p21 protein-activated kinase 1 is associated with severe regressive autism, and epilepsy

Antagonistic actions of PAK1 and NF2/Merlin drive myelin membrane expansion in oligodendrocytes

In the central nervous system, the formation of myelin by oligodendrocytes (OLs) relies on the switch from the polymerization of the actin cytoskeleton to its depolymerization. The molecular mechanisms that trigger this switch have yet to be elucidated. Here, we identified P21-activated kinase 1 (PAK1) as a major regulator of actin depolymerization in OLs. Our results demonstrate that PAK1 accumulates in OLs in a kinase-inhibited form, triggering actin disassembly and, consequently, myelin membrane expansion. Remarkably, proteomic analysis of PAK1 binding partners enabled the identification of NF2/Merlin as its endogenous inhibitor. Our findings indicate that Nf2 knockdown in OLs results in PAK1 activation, actin polymerization, and a reduction in OL myelin membrane expansion. This effect is rescued by treatment with a PAK1 inhibitor. We also provide evidence that the specific Pak1 loss-of-function in oligodendroglia stimulates the thickening of myelin sheaths in vivo. Overall, our data indicate that the antagonistic actions of PAK1 and NF2/Merlin on the actin cytoskeleton of the OLs are critical for proper myelin formation. These findings have broad mechanistic and therapeutic implications in demyelinating diseases and neurodevelopmental disorders.

Loss of the polarity protein Par3 promotes dendritic spine neoteny and enhances learning and memory

The Par3 polarity protein is critical for subcellular compartmentalization in different developmental processes. Variants of PARD3, encoding PAR3, are associated with intelligence and neurodevelopmental disorders. However, the role of Par3 in glutamatergic synapse formation and cognitive functions in vivo remains unknown. Here, we show that forebrain-specific Par3 conditional knockout leads to increased long, thin dendritic spines in vivo. In addition, we observed a decrease in the amplitude of miniature excitatory postsynaptic currents. Surprisingly, loss of Par3 enhances hippocampal-dependent spatial learning and memory and repetitive behavior. Phosphoproteomic analysis revealed proteins regulating cytoskeletal dynamics are significantly dysregulated downstream of Par3. Mechanistically, we found Par3 deletion causes increased Rac1 activation and dysregulated microtubule dynamics through CAMSAP2. Together, our data reveal an unexpected role for Par3 as a molecular gatekeeper in regulating the pool of immature dendritic spines, a rate-limiting step of learning and memory, through modulating Rac1 activation and microtubule dynamics in vivo.

Control of OPC proliferation and repopulation by the intellectual disability gene PAK1 under homeostatic and demyelinating conditions

Appropriate proliferation and repopulation of oligodendrocyte progenitor cells (OPCs) determine successful (re)myelination in homeostatic and demyelinating brains. Activating mutations in p21-activated kinase 1 (PAK1) cause intellectual disability, neurodevelopmental abnormality, and white matter anomaly in children. It remains unclear if and how PAK1 regulates oligodendroglial development. Here, we report that PAK1 controls proliferation and regeneration of OPCs. Unlike differentiating oligodendrocytes, OPCs display high PAK1 activity which maintains them in a proliferative state by modulating PDGFRa-mediated mitogenic signaling. PAK1-deficient or kinase-inhibited OPCs reduce their proliferation capacity and population expansion. Mice carrying OPC-specific PAK1 deletion or kinase inhibition are populated with fewer OPCs in the homeostatic and demyelinated CNS than control mice. Together, our findings suggest that kinase-activating PAK1 mutations stall OPCs in a progenitor state, impacting timely oligodendroglial differentiation in the CNS of affected children and that PAK1 is a potential molecular target for replenishing OPCs in demyelinating lesions.

A PAK1 Mutational Hotspot Within the Regulatory CRIPaK Domain is Associated With Severe Neurodevelopmental Disorders in Children

BACKGROUND

P-21-activated kinases (PAKs) are protein serine/threonine kinases, part of the RAS/mitogen-activated protein kinase pathway. PAK1 is highly expressed in the central nervous system and crucially involved in neuronal migration and brain developmental processes. Recently, de novo heterozygous missense variants in PAK1 have been identified as an ultrarare cause of pediatric neurodevelopmental disorders.

