Dual Mkk4 and Mkk7 Gene Deletion in Adult Mouse Causes an Impairment of Hippocampal Immature Granule Cells.

(1) Background: The c-Jun-NH2-terminal protein kinase (JNK) is a mitogen-activated protein kinase involved in regulating physiological processes in the central nervous system. However, the dual genetic deletion of Mkk4 and Mkk7 (upstream activators of JNK) in adult mice is not reported. The aim of this study was to induce the genetic deletion of Mkk4/Mkk7 in adult mice and analyze their effect in hippocampal neurogenesis. (2) Methods: To achieve this goal, Actin-CreERT2 (Cre+/-), Mkk4flox/flox, Mkk7flox/flox mice were created. The administration of tamoxifen in these 2-month-old mice induced the gene deletion (Actin-CreERT2 (Cre+/-), Mkk4∆/∆, Mkk7∆/∆ genotype), which was verified by PCR, Western blot, and immunohistochemistry techniques. (3) Results: The levels of MKK4/MKK7 at 7 and 14 days after tamoxifen administration were not eliminated totally in CNS, unlike what happens in the liver and heart. These data could be correlated with the high levels of these proteins in CNS. In the hippocampus, the deletion of Mkk4/Mkk7 induced a misalignment position of immature hippocampal neurons together with alterations in their dendritic architecture pattern and maturation process jointly to the diminution of JNK phosphorylation. (4) Conclusion: All these data supported that the MKK4/MKK7-JNK pathway has a role in adult neurogenic activity.

c-Jun N-Terminal Kinases in Alzheimer's Disease: A Possible Target for the Modulation of the Earliest Alterations.

Given the highly multifactorial origin of Alzheimer's disease (AD) neuropathology, disentangling and orderly knowing mechanisms involved in sporadic onset are arduous. Nevertheless, when the elements involved are dissected into smaller pieces, the task becomes more accessible. This review aimed to describe the link between c-Jun N-terminal Kinases (JNKs), master regulators of many cellular functions, and the early alterations of AD: synaptic loss and dysregulation of neuronal transport. Both processes have a role in the posterior cognitive decline observed in AD. The manuscript focuses on the molecular mechanisms of glutamatergic, GABA, and cholinergic synapses altered by the presence of amyloid-ß aggregates and hyperphosphorylated tau, as well as on several consequences of the disruption of cellular processes linked to neuronal transport that is controlled by the JNK-JIP (c-jun NH2-terminal kinase (JNK)-interacting proteins (JIPs) complex, including the transport of AßPP or autophagosomes.

Involvement of JNK1 in Neuronal Polarization During Brain Development.

The c-Jun N-terminal Kinases (JNKs) are a group of regulatory elements responsible for the control of a wide array of functions within the cell. In the central nervous system (CNS), JNKs are involved in neuronal polarization, starting from the cell division of neural stem cells and ending with their final positioning when migrating and maturing. This review will focus mostly on isoform JNK1, the foremost contributor of total JNK activity in the CNS. Throughout the text, research from multiple groups will be summarized and discussed in order to describe the involvement of the JNKs in the different steps of neuronal polarization. The data presented support the idea that isoform JNK1 is highly relevant to the regulation of many of the processes that occur in neuronal development in the CNS.

Epigallocatechin-3-Gallate (EGCG) Improves Cognitive Deficits Aggravated by an Obesogenic Diet Through Modulation of Unfolded Protein Response in APPswe/PS1dE9 Mice.

Epigallocatechin-3-gallate (EGCG), a catechin found in green tea, has been previously investigated for its neuroprotective effects in vitro and in vivo. In the present study, we aimed to evaluate its possible beneficial effects in a well-established preclinical mixed model of familial Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) based on the use of transgenic APPswe/PS1dE9 (APP/PS1) mice fed with a high fat diet (HFD). C57BL/6 wild-type (WT) and APP/PS1 mice were used in this study. APP/PS1 mice were fed with a palmitic acid-enriched HFD (APP/PS1 HFD) containing 45% of fat mainly from hydrogenated coconut oil. Intraperitoneal glucose tolerance tests (IP-GTT) and insulin tolerance tests (IP-ITT) were performed. Western blot analyses were performed to analyse protein expression, and water maze and novel object recognition test were done to evaluate the cognitive process. EGCG treatment improves peripheral parameters such as insulin sensitivity or liver insulin pathway signalling, as well as central memory deficits. It also markedly increased synaptic markers and cAMP response element binding (CREB) phosphorylation rates, as a consequence of a decrease in the unfolded protein response (UPR) activation through the reduction in the activation factor 4 (ATF4) levels and posterior downregulation of protein tyrosine phosphatase 1B (PTP1B). Moreover, EGCG significantly decreased brain amyloid ß (Aß) production and plaque burden by increasing the levels of α-secretase (ADAM10). Also, it led to a reduction in neuroinflammation, as suggested by the decrease in astrocyte reactivity and toll-like receptor 4 (TLR4) levels. Collectively, evidence suggests that chronic EGCG prevents distinct neuropathological AD-related hallmarks. This study also provides novel insights into the metabolic and neurobiological mechanisms of EGCG against cognitive loss through its effects on UPR function, suggesting that this compound may be a promising disease-modifying treatment for neurodegenerative diseases.

c-Jun N-terminal Kinase 1 ablation protects against metabolic-induced hippocampal cognitive impairments.

