JNK signaling activation in the Ube3a maternal deficient mouse model: its specific inhibition prevents post-synaptic protein-enriched fraction alterations and cognitive deficits in Angelman Syndrome model

Multiscale spatio-temporal dynamics of UBE3A gene in brain physiology and neurodevelopmental disorders

The UBE3A gene, located in the chromosomal region 15q11-13, is subject to neuron-specific genomic imprinting and it plays a critical role in brain development. Genetic defects of UBE3A cause severe neurodevelopmental disorders, namely the Angelman syndrome (AS) and the 15q11.2-q13.3 duplication syndrome (Dup15q). In the last two decades, the development of in vitro and in vivo models of AS and Dup15q were fundamental to improve the understanding of UBE3A function in the brain. However, the pathogenic mechanisms of these diseases remain elusive and effective treatments are lacking. Recent evidence suggests that UBE3A functions are both spatially and temporally specific, varying across subcellular compartments, brain regions, and neuronal circuits. In the present review, we summarize current knowledge on the role of UBE3A in neuronal pathophysiology under this spatio-temporal perspective. Additionally, we propose key research questions that will be instrumental to better understand the pathogenic mechanisms underpinning AS and Dup15q disorders and provide the rationale to develop novel therapies.

Imbalanced expression of cation-chloride cotransporters as a potential therapeutic target in an Angelman syndrome mouse model

Angelman syndrome is a neurodevelopmental disorder caused by loss of function of the maternally expressed UBE3A gene. Treatments for the main manifestations, including cognitive dysfunction or epilepsy, are still under development. Recently, the Cl^- importer Na⁺-K⁺-Cl^- cotransporter 1 (NKCC1) and the Cl^- exporter K⁺-Cl^- cotransporter 2 (KCC2) have garnered attention as therapeutic targets for many neurological disorders. Dysregulation of neuronal intracellular Cl^- concentration ([Cl^-]_i) is generally regarded as one of the mechanisms underlying neuronal dysfunction caused by imbalanced expression of these cation-chloride cotransporters (CCCs). Here, we analyzed the regulation of [Cl^-]_i and the effects of bumetanide, an NKCC1 inhibitor, in Angelman syndrome models (Ube3a^m-/p+ mice). We observed increased NKCC1 expression and decreased KCC2 expression in the hippocampi of Ube3a^m-/p+ mice. The average [Cl^-]_i of CA1 pyramidal neurons was not significantly different but demonstrated greater variance in Ube3a^m-/p+ mice. Tonic GABA_A receptor-mediated Cl^- conductance was reduced, which may have contributed to maintaining the normal average [Cl^-]_i. Bumetanide administration restores cognitive dysfunction in Ube3a^m-/p+ mice. Seizure susceptibility was also reduced regardless of the genotype. These results suggest that an imbalanced expression of CCCs is involved in the pathophysiological mechanism of Ube3a^m-/p+ mice, although the average [Cl^-]_i is not altered. The blockage of NKCC1 may be a potential therapeutic strategy for patients with Angelman syndrome.

JNK Activation Correlates with Cognitive Impairment and Alteration of the Post-Synaptic Element in the 5xFAD AD Mouse Model

The c-Jun N-terminal kinases (JNKs) are a family of proteins that, once activated by stress stimuli, can alter neuronal functions and survival. The JNK cascade plays a crucial role in the post-synaptic neuronal compartment by altering its structural organization and leading, at worst, to an overall impairment of neuronal communication. Increasing evidence suggests that synaptic impairment is the first neurodegenerative event in Alzheimer’s disease (AD). To better elucidate this mechanism, we longitudinally studied 5xFAD mice at three selected time points representative of human AD symptom progression. We tested the mice cognitive performance by using the radial arm water maze (RAWM) in parallel with biochemical evaluations of post-synaptic enriched protein fraction and total cortical parenchyma. We found that 5xFAD mice presented a strong JNK activation at 3.5 months of age in the post-synaptic enriched protein fraction. This JNK activation correlates with a structural alteration of the post-synaptic density area and with memory impairment at this early stage of the disease that progressively declines to cause cell death. These findings pave the way for future studies on JNK as a key player in early neurodegeneration and as an important therapeutic target for the development of new compounds able to tackle synaptic impairment in the early phase of AD pathology.

JNK signaling provides a novel therapeutic target for Rett syndrome

Background

Rett syndrome (RTT) is a monogenic X-linked neurodevelopmental disorder characterized by loss-of-function mutations in the MECP2 gene, which lead to structural and functional changes in synapse communication, and impairments of neural activity at the basis of cognitive deficits that progress from an early age. While the restoration of MECP2 in animal models has been shown to rescue some RTT symptoms, gene therapy intervention presents potential side effects, and with gene- and RNA-editing approaches still far from clinical application, strategies focusing on signaling pathways downstream of MeCP2 may provide alternatives for the development of more effective therapies in vivo. Here, we investigate the role of the c-Jun N-terminal kinase (JNK) stress pathway in the pathogenesis of RTT using different animal and cell models and evaluate JNK inhibition as a potential therapeutic approach.

