Cell cloning-based transcriptome analysis in cyclin-dependent kinase-like 5 mutation patients with severe epileptic encephalopathy

A homozygous variant in INTS11 links mitosis and neurogenesis defects to a severe neurodevelopmental disorder

The INTS11 endonuclease is crucial in modulating gene expression and has only recently been linked to human neurodevelopmental disorders (NDDs). However, how INTS11 participates in human development and disease remains unclear. Here, we identify a homozygous INTS11 variant in two siblings with a severe NDD. The variant impairs INTS11 catalytic activity, supported by its substrate's accumulation, and causes G2/M arrest in patient cells with length-dependent dysregulation of genes involved in mitosis and neural development, including the NDD gene CDKL5. The mutant knockin (KI) in induced pluripotent stem cells (iPSCs) disturbs their mitotic spindle organization and thus leads to slow proliferation and increased apoptosis, possibly through the decreased neurally functional CDKL5-induced extracellular signal-regulated kinase (ERK) pathway inhibition. The generation of neural progenitor cells (NPCs) from the mutant iPSCs is also delayed, with long transcript loss concerning neurogenesis. Our work reveals a mechanism underlying INTS11 dysfunction-caused human NDD and provides an iPSC model for this disease.

CDKL5 promotes proliferation, migration, and chemotherapeutic drug resistance of glioma cells via activation of the PI3K/AKT signaling pathway

Gliomas, the most prevalent cancer in the central nervous system, are characterized by high morbidity and mortality, emphasizing the need to understand their etiology. Here, we report that cyclin-dependent kinase-like 5 (CDKL5) is highly expressed in gliomas, and CDKL5 overexpression promotes invasion, proliferation, migration and drug (β-lapachone) resistance of glioma cells. In vitro, CDKL5 overexpression enhanced invasion, growth and migration of glioma cells, and stimulated the phosphoinositide 3-kinase (PI3K)/AKT axis. Furthermore, CDKL5 overexpression in vivo promoted glioma proliferation, whereas CDKL5 knockdown had opposing effects. The effect of CDKL5 on drug resistance was eliminated if the PI3K/AKT axis was suppressed, and cisplatin combined with the PI3K/AKT suppressor XL147 remarkably prohibited proliferation in xenografts overexpressing CDKL5. Collectively, our findings suggest that CDKL5 acts through the PI3K/AKT axis in glioma cells, and indicate a possible role for CDKL5 in glioma therapy.

Kinases in synaptic development and neurological diseases

Neuronal morphogenesis and synapse development is essential for building a functioning nervous system, and defects in these processes are associated with neurological disorders. Our understanding of molecular components and signalling events that contribute to neuronal development and pathogenesis is limited. Genes associated with neurodevelopmental and neurodegenerative diseases provide entry points for elucidating molecular events that contribute to these conditions. Several protein kinases, enzymes that regulate protein function by phosphorylating their substrates, are genetically linked to neurological disorders. Identifying substrates of these kinases is key to discovering their function and providing insight for possible therapies. In this review, we describe how various methods for kinase-substrate identification helped elucidate kinase signalling pathways important for neuronal development and function. We describe recent advances on roles of kinases TAOK2, TNIK and CDKL5 in neuronal development and the converging pathways of LRRK2, PINK1 and GAK in Parkinson's Disease.

The regulatory and signaling mechanisms of the ASK family

Apoptosis signal-regulating kinase 1 (ASK1) was identified as a MAP3K that activates the JNK and p38 pathways, and subsequent studies have reported ASK2 and ASK3 as members of the ASK family. The ASK family is activated by various intrinsic and extrinsic stresses, including oxidative stress, ER stress and osmotic stress. Numerous lines of evidence have revealed that members of the ASK family are critical for signal transduction systems to control a wide range of stress responses such as cell death, differentiation and cytokine induction. In this review, we focus on the precise signaling mechanisms of the ASK family in response to diverse stressors.

Recent advances in understanding synaptic abnormalities in Rett syndrome

Rett syndrome is an extremely disabling X-linked nervous system disorder that mainly affects girls in early childhood and causes autism-like behavior, severe intellectual disability, seizures, sleep disturbances, autonomic instability, and other disorders due to mutations in the MeCP2 (methyl CpG-binding protein 2) transcription factor. The disorder targets synapses and synaptic plasticity and has been shown to disrupt the balance between glutamate excitatory synapses and GABAergic inhibitory synapses. In fact, it can be argued that Rett syndrome is primarily a disorder of synaptic plasticity and that agents that can correct this imbalance may have beneficial effects on brain development. This review briefly summarizes the link between disrupted synaptic plasticity mechanisms and Rett syndrome and early clinical trials that aim to target these abnormalities to improve the outcome for these severely disabled children.

