiation in the subgranular zone of the dentate gyrus (SZDG) in normal C57BL/6 mice using Ki67 and doublecortin (DCX) immunohistochemical staining, respectively. At 8 weeks of age, vehicle (physiological saline) or CsA was daily administered (40 mg/kg, i.p.) for 1 week. Animals were sacrificed at 2 weeks after last administration. CsA treatment did not show any influences in neurons, astrocytes and microglia based on immunohistochemistry for its markers, respectively. However, in the CsA-treated group, Fluoro-Jade B, a marker for neurodegeneration, positive cells were found in the SZDG, not in the vehicle-treated group. In the vehicle-treated group, Ki67 immunoreactive (+) nuclei were clustered in the SZDG, whereas in the CsA-treated group Ki67(+) nuclei were scattered in the SZDG, showing no difference in cell numbers. Numbers of DCX(+) neuroblasts with well-developed processes (tertiary dendrites) were much lower in the CsA-treated group than those in the vehicle-treated group; however, numbers of DCX(+) neuroblasts with secondary dendrites were similar in both the groups. These results suggest that CsA significantly reduces dendritic outgrowth and complexity from neuroblasts in the SZDG without any affecting in neurons, astrocytes and microglia in normal mice.