Results

We discovered that the c-Jun N-terminal kinase (JNK) stress pathway is activated in Mecp2-knockout, Mecp2-heterozygous mice, and in human MECP2-mutated iPSC neurons. The specific JNK inhibitor, D-JNKI1, promotes recovery of body weight and locomotor impairments in two mouse models of RTT and rescues their dendritic spine alterations. Mecp2-knockout presents intermittent crises of apnea/hypopnea, one of the most invalidating RTT pathological symptoms, and D-JNKI1 powerfully reduces this breathing dysfunction. Importantly, we discovered that also neurons derived from hiPSC-MECP2 mut show JNK activation, high-phosphorylated c-Jun levels, and cell death, which is not observed in the isogenic control wt allele hiPSCs. Treatment with D-JNKI1 inhibits neuronal death induced by MECP2 mutation in hiPSCs mut neurons.

Conclusions

As a summary, we found altered JNK signaling in models of RTT and suggest that D-JNKI1 treatment prevents clinical symptoms, with coherent results at the cellular, molecular, and functional levels. This is the first proof of concept that JNK plays a key role in RTT and its specific inhibition offers a new and potential therapeutic tool to tackle RTT.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01190-2.

Pathophysiological Significance of WDR62 and JNK Signaling in Human Diseases

The c-Jun N-terminal kinase (JNK) is highly evolutionarily conserved and plays important roles in a broad range of physiological and pathological processes. The WD40-repeat protein 62 (WDR62) is a scaffold protein that recruits different components of the JNK signaling pathway to regulate several human diseases including neurological disorders, infertility, and tumorigenesis. Recent studies revealed that WDR62 regulates the process of neural stem cell mitosis and germ cell meiosis through JNK signaling. In this review we summarize the roles of WDR62 and JNK signaling in neuronal and non-neuronal contexts and discuss how JNK-dependent signaling regulates both processes. WDR62 is involved in various human disorders via JNK signaling regulation, and may represent a promising therapeutic strategy for the treatment of related diseases.

Adenosine A2A receptors format long-term depression and memory strategies in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder caused by loss of function of the maternally inherited Ube3a neuronal protein, whose main features comprise severe intellectual disabilities and motor impairments. Previous studies with the Ube3a^m-/p+ mouse model of AS revealed deficits in synaptic plasticity and memory. Since adenosine A_2A receptors (A_2AR) are powerful modulators of aberrant synaptic plasticity and A_2AR blockade prevents memory dysfunction in various brain diseases, we tested if A_2AR could control deficits of memory and hippocampal synaptic plasticity in AS. We observed that Ube3a^m-/p+ mice were unable to resort to hippocampal-dependent search strategies when tested for learning and memory in the Morris water maze; this was associated with a decreased magnitude of long-term depression (LTD) in CA1 hippocampal circuits. There was an increased density of A_2AR in the hippocampus of Ube3a^m-/p+ mice and their chronic treatment with the selective A_2AR antagonist SCH58261 (0.1 mg/kg/day, ip) restored both hippocampal-dependent learning strategies, as well as LTD deficits. Altogether, this study provides the first evidence of a role of A_2AR as a new prospective therapeutic target to manage learning deficits in AS.

JNK3 as Therapeutic Target and Biomarker in Neurodegenerative and Neurodevelopmental Brain Diseases

The c-Jun N-terminal kinase 3 (JNK3) is the JNK isoform mainly expressed in the brain. It is the most responsive to many stress stimuli in the central nervous system from ischemia to Aβ oligomers toxicity. JNK3 activity is spatial and temporal organized by its scaffold protein, in particular JIP-1 and β-arrestin-2, which play a crucial role in regulating different cellular functions in different cellular districts. Extensive evidence has highlighted the possibility of exploiting these adaptors to interfere with JNK3 signaling in order to block its action. JNK plays a key role in the first neurodegenerative event, the perturbation of physiological synapse structure and function, known as synaptic dysfunction. Importantly, this is a common mechanism in many different brain pathologies. Synaptic dysfunction and spine loss have been reported to be pharmacologically reversible, opening new therapeutic directions in brain diseases. Being JNK3-detectable at the peripheral level, it could be used as a disease biomarker with the ultimate aim of allowing an early diagnosis of neurodegenerative and neurodevelopment diseases in a still prodromal phase.