CDKL5's role in microtubule-based transport and cognitive function

Abstract Cyclin-dependent kinase like 5 (CDKL5) is a serine-threonine kinase highly enriched in mammalian neurons. CDKL5 is located on the X-chromosome and its loss-of-function leads to a severe neurodevelopmental disorder called CDKL5 deficiency disorder (CDD). CDKL5 phosphorylates microtubule-associated protein MAP1S and regulates its binding to microtubules. How MAP1S phosphorylation affects microtubule function is not well understood. To address this question, we generated MAP1S phosphomutant mice, in which the CDKL5 phosphorylation sites S786 and S812 are mutated to Alanine (MAP1S S786/812A or MAP1S SA). Using a microtubule co-sedimentation assay, we showed that dynein binding to microtubules is severely reduced in CDKL5 knockout (KO) and MAP1S SA brains. Time-lapse imaging in primary neurons showed impaired dynein motility in both Cdkl5 KO and MAP1S SA. Dynein-driven cargo transport was affected in mutant neuron dendrites, including the delivery of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. We next studied tubulin tyrosination in Cdkl5 KO and MAP1S SA neurons and found that both mutants had a reduced tubulin tyrosination when compared to WT neurons. Since dynein-dynactin has a higher affinity for tyrosinated microtubules, we hypothesized that reduced tyrosination in MAP1S phosphomutant mice could be the mechanistic cause of impaired dynein motility. In support of this, we show that upon expression of tubulin tyrosine kinase TTL, we rescued dynein motility defects in MAP1S phosphomutant neurons. Hippocampal neurons derived from MAP1S SA mice revealed a significant reduction in spine density and synapses, and altered spine morphology. Finally, behavioral phenotyping of MAP1S phosphomutant mice showed increased anxiety, impaired motor performance, social and memory deficits, mirroring to some extent the clinical manifestations present in CDD patients. Our results reveal MAP1S phosphorylation to be an important contributor to dynein-mediated transport and synapse formation. Graphical abstract