A mouse model for creatine transporter deficiency reveals early onset cognitive impairment and neuropathology associated with brain aging.

Mutations in the creatine (Cr) transporter (CrT) gene lead to cerebral creatine deficiency syndrome-1 (CCDS1), an X-linked metabolic disorder characterized by cerebral Cr deficiency causing intellectual disability, seizures, movement and autistic-like behavioural disturbances, language and speech impairment. Since no data are available about the neural and molecular underpinnings of this disease, we performed a longitudinal analysis of behavioural and pathological alterations associated with CrT deficiency in a CCDS1 mouse model. We found precocious cognitive and autistic-like defects, mimicking the early key features of human CCDS1. Moreover, mutant mice displayed a progressive impairment of short and long-term declarative memory denoting an early brain aging. Pathological examination showed a prominent loss of GABAergic synapses, marked activation of microglia, reduction of hippocampal neurogenesis and the accumulation of autofluorescent lipofuscin. Our data suggest that brain Cr depletion causes both early intellectual disability and late progressive cognitive decline, and identify novel targets to design intervention strategies aimed at overcoming brain CCDS1 alterations.

Mir-132/212 is required for maturation of binocular matching of orientation preference and depth perception.

MicroRNAs (miRNAs) are known to mediate post-transcriptional gene regulation, but their role in postnatal brain development is still poorly explored. We show that the expression of many miRNAs is dramatically regulated during functional maturation of the mouse visual cortex with miR-132/212 family being one of the top upregulated miRNAs. Age-downregulated transcripts are significantly enriched in miR-132/miR-212 putative targets and in genes upregulated in miR-132/212 null mice. At a functional level, miR-132/212 deletion affects development of receptive fields of cortical neurons determining a specific impairment of binocular matching of orientation preference, but leaving orientation and direction selectivity unaltered. This deficit is associated with reduced depth perception in the visual cliff test. Deletion of miR-132/212 from forebrain excitatory neurons replicates the binocular matching deficits. Thus, miR-132/212 family shapes the age-dependent transcriptome of the visual cortex during a specific developmental window resulting in maturation of binocular cortical cells and depth perception.

Experience-dependent DNA methylation regulates plasticity in the developing visual cortex.

DNA methylation is an epigenetic repressor mark for transcription dynamically regulated in neurons. We analyzed visual experience regulation of DNA methylation in mice and its involvement in ocular dominance plasticity of the developing visual cortex. Monocular deprivation modulated the expression of factors controlling DNA methylation and exerted opposite effects on DNA methylation and hydroxymethylation in specific plasticity genes. Inhibition of DNA methyltrasferase (DNMT) blocked molecular and functional effects of monocular deprivation, partially reversing the monocular deprivation transcriptional program.

A novel mouse model of creatine transporter deficiency.

Mutations in the creatine (Cr) transporter (CrT) gene lead to cerebral creatine deficiency syndrome-1 (CCDS1), an X-linked metabolic disorder characterized by cerebral Cr deficiency causing intellectual disability, seizures, movement  and behavioral disturbances, language and speech impairment ( OMIM #300352). CCDS1 is still an untreatable pathology that can be very invalidating for patients and caregivers. Only two murine models of CCDS1, one of which is an ubiquitous knockout mouse, are currently available to study the possible mechanisms underlying the pathologic phenotype of CCDS1 and to develop therapeutic strategies. Given the importance of validating phenotypes and efficacy of promising treatments in more than one mouse model we have generated a new murine model of CCDS1 obtained by ubiquitous deletion of 5-7 exons in the Slc6a8 gene. We showed a remarkable Cr depletion in the murine brain tissues and cognitive defects, thus resembling the key features of human CCDS1. These results confirm that CCDS1 can be well modeled in mice. This CrT (-/y) murine model will provide a new tool for increasing the relevance of preclinical studies to the human disease.