Qizhu Wu

MR diffusion changes correlate with ultra-structurally defined axonal degeneration in murine optic nerve

Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are widely used to investigate central nervous system (CNS) white matter structure and pathology. Changes in principal diffusivities parallel and perpendicular to nerve fibers or axonal tracts have been associated with axonal pathology and de/dysmyelination respectively. However, the ultra-structural properties and the pathological alterations of white matter responsible for diffusivity changes have not been fully elucidated. We examined the relationship between the directional diffusivities and ultra-structural properties in mouse optic nerve using healthy animals, and mice with optic neuritis (ON) that exhibited marked inflammatory changes and moderately severe axonal pathology. Progressive axonal degeneration in ON resulted in a 23% reduction of parallel diffusivity as detected by diffusion MRI (P<10(-5)), but no change in perpendicular diffusivity. Parallel diffusion changes were highly correlated with the total axolemmal cross-sectional area in the pre-chiasmal portion of the optic nerve (r=0.86, P<0.001). This study provides quantitative evidence that reduced parallel diffusivity in the optic nerve correlates significantly with axolemmal cross-sectional area reductions. MRI-based assessment of axonal degeneration in murine ON is feasible and potentially useful for monitoring of neuro-protective therapies in preclinical trials in animals.

Leukemia inhibitory factor signaling modulates both central nervous system demyelination and myelin repair

Leukemia inhibitory factor (LIF) receptor signaling limits the severity of inflammatory demyelination in experimental autoimmune encephalomyelitis, a T‐cell dependent animal model of multiple sclerosis (MS) [Butzkueven et al. ( 2002 ) Nat Med 8:613–619]. To identify whether LIF exerts direct effects within the central nervous system to limit demyelination, we have studied the influence of LIF upon the phenotype of mice challenged with cuprizone, a copper chelator, which produces a toxic oligodendrocytopathy. We find that exogenously administered LIF limits cuprizone‐induced demyelination. Knockout mice deficient in LIF exhibit both potentiated demyelination and oligodendrocyte loss after cuprizone challenge, an effect that is ameliorated by exogenous LIF, arguing for a direct beneficial effect of endogenous LIF receptor signaling. Numbers of oligodendrocyte progenitor cells in cuprizone‐challenged mice are not influenced by either exogenous LIF or LIF deficiency, arguing for effects directed to the differentiated oligodendrocyte. Studies on the influence of LIF upon remyelination after cuprizone challenge fail to reveal any significant effect of exogenous LIF. The LIF‐knockout mice do, however, display impaired remyelination, although oligodendrocyte replenishment, previously identified to occur from the progenitor pool, is not significantly compromised. Thus endogenous LIF receptor signaling is not only protective of oligodendrocytes but can also enhance remyelination, and exogenous LIF has therapeutic potential in limiting the consequences of oligodendrocyte damage.

MRI identification of the rostral-caudal pattern of pathology within the corpus callosum in the cuprizone mouse model.

To characterize and compare histological and MRI‐based changes within the corpus callosum (CC) in the cuprizone mouse model of multiple sclerosis (MS).

Early Detection of Ventilation-Induced Brain Injury Using Magnetic Resonance Spectroscopy and Diffusion Tensor Imaging: An In Vivo Study in Preterm Lambs

Background and Aim High tidal volume (VT) ventilation during resuscitation of preterm lambs results in brain injury evident histologically within hours after birth. We aimed to investigate whether magnetic resonance spectroscopy (MRS) and/or diffusion tensor imaging (DTI) can be used for early in vivo detection of ventilation-induced brain injury in preterm lambs. Methods Newborn lambs (0.85 gestation) were stabilized with a “protective ventilation” strategy (PROT, n = 7: prophylactic Curosurf, sustained inflation, VT 7 mL/kg, positive end expiratory pressure (PEEP) 5 cmH2O) or an initial 15 minutes of “injurious ventilation” (INJ, n = 10: VT 12 mL/kg, no PEEP, late Curosurf) followed by PROT ventilation for the remainder of the experiment. At 1 hour, lambs underwent structural magnetic resonance imaging (Siemens, 3 Tesla). For measures of mean/axial/radial diffusivity (MD, AD, RD) and fractional anisotropy (FA), 30 direction DTI was performed. Regions of interests encompassed the thalamus, internal capsule, periventricular white matter and the cerebellar vermis. MRS was performed using a localized single-voxel (15×15×20 mm3, echo time 270 ms) encompassing suptratentorial deep nuclear grey matter and central white matter. Peak-area ratios for lactate (Lac) relative to N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) were calculated. Groups were compared using 2-way RM-ANOVA, Mann-Whitney U-test and Spearmans correlations. Results No cerebral injury was seen on structural MR images. Lambs in the INJ group had higher mean FA and lower mean RD in the thalamus compared to PROT lambs, but not in the other regions of interest. Peak-area lactate ratios >1.0 was only seen in INJ lambs. A trend of higher mean peak-area ratios for Lac/Cr and Lac/Cho was seen, which correlated with lower pH in both groups. Conclusion Acute changes in brain diffusion measures and metabolite peak-area ratios were observed after injurious ventilation. Early MRS/DTI is able to detect the initiation of ventilation-induced brain injury.

