PP2A ligand ITH12246 protects against memory impairment and focal cerebral ischemia in mice

C-glycosides analogues of the okadaic acid central fragment exert neuroprotection via restoration of PP2A-phosphatase activity: A rational design of potential drugs for Alzheimer's disease targeting tauopathies

Protein phosphatase 2A (PP2A) is an important Ser/Thr phosphatase that participates in the regulation of multiple cellular processes. This implies that any deficient activity of PP2A is the responsible of severe pathologies. For instance, one of the main histopathological features of Alzheimer's disease is neurofibrillary tangles, which are mainly comprised by hyperphosphorylated forms of tau protein. This altered rate of tau phosphorylation has been correlated with PP2A depression AD patients. With the goal of preventing PP2A inactivation in neurodegeneration scenarios, we have aimed to design, synthesize and evaluate new ligands of PP2A capable of preventing its inhibition. To achieve this goal, the new PP2A ligands present structural similarities with the central fragment C19-C27 of the well-established PP2A inhibitor okadaic acid (OA). Indeed, this central moiety of OA does not exert inhibitory actions. Hence, these compounds lack PP2A-inhibiting structural motifs but, in contrast, compete with PP2A inhibitors, thus recovering phosphatase activity. Proving this hypothesis, most compounds showed a good neuroprotective profile in neurodegeneration models related to PP2A impairment, highlighting derivative 10, named ITH12711, as the most promising one. This compound (1) restored in vitro and cellular PP2A catalytic activity, measured on a phospho-peptide substrate and by western-blot analyses, (2) proved good brain penetration measured by PAMPA, and (3) prevented LPS-induced memory impairment of mice in the object recognition test. Thus, the promising outcomes of the compound 10 validate our rational approach to design new PP2A-activating drugs based on OA central fragment.

Promising Molecular Targets in Pharmacological Therapy for Neuronal Damage in Brain Injury

The complex etiopathogenesis of brain injury associated with neurodegeneration has sparked a lot of studies in the last century. These clinical situations are incurable, and the currently available therapies merely act on symptoms or slow down the course of the diseases. Effective methods are being sought with an intent to modify the disease, directly acting on the properly studied targets, as well as to contribute to the development of effective therapeutic strategies, opening the possibility of refocusing on drug development for disease management. In this sense, this review discusses the available evidence for mitochondrial dysfunction induced by Ca2+ miscommunication in neurons, as well as how targeting phosphorylation events may be used to modulate protein phosphatase 2A (PP2A) activity in the treatment of neuronal damage. Ca2+ tends to be the catalyst for mitochondrial dysfunction, contributing to the synaptic deficiency seen in brain injury. Additionally, emerging data have shown that PP2A-activating drugs (PADs) suppress inflammatory responses by inhibiting different signaling pathways, indicating that PADs may be beneficial for the management of neuronal damage. In addition, a few bioactive compounds have also triggered the activation of PP2A-targeted drugs for this treatment, and clinical studies will help in the authentication of these compounds. If the safety profiles of PADs are proven to be satisfactory, there is a case to be made for starting clinical studies in the setting of neurological diseases as quickly as possible.

The involvement of TRPV4 on the hypoxia-induced oxidative neurotoxicity and apoptosis in a neuronal cell line: Protective role of melatonin

The hypoxia (HYPX)-mediated excessive generation of mitochondrial free reactive oxygen species (mROS) and the overload Ca²⁺ influx via the inhibition of TRPV4 are controlled by the treatment of antioxidants. However, the molecular mechanisms underlying melatonin (MLT)'s neuroprotection remains elusive. We investigated the role of MLT via modulation of TRPV4 on oxidative neurodegeneration and death in SH-SY5Y neuronal cells. The SH-SY5Y cells were divided into five groups as follows: control, MLT (1 mM for 2 h), HYPX (200 μM CoCl₂ for 24 h), HYPX + MLT, and HYPX + TRPV4 blockers (ruthenium red-1 μM for 30 min). The HYPX caused to the increase of TRPV4 current density and overload Ca²⁺ influx with an increase of mitochondrial membrane potential and mROS generation. The changes were not observed in the absence of TRPV4. When HYPX exposure and TRPV4 agonist (GSK1016790A)-induced TRPV4 activity were inhibited by the treatment of ruthenium red or MLT, the increase of mROS, lipid peroxidation, apoptosis, Zn²⁺ concentrations, TRPV4, caspase -3, caspase -9, Bax, and Bcl-2 expressions were restored via upregulation of reduced glutathione, glutathione peroxidase, and total antioxidant status. The levels of apoptosis and cell death in the cells were enriched with increases of caspase -3 and -9 activations, although they were decreased by MLT treatment. In conclusion, the treatment of MLT modulates HYPX-mediated mROS, apoptosis, and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting HYPX-mediated neurological diseases associated with the increase of mROS, Ca²⁺, and Zn²⁺ concentration.