METHODS

We report a series of children affected with postnatal macrocephaly, neurodevelopmental impairment, and drug-resistant epilepsy. Repeated electroencephalographic (EEG) and video-EEG evaluations were performed over a two- to 10-year period during follow-up to delineate electroclinical histories. Genetic sequencing studies and computational evaluation of the identified variants were performed in our patient cohort.

RESULTS

We identified by whole-exome sequencing three novel de novo variants in PAK1 (NM_001128620: c.427A>G, p.Met143Val; c.428T>C, p.Met143Thr; c.428T>A, p.Met143Lys) as the underlying cause of the disease in our families. The three variants affected the same highly conserved Met143 residue within the cysteine-rich inhibitor of PAK1 (CRIPaK) domain, which was identified before as a PAK1 inhibitor target. Computational studies suggested a defective autoinhibition presumably due to impaired PAK1 autoregulation as a result of the recurrent substitution.

CONCLUSIONS

We delineated the electroclinical phenotypes of PAK1-related neurological disorders and highlight a novel mutational hotspot that may involve defective autoinhibition of the PAK1 protein. The three novel variants affecting the same hotspot residue within the CRIPaK domain highlight potentially impaired PAK1-CRIPaK interaction as a novel disease mechanism. These findings shed light on possible future treatments targeted at the CRIPaK domain, to modulate PAK1 activity and function.

PLPP/CIN-mediated NF2 S10 dephosphorylation distinctly regulates kainate-induced seizure susceptibility and neuronal death through PAK1-NF-κB-COX-2-PTGES2 signaling pathway

BACKGROUND

Pyridoxal-5'-phosphate phosphatase/chronophin (PLPP/CIN) selectively dephosphorylates serine (S) 10 site on neurofibromin 2 (NF2, also known as merlin (moesin-ezrin-radixin-like protein) or schwannomin). p21-activated kinase 1 (PAK1) is a serine/threonine protein kinase, which is involved in synaptic activity and plasticity in neurons. NF2 and PAK1 reciprocally regulate each other in a positive feedback manner. Thus, the aim of the present study is to investigate the effects of PLPP/CIN-mediated NF2 S10 dephosphorylation on PAK1-related signaling pathways under physiological and neuroinflammatory conditions, which are largely unknown.

METHODS

After kainate (KA) injection in wild-type, PLPP/CIN^-/- and PLPP/CIN^Tg mice, seizure susceptibility, PAK1 S204 autophosphorylation, nuclear factor-κB (NF-κB) p65 S276 phosphorylation, cyclooxygenase-2 (COX-2) upregulation, prostaglandin E synthase 2 (PTGES2) induction and neuronal damage were measured. The effects of 1,1'-dithiodi-2-naphthtol (IPA-3, a selective inhibitor of PAK1) pretreatment on these responses to KA were also validated.

RESULTS

PLPP/CIN overexpression increased PAK1 S204 autophosphorylation concomitant with the enhanced NF2 S10 dephosphorylation in hippocampal neurons under physiological condition. Following KA treatment, PLPP/CIN overexpression delayed the seizure on-set and accelerated PAK1 S204 phosphorylation, NF-κB p65 S276 phosphorylation, COX-2 upregulation and PTGES2 induction, which were ameliorated by PLPP/CIN deletion or IPA-3. Furthermore, IPA-3 pretreatment shortened the latency of seizure on-set without affecting seizure severity (intensity) and ameliorated CA3 neuronal death induced by KA.

CONCLUSIONS

These findings indicate that PLPP/CIN may regulate seizure susceptibility (the latency of seizure on-set) and CA3 neuronal death in response to KA through NF2-PAK1-NF-κB-COX-2-PTGES2 signaling pathway.