The development of metabolic alterations like insulin resistance has been associated with dysfunctions in mitochondrial oxidative capacity, induction of neuroinflammatory responses, and the appearance of cognitive impairments in the brain. The c-Jun N-terminal Kinase 1 (JNK1) is a potential key modulator of these mechanisms. The current study identifies a protective effect of whole-body JNK1 knockout in the presence of a high-fat diet (HFD). Specifically, the data suggest that mice missing JNK1 show increased insulin sensitivity and mitochondrial activity, as well as reduced body weight, and astrocyte and microglial reactivity. Finally, these animals are also protected against HFD-induced cognitive impairments as assessed through novel object recognition test, the observation of dendritic spines, and the levels of BDNF or other proteins like spinophilin and ARC. Thus, modulation of JNK1 activity seems like a promising approach for the design of therapies aimed at treating metabolic-induced cognitive impairments. KEY MESSAGES: JNK1 is a link between obesity/type 2 diabetes and cognitive loss Inhibition of JNK1 is neuroprotective JNK1 constitutes a therapeutic strategy for cognitive loss.

Memantine for the Treatment of Dementia: A Review on its Current and Future Applications.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of extracellular amyloid-ß protein (Aß) and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. The N-Methyl-D-aspartate receptors (NMDAR), ionotropic glutamate receptor, are essential for processes like learning and memory. An excessive activation of NMDARs has been associated with neuronal loss. The discovery of extrasynaptic NMDARs provided a rational and physiological explanation between physiological and excitotoxic actions of glutamate. Memantine (MEM), an antagonist of extrasynaptic NMDAR, is currently used for the treatment of AD jointly with acetylcholinesterase inhibitors. It has been demonstrated that MEM preferentially prevents the excessive continuous extrasynaptic NMDAR disease activation and therefore prevents neuronal cell death induced by excitotoxicity without disrupting physiological synaptic activity. The problem is that MEM has shown no clear positive effects in clinical applications while, in preclinical stages, had very promising results. The data in preclinical studies suggests that MEM has a positive impact on improving AD brain neuropathology, as well as in preventing Aß production, aggregation, or downstream neurotoxic consequences, in part through the blockade of extrasynaptic NMDAR. Thus, the focus of this review is primarily to discuss the efficacy of MEM in preclinical models of AD, consider possible combinations of this drug with others, and then evaluate possible reasons for its lack of efficacy in clinical trials. Finally, applications in other pathologies are also considered.

Neuroprotective Effects of the Absence of JNK1 or JNK3 Isoforms on Kainic Acid-Induced Temporal Lobe Epilepsy-Like Symptoms.

The activation of c-Jun-N-terminal kinases (JNK) pathway has been largely associated with the pathogenesis and the neuronal death that occur in neurodegenerative diseases. Altogether, this justifies why JNKs have become a focus of screens for new therapeutic strategies. The aim of the present study was to identify the role of the different JNK isoforms (JNK1, JNK2, and JNK3) in apoptosis and inflammation after induction of brain damage. To address this aim, we induced excitotoxicity in wild-type and JNK knockout mice (jnk1 -/- , jnk2 -/- , and jnk3 -/- ) via an intraperitoneal injection of kainic acid, an agonist of glutamic-kainate-receptors, that induce status epilepticus.Each group of animals was divided into two treatments: a single intraperitoneal dose of saline solution, used as a control, and a single intraperitoneal dose (30 mg/kg) of kainic acid. Our results reported a significant decrease in neuronal degeneration in the hippocampus of jnk1 -/- and jnk3 -/- mice after kainic acid treatment, together with reduced or unaltered expression of several apoptotic genes compared to WT treated mice. In addition, both jnk1 -/- and jnk3 -/- mice exhibited a reduction in glial reactivity, as shown by the lower expression of inflammatory genes and a reduction of JNK phosphorylation. In addition, in jnk3 -/- mice, the c-Jun phosphorylation was also diminished.Collectively, these findings provide compelling evidence that the absence of JNK1 or JNK3 isoforms confers neuroprotection against neuronal damage induced by KA and evidence, for the first time, the implication of JNK1 in excitotoxicity. Accordingly, JNK1 and/or JNK3 are promising targets for the prevention of cell death and inflammation during epileptogenesis.