Leukemia Inhibitory Factor Protects Axons in Experimental Autoimmune Encephalomyelitis via an Oligodendrocyte-Independent Mechanism

Leukemia inhibitory factor (LIF) and Ciliary Neurotrophic factor (CNTF) are members of the interleukin-6 family of cytokines, defined by use of the gp130 molecule as an obligate receptor. In the murine experimental autoimmune encephalomyelitis (EAE) model, antagonism of LIF and genetic deletion of CNTF worsen disease. The potential mechanism of action of these cytokines in EAE is complex, as gp130 is expressed by all neural cells, and could involve immuno-modulation, reduction of oligodendrocyte injury, neuronal protection, or a combination of these actions. In this study we aim to investigate whether the beneficial effects of CNTF/LIF signalling in EAE are associated with axonal protection; and whether this requires signalling through oligodendrocytes. We induced MOG35–55 EAE in CNTF, LIF and double knockout mice. On a CNTF null background, LIF knockout was associated with increased EAE severity (EAE grade 2.1±0.14 vs 2.6±0.19; P<0.05). These mice also showed increased axonal damage relative to LIF heterozygous mice, as indicated by decreased optic nerve parallel diffusivity on MRI (1540±207 µm2−/s vs 1310±175 µm2−/s; P<0.05), and optic nerve (−12.5%) and spinal cord (−16%) axon densities; and increased serum neurofilament-H levels (2.5 fold increase). No differences in inflammatory cell numbers or peripheral auto-immune T-cell priming were evident. Oligodendrocyte-targeted gp130 knockout mice showed that disruption of CNTF/LIF signalling in these cells has no effect on acute EAE severity. These studies demonstrate that endogenous CNTF and LIF act centrally to protect axons from acute inflammatory destruction via an oligodendrocyte-independent mechanism.

Influence of methylprednisolone on magnetic resonance and histological measures during cuprizone-induced demyelination.

MRI is widely used for routine assessment of the progression of white matter injury while patients receive therapeutic agents, such as the glucocorticoid agonist methylprednisolone (MP). Given this, it is important to determine whether MRI parameters are altered by MP treatment in the absence of changes in cellular and myelin pathology. In this study, we compared magnetic resonance and histological measures during myelin injury in mice with and without short duration MP administration. Mice were scanned with a 4.7T MRI scanner before and after MP or vehicle injections using T2WI and DTI sequences and histology was performed on the brains following the second scan. Comparison of post-injection to pre-injection MRI showed a reduced T2WI intensity in the CC and an attenuated response in ADC|| and ADC perpendicular in the MP group in comparison with the vehicle group. However, quantitative analyses of myelin staining, neurofilament intensity and oligodendrocyte and microglial density were not different between the MP and the vehicle groups, indicating that the short duration MP treatment did not alter cellular and myelin pathology. These data suggest that MP could confound the validity of paraclinical measures such as ADC|| and ADC perpendicular that are otherwise being touted as markers of either axonal integrity or myelin repair.

Microvascular leakage in acute myocardial infarction: characterization by histology, biochemistry, and magnetic resonance imaging

Cardiac microvascular obstruction (MVO) after ischemia-reperfusion (I/R) has been well studied, but microvascular leakage (MVL) remains largely unexplored. We characterized MVL in the mouse I/R model by histology, biochemistry, and cardiac magnetic resonance (CMR) imaging. I/R was induced surgically in mice. MVL was determined by administrating the microvascular permeability tracer Evans blue (EB) and/or gadolinium-diethylenetriaminepentaacetic acid contrast. The size of MVL, infarction, and MVO in the heart was quantified histologically. Myocardial EB was extracted and quantified chromatographically. Serial CMR images were acquired from euthanized mice to determine late gadolinium enhancement (LGE) for comparison with MVL quantified by histology. I/R resulted in MVL with its severity dependent on the ischemic duration and reaching its maximum at 24-48 h after reperfusion. The size of MVL correlated with the degree of left ventricular dilatation and reduction in ejection fraction. Within the risk zone, the area of MVL (75 ± 2%) was greater than that of infarct (47 ± 4%, P < 0.01) or MVO (36 ± 4%, P < 0.01). Contour analysis of paired CMR-LGE by CMR and histological MVL images revealed a high degree of spatial colocalization (r = 0.959, P < 0.0001). These data indicate that microvascular barrier function is damaged after I/R leading to MVL. Histological and biochemical means are able to characterize MVL by size and severity while CMR-LGE is a potential diagnostic tool for MVL. The size of ischemic myocardium exhibiting MVL was greater than that of infarction and MVO, implying a role of MVL in postinfarct pathophysiology.NEW & NOTEWORTHY We characterized, for the first time, the features of microvascular leakage (MVL) as a consequence of reperfused myocardial infarction. The size of ischemic myocardium exhibiting MVL was significantly greater than that of infarction or no reflow. We made a proof-of-concept finding on the diagnostic potential of MVL by cardiac magnetic resonance imaging.

