Yun-Feng Li

Phosphodiesterase-4D Knock-Out and RNA Interference-Mediated Knock-Down Enhance Memory and Increase Hippocampal Neurogenesis via Increased cAMP Signaling

Phosphodiesterase-4 (PDE4) plays an important role in mediating memory via the control of intracellular cAMP signaling; inhibition of PDE4 enhances memory. However, development of PDE4 inhibitors as memory enhancers has been hampered by their major side effect of emesis. PDE4 has four subtypes (PDE4A–D) consisting of 25 splice variants. Mice deficient in PDE4D displayed memory enhancement in radial arm maze, water maze, and object recognition tests. These effects were mimicked by repeated treatment with rolipram in wild-type mice. In addition, similarly as rolipram-treated wild-type mice, PDE4D-deficient mice also displayed increased hippocampal neurogenesis and phosphorylated cAMP response element-binding protein (pCREB). Furthermore, microinfusion of lentiviral vectors that contained microRNAs (miRNAs) targeting long-form PDE4D isoforms into bilateral dentate gyri of the mouse hippocampus downregulated PDE4D4 and PDE4D5, enhanced memory, and increased hippocampal neurogenesis and pCREB. Finally, while rolipram and PDE4D deficiency shortened α2 adrenergic receptor-mediated anesthesia, a surrogate measure of emesis, miRNA-mediated PDE4D knock-down in the hippocampus did not. The present results suggest that PDE4D, in particular long-form PDE4D, plays a critical role in the mediation of memory and hippocampal neurogenesis, which are mediated by cAMP/CREB signaling; reduced expression of PDE4D, or at least PDE4D4 and PDE4D5, in the hippocampus enhances memory but appears not to cause emesis. These novel findings will aid in the development of PDE4 subtype- or variant-selective inhibitors for treatment of disorders involving impaired cognition, including Alzheimers disease.

Antidepressant- and Anxiolytic-like Effects of the Phosphodiesterase-4 Inhibitor Rolipram on Behavior Depend on Cyclic AMP Response Element Binding Protein-Mediated Neurogenesis in the Hippocampus

Inhibition of phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP (cAMP), increases phosphorylation of the cAMP response element binding protein (pCREB) and hippocampal neurogenesis, and produces antidepressant-like effects on behavior; however, causal links among these actions have not been established. In this study, chronic administration of rolipram (0.31–1.25u2009mg/kg, 16–23 days) produced antidepressant- and anxiolytic-like effects on behavior in mice. It also increased cAMP and pCREB levels in the hippocampus and prefrontal cortex, but increased Sox2, a marker for mitotic progenitor cells, only in the hippocampus. Chronic rolipram treatment also increased hippocampal neurogenesis, as evidenced by increased bromodeoxyuridine (BrdU)-positive cells in the hippocampal dentate gyrus. Methylazoxymethanol (MAM), which is toxic to proliferating cells, reversed rolipram-induced increases in BrdU-positive cells and pCREB in the hippocampus and partially blocked its behavioral effects. Approximately 84% of BrdU-positive cells became newborn neurons, 93% of which co-expressed pCREB; these proportions were not altered by rolipram or MAM, either alone or in combination. Finally, 3 weeks after the end of the MAM treatment, when neurogenesis was no longer inhibited, rolipram again increased hippocampal pCREB and its antidepressant- and anxiolytic-like effects were restored. Overall, these results suggest that rolipram produces its effects on behavior in a manner that at least partially depends on its neurogenic action in the hippocampus, targeting mitotic progenitor cells rather than newborn or mature neurons; cAMP/CREB signaling in hippocampal newborn neurons is critical for neurogenesis and contributes to the behavioral effects of rolipram.

Anxiogenic-Like Behavioral Phenotype of Mice Deficient in Phosphodiesterase 4B (PDE4B)

Phosphodiesterase-4 (PDE4), an enzyme that catalyzes the hydrolysis of cyclic AMP and plays a critical role in controlling its intracellular concentration, has been implicated in depression- and anxiety-like behaviors. However, the functions of the four PDE4 subfamilies (PDE4A, PDE4B, PDE4C, and PDE4D) remain largely unknown. In animal tests sensitive to anxiolytics, antidepressants, memory enhancers, or analgesics, we examined the behavioral phenotype of mice deficient in PDE4B (PDE4B−/−). Immunoblot analysis revealed loss of PDE4B expression in the cerebral cortex and amygdala of PDE4B−/− mice. The reduction of PDE4B expression was accompanied by decreases in PDE4 activity in the brain regions of PDE4B−/− mice. Compared to PDE4B+/+ littermates, PDE4B−/− mice displayed anxiogenic-like behavior, as evidenced by decreased head-dips and time spent in head-dipping in the holeboard test, reduced transitions and time on the light side in the light–dark transition test, and decreased initial exploration and rears in the open-field test. Consistent with anxiogenic-like behavior, PDE4B−/− mice displayed increased levels of plasma corticosterone. In addition, these mice also showed a modest increase in the proliferation of neuronal cells in the hippocampal dentate gyrus. In the forced-swim test, PDE4B−/− mice exhibited decreased immobility; however, this was not supported by the results from the tail-suspension test. PDE4B−/− mice did not display changes in memory, locomotor activity, or nociceptive responses. Taken together, these results suggest that the PDE4B subfamily is involved in signaling pathways that contribute to anxiogenic-like effects on behavior.