Pirfenidone Attenuates Microglial Reactivity and Reduces Inducible Nitric Oxide Synthase mRNA Expression After Kainic Acid-Mediated Excitotoxicity in Pubescent Rat Hippocampus.

Excitotoxicity and neuroinflammation are strongly linked to the progressions of neurodegenerative diseases and acute injuries in the brain. Systematic administration of kainic acid (KA) in rodents causes severe limbic seizures, selective neuronal loss, and neuroinflammation in the hippocampus that are attributed to the excitotoxic process. Our previous report demonstrated the antioxidant and neuroprotective effects of pirfenidone (PFD) after the seizure onset induced by KA intraperitoneal injection. However, the aim of the present study is to analyze whether PFD has anti-inflammatory properties. Thus, pubescent male Wistar rats (30 days old) were exposed to 12 mg/Kg of KA, and the experimental group received KA and a single dose of 325 mg/Kg PFD in an orogastric tube at 90 min after KA exposure. The PFD treatment dramatically reduces the microglial activation observed by isolectin B4 staining and major histocompatibility complex II immunohistochemistry. We also determined that the messenger RNA of inducible nitric oxide synthase was downregulated by PFD treatment as measured 6 h after the KA injection. Our results indicate that the mechanism of neuroprotection after PFD treatment may include a decreased expression of the inducible nitric oxide synthase and reduced microglial activation. These findings suggest that PFD is a potentially useful strategy of the treatment for acute or chronic neurodegenerative diseases.

P38 MAPK inhibition protects against glutamate neurotoxicity and modifies NMDA and AMPA receptor subunit expression.

NMDA and AMPA receptors are thought to be responsible for Ca(++) influx during glutamate-induced excitotoxicity and, therefore, hippocampal neuronal death. We assessed whether excitotoxicity induced by neonatal treatment with monosodium glutamate in rats at postnatal age of 1, 3, 5, and 7 modifies the hippocampal expression of the NMDAR subunit NR1 and the AMPAR subunits GluR1/GluR2 at postnatal days 8, 10, 12, and 14. We also assessed the involvement of MAPK signaling by using the p38 inhibitor SB203580. Our results showed that monosodium glutamate induces neuronal death and alters the expression of the subunits evaluated in the hippocampus at all ages studied, which could be prevented by SB203580 treatment.Furthermore, expression of the NRSF gene silencing factor also increased in response to excitotoxicity, suggesting a relationship in suppressing GluR2-expression, which was regulated by the p38-MAPK pathway inhibitor SB203580. This result suggests that selectively blocking the pro-death signaling pathway may reduce neuronal death in some neurodegenerative diseases in which these neurotoxic processes are present and produce major clinical benefits in the treatment of these pathologies.

A single dose of pirfenidone attenuates neuronal loss and reduces lipid peroxidation after kainic acid-induced excitotoxicity in the pubescent rat hippocampus.

Systemic administration of kainic acid (KA) in rodents triggers limbic seizures following selective neuronal loss in the hippocampus attributed to the excitotoxic process. Lipid peroxidation products, such as 4-hydroxynonenal, are produced by oxidative stress and are present on the hippocampus, which contribute to neuronal death in the KA excitotoxicity model. Several antioxidants are neuroprotective agents. The aim of the present study was to analyse whether pirfenidone (PFD, 5-methyl-1-phenyl-2-(1H)-pyridone), an antioxidant drug, protects the neurons in the hippocampus of pubescent rats administered with KA. We evaluated the neuroprotective effect of PFD by quantifying the surviving neurons under hematoxilin-eosin staining after using three different doses of 100, 250, and 325 mg/kg administered via an orogastric tube 90 min after KA intraperitoneal injection (12 mg/kg). Only 325 mg/kg of PFD-attenuated neuronal loss in the hippocampal areas cornu ammonis field 1 (CA1) and cornu ammonis field 3 (CA3c) was observed; therefore, this dose was used in our subsequent studies. Later, we established that PFD reduces neuronal degeneration using Fluoro-Jade B stain in the CA3c but not in the CA1, and PFD reduces the presence of 4-hydroxynonenal, a lipid peroxidation product, in the CA3 by tissue immunohistochemistry. We concluded that only a single 325 mg/kg PFD dose had a neuroprotective effect after KA brain injury. This treatment may be advantageous because adequate pharmacological therapy with PFD can be developed to protect the neuron even after an acute neuronal disorder such as seizures or hypoxic/ischemic damage.