GluD1 is a common altered player in neuronal differentiation from both MECP2-mutated and CDKL5-mutated iPS cells

Rett syndrome is a monogenic disease due to de novo mutations in either MECP2 or CDKL5 genes. In spite of their involvement in the same disease, a functional interaction between the two genes has not been proven. MeCP2 is a transcriptional regulator; CDKL5 encodes for a kinase protein that might be involved in the regulation of gene expression. Therefore, we hypothesized that mutations affecting the two genes may lead to similar phenotypes by dysregulating the expression of common genes. To test this hypothesis we used induced pluripotent stem (iPS) cells derived from fibroblasts of one Rett patient with a MECP2 mutation (p.Arg306Cys) and two patients with mutations in CDKL5 (p.Gln347Ter and p.Thr288Ile). Expression profiling was performed in CDKL5-mutated cells and genes of interest were confirmed by real-time RT-PCR in both CDKL5- and MECP2-mutated cells. The only major change in gene expression common to MECP2- and CDKL5-mutated cells was for GRID1, encoding for glutamate D1 receptor (GluD1), a member of the δ-family of ionotropic glutamate receptors. GluD1 does not form AMPA or NMDA glutamate receptors. It acts like an adhesion molecule by linking the postsynaptic and presynaptic compartments, preferentially inducing the inhibitory presynaptic differentiation of cortical neurons. Our results demonstrate that GRID1 expression is downregulated in both MECP2- and CDKL5-mutated iPS cells and upregulated in neuronal precursors and mature neurons. These data provide novel insights into disease pathophysiology and identify possible new targets for therapeutic treatment of Rett syndrome.

MeCP2 deficiency is associated with impaired microtubule stability

Rett syndrome (RTT) is a neurodevelopmental disorder caused by MECP2 mutations. Previous studies performed on Mecp2-deficient brain showed striking changes in neuronal maturation. We recently showed that MeCP2 deficiency affects microtubule (MT) dynamics in RTT astrocytes. Here, we analyze MT stability in primary fibroblast cultures from patients with RTT syndrome and identify a significant decrease in stability compared to controls. Furthermore, we found that MT stability was reduced both in cells expressing the mutant or the wild-type allele in RTT fibroblasts, suggesting that mutated cells could damage wild-type ones through a non-cell-autonomous pathway. These results suggest that MeCP2 has a stabilizing role on MT dynamics and that its deficiency could lead to impaired MT stability that may explain in part the dendritic abnormalities observed in RTT brains.

Angiotensin II facilitates breast cancer cell migration and metastasis

Breast cancer metastasis is a leading cause of death by malignancy in women worldwide. Efforts are being made to further characterize the rate-limiting steps of cancer metastasis, i.e. extravasation of circulating tumor cells and colonization of secondary organs. In this study, we investigated whether angiotensin II, a major vasoactive peptide both produced locally and released in the bloodstream, may trigger activating signals that contribute to cancer cell extravasation and metastasis. We used an experimental in vivo model of cancer metastasis in which bioluminescent breast tumor cells (D3H2LN) were injected intra-cardiacally into nude mice in order to recapitulate the late and essential steps of metastatic dissemination. Real-time intravital imaging studies revealed that angiotensin II accelerates the formation of metastatic foci at secondary sites. Pre-treatment of cancer cells with the peptide increases the number of mice with metastases, as well as the number and size of metastases per mouse. In vitro, angiotensin II contributes to each sequential step of cancer metastasis by promoting cancer cell adhesion to endothelial cells, trans-endothelial migration and tumor cell migration across extracellular matrix. At the molecular level, a total of 102 genes differentially expressed following angiotensin II pre-treatment were identified by comparative DNA microarray. Angiotensin II regulates two groups of connected genes related to its precursor angiotensinogen. Among those, up-regulated MMP2/MMP9 and ICAM1 stand at the crossroad of a network of genes involved in cell adhesion, migration and invasion. Our data suggest that targeting angiotensin II production or action may represent a valuable therapeutic option to prevent metastatic progression of invasive breast tumors.

CDKL5-Related Disorders: From Clinical Description to Molecular Genetics

Mutations in the cyclin-dependent kinase-like 5 gene (CDKL5) have been described in girls with Rett-like features and early-onset epileptic encephalopathy including infantile spasms. To date, with more than 80 reported cases, the phenotype of CDKL5-related encephalopathy is better defined. The main features consist of early-onset seizures starting before 5 months of age, severe mental retardation with absent speech and Rett-like features such as hand stereotypies and deceleration of head growth. On the other hand, neuro-vegetative signs and developmental regression are rare in CDKL5 mutation patients. The CDKL5 gene encodes a serine threonine kinase protein which is characterized by a catalytic domain and a long C-terminal extension involved in the regulation of the catalytic activity of CDKL5 and in the sub-nuclear localization of the protein. To our knowledge, more than 70 different point mutations have been described including missense mutations within the catalytic domain, nonsense mutations causing the premature termination of the protein distributed in the entire open reading frame, splice variants, and frameshift mutations. Additionally, CDKL5 mutations have recently been described in 7 males with a more severe epileptic encephalopathy and a worse outcome compared to female patients. Finally, about 23 male and female patients have been identified with gross rearrangements encompassing all or part of the CDKL5 gene, with a phenotype reminiscent of CDKL5-related encephalopathy combined with dysmorphic features. Even if recent data clearly indicate that CDKL5 plays an important role in brain function, the protein remains largely uncharacterized. Phenotype-genotype correlation is additionally hampered by the relatively small number of patients described.