A Mechanistic Rationale for PDE-4 Inhibitors to Treat Residual Cognitive Deficits in Acquired Brain Injury

Effects of exercise-targeted hippocampal PDE-4 methylation on synaptic plasticity and spatial learning/memory impairments in D-galactose-induced aging rats

Physical exercise reduces the effects of aging and cognitive decline by improving synaptic plasticity and spatial learning. However, the underlying neurobiological mechanisms are unclear. A total of 45 Male SPF Sprague-Dawley rats were acclimatized and then allocated into three groups, 15 in each group: the saline control (DC) group, D-gal-induced aging (DA) group, and D-gal-induced aging + exercise (DE) group. Six weeks of intraperitoneal injections of D-gal at a concentration of 100 mg/kg body weight/d was injected to establish model of aging in the DA and DE groups. Morris water maze test was implemented to evaluate the hippocampus related cognition. SOD activity and MDA was tested to assess the aging in all groups. H&E and Nissl staining was used to observe the histopathological changes of hippocampal neurons in aging rats. Quantitative real-time polymerase chain reaction, western blotting and immunofluorescence staining techniques were used to investigate the expression of synaptic genes and proteins in the hippocampus. Massarray methylation system was employed to measure the PDE-4 gene methylation level in rat hippocampal tissues. Our results demonstrated that exercise intervention improves cognitive function in D-gal-induced aging rats. The methylation of CpG sites in PDE-4 in the hippocampus was significantly increased. The physical exercise significantly increased PDE-4 gene methylation and effectively decreased PDE-4 gene and protein expression. These beneficial behavioral and morphological effects were attributed to PDE-4 methylation, which was activated cAMP/PKA/CREB pathway and improved synaptic plasticity. Exercise induced PDE-4 methylation is key mechanism underpinning the amelioration of learning/memory impairment, suggesting the potential efficacy of physical exercise training in delaying brain aging.

Phosphodiesterase inhibitor, ibudilast alleviates core behavioral and biochemical deficits in the prenatal valproic acid exposure model of autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is categorized as a neurodevelopmental disorder, presenting with a variety of aetiological and phenotypical features. Ibudilast is known to produce beneficial effects in several neurological disorders including neuropathic pain, multiple sclerosis, etc. by displaying its neuroprotective and anti-inflammatory properties. Here, in our study, the pharmacological outcome of ibudilast administration was investigated in the prenatal valproic acid (VPA)-model of ASD in Wistar rats.

METHODS

Autistic-like symptoms were induced in Wistar male pups of dams administered with Valproic acid (VPA) on embryonic day 12.5. VPA-exposed male pups were administered with two doses of ibudilast (5 and10 mg/kg) and all the groups were evaluated for behavioral parameters like social interaction, spatial memory/learning, anxiety, locomotor activity, and nociceptive threshold. Further, the possible neuroprotective effect of ibudilast was evaluated by assessing oxidative stress, neuroinflammation (IL-1β, TNF-α, IL-6, IL-10) in the hippocampus, % area of Glial fibrillary acidic protein (GFAP)-positive cells and neuronal damage in the cerebellum.

KEY FINDINGS

Treatment with ibudilast significantly attenuated prenatal VPA exposure associated social interaction and spatial learning/memory deficits, anxiety, hyperactivity, and increased nociceptive threshold, and it decreased oxidative stress markers, pro-inflammatory markers (IL-1β, TNF-α, IL-6), and % area of GFAP-positive cells and restored neuronal damage.

CONCLUSIONS

Ibudilast treatment has restored crucial ASD-related behavioural abnormalities, potentially through neuroprotection. Therefore, benefits of ibudilast administration in animal models of ASD suggest that ibudilast may have therapeutic potential in the treatment of ASD.

Re-Addressing Dementia by Network Medicine and Mechanism-Based Molecular Endotypes

Alzheimer's disease (AD) and other forms of dementia are together a leading cause of disability and death in the aging global population, imposing a high personal, societal, and economic burden. They are also among the most prominent examples of failed drug developments. Indeed, after more than 40 AD trials of anti-amyloid interventions, reduction of amyloid-β (Aβ) has never translated into clinically relevant benefits, and in several cases yielded harm. The fundamental problem is the century-old, brain-centric phenotype-based definitions of diseases that ignore causal mechanisms and comorbidities. In this hypothesis article, we discuss how such current outdated nosology of dementia is a key roadblock to precision medicine and articulate how Network Medicine enables the substitution of clinicopathologic phenotypes with molecular endotypes and propose a new framework to achieve precision and curative medicine for patients with neurodegenerative disorders.