Inhibition of phosphodiesterase-4 reverses memory deficits produced by Aβ25–35 or Aβ1–40 peptide in rats

RationaleCyclic AMP signaling plays an important role in memory loss associated with Alzheimer’s disease (AD). However, little is known about whether inhibition of phosphodiesterase-4 (PDE4), which increases intracellular cAMP, reverses β-amyloid peptide (Aβ)-induced memory deficits.ObjectiveExperiments were performed to demonstrate the effect of the PDE4 inhibitor rolipram on memory impairment produced by Aβ1–40 (Aβ40) or its core fragment Aβ25–35.MethodsWe tested memory using Morris water-maze and passive avoidance tasks and examined expression of phosphorylated cAMP response-element binding protein (pCREB) in the hippocampus in rats treated with Aβ25–35 or Aβ40 into bilateral CA1 subregions, with or without rolipram administration.ResultsAβ25–35 (10xa0μg/side) increased escape latency during acquisition training and decreased swimming time and distance in the target quadrant in the water-maze probe trial; it also decreased 24-h retention in the passive avoidance paradigm. All these were reversed by chronic administration of rolipram (0.5xa0mg/kg). Similarly, Aβ40 (4xa0μg/side) produced memory impairment, as demonstrated by decreased retention in passive avoidance; this was also reversed by repeated treatment with rolipram. In addition, rolipram blocked extinction of memory during the 32-day testing period in the passive avoidance test. Further, Aβ40 decreased pCREB expression in the hippocampus, which was also reversed by rolipram; the changes in pCREB were highly correlated with those in memory.ConclusionsThese results suggest that the PDE4 inhibitor rolipram reverses cognitive deficits associated with AD most likely via increased cAMP/CREB signaling in the hippocampus; PDE4 could be a target for drugs that improve cognition in AD.

RNA interference-mediated phosphodiesterase 4D splice variants knock-down in the prefrontal cortex produces antidepressant-like and cognition-enhancing effects.

Phosphodiesterase 4 (PDE4) inhibitors produce potent antidepressant‐like and cognition‐enhancing effects. However, their clinical utility is limited by the major side effect of emesis, which appears to be PDE4 isoform‐specific. Although PDE4D subtype plays the pivotal role in these therapeutic profiles, it is also the primary subtype responsible for emesis. Therefore, the aim of present research was to investigate whether long‐form PDE4D variants mediate antidepressant‐like and cognition‐enhancing effects, but are irrespective with emesis.

Anxiolytic effects of ketamine in animal models of posttraumatic stress disorder

This study investigated the effectiveness of ketamine, a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, in alleviating the enhanced anxiety and fear response in both a mouse model of PTSD induced by inescapable electric foot shocks and a rat model of PTSD induced by a time-dependent sensitization (TDS) procedure. First, we evaluated the effect of ketamine on behavioral deficits in a mouse model of PTSD that consisted of foot shocks followed by three situational reminders. Our results showed that the aversive procedure induced several behavioral deficiencies, such as increased freezing behavior and anxiety, as well as reduced time spent in an aversive-like context, which were reversed by repeated treatment with ketamine. The effect of ketamine on behavioral changes after exposure to TDS was also investigated, and the levels of brain-derived neurotrophic factor (BDNF) in the hippocampus were measured. The results revealed that after TDS, the rats showed a significant increase in contextual freezing and a decrease in the percentage of time spent in and numbers of entries into open arms in the elevated plus maze test. As a positive control drug, sertraline (Ser, 15xa0mg/kg, i.g.), a selective serotonin reuptake inhibitor (SSRI) ameliorated these behavioral deficits. These behavioral effects were mimicked by chronic ketamine treatment. Furthermore, ketamine normalized the decreased BDNF level in the hippocampus in post-TDS rats. Taken together, these results suggest that ketamine exerts a therapeutic effect on PTSD that might be at least partially mediated by an influence on BDNF signaling in the hippocampus.

