The green tea polyphenol epigallocatechin-3-gallate (EGCG) restores CDKL5-dependent synaptic defects in vitro and in vivo.

CDKL5 deficiency disorder (CDD) is a rare X-linked neurodevelopmental disorder that is characterised by early-onset seizures, intellectual disability, gross motor impairment, and autistic-like features. CDD is caused by mutations in the cyclin-dependent kinase-like 5 (CDKL5) gene that encodes a serine/threonine kinase with a predominant expression in the brain. Loss of CDKL5 causes neurodevelopmental alterations in vitro and in vivo, including defective dendritic arborisation and spine maturation, which most likely underlie the cognitive defects and autistic features present in humans and mice. Here, we show that treatment with epigallatocathechin-3-gallate (EGCG), the major polyphenol of green tea, can restore defects in dendritic and synaptic development of primary Cdkl5 knockout (KO) neurons. Furthermore, defective synaptic maturation in the hippocampi and cortices of adult Cdkl5-KO mice can be rescued through the intraperitoneal administration of EGCG, which is however not sufficient to normalise behavioural CDKL5-dependent deficits. EGCG is a pleiotropic compound with numerous cellular targets, including the dual-specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A) that is selectively inhibited by EGCG. DYRK1A controls dendritic development and spine formation and its deregulation has been implicated in neurodevelopmental and degenerative diseases. Treatment with another DYRK1A inhibitor, harmine, was capable of correcting neuronal CDKL5-dependent defects; moreover, DYRK1A levels were upregulated in primary Cdkl5-KO neurons in concomitance with increased phosphorylation of Tau, a well-accepted DYRK1A substrate. Altogether, our results indicate that DYRK1A deregulation may contribute, at least in part, to the neurodevelopmental alterations caused by CDKL5 deficiency.

Pregnenolone and pregnenolone-methyl-ether rescue neuronal defects caused by dysfunctional CLIP170 in a neuronal model of CDKL5 Deficiency Disorder.

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene are responsible for the onset of CDKL5 Deficiency Disorder (CDD), a neurological pathology characterised by severe infantile seizures, intellectual disability, impairment of gross motor skills, sleep and gastrointestinal disturbances. CDKL5 is a serine/threonine kinase the molecular network of which is not yet fully understood. Loss of CDKL5 both in vitro and in vivo leads to altered neuronal morphology including axon specification and outgrowth, dendritic arborisation and spine morphology suggesting a link between CDKL5 and the regulation of proper cytoskeleton functioning. Recently, we found that CDKL5 regulates the binding of CLIP170 to microtubules (MT). CLIP170 is a MT-plus end tracking protein (+TIP) that associates with MTs when present in its open, active conformation. Here we present evidence suggesting CLIP170 contributes to neuronal CDKL5-dependent defects and that it represents an important novel druggable target for CDD; indeed, CLIP170 is directly targeted by the neuroactive steroid pregnenolone (PREG), which induces the active conformation of the protein thus promoting MT-dynamics. We here show that PREG and a synthetic derivative pregnenolone-methyl-ether (PME) can restore the MT association of CLIP170 and revert morphological and molecular defects in Cdkl5-KO neurons at different stages of maturation. All together, these findings identify CLIP170 as possible novel druggable target for CDKL5 related disorders providing an intriguing prospective for future disease-modifying drug-based therapies.