The protective effect of Palmatine on depressive like behavior by modulating microglia polarization in LPS-induced mice

The purpose of the present study was to evaluate the protective effect of Palmatine on LPS-induced depressive like behavior and explore its potential mechanism. The mice were intragastrically treated with Fluoxetine or Palmatine once daily for 1 week. After the last drug administration, the mice were intraperitoneally challenged with LPS and suffered for Sucrose preference test, Tail suspension test, Forced swimming test and Open field test. The pro-inflammatory biomarkers were measured by ELISA, qPCR, WB and immunofluorescence. As a result, the administration of Palmatine effectively lessened depressive-like behavior. Palmatine could decrease the levels of pro-inflammatory cytokines TNF-α, IL-6, the expressions of CD68, iNOS mRNA, as well as increase the levels of anti-inflammatory cytokines IL-4, IL-10, the expressions of CD206, Arg1 mRNA, Ym1 mRNA both in LPS-induced mice and in LPS-induced BV2 cells. The beneficial effect of Palmatine might be attributed to the suppression of M1 microglia polarization and the promotion of M2 microglia polarization via PDE4B/KLF4 signaling. The similar results were observed in CUMS-induced depressive mice. The transfection with PDE4B SiRNA or KLF4 SiRNA indicated that PDE4B and KLF4 were both involved in the Palmatine-mediated microglia polarization. Molecular docking indicated that Palmatine could interact with PDE4B. In conclusion, this research demonstrated that Palmatine attenuated depressive like behavior by modulating microglia polarization via PDE4B/KLF4 signaling.

Roflupram protects against rotenone-induced neurotoxicity and facilitates α-synuclein degradation in Parkinson's disease models

We have previously shown that roflupram (ROF) protects against MPP+-induced neuronal damage in models of Parkinson's disease (PD). Since impaired degradation of α-synuclein (α-syn) is one of the key factors that lead to PD, here we investigated whether and how ROF affects the degradation of α-syn in rotenone (ROT)-induced PD models in vivo and in vitro. We showed that pretreatment with ROF (10 μM) significantly attenuated cell apoptosis and reduced the level of α-syn in ROT-treated SH-SY5Y cells. Furthermore, ROF significantly enhanced the lysosomal function, as evidenced by the increased levels of mature cathepsin D (CTSD) and lysosomal-associated membrane protein 1 (LAMP1) through increasing NAD+/NADH and the expression of sirtuin 1 (SIRT1). Pretreatment with an SIRT1 inhibitor selisistat (SELI, 10 μM) attenuated the neuroprotection of ROF, ROF-reduced expression of α-syn, and ROF-increased expression levels of LAMP1 and mature CTSD. Moreover, inhibition of CTSD by pepstatin A (20 μM) attenuated ROF-reduced expression of α-syn. In vivo study was conducted in mice exposed to ROT (10 mg·kg-1·d-1, i.g.) for 6 weeks; then, ROT-treated mice received ROF (0.5, 1, or 2 mg·kg-1·d-1; i.g.) for four weeks. ROF significantly ameliorated motor deficits, which was accompanied by increased expression levels of tyrosine hydroxylase, SIRT1, mature CTSD, and LAMP1, and a reduced level of α-syn in the substantia nigra pars compacta. Taken together, these results demonstrate that ROF exerts a neuroprotective action and reduces the α-syn level in PD models. The mechanisms underlying ROF neuroprotective effects appear to be associated with NAD+/SIRT1-dependent activation of lysosomal function.

The Dual Dose-Dependent Effects of Corticosterone on Hippocampal Cell Apoptosis After Traumatic Brain Injury Depend on the Activation Ratio of Mineralocorticoid Receptors to Glucocorticoid Receptors