Cerebrovascular Disease in the Young Adult: Examining Melatonin's Possible Multiple Roles

In the last decade or more, there have been reports suggesting a rise in the incidence of stroke in young adults. Presently, it appears that the risk factors associated with the cause of stroke in young adults remain relatively constant across different geographic regions of the world. Moreover, the endogenous rhythm of a neurohormone such as melatonin is known to play certain roles in the modulation of some of the risk factors that are associated with an increased risk of stroke in young people. Whereas animal studies have shown that melatonin plays diverse roles in stroke, only a limited number of human studies examined the roles of exogenous melatonin administration in the prevention of stroke, attenuation of neuronal damage, and improving outcome or well-being in stroke patients. In this review, first we summarize existing studies of stroke in the young adult and then provide insights on melatonin and stroke. Thereafter, we discuss the role of melatonin in models of stroke and how melatonin can be regulated to prevent stroke in young adults. Finally, we highlight the possible roles of melatonin in the management and outcome of stroke, especially in the young adult stroke population.

Senkyunolide A protects neural cells against corticosterone-induced apoptosis by modulating protein phosphatase 2A and α-synuclein signaling

Background

Depression is characterized by a pathological injury to the hippocampal neurons. Senkyunolide A (SenA) is one of the major active components of Dan-zhi-xiao-yao-san, which is widely used in the treatment of depression-related disorders.

Materials and methods

In the present study, it was hypothesized that the antidepressant effect of Dan-zhi-xiao-yao-san depended on the function of SenA and the authors attempted to reveal the molecular mechanism associated with the treatment. An in vitro depression model was induced using corticosterone (Cort), and the effect of SenA on the cell viability, apoptosis, and protein phosphatase 2A/α-synuclein (PP2A/α-syn) signaling was detected. To validate the mechanism driving the therapeutic effect of SenA, activity of PP2A and α-syn was modulated and the effect on neural cells was evaluated.

Results

The results showed that SenA protects Cort-induced cell apoptosis in PC12 cells. In addition, SenA increased Cort-induced reduction of PP2A activity, while it decreased the expression of p-PP2A, α-syn, and p-α-syn (Ser129). Further, modulation of PP2A activity with specific inhibitor okadaic acid (OA) increased Cort-induced cell apoptosis, while PP2A activator D-erythro-sphingosine (SPH) exhibited an opposite effect. The neuroprotective effects of SenA on neural cells also depended on inhibition of α-syn function, the regulation of which would influence the activity of PP2A in a negative loop.

Conclusion

Collectively, the results suggested that the neuroprotective effects of SenA were exerted by modulating activities of PP2A activities and α-syn. The findings partially explained the mechanism associated with the neuroprotective effect of SenA.

Analysis of gene expression profiles of CR80, a neuroprotective 1,8-Naphthyridine

Aim: The 1,8-naphthyridine CR80 (ethyl 5-amino-2-methyl-6,7,8,9-tetrahydrobenzo[b] [1,8]naphthyridine-3-carboxylate) has shown interesting neuroprotective properties in in vitro and in vivo models of neurodegeneration. In spite of these promising outcomes, the molecular and cellular mechanisms underlying CR80 actions need to be further explored. Materials & methods: We herein report the signal transduction pathways involved in developmental, neuroprotective and stress-activated processes, as well as the gene expression regulation by CR80 in SH-SY5Y neuroblastoma cells. Results: The CR80 exposure upregulated several antioxidant enzymes (HO-1, GSR, SQSTM1, and TRXR1) and anti-apoptotic proteins (Bcl-xL, Bcl-2, P21, and Wnt6). Conclusion: The observed changes in gene expression would afford new insights on the neuroprotective profile of CR80.

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

Gramine Derivatives Targeting Ca(2+) Channels and Ser/Thr Phosphatases: A New Dual Strategy for the Treatment of Neurodegenerative Diseases

We describe the synthesis of gramine derivatives and their pharmacological evaluation as multipotent drugs for the treatment of Alzheimer's disease. An innovative multitarget approach is presented, targeting both voltage-gated Ca(2+) channels, classically studied for neurodegenerative diseases, and Ser/Thr phosphatases, which have been marginally aimed, even despite their key role in protein τ dephosphorylation. Twenty-five compounds were synthesized, and mostly their neuroprotective profile exceeded that offered by the head compound gramine. In general, these compounds reduced the entry of Ca(2+) through VGCC, as measured by Fluo-4/AM and patch clamp techniques, and protected in Ca(2+) overload-induced models of neurotoxicity, like glutamate or veratridine exposures. Furthermore, we hypothesize that these compounds decrease τ hyperphosphorylation based on the maintenance of the Ser/Thr phosphatase activity and their neuroprotection against the damage caused by okadaic acid. Hence, we propose this multitarget approach as a new and promising strategy for the treatment of neurodegenerative diseases.