Occipital GABA levels in older adults and their relationship to visual perceptual suppression

Several studies have attributed certain visual perceptual alterations in older adults to a likely decrease in GABA (Gamma Aminobutyric Acid) concentration in visual cortex, an assumption based on findings in aged non-human primates. However, to our knowledge, there is no direct evidence for an age-related decrease in GABA concentration in human visual cortex. Here, we estimated visual cortical GABA levels and Glx (combined estimate of glutamate and glutamine) levels using magnetic resonance spectroscopy. We also measured performance for two visual tasks that are hypothesised to be mediated, at least in part, by GABAergic inhibition: spatial suppression of motion and binocular rivalry. Our results show increased visual cortical GABA levels, and reduced Glx levels, in older adults. Perceptual performance differed between younger and older groups for both tasks. When subjects of all ages were combined, visual cortical GABA levels but not Glx levels correlated with perceptual performance. No relationship was found between perception and GABA levels in dorsolateral prefrontal cortex. Perceptual measures and GABA were not correlated when either age group was considered separately. Our results challenge current assumptions regarding neurobiological changes that occur within the aging human visual cortex and their association with certain age-related changes in visual perception.

Point mutations in murine Nkx2-5 phenocopy human congenital heart disease and induce pathogenic Wnt signaling

Mutations in the Nkx2-5 gene are a main cause of congenital heart disease. Several studies have addressed the phenotypic consequences of disrupting the Nkx2-5 gene locus, although animal models to date failed to recapitulate the full spectrum of the human disease. Here, we describe a new Nkx2-5 point mutation murine model, akin to its human counterpart disease-generating mutation. Our model fully reproduces the morphological and physiological clinical presentations of the disease and reveals an understudied aspect of Nkx2-5-driven pathology, a primary right ventricular dysfunction. We further describe the molecular consequences of disrupting the transcriptional network regulated by Nkx2-5 in the heart and show that Nkx2-5-dependent perturbation of the Wnt signaling pathway promotes heart dysfunction through alteration of cardiomyocyte metabolism. Our data provide mechanistic insights on how Nkx2-5 regulates heart function and metabolism, a link in the study of congenital heart disease, and confirms that our models are the first murine genetic models to our knowledge to present all spectra of clinically relevant adult congenital heart disease phenotypes generated by NKX2-5 mutations in patients.

Diffusion Tensor Imaging Colour Mapping Threshold for Identification of Ventilation-Induced Brain Injury after Intrauterine Inflammation in Preterm Lambs

Purpose The aim of this study is to examine whether advanced magnetic resonance imaging (MRI) techniques can detect early brain injury caused by intrauterine inflammation and inappropriate initial respiratory support in preterm lambs. Hypothesis Neuropathology caused by intrauterine inflammation is exacerbated by mechanical ventilation at birth and is detectable with advanced MRI techniques. Methods Pregnant ewes received intra-amniotic lipopolysaccharide (LPS) 7 days prior to delivery at ~125 days of gestation (85% of gestation), whereupon lambs were delivered and randomised to receive an injurious (LPS + INJ, n = 6) or protective (LPS + PROT, n = 6) ventilation strategy. MRI of the brain was conducted 90 min after preterm delivery, using structural, diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS) techniques. A colour map threshold technique was utilised to compare distributions of low diffusivity voxels in the brains of LPS-exposed lambs with those not exposed to LPS (PROT, n = 7 PROT and INJ, n = 10). Results No overt cerebral injury was identified on structural MRI images of any lamb. However, on DTI, axial diffusivity, radial diffusivity, and mean diffusivity values were lower and significantly more heterogeneous in specific brain regions of lambs in the LPS + INJ group compared to the LPS + PROT group. Colour mapping revealed lower diffusivity in the thalamus, periventricular white matter, internal capsule, and frontal white matter in the LPS + INJ group compared to LPS + PROT group. The MRS peak area ratios of lactate, relative to those for the metabolites creatine, choline, and N-acetylaspartate, were not different between LPS-exposed groups. Lambs exposed to LPS had lower diffusivity within the white matter regions assessed than non-LPS-treated control lambs. Conclusion DTI colour map threshold techniques detected early brain injury in preterm lambs exposed to intrauterine inflammation and detected differences between injurious and protective ventilation strategies. DTI mapping approaches are potentially useful for early detection of subtle brain injury in premature infants.