The molecular basis of p21-activated kinase-associated neurodevelopmental disorders: From genotype to phenotype

Although the identification of numerous genes involved in neurodevelopmental disorders (NDDs) has reshaped our understanding of their etiology, there are still major obstacles in the way of developing therapeutic solutions for intellectual disability (ID) and other NDDs. These include extensive clinical and genetic heterogeneity, rarity of recurrent pathogenic variants, and comorbidity with other psychiatric traits. Moreover, a large intragenic mutational landscape is at play in some NDDs, leading to a broad range of clinical symptoms. Such diversity of symptoms is due to the different effects DNA variations have on protein functions and their impacts on downstream biological processes. The type of functional alterations, such as loss or gain of function, and interference with signaling pathways, has yet to be correlated with clinical symptoms for most genes. This review aims at discussing our current understanding of how the molecular changes of group I p21-activated kinases (PAK1, 2 and 3), which are essential actors of brain development and function; contribute to a broad clinical spectrum of NDDs. Identifying differences in PAK structure, regulation and spatio-temporal expression may help understanding the specific functions of each group I PAK. Deciphering how each variation type affects these parameters will help uncover the mechanisms underlying mutation pathogenicity. This is a prerequisite for the development of personalized therapeutic approaches.

Transcription factors are potential therapeutic targets in epilepsy

Academics generally believe that imbalance between excitation and inhibition of the nervous system is the root cause of epilepsy. However, the aetiology of epilepsy is complex, and its pathogenesis remains unclear. Many studies have shown that epilepsy is closely related to genetic factors. Additionally, the involvement of a variety of tumour‐related transcription factors in the pathogenesis of epilepsy has been confirmed, which also confirms the heredity of epilepsy. In this review, we summarize the existing research on a variety of transcription factors and epilepsy and present relevant evidence related to transcription factors that may be targets in epilepsy. This information is of great significance for revealing the in‐depth molecular and cellular mechanisms of epilepsy.

Sodium Benzoate—Harmfulness and Potential Use in Therapies for Disorders Related to the Nervous System: A Review

Currently, due to the large number of reports regarding the harmfulness of food additives, more and more consumers follow the so-called “clean label” trend, i.e., prefer and choose the least-processed food products. One of the compounds known as a preservative with a high safety profile is sodium benzoate. While some studies show that it can be used to treat conditions such as depression, pain, schizophrenia, autism spectrum disorders, and neurodegenerative diseases, others report its harmfulness. For example, it was found to cause mutagenic effects, generate oxidative stress, disrupt hormones, and reduce fertility. Due to such disparate results, the purpose of this study is to comprehensively discuss the safety profile of sodium benzoate and its potential use in neurodegenerative diseases, especially in autism spectrum disorder (ASD), schizophrenia, major depressive disorder (MDD), and pain relief.

Group I PAKs in myelin formation and repair of the central nervous system: what, when, and how

p21-activated kinases (PAKs) are a family of cell division control protein 42/ras-related C3 botulinum toxin substrate 1 (Cdc42/Rac1)-activated serine/threonine kinases. Group I PAKs (PAK1-3) have distinct activation mechanisms from group II PAKs (PAK4-6) and are the focus of this review. In transformed cancer cells, PAKs regulate a variety of cellular processes and molecular pathways which are also important for myelin formation and repair in the central nervous system (CNS). De novo mutations in group I PAKs are frequently seen in children with neurodevelopmental defects and white matter anomalies. Group I PAKs regulate virtually every aspect of neuronal development and function. Yet their functions in CNS myelination and remyelination remain incompletely defined. Herein, we highlight the current understanding of PAKs in regulating cellular and molecular pathways and discuss the status of PAK-regulated pathways in oligodendrocyte development. We point out outstanding questions and future directions in the research field of group I PAKs and oligodendrocyte development.