RNA interference-mediated phosphodiesterase 4D splice variants knock-down in the prefrontal cortex produces antidepressant-like and cognition-enhancing effects

Phosphodiesterase 4 (PDE4) inhibitors produce potent antidepressant‐like and cognition‐enhancing effects. However, their clinical utility is limited by the major side effect of emesis, which appears to be PDE4 isoform‐specific. Although PDE4D subtype plays the pivotal role in these therapeutic profiles, it is also the primary subtype responsible for emesis. Therefore, the aim of present research was to investigate whether long‐form PDE4D variants mediate antidepressant‐like and cognition‐enhancing effects, but are irrespective with emesis.

Phosphodiesterase-4D Knock-down in the Prefrontal Cortex Alleviates Chronic Unpredictable Stress-Induced Depressive-Like Behaviors and Memory Deficits in Mice

Phosphodiesterase 4 (PDE4) has four isoforms (PDE4A-D) with at least 25 splice variants. PDE4 subtype nonselective inhibitors produce potent antidepressant-like and cognition-enhancing effects via increased intracellular cyclic AMP (cAMP) signaling in the brain. Our previous data have demonstrated that long-form PDE4Ds appear to be involved in these pharmacological properties of PDE4 inhibitors in the normal animals. However, it is not clear whether long-form PDE4Ds are critical for the behaviors and related cellular signaling/neuronal plasticity/neuroendocrine alterations in the depressed animals. In the present study, animals exposed to the chronic unpredictable stress (CUS), a rodent model of depression, exhibited elevated corticosterone, depressive-like behavior, memory deficits, accompanied with decreased cAMP-PKA-CREB and cAMP-ERK1/2-CREB signaling and neuroplasticity. These alterations induced by CUS were reversed by RNA interference (RNAi)-mediated prefrontal cortex long-form PDE4Ds (especially PDE4D4 and PDE4D5) knock-down, similar to the effects of the PDE4 subtype nonselective inhibitor rolipram. Furthermore, these effects of RNAi were not enhanced by rolipram. These data indicate a predominant role of long-form PDE4Ds in the pharmacotherapies of PDE4 inhibitors for depression and concomitant memory deficits. Long-form PDE4Ds, especially PDE4D4 and PDE4D5, appear to be the promising targets for the development of antidepressants with high therapeutic indices.

Systematic review of traditional chinese medicine for depression in Parkinson's disease.

Depression is the most common non-motor symptom of Parkinsons disease (PD). Recent clinical trials have evaluated the effectiveness of traditional Chinese medicine (TCM) in the treatment of depression in PD (dPD). However, the results are conflicting rather than conclusive. To investigate the effectiveness of TCM for the treatment of dPD, a systematic review was conducted. Literature searches and collections were performed to identify studies addressing the treatment of TCM for dPD. The methodological quality and risk of bias in all studies included were evaluated. Weighted mean difference (WMD) with 95% confidence interval (CI) was used as the effect measure. Finally, a total of 10 studies involving 582 patients were identified. The pooled results revealed that TCM combined with conventional drugs significantly improved the total scores of the unified Parkinsons disease rating scale (WMD = -7.35, 95% CI: -11.24 to -3.47) and the score of the Hamilton rating scale for depression (HAM-D) (WMD = -4.19, 95% CI: -5.14 to -3.24) compared with conventional drug, respectively. Conclusively, there is evidence that TCM may be beneficial to the treatment of dPD in spite of the methodological weakness of the included studies.

Phosphodiesterase: An Interface Connecting Cognitive Deficits to Neuropsychiatric and Neurodegenerative Diseases

Phosphodiesterases (PDEs) are the only known enzymes to degrade intracellular cyclic AMP and/or cyclic GMP. The PDE superfamily consists of 11 families (PDE1- PDE11), each of which has 1 to 4 subtypes. Some of the subtypes may have multiple splice variants (e.g. PDE4D1-PDE4D11), leading to a total of more than 100 known proteins to date. Growing attention has been paid to the potential of PDEs as therapeutic targets for mood disorders and/or diseases affecting cognitive activity by controlling the rate of hydrolysis of the two aforementioned second messengers in recent years. The loss of cognitive functions is one of the major complaints most patients with CNS diseases face; it has an even more prominent negative impact on the quality of daily life. Cognitive dysfunction is usually a prognosis in patients suffering from neuropsychiatric and neurodegenerative diseases, including depression, schizophrenia, and Alzheimers disease. This review will focus on the contributions of PDEs to the interface between cognitive deficits and neuropsychiatric and neurodegenerative disorders. It is expected to make for the understanding and discovery that selective PDE inhibitors have the therapeutic potential for cognitive dysfunctions associated with neuropsychiatric and neurodegenerative disorders.