Age-Related Cognitive and Motor Decline in a Mouse Model of CDKL5 Deficiency Disorder is Associated with Increased Neuronal Senescence and Death

Abstract

CDKL5 deficiency disorder (CDD) is a severe neurodevelopmental disease caused by mutations in the X-linked <i>CDKL5</i> gene. Children affected by CDD display a clinical phenotype characterized by early-onset epilepsy, intellectual disability, motor impairment, and autistic-like features. Although the clinical aspects associated with <i>CDKL5</i> mutations are well described in children, adults with CDD are still under-characterized. Similarly, most animal research has been carried out on young adult <i>Cdkl5</i> knockout (KO) mice only. Since age represents a risk factor for the worsening of symptoms in many neurodevelopmental disorders, understanding age differences in the development of behavioral deficits is crucial in order to optimize the impact of therapeutic interventions. Here, we compared young adult <i>Cdkl5</i> KO mice with middle-aged <i>Cdkl5</i> KO mice, at a behavioral, neuroanatomical, and molecular level. We found an age-dependent decline in motor, cognitive, and social behaviors in <i>Cdkl5</i> KO mice, as well as in breathing and sleep patterns. The behavioral decline in older <i>Cdkl5</i> KO mice was not associated with a worsening of neuroanatomical alterations, such as decreased dendritic arborization or spine density, but was paralleled by decreased neuronal survival in different brain regions such as the hippocampus, cortex, and basal ganglia. Interestingly, we found increased β-galactosidase activity and DNA repair protein levels, γH2AX and XRCC5, in the brains of older <i>Cdkl5</i> KO mice, which suggests that an absence of Cdkl5 accelerates neuronal senescence/death by triggering irreparable DNA damage. In summary, this work provides evidence that CDKL5 may play a fundamental role in neuronal survival during brain aging and suggests a possible worsening with age of the clinical picture in CDD patients.