RHO GTPases: from new partners to complex immune syndromes

Ras homology (RHO) GTPases are signalling proteins that have crucial roles in triggering multiple immune functions. Through their interactions with a broad range of effectors and kinases, they regulate cytoskeletal dynamics, cell polarity and the trafficking and proliferation of immune cells. The activity and localization of RHO GTPases are highly controlled by classical families of regulators that share consensus motifs. In this Review, we describe the recent discovery of atypical modulators and partners of RHO GTPases, which bring an additional layer of regulation and plasticity to the control of RHO GTPase activities in the immune system. Furthermore, the development of large-scale genetic screening has now enabled researchers to identify dysregulation of RHO GTPase signalling pathways as a cause of many immune system-related diseases. We discuss the mutations that have been identified in RHO GTPases and their signalling circuits in patients with rare diseases. The discoveries of new RHO GTPase partners and genetic mutations in RHO GTPase signalling hubs have uncovered unsuspected layers of crosstalk with other signalling pathways and may provide novel therapeutic opportunities for patients affected by complex immune or broader syndromes.

Kinase Signaling in Dendritic Development and Disease

Dendrites undergo extensive growth and remodeling during their lifetime. Specification of neurites into dendrites is followed by their arborization, maturation, and functional integration into synaptic networks. Each of these distinct developmental processes is spatially and temporally controlled in an exquisite fashion. Protein kinases through their highly specific substrate phosphorylation regulate dendritic growth and plasticity. Perturbation of kinase function results in aberrant dendritic growth and synaptic function. Not surprisingly, kinase dysfunction is strongly associated with neurodevelopmental and psychiatric disorders. Herein, we review, (a) key kinase pathways that regulate dendrite structure, function and plasticity, (b) how aberrant kinase signaling contributes to dendritic dysfunction in neurological disorders and (c) emergent technologies that can be applied to dissect the role of protein kinases in dendritic structure and function.

Sterically stabilized liposomes targeting P21 (RAC1) activated kinase-1 and secreted phospholipase A2 suppress prostate cancer growth and metastasis

Metastatic prostate cancer (PCa) has a very high mortality rate in men, in Western countries and lacks reliable treatment. The advanced-stage PCa cells overexpress P21 (RAC1) activated kinase-1 (PAK1) and secreted phospholipase A2 (sPLA2) suggesting the potential utility of pharmacologically targeting these molecules to treat metastatic PCa. The small molecule, inhibitor targeting PAK1 activation-3 (IPA3) is a highly specific allosteric inhibitor of PAK1; however, it is metabolically unstable once in the plasma thus, limiting its utility as a chemotherapeutic agent. In the present study, the efficacy and specificity of IPA3 were combined with the stability and the sPLA2-targeted delivery method of two sterically stabilized liposomes [sterically stabilized long-circulating liposomes (SSL)-IPA3 and sPLA2 responsive liposomes (SPRL)-IPA3, respectively] to inhibit PCa growth and metastasis. It was found that twice-a-week administration of either SSL-IPA3 or SPRL-IPA3 for 3 weeks effectively suppressed the growth of PC-3 cell tumor xenografts implanted in athymic nude mice. Both drug formulations also inhibited the metastasis of intravenously administered murine RM1 PCa cells to the lungs of C57BL/6 mice. Whereas the twice-a-week administration of SSL-IPA3 significantly inhibited the spontaneous PCa metastasis to the lungs in Transgenic Adenocarcinoma of the Mouse Prostate mice, the administration of free IPA3 had no significant therapeutic benefit. The results present two novel IPA3 encapsulated liposomes to treat metastatic PCa.

A novel PAK1 variant causative of neurodevelopmental disorder with postnatal macrocephaly

p21-activated kinases (PAKs) are protein serine/threonine kinases stimulated by Rho-family p21 GTPases such as CDC42 and RAC. PAKs have been implicated in several human disorders, with pathogenic variants in PAK3 associated with intellectual disability and several PAK members, especially PAK1 and PAK4, overexpressed in human cancer. Recently, de novo PAK1 variants were reported to be causative of neurodevelopmental disorder (ND) with secondary macrocephaly in three patients. We herein report a fourth patient with ND, epilepsy, and macrocephaly caused by a de novo PAK1 missense variant. Two previously reported missense PAK1 variants functioned as activating alleles by reducing PAK1 homodimerization. To examine the pathogenicity of the identified novel p.Ser110Thr variant, we carried out in silico structural analysis. Our findings suggest that this variant also prevents PAK1 homodimerization, leading to constitutive PAK1 activation.