Brain ischaemia induces shedding of a BDNF-scavenger ectodomain from TrkB receptors by excitotoxicity activation of metalloproteinases and γ-secretases

Stroke remains a leading cause of death and disability in the world with limited therapies available to restrict brain damage or improve functional recovery after cerebral ischaemia. A promising strategy currently under investigation is the promotion of brain-derived neurotrophic factor (BDNF) signalling through tropomyosin-related kinase B (TrkB) receptors, a pathway essential for neuronal survival and function. However, TrkB and BDNF-signalling are impaired by excitotoxicity, a primary pathological process in stroke also associated with neurodegenerative diseases. Pathological imbalance of TrkB isoforms is critical in neurodegeneration and is caused by calpain processing of BDNF high affinity full-length receptor (TrkB-FL) and an inversion of the transcriptional pattern of the Ntrk2 gene, to favour expression of the truncated isoform TrkB-T1 over TrkB-FL. We report here that both TrkB-FL and neuronal TrkB-T1 also undergo ectodomain shedding by metalloproteinases activated after ischaemic injury or excitotoxic damage of cortical neurons. Subsequently, the remaining membrane-bound C-terminal fragments (CTFs) are cleaved by γ-secretases within the transmembrane region, releasing their intracellular domains (ICDs) into the cytosol. Therefore, we identify TrkB-FL and TrkB-T1 as new substrates of regulated intramembrane proteolysis (RIP), a mechanism that highly contributes to TrkB-T1 regulation in ischaemia but is minor for TrkB-FL which is mainly processed by calpain. However, since the secreted TrkB ectodomain acts as a BDNF scavenger and significantly alters BDNF/TrkB signalling, the mechanism of RIP could contribute to neuronal death in excitotoxicity. These results are highly relevant since they reveal new targets for the rational design of therapies to treat stroke and other pathologies with an excitotoxic component.

Epigenetic regulation of estrogen-dependent memory

Hippocampal memory formation is highly regulated by post-translational histone modifications and DNA methylation. Accordingly, these epigenetic processes play a major role in the effects of modulatory factors, such as sex steroid hormones, on hippocampal memory. Our laboratory recently demonstrated that the ability of the potent estrogen 17β-estradiol (E2) to enhance hippocampal-dependent novel object recognition memory in ovariectomized female mice requires ERK-dependent histone H3 acetylation and DNA methylation in the dorsal hippocampus. Although these data provide valuable insight into the chromatin modifications that mediate the memory-enhancing effects of E2, epigenetic regulation of gene expression is enormously complex. Therefore, more research is needed to fully understand how E2 and other hormones employ epigenetic alterations to shape behavior. This review discusses the epigenetic alterations shown thus far to regulate hippocampal memory, briefly reviews the effects of E2 on hippocampal function, and describes in detail our work on epigenetic regulation of estrogenic memory enhancement.

ITH12410/SC058: a new neuroprotective compound with potential in the treatment of Alzheimer's disease

The neuroprotective profile of the dibenzothiadiazepine ITH12410/SC058 (2-chloro-5,6-dihydro-5,6-diacetyldibenzo[b,f][1,4,5]thiadiazepine) against several neurotoxicity models related to neurodegenerative diseases is herein described. ITH12410/SC058 protected SH-SY5Y cells against the loss of cell viability elicited by amyloid beta peptide and okadaic acid, a selective inhibitor of phosphoprotein phosphatase 2A that induces neurofibrillary tangle formation. Furthermore, ITH12410/SC058 is neuroprotective against several in vitro models of oxidative stress, that is, H2O2 exposure or incubation with rotenone plus oligomycin A in SH-SY5Y cells, and oxygen and glucose deprivation followed by reoxygenation in rat hippocampal slices. By contrast, ITH12410/SC058 was unable to significantly protect SH-SY5Y neuroblastoma cells against the toxicity elicited by Ca(2+) overload. Our results confirm the hypothesis that the dibenzothiadiazepine ITH12410/SC058 features its neuroprotective actions in a multitarget fashion, and is a promising drug for the treatment of neurodegenerative diseases.