Searching for biomarkers of CDKL5 disorder: early-onset visual impairment in CDKL5 mutant mice.

CDKL5 disorder is a neurodevelopmental disorder still without a cure. Murine models of CDKL5 disorder have been recently generated raising the possibility of preclinical testing of treatments. However, unbiased, quantitative biomarkers of high translational value to monitor brain function are still missing. Moreover, the analysis of treatment is hindered by the challenge of repeatedly and non-invasively testing neuronal function. We analyzed the development of visual responses in a mouse model of CDKL5 disorder to introduce visually evoked responses as a quantitative method to assess cortical circuit function. Cortical visual responses were assessed in CDKL5 null male mice, heterozygous females, and their respective control wild-type littermates by repeated transcranial optical imaging from P27 until P32. No difference between wild-type and mutant mice was present at P25-P26 whereas defective responses appeared from P27-P28 both in heterozygous and homozygous CDKL5 mutant mice. These results were confirmed by visually evoked potentials (VEPs) recorded from the visual cortex of a different cohort. The previously imaged mice were also analyzed at P60-80 using VEPs, revealing a persistent reduction of response amplitude, reduced visual acuity and defective contrast function. The level of adult impairment was significantly correlated with the reduction in visual responses observed during development. Support vector machine showed that multi-dimensional visual assessment can be used to automatically classify mutant and wt mice with high reliability. Thus, monitoring visual responses represents a promising biomarker for preclinical and clinical studies on CDKL5 disorder.

Foxg1 localizes to mitochondria and coordinates cell differentiation and bioenergetics.

Forkhead box g1 (Foxg1) is a nuclear-cytosolic transcription factor essential for the forebrain development and involved in neurodevelopmental and cancer pathologies. Despite the importance of this protein, little is known about the modalities by which it exerts such a large number of cellular functions. Here we show that a fraction of Foxg1 is localized within the mitochondria in cell lines, primary neuronal or glial cell cultures, and in the mouse cortex. Import of Foxg1 in isolated mitochondria appears to be membrane potential-dependent. Amino acids (aa) 277-302 were identified as critical for mitochondrial localization. Overexpression of full-length Foxg1 enhanced mitochondrial membrane potential (ΔΨm) and promoted mitochondrial fission and mitosis. Conversely, overexpression of the C-term Foxg1 (aa 272-481), which is selectively localized in the mitochondrial matrix, enhanced organelle fusion and promoted the early phase of neuronal differentiation. These findings suggest that the different subcellular localizations of Foxg1 control the machinery that brings about cell differentiation, replication, and bioenergetics, possibly linking mitochondrial functions to embryonic development and pathological conditions.

Binding of the Anti-FIV Peptide C8 to Differently Charged Membrane Models: From First Docking to Membrane Tubulation.

Gp36 is the virus envelope glycoproteins catalyzing the fusion of the feline immunodeficiency virus with the host cells. The peptide C8 is a tryptophan-rich peptide corresponding to the fragment 770W-I777 of gp36 exerting antiviral activity by binding the membrane cell and inhibiting the virus entry. Several factors, including the membrane surface charge, regulate the binding of C8 to the lipid membrane. Based on the evidence that imperceptible variation of membrane charge may induce a dramatic effect in several critical biological events, in the present work we investigate the effect induced by systematic variation of charge in phospholipid bilayers on the aptitude of C8 to interact with lipid membranes, the tendency of C8 to assume specific conformational states and the re-organization of the lipid bilayer upon the interaction with C8. Accordingly, employing a bottom-up multiscale protocol, including CD, NMR, ESR spectroscopy, atomistic molecular dynamics simulations, and confocal microscopy, we studied C8 in six membrane models composed of different ratios of zwitterionic/negatively charged phospholipids. Our data show that charge content modulates C8-membrane binding with significant effects on the peptide conformations. C8 in micelle solution or in SUV formed by DPC or DOPC zwitterionic phospholipids assumes regular ß-turn structures that are progressively destabilized as the concentration of negatively charged SDS or DOPG phospholipids exceed 40%. Interaction of C8 with zwitterionic membrane surface is mediated by Trp1 and Trp4 that are deepened in the membrane, forming H-bonds and cation-π interactions with the DOPC polar heads. Additional stabilizing salt bridge interactions involve Glu2 and Asp3. MD and ESR data show that the C8-membrane affinity increases as the concentration of zwitterionic phospholipid increases. In the lipid membrane characterized by an excess of zwitterionic phospholipids, C8 is adsorbed at the membrane interface, inducing a stiffening of the outer region of the DOPC bilayer. However, the bound of C8 significantly perturbs the whole organization of lipid bilayer resulting in membrane remodeling. These events, measurable as a variation of the bilayer thickness, are the onset mechanism of the membrane fusion and vesicle tubulation observed in confocal microscopy by imaging zwitterionic MLVs in the presence of C8 peptide.

Dendritic Spine Instability in a Mouse Model of CDKL5 Disorder Is Rescued by Insulin-like Growth Factor 1.

BACKGROUND: CDKL5 (cyclin-dependent kinase-like 5) is mutated in many severe neurodevelopmental disorders, including atypical Rett syndrome. CDKL5 was shown to interact with synaptic proteins, but an in vivo analysis of the role of CDKL5 in dendritic spine dynamics and synaptic molecular organization is still lacking. METHODS: In vivo two-photon microscopy of the somatosensory cortex of Cdkl5(-/y) mice was applied to monitor structural dynamics of dendritic spines. Synaptic function and plasticity were measured using electrophysiological recordings of excitatory postsynaptic currents and long-term potentiation in brain slices and assessing the expression of synaptic postsynaptic density protein 95 (PSD-95). Finally, we studied the impact of insulin-like growth factor 1 (IGF-1) treatment on CDKL5 null mice to restore the synaptic deficits. RESULTS: Adult mutant mice showed a significant reduction in spine density and PSD-95-positive synaptic puncta, a reduction of persistent spines, and impaired long-term potentiation. In juvenile mutants, short-term spine elimination, but not formation, was dramatically increased. Exogenous administration of IGF-1 rescued defective rpS6 phosphorylation, spine density, and PSD-95 expression. Endogenous cortical IGF-1 levels were unaffected by CDKL5 deletion. CONCLUSIONS: These data demonstrate that dendritic spine stabilization is strongly regulated by CDKL5. Moreover, our data suggest that IGF-1 treatment could be a promising candidate for clinical trials in CDKL5 patients.

Synaptic plasticity and signaling in Rett syndrome.

Rett syndrome (RTT) is a disorder that is caused in the majority of cases by mutations in the gene methyl-CpG-binding protein-2 (MeCP2). Children with RTT are generally characterized by normal development up to the first year and a half of age, after which they undergo a rapid regression marked by a deceleration of head growth, the onset of stereotyped hand movements, irregular breathing, and seizures. Animal models of RTT with good construct and face validity are available. Their analysis showed that homeostatic regulation of MeCP2 gene is necessary for normal CNS functioning and that multiple complex pathways involving different neuronal and glial cell types are disrupted in RTT models. However, it is increasingly clear that RTT pathogenetic mechanisms converge at synaptic level impairing synaptic transmission and plasticity. We review novel findings showing how specific synaptic mechanisms and related signaling pathways are affected in RTT models.

Novel metabolic aspects related to adenosine deaminase inhibition in a human astrocytoma cell line.

Adenosine deaminase, which catalyzes the deamination of adenosine and deoxyadenosine, plays a central role in purine metabolism. Indeed, its deficiency is associated with severe immunodeficiency and abnormalities in the functioning of many organs, including nervous system. We have mimicked an adenosine deaminase-deficient situation by incubating a human astrocytoma cell line in the presence of deoxycoformycin, a strong adenosine deaminase inhibitor, and deoxyadenosine, which accumulates in vivo when the enzyme is deficient, and have monitored the effect of the combination on cell viability, mitochondrial functions, and other metabolic features. Astrocytomas are the most common neoplastic transformations occurring in glial cell types, often characterized by a poor prognosis. Our experimental approach may provide evidence both for the response to a treatment affecting purine metabolism of a tumor reported to be particularly resistant to chemotherapeutic approaches and for the understanding of the molecular basis of neurological manifestations related to errors in purine metabolism. Cells incubated in the presence of the combination, but not those incubated with deoxyadenosine or deoxycoformycin alone, underwent apoptotic death, which appears to proceed through a mitochondrial pathway, since release of cytochrome c has been observed. The inhibition of adenosine deaminase increases both mitochondrial reactive oxygen species level and mitochondrial mass. A surprising effect of the combination is the significant reduction in lactate production, suggestive of a reduced glycolytic capacity, not ascribable to alterations in NAD⁺/NADH ratio, nor to a consumption of inorganic phosphate. This is a hitherto unknown effect presenting early during the incubation with deoxyadenosine and deoxycoformycin, which precedes their effect on cell viability.