In our recent studies, we reported that mineralocorticoid receptor (MR) had the opposite effects of glucocorticoid receptor (GR) on neural cell survival after traumatic brain injury (TBI). However, whether short-term use of high-dose natural glucocorticoids, which are mixed agonists of both MR and GR, leads to neurotoxic effects by inducing excessive GR activation is unclear, as is the threshold GR activation level and the possible signaling pathways remain unclear. In this study, we examined the dual dose-dependent effects of corticosterone (CORT) on spatial memory, hippocampal cell survival and receptor-mediated downstream signaling pathways after TBI. We found that different doses of CORT exhibited dual effects on hippocampal cell survival and rat spatial memory. Low doses of CORT (0.3 and 3 mg/kg) significantly increased MR activation, upregulated Akt/CREB/Bad phosphorylation and Bcl-2 concentration, reduced the number of apoptotic neural cells, and subsequently improved rat spatial memory. In contrast, a high dose of CORT (30 mg/kg) exerted the opposite effects by overactivating GR, upregulating P53/Bax levels, and inhibiting Erk/CREB activity. The results suggest that the neuroprotective and neurotoxic effects of endogenous GC depend on a threshold level and that a higher dose of GC, even for short-term use, should be avoided after TBI.

Roflumilast prevents ischemic stroke-induced neuronal damage by restricting GSK3β-mediated oxidative stress and IRE1α/TRAF2/JNK pathway

Inhibition of phosphodiesterase 4 (PDE4) protects against neuronal apoptosis induced by cerebral ischemia. However, the exact mechanisms responsible for the protection of PDE4 inhibition have not been completely clarified. Roflumilast (Roflu) is an FDA-approved PDE4 inhibitor for the treatment of chronic obstructive pulmonary disease. The potential protective role of Roflu against ischemic stroke-associated neuronal injury remains unexplored. In this study, we investigated the effect and mechanism of Roflu against ischemic stroke using in vitro oxygen-glucose deprivation reperfusion (OGD/R) and in vivo rat middle cerebral artery occlusion (MCAO) models. We demonstrated that Roflu significantly reduced the apoptosis of HT-22 cells exposed to OGD/R, enhanced the nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2), and reduced oxidative stress. Treatment with Roflu increased the phosphorylation of protein kinase B (Akt) and glycogen synthase kinase 3β (GSK3β) but decreased the level of phosphorylated inositol requiring enzyme 1α (IRE1α). Interestingly, constitutively active GSK3β (S9A) mutation abolished the effects of Roflu on oxidative stress and IRE1α phosphorylation. Moreover, Roflu decreased the binding of IRE1α to tumor necrosis factor receptor-associated factor 2 (TRAF2) and attenuated the phosphorylation of c-Jun N-terminal kinase (JNK). We also found that PDE4B knockdown reduced the phosphorylation of both IRE1α and JNK, while overexpression of PDE4B antagonized the role of PDE4B knockdown on the activation of IRE1α and JNK. Besides, the inhibition of PDE4 by Roflu produced similar effects in primary cultured neurons. Finally, Roflu ameliorated MCAO-induced cerebral injury by decreasing infarct volume, restoring neurological score, and reducing the phosphorylation of IRE1α and JNK. Collectively, these data suggest that Roflu protects neurons from cerebral ischemia reperfusion-mediated injury via the activation of GSK3β/Nrf-2 signaling and suppression of the IRE1α/TRAF2/JNK pathway. Roflu has the potential as a protective drug for the treatment of cerebral ischemia.

Roflumilast protects against spatial memory impairments and exerts anti-inflammatory effects after transient global cerebral ischemia

Phosphodiesterase 4 (PDE4) inhibitors have been shown to present beneficial effects in cerebral ischemic injury because of their ability to improve cognition and target different phases and mechanisms of cerebral ischemia, including apoptosis, neurogenesis, angiogenesis, and inflammation. The present study investigated whether repeated treatment with the PDE4 inhibitor roflumilast rescued memory loss and attenuated neuroinflammation in rats following transient global cerebral ischemia (TGCI). TGCI caused memory impairments, neuronal loss (reflected by Neuronal nuclei (NeuN) immunoreactivity), and compensatory neurogenesis (reflected by doublecortin (DCX) immunoreactivity) in the hippocampus. Also, increases in the protein expression of the phosphorylated response element-binding protein (pCREB) and inflammatory markers such as the glial fibrillary acidic protein (GFAP) and ionized calcium-binding adaptor molecule 1 (Iba-1), were detected in the hippocampus in TGCI rats. Repeated treatment with roflumilast (0.003 and 0.01 mg/kg) prevented spatial memory deficits without promoting hippocampal protection in ischemic animals. Roflumilast increased the levels of pCREB, arginase-1, interleukin (IL) 4, and IL-10 in the hippocampus 21 days after TGCI. These data suggest a protective effect of roflumilast against functional sequelae of cerebral ischemia, which might be related to its anti-inflammatory properties.