Structural microtubule associated proteins (MAPs) stabilize microtubules, a property that was thought to be essential for development, maintenance and function of neuronal circuits. However, deletion of the structural MAPs in mice does not lead to major neurodevelopment defects. Here we demonstrate a role for MAP6 in brain wiring that is independent of microtubule binding. We find that MAP6 deletion disrupts brain connectivity and is associated with a lack of post-commissural fornix fibres. MAP6 contributes to fornix development by regulating axonal elongation induced by Semaphorin 3E. We show that MAP6 acts downstream of receptor activation through a mechanism that requires a proline-rich domain distinct from its microtubule-stabilizing domains. We also show that MAP6 directly binds to SH3 domain proteins known to be involved in neurite extension and semaphorin function. We conclude that MAP6 is critical to interface guidance molecules with intracellular signalling effectors during the development of cerebral axon tracts.

Manganese enhanced MRI (MEMRI) offers many possibilities such as tract tracing and functional imaging in vivo. Mn is however neurotoxic and may induce symptoms similar to those associated with Parkinson's disease (manganism). The mechanisms of Mn-induced neurotoxicity are not clear. In this study, we combine synchrotron X-ray fluorescence microprobe (SR-XRF) and MEMRI techniques to investigate spatial distribution of Mn within the rat hippocampus and how Mn interacts with Ca, Fe and Zn at a cellular level. Images were acquired in the rat hippocampus (n=23) and using two injection routes: intra-cerebral (MnCl(2): 50 mM, 10 μL) and intra-peritoneal (MnCl(2): 100 mM, 30 mg/kg). For both injection routes, Mn is found in dentate gyrus and in CA3: control: 2.5 ± 1.6, intra-peritoneal: 5.0 ± 2.4, and intra-cerebral: 25.1 ± 9.2 μg/g. Mn follows Zn distribution and has a negative impact on the total amount of Zn and Fe. The Mn-enhanced MRI contrast is well correlated with the total Mn amount measured with SR-XRF (R(2)=0.93; p<0.002). After intra-cerebral injection, the hippocampal fissure is found to accumulate a large amount of Mn and yields a hypointense MRI signal, which may be ascribed to a reduction in T2. This study shows that SR-XRF is well suited to investigate Mn distribution at a mesoscale and that MRI is sensitive to low Mn concentrations. As perturbations in metal homeostasis may alter brain function, the injected dose of Mn in MEMRI studies needs to be carefully adjusted to obtain reliable functional information.

This study opens the possibility of monitoring glucose regulation of CSF at the resolution of MRI by quantitating T.

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The MAP6 (microtubule-associated protein 6) KO mouse is a microtubule-deficient model of schizophrenia that exhibits severe behavioral disorders that are associated with synaptic plasticity anomalies. These defects are alleviated not only by neuroleptics, which are the gold standard molecules for the treatment of schizophrenia, but also by Epothilone D (Epo D), which is a microtubule-stabilizing molecule. To compare the neuronal transport between MAP6 KO and wild-type mice and to measure the effect of Epo D treatment on neuronal transport in KO mice, MnCl2 was injected in the primary somatosensory cortex. Then, using manganese-enhanced magnetic resonance imaging (MEMRI), we followed the propagation of Mn(2+) through axonal tracts and brain regions that are connected to the somatosensory cortex. In MAP6 KO mice, the measure of the MRI relative signal intensity over 24h revealed that the Mn(2+) transport rate was affected with a stronger effect on long-range and polysynaptic connections than in short-range and monosynaptic tracts. The chronic treatment of MAP6 KO mice with Epo D strongly increased Mn(2+) propagation within both mono- and polysynaptic connections. Our results clearly indicate an in vivo deficit in neuronal Mn(2+) transport in KO MAP6 mice, which might be due to both axonal transport defects and synaptic transmission impairments. Epo D treatment alleviated the axonal transport defects, and this improvement most likely contributes to the positive effect of Epo D on behavioral defects in KO MAP6 mice.

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Manganese-enhanced magnetic resonance imaging (MEMRI) is a powerful tool for in vivo tract tracing or functional imaging of the central nervous system. However Mn(2+) may be toxic at high levels. In this study, we addressed the impact of Mn(2+) on mouse hippocampal neurons (HN) and neuron-like N2a cells in culture, using several approaches. Both HN and N2a cells not exposed to exogenous MnCl2 were shown by synchrotron X-ray fluorescence to contain 5 mg/g Mn. Concentrations of Mn(2+) leading to 50% lethality (LC50) after 24 h of incubation were much higher for N2a cells (863 mM) than for HN (90 mM). The distribution of Mn(2+) in both cell types exposed to Mn(2+) concentrations below LC50 was perinuclear whereas that in cells exposed to concentrations above LC50 was more diffuse, suggesting an overloading of cell storage/detoxification capacity. In addition, Mn(2+) had a cell-type and dose-dependent impact on the total amount of intracellular P, Ca, Fe and Zn measured by synchrotron X-ray fluorescence. For HN neurons, immunofluorescence studies revealed that concentrations of Mn(2+) below LC50 shortened neuritic length and decreased mitochondria velocity after 24 h of incubation. Similar concentrations of Mn(2+) also facilitated the opening of the mitochondrial permeability transition pore in isolated mitochondria from rat brains. The sensitivity of primary HN to Mn(2+) demonstrated here supports their use as a relevant model to study Mn(2+) -induced neurotoxicity.

Background Heart failure (HF) with reduced ejection fraction represents approximately 50% of the 600,000 Canadians currently living with HF and over 90,000 new cases diagnosed each year. The angiotensin receptor neprilysin inhibitor, sacubitril/valsartan, demonstrated superior efficacy in reducing cardiovascular death and HF hospitalization over standard of care therapy. Methods The potential magnitude of benefit in Canada with respect to preventing or postponing deaths and reducing hospitalizations resulting from its optimal implementation in patients with HF with an ejection fraction <40% was estimated based on published sources. Results Of the potentially eligible 225,562 patients, this would amount to the prevention of 4699 cardiovascular deaths and first HF hospitalizations, 3698 thirty-day HF readmissions, and 2820 deaths due to all-cause mortality. The number of patients receiving sacubitril/valsartan nationally in 2018 was 27,267. This represents approximately 12% of the calculated eligible population for this therapy in Canada. Conclusions The findings from this analysis suggest that a substantial number of deaths, hospitalizations, and HF readmissions could potentially be avoided by optimal usage of sacubitril/valsartan therapy in Canada. This emphasizes the importance of rapidly and appropriately implementing evidence-based medications into routine clinical practice, to achieve the best possible outcomes for our patients with HF and to reduce the high burden and cost of